Title of Invention	A SNAP ACTION ROTARY SWITCH
Abstract	In a snap action rotary switch, incorporating a novel locking and indexing means motion of the switch selector means (knob, handle or others) is transmitted to the contacts through a drive and a driven wheel rotatably coupled together by spring means, the rotation of the latter being prevented upto the release point(s) by ratchet engagement between the latter and a ring assembly anchored to the snap action mechanism housing by spline means which prevent rotation but allow vertical movement thereof • Downward movement of said ring assembly causes the disengagement of said ratchet means and this occurs when a set of cams located on said drive wheel bears down on a set of vertical pins which in turn pushes down the spring loaded ring assembly. A new set of contact gaps are indicated which considerably reduce the derating involved in inductive and/or DC applications of the switches.

Title of Invention

A SNAP ACTION ROTARY SWITCH

Abstract

In a snap action rotary switch, incorporating a novel locking and indexing means motion of the switch selector means (knob, handle or others) is transmitted to the contacts through a drive and a driven wheel rotatably coupled together by spring means, the rotation of the latter being prevented upto the release point(s) by ratchet engagement between the latter and a ring assembly anchored to the snap action mechanism housing by spline means which prevent rotation but allow vertical movement thereof • Downward movement of said ring assembly causes the disengagement of said ratchet means and this occurs when a set of cams located on said drive wheel bears down on a set of vertical pins which in turn pushes down the spring loaded ring assembly. A new set of contact gaps are indicated which considerably reduce the derating involved in inductive and/or DC applications of the switches.

Full Text	This invention relates to (snap action) switches and more particularly to rotary snap action switcnes. In the specification hereinbelow, when referring to electrical terms such as 'electric current , 'electrical load' and others the words 'electric' and 'electrical' have been dropped in the interests of conciseness. A switch is an electromechanical component which is used to control one or more circuits. In its simplest form, a circuit comprises a source of electrical energy such as a primary or secondary cell(battery), a generator, and load(s) that use electrical energy, such as, for example, fans, tubelights, incandescent bulbs, motors, instruments or others. Circuits further comprise conductors extending from said source to load and back such as to provide a path for the current to flow from and to the source, that is, round a path(circuit). Control of a circuit is exercised by interposing a switch in a circuit, in one position whereof said circuit(path) is broken(opened) and in the other it is made(closed). Circuits in practice, possess varying degrees of complexity such as, for example, having a plurality of loads and/or sources and/or switches and the switches themselves may be more complex than the simple one referred to hereinabove. Circuits may comprise other components such as relays, fuses, indicators, inductors, capacitors and others. The wide variation in types of circuits is described so as to emphasise that the rotary switches of the invention can be easily and simply adapted for use in any of them. A simple source has two poles, one for the outgoing conductor and one for the incoming conductor. Examples of such two-pole sources are DC power sources and single phase AC where the poles arc referred to as positive and negative in the former and phase(live) and neutral in the latter. In the descriptiofurther hereinbelow, only two pole sources are considered. This is in the interests of simplicity and the rotary snap action switches of the invention are simply and easily adapted to other sources. A switch is interposed in a circuit more commonly in said outgoing conductor. This is the arrangement adopted in the description hereinbelow. In such an arrangement, the switch terminal which is closer circuitwise to the positive or phase(live) of the source is referred to as the pole and other as the load terminal Hence, unless otherwise specified, the term 'pole'; in the further specification hereinbelow refers to said switch pole. This is the convention adopted in this specification. A switch as mentioned hereinabove, is an electromechanical component and comprises an electrical part and a mechanical one. The former comprises one or more contacts which make and break the circuit while the latter an actuator linked to the switch mechanism, by means of which the opening and closing of the switch is carried out. In a rotary switch, said actuator comprises a knob, handle or other similar means which are hereinafter referred to as selector means. The switch mechanism in a rotary switch comprises a shaft and one or more rotatable members which rotate therewith and cause the opening and closing of said contacts. Operation of said selector means causes rotation of said shaft and rotatable members. Said rotatable members may comprise arms(referred to hereinafter as rotary arms) or alternatively wheels/discs provided with cam portions on the circumferences thereof Thus we have two types of rotary' switches: rotarv- arm type and cam type. A rotary arm type rotary' switch comprises one or more said load terminals located circumferentially around said shaft. Each said load terminal is associated with a contact. Upon operation of the switch, said rotary arm moles establishing contact with the contacts of successive load terminals. Said rotary' arm is in contact with said pole and when it makes contact with a load terminal path is provided between said pole and load terminal A said contact can be conceived of as a pair of contact elements(surfaces) which come into face to face contact upon operation of the switch. One said surface is common to all said contacts and is located on said rotary- arm and other is associated one each with each said load terminal Said surface located on the rotary- arm is called the moving contact surface and others the stationer) ones. As the rotary arm moves into position against a load terminal said moving surface slides over said stationery surface associated with that load terminal and comes to rest substantially in full face to face contact. In view of said sliding, said contacts are referred to as wiping type contacts as a ceRtain amount of wiping occurs during said sliding. This results in a certain amount of cleaning of said surfaces and improves the contact therebetween but also adds to the friction and to the effort required in operation of the switch. A rotary arm together with its associated pole(s) and load terminal(s) is referred to as a stage, deck, packet and by other terms. A stage may comprise more than one pole and if so it may have different pole-load terminal combinations. A stage is often enclosed in a container to form a switching module which is mounted on said switch shaft extending from said selector means. A rotary arm type rotary switch may comprise more than one said stage either in the form of said modules or otherwise. Between the selector means and the first switching module is located detent means the purpose whereof is to provide firm location for said rotary arm(s) in the switching positions thereof, that is, in the contacting positions or angular positions wherein said contact between said surfaces takes place. Often said selector means, detent means and switch shaft form one self-contained unit with said shaft extending therefrom. In an alternative design, said arm comprises two said moving surfaces. Correspondingly, each load terminal is provided with two said stationary surfaces and during operation said arm wedges itself therebetween. Contact is established, then between two pairs of surfaces such that current from pole to load terminal flows through two parallel paths. Said parallel double wiping contacts are common in rotary-arm type rotary switches. Series double wiping contacts are not found in the art, altHough feasible. In a yet another alternative design, said moving contact moves frontally towards the stationary one and said sliding is not involved. Such contacts are called butt type contacts and although they are feasible in rotary arm type rotary switches they are commonly found in cam type rotary switches. A load terminal in cam type rotary switches is associated with one said butt contact or two. the latter being referred to as a double butt contact. Said double butt contacts in cam type rotary switches are commonly in series although parallel arrangement is also feasible. The various features referred to in the description of said rotary arm type rotary switches are also found or are feasible in cam type rotary switches. However, the design of the latter common in the art, comprises a self-contained unit comprising of selector means, detent means and switch shaft, said shaft extending therefrom along which are mounted one or more cam type switching modules. Each said cam type switching module has two poles and two load terminals, each of the latter being associated with one of the former. Said pole-load terminal pairs are located circumferentially around said shaft and each pair is associated with, and activated by, its own cam wheel/disc which is mounted upon and rotatable by said shaft. Each said pair is also associated with its own double butt contact. The periphery of a cam wheel/disc is divided into radial segments, each segment corresponding to a setting of the switch. A segment may be active or inactive, the former having a profiled cam portion while the latter having none. An active segment when aligned with a said butt contact, double or otherwise, activates the latter changing it from closed to open position said butt contacts being spring -loaded. Suitable coupling means are provided on said shaft and said selector means and rotary arms(said cam wheels/discs in cam type rotary switches) such that the movement of the various components is in synchronisation with said settings and load terminal position. Said segments may be notional, in that, said cam wheels/discs are not required to be physically and actually divided into segments. In practice, in the art, said cam wheels/discs are moulded out of plastics and said cam portions are integral therewith but could be separate and attached thereto. Where said butt contacts are required to be NO(normally open) the cam wheels/discs are provided with slots in place of said projecting profiled cam portions. Cam type rotary switches having three or more said pole-load terminal pairs in a stage are also found in the art or are feasible. Rotary switches are mounted on control panels or other surfaces by means of screw or suitable other means located on the switch bodies. Mounting practices are. front, rear and dual mountings. A rotary switch may have a face plate indicating said switch settings and other information. Mounting of a rotary switch by means of the faceplate is also practiced. A typical rotary arm type and a cam type rotary switch of prior art have been described as also several design variations thereof It is stressed that the novel rotary switches of the invention incorporating a novel snap-action mechanism can be simply and easily adapted to provide all said design features and said variations. That is, the novel snap-action mechanism of the invention can be simply and easily adapted for incorporation in said designs and said variations thereof. The snap-action mechanism of the invention also provides for firm location of the switch shaft in various angular positions thereof corresponding to the switch settings that is, the function of the detent means is performed by the snap action mechanism. Snap-action mechanisms of the invention, therefore, replace said detent means and eliminate the need thereof. In fact, the snap-action mechanism is placed in the position normally occupied by said detent means in a rotary switch, that is, next to said selector means. It is therefore, not necessary to discuss detent means in detail in this specification. Snap action mechanisms of the invention further provide the quick make and quick break feature which is very necessary for Rotan' switches for DC. applications. This is further discussed hereinbelow. Classification of rotary- switches is based on the following criteria: 1. the number of poles in a switch, that is, the number of separate conductors that can be controlled by the switch: 2. the number of throws of the switch, that is. the number of circuits the switch can control with respect to each pole: 3. the number of breaks, that is. the number of contacts at which said making and breaking occurs in respect of a circuit, that is. in respect of a single load terminal. 4 • the speed of said making and breaking; and 5. the normal position of said contacts prior to actuation of the switch. Criterion 1 relates to the number of poles in a deck and has been discussed already and elaborated hereinab-above The number of load terminals associated with a deck represents the number of throws of the switch. A rotary arm type switch may have, for example, two poles and four throws which would be capable of being arranged in different pole-throw combinations by suitable internal or external wiring. In a cam type rotary switch by construction each pole has only a single tluow. Here too, by suitable internal or external wiring different pole-throw combinations can be achieved. With reference to criterion 3, single and double wiping type and butt type contacts have been considered. These may be in series or parallel Breaks are further discussed hereinbelow in reference to the arcing phenomenon in switches. Criterion 4 relates to the speed of making and breaking of said contacts in a switch. There are two types of actions: slow and quick. Thus there are slow make slow break switches and quick make quick break switches. Detent means in rotary' switches proxide slow make slow break action. Such switches are quite adequate, indeed preferable, for AC circuits while DC circuits generally require quick make quick break action. Snap action mechanisms provide quick make quick break action. Snap action switches are furthermore partly autonomous in the sense that when said selector means are operated and reach the release point thereafter the movement of said contact(s) from one position to another is substantially independent of the selector means. That is, beyond the release point, said moving contact accelerates rapidly from one position to the next without further intervention by the switch operator Two other types of action slow make quick break and quick make and slow break are also feasible but not common in the art. Under criterion 5, there are normally open(NO) and NC(normally closed) switches. Snap action rotary switches of the invention can be easily and simply adapted to all types elaborated under criteria 1, 2, 3 and 5 and under criterion 4 they can provide quick make quick break switches. The snap action mechanism of the invention has been adapted by this invention to both rotary arm type and cam type rotary switches. The rotary switches considered so far hereinabove have each a single said switch shaft extending from selector means, through detent means to the switching module(s). There are several advantages in segmentising said switch shaft: one segment covering the selector means and detent means and a segment each for each of the switching modules. The advantages offered by said segmentation relate to design, manufacturing, operation and standardisation. It also offers the possibility of use of plastics for said shaft segments which provides further cost benefit and manufacturing convenience. The development of said segmental shafts is novel and is the subject of an application for patent No. 1995/MAS/98 dated 4th Sept. '98 by this applicant. A rotary switch of the invention incorporating the novel snap action mechanism of the invention comprises two shafts called the drive and driven shafts each extending from said snap action mechanism, that is. from the sides thereof The two parts of the snap action mechanism are hereinafter referred to as the drive and driven sides thereof Said two shafts, the drive and driven are coupled together by spring means and an indexing means which are elaborated further hereinbelow. Said selector means are mounted on the drive shaft and the one or more switching modules of the switch on the driven shaft extending on the other side of the snap action mechianism. Said indexing means are also referred to hereinafter as locking and release means. Said concept of segmentisation can also be applied to rotary switches of the invention incorporating the novel snap action mechanism. That is, rotary switches of the invention were adapted to have a single said driven shaft or alternatively segmentised driven shaft comprising of a segment for each of the switching modules associated with the switch, suitable coupling means being provided between the drive shaft segment extending from the snap action mechanism and the segment shafts of the switching modules and between said segment shafts of the modules such as to provide co-ordinated movement. The embodiment of the cam type rotary switch described in detail further hereinbelow incorporates the novel snap action mechanism of the invention and is provided with said segmental shafts for the switching modules thereof. The utihty of snap action rotary switches of the invention is better understood in context of the arcing phenomena in switches. During the closing of a switch, an arc forms when said contact surfaces are sufficiently close and last till said contact surfaces make adequate contact. Similarly, when said contact surfaces separate during switch opening an arc forms which extinguishes when the gap between said surfaces becomes too large to be able to sustain an arc. The picture of arcing presented herein is somewhat simplified in the interests of conciseness. Some characteristics of arcing are: i. arcing is more severe during contact breaking than making because of the induced current created by the collapsing magnetic field, ii. arcing is more severe in a DC circuit than in an equivalent AC circuit; and iii. if a DC circuit has inductive loads then arcing is more severe than otherwise. In switch design, the objective is to minimise the duration of arcing and heat release associated therewith. This is done by increasing the speed of the closing and opening of said contacts in switches. Thus we ha\ e slow make, slow break and quick make quick break rotary switches. A snap action rotary switch is a quick make and quick break switch wherein when the selector means are operated, beyond the operating point said contacts come together or spring apart rapidly with a snap under the influence of strong spring means. Provision of multiple contacts in rotary switches offers greater mass for heat absorption and greater area for heat dissipation. As mentioned hereinabove, rotary switches are found in the art having double wiping contacts or with double butt contacts the former being usually in parallel and the latter in series. Series double contacts offer the further advantage of a voltage breaking capacity twice that of a single contact with the same contact gap. Triple and higher order contacts are also found in the art particularly of the butt type in cam type switches. Said higher order contacts are commonly in series so as to enhance their overall(total) voltage breaking capacity. In an AC circuit, the current falls to zero twice in a cycle. Hence an arc formed during switching in an AC circuit dies down in a short interval of time. The problems associated with arcing are therefore, not so pronounced in AC circuits and slow make slow break switches are quite adequate for AC circuits. On the other hand, snap action switches are almost indispensable for DC circuits. A snap action rotary switch of the prior art will now be described. A snap action rotary switch of prior art comprises a drive wheel or disc and driven wheel or disc rotatably coupled together by spring means which transmit rotating motion from the former to the latter, said transmission of motion being controlled by suitable indexing means which are also sometimes referred to as locking means or locking and release means. Rotation of said drive wheel is carried out by operation of said selector means of the switch. When said drive wheel(disc) is made to move from one position to an adjacent(next) one by operation of said selector means, during first part of the movement thereof said indexing means prevent corresponding rotation of said driven wheel. During said first part of movement, potential energy is built up in said spring means. This situation continues till the release point is reached whereat said indexing means get activated such as to release said driven wheel(disc) which under the influence of the energy stored in said spring means accelerates from one position to the next. As the driven wheel(disc) is rotatably linked to the switching modules, the motion is transmitted all the way to the contacts in the modules, which move rapidly with a snap from one position to the other, say from closed to open or open to closed depending on the design of the switch. In a snap action switch of the prior art, said drive and driven wheels/discs are of metal and said spring means comprise two coiled springs one oriented for clockwise and other for anti-clockwise operation thereof Said drive wheel is rigid with a drive shaft, which extends outwards from the snap action housing and whereupon is mounted said selector means which may be a knob, handle, wheel or other suitable member. Said indexing means in prior art comprise circular ring segments of non-ferrous material. Said ring segments are substantially flat and are mounted flat on the upper face of said driven wheel along a circumference round the axis thereof References to directions in this specification relate to the switch axis and the direction towards said selector means of the switch is referred to as upward or vertical and perpendicular to that as the horizontal Said ring segments are rigid with the driven wheel and one end of each thereof, hereinafter called the free ends, extend upwards from said upper face substantially in a diagonal direction, that is, neither vertically nor horizontally. Said free ends abut against stops located upon body of said housing. Said ring segments, free ends and said stops form said indexing means, said stops preventing the rotation of said driven wheel upto said release point. Said ring segments therefore, lock said driven wheel in a position and are also referred to as locking strips. Said indexing means also comprise cy cylindrical shaped cams mounted at appropriate locations on said drive wheel such that at said release point they press upon and depress said free ends in a downward direction. When pushed down, said free ends get clear of said stops and release the driven wheel which then under the effect of the stored potential energy of said spring means rapidly moves with a snap to the next position thereof where it is brought to rest by the said system of stops. Said driven wheel is rigid with said driven shaft which forms said switch shaft. The rotation of said driven wheel thereby gets transmitted to the switching modules located on said switch shaft. It will be observed that with each position change of the switch, said free ends impact on said stops and these impacts are borne by the small cross sectional area of said free ends. This results in somewhat noisy operation and distortion and rapid wear of said free ends. This is one of the drawbacks of the prior art snap action mechanism. Another observation is that said free ends are subjected to repeated operations of bending and unbending which also increase the wear and decrease working life thereof. This in\'ention offers a novel rotary switch incorporating a novel snap action mechanism which is not subjected to such distortion and rapid wear as the snap action mechanism of prior art. The novel snap action mechanism of the invention has been adapted to both rotary arm type and cam type rotary switches. As cam type switching modules are superior to rotary arm type switching modules in respect of design, scope for standardisation, use of plastics, ease of operation, durability, manufacturing cost and other factors, this invention has paid special attention to the development thereof Furthermore, inclusion of the novel snap action mechanism of the invention in cam type rotary switches makes them particularly relevant for DC applications. This invention has therefore further developed said cam type rotary switches by applying a novel range of contact gaps particularly relevant for DC applications. This is further elaborated hereinbelow. Thus the cam type rotary switch of this invention incorporates the following two novel features which are of special relevance to DC applications: i. the novel snap action mechanism: and ii. a novel range of contact gaps. In the snap action mechanism of the invention, said locking means comprise: i. a ring assembly; and ii. a set of vertically oriented pins. Said ring assembly comprises a pair of ring like members which are concentric with each other one cylindrical face of one said member abutting against a cylindrical face of the other. This said two members upon assembly substantially constitute a single substantially cylindrical shaped ring referred to hereinabove as said ring assembly. Said members are referred to as inner and outer rings and also as inner and outer locking rings hereinbelow. Said ring assembly is housed in a suitably shaped ring slot in the snap action mechanism housing. A radially outer and inner cylindrical face of said ring assembly are provided with spline means which engage with similar spline means located in said ring slot and prevent rotation of said ring assembly but allowing upward and downward movement thereof Said pins extend substantially vertically upward passing through holes provided in said driven wheel. At the lower ends thereof, said pins abut said ring assembly while the upper ends thereof terminate at an appropriate distance below the underface of said drive wheel. Said underface is provided with suitably located cam portions at appropriate points on a circumference{around said switch axis) such that when said drive wheel is rotated(by operation of the switch) said cam portions engage with said pins pushing them downwards. Said pins, in turn, push down said ring assembly. Such appropriate points constitute said release points of the snap action mechanism. In the embodiment described in detail hereinbelow, said pins are substantially cylindrical members but can be of other shapes and cross sections and may be hollow or solid. They are therefore, broadly referred to as pin type members and may have for example, square, hexagonal, elliptical or other section shape and may have splines, slots, keys or flutes thereupon within the scope of the invention. The downward movement of said assembly takes place against the resistive force provided by a set of springs located below said assembly and within said ring slot such that when the engagement of said cam portions with said ring assembly ceases said ring assembly springs back upwards to the normal(locking) position thereof A further pair of radially outer and inner cylindrical faces located on said ring assembly is provided with ratchet means which engage with corresponding ratchet means located on corresponding cylindrical faces provided on the underside of said driven wheel. Said two pairs of corresponding ratchet means constitute said locking means and upon mutual engagement lock said driven wheel in positions corresponding to said switch settings. Said ratchet means also provide said indexing in that upon operation of the switch said driven wheel is brought to rest precisely at a position which corresponds with the next said switch setting. One said ratchet means provide locking/indexing for clockwise motion of said driving wheel and the other for the anti-clockwise motion thereof Motion orientations of said drive and driven wheel and other switch components, that is, clockwise and anti-clockwise (C and AntiC) are based on looking downwards from top along the switch axis. As in the prior art. The drive and driven wheels in the snap action mechanism of the invention are rotatably coupled by two spring means, one for clockwise and the other for anti-clockwise motion thereof Thus. when said switch knob(sector means) is moved from one position to the next one. during part of the motion thereof, said coupling spring means absort energy til said release point is reached whereat said cam portions engage said set of pins causing the latter along with said ring assembly to move downwards. This causes the disengagement of said pair of ratchet means resulting motion being transmitted from said drive wheel to said driven by means of said coupling spring means. During the brief interval that said pair of ratchet means remain disengaged the stored energy of said coupling spring means-acts upon said drive wheel causing accelerated motion thereof to the next position thereof. Thus said driven w heel together with said pins moves rapidly with a snap to the next position thereof corresponding to the next setting of the switch. The motion of the driven wheel is transmitted through said switch shaft(driven shaft) to all the modules located thereupon wherein appropriate contacts thereof move from one position(NO or NC) lo the other positions thereof with a snap, Where said modules comprise segmental shafts it will be observed that similar action takes place. It is interesting to note that at said release point said drive wheel has covered substantially halt of its angular journey from one position to the next while said driven wheel is just about to commence its journey and therefore has the full angular distance to be covered from one position to the next. Just past the release point, therefore, there are two somewhat independent motions to reckon with, that of said drive and driven wheels, the impulse for the former being substantially that provided by the switch operator. The impulse for the latter is provided by the said stored energy held in said coupling means which makes said second motion substantially autonomous of the switch operator. However, if said forward motion is further accelerated by said operator a further impulse may pass on to said second motion. Under the combined influence of said two motions at some point, disengagement of said cam portions and pins occurs resulting in the springing back of said ring assembly upwards. This results in the re-engagement of said ratchet means which provides the indexing of said driven wheel into the next position thereof. In the snap action mechanism of the invention, the forces acting on said drive and driven wheels are much less severe. In fact, the said drive and driven wheels of the invention are substantially free of the forces perpendicular to the faces thereof which, as observed hereinabove are in the prior art design. Also, the forces arising out of said locking(indexing) and said snap movement of the driven assembly are distributed over a larger surface area and not concentrated as in the prior art design. This favourable situation enables the wide use of plastics in the snap action mechanism of the invention offering considerable saving in material and manufacturing costs and in weight. In fact, in the embodiment of the invention described in detail further hereinbelow, the entire snap action mechanism including the housing thereof comprises plastics mouldings with the exception of said spring means interposed between the drive and driven wheels and said set of springs that support said ring assembly. The snap action mechanisms of the intention also ensures a less noisy operation of the switch. It may be mentioned that the snap action mechanism of the invention further provides the following advantages; 1. longer life of the components and of the switch as a whole: 2. quicker operation; 3. lesser problems of corrosion; and 4. smoother operation as component friction in the locking means and release mechanism is minimised. Contact gap is the distance between said two contact surfaces of a contact in the open position thereof The magnitude of said gap is one of the switch design factors which determines the maximum operational voltage and current of a switch. All other parameters being the same, the maximum operational parameters of a switch are lower for inductive loads than for pure resistive loads. Similarly, for a particular type of load the maximum operational parameters are lower for DC applications than for AC applications. As mentioned hereinabove, these differences in maximum operational parameters arise because of differences in the severity of arcing encountered with different types of loads and between AC and DC applications. Thus a switch rated for a particular voltage and current for AC resistive loads has to be derated for application involving AC inductive loads. Similar derating is also involved when going from AC resistive loads to DC resistive loads and going from DC resistive to DC inductive loads. The degree of derating involved in changing from AC resistive to AC inductive loads is much less than that involved in changing from DC resistive to DC inductive and in general from AC to DC applications. That is, broadly the derating inolved in DC applications is considerable. Figures given in Table I hereinbelow give an idea of the extent of derating imolved in various applications for switches manufactured by the applicants. Table I refers to cam type rotary switches. Similar situation is observed in rotary switches of other makes also. Clearly derating involves lesser utilisation of switch equipment, in other words, use of bulkier equipment which adds to the cost of an installation. Any innovation therefore, which would reduce the amount of said derating would provide cost benefits particularly for DC applications. This invention provides for such an innovation. This invention has provided a novel system of said gaps which was observed to considerably reduce the amount of derating involved when considering DC applications. As mentioned hereinabov e. cam type rotar\yswitches are commonly associated with butt contacts and each load terminal and pole thereof is provided usually with a double butt contact, that is, two butt contacts in series. The range of contact gaps observed in the butt contacts of cam switches of prior art are presented in Table 11 hereinbelow. Table 11 gives the magnitude of said contact gaps and the voltage and current ratings associated therewith and is based on several prior art switches a\'ailable in the market. Said gaps in rotary switches of prior art were all uniformly equal to the values prescribed in Table II or were lower. Table II refers to ccam type switches. No instances were observed of values larger than that shown in Table II. Thus consideration of larger said gaps and adaptation thereof to cam type rotary switches of the invention is novel. Said system of novel gaps has been applied by this invention both to the switches of the invention and to prior art switches, that is, both rotary switches incorporating the novel snap action mechanism of the invention or snap action mechanism of prior art. Thus, it was found that it was feasible to provide the novel system of gaps also in a rotary cam switch of the prior art having the prior art snap action mechanism and bring down the required derating thereof Table - n One of the approaches of prior art to reduce the amount of said derating involved in DC applications is to have higher order butt contacts. Thus, there are cam type rotary' switches in prior art that have three or more butt contacts in series associated with each load tenninal(or pole) thereof The disadvantage associated with this approach is that switches having higher order butt contacts are considerably bulkier. Said approach to a certain extent defeats the purpose of reducing said derating. The notable feature of this invention is that use of the novel system of gaps of the invention does not involve any significant increase in the size, volume and weight of the switch and in some cases no increase whatsoever. The novel range of said contact gaps according to this invention is presented herein in the last line of Table II. This invention has established by experimentation that said novel range of gaps is both practical and workable. Thus one obtains a substantial reduction in said derating for DC applications without any substantial modification of the switches. Furthermore, butt contacts having said novel range of gaps when placed in a multiple configuration, that is, more than two contacts in series offer even greater reduction in derating. According to the invention, therefore, there is provided a rotary switch comprising: i • a selector means; i i • a snap action mechanism; and i i i • one or more switching modules, said snap action mechanism comprising a housing with a drive and a driven wheel/disc located therein said drive and driven wheels/discs being rigid respectively with the drive and driven shafts, and being rotatabiy coupled together by spring means and provided with locking and release means that prevent rotation of said driven shaft(switch shaft) upto a release point but allow said rotation thereafter characterised in said locking and release means comprising a spring loaded substantially cylindrical ring assembly, a set of substantially vertically oriented pin hke members and a set of cam like members located on said driven wheel, a pair comprising an inner and an outer cylindrical face of said ring assembly being provided with spline means and another with ratchet means, the former engaging with similar means located in said housing and the latter with snnilar means on said driven wheel, said pin like members extending between said ring assembly and drive wheel and passing through said driven wheel, such that at said release points said cam Uke members push down said pin like members and ring assembly, causing disengagement of said ratchet means and allowing rotation of said driven wheel. The scope of the invention extends to rotary arm type and cam type rotary switches as the novel snap action mechanism can be simply and easily adapted to both designs. Several design variations of both these types of switches have been considered hereinabove and it will be observed that the novel snap action mechanism can be easily and simply incorporated therein. The rotary switches of the invention may comprise one said switching module or more. Said switching stages may be modular or non-modular as described. The rotary switch of the invention is easily adaptable for use in the wide range of circuits considered hereinabove. Segmentation of shafts has been referred to. The rotary switch of the invention may comprise one said drive shaft and one said driven shaft with said modules located on said driven shaft. Alternatively, each said module may have its own segmental shaft. Said scope also covers the various mounting arrangements for rotary switches considered hereinabove. The drive and driven wheels are circular but within the scope of the invention may take other shapes. They may be substantially like a wheel or thin like a disc. Also the shape thereof may be substantially cy1indrical or a complex shape within the scope of the invention. Said wheels/discs may be metallic or non-metallic the latter construction offering the advantages of considerable manufacturing and handling con\ enience and cost benefits. Said wheels are of plastics in the embodiment described in detail further hereinbelow. Said coupling spring means comprise spiral shaped wire springs in the embodiment described but can be of strip also. Said ring assembly in the embodiment described comprised two Concentric nngs made of plastics. The construction of said ring assembly in two parts is for manufacturing and assembling convenience and cost benefit and within the scope of the invention said ring assembly may be a single piece construction also. The spring means supporting said ring assembly comprise a set of helical springs but other spring means can also be used. Construction of said pin type members has ah-easily been elaborated hereinabove. In the embodiment described, said pins are of plastics and are generally cylindrical in shape. In order to provide a clearer understanding of the invention an embodiment thereof will now be described in detail hereinbelow without limitation to the scope of the invention. In the accompanying drawings; Fig. 1 shows the axial sectional view of the rotary switch of the invention; Fig. 2 shows a sectional view of the switching module incorporated in the rotary switch of the invention the section being in a plane perpendicular to the switch axis; and Fig. 3 show s the profile of a part of the ratchet means. The embodiment described in detail comprises a cam type rotary switch having one cam type switching module. The switching module comprises two pole-load terminal sets and is provided with a segmental shaft. A double butt contact with the two contacts in series is associated with each said pair of pole-load terminal and is activated by its own cam wheel/disc. It follows that each said module comprises two cam wheel/discs. It will be observed that within the scope of the invention the switch can have one. two or more of said modules. Reference numerals 1,2 in the accompanying drawings denote the upper and lower parts of the snap action housing, which are fastened together and niounted on mounting plate 10 by fastening means 3. Drive wheel 4 and driven shaft 5 are rigid respectively with the drive shaft 6 and driven shaft 7. Drive shaft 6 is hexagonal in section and at upper end thereof is provided with a threaded hole 8 by means of which handle 9 is fastened to shaft 6. The switch is operated by handle 9 which constitutes said selector means in the present embodiment. Shaft 6 is provided with orientation slots to ensure correct angular correspondence between handle 9 and the switch shaft(driven shaft) 7. The end portion 12 of shaft 6 is of circular cross section and the upper end of shaft 7 is provided with a suitably shaped hollow 13 for location of said end portion 12 sufficient clearance being provided therein to allow independent rotation of shafts 6 and 7. Circlip ensures retention of shaft 6 in drive wheel 4. Coupling springs 16,17 provide rotatable coupling between drive wheel 4 and driven wheel 5. One said spring provides said coupling for clockwise movement of handle 9 and the other for anticlockwise movement thereof Suitable holes are provided on wheels 4,5 for anchoring ends of springs 16,17 and slots extending in the appropriate direction for providing room for movement of the appropriate spring ends with reference to the clockwise and anti-clockwise operation of handle 9. The rotary' switch of the embodiment comprises one switching module 18 but the number thereof can be more within the scope of the invention. Said locking and release means comprise inner locking ring 19 and outer locking ring 20 and are shown assembled together to form said ring assembly 21 which is housed in a ring slot 22 in the housing 1.2. Locking ring assembly 21 is supported by helical springs 23, four numbers of which are provided in this embodiment. Face 24 of ring assembly 21 is provided with spline means that engage with similar means on face 26 located in ring slot 22. Similar face 25 of ring assembly engages with face 27 of ring slot by means of similar spline means. Said set of spline means prevent rotation of ring assembly 21 but allow upw ard and downward motion thereof Faces 28 and 29, respectively an outer an inner face of ring assembly 21 are provided with ratchet means which engage with similar ratchet systems on outer face 30 and inner face 31 of driven wheel 5. One of said ratchet means(systems) is oriented for providing indexing for driven shaft 5 during clockwise rotation thereof and other for anti-clockwise rotation thereof A cutout of the ratchet systems is shown in Fig. 3. Pins 32 extend from said ring assembly 21 to drive wheel 4 and pass through drive wheel 5. Cam portions 33 are located at appropriate angular positions on an undersurface of drive wheel 4. Said angular positions correspond to said release points whereat said cam portions push down pins 32 and therewith the ring assembly 21. The downward movement of the ring assembly 21 disengages said ratchet means whereupon drive wheel 5 becomes free to rotate. Driven wheel 5 remains free to rotate during the short time interval in which said cam portions 33 engage pins 32. With further angular movement of handle 9 and drive wheel 4 therewith, said engagement of cam portions 33 and pins 32 ceases whereupon under action of springs 23 the ring assembly 21 springs back upwards and causes, once again, the engagement of said ratchet means. Pins 32 are solid and of circular cross-section and four nmnbers thereof are pro\ided in the embodiment. Pins 32 are of glass filled polyamide construction. The number of pins depends on the switching angle. Feasibility of said pins having other shapes and cross-sections within the scope of the invention has been elaborated hereinabove. Drive wheel 4 and driven wheel 5 are substantially solid members in the embodiment described but can be in the form of a disc, that is, substantially thin and slat within the scope of the invention. Item 34 is the front plate of the switch which is mounted on a control panel with the front plate 34 in front of and mounting plate 10 behind said panel. Fastening of front plate 34 and mounting plate with each other and with said panel is by fastening screws 35. Stop means 11 provide for a limiting stop for handle 9 but are dispensed with in switches where full 360 degrees movement of handle 9 is desired Script plate 37 is provided to display the switch setting for handle 9 and any other desired information connected with the switch such as operational parameters of the switch and/or loads operated thereby. Script plate 37 is retained by script plate ring 38. Fig. 2 shows cam wheel/disc 39 the active segments whereof are provided with profiled cam portions. It will be observed that the switch shown is of NC type such that when one of said active segments comes into position said contacts change from closed(NC) to open position. It will also be observed that the double butt contact 40 connects terminals 41 and 42 one of which can be desiginted the pole and other the load terminal and appropriately marked on the switch. Contact slide 43 moves up when an active segment comes into position. When an inactive segment comes into position slide 43 moves down under effect of spring 44. Contact surfaces 46 are the stationery surfaces in respect of one pole-load terminal pair. Similar arrangement exists for the other pole-load terminal pair of the module. Moving contact surfaces 47 are located on contact slide 43. The invention provides for the driven wheel being rigid with the driven shaft at the lower end of which coupling means are provided to enable coupling between said driven shaft and the shaft of the switching module(s) or the segmental shaft of the first switching module. In the embodiment described, the driven wheel is rigid with the said coupling means and said driven shaft between the former and latter is notional.. This has been done to make the switch as compact as possible and it is stressed that within the scope of the invention said driven shaft may be small, large or of zero length as is the case in the embodiment described. We claims: 1. A rotary switch comprising: i. a selector means; ii. a snap action mechanism, and ill. one or more switching modules; said snap action mechanism comprising a housing with a drive and a driven wheel/disc located therein, said drive and driven wheels/discs being rigid respectively with the drive and driven shafts and being rotatably coupled together by spring means and provided with locking and release means that prevent rotation of said driven shaft(switch shall) upto a release point but allow said rotation thereafter cliaracterised in said locking and release means comprising a spring loaded substantially cylindrical ring assembly, a set of substantially vertically oriented pin like members and a set of cam like members located on said driven wheel, a pair comprising an inner and an outer cylindrical face of said ring assembly being provided with spline means and another with ratchet means, the former engaging with similar means located in said housing and the latter With similar means on said drive wheel, said pin like members extending between said ring assembly and drive wheel and passing through said driven wheel, such that at said release points said cam like members push down said pin like members and ring assembly, causing disengagement of said ratchet means and allowing rotation of said driven wheel. 2. Tlie rotary switch as claimed in preceding Claim 1 wherein said switching modules are cam type. 3. The rotary switch as claimed in preceding Claim 2 wherein said ring assembly comprises two concentric, substantially cylindrical rings. 4. The rotary switch as claimed in any of preceding Claims 2 and 3 wherein said contacts in said modules are of double butt type. 5. The rotary switch as claimed in any of preceding Claims 2 to 4 wherein said contact gaps range from about 2,5 mm to 5 mm for current ratings from about 16 A to 63 A. A rotary switch substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

Full Text

This invention relates to (snap action) switches and more particularly to rotary snap action switcnes.
In the specification hereinbelow, when referring to electrical terms such as 'electric current , 'electrical load' and others the words 'electric' and 'electrical' have been dropped in the interests of conciseness.
A switch is an electromechanical component which is used to control one or more circuits. In its simplest form, a circuit comprises a source of electrical energy such as a primary or secondary cell(battery), a generator, and load(s) that use electrical energy, such as, for example, fans, tubelights, incandescent bulbs, motors, instruments or others. Circuits further comprise conductors extending from said source to load and back such as to provide a path for the current to flow from and to the source, that is, round a path(circuit). Control of a circuit is exercised by interposing a switch in a circuit, in one position whereof said circuit(path) is broken(opened) and in the other it is made(closed). Circuits in practice, possess varying degrees of complexity such as, for example, having a plurality of loads and/or sources and/or switches and the switches themselves may be more complex than the simple one referred to hereinabove. Circuits may comprise other components such as relays, fuses, indicators, inductors, capacitors and others. The wide variation in types of circuits is described so as to emphasise that the rotary switches of the invention can be easily and simply adapted for use in any of them.
A simple source has two poles, one for the outgoing conductor and one for the incoming conductor. Examples of such two-pole sources are DC power sources and single phase AC where the poles arc referred to as positive and negative in the former and phase(live) and neutral in the latter. In the descriptiofurther hereinbelow, only two pole sources are considered. This is in the interests of simplicity and the rotary snap action switches of the invention are simply and easily adapted to other sources.
A switch is interposed in a circuit more commonly in said outgoing conductor. This is the arrangement adopted in the description hereinbelow. In such an arrangement, the switch terminal which is closer circuitwise to the positive or phase(live) of the source is referred to as the pole and other as the load

terminal Hence, unless otherwise specified, the term 'pole'; in the further specification hereinbelow refers

to said switch pole. This is the convention adopted in this specification.
A switch as mentioned hereinabove, is an electromechanical component and comprises an electrical part and a mechanical one. The former comprises one or more contacts which make and break the circuit while the latter an actuator linked to the switch mechanism, by means of which the opening and closing of the switch is carried out.
In a rotary switch, said actuator comprises a knob, handle or other similar means which are hereinafter referred to as selector means. The switch mechanism in a rotary switch comprises a shaft and one or more rotatable members which rotate therewith and cause the opening and closing of said contacts. Operation of said selector means causes rotation of said shaft and rotatable members. Said rotatable members may comprise arms(referred to hereinafter as rotary arms) or alternatively wheels/discs provided with cam portions on the circumferences thereof Thus we have two types of rotary' switches: rotarv- arm type and cam type.
A rotary arm type rotary' switch comprises one or more said load terminals located circumferentially around said shaft. Each said load terminal is associated with a contact. Upon operation of the switch, said rotary arm moles establishing contact with the contacts of successive load terminals. Said rotary' arm is in contact with said pole and when it makes contact with a load terminal path is provided between said pole and load terminal A said contact can be conceived of as a pair of contact elements(surfaces) which come into face to face contact upon operation of the switch. One said surface is common to all said contacts and is located on said rotary- arm and other is associated one each with each said load terminal
Said surface located on the rotary- arm is called the moving contact surface and others the stationer) ones. As the rotary arm moves into position against a load terminal said moving surface slides over said stationery surface associated with that load terminal and comes to rest substantially in full face to face

contact. In view of said sliding, said contacts are referred to as wiping type contacts as a ceRtain amount of wiping occurs during said sliding. This results in a certain amount of cleaning of said surfaces and improves the contact therebetween but also adds to the friction and to the effort required in operation of the switch.
A rotary arm together with its associated pole(s) and load terminal(s) is referred to as a stage, deck, packet and by other terms. A stage may comprise more than one pole and if so it may have different pole-load terminal combinations. A stage is often enclosed in a container to form a switching module which is mounted on said switch shaft extending from said selector means. A rotary arm type rotary switch may comprise more than one said stage either in the form of said modules or otherwise.
Between the selector means and the first switching module is located detent means the purpose whereof is to provide firm location for said rotary arm(s) in the switching positions thereof, that is, in the contacting positions or angular positions wherein said contact between said surfaces takes place. Often said selector means, detent means and switch shaft form one self-contained unit with said shaft extending therefrom.
In an alternative design, said arm comprises two said moving surfaces. Correspondingly, each load terminal is provided with two said stationary surfaces and during operation said arm wedges itself therebetween. Contact is established, then between two pairs of surfaces such that current from pole to load terminal flows through two parallel paths. Said parallel double wiping contacts are common in rotary-arm type rotary switches. Series double wiping contacts are not found in the art, altHough feasible.
In a yet another alternative design, said moving contact moves frontally towards the stationary one and said sliding is not involved. Such contacts are called butt type contacts and although they are feasible in rotary arm type rotary switches they are commonly found in cam type rotary switches. A load terminal in cam type rotary switches is associated with one said butt contact or two. the latter being referred to as a double

butt contact. Said double butt contacts in cam type rotary switches are commonly in series although parallel arrangement is also feasible.
The various features referred to in the description of said rotary arm type rotary switches are also found or are feasible in cam type rotary switches. However, the design of the latter common in the art, comprises a self-contained unit comprising of selector means, detent means and switch shaft, said shaft extending therefrom along which are mounted one or more cam type switching modules. Each said cam type switching module has two poles and two load terminals, each of the latter being associated with one of the former. Said pole-load terminal pairs are located circumferentially around said shaft and each pair is associated with, and activated by, its own cam wheel/disc which is mounted upon and rotatable by said shaft. Each said pair is also associated with its own double butt contact. The periphery of a cam wheel/disc is divided into radial segments, each segment corresponding to a setting of the switch. A segment may be active or inactive, the former having a profiled cam portion while the latter having none. An active segment when aligned with a said butt contact, double or otherwise, activates the latter changing it from closed to open position said butt contacts being spring -loaded. Suitable coupling means are provided on said shaft and said selector means and rotary arms(said cam wheels/discs in cam type rotary switches) such that the movement of the various components is in synchronisation with said settings and load terminal position. Said segments may be notional, in that, said cam wheels/discs are not required to be physically and actually divided into segments. In practice, in the art, said cam wheels/discs are moulded out of plastics and said cam portions are integral therewith but could be separate and attached thereto. Where said butt contacts are required to be NO(normally open) the cam wheels/discs are provided with slots in place of said projecting profiled cam portions. Cam type rotary switches having three or more said pole-load terminal pairs in a stage are also found in the art or are feasible.
Rotary switches are mounted on control panels or other surfaces by means of screw or suitable other means located on the switch bodies. Mounting practices are. front, rear and dual mountings. A rotary switch may

have a face plate indicating said switch settings and other information. Mounting of a rotary switch by means of the faceplate is also practiced.
A typical rotary arm type and a cam type rotary switch of prior art have been described as also several design variations thereof It is stressed that the novel rotary switches of the invention incorporating a novel snap-action mechanism can be simply and easily adapted to provide all said design features and said variations. That is, the novel snap-action mechanism of the invention can be simply and easily adapted for incorporation in said designs and said variations thereof.
The snap-action mechanism of the invention also provides for firm location of the switch shaft in various angular positions thereof corresponding to the switch settings that is, the function of the detent means is performed by the snap action mechanism. Snap-action mechanisms of the invention, therefore, replace said detent means and eliminate the need thereof. In fact, the snap-action mechanism is placed in the position normally occupied by said detent means in a rotary switch, that is, next to said selector means. It is therefore, not necessary to discuss detent means in detail in this specification. Snap action mechanisms of the invention further provide the quick make and quick break feature which is very necessary for Rotan' switches for DC. applications. This is further discussed hereinbelow.
Classification of rotary- switches is based on the following criteria:
1. the number of poles in a switch, that is, the number of separate conductors that can be controlled by
the switch:
2. the number of throws of the switch, that is. the number of circuits the switch can control with
respect to each pole:
3. the number of breaks, that is. the number of contacts at which said making and breaking occurs in
respect of a circuit, that is. in respect of a single load terminal.
4 • the speed of said making and breaking; and

5. the normal position of said contacts prior to actuation of the switch.
Criterion 1 relates to the number of poles in a deck and has been discussed already and elaborated hereinab-above
The number of load terminals associated with a deck represents the number of throws of the switch. A rotary arm type switch may have, for example, two poles and four throws which would be capable of being arranged in different pole-throw combinations by suitable internal or external wiring. In a cam type rotary switch by construction each pole has only a single tluow. Here too, by suitable internal or external wiring different pole-throw combinations can be achieved.
With reference to criterion 3, single and double wiping type and butt type contacts have been considered. These may be in series or parallel Breaks are further discussed hereinbelow in reference to the arcing phenomenon in switches.
Criterion 4 relates to the speed of making and breaking of said contacts in a switch. There are two types of actions: slow and quick. Thus there are slow make slow break switches and quick make quick break switches. Detent means in rotary' switches proxide slow make slow break action. Such switches are quite adequate, indeed preferable, for AC circuits while DC circuits generally require quick make quick break action. Snap action mechanisms provide quick make quick break action. Snap action switches are
furthermore partly autonomous in the sense that when said selector means are operated and reach the
release point thereafter the movement of said contact(s) from one position to another is substantially independent
of the selector means. That is, beyond the release point, said moving contact accelerates rapidly from one
position to the next without further intervention by the switch operator Two other types of action slow
make quick break and quick make and slow break are also feasible but not common in the art.

Under criterion 5, there are normally open(NO) and NC(normally closed) switches.
Snap action rotary switches of the invention can be easily and simply adapted to all types elaborated under criteria 1, 2, 3 and 5 and under criterion 4 they can provide quick make quick break switches. The snap action mechanism of the invention has been adapted by this invention to both rotary arm type and cam type rotary switches.
The rotary switches considered so far hereinabove have each a single said switch shaft extending from selector means, through detent means to the switching module(s). There are several advantages in segmentising said switch shaft: one segment covering the selector means and detent means and a segment each for each of the switching modules. The advantages offered by said segmentation relate to design, manufacturing, operation and standardisation. It also offers the possibility of use of plastics for said shaft segments which provides further cost benefit and manufacturing convenience. The development of said segmental shafts is novel and is the subject of an application for patent No. 1995/MAS/98 dated 4th Sept. '98 by this applicant.
A rotary switch of the invention incorporating the novel snap action mechanism of the invention comprises two shafts called the drive and driven shafts each extending from said snap action mechanism, that is. from the sides thereof The two parts of the snap action mechanism are hereinafter referred to as the drive and driven sides thereof Said two shafts, the drive and driven are coupled together by spring means and an indexing means which are elaborated further hereinbelow. Said selector means are mounted on the drive shaft and the one or more switching modules of the switch on the driven shaft extending on the other side of the snap action mechianism. Said indexing means are also referred to hereinafter as locking and release
means.

Said concept of segmentisation can also be applied to rotary switches of the invention incorporating the novel snap action mechanism. That is, rotary switches of the invention were adapted to have a single said driven shaft or alternatively segmentised driven shaft comprising of a segment for each of the switching modules associated with the switch, suitable coupling means being provided between the drive shaft segment extending from the snap action mechanism and the segment shafts of the switching modules and between said segment shafts of the modules such as to provide co-ordinated movement. The embodiment of the cam type rotary switch described in detail further hereinbelow incorporates the novel snap action mechanism of the invention and is provided with said segmental shafts for the switching modules thereof.
The utihty of snap action rotary switches of the invention is better understood in context of the arcing phenomena in switches. During the closing of a switch, an arc forms when said contact surfaces are sufficiently close and last till said contact surfaces make adequate contact. Similarly, when said contact surfaces separate during switch opening an arc forms which extinguishes when the gap between said surfaces becomes too large to be able to sustain an arc. The picture of arcing presented herein is somewhat simplified in the interests of conciseness. Some characteristics of arcing are:
i. arcing is more severe during contact breaking than making because of the induced current created by the collapsing magnetic field,
ii. arcing is more severe in a DC circuit than in an equivalent AC circuit; and iii. if a DC circuit has inductive loads then arcing is more severe than otherwise.
In switch design, the objective is to minimise the duration of arcing and heat release associated therewith. This is done by increasing the speed of the closing and opening of said contacts in switches. Thus we ha\ e slow make, slow break and quick make quick break rotary switches. A snap action rotary switch is a quick make and quick break switch wherein when the selector means are operated, beyond the operating point said contacts come together or spring apart rapidly with a snap under the influence of strong spring means.

Provision of multiple contacts in rotary switches offers greater mass for heat absorption and greater area for heat dissipation. As mentioned hereinabove, rotary switches are found in the art having double wiping contacts or with double butt contacts the former being usually in parallel and the latter in series. Series double contacts offer the further advantage of a voltage breaking capacity twice that of a single contact with the same contact gap. Triple and higher order contacts are also found in the art particularly of the butt type in cam type switches. Said higher order contacts are commonly in series so as to enhance their overall(total) voltage breaking capacity.
In an AC circuit, the current falls to zero twice in a cycle. Hence an arc formed during switching in an AC circuit dies down in a short interval of time. The problems associated with arcing are therefore, not so pronounced in AC circuits and slow make slow break switches are quite adequate for AC circuits. On the other hand, snap action switches are almost indispensable for DC circuits.
A snap action rotary switch of the prior art will now be described. A snap action rotary switch of prior art comprises a drive wheel or disc and driven wheel or disc rotatably coupled together by spring means which transmit rotating motion from the former to the latter, said transmission of motion being controlled by suitable indexing means which are also sometimes referred to as locking means or locking and release means. Rotation of said drive wheel is carried out by operation of said selector means of the switch. When said drive wheel(disc) is made to move from one position to an adjacent(next) one by operation of said selector means, during first part of the movement thereof said indexing means prevent corresponding rotation of said driven wheel. During said first part of movement, potential energy is built up in said spring means. This situation continues till the release point is reached whereat said indexing means get activated such as to release said driven wheel(disc) which under the influence of the energy stored in said spring means accelerates from one position to the next. As the driven wheel(disc) is rotatably linked to the switching modules, the motion is transmitted all the way to the contacts in the modules, which move

rapidly with a snap from one position to the other, say from closed to open or open to closed depending on the design of the switch.
In a snap action switch of the prior art, said drive and driven wheels/discs are of metal and said spring means comprise two coiled springs one oriented for clockwise and other for anti-clockwise operation thereof Said drive wheel is rigid with a drive shaft, which extends outwards from the snap action housing and whereupon is mounted said selector means which may be a knob, handle, wheel or other suitable member.
Said indexing means in prior art comprise circular ring segments of non-ferrous material. Said ring segments are substantially flat and are mounted flat on the upper face of said driven wheel along a circumference round the axis thereof References to directions in this specification relate to the switch axis and the direction towards said selector means of the switch is referred to as upward or vertical and perpendicular to that as the horizontal Said ring segments are rigid with the driven wheel and one end of each thereof, hereinafter called the free ends, extend upwards from said upper face substantially in a diagonal direction, that is, neither vertically nor horizontally. Said free ends abut against stops located upon body of said housing. Said ring segments, free ends and said stops form said indexing means, said stops preventing the rotation of said driven wheel upto said release point. Said ring segments therefore, lock said driven wheel in a position and are also referred to as locking strips. Said indexing means also comprise cy cylindrical shaped cams mounted at appropriate locations on said drive wheel such that at said release point they press upon and depress said free ends in a downward direction. When pushed down, said free ends get clear of said stops and release the driven wheel which then under the effect of the stored potential energy of said spring means rapidly moves with a snap to the next position thereof where it is brought to rest by the said system of stops. Said driven wheel is rigid with said driven shaft which forms said switch shaft. The rotation of said driven wheel thereby gets transmitted to the switching modules located on said switch shaft.

It will be observed that with each position change of the switch, said free ends impact on said stops and these impacts are borne by the small cross sectional area of said free ends. This results in somewhat noisy operation and distortion and rapid wear of said free ends. This is one of the drawbacks of the prior art snap action mechanism. Another observation is that said free ends are subjected to repeated operations of bending and unbending which also increase the wear and decrease working life thereof.
This in\'ention offers a novel rotary switch incorporating a novel snap action mechanism which is not subjected to such distortion and rapid wear as the snap action mechanism of prior art. The novel snap action mechanism of the invention has been adapted to both rotary arm type and cam type rotary switches. As cam type switching modules are superior to rotary arm type switching modules in respect of design, scope for standardisation, use of plastics, ease of operation, durability, manufacturing cost and other factors, this invention has paid special attention to the development thereof Furthermore, inclusion of the novel snap action mechanism of the invention in cam type rotary switches makes them particularly relevant for DC applications. This invention has therefore further developed said cam type rotary switches by applying a novel range of contact gaps particularly relevant for DC applications. This is further elaborated hereinbelow.
Thus the cam type rotary switch of this invention incorporates the following two novel features which are of special relevance to DC applications:
i. the novel snap action mechanism: and
ii. a novel range of contact gaps.
In the snap action mechanism of the invention, said locking means comprise:
i. a ring assembly; and
ii. a set of vertically oriented pins.

Said ring assembly comprises a pair of ring like members which are concentric with each other one cylindrical face of one said member abutting against a cylindrical face of the other. This said two members upon assembly substantially constitute a single substantially cylindrical shaped ring referred to hereinabove as said ring assembly. Said members are referred to as inner and outer rings and also as inner and outer locking rings hereinbelow. Said ring assembly is housed in a suitably shaped ring slot in the snap action mechanism housing. A radially outer and inner cylindrical face of said ring assembly are provided with spline means which engage with similar spline means located in said ring slot and prevent rotation of said ring assembly but allowing upward and downward movement thereof
Said pins extend substantially vertically upward passing through holes provided in said driven wheel. At the lower ends thereof, said pins abut said ring assembly while the upper ends thereof terminate at an appropriate distance below the underface of said drive wheel. Said underface is provided with suitably located cam portions at appropriate points on a circumference{around said switch axis) such that when said drive wheel is rotated(by operation of the switch) said cam portions engage with said pins pushing them downwards. Said pins, in turn, push down said ring assembly. Such appropriate points constitute said release points of the snap action mechanism.
In the embodiment described in detail hereinbelow, said pins are substantially cylindrical members but can be of other shapes and cross sections and may be hollow or solid. They are therefore, broadly referred to as pin type members and may have for example, square, hexagonal, elliptical or other section shape and may have splines, slots, keys or flutes thereupon within the scope of the invention.
The downward movement of said assembly takes place against the resistive force provided by a set of springs located below said assembly and within said ring slot such that when the engagement of said cam portions with said ring assembly ceases said ring assembly springs back upwards to the normal(locking) position thereof

A further pair of radially outer and inner cylindrical faces located on said ring assembly is provided with ratchet means which engage with corresponding ratchet means located on corresponding cylindrical faces provided on the underside of said driven wheel. Said two pairs of corresponding ratchet means constitute said locking means and upon mutual engagement lock said driven wheel in positions corresponding to said switch settings. Said ratchet means also provide said indexing in that upon operation of the switch said driven wheel is brought to rest precisely at a position which corresponds with the next said switch setting. One said ratchet means provide locking/indexing for clockwise motion of said driving wheel and the other for the anti-clockwise motion thereof Motion orientations of said drive and driven wheel and other switch components, that is, clockwise and anti-clockwise (C and AntiC) are based on looking downwards from top along the switch axis.
As in the prior art. The drive and driven wheels in the snap action mechanism of the invention are rotatably coupled by two spring means, one for clockwise and the other for anti-clockwise motion thereof Thus. when said switch knob(sector means) is moved from one position to the next one. during part of the
motion thereof, said coupling spring means absort energy til said release point is reached whereat said cam
portions engage said set of pins causing the latter along with said ring assembly to move downwards. This
causes the disengagement of said pair of ratchet means resulting motion being transmitted from said drive
wheel to said driven by means of said coupling spring means. During the brief interval that said pair of
ratchet means remain disengaged the stored energy of said coupling spring means-acts upon said drive
wheel causing accelerated motion thereof to the next position thereof. Thus said driven w heel together
with said pins moves rapidly with a snap to the next position thereof corresponding to the next setting of
the switch. The motion of the driven wheel is transmitted through said switch shaft(driven shaft) to all the
modules located thereupon wherein appropriate contacts thereof move from one position(NO or NC) lo the
other positions thereof with a snap, Where said modules comprise segmental shafts it will be observed that
similar action takes place.

It is interesting to note that at said release point said drive wheel has covered substantially halt of its angular journey from one position to the next while said driven wheel is just about to commence its journey and therefore has the full angular distance to be covered from one position to the next. Just past the release point, therefore, there are two somewhat independent motions to reckon with, that of said drive and driven wheels, the impulse for the former being substantially that provided by the switch operator. The impulse for the latter is provided by the said stored energy held in said coupling means which makes said second motion substantially autonomous of the switch operator. However, if said forward motion is further accelerated by said operator a further impulse may pass on to said second motion. Under the combined influence of said two motions at some point, disengagement of said cam portions and pins occurs resulting in the springing back of said ring assembly upwards. This results in the re-engagement of said ratchet means which provides the indexing of said driven wheel into the next position thereof.
In the snap action mechanism of the invention, the forces acting on said drive and driven wheels are much less severe. In fact, the said drive and driven wheels of the invention are substantially free of the forces perpendicular to the faces thereof which, as observed hereinabove are in the prior art design. Also, the forces arising out of said locking(indexing) and said snap movement of the driven assembly are distributed over a larger surface area and not concentrated as in the prior art design. This favourable situation enables the wide use of plastics in the snap action mechanism of the invention offering considerable saving in material and manufacturing costs and in weight. In fact, in the embodiment of the invention described in detail further hereinbelow, the entire snap action mechanism including the housing thereof comprises plastics mouldings with the exception of said spring means interposed between the drive and driven wheels and said set of springs that support said ring assembly. The snap action mechanisms of the intention also ensures a less noisy operation of the switch.
It may be mentioned that the snap action mechanism of the invention further provides the following advantages;

1. longer life of the components and of the switch as a whole:
2. quicker operation;
3. lesser problems of corrosion; and
4. smoother operation as component friction in the locking means and release mechanism is minimised.
Contact gap is the distance between said two contact surfaces of a contact in the open position thereof The magnitude of said gap is one of the switch design factors which determines the maximum operational voltage and current of a switch.
All other parameters being the same, the maximum operational parameters of a switch are lower for inductive loads than for pure resistive loads. Similarly, for a particular type of load the maximum operational parameters are lower for DC applications than for AC applications. As mentioned hereinabove, these differences in maximum operational parameters arise because of differences in the severity of arcing encountered with different types of loads and between AC and DC applications. Thus a switch rated for a particular voltage and current for AC resistive loads has to be derated for application involving AC inductive loads. Similar derating is also involved when going from AC resistive loads to DC resistive loads and going from DC resistive to DC inductive loads. The degree of derating involved in changing from AC resistive to AC inductive loads is much less than that involved in changing from DC resistive to DC inductive and in general from AC to DC applications. That is, broadly the derating inolved in DC applications is considerable. Figures given in Table I hereinbelow give an idea of the extent of derating imolved in various applications for switches manufactured by the applicants. Table I refers to cam type rotary switches. Similar situation is observed in rotary switches of other makes also.

Clearly derating involves lesser utilisation of switch equipment, in other words, use of bulkier equipment which adds to the cost of an installation. Any innovation therefore, which would reduce the amount of said derating would provide cost benefits particularly for DC applications.
This invention provides for such an innovation. This invention has provided a novel system of said gaps which was observed to considerably reduce the amount of derating involved when considering DC applications.
As mentioned hereinabov e. cam type rotar\yswitches are commonly associated with butt contacts and each load terminal and pole thereof is provided usually with a double butt contact, that is, two butt contacts in series. The range of contact gaps observed in the butt contacts of cam switches of prior art are presented in Table 11 hereinbelow. Table 11 gives the magnitude of said contact gaps and the voltage and current ratings associated therewith and is based on several prior art switches a\'ailable in the market. Said gaps in rotary switches of prior art were all uniformly equal to the values prescribed in Table II or were lower. Table II refers to ccam type switches. No instances were observed of values larger than that shown in Table II. Thus

consideration of larger said gaps and adaptation thereof to cam type rotary switches of the invention is novel. Said system of novel gaps has been applied by this invention both to the switches of the invention and to prior art switches, that is, both rotary switches incorporating the novel snap action mechanism of the invention or snap action mechanism of prior art. Thus, it was found that it was feasible to provide the novel system of gaps also in a rotary cam switch of the prior art having the prior art snap action mechanism and bring down the required derating thereof
Table - n

One of the approaches of prior art to reduce the amount of said derating involved in DC applications is to have higher order butt contacts. Thus, there are cam type rotary' switches in prior art that have three or more butt contacts in series associated with each load tenninal(or pole) thereof The disadvantage associated with this approach is that switches having higher order butt contacts are considerably bulkier. Said approach to a certain extent defeats the purpose of reducing said derating. The notable feature of this

invention is that use of the novel system of gaps of the invention does not involve any significant increase in the size, volume and weight of the switch and in some cases no increase whatsoever.
The novel range of said contact gaps according to this invention is presented herein in the last line of Table II. This invention has established by experimentation that said novel range of gaps is both practical and workable. Thus one obtains a substantial reduction in said derating for DC applications without any substantial modification of the switches. Furthermore, butt contacts having said novel range of gaps when placed in a multiple configuration, that is, more than two contacts in series offer even greater reduction in derating.
According to the invention, therefore, there is provided a rotary switch comprising:
i • a selector means;
i i • a snap action mechanism; and
i i i • one or more switching modules,
said snap action mechanism comprising a housing with a drive and a driven wheel/disc located therein said drive and driven wheels/discs being rigid respectively with the drive and driven shafts, and being rotatabiy coupled together by spring means and provided with locking and release means that prevent rotation of said driven shaft(switch shaft) upto a release point but allow said rotation thereafter characterised in said locking and release means comprising a spring loaded substantially cylindrical ring assembly, a set of substantially vertically oriented pin hke members and a set of cam like members located on said driven wheel, a pair comprising an inner and an outer cylindrical face of said ring assembly being provided with spline means and another with ratchet means, the former engaging with similar means located in said housing and the latter with snnilar means on said driven wheel, said pin like members extending between said ring assembly and drive wheel and passing through said driven wheel, such that at said release points

said cam Uke members push down said pin like members and ring assembly, causing disengagement of said ratchet means and allowing rotation of said driven wheel.
The scope of the invention extends to rotary arm type and cam type rotary switches as the novel snap action mechanism can be simply and easily adapted to both designs. Several design variations of both these types of switches have been considered hereinabove and it will be observed that the novel snap action mechanism can be easily and simply incorporated therein. The rotary switches of the invention may comprise one said switching module or more. Said switching stages may be modular or non-modular as described. The rotary switch of the invention is easily adaptable for use in the wide range of circuits considered hereinabove. Segmentation of shafts has been referred to. The rotary switch of the invention may comprise one said drive shaft and one said driven shaft with said modules located on said driven shaft. Alternatively, each said module may have its own segmental shaft. Said scope also covers the various mounting arrangements for rotary switches considered hereinabove.
The drive and driven wheels are circular but within the scope of the invention may take other shapes. They may be substantially like a wheel or thin like a disc. Also the shape thereof may be substantially cy1indrical or a complex shape within the scope of the invention. Said wheels/discs may be metallic or non-metallic the latter construction offering the advantages of considerable manufacturing and handling con\ enience and cost benefits. Said wheels are of plastics in the embodiment described in detail further hereinbelow.
Said coupling spring means comprise spiral shaped wire springs in the embodiment described but can be of strip also.

Said ring assembly in the embodiment described comprised two Concentric nngs made of plastics. The construction of said ring assembly in two parts is for manufacturing and assembling convenience and cost benefit and within the scope of the invention said ring assembly may be a single piece construction also.
The spring means supporting said ring assembly comprise a set of helical springs but other spring means can also be used.
Construction of said pin type members has ah-easily been elaborated hereinabove. In the embodiment described, said pins are of plastics and are generally cylindrical in shape.
In order to provide a clearer understanding of the invention an embodiment thereof will now be described in detail hereinbelow without limitation to the scope of the invention. In the accompanying drawings;
Fig. 1 shows the axial sectional view of the rotary switch of the invention;
Fig. 2 shows a sectional view of the switching module incorporated in the rotary switch of the invention the section being in a plane perpendicular to the switch axis; and
Fig. 3 show s the profile of a part of the ratchet means.
The embodiment described in detail comprises a cam type rotary switch having one cam type switching module. The switching module comprises two pole-load terminal sets and is provided with a segmental shaft. A double butt contact with the two contacts in series is associated with each said pair of pole-load terminal and is activated by its own cam wheel/disc. It follows that each said module comprises two cam wheel/discs. It will be observed that within the scope of the invention the switch can have one. two or more of said modules.

Reference numerals 1,2 in the accompanying drawings denote the upper and lower parts of the snap action housing, which are fastened together and niounted on mounting plate 10 by fastening means 3. Drive wheel 4 and driven shaft 5 are rigid respectively with the drive shaft 6 and driven shaft 7. Drive shaft 6 is hexagonal in section and at upper end thereof is provided with a threaded hole 8 by means of which handle 9 is fastened to shaft 6. The switch is operated by handle 9 which constitutes said selector means in the present embodiment. Shaft 6 is provided with orientation slots to ensure correct angular correspondence between handle 9 and the switch shaft(driven shaft) 7. The end portion 12 of shaft 6 is of circular cross section and the upper end of shaft 7 is provided with a suitably shaped hollow 13 for location of said end portion 12 sufficient clearance being provided therein to allow independent rotation of shafts 6 and 7. Circlip ensures retention of shaft 6 in drive wheel 4.
Coupling springs 16,17 provide rotatable coupling between drive wheel 4 and driven wheel 5. One said spring provides said coupling for clockwise movement of handle 9 and the other for anticlockwise movement thereof Suitable holes are provided on wheels 4,5 for anchoring ends of springs 16,17 and slots extending in the appropriate direction for providing room for movement of the appropriate spring ends with reference to the clockwise and anti-clockwise operation of handle 9.
The rotary' switch of the embodiment comprises one switching module 18 but the number thereof can be more within the scope of the invention.
Said locking and release means comprise inner locking ring 19 and outer locking ring 20 and are shown assembled together to form said ring assembly 21 which is housed in a ring slot 22 in the housing 1.2. Locking ring assembly 21 is supported by helical springs 23, four numbers of which are provided in this embodiment. Face 24 of ring assembly 21 is provided with spline means that engage with similar means on face 26 located in ring slot 22. Similar face 25 of ring assembly engages with face 27 of ring slot by means of similar spline means. Said set of spline means prevent rotation of ring assembly 21 but allow upw ard

and downward motion thereof Faces 28 and 29, respectively an outer an inner face of ring assembly 21 are provided with ratchet means which engage with similar ratchet systems on outer face 30 and inner face 31 of driven wheel 5. One of said ratchet means(systems) is oriented for providing indexing for driven shaft 5 during clockwise rotation thereof and other for anti-clockwise rotation thereof A cutout of the ratchet systems is shown in Fig. 3.
Pins 32 extend from said ring assembly 21 to drive wheel 4 and pass through drive wheel 5. Cam portions 33 are located at appropriate angular positions on an undersurface of drive wheel 4. Said angular positions correspond to said release points whereat said cam portions push down pins 32 and therewith the ring assembly 21. The downward movement of the ring assembly 21 disengages said ratchet means whereupon drive wheel 5 becomes free to rotate.
Driven wheel 5 remains free to rotate during the short time interval in which said cam portions 33 engage pins 32. With further angular movement of handle 9 and drive wheel 4 therewith, said engagement of cam portions 33 and pins 32 ceases whereupon under action of springs 23 the ring assembly 21 springs back upwards and causes, once again, the engagement of said ratchet means. Pins 32 are solid and of circular cross-section and four nmnbers thereof are pro\ided in the embodiment. Pins 32 are of glass filled polyamide construction. The number of pins depends on the switching angle. Feasibility of said pins having other shapes and cross-sections within the scope of the invention has been elaborated hereinabove.
Drive wheel 4 and driven wheel 5 are substantially solid members in the embodiment described but can be in the form of a disc, that is, substantially thin and slat within the scope of the invention.
Item 34 is the front plate of the switch which is mounted on a control panel with the front plate 34 in front of and mounting plate 10 behind said panel. Fastening of front plate 34 and mounting plate with each other and with said panel is by fastening screws 35. Stop means 11 provide for a limiting stop for handle 9 but are dispensed with in switches where full 360 degrees movement of handle 9 is desired

Script plate 37 is provided to display the switch setting for handle 9 and any other desired information connected with the switch such as operational parameters of the switch and/or loads operated thereby. Script plate 37 is retained by script plate ring 38.
Fig. 2 shows cam wheel/disc 39 the active segments whereof are provided with profiled cam portions. It will be observed that the switch shown is of NC type such that when one of said active segments comes into position said contacts change from closed(NC) to open position. It will also be observed that the double butt contact 40 connects terminals 41 and 42 one of which can be desiginted the pole and other the load terminal and appropriately marked on the switch. Contact slide 43 moves up when an active segment comes into position. When an inactive segment comes into position slide 43 moves down under effect of spring 44. Contact surfaces 46 are the stationery surfaces in respect of one pole-load terminal pair. Similar arrangement exists for the other pole-load terminal pair of the module. Moving contact surfaces 47 are located on contact slide 43.
The invention provides for the driven wheel being rigid with the driven shaft at the lower end of which coupling means are provided to enable coupling between said driven shaft and the shaft of the switching module(s) or the segmental shaft of the first switching module. In the embodiment described, the driven wheel is rigid with the said coupling means and said driven shaft between the former and latter is notional.. This has been done to make the switch as compact as possible and it is stressed that within the scope of the invention said driven shaft may be small, large or of zero length as is the case in the embodiment described.

We claims:
1. A rotary switch comprising:
i. a selector means;
ii. a snap action mechanism, and
ill. one or more switching modules;
said snap action mechanism comprising a housing with a drive and a driven wheel/disc located therein, said drive and driven wheels/discs being rigid respectively with the drive and driven shafts and being rotatably coupled together by spring means and provided with locking and release means that prevent rotation of said driven shaft(switch shall) upto a release point but allow said rotation thereafter cliaracterised in said locking and release means comprising a spring loaded substantially cylindrical ring assembly, a set of substantially vertically oriented pin like members and a set of cam like members located on said driven wheel, a pair comprising an inner and an outer cylindrical face of said ring assembly being provided with spline means and another with ratchet means, the former engaging with similar means located in said housing and the latter With similar means on said drive wheel, said pin like members extending between said ring assembly and drive wheel and passing through said driven wheel, such that at said release points said cam like members push down said pin like members and ring assembly, causing disengagement of said ratchet means and allowing rotation of said driven wheel.
2. Tlie rotary switch as claimed in preceding Claim 1 wherein said switching modules are cam
type.
3. The rotary switch as claimed in preceding Claim 2 wherein said ring assembly comprises two concentric, substantially cylindrical rings.
4. The rotary switch as claimed in any of preceding Claims 2 and 3 wherein said contacts in said modules are of double butt type.

5. The rotary switch as claimed in any of preceding Claims 2 to 4 wherein said contact gaps range from about 2,5 mm to 5 mm for current ratings from about 16 A to 63 A.
A rotary switch substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

Documents:

433-mas-2000 abstract granted.pdf

433-mas-2000 claims granted.pdf

433-mas-2000 description (complete) granted.pdf

433-mas-2000 drawings granted.pdf

433-mas-2000-abstract.pdf

433-mas-2000-claims.pdf

433-mas-2000-correspondence others.pdf

433-mas-2000-correspondence po.pdf

433-mas-2000-description complete.pdf

433-mas-2000-drawings.pdf

433-mas-2000-form 1.pdf

433-mas-2000-form 19.pdf

433-mas-2000-form 26.pdf

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Patent Number

228500

Indian Patent Application Number

433/MAS/2000

PG Journal Number

10/2009

Publication Date

06-Mar-2009

Grant Date

05-Feb-2009

Date of Filing

07-Jun-2000

Name of Patentee

SALZER ELECTRONICS LIMITED

Applicant Address

SAMICHETTIPALAYAM, COIMBATORE - 641 047,

Inventors:

#	Inventor's Name	Inventor's Address
1	RANGASWAMY DORAISWAMY	S/O MR. RANGASWAMY NAIDU, 9/175, RAILWAY STATION ROAD, PERIANAICKENPALAYAM, COIMBATORE - 641 020,
2	RAMASWAMY HARIHARAN	S/O. MR. RAMASWAMY IYER, 473/T, PARSM UNIQUE APARTMENTS, 4TH STREET, K.K PUDUR, COIMBATORE - 641 020,
3	BHUPALAN ARAVINDAN	S/O MR. R. BHUPALAN, 70B, VIDHYANAGAR, VEERAPANDI PIRIVU, JYOTIPURAM P.O., COIMBATORE - 641 047,

PCT International Classification Number

H01H19/54

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA