Self-tuning controller

In a self tuning controller having PI controlling means for effecting at least proportional integral arithmetic on a deviation signal between a process variable and a control set value,the improvement comprising

• waveform observing means for seeking an evaluation index of a response waveform of said process variable or said deviation signal by observing said response waveform of said process variable or said deviation signal;
• arithmetic segment setting means for selecting operational expressions for obtaining PI arithmetic parameters on the basis of said measurement evaluation index of said response waveform obtained by said waveform observing means;
• parameter arithmetic means for computing said PI arithmetic parameters to be set in said PI controlling means by using said operational expressions selected by said arithmetic segment setting means;
• and
• tuning quantity correcting means for correcting a tuning quantity of said PI arithmetic parameters obtained by said parameter arithmetic means in accordance with an amplitude of said response waveform.

A self tuning controller comprising

• PI controlling means for performing at least proportional integral arithmetic on a deviation between a control set value and a process variable from a controlled system, and comprising a pre-adapter comprising an outputting means for outputting a step variation to a process;
• an observing means for observing a step response from said process;
• and a PI calculating means for calculating proportional integral arithmetic parameters on the basis of an observed result given by said observing unit and setting said proportional integral arithmetic parameters in said PI controlling means;
• said observing means obtaining a maximum gradient line from timings (.DELTA.t) at which said step response passes through a plurality of different set values (.DELTA.PVn and .DELTA.PVn-1) and from a different (.DELTA.Pvn-.DELTA.PVn-1) between said different set values after observing said step response and further obtaining a correction coefficient (E) by performing a predetermined arithmetic operation on the basis of said set values (.DELTA.PVn and .DELTA.PVn-1) , a step variation quantity .DELTA.MV and a step response fluctuation quantity .DELTA.PV;
• said PI calculating unit calculating said PI arithmetic parameters by making use of information obtained from said maximum gradient and said correction coefficient (E).

A method for automatically tuning the proportional (P) and integral (I) arithmetic parameters of a self tuning controller of a process having a process variable signal, comprising the steps of

• generating a deviation signal between a control set value and the process variable signal;
• computing a first area associated with said process variable signal or said deviation signal extending from a first generation timing (t.sub.1) of a first peak of said process variable signal of said deviation signal to a subsequent second generation timing (t.sub.2) of a second peak;
• computing a second area associate with said process variable signal or said deviation signal extending from said second generation timing to a subsequent timing given by t.sub.2 +(t.sub.2 -t.sub.1);
• outputting an area ratio of said first area to said second area, as one of a plurality of evaluation indexes representing wave form patterns;
• computing said PI arithmetic parameters on basis of said evaluation indexes, including said area ratio;
• and
• automatically tuning PI arithmetic parameters of the self tuning controller.