JP4952902B2 - Electric motor control device - Google Patents

Description

  The present invention relates to an electric motor control device that drives a machine or the like with a servo motor and a torque constant correction method thereof.

The first prior art relates to a servo motor control device used as a drive source for a feed axis of a machine tool or industrial machine or a robot arm, etc., and keeps a constant torque constant in the servo motor speed control. In addition, a servo motor control device that can prevent a decrease in speed loop gain due to a decrease in torque constant is provided (see, for example, Patent Document 1).
The second prior art relates to an auto-tuning servo device that always maintains good control performance even if the parameters of the mechanical system and servo motor are unknown or change. When the parameters of the mechanical system and servo motor are unknown However, an auto-tuning servo device is provided that can be automatically adjusted by estimating parameters and can be automatically readjusted even if the characteristics of the mechanical system fluctuate (for example, Patent Document 2). reference).

FIG. 6 is a schematic block diagram for explaining a servo motor control apparatus according to the first prior art. In the figure, the servo motor control device is a control device that controls the servo motor including at least the speed control loop 100, and forms a corrected torque command that compensates for a decrease in the torque constant according to the control state of the servo motor. In the control of the servo motor that performs the speed control, the servo control circuit estimates a decrease in the torque constant, and the torque constant is reduced. The torque constant of the servo motor is made constant by obtaining a corrected torque command that compensates for the current, performing current control by the current control loop 102 based on this corrected torque command, and keeping the torque constant viewed from the control loop equivalently constant. Was holding.
As described above, in the first conventional technique, a decrease in the torque constant is determined based on the actual current amplitude value with respect to the torque command, and the torque correction value is calculated.

FIG. 7 is a block diagram showing a configuration of an auto-tuning servo device that is the second prior art. In the figure, an auto-tuning servo device is a servo device that controls the position and speed, and a parameter estimation unit 230 that estimates the inertia term, viscosity term, coulomb friction, steady disturbance force, and torque constant of the servo motor of the mechanical system 220. And a control calculation unit 210 that changes the parameters of the control system based on the numerical values of the parameters estimated by the parameter estimation unit 230, even if the parameters of the mechanical system 220 and the torque constant of the servo motor are unknown. These parameters are estimated by the parameter estimation unit 230, and the control system is adaptively changed to always maintain good control performance.
As described above, the second prior art performs a parameter estimation calculation based on the torque command Ic output from the control calculation unit 210 and the angular velocity ω measured by the mechanical system 220, and calculates the torque constant Kt of the servo motor and the like. A parameter estimate was calculated.
As described above, in the conventional apparatus, a procedure of calculating and compensating the actual current amplitude value and parameter has been taken.
Japanese Patent Laid-Open No. 11-191990 (page 3-6, FIG. 1) Japanese Patent Laid-Open No. 11-065608 (page 2-7, FIG. 1)

In the first prior art, since the torque correction value is calculated based on the actual current amplitude value with respect to the torque command, the actual torque with respect to the torque command is caused by the temperature change (winding temperature rise) of the motor caused by driving the motor. Changes (when the torque constant changes), the actual current amplitude value changes with the change of the actual torque, and the torque command also changes by the servo control loop due to the change of the actual current amplitude value. Since the torque command and the actual current amplitude value change, there is a problem that the torque correction value cannot be calculated based on the actual current amplitude value with respect to the torque command.
The second prior art has a problem that the estimated parameter cannot be changed frequently because the disturbance is calculated and corrected from the estimated parameter and the state variable for auto-tuning. In addition, the parameters to be estimated are related to each other and there are a large number of parameters. Therefore, in order to obtain the parameters to be estimated, several different conditions are necessary, and if the conditions are not met, it cannot be obtained accurately. There was also.

The present invention has been made in view of such a problem. When the actual torque with respect to the torque command changes (when the torque constant changes) due to a change in the temperature of the motor (winding temperature rise) or the like, It is an object of the present invention to provide an electric motor control device and a torque constant correcting method thereof that can always correct a torque command accurately by easily calculating a change and correcting a torque constant.

In order to solve the above problem, the present invention is as follows.
An electric motor control device according to one aspect of the present invention drives an electric motor according to a torque command that is controlled and calculated based on a position or speed command and a current position of the electric motor that is a detection value of a position detector. The control device calculates a moving average value of acceleration / deceleration at a predetermined time interval during driving of the electric motor, and when the moving average value of the acceleration / deceleration and a current acceleration / deceleration value are within a predetermined range, the electric motor An acceleration / deceleration detecting unit that determines that the driving of the motor is a driving at a constant acceleration / deceleration, and the acceleration / deceleration detecting unit determines that the driving of the electric motor is a driving at a constant acceleration / deceleration. The acceleration and deceleration average torque commands, which are moving average values of the torque command at the time, are detected, respectively, and the difference between the absolute values of the acceleration average torque command and the deceleration average torque command is 1 2 to calculate the friction torque, subtract the friction torque from the acceleration or deceleration average torque command to calculate the acceleration or deceleration torque, and the reciprocal of the inertia moment value of the motor, A torque constant correction unit that multiplies a current acceleration / deceleration value by a reference torque constant, and calculates a torque constant correction value by dividing the acceleration or deceleration torque by the acceleration or deceleration torque, wherein the torque constant used in the control calculation is the torque An electric motor control device that updates the constant correction value is applied .

According to the motor control device of one aspect of the present invention, when the actual torque with respect to the torque command changes (when the torque constant changes) due to a temperature change of the motor (winding temperature rise) or the like, an accurate change of the torque constant can be obtained. By simply calculating and correcting the torque constant, the torque command can always be accurately corrected.
Further, it is possible to avoid the use of a torque command that slightly changes in a transient state during acceleration / deceleration, and by averaging, a detection error is small and a stable torque command can be obtained. In addition, it is possible to avoid the use of acceleration / deceleration and torque commands in the vicinity of the low speed during acceleration, which is a transitional state due to the influence of friction and gain and the like, near the low speed during acceleration.
Further, the influence of the friction torque can be ignored, and the correct torque constant can be corrected.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a schematic block diagram showing a configuration of an electric motor control device of the present invention. In the figure, 1 is an electric motor control device, 2 is an electric motor (motor), 3 is a position detector such as an encoder, 11 is a position or speed control unit, 12 is a current control unit, 13 is a power conversion unit, 14 is an encoder signal input. An output unit, 15 is a torque constant correction unit, 16 is a torque command detection unit, and 17 is an acceleration / deceleration detection unit.
A configuration in which the motor 2 is driven according to the position detection signal or the speed detection signal that is output from the command and the encoder signal input / output unit 14 (the motor 2, the position detector 3, the position) is input. Alternatively, the speed control unit 11, the current control unit 12, the power conversion unit 13, and the encoder signal input / output unit 14) are configurations obtained by a well-known technique, and thus detailed description thereof is omitted.
The present invention is different from the prior art in that it includes an acceleration / deceleration detection unit 17 and a torque command detection unit 16, and is a torque constant correction method implemented by the acceleration / deceleration detection unit 17, torque command detection unit 16, and torque command correction unit 15. Part.
The torque constant correction unit 15 calculates a torque constant from a constant acceleration during acceleration and deceleration and an average torque command thereof, and corrects the torque command with the torque constant. The torque detector 16 detects the final average torque command for the acceleration / deceleration during a constant acceleration / deceleration. The acceleration / deceleration detector 17 detects a constant acceleration / deceleration and detects the final average acceleration / deceleration of the acceleration / deceleration.

FIG. 2 is a flowchart showing the processing procedure of the torque constant correction method of the present invention. The method of the present invention will be described step by step with reference to this figure.
(Step 1: S1)
The acceleration / deceleration detector 17 determines whether or not the current driving of the electric motor 2 is driving at a constant acceleration / deceleration. If the acceleration / deceleration is constant, the process proceeds to Step 2, and if not, the series of processing is terminated.
FIG. 3 is a waveform diagram for explaining the timing for detecting the acceleration / deceleration and the torque command in the motor control device of the present invention.
For example, if the moving average value of acceleration / deceleration for 10 ms and the current acceleration / deceleration are within a certain range, the constant acceleration / deceleration is determined to be constant acceleration / deceleration. In the calculation, as shown by points A and B in FIG. 3, the moving average value of the acceleration / deceleration near the end of acceleration / deceleration is used. This is to prevent detection of a transient state due to the influence of friction and the dependence of gain or the like in the vicinity of a low speed during acceleration. The detection method uses, for example, a moving average value of acceleration / deceleration before the acceleration or deceleration changes from constant acceleration to 0 near the end. Therefore, the acceleration is always averaged until the acceleration / deceleration is detected.

(Step 2: S2)
The torque command detection unit 16 calculates a moving average value of the torque command and proceeds to step 3.
The torque command detection unit 16 integrates the torque command of the portion indicated by points C and D in FIG. 3, which is the time axis portion used for the above-described calculation of the constant acceleration / deceleration, for example, by averaging for a fixed time with a moving average. Torque command is detected. The average torque command is a transitional state during acceleration / deceleration, and the torque command changes slightly finely. Therefore, averaging allows a small detection error and a stable torque command can be obtained.
As described above, in the moving average process of acceleration / deceleration and torque command in step 1 and step 2, acceleration / deceleration and torque command are detected in a portion where the transient change of acceleration / deceleration indicated by points A to D in FIG. 3 is small. .

(Step 3: S3)
Further, the torque command detection unit 16 corrects the friction torque from the moving average value of the torque command, and the process proceeds to Step 4.
Above a certain speed, the torque command at acceleration is expressed by equation (1), and the torque command at deceleration is expressed by equation (2).
Torque command during acceleration = acceleration torque + friction torque (static friction + viscous friction) (1)
Deceleration torque command = Deceleration torque-Friction torque (static friction + viscous friction) (2)
Here, if the acceleration and the deceleration are the same, it is expressed by equation (3). Therefore, the friction torque is obtained by halving the difference between the absolute values of the acceleration torque command and the deceleration torque command.
| Expression (1) |-| Expression (2) |
= | Acceleration torque + Friction torque |-| Deceleration torque-Friction torque |
= 2 x friction torque (3)
Thus, the friction torque is calculated based on the average torque command value during acceleration and deceleration, and the torque can be obtained by subtracting (correcting) the friction torque from the average torque command value during acceleration and deceleration. . The method for obtaining and subtracting the friction torque is not limited to this method, and another method may be used. For example, the friction torque may be a preset value.

(Step 4: S4)
The torque constant correction unit 15 calculates and corrects the torque constant, and ends the series of processes. The torque constant Kt is calculated as in equations (4) to (6). Here, τ is torque obtained by subtracting friction torque, i is current, dω / dt is acceleration, J is moment of inertia, and Kt ₀ is torque under a certain condition (for example, a typ. Value at a motor temperature of 20 ° C.). It is a constant.
Kt = τ / i (4)
τ = 1 / J × dω / dt (5)
Kt = 1 / J × dω / dt × Kt ₀ / τ (6)
That is, if the acceleration dω / dt is the same (constant), a change in torque becomes a change in torque constant.

Thus, the torque constant can be detected and corrected from the acceleration / deceleration during constant acceleration / deceleration and the average torque command at that time. The corrected torque constant is used by changing the original torque constant in the position or speed control for driving the electric motor 2.
FIG. 5 is a diagram illustrating a change in the torque command with respect to the armature temperature in a motor having a constant acceleration. In the figure, it can be seen that the torque command changes depending on the armature temperature.
In a motor using a magnet such as a synchronous motor, the magnetic force changes depending on the temperature. As a result, the torque obtained even with the same current changes and the torque constant changes. Therefore, if the motor is controlled with the temperature changed, the actual torque will change even with the same torque command. Conversely, when trying to perform a certain acceleration / deceleration, the actual acceleration / deceleration torque does not change with temperature or the like (since it follows the equation of motion), but the torque command changes. Therefore, the torque constant can be calculated from the acceleration / deceleration and the current (torque command). In addition, the actual torque and acceleration / deceleration are proportional to each other as shown in Equation (5). In order to reduce variations and detection errors by averaging, even if constant acceleration / deceleration is not always the same acceleration / deceleration good.

The difference between the second embodiment and the first embodiment is not the calculation of the torque constant itself, but a method of calculating and correcting a change in the torque constant from a certain reference torque value, for example, when the power is turned on. Instead of (Step 4: S4) in Example 1, the processing of (Step 11: S11) described later is performed.

(Step 11: S11)
The torque constant correction unit 15 calculates a torque constant from the reference torque value. Here, as the reference torque value, for example, a torque constant calculated value when the power is turned on is used. The torque constant Kt is calculated by the equation (6) in the first embodiment.
FIG. 5 is a speed control block diagram in the motor control device 1 of the present invention. In the figure, 21 is a speed control unit, 22 is a reciprocal of a torque constant Kt, 23 is a motor equivalent circuit, 24 is a torque constant Kt, and 25 is a motor and a load. Vref is a speed command, τref is a torque command, iref is a current command, and ω is a speed.
When the torque constant Kt24 is changed by changing the motor temperature (winding temperature rise), the torque required for the motor is not generated. That is, since the magnetic force of a motor using a magnet such as a synchronous motor changes depending on the temperature, the resulting torque changes even with the same current, and the torque constant changes. If the motor is controlled with the temperature changed, the actual torque will change even with the same torque command (current).
In this case, the reciprocal 22 of the torque constant Kt is corrected, for example, by correcting the current command as a current command = (1 + α) current command (α is a correction coefficient) to correct the torque.

It is a schematic block diagram which shows the structure of the electric motor control apparatus of this invention. It is a flowchart which shows the process sequence of the torque constant correction method of this invention. It is a wave form diagram for demonstrating the timing which detects the acceleration / deceleration and torque command in the electric motor control apparatus of this invention. It is a figure which shows the change of the torque command with respect to the armature temperature in the motor with a constant acceleration. It is a speed control block diagram in the electric motor control apparatus 1 of this invention. FIG. 6 is a schematic block diagram for explaining a servo motor control apparatus according to the first prior art. FIG. 7 is a block diagram showing a configuration of an auto-tuning servo device that is the second prior art.

Explanation of symbols

1 Electric motor control device 2 Electric motor (motor)
3 Position detector 11 Position or speed control unit 12 Current control unit 13 Power conversion unit 14 Encoder signal input / output unit 15 Torque command correction unit 16 Torque command detection unit 17 Acceleration / deceleration detection unit 21 Speed control unit 22 Reciprocal 23 of torque constant Kt Motor equivalent circuit 24 Torque constant Kt
25 Motor and load

Claims (2)

A motor control device that drives the motor in accordance with a torque command that is calculated based on a position or speed command and a current position of the motor that is a detection value of a position detector ,
While driving the motor, the moving average value of acceleration / deceleration at a predetermined time interval is calculated, and when the moving average value of acceleration / deceleration and the current acceleration / deceleration value are within a predetermined range, the driving of the motor is controlled at a constant level. An acceleration / deceleration detector that determines that the speed is driven;
When the acceleration / deceleration detecting unit determines that the driving of the electric motor is a constant acceleration / deceleration, an acceleration and deceleration average torque command, which is a moving average value of the torque command during acceleration and deceleration, respectively. In addition, the friction torque is calculated by halving the absolute value difference between the average torque command during acceleration and the average torque command during deceleration, and the friction torque is subtracted from the average torque command during acceleration or deceleration. A torque command detection unit for calculating acceleration or deceleration torque,
A torque constant correction unit that calculates a torque constant correction value by multiplying the reciprocal of the moment of inertia value of the electric motor by the current acceleration / deceleration value and a reference torque constant and dividing by the acceleration or deceleration torque; ,
A motor control device that updates a torque constant used in the control calculation to the torque constant correction value. The acceleration / deceleration detector calculates a moving average value of the acceleration / deceleration at the predetermined time interval near the end of acceleration and deceleration of the motor;
The motor control device according to claim 1, wherein the torque command detection unit detects the acceleration and deceleration average torque commands near the end of acceleration and deceleration of the motor, respectively.

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