US3558927A

US3558927A - Apparatus for controlling the effects of backlash

Info

Publication number: US3558927A
Application number: US795377A
Authority: US
Inventors: Joseph Colin Whitehouse
Original assignee: Rank Organization Ltd
Current assignee: Rank Organization Ltd
Priority date: 1968-12-09
Filing date: 1968-12-09
Publication date: 1971-01-26
Anticipated expiration: 1988-01-26

Abstract

This disclosure describes an apparatus for controlling the rate at which the backlash of a mechanism is taken up. A demand signal causing rapid acceleration or rapid deceleration is modified prior to its application to the drive portion of the mechanism in an electrical or mechanical modifying system. The demand signal is modified in such a manner that it reduces or eliminates backlash to thereby reduce or eliminate the damage or noise caused by backlash.

Description

United States Patent I Joseph Colin Whitehouse Humberstone, Leicester, England Dec. 9, 1968 Jan. 26, l 971 The Rank Organisation Limited London, England Continuation-impart of application Ser. No. 578,082, Sept. 8, 1966, now abandoned.

Inventor Appl. No. Filed Patented Assignee APPARATUS FOR CONTROLLING THE EFFECTS OF BACKLASH 11 Claims, 29 Drawing Figs.

vs. C! 307/264; 74/583, 307/237, 328/169, 328/172 Int. Cl H03k 5/01, 605g 7/00 Field of Search 74/1 583, (Inquired); 328/69, 1, 127, 132, 168, 169, 172; 307/237, 264

[56] References Cited UNlT ED STATES PATENTS 1,738,281 12/1929 Bucklen et al. 74/583 2,449,035 9/1948 Coffin, Jr. et al. 328/l65X 3,030,054 4/1962 Lee et al. 328/127X 3,219,936 11/1965 Eksten et a1. 328/1X Primary Examiner- Donald D. Forrer Assistant Examiner-John Zazworsky Attorney Griffin, Branigan and Kindness ABSTRACT: This disclosure describes an apparatus for controlling the rate at which the backlash of a mechanism is taken up. A demand signal causing rapid acceleration or rapid deceleration is modified prior to its application to the drive portion of the mechanism in an electrical or mechanical modifying system. The demand signal is modified in such a manner .that it reduces or eliminates backlash to thereby reduce or eliminate the damage or noise caused by backlash.

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APPARATUS FOR CONTROLLING THE EFFECTS OF BACKLASI-I BACKGROUND OF THE INVENTION rate at which the backlash of a mechanism is taken up. When mechanisms which exhibit backlash are subject to rapid accelerations or decelerations, noise results. In addition, the pos sibility of damage exists due to the large impact forces which are created. For example, when a load driven through a mechanical gear arrangement from a power source requires more (orless) power, backlash effects occur. Similarly, when a servo control system requires more (or less) electrical power, backlash effects occur. The amount of backlash effect involved is related to the amount of power increase (or decrease) applied and the type of system involved, (i.e., mechanical gears, electrical servo, etc.).

There are two primary factors that contribute to backlash effects. The first factor is the application of the power as a step function, (i.e., power changes are rapidly applied). The second factor is the lost motion between the time of application of a power increase (or decrease) to the drive means and the application of power by the drive means to the load. This lost motion period of time results in a shock when the drive means engages the load. This shock creates backlash resulting in undesirable noise and possible damage to the overall system.

Therefore, it is an object of this invention to provide an apparatus for reducing or eliminating the undesirable effect of backlash.

It is also an object of this invention to provide an apparatus for controlling backlash by modifying demanded power changes so that backlash is reduced or eliminated.

It is a still further object of this invention to provide an ap paratus for controlling the application of power to a mechanism so that the shock which occurs when a drive means engages a load is reduced or eliminated.

SUMMARY OF THE INVENTION According to the present invention, an apparatus for use with mechanisms which employ drive and driven members (loads) that are subject to backlash effects is provided. The apparatus basically comprises a means for modifying the input signal to the drive member in a predetermined manner for a predetermined period of time so that the relative velocity of the drive and driven member is small at the instant of engagement. Thereafter, the full effect of the drive signal (input signal) is restored to its unmodified form. That is, after the predetermined period of time has elapsed, the drive signal is allowed to reach its unmodified level.

While the invention may be used with various mechanisms that are controlled by electrical, mechanical, hydraulic, and other signals, the following description refers in particular to the use of the invention with a speed control closed loop system that has a high inertia load and is controlled by a signal voltage through an amplifying device. Clearly, this system is such that backlash effects are severe. Following the description of the various arrangements for such a system, a particular example of a speed controlled servooperating a zoom lens is described. In conclusion, various hydromechanical embodiments of the invention are described.

BRIEF DESCRIPTION OF THE DRAWINGS The preferred embodiments of the invention will now be particularly described with reference to the accompanying drawings wherein:

FIG. 1 is a pictorial diagram of a mechanical demand source coupled to an actuator through a backlash effect control;

FIG. 2 is an alternative pictorial diagram of a demand signal source coupled to an actuator through a backlash effect control;

FIG. 3 is a pictorial diagram of a demand signal source coupled through a backlash effect control to an actuator that controls the movement of a zoom lens mechanism;

FIG. 4 is a pictorial diagram of a drive and a load at rest; FIG. 5a is a velocity versus time diagram of the drive of FIG. 4 when a step input is applied to said drive;

FIG. 5b is a velocity versus distance or phase plane diagram of the drive load system of FIG. 4 when a step input is applied to drive;

FIG. 50 is a phase plane diagram of a drive-load system of FIG. 4 when the drive signal is modified;

FIG. 5d is a velocity versus time diagram illustrating the velocity that must be applied to the drive of FIG. 4 to result in the phase plane diagram illustratedin FIG. 5c,

FIG. 6 is a pictorial diagram of the drive and the load under constant velocity just prior to deceleration;

FIG. 7 is a velocity versus time diagram of the drive-load system of FIG. 6 when a sudden deceleration is applied;

FIG. 8 is a phase plane diagram of the drive-load system of FIG. 6 for a sudden deceleration;

FIG. 9 is a phase plane diagram of thedrive-load system of FIG. 6 wherein the deceleration is modified;

FIG. 10 is a velocity versus time diagram for a modified deceleration resulting in a phase plane diagram of FIG. 9;

FIG. 11 is an optimum or ideal velocity or voltage versus time diagram including an acceleration backlash area; FIG. 11b is an optimum or ideal velocity voltage versus time diagram including a deceleration backlash area;

FIG. is a phase plane diagram for either an 110 or an llb type of backlash;

FIG. 11d is an actual as opposed to an optimum (11b) diagram of voltage or velocity versus time for deceleration backlash;

FIG. 12 is a block diagram illustrating the overall concept of the invention;

FIG. 13 is a schematic diagram illustrating one embodiment of the invention;

FIG. 14 is a pictorial diagram illustrating the incoming demand signal for the embodiment of the invention illustrated in FIG. 13;

FIG. 15 is a pictorial diagram of the modified demand signal generated at the output of the embodiment of the invention illustrated in FIG. 13;

FIG. 16 is a pictorial diagram of a decelerating demand signal suitable for application to the embodiment of the invention illustrated in FIG. 13;

FIG. 17 is a phase plane diagram illustrating the modified output signal for an embodiment of the invention of the type illustrated in FIG. 18;

FIG. 18 is a schematic diagram of an alternative embodiment of the invention;

FIG. 19 is a schematic diagram of a still further embodiment of the invention;

FIG. 20 is a schematic diagram of an embodiment of the invention suitable for use in the servo control system of a zoom lens;

FIG. 21 is a diagram of a mechanical embodiment of the invention;

FIG. 22 is a diagram of an alternative mechanical embodiment of the invention; and

FIG. 23 is phase plane diagram for the embodiment of the invention illustrated in FIG. 22.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS. 1, 2 and 3 illustrate various environments wherein backlash occurs. Specifically, FIG. 1 illustrates a system wherein a demand signal source 11 is coupled to an actuator 13 via a backlash effect control 15 of the type illustrated in FIGS. 21 and 22, and hereinafter described. The demand signal source includes a manually operable handle 17 coupled via a horizontally movable rod 19 to the mechanical backlash effect control 15. The backlash effect control 15 is coupled to the actuator 13 via a horizontally movable connecting rod 21.

When the manually operable handle 17 is moved to the right or left as viewed in FIG. 1, the movement is applied to the actuator 13 via the backlash effect control 15. The backlash effect control modifies mechanical signal in accordance with the principles herein described.

FIG. 2 illustrates an alternative system wherein a demand signal source 23 is connected to an actuator 25 via a backlash effect control 27 of the type illustrated in FIGS. 21 and 22. The demand signal source includes a rod 29 having a manually moveable handle 31. The rod 29 is attached at about its center to one end of a shaft 33 which is connected to the backlash effect control 27. The backlash effect control 27 is connected to the actuator via a further shaft 35. In addition a mechanical feedback rod 37, connected to the mechanism to be actuated, is connected to the lower end of the rod 29. As the manually moveable handle 31 is moved back and forth, in the direction illustrated in FIG. 2, the thusly created mechanical signal is applied via the backlash effect control 27 to the actuator 25.

FIG. 3 illustrates a system that utilizes an electronic backlash effect control 39 of the type herein described. The electronic backlash effect control 39 interconnects a demand signal source 41 to an actuator 43. The actuator 43 may be a servo motor having means for transferring rotary motion to lateral motion. The lateral motion is connected to a zoom lens mechanism 45 via a rotatable coupling rod 47. In this manner, as the shaft 49 of the actuator 43 moves back and forth, the zoom lens element 45 moves back and forth inside of a lens barrel 53.

It will be appreciated from viewing FIGS. 1-3, that the inventive system includes means for modifying a demand signal by a backlash effect control. The backlash effect control, as hereinafter described, is either mechanical or electrical and modifies the demand signal in such a manner that the effect of actuator backlash is reduced or entirely eliminated.

Prior to describing an actual embodiment of the invention, the conditions existing when acceleration is taking place will be first considered. FIGS. 4 and 5a thru 5d illustrate functionally and diagrammatically certain of these conditions.

FIG. 1 illustrates a drive, D, adapted to drive a load. X represents the distance that the drive moves through prior to engaging the load when the drive and the load initially are at rest. Hence, the drive could be the shaft of a motor and the load could be a zoom lens, for example. X then represents lost motion distance between the shaft and the lens through a gear coupling means.

Assuming the drive and the load to be stationary, as illustrated in FIG. 4, before the time (t=O) of engagement between the drive and the load, then for normal operation, the application of an input signal to the drive produces a step input of velocity to the drive D as illustrated in FIG. a. The phase plane diagram of X distance between drive and load) and (velocity of approach between drive and load) is as shown in FIG. 5b. It will be appreciated that, under these conditions, the drive moves to the right (as viewed in FIG. 5a) at a constant speed and strikes the load at a velocity V thereby producing noise and possible damage.

The apparatus of the invention prevents the foregoing situation by modifying the signal applied to the drive in such a way so as to produce a very small value of =V (velocity at time of striking) when the displacement, X, is small. The resultant phase plane diagram is illustrated in FIG. 50. It will be appreciated that the value of the velocity signal (V should be adjustable to suit the precise operating conditions of the particular environment in which the invention is being used. The velocity signal required at the drive D for the case illustrated in FIG. 4 is shown in FIG. 5d with the time of operation of the modification of the input signal depending upon the distance to the region AA (where backlash is removed) from the point of starting.

Referring now to FIGS. 6 to 10, the conditions existing when a deceleration, as opposed to an acceleration, signal is applied to the drive means is considered. Assuming the drive D and the load to be moving toward the left of FIG. 6 at velocity V a sudden deceleration to zero velocity of the drive D is produced by an input signal on the drive D of the type illustrated in FIG. 7. The resulting phase plane diagram is illus trated in FIG. 8, from which it can be seen that there is again an impact velocity equal to V (assuming the load continues moving at V To obtain the desired result (i.e., a velocity of near zero after distance X has been traveled), the signal to the drive means must be modified so that a phase plane diagram of the type illustrated in FIG. 9 results. FIG. 10 illustrates how the signal to the drive means must be modified to achieve this result.

Referring now to FIGS. 5d and 10, the shaded areas under these graphs represent a distance that is just greater than the backlash in the mechanism involved. It is clear from the shape of the areas concerned, that the maximum acceptable value of V, and the amount of backlash govern the time that the modifying device need be operative. FIGS. 11a and 11b show the optimum type of demand signal for acceleration and deceleration, respectively, resulting in smaller application time and, hence, better frequency response than a less optimum type of demand signal. The corresponding phase plane diagram for FIG. 11b is illustrated in FIG. 110. Several embodiments of the invention resulting in a nearly optimum modify demand signal are hereinafter described.

FIG. 12 illustrates, in block form, how the demand signal is modified prior to the application to the demand element. More specifically, from FIG. 12 it can be seen that a demand signal which is to be applied to a particular mechanism in response to a particular demand is fed through a modifying system to produce a modified input signal for the mechanism. Depending upon the type of demand signal, the modifying system can be electrical, mechanical, hydrostatic, or pneumatic, for example. The modifying system operates in accordance with the principles outlined in connection with FIGS. 4-11. That is, the demand signal which is to operate the mechanism, is modified in accordance with a predetermined signal modification prior to application to the mechanism. For example, when the demand signal is an electric voltage, an electric modifying system is used. Alternatively, the demand signal could be a mechanically generated demand signal, used in combination with a mechanically powered actuator.

The least complex embodiment of the invention is illustrated in FIG. 18 and comprises a two stage RC filter with ganged variable resistors. The filters are L-stage filters with the resistor being connected in series and the capacitor being connected in shunt. This embodiment of the invention is con nected as illustrated in FIG. 18 so that the electrical demand input is connected across one filter combination and the modified input electrical signal to the mechanism is taken across the capacitor of the second filter. This embodiment modifies electrical signals for both accelerating and decelerating demands. The action of the filter is that of a double integrator and by the choice of a suitable time constant, a decelerating step input signal (FIG. 16) is modified to that shown in FIG. 17 so that the velocity is reduced to prevent backlash. It will be understood that varying the settings of the variable resistors R will alter the time period over which the velocity reduction occurs. A similar diagram to that illustrated in FIG. 17 can be drawn for an accelerating step input electrical signal. It will be appreciated by those skilled in the art and others, that the FIG. 18 embodiment is relatively slow acting, hence, it finds its greatest use when a large backlash is involved.

In many applications the sluggishness resulting from a large delay is unacceptable. For such systems, the embodiment of the invention illustrated in FIG. 13 and hereinafter described which results in conditions approximating more clearly those described in connection with FIGS. 11a and 11b can be used. In this embodiment, the accelerating and decelerating demand signals are modified separately by different devices for convemence.

For a positive step input at terminal X, a positive signal is transmitted through a variable resistor R31 and a capacitor 13C to the bases of two transistors, Q1 and Q2. The emitters of Q1 and Q2 are connected to ground. O1 is a PNP transistor and O2 is an NPN transistor. A resistor, R4], is connected between the input terminal X and the output terminal Y. A second variable resistor R11, is connected between the collector of Q1 and terminal Y and a third variable resistor, R21, is connected between the collector of Q2 and terminal Y. If the input signal has a significant magnitude, for example more than one-half volt, O2 is switched on (saturated) and the modified signal voltage applied to output terminal Y is the bottoming voltage of Q2. PNP transistor Q1, remains off because the positive input at its base is ineffective to turn it on.

Transistor Q2 remains saturated on until the voltage on its base becomes less than approximately one-half volt (in this example) or,. according to the V of the transistor used, becomes less that the saturating base voltage. This occurs when capacitor 13C is charged up to the demand signal voltage level through variable resistor, R31. The time constant of this charging period is governed by the adjustment of the variable resistor R31. When transistor Q2 is saturated, the magnitude of the modified signal voltage produced is adjusted by varying the third variable resistor R21.

For a significant negative signal, transistor O2 is switched off and transistor Q1 is switched on. The demand signal and the modified demand signal for the embodiment shown in FIG. 13 are illustrated in FIGS. 14 and 15, respectively. The shaded portion in FIG. 15 is related to the distance traveled if the drive is a speed controlled device. Consequently, from the foregoing discussion, it will be appreciated that this area should represent a distance slightly greater than the backlash of the system. It can be seen that the modified demand signal illustrated in FIG. 15 more clearly approaches the optimum demand signal illustrated in FIG. 11a than a modified signal which results from the use of the embodiment of the invention illustrated in FIG. 18.

For decelerating demands to zero, the sluggishness introduced by the filters contained in the embodiment of the invention illustrated in FIG. 18 is largely overcome by using a smaller capacitor charged up toa voltage V while the demand is on and applying this voltage to a system having a time delay 8 after the demand ceases. The voltage V, is obtained by the linear amplification of the demand voltage and is therefore proportional to and, in general, larger than the V voltage. The resulting signal is illustrated in FIG. 11d. It can be seen that this signal approximates the 11b signal provided area B is small compared with area A. The backlash of this system is A+c-B. This modified RC only embodiment of the invention results in reduced application time of the modified signal. As the capacitance is now smaller than in the previous embodiment (FIG. 18) the sluggishness of the overall system is substantially reduced.

In the modified RC only embodiment, the capacitor is made ineffective in the demand lead while the demand is on and is charged during this time. When the demand ceases, the capacitor is switched into the demand lead by the action of a relay or other suitable switch. Such an embodiment is illus trated in FIG. 19.

During the time the demand exists, the relay in FIG. 19 is in the position illustrated and the capacitor 19C is charged up to a voltage equivalent to V and proportional to V The magnitude of V is determined by the values of R20 and R and the resistance of a linear amplifier (not shown). The amplifier is connected to receive the demand signal. And, R30 and R20 form a voltage divider which applies this signal to capacitor 19C. On relaxing the demand signal, the relay contacts switch positions and the voltage previously applied to the capacitor becomes the demand signal after a fixed time delay 8 governed by either electrically slugging the relay coil or adjusting the relay mechanics. The voltage across the capacitor 19C then decays exponentially with a time constant depending upon the value of its discharge resistor R10 and the parallel input impedance of the amplifier receiving the modified signal (if one is used). Adjustment for different amounts of backlash are made by altering the values of V 8, and the time constant of the capacitor decay either singly or together.

The electrical arrangement previously described can be used with any mechanism that is electrically energized. The arrangement can be used in connection with simple motorized mechanisms, but its important uses are in connection with the servocontrol of guns, and in connection with zoom lenses.

FIG. 20 shows a circuit diagram of an arrangement for applying the invention to a servo-controlled zoom lens and enables simple speed control and position control. From observing FIG. 20, it will be seen that the arrangement is essentially a combination of the embodiments of the invention described above and illustrated in FIGS. 13 and 19. For position demand control, a demand potentiometer DP, included in a demand position servo, is variable to supply a position demand signal. That is, when the position of the demand potentiometer is changed, a demand signal occurs. The position demand signal drops across a summing resistor SR in an amount determined by a signal originating at a reset position potentiometer RP. The reset position potentiometer has its tap connected to the load so as to sense the position of the load. The signal from RP is connected to the other end of SR via a pick off network N which preferably includes a compensation capacitor as shown by the dashed line. The signal from the summing point S serves to maintain, for a given position demand signal, a load at a substantially constant position. The load being driven by a rate servomechanism or velodyne from a terminal TD. During an interval between the initial application of a desired position demand signal by the demand potentiometer and the achievement final equilibrium, the voltage error to earth from the summing point S is limited by a voltage limiting circuit VLT. Due to the backlash present in the load, it is advantageous to control the signal at terminal TD in the manner indicated herein, thereby, preventing noise and possible damage. That is, as hereinafter described, means of the type previously described, are included to modify the demand signal during its application to the load (zoom lens) connected to point TD so as to prevent backlash from occurring.

To the foregoing end, an arrangement A in accordance with that illustrated in FIG. 13 is included so as to operate substantially as described in connection with FIGS. 14 and 15 with respect to sudden changes in the signal from the demand potentiometer DP. Conduction of one of the transistors of the arrangement A is caused according to the polarity of the sufficiently large new position demand signal relative to the previous steady condition. When either of these transistors is switched on for the period determined by the discharge time of the capacitance of the arrangement A, its emitter-collector voltage is small. Because the emitter-collector voltage is small and because the variable resistance connected to its collector is small; the voltage from the summing point to earth is also small. Hence, a small signal exists at TD.

With the relay control contacts RC of arrangement B in the position shown, the voltage at terminal TD constitutes a small demand input to the rate servomechanism so that the speed of the load is small. After a time sufficient for backlash to be taken up, the transistor A switches off and the speed of the load is determined by the voltage limiting circuit VLT until such time as the desired new position is reached and the voltage at the summing point S is insufficient to actuate the voltage limiting circuit VLT. Movement of the load then stops. The variable resistor VR affords a means for varying the time of application of the modified rate demand signal.

The remainder of the circuit illustrated in FIG. 20 comprises a circuit of the type shown in FIG. 19 for controlling the rate demand signal at terminal TD due to operation of a zoom control potentiometer ZR when the relay contacts RC are shifted from the position shown to their other position. Prior to this relay operation, which is preferably pushbutton controlled, the voltage across' capacitor 20C is substantially proportional to the speed of the position servo because the voltage across the resistor VR is substantially proportional to speed of transverse of the moving contact of the reset potentiometer RP due to differentiating capacitor-resistor elements (R1 and Cl) illustrated in FIG. 20. Thus, if such relay operation occurs at a time when the signal at the terminal TD is being adjusted for a changed position demand signal, the voltage across the capacitor C is fed to the terminal TD and causes the rate servo to come to rest in a manner tending to reduce the relative velocity between the drive and the driven members thereof, thereby reducing the unwanted effects due to backlash.

As with the arrangement of FIG. 19, a delay equal to the drop out time of the relay combined with a relatively small capacitance 20C (compared as before with the arrangement of FIG. 18) results in operation substantially as shown in FIG. 11d. It should be noted that, due to the nature of the drive and driven members generally the drop in the velocity of the drive members in the interval '0 will, in practice, be exponential and the rise after the interval will also not be instantaneous. During this time, the velocity of the driven member will also be falling slightly in a substantially linear manner.

Mechanical, hydraulic, or pneumatic systems operating analogously to the above described electrical systems may be used for appropriate type of demand signals, one such mechanical system is illustrated in FIG. 21. This system incorporates two mechanical filters connected in series each comprising an oil dashpot 100, 100' and a spring 101, 101, which are the analogue of the electric filter illustrated in FIG. 18. The time constants of the filters can be changed by altering the viscosity of the oil 102, 102 in the dashpots or the rates of the springs.

Each dashpot 100, 100' has a plunger 103, 103 bored at 104, 104 for operation in its oil chamber. The plunger shafts 105, 105 are sealed at 106, 106 on each end of the respective oil chamber and protrude at 107, 107 into a closed end 108, 108' of the respective dashpot body. The spaces between the ends 108, 108' and the plunger parts 107, 107' are arranged so that the maximum plunger travel is, preferably, just greater than the backlash of the load driven from the shaft 109. A friction loading 110, on the shaft 109 is also provided.

In operation, the full effect of the sudden change of a demand signal applied to the shaft 105 is not transmitted to the shaft 109 until movement of the plunger shafts 105, 105 toward the ends 108, 108 has taken place. As this is greater than the backlash in the load, the characteristics of this system will, as described above, be similar to those for FIG. 18.

In order to obtain a mechanical device exhibiting the delay characteristics similar to those associated with FIGS. 11a and 11b, it is convenient to use a mechanism which itself has controlled backlash, such as a device of the type illustrated in FIG. 22. This arrangement comprises a dashpot 111 filed with oil 112 with an input shaft 113 having a plunger 114 protruding as illustrated in FIG. 22. The axial movement of the plunger 114 within the dashpot 111 is limited by the position of adjustable end stops 115 located at one end of the dashpot 111. The force transferred to the output shaft 116 when the plunger 114 is not at the end stops 115 is altered by moving the oil 112 in the dashpot 111.

Considering the device illustrated in FIG. 22, it will be appreciated that the application of a force to the input or demand shaft 113 forces the plunger 114 into the body of the dashpot 111 providing the friction loading 117 on the output shaft 116 is just greater than the loading between the demand shaft 113 and the dashpot case seals 118. The movement of the plunger 114 due to the oil holes 119 exerts a viscous force on the walls of the dashpot 111 proportional to the relative velocity between the dashpot 111 and the plunger 114. Equilibrium occurs when the sum of the friction forces (i.e., the forces between the dashpot 111 and the plunger 114 and between the output shaft 116 and the frictional clutch or loading 117) equals the applied force. In this condition, the input shaft 113 moves at a constant speed. The friction loading on the output shaft 116 is composed of two parts. one being friction and the other viscous. The friction controls the large velocity differentials between the input and output shafts of the device.

Application of a force to the input shaft 113 initially produces a modified velocity demand on the output shaft 116 which is much less than a demand velocity. This operation continues until the plunger 114 transverses the backlash in the dashpot 111. At this point, the modified demand velocity becomes equal to the input demand velocity. Adjustment of the dashpot 111 to suit different degrees of system backlash is made by alternating the amount of travel in the dashpot 111 using the adjustable end stops 115. The speed differential between the input and output shafts 113 and 116 is varied by altering the viscosity of the oil 1 12 in the dashpot 111.

The device illustrated in FIG. 22 is used for both accelerating and decelerating demand signals, the resulting phase plane diagram in both cases is illustrated in FIG. 23. If this mechanism is to suffer fairly large impact velocities between the plunger 114 and the end stops 115, it may be necessary to terminate the end stops with shock absorbent pads 120, thus reducing the risk of noise and damage in the device itself. It will be appreciated that the backlash in the device is set to be only just greater than that in the system wherein it is being used.

I claim:

1. Apparatus including a backlash effect control comprising:

an electrically operated actuator for moving a mechanism,

said actuator having backlash generating elements;

a demand signal source for generating an electrical demand signal in response to a demand; and

a backlash effect control connected to said demand signal source to receive said demand signal and connected to said actuator for applying a modified demand signal to said actuator, said backlash effect control modifying said demand signal for a predetermined period of time after it has been generated in response to a demand so that a low relative velocity occurs between the backlash generating elements of said actuator upon impact, said modified demand signal changing to an unmodified level after said impact has occurred, said backlash effect control comprising: switch means having a pair of two position contacts, each pair including a common contact for controlling the passage of current in an electric circuit, said switch means connected to receive the electrical demand signal generated by said demand signal source;

a resistor;

a first variable resistor, said resistor and said first variable resistor connected in series one end of said series connection adapted to receive the electrical demand signal generated by said demand signal source, the junction between said series connection being connected to one terminal of the first of said two position contacts, the other end of said series connection being connected to ground and to the other terminal of said first of said two position contacts;

a capacitor, one end of said capacitor connected to the common contact of said first of said two position contacts; and

a second variable resistor, said second variable resistor being connected between the other side of said capacitor and ground, the junction between said capacitor and said second variable resistor being connected to one terminal of the second of two position contacts, the other terminal of said second of said two position contacts being connected to said demand signal source and the common terminal of said second of said two position contacts being connected to said electrically operated actuator.

2. Apparatus including a backlash effect control comprismg:

an electrically operated actuator for moving a mechanism,

said actuator having backlash generating elements;

a demand signal source for generating an electrical demand signal in response to a demand; and,

a backlash effect control connected to said demand signal source to receive said demand signal and connected to said actuator for applying a modified demand signal to said actuator, said backlash effect control modifying said demand signal for a predetermined period of time after it has been generated in response to a demand so that a low relative velocity occurs between the backlash generating elements of said actuator upon impact, said modified demand signal changing to an unmodified level after said impact has occurred, said backlash effect control comprising:

a first resistor having one end connected to said demand signal source and the other end connected to said electrically operated actuator;

a first variable resistor;

a capacitor, said first variable resistor and said capacitor connected in series with the other end of said first variable resistor being connected to said demand signal source;

an NPN transistor having its base connected to the other side of said capacitor and having its emitter connected to ground;

a PNP transistor having its base connected to the other side of said capacitor and its emitter connected to ground;

a second variable resistor having one end connected to the collector of said NPN transistor and the other end connected to said electrically operated actuator; and

a third variable resistor having one end connected to the collector of said PNP transistor and the other end connected to said electrically operated actuator.

3. Apparatus including a backlash effect control comprismg:

an electrically operated actuator for moving a mechanism,

said actuator having backlash generating elements;

a backlash effect control connected to said demand signal source to receive said demand signal and connected to said actuator for applying a modified demand signal to said actuator, said backlash efiect control modifying said demand signal for a predetermined period of time after it has been generated in response to a demand so that a low relative velocity occurs between the backlash generating elements of said actuator upon impact, said modified demand signal changing to an unmodified level after said impact has occurred, said backlash effect control comprising:

a position indicating means connected to said electrically operated actuator for indicating the position of said actuator;

a summing means connected to said demand signal source and to said position means for summing signals from said demand signal source and from said position means; and

signal modifying means connected to said summing means for modifying the signal from said summing means and for applying said modified signal to said electrically operated actuator.

4. Apparatus including a backlash effect control as claimed in claim 3 wherein said position means comprises a potentiometer connected across a positive and negative source of voltage and having its wiper arm connected to said actuator so that said wiper arm moves as said actuator output moves and wherein said summing means comprises a resistive network connected to said wiper arm and to said demand signal source.

5. Apparatus including a backlash effect control as claimed in claim 4 wherein said modifying means comprises:

transistor means connected to said resistive network and to said actuator for modifying said demand signal in a predetermined manner. 6. Apparatus including a backlash effect control as claimed in claim 5 wherein said transistor means comprises: a first resistor having one end connected to said resistive network and the other end connected to said actuator;

a first variable resistor;

a capacitor, said first variable resistor and said capacitor connected in series with the other end of said capacitor being connected to said resistive network;

an NPN transistor having its base connected to the other side of said first variable resistor and having its emitter connected to ground;

a PNP transistor having its base connected to the other side of said first variable resistor and its emitter connected to ground;

a second variable resistor having one end connected to the collector of said NPN transistor and the other end connected to said actuator; and,

a third variable resistor having one end connected to the collector of said PNP transistor and the other end connected to said actuator.

7. Apparatus including a backlash effect control as claimed in claim 6 comprising a voltage limiting means connected between said modifying means and said actuator.

8. Apparatus including a backlash effect control as claimed in claim 7 wherein said modifying means also includes:

switch means having a pair of two position contacts, each pair having a common contact, for controlling the passage of current in an electric circuit;

a first capacitor;

a first resistor;

a variable resistor, said first capacitor, said first resistor and said variable resistor connected in series, one end of said series connection adapted to receive the sum signal from said resistive network, the junction between said variable resistor and said first resistor being connected to one terminal of the first of said two position contacts, the other end of said variable resistor being connected to ground;

a second capacitor, one end of said second capacitor being connected to the common contact of said first of said two position contacts; and

a second resistor, said second resistor being connected between the other end of said second capacitor and ground, the junction between said second capacitor and said second resistor being connected to one terminal of the second of said two position contacts, the other terminal of said second of said two position contacts being connected to said voltage limiting means and the common terminal of said second of said two position contacts being connected to said actuator.

9. Apparatus including a backlash effect control comprisa mechanically powered actuator for moving a mechanism,

said actuator having backlash generating elements;

a demand signal source for generating a mechanical power demand signal in response to a demand;

a backlash effect control connected to said demand signal source to receive said demand signal and connected to said actuator for applying a modified demand signal to said actuator, said backlash effect control modifying said demand signal for a predetermined period of time after it has been generated in response to a demand so that a low relative velocity occurs between the backlash generating elements of said actuator upon impact, said modified demand signal changing to an unmodified level after said impact has occurred.

10. Apparatus including a backlash effect control as claimed in claim 9 wherein said backlash effect control comprises first and second dashpots and first and second springs connected in series between said demand signal source and said actuator, each of said dashpots comprising a housing having a plunger mounted therein with oil located between said plunger and said housing.

11. Apparatus including a backlash efiect control as claimed in claim 9 wherein said backlash effect control comprises a dashpot, said dashpot including a housing connected by a shaft to said actuator and further including a plunger conn nected by a second shaft to said demand signal source, said housing including oil located therein about said plunger so that the demand signal applied by said plunger to said housing is modified by the viscosity of said oil.

Claims

1. Apparatus including a backlash effect control comprising: an electrically operated actuator for moving a mechanism, said actuator having backlash generating elements; a demand signal source for generating an electrical demand signal in response to a demand; and a backlash effect control connected to said demand signal source to receive said demand signal and connected to said actuator for applying a modified demand signal to said actuator, said backlash effect control modifying said demand signal for a predetermined period of time after it has been generated in response to a demand so that a low relative velocity occurs between the backlash generating elements of said actuator upon impact, said modified demand signal changing to an unmodified level after said impact has occurred, said backlash effect control comprising: switch means having a pair of two position contacts, each pair including a common contact for controlling the passage of current in an electric circuit, said switch means connected to receive the electrical demand signal generated by said demand signal source; a resistor; a first variable resistor, said resistor and said first variable resistor connected in series one end of said series connection adapted to receive the electrical demand signal generated by said demand signal source, the junction between said series connection being connected to one terminal of the first of said two position contacts, the other end of said series connection being connected to ground and to the other terminal of said first of said two position contacts; a capacitor, one end of said capacitor connected to the common contact of said first of said two position contacts; and a second variable resistor, said second variable resistor being connected between the other side of said capacitor and ground, the junction between said capacitor and said second variable resistor being connected to one terminal of the second of two position contacts, the other terminal of said second of said two position contacts being connected to said demand signal source and the common terminal of said second of said two position contacts being connected to said electrically operated actuator.

2. Apparatus including a backlash effect control comprising: an electrically operated actuator for moving a mechanism, said actuator having backlash generating elements; a demand signal source for generating an electrical demand signal in response to a demand; and, a backlash effect control connected to said demand signal source to receive said demand signal and connected to said actuator for applying a modified demand signal to said actuator, said backlash effect control modifying said demand signal for a predetermined period of time after it has been generated in response to a demand so that a low relative velocity occurs between the backlash generating elements of said actuator upon impact, said modified demand signal changing to an unmodified level after said impact has occurred, said backlash effect control comprising: a first resistor having one end connected to said demand signal source and the other end connected to said electrically operated actuator; a first variable resistor; a capacitor, said first variable resistor and said capacitor connected in series with the other end of said first variable resistor being connected to said demand signal source; an NPN transistor having its base connected to the other side of said capacitor and having its emitter connected to ground; a PNP transistor having its base connected to the other side of said capacitor and its emitter connected to ground; a second variable resistor having one end connected to the collector of said NPN transistor and the other end connected to said electrically operated actuator; and a third variable resistor having one end connectEd to the collector of said PNP transistor and the other end connected to said electrically operated actuator.

3. Apparatus including a backlash effect control comprising: an electrically operated actuator for moving a mechanism, said actuator having backlash generating elements; a demand signal source for generating an electrical demand signal in response to a demand; and a backlash effect control connected to said demand signal source to receive said demand signal and connected to said actuator for applying a modified demand signal to said actuator, said backlash effect control modifying said demand signal for a predetermined period of time after it has been generated in response to a demand so that a low relative velocity occurs between the backlash generating elements of said actuator upon impact, said modified demand signal changing to an unmodified level after said impact has occurred, said backlash effect control comprising: a position indicating means connected to said electrically operated actuator for indicating the position of said actuator; a summing means connected to said demand signal source and to said position means for summing signals from said demand signal source and from said position means; and signal modifying means connected to said summing means for modifying the signal from said summing means and for applying said modified signal to said electrically operated actuator.

5. Apparatus including a backlash effect control as claimed in claim 4 wherein said modifying means comprises: transistor means connected to said resistive network and to said actuator for modifying said demand signal in a predetermined manner.

6. Apparatus including a backlash effect control as claimed in claim 5 wherein said transistor means comprises: a first resistor having one end connected to said resistive network and the other end connected to said actuator; a first variable resistor; a capacitor, said first variable resistor and said capacitor connected in series with the other end of said capacitor being connected to said resistive network; an NPN transistor having its base connected to the other side of said first variable resistor and having its emitter connected to ground; a PNP transistor having its base connected to the other side of said first variable resistor and its emitter connected to ground; a second variable resistor having one end connected to the collector of said NPN transistor and the other end connected to said actuator; and, a third variable resistor having one end connected to the collector of said PNP transistor and the other end connected to said actuator.

8. Apparatus including a backlash effect control as claimed in claim 7 wherein said modifying means also includes: switch means having a pair of two position contacts, each pair having a common contact, for controlling the passage of current in an electric circuit; a first capacitor; a first resistor; a variable resistor, said first capacitor, said first resistor and said variable resistor connected in series, one end of said series connection adapted to receive the sum signal from said resistive network, the junction between said variable resistor and said first resistor being connected to one terminal of the first of said two position contacts, the other end of said variable resistor being connected to grOund; a second capacitor, one end of said second capacitor being connected to the common contact of said first of said two position contacts; and a second resistor, said second resistor being connected between the other end of said second capacitor and ground, the junction between said second capacitor and said second resistor being connected to one terminal of the second of said two position contacts, the other terminal of said second of said two position contacts being connected to said voltage limiting means and the common terminal of said second of said two position contacts being connected to said actuator.

9. Apparatus including a backlash effect control comprising: a mechanically powered actuator for moving a mechanism, said actuator having backlash generating elements; a demand signal source for generating a mechanical power demand signal in response to a demand; a backlash effect control connected to said demand signal source to receive said demand signal and connected to said actuator for applying a modified demand signal to said actuator, said backlash effect control modifying said demand signal for a predetermined period of time after it has been generated in response to a demand so that a low relative velocity occurs between the backlash generating elements of said actuator upon impact, said modified demand signal changing to an unmodified level after said impact has occurred.

11. Apparatus including a backlash effect control as claimed in claim 9 wherein said backlash effect control comprises a dashpot, said dashpot including a housing connected by a shaft to said actuator and further including a plunger connected by a second shaft to said demand signal source, said housing including oil located therein about said plunger so that the demand signal applied by said plunger to said housing is modified by the viscosity of said oil.