JPH02211085A - Automatic zero adjuster for speed command - Google Patents

Abstract

PURPOSE:To improve accuracy of a speed control without using a precise and expensive component by correcting the offset and gain of an operational amplifier, an analog/digital converter at every predetermined time in a speed command input circuit of a servo unit using a digital control. CONSTITUTION:A microprocessor 4 closes a switch 1b, opens switches 1a, 1c, and reads a zero speed command V0 (= zero volt) as digital value of an offset through an A/D converter 3. Then, it closes the switch 1c, opens the switches 1a, 1b, and reads a reference voltage Vref as a digital value through the converter 3. Then, it closes the switch 1a, opens the switches 1b, 1c, reads a speed command Vcmd as a digital value Vcmd through the converter 3, calculates a corrected speed command, and controls the speed with it as a final speed command value.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to an automatic zero adjustment device for a speed command in a servo device that controls the speed of an electric motor.

(Prior Art) FIG. 2 shows a block diagram of a general servo device that performs speed control.

In FIG. 2, the speed command Vend is matched with the speed feedback signal Vfb detected by the speed detector 8 at the input circuit 9A, the difference is proportionally integrated by the proportional integrator 5, and the output thereof is amplified by the current amplifier 6. A current proportional to the output of the proportional integrator 5 is caused to flow through the motor 7.

FIG. 3 shows an example of a speed command input circuit 9A constructed of an analog circuit.

In FIG. 3, operational amplifier 9 is adjusted by variable power supply 11 so as to cancel out the offset of speed command Vend and the offset of operational amplifier 9. In FIG.

The adjustment resistor 12 is for adjusting the gain of the operational amplifier 9,
It is used to adjust the motor speed with respect to the speed command Vend.

(Problem to be solved by the invention) In this case, the offset and gain may change depending on environmental conditions such as temperature, and this change directly affects speed control accuracy, so an operational amplifier with small drift is used. There is a need.

Figure 4 shows the case of digital control using a microprocessor, but in this case as well, speed commands are often input in analog form;
Using the digital converter 3, the analog speed command Ven
d is converted into a digital value and input to the microprocessor.

In this case, changes in offset and gain need to be considered not only for the operational amplifier but also for the analog/digital converter.

The present invention corrects the offset and gain of the operational amplifier and analog/digital converter at regular intervals in a speed command input circuit for a servo device using digital control, thereby making it possible to use highly accurate and expensive components. The purpose of the present invention is to provide an automatic zero adjustment device for a rational speed command that can improve speed control accuracy.

[Structure of the invention]

(Means and operations for solving the problem) In order to achieve the above object, the present invention provides a servo device that performs speed control, a means for detecting a zero speed command, a means for detecting a speed command reference, and a means for detecting a speed command reference, and a means for detecting a speed command standard. An analog/digital converter for analog/digital conversion of commands and speed commands and a microprocessor for calculation are provided, and the output of the analog/digital converter is used to enable the microprocessor to automatically zero-adjust the speed command. .

(Example) An embodiment of the present invention is shown in FIG.

In Figure 1, la, lb, and lc are switches, 2
is an operational amplifier, 3 is an analog/digital converter, and 4 is a microprocessor.

The microprocessor 4 takes in the analog value of the speed command VC Yod as a digital value according to the flowchart of FIG.

That is, the microprocessor 4 closes the switch 1b and opens the switches la and lc at appropriate timing.

The zero speed command v0 (=zero volts) is converted to an offset digital value v0 via the analog/digital converter 3.
Read as .

Next, the microprocessor 4 closes the switch 1c and opens the switches la and lb at a timing different from that described above, and reads the reference voltage Vraf as a digital value Vref via the analog/digital converter 3.

If the value of Vref changes, the target value Vrefo set in the microprocessor 4
should match, and if they do not match, operational amplifier 2
This is the error between the input resistance R1 and the feedback resistance Rf, that is, the gain error, so this is calculated.

Next, close the switch la, open lb and fc, read the speed command Vend as a digital value Ve+md via the analog/digital converter 3, and calculate the corrected speed command Vcmdo as Vcmdo = (Vcs*d - Vo) X E
This is calculated as the final speed command value and speed control is performed.

〔Effect of the invention〕

As explained above, according to the present invention, even if an inexpensive resistor with poor precision or an operational amplifier with an offset is used, it is possible to always automatically correct the gain and offset and obtain the correct command value. Furthermore, an automatic zero adjustment device with a reasonable speed command that is not affected by temperature drift can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of the present invention. Figure 2 is a block diagram showing the general configuration of the servo device;
3 is a general speed command input circuit for analog control, FIG. 4 is a general speed command input circuit for digital control, and FIG. 5 is a flowchart showing the operation of the present invention. la, lb, lc-switches. 2.9.10...Operation amplifier. 3...Analog/digital converter, 4...Microprocessor. 5...Proportional integrator, 6...Current amplifier, 7.
...Electric motor, 8...Speed detector.

Claims (1)

[Claims] In an automatic zero adjustment device for a speed command that adjusts the zero point of a speed command obtained by converting an analog value speed command input to an analog input circuit into a digital value via an analog/digital converter, the speed command is provided in the analog input circuit. There are three switches for inputting the speed command, zero speed command, and speed command reference voltage respectively, and the three switches are opened and closed in sequence at predetermined timing, and the offset and offset of the analog input circuit are calculated from the digital value corresponding to the analog input. An automatic zero adjustment device for a speed command, characterized in that it is provided with a microprocessor that calculates a change in gain and corrects the zero point of an analog speed command based on this.