Bidirectional self balancing bridge

• US 4,112,343 A
• Filed: 04/27/1977
• Issued: 09/05/1978
• Est. Priority Date: 01/29/1975
• Status: Expired due to Term

• Current Assignee: Cornell-Dubilier Electronics Incorporated
• Original Assignee: Cornell-Dubilier Electric Corp.
• Inventors: Douglas, Philip N.
• Primary Examiner(s): Dobeck, B.
• Application Number:
  US05/791,554
• Time in Patent Office: 496 Days
• Field of Search: 318/674, 318/678, 318/663, 323/75 E
• US Class Current: 318/674
• CPC Class Codes: G05D 3/16 whose output amplitude can only take a number of discrete values G05D3/18 takes precedence

Abstract

The disclosed system includes a direct-current bridge circuit and a bridge-balancing reversible motor coupled to the bridge circuit, together with a differential high-gain amplifier which is responsive to even slight bridge unbalance to polarize the motor for rotation in the direction toward rebalance of the bridge circuit and also interrupts the motor operation when balance of the bridge is passed in either direction. Apparatus is included responsive to both positive and negative reversals in the polarity of unbalance of the bridge for deenergizing the motor when the null of the bridge is crossed in either direction.

Claims

1. A self-balancing direct current bridge system, including a mechanical output device;

a position sensor coupled to said output device to provide a signal representing the actual position of said device;

a reversible motor for operating said output device;

a first relay effective when energized to connect said motor to a power source;

means for energizing said first relay;

a second relay arranged when de-energized to permit motor rotation in one direction and when energized to permit motor rotation in the opposite direction;

direct-current bridge means;

an output circuit for said bridge means;

an adjustable control element to provide a signal representing a desired position for said output device, means coupling said actual and desired position signals in said bridge means whereby said bridge means is balanced when said position signals represent like desired and actual positions and is unbalanced otherwise;

means connected to said bridge output circuit for selectivity energizing or deenergizing said second relay such that the motor operates to restore the bridge means to its balanced condition;

said output circuit including means responsive to the rate of change of bridge balance to produce a control signal; and

means responsive to any polarity reversal of the rate of change of bridge balance for de-energizing said first relay and thereby de-energizing said motor.

2. A self-balancing direct current bridge system in accordance with claim 1, wherein said means for de-energizing said first relay includes means to interrupt the current flow path of said relay whenever said control signal changes polarity.

3. A self-balancing direct current bridge system in accordance with claim 1, wherein said bridge output circuit includes a high-gain differential amplifier and the means for de-energizing said first relay includes series-coupled capacitance means.

4. A self-balancing bridge circuit in accordance with claim 1, wherein said bridge output circuit includes a high-gain direct-current amplifier and wherein said control signal generating means includes pulse generating means and wherein said means for de-energizing said first relay includes means separately responsive to positive and negative control signal pulses.

5. A self-balancing bridge circuit in accordance with claim 1, wherein said bridge output means inclues a differential high-gain direct-current amplifier whose output is at the positive or negative power supply level when the bridge circuit is even slightly unbalanced, the amplifier output being of one polarity or the opposite according to the polarity of said unbalance, and wherein said means for de-energizing the first relay includes means that are polarized and responsive to control signals corresponding to different directions of reversal of the output of the amplifier whereby the motor is de-energized in response to each polarity reversal.

6. A self-balancing bridge system in accordance with claim 1 wherein said position sensor is an adjustable resistor operated by said motor coordinately with the output device, and coupled into said bridge means, and wherein said adjustable control element is an adjustable resistor coupled into said bridge means.

7. A control system comprising a d-c bridge;

an adjustable control resistance;

an adjustable slave resistance;

a motor for controlling the slave resistance;

current conduction means for applying power to the motor, current controlling means maintaining said current conduction means normally conducting, a high-gain direct current amplifier hving an input circuit connected across the bridge; and

differentiating means coupled between the amplifier output circuit and the current controlling means;

said current controlling means including means for disabling the current conduction means responsive to both positive and negative transitions in the output of said differentiating means corresponding to the crossing of the null of the bridge in opposite directions.

8. A self-balancing bridge circuit as in claim 7 wherein said current conduction means comprises a relay having contacts for applying power to the motor.

9. A self-balancing bridge circuit as in claim 8 wherein said differentiating means includes a series capacitor whereby to generate positive and negative pulses responsive to positive and negative going transitions of the amplifier output for disabling the current conduction means.

10. A self-balancing bridge circuit as in claim 7 wherein the current controlling means includes means that are polarized and responsive to signals of different polarity received from the differentiating means for de-energizing the motor responsive to each polarity transition of the output of said amplifier.

11. A bridge circuit according to claim 7 wherein said current conduction means comprises a relay having contacts for applying power to the motor, wherein said current control means includes a polarity-sensitive switching device in series with the coil of said relay and means providing bias for maintaining said switching device in its relay-energizing state;

wherein said differentiating means includes a capacitor coupled to the output of said amplifier, said current control device further including a second polarity sensitive device for removing the bias on said switching device in response to an output of said differentiating device corresponding to a crossing of the null of the bridge in one direction, and a third polarity sensitive device for removing the bias on said switching device in response to an output of said differentiating device corresponding to a crossing of the null of the bridge in the opposite direction.

12. A bridge circuit according to claim 11, wherein said switching device comprises a transistor, including a signal path defined by two terminals in series with said relay coil and a control input defined by a separate third terminal connected to said second and third polarity sensitive devices.

13. A bridge circuit according to claim 12, wherein said second polarity sensitive device comprises a diode coupled between said capacitor and said transistor control terminal.

14. A bridge circuit according to claim 7, further including motor reversing means for controlling the sense of adjustment of said slave resistance, including means responsive to a positive output of said amplifier to condition said motor for operation in one direction and responsive to a negative output of said amplifier to condition said motor for operation in the opposite direction.

15. A bridge circuit according to claim 14, wherein said motor reversing means comprises a relay having normally open and normally closed contact means connecting said motor to said power source for rotation in opposite directions, said relay being responsive to one polarity output of said amplifier to close said normally open contacts, but remaining unenergized in response to the opposite polarity output of said amplifier.

16. A d-c feedback control system including a mechanical output device;

a power source;

reversible drive means for said output device operable by said power source;

first switch means effective when energized to maintain said power source in operation;

means for energizing said first switch means;

second switch means operative when de-energized to permit operation of said drive means in one direction and when energized to permit operation of said drive means in the opposite direction;

first means to generate a d.c. signal representative of the desired position of said output device;

second means to generate a d-c signal representative of the actual position of said output device;

circuit means providing a first output when said d-c signals represent one sense of difference between the desired and actual positions of said output means, and for providing a second output when the d-c isgnals represent the opposite sense of difference between the desired and actual positions of said output means;

differentiating means coupled to the output of said circuit means;

means responsive to the first output of said circuit means to de-energize said second switch means and responsive to the second output of said circuit means to energize said second switch means; and

means responsive to an output of said differentiating means corresponding to reversal of the polarity of the circuit means output in either direction for de-energizing said first switch means and thereby deactivating said power supply.

17. A feedback control system according to claim 16, wherein said drive means comprises a reversible motor;

and wherein said second switch means comprises a relay having first and second contact means, said first contact means coupling said power source to said motor for operation in one direction, and said second contact means coupling said power source to said motor for operation in the opposite direction.

18. A control system according to claim 16, wherein said first switch means comprises a relay with a normally open contact pair through which power is supplied to the remainder of the system, the energizing means coupling said relay coil to said power supply;

and means for by-passing the normally open relay contacts for at least long enough to allow the relay to be energized.

19. A control system according to claim 18, wherein said by-passing means comprises a manually operable momentary contact switch.

20. A control system according to claim 18, wherein said differentiating means comprises a series capacitor, and wherein said means for de-energizing said first switch means comprises means for disconnecting the coil of said relay from said power supply.

21. A control system according to claim 20, wherein said first means to generate a d-c signal representative of the desired position of said output device comprises an adjustable resistor;

and wherein said second means to generate a d-c signal representative of the actual position of said output device comprises an adjustable resistor connected to said output device and arranged for adjustment in accordance with motion of said output device.

22. A control system according to claim 21, wherein said circuit means comprises a d-c bridge including said adjustable resistors and further means responsive to even a small bridge unbalance of one polarity to provide said first output and responsive to even a small bridge unbalance of the opposite polarity to provide said second output.

23. A control system according to claim 22, wherein said further means comprises a high gain d-c differential amplifier connected in open loop configuration.

24. A control system according to claim 17, wherein said means to energize and de-energize said second switch means comprises a transistor having a signal path connected in series with said relay coil, and having a control terminal coupled to the output of said circuit means.

25. A control system according to claim 16, wherein said means for de-energizing said first switch means comprises a transistor having its current path connected to energize said first switch means, a control terminal means connected to said control terminal for biasing said transistor into conduction when said system is energized, and first and second polarity sensitive means connected to said differentiating means and each responsive to an output from said differentiating means of different polarity for overcoming the bias at said transistor control terminal.