Inertia and load torque estimating method and apparatus

• US 7,627,440 B2
• Filed: 08/28/2007
• Issued: 12/01/2009
• Est. Priority Date: 08/28/2007
• Status: Active Grant

• Current Assignee: Rockwell Automation Technologies Incorporated (Allen-Bradley Co., Inc.)
• Original Assignee: Rockwell Automation Technologies Incorporated (Allen-Bradley Co., Inc.)
• Inventors: Schmidt, Peter B., Golownia, John Joseph Jr., Rehm, Thomas J.
• Primary Examiner(s): Bui; Bryan
• Application Number:
  US11/846,159
• Publication Number:
  US 20090063058A1
• Time in Patent Office: 826 Days
• Field of Search: 702/41, 702/141, 702/142, 702/145, 318/563, 318/624, 318/626, 318/632
• US Class Current: 702/41
• CPC Class Codes: G05B 19/416 characterised by control of velocity, acceleration or deceleration G05B19/19 takes precedence
• CPC Class Codes: G05B 2219/41123 Correction inertia of servo
• CPC Class Codes: G05B 2219/41163 Adapt gain to friction, weight, inertia
• CPC Class Codes: G05B 2219/41381 Torque disturbance observer to estimate inertia

Abstract

A method and apparatus for estimating a system inertia and a load torque in a motor controller, the method comprising the steps of providing an acceleration command signal, determining a motor position, using the motor position to generate an acceleration feedback signal, mathematically combining the acceleration feedback signal and a load torque signal to generate a system inertia estimate, mathematically combining the system inertia estimate and the acceleration command signal to generate a motor torque signal, mathematically combining the system inertia estimate and the acceleration feedback signal to generate an inertia torque and mathematically combining the inertia torque and the motor torque signal to generate the load torque estimate.

Claims

1. A method for estimating a system inertia and a load torque in a motor controller, the method comprising using a motor controller processor to perform the steps of:

providing an acceleration command signal;

determining a motor position;

using the motor position to generate an acceleration feedback signal;

mathematically combining the acceleration feedback signal and a load torque signal to generate a system inertia estimate;

mathematically combining the system inertia estimate and the acceleration command signal to generate a motor torque signal;

mathematically combining the system inertia estimate and the acceleration feedback signal to generate an inertia torque; and

mathematically combining the inertia torque and the motor torque signal to generate the load torque estimate.

2. The method of claim 1 wherein the step of providing an acceleration command signal includes providing a velocity command signal, deriving a velocity feedback signal from the motor position and subtracting the motor velocity feedback signal from the velocity command signal.

3. The method of claim 1 wherein the step of mathematically combining the acceleration feedback signal and the load torque signal includes filtering the load torque signal to generate a load torque difference signal, multiplying the acceleration feedback signal and the load torque difference signal to generate an inertia product signal and integrating a derivative of the inertia product signal to generate the system inertia estimate.

4. The method of claim 1 wherein the step of mathematically combining the system inertia estimate and the acceleration command signal to generate a motor torque signal includes multiplying a derivative of the system inertia estimate and the acceleration command signal to generate a torque command signal and limiting the torque command signal to generate the motor torque signal.

5. The method of claim 4 wherein the step of multiplying a derivative of the system inertia estimate and the acceleration command signal includes low pass filtering the system inertia estimate to generate the derivative of the system inertia estimate.

6. The method of claim 1 wherein the step of mathematically combining the system inertia estimate and the acceleration feedback signal to generate an inertia torque includes multiplying the system inertia estimate by the acceleration feedback signal to generate the inertia torque.

7. The method of claim 1 wherein the step of mathematically combining the inertia torque and the motor torque signal to generate a load torque estimate includes subtracting the inertia torque from the motor torque signal to generate the load torque estimate.

8. A method for deriving a system inertia estimate and a load torque estimate in a motor controller, the method comprising using a motor controller processor to perform the steps of:

providing a velocity command signal;

sensing a motor position;

using the motor position to generate a velocity feedback signal and an acceleration feedback signal;

subtracting the velocity feedback signal from the velocity command signal to generate a velocity error signal;

using the velocity error signal to generate an acceleration command signal;

multiplying the acceleration feedback signal and a load torque difference signal to generate an inertia product signal;

using the inertia product signal to generate the system inertia estimate;

multiplying the system inertia estimate and the acceleration command signal to generate a motor torque signal;

multiplying the acceleration feedback signal and the system inertia estimate to generate an inertia torque;

subtracting the inertia torque from the motor torque signal to generate the load torque estimate; and

filtering the load torque estimate to generate the load torque difference signal.

9. The method of claim 8 wherein the step of using the inertia product signal to generate the system inertia estimate includes scaling the inertia product signal and integrating the scaled product signal to derive the system inertia estimate.

10. The method of claim 8 wherein the step of filtering the load torque estimate includes band pass filtering the load torque estimate.

11. An apparatus for estimating a system inertia and a load torque in a motor controller, the apparatus comprising:

a sensing device for determining a motor position;

at least a first derivative module using the motor position to generate an acceleration feedback signal;

a module for mathematically combining the acceleration feedback signal and a load torque signal to generate a system inertia estimate;

a module for mathematically combining the system inertia estimate and an acceleration command signal to generate a motor torque signal;

a module for mathematically combining the system inertia estimate and the acceleration feedback signal to generate an inertia torque; and

a module for mathematically combining the inertia torque and the motor torque signal to generate the load torque estimate.

12. The apparatus of claim 11 further including a second derivative module for deriving a velocity feedback signal from the motor position, a summer for subtracting the motor velocity feedback signal from a velocity command signal to generate the acceleration command signal.

13. The apparatus of claim 11 wherein the module for mathematically combining the acceleration feedback signal and the load torque signal includes a filter for by filtering the load torque signal to generate a load torque difference signal, a multiplier for multiplying the acceleration feedback signal and the load torque difference signal to generate an inertia product signal and an integrator for integrating a derivative of the inertia product signal to generate the system inertia estimate.

14. The apparatus of claim 11 wherein the module for mathematically combining the system inertia estimate and the acceleration command signal to generate a motor torque signal includes a multiplier for multiplying a derivative of the system inertia estimate and the acceleration command signal to generate a torque command signal and a limiter for limiting the torque command signal to generate the motor torque signal.

15. The apparatus of claim 14 wherein the multiplier multiplies the derivative of the system inertia estimate and the acceleration command signal by low pass filtering the system inertia estimate to generate the derivative of the system inertia estimate.

16. The apparatus of claim 11 wherein the module for mathematically combining the system inertia estimate and the acceleration feedback signal to generate an inertia torque includes a multiplier for multiplying the system inertia estimate by the acceleration feedback signal to generate the inertia torque.

17. The apparatus of claim 11 wherein the module for mathematically combining the inertia torque and the motor torque signal to generate a lead torque estimate includes a summer for subtracting the inertia torque from the motor torque signal to generate the load torque estimate.