US2392889A - Motion reproducing mechanism - Google Patents

Description

Jan. 15, 1946. J. D. TEAR MoTIoN REPRODUGING MEGHANlsM v 32033 .luws...

4 Sheets-Sheet' 1 Filed April 14,. 1943 lllllllllllllllllll llllllllllllll ATTORNEY Jan. 15, 1946. J. D. TEAR MOTION REPRODUCING MECHANISM Filed lApril 14, 1943 4 She'ets-Sheetr 2 l IN VEN TOR J A M Las DTE AR 4i/@HW- ATTORNEY Jan. 15, 1946. J. D. TEAR MOTION REPRODUG ING MECHANISM Filed April 14, 1943 4 Sheets-Sheet 3 v ATTORNEY MOTION REPRODUCING MECHANISVI Filed April 14, 1943 4 Sheets-Shree*I 4 fr oo` p (\'l H v f 'l I INVENTOR JAMES D..TEAR

` ATTORNEY J. D. TEARl l2,392,889

Patented Jan. 15, 1946` UNITED STATES -PATENT DFFI'CE Monos nnrnonucmc MnonANrsM Janes n. rear, Great Neer. N. Y., mignonuv Ford Instrument Company, Inc., Long Island City, N. Y., a corporation of New York Application April 14, 1943, Serial No. 482,971 (ci. ca -53) 7Claims.

This invention relates to motion reproducing or follow-up mechanism in which the movement of one member, herein referred to as the primary element, is to be reproduced by another member, herein termed the secondary or follower element.

More particularly this invention has to do with v such mechanism in which the primary element is onein which the power device is a variable speed motor or drive and the error, represented by the output of the differential, is utilized directly to control the speed so as vto obtain the desired reproduction of motion. customarily the diierential output controls a speed regulating device for the motor or drive through a fixed ratio connection so that the speed oi the response and hence of the elimination of the error is a direct function of the error. Conversely, when the secondary element is being driven at the same speed as the primary element there is an inherent positional error proportional to the speed.

It is recognized that such controls are not ideal in eilecting synchronization when there is a substantial error to be erased. Acdording to the.'

characteristicsgof the system they either result in too rapid acceleration of the response'when the error islarge or they are `sluggish and require an undue time to synchronize:

The object vof this invention is to provide a control in such,` systems which will eect synchronization in a minimum. of time and at a predetermined acceleration which will be best suited to the characteristics of the system. Specically it is an object to make the acceleration substantially uniform while synchronizing and of a value suited to the power device and load conditions and which will bring the members into synchronism promptly and at the maximum speedconsistent with the synchronizing conditions.

According to the invention the improvement in synchronizing is obtained by making the speed-of the response or in certain forms, the rate of removal of the error proportional to the square root oi the error. This is according to the law of uniformly accelerated motion, wherein the instant velocity is proportional to the square root of the distance moved. To apply this to the problem under consideration. if the `Aspeed of the responseor the speed at which the error is being removed be represented by V, and the error or distance from synchronous relation of the elements be D, and the predetermined or chosen acceleration be denoted by a, then the equation which it is desired to apply in the control mechanism is V=\/2aD.

To maintain this condition the ratio between Athe error D and the rate of the response or the rate ofI removal of the error V must constantly change as synchronism is approached. By the invention thischange in ratio is accomplished by a cam mechanism introduced in the mechanical connection between the output of the diilerential means and the control member of the speed regulating device. The cam surface is so formed that the control member is positioned to provide a velocity of output ofthe speed regulating device which is proportional to the square root of the error D. .The acceleration is chosen according to the characteristics of the particular system.

The invention lwill now be explained in connection with the diagrams and apparatus illustrated in the accompanying drawings and will be thereafter pointed out in claims.

Fig. 1 is a schematic representation of an a paratus embodying the invention;

Fig. V2 is a graph showing curves representing the ratio between the error, D, and the rate of removal of the error, V, both when the rate of removal is proportional to thesquare root of the error, according to the present' invention and, by

y way of comparison, when the rate of removaLV.

modiilcation of the hydraulically operated mechanism.

is proportional to the error, D, as in prior systems;

Fig. 3 is a graph showing curves representing the progressive values of the error, D, during the synchronizing period for the two conditions depicted in the graph of Fig. 2, and also a curve representing the progressive values of the rate V under the depicted condition when, as contemplated by the invention, the rate of removal of the error or the speed of the response is proportional to the square root of the error;

Fig. 4 is a schematic representation of an embodiment of the invention in which the speed regulating member of the variable speed power device is positioned by an hydraulically operated relay mechanism;

Fig. 5- is a view similar to Fig. 4 but showing a modication of the hydraulically operated mechanism; and

Fig. 6 is a similar view showing a still further The principle will be explained rst by reference to the form of mechanism represented inthe diagram of Fig. 1. The shaft I represents the primary element and the shaft 2 represents the secondary element. 'I'he differential 3 is connected between these and the output of the diierential drives shaft 4. The constant-speed power motor 5 operates the shaft 2 through a variable speed drive 6 the rate element or control member of which is a ball carriage 'I the position of which is determined 4by the diiferential output shaft 4.

Heretofore the positioning of the speed element has been in direct proportion to the error, that is, V=kD in which 1c is a selected conversion curve. When the error becomes small the slope of Y the curve following the equation V=\/2aD ap" constant. In other words there has been a fixed,

drive ratio between'the members corresponding to the shaft 4 and ball carriage 1, such as would be the case, for example, if the arm 8 oi' the ball carriage were provided with a rack coacting with a pinion on the shaft 4.l Such a drive gives accelerations and speeds varying with the error when synchronizing, and introduces an error proportional to the speed while following.

According to the invention the ratio of movement between the members corresponding to the shaft 4 and the ball carriage or speed regulating member 1 is a variable such that,l when synchronizing, the acceleration of the output of the variable speed drive is a predetermined constant. As shown this is effected through a cam and cam follower introduced in the drive, the cam surface being shaped to correspond to the curve repre.

senting the ratio V=\/2aD. As shown in Fig. 1 this cam surface is a groove 9 on the cylindrical cam inf and a pin II on the arm 8 serves as a cam follower. The positioning of the speed element will therefore be such as to effect the ratio represented by the stated equation.

This ratio for a given value of acceleration is shown in Fig. 2. There by way of illustration a value of eight is selected for the acceleration. That makes the value of V, which may be taken as the position of the ball carriage 'l, or the velocity of the response as represented by the rate of movement of the shaft 2 or the rate of erasure of the error as represented by the movement of shaft 4, all three of which are proportional, equal to four times the square root of the pp sition of the shaft 4, that is, V=\/28D or V=4\/D. This assumes for the sake of simplicity, that the shaft I is stationary for the time being, or, in other words, that the shaft I has introduced a certain primary movement which moved the ball carriage Thehcurve of Fig. 2 which satisfies the equation V=4\/D is numbered 9 for the reason that it determines the shape of cam groove 9 for this selected value of a, it being understood that the curve of Fig. 2 represents only one-half of the cam groove, the other half being the reverse preaches so near the vertical that a cam made strictly in accordance therewith would be inoperative, for this reason the groove 8 on the cam I0 is made of uniform lead near the center or zero positionl so that the operation over this portion of the cam is in accordance with the equation Assuming twenty-five to be the maximum value of error D and twenty' to be the maximum-value of velocity V, a constant ratio between V and D as previously used would be represented by the curve 9a of Fig. 2, in this case of course a straight off center a certain amount, and that the motor 5 through the variable speed drive is moving the shaft 2 a corresponding amount. At the end of this response movement the shaft 2 will be in agreement with the movement introduced by shaft I and the ball carriage will be back at the center position. The principle is the same, of course, if shaft I continues to move and shaft 2 accelerates to come into speed synchronism with it.`

for the assumed acceleration.

line. The ratio or constant lc in this case is eight tenths, that is, V=kD or V=.8D.

By the use in connection with the invention of the selected acceleration of eight (say 8 per second per second), the value of V will decrease from 20 per second to zero in 21/2 seconds. This is shown by the curve I2 of Fig. 3, which is in accordance with the equation V=(2 lyz-tm or V=208t.

The value of D during the synchronization when a cam groove corresponding to the curve 9 is used is shown bythe curve I3, which is in accordance with the equation D=2520t+4t'`. The curve I4 represents-the value of D during. synchronization when the ratio between V andD is kept constant. It will be seen that in such case, as when a gear drive is used, the error approaches zero at a much slower. rate and theoretically never actually reaches zero. The error resulting from this condition is minimized when the cam is used because of the relatively large eiIect of a small change of error near synchronization, because the constant 7c of the equation V=kD, which is effective over the portion of the cam near zero error, can be made relatively large.

As has previously been explained the error of the follow-up shown in Fig. 1 when following a moving signal or primary element is substantially proportional to the square of the velocity; In many instances .this error is objectionable, however, it may be overcome by utilizing forms of control in which the error is a function of the acceleration or change of acceleration. In the embodiment of the invention shown in Figs. 4, 5 and 6 the error when following a moving signal is a function of the changes in velocity but when the response is synchronizing with.the incoming signal the velocity of removing the error is substantially proportional to the square root of the ing application of William H. Newell, Serial No.

- through a pilot valve.

313,678 and assigned to the same assignee.

'I'he construction of Fig. 4 is a simple construction in which the cam III operates the main valve of the hydraulic control directly instead of This assumes sufficient power in the incoming movement to do this work.

A handle is shown in Fig. 4 as representative of any source of primary movement applied to the shaft I constituting the primary element, and a secondary element, as in Fig. 1 consists of a shaft 2, a diiferential 3 being connected between the two shafts and driving the cam I through the output shaft 4. Dials are shown -to indicate the positions of the primary and secondary elements.

'I'he variable speed drive 6 in this case is an hydraulic speed gear of well known form which includes an hydraulic pump known as the A" end and an hydraulic motor known as the B end which is connected to the response shaft 2. The pump is rotated at constant speed by the motor 5 and the speed of the motor or B end is determined by the position of a tilting box or swash plate in the A end actuated by a'crank arm I5.

The crank arm I5 is positioned by a reciprocating hydraulic piston I'6 slidable in a cylinder AI'I having ports at its opposite ends connected to high and low pressure hydraulic fluid through valve means to be described. The left end of the piston I6 has a reduced extension slidable in a reduced axial extension of the cylinder Il, so that the active area of the left end of the piston is, say, one-half that of the right end. The pressures will therefore be balanced when that on the right end is one-half that on the left end. A high pressure conduit I8 leads into the cylinder I'I on the left end of the piston, and a low pressure conduit I9 leads into the cylinder on the right end of the piston. These conduits lead from a valve block 20 provided with passages and valves.

The passages referred to are the high pressure passage 2| connected to the pressure side of a pump (not shown), and an exhaust passage 22 connected to the exhaustlpressure or intake side of the pump through a suitable supply reservoir. The high pressure conduit I8 of cylinder I'I communicates with the high pressure passage 2|, and that passage also has two spaced branches 2Ia leading to-a valve bore 23 in the block 20. The exhaust passage 2'2 has two spaced branches 22a leading to the bore 23, the two exhaust branches being outside the two pressure branches.

Two piston valves 24 and 25 slide in the bore 23, their mid portions being reduced and their length being such as to just lap the ports of the pressure and exhaust branches on their respective sections of the bore when the valves are in their central positions. The bore is closed at its ends and the conduit I9- leads to the left end adjacent the main valve 24 so that the conduit and the connected ends of the cylinder I'I and bore 23 constitute av closed chamber that contains hydraulic fluid. A

- extension o'f the bore 23, thereby making the active area on that end one-half that on the inner end. The pressure passage 2| has a branch 2lb leading to the end of the bore 23 at the reduced end of the valve 25. y

A conduit 26 that includes passages in the valve block and an outside pipe connecting the passages, connects the bore 23 at a point opposite the valve 24 midway between the pressure and exhaust ports lapped thereby to the space in the bore between the valves 26 and 25.

The arm 8 in this case is a pivoted lever ful'- crumed at its lower end and extending transends so as to be reciprocated thereby, and the link 2'I has one end pivotally attached to a rod 28 axially fixed tothe valve 24 and slidable through a bearing in the block 2U. Thus rock- Ing movement of the lever 8 is transmitted di- -rectly to produce longitudinal movement of the valve 24.

Assume the parts in zero position, as shown in Fig. 4, and movement of the handle on the shaft I in a clockwise directionas viewed from the left. The shaft 4 will turn in a counter-clockwise direction. This will turn the cam I0 in the same direction and cause the upper end of the lever 8 to move to the right. This will movethe valve 24 to the right ,and reduce the pressure on the fluid in conduit IS'and the chamber at the right end on piston I6. The high pressure from conduit I8 acting on the left end of piston I6 causes a movement of piston I6 to the right to restore a balance of pressures on the piston, and hence a movement of crank I5 and the tilting box of the A" end of the variable speed gear. The B end is thus caused to rotate at a speed proportiona1 to the displacement of the tilting box, which movement is transmitted as a response through shaft 2 to the differential 3 to neutralize the input movement of'shaft'l. Eventually the followerII is again centralized thereby, and the valve 24 is brought back to its original position and the state of equilibrium represented in Fig. 4 is again restored.

The above explanation neglects the compensations or corrections for the speed and acceleration errors and therefore the operation is the same as explained for Fig. 1. The conduit 26 and the space between the valves 24. and 25 contains hydraulic fluid. The movement of the main valve 24 to the right imparts similar motion to the regulator valve 25 through the intervening hydraulic uid. At the same time the valve 24 uncovers 'the port of the' adjacent pressure passage 2 Ia and admits pres'sure fluid to the conduit versely of the axis of the cam I6, so that it is 26 at a rate representing a function ofthe displacement of valve 24 from its central position. A restriction inthe conduit 26 and the shape of the intermediate reduced portion of valve 24 are designed to eiect the desired function. The displacement of the piston 25 is therefore proportional to the square root of the error, that is, the

movement of valve 24, plus the amount of pressure uid admitted through the conduit 26 dueg.:

to the displacement of valve 2,4.

'Ihis displacement of valve 25 uncovers the ex;vlv I haust port an amount proportional to the sum of the two quantities, namely the square root of the error,`represented by movement of valve 2d,

and the flow through conduit 26 due to the displacement of valve 24, and t0 that extent branch I9a is connected to exhaust. The conduit I9a has a restriction to modify the flow of iluid from the conduit I9 to exhaust. The ow of hydraulic iiuid from the conduit I9 to exhaust reduces the Volume of hydraulic fluid contained in the normally closed chamber so that as the valve 26 is brought back to its original position due to the movement of the shaft 2 the crank I5 of the A end of the variable speed gear remains displaced at an angle which causes the B end to continue to drive the shaft 2 at a speed corresponding to the rate of rotation offshaft I but without-the speed erroror the lack of complete synchronism found with the construction of Fig. 1. Although valve 24 is now back at its central position 'the valve 25 is still displaced due to the previous flow through conduit 26 and therefore fluid continues to now from conduit ls through conduit Ila so that the control arm of the "A end of the vari? able speed gear is displaced still further and shaft 2 not only overtakes but slightly passes' shalt I. This causes valve 24 to move to the left of its central position and the increased pressure to the left of valve`24 causes the piston I6 to move to the left to slow down shaft 2 because the rate of'reduction of the volume o! the chamber to the left of valve 24 exceeds the outward ilow of iluid through the conduit Isa. The movement of valve 24 to the left likewise moves the valve 25 to the left until it reaches its central position and the w through conduit Ila ceases. While the valve 24 is to the left of its central position the exhaust port 22a is connected to the conduit 26 so that iiuid ows from the space between the valves 24 and 25. As the main valve 24 then I returns to its central position the shaft 2 slows down slightly and the valve 25 remains substantially in its central position because the constants of the system are so selected that the rate of ow through conduit 25 from the space between valves Instead of being pivoted at its lower end to a fixed' iulcrum, the lever t is pivoted at its lower end to the stem 29 of a pilot valve lo. This pilot valve through a passage 20a controls the pres, sure at the right end of valve 25a which in this case, unlike the corresponding valve 25, has its two ends of equal active area. i

The pilot valve l0 slides in a bore II and con- .trols ports of pressure passage 2i and of an exhaust passage 32. An exhaust passage 33 also communicates with the space behind the pilot valve and with the exhaust port lapped `by valve a. v

The piston Ita, unlike piston I5, has both ends of equal active area. and the left end, instead of being opposed by full pressure iluid is opposed by a reduced pressure controlled by reducing valve 34. Y This valve has full pressure on one end which is of reduced area and its other` end, which communicates with the left end of cylinder space Il, is alternately connected with pres- Y sure from passage 2I and exhaust in passage I5 24 and-25 neutralires the eiect on the valve 25 of the movement of valve 24 toward its central position. When the valve 24 has thus returned to its central position the valve 25 is also at its normal central position and the low pressure hydraulic system of conduit I! is again stabilized as shown in Fig. 4 except that the crank I5 is displaced an appropriate amonmt.

During normal following operation of the apparatus of Fig.` 4 the follower II remains substantiallv at the center of the groove 9 of cam III.V .If forany reason the error exceeds that due to through ports controlled by the valve I4, thus maintaining a. constant reduced pressure on the left end of piston lia. When the pressure in conduit I9 on the right end of piston IBa equals that on the left end, the piston is in equilibrium.

As before; let us assumev an incoming primary movement in a clockwise direction. 'I'he cam l0 is turned counterclockwise and the upper end of lever l is moved tothe right. The lever is now fulcrumed at the center pivot and its lower end therefore moves to the left` pulling pilot valve 30 to the left. This opens the passage 35a to exhaust and valve 25a moves to the right under the influence of the pressure in conduit I5 acting through the valve 24 and the hydraulic huid between the valves 24 and 25a. 'The valve 24 thus moves to the right and through the rod 28 and link 21 moves the lever 8 to the right about the follower II as a fulcrum until the pilot valve 30 is returned to its central position. Simultaneously with the movement of valve 24 to the right the piston Ita and the crank arm I5 move to the arm I5 andthe tilting box o! the A end are set for maximum speed of the response shaft 2 in the direction to remove the error. As the shaft 2 now turns, the follower II follows the cam groove 9 toward the center of the cam, the main valve 24 moves toward its center position thus forcing uid through conduit I9 to return-the piston I6 and crank arm I5 to their central position. It will be seen that as the follower II apis greater, then the rate of rotation of the shaft 2 and the cam I0 becomes slower and slower with the combined eifect that the movement of the valve 24 and crank arm I5 are substantially uniform, that is, the rate of change of the velocity of the output of the "B end or the acceleration is a constant. During the operation of synchronizing the effect of the movement of valve 24 on the movement of the crank arm I5 so predomi nates over the eiect of the ow through passage I9a.that this iiow has very little eilect on the overall operation and for practical consideration may be neglected.

The control mechanism of Fig. 5 diners from that of Fig. 4 principally in that it employs a pilot valve and thus relieves the primary moving part of the load of adjusting the main control valve.

right under the effect of the pressure on the left end of piston Ilia. As with' the construction of Fig. 4 the movement of iiuid throughpassage 25 due to the displacement o! valve 24- changes the volume of fluid between valves 24 and 25a and -the displacement of valve 25a permits ilow of fluid through passage I9a to vary the volume of iluid in the normally closed chamber including the conduit i9.

As explained in connection with Fig. 4 the follower Il during normal operation remains substantially at the center of the cam Il! and the flow of fluid through passage I9a varies the volume of uid in the closed chamber so that the piston Isa and the-crank arm I5 take the proper position to cause the shaft 2 to be rotated at a rate corresponding to the rate of the shaft I. When synchronizing from a. large error the piston IGa is moved at a uniform rate the same as explained regarding Fig. 4 except that the return movement of valve 24 is controlled by the cam- I0 acting through the pilot valve 30 instead of directly through the link 21 and the rod 28.

'Ihe construction of Fig. 6 adds a relay valve to lthe construction of Fig. 5, thereby making more power available to operate the tilting box, but the principle and general eiect are the same.

A piston ISb corresponding to the piston Ila is in this case operated by full pressure, the control o! the admission of pressure on one side valve block 20, and the conduit I9 leads to one sure from passage 2| or exhaust through passage 39. 'Ihis reduced pressure onthe end of valve 38 is balanced by the fullpressure on the reduced 'area of the other end. The valve 31 has three reduced portions separating four piston valve portions, the center reduced portion communicating withv full pressure from passage 2|,

and the two outside reduced portions communieating with exhaust passage 40. Thus axial movement of the relay valve 36 connects the ports of the passages leading to the opposite end -of piston I6b either with pressure or exhaust.

As with the previous construction, a clockwise incoming movement moves the upperv end of lever 8 to the lright and pulls the pilot valve 30 tothe left thereby causing the main valve 24 to move to the right and the yrelay valve 36 to move .to the left under the influence of the pressure acting on the right-hand end of valve 36. This movement of valve 36 connects'the left end of piston |6b with pressure and the right end to exhaust, thereby tilting the speed regulator to the right and turning shaft 2 in the direction to subtract from the movement introduced into the diierential by shaft l. The effect of the cam I0 during normal following and synchronizing is the same as for the construction of Fig. 5.

Other embodiments of the invention will readily occur to those" skilled in the art and it is not the intent that the invention shall be limited to the constructions used forillustration but only as required by the following claims.

1. A motion reproducing mechanism including a primary element and a secondary element and means to cause the secondary element to reproduce the motion of the primary element comprising a power device for driving the secondary element, a speed regulating member for the power device, means for comparing the motion of the primary and secondary elements', and control means for the speed regulating member including a cam actuated by the output of the comparing means and a cam follower operatively connected to the speed regulating member.

2. A motion reproducing mechanism including a primary element and a secondary element and means to cause the secondary element `to reproduce the motion of the primary element comprising a power device for driving the secondary element, a speed regulating member for the power device, means for comparing the motion of the primary and secondary elements, and control means for the speed regulating member including a cam actuated by the output of the vcomparing means and having a cam surface representing the ratio between the positional out-` put of the comparing means and the speed of the power device when the latter is proportional to the square root of the former, and a cam folmeans to cause the secondary element to reproduce the motion of the primary element comprising a power device for driving the secondary element, a speed regulating member for `the power device, means for comparing the motion ofthe primary and secondary elements, and control means for the speed regulating member including a cam actuated by the output of the comparing means and having a cam surface representing the ratio V=\/2aD, and a cam follower operatively connected to the speed regulating member. Y

4. A motion reproducing mechanism including a primary element and a secondary element and means to cause the secondary element to reproduce the motion of the primary element comprising a variable speed power device for driving the secondary element, a speed regulating member for the power device, a differential connected between the primary and secondary elements, a hydraulically operated piston connected to operate the speed regulating member, a valve block having passages communicating with opposite ends of the pistonand connected respectively with high and low hydraulic pressure, a slide valve in the block in control of the passages, an actuating link for the valve, and means operatively connecting the output of the differential with the link including means automatically operable to vary the ratio of movement of the output and of the link. l

5. A motion reproducing mechanism including a primary element and a secondary element and means to cause the secondary element to reproduce the motion ofthe primary element comprising a variable speed power device for driving the secondary element, a speed regulating member for the power device, a differential connected between the primary and secondary elements, a hydraulically operated piston connected to operate the speed regulating member, a valve block having passages communicating with ODDOsite ends of the piston and connected respectively' with high and low hydraulic pressure, a slide valve in the block in control of the passages, an

actuating link for the valve, and means opera hydraulically operated piston connected to operlower operatively connected to the speed reguv lating member.

' 3. A motion reproducing mechanism including a primary element and a secondary element and means to cause' the secondary element to repro- -Y ate the speed regulating member, a valve block having passages communicating with opposite ends of the piston and connected respectively with high and low hydraulic pressure, a slide valve in the block in control of the passages, an actuating link for the valve, and means operatively connecting the output of the differential with the link including a cam operated by the output and having a cam surface representing theA ratio between the' positional output of thev differential and the rate of movement of the secondary element when the latter is proportional to the square root of the former, and a cam follower on the link.

'1. A motion reproducing mechanism including a primary element and a secondary element and n 6 aaneen with high and low hydraulic pressure, a slide valve in the block in control o! the passages. an

Yactuating link for the valve, and means operatively connecting the output o! the differential with the link including a cam operated by the output and having a cam sm'iace representing the ratio V=v' 2aB. and a cam follower on the link.

Tm D. TEAR.

Images