JPH06106456A - Feed control device - Google Patents

Abstract

PURPOSE:To restrain proper vibration of a slider by arranging an acceleration detecting sensor to detect acceleration of the slider and a band-pass filter to extract only a proper vibration component caused by elasticity of a feed screw from output of the acceleration sensor. CONSTITUTION:A speed command O is inputted to the second feed control device 110, and speed of a slider 5 created by a hollow servomotor 60 is kept in zero. When vibration is generated in the slider 5 due to elasticity of a ball screw 3, an acceleration sensor 7 detects acceleration of the slider 5, and a band-pass filter BPF extracts a proper vibration component of the slider 5 in the detected acceleration. The extracted proper vibration component is fed back to a target electric current value based on the speed command O of the second feed control device 110, and the hollow servomotor 60 is rotated by an extremely small angle so as to negate this proper vibration.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a feed control device, and more particularly to a control system for a uniaxial feed mechanism such as a grinder.

[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, the feed nut is fed by this, and a slider such as a grindstone fixed to the feed nut 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, according to the present invention, a first servomotor, a feed screw rotatably driven by the first servomotor, and a feed nut screwed to the feed screw. A second servo motor fixed to a slider for rotating the feed nut; a position detecting means for detecting a position of the slider; a first speed detecting means for detecting a feed speed of the slider; and a current of the servo motor. And a first feed control device for controlling a first servo motor having a triple feedback loop of position feedback, velocity feedback, and current feedback, and a slider feed velocity by the second servo motor. A second speed detecting means for detecting and a second current detecting means for detecting a current of the second servomotor. Second controlling to keep the second servo motor to zero speed of the slider by the second servo motor
Feed control device, an acceleration detection sensor for detecting the acceleration of the slider, a bandpass filter for extracting only the natural vibration component due to the elasticity of the feed screw from the output of the acceleration sensor, and the output of the bandpass filter for the second feed control device. And a feedback loop for subtracting the acceleration from the current command of 1.

[0005]

In the feed control device constructed as described above, the second feed control device keeps the second servomotor to keep the slider speed by the second servomotor to zero, that is, the slider and the nut are relatively moved. Control not to rotate. When the slider vibrates due to the elasticity of the feed screw (ball screw), the acceleration sensor detects the acceleration, and the bandpass filter extracts the natural vibration component of the slider in the detected acceleration. The natural vibration component is fed back to the current command of the second feed control device, and the second servomotor is rotated by a small angle so as to cancel this natural vibration, thereby suppressing the vibration peculiar to the slider.

[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 nut (not shown) is screwed onto the ball screw 3.
The hollow servomotor 60 holds the nut so that the nut can be driven. A grindstone (slider) 5 is fixed to the hollow servomotor 60, and a grindstone wheel 6 is rotatably mounted on the grindstone 5. Further, the acceleration sensor 7 is fixed to the grindstone 5, and the rotary encoder 102 is directly connected to the hollow servomotor 60.

The hollow servomotor 60 will be described in more detail with reference to FIG. A nut 4 is screwed onto the ball screw 3. A rotor 61 is attached to the nut 4 by shrink fitting, a stator 62 is attached to a hollow servo motor housing 60b at a position facing the nut 62, and the rotor 61 and the stator 62 are connected via a power line 64 to a second feed control device. The hollow servomotor housing 60b is moved in the left-right direction in the figure by the electric power applied from 110 (FIG. 1)
And the slider flange 5a attached to the flange 60a at the end of the hollow servomotor housing 60b.
The slider 5 is moved along the ball screw 3 via. Further, the rotary encoder 102 is attached to the other end of the hollow servo motor housing 60b, detects the rotation of the hollow servo motor 60, that is, the speed of the slider 5, and sends it to the second feed control device 110 via the signal line 63. It is designed to output.

The feed control device of this embodiment comprises a first feed control device 10 for controlling the position and speed of the servomotor 1,
The second feed control device 110 that controls the speed of the hollow servomotor 60. First, in the first feed control device 10, the position feedback value output from the current position counter Σ is subtracted from the position command 70 and amplified by the position loop gain Kp to become a 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. After the current feedback value is subtracted from the current command, it is amplified by the current loop gain Ki and the servo motor 1 is driven.

In the second feed controller 110, the speed command value 0 is input from the input 80 in order to keep the speed of the slider 5 by the hollow servomotor 60 at 0, and the speed feedback value from the rotary encoder 102 is subtracted from this. It is amplified by the velocity loop proportional gain K'vp and integrated by the velocity loop integral gain K'vi to become a current command.
On the other hand, the acceleration of the slider 5 is detected by the acceleration sensor 7, from which the vibration component (natural vibration component) due to the elasticity of the ball screw 3 is extracted by the bandpass filter BPF, and this is amplified by the acceleration feedback gain Ka to obtain the acceleration feedback value. Used. This acceleration feedback value is subtracted from the current command, and after the current feedback value is further subtracted, it is amplified by the current loop gain K'i and the hollow servomotor 60 is driven.

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 (first feed control device) 10 for controlling the position and speed of the servo motor 1 mainly includes the CPU 1
1, ROM 12, RAM 13, digital signal processor 14 (hereinafter referred to as DSP 14), common RAM 1
7, A / D converters 15a and 15b and current value counter 1
It is composed of 6. 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 the inverter 25
The inverter 25 drives the servo motor 1 in accordance with the output signal of the DSP 14. Servo motor 1
A synchronous motor is used for this, the load current of the servomotor 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 load current feedback value.
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.

The output signal of the rotary encoder 2 input to the current position counter 16 via the waveform shaping / direction discriminating 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 compared with the target value output from the CPU 11 to calculate the position deviation. Then, the DSP 14 calculates the speed command value based on the position deviation.

The current position feedback value input to the DSP 14 is differentiated to calculate a speed feedback value. The DSP 14 compares the speed command value determined according to the position deviation with the speed feedback value to calculate the speed deviation, and calculates the current command value based on the speed deviation. This current command value is compared with the above-mentioned current feedback value to calculate the current deviation, and the voltage command value is calculated based on this current deviation. Based on this voltage command value, a voltage control PWM signal for controlling on / off of each phase transistor 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 servomotor 1 is performed by the CPU
According to 11, it is completed when it is determined that the output value of the current position counter 16 becomes equal to the target value of the position. 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.

Next, a digital servo control device (second feed control device) 1 for controlling the speed of the hollow servo motor 60.
10 will be described. The digital servo control device 110 mainly includes a CPU 111, a ROM 112, a RAM 113,
Digital signal processor 114 (hereinafter DSP 11)
4), A / D converters 115a, 115b, 115
c and the current value counter 116. DS
The output of P114 is input to the inverter 125, and the inverter 125 drives the hollow servomotor 60 according to the output signal of the DSP 114. A synchronous motor having the shape described with reference to FIG. 4 is used as the hollow servo motor 60, and the load voltage of the hollow servo motor 60 is controlled by the PWM voltage control of the inverter 125, and as a result, the output torque is controlled.

The U-phase and V-phase load currents of the hollow servomotor 60 are detected by the current transformers (CT) 132a, 132b and amplified by the amplifiers 118a, 118b. The outputs of the amplifiers 118a and 118b are the A / D converter 1
Input to 15a and 115b, sampled at a predetermined cycle, and converted into a digital value. The sampled value is used as the feedback value of the load current, DS
It is input to P114. A rotary encoder 102 is connected to the hollow servomotor 60, and its output is connected to a current position counter 116. Further, the output of the acceleration sensor 7 fixed to the grindstone base 5 is extracted by the bandpass filter 152 by only the vibration component (natural vibration component) due to the elasticity of the ball screw 3, and the A / D converter 115.
It is input to c, sampled at a predetermined cycle, and converted into a digital value. The sampled value is D
Input to SP114, acceleration feedback gain K
A value obtained by multiplying a is calculated as an acceleration feedback value.

The output signal of the rotary encoder 102 adjusts the value of the current position counter 116. DSP114
Thus, the value of the current position counter 116 is read to calculate the current speed feedback value, and the CPU 111
Is compared with the value of the speed command 0 output from to calculate the speed deviation. Then, the DSP 114 calculates the current target value based on the speed deviation.

Then, the DSP 114 compares the current target value with the acceleration feedback value and the current feedback value to calculate the current deviation. A current command value is calculated based on the current deviation, the current command value is compared with a high frequency triangular wave, and a voltage control PWM signal for controlling on / off of each phase transistor of the inverter 125 is generated. The voltage control PWM signal is output to the inverter 125, and the transistors of each phase of the inverter 125 are driven. By this switching of the inverter 125, the load current of each phase is controlled to the current target value. In addition, the U-phase and V-phase load current values sampled by the A / D converters 115a and 115b are
Dq conversion is performed by the DSP 114.

As described above, the speed command 0 is input to the second feed control device (digital servo motor control device 110), and the speed of the slider 5 generated by the second servo motor is maintained at zero. On the other hand, if the slider 5 vibrates due to the elasticity of the ball screw 3, the acceleration sensor 7
Detects the acceleration of the slider 5, and the bandpass filter 1
52 extracts the natural vibration component of the slider in the detected acceleration. In a servo motor, current, torque, and angular acceleration are proportional to each other, so current and angular acceleration can be regarded as the same type of signal. Therefore, the extracted natural vibration component is fed back to the current target value based on the speed command 0 of the second feed control device, and the hollow servomotor 60 is rotated by a minute angle so as to cancel this natural vibration. Suppress vibration.

As described above, the hollow servomotor 6 is included in the second feed control device (digital servomotor control device 110).
A speed command of 0 is always given so that the slider speed due to 0 does not occur. Therefore, even if the servo motor 1 is rotated by the command of the first feed control device (digital servo motor control device 10) and inertia occurs in the slider 5, the nut 4 and the hollow servo motor 60 do not rotate due to this.

As described above, the feed control device 110 of this embodiment is provided with an acceleration feedback loop in addition to the two feedback loops of speed and current. Higher responsiveness is required for the lower feedback loop. For example, the lowest current feedback loop and the acceleration feedback loop are synchronized every 100 μS, and the velocity feedback loop is synchronized with the data at several time intervals. Sampling is executed and the processing of each feedback loop is executed.

The operation will be described based on the above configuration. FIG. 3 is a flowchart showing a process repeatedly executed by the DSP 114 at each predetermined minimum cycle. First, when the processing is started, it is determined in step 300 whether or not 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, the current value (electrical angle) θ (p) of the position held in the current position counter 116 is read in the next step 302. Next, at step 304, the current value (electrical angle) of the position read at the time of the speed deviation calculation timing in the p-1st speed control cycle last time.
From θ (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 0, that is, the speed deviation is calculated.

In the next step 306, 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 308, 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. A (p) = [ω (p) −ω (p−1)] / D (2)

Next, the routine proceeds to step 310, 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 process proceeds to step 312. From step 312 onward, current and acceleration feedback control is executed.

In step 312, 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. 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 314, the current values Iu (n), Iv (n) of the u-phase and v-phase instantaneous load currents are calculated as A / D converter 11.
5a, 115b. The current value Iw (n) of the w-phase instantaneous load current is Iw (n) =-[Iu (n) + Iv
(n)]. In step 316,
The acceleration Asp (n) of the grinding wheel stand 5 is the A / D converter 115c.
Read from.

Next, at step 318, the current values Iu (n), Iv (n), Iw (n) of the currents are dq-converted, and 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, at step 320, from the current target 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. Vd (n) = Ki [Idc (p) -Id (n)] (6) Vq (n) = Ki [Iqc (p) -Iq (n) -Ka.Asp (n)] (7)

Next, at step 322, the voltage commands Vd (n) and Vq (n) are inversely dq-converted by the following equations, and the respective phase voltage command values Vu (n) and Vv (at the voltage control time (n) are converted. n), V
w (n) is calculated.

[Equation 8]

Next, at step 324, 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 326, the on-time is set in each timer incorporated in the DSP 114, so that the PWM signal of each phase that becomes high level for the set time is output to the inverter 125.
Is output to. Although not explicitly shown, PWM for each phase
When generating a signal, dead time processing is performed so that two transistors in the same phase do not turn on at the same time.

In this way, the processing of one execution cycle is completed. This execution cycle is executed with the minimum control cycle, and it is determined in steps 300 and 310 that the current feedback loop and the acceleration feedback loop are controlled by an integral multiple thereof and the velocity feedback loop is controlled by an integral multiple thereof. The number of times that becomes the standard of is set. By repeatedly executing the above cycle, feedback control of speed, current and acceleration is performed.

In the embodiment of the present invention, the first feed control device for driving the ball screw has been described in detail with reference to a specific example, but the present invention is not limited to this and other embodiments are possible. It is of course possible to configure the present invention by applying the second feed control device of the present embodiment to a single-axis feed control device of the type. Further, in the above-described embodiment, the second feed control device is configured to control the speed of the slider to 0, but instead, the second feed control device is configured to control the position of the slider. However, by setting the position command to 0, the relative position between the ball screw and the slider can be maintained. Further, in the present embodiment, the feedback of subtracting the output of the bandpass filter from the current command of the second feed control device is performed. Alternatively, the output of the bandpass filter may be added to the current command to suppress the vibration. It is possible.

In this embodiment, a hollow servomotor is newly provided on the feed nut side in order to cancel the vibration of the slider,
This was controlled by a newly provided servo mechanism. As a method of canceling this vibration, it is conceivable to add a mechanism for canceling the vibration to the side of the servomotor that rotates the feed screw, but in this case, the feed screw is included in the controlled object. This embodiment has an advantage over this method in that the controlled object is lighter by the inertial weight of the feed screw.

[0035]

According to the present invention having the above-mentioned structure, the second feed control device controls the second servo motor so as to keep the speed of the slider generated by the second servo motor at zero. When the slider vibrates due to the elasticity of the feed screw (ball screw), the acceleration sensor detects the acceleration, and the bandpass filter extracts the natural vibration component of the slider of the detected acceleration. There is an excellent effect that the vibration peculiar to the slider can be suppressed by feeding back the natural vibration component to the current command value of the second feed control device and rotating the second servo motor by a minute angle so as to cancel this natural vibration.

[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.

FIG. 4 is a vertical sectional view of a hollow servomotor 60 according to an embodiment.

[Explanation of symbols]

 1 Servo Motor 2 Rotary Encoder 3 Feed Screw (Ball Screw) 4 Feed Nut 5 Wheel Head (Slider) 7 Accelerometer 10 Digital Servo Controller 11 CPU 14 DSP (Digital Signal Processor) 60 Hollow Servo Motor 102 Rotary Encoder 110 Digital Servo Control Device 111 CPU 114 DSP (Digital Signal Processor) 152 Bandpass Filter

Claims (1)

[Claims] 1. A first servomotor, a feed screw rotatably driven by the first servomotor, a feed nut screwed to the feed screw, and a second screw fixed to a slider to rotatably drive the feed nut.
A servo motor, a position detecting means for detecting the position of the slider, a first speed detecting means for detecting the feed speed of the slider, and a first current detecting means for detecting the current of the servo motor, and position feedback, speed feedback, A first feed control device for controlling a first servo motor having a triple feedback loop of current feedback, a second speed detection means for detecting a slider feed speed by the second servo motor, and a second servo motor of the second servo motor. A second feed control device for controlling the second servo motor so as to keep the feed speed of the slider by the second servo motor to zero; The acceleration detection sensor and the van that extracts only the natural vibration component due to the elasticity of the feed screw from the output of the acceleration sensor. A feed control device comprising: a de-pass filter; and an acceleration feedback loop for subtracting the output of the band-pass filter from the current command of the second feed control device.