METHOD AND APPARATUS FOR PULSE-MODULATED FEEDBACK CONTROL

• US 20120046793A1
• Filed: 08/17/2010
• Published: 02/23/2012
• Est. Priority Date: 08/17/2010
• Status: Active Grant

• Current Assignee: Massachusetts Institute of Technology
• Original Assignee: Massachusetts Institute of Technology
• Inventors: Song, Yun Seong, Hogan, Neville John
• Granted Patent: US 9,488,974 B2
• Time in Patent Office: Days
• US Class Current: 700/282
• CPC Class Codes: G05B 19/4142 characterised by the use of a microprocessor G05B19/4141 takes precedence
• CPC Class Codes: G05B 2219/34217 Microprocessor with build in pwm
• CPC Class Codes: G05B 2219/41158 Use of pwm signal against friction

Abstract

A PM system for overcoming friction stickiness and which also remains stable is described.

Claims

1. A method of controlling a system, the method comprising a repetitive sequence of the following:

(a) obtaining an actual value signal corresponding to a quantity which is controllable by the system;

(b) comparing the actual value signal to a command value;

(c) in response to the command value minus the actual value being greater than an upper bound of error, generating a first control signal having a first value which causes the system to produce a maximum system response; and

(d) in response to the command value minus the actual value being smaller than the lower bound of error generating a second control signal having a second, different value which causes the system to produce a minimum system response;

(e) in response to the command value minus the actual value signal being neither greater than the upper margin of error nor less than the lower margin of error, generating a third control signal having a third value which causes the system to produce substantially no response; and

(f) supplying one of the first, second or third control signals to the system for controlling the same.

2. The method of claim 1, wherein:

the first value corresponds to a first non-zero value;

the second value corresponds to a second, different non-zero value; and

the third value corresponds to a zero or substantially zero value.

3. The method of claim 1, wherein one of the first, second or third control signals is supplied at each repetitive sequence of (a)-(f).

4. The method of claim 2, wherein the value of the first control signal is selected to be greater than a system input value which produces a non-repeatable system output.

5. The method of claim 2, wherein the value of the second control signal is selected to be less than a system input value which produces a non-repeatable system output.

6. The method of claim 3, wherein the time interval between the repetitive sequences is constant.

7. The method of claim 1, wherein the signal compensating for the non-linearity has a substantially constant amplitude.

8. The method of claim 1 for controlling one or more of:

a motor;

an engine;

a pump; and

a control valve.

9. The method of claim 8, wherein the motor is a rotary electric motor.

10. The method of claim 1 wherein obtaining an actual value signal comprises measuring the actual value signal.

11. A system comprising:

a plant;

a sensor coupled to sense an actual value signal corresponding to a quantity which is controllable by the plant; and

a controller coupled to the plant for providing control signals to the plant and coupled to receive a signal from said sensor corresponding to the actual value signal, the controller comprising;

a processor which receives a signal representative of a difference between a command signal value and actual signal value and in response to the value of the command value minus the actual value signal being greater than the upper margin of error, generating a first control signal having a first value; and

in response to the value of the command signal minus the actual value signal being less than the lower margin of error, generating a second control signal having a second, different value and in response to the value of the actual value signal being neither greater than the command value plus the margin of error nor less than the command value minus the margin of error, generating a third control signal having a third value; and

means for supplying one of the first, second or third control signals to an output port.

12. The system of claim 11 wherein the controller further comprises a comparator which receives the command signal value and the actual signal value and provides the signal representative of the difference therebetween.

13. A controller comprising:

a processor having an input coupled to receive a signal representative of a difference between a characteristic of a command signal and a characteristic of an actual signal and in response to the signal being greater than an upper margin of error, generating a first control signal having a first value which causes the system to produce a maximum system response; and

in response to the signal being less than a lower margin of error, generating a second control signal having a second, different value which causes the system to produce a minimum system response and in response to the signal being neither greater than the upper margin of error nor less than the lower margin of error, generating a third control signal having a third value which causes the system to produce a substantially no response; and

control signal output means for supplying one of the first, second or third control signals to an output port.

14. The controller of claim 13 further comprising repeating means, coupled to said processor and to said control signal output means, said repeating means for ensuring that said control signal output means provides an output signal at each of a plurality of sampling intervals until asked to stop.

15. The controller of claim 14 wherein said repeating means is provided as part of said processor.

16. The controller of claim 13 wherein the signal is computed as the command value minus the actual value signal.

17. The system of claim 13 wherein the controller further comprises a comparator which receives the command signal value and the actual signal value and provides the signal representative of the difference therebetween.

18. A method of controlling a system, the method comprising a repetitive sequence of the following:

(a) obtaining an actual value signal corresponding to a quantity which is controllable by the system;

(b) computing a difference value corresponding to a difference between a command value and the actual value;

(c) in response to the difference value being greater than an upper margin of error, generating a first control signal having a first value;

(d) in response to the difference value being smaller than a lower bound of error, generating a second control signal having a second, different value;

(e) in response to the difference value being neither greater than the upper margin of error nor less than the lower margin of error, generating a third control signal having a third value; and

(f) supplying one of the first, second or third control signals to the system for controlling the same.

19. The method of claim 18 wherein the difference value is computed as the command value minus the actual value.