Circuit for controlling the motion of a moving object

• US 4,792,737 A
• Filed: 06/15/1987
• Issued: 12/20/1988
• Est. Priority Date: 06/15/1987
• Status: Expired due to Term

• Current Assignee: Performance Controls, Inc. (Fujifilm Holdings Corporation)
• Original Assignee: Performance Controls, Inc. (Fujifilm Holdings Corporation)
• Inventors: Chizever, Gary E., Goff, Kenneth W.
• Primary Examiner(s): Shoop, Jr., William M.
• Assistant Examiner(s): Young, Brian
• Application Number:
  US07/062,189
• Time in Patent Office: 554 Days
• Field of Search: 318/619, 318/629, 318/611, 318/615-618, 318/561, 318/560, 318/628, 318/327, 318/632, 360/71, 360/74.2
• US Class Current: 318/615
• CPC Class Codes: G05B 13/04 involving the use of models or simulators

Abstract

A circuit is disclosed for controlling the position or velocity of a moving object. The motion of the object may be linear or rotational. The object is moved by an electric motor, or linear actuator, which is driven by a power amplifier. The current output of the amplifier, which drives the motor or linear actuator, is controlled by an input signal based at least in part on the estimated velocity of the object. The control circuit includes a pair of integrators connected in series, the inputs to the integrators being dependent both on the current output from the amplifier, and on the difference between the output of the second integrator and the actual sensed position of the object. The velocity estimation circuit is thus based on a form of Kalman filter. The velocity estimator uses a model of the motor which is extremely simple, and which contains only constants. The velocity estimator can control the motor very accurately without detailed knowledge of the model of the motor. The present invention replaces relatively expensive device, such as tachometers, with comparatively inexpensive electronic circuity. The invention also includes a method and apparatus which enable the device to calculate automatically the constants needed for efficient operation. The device therefore has the advantage that it can calibrate itself. The circuit can be implemented in either analog or digital form.

Claims

1. In an apparatus for control of the motion of an object, the object being moved by an electric motor, the apparatus including means for sensing the position of the object, the motor being controlled by a control current which is dependent, at least in part, on a velocity feedback signal, the improvement comprising means for sampling the control current, means for measuring the actual position of the object, means for multiplying the control current by a motor model constant, the output of the multiplying means being connected to the input of a first integrating means, the output of the first integrating means being connected to the input of a second integrating means, the output of the second integrating means being connected to a means for comparing the output of the second integrating means with the output of the measuring means, means for multiplying the output of the comparing means by a first constant, and for adding the resulting product signal to the input of the second integrating means, the output of the latter multiplying means being permanently connected to the input of the second integrating means, means for multiplying the output of the comparing means by a second constant, and for adding the resulting product signal to the input of the first integrating means, wherein the output of the first integrating means comprises the input signal which is the estimated velocity of the object.

2. The improvement of claim 1, wherein the motor generates rotational motion, and wherein the motor model constant is the torque constant of the motor divided by the moment of inertia of the motor.

3. The improvement of claim 1, wherein the motor generates linear motion, and wherein the motor model constant is the force constant of the motor divided by the mass of the motor.

4. The improvement of claim 1, wherein the first constant is proportional to the product of a frequency constant and a damping factor.

5. The improvement of claim 4, wherein the second constant is the square of the frequency constant.

6. In an apparatus for control of the motion of an object, the object being moved by an electric motor, the apparatus including means for sensing the position of the object, the motor being controlled by a control current which is dependent, at least in part, on a velocity feedback signal, the improvement comprising means for sampling the control current, means for measuring the actual position of the object, means for multiplying the control current by a motor model constant, the output of the multiplying means being connected to the input of a first integrating means, the output of the first integrating means being connected to the input of a second integrating means, the output of the second integrating means being connected to a means for comparing the output of the second integrating means with the output of the measuring means, means for multiplying the output of the comparing means by a first constant, and for adding the resulting signal to the input of the second integrating means, the output of the latter multiplying means being permanently connected to the input of the second integrating means, means for multiplying the output of the comparing means by a second constant, and for adding the resulting signal to the input of the first integrating means, wherein the input to the second integrating means comprises the signal which is the estimated velocity of the object.

7. The improvement of claim 6, wherein the motor generates rotational motion, and wherein the motor model constant is the torque constant of the motor divided by the moment of inertia of the motor.

8. The improvement of claim 6, wherein the motor generates linear motion, and wherein the motor model constant is the force constant of the motor divided by the mass of the motor.

9. The improvement of claim 6, wherein the first constant is proportional to the product of a frequency constant and a damping factor.

10. The improvement of claim 9, wherein the second constant is the square of the frequency constant.

11. In an apparatus for control of the motion of an object, the object being moved by an electric motor, the apparatus including means for sensing the position of the object, the object being controlled by a control current which is dependent, at least in part, on a velocity feedback signal, the improvement comprising a velocity estimator circuit, the circuit comprising first and second integrators, the input to the first integrator being dependent, at least in part, on the control current, and on the difference between the actual position and the position indicated by the output of the second integrator, the input to the second integrator being dependent, at least in part, on the output of the first integrator, the input to the second integrator being permanently connected to means for measuring the difference between the actual position and the position indicated by the output of the second integrator, wherein the estimator circuit includes means for multiplying the control current by at least one value which is characteristic of the motor, said value being a constant, and wherein the output of the first integrator comprises the estimated velocity.

12. The improvement of claim 11, further comprising means for determining the value characteristic of the motor, said determining means including means for displacing the object, from rest, with a given current applied to the motor, and means for measuring the time elapsed and displacement of the object.

13. In an apparatus for control of the motion of an object, the object being moved by an electric motor, the apparatus including means for sensing the position of the object, the object being controlled by a control current which is dependent, at least in part, on a velocity feedback signal, the improvement comprising a velocity estimator circuit, the circuit comprising first and second integrators, the input to the first integrator being dependent, at least in part, on the control current, and on the difference between the actual position and the output of the second integrator, the input to the second integrator being dependent, at least in part, on the output of the first integrator, the input to the second integrator being permanently connected to means for measuring the difference between the actual position and the output of the second integrator, wherein the estimator circuit includes means for multiplying the control current by at least one value which is characteristic of the motor, said value being a constant, and wherein the signal at the input to the second integrator comprises the estimated velocity.

14. The improvement of claim 13, further comprising means for determining the value characteristic of the motor, said determining means including means for displacing the object, from rest, with a given current applied to the motor, and means for measuring the time elapsed and displacement of the object.

15. A method of controlling the motion of an object, the object being moved by a motor which is powered by a current-driven amplifier, comprising the steps of:

(a) sampling the current output of the amplifier and the position of the object,

(b) multiplying the current signal by at least one constant relating to the structure of the motor,

(c) integrating the resulting signal twice in succession, each integrating step including the step of adding, to the input to the integrator, a signal proportional to the difference between the output of the second integrating step and the actual position of the object, the adding step being performed without interruption, and

(d) connecting the output of the first integrating step to the amplifier.

16. The method of claim 15, wherein the constant in step (b) is determined by (2s_M)/(I_o T²), where s_M is the total displacement of the object during period T, when the object is accelerated from rest due to current I_o applied to the motor.

17. A method of controlling the motion of an object, the object being moved by a motor which is powered by a current-driven amplifier, comprising the steps of:

(a) sampling the current output of the amplifier and the position of the object,

(b) multiplying the current signal by at least one constant relating to the structure of the motor,

(c) integrating the resulting signal twice in succession, each integrating step including the step of adding, to the input to the integrator, a signal proportional to the difference between the output of the second integrating step and the actual position of the object, the adding step being performed without interruption, and

(d) connecting the sum of the output of the first integrating step, and the difference signal, to the amplifier.

18. The method of claim 17, wherein the constant in step (b) is determined by (2s_M)/(I_o T²), where s_M is the total displacement of the object during period T, when the object is accelerated from rest due to current I_o applied to the motor.

19. In an apparatus for control of the motion of an object, the object being moved by an electric motor, the apparatus including means for sensing the position of the object, the motor being controlled by a control current which is dependent, at least in part, on a velocity feedback signal, the improvement comprising means for sampling the control current, means for measuring the actual position of the object, means for multiplying the control current by a motor model constant, the output of the multiplying means being connected to the input of a first integrating means, the output of the first integrating means being connected to the input of a second integrating means, the output of the second integrating means being connected to a means for comparing the output of the second integrating means with the output of the measuring means, means for multiplying the output of the comparing means by a first constant, and for adding the resulting product signal to the input of the second integrating means, means for multiplying the output of the comparing means by a second constant, and for adding the resulting product signal to the input of the first integrating means, wherein the output of the first integrating means comprises the input signal which is the estimated velocity of the object, wherein the first constant is proportional to the product of a frequency constant and a damping factor.

20. The improvement of claim 19, wherein the second constant is the square of the frequency constant.

21. In an apparatus for control of the motion of an object, the object being moved by an electric motor, the apparatus including means for sensing the position of the object, the motor being controlled by a control current which is dependent, at least in part, on a velocity feedback signal, the improvement comprising means for sampling the control current, means for measuring the actual position of the object, means for multiplying the control current by a motor model constant, the output of the multiplying means being connected to the input of a first integrating means, the output of the first integrating means being connected to the input of a second integrating means, the output of the second integrating means being connected to a means for comparing the output of the second integrating means with the output of the measuring means, means for multiplying the output of the comparing means by a first constant, and for adding the resulting signal to the input of the second integrating means, means for multiplying the output of the comparing means by a second constant, and for adding the resulting signal to the input of the first integrating means, wherein the input to the second integrating means comprises the signal which is the estimated velocity of the object, wherein the first constant is proportional to the product of a frequency constant and a damping factor.

22. The improvement of claim 21, wherein the second constant is the square of the frequency constant.

23. In an apparatus for control of the motion of an object, the object being moved by an electric motor, the apparatus including means for sensing the position of the object, the object being controlled by a control current which is dependent, at least in part, on a velocity feedback signal, the improvement comprising a velocity estimator circuit, the circuit comprising first and second integrators, the input to the first integrator being dependent, at least in part, on the control current, and on the difference between the actual position and the position indicated by the output of the second integrator, the input to the second integrator being dependent, at least in part, on the output of the first integrator and on the difference between the actual position and the position indicated by the output of the second integrator, wherein the estimator circuit includes means for multiplying the control current by at least one value which is characteristic of the motor, said value being a constant, and wherein the output of the first integrator comprises the estimated velocity,

further comprising means for determining the value characteristic of the motor, said determining means including means for displacing the object, from rest, with a given current applied to the motor, and means for measuring the time elapsed and displacement of the object.

24. In an apparatus for control of the motion of an object, the object being moved by an electric motor, the apparatus including means for sensing the position of the object, the object being controlled by a control current which is dependent, at least in part, on a velocity feedback signal, the improvement comprising a velocity estimator circuit, the circuit comprising first and second integrators, the input to the first integrator being dependent, at least in part, on the control current, and on the difference between the actual position and the output of the second integrator, the input to the second integrator being dependent, at least in part, on the output of the first integrator and on the difference between the actual position and the output of the second integrator, wherein the estimator circuit includes means for multiplying the control current by at least one value which is characteristic of the motor, said value being a constant, and wherein the signal at the input to the second integrator comprises the estimated velocity,

further comprising means for determining the value characteristic of the motor, said determining means including means for displacing the object, from rest, with a given current applied to the motor, and means for measuring the time elapsed and displacement of the object.

25. A method of controlling the motion of an object, the object being moved by a motor which is powered by a current-driven amplifier, comprising the steps of:

(a) sampling the current output of the amplifier and the position of the object,

(b) multiplying the current signal by at least one constant relating to the structure of the motor,

(c) integrating the resulting signal twice in succession, each integrating step including the step of adding, to the input to the integrator, a signal proportional to the difference between the output of the second integrating step and the actual position of the object, and

(d) connecting the output of the first integrating step to the amplifier,

wherein the constant in step (b) is determined by (2s_M)/(I_o T²), where s_M is the total displacement of the object during period T, when the object is accelerated from rest due to current I_o applied to the motor.

26. A method of controlling the motion of an object, the object being moved by a motor which is powered by a current-driven amplifier, comprising the steps of:

(a) sampling the current output of the amplifier and the position of the object,

(b) multiplying the current signal by at least one constant relating to the structure of the motor,

(c) integrating the resulting signal twice in succession, each integrating step including the step of adding, to the input to the integrator, a signal proportional to the difference between the output of the second integrating step and the actual position of the object, and

(d) connecting the sum of the output of the first integrating step, and the difference signal, to the amplifier,

wherein the constant in step (b) is determined by (2s_M)/(I_o T²), where s_M is the total displacement of the object during period T, when the object is accelerated from rest due to current I_o applied to the motor.

27. In an apparatus for controlling the motion of an object, the object being moved by a motor powered by a current-driven amplifier, the improvement comprising a damped simple harmonic oscillator circuit, at least one input of the circuit being proportional to the current in said amplifier, multiplied by a constant relating the acceleration of the motor to the current applied the output of the circuit being an estimate of the velocity of the object, wherein the bandwidth of the simple harmonic oscillator circuit exceeds the bandwidth of the amplifier,

and including means for determining said constant, said determining means including means for displacing the object, from rest, with a given current applied to the motor, and means for measuring the time elapsed and displacement of the object.

28. In an apparatus for controlling the motion of an object, the object being moved by a motor powered by a current-driven amplifier, the improvement comprising a damped simple harmonic oscillator circuit, at least one input of the circuit being proportional to the current in said amplifier, multiplied by a constant relating the acceleration of the motor to the current applied the output of the circuit being an estimate of the velocity of the object, wherein the bandwidth of the simple harmonic oscillator circuit exceeds the bandwidth of the amplifier,

wherein the simple harmonic oscillator circuit comprises two integrators, and wherein the output signal is a linear combination of the output signal of the first integrator and the input signal to the second integrator.

29. In an apparatus for controlling the motion of an object, the object being moved by a motor powered by a current-driven amplifier, the improvement comprising a damped simple harmonic oscillator circuit, at least one input of the circuit being proportional to the current in said amplifier, multiplied by a constant relating the acceleration of the motor to the current applied the output of the circuit being an estimate of the velocity of the object, wherein the bandwidth of the simple harmonic oscillator circuit exceeds the bandwidth of the amplifier,

wherein the motion of the object is rotational, and wherein said constant is the torque constant of the motor divided by the moment of inertia of the motor.

30. In an apparatus for controlling the motion of an object, the object being moved by a motor powered by a current-driven amplifier, the improvement comprising a damped simple harmonic oscillator circuit, at least one input of the circuit being proportional to the current in said amplifier, multiplied by a constant relating the acceleration of the motor to the current applied the output of the circuit being an estimate of the velocity of the object, wherein the bandwidth of the simple harmonic oscillator circuit exceeds the bandwidth of the amplifier,

wherein the motion of the object is linear, and wherein said constant is the force constant of the motor divided by the mass of the motor.