JPS6156523B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a process control device that performs feedback control of a process using an electronic computer.

To perform feedback control of a process using an electronic computer, input the process quantity through an input device connected to the electronic computer, perform appropriate calculations on it to obtain the control output, and output it to the output connected to the electronic computer. It is necessary to output to the process by the device.

FIG. 1 shows a block diagram of conventional process feedback control using an electronic computer.

In FIG. 1, an input device 3 inputs an analog quantity Au from a process 1, converts it into a digital quantity Du by an A/D converter, and supplies it to a computer 5. The electronic computer 5 calculates the deviation Dδu between Du and the control target value Du ₀ . Next, based on the deviation Dδu, the control output calculation unit 4 calculates proportional, integral,
Perform differential calculations, etc. to obtain control output DY. The obtained control output DY is converted into an analog quantity AY by a D/A converter in the output device 2 and output to the process 1. Normally, the input Du from the input device 3 and the output DY to the output device 2 are expressed in fixed point numbers, and the calculations performed by the control output calculation section 4 are performed in floating point numbers. To do this, Dδu, which is expressed as a fixed point number, is converted into a floating point number by converting it into a floating point number, and then the control output calculation section 4 performs floating point processing, and the result is converted back to a fixed point number.
It is necessary to obtain

Recently, there has been a tendency to use microcomputers to perform such simple feedback control, but most microcomputers do not have floating-point arithmetic functions, and even if they do, they cannot process floating-point arithmetic. It takes time to perform calculations and convert fixed-point numbers to floating-point numbers or vice versa, making it unsuitable for fast cycle control.

The present invention has been made in view of this point,
To provide a process control device that enables fast-cycle feedback control even in an electronic computer that does not have a floating-point arithmetic function, or even if it does have it, the computer has a slower control cycle than the process control cycle.

The basic configuration of the present invention is shown in FIG.

The difference between FIG. 2 and FIG. 1 is that the control output calculation section 4 in FIG. 1 is replaced with a table search section 6.

The analog quantity Au of the process is converted by an A/D converter in the input device 3 into a digital quantity Du. The number of bits of the digital quantity Du depends on the number of bits of the A/D converter, but if the A/D converter is 11 bits including the sign bit, Du is -
It is an integer in the range of 1024≦Du≦+1023. Therefore, Dδu also becomes an integer in the range of −1024≦Dδu≦+1023. Since the number of bits of the D/A converter of output device 2 does not need to be greater than the number of bits of the A/D converter of input device 3, suppose that the number of bits of the D/A converter of output device 2 also includes the sign bit. Assuming that there are 11 bits, DY is an integer in the range -1024≦DY≦+1023.

That is, to obtain the final control output DY, −
The control output DY, which is an integer value in the range -1024≦DY≦+1023, may be obtained by inputting an integer value in the range of 1024≦Dδu≦+1023.

Since the relationship between Dδu and DY has already been known, there is no need to calculate it in real time as in the past, but instead create a table like the one shown in Figure 3 and store it in the computer's storage device. You can save it to . The absolute address in FIG. 3 is an address in the storage device, and according to FIG. 3, the above table is stored starting from address _A0 in the storage device.
DY(Dδu) represents the output corresponding to Dδu. For example, when Dδu=0, DY(0) at address A ₀ +1024 may be taken out from the storage device and output. Using this table, the address A where DY (Dδu) corresponding to Dδu is stored can be found using the following formula.

A=A ₀ +1024+Dδu ...(1) Since A ₀ in the above equation is known in advance, if A ₁ =A ₀ +1024, A=A ₁ +Dδu ...(2) Dδu can be obtained by one addition. Output DY corresponding to
The address of (Dδu) can be found.

FIG. 4 is a flowchart showing the flow of the above processing performed by an electronic computer.

The part indicated by the dotted line is the table search section 6 in Fig. 2.
This is the process. Dδu input from input device 3
Calculate the deviation Dδu based on . The output DY corresponding to D.delta.u is the contents of the table search section stored in accordance with the table of FIG. 3 at the address determined by equation (2). Therefore, according to the present invention, by storing the relationship between the input from the process and the control output as a table, the process can be controlled at a faster cycle without requiring complicated calculations when determining the control output. I can do things.

In the above explanation, the case has been described where the deviation Dδu and the control output DY have a one-to-one correspondence. This is the case, for example, in the case of so-called proportional control (P control) in which the control output DY is obtained by multiplying the deviation Dδu by a constant proportionality constant K.

The present invention further provides that the control output DY is equal to the past deviation D
It can also be applied to integral control (I control) that is proportional to the integrated value of δu. It goes without saying that the integral control may be multiple integral control of double integral or more.

An example of a flowchart when applied to integral control is shown in FIG. A portion 6 surrounded by a dotted line in FIG. 5 is the flow of processing performed by the table search section 6 of FIG. 2. In FIG. 5, the deviation Dδu is integrated by the deviation integration section 7. The absolute address A is set so that this integrated value ΣDδu and the control output DY correspond one-to-one.
Instead of formula (2), it is configured to be obtained by A=A ₁ +ΣDδu...(3). Fifth
The figure is the same as in Figure 4 except that the deviation accumulator 7 is added, and the accumulation of the deviation Dδu does not require floating-point addition and can be done as a fixed-point number. It is easy to apply to a computer or an electronic computer whose speed is slower than the control cycle even if it has one.

The above mentioned proportional control and integral control, but
Similarly, it can be applied to differential control (D control).

An example of a flowchart when applied to differential control is shown in FIG. A portion 6 surrounded by a dotted line in FIG. 6 is the flow of processing performed by the table search section 6 of FIG. 2. The only difference between FIG. 4 and FIG. 6 is that in FIG. 6, an arithmetic unit 8 for performing differential control is added. In the calculation unit 8, DDδu=
The calculation Dδu-Dδu ^* is performed. Here Dδu
^* is the previous deviation. In other words, the current deviation D
Find the difference DDδu between δu and the previous deviation Dδu ^* ,
The absolute address A is determined by A=A ₁ +DDδu (4) instead of equation (2) so that DDδu and control output DY correspond one-to-one. Since the subtraction performed in the arithmetic unit 8 for performing differential control can be performed using fixed-point numbers, it is suitable for electronic computers that do not have floating-point arithmetic functions or whose speed is slower than the control cycle even if they do have floating-point arithmetic functions. It is also easy to apply. Note that it goes without saying that the differential control may be multi-order differential control that is higher than second-order differential control.

Next, FIG. 7 shows a flowchart when performing proportional/integral/derivative control (PID control) by combining FIGS. 4, 5, and 6.

In this case, generally a table for proportional control, a table for integral control,
Three types of tables are required for differential control. A portion 6 surrounded by a dotted line in FIG. 7 is the flow of processing performed by the table search unit 6 in FIG. 2. The table for proportional control is stored starting from address _A'0 in the computer's storage device.
It is assumed that the table for performing integral control is stored from address _A'1 and the table for performing differential control is stored from address _A'2 . At each table, Dδu=
Address corresponding to 0, ΣDδu=0, DDδu=0
Using A ₀ , A ₁ , A ₂ , the storage address A P of the proportional control output DY _P corresponding to Dδu and the storage address A _P of the integral control output DY _I corresponding to ΣDδu and _the differential control output DY corresponding to DDδu The storage address A _D of _D can be calculated using the following formula.

A _P =A ₀ +Dδu A _I =A ₁ +ΣDδu A _D =A ₂ +DDδu Proportional control output DY _P obtained by searching each table using the above A _P , A _I , and A _D ,
The output DY _I of the integral control and the output DY _D of the differential control are finally added together to form a control output DY, which is output to an output device 2 connected to a computer.

As described above, according to the present invention, by storing the relationship between the input from the process and the control output as a table, there is no need for complex calculations when determining the control output, and the process can be controlled at a faster cycle. can be done.

[Brief explanation of the drawing]

Figure 1 is a block diagram showing conventional feedback control using a computer, Figure 2 is a block diagram showing the basic configuration of the present invention, and Figure 3 is the relationship between input and output stored in the storage device of the computer. 4 to 7 are flowcharts when the present invention is applied to proportional control, integral control, differential control, and PID control, respectively. DESCRIPTION OF SYMBOLS 1...Process, 2...Output device, 3...Input device, 4...Control output calculation unit, 5...Electronic computer, 6...Table search unit.

Claims (1)

[Claims] 1. Converting the analog signal obtained from the process into a digital quantity and inputting it into a computer, calculating a deviation signal from the feedback amount and the control target value within the computer, calculating a control output according to this deviation signal, In a process control device that converts this control output into an analog quantity and outputs it to the process, thereby providing feedback control of the process, the process deviation signal, the integral value of the process deviation signal, or the process deviation signal obtained as a digital quantity is used. Separate tables of control outputs corresponding to a plurality of values including at least a process deviation signal among the differential values are provided separately, and appropriate control outputs are searched from the plurality of tables using each of these plurality values as arguments. A process control device that combines a plurality of control outputs to obtain an output value for a process, converts this output value into an analog quantity, and outputs the converted value.