JPH0691482A - Feed control device - Google Patents

Abstract

PURPOSE:To suppress the vibration of a slider generated by the vibration of a ball screw in the acceleration or the deceleration of the slider, by providing an acceleration feedback loop to subtract the signal from an acceleration sensor from the current instruction of the current feedback. CONSTITUTION:An acceleration sensor 7 installed to a slider 5 and to detect the acceleration of the slider 5, and an acceleration feedback loop to subtract the signal from the acceleration sensor 7 from the current instruction of the current feedback are provided. The acceleration of the slider 5 operates to follow the current instruction. When a vibration of the slider 5 is generated by the elasticity of a feed screw 3, the vibration component of the acceleration signal of the slider 5 is made as an error to the current instruction, and thereby, the signal from the acceleration sensor 7 is regulated by an acceleration feedback gain Ka, and the current is fed to a servomotor 1 so as to suppress the vibration.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control system for a feed control device.

[0002]

2. Description of the Related Art In a conventional device of this type, a current detector, a velocity detector, and a position detector are attached to a servomotor to form a triple feedback loop. The feed screw is rotationally driven by the servo motor, and the slider such as a grindstone base to which the feed nut is fixed is positioned. Ball screws were often used as feed screws.

[0003]

However, the above-mentioned conventional device has a problem that vibration may occur in the slider (stone head) when the angular acceleration of the servo motor changes abruptly. This vibration was particularly remarkable when the slider was supported by a guide such as a linear way with low friction. This is because the slider (grind head) vibrates due to the elasticity of the ball screw between the servo motor and the slider. Since the damping constant of the ball screw alone is not large, this vibration (natural vibration) was not immediately damped.
The present invention has been made to solve the above problems, and an object of the present invention is to provide a feed control device capable of suppressing vibration of a slider during acceleration / deceleration.

[0004]

In order to achieve the above object, in the present invention, a servomotor, a feed screw rotationally driven by the servomotor, a feed nut screwed to the feed screw, and a feed nut thereof. A slider fixed to the nut, position detecting means for detecting the position of the slider, speed detecting means for detecting the speed of the slider, current detecting means for detecting the current of the servo motor, position feedback, speed feedback, and current In a feed controller having a triple feedback loop of feedback,
There is provided a feed control device comprising an acceleration sensor attached to the slider for detecting the acceleration of the slider, and an acceleration feedback loop for subtracting a signal from the acceleration sensor from a current command of the current feedback.

[0005]

In the servo motor, the electric current is proportional to the torque and the angular acceleration, so that the electric current and the angular acceleration can be regarded as the same kind of signal. In the feed control device configured as described above, the acceleration of the slider works so as to follow the current command. Then, when the slider vibrates due to the elasticity of the feed screw (ball screw), the vibration component in the acceleration signal of the slider causes an error with respect to the current command. Suppress.

[0006]

Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing a servo configuration of a feed control device according to the present invention. An incremental rotary encoder 2 is directly connected to the servomotor 1. A ball screw 3 is connected to the output shaft of the servomotor 1, and a feed nut 4 fixed to a grindstone 5 is screwed onto the ball screw 3. A grinding wheel 6 is rotatably mounted on the grinding wheel base 5. In addition, the grindstone 5 has an acceleration sensor 7
Is fixed. The position feedback value, which is the output of the integration counter Σ, is subtracted from the position command and is amplified by the position loop gain Kp to become the speed command. The speed feedback value from the rotary encoder 2 is subtracted from the speed command, amplified by the speed loop proportional gain Kvp, and integrated by the speed loop integral gain Kvi to become a current command. The acceleration feedback value, which is the output of the acceleration feedback gain Ka, is subtracted from the current command, and further, the current feedback value is subtracted, and then the current loop gain Ki
The servo motor 1 is driven by being amplified by. The characteristic of the present invention is that the signal from the acceleration sensor 7 is adjusted by the acceleration feedback gain Ka and is returned to the current loop.

FIG. 2 is a block diagram showing a hardware structure of a feed control device for realizing the above servo structure. The digital servo control device 10 mainly includes a CPU 11 and a ROM.
12, RAM 13, digital signal processor 14
It is composed of a common RAM 17, A / D converters 15a and 15b, and a current value counter 16 (hereinafter referred to as DSP 14). A keyboard 21 and a CRT display device 22 are connected to the CPU 11 via an interface 19. The output of the DSP 14 is input to the inverter 25,
The inverter 25 drives the servo motor 1 according to the output signal of the DSP 14. A synchronous motor is used as the servo motor 1, and the load voltage of the servo motor 1 is controlled by the PWM voltage control of the inverter 25, and as a result, the output torque is controlled.

The U-phase and V-phase load currents of the servomotor 1 are detected by the current transformers (CT) 32a, 32b and amplified by the amplifiers 18a, 18b. The amplifier 18
The outputs of a and 18b are input to A / D converters 15a and 15b, sampled at a predetermined cycle, and converted into digital values. The sampled value is input to the DSP 14 as a feedback value of the instantaneous load current. Further, a rotary encoder 2 is connected to the servo motor 1 and its current position is detected. The output of the rotary encoder 2 is connected to the current value counter 16 via a waveform shaping / direction discriminating circuit 34. Furthermore, grinding wheel stand 5
The output of the acceleration sensor 7 fixed to the A / D converter 1 is
5c is input, sampled at a predetermined cycle, and converted into a digital value. Its sampled value is
It is input to the DSP 14 as a feedback value of acceleration.

The output signal of the rotary encoder 2 input to the current position counter 16 via the waveform shaping / direction discrimination circuit 34 adjusts the value of the current position counter 16. D
The value of the current position counter 16 is read by the SP 14 as a current position feedback value, and the position deviation is calculated by comparing with the target value output from the CPU 11 by the DSP 14. Then, the DSP 14 calculates the speed command value based on the position deviation. In addition, DSP14
The current position feedback value input to is differentiated to calculate the speed feedback value. By DSP14,
The speed command value determined according to the position deviation is compared with the speed feedback value to calculate the speed deviation, and the current command value is calculated based on the speed deviation.

On the other hand, the acceleration of the grindstone 5 detected by the acceleration sensor 7 is sent to the DSP 14 via the A / D converter 15c.
To enter. Then, the acceleration feedback gain Ka
A value obtained by multiplying by is calculated as an acceleration feedback value. The load currents detected by the current transformers (CT) 32a and 32b are input to the DSP 14 via the amplifiers 18a and 18b and the A / D converters 15a and 15b. Then, the current value at the current control time is calculated as the current feedback value based on the detected current value at the current sampling time. Then, the DSP 14 compares the current command value with the acceleration feedback value and the current feedback value to calculate the current deviation. A voltage command value is calculated based on the current deviation, the voltage command value is compared with a high frequency triangular wave, and a voltage control PWM signal for controlling on / off of the transistors of each phase of the inverter 25 is generated. The voltage control PWM signal is output to the inverter 25, and the transistors of each phase of the inverter 25 are driven. By the switching of the inverter 25, the load current of each phase is controlled to the current target value.

The positioning of the servo motor 1 is performed by the CPU
According to 11, the process is completed when it is determined that the output value of the current position value counter 16 becomes equal to the position command value. Further, the U-phase and V-phase load current values sampled by the A / D converters 15a and 15b are d by the DSP 14.
q converted.

As described above, the feed control device of this embodiment has an acceleration feedback loop in addition to the three feedback loops of position, velocity and current. Higher responsiveness is required for the lower feedback loops. For example, the lowest current feedback loop and the acceleration feedback loop are every 100 μS, the velocity feedback loop is several times that, and the position feedback loop is several times that multiple. Data sampling is performed in synchronization at time intervals, and the processing of each feedback loop is performed.

The operation will be described based on the above configuration. FIG. 3 is a flowchart showing a process repeatedly executed by the DSP 14 at each predetermined minimum cycle.
First, when the process is started, it is determined in step 100 whether or not the current execution cycle is the position deviation calculation timing. If it is the position deviation calculation timing, the process proceeds to step 102 and the position held in the current position value counter 16 is determined. The current position value of is read and the position deviation with respect to the target value is calculated.
Next, at step 104, a speed command value according to the position deviation is calculated.

Next, at step 106, it is judged if the current execution cycle is the speed deviation calculation timing. If the current execution cycle is the speed deviation calculation timing in the p-th speed control cycle, in the next step 108, the current value (electrical angle) θ of the position held in the current position value counter 16
(P) is read. Next, at step 110, the current value (electrical angle) θ of the position read at the time of the speed deviation calculation timing in the p−1-th speed control cycle last time.
From (p-1) and the speed control period D, the current value ω (p) of the electrical angular speed in the current speed control period is calculated by the following equation.

Ω (p) = [θ (p) −θ (p−1)] / D (1) Then, the deviation from the speed command value calculated in step 104, that is, the speed deviation is calculated. It

In the next step 112, the current target values Idc (p), Iqc of the d-axis component and the q-axis component are calculated according to the speed deviation.
(p) is calculated. Next, at step 114, the angular velocity ω (p-1) detected in the previous velocity control cycle.
And the angular velocity ω detected in this velocity control cycle
Using (p), the current electrical angular acceleration A (p) is calculated by the following equation.

## EQU00002 ## A (p) = [. Omega. (P)-. Omega. (P-1)] / D (2)

Next, the routine proceeds to step 116, where it is judged if the current execution cycle is the current deviation calculation timing in the nth current control cycle. Note that n is a value that changes to 1, 2, ... In one speed control cycle, and is related to the time of current detection and current control. If it is the current deviation calculation timing, the routine proceeds to step 118. In step 118 and subsequent steps, current and acceleration feedback control is executed.

In step 118, the electrical angle θ (n) at the time of current detection in the nth current control cycle in the pth speed control cycle.
Is calculated by the following equation.

## EQU3 ## θ (n) = θ (p) + ω (p) nT (3) where T is the current control period. Further, the electrical angular velocity ω (n) at the current detection time is complemented by the following equation.

Ω (n) = ω (p) + A (p) nT (4)

Next, at step 120, the current values Iu (n) and Iv (n) of the u-phase and v-phase instantaneous load currents are calculated by the A / D converter 15.
It is read from a and 15b. The current value Iw (n) of the w-phase instantaneous load current is calculated by Iw (n) =-[Iu (n) + Iv (n)]. In step 122, the grindstone 5
The acceleration Asp (n) is read from the A / D converter 15c.

Next, at step 124, the current values Iu (n), Iv (n), and Iw (n) of the current are dq-converted to obtain the d-axis component Id (n) and the q-axis component Iq at the current detection time. (n) is calculated by the following equation.

[Equation 5]

In the dq coordinate system, the d axis is in phase with the exciting magnetic field, as is well known in vector control.
The q-axis is a coordinate system with a phase difference of 90 ° in electrical angle from the exciting magnetic field. The d-axis component represents the ineffective component, and the q-axis component represents the effective component.

Next, in step 126, from the current command values Idc (p), Iqc (p) current values Id (n), Iq (n), the grindstone acceleration Asp (n) acceleration feedback gain Ka, and the current loop gain Ki. The voltage command values Vd (n) and Vq (n) are calculated by the following equation.

## EQU00006 ## Vd (n) = Ki [Idc (p) -Id (n)] (6)

## EQU7 ## Vq (n) = Ki [Iqc (p) -Iq (n) -KaAsp (n)] (7)

Next, at step 128, the voltage commands Vd (n) and Vq (n) are inversely dq-converted by the following equations, and the voltage command values Vu (n) and Vv (for each phase at the voltage control time (n) are converted. n), V
w (n) is calculated.

[Equation 8]

Next, in step 130, the level relationship between each phase voltage command value Vu (n), Vv (n), Vw (n) and the high frequency triangular wave is utilized, that is, the average voltage method is used. Then, the ON time of the PWM signal of each phase is calculated. Then, in step 132, the on-time is set in each timer incorporated in the DSP 14, so that the PWM signal of each phase which becomes high level for the set time is output to the inverter 25. Although not explicitly shown, dead time processing is performed so that two transistors in the same phase do not turn on at the same time when the PWM signal for each phase is generated.

In this way, the processing of one execution cycle is completed. This execution cycle is executed with the minimum control period, the current feedback loop and the acceleration feedback loop are controlled by an integral multiple thereof, the velocity feedback loop is controlled by an integral multiple thereof, and the position feedback loop is further multiplied by the integral multiple thereof. In order to be controlled, the number of times to be the reference for determination is set in steps 100, 106 and 116. By repeatedly executing the above cycle, feedback control of position, velocity, current and acceleration is performed.

[0025]

Since the present invention has the above-mentioned construction and detects the acceleration of the slider by the acceleration sensor and feeds it back to the current, when the slider vibrates due to the elasticity of the feed screw (ball screw), the slider is moved. Since the vibration component in the acceleration signal of becomes an error with respect to the current command,
There is an excellent effect that a current is passed through the servo motor so as to eliminate this error and vibration of the feed screw is suppressed.

[Brief description of drawings]

FIG. 1 is a block diagram showing a servo configuration of an embodiment.

FIG. 2 is a block diagram showing a hardware configuration of the embodiment.

FIG. 3 is a flowchart showing a processing procedure.

[Explanation of symbols]

 1 Servo Motor 2 Rotary Encoder 3 Feed Screw (Ball Screw) 4 Feed Nut 5 Grindstone (Slider) 7 Accelerometer 10 Digital Servo Controller 11 CPU 14 DSP (Digital Signal Processor)

Claims (1)

[Claims] 1. A servo motor, a feed screw rotationally driven by the servo motor, a feed nut screwed to the feed screw, a slider fixed to the feed nut, and position detection for detecting the position of the slider. Means, a speed detecting means for detecting the speed of the slider, a current detecting means for detecting the current of the servo motor, and a feed control device having a triple feedback loop of position feedback, speed feedback, and current feedback, wherein the slider is A feed control device comprising: an acceleration sensor that detects the acceleration of a slider that is attached; and an acceleration feedback loop that subtracts a signal from the acceleration sensor from a current command of the current feedback.