Title of Invention	APPARATUS FOR CONVERTING LARGE LINEAR DISPLACEMENT INTO SMALL LINEAR DISPLACEMENT AND METHODS FOR MEASURING THE SAME
Abstract	Disclosed herein is an apparatus for converting large linear displacement into smaller proportional linear displacement and method thereof. In this method plunger and ball arrangement is used for the conversion. The lever attached to the valve whose linear displacement is to be measured is attached to a shaft which rotates as the lever moves about the hexagonal nut. This rotational movement of the shaft rotates the plate attached to it at one end. A plunger and ball arrangement attached to the plate. The rotational movement of the shaft with corresponding plate rotation moves the plunger linearly and thereby the large linear displacement gets converted to small linear displacement which is measured by small range LVDT. The error associated with the conversion is also disclosed. Using 2mm range LVDT, 50 mm valve stoke length is measured with less than 1% linearity error.

Title of Invention

APPARATUS FOR CONVERTING LARGE LINEAR DISPLACEMENT INTO SMALL LINEAR DISPLACEMENT AND METHODS FOR MEASURING THE SAME

Abstract

Disclosed herein is an apparatus for converting large linear displacement into smaller proportional linear displacement and method thereof. In this method plunger and ball arrangement is used for the conversion. The lever attached to the valve whose linear displacement is to be measured is attached to a shaft which rotates as the lever moves about the hexagonal nut. This rotational movement of the shaft rotates the plate attached to it at one end. A plunger and ball arrangement attached to the plate. The rotational movement of the shaft with corresponding plate rotation moves the plunger linearly and thereby the large linear displacement gets converted to small linear displacement which is measured by small range LVDT. The error associated with the conversion is also disclosed. Using 2mm range LVDT, 50 mm valve stoke length is measured with less than 1% linearity error.

Full Text	APPARATUS FOR CONVERTING LARGE LINEAR DISPLACEMENT INTO SMALL LINEAR DISPLACEMENT AND METHODS FOR MEASURING THE SAME (1) Field of the Invention (2) In general the present invention relates to methods for linear displacement measurement in the process control and other industrial and laboratory applications. The present invention relates to an apparatus for converting large linear displacement into small linear displacement and methods for measuring the same. More specifically, but without restriction to the particular embodiments hereinafter described in accordance with the best mode of practice the present invention relates the measurement of large linear displacement of control valve travel pin using small range conventionally called position transmitter when 4-20 ma current transmitter is used for the transmission of displacement. (3) Background of the Invention (4) In the process control industry, the control valve opening is measured by measuring the linear displacement of the travel pin. The linear displacement is normally measured using the electronic sensors and transmitted over a long distance. For the electronic measurement of linear displacement, sensors like LVDT (linear variable differential transformer), potentiometer, proximity sensors etc are used. Normal measurement range of these sensors is only few mm distances. So, for large mechanical movement measurement like over 100 mm in control valve etc., it is essential to convert this large mechanical movement into proportionally small mechanical movement. (5) Conventionally, mechanical cam with lever arrangement is used to convert large linear displacement into smaller displacement. In the cam method, one end of the lever is connected to the valve travel pin whose linear displacement is to be measured and the other end of the lever is connected to the shaft. The shaft is so arranged that whenever the travel pin moves linearly, the shaft rotates along its axis. To this rotating axis, the off centered cam is fixed. So, along with the shaft, the off centered cam also rotates. Whenever the cam rotates, it pushes the plunger, which is making contact with it. In effect, whenever the valve travel pin moves the cam rotates and correspondingly the plunger also moves. However to make the plunger movement liner with valve travel pin movement it is essential to shape the cam profile. This demands precision cam profiling work, which is costly. (6) The present invention provides for a new method for the conversion of large linear mechanical movement into smaller linear movement. The present apparatus needs no cam and it produces linear conversion with a simpler arrangement. In this method with out using the cam the linear scaling is obtained. The linear displacement of the valve can be large up to several 100 mm. This large linear displacement can be measured using the transducer like LVDT even though the range of these transducers is only few mm. Then using the LVDT of small range itself large linear displacements can be measured. (7) Related Art (8) Various patented methods and systems are available for the linear displacement measurement for use in the process control industry. (9) US Patent No. 6,694,861 to Glasson titled "Precision Sensor for a Hydraulic Cylinder" dated February 24, 2004 describes a linear displacement measurement method for the piston movement using a corresponding arrangement of a sensor. In this patent, piston movement is converted into rotary motion using a pick-up spool. The pick-up spool rotates due to the motion of the piston. A lead screw is threaded on the spool. The lead screw moves linearly with the linear movement of the piston. Using the LVDT, linear movement is measured. The patent does not disclose any conversion of large linear displacement into small linear displacement. (10) US Patent No. 5,469,053 titled "E/U Core Linear Variable Differential Transformer for Precise Displacement Measurement" to Laughlin dated November 21,1995 discloses E and U core based LVDT based position transmitter. In the present arrangement, in the E core all the three coils of the LVDT is wound and U core is mechanically moved in step with the displacement. There is no linear to angular conversion and thereby conversions of large linear displacement into small linear displacement in this method. (11) US Patent No. 5,277,223 titled "Valve Position Transmitter" to Glockner et.al dated January 11, 1994 discloses a mechanical position indicator for the valve. The patent discloses a mechanical shaft assembly extending from the point where it may be coupled to a valve through the aperture in the base of the indicator assembly to a point where it engages with the indicator member such that any rotation of the shaft assembly is sensed by the said indicator member and some display with respect to such rotation is made. The position of the valve is indicated using the calibrated dial. Herein also there is no conversion of large linear movement to corresponding small linear movement and thereafter measuring the same. (12) US Patent No. 5,056,049 titled "Position Transmitter" to O'Neill dated October 8, 1991 discloses a digital position transmitter. In this, fixed array of physico electric Proximity switches are arranged to locate a physical exciter. The physical exciter is linked to the valve movement, which is to be measured. Using this method, movements in the range from one inch to hundreds of feet can be detected, but the patent does not disclose about the conversion of the large linear displacement into small linear displacement. (13) US Patent No. 4,769,546 titled "Digital Position Transmitter" by Kniffler et.al. dated September 6, 1988 discloses a position transmitter based on diode array. In this method, the diode array detects the point of incidence of light. The diode output indicates the position of the light. The light source is attached to the moving object and the diode position indicates the displacement. In this patent, no linear to angular conversion or angular to linear conversion is done. (14) US Patent No. 4,731,996 by Smith et. al. dated March 22, 1988 discloses potentiometer based position transmitter. In this disclosure a rotary potentiometer is connected to the valve using the conventional mechanical linkages. Independent zero and span adjustment for the 4 to 20 ma current transmitter is the main focus in this patent. The patent does not claim the linkages or for the linearity. (15) Summary of the Invention (16) In accordance with the principal aspect of the present invention disclosed is an apparatus for converting large linear displacement into small linear displacement and methods for measuring the same. (17) In accordance with yet another aspect of the present invention disclosed herein is an apparatus for converting large linear displacement into small linear displacement, the apparatus comprises a lever coupled to a valve the linear displacement of which is to be measured, a shaft mounted on a base connected on one end to the lever by a hexagonal nut and the other end coupled to a plate, the plate being fixed onto the shaft, a plunger operably attached to said fixed plate, wherein the shaft when rotates about an axis at an angle causes the plate to rotate at the same angle, the rotational movement of the shaft causes the plunger to linearly move about its axis enabling the apparatus to convert large linear displacement into small linear displacement. (18) In one another aspect, disclosed herein is an apparatus for converting large linear displacement into small linear displacement wherein the shaft is placed perpendicular to the lever. (19) It is yet another aspect !of the present invention to configure an apparatus for converting large linear displacement into small linear displacement wherein the plate is press fitted on to the shaft. (20) It is yet another aspect of the present invention to configure an apparatus for converting large linear displacement into small linear displacement wherein the plate is fixed on the shaft perpendicular to the longitudinal axis of the lever. (21) It is yet another aspect of the present invention to configure an apparatus for converting large linear displacement into small linear displacement wherein the plunger is conical on the plate end and having a ball attached to the plunger on the conical tip and is connected to the LVDT unit by means of a compression spring. (22) It is yet another aspect of the present invention to configure an apparatus for converting large linear displacement into small linear displacement wherein the ball attached to the conical tip of the plunger is always touching the hardened plate. (23) In yet another aspect of the present invention disclosed herein is an apparatus which converts the large linear displacement to small linear displacement wherein, the shaft is so arranged that whenever the valve stem moves linearly the shaft rotate about its axis. For a linear movement of the valve stem, the stem rotates a certain angle. The angle of rotation of the shaft is related to the stem linear movement by L/X = Tan Q, where L is the linear stem movement and X is the distance between the shaft and the valve stem. Here, the stem movement and the angle of rotation of the shaft are not linear. To convert the stem linear movement into scaled linear movement, a thin metallic plate is attached to the shaft in such a way that whenever the shaft rotates the attached plate also made to rotate in the same axis by the same angle. To a plunger a 1 mm diameter ball is attached to its tip. Whenever the ball is pushed, the plunger also moves along with the ball. The plunger and the ball arrangement are required for the conversion of angular movement in to linear movement. (24) In accordance with yet another preferred embodiment disclosed herein is a method for the measurement of valve stem linear displacement. The method comprises converting the large linear displacement into smaller proportional linear displacement thereby using small range transducers for measuring the same. (25) In another principal aspect of the present invention a method for converting large linear displacement into small linear displacement using the apparatus as disclosed wherein when the lever connected to the valve whose linear displacement to be measured moves linearly, it rotates the lever about the hexagonal nut and inturn the shaft connected to the lever also rotates about the same angle thereby rotating the plate attached to the shaft and the rotational movement of the shaft causes the plunger to linearly move about its axis enabling the apparatus to convert the large linear displacement into small linear displacement. (26) In yet another aspect the present invention discloses a method for converting the large linear displacement into smaller proportional linear displacement wherein when the lever connected to the valve whose linear displacement to be measured moves, it rotates the lever about the and shaft connected to the lever also rotates about the same angle thereby rotating the plate attached to the shaft. The rotation of the shaft pushes the ball and the attached plunger thereby converting the angular movement of the plate to scaled linear movement of the plunger. This linear movement of the plunger pushes the compression springs and the LVDT core in the LVDT unit and the corresponding linear displacement is measured. (27) Brief Description of the Accompanying Drawings (28) FIG 1 is a detailed configuration of the apparatus of the present invention. (29) FIG 2 shows the detailed configuration of the LVDT unit. (30) FIG 3 is a top view of the apparatus showing the attachment of the plunger alongwith the LVDT unit to the hardened plate on the shaft. (31) FIG 4 is a bottom view shows the complete apparatus illustrating the attachment of the lever to the shaft using a hexagonal nut. (32) FIG 5 is an enlarged view showing in detail the attachment of the plunger ball to the hardened plate fitted on the shaft. (33) FIG 6 explains the movement of the plate as the shaft rotates and thereby the plunger taking a new position. (34) FIG 7 explains the errors associated with the plunger and ball arrangement, give the typical measurement scenario. To reduce the error the angle of rotation can be made half by splitting the large linear displacement h about its midpoint. (35) FIG 8 and 9 explains the principle of operation of the apparatus of the present invention. (36) Detailed Description of the Preferred Embodiment (37) FIG 1 shows the detailed configuration of the apparatus of the present invention. A lever 100 having a valve end and a shaft end and the lever is connected to the valve whose linear displacement is to be measured. The shaft 110 is connected to the lever at one end using a hexagonal nut 120 and on the other end a hardened [HSS] plate 130 is press fitted and ground. This plate 130 is also pasted to the shaft 110 using araldite. The shaft 110 is mounted on the base 140. A plunger 150 having a plate end and a LVDT end is also configured. The LVDT unit is configured to measure the linear displacement of the valve stem. The plate end of the plunger is conical and is having a ball attached to the plunger. The ball 170 is a hardened carbide ball partially inserted at the tip of the plunger, which is about a one mm in diameter. The LVDT unit 160 is fitted to the case 180 using the screw 190. A compression spring 200 holds the LVDT unit 160 in its place. An adjustable screw 210 is fixed on the end plate 220. The LVDT unit 160 is connected to the connector 230. (38) FIG 2 explains in detail the configuration of the LVDT unit 160 connected to the plunger. The plunger 150 is connected to a non-metallic core holder 240, which is further coupled to the LVDT core 250. The LVDT consists of a first secondary 260 and a second secondary 270 and the primary 280. The three coils namely the first secondary 260, the second secondary 270 and the primary 280 are wound on the bobbin 290. The outer metallic shell 300 of the LVDT unit 160 is held by the metallic block 310. The end plate 220 holds the adjusting screw 210. The compression spring 200 holds the outer metallic shell 300 of the LVDT unit. (39) The travel pin of the valve is attached to the lever 100. The linear movement of the travel pin rotates the lever 100. The lever 100 in turn rotates the shaft 110 connected to it. The shaft 110 in turn rotates the hardened plate 130. The rotation of the hardened plate 130 pushes the plunger 150 linearly. The axis of rotation of the shaft 110 and the axis of movement of the plunger 150 are perpendicular. The linear movement of the plunger 150 moves the LVDT core 250 inside the LVDT unit 160. (40) FIG 3 and FIG 4 shows the arrangement of the entire apparatus from the top view and the bottom view illustrating in detail the attachments of the plunger 150 and-the ball 170 arrangement to the hardened plate 130 and the lever 100 and shaft 110 arrangement using a circlip 121. (41) FIG 5 shows the closer detailed view of the plunger 150 and ball 170 arrangement and the configurational attachment of the arrangement to the hardened plate 130. The tip of the ball 170 is always in attachment to the hardened plate 130. (42) FIG 6 explains the movement of the plate as the shaft rotates and thereby the plunger taking a new position. As shown in the figure the plunger 150 moves horizontally along the line A. The rotational axis of the shaft 110 is vertical and its center is at Z on the line B. The line A and B are separated by a distance k. Two stoppers 320 are provided to limit the angle of rotation of the plate 130. (43) The free end of the lever 100 is attached to the valve travel pin or to any other linearly moving object. As shown in FIG 9 the valve travel pin move from position B to C. The lever 100 moves from the position OB to OC. The lever used is slotted and hence as the travel pin moves from B to C the lever 100 slide through and hence OC is greater than OB. The angle of rotation of the lever 100 for a displacement of linear distance his P. The plunger 1500 correspondingly moves linearly for an amount X and it is indicated as AD in FIG 9. The distance K is the distance between the axis of rotation of the shaft 110 at point O in -FIG 9 and the point of contact of the ball 170 of the plunger 150 in the plate. In FIG 9 the triangles OAD and OBC are concurrent. So L/K=h/X. So h = (L/K)X. (44) For a given system (L/K) is constant and hence to measure the value of h, we need to measure only X. The displacement X can be measured using the LVDT. The displacement X can be made very small for a large displacement h by a suitable scale factor. It is to be noted that the displacement X is linearly related to h. There is no error at all mathematically as far as conversion large linear displacement in to smaller linear displacement. (45) The angle of rotation of the lever 100 should be less than 90 degree. However when the lever 100 rotates 90 degree, the plate 130 attached to lever 100 also rotates 90 degree. But the plate will not be able to push the plunger 150 and the -ball 170 arrangement when the angle of rotation is above 45 degree. So, it is essential to reduce the angle of rotation. To reduce the angle of rotation the arrangement shown in FIG 8 is used. In this figure the lever OB is 75 mm length. The total displacement his 50 mm. The value of K is 3mm. At mid point of displacement the lever 100 is perpendicular to valve travel h. So the lever moves as shown in the example 18.4 degree both sides, corresponding to 25 mm displacement of valve travel pin in each side. In effect the lever 100 rotates only 18.4 degree for the displacement of 25 mm. For 18.4 degree lever rotation the attached plate 400 also rotates only 18.4 degree. For up to 45 degree rotation the plate 400 easily pushes the plunger -ball arrangement. As shown in FIG 8 corresponding to 25 mm displacement of the valve travel pin the displacement of the plunger 500 is 1mm. (46) In -FIG 7 the plunger 150 and ball 170 arrangement is shown in detail. O is the center of the ball 170, which is partly attached to the plunger 150, as described before. In FIG 7 the line S is the plate 130 which rotates along with shaft 110. As shown in FIG 8 at the midpoint of the displacement h the plate 130 is perpendicular to the plunger 150 and ball 170 assembly. In that case the plate 130 position is S and it makes contact with the ball 170 at point N. As the valve moves the plate 130 also rotates and it makes contact for example at M for the new position SI of the platel30. Actually, plunger 150 is fitted to move only in the horizontal position i.e. along the line ON only. That means as the plate 130 rotates it is pushing the plunger 150 andball 170 arrangement and in the process the point of contact of the ball 170 and the plate 130 also changes. Ideally, the plate 130 should always touch the ball 170 only at N. As the plate 130 rotates, if the ball 170 always touches at point N then displacement produced by the plunger 150 corresponding to the rotation of the plate S will be ideal. That is, the displacement of the plunger 150 will be linear with the displacement of the valve travel pin. When the point of contact of the ball 170 and the plate is at M, then the loss of displacement of the plunger 150 is EN. In effect, the actual displacement of the plunger 150 will be less than what is shown as per our earlier equation. (0047) The loss of distance EN will be there at both sides of N corresponding to the plate 130 movement. That is, if the plate 130 touches at M it looses the distance EN and when it touches at other end at T again it looses the distance EN. This distance loss is an error as shown in FIG 7 The angle of rotation of the plate 130 is P. i.e. Angle SRS is P. So angle MRN = (180-P) Angle ONR =90 degree Angle OMR =90 So angle MON=P So OE =rcos P So EN=r(l-cos P) r is the radius of the ball attached to the plungerl50. The loss of distance is more for more angle of rotation. In this method the angle of rotation is limited to less than 45 degree each side beyond with the shaft plate 400 will not able to exert enough force on the plunger 150. This means shaft 110 can rotate up to little less than 45 degree in each side with respect to point N. In effect the total movement of the shaft is less than 90 degree. If the rotation of the shaft 110 is for example 35 degree in each side then error in displacement measurement is = 0.5(1- cos 35)=0.090 mm. (radius of the ball is taken as 0.5 mm). This measurement error is after scaling. So if the scale factor is 20 then the error in the control valve travel pin measurement would be 20x 0.09 =1.8 mm. (48) As shown in FIG 8 when the travel pin of the valve is in the mid way, the system is adjusted so that the shaft plate 130 touches the extreme point of the ball 170 attached to the plunger 150. That is, it corresponds to the position S;(in FIG 7. The lever length is taken as 75 mm. The travel pin is made to move both sides by 25 mm so that at one end the shaft plate 130 touches the ball 170 at M and at the other end it touches the point T as in FIG 7. As shown in FIG 8, the movement of 25 mm produces 1 mm movement in the plunger 150 for the 75 mm lever length. The total movement of 50 mm of travel pin produces 1 mm movement of the plunger 150 in each side and hence total plunger 150 movement is 2mm. For this the total rotation of the shaft is only 18.4 degree in each side. The displacement error for the angle of 18.4 degree rotation is 0.5 mm for 0.5 mm radius ball. (49) In case if the entire 50mm displacement of the travel pin is only one side with respect to the point N the angle of rotation of the shaft 110 would be 33.66 degree for the same 75 mm lever. For 33.66 degree rotation the error at the plunger end would be 0.2 mm. Clearly the split range gives lesser conversion error. (50) In an actual practical experimental measurement 50 mm valve stroke measurement was carried out using the above ball-plunger arrangement. In case 2mm movement LVDT and its associated circuit was used for the measurement. The valve of K is fixed at 3mm. The lever length is taken as 75 mm. The valve movement is adjusted such that the 25 mm movement of the valve position, the lever was parallel to the ground. That is at mid point of the valve stoke the ball touches the plate at N as shown in figure-6. Then valve is made to move up words 25 mm from the midpoint and similarly the valve was made to move 25 mm down words from the midpoint. The L VDT movement was 2mm. The L VDT core movement is converted in to 4-20 ma output. The open position of the valve was adjusted to 4 ma and the close position of the valve was adjusted to 20 ma. The valve travel pin movement was separately measured using the separate dial gauge of 0.01mm accuracy. The current output was compared with the dial gauge reading. The maximum deviation of the current with respect to dial gauge reading was less than 1%. This much of less error was possible because of the split range operation. In the split range the error in length measurement at the plunger end in the above experiment is 0.025 mm. Total movement of the plunger is only one mm in each side. This corresponds to 2.5 % error in each side. Since the error is symmetrical with respect to the center the total linearity error was less than 1% in the 4 to 20 ma current output. We Claim: 1. An apparatus for converting large linear displacement into small linear displacement, the apparatus comprising: a lever coupled to a valve the linear displacement of which is to be ' measured; a shaft mounted on a base connected on one end to the lever by a hexagonal nut arid the other end coupled to a plate, the plate being fixed onto the shaft; a plunger operably attached to said fixed plate, wherein the shaft when rotates about an axis at an angle causes the plate to rotate at the same angle, the rotational movement of the shaft causes the plunger to linearly move about its axis enabling the apparatus to convert large linear displacement into small linear displacement. 2. The apparatus as claimed in claim 1 wherein the shaft is placed perpendicular to the lever. 3. The apparatus as claimed in claim 1 wherein the plate is press fitted on to the shaft. 4. The apparatus as claimed in claim 1 wherein the plate fixed on the shaft is perpendicular to the longitudinal axis of the lever. 5. The apparatus as claimed in claim 1 wherein the plunger is conical towards the plate end and is connected to the LVDT unit by a compression spring. 6. The apparatus as claimed in claim 5 wherein a ball is attached to the plunger on the conical tip. 7. The apparatus as claimed in claim 5 wherein the ball attached to the conical tip of the plunger is always touching the hardened plate. 8. The apparatus as claimed in claim 1 wherein the LVDT unit is fitted in a case by means of a screw, the LVDT unit is further connected to a connector. 9. A method for converting large linear displacement into small linear displacement using the apparatus as claimed in claim 1 wherein when the lever connected to the valve whose linear displacement to be measured moves linearly, it rotates the lever about the hexagonal nut and inturn the shaft connected to the lever also rotates about the same angle thereby rotating the plate attached to the shaft and the rotational movement of the shaft causes the plunger to linearly move about its axis enabling the apparatus to convert the large linear displacement into small linear displacement.

Full Text

APPARATUS FOR CONVERTING LARGE LINEAR DISPLACEMENT INTO SMALL LINEAR DISPLACEMENT AND METHODS FOR MEASURING
THE SAME
(1) Field of the Invention
(2) In general the present invention relates to methods for linear displacement measurement in the process control and other industrial and laboratory applications. The present invention relates to an apparatus for converting large linear displacement into small linear displacement and methods for measuring the same. More specifically, but without restriction to the particular embodiments hereinafter described in accordance with the best mode of practice the present invention relates the measurement of large linear displacement of control valve travel pin using small range conventionally called position transmitter when 4-20 ma current transmitter is used for the transmission of displacement.
(3) Background of the Invention
(4) In the process control industry, the control valve opening is measured by measuring the linear displacement of the travel pin. The linear displacement is normally measured using the electronic sensors and transmitted over a long distance. For the electronic measurement of linear displacement, sensors like LVDT (linear variable differential transformer), potentiometer, proximity sensors etc are used. Normal measurement range of these sensors is only few mm distances. So, for large mechanical movement measurement like over 100 mm in control valve etc., it is essential to convert this large mechanical movement into proportionally small mechanical movement.
(5) Conventionally, mechanical cam with lever arrangement is used to convert large linear displacement into smaller displacement. In the cam method,

one end of the lever is connected to the valve travel pin whose linear displacement is to be measured and the other end of the lever is connected to the shaft. The shaft is so arranged that whenever the travel pin moves linearly, the shaft rotates along its axis. To this rotating axis, the off centered cam is fixed. So, along with the shaft, the off centered cam also rotates. Whenever the cam rotates, it pushes the plunger, which is making contact with it. In effect, whenever the valve travel pin moves the cam rotates and correspondingly the plunger also moves. However to make the plunger movement liner with valve travel pin movement it is essential to shape the cam profile. This demands precision cam profiling work, which is costly.
(6) The present invention provides for a new method for the conversion of large linear mechanical movement into smaller linear movement. The present apparatus needs no cam and it produces linear conversion with a simpler arrangement. In this method with out using the cam the linear scaling is obtained. The linear displacement of the valve can be large up to several 100 mm. This large linear displacement can be measured using the transducer like LVDT even though the range of these transducers is only few mm. Then using the LVDT of small range itself large linear displacements can be measured.
(7) Related Art
(8) Various patented methods and systems are available for the linear displacement measurement for use in the process control industry.
(9) US Patent No. 6,694,861 to Glasson titled "Precision Sensor for a Hydraulic Cylinder" dated February 24, 2004 describes a linear displacement measurement method for the piston movement using a corresponding arrangement of a sensor. In this patent, piston movement is converted into rotary motion using a pick-up spool. The pick-up spool rotates due to the motion of the piston. A lead screw is threaded on the spool. The lead screw moves linearly with the linear

movement of the piston. Using the LVDT, linear movement is measured. The patent does not disclose any conversion of large linear displacement into small linear displacement.
(10) US Patent No. 5,469,053 titled "E/U Core Linear Variable Differential Transformer for Precise Displacement Measurement" to Laughlin dated November 21,1995 discloses E and U core based LVDT based position transmitter. In the present arrangement, in the E core all the three coils of the LVDT is wound and U core is mechanically moved in step with the displacement. There is no linear to angular conversion and thereby conversions of large linear displacement into small linear displacement in this method.
(11) US Patent No. 5,277,223 titled "Valve Position Transmitter" to Glockner et.al dated January 11, 1994 discloses a mechanical position indicator for the valve. The patent discloses a mechanical shaft assembly extending from the point where it may be coupled to a valve through the aperture in the base of the indicator assembly to a point where it engages with the indicator member such that any rotation of the shaft assembly is sensed by the said indicator member and some display with respect to such rotation is made. The position of the valve is indicated using the calibrated dial. Herein also there is no conversion of large linear movement to corresponding small linear movement and thereafter measuring the same.
(12) US Patent No. 5,056,049 titled "Position Transmitter" to O'Neill dated October 8, 1991 discloses a digital position transmitter. In this, fixed array of physico electric Proximity switches are arranged to locate a physical exciter. The physical exciter is linked to the valve movement, which is to be measured. Using this method, movements in the range from one inch to hundreds of feet can be detected, but the patent does not disclose about the conversion of the large linear displacement into small linear displacement.

(13) US Patent No. 4,769,546 titled "Digital Position Transmitter" by Kniffler et.al. dated September 6, 1988 discloses a position transmitter based on diode array. In this method, the diode array detects the point of incidence of light. The diode output indicates the position of the light. The light source is attached to the moving object and the diode position indicates the displacement. In this patent, no linear to angular conversion or angular to linear conversion is done.
(14) US Patent No. 4,731,996 by Smith et. al. dated March 22, 1988 discloses potentiometer based position transmitter. In this disclosure a rotary potentiometer is connected to the valve using the conventional mechanical linkages. Independent zero and span adjustment for the 4 to 20 ma current transmitter is the main focus in this patent. The patent does not claim the linkages or for the linearity.
(15) Summary of the Invention
(16) In accordance with the principal aspect of the present invention disclosed is an apparatus for converting large linear displacement into small linear displacement and methods for measuring the same.
(17) In accordance with yet another aspect of the present invention disclosed herein is an apparatus for converting large linear displacement into small linear displacement, the apparatus comprises a lever coupled to a valve the linear displacement of which is to be measured, a shaft mounted on a base connected on one end to the lever by a hexagonal nut and the other end coupled to a plate, the plate being fixed onto the shaft, a plunger operably attached to said fixed plate, wherein the shaft when rotates about an axis at an angle causes the plate to rotate at the same angle, the rotational movement of the shaft causes the plunger to linearly move about its axis enabling the apparatus to convert large linear displacement into small linear displacement.

(18) In one another aspect, disclosed herein is an apparatus for converting large linear displacement into small linear displacement wherein the shaft is placed perpendicular to the lever.
(19) It is yet another aspect !of the present invention to configure an apparatus for converting large linear displacement into small linear displacement wherein the plate is press fitted on to the shaft.
(20) It is yet another aspect of the present invention to configure an apparatus for converting large linear displacement into small linear displacement wherein the plate is fixed on the shaft perpendicular to the longitudinal axis of the lever.
(21) It is yet another aspect of the present invention to configure an apparatus for converting large linear displacement into small linear displacement wherein the plunger is conical on the plate end and having a ball attached to the plunger on the conical tip and is connected to the LVDT unit by means of a compression spring.
(22) It is yet another aspect of the present invention to configure an apparatus for converting large linear displacement into small linear displacement wherein the ball attached to the conical tip of the plunger is always touching the hardened plate.
(23) In yet another aspect of the present invention disclosed herein is an apparatus which converts the large linear displacement to small linear displacement wherein, the shaft is so arranged that whenever the valve stem moves linearly the shaft rotate about its axis. For a linear movement of the valve stem, the stem rotates a certain angle. The angle of rotation of the shaft is related to the stem linear movement by L/X = Tan Q, where L is the linear stem movement and X is the distance between the shaft and the valve stem. Here, the

stem movement and the angle of rotation of the shaft are not linear. To convert the stem linear movement into scaled linear movement, a thin metallic plate is attached to the shaft in such a way that whenever the shaft rotates the attached plate also made to rotate in the same axis by the same angle. To a plunger a 1 mm diameter ball is attached to its tip. Whenever the ball is pushed, the plunger also moves along with the ball. The plunger and the ball arrangement are required for the conversion of angular movement in to linear movement.
(24) In accordance with yet another preferred embodiment disclosed herein is a method for the measurement of valve stem linear displacement. The method comprises converting the large linear displacement into smaller proportional linear displacement thereby using small range transducers for measuring the same.
(25) In another principal aspect of the present invention a method for converting large linear displacement into small linear displacement using the apparatus as disclosed wherein when the lever connected to the valve whose linear displacement to be measured moves linearly, it rotates the lever about the hexagonal nut and inturn the shaft connected to the lever also rotates about the same angle thereby rotating the plate attached to the shaft and the rotational movement of the shaft causes the plunger to linearly move about its axis enabling the apparatus to convert the large linear displacement into small linear displacement.
(26) In yet another aspect the present invention discloses a method for converting the large linear displacement into smaller proportional linear displacement wherein when the lever connected to the valve whose linear displacement to be measured moves, it rotates the lever about the and shaft connected to the lever also rotates about the same angle thereby rotating the plate attached to the shaft. The rotation of the shaft pushes the ball and the attached plunger thereby converting the angular movement of the plate to scaled linear

movement of the plunger. This linear movement of the plunger pushes the compression springs and the LVDT core in the LVDT unit and the corresponding linear displacement is measured.
(27) Brief Description of the Accompanying Drawings
(28) FIG 1 is a detailed configuration of the apparatus of the present invention.
(29) FIG 2 shows the detailed configuration of the LVDT unit.
(30) FIG 3 is a top view of the apparatus showing the attachment of the plunger alongwith the LVDT unit to the hardened plate on the shaft.
(31) FIG 4 is a bottom view shows the complete apparatus illustrating the attachment of the lever to the shaft using a hexagonal nut.
(32) FIG 5 is an enlarged view showing in detail the attachment of the plunger ball to the hardened plate fitted on the shaft.
(33) FIG 6 explains the movement of the plate as the shaft rotates and thereby the plunger taking a new position.
(34) FIG 7 explains the errors associated with the plunger and ball arrangement, give the typical measurement scenario. To reduce the error the angle of rotation can be made half by splitting the large linear displacement h about its midpoint.
(35) FIG 8 and 9 explains the principle of operation of the apparatus of the present invention.

(36) Detailed Description of the Preferred Embodiment
(37) FIG 1 shows the detailed configuration of the apparatus of the present invention. A lever 100 having a valve end and a shaft end and the lever is connected to the valve whose linear displacement is to be measured. The shaft 110 is connected to the lever at one end using a hexagonal nut 120 and on the other end a hardened [HSS] plate 130 is press fitted and ground. This plate 130 is also pasted to the shaft 110 using araldite. The shaft 110 is mounted on the base 140. A plunger 150 having a plate end and a LVDT end is also configured. The LVDT unit is configured to measure the linear displacement of the valve stem. The plate end of the plunger is conical and is having a ball attached to the plunger. The ball 170 is a hardened carbide ball partially inserted at the tip of the plunger, which is about a one mm in diameter. The LVDT unit 160 is fitted to the case 180 using the screw 190. A compression spring 200 holds the LVDT unit 160 in its place. An adjustable screw 210 is fixed on the end plate 220. The LVDT unit 160 is connected to the connector 230.
(38) FIG 2 explains in detail the configuration of the LVDT unit 160 connected to the plunger. The plunger 150 is connected to a non-metallic core holder 240, which is further coupled to the LVDT core 250. The LVDT consists of a first secondary 260 and a second secondary 270 and the primary 280. The three coils namely the first secondary 260, the second secondary 270 and the primary 280 are wound on the bobbin 290. The outer metallic shell 300 of the LVDT unit 160 is held by the metallic block 310. The end plate 220 holds the adjusting screw 210. The compression spring 200 holds the outer metallic shell 300 of the LVDT unit.
(39) The travel pin of the valve is attached to the lever 100. The linear movement of the travel pin rotates the lever 100. The lever 100 in turn rotates the shaft 110 connected to it. The shaft 110 in turn rotates the hardened plate 130. The

rotation of the hardened plate 130 pushes the plunger 150 linearly. The axis of rotation of the shaft 110 and the axis of movement of the plunger 150 are perpendicular. The linear movement of the plunger 150 moves the LVDT core 250 inside the LVDT unit 160.
(40) FIG 3 and FIG 4 shows the arrangement of the entire apparatus from the top view and the bottom view illustrating in detail the attachments of the plunger 150 and-the ball 170 arrangement to the hardened plate 130 and the lever 100 and shaft 110 arrangement using a circlip 121.
(41) FIG 5 shows the closer detailed view of the plunger 150 and ball 170 arrangement and the configurational attachment of the arrangement to the hardened plate 130. The tip of the ball 170 is always in attachment to the hardened plate 130.
(42) FIG 6 explains the movement of the plate as the shaft rotates and thereby the plunger taking a new position. As shown in the figure the plunger 150 moves horizontally along the line A. The rotational axis of the shaft 110 is vertical and its center is at Z on the line B. The line A and B are separated by a distance k. Two stoppers 320 are provided to limit the angle of rotation of the plate 130.
(43) The free end of the lever 100 is attached to the valve travel pin or to any other linearly moving object. As shown in FIG 9 the valve travel pin move from position B to C. The lever 100 moves from the position OB to OC. The lever used is slotted and hence as the travel pin moves from B to C the lever 100 slide through and hence OC is greater than OB. The angle of rotation of the lever 100 for a displacement of linear distance his P. The plunger 1500 correspondingly moves linearly for an amount X and it is indicated as AD in FIG 9. The distance K is the distance between the axis of rotation of the shaft 110 at point O in -FIG 9

and the point of contact of the ball 170 of the plunger 150 in the plate. In FIG 9 the triangles OAD and OBC are concurrent. So L/K=h/X. So h = (L/K)X.
(44) For a given system (L/K) is constant and hence to measure the value of h, we need to measure only X. The displacement X can be measured using the LVDT. The displacement X can be made very small for a large displacement h by a suitable scale factor. It is to be noted that the displacement X is linearly related to h. There is no error at all mathematically as far as conversion large linear displacement in to smaller linear displacement.
(45) The angle of rotation of the lever 100 should be less than 90 degree. However when the lever 100 rotates 90 degree, the plate 130 attached to lever 100 also rotates 90 degree. But the plate will not be able to push the plunger 150 and the -ball 170 arrangement when the angle of rotation is above 45 degree. So, it is essential to reduce the angle of rotation. To reduce the angle of rotation the arrangement shown in FIG 8 is used. In this figure the lever OB is 75 mm length. The total displacement his 50 mm. The value of K is 3mm. At mid point of displacement the lever 100 is perpendicular to valve travel h. So the lever moves as shown in the example 18.4 degree both sides, corresponding to 25 mm displacement of valve travel pin in each side. In effect the lever 100 rotates only 18.4 degree for the displacement of 25 mm. For 18.4 degree lever rotation the attached plate 400 also rotates only 18.4 degree. For up to 45 degree rotation the plate 400 easily pushes the plunger -ball arrangement. As shown in FIG 8 corresponding to 25 mm displacement of the valve travel pin the displacement of the plunger 500 is 1mm.
(46) In -FIG 7 the plunger 150 and ball 170 arrangement is shown in detail. O is the center of the ball 170, which is partly attached to the plunger 150, as described before. In FIG 7 the line S is the plate 130 which rotates along with shaft 110. As shown in FIG 8 at the midpoint of the displacement h the plate 130 is perpendicular to the plunger 150 and ball 170 assembly. In that case the plate

130 position is S and it makes contact with the ball 170 at point N. As the valve moves the plate 130 also rotates and it makes contact for example at M for the new position SI of the platel30. Actually, plunger 150 is fitted to move only in the horizontal position i.e. along the line ON only. That means as the plate 130 rotates it is pushing the plunger 150 andball 170 arrangement and in the process the point of contact of the ball 170 and the plate 130 also changes. Ideally, the plate 130 should always touch the ball 170 only at N. As the plate 130 rotates, if the ball 170 always touches at point N then displacement produced by the plunger 150 corresponding to the rotation of the plate S will be ideal. That is, the displacement of the plunger 150 will be linear with the displacement of the valve travel pin. When the point of contact of the ball 170 and the plate is at M, then the loss of displacement of the plunger 150 is EN. In effect, the actual displacement of the plunger 150 will be less than what is shown as per our earlier equation.
(0047) The loss of distance EN will be there at both sides of N
corresponding to the plate 130 movement. That is, if the plate 130 touches at M it looses the distance EN and when it touches at other end at T again it looses the distance EN. This distance loss is an error as shown in FIG 7 The angle of rotation of the plate 130 is P. i.e. Angle SRS is P.
So angle MRN = (180-P) Angle ONR =90 degree Angle OMR =90 So angle MON=P So OE =rcos P So EN=r(l-cos P)
r is the radius of the ball attached to the plungerl50. The loss of distance is more for more angle of rotation. In this method the angle of rotation is limited to less than 45 degree each side beyond with the shaft plate 400 will not able to exert enough force on the plunger 150. This means shaft 110 can rotate up to little less than 45 degree in each side with respect to point N. In

effect the total movement of the shaft is less than 90 degree. If the rotation of the shaft 110 is for example 35 degree in each side then error in displacement measurement is = 0.5(1- cos 35)=0.090 mm. (radius of the ball is taken as 0.5 mm). This measurement error is after scaling. So if the scale factor is 20 then the error in the control valve travel pin measurement would be 20x 0.09 =1.8 mm.
(48) As shown in FIG 8 when the travel pin of the valve is in the mid way, the system is adjusted so that the shaft plate 130 touches the extreme point of the ball 170 attached to the plunger 150. That is, it corresponds to the position S;(in FIG 7. The lever length is taken as 75 mm. The travel pin is made to move both sides by 25 mm so that at one end the shaft plate 130 touches the ball 170 at M and at the other end it touches the point T as in FIG 7. As shown in FIG 8, the movement of 25 mm produces 1 mm movement in the plunger 150 for the 75 mm lever length. The total movement of 50 mm of travel pin produces 1 mm movement of the plunger 150 in each side and hence total plunger 150 movement is 2mm. For this the total rotation of the shaft is only 18.4 degree in each side. The displacement error for the angle of 18.4 degree rotation is 0.5 mm for 0.5 mm radius ball.
(49) In case if the entire 50mm displacement of the travel pin is only one side with respect to the point N the angle of rotation of the shaft 110 would be 33.66 degree for the same 75 mm lever. For 33.66 degree rotation the error at the plunger end would be 0.2 mm. Clearly the split range gives lesser conversion error.
(50) In an actual practical experimental measurement 50 mm valve stroke measurement was carried out using the above ball-plunger arrangement. In case 2mm movement LVDT and its associated circuit was used for the measurement. The valve of K is fixed at 3mm. The lever length is taken as 75 mm. The valve movement is adjusted such that the 25 mm movement of the valve position, the lever was parallel to the ground. That is at mid point of the valve

stoke the ball touches the plate at N as shown in figure-6. Then valve is made to move up words 25 mm from the midpoint and similarly the valve was made to move 25 mm down words from the midpoint. The L VDT movement was 2mm. The L VDT core movement is converted in to 4-20 ma output. The open position of the valve was adjusted to 4 ma and the close position of the valve was adjusted to 20 ma. The valve travel pin movement was separately measured using the separate dial gauge of 0.01mm accuracy. The current output was compared with the dial gauge reading. The maximum deviation of the current with respect to dial gauge reading was less than 1%. This much of less error was possible because of the split range operation. In the split range the error in length measurement at the plunger end in the above experiment is 0.025 mm. Total movement of the plunger is only one mm in each side. This corresponds to 2.5 % error in each side. Since the error is symmetrical with respect to the center the total linearity error was less than 1% in the 4 to 20 ma current output.

We Claim:
1. An apparatus for converting large linear displacement into small
linear displacement, the apparatus comprising:
a lever coupled to a valve the linear displacement of which is to be ' measured;
a shaft mounted on a base connected on one end to the lever by a hexagonal nut arid the other end coupled to a plate, the plate being fixed onto the shaft;
a plunger operably attached to said fixed plate, wherein the shaft when rotates about an axis at an angle causes the plate to rotate at the same angle, the rotational movement of the shaft causes the plunger to linearly move about its axis enabling the apparatus to convert large linear displacement into small linear displacement.
2. The apparatus as claimed in claim 1 wherein the shaft is placed perpendicular to the lever.
3. The apparatus as claimed in claim 1 wherein the plate is press fitted on to the shaft.
4. The apparatus as claimed in claim 1 wherein the plate fixed on the shaft is perpendicular to the longitudinal axis of the lever.
5. The apparatus as claimed in claim 1 wherein the plunger is conical towards the plate end and is connected to the LVDT unit by a compression spring.
6. The apparatus as claimed in claim 5 wherein a ball is attached to the plunger on the conical tip.
7. The apparatus as claimed in claim 5 wherein the ball attached to

the conical tip of the plunger is always touching the hardened plate.
8. The apparatus as claimed in claim 1 wherein the LVDT unit is
fitted in a case by means of a screw, the LVDT unit is further connected to a
connector.
9. A method for converting large linear displacement into small linear
displacement using the apparatus as claimed in claim 1 wherein when the lever
connected to the valve whose linear displacement to be measured moves linearly,
it rotates the lever about the hexagonal nut and inturn the shaft connected to the
lever also rotates about the same angle thereby rotating the plate attached to the
shaft and the rotational movement of the shaft causes the plunger to linearly move
about its axis enabling the apparatus to convert the large linear displacement into
small linear displacement.

Documents:

1054-che-2003 description (complete) granted.pdf

1054-che-2003-abstract.pdf

1054-che-2003-claims.pdf

1054-che-2003-correspondnece-others.pdf

1054-che-2003-correspondnece-po.pdf

1054-che-2003-description(complete).pdf

1054-che-2003-description(provisional).pdf

1054-che-2003-drawings.pdf

1054-che-2003-form 1.pdf

1054-che-2003-form 18.pdf

1054-che-2003-form 5.pdf

« Previous Patent

Next Patent »

Patent Number

229188

Indian Patent Application Number

1054/CHE/2003

PG Journal Number

12/2009

Publication Date

20-Mar-2009

Grant Date

13-Feb-2009

Date of Filing

26-Dec-2003

Name of Patentee

JOSE, MATTAPPALLIL

Applicant Address

41, KEREGUDDADAHALLI, CHIKKABANAVARA, P.O., BANGALORE 560 090,

Inventors:

#	Inventor's Name	Inventor's Address
1	JOSE, MATTAPPALLIL	41, KEREGUDDADAHALLI, CHIKKABANAVARA, P.O., BANGALORE 560 090,
2	GUNASEKARAN, KALAIMATHI	41, KEREGUDDADAHALLI, CHIKKABANAVARA, P.O., BANGALORE 560 090,

PCT International Classification Number

G01B5/02

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA