JPH07295652A - Position controller - Google Patents

Abstract

PURPOSE:To prevent overshooting without lowering tracking performance and to perform position control with high precision by a simple configuration by providing a speed control loop which controls the speed of a motor according to a speed command outputted from an accelerator. CONSTITUTION:A subtracter 8 calculates a position error S7 from the position command S20 after time correction from a position command correcting means 20 and the position detected value S5 from a position detector 6. A position controller 1 multiplies the position error S7 by a position control loop gain and outputs the result. A feedforward means 2, on the other hand, differentiates a position command S1 and multiplies it by a feedforward gain to calculate a feedforward controlled variable S6. An adder 9 adds the output of the position controller 1 to the feedforward controlled variable S6 to obtain a speed command S2. Then this controller is equipped with a speed control loop which controls the speed of a motor 5 according to the speed command S2 outputted from the adder 9.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a position control device,
In particular, the present invention relates to a position control device suitable for controlling the position of a feed shaft motor of a machine tool.

[0002]

2. Description of the Related Art A position control device for controlling the position of a feed shaft motor of a machine tool, for example, as shown in Japanese Unexamined Patent Publication No. 5-19861, performs a feedforward control for enhancing the following performance. There is something I did.

FIG. 6 is a block diagram showing a schematic configuration of a conventional position control device having a position control loop and a speed control loop for controlling the position of a feed shaft motor of a machine tool.

This position control device comprises a position detector 6 for detecting the position of the motor 5, and a speed detecting means 7 for obtaining a speed detection value S4 from the position detection value S5 output by the position detector 6. . The position control device further includes a subtracter 8 that calculates a position error S7 by subtracting the position detection value S5 from the position command S1 output from the higher-order controller, and a position control loop based on the position error S7 from the subtractor 8. The position controller 1 that multiplies the gain and outputs the position command S1 is differentiated, the feed forward means 2 that multiplies the feed forward gain to calculate the feed forward control amount S6, and the output of the position controller 1 is feed forward controlled. Depending on the speed error S8, an adder 9 for adding the amount S6 and outputting the speed command S2, a subtractor 10 for subtracting the speed detection value S4 from the speed detection means 7 from the speed command S2 to calculate a speed error S8, and The speed controller 3 that calculates the torque command S3 and outputs it to the amplifier 4 is provided. The amplifier 4 drives the motor 5 with a current according to the torque command S3.

In this position control device, the subtracter 8 calculates the position error S7 from the position command S1 output from the host controller and the position detection value S5 from the position detector 6.
On the other hand, the feedforward means 2 differentiates the position command S1 and multiplies the feedforward gain to calculate the feedforward control amount S6. The position controller 1 multiplies the position error S7 by the position control loop gain and outputs it to the adder 9. The adder 9 adds the feedforward control amount S6 to the output of the position controller 1 to obtain the speed command S2. Subtractor 10
Inputs the speed command S2 and the speed detection value S4 to obtain the speed error S
8 is calculated, and the speed controller 3 calculates the torque command S3 according to the speed error S8. Further, the amplifier 4 drives the motor 5 with a current according to the torque command S3.

In the conventional position control device, in the calculation of the feedforward control amount S6, the differential processing of the position command S1 is approximated by the differential processing between sampling points. When the sampling period is T, the transfer function of the feedforward means 2 is expressed by the following equation (1). Here, the feedforward gain is 1.

[0007]

## EQU1 ## {1- [e-sT]} / T (1) In the above equation, the symbol [e-sT] is an exponential function with base e of the natural logarithm, and -sT is Indicates an index. Also, s is an operator.

Here, the transfer function of the speed control loop in FIG. 6 is set to 1, the position control loop gain is set to K, and the block diagram is rewritten to be FIG. 7, and FIG. 8 is a simple block diagram conversion. . In FIG. 7, reference numeral 1
1 is an element for obtaining the position detection value S5 from the speed command S2, and the transfer function is represented by 1 / s. In the configuration shown in FIG. 8, the element 12 that inputs the position command S1, the adder 13 that adds the output of the element 12 and the position command S1, and the output of the element 11 is subtracted from the output of the adder 13. It is provided with a subtracter 14, an element 15 for multiplying the output of the subtractor 14 by the position control loop gain K, and an element 11 for obtaining the position detection value S5 from the output of the element 15. The transfer function of the element 12 is represented by (1- [e-sT]) / TK.

When the transfer function G having the configuration shown in FIG. 8 is calculated, the following equation (2) is obtained.

[0010]

## EQU2 ## G = {(1- [e-sT]) / TK + 1} * {K / (K + s)} = {K + T [K2] -Kcos (ωT) + ωsin (ωT)} / {T ([ K2] + [ω2])} + j {-ω-ωTK + Ksin (ωT) + ωcos (ωT)} / {T ([K2] + [ω2])} (2) In the above equation, the symbol [K2 ] Is an exponential function with K as the base, and 2 indicates the exponent. Also, j is an imaginary unit. Also,
* Indicates a multiplication symbol.

The amplitude characteristic | G | of G is given by the following equation (3).

[0012]

[Equation 3] | G | = √ {[T2] [K2] +2 (1 + TK) (1-cos (ωT)) / ([T2] [K2] ＋ [T2] [ω2])} ・ ・(3) In the above equation, the symbol √ {} means the square root of the value in brackets {}.

Here, suppose that the sampling cycle is T = 0.0016se.
When the amplitude characteristic | G | is calculated with c (sec) and position loop gain K = 75 / sec, the peak is 0.4 dB at ω = 200 rad / sec, which is an overshoot on the real-time waveform. Is generated.

[0014]

The overshoot is due to
It appears as a trajectory error during synchronous position control of machine tools,
This is a problem because it may reduce the shape accuracy of the work piece or the surface roughness. For this reason, overshoot is extremely disliked in the feed axis control of machine tools. On the other hand, conventionally, measures for preventing overshoot by a method of reducing the feedforward gain or a method of smoothing the feedforward control amount have been considered.

However, when the feedforward gain is reduced, there is a drawback that the response to the position command S1 becomes slow and the positioning time increases, that is, the tracking performance deteriorates. In addition, the method of smoothing the feedforward control amount requires a high-performance and expensive host controller because the processing is complicated and prefetching is required.
There is a drawback that the cost becomes high.

Therefore, an object of the present invention is to provide a position control device using feedforward control, which has a simple structure and prevents overshoot without deteriorating the tracking performance, thereby achieving highly accurate position control. It is to provide a position control device capable of performing.

[0017]

A position control device according to claim 1 calculates a feedforward control amount from a position detector which detects a position of a motor and outputs a position detection value, and a position command from a host controller. Feed forward means, position command correction means for correcting the time by shifting the position command for a predetermined time, corrected position command output from the position command correction means, and position detection value output from the position detector. , A position controller that outputs the position error output from this subtractor by multiplying the position error by the position control loop gain, and the output of this position controller and the feed output from the feedforward means. An adder that calculates a speed command based on the forward control amount and a speed control that controls the motor speed in accordance with the speed command output from this adder. It is obtained by a loop.

A position control device according to a second aspect of the present invention is the first aspect.
In the position control device described above, the position command correction means delays the position command from the host controller by a time half the sampling cycle of the position command.

[0019]

In the position control device according to the first aspect of the present invention, the feedforward means calculates the feedforward control amount from the position command from the host controller. Also,
The position command correction means shifts the position command from the host controller for a predetermined time and corrects the time. Then, the subtracter calculates the position error from the corrected position command and the position detection value output from the position detector,
The position controller multiplies the position error by the position control loop gain and outputs the result. Further, the adder calculates a speed command from the output of the position controller and the feedforward control amount from the feedforward means, and the speed control loop controls the speed of the motor according to the speed command output from the adder. To be done. By thus correcting the position command with time and using it for calculating the position error, the transfer function of the position control device is suppressed, and overshoot is prevented.

In the position control device according to the second aspect of the present invention, the position command correction means delays the position command from the host controller by half the sampling period of the position command.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the position control device of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing a schematic configuration of a position control device according to a first embodiment of the present invention. Note that, in FIG. 1, the same components and signals as those of the position control device shown in FIG. 6 are denoted by the same reference numerals as those in FIG. 6, and description thereof will be omitted.

In this embodiment, in the position control device shown in FIG. 6, a position command correction means as a position command correction means for correcting the position command S1 from the host controller by a predetermined time before the subtractor 8 for time correction. Means 20 are provided. The position command correction means 20 delays the position command S1 from the host controller by a time half the sampling cycle of the position command S1 and outputs the position command S1 as a time-corrected position command S20. Other configurations are similar to those of the position control device shown in FIG.

FIG. 2 is a characteristic diagram showing a state of the position command S1 from the host controller and the time-corrected position command S20 which is the output of the position command correction means 20. In the figure,
Circles and squares respectively indicate the position command S1 and the time-corrected position command S20 at each sampling point.

FIG. 3 is a block diagram showing an example of the configuration of the position command correction means 20. This position command correction means 20
Is a register 21 that stores the position command S1 for each sampling, an adder 22 that adds the position command of one sampling before and the latest position command S1 output from the register 21, and an output of the adder 22. Multiplier 2 that multiplies by a factor of 1/2 and outputs as time-corrected position command S20
3 and 3.

In the position command correcting means 20, the register 21 stores the position command S1 for each sampling, and the adder 22 adds the position command one sampling before and the latest position command S1. Then, the multiplier 23 multiplies it by a coefficient of 1/2,
It is output as a position command S20 after time correction. With the simple configuration as described above, it is possible to calculate the position command S20 delayed by half the sampling period.

Next, the operation of the position control device of this embodiment will be described.

In the position control device of the present embodiment, the position command correction means 20 uses the position command S1 from the host controller.
Is delayed by half the sampling period of the position command S1 and is output as the position command S20 after time correction. The subtractor 8 receives the time-corrected position command S20 from the position command correction means 20 and the position detection value S5 from the position detector 6.
Then, the position error S7 is calculated. The position controller 1 multiplies the position error S7 by the position control loop gain and outputs it. on the other hand,
The feedforward means 2 differentiates the position command S1 and multiplies the feedforward gain to calculate the feedforward control amount S6. The adder 9 adds the output of the position controller 1 and the feedforward control amount S6 to obtain a speed command S2. The subsequent operation is the same as that of the position control device shown in FIG.

Next, in the present embodiment, it will be described that the position command S1 is time-corrected by the position command correction means 20 to change the amplitude characteristic of the transfer function of the position control device to prevent overshoot. In order to make FIG. 1 correspond to FIG. 7, the transfer function of the speed control loop is set to 1, the position control loop gain is set to K, and the block diagram is rewritten as shown in FIG. The configuration shown in FIG. 4 is obtained by inserting a delay unit 23 corresponding to the position command correction unit 20 in the preceding stage of the subtractor 8 in the conventional configuration shown in FIG. The delay means 23 shifts the position command S1 by D time and outputs it to the subtractor 8. At this time, the transfer function G2 having the configuration shown in FIG. 4 becomes the following expression (4).

[0030]

## EQU00004 ## G2 = {(1- [e-sT]) / TK + [e-sD]} * {K / (K + s)} = {K + T [K2] cos (ωD) -Kcos (ωT ) ＋ ωsin (ωT) -TK ωsin (ωD)} / {T ([K2] + [ω2])} ＋ j {-ω-ωTKcos (ωD) + Ksin (ωT) ＋ ωcos (ωT) -T [K2] sin ( ωD)} / {T ([K2] + [ω2])} (4) Further, the amplitude characteristic | G2 | of G2 is expressed by the following equation (5).

[0031]

[Equation 5] | G2 | = √ {{2+ [T2] [K2] -2cos (ωT) -2TKsin (ωT) sin (ωD) -2TKcos (ωT) cos (ωD) + 2TKcos (ωD)} / [ T2] ([K2] + [ω2])} (5) Here, replacing the sampling period T with the delay time D (assuming T = 2D) and rearranging the equation (5), the following (6) ) Becomes the formula.

[0032]

[Equation 6] | G2 | = √ {([T2] [K2] +4 [sin (ωD) 2]) / ([T2] [K2] + [T2] [ω2])} ・ ・ ・ (6) Here, in order to compare 4 [sin (ωD) 2] of the numerator and [T2] [ω2] of the denominator, the following expression (7), which is the difference between them, is evaluated. Note that 2D = T is used in the modification of the following equation.

[0033]

[Equation 7] 4 [sin (ωD) 2]-[T2] [ω2] = 4 [sin (ωD) 2] -4 [D2] [ω2] = 4 (sin (ωD) + ωD) (sin (ωD )-ωD) (7) Here, since D> 0 and ω ≧ 0, ωD ≧ 0. Furthermore, the following holds.

When ωD = 0, sin (ωD) = ωD = 0, so 4
[sin (ωD) 2]-[T2] [ω2] = 0 0 <ωD ≤ 1, so sin (ωD) <ωD, so 4 [sin (ωD)
2]-[T2] [ω2] <0 1 <ωD, sin (ωD) <ωD, so 4 [sin (ωD) 2]-
[T2] [ω2] <0 Therefore, the value of the expression (7) becomes 0 or negative, and the following expression (8) is established.

[0035]

[Equation 8] ([T2] [K2] +4 [sin (ωD) 2]) ≤ ([T2] [K2] + [T2] [ω2]) (8) Therefore, the numerator is smaller than the denominator. Therefore, the following expression (9) is established.

[0036]

[Expression 9] √ {([T2] [K2] +4 [sin (ωD) 2]) / ([T2] [K2] + [T2] [ω2])} ≤ 1 ... (9) Therefore, | G2 | ≦ 1 and overshoot can be prevented.

As described above, according to the present embodiment, the position control device using the feedforward control is provided with the position command correction means 20 for correcting the time by shifting the position command for a predetermined time. Since the position command S1 is time-corrected by 20 and used for calculating the position error, the structure is simple and the feed-forward gain is not lowered to lower the tracking performance as in the conventional case.
It is possible to prevent overshoot and perform highly accurate position control. Therefore, when applied to control the position of the feed shaft motor of a machine tool or the like, it is possible to perform high-accuracy and high-speed machining, and prevent deterioration of shape accuracy and surface roughness. Further, since it has a simple structure, it can be realized at low cost.

FIG. 5 is a block diagram showing the configuration of the position command correction means 20 in the position control device of the second embodiment of the present invention.

Position command correction means 20 in this embodiment
Is a register 21 that stores the position command S1 for each sampling, and a multiplier 26 that multiplies the position command output from the register 21 one sampling before by a coefficient (1-α).
And a multiplier 27 that multiplies the position command S1 by a coefficient α, and an adder 22 that adds the output of the multiplier 26 and the output of the multiplier 27 and outputs the time-corrected position command S20.

In this position command correcting means 20, the register 21 stores the position command S1 for each sampling,
This is multiplied by the coefficient (1-α) by the multiplier 26, while the latest position command S1 is multiplied by the coefficient α by the multiplier 27, and the adder 22 outputs the output of the multiplier 26 and the output of the multiplier 27. And are added to the position command S after time correction
Output as 20. As a result, the position command S1 can be changed within the sampling cycle according to the coefficient α. That is, the time for which the position command S1 is changed can be changed by changing the coefficient α.

In this embodiment, the number of multipliers by which the coefficient is multiplied is increased as compared with the first embodiment, but in an actual system, there is also a delay in the speed control loop and the like, so in order to optimally prevent overshoot. In some cases, the transition time of the position command S1 may need to be adjusted, and this embodiment is effective in that the transition time can be easily adjusted by changing the coefficient α.

When the position command correction means 20 is composed of a digital computer and software,
The coefficient α can be easily set by a host controller or another method, and the adjustment is very easy. Other configurations, operations and effects are similar to those of the first embodiment.

[0043]

As described above, according to the present invention, in the position control device using the feedforward control,
Position command correction means for correcting the time by moving the position command by a predetermined time is provided, and the position command correction means is used for time correction of the position command to calculate the position error. There is an effect that overshoot can be prevented and position control can be performed with high accuracy without degrading performance.

[Brief description of drawings]

FIG. 1 is a block diagram showing a schematic configuration of a position control device according to a first embodiment of the present invention.

FIG. 2 is a characteristic diagram for explaining the operation of the position command correction means in FIG.

FIG. 3 is a block diagram showing an example of a configuration of a position command correction means in FIG.

FIG. 4 is a block diagram for explaining the operation of the position control device shown in FIG.

FIG. 5 is a block diagram showing a configuration of a position command correction means in a position control device according to a second embodiment of the present invention.

FIG. 6 is a block diagram showing a schematic configuration of a conventional position control device.

FIG. 7 is a block diagram in which the position control device shown in FIG. 6 is idealized.

FIG. 8 is a block diagram obtained by modifying the block diagram shown in FIG. 7.

[Explanation of symbols]

 1 Position Controller 2 Feed Forward Means 3 Speed Controller 4 Amplifier 5 Motor 6 Position Detector 7 Speed Detection Means 8 Subtractor 9 Adder 10 Subtractor 20 Position Command Correction Means S1 Position Command S2 Speed Command S3 Torque Command S4 Speed Detection Value S5 Position detection value S6 Feedforward control amount S7 Position error S8 Speed error S20 Time-corrected position command

Claims (2)

[Claims] 1. A position detector that detects a motor position and outputs a position detection value, a feedforward unit that calculates a feedforward control amount from a position command from a host controller, and the position command changes for a predetermined time. Position command correcting means for time correction, a subtracter for calculating a position error based on the corrected position command output from the position command correcting means and the position detection value output from the position detector, and the subtractor Position controller that outputs the position error output from the position multiplier by a position control loop gain, and an addition that calculates a speed command from the output of this position controller and the feedforward control amount output from the feedforward means. And a speed control loop for controlling the speed of the motor according to the speed command output from this adder. Position controller according to. 2. The position control device according to claim 1, wherein the position command correction means delays the position command from the host controller by a time half the sampling cycle of the position command.