PiD control unit

• US 5,331,541 A
• Filed: 09/18/1992
• Issued: 07/19/1994
• Est. Priority Date: 09/20/1991
• Status: Expired due to Term

• Current Assignee: Omron Corporation
• Original Assignee: Omron Corporation
• Inventors: Saito, Yumi, Nagami, Yoshihiro, Ueda, Tamio, Zhiming, Zhang
• Primary Examiner(s): Smith, Jerry
• Assistant Examiner(s): GORDON, PAUL P
• Application Number:
  US07/947,333
• Time in Patent Office: 669 Days
• Field of Search: 364/162, 364/152, 364/153, 364/148
• US Class Current: 700/42
• CPC Class Codes: G05B 11/42 for obtaining a characteristic which is both proportional and time-dependent, e.g. P. I., P. I. D.
• CPC Class Codes: G05B 13/024 in which a parameter or coefficient is automatically adjusted to optimise the performance

Abstract

A PID control device identifies rise characteristics of a controlled system by a step response method on changing a reference, moves to PID control when idle time and slope successively obtained at the rise reach a predetermined condition, and computes PID control parameters based on the idle time and slope obtained up to that point. If the identification is fully executed, the computed PID control parameters are immediately set. If it is not fully executed, the PID control device 1 further watches the state to compare a proportional gain of the newly computed PID control parameters with the proportional gain of previously set PID control parameters, and the currently computed PID control parameters are set when the parameters are on a safe side.

Claims

1. A self control type PID control unit for controlling a controlled system comprising:

step manipulated variable output means for outputting a step manipulated variable,

PID control means for generating a manipulated variable based on an error between a reference and a controlled variable obtained from the controlled system,

control mode switching means for applying said step manipulated variable to the controlled system and for stopping the application of the step manipulated variable to move to PID control by said PID control means when idle time and slope successively obtained in accordance with a change of said controlled variable reach a predetermined condition,

identification means for successively computing by a predetermined sampling period the idle time and the slope according to a change of the controlled variable by a step response of the controlled system applied by the step manipulated variable to provide an output, and

setting means for computing PID control parameters based on said idle time and said slope computed by said identification means after reaching said predetermined condition to be set to said PID control means.

2. A PID control unit according to claim 1 in which said step manipulated variable output means generates a maximum step manipulated variable.

3. A PID control unit according to claim 2 in which said setting means sets said computed PID control parameters only when a proportional gain of said computed PID control parameters is smaller than a proportional gain of PID control parameters previously set in said PID control means.

4. A PID control unit according to claim 1 in which said setting means sets said computed PID control parameters only when a proportional gain of said computed PID control parameters is smaller than a proportional gain of PID control parameters previously set in said PID control means.