JP2000194421A - Method and device for srevo control - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide servo controlling method and device capable of performing high-speed control with high accuracy without providing two position detectors for high and low speeds. SOLUTION: In this servo controlling method in which the position of a member which is driven by a servo motor 31 is detected by a position detector 33 and the position information signal for the member to be driven which comprises analog signals detected by the detector 33 is fed back to a servo amplifier 41 to control the servo motor 31, the position information signal is analyzed with low resolution to generate a feedback signal to the amplifier 41 while the member to be driven operates at a speed being higher than a prescribed reference speed, and the position information signal is analyzed with high resolution to generate a feedback signal to the amplifier 41 while the member to be driven operates at a speed being slower than the prescribed reference speed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a servo control method and apparatus for controlling a servo motor for driving a machine tool or an industrial robot.

[0002]

2. Description of the Related Art A servo mechanism is usually provided with a position detector for detecting the position of a driven member, an amplifying device for amplifying a difference between a value detected by the position detector and a predetermined reference value, and a servo device driven based on the amplified signal. A servo motor for correcting the position of the member is provided. 2. Description of the Related Art Servo mechanisms are used in a wide range of application fields such as relative positioning between a workpiece of a machine tool and a spindle, positioning of a robot arm of an industrial robot, and automatic control of a ship or an aircraft. In recent years, a digital servo in which an A / D converter for converting an analog signal into a digital signal is incorporated in a servo mechanism has become mainstream.

FIG. 6 shows a conventional servo control device. This servo control device is an electric servo, and controls and drives a servo motor 111 by a servo amplifier 121 based on a movement command 101 from an NC device (not shown) or the like and a detection value of a position detector 113. . The servo amplifier 121 is known in the art, and includes a position amplifier 103, a speed amplifier 105,
A current amplifier 107 is included. On the output side of the current amplifier 107, a current detector 109 for detecting a current supplied to the servo motor 111 is provided.

The position detector 113 generally has a linear scale or a rotary encoder. The linear scale or rotary encoder of the position detector 113 detects a position information signal of a driven member (not shown) such as a work table of a machine tool or a robot arm. A linear scale or a rotary encoder usually outputs a detected position information signal as an analog signal,
Reference numeral 3 internally converts an analog signal into a digital signal and feeds it back to the servo amplifier 121.

A position information signal composed of a digital signal fed back from the position detector 113 is compared with a movement command signal 101 sent from an NC unit (not shown) or the like, and the difference is amplified by a position amplifier 103. . The amplified output signal has information equivalent to speed in a physical sense. On the other hand, the detected value from the position detector 113 is differentiated by the speed converter 115 and converted into a speed value. The converted speed value is compared with the output value amplified by the position amplifier 103, and the difference is further amplified by the speed amplifier 105. The output amplified by the speed amplifier 105 has information equivalent to a current or a torque as a physical meaning. The power supplied to the servomotor 111 is detected by the current detector 109, the value is compared with the output value amplified by the speed amplifier 105, and the difference is amplified by the current amplifier 107 and supplied as power to the servomotor 111. Is done.

[0006]

Recently, particularly in the field of machine tools and industrial robots, high-speed positioning has been achieved.
The demand for higher precision is increasing further, and with this,
Servo controllers also need to be faster and more accurate. On the other hand, a converter used when the position detector converts an analog signal into a digital signal, that is, a so-called A / D converter, does not have a high frequency responsiveness that can sufficiently cope with a recent increase in positioning accuracy. . In order to solve this, two position detectors are provided as a position detector: a high-speed position detector with low resolution and a low-speed position detector with high resolution for analog signal processing from a rotary encoder and a linear scale. When the driven member is moved at a high speed, a low-precision position detector for a high speed is used, and a high-precision position detector is used at a low speed. However, in order to switch between the high-speed position detector and the low-speed position detector, the servo mechanism must be temporarily stopped to perform zero point adjustment, and there is a problem that the continuity of the process cannot be maintained.

Further, if the detection signal of the position detector is analyzed with high precision in order to position the driven member with high precision, the data amount of the digital signal output from the position detector increases. Digital communication means with a high communication speed, for example, a parallel communication device is required to transmit the signal to the servo amplifier, which increases the cost of the servo control device and increases the number of communication cables. An object of the present invention is to solve such a problem of the prior art, and a servo control method and apparatus capable of performing high-speed and high-accuracy control without providing two position detectors for high speed and low speed. It is intended to provide.

[0008]

According to the present invention, a position of a driven member driven by a servomotor is detected by a position detector, and the position of the driven member is determined by an analog signal detected by the position detector. In the servo control method of controlling the servo motor by feeding back a position information signal to a servo amplifier, the position information signal is analyzed at a low resolution while the driven member is operating at a speed higher than a predetermined reference speed. To generate a feedback signal to the servo amplifier, and while the driven member is operating at a speed lower than a predetermined reference speed, analyze the position information signal with high resolution to generate a feedback signal to the servo amplifier. The gist is a servo control method to be generated.

According to another feature of the present invention, the position of the driven member driven by the servomotor is detected by the position detector, and the position of the driven member is determined by the analog signal detected by the position detector. In a servo control device that controls the servomotor by feeding back a position information signal to a servo amplifier, a rectangular wave shaping counting unit that converts the position information signal into a rectangular wave and counts the number of pulses, Interpolating means for obtaining the phase of the position information signal from the value of the converted digital signal, and the pulse of the rectangular wave while the driven member is operating at a speed higher than a predetermined reference speed. Generating a feedback signal based on the number of pulses, while the driven member is operating at a speed lower than the reference speed, the number of pulses and the phase of the position information signal. Servo control device is provided which is adapted to generate a feedback signal based.

[0010]

Preferred embodiments of the present invention will be described below with reference to the accompanying drawings. In the embodiment of the present invention shown in FIG.
1 is driven based on a feedback signal from a position detector 33 that detects the position of a driven member (not shown) driven, and a movement command 21 from, for example, an NC device (not shown) of a machine tool or an industrial robot. Thus, it is driven and controlled by the servo amplifier 41.

The servo amplifier 41 has substantially the same configuration as the conventional servo amplifier 121 shown in FIG. 6, and includes a subtracter 35 for comparing a movement command 21 from an NC device (not shown) with a feedback signal. A position amplifier 23 that amplifies the output from the subtractor 35, a subtractor 37 that compares the output value of the position amplifier 23 with the feedback signal,
Speed amplifier 25, which amplifies the output of the motor, a current detector 29, which detects the current value supplied to the servo motor 31, a subtractor 39, which compares the output of the speed amplifier 25 and the current value to the servo motor 31, and a subtractor 39 Is included in the current amplifier 27 for amplifying the output.

The position detector 33 includes a conventionally known linear scale or rotary encoder. The position detector 33 detects the position coordinates of the driven member (not shown) as is well known in the art, and includes a multiplex analog signal including a sine wave and a cosine wave as position information signals indicating the position coordinates. Output a signal. This position information signal is used as an input signal in the waveform analyzer 11 according to the embodiment of the present invention.
Sent to The waveform analyzer 11 includes a buffer amplifier 11a as an input unit, a square wave shaping / counting unit 13, an interpolation unit 15, and a timing controller 11b for adjusting the timing of the square wave shaping / counting unit 13 and the interpolation unit 15.
And

As shown in FIG. 2, a rectangular wave shaper / counter 13 converts the input signal into a rectangular wave by a waveform shaper 13a.
And a counter 13b for counting the number of rectangular waves formed by the waveform shaper 13a, and a latch 13c. The interpolation unit 15 includes an A / D converter 15a that converts an input signal composed of an analog signal into a digital signal, an interpolation unit 15b described later, and a latch 15c.

In the rectangular wave shaping / counting unit 13, as shown in FIG. 2, the input signal from the buffer amplifier 11a is converted into a rectangular wave by the waveform shaper 13a, and the counter 13b
Counts the number of pulses of the rectangular wave, that is, the number of falling and rising edges of the rectangular wave. This counted number is referred to as a pulse number P in this specification. Although FIG. 2 shows only one of the input signals composed of the sine wave and cosine wave multiplexed analog signals,
In practice, both signals are processed in the same way and the servomotor 3
Needless to say, one moving direction is considered.

In the interpolation section 15, an input signal from the buffer amplifier 11a is first converted into a digital signal by an A / D converter 15a. The interpolator 15b is composed of a ROM (read only memory) table in which the value of the converted digital signal is associated with the phase in one cycle of the input signal, in actuality, the number of pulses indicating the phase or an integer value. . This pulse number or an integer value is defined as an interpolation value I. Typically,
In the rotary encoder and the linear scale provided in the position detector 33, as shown in FIG. 3, the amount of movement of the output sine wave (or cosine wave) per cycle, that is, the movement distance and movement of the driven member. Although the angle L0 is determined, the table stored in the interpolator 15b has the function of dividing the output signal of the rotary encoder or the linear scale by a predetermined division number or resolution and interpolating the movement amount L0. . This division number is defined as an interpolation number N, and is a constant appropriately given according to the accuracy required for the servo system. The interpolation number can be an arbitrary integer value. In FIG. 3, the movement amount L0 per cycle is divided into 16 as an example, but it is needless to say that the number of interpolation is not limited to this.

The number of pulses P counted by the counter 13b and the interpolated value I output from the interpolator 15b are used for estimating the speed by adjusting the timing by the signals from the timing controller 11b via the latches 13c and 15c. The feedback pulse is sent to the FB (feedback) signal calculator 17.

On the other hand, the signal from the speed estimation / FB signal calculator 17 is sent to a subtractor 35 to be moved to a movement command 21.
And the difference is amplified by the speed amplifier 23. The other of the signals output from the speed estimation / FB signal calculator 17 is differentiated by a speed calculator 19 and converted into a signal corresponding to the speed. The signal amplified by the position amplifier 23 is compared with the signal converted by the speed converter 19 in the subtractor 37, and the difference is compared with the speed amplifier 2
Amplified by 5. Next, in the subtractor 39, the signal amplified by the speed amplifier 25 is supplied to the current detector 29.
The current value supplied to the servo motor 31 is compared with the current value detected, and the difference is amplified by the current amplifier 27, and the output becomes the supply current to the servo motor 31.

The operation of the embodiment of the present invention will be described below with reference to FIGS. FIG. 4 is a main routine of the feedback control method according to the present embodiment, and FIG. 5 is a subroutine for reading a feedback pulse. When the main routine of FIG. 4 is started, first, in step S
At 11, a feedback pulse is read from the waveform analyzer 11 to the speed estimation / FB signal calculator 17 according to a subroutine shown in FIG. That is, step S31
In step S33, the feedback pulse reading subroutine is started. In step S33, the interpolation value I is read from the interpolator 15b via the latch 15c of the interpolation unit 15, and in step S35, the square wave shaping count unit 1 is read.
The pulse number P is read from the counter 13b via the third latch 13c. Step S33 and step S35 may be interchanged in order. Next, speed estimation / FB
In the signal calculator 17, ΔP, which is the difference between the pulse number P read in the previous routine and the current pulse number P, is calculated by the following equation (step S37). ΔP = P (current value) −P (previous value) (1)

Since the routine shown in FIGS. 2 and 3 is repeated at regular time intervals, ΔP can be regarded as representing the speed of the servomotor 31 or the driven member. When the speed of the servomotor 31 or the driven member increases, the frequency of the sine wave, which is an input signal from the position detector 33 to the waveform analyzer 11, increases. In general, the waveform shaping from a sine wave to a rectangular wave and counting of the number of pulses have high frequency response characteristics. However, since the frequency response characteristics of the A / D converter 15a are low, when the frequency of the input signal increases, A The reliability of the output value of the / D converter 15a decreases. Then, in step S39, ΔP is compared with the reference pulse number P (reference), and if ΔP is larger than P (reference), that is, if Yes in step S39, the interpolated value I ( The value of ΔI, which is the difference between the previous value) and the current interpolated value I (current value), is forcibly set to 0 (zero) (step S41).
If ΔP is smaller than P (reference), that is, if No in step S39, the value of ΔI is calculated by the following equation (step S43). ΔI = I (current value) −I (previous value) (2)

Next, in step S45, a feedback pulse is calculated by the following equation. FB = ΔP × N + ΔI (3) According to equation (3), while the servo motor 31 is operating at a low speed, the value of the FB is the output signal of the low-speed position detector 33 (the input signal to the waveform analyzer 11). ) Is equivalent to the increment amount obtained by digitizing the servo motor with high resolution.
While 1 is operating at a high speed, ΔI becomes zero, so that the increment amount is digitized to a low resolution.

The feedback pulse FB calculated by the speed estimating / FB signal calculator 17 as described above is output from the speed estimating / FB signal calculator 17 to the subtractor 35 and the speed converter 19, and the feedback pulse is read. The subroutine ends.

When the feedback pulse reading subroutine is completed, the main routine proceeds to step S13, where the movement command 21 (see FIG. 1) from the NC device or the like is read as described above, and the read feedback pulse FB is subtracted. The movement is compared with the movement command in the device 35 (step S15), and the difference is amplified by the position amplifier 23. On the other hand, in the speed converter 19, the feedback pulse from the speed estimation / FB signal calculator 17 is differentiated and converted into a speed (step S17). Next, in the subtracter 37, the output signal from the position amplifier 23 is compared with the signal obtained by differentiating the feedback signal FB by the speed converter 19, and the difference is amplified by the speed amplifier 25 (step S19). Next, in step S21, the current supplied to the servomotor 31 is detected by the current detector 29. The signal amplified by the speed amplifier 25 is output to a subtractor 39 by a current detector 29.
Is compared with the detected current value, and the difference is amplified by the current amplifier 27 (step S23). This output is supplied to the servo motor 31.

According to the present embodiment, while the member driven by the servo motor 31 is moving at a high speed, the position information signal from the position detector 33 is analyzed at a low resolution and fed back to the servo amplifier 41. While the driven member is moving at a low speed, the position information signal from the position detector 33 is analyzed with high resolution and fed back to the servo amplifier 41. In this regard, while the driven member is moving at high speed, generally high-precision control is not necessary,
For example, high-precision control is required when the speed of the driven member is reduced to stop or change its direction. Therefore, according to the present embodiment, it is possible to speed up the operation of these driven members while maintaining high positioning accuracy of, for example, a work table of a machine tool or a robot arm of an industrial robot.

Further, even if a hardware configuration in which the waveform analyzer 11 is disposed near the position detector 33 and the speed estimation / FB signal calculator 17 is disposed near the servo amplifier 41, the waveform Since the signal transmitted from the analyzer 11 to the speed estimation / FB signal calculator 17 is the pulse number P and the interpolation value I of the rectangular wave, the position information signal from the position detector 33 is analyzed with high resolution. However, the amount of data can be significantly reduced while eliminating the need for high-speed digital communication means requiring a high-speed and large cable such as parallel communication.

Further, the waveform analyzer 11 and the speed estimator F
When a hardware configuration in which the B signal calculator 17 is integrated with the servo amplifier 41 or is disposed in the same housing is adopted, the communication from the position detector 33 to the waveform analysis 11 is performed by analog communication. No digital communication means is required, and relatively long-distance communication is facilitated. In this embodiment, the waveform analyzer 11 and the speed estimation / FB signal calculator 17 can be further connected to the servo amplifier 41 by bus.

[0026]

According to the present invention, as in the prior art, two position detectors, a high-speed position detector and a low-speed position detector, are provided, and the driven member is automatically moved at a high speed without switching. When the motor is moved to a low speed, the servomotor can be controlled with low precision, and at low speed, the servomotor can be controlled with high precision.

According to the present invention, the data amount of the feedback signal can be significantly reduced while analyzing the position information signal from the position detector with high accuracy, and a high-speed and large cable such as parallel communication is required. It does not require high-speed digital communication means.

[Brief description of the drawings]

FIG. 1 is a block diagram of a servo control device according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing an operation of a waveform shaper.

FIG. 3 is an explanatory diagram showing the operation of the interpolator.

FIG. 4 is a flowchart showing a main routine of the servo control method of the present invention.

FIG. 5 is a subroutine for reading a feedback pulse according to the embodiment of the present invention.

FIG. 6 is a block diagram of a conventional servo control device.

[Explanation of symbols]

 11: Waveform analyzer 11a: Buffer amplifier 11b: Timing controller 13: Rectangular wave shaping / counting unit 13a: Waveform shaper 13b: Counter 13c: Latch 15: Interpolation unit 15a: A / D converter 15b: Interpolator 15c ... Latch 17: Speed estimation / FB signal calculator 19: Speed converter 31: Servo motor 33: Position detector 41: Servo amplifier

 ──────────────────────────────────────────────────続 き Continued on the front page F-term (reference) 2F069 AA01 BB01 BB04 BB40 DD30 GG06 HH14 HH15 JJ01 JJ11 NN00 NN08 NN21 5H004 GA18 GA34 GB15 HA07 HB07 JA03 JA09 JB02 JB15 JB17 JB19 JB30 KA01 MA08 AMA MAA MAA BB01 BB06 BB14 EE03 EE09 FF05 GG20 GG27 JJ02 KK01 KK17 KK37

Claims (4)

[Claims] 1. A position detector detects a position of a driven member driven by a servomotor, and feeds back a position information signal of the driven member comprising an analog signal detected by the position detector to a servo amplifier. In the servo control method of controlling the servo motor, while the driven member is operating at a speed higher than a predetermined reference speed, the position information signal is analyzed at a low resolution, and a feedback signal to the servo amplifier is analyzed. And a servo control method for analyzing the position information signal with high resolution and generating a feedback signal to a servo amplifier while the driven member is operating at a speed lower than a predetermined reference speed. . 2. The servo control method according to claim 1, wherein the position information signal is converted into a rectangular wave, the number of pulses is counted, the position information signal is converted, and the position information signal is converted from a value of the converted digital signal. Determining the phase of the driven member, while the driven member is operating at a speed higher than the reference speed, generates a feedback signal based on the number of pulses of the rectangular wave, the driven member is higher than the reference speed 2. The servo control method according to claim 1, wherein a feedback signal is generated based on the number of pulses and the phase of the position information signal during operation at a low speed. 3. A position of a driven member driven by a servomotor is detected by a position detector, and a position information signal of the driven member comprising an analog signal detected by the position detector is fed back to the servo amplifier. A servo control device that controls the servo motor and converts the position information signal into a rectangular wave and counts the number of pulses thereof; a rectangular wave shaping / counting unit that converts the position information signal; and a converted digital signal. And interpolation means for calculating the phase of the position information signal from the value of the position information signal. While the driven member is operating at a speed higher than a predetermined reference speed, a feedback signal is generated based on the number of pulses of the rectangular wave. While the driven member is operating at a speed lower than the reference speed, feedback is performed based on the pulse number and phase of the position information signal. Servo control apparatus designed to generate a signal. 4. The servo control device according to claim 3, wherein said interpolation means includes a table in which a value of said digital signal is associated with a phase of said position information signal.