Damping for electromechanical actuators

• US 7,109,679 B2
• Filed: 03/09/2004
• Issued: 09/19/2006
• Est. Priority Date: 03/09/2004
• Status: Expired due to Fees

• Current Assignee: HR Textron, Inc.
• Original Assignee: HR Textron, Inc.
• Inventors: Edson, Ralph D., Mock, M. Robert
• Primary Examiner(s): Ro, Bentsu
• Application Number:
  US10/797,787
• Publication Number:
  US 20050200328A1
• Time in Patent Office: 924 Days
• Field of Search: 318/560, 318/561, 318/566, 318/568.22, 318/611, 318/615, 318/619, 318/621, 318/623, 318/632, 318650-653
• US Class Current: 318/611
• CPC Class Codes: G05B 19/404 characterised by control arrangements for compensation, e.g. for backlash, overshoot, tool offset, tool wear, temperature, machine construction errors, load, inertia G05B19/19, G05B19/41 take precedence
• CPC Class Codes: G05B 2219/49054 Active damping of tool vibration

Abstract

Oscillation and other disturbance damping is provided for a system having a load driven by an electric motor, e.g., an electromagnetic actuator. Damping is achieved using feedback in an active mode, where power is supplied in a normal operation mode of the electromagnetic actuator. Feedback may be provided by measured force (or torque) transmitted between the actuator and load mass. A gear train or other mechanical advantage device may be connected between the electromagnetic actuator output and load, this combination forming an electromechanical actuator (EMA). Instead of force or torque, acceleration of the load may be used as a feedback signal. In one embodiment, active mode damping uses the motor'"'"'s actual current as a feedback signal. In certain or all active damping versions of the invention, a high pass filter is preferably used to receive feedback signals and filter out low frequency feedback. Alternatively, damping is achieved in an inactive (passive) mode of motor operation, e.g., where the electric motor is not receiving power drive signals. The motor coils are shorted, e.g., using a switch. The induced motor currents act to inhibit load oscillations. Preferably, a resistance, e.g., a number of resistors, are in the short circuit to tailor the damping characteristics of the motor. In at least the active current feedback and passive modes of operation, inertia of the electric motor is substantially reduced in relation to typical motor inertia, by changing the stator to rotor diameter ratio from a typical ratio of at or about 2:1 or less, to a substantially higher ratio than 2:1.

Claims

1. A damped system for moving a load, comprising:

an electric motor having damping means;

a mechanical connection between the electric motor and the load;

a transducer to sense an indicator related to load force or torque and produce a feedback signal; and

a controller connected to the electric motor and providing a motor control signal to move the load to a desired position, and connected to the transducer for receiving the feedback signal and adjusting the motor control signal based on the feedback signal whereby disturbances to the position of the load are damped;

wherein the damping means comprises a resistance and a switch for connecting the motor windings in a short circuit with the resistance in response to loss of power to the motor, whereby oscillating disturbances to the position of the load are damped even when there is no power to the motor.

2. The damped system of claim 1, wherein the electric motor is a servo motor comprising an electromagnetic actuator.

3. The damped system of claim 1, wherein the transducer is one of a force transducer, a torque transducer, and an accelerometer.

4. The damped system of claim 3, further comprising a high pass filter which filters the feedback signals.

5. The damped system of claim 1, wherein the transducer is a current sensor.

6. The damped system of claim 5, wherein the electric motor has a stator and a rotor, and a diameter of the stator divided by a diameter of the rotor is set for damping to at least 2.75.

7. The damped system of claim 6, wherein the diameter of the stator divided by the diameter of the rotor is at least about five.

8. The damped system of claim 6, wherein the diameter of the stator divided by the diameter of the rotor is at least about ten.

9. The damped system of claim 1, wherein the resistance comprises two resistors.

10. The damped system of claim 1, wherein the resistance comprises three resistors.

11. The damped system of claim 1, wherein the motor comprises a stator and a rotor, and the feedback means further includes setting the diameter of the stator divided by a diameter of the rotor equal to at least about 2.75.

12. The damped system of claim 11, wherein the diameter of the stator divided by the diameter of the rotor is at least about five.

13. The damped system of claim 11, wherein the diameter of the stator divided by the diameter of the rotor is at least about ten.

14. The damped system of claim 1, wherein the mechanical connection includes a power train which has a gear ratio of at least about fifty.

15. The damped system of claim 1, wherein the load comprises a front wheel of a vehicle.

16. The damped system of claim 1, wherein the electric motor forms at least a portion of an electromechanical actuator which is configured to stabilize the mechanical connection at a fixed orientation when the load is coupled to the mechanical connection and when the load is moved to the desired position, the disturbances being damped when the electromechanical actuator stabilizes the mechanical connection at the fixed orientation.

17. The damped system of claim 1, wherein the electromechanical actuator is configured to stabilize the mechanical connection at a fixed orientation when the load is coupled to the mechanical connection and when the load is moved to the desired position, the disturbances being damped when the electromechanical actuator stabilizes the mechanical connection at the fixed orientation.

18. A damped system for moving a load, comprising:

an electric motor having damping means;

a mechanical connection between the electric motor and the load;

a transducer to sense an indicator related to load force or torque and produce a feedback signal; and

a controller connected to the electric motor and providing a motor control signal to move the load to a desired position, and connected to the transducer for receiving the feedback signal and adjusting the motor control signal based on the feedback signal whereby disturbances to the position of the load are damped;

wherein the electric motor has a stator and a rotor, and wherein a diameter of the stator divided by a diameter of the rotor is set for damping, the ratio being set at least 2.75.

19. The damped system of claim 18, wherein the diameter of the stator divided by the diameter of the rotor is at least about five.

20. The damped system of claim 18, wherein the ratio of the diameter of the stator divided by the diameter of the rotor is at least about ten.

21. A method of providing damping to disturbances to the position of a load in a load moving system, the method comprising the steps of:

moving a load with an electric motor;

sensing an indicator of load movement and feeding back a feedback signal indicative of the sensed indicator; and

controlling the electric motor by providing a motor control signal to move the load to a desired position based on the feedback signal, whereby disturbances to the position of the load are damped;

wherein the motor has windings, and the method further comprises a step of providing a resistance, and a step of connecting the motor windings in a short circuit with the resistance in response to loss of power to the motor, whereby disturbances to the position of the load are damped even when there is no power to the motor.

22. The method of claim 21, wherein the electric motor forms at least a portion of an electromechanical actuator which is configured to stabilize a mechanical connection at a fixed orientation when the load is coupled to the mechanical connection and when the load is moved to the desired position, and wherein the step of controlling the electric motor includes the step of:

damping the disturbances when the electromechanical actuator stabilizes the mechanical connection at the fixed orientation.

23. A damped system for moving a load, comprising:

an electromagnetic actuator;

a mechanical connection between the electromagnetic actuator and the load;

a controller connected to the electromagnetic actuator and providing a motor control signal to move the load to a desired position; and

a damping mechanism electrically responsive to an indicator related to force or torque oscillations of the load from the desired position in response to disturbances to the position of the load;

wherein the electromagnetic actuator comprises an electrical motor having windings, and the damping mechanism comprises a resistance, and a switch for connecting the motor windings in a short circuit with the resistance in response to loss of power to the motor whereby disturbances to the position of the load are damped even when there is no power to the motor.

24. The damped system of claim 23, wherein the damping mechanism further comprises a transducer to sense an indicator related to load force or torque oscillations, and produce a feedback signal, and the controller is also connected to the transducer for receiving the feedback signal and adjusting the control signal to the motor based on the feedback signal whereby disturbances to the position of the load are damped.