JP7358942B2 - Motor control device and motor control method - Google Patents

Description

The present invention relates to a motor control device and a motor control method for controlling the speed or rotor position of a motor that drives a mechanical load having frictional torque.

When driving a mechanical load with a motor, the desired movement may be hindered by the frictional torque of the mechanical load. In particular, when a motor is caused to move with a reversal of direction, the direction of friction torque is also reversed due to the reversal of the direction of movement, so that the movement of the mechanical load often deviates temporarily from a desired state. In order to suppress this phenomenon, the following techniques have been conventionally provided.

For example, Patent Document 1 describes a technique for compensating the Coulomb friction torque of a controlled object 200 in a system including a control device 100 and a controlled object (motor + mechanical load) 200, as shown in FIG. . That is, in FIG. 9, the speed control unit 110 generates a torque command that causes the motor speed detection value to follow the speed command, and also generates a Coulomb friction that is a function with a sign opposite to the Coulomb friction torque F of the controlled object 200. By identifying the compensation torque F' based on the detected speed value and adding it to the torque command, speed control is performed while canceling the Coulomb friction torque. This method is a well-known friction compensation method.

Also, instead of friction compensation using the sign function described above, as shown in FIG. 10, the result of multiplying the friction compensation input (speed command or detected speed value) by a first constant is limited by a second constant. A compensation method using a so-called polygonal function that obtains a friction compensation output (friction compensation value) is also known. FIG. 11 shows the input and output when friction compensation is performed using the above-mentioned polygonal linear function, and the friction compensation output changes linearly while being limited by the second constant according to changes in the friction compensation input. It's going to change.

Patent No. 3463355 ([0023], [0024], Fig. 4, Fig. 5, etc.)

When driving a mechanical load with friction torque, the method of compensating using the friction compensation torque of the sign function type shown in Fig. 9 causes the sign to reverse too quickly when the friction compensation torque is determined using the motor speed command as input. This may cause temporary overcompensation and speed disturbance. If the friction compensation torque is determined by inputting the speed detection value instead of the speed command, there is no risk of the sign reversing too quickly, but if the motor rotation stops due to friction during direction reversal, the friction compensation torque cannot be output correctly.

On the other hand, in the compensation method using the polygonal function shown in FIGS. 10 and 11, the disturbance of the friction compensation torque at the time of sign reversal as described above is reduced, but as is clear from FIG. Since the friction compensation output is weakened from time t _a before the reversal time t ₀ , the speed becomes zero before reaching time t ₀ , and sufficient friction compensation is achieved even if the slope of the polygonal function is adjusted. There is a possibility that it cannot be done.
Further, since the optimum value of the slope of the polygonal function depends on the acceleration during direction reversal, it is difficult to obtain satisfactory friction compensation even when the motion is performed in which this acceleration is not uniquely given.

SUMMARY OF THE INVENTION An object of the present invention is to provide a motor control device and a motor control method that can achieve better friction compensation than the prior art when driving a mechanical load having frictional torque.

In order to solve the above problem, a motor control device according to claim 1 is a motor control device that controls the speed or rotor position of a motor that drives a mechanical load having frictional torque, wherein the actual speed value of the motor is A motor control device comprising a speed feedback control means that operates to follow a speed command, and a current control means that controls a current of the motor based on a torque command output from the speed feedback control means,
Friction compensation means for calculating a friction compensation value from the speed command of the motor;
addition means for adding the friction compensation value output from the friction compensation means to the torque command;
Equipped with
The friction compensation means includes:
The absolute value of the sum of the product of the speed command subjected to low-pass filter calculation and the first constant and the previous value of the friction compensation value one calculation cycle ago is calculated as a second constant. The present invention is characterized in that it is output as the current value of the friction compensation value.

According to a second aspect of the present invention, in the motor control device according to the first aspect, the low-pass filter is configured to perform speed feedback control on the mechanical load having no load torque other than inertia. It is characterized in that it has a transfer characteristic equal to the actual speed value with respect to the speed command.

According to a third aspect of the present invention, in the motor control device according to the first or second aspect, the first constant increases monotonically with respect to the absolute value of the speed command change rate near the time when the direction of the motor is reversed. It is characterized by being set to do so.

According to a fourth aspect of the present invention, in the motor control device according to any one of the first to third aspects, the second constant is set such that the load torque when driving the mechanical load is the speed of the motor. The present invention is characterized in that the load torque is set as an intercept of a straight line approximated by a linear function with respect to the speed of the motor in a range where the load torque changes linearly without hysteresis.

A motor control method according to claim 5 is a motor control method for controlling the speed or rotor position of a motor that drives a mechanical load having frictional torque, and the method includes speed feedback control so that an actual speed value follows a speed command. In the motor control method, the motor current is controlled based on the addition result of the friction compensation value calculated from the speed command and the torque command, while generating a torque command by performing the following steps:
The absolute value of the sum of the product of the speed command subjected to low-pass filter calculation and the first constant and the previous value of the friction compensation value one calculation cycle ago is calculated as a second constant. The current value of the friction compensation value is set by limiting the friction compensation value.

According to the present invention, when a mechanical load having frictional torque is driven by a motor, it is possible to appropriately compensate for friction especially when the direction of the motor is reversed, thereby realizing excellent speed control and position control.

FIG. 1 is a block diagram showing main parts of a motor control device according to a first embodiment of the present invention. FIG. 2 is a configuration diagram of friction compensation means in FIG. 1; 3 is a configuration diagram of a low-pass filter in FIG. 2. FIG. FIG. 6 is a diagram for explaining changes in the low-pass filter output and friction compensation output with respect to changes in the friction compensation input. FIG. 7 is a diagram illustrating a method of setting a second constant. It is a block diagram of the friction compensation means in 2nd Embodiment of this invention. FIG. 3 is a block diagram showing main parts of a motor control device according to a third embodiment of the present invention. 3A and 3B are waveform diagrams of experimental results comparing friction compensation effects, in which (a) is a case without compensation, (b) is a case according to the prior art, and (c) is a case according to the present invention. FIG. 2 is a block diagram showing the conventional technology described in Patent Document 1. FIG. 2 is a block diagram of a conventional technique that performs friction compensation using a polygonal function. FIG. 6 is an explanatory diagram of friction compensation input and friction compensation output when friction compensation is performed using a polygonal function.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a block diagram showing the main parts of a motor control device according to a first embodiment of the present invention. This embodiment relates to speed control of a motor that drives a mechanical load with frictional torque.

In FIG. 1, the deviation between the motor speed command and the actual speed value is determined by the subtraction means 51, and the speed feedback control means 20 operates to eliminate this deviation to generate a torque command and input the speed command. A friction compensation value is calculated by the friction compensation means 10.
The friction compensation value is added to the torque command output from the speed feedback control means 20 by the addition means 52. Then, the current control means 30 consisting of a driver and a motor performs current control to drive the mechanical load 40 so that the output torque of the motor follows this torque command.

Next, the structure and operation of the friction compensating means 10, which is the main part of this embodiment, will be explained.
FIG. 2 is a block diagram showing the configuration of the friction compensating means 10. As shown in FIG.
In FIG. 2, the first variable is the value calculated by the low-pass filter 11 on the motor speed command as the friction compensation input, and the second variable obtained by multiplying this variable by the first constant is It is input to the adding means 12.
On the other hand, by adding a value obtained by limiting the absolute value of the output of the adding means 12 by a second constant by the limiting means 13 to the second variable as the previous value of the friction compensation value calculated one cycle ago, Obtain the current value of the friction compensation value. This current value of the friction compensation value is input to the addition means 52 of FIG. 1 described above.

FIG. 3 shows a specific example of the low-pass filter 11 in FIG. 2. Here, assuming that the speed feedback control means 20 in FIG. 1 performs proportional-integral control, the proportional gain is k _vp and the integral gain is k _vi . Note that s is a Laplace operator.
Assuming that the mechanical load 40 does not have any load torque other than inertia, performing the proportional-integral control will achieve an ideal response speed that is the same as when performing the filter calculation in FIG. 3. Although friction torque exists in the mechanical load 40 that is actually driven, in this embodiment, the friction compensation means 10 adds the friction compensation value calculated according to the speed command to the torque command, thereby achieving an ideal response speed. can be realized.

In this embodiment, instead of giving the friction compensation value as a single-valued function to the speed command, the previous value of the friction compensation value is added to the second variable to update the friction compensation value, as shown in FIG. That's what I do.
As a result, for example, when the speed command changes to zero at time _t0 as shown in FIG. The friction compensation value changes as shown in FIG. 4(b), and the friction compensation value changes as shown in FIG. 4(c). Here, if the second constant given to the limiting means 13 is set in accordance with the actual measured value of the friction torque of the mechanical load 40, the friction equal to the actual friction torque until the actual speed value becomes zero at time _t0 '. A compensation value can be output, and it is possible to prevent the motor from stopping before the expected timing, time _t0 '. Then, the friction compensation value starts changing from time t ₀ ' when the actual speed value of the motor becomes zero, and at the subsequent time t ₀ ', the value has the opposite polarity (the positive value of the second constant). By reaching , near-ideal friction compensation can be achieved.

Regarding the specific method of giving the second constant, that is, the method of actually measuring the friction torque, the range in which the load torque when driving the mechanical load 40 changes linearly without hysteresis when plotted against the motor speed is as follows. In this case, the load torque may be given as the intercept of a straight line approximated by a linear function with respect to the motor speed. For example, when the load torque with respect to the motor speed is drawn as shown in Figure 5(a), a linear approximation is made as shown in Figure 5(b) in a linearly changing range outside the hysteresis range, and this straight line is The value that intersects with the load torque axis may be regarded as the friction torque, and this value may be set as the second constant.

Note that the functions shown in FIGS. 1 to 3 according to the first embodiment may be realized by a single speed control device that inputs a motor speed command, or outputs a speed command and a feedforward torque. It may be realized as a system that combines a host controller and a speed control device that receives speed commands and feedforward torque as inputs.

Further, the first constant in FIG. 2 corresponds to the ratio of the change in the friction compensation value to the output (first variable) of the low-pass filter 11, but the rate of change in speed at the time of direction reversal is uniquely given. If so, the first constant may be adjusted so that the disturbance in the speed waveform when the direction is actually reversed is minimized depending on the speed change rate.
If the speed change rate at the time of direction reversal is not uniquely given, the first constant may be set to increase monotonically with respect to the absolute value of the speed change rate. An example of friction compensation means in this case is shown in FIG. 6 as a second embodiment.

In the friction compensation means 10A shown in FIG. 6, the friction compensation input (speed command) is input to the change rate absolute value calculation means 14 to obtain the absolute value of the speed change rate, and this absolute value is multiplied by a third constant. is a value corresponding to the first constant in FIG. In this case, the third constant is preferably adjusted so that the disturbance of the speed waveform when the rotational direction of the motor is reversed at a certain speed change rate is minimized.

Next, FIG. 7 is a block diagram showing the main parts of the third embodiment of the present invention. This third embodiment is a case where the present invention is applied to position control that controls the rotor position of a motor.
In FIG. 7, a speed feedback similar to that described above is added to a position control loop including a subtraction means 53 into which a motor position command and an actual position are input, a proportional gain _Kp , and a differentiation means 60 that calculates an actual speed value. It includes a control means 20, a friction compensation means 10 (or 10A), and a block 70 (current control means 30 and mechanical load 40), and the friction torque of the mechanical load 40 is controlled by the same operation as in the first or second embodiment. Desired position control can be performed while compensating for

Next, in order to confirm the effects of the present invention, experimental results when a mechanical load having frictional torque was actually driven by a motor are shown in FIGS. 8(a), (b), and (c). The maximum speed of each motor is 1200 [r/min], and two types of trapezoidal acceleration/deceleration patterns ([large speed change rate] and [small speed change rate]) are prepared, and the position is determined using the configuration shown in Fig. 7. The motor was operated reciprocally while being controlled, and the disturbance in the speed waveform was observed when the direction was reversed.
FIG. 8(a) shows the case where no friction compensation is performed, and FIG. 8(b) shows the conventional technology in which the friction compensation means 10 of FIG. 7 is realized by the polygonal linear function of FIG. (limited by a second constant), and FIG. 8(c) shows the case where friction compensation is performed using the configuration of FIG.
Note that the feedback control gain in position control was set to the same value in all of FIGS. 8(a), (b), and (c).

In contrast to FIG. 8(a) where friction compensation is not performed, in FIG. 8(b) with the conventional technology, when comparing parts a and b circled by solid lines, the disturbance in the velocity waveform at the time of direction reversal is reduced to some extent. However, some disturbances still remain. On the other hand, in FIG. 8(c) where the friction compensation according to the present invention has been performed, it is confirmed that the disturbance in the speed waveform is further reduced compared to FIG. 8(b), as is clear from the part c circled by the broken line. It was done.

INDUSTRIAL APPLICATION This invention can be utilized for the motor control apparatus which controls the position and speed of various mechanical loads which have frictional torque, including the servo system of machine tools, industrial robots, etc.

10, 10A: Friction compensation means 11: Low pass filter 12: Adding means 13: Limiting means 14: Rate of change absolute value calculation means 15: Multiplying means 20: Speed feedback control means 30: Current control means (driver and motor)
40: Mechanical load 51, 53: Subtraction means 52: Addition means 60: Differentiation means 70: Current control means and mechanical load

Claims (5)

A motor control device for controlling the speed or rotor position of a motor that drives a mechanical load having frictional torque, the speed feedback control means operating such that the actual speed value of the motor follows a speed command; and the speed A motor control device comprising: current control means for controlling the current of the motor based on a torque command output from a feedback control means,
Friction compensation means for calculating a friction compensation value from the speed command of the motor;
addition means for adding the friction compensation value output from the friction compensation means to the torque command;
Equipped with
The friction compensation means includes:
The absolute value of the sum of the product of the speed command subjected to low-pass filter calculation and the first constant and the previous value of the friction compensation value one calculation cycle ago is calculated as a second constant. A motor control device characterized in that the current value of a friction compensation value is outputted as a current value of a friction compensation value. The motor control device according to claim 1,
A motor control device characterized in that the low-pass filter has a transmission characteristic equal to an actual speed value in response to the speed command when speed feedback control is performed on the mechanical load that has no load torque other than inertia. . The motor control device according to claim 1 or 2,
A motor control device characterized in that the first constant is set to increase monotonically with respect to an absolute value of a speed command change rate near a time when the direction of the motor is reversed. In the motor control device according to any one of claims 1 to 3,
The second constant is approximated by a linear function of the load torque with respect to the speed of the motor in a range where the load torque when driving the mechanical load changes linearly with respect to the speed of the motor without hysteresis. A motor control device characterized in that the motor control device is set as an intercept of a straight line. A motor control method for controlling the speed or rotor position of a motor that drives a mechanical load having frictional torque, the method comprising performing speed feedback control so that an actual speed value follows a speed command and generating a torque command, In the motor control method, the current of the motor is controlled based on the addition result of the friction compensation value calculated from the speed command and the torque command,
The absolute value of the sum of the product of the speed command subjected to low-pass filter calculation and the first constant and the previous value of the friction compensation value one calculation cycle ago is calculated as a second constant. A method for controlling a motor, characterized in that the current value of a friction compensation value is set by limiting the current value.

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