JPS63253886A - Rotational speed controller for motor - Google Patents

Abstract

PURPOSE:To stably control a speed, by using a speed feedback signal at a higher frequency, at the time of the low-speed rotation of a motor. CONSTITUTION:A speed feedback section 1 is composed of a first and a second speed feedback signal generating sections 11, 12, a signal change-over controlling section 13, and a signal change-over section 14. From the signal change-over controlling section 13, according to whether or not the rotational speed of a motor 2 exceeds a specified value, the output of selection signal controlling the signal change-over section 14 is generated so that the output of each signal at a higher frequency and a lower frequency among the first or the second speed feedback signal may be generated. To a speed controlling means 4, at the time of the low-speed rotation of the motor 2, the input of the speed feedback signal of higher frequency, namely, of dense pulse train is provided.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a motor rotation speed control device, and particularly to a motor rotation speed control device using digital signals.

In servo motors used in NC machine tools and the like, the rotational position, speed, and drive current of the motor are controlled by digital numerical control using an NC device. The present invention relates to a device for speed control therein.

[Conventional technology]

Conventionally, in order to control the rotational speed of a motor to a predetermined value,
The rotational speed of the motor is detected and fed back.

FIG. 8 is a diagram showing the configuration of a conventional motor rotation speed control device. In this figure, 2 is a motor, 3 is a motor drive means, 4 is a speed control means, and 10 is a speed feed bank section. The motor 2 is driven by a drive current output by a motor drive means 3. The motor drive means 3 outputs the drive current in accordance with a current command output from the speed control means 4 as a digital data signal. In reality, the motor drive means 3 includes current control means for feedback controlling the drive current of the motor 2, an amplifier, and the like.

The speed feedback unit 10 detects the rotational speed of the motor 2, converts this rotational speed into a frequency of a digital signal, and outputs a signal in the form of a digital signal having such a frequency.
Information on the rotational speed of the motor 2 is transmitted to the speed control means 4. The speed control means 4 receives a speed command from another in the form of a digital signal, and transmits the speed command and the speed feedback section l.
A deviation from the rotational speed of the motor 2 obtained from the rotational speed of the motor 2 is determined, and a current command corresponding to this deviation is output to the motor driving means 3.

In the above configuration, the speed feedback section 10 is composed of, for example, a pulse encoder or a combination of a tacho generator and a V/F converter. In a pulse encoder, the rotational speed of the motor is determined by its detection section (
has already been converted into a signal frequency at the output (light receiving section). Additionally, the tachogenerator generates a voltage proportional to the rotational speed of the motor, and the V/F converter converts this voltage into a frequency. Further, the speed control means 4 and the current control means included in the motor drive means 3 are parts for calculating digital values, and are usually realized by a microcomputer.

The motor rotational speed control device as described above is used, for example, in a digital servo system. In this case, a feedback loop for position control exists outside the loop of the velocity feedbank described above.

[Problem that the invention seeks to solve]

By the way, in the speed control means 4 of FIG. 8, when obtaining the rotational speed of the motor from the digital signal having a frequency corresponding to the rotational speed of the motor, as shown in FIG. A method is used in which the number of digital pulses input within T) is counted and the average rotational speed of the motor within the predetermined time is determined from the counted value. Therefore, the obtained rotational speed information +1 becomes discrete.

When trying to obtain the rotational speed using the method described above, when the motor rotates at low speed, the weight of one pulse increases relatively, so the influence of the discretization described above becomes significant and the control system becomes unstable. There is a problem.

For example, as shown in FIG. 1O, a section in which no pulses from the speed feed bank section lO in FIG. 8 are input and the motor rotational speed is considered to be zero, and a section in which pulses are input appear repeatedly. A situation occurs. In such a case, for the section where the rotational speed of the motor is considered to be zero, the deviation from the speed command value is large, so a current command with a relatively large current value is output, and the section where the pulse was input is output. In this case, it is assumed that the deviation is relatively small, and a relatively small value of the current command is output repeatedly, which causes vibration and uneven feeding in the control system.

The present invention has been made in view of the above-mentioned problems. Even when the motor rotates at low speed, vibrations, uneven feed, etc. do not occur, and the control system does not become unstable due to the effects of discretization. The object of the present invention is to provide a motor rotation speed control device.

[Means for solving problems]

FIG. 1 is a diagram showing the basic configuration of a motor rotation speed control device according to the present invention. In this figure, 1 is a speed feed bank section, 2 is a motor, 3 is a motor drive means, and 4 is a speed control means.

The motor drive means 3 supplies a drive current to the motor 2 under control by a current command from the speed control means 4. The speed feedback section 1 detects the rotational speed of the motor 2, converts the rotational speed into a frequency of a digital signal, and transmits it to the speed control means 4 as a speed feedback signal.

The speed control means 4 performs calculations based on a speed command that teaches a target value of the rotation speed from the outside and the rotation speed of the motor 2 read from the speed feedback signal, and outputs a current command to drive the motor drive means 3. Control.

According to the invention, the speed feedback section I further comprises:
First and second speed feedback signal generators 11.
12, a signal switching control section 13, and a signal switching section 14.

First and second speed feedback signal generators 11
．． 12 detects the rotational speed of the motor 2, and the first and second speed feed bank signal generators (
11, 12) output first and second velocity feedbank signals, respectively. The first and second speed feedback signals are both digital signals having frequencies converted from the rotational speed, one frequency being a predetermined times higher than the other. The signal switching section 14
and a second speed feedback signal, and is controlled by the selection signal from the signal switching control section 13.
Either one of the first and second speed feedback signals is selected and output to the speed control means 4. The signal switching control unit 13 monitors the rotational speed using the first or second speed feedback signal, and depending on whether or not the rotational speed exceeds a predetermined value, switches the rotational speed to the first or second speed feedback signal. It outputs a selection signal that controls the signal switching section 14 to output the lower and higher frequency signals, respectively, and also transmits this selection signal to the speed control means 4. Based on this selection signal, the speed control means 4 reads the rotational speed of the motor 2 from the inputted first or second speed feedback signal.

[For production]

The rotation speed of the motor 2 is detected by both or one of the first and second speed feedback signal generation sections 11.12, and the detected rotation speed is detected by the first and second speed feedback signal generation sections 11.12. From each of
The first digital signals each have a different frequency.
and is output as a second velocity feed bank signal. The frequency of one of the first and second velocity feedhack signals is a predetermined multiple of the frequency of the other. That is, the output of one of the first and second speed feedback signal generators 11.12 is a digital signal with finer pulse intervals that is the predetermined times as dense as the output of the other. The signal switching control section 13
While monitoring the rotational speed of the motor 2 using the speed feedback signal, the output of the signal switching unit 14 is controlled to be selected according to the rotational speed. This control is performed when the rotational speed of the motor 2 decreases to a predetermined value or less and the pulses of the first or second speed feedback signal become sparse.
In other words, when the pulse interval increases, the signal switching section 14 outputs the predetermined times denser (higher frequency) one of the first or second speed feedback signals to the speed control section 14. conversely, when the rotational speed of the motor 2 increases and exceeds the predetermined value and the pulses of the first or second speed feedback signal become dense, that is,
When the pulse interval becomes shorter, the signal controller 14 outputs the predetermined multiplication (lower frequency) of the first or second speed feedback signal to control the speed control means 4. is input. At this time, a selection signal indicating which of the first and second speed feed bank signals has been input to the speed control means 4 is also transmitted to the speed control means 4, so that the first and second speed feed bank signals are The speed control means 4, which stores the relationship between the frequency of the speed feed bank signal and the rotational speed of the motor 2, can read the rotational speed of the motor from the inputted first or second speed feedback signal. can.

In this way, when the motor 2 is rotating at a low speed, the speed control means 4 receives a speed feedback signal having a higher frequency, that is, consisting of a dense pulse train, so that the rotation speed of the motor can be controlled evenly and stably. can be read. Therefore, the current command calculated based on the rotational speed thus read is also stable, and the driving of the motor 2 is also stable.

〔Example〕

FIG. 3A is a block diagram of an embodiment of the present invention. In this figure, 2 is a motor, 31 is an amplifier, 32 is a current detection section, and 3
3 is an A/D converter, 15 is a tacho generator, 16 is a pulse encoder, 17 is a V/F converter, 10 is an NC device, 20 is a microcomputer, 21 is a comparison circuit, 22
is a selector.

The motor 2 receives a drive current from the amplifier 31, the current detection section 32 detects this drive current, and the A/D converter 33 detects the drive current.
converts the detected analog data of the drive current into digital data and feeds it back to the microcomputer within the NCC device (current feedback).

The microcomputer 20 calculates the deviation of a current command value, which will be described later, from the above-mentioned fed-back current value, and controls the amplifier 31 to output a drive current according to this deviation.
Outputs a control signal to control the The configuration consisting of the current control function by the microcomputer 20, the amplifier 31, the current detection section 32, and the A/D converter 33 corresponds to the motor driving means 3 in FIG. 1 described above.

The rotational speed of the motor 2 is detected independently by the tacho generator 15 and the pulse encoder 16. The analog output of the tacho generator 15 is further V
/F converter 17 digitizes the signal. The pulse encoder 16 is connected to the first speed feedback signal generator 11 in FIG.
The configuration consisting of the V/F converter 17 and the V/F converter 17 corresponds to the second speed feedback signal generating section 12 in FIG.

The pulse encoder 16 is attached to the rotating shaft of the motor 2 and outputs an incremental digital pulse train as the motor 2 rotates. This incremental digital pulse train corresponds to the amount of light passing through slits provided at equal intervals on a rotating slit plate (not shown) of a pulse encoder that rotates with the rotation of the motor, and corresponds to the rotational speed of the motor 2. It has a frequency (number of pulses per unit time) proportional to . tacho generator 15
is also attached to the rotating shaft of the motor 2, and outputs a voltage proportional to the rotational speed of the motor.

The V/F converter 17 outputs a train of digital pulses having a frequency proportional to the output voltage of the tachogenerator 15. In this way, the V/F converter 17 also outputs a train of digital pulses having a frequency proportional to the rotational speed of the motor 2.

For example, if the highest frequency of the V/F converter 17 is set to correspond to the rotational speed of the motor 2 when it rotates at a low speed, then when the motor 2 rotates at a high speed higher than this rotational speed, the V/F converter 17
The converter 17 cannot output a speed feedback signal that accurately reflects the rotational speed, but in the region below the rotational speed described above, it outputs a speed feedback signal consisting of a very dense (high frequency) pulse train. Therefore, for example, when reading the rotational speed of the motor from the speed feedback signal by counting the number of pulses over a certain period of time T, there will be no variation in the read rotational speed value even when the motor rotates at a fairly low speed. . On the other hand, the (first) speed feedback signal from the pulse encoder 16 is in this case coarse and sparse so that the reader (for example, an NC device) can follow it even when the motor 2 rotates at high speed. ing. These first and second velocity feedback signals (the output of the pulse encoder 16 and the output of the V/F converter 17) are as shown in (1) and (2) in FIG. 2, for example. Second
(1) and (2) in the figure correspond to the same rotation of the motor 2. In FIG. 2, the pulse train of the second speed feedback signal is five times finer than the pulse train of the first speed feedback signal. That is, for the same rotational speed of the motor 2, the frequency of the second speed feedback signal is five times the frequency of the first speed feedbank signal.

The comparison circuit 21 corresponds to the signal switching control section 13 in FIG. 1, and reads the rotational speed of the motor 2 from the output of the V/F converter 17, and compares it with a reference speed stored in advance. , outputs a selection signal according to the comparison result (for example, "l" if rotational speed>reference speed, "0" if rotational speed≦reference speed).

The configuration of this comparison circuit 21 is shown in FIG. 3B.

In this figure, 21a is a counter with a cycle T (
It is reset every certain period of time when counting the number of pulses. The output of the V/F converter 17 is input to the clock input terminal IN of the counter 2r, and the output terminal Qj of the counter 21a for the count number corresponding to the rotation speed exceeding the reference speed is It becomes the output terminal of the circuit 21. While the rotational speed of the motor 2 is low, the number of pulses input from the V/F converter 17 within the period T is small, so the output Qj of the counter 21a, that is, the selection signal remains "O". , rotation speed≦reference speed. The rotational speed of motor 2 increases and V
When the frequency of the output of the /F converter 17 becomes higher and the number of pulses counted within the above period T increases, the above output Qj finally becomes "l", and rotation speed>reference speed,
It is detected that

In FIG. 3, the analog output of the tacho generator 15 indicating the rotational speed of the motor 2 is once converted into a digital signal by the V/F converter 17, and then in the comparison circuit 21.
This is compared with a reference speed, or alternatively, although not shown, a reference voltage corresponding to the reference speed is set, and an analog input comparator is provided that uses this reference voltage as a comparison standard. The output may be directly compared with the reference voltage using the comparator.

The selector 22 corresponds to the signal switching section 14 in FIG.
The control input terminal receives a selection signal which is the output of , and in response to the selection signal, selects and outputs one of the two manual forces and sends it to the microcomputer 20 .

Depending on the selection signal, the microcomputer 20 determines whether the output from the selector 22 is the first speed feedback signal (output of the pulse encoder 16) or the second speed feedback signal (the output of the V/F converter 17). ), and read the rotational speed of the motor 2 from these signals with weights depending on the respective signals. Then, the microcomputer 20 calculates the deviation between the speed command value taught as a target value from the outside and the read rotation speed,
A current command value is determined according to this deviation.

This current command value is used in the current control function of the microcomputer that forms part of the motor drive means 3, as described above. The above functions of the microcomputer 20 correspond to the speed control means 4 of FIG. 1 described above.

Note that the speed command value taught as a target value from the outside in the microcomputer 20 is, for example,
It is as follows. In a normal servo motor system, in addition to the current control function using current feedback and the speed control function using speed feedback as shown in the configuration of Fig. 3, the system also has a position control function using position feedback. The microcomputer determines the deviation between the position command value and the position feedback value taught by an external source, such as a host computer, tape input, manual input, etc., and the speed command value is determined in accordance with this deviation. Alternatively, when the purpose is not position control but simply speed control, the speed command value itself may be input via an external host computer or tape. In any case, since the present invention relates to a motor rotational speed control device, the speed command value can be considered to be given from the outside.

According to the configuration shown in FIG. 3, when the motor 2 rotates at a low speed, the speed control means 4 of the microcomputer 20
However, since the speed feedback signal consisting of a high-frequency, dense pulse train is supplied to the motor, the rotational speed of the motor read at regular intervals from the speed feedback signal is stable and free from unevenness and variation. The current command value calculated and outputted based on this value is also stable, and the motor is driven stably without uneven driving or feeding.

FIG. 4A is a block diagram of a second embodiment of the present invention.

In the configuration shown in this figure, the first and second speed feed bank signal generators 11.12 in FIG.
This is realized by a frequency dividing circuit 19 connected to the pulse encoder 16.

The output of the frequency divider circuit 19 corresponds to a first velocity feedback signal, and the output of the pulse encoder 16 corresponds to a second velocity feedbank signal.

An example of the structure of the frequency dividing circuit 19 is shown in FIG. 4B. The frequency dividing circuit 19 in this figure consists of a counter 19a, and the frequency dividing circuit 1
The input terminal 9 is the clock input terminal I of the counter 9a.
N, and the output terminal of the frequency dividing circuit 19 is the counter 9'
This is the Nth output terminal QN. The output terminal Q, is also connected to the clear terminal CLR of the counter 9. Since the frequency divider 819 outputs one pulse every time N pulses from the pulse encoder 16 are input,
The frequency of the output of the frequency dividing circuit 19 is determined by the pulse encoder 16
The output of is -. Therefore, the frequency of the first velocity feedback signal becomes - of the second velocity feedback signal.

The other configuration and operation of FIG. 4A are similar to the configuration of FIG. 3 described above. Note that in the configuration of FIG. 4A, the pulse encoder described above may be replaced with a series connection of a tacho generator and a V/F converter.

FIG. 5 is a block diagram of a third embodiment of the present invention.

In the configuration shown in this figure, the first and second speed feedback signal generators 11.12 in FIG. , 16-2. Although not shown, the first pulse encoder 16-
The pinch of the slit of the rotating slit plate 1 is N times the pinch of the slit of the rotating slit plate of the second pulse encoder 16-2. Therefore, the frequency of the output of the first pulse encoder 16-1 is It becomes - of the frequency of the output of the second pulse encoder 16-2.

In the configurations shown in FIGS. 4A and 5, the output of the pulse encoder 16 or 16-2 is used to measure the rotational speed of the motor 2 when it rotates at low speed. , high resolution with small slit pinch is required.

FIG. 6 is a block diagram of a fourth embodiment of the present invention.

In the configuration shown in this figure, 16-1 is a first pulse encoder, 16-2 is a second pulse encoder, and 18 is a gear transmission section. The first pulse encoder 16-1 is attached to the rotating shaft of the motor 2, and realizes the first speed feedback signal generating section 11 shown in FIG. The gear transmission unit 18 is a part that uses gears to transmit the rotation of the rotating shaft of the motor 2 to a high-speed rotating shaft that rotates at a higher speed. The second pulse encoder 16-2 is attached to the high-speed rotation shaft, and the gear transmission section 18 and the second pulse encoder 16-2 realize the second speed feedback signal generation section 12 in FIG. do. Even if the first pulse encoder 16-1 and the second pulse encoder 16-2 have the same resolution, the gear transmission section 18
As a result, the frequency of the output of the second pulse encoder 16-2 becomes higher than the frequency of the output of the first pulse encoder 16-1 by the gear shift.

FIG. 7 is a block diagram of a fifth embodiment of the present invention.

In the configuration of this figure, 15-1 and 15-2 are the first and second tacho generators, respectively, 17-1 and 17-
2 are V/F converters, respectively. The first tacho generator 15-1 is attached to the rotating shaft of the motor 2,
First tacho generator 15-1 and V/F converter 1
The configuration consisting of 7-1 realizes the first speed feedback signal generating section 11 shown in FIG. The role of the gear transmission section 18 is exactly the same as that shown in FIG. 6 described above. The configuration consisting of the second tacho generator 15-2 and the V/F converter 17-2 corresponds to the 22nd pulse encoder 16-2 in the configuration shown in FIG. The configuration consisting of the gear transmission section 18 realizes the second speed feedback signal generation section 2 shown in FIG.

If the first tacho generator 15-1 and the second tacho generator 15-2 have the same function, the V/F converters 17-1 and 17-2 are set in the same way. Assuming that, as in the configuration of FIG. 6, the frequency of the output of the V/F converter 17-2 is V/F
The frequency of the output of the converter 17-1 is multiplied by the gear ratio.

In the above description, it has been assumed that there are two types of speed feedback signals, the first and second types, but these can be easily expanded to any plurality of types.

〔Effect of the invention〕

According to the present invention, there is provided a motor rotational speed control device that does not cause vibration or uneven feeding even when the motor rotates at low speed, and does not cause the system to become unstable.

[Brief explanation of the drawing]

FIG. 1 is a basic configuration diagram of the present invention, FIG. 2 is a diagram showing an example of output waveforms of the first and second speed feedback signal generators, and FIG. 3A is a diagram showing the first example of the present invention.
3B is a diagram showing a configuration example of the comparator circuit 21 of FIG. 3A, FIG. 4A is a configuration diagram of the second embodiment of the present invention, and FIG. 4B is the frequency dividing circuit of FIG. 4A. 19, FIG. 5 is a diagram showing the configuration of the third embodiment of the present invention, FIG. 6 is a diagram showing the configuration of the fourth embodiment of the present invention, and FIG. 7 is a diagram showing the configuration of the fifth embodiment of the present invention. A configuration diagram, FIG. 8 is a diagram showing the conventional configuration of a motor rotation speed control device, FIG. 9 is an output waveform diagram of the speed feedback section of FIG. 8,
FIG. 10 is a diagram of the output waveform of the speed feedback section during the conventional low-speed rotation. (Explanation of symbols) 1. IQ...speed feed bank unit, 2...motor, 3...motor drive means, 4...speed control means, 10...NC device, 11...th 1 speed feed bank signal generator, 12
...Second speed feedback signal generating section, 13...
- Signal switching control unit, 14... Signal switching unit, 15, 15-1.15-2... Tacho generator, 1
6, 16-1.16-2...pulse encoder, 17
, 17-1.17-2...V/F converter, 18...
Gear transmission section, 19... Frequency dividing circuit, 19a... Counter, 20... Microcomputer, 21... Comparison circuit, 21a... Counter, 22... Selector, 31... Amplifier, 32... Current detection section, 33... A/D converter.

Claims (1)

[Claims] 1. A motor (2), a motor drive means (3) for supplying a drive current to the motor (2), and a motor drive means (3).
and a speed feedback unit that detects the rotation speed of the motor (2), converts the rotation speed into a frequency of a digital signal, and transmits the same as a speed feedback signal to the speed control means (4). (1), and the speed control means (4) performs calculations based on a speed command that externally teaches a target value of rotation speed and the rotation speed of the motor (2) read from the speed feedback signal. In the rotational speed control device for a motor (2), which controls the motor drive means (3) by outputting a current command, the speed feedback section (1) includes first and second speed feedback signal generation sections. (11, 12), a signal switching control section (13), and a signal switching section (14), the first and second speed feedback signal generating section (1
1 and 12) output first and second speed feedback signals, each of which is a digital signal having a frequency converted from the rotational speed, one of which is a predetermined times higher in frequency than the other; The switching unit (14) selects one of the first and second speed feedback signals and outputs it to the speed control means (4) under the control of the signal switching control unit (13), and outputs the selected signal to the speed control means (4). The switching control unit (13) monitors the rotational speed using the first or second speed feedback signal, and depending on whether the rotational speed exceeds a predetermined value, changes the rotational speed to the first or second speed feedback signal.
Alternatively, it outputs a selection signal that controls the signal switching section (14) to output the lower frequency one and the higher frequency one of the second speed feedback signals, respectively, and outputs the selection signal to the speed control means (14). 4), and the speed control means (4) controls the motor (2) by reading the rotational speed of the motor (2) from the inputted first or second speed feedback signal based on the selection signal. (2) A rotation speed control device for a motor, characterized in that the frequency of the speed feedback signal input to the speed control means (4) is increased during low speed rotation. 2. The first speed feedback signal generator (11)
is the second speed feedback signal generator (12)
2. The device according to claim 1, further comprising a frequency dividing circuit (19) for frequency dividing the output of the circuit to a predetermined ratio. 3. At least one of the first and second speed feedback signal generators (11, 12) is connected to the motor (
2. The device according to claim 1, further comprising means for detecting the rotational speed of the rotational speed of the item 2) which is changed by a gear. 4. One of the first and second speed feedback signal generators (11, 12) is a pulse encoder (16) that detects the rotation speed of the motor (2), and the other is a pulse encoder (16) that detects the rotation speed of the motor (2). Tacho generator (1
5) and a V/F converter (17) for converting the analog output of the tacho generator (15) into a digital signal having a frequency proportional to the analog output level. 5. The first and second speed feedback signal generators (11, 12) each include a pulse encoder (16-1) having a rotating slit plate with a different slit pitch.
, 16-2).