Feedback control method and system having variable deadband

• US 4,604,681 A
• Filed: 08/13/1985
• Issued: 08/05/1986
• Est. Priority Date: 03/05/1982
• Status: Expired due to Term

• Current Assignee: Mitsubishi Denki Kabushiki Kaisha (Mitsubishi Electric Corporation)
• Original Assignee: Mitsubishi Denki Kabushiki Kaisha (Mitsubishi Electric Corporation)
• Inventors: Sakashita, Ryuji
• Primary Examiner(s): Harkcom, Gary V.
• Application Number:
  US06/765,189
• Time in Patent Office: 357 Days
• Field of Search: 364/140-143, 364/148, 364/152-155, 364/176-177, 364/180-183, 364/160, 364/420, 364/505-506, 364/509-510, 318/590-596, 318/611, 318/624, 405/80, 405/92, 405/107
• US Class Current: 700/78
• CPC Class Codes: G05B 5/01 electric
• CPC Class Codes: G05D 9/12 characterised by the use of electric means

Abstract

An automatic feedback controller for maintaining water level in a dam initially compares target and sensed water levels to derive a deviation value. Simultaneously, a first dead zone having a relatively wide width contiguous to the target level is set. The first set dead zone is compared with the deviation value to open and close a dam gate such that the deviation value becomes smaller than the first dead zone width. When a predetermined time has elapsed, a second dead zone having a width narrower than that of the first dead zone is set. The second dead zone is then compared with the deviation value to open or close the gate such that the deviation value becomes smaller than the second dead zone width.

Claims

1. A feedback automatic control apparatus for performing feedback control such that a control amount with which an object being controlled may correspond with a target value, comprising:

first dead zone setting means for setting a first dead zone including said target value and having a first width,

second dead zone setting means for setting a second, non-zero dead zone including said target value and having a width narrower than that of said first dead zone and being entirely within the first dead band,

means for measuring time elapsed from a start of control toward the target value, and

control means for controlling said object being controlled such that the control amount of said object being controlled falls within the range of said first dead zone as derived from said first dead zone setting means at the start of control and for controlling said object being controlled such that said control amount of said object being controlled falls within the range of the second dead zone as derived from said second dead zone setting means after the lapse of a predetermined time period after said start of control measured by said elapsed time measuring means, said control means comprising means responsive to (a) said target value, (b) the first dead zone as derived from said first dead zone setting means and (c) a current control amount for gradually decreasing as a function of time the width of said first dead zone set in said first dead zone setting means to the width of said second dead zone set in said second dead zone setting means.

2. A feedback automatic control apparatus in accordance with claim 1, wherein

said control means comprises timer means responsive to a time dependent change of a current control amount and said target value for providing a timing signal for gradually decreasing as a function of time the width of said first dead zone to the width of the second dead zone.

3. A feedback control method for controlling a variable parameter to obtain a target value, comprising the steps of:

presetting a first dead zone having a first width and including the target value of said parameter;

measuring elapsed time following a start of control toward the target value;

controlling, with the first dead zone, the parameter to approach said target value so the parameter is within the first dead zone; and

after a predetermined time period after said start of control, controlling, with a second, non-zero dead zone having a width wholly within and narrower than that of the first dead zone and including said target value, the parameter to approach said target value so the parameter is within the second dead zone, said second dead zone being obtained by gradually decreasing as a function of time the width of said first dead zone after said predetermined time period.

4. A feedback control apparatus for energizing an actuator so a variable controlled by the actuator approaches a set point value comprising means responsive to a signal having a magnitude indicative of a monitored value of the variable and the set point value for deriving an error signal having a magnitude indicative of the deviation of the set point and monitored values, means responsive to the error signal for controlling the actuator to cause the variable to approach the set point value, said controlling means including:

means for establishing a series of N successive time dependent dead band values for the error signal, where N is an integer greater than 1, the dead band values decreasing only monotonically as the successive time dead band values are derived during a particular series, the actuator being energized only while the error signal magnitude is greater than each of the successive time dependent dead band values.

5. The apparatus of claim 4 wherein the means for controlling the actuator drives the actuator to fully on and off conditions in response to the error signal magnitude being respectively greater than and less than each of the successive time dependent dead band values.

6. The apparatus of claim 4 wherein the variable is height of water in a dam and the actuator is a gate of the dam, the means for controlling the gate driving the gate to fully opened and fully closed positions in response to the error signal magnitude being respectively greater than and less than each of the successive time dependent dead band values.

7. The apparatus of claim 6 further including means for measuring the height of water in the dam.

8. The apparatus of claim 4 wherein N is greater than 2.

9. A feedback control method for energizing an actuator so a variable controlled by the actuator approaches a set point value comprising monitoring the value of the variable, responding to the monitored value of the variable and the set point value to derive an error signal having a magnitude indicative of the deviation of the set point and monitored values, in response to the error signal controlling the actuator to cause the variable to approach the set point value, said controlling step including:

establishing a series of N successive time dependent dead band values for the error signal, where N is an integer greater than 1, the dead band values decreasing only monotonically as the successive time dependent dead band values are derived during a particular series, the actuator being energized only while the error signal magnitude is greater than each of the successive time dependent dead band values.

10. The method of claim 9 wherein the actuator is driven to fully on and off conditions in response to the error signal magnitude being respectively greater than and less than each of the successive time dependent dead band values.

11. The method of claim 10 wherein the variable is height of water in a dam and the actuator is a gate of the dam, the gate being driven to fully opened and fully closed positions in response to the error signal magnitude being respectively greater than and less than each of the successive time dependent dead band values.

12. The method of claim 11 wherein the monitoring step includes measuring the height of water in the dam.

13. The method of claim 9 wherein N is greater than 2.

14. A method of controlling a parameter with an actuator comprising the steps of:

(a) establishing a target value for the parameter,

(b) monitoring the value of the parameter,

(c) setting an initial dead band zone including the set point value for the actuator at the time the target value is established,

(d) gradually reducing in only a monotonic manner the width of the dead band zone for the established target value from the intial dead band zone as control time for the parameter increases, whereby the dead band zone has a time dependent gradually decreasing monotonic variable value,

(e) comparing the monitored and target values for the parameters to derive an indication of an error between them,

(f) comparing the indicated error between the monitored and target values with the time dependent gradually decreasing monotonic variable value for the dead band zone, and

(g) in response to comparing step (f) controlling said actuator so the parameter is varied toward the target value only when the error indication of step (e) is greater than the time dependent decreasing monotonic variable value for the dead band.

15. The method of claim 14 wherein the target value is at one extreme end of values in the dead band zone.

16. The method of claim 14 wherein the actuator is respectively driven to fully activated and fully de-activated states when the error indication of step (e) is greater and less than the time dependent gradually decreasing monotonic variable value for the dead band.

17. The method of claim 14 wherein the parameter is height of water in a dam, and the actuator includes a gate of the dam, the gate being respectively driven to fully open and fully closed states when the error indication of step (e) is greater and less than the time dependent gradually decreasing monotonic variable value for the dead band.

18. Apparatus for controlling a parameter with an actuator in response to an indication of a value of the parameter comprising:

(a) means for establishing a target value for the parameter,

(b) means for setting an initial dead band zone including the set point value for the actuator at the time the target value is established,

(c) means for gradually reducing in only a monotonic manner the width of the dead band zone for the established target value from the initial dead band zone as control time for the parameter increases, whereby the dead band zone has a time dependent gradually decreasing monotonic variable value,

(d) means for comparing the monitored and target values for the parameters to derive an indication of an error between them,

(e) means for comparing the indicated error between the monitored and target values with the time dependent gradually decreasing monotonic variable value for the dead band zone, and

(f) means responsive to comparing means (e) for controlling said actuator so the parameter is varied toward the target value only when the error indication derived by comparing means (d) is greater than the time dependent gradually decreasing monotonic variable for the dead band.

19. The apparatus of claim 18 wherein said controlling means includes means for energizing the actuator so that the actuator is respectively driven to fully activated and fully deactivated states when the error indication of comparing means (d) is greater and less than the time dependent gradually decreasing monotonic variable value for the dead band.

20. The apparatus of claim 18 wherein the parameter is height of water in a dam, the target value being a maximum value for the water height in the dead band zone, said controlling means including means for energizing the gate so the gate is respectively fully open and fully closed when the error indication of comparing means (d) is greater and less than the time dependent gradually decreasing monotonic variable value for the dead band.