JP2000337926A - Initial position-detecting device for encoder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To precisely detect the initial position of a rotor irrespectively whether the rotor rotates fast or slow. SOLUTION: To detect the initial position of a rotary body with the value obtained by converting an M-series signal obtained through a resistance 4 by a table 80 when the power source is turned on and adding the outputs of an A and B pulse counter 81 to the initial position detection value thereafter, a slow/fast-speed judging circuit 83 is added, when the rotary body is rotating slow including a stop, the initial position is detected from the output of the table 80 and when fast, the initial position is detected by using a Z-pulse signal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an encoder initial position detecting device suitable for use in a servomotor or the like.

[0002]

2. Description of the Related Art FIG. 4 shows a conventional example of an N-bit (N-bit) encoder. In the figure, 1 is a slit plate, 2
Is an LED (light emitting diode), 3 is a light receiving element group, 4 is a resistor, 5 is an I / V (current / voltage) conversion circuit, 6 is a comparator, 8 is a conversion table 80 for converting an M-sequence code into a position signal, and a counter. 81, latch 82 and adder 84
And the like.

[0003] The slit plate 1, shading based on M-sequence signal is a binary random signal such that one period in one rotation, and the pattern repeating transmission, equidistant one revolution 2 N with (2 ^N ) A and B pulse patterns that repeat light shielding and transmission only once. Light emitted from the LED 2 is received by the light receiving element group 3 via the slit plate 1. Light receiving element group 3
Are N M-sequence light-receiving elements 31 for receiving light passing through the M-sequence pattern of the slit plate 1 and converting the light into current, and A for receiving light passing through the A and B pulse patterns of the slit plate 1.
A pulse light receiving element, a B pulse light receiving element that obtains an output having a cycle shifted by 1/4 cycle from the cycle of the A pulse (hereinafter collectively referred to as A and B pulse light receiving elements 32), and an M series light receiving element 31. It is composed of N transistors 34 for amplifying the converted current.

The current output from the N transistors 34 is converted into a voltage by the N resistors 4, and the current output from the A and B pulse light receiving elements 32 is converted into a voltage by the I / V conversion circuit 5. Is done. The signal converted to the voltage is output from the comparator 6 to the amplitudes (P
−P), and the waveform is shaped into a pulse. The N (N-bit) M-sequence signals and the A and B pulses converted into these voltages are input to the digital processing unit 8 and processed as follows.

[0005] As shown in FIG. 5, for example, a conversion table 80 is an N × N table for converting an N-bit M-sequence signal into N-bit position data. A, B
The pulse counter 81 has a phase of 90 as shown in FIG.
A pulse and B pulse shifted by one degree are multiplied by 1 (multiplication),
It is a counter that counts up / down.

The processing in the digital processing section 8 is performed as follows. First, the M-sequence / position conversion is performed by the M-sequence / position conversion table 80 immediately after the power is turned on. When this is completed, the M-sequence / position conversion end flag is set, the output of the table 80 is held in the latch 82 as the initial position detection value, and the A and B pulse counter 81 is cleared (clr). The latch output of the table output by the adder 84 (also referred to as an M-sequence position detection value)
, And the counter values of the A and B pulses are added, and the addition result becomes the position detection value of the encoder.

[0007]

In the above configuration, when it is desired to obtain a high resolution (increase N) in the slit plate 1 having a limited diameter, the LED 2 has a limited irradiation area within a limited irradiation area. Since the light receiving element group 3 having a shape corresponding to the pattern of the slit plate must be arranged, the area per light receiving element becomes small. In particular, since the number of output signals of the M-sequence light receiving element is large, it is often necessary to reduce the area as compared with the A and B pulse light receiving elements.
The output signal is also very small. Therefore, it is necessary to perform amplification using the transistor 34 and the like. As described above, when amplification is performed using a transistor, the transistor has a capacitance between the base and the emitter, and a delay occurs in an output signal between the transistor and the resistor 4 for current / voltage conversion.

For this reason, when the rotating body of the encoder rotates at a high speed, the M-sequence signal is delayed due to the influence of the delay, and there is a possibility that an erroneous detection may occur. For this reason, in the related art, when the power supply for detecting the position of the M-sequence is turned on, there is often a restriction on the use such that the rotating body of the encoder is at a certain rotational speed or less. Therefore, an object of the present invention is to enable accurate position detection without being limited by the number of revolutions of a rotating body of an encoder.

[0009]

In order to solve the above-mentioned problems, according to the present invention, a binary random number signal (hereinafter, referred to as an M-sequence signal) which is one cycle per rotation of a rotating body of an encoder is provided. An M-sequence signal output means for outputting, and an output of an arbitrary number of resolutions per rotation of the rotary body of the encoder; and
Pulse signal output means for outputting an A pulse signal having a duty of 50% and a B pulse signal shifted from the A pulse signal by 1/4 of one cycle; conversion means for converting the M-sequence signal into position data; The A pulse signal and B
And counting means for counting pulse signals, and performs initial position detection using the conversion means when power is turned on.
Z-pulse signal output means for outputting a Z-pulse signal generated at the same position by one rotation per rotation in an encoder which always enables position detection by adding the output from the counting means to the initial position detection value. And a position detecting means for detecting a position from the Z pulse signal, and when the rotating body of the encoder is rotating at a low speed including a stop, the initial position is detected using the M-sequence signal, and When the rotating body is rotating at a high speed, the initial position is detected using the Z pulse signal.

According to the first aspect of the present invention, whether the rotating body of the encoder is low speed or high speed is determined by an output value (counter value) from the counting means during a certain sampling period.
Can be determined by comparing the absolute value of the difference value obtained by subtracting the previous value from the current value with a predetermined value (the invention of claim 2), or the output value (counter value) from the counting means can be determined. When the amount of change is equal to the amount of change in the output from the conversion means, the output from the conversion means can be determined to be correct (the invention of claim 3), or the Z pulse is detected last time. Between detection and this time,
When the output value from the counting means is equal to the number of A and B pulses corresponding to one rotation of the rotary body of the encoder, the output from the position detecting means for detecting the position using the Z pulse can be determined to be correct. .

That is, according to the first aspect of the present invention, when the rotating body of the encoder such as the slit plate is rotating at a low speed when the power is turned on, the position is detected by using the M-sequence signal, and the rotating body is rotated at a high speed. In such a state, the initial position can be detected at a low speed or a high speed by detecting the position using the Z pulse. Furthermore, position detection using the M sequence
While the position detection time for reading the N M-sequence signals instantaneously is short, the position detection using the Z pulse requires the time until the rotating body of the encoder makes one rotation at worst. However, in the present invention, the position detection using the M-sequence is performed at a low speed, and the position detection using the Z pulse is performed at a high speed. Therefore, even when the Z-pulse position detection is performed, the rotating body rotates once. This time is short, and the time required for initial position detection is short.

According to the second aspect of the present invention, in the initial position detection, the high / low speed is newly determined because the change amount of the A and B pulse count values during a certain sampling period is large / small. This can be realized without providing a judging means. In the invention according to claim 3, the amount of change in the M-sequence position detection value during a certain sampling period;
When the change amounts of the A and B pulse count values match, M
The sequence position detection value is adopted as correct. In order to compare the signals obtained from different light receiving elements and the results obtained by different detection means, even if one detection means fails due to noise, the other detection means may be normal. In addition, the possibility that the encoder erroneously detects the initial position can be greatly reduced. Also, if the above comparisons do not match, if this operation is retried, the fact that the initial position detection value is not easily established means that one of the detection means is not normal, and this indicates that the encoder has failed. Can be detected.

According to the present invention, the count value of the A and B pulses changes by the number of pulses for one rotation between the detection of the Z pulse immediately after the power is turned on and the detection of the next Z pulse. Thus, the Z pulse position detection value is adopted as the initial position detection value. This is because signals from different light receiving elements and results obtained by different detection means are compared, so that even if one detection means fails due to noise or the like, the other detection means is normal. In some cases, the possibility that the encoder erroneously detects the initial position can be greatly reduced. Further, similarly to the invention of claim 3, if the retry is performed when the comparisons do not match, the initial position detection value is not easily established.
This means that one of the detection means is not normal, and from this it is possible to detect a failure of the encoder.

[0014]

FIG. 1 is a configuration diagram showing a first embodiment of the present invention. The slit plate 1 has one rotation
N-bit M-sequence signal pattern having a period, A and B pulse signal patterns that repeat light-shielding / transmission at equal intervals,
It is assumed that a Z-pulse signal pattern that transmits light only once at the same position in one rotation is formed. LED2
The emitted light is converted into a current by the light receiving element group 3 through the slit plate 1. Therefore, the light receiving element group 3 includes N light receiving element rows 31 and a B pulse light receiving element arranged to output a waveform having a phase shifted by 1/4 cycle from the output signals of the A pulse light receiving element and the A pulse light receiving element. A containing
B pulse light receiving element 32, Z pulse light receiving element 33, M
It comprises N transistors 34 and the like for amplifying the current output from the series light receiving element 31.

The currents output from the N transistors 34 are converted from currents to voltages by the N resistors 4. The current output from the Z-pulse light receiving element 33 is converted into a voltage by the I / V conversion circuit 5A.
The Z pulse signal converted into the voltage is supplied to the comparator 6A
Then, the output (pulse width of the Z pulse) is compared with the comparison voltage E1 such that the pulse width becomes about the pulse width of the A and B pulses, and the waveform is shaped into a Z pulse signal as shown in FIG. Similarly,
The current output from the A and B pulse light receiving elements 32 is I /
The voltage is converted by the V conversion circuit 5 into a voltage. The voltage-converted A and B pulse signals are compared with the voltage E by the comparator 6 and shaped into A and B pulse signals as shown in FIG.

The N M-sequence signals, A, B pulse signals, and Z pulse signals are input to the digital processing unit 8 and processed as described below to be processed into position detection values. The M-sequence / position conversion table 80 is similar to FIG.
It is a table of the size of N rows × N columns for converting the input of the M-sequence signal into N-bit position data. 81
4, is a counter for multiplying the A and B pulses by 1 as shown in FIG. 6 and counting up / down, and "0" is preset when the power is turned on.

When the power is turned on, first, the low speed / high speed determination circuit 83 determines whether the slit plate 1 is stopped, rotating at a low speed, or rotating at a high speed. When the speed is low, the judgment circuit 83 outputs "1" and selects the output of the table 80 by the switch (SW) 86. When the speed is high, the judgment circuit 83 outputs "0" and the switch (SW) 86 To select "0", that is, the position detection value (0) based on the Z pulse. Next, the data selected by 86 is at the rising timing of the initial position detection end signal output from the logic circuit 85 by the latch 82,
Latched as the initial position detection value. The initial position detection end signal is cleared by the logic circuit 85 when the power is turned on, and is set at low speed and when M-sequence / position detection conversion is completed, and at high speed and when a Z pulse is detected. After the initial position detection end signal is set, the initial position detection value latched by the latch 82 and the output of the counter 81 cleared at the rising edge of the initial position detection end signal are added by the adder 84, and the position detection is always performed. Will be performed.

FIG. 2 is a configuration diagram showing a second embodiment of the present invention. What is different from FIG. 1 is a low speed / high speed judgment circuit 8.
Since only part 3 is described, only this will be described, and the description of the other parts will be omitted. As shown in the figure, a low speed / high speed determination circuit 83 includes a buffer 832 for holding the previous value of the output of the counter 81, and a subtractor 831 for subtracting the current value from the previous value.
It is composed of an absolute value calculator 833 for calculating the absolute value of the subtraction result, a comparator 834, and the like. The input A of the comparator 835 indicates a threshold value for determining whether the speed is low or high.

That is, the output of the counter 81 is applied to the subtractor 8
31, the value is subtracted from the value of the buffer 832, and the absolute value calculator 833 takes the absolute value. This absolute value is the amount of change in A and B pulses between samplings. The amount of change is compared with a threshold value A for determining whether the speed is low or high in the comparator 834. Thus, the low speed / high speed judgment circuit 83 outputs "1" if the speed is low and "0" if the speed is high. Here, the threshold value A for determining whether the speed is low or high is a constant determined from the response of the M-sequence signal.

FIG. 3 is a block diagram showing a third embodiment of the present invention. In FIG. 3, an M-sequence position detection value check circuit 87 and a Z pulse position detection value check circuit 8 are different from those shown in FIG.
8 is added. First, the M-sequence position detection value check circuit 87 includes a buffer 871 for holding the previous value of the M-sequence position detection value, a subtractor 872 for subtracting the current value from the previous value of the M-sequence position detection value, A buffer 874 for holding the value, a subtractor 875 for subtracting the current value from the previous value of the output of the counter 81, and a subtractor 872
Subtracter 873, which subtracts the output of subtractor 875 from the output of
And a judgment circuit 876 for judging whether the output of the subtracter 873 is "0" or not.

The operation of the M-sequence position detection value check circuit 87 will be described. The M-sequence position detection value output from the table 80 is subtracted by the subtractor 872 from the output of the buffer 871 holding the previous value. This subtraction result is the amount of change in the M-sequence position detection value between samplings. on the other hand,
The output of the A and B pulse counters 81 is subtracted by a subtractor 875 from the output of the buffer 874 holding the previous value. The result of this subtraction is the number of A and B pulses between samplings. From the amount of change in the M-sequence position detection value between samplings, the number of A and B pulses between samplings is subtracted by
Is subtracted by The determination circuit 876 determines that the result of the subtraction is "0", that is, the number of A and B pulses between samplings and the amount of change in the M-sequence position detection value match. Outputs “0”.
If this output is “1”, the check of the M-sequence position detection value is OK, and the initial position detection end flag is set by the logic circuit 85 at low speed. If the output is "0", the initial position detection end flag remains cleared even in the case of low speed, so that the check operation of the M-sequence position detection value is retried in the next sampling.

On the other hand, Z pulse position detection value check circuit 8
8 is a counter 81 at the timing of the current Z pulse detection.
A latch 881, a latch 882 for latching the output of the counter 81 at the previous Z pulse detection timing, and a subtractor 88 for subtracting the current value from the previous value.
3, and a judgment circuit 884 for judging whether or not the subtraction result is 2 N (2 ^N ). The operation is as follows. After the power is turned on, the output value of the counter 81 when the Z pulse is detected first is latched by the latch 882, and the output value of the counter 81 when the Z pulse is detected is latched by the latch 881 and the difference is subtracted. Vessel 883
Ask by The judgment circuit 884 judges whether the difference is 2 ^N corresponding to the number of A and B pulses for one rotation of the slit plate 1, and if the result is "1", the check of the Z pulse position detection is OK. In the case of high speed, the logic circuit 85 sets an initial position detection end flag.
If the output is "0", the initial position detection end flag is not set even at high speed, and the operation of checking the Z pulse position detection value is retried.

[0023]

According to the first aspect of the present invention, the initial position upon power-on is detected at low speed using the M-sequence signal, and the Z pulse is used at high speed. Detection becomes possible. According to the second aspect of the present invention, it is possible to determine the low speed / high speed by using the conventional A and B pulse count values without providing a means for newly detecting the number of revolutions. According to the third aspect of the present invention, the M-sequence position detection value is determined to be correct when the M-sequence position detection value and the change amount of the A and B pulse count values in a certain sampling period match, and the initial position detection value is determined. , The noise resistance of M-sequence position detection can be improved. According to the fourth aspect of the present invention, between the detection of the Z pulse immediately after the power is turned on and the detection of the next Z pulse, the A and B pulse count values change by the number of pulses for one rotation. By determining that the Z pulse position detection value is correct and adopting it as the initial position detection value, the noise resistance of the Z pulse position detection can be improved.

[Brief description of the drawings]

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

FIG. 2 is a configuration diagram showing a second embodiment of the present invention.

FIG. 3 is a configuration diagram showing a third embodiment of the present invention.

FIG. 4 is a configuration diagram showing a conventional example.

FIG. 5 is an explanatory diagram of an example of a table for converting an M-sequence signal into position data.

FIG. 6 is an operation explanatory diagram of FIGS.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Slit board, 2 ... LED (light emitting diode), 3 ...
Light receiving element group, 31, 32, 33: light receiving element, 34: transistor, 4: resistor, 5, 5A: current / voltage (I / V)
Conversion circuit, 6, 6A, 834 Comparator, 8 Digital processing unit, 81 Counter, 82, 881, 882
... Latch, 83 ... Low speed / high speed judgment circuit, 84 ... Adder,
85: logic 0886: switch, 87: M-sequence position detection value check circuit, 88: Z pulse position detection value check circuit, 831, 872, 875, 883: subtractor, 8
32, 871, 874: buffer; 833: absolute value calculator; 876, 884: determination circuit.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Takashi Aihara 1-1-1 Tanabeshinda, Kawasaki-ku, Kawasaki-shi, Kanagawa F-term in Fuji Electric Co., Ltd. (Reference) 2F077 AA38 NN02 NN30 PP19 QQ05 QQ11 RR17 TT32 TT61 TT66 TT71 2F103 BA32 CA02 DA01 DA13 EA02 EA12 EB06 EB33 ED06 ED12 ED18 ED21

Claims (4)

[Claims] 1. An M-sequence signal output means for outputting a binary random number signal (hereinafter, referred to as an M-sequence signal) such that one cycle is obtained by one rotation of the rotating body of the encoder, and an arbitrary resolution by one rotation of the rotating body of the encoder. And A pulse signal output means for outputting an A pulse signal having a duty ratio of 50% and a B pulse signal shifted from the A pulse signal by one-fourth of one cycle; A conversion unit for converting the data into data; and a counting unit for counting the A pulse signal and the B pulse signal. When the power is turned on, an initial position is detected by using the conversion unit. In an encoder that always enables position detection by adding outputs from the means, a Z pulse that outputs a Z pulse signal generated at the same position by one pulse per rotation No. output means, and a position detecting means for detecting a position of the Z pulse signal provided, if the rotation of the encoder is rotating at a low speed including when stopped, the M
An initial position detecting device for an encoder, wherein the initial position is detected by using a series signal, and the initial position is detected by using the Z pulse signal when the rotating body of the encoder is rotating at a high speed. 2. The method according to claim 1, wherein the rotating body of the encoder is at a low speed or a high speed by determining the absolute value of a difference value obtained by subtracting a previous value from a current value of an output value (counter value) from the counting means during a certain sampling period. The initial position detecting device for an encoder according to claim 1, wherein the determination is made by comparing with a predetermined value. 3. When the amount of change in the output value (counter value) from the counting means is equal to the amount of change in the output from the converting means, the output from the converting means is determined to be correct. The encoder initial position detecting device according to claim 1, wherein: 4. When the output value from the counting means is equal to the number of A and B pulses corresponding to one rotation of the rotating body of the encoder during a period from the previous detection of the Z pulse to the present detection thereof, the Z pulse The initial position detecting device for an encoder according to claim 1, wherein the output from the position detecting means for detecting the position using is determined to be correct.