JPS61203885A - Motor control system - Google Patents

Abstract

PURPOSE:To improve a torque ripple by storing a torque constant correction value in response to the rotating position of a motor in advance in a control table memory. CONSTITUTION:A counter 8 counts clock signal ch2 output from a digital tachometer 2, and outputs an absolute position signal of the shaft rotation of a DC motor 1. The output of the counter 8 is used as an address for accessing a control table memory 9. The memory 9 stores the value for correcting the variation of the torque constant generated by the structure of a motor in a table format. The correction value read out from the memory 9 is compared with a reference value Es, and output to a D/A converter 13. The converter 13 multiplies the drive signal output from a servo main circuit 14 by the correction signal, and outputs a drive analog signal.

Description

[Detailed Description of the Invention] [Summary] In order to improve the torque ripple of the motor, fluctuations and deviations of the torque constant for each rotational position of the motor are made into a table in advance and stored in a memory.

A table is referred to based on the motor rotation position, the motor drive current is corrected, and the motor is driven so that a constant torque is generated regardless of the two rotation positions.

[Industrial application field]

The present invention relates to a control system for a DC motor or a brushless motor, and more particularly to a motor control system that minimizes control errors caused by torque ripple and differences in torque constants between a plurality of motors.

[Conventional technology]

In DC motors and brushless motors, motor torque is generated by the current flowing through the motor windings.

Widely used as a driving element in high-precision servo systems.

However, in the case of these motors, as the servo accuracy increases, control errors due to unevenness in the torque constant and friction torque based on the slot arrangement of the motor, that is, torque ripples that occur as a function of the rotation angle, increase.

Figure 2 shows this conceptually, and 21 in Figure 2 (a)
is the magnetic pole of the stator, 22 is the rotor, 23 is the slot, θ
is the rotational position. The figure (bl represents the fluctuation of the generated torque due to the 9-rotation position θ, that is, the torque ripple.

To improve this, there is a method of increasing the gain of the servo amplifier, but there is a limit because it also increases unstable factors such as single oscillation.

For this reason, in the past, many methods have been used to reduce the torque ripple of the motor by improving the motor structure, such as making the rotor cup-shaped or using a ski-loft.

However, this method has the disadvantage of complicating the motor structure and increasing the price of the motor.

Furthermore, when a reel-to-reel direct drive system is adopted in a magnetic tape device for computers, the torque position and friction torque between the two reel motors must be made approximately equal, but this requires reducing the variation in the motors. was required, which caused manufacturing difficulties.

[Problem that the invention seeks to solve]

The present invention provides a means for easily improving torque ripple in a DC motor or brushless morph servo system by using an electrical method, without using the conventional method of improving the motor structure, and thereby achieving high precision. The aim is to enable servo control.

[Means to improve problems]

Torque ripple in a motor occurs due to the structure of the motor, and in particular, the biggest factor is that the torque constant varies depending on the motor shaft position.

Therefore, by correcting the motor drive current value only by the variation in the torque constant, the torque ripple of the motor can be canceled out in a pseudo manner.

Therefore, in the present invention, a table is created by calculating the torque constant correction value according to the rotational position of the motor in advance and stored in the control table memory during operation.

Detect the rotation of the motor with a digital tachometer.

A torque constant correction value corresponding to the rotational position is read from the control table memory, and the motor current is corrected via the power amplifier.

[Effect]

According to the present invention, motor current correction is performed for each rotational position of the motor so as to generate a torque change in the opposite direction that cancels the torque ripple.

Additionally, when multiple motors are operated together.

By determining the torque constant deviation between each motor and correcting the torque constant correction value for each motor,
Variations in torque constant between motors can be reduced.

(Example) The details of the present invention will be explained below according to an example. In Fig. 1, 1 is a DC motor, 2 is an optical decimal tachometer, and 3 is an index output (c
hi), 4 is the tachometer clock output (ch2)
, 5 and 6 are photodetection circuits, 7 is a differentiation circuit, 8 is a counter, and 9 is a control table memory.

10 is a multiplication type DAC (DA converter), 11 is a variable voltage (Es), 12 is a filter circuit, and 13 is a multiplication type D
AC, 14 is a servo main circuit, 15 is a power amplifier, 16 is a motor current, and 17 is a feedback signal.

18 indicates a feedback resistor (R).

The deci7 tartachometer 2 is attached to the rotating shaft of the DC motor 1, and has an index output (chi) that generates one pulse per rotation and a clock output (ch2) that generates multiple pulses (ch2) per rotation. . These are converted into electrical signal pulses by photodetection circuits 5 and 6, and ch
i is further differentiated by a differentiating circuit 7 and applied to a counter 8, respectively.

The rotational position of the DC motor 1 can be detected by clearing the counter 8 with chl and counting up with ch2. The main force of the counter 8 indicates the absolute position of the shaft rotation of the DC motor 1. The output of this counter 8 is also used as an address for accessing the control table memory 9.

The control table memory 9 is composed of, for example, a ROM, and stores in advance in table form values for correcting variations in the torque constant that occur due to the structure of the motor (number of slots, number of magnetic poles, etc.).

Note that the average value of torque constant fluctuations measured for several sample motors is used as the value stored in this table.

The data output of the correction value read from the control table memory 9 is input to the DACIO and converted into a correction analog signal. This DACIO is a multiplication type, and a variable voltage (ES) is applied to a reference voltage input terminal.

This variable voltage (Es) is for correcting variations in the magnitude of the torque constant among individual motors. In other words, increasing E's increases the torque constant correction value, resulting in overcompensation, while decreasing Es results in undercompensation, so if Es is selected to the optimal value, variations in torque constant between motors can be absorbed. I can do it.

The filter circuit 12 performs torque ripple compensation.

This is to constantly optimize the motor rotation speed against changes.

The multiplication type DAC 13 connects the correction analog signal generated by the DACIO to the basic voltage input terminal, and thereby multiplies the digital drive signal output from the servo main circuit 14 by the correction analog signal. , it is possible to output a compensated drive analog signal.

Since the power amplifier 15 is subjected to current feedback by the feedback signal 17 and the resistor (R) 18, it is possible to flow a current proportional to the drive analog signal output from the DAC 13 to the motor.

Note that in the above-described embodiment, the 9-multiplying type DACIO and DAC 13 can be a combination of a 2-multiplier and a DAC, and the multiplier and control table memory 9 can also be combined together to form an MPU. It is possible. Further, the control table memory 9 may be constructed of either ROM or RAM.

Furthermore, a similar method can be applied to a system using a brushless motor instead of a DC motor to correct torque fluctuations.

〔Effect of the invention〕

High-precision servo motors are expensive, but according to the present invention, equivalent servo precision can be achieved using a low-precision, low-cost motor.

This is particularly effective when applied to a reel-to-reel direct drive type magnetic tape device because the torque motor current characteristics between the two reel motors can be easily matched.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram of a system according to an embodiment of the present invention. FIG. 2 is an explanatory diagram of the torque ripple of the DC motor. In Fig. 1, 1 is a DC motor, 2 is an optical digital tachometer, 8 is a counter, 9 is a control table memory, 10.13 is a multiplication type DAC, and 11 is a variable voltage (Es
), 12 is a filter circuit, 14 is a servo main circuit, and 15 is a power amplifier.

Claims (1)

[Claims] A DC motor or brushless motor with a digital tachometer, a power amplifier for controlling the motor current that drives these motors, and a position detector that generates a digital signal indicating the rotational position of the motor shaft based on the output of the digital tachometer. circuit, and a control table memory which takes the digital signal output from the position detection circuit as an address input and outputs a motor torque correction value, and controls the output of the power amplifier according to the motor torque correction value output from the control table memory. A motor control method characterized by correction.