US 3714535 A
A servo system includes power turn-off, position and direction controlled limit switching for removing excitation to the servo motor at the stop position, while permitting reversing of rotational direction upon command, to eliminate heat generation and the necessity for dissipating the heat.
Description (OCR text may contain errors)
United States Patent IIH Krivak'et al.
1 1 Jan. 30, 1973 SERVO DISPLACEMENT LIMITER WITH REVERSING CAPABILITIES Inventors: Michael T. Krivak, Hasbrouck Heights, N.J.; Gibson Reynolds, Tuxedo Park, N.Y.; Frank Prapis, Paterson,.N.J.
Assignee: The Bendix Corporation Filed: June 25, 1971 App1.No.: 156,635
Int. Cl. ..G05b 5/01 Field of Search ..3 18/266, 280, 286, 289
26 E 4 F V25 36 a 30 s 12 j /\V a W K r as 20 16 13 [561 References Cited UNITED STATES PATENTS 3.119356 1/1964 Cibelius. Jr. et al ...318/468 X 3,525,918 8/1970 Parnell ..318/626 X Primary ExaminerBernard A. Gilheany Assistant ExaminerW. E. Duncanson, .lr. AttorneyAnthony F. Cuoco  ABSTRACT A servo system includes power turn-off, position and direction controlled limit switching for removing excitation to the servo motor at the stop position, while permitting reversing of rotational direction upon command, to eliminate heat generation and the necessity for dissipating the heat.
7 Claims, 1 Drawing Fignre PAIENTEBJMSO I973 V 3,714,535
80V LOAD I INVENTORS LL M/CHAEL r KR/l/AK w y c/sso/v REYNOLDS SERVO DISPLACEMENT LIMITER WITH REVERSING CAPABILITIES BACKGROUND OF THE INVENTION This invention relates generally to servo systems and, particularly, to servo systems including output element limiting means. More particularly, this invention relates to a servo system of the type described, including electrical limiting means effective without generating heat which must be dissipated.
DESCRIPTION OF THE PRIOR ART Positioning servo and torquing devices are often designed so that the excursion of the output element is limited by mechanical stops. Under stop conditions, the servo motor and its associated amplifier generate full power and the system components must be large and rugged enough to dissipate the resulting heat.
SUMMARY OF THE INVENTION This invention contemplates position controlled limit switches in the amplifier circuit which eliminate the generation of such heat. An alternating signal is applied to the servo motor to rotate the motor shaft in a particular direction and for reversing the sense of the input signal to provide shaft rotation in the opposite direction. Rotation is stopped by position controlled limit switches actuated by cams on the motor shaft. The limit switches are further effective for commanding shaft rotation in an opposite direction.
One object of this invention is to provide limit switches for stopping the rotation of a motor and for reversing the direction of rotation without the generation of large quantities of heat which must be dissipated.
Another object of this invention is to prevent the servo system from generating full power under stop conditions.
Another object of this invention is to provide, in a servo system of thetype described, means for reversing servo motor shaft rotation when the motor is under stop conditions.
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 drawing 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 an electrical schematic diagram of a servo system according to the invention.
DESCRIPTION OF THE INVENTION An alternating command signal E and an alternating follow-up signal 13,-, out of phase with signal E, are applied through resistors 2 and 4, respectively to a summing point 6 and summed thereat. The signal from summing point 6 is applied through a coupling 28 8 to an input terminal 10 of an operational amplifier 12. Operational amplifier 12 has another input terminal 14 connected to a biasing circuit including a resistor 16 connected to the positive terminal of a battery 18, and which battery 18 has a negative terminal connected to ground, and a resistor 20 connected in parallel with resistor l6 and battery 18. A power conductor 13 is connected to an amplifier power terminal 15 and is connected intermediate resistor 16 and battery 18.
Amplifier 12 has an output terminal 22 connected to input terminal 10 through a feedback circuit including a capacitor 24 and a resistor 26. A resistor 28 is con nected intermediate resistor 26 of amplifier 12, and is connected to a grounded capacitor 30. A resistor 32 is connected intermediate resistor 28. and capacitor 30 and intermediate output terminal 22 of amplifier l2 and capacitor 24. The feedback circuit provides dc bias feedback to amplifier 12.
A transformer 36 has a primary winding 38 connected to capacitor 24 and a pair of reversing secondary windings 40 and 42 inductively coupled to primary winding 38. Secondary winding 40 has one leg connected to a base 42 of a transistor 44 and another leg connected through a resistor 46 to emitter 48 of transistor 44. Transistor 44 has a collector element 50. Secondary winding 42 has one leg connected to a base 52 of a transistor 54 and another leg connected through a resistor 56 to an emitter element 58 of transistor 54. Transistor 54 has a collector element 53.
Emitter element 46 of transistor 44 is connected through resistor 46 to a winding 60 of a servo motor 62 and collector element 53 of transistor 54 is connected to winding 60. A capacitor 64 is connected across winding 60.
Motor 62 has another winding 66 connected to an energizing alternating voltage 68. Motor 62has an output shaft 70 connected through suitable gearing means 72 to a load 80. Shaft 72 has mounted thereon a cam 74 and a cam 76.
A transformer 82 has a primary winding 84 energized by a suitable source of alternating voltage 86 and a secondary winding 88 inductively coupled to primary winding 84. Secondary winding 88 has one leg connected to a switch 90 and another leg connected to a switch 92. Switch 90 is actuated by cam 74 and switch 92 is actuated by cam 76 on motor shaft 70.
Switch 90 is connected to diodes and 102 connected in opposing relation and switch 92 is connected to diodes 104 and 106 connected in opposing relation. Diodes 100 and 106 are connected to resistor 56 lead ing from emitter 58 of transistor 54 and diodes 102 and 104 are connected to collector 50 of transistor 44. The signal applied from transformer 82 through switch 90 and diodes 100, 106 to emitter 58 of transistor 54 has 'a waveform a, b shown in the FIGURE, and the signal applied from the transformer through switch 92 and diodes 102, 104 has a waveform c, d as shown in the FIGURE.
OPERATION OF THE INVENTION Assuming signal E is the dominant input signal, the positive half cycle of the signal drives base 42 of transistor 44 positive and base 52 of transistor 54 negative and half-cycle c is applied to motor 62. During the negative half-cycle of input signal E base 52 of transistor 54 becomes positive and half-cycle b is applied to motor 62. Thus, a full cycle is developed across the motor to rotate the motor in a particular direction which may, for example, be clockwise. Reversing the phase of the input signal will apply half-cycles a and d to motor 62 providing counterclockwise rotation.
To stop clockwise rotation, it is merely required to interrupt half-cycles c and b by opening limit switch 90 through cam 74. Half-cycles a and d remain connected to the transistor in preparation for applying power to the motor upon a reverse rotation command. Similarly, limit switch 92 may be opened to interrupt counterclockwise power while switch 90, remaining closed, applies half-cycles c and b for clockwise commanded rotation.
It will now be seen from the foregoing description of the invention that the inclusion of position controlled limit switches 90 and 92 in the amplifier circuit is effective for eliminating generation of heat during stop conditions, and thus eliminates the necessity for dissipation of said heat in the motor and amplifier. Moreover, the system is capable of reverse rotation when in the stop position.
While one embodiment of the invention has been illustrated and described in detail, it is to be expressly understood that the invention is not limited thereto. Various changes may also be made in the design and arrangement of the parts without departing from the spirit and scope of the invention as the same will now be understood by those skilled in the art.
What is claimed is:
l. A servo system, comprising:
a motor having a shaft connected to a load for driving the load; means for providing a control signal; means for providing a motor driving signal; means connected to the control signal means and to the driving signal means and responsive to the signals therefrom for applying a signal to the motor for rotating the motor shaft in a predetermined direction; motor shaft displacement responsive means as sociated with the motor driving signal means and effective upon a predetermined shaft displacement for disconnecting the driving signal means from the signal applying means to stop the motor; and
said control signal means including means for providing a servo command signal; means for providing a servo follow-up signal; means for combining the command and follow-up signals; and operational amplifier having a first input terminal, a first output terminal connected to the signal applying means, a grounded second output terminal and a power terminal; an amplifier biasing circuit connected to the second input terminal; a feedback circuit connected to the first output terminal and to the first input terminal; and a power conductor connected to the biasing circuit and to the power terminal.
2. A servo system as described by claim 1, wherein:
the control signal is an alternating signal having positive and negative half-cycles;
the means for providing driving signals includes means for providing a first signal having positive half-cycles and means for providing a second signal having negative half-cycles;
the means connected to the control signal means and to the driving signal means and responsive to the signals therefrom for applying a signal to the motor for rotating the motor shaft in a predetermined 5 direction includes a first current flow control device affected by the positive half-cycle of the alternating signal for applying a positive half-cycle of the first signal to the motor and a second current flow control device affected by the negative half-cycle of the alternating signal for applying a negative half-cycle of the second signal to the motor; and
the motor is responsive to the full cycle signal including the positive and negative half-cycles of the first and second signals so that the motor shaft rotates in the predetermined direction.
3. A servo system as described by claim 2, wherein the means for providing driving signals including means 0 for providing a first signal having positive half-cycles and means for providing a second signal having negative half-cycles comprises:
means for providing an alternating signal;
a transformer having a primary winding connected to the alternating signal means and a secondary winding inductively coupled to the primary winding;
a third current flow control device connected to one of the legs of the secondary winding and a fourth current flow control device connected to the other leg in opposing relation to the third device;
a fifth current flow control device connected to the one leg in opposing relation to the third device and a sixth current flow control device connected to the other leg in opposing relation to the fourth device; and
the fourth and fifth devices cooperating to provide the first signal having positive half-cycles and the third and sixth devices cooperating to provide the second signal having negative half-cycles.
4. A servo system as described by claim 3, wherein the motor shaft displacement responsive means associated with the motor driving signal means and effective upon a predetermined shaft displacement for disconnecting the driving signal means from the signal applying means to stop the motor includes:
a normally closed first switch connected between the one leg of the secondary winding and the third and fifth current flow control devices;
a normally closed second switch connected between the other leg of the secondary winding and the fourth and sixth current flow control devices;
first switch actuating means coupled to the motor shaft and to the first switch for opening the first switch when the motor shaft displacement is at a predetermined limit in one sense; and
second switch actuating means coupled to the motor shaft and to the second switch for opening the second switch when the motor shaft displacement is at a predetermined limit in an opposite sense.
5. A servo system as'described by claim 1, wherein the biasing circuit includes:
a first resistor connected to the second input terminal; Q
a power supply serially connected to the first resistor; and
a second resistor connected in parallel with the first resistor and the battery.
a first capacitor connected to the first output terminal; a first resistor connected to the capacitor and to the first input terminal;
a second resistor and a second capacitor connected in series between the first resistor and the first input terminal; and
a third resistor'connected between the secondfresistor and the second capacitor and connected between the first output terminal and the first capacitor. p
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