Positioning Control System and Filter

Abstract

A positioning control system has a disturbance observer for estimating a disturbance from a displaced distance of a cylinder of a controlled object, and feeding back an estimated disturbance. The positioning control system also includes a saturation element and a low-pass element disposed in a feedback loop including the disturbance observer, and a saturated value changer for changing a saturated value of the saturation element based on a deviation. The saturation element is disposed in a forward path of a positive-feedback minor loop, whereas the low-pass element is disposed in a feedback path of the positive-feedback minor loop.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram, partly in cross section, of a positioning control system according to an embodiment of the present invention;

FIG. 2 is an enlarged fragmentary cross-sectional view of a piston;

FIG. 3 is a block diagram of a controller;

FIG. 4 is a block diagram of a positive-feedback filter;

FIG. 5 is a Bode diagram showing gain characteristics of the positive-feedback filter;

FIG. 6 is a Bode diagram showing phase characteristics of the positive-feedback filter;

FIG. 7 is a block diagram of a saturated positive-feedback filter;

FIG. 8 is a diagram showing gain characteristics of the saturated positive-feedback filter;

FIG. 9 is a diagram showing simulated outputs of the positive-feedback filter and the saturated positive-feedback filter at the time an input amplitude X is 0.31 at a low frequency;

FIG. 10 is a diagram showing simulated outputs of the positive-feedback filter and the saturated positive-feedback filter at the time an input amplitude X is 0.35 at a low frequency;

FIG. 11 is a diagram showing simulated outputs of the positive-feedback filter and the saturated positive-feedback filter at the time an input amplitude X is 0.5 at a low frequency;

FIG. 12 is a diagram showing simulated outputs of the positive-feedback filter and the saturated positive-feedback filter at the time an input amplitude X is 1.0 at a low frequency;

FIG. 13 is a diagram showing simulated outputs of the positive-feedback filter and the saturated positive-feedback filter at the time an input amplitude X is 2.35 at a low frequency;

FIG. 14 is a diagram showing simulated outputs of the positive-feedback filter and the saturated positive-feedback filter at the time an input amplitude X is 2.8 at a low frequency;

FIG. 15 is a diagram showing simulated outputs of the positive-feedback filter and the saturated positive-feedback filter at the time an input amplitude X is 3.5 at a low frequency;

FIG. 16 is a diagram showing simulated outputs of the positive-feedback filter and the saturated positive-feedback filter at the time an input amplitude X is 5.0 at a low frequency;

FIG. 17 is a block diagram of a positioning system employing a PID controller;

FIG. 18 is a block diagram of a positioning system similar to the control system shown in FIG. 17, except that a positive-feedback filter is used instead of the integrator that is used in the control system shown in FIG. 17;

FIG. 19 is a block diagram of a positioning system similar to the control system shown in FIG. 17, except that a saturated positive-feedback filter is used instead of the integrator that is used in the control system shown in FIG. 17;

FIG. 20 is a diagram showing simulated outputs at the time a saturation element is not saturated in the positioning systems shown in FIGS. 17 and 18;

FIG. 21 is a diagram showing a simulated input signal of the saturation element, which produces the simulated outputs shown in FIG. 20 at the time the saturation element is not saturated;

FIG. 22 is a diagram showing simulated outputs at the time a saturation element is saturated in the positioning systems shown in FIGS. 17 and 18;

FIG. 23 is a diagram showing a simulated input signal of the saturation element, which produces the simulated outputs shown in FIG. 20 at the time the saturation element is saturated;

FIG. 24 is a diagram showing simulated outputs at the time a saturation element is saturated in the positioning systems shown in FIGS. 17 and 18, wherein the saturated value of the saturation element is smaller than a disturbance;

FIG. 25 is a diagram showing a simulated input signal of the saturation element, which produces the simulated outputs shown in FIG. 24 at the time the saturation element is saturated;

FIG. 26 is a block diagram of a system wherein a saturated positive-feedback filter is not incorporated in a disturbance observer;

FIG. 27 is a block diagram of a system wherein a saturated positive-feedback filter is incorporated in a disturbance observer;

FIG. 28 is a diagram showing simulated outputs at the time a saturation element is not saturated in the systems shown in FIGS. 26 and 27;

FIG. 29 is a diagram showing a simulated estimated disturbance value at the time a saturation element is not saturated in the systems shown in FIGS. 26 and 27;

FIG. 30 is a diagram showing simulated outputs at the time a saturation element is saturated in the systems shown in FIGS. 26 and 27;

FIG. 31 is a diagram showing a simulated estimated disturbance value at the time a saturation element is saturated in the system shown in FIG. 26;

FIG. 32 is a diagram showing a simulated estimated disturbance value at the time a saturation element is saturated in the system shown in FIG. 27;

FIG. 33 is a graph showing saturated values set by a saturated value changer;

FIG. 34 is a graph showing modified saturated values set by the saturated value changer; and

FIG. 35 is a timing chart of integrals produced by an integrator, which are illustrative of integrator windup.

Claims

1. A positioning control system comprising: a disturbance observer for estimating a disturbance from at least one observed value of a controlled object and feeding back an estimated disturbance; anda saturation element disposed in a feedback loop for feeding back the estimated disturbance from said disturbance observer;said feedback loop having a main loop based on an output value of said controlled object, and a minor loop for performing positive feedback based on a predetermined parameter;said saturation element being disposed in said minor loop.

2. A positioning control system according to claim 1, wherein said minor loop performs said positive feedback through two subtractors.

3. A positioning control system according to claim 1, wherein said saturation element is saturated with positive and negative values whose absolute values are equal to each other.

4. A positioning control system according to claim 1, further comprising a saturated value changer for changing a saturated value of said saturation element based on a control deviation.

5. A positioning control system according to claim 4, wherein said controlled object comprises a cylinder having a seal on a slidable component thereof, and said saturated value of said saturation element has an absolute value that is greater when said control deviation falls outside of the viscoelastic displacement range of said seal than when said control deviation falls within a viscoelastic displacement range of said seal.

6. A positioning control system according to claim 5, wherein said cylinder comprises a pneumatic cylinder.

7. A positioning control system according to claim 5, wherein said seal comprises a piston seal and a cap seal.

8. A positioning control system according to claim 5, wherein said cylinder is bidirectionally actuatable by a proportional valve.

9. A positioning control system according to claim 4, wherein said saturated value changer changes said saturated value stepwise based on said control deviation.

10. A filter in a control system having a main feedback loop, comprising: a minor loop for performing positive feedback within said main feedback loop;a low-pass element disposed in a feedback path of said minor loop; anda saturation element disposed in a forward path of said minor loop.