Method and apparatus for tuning a motion control system having an external velocity loop

• US 5,684,374 A
• Filed: 07/27/1995
• Issued: 11/04/1997
• Est. Priority Date: 07/27/1995
• Status: Expired due to Term

• Current Assignee: Allen-Bradley Company (Rockwell Automation, Inc.)
• Original Assignee: Allen-Bradley Company (Rockwell Automation, Inc.)
• Inventors: Chaffee, Mark A.
• Primary Examiner(s): Cabeca, John W.
• Application Number:
  US08/508,012
• Time in Patent Office: 831 Days
• Field of Search: 318/610-612, 318/567, 318/569, 318/609, 318/432, 318/615, 318/618, 318/629, 318/619, 318/616, 318/632, 388/809, 388/806, 388/815
• US Class Current: 318/616
• CPC Class Codes: G05B 19/19 characterised by positioning or contouring control systems, e.g. to control position from one programmed point to another or to control movement along a programmed continuous path
• CPC Class Codes: G05B 2219/41016 Adjust gain to maintain operating bandwith for guaranteed servo performance
• CPC Class Codes: G05B 2219/42018 Pid learning controller, gains adapted as function of previous error
• CPC Class Codes: G05B 2219/42128 Servo characteristics, drive parameters, during test move

Abstract

A method and apparatus for tuning an external velocity loop servo drive of the type including a controller, a command device, an external velocity servo amplifier, an actuator and a position feedback device. The tuning technique include the use of three unidirectional motion events of descending duration. In the first motion event the controller applies a control signal of known amplitude to the actuator and monitors the actuator velocity based upon the position feedback signals. The controller determines the actuator steady state velocity during the motion event and uses this value to determine a scaling factor for the servo amplifier. In a second motion event, the controller drives the actuator in acceleration and deceleration in response to a control signal of known amplitude. Based upon the times at which the actuator reaches certain anticipated velocities, the controller determines system dynamic characteristics. In a third motion event the controller pulses the actuator for a short interval and monitors the actuator velocity to determine the rise time in response to a control signal of known amplitude. The rise time is used to determine the velocity loop bandwidth. The velocity loop bandwidth is then used to tune the position loop gains to appropriate levels.

Claims

1. A method for tuning a motion control system of the type including an input device for generating position command signals, an actuator for displacing a physical element to a desired location in response to drive signals, a servo amplifier circuit implementing a velocity control loop for converting control signals to drive signals for driving the actuator, a sensor for generating feedback signals representative of the position of the physical element, and a controller coupled to the input device, the sensor and the amplifier circuit for processing the command and feedback signals and generating the control signals, the controller implementing a position control loop wherein at least one parameter error signal derived from the command and feedback signals is multiplied by a position loop gain value, the method including the steps of:

(a) applying a control signal at a predetermined level to the amplifier circuit to accelerate the actuator in a predetermined direction;

(b) monitoring the feedback signals from the sensor during acceleration of the actuator;

(c) generating a value representative of velocity loop bandwidth based upon the feedback signals; and

(d) generating a desired value for the position loop gain value based upon velocity loop bandwidth value.

2. The method of claim 1, wherein the velocity loop bandwidth value is generated based upon a rise time value determined from the feedback signals.

3. The method of claim 1, wherein the position loop gain value is a position loop proportional gain value and the error signal is representative the difference between the position command signals and the feedback signals.

4. The method of claim 1, wherein the predetermined level of the control signals applied at step (a) is determined based upon a scaling factor for the amplifier circuit.

5. The method of claim 1, wherein step (d) includes generating a position loop proportional gain value and a position loop integral gain value.

6. A method for tuning a motion control system of the type including an input device for generating position command signals, an actuator for displacing a physical element to a desired location in response to drive signals, a servo amplifier circuit implementing a velocity control loop for converting control signals to drive signals for driving the actuator through multiplication of the drive signals by a scaling factor, a sensor for generating feedback signals representative of the position of the physical element, and a controller coupled to the input device, the sensor and the amplifier circuit for processing the command and feedback signals and generating the control signals, the method including the steps of:

(a) applying a control signal at a predetermined level to the amplifier circuit to drive the actuator at a steady state velocity;

(b) monitoring the feedback signals;

(c) generating a value representative of the steady state velocity based upon the feedback signals; and

(d) generating the scaling factor from the predetermined level of the control signals and from the steady state velocity value.

7. The method of claim 6, wherein the controller implements a position control loop wherein at least one position error value is multiplied by a predetermined gain value, the method including the further steps of applying a control signal to the amplifier circuit to accelerate the actuator in a predetermined direction, monitoring the feedback signals from the sensor during acceleration of the actuator and generating a desired value for the gain based upon the feedback signals.

8. The method of claim 7, wherein the feedback signals are used to generate a value representative of velocity loop bandwidth and the desired value for the gain is derived from the velocity loop bandwidth value.

9. The method of claim 8, wherein the velocity loop bandwidth value is generated based upon a rise time value and derived from the feedback signals.

10. The method of claim 7, wherein the gain value is a position loop proportional gain value.

11. The method of claim 6 including the further steps of applying control signals to the amplifier circuit to accelerate and decelerate the actuator, monitoring the feedback signals during acceleration and deceleration of the actuator and generating values representative of maximum system acceleration and deceleration rates based upon the feedback signals.

12. An apparatus for tuning a motion control system of the type including an input device for generating position command signals, an actuator for displacing a physical element to a desired location in response to drive signals, a servo amplifier circuit implementing a velocity control loop for converting control signals to drive signals for driving the actuator, a sensor for generating feedback signals representative of the position of the physical element, and a controller coupled to the input device, the sensor and the amplifier circuit for processing the command and feedback signals and generating the control signals, the controller implementing a position control loop wherein at least one parameter error signal derived from the command and feedback signals is multiplied by a position loop gain value, the apparatus comprising:

a control signal generating circuit coupled to the amplifier circuit and configured to generate and apply a control signal to the amplifier circuit to accelerate the actuator during a tuning sequence;

a monitoring circuit coupled to the sensor for monitoring the feedback signals during the tuning sequence;

a signal processing circuit coupled to the monitoring circuit and configured to generate a velocity loop bandwidth value based upon the feedback signals monitored during the tuning sequence and to derive the position loop gain value from the velocity loop bandwidth value; and

a memory circuit for storing the position loop gain value.

13. The apparatus of claim 12, wherein the control signal generating circuit, the signal processing circuit and the memory circuit are included in a programmed microprocessor.

14. The apparatus of claim 12, wherein the signal processing circuit is configured to generate a rise time value based upon the feedback signals monitored during the tuning sequence and to derive the velocity loop bandwidth value from the rise time value.

15. The apparatus of claim 12, wherein the actuator includes an electric motor.

16. The apparatus of claim 12, wherein the sensor includes a quadrature-type incremental encoder.

17. The apparatus of claim 12, further comprising an operator interface coupled to the signal processing circuit for monitoring operation of the controller.