Title of Invention

SEWING MACHINE COMPRISING A SENSOR FOR WORK-PIECE-THICKNESS DETECTION.

Abstract

A sewing machine with a sensor for the detection of the thickness of a work piece, characterized in that the sensor is an ultrasonic sensor, comprising the following features: a base plate (2) with a bearing plate (23) for a work piece (24; 24, 25); a standard (3) which is formed on the bearing plate (23), having an adjoining arm (4) comprising a head (5); a stitch-forming place (21) with a sewing needle (11); a feed arrangement (30) for feeding the work piece (24; 24, 25) in a feed direction (31); the sensor (34) having a circuit (36) for transmission, to an electric control system (38), of a measured value that corresponds to the thickness (dl; d2) of the work piece (24; 24, 25) upstream of the stitch-forming place (21); the control system (38) comprising a unit (37) for transmission of alter commands in dependence on the detected thickness (dl, d2) to at least one servo component (15,29) and/or a driving motor (9) on the sewing machine (1); wherein the sensor is an ultrasonic sensor (34) which comprises a transmitter part (34a) and a receiver part (34b); and wherein the transmitter part (34a) and the receiver part (34b) are disposed upstream of the stitch-forming place (21) in the feed direction (31) and above the bearing plate (23) at a distance (a) therefrom on the head (5) of the sewing machine (1).

Full Text

Sewing Machine Comprising a Sensor for Work-Piece-Thickness Detection The invention relates to a sewing machine comprising a sensor for work- piece-thickness detection, comprising the following features: a base plate with a bearing plate for a work piece; a standard which is formed on the bearing plate, having an adjoining arm including a head; a stitch-forming place with a sewing needle; a feed arrangement for feeding the work piece in a feed direction; the sensor having a circuit for transmission, to an elec- tric control system, of a measured value that corresponds to the thickness of the work piece upstream of the stitch-forming place; the control system comprising a unit for transmission of alter commands in dependence on the detected thickness to at least one servo component and/or a driving motor on the sewing machine. A sewing machine of the generic type is known from DE 35 28 295 C2 (corresponding to U.S. patent 4 686 917), in which the thickness of a work piece is sensed by a sensing lever that is disposed upstream of the point where the stitch is formed, seen in the direction of sewing, the angular po- sition of the sensing lever being converted by an electronic measuring ele- ment, into corresponding measured values. Depending on a measured value, alter commands are transmitted via an electronic control system to servo motors of the sewing machine, for instance for adjusting the lifting stroke of pressure feet of alternating operation. Drawbacks reside in that the sensing lever is located in the working area directly upstream of the pressure feet where the operator handles the work piece. Inserting the work piece in the stitch forming area of the sewing ma- chine must take place carefully for the work piece to be positioned under the sensing lever. When sewing, the operator must ensure unimpeded op- eration of the sensing lever. Moreover, the sensing lever interferes with work piece supply when arch-shaped seams are produced. Concluding it can be said that disturbing effects of the sensing lever on an operator's working area cannot be avoided. DE 37 17 601 Al teaches a work piece detector for a sewing machine, in which the position of a sensing lever that is located upstream of the stitch forming place of the sewing machine is kinematically coupled with a po- tentiometer. Measured values are emitted corresponding to the thickness of the scanned work piece. Although work-piece thickness is detectable in this way, the drawbacks of a sensing lever also apply in the case of this work piece detector. It is an object of the invention to provide a sewing machine of the generic type with a sensor, ensuring an unimpeded mode of operation. According to the invention, this object is attained by the features which consist in that the sensor is an ultrasonic sensor which comprises a trans- mitter part and a receiver part; and in that the transmitter part and the re- ceiver part are disposed upstream of the stitch-forming place in the feed direction and above the bearing plate at a distance therefrom on the head of the sewing machine. The measures according to the invention ensure that the distance from the sewing-machine bearing plate and from a work piece placed thereon can be determined on the basis of an interval between emit- ted sound pulses and the receipt of an echo signal. This renders an opera- tor's working area free from any influences. The property of the ultrasonic sensor of timing the interval between transmission and echo-return instead of sensing sound intensity ensures that interfering environmental effects are nearly precluded, making a wide spectrum of materials detectable, such as leather or velvet, regardless of their color, transparency and other physical properties. Another advantage results from the fact that thickness meas- urement may take place even in dusty surroundings. The transmitter part and the receiver part being disposed in a casing helps put into practice a space-saving way of construction so that an operator's view of the working area is nearly unimpeded. The improvement, according to which the control system comprises a first memory for recording a value that represents the distance between the sen- sor and the bearing plate of the sewing machine, and a second memory for recording a second value that represents the thickness of the work piece, enables the distance by which the sensor is disposed above the bearing plate of the sewing machine to be detected automatically. This is accompa- nied with the advantage that the sensor can be mounted on the arm of the sewing machine, using components of dimensional variation. Mounting the sensor after the machine has been repaired is also possible, needing no spe- cial alignment job. Furthermore, this improvement enables the value that represents the distance between the sensor and bearing plate of the sewing machine to be updated permanently, precluding any effects of modified air properties (pressure, temperature, humidity) on the measured result. When the control system comprises a third memory for recording a third value that represents the total thickness of the first work piece plus a sec- ond work piece, this offers the possibility of processing thickenings - which means quite generally work pieces of varying thickness - by a cor- responding alter function being triggered. A special advantage is accomplished by the further development compris- ing the features which consist in that the control system comprises a fourth memory for recording a maximum thickness as a fourth value, and a com- parator circuit for determining the difference between the fourth value and the second value or the third value, and for preventing an alter command from being triggered when the difference is less than or equal to zero, which enables a person, for feed of a work piece, to operate in the working area of the sensor directly upstream of the stitch forming place. In this case, measured results are disregarded which the ultrasonic sensor passes to the control system upon detection of an operator's finger or hand and which exceed a given maximum thickness. Further advantages, features and details of the invention will become ap- parent from the ensuing description of an exemplary embodiment, taken in conjunction with the accompanying drawings in which Fig. 1 is a view of the head of a sewing machine; Fig. 2 is an elevation of the sewing machine, on a reduced scale, in ac- cordance with the arrow II of Fig. 1; and Fig. 3 is a diagrammatic illustration of part of the sewing-machine control system. A sewing machine 1 comprises a base plate 2 with a standard 3 which ex- tends upwards therefrom and an elbowed arm 4 which ends in a head 5. An arm shaft 6 is run rotatably in the arm 4; on the side of the standard, it is joined to a handwheel 7. By way of a belt drive 8, the handwheel 7 is con- nected to a driving motor 9 which is fixed to the arm 4. Within the head 5, the free end of the arm shaft 6 is conventionally con- nected to a crank drive (not shown) for actuation of a needle bar 10, the end of which facing the base plate 2 being provided with a sewing needle 11. A thread lever 12 is in driving connection with the crank drive, its free end 13 projecting through a hole 14 in the head 5. By the side of the hole 14, provision is made on the head 5 for an electromagnetically actuated thread tightener 15. Eyelets 16, 17 are disposed on the arm 4. A thread 18 is sup- plied from a bobbin (not shown) to the sewing machine 1, this thread 18 being led through the eyelet 16 to the thread tightener 15, from where it is led through an eyelet in the end 13 of the thread lever 12 and from there through the eyelet 17 and finally through the eye of the sewing needle 11. A needle plate 19 is mounted on the base plate 2, having a stitch hole 20 for the needle 11 to pass through. A hook (not shown) is located under- neath the needle plate 19, working as a stitch forming element that cooper- ates with the sewing needle 11. The needle 11 and the stitch hole 20 consti- tute a stitch forming place 21. In the vicinity of the stitch hole 20, provision is made for a feeder 22 which passes through corresponding recesses in the needle plate 19. A first work piece 24 of a thickness dl is placed on the top side of the base plate 2 which is also called the bearing plate 23. As seen in Fig. 1, a second work piece 25 of a width b lies on top of the first work piece 24. The sec- ond work piece 25 can for example be a stripe or piping that is to be sewn on the first work piece 24 or generally any other type of work piece thick- ening. This work piece thickening of two work pieces 24, 25 placed on top of each other has a thickness d2. A pressure foot 26 supports itself on the work piece 24 while a second pressure foot 27 is in an elevated position as seen in Fig. 1. The pressure feet 26, 27 are components of a so-called pressure arrangement 28 of alter- nating operation which is in driving connection with the arm shaft 6. The pressure feet 26, 27 can be lifted alternately off the top side of the work piece 24 or 24 and 25 by a lift c, the lift c being modifiable by a servo component 29 during the run of the sewing machine 1. The pressure ar- rangement 28 is known from the document mentioned at the outset. The mentioned feeder 22 is part of a feed arrangement 30 which is in driv- ing connection with the arm shaft 6. In combination with the pressure ar- rangement 28, the feed arrangement 30 exercises a feed motion on the work piece 24 or the work pieces 24, 25 in a feed direction 31. A holding arm 33 is tightly mounted on a bottom surface 32 of the head 5, the free end of which extends counter to the feed direction 31 where it is provided with a sensor 34. The sensor 34 is an ultrasonic sensor, emitting sound waves in a frequency range of 0.1 to 1 megahertz and receiving cor- responding reflected waves. Ultrasonic sensors of this type are commercial in the market. A dashed line in Fig. 1 symbolically illustrates a beam path 35 of these sound waves. Seen in the feed direction 31, the beam path 35 is located at a distance e upstream of the stitch forming place 21. According to Fig. 3, the sensor comprises a transmitter part 34a and a re- ceiver part 34b, both parts being triggered by an electronic circuit 36. Cor- respondingly, an emitted beam 35a is illustrated on the transmitter part 34a and a reflected beam 35b on the receiver part 34b. In the preferred embodiment seen in Figs. 1 and 2, the sensor 34 is config- ured in such a way that the transmitter part 34a, the receiver part 34b and the circuit 36 are accommodated in a single casing. In this case, the sensor body of sintered material is used as a receiver part as well as a transmitter part, alternately switching from one to the other in high-frequency se- quence. Sensors of this type excel by needing comparatively little space. Accordingly, Fig. 3 shows the sensor 34 with the beam path 35 roughly outlined by a dashed line with arrows at both ends. The circuit 36, the driving motor 9 (diagrammatically illustrated as a block 9a in Fig. 3), the thread tightener 15 (diagrammatically illustrated as a block 15a in Fig. 3), and the servo component 29 (diagrammatically illus- trated as a block 29a in Fig. 3) are electrically connected to an input-output unit 37 which is part of an electronic control system 38. The input-output unit 37 is connected to a microprocessor 39 which comprises a computer part 40 having a computer circuit 41, a comparator circuit 42 and a mem- ory area 43 with a first memory 44, a second memory 45, a third memory 46 and a fourth memory 47. The control system 38 is electrically connected to an operating panel 48 which is equipped with a display unit 49 and a keyboard 50. The mode of operation of the sewing machine 1 is as follows: It is assumed that, with the current turned on and compressed air provided for any possible pneumatic servo components, the sewing machine 1 is ready for operation, in which condition the bearing plate 23 is free, without any work piece placed thereon for sewing. Correspondingly, the emitted beam path 35 of the sensor 34 acts on the bearing plate 23. This is effected by the sensor 34 being triggered, whereby a pre-determined number of sound waves is emitted by the transmitter part 34a and the sound waves reflected by the bearing plate 23 are then received as an echo by the re- ceiver part 34b. During this process, the time interval between the begin- ning of sound wave emission and echo receipt is measured. The interval is a value that is proportional to the distance a of the sensor 34 from the bear- ing plate 23, the distance a thus being measured and then recorded in the first memory 44. This described process is steadily repeated. Upon insertion of the work piece 24, the difference in distance, a - dl, is measured in the same way, from which the computer circuit 41, in combi- nation with the distance a determined before, can calculate the thickness dl which is then recorded in the second memory 45. Upon determination of the thickness dl of the work piece 24, the control system 38 causes regula- tion variables of the motor 9 and the servo components 15 and 29 to be set so that the sewing machine is automatically adjusted for sewing the work piece 24. Depending on the respective thickness of the work piece, pre- selected adjustment data are activated which are allocated to the respective thickness; these data are contained in a table that is stored in the memory area 43. As the work piece 24 advances during sewing, an approaching edge 51 will arrive in the working range of the sensor 34 which determines the thickness d2 in the manner specified and records it in the third memory 46. Being aware of the constructionally given distance e of the sensor 34 from the stitch forming place 21, the control system 38 takes into account that a de- fined number of stitches must still be sewn with the motor 9 and servo components 15 and 29 adjusted as before. Once this number of stitches has been worked, the control system 38 causes the motor 9 and servo compo- nents 15 and 29 to be adjusted anew, this renewed adjustment correspond- ing to the sewing conditions that allow for the thickness d2 of the work pieces 24 and 25. As the sewing process proceeds, a tail edge 52 of the work piece 25 arrives in the working range of the sensor 34, which again causes the motor 9 and the servo components 15 and 29 to be adjusted correspondingly as upon detection of the approaching edge 51. Upon operation of the sewing machine 1, the computer part 40, together with the comparator circuit 42, permanently compares the determined dis- tances d 1 and d2 to a distance D which is a maximum recorded in the fourth memory 47. Fig. 1 illustrates the maximum by a dot-dashed line 53. This proceeding ensures that measured results, which are sensed when an operator handles the work piece in the working range of the sensor 34, will be ignored ultimately so that these measured results prevent an alter func- tion of the servo components 9, 15, 29 from being triggered when the dif- ference between the determined work piece thickness dl or d2 is less than or equal to zero. List of Reference Numerals 1 sewing machine 2 base plate 3 standard 4 arm 5 head 6 arm shaft 7 handwheel 8 belt drive 9 driving motor 10 needle bar 11 sewing needle 12 thread lever 13 end 14 hole 15 thread tightener 16 eyelet 17 eyelet 18 thread 19 needle plate 20 stitch hole 21 stitch-forming place 22 feeder 23 bearing plate 24 first work piece 25 second work piece 26 pressure foot 27 pressure foot 28 pressure arrangement 29 servo component 30 feed arrangement 31 feed direction 32 surface 33 holding arm 34 sensor,, 34a transmitter part, 34b receiver part 35 beam path 36 circuit 37 input-output unit 38 control system 39 microprocessor 40 computer part 41 computer circuit 42 comparator circuit 43 memory area 44 first memory 45 second memory 46 third memory 47 fourth memory 48 operating panel 49 display unit 50 keyboard 51 approaching edge 52 tail edge 53 line dl,d2, D thickness a, e distance b width c lift of stroke WE CLAIM: 1. A sewing machine with a sensor for the detection of the thickness of a work piece, characterized in that the sensor is an ultrasonic sensor, comprising the following features: (a) a base plate (2) with a bearing piate (23} for a work piece (24; 24, 25); (b) a standard (3) which is formed on the bearing plate (23), having an adjoining arm (4) comprising a head (5); (c) a stitch-forming place (21) with a sewing needle (11); (d) a feed arrangement (30) for feeding the work piece (24; 24, 25) in a feed direction (31); (e) the sensor (34) having a circuit (36) for transmission, to an electric control system (38), of a measured value that corresponds to the thickness (dl; d2) of the work piece (24; 24, 25) upstream of the stitch-form ing place (21); (0 the control system (38) comprising a unit (37) for transmission of alter commands in dependence on the detected thickness (dl,d2) to at least one servo component (15,29) and/or a driving motor (9) on the sewing machine (1); (g) wherein the sensor is an ultrasonic sensor (34) which comprises a transmitter part (34a) and a receiver part (34b); and (h) wherein the transmitter part (34a) and the receiver part (34b) are disposed upstream of the stitch-forming place (21) in the feed direction (31) and above the bearing plate (23) at a distance (a) therefrom on the head (5) of the sewing machine (1). 2. A sewing machine as claimed in claim 1, wherein the transmitter part (34a) and the receiver part (34b) are disposed in a casing. 3. A sewing machine as claimed in claim 1, wherein the control system (38) comprises a first memory (44) for recording a value that represents the distance (a) between the sensor (34) and the bearing plate (23) of the sewing machine (1), and a second memory {45} for recording a second value that represents the thickeness (dl) of the work piece (24), 4. A sewing machine as claimed in claim3, wherein the control system (38) comprises a third memory (46) for recording a third value that represents the total thickness of the first work piece (24) plus a second work piece (25). 5. A sewing machine as claimed in claim 3, wherein the control system (38) comprises a fourth memory (47) for recording a maximum thickness (D) as a fourth value, and a comparator circuit (42) for determining the difference between the fourth value and the second value or the third value, and for preventing an alter command from being triggered when the difference is less than or equal to zero. A sewing machine with a sensor for the detection of the thickness of a work piece, characterized in that the sensor is an ultrasonic sensor, comprising the following features: a base plate (2) with a bearing plate (23) for a work piece (24; 24, 25); a standard (3) which is formed on the bearing plate (23), having an adjoining arm (4) comprising a head (5); a stitch-forming place (21) with a sewing needle (11); a feed arrangement (30) for feeding the work piece (24; 24, 25) in a feed direction (31); the sensor (34) having a circuit (36) for transmission, to an electric control system (38), of a measured value that corresponds to the thickness (dl; d2) of the work piece (24; 24, 25) upstream of the stitch-forming place (21); the control system (38) comprising a unit (37) for transmission of alter commands in dependence on the detected thickness (dl, d2) to at least one servo component (15,29) and/or a driving motor (9) on the sewing machine (1); wherein the sensor is an ultrasonic sensor (34) which comprises a transmitter part (34a) and a receiver part (34b); and wherein the transmitter part (34a) and the receiver part (34b) are disposed upstream of the stitch-forming place (21) in the feed direction (31) and above the bearing plate (23) at a distance (a) therefrom on the head (5) of the sewing machine (1).

Documents:

250-kol-2004-granted-abstract.pdf

250-kol-2004-granted-claims.pdf

250-kol-2004-granted-correspondence.pdf

250-kol-2004-granted-description (complete).pdf

250-kol-2004-granted-drawings.pdf

250-kol-2004-granted-examination report.pdf

250-kol-2004-granted-form 1.pdf

250-kol-2004-granted-form 18.pdf

250-kol-2004-granted-form 2.pdf

250-kol-2004-granted-form 3.pdf

250-kol-2004-granted-form 5.pdf

250-kol-2004-granted-pa.pdf

250-kol-2004-granted-priority document.pdf

250-kol-2004-granted-reply to examination report.pdf

250-kol-2004-granted-specification.pdf

250-kol-2004-granted-translated copy of priority document.pdf