US3600659A

US3600659A - Solid-state compact servosystem

Info

Publication number: US3600659A
Application number: US862208A
Authority: US
Inventors: Alex Danchuk
Original assignee: Bendix Corp
Current assignee: Bendix Corp
Priority date: 1969-09-30
Filing date: 1969-09-30
Publication date: 1971-08-17
Anticipated expiration: 1988-08-17

Abstract

A servosystem having solid-state components includes means for summing an alternating command signal with a motor shaft position signal and when the resulting difference signal exceeds a predetermined threshold drivers are actuated for applying to the motor a voltage having a polarity in accordance with the phase of the difference signal relative to a reference. The voltage is cut off when the motor is at null, whereupon inertia drives the motor past null to provide a difference signal of opposite polarity so that the motor is driven in the opposite direction until it again passes through null, reversing the voltage thereto with the result being that full voltage is applied to the motor until the null is reached.

Description

Unite States mm [72] Inven or A x D ll h k 3,406,309 10/1968 Martens 3 18/18 X (20.835) Livingston, NJ. 3,260,912 7/1966 Gregory 318/599 [21] Appl. No. 862,208 3,363,158 l/1968 Potma 318/616 [22] Filed Sept. 30, 1969 3,391,317 7/1968 Bell 318/619 [45] Patented Aug. 17, 1971 Primary Examiner-Ben amin Dobeck [73] Asslgnee The Bendix Cnrporafion Attorneys-Anthony F. Cuoco and Flame, Arens, Ham,

Smith and Thompson [54] SOLID-STATE COMPACT SERVOSYSTEM 2 Claims, 1 Drawing Fig.

ABSTRACT: A servosystem having solid-state components in- [52] 11.5. CI. 318/608, eludes means for Summing an alternating command Signal 318/614, 3318/65 with a motor shaft position signal and when the resulting dif- [51] Int. Cl. Gosh 5/01 ference Signal exceeds a predetermined threshold drivers are of Search 1 t t d f t th motor a lt g h i g a p l ity 20-41 ZOAZO' 20-370 in accordance with the phase of the difference signal relative [56] Reerences Cited to a reference. The voltage is cut off when the motor is at null,

whereupon inertia drives the motor past null to provide a dif- UNITED STATES PATENTS ference signal of opposite polarity so that the motor is driven 3,940,028 6/ 1960 Parzen 3.18/28 X (20.440) in the opposite direction until it again passes through null, 3,237,070 2/1966 lnaba et al. .318/ 18 X (20.415) reversing the voltage thereto with the result being that full 3,239,735 3/1966 Raider et a1. 3.18/18 X (20.415) voltage is applied to the motor until the null is reached.

. g2 POWgR l I5 SUPPLY DRIVER 2 IOA 10 i I? as 34 c 9 l JPHASE SWITCH T DV 7 DET. I |0B l DRIVER-Y l3 7 I I 12 T 16 I 7 4 DEVICE DELAY NETWORK PATENIED mm 7 l9?! v 3, 600, 659

POWER H '5 SUPPLY DRIVER 3 IO 36 34 j PHASE swncn M on BRAKE DRIVER I 13 T7 ,6 g 4 6 I POSITION SENSING DEVICE DELAY NETWORK IN VENTOR.

ALEX DANCHUK A rroM/E SOLID-STATE COMPACT SERVOSYSTEM BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to servosystems and, more particularly, to servosystems having solid state components, and having reduced size and weight and minimal power losses.

2. Description of the Prior Art Servosystems now known in the art use servoamplifiers which, for high power applications, are large in size and incur considerable power losses. Modern requirements call for smaller and lighter systems and systems which operate with increased accuracy.

SUMMARY OF THE INVENTION This invention contemplates a servosystem of solid-state construction and having means for summing an AC command signal with a servomotor shaft position signal for providing a difference signal. The phase of the difference signal relative to a reference signal is detected, and when the difference signal exceeds a predetermined threshold clockwise or counterclockwise drivers, depending on said detected phase, are actuated. The drivers operate a switch for applying a voltage of appropriate polarity to the servomotor. When the servomotor is at null the voltage is cutoff, but inertia drivers the motor past null so that a difference signal of opposite polarity is detected. The voltage to the motor is thereupon reversed to initially slow the motor and to ultimately drive the motor in the opposite direction until the motor again drives through null reversing the voltage to the motor. In this manner full voltage is applied to the motor until null is reached to provide a servosystem having improved accuracy. Improved null stability is achieved by applying braking action to the motor at null conditions.

One object of this invention is to provide a servosystem of solid state construction having reduced size, minimal power losses and increased accuracy.

Another object of this invention is to provide a servosystem of the type described having improved null stability.

Another object of this invention is to provide a servosystem having small power consumption components for minimizing power losses and for substantially reducing the cost of the system.

The foregoing and other objects and advantages of the invention will appear more fully hereinafter from a consideration of the detailed description which follows, taken together with the accompanying drawings wherein one embodiment of the invention is illustrated by way of example. It is to be expressly understood, however, that the drawings are for illustration purposes only and are not to be construed as defining the limits of the invention.

DESCRIPTION OF THE DRAWINGS The single figure in the drawing is a block diagram of a servosystem according to the invention.

An AC command signal E, which may correspond, for purposes of example, to an aircraft flight condition signal is applied to a summing means 2. Signal E has a phase in accordance with the direction of the command. A position sensing device 4 is connected by suitable mechanical means 6 to a torquer motor 8 and is connected by a conductor 7 to summing means 2. Position sensor 4 may be a linear potentiometer for sensing the angular position of the motor shaft and for providing at conductor 7 a corresponding electrical signal. Summing means 2, which may be a simple resistance, transformer or operational amplifier in differential amplifier configuration sums signal E and the signal from position sensing device 4 and provides at an output conductor 9 an AC signal corresponding to the difference therebetween. Solid state differential amplifiers suitable for purposes of the inven tion are described at pages 111-120, Transistor Manual published in 1964 by the General Electric Company.

Summing means 2 is connected through conductor 9 to an input terminal 10A of a phase detector 10. Phase detector 10 has another input terminal 108 connected to a suitable AC reference source 12. When the signal from summing means 2 exceeds a predetermined threshold, phase detector 10 provides an output at either an output conductor 11 or at an output conductor 13, depending on the phase of the signal from summing means 2. Phase detector 10 is of the type which includes an operational amplifier used as a threshold device for comparing the signal from summing means'2 to a fixed level reference voltage and further includes a pair of operational amplifiers for phase detection whereby AC signal proportional to the phase difference between the signal from summing means 2 and the reference voltage from source 12 is provided at one of the conductors 11 or 13, depending on the phase of the signal from summing means 2. A solid-state device suitable for the purposes of phase detector 10 is shown in FIG. 7-26, Pulse, Digital and Switching Waveforms, Milman and Taub, McGraw-l-lill 1965, modified as will be understood by those skilled in the art and as indicated at page 260.

Conductorsll and 13 are connected to

corresponding drivers

14 and 16, and which drivers include high input impedance amplifiers which may be described at page 102, FIG. 4.7, 4.8, Transistor Manual, supra, for protecting the signal channel from loading effects.

Drivers

14 and 16 further include demodulators or converters for providing DC voltages at

respective output conductors

15 and 17. A device employing semiconductors and suitable for the purposes of

drivers

14 and 16 is described in U.S. Pat. No. 3,525,921 issued Aug. 25, 1970 to H. B. Wattson and assigned to The Bendix Corporation, assignee of the present invention. It will be understood that driver 14 will provide a voltage at output conductor 15 if phase detector 10 provides an output at conductor 11 and driver 16 will provide a voltage at conductor 17 if phase detector 10 provides an output at conductor 13. The effect of

drivers

14 and 16 is to drive motor 8 in either clockwise or counterclockwise directions as will hereinafter become evident.

Conductors

15 and 17 are connected to a switch 23, and which switch 23 is connected to a power supply 22 providing suitable positive and negative DC motor driving voltages. Switch 23 may be an electrical mechanical relay or transistorized switch such as. described at Chapter 6, Transistor Manual, supra, responsive to the voltages at

conductors

15 or 17 to apply voltage of proper polarity from power supply 22 to motor 8 to drive the motor. It will be understood that when voltage of one polarity is applied to motor 8, the motor is driven clockwise and when voltage of the opposite polarity is applied, the motor is driven counterclockwise.

Drivers

14 and 16, are also connected through

output conductors

15 and 17 to a summing means 24, and which summing means 24 may be an operational amplifier such as described with reference to summing means 2 for summing the signals from the drivers and for providing a signal corresponding to the difference therebetween.

Summing means 24 is connected to a delay network 26, and which delay network 26 is connected to a voltage level detector 28. Delay network 26 is a low pass filter such as described at pages 42-47, Pulse, Switching and Digital Waveforms, supra for smoothing and delaying the signal from summing means 24 before applying said signal to the level detector. Level detector 28 is an operational amplifier connected as described in copending U.S. application Ser. No. 691,376, filed Dec. 18, 1967 by Steven D. Stolman and assigned to The Bendix Corporation, assignee of the present invention, which compares the signal from delay network 26 to a preselected reference signal provided by a battery 29, and provides a triggering output when the difference between said signals exceeds a predetermined level. The driver 32, which may be a high input impedance amplifier such as described with reference to

drives

15 and 17, is connected to level detector 28 and is connected to a brake 34. Brake 34 is coupled by suitable mechanical means 36 to the shaft of Motor 8. The

triggering output from level detector 28 is applied through driver 32 to brake 34, and which brake 34 imparts a holding action to motor 18 for better null stability, and during intervals when power to the system is cutoff.

OPERATION As command signal E is received, it is compared by summing means 2 with the signal from position sensing device 4 to determine the difference between the two signals. The difference signal is applied to phase detector which, in accordance with phase of the difference signal, applies a signal to either clockwise driver 14 or counterclockwise 16. The drivers, in turn, actuate switch 23 which delivers full voltage of appropriate polarity directly to motor 8 for driving said motor clockwise or counterclockwise. Motor 8 receives full voltage as long as an input signal is provided at input 10A of phase detector 10, and as soon as the motor drives through a null, power is cut off. However, inertia carries the motor load past null for providing at the output of summing device 2 an opposing signal which reverses the polarity of the motor driving voltage. This first slows down the motor and finally drivers the motor in the opposite direction until null is again achieved. In contrast to servosystems now shown in the art, the system of the invention thus provides full voltage to the motor until null is reached and thereby imparts greater accuracy to the system.

At the same time, clockwise and

counterclockwise drivers

14 and 16 apply signals to summing device 24 and which device 24 sums the signals and applies the resulting difference signal to delay network 26 and therefrom to level detector 28. When the delayed difference signal exceeds a predetermined threshold established by level detector 28, driver 32 actuates brake 34 for better null stability, and also for holding the system at time when power is off.

- Although only one embodiment of the invention has been illustrated and described, various changes in the form and relative arrangements of the parts, which will now appear obvious to those skilled in the art may be made without departing from the scope of the invention. Reference is, therefore, to be had to the appended claims for a definition of the limits of the invention.

What I claim is:

1. A servosystem, comprising:

a servomotor;

means connected to the servomotor for providing a motor shaft position signal;

means for providing a command signal;

means connected to the shaft position signal means and to the command signal means for summing the signals therefrom and providing a difference signal;

a voltage source;

switching means connecting the voltage source to the servomotor;

driving means connected to the switching means;

means for connecting the driving means to the difference signal means, with the driving means responsive to the difference signal above a predetermined level in one sense for rendering the switching means effective to apply voltage from the voltage source to the motor;

means for providing an AC reference signal;

the means for connecting the difference signal means to the driving means being connected to the reference signal means for providing a first signal when the difference signal is of one phase relative to the reference signal and for providing a second signal when said difference slgnal is of another phase;

the driving means including means responsive to the first signal for providing a signal for driving the motor in one direction and responsive to the second signal for providing a signal for driving the motor in an opposite direction;

means connected to the means for providing the motor driving signals for summing the signals therefrom and for providing a signal corresponding to the difference therebetween; means connected to the difference signal for filtering said signal;

means for providing a reference signal;

means for comparing the reference signal and the filtered signal to provide a triggering signal when the difference between the compared signals exceeds a predetermined level; and

braking means connected to the triggering signal means and to the motor for braking the motor in response to the triggering signal.

2. A system as described by claim 1, wherein:

the vgltage source provides voltages of opposite polarities;

the switching means is affected by the signal for driving the motor in the one direction for applying voltage of one polarity to the motor, and is affected by the signal for driving the motor in the opposite'direction for applying voltage of opposite polarity to the motor.

Claims

1. A servosystem, comprising: a servomotor; means connected to the servomotor for pRoviding a motor shaft position signal; means for providing a command signal; means connected to the shaft position signal means and to the command signal means for summing the signals therefrom and providing a difference signal; a voltage source; switching means connecting the voltage source to the servomotor; driving means connected to the switching means; means for connecting the driving means to the difference signal means, with the driving means responsive to the difference signal above a predetermined level in one sense for rendering the switching means effective to apply voltage from the voltage source to the motor; means for providing an AC reference signal; the means for connecting the difference signal means to the driving means being connected to the reference signal means for providing a first signal when the difference signal is of one phase relative to the reference signal and for providing a second signal when said difference sIgnal is of another phase; the driving means including means responsive to the first signal for providing a signal for driving the motor in one direction and responsive to the second signal for providing a signal for driving the motor in an opposite direction; means connected to the means for providing the motor driving signals for summing the signals therefrom and for providing a signal corresponding to the difference therebetween; means connected to the difference signal for filtering said signal; means for providing a reference signal; means for comparing the reference signal and the filtered signal to provide a triggering signal when the difference between the compared signals exceeds a predetermined level; and braking means connected to the triggering signal means and to the motor for braking the motor in response to the triggering signal.

2. A system as described by claim 1, wherein: the voltage source provides voltages of opposite polarities; and the switching means is affected by the signal for driving the motor in the one direction for applying voltage of one polarity to the motor, and is affected by the signal for driving the motor in the opposite direction for applying voltage of opposite polarity to the motor.