Controller having PID selection function

Details Controller having PID selection function Controller having PID selection function

2003-01-14

2004-05-18

Wayner, William (Department: 2121)

Data processing: generic control systems or specific application

Generic control system, apparatus or process

Optimization or adaptive control

C236S07800D, C318S610000, C700S050000

Reexamination Certificate

active

06738676

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a controller having a PID selection function capable of performing stable PID control during a change of a PID value.
2. Description of the Related Art
FIG. 6
is a block diagram showing a configuration of a conventional controller having a PID selection function. In the diagram, reference number
100
designates a controller having a PID selection function,
200
denotes an object device or system to be controlled,
101
indicates a PID set selection means for selecting a set of a P (Proportional) value, an I (Integral) value, and a D (Derivative) value. Reference number
102
designates a PID value storage means for storing P, I, and D values,
103
denotes a PID value input means through which P values, I values, and D values are inputted. Reference number
104
designates a PID value determination means for determining a set of the P, I, and D values,
105
denotes PID calculation means for calculating an operation value MV based on the P, I, and D values transferred from the PID value determination means
103
and a deviation value (measured value PV−set value SP), and outputting the operation value MV to the object device
200
in order to perform the PID control for the object device
200
. Reference number
106
indicates a set value input means for inputting and outputting a set value, and
107
denotes a subtracter for subtracting a set value SP from a measured value PV as an actual process variable.
Next, a description will be given of the operation of the conventional controller having the PID selection function.
In this controller, the PID calculation means
105
performs the PID calculation based on the deviation value (PV−SP) so that the measured value PV of the object device becomes equal to the set value SP, and then calculates the operation value MV. For example, the controller supplies the current corresponding to the operation value MV to a heater (not shown) equipped in the object device
200
so that the temperature of a high-temperature tank measured becomes equal to the desired set temperature.
Generally, in cases where the object device
200
includes different works to be controlled and where different set values SP are used, because the object device
200
is in different environment, it is necessary to use different PID values. That is, it is necessary to change the PID value every changing of the work and the set value SP. In such a conventional controller, the PID value determination means
104
reads the PID value stored in the PID value storage means
102
corresponding to the set number selected by the PID set selection means
101
, and outputs the read one to the PID calculation means
105
. The PID value storage means
102
stores the PID values in advance, each of which corresponds to its PID set number.
Through the PID value input means
103
incorporated in the controller, the PID values stored in the PID value storage means
102
corresponding to the PID numbers are stored in advance.
The PID set selection means
101
determines the PID set number based on the input through an external input switch or the PID set selection means placed in the controller. For example, the PID set selection means
101
so determines that the PID set number is the value “1” when the external input switch is ON, and determines that the PID set number is the value “2” when OFF.
FIG. 7
is a flow chart showing the operation of the PID value determination process in the conventional controller when the PID value is changed.
First, the PID set selection means
101
reads a set number (Step ST
100
). It is judged whether the set number read is “1” or “2” (Step ST
101
). When the set number is “1”, the PID value storage means
102
reads the PID value corresponding to the set number “1” (Step ST
102
). On the contrary, the judgment result in the Step ST
101
indicates the set number is “2”, the PID value corresponding to the set number “2” is read from the PID value storage means
102
(Step ST
103
). The PID value read in Step ST
102
or ST
103
is outputted to the PID calculation means
105
. When receiving the PID value, the PID calculation means
105
calculates new operation value MV (Step ST
104
), and then outputs the calculated one to the object device
200
.
Because the conventional controller having the PID selection function has the configuration described above, the PID value to be supplied to the PID calculation means
105
is rapidly changed in the changing process of the PID value. This causes that a new operation value MV from the PID calculation means
105
is rapidly changed, so that it is difficult to perform the correct control for the object device in the changing process of the PID value.
SUMMARY OF THE INVENTION
The present invention has been made to solve the drawback involved in the conventional controller having the PID selection function. It is therefore an object of the present invention to provide a controller having a PID selection function capable of suppressing the rapid change of the operation value to be supplied to an object device or system when the PID value is changed and capable of controlling the object device or system smoothly and continuously.
According to an aspect of the present invention, there is provided a controller having a PID selection function of performing PID calculation so that a measured value of an object device or system to be controlled is reached to a set value and of calculating an operation value to be supplied to the object device or system based on the PID value calculated. The controller of the present invention has a PID set selection means and a PID value determination means. The PID set selection means selects a set number of the PID value. The PID value determination means performs PID calculation in order to determine a PID value based on a current PID value of the set number currently selected by the PID set selection means, a previous PID value of the set number previously selected by the PID set selection means, and a switch time to switch the previous PID value to the current PID value.
Further, according to another aspect of the present invention, the PID value determination means in the controller determines the PID value based on fuzzy inference using a switch time as a parameter, the PID value corresponding to the PID set number currently selected, and the PID value of the set number previously selected.
Still further, according to another aspect of the present invention, the PID value determination means in the controller calculates the switch time based on a D value as a derivative time of the PID value corresponding to the set number selected by the PID set selection means.


REFERENCES:
patent: 5748467 (1998-05-01), Qin et al.
patent: 6081751 (2000-06-01), Luo et al.
patent: 0263516 (1987-11-01), None

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