JP3339214B2 - Servo motor control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a servo motor control device, and more particularly to a servo motor control device for controlling speed and position with high accuracy depending on the resolution of a free running counter.

[0002]

2. Description of the Related Art As a conventional servo motor control device,
For example, there is one disclosed in JP-A-3-111913. This conventional servo motor control device inputs and processes a position signal and a speed signal from a linear scale that detects the position of a movable part, a pulse encoder that detects the speed of the servo motor, and a linear scale and a pulse encoder. It has a servo circuit (CPU) that controls the servomotor based on the processing result, and uses a pulse encoder with higher accuracy than a linear sensor.

In the above arrangement, every time the position of the movable part changes based on the position signal of the linear scale, the speed signal of the pulse encoder is integrated, and the obtained integrated value is converted into the unit of the position signal, and the conversion result is obtained. Is added to the position signal to obtain a servo motor control signal. The position of the movable part is controlled with high accuracy by controlling the servomotor with this control signal.

[0004]

However, according to the conventional servo motor control device, since the position accuracy of the movable portion depends on the resolution of the linear scale or the pulse encoder, an increase in the position accuracy increases the cost. And there is a limit to the improvement of the positional accuracy. Therefore, an object of the present invention is to provide a servomotor control device that controls speed and position with high accuracy while suppressing an increase in cost.

Another object of the present invention is to provide a control device for a servomotor which eliminates the limit of improvement in accuracy.

[0006]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides an encoder provided on a servomotor.
Based on the encoder pulse of the frequency corresponding to the output speed
A servomotor for controlling the speed and position of the servomotor.
The control device Bomota a sampling timing setting circuit for setting a sampling timing of the encoder pulse, the counter circuit for counting using decimal values several integer value and a predetermined number of digits of said encoder pulses generated in the sampling timing When the error calculation circuit for calculating an error consisting decimals integer value and a predetermined number of digits as compared to the reference value of the count value consisting of decimals integer value and a predetermined number of digits of the counter circuit, the error to provide a control apparatus of a servo motor, comprising the drive circuit the pulse-width-modulated signal output to the driving of the servo motor having a pulse width modulation in accordance with the.

[0007]

When the sampling time limit is set by the sampling time setting circuit, the counter circuit counts the number of encoder pulses generated in that time period and outputs a count value having a predetermined number of decimal digits. The encoder arithmetic circuit compares the decimal value with a reference value having the decimal value in the same manner, and calculates an error having the decimal value. The drive circuit controls the degree of pulse modulation of the pulse width modulation signal according to the error having a decimal value, and drives the servo motor with the pulse width modulation signal. The control of the present invention is not a control for counting encoder pulses only by an integer value and discarding a portion less than one pulse, but a control for increasing accuracy by counting a portion less than one pulse with a decimal number.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a servo motor control device according to the present invention will be described in detail. FIG. 1 shows an embodiment of the present invention, a microcomputer 100 constituted by one chip, an amplifier 11 for amplifying an output of the microcomputer 100,
A servo motor (hereinafter, simply referred to as a motor) 12 driven by an output of an amplifier 11, an encoder 13 for generating a pulse corresponding to a rotation speed of the motor 12, and an interface circuit for inputting an output of the encoder 13 to a microcomputer 100 14.

The microcomputer 100 includes a reference pulse generating circuit 1 for generating a reference pulse REF shown in FIG.
When a edge detection circuit 2 for detecting the edge of the reference pulse REF, a sufficiently high frequency compared to the reference pulse REF, for example, a clock generating circuit 3 for generating a clock of 1 MH _Z, an encoder pulse ENC encoder 13
An edge detection circuit 6 for detecting an edge of FIG. 2; counter circuits 4 and 5 for counting clocks of a clock generation circuit 3 based on edge signals of the edge detection circuits 2 and 6 to constitute a free running counter; Counter circuits 4, 5
A memory 7 for storing the count value of the above and other data, for example, the number of detected edges, the ratio (decimal value) of the portion of the reference pulse REF and the encoder pulse ENC that is less than one pulse to one pulse, and the storage contents of the memory 7. An error calculation circuit 8 for calculating a speed error and a position error of the motor 12 based on the calculation result; a compensation calculation processing circuit 9 for compensating a speed and a position error based on the calculation result of the error calculation circuit 8; PW based on compensation result
It comprises a PWM circuit 10 for generating an M signal, and a sampling time setting circuit 15 for setting sampling times T _{k − 1} , T _k , and T _{k + 1} (FIG. 2). The counter circuits 4 and 5 count the number of detected edges and the ratio (decimal value) described above.
Is also calculated.

FIG. 2 shows a reference pulse REF and an engorder pulse ENC input to the edge detection circuits 2 and 6.
In the figure, each symbol is defined as follows. (1) T _k-1 , T _k , T _{k + 1} sampling time (2) T ' _ENC , T _{ENC The} time from the start of the sampling time T _k to the rise of each reference pulse REF. . (3) N ' _ENC , N _ENC encoder time limit T' _ENC , clock count value of counter circuit 4 in T _ENC . _{^{(4) N 'P, N}} P, N'' is a clock count value of the counter circuit 4 in one cycle of _P reference clock REF, N _P is that of a sampling time period T _k. N _^'P those from the last rising edge of the sampling time period T _k-1 of over the start of T _k. N ^'' _P is T from the last rising edge of the sampling time period T _{k
It is about} the start of _{k + 1} . (5) The clock count value of the counter circuit 4 in the time period from the last rising edge of the N ^′ _fr and N _fr reference pulses REF to the end of the sampling time periods T _k−1 and T _k . (6) θ ′, θ, θ ″ Distance (position change) in one cycle of reference pulse REF. In FIG. 2, each of the symbols (1) to (6) is a reference pulse RE.
Although shown only at F, it is assumed that the same applies to the encoder pulse ENC.

In addition to the definitions of the above codes, the fractional value coefficient K
_fr and K ′ _fr are defined as follows. K _fr = N _fr / N _P K ' _fr = N ^' _fr / N ^' _P

The operation of the above configuration will be described. The motor 12 converts the PWM signal from the PWM circuit 10 into an amplifier 1
When the signal is input via the signal 1, the motor rotates at a speed corresponding to the duty ratio (pulse width modulation) of the PWM signal. When the motor 12 rotates, an encoder pulse ENC having a frequency corresponding to the rotation speed is output from the encoder 13 and input to the microcomputer 100 via the interface circuit 14. In the microcomputer 100, the edge detection circuit 6 detects the edge of the encoder pulse ENC, and the counter circuit 5 counts the clock counts N ′ _P , N _P , N ^′ from the clock generation circuit 3 based on the edge detection signal. _fr ,
N _fr is counted, and a predetermined operation is performed. At the same time, the counter circuit 5 edge number n of pulses is full of one period of the encoder pulse ENC sampling time period T _k (FIG. 2
Then, n = 2) is counted. The above counting result is stored in the memory 7.

[0013] Similarly, edge detector 2 also reference pulse REF output from the reference pulse generating circuit 1 detects the edge, the counter circuit 4 clocks from the clock generating circuit 3 based on it N _^'P , N _P , N ^' _fr , N
_{The fr} is counted, the edge number n (n = 2 in the figure) of the reference pulse REF is counted, and a predetermined operation is performed.
The above counting result is stored in the memory 7.

Reference pulse REF stored in memory 7
Is as follows, for example. _{n = 2 N P = 300 N} fr = 185 K fr = N fr / N P = 185/300 = 0.616666
6 N ' _P = 300 N' _fr = 242 K ' _fr = N' _fr / N ' _P = 242/300 = 0.806
6666

As described above, the error operation circuit 8 is a
Time period T_kReference position signal P at _REFIs calculated as
Put out. P_REF= [N + K_fr+ (1-K '_fr)]. Theta. = [2 + 0.6166666 + (1-0.8066666)]. Theta. = 2.8100000.theta.

Similarly, the error calculation circuit 8 calculates the measured position signal _PENC based on the counting result of the encoder pulse ENC stored in the memory 7 as follows. P _ENC = 2.56700000 · θ

The error calculation circuit 8 calculates (P_ENC-P_REF)of
The position error P is calculated as follows as follows: _ERRORIs calculated. P_ERROR= P_ENC-P_REF= −0.2430000 · θ

[0018] In the same manner, obtained as the difference between the velocity error V _ERROR also reference speed signal V _REF and the measured velocity signal V _{EN C.} V _REF , V _ENC = [n + K _fr + (1−K ′ _fr )] / T _k V _ERROR = V _ENC −V _REF = −0.2430000 / T
_k

As is clear from the above, the position error and the velocity error have a measurement accuracy corresponding to the fractional value coefficient K _fr based on the clock resolution of the clock generation circuit 3.

The compensation operation processing circuit 9 to which the above error has been input.
Outputs a compensation signal corresponding to the error to the PWM circuit 10,
The WM circuit 10 drives the motor 12 by outputting a PWM signal having a pulse modulation degree according to the error.

FIG. 5 is a flowchart of the operation described above.
It is a chart. In Figure 3, the sampling interrupt
Occurs, for example, the sampling time T_kStar of
Time T 'from encoder to the edge of each edge
_ENC, T _ENCClock number N ′_ENC, N_ENCIs counted,
(N_ENC-N '_ENC) During one encoder pulse
Clock number N_PGet. Next, the sampling time T_k
Number of encoder pulses (edge number) that fills one cycle of
Count n. Each is stored in the memory 7. same
Sometimes it is reset to n = 0. Stored in memory 7
The above-described error calculation based on the data is performed by the error calculation circuit 8.
The compensation calculation processing is performed by the compensation calculation processing circuit 9.
You.

FIG. 4 shows the operation of the error calculation circuit 8, in which the number of clocks N _ENC of the encoder time period T _ENC is subtracted from the number of clocks N of the sampling time period T _k to obtain a fraction time period, that is, less than one cycle. The number of clocks N _{fr of the} pulse time period (T _k −T _ENC ) is obtained. 1
From the number of clocks N _P in the encoder pulse and the number of clocks N _fr obtained here, the above-described fractional value coefficient K _fr , in other words, the fraction coefficient K _fr is obtained. From the current fractional value coefficient K _fr , the previous fractional value coefficient K ′ _fr , and the encoder pulse number (edge number) n, the measured speed signal V
_ENC is calculated, and then the current fractional value coefficient K _fr is replaced with the previous fractional value coefficient K ′ _fr . The aforementioned speed error V _ERROR is the reference speed signal V calculated in the same manner.
It is calculated by subtracting _REF from the measured speed signal V _ENC .

Next, when the control is in the speed mode, the speed error V _ERROR becomes the input I _C of the compensation operation processing circuit 9.
On the other hand, when the control is in the position mode, the sum of the position error P _{ER ROR} and the speed error V _ERROR is calculated by the compensation operation processing circuit 9.
Input I _C next, also, the sum is a position error P _ERROR in the next control.

FIG. 5 shows the encoder time period T 'described above._ENC,
T_ENCClock number N ′_ENC, N_{EN C}Showing the count of
And the encoder pulse number n becomes (n + 1) and increases by one.
When added, the number of clocks N_ENCCount, then one before
Clock number N ′ in the encoder pulse of_ENCSubtract
The number of clocks in one encoder pulse N _P
Get. Encoder based on current encoder pulse
Number of clocks N_ENCIs N '_ENCIt becomes.

[0025] In the above embodiment, the clock frequency of the clock generation circuit 3 is, for example, a 1 MH _Z, the frequency of the encoder 13 in the motor standard speed, for example, assuming that the 1.7KH _Z, conventional servo In the motor control device, the number of encoder pulses per rotation of the servo motor 12 is 100 ± n (n = 1, 2──).
However, according to the present invention,
For example, the data can be input as data having a decimal value of a predetermined number of digits, and the accuracy can be significantly improved.

Further, do not be such as to preserve the number of clocks in the sampling time period T _k as data,
Since the number n of encoder pulses can be stored as data, the number of bits can be reduced to save the storage capacity of the memory, and the precision can be increased using the fractional value coefficient K _fr .

Further, the errors P _ERROR and V _ERROR are both the reference values P obtained by measuring the reference pulse REF.
_Although calculated by comparing _REF and V _REF , the reference value may be a preset reference value in each of the sampling time periods without depending on the measurement.

[0028]

As described above, according to the servo motor control device of the present invention, it is not necessary to improve the accuracy of the encoder, so that the cost can be reduced, and the accuracy depends on the resolution of the free running counter. Since it can be increased, the limit of improvement in accuracy can be eliminated.

[Brief description of the drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention.

FIG. 2 is a waveform chart showing an example of counting reference pulses and encoder pulses in the operation of one embodiment of the present invention.

FIG. 3 is a flowchart showing the operation of one embodiment of the present invention.

FIG. 4 is a flowchart showing the operation of one embodiment of the present invention.

FIG. 5 is a flowchart showing the operation of one embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Reference pulse generation circuit 2.6 Edge detection circuit 3 Clock generation circuit 4.5 Counter circuit 7 Memory 8 Error calculation circuit 9 Compensation calculation processing circuit 10 PWM circuit 11 Amplifier 12 Servo motor 13 Encoder 14 Interface circuit 15 Sampling time setting circuit 100 microcomputer

Continuation of front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H02P 5/00 G01D 5/245

Claims (3)

(57) [Claims] 1. A servomotor control device for controlling the speed and position of the servomotor based on an encoder pulse having a frequency corresponding to the speed output from an encoder provided in the servomotor, wherein a sampling time of the encoder pulse And a sampling time setting circuit for setting the encoder pulse generated in the sampling time
A counter circuit that counts the number of integers using a decimal value of a predetermined number of digits, and the integer value by comparing the count value of the counter circuit with a reference value consisting of an integer value and a decimal value of a predetermined number of digits. An error calculation circuit for calculating an error consisting of a decimal value of a predetermined number of digits; and a drive circuit for outputting a pulse width modulation signal having a pulse width modulation degree corresponding to the error and driving the servo motor. A control device for a servomotor, characterized in that: 2. The error calculation circuit calculates the error based on the reference value obtained by counting the number of reference pulses generated in the sampling time period using an integer value and a decimal value of a predetermined number of digits. The control device for a servomotor according to claim 1, wherein the control device performs a calculation. 3. The first counting value obtained by counting a clock signal having a frequency higher than the frequency of the encoder pulse in one period of the encoder pulse in the sampling period, and 2. The servo motor according to claim 1, wherein the decimal value is calculated based on a ratio of a second count value obtained by counting the clock signal in a period corresponding to the decimal value in the sampling period. 3. Control device.