JP3253022B2 - Servo motor backlash compensation control method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control method of a servomotor for driving a feed shaft such as a table of a machine tool, and more particularly, to a quadrant projection caused by backlash when the movement of the feed shaft is reversed. The present invention relates to a servomotor control method for reducing the power consumption.

2. Description of the Related Art When reversing the driving direction of a servomotor for driving a table or the like in a machine tool, the machine cannot usually be reversed immediately due to backlash or friction of a feed screw. Therefore, when a quadrant is changed while performing arc cutting or the like with a machine tool, a projection (hereinafter, referred to as a quadrant projection) is generated on the cut arc surface. For example, a circular arc cutting is performed on the workpiece on the X, Y2 axis plane, the X axis is set in the plus direction,
The quadrant changes when the axis is moved in the minus direction,
When the Y-axis is driven in the minus direction and the X-axis is switched in the minus direction, cutting is performed on the Y-axis at the same speed as before, but the X-axis has a position deviation of “0”. ), The torque command value becomes smaller, and the servo motor cannot be immediately reversed due to friction.
Since the movement of the table cannot be reversed immediately due to the backlash of the feed screw for feeding the table, the movement of the work in the X-axis direction cannot be followed to the movement command and is delayed. As a result, a quadrant projection is formed on the cutting arc surface.

Conventionally, in order to eliminate or reduce the quadrant projection, a position correction amount for backlash is corrected to a position command when the moving direction is reversed. In addition, for a predetermined period,
The set correction amount is added to the speed command in order to speed up the reversal of the speed loop integrator. Hereinafter, the correction for adding the set correction amount for the predetermined period to the speed command is referred to as backlash acceleration correction. The correction amount corrected by the backlash acceleration correction is called a backlash acceleration amount.

After the start of the backlash acceleration correction, a feedback pulse of the position is integrated, and when the integrated value becomes a certain value or more, control such as stopping the backlash acceleration correction is performed.

Problems to be Solved by the Invention However, there is a problem that it is difficult to find an optimal amount of backlash acceleration because the amount of backlash and the magnitude of friction vary depending on the machine.

If the amount of backlash acceleration is small, a quadrant projection is generated as described above. On the other hand, if the backlash acceleration amount is too large, the inverted shaft moves more than the backlash or friction torque is corrected, and the cut arc surface is cut inward. Therefore, there is a difficult problem that the backlash acceleration amount must be strictly set for each machine.
Further, when the conditions such as the cutting speed change, there is a problem that the optimum backlash acceleration amount also changes.

SUMMARY OF THE INVENTION An object of the present invention is to provide a servo motor backlash correction control method capable of reducing the load of the control of the backlash acceleration and preventing the quadrant projection and the inward cut.

Means for Solving the Problems According to the present invention, during the period in which the backlash acceleration amount is added to the speed command, only the gain of the integral control of the speed loop is increased by a predetermined amount to perform the speed control. In particular, during the period in which the backlash acceleration amount is added, the backlash acceleration amount is added to a value obtained by multiplying a speed deviation obtained by subtracting the actual speed of the servo motor from the speed command by a predetermined value, and the added value is integrated. The value obtained by multiplying this integral value by the integral gain is used as the output of the integrator of the speed loop, thereby increasing the influence of the integrator of the speed loop and controlling the speed so that cutting without quadrant protrusion and excessive cutting can be performed. did.

Operation For example, assume that the servo motor is driven in the forward direction. Then, immediately before the quadrant changes and the driving direction of the servo motor is switched to the negative direction, the position deviation value approaches “0”. Then, the actual speed of the servomotor is reduced, and the output of the integrator of the speed loop is the main ratio of the torque command value to the servomotor. When the position deviation value becomes “0”, the integrator of the speed loop outputs an output for driving the servomotor in the positive direction, and the servomotor is driven by the torque command value based on the output of the integrator. Direction, but the servomotor is stopped due to friction. Therefore, the backlash correction amount of the position is added to the error counter, and the backlash acceleration amount is added to the speed command to perform the backlash correction. However, as described above, the positive value is given to the integrator of the speed loop. In order to cancel the positive integral value and further drive the servo motor in the negative direction, the integral value of the integrator should be quickly changed to a negative value, and the torque command to overcome the static friction The value must be output to the servo motor. Therefore, the present invention increases the influence of the integrator by increasing only the gain of the integral control of the speed loop during the backlash correction period (the period during which the backlash acceleration amount is added), and rapidly increases the integral value of the integrator. Then, a negative integrator output that overcomes the static friction is output, and the servo motor is driven as a torque command value. As a result, there is no need to strictly set the backlash acceleration amount, and the burden of the backlash acceleration amount can be reduced. Also, even if the backlash acceleration amount is too large and the servomotor overshoots during reversal and overshoot occurs, the overshoot reverses the position deviation and raises the reversal value. Since the integrated value of the integrator is rapidly reduced by the gain, the overshoot is also quickly corrected, and it is possible to prevent the incision from being generated inside the processing surface.

In addition, during the backlash correction period, the backlash acceleration amount is added to the value obtained by multiplying the speed deviation by the set predetermined value to perform the backlash acceleration correction, and the integral value of the integrator is quickly increased, and the negative friction that overcomes the static friction is overcome. The output of the integrator was output.

Embodiment FIG. 1 is a block diagram of an embodiment of the present invention, showing an example in which the speed loop control is performed by IP control (integral and proportional control). The difference from the block diagram of the conventional servo system is that a transfer function denoted by reference numeral 2 is added.

That is, KP of the transfer function 1 is the position gain in the position loop, and the transfer function 2 is such that the value of the parameter α is set to “0” when the backlash correction is not performed, and the value of the parameter α is set when the backlash correction is performed. It is set to a set value to increase the gain of the integral control of the speed loop. Transfer functions 3 and 4 are transfer functions of the integrator of the speed loop, and k1 represents a fixed integral gain. K2 of the transfer function 5 represents a proportional gain of the speed loop, transfer function 6 represents a current loop, and the gain is normally "1". Further, the transfer function 7 represents a transfer function of the servomotor, where Jm is motor inertia and Kt is a torque constant. The transfer function 8 is a transfer function for calculating the position by integrating the speed of the motor.

When the backlash correction is not performed, the value of the parameter α is set to “0”, and the same servo motor control as in the related art is performed.

When the backlash correction is not performed, the position deviation is obtained by subtracting the position feedback signal Pf detected by a detector such as a pulse coder attached to the servo motor from the position command Pc output from the numerical controller, and obtaining the position gain. The speed command Vc is obtained by multiplying by KP.
From the feedback signal Vf of the actual speed of the motor detected by a pulse coder or the like to determine the speed deviation. When the backlash correction is not being performed, the parameter α = 0 and the backlash acceleration BA = 0. Integrate (accumulate) to determine the integral value I, subtract the value obtained by multiplying the integral gain k1 by the value obtained by multiplying the speed feedback signal Vf by the proportional gain k2 to obtain the torque command value Tc, and deliver it to the current loop 6. Control the servo motor.

Further, when the sign of the position command Pc changes, that is, when the rotation direction of the servo motor is reversed, the backlash correction amount of the position is output from the numerical controller, and when the position deviation becomes “0”, The backlash correction amount is added to the position deviation, and the set backlash acceleration amount is added. The operation so far is the same as the conventional backlash correction, but in the present invention, the value of the parameter α is further set to the set value, and the gain of the integral control of the speed loop is increased. Immediately before the rotation direction of the servomotor is reversed, the rotation speed of the servomotor approaches “0”, the servomotor is driven by the torque command value Tc by the output of the integrator of the speed loop, and in a state where the rotation of the servomotor is stopped. Therefore, the motor stops in a state where the output torque of the servo motor is canceled by the frictional resistance. That is, the output of the integrator is an output (for example, an output in the plus direction) for driving the servo motor in the same direction as before. Then, the backlash correction amount of the position is added to the position deviation, the position deviation is multiplied by the position gain KP, a speed command is obtained, and the speed command is multiplied by (1 + α) by the set parameter α (speed feedback). The signal is "0"), and the backlash acceleration amount is added to the signal. Therefore, the integrated value of the integrator rapidly reverses, and only drives the servo motor in the reverse direction (for example, the minus direction) by overcoming the frictional resistance. The torque command value Tc is issued. As a result, the rotation direction of the servomotor is quickly reversed, and the number of quadrant projections is reduced. Even if the backlash acceleration amount is set slightly larger and the motor speed at the time of reversal of the servomotor becomes faster than the speed command Vc, the gain of the speed loop integration control is increased by the parameter α. The integrated value of the vessel rapidly decreases, the overshoot is immediately improved, and the inward cut of the cutting surface is reduced.

FIG. 2 is a block diagram of an NC machine tool for implementing one embodiment of the present invention. Numeral 11 denotes a numerical controller (hereinafter referred to as CNC) built in a computer, and numeral 12 denotes a shared memory, and a position outputted from the CNC 11. Command or the like to the digital servo circuit 13 or the signal output from the digital servo circuit 13
Performs the function of handing over to CNC11. The digital servo circuit 13 has a processor (CPU), a ROM, a RAM, and the like, executes a process of a servo circuit that drives a servomotor of the machine tool 14 by software, and controls the drive of the servomotor of each axis. Since the NC machine tool with a digital servo circuit as shown in FIG. 2 is already known, a detailed description thereof will be omitted.

FIG. 3 is a flowchart of a speed loop process executed by the processor of the digital servo circuit 13 in the embodiment at predetermined intervals.

First, it is determined whether or not a backlash correction amount of a position has been sent as a backlash correction command from the CNC 11 (step S1). If not, it is determined whether or not the timer T is "0" (step S1). S6), Timer T is "0"
Then, a speed deviation is obtained by subtracting the speed feedback signal Vf from a pulse coder or the like from the speed command Vc calculated in the position loop, and a register R (I) for integrating the speed deviation.
To obtain an integral value I (step S9). Then, an integral gain is added to the integral value I stored in the register R (I).
The torque command value Tc is obtained by subtracting the value obtained by multiplying the speed feedback signal Vf by the proportional gain k2 from the value obtained by multiplying the speed feedback signal Vf by k1 and passing the specified torque value Tc to the current loop (steps S10 and S1).
1), end the processing of the speed loop of the cycle. That is, a speed loop process similar to the conventional one is performed.

On the other hand, when the backlash correction command is output from the CNC 11 and detected in step S1, the processor determines whether the sign of the position deviation value stored in the error counter has been inverted (step S2). That is, if the sign of the backlash correction amount is positive, it is determined whether the position deviation value is “0” or a positive value. If the sign of the backlash correction amount is negative, the position deviation value is “0”. Or a negative value, and if the sign of the position deviation value is not inverted, the above-described processing of steps S6, S9 to S11 is performed. If the sign of the position deviation value is inverted, the timer T is set to the set value, the backlash correction data (correction amount) of the position is added to the error counter, and the backlash correction data is cleared (steps S3 to S5). ). Next, the timer T
Is determined to be "0" or not, and since it is not "0", the speed command Vc
A value obtained by multiplying the value obtained by subtracting the speed feedback signal Vf from the set value and the value obtained by adding “1” to the setting parameter α is added to the register R (I) as an integrator, and the set backlash acceleration amount BA is added. "1" is subtracted from the timer T (steps S6 to S8). Then, the value obtained by multiplying the value of the register R (I) by the integral gain k1 is subtracted by the value obtained by multiplying the speed feedback signal Vf by the proportional gain k2 to obtain a torque command value Tc.
Is obtained and passed to the current loop (steps S10 and S11),
The speed loop process of the cycle ends.

In the next cycle, the backlash correction data
Since it was cleared in S5, steps S1 to S6
If the timer T is not "0", the processes of steps S7, S8, S10, and S11 are performed as described above. That is, until the time set in the timer T is reached, the backlash acceleration correction is performed, and the process of increasing the gain of the integration control by the parameter α (step S7) is performed to perform the integration process.

When the timer T becomes "0", the process proceeds from step S6 to step S9, and returns to the normal speed loop process.

The above is the operation processing of the present embodiment. In the above embodiment, the control of the speed loop is performed by IP control (integral and proportional control).
The same applies to PI control (proportional / integral control), and the speed deviation input to the integrator for rapidly inverting the integral value of the integrator when the servomotor is inverted is described. What is necessary is just to multiply (1 + α) times during the set backlash correction period and add the backlash acceleration amount.

Further, the backlash acceleration amount may be added to the speed command value.

Effect of the Invention In the first invention of the present application, when the rotation direction of the servomotor is reversed, the gain of the integral control of the speed loop is increased, the integrated value output of the integrator of the speed loop is rapidly reversed, and the torque command value is rapidly reversed. Since the servo motor is driven in such a manner, the delay of the reversing servo motor is reduced and the number of quadrant protrusions can be reduced. Moreover, since only the gain of the integral control of the speed loop is increased, and the proportional gain is not increased, the speed loop does not oscillate due to mechanical resonance in a short time caused by increasing the proportional gain. Furthermore, since the period during which the gain of the integral control is increased is a short period in which the direction is reversed, vibration at a low frequency such as hunting caused by an increase in the gain of the integral control is not induced. And, since the gain of the integral control is increasing, even if the backlash acceleration amount is too large and the speed of the servo motor at the time of reversal overshoots, the overshoot is stopped quickly, so the cutting surface The number of cuts on the inside is reduced, and the quadrant projections and cuts can be reduced too much without setting the backlash acceleration amount strictly for each machine, and the burden of backlash acceleration can be reduced.

Further, in the second invention of the present application, when the rotation direction of the servo motor is reversed, the value obtained by multiplying the speed deviation by a predetermined value is added to the backlash acceleration amount and integrated, and the integrated value output of the integrator of the speed loop is rapidly increased. Since the servo motor is driven by reversing the torque command value rapidly, the delay of the reversing servo motor is reduced and the number of quadrant protrusions can be reduced.

[Brief description of the drawings]

FIG. 1 is a block diagram of a servo system according to an embodiment of the present invention, FIG. 2 is a block diagram of a CNC machine tool for implementing the embodiment, and FIG. 3 is performed by a processor of a digital servo circuit according to the embodiment. It is a flowchart of a speed loop process. KP …… Position gain, α …… Parameter, BA ……
Backlash acceleration amount, k1 ... integral gain, k2 ... proportional gain.

Continuation of front page (56) References JP-A-63-269212 (JP, A) JP-A-58-144822 (JP, A) JP-A-60-116004 (JP, A) JP-A-57-139820 (JP, A) , A) JP-A-62-182803 (JP, A) JP-A-59-8008 (JP, A)

Claims (2)

(57) [Claims] 1. A backlash correction control method for a servomotor that drives a feed shaft of a machine tool, wherein when a rotation direction of the servomotor is reversed, a correction amount of a position for backlash is corrected to a position command, and In order to accelerate the reversal of the speed loop integrator, the backlash acceleration correction is performed by increasing only the gain of the speed loop integration control by a predetermined amount and adding the set correction amount to the speed command for a predetermined period. Backlash compensation control method for servomotors. 2. A backlash correction control method for a servomotor that drives a feed shaft of a machine tool, wherein when a rotation direction of the servomotor is reversed, a position correction amount for the backlash is corrected to a position command. During a predetermined period, a set correction amount is added to a value obtained by multiplying a speed deviation obtained by subtracting the actual speed of the servo motor from the speed command by one or more set predetermined values, and the added value is integrated. A backlash correction control method for a servomotor, wherein a value multiplied by an integral gain is used as an output of an integrator of a speed loop.