US2716208A - Long time constant servo system - Google Patents

Description

United States Patent LONG TIME CONSTANT SERVO SYSTEM Francis P. Coflin, Jr., Schenectady, N. Y., assignor, by mesne assignments, to the United States of America as represented by the Secretary of the Navy Application April 11, 1946, Serial No. 661,207

8 Claims. Cl. 318-19) This invention relates to servo systems and particularly to long time constant servo systems.

A servo system accurately transmits mechanical information from one point to a remote location without mechanical connections. In some systems, the transmitted information may fade or entirely disappear for short intervals of time thereby causing the remote indicator indication to jitter and fall out of synchronization with the transmitter.

It is an object of this invention to provide an electrical servo system having means for smoothing the remote indicator indication, effectively the equivalent of a flywheel in mechanical systems.

Another object of this invention is to provide a long time constant servo system with adjustable time constant.

These and other objects will be apparent to one skilled in the art from the following specification when taken with the accompanying drawing which is generally a schematic diagram of an embodiment of the invention.

Referring to the drawing, the output of shaft rotation data source and detector 10, is connected through resistor 11 to the grids of amplifier tube 12 and cathode follower tube 13. The cathode of tube 12 is returned to a positive bias source, determined by voltage division across resistors 14 and 15, through resistor 16. The anode of tube 12 is connected to B+ through resistor 17 and to the grid of cathode follower tube 18 whose anode is returned to +B. The cathode of tube 18 is returned to ground through resistor 20 and to the grid of tube 12 through condenser 21 and ganged switch 22A, completing a conventional Miller feedback circuit for amplifying in effect, the size of condenser 21. The anode of cathode follower 13 is connected to B+ and the cathode is returned to ground through resistors 23 and 24 and bias control potentiometer 25. From the cathode of tube 13 condenser 26, ganged switch 22B, and resistor 27 are connected in series to the movable arm of potentiometer 25. Resistor 28 connects the junction of switch 22B and resistor 27 to the grid of tube 30. Converter 31, comprising a synchronous vibrator, connects and disconnects the previously described bias source at the junction of resistors 14, 15, and 16 to the grid of tube 30 rapidly, for example, 60 times per second, thereby supplying a 60 cycle carrier, modulated by the incoming signal from source 10 to the grid. The cathode of tube 30 is returned to ground through resistor 32 in parallel with potentiometer 33 and cathode resistor 34 of tube 35. The anode of tube 30 is connected to B+ through potentiometer 36. Capacitor 37 in series with resistor 38 join the anode of tube 30 and the grid of tube whose anode is returned to B+. Resistors 40 and 41 form a voltage divider, and the junction thereof connects to the grid of tube 35 through potentiometer 42, the grid of tube 46 through resistor 44, and the grid of tube 47 through resistor 45. Resistors 38 and 41 together with potentiometer 42 and capacitor 43 form a low pass filter with variable phase shift for the filter network composed of tubes 30 and 35 and their associated circuits.

2,716,208" Patented Aug. 23, 1955 Capacitor couples the 60 cycle amplitude modulated sine wave to the grid to amplifier tube 46 whose anode is connected to B through resistor 51. The cathodes of tubes 46 and 47 are returned to ground through the common resistor 52. The grid of tube 47 is bypassed to ground by condenser 53 and its plate is connected to B+ through resistor 54. The push-pull output of tubes 46 and 47 is connected to the grids of push-pull output tubes 70 and 71 through condenser 56 and resistor 61 and condenser and resistor respectively. The cathodes of tubes 70 and 71 are returned to ground through feedback windings 65 and 66 and a common cathode resistor 64. Screen grid and plate voltage is supplied to the outpug tubes 70 and 71 in conventional manner for push-pull operation. Secondary 73 of output transformer 72 connects to one winding 75 of two phase motor 76. Winding 77 of motor 76 is connected to the same 60 cycle supply as converter 31 through phase shifting condenser 80 so that the voltages applied to motor 76 are essentially in quadrature. Direction of rotation of motor 76 is determined by the phase relationships of the voltages applied to its windings. Since the phase of the voltage applied to winding 77 is fixed, it is obvious that the phase of the voltage applied to winding 75 must shift 180 degrees for a reversal of motor 76. The phase of the voltage applied to winding 75 is determined by the relative amplitude of the voltage applied to the grid of tube 30 from shaft rotation data source and detector 10 and the bias voltage appearing across resistor 15 of the voltage divider resistors 14 and 15. Motor 76 mechanically drives tachometer 81 which generates a voltage to balance out the applied voltage so that the speed of motor 76 is proportional to the applied voltage. Tachometer 81 is electrically connected to the grid of tube 30 through resistor 82 and to the bias voltage supply appearing across resistor 15.

Motor 76 also drives conventional servo 83 causing motor 84 to operate and turn rotatable element 85 in synchronism with the rotated element, not shown, from which shaft rotation data source and detector 10 receives rotational information. A conventional servo feedback loop is provided from motor 84 to shaft rotation data source and detector 10.

In operation, shaft rotation data source and detector 10 supplies positive or negative pulses of voltage when the shaft connected to the transmitter, not shown, is not in synchronism with the remote rotatable element 85. The amplitude and polarity of the voltage pulses depends upon the amount rotatable element 85 is ahead or behind the transmitter rotating element, not shown.

One type of device which may be used for this purpose is a synchro control transformer such as set forth at page 12-17 of Principles of Radar by the Staff of the M. I. T. Radar School published in 1944. When an error exists and the transmitted information is continuous, the error voltage pulses are applied to the grid of tube 30 to modulate the 60 cycle carrier supplied by converter 31. This voltage is filtered by tubes 30 and 35 and the associated circuit elements. Potentiometer 36 determines the amplitude of the sine wave voltage fed to amplifier tube 46 and inverter tube 47. The push-pull output tubes 70 and71 provide a voltage to winding 75 either leading or lagging by approximately degrees the voltage applied to motor winding 77 for rotating motor 76. The feedback loop to tachometer 81 supplies sufficient negative feedback to the modulating signal for motor 76 to run at a speed proportional to the amplitude of the input voltage ulses. p The Miller feedback circuit composed of tubes 12 and 18, and associated circuit elements, and condenser 21 as described above amplifies the effective size of condenser 21 to produce a long time constant integrating circuit.

If the input signal from source fades or disappears for a short period of time, this long time constant input circuit will keep the voltage at the grid of tube at approximately constant potential thus producing smooth rotation at rotatable element 85 instead of irregular rotation or jitter. As soon as the information from source 10 becomes steady any lag at rotatable element 85 will be almost instantly removed.

Ganged switch 22A and 22B. is adjusted to the position giving the desired time constant, for example, A, /2 and 1 second positions. Potentiometer 25 is adjusted so that motor 76 does not operate when no information is being supplied by source 10. Potentiometers 33 and 42 are adjusted so that the filter output at potentiometer 36 is a sine wave. Potentiometer 36 is the gain control for adjusting the speed of motor 76.

It is to be understood that the invention may be substituted for a conventional servo system as well as inserted into a working system as is indicated on the drawing.

While the specification describes what is now considered to be the most desirable form of the invention it will be apparent to one skilled in the art that various changes and modifications may be made therein without departing from the scope of the invention as set forth in the appended claims.

What is claimed is:

l. A long time constant servo system comprising a source of shaft rotation data, a source of alternating voltage, a long time constant input circuit, means for combining a carrier signal and said shaft rotation data voltage. means for filtering said combined shaft rotation data and carrier signal, means for obtaining a push-pull output voltage from said filtered signal, a two phase motor energized by said source of alternating voltage and said push-pull output voltage, means for obtaining feedback from said motor to said shaft rotation data source, and a tachometer feedback circuit mechanically connected to said motor and electrically connected to the input of said filter for smoothing said motor rotation when said shaft rotation data information fades or disappears for short periods of time.

2. Apparatus as in claim 1 and including a conventional servo system connected to said motor, a second motor connected to said conventional servo system.

3. A long time constant servo system providing smoothing of data from remote shaft rotation comprising, a source of shaft rotation data, a source of alternating voltage, an input from said data source connected to a long time constant resistor and capacitor network, said capacitor connected to a first cathode follower, a feedback circuit connected to said first cathode follower and said capacitor, means for changing the size of said capacitor and said long time constant, a second cathode follower connected to said resistor, a filter connected to said second cathode follower, a converter connected to said source of alternating voltage, a tachometer electrically connected to said filter, contacts of said converter shunting said tachometer, an amplifier phase converter connected to said filter output, push-pull output amplifiers connected to said amplifier phase inverter, a two phase motor, a first winding of said motor connected to said push-pull output amplifier, second winding of said motor connected to a phase shifting condenser and to said source of alternating potential, a feedback loop connected between said motor and said shaft rotation data source, said motor being mechanically connected to said tachometer, said motor speed being proportional to said input data voltage.

4. Apparatus as in claim 3 and including a conventional servo system connected to said motor, a second motor connected to said conventional servo system, said second motor providing smooth operation when said input data fades or momentarily disappears.

5. A long time constant servo system comprising, a source of shaft rotation data signals, said shaft rotation data signals being in the form of pulses of varying polarity and magnitude, an input integrating circuit coupled to said source of shaft rotation data signals, said input integrating circuit having a time constant long compared to the repetition frequency of said pulses, means for generating a relatively square wave of fixed frequency and of variable amplitude, the amplitude of said square wave being a function of a signal applied to said generating means, a combined filter and amplifier coupled to the output of said square wave generating means for passing only a signal having the fundamental frequency of said square wave, a two phase motor having first and second windings, means for supplying one winding thereof with alternating current energy having a frequency equal to said fundamental frequency and a phase in quadrature with said signal output from said combined filter and amplifier, means coupling said second winding of said motor to said combined filter and amplifier, a tachometer generator mechanically coupled to said motor so as to be rotated thereby, and means coupling the output of said input integrating circuit and said tachometer generator to said square wave generating means, said tachometer generator being coupled in a direction providing negative feedback.

6. A long time constant servo system comprising, a source of shaft rotation data signals. said shaft rotation data signals having the form of pulses of varying polarity and magnitude, an input integrating circuit coupled to said source of shaft rotation data signals, said input integrating circuit having a time constant long compared to the repetition frequency of said pulses, means for generating a periodic signal of fixed fundamental frequency, the output of said input integrating circuit being coupled to said periodic signal generating means to modulate the amplitude of the signal generated thereby, means coupled to the output of said periodic signal generating means for generating a second periodic signal having a variable amplitude and one of two phases, said phases differing by electrical degrees, the phase and amplitude of said second periodic signal being a function of the amplitude modulation of said first periodic signal, a two phase motor, means for supplying one phase winding of said two phase motor with alternating current energy having a frequency equal to the frequency of said second periodic signal and a phase in quadrature with said second periodic signal, means coupling a second phase winding of said motor to said means for generating said second periodic signal, a tachometer generator mechanically coupled to said motor to be rotated thereby, the output of said tachometer generator being coupled back to the output of said integrating means in a direction to provide negative feedback.

7. A long time constant servo system comprising a source of shaft rotation data signals, said shaft rotation data signals having the form of pulses of varying polarity and magnitude, an input integrating circuit coupled to said source of shaft rotation data signals, said integrating circuit having a time constant long compared to the repetition frequency of said pulses, means for generating a periodic signal of fixed fundamental frequency, the output of said input integrating circuit being coupled to said periodic signal generating means to modulate the amplitude of the signal generated thereby, a filter circuit for passing only the fundamental frequency of said modulated periodic signal, a phase splitting amplifier circuit coupled to the output of said filter, said phase splitting amplifier being adapted to generate second and third periodic signals at said fundamental frequency, the relative amplitudes of said second and third periodic signals being dependent upon the amplitude of the signal in the output of said filter, a reversible motor, means coupling said reversible motor to said phase splitting amplifier in a manner to cause said motor to rotate in a direction dependent upon the direction of unbalance of said first and second signals and at a speed proportional to the amount of said unbalance, a tachometer generator coupled to said motor so as to rotate therewith, the output of said tachometer generator being coupled back to said means for generating said first periodic signal in a direction to oppose the amplitude modulation of said first periodic signal.

8. A long time constant servo system comprising a source of shaft rotation data signals, said shaft rotation data signals having the form of pulses of varying polarity and magnitude, a capacitor type input integrating circuit including electronic means for amplifying the effective capacity of the capacitor in said input integrating circuit, said input integrating circuit having a time constant long compared to the repetition frequency of said pulses, means for generating a periodic signal of fixed fundamental frequency, the output of said input integrating circuit being coupled to said periodic signal generating means to modulate the amplitude of the signal generated thereby, a vacuum tube filter circuit for passing only the fundamental frequency of said modulated periodic signal, a phase splitting amplifier circuit coupled to the output of said filter, said phase splitting amplifier being adapted to generate second and third periodic signals at said fundamental frequency, the relative amplitudes of said second and third periodic signals being dependent upon the amplitude of the signal in the output of said filter, a reversible motor having a difierential winding, means coupling said difierential winding of said motor to said phase splitting amplifier in a manner to cause said motor to rotate in a direction dependent upon the direction of unbalance of said first and second signals and at a speed proportional to the amount of said unbalance, a tachometer generator coupled to said motor so as to rotate therewith, the output of said tachometer generator being coupled back to said means for generating said first periodic signal in a direction to oppose the amplitude modulation of said first periodic signal.

References Cited in the file of this patent UNITED STATES PATENTS 2,105,598 Hubbard Jan. 18, 1938 2,300,742 Harrison et a1. Nov. 3, 1942 2,449,035 Coflin et a1 Sept. 7, 1948 2,470,099 Hall May 17, 1949

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