JPH0326771B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an incremental encoder capable of reporting an abnormal output value and/or a phase difference abnormality of a detection signal.

Encoders can be divided into absolute type and incremental type. Although the absolute type is highly reliable, it has a complicated structure and is expensive. Therefore, incremental encoders, which have a simple structure and are inexpensive, are widely used, but they have the drawback of accumulating miscounts, and are said to be less reliable than absolute encoders. Various alarm circuits have been proposed to compensate for this drawback.

The applicant filed Japanese Patent Application No. 57-52647 (Japanese Unexamined Patent Publication No. 58-58
169027) has already proposed an alarm circuit. The encoder has a detection section that detects a first signal and a second signal having a phase difference of 90 degrees from a main code section that is formed at a predetermined pitch and moves relative to each other, and an index code section. Here, it is assumed that the first signal leads the second signal by 90 degrees in phase. Abnormality detection of the first signal is performed at the rising edge of the second rectangular wave signal obtained by converting the second signal into a rectangular wave.
This is performed by a circuit that compares the first signal with a reference level and determines whether the first signal exceeds the first reference level or is below the second reference level. Abnormality detection for the second signal is also performed using similar means.

However, if the configuration is such that the second rectangular wave signal is required to detect an abnormality in the first signal, and the first rectangular wave signal is required to detect an abnormality in the second signal, as described above, , the first signal and the second signal, or either one of them, is significantly deviated and no rectangular wave signal is generated, or if the rectangular wave signal is no longer generated for some reason, the abnormality detection function will not be fulfilled. It disappears.

Therefore, the reliability of this abnormality detection circuit cannot be said to be sufficient.

The present invention enables each abnormality detection to be performed independently without using the second signal to detect an abnormality in the first signal that is the output of the detection unit, and without using the first signal to detect an abnormality in the second signal. It is an object of the present invention to provide an incremental encoder that improves reliability by performing the following steps and can notify an abnormal output value and an abnormal phase difference of the output of a detection section with a simple structure.

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a digital transmission having an incremental rotary encoder according to the present invention will be described below with reference to the drawings. As shown in FIG. 1, the digital transit includes a cradle 2 having supports 2a and 2b that rotatably support a telescope 1.
and a base 3 that supports the stand 2 rotatably around a vertical axis, and a photoelectric encoder 4 for reading horizontal degrees is built in the lower part of the stand 2. This encoder 4 is connected to an index code plate 4b which is an index code section that is fixed to the rack section 2 and rotates with the rotation of the rack section 2.
, a main code plate 4a which is a main code part fixed to the base part 3, and a light emitting part 4 for illuminating the main code plate 4a and the index code plate 4b.
c, and a light receiver 4d that receives the illumination light. Furthermore, an encoder 5 having a similar structure and for reading the elevation angle from the rotation angle of the telescope 1 is attached to one of the support columns 2b. On the main code plate 4a, slits of equal pitch are formed all around the circumference. On the index code 4b, two groups of slits are formed which have the same slits as the main code (not shown) and are 1/4 pitch apart from each other. The light receiving section 4d is connected to the slit on the main code plate 4a and the index code plate 4.
Figure 3a includes two light-receiving elements that receive the respective light fluxes that have passed through the two slit groups formed on The two sine waves shown in can be obtained. Further, on the pillar 2a, there is a processing section 6 for processing the read signals from the encoders 4 and 5 into angle values, and a digital display of the angle values from the processing section 6 as horizontal and elevation angles. A display 7 is arranged to display the information.

As shown in FIG. 2, the processing section 6 includes a rectangular wave converting section 8, a counting section 9, a calculation display 10, and an abnormality detecting section 11. Hereinafter, the detection of the horizontal minute angle will be described, and the explanation of the detection of the elevation minute angle based on the same structural effect will be omitted.

The rectangular wave converter 8 converts the first signal and the second signal having a phase difference of 90° from each other obtained by the light receiving unit 4d into rectangular waves, and amplifies the first signal to a level suitable for signal processing. a first amplifier 12 and a second amplifier 12;
a second amplifier 13 that amplifies the signal; a first Schmitt trigger circuit 14 that converts the first signal into a rectangular wave;
A second Schmitt trigger circuit 15 converts the second signal into a rectangular wave.

The first Schmitt trigger circuit 14 receives the first signal,
Further, the second Schmitt trigger circuit 15 converts the second signal into a rectangular wave at the same predetermined threshold level, and outputs the converted signal to the direction discrimination circuit 16 and pulse generator 17 of the counting section 9.

The outputs of the first amplifier 12 and the second amplifier 13 are
Also, the abnormality detection circuit 1 of the abnormality detection unit 11, respectively.
8 is entered.

The counting section 9 generates narrow pulses at the rise and fall of the rectangular wave output signals of the direction discrimination circuit 16 that discriminates the rotating direction of the main code plate 4a, and the first and second Schmitt trigger circuits 14 and 15. It is composed of a pulse generator 17 that generates pulses, and a counting circuit 20 that increases or decreases the number of pulses generated by the pulse generator 17 based on the direction signal discriminated by the direction discrimination circuit 16. The count value counted by the counting circuit 20 corresponds to the amount of rotational movement of the main code plate 4a.
The counted value is sent to the microprocessor 21 of the calculation display section 10.

The calculation display unit 10 includes a microprocessor 21
and a display 7. The microprocessor 21 performs a predetermined calculation on the counter received from the counting circuit 20, converts it into an angle value, and displays the result.
The microprocessor 21 further includes an abnormality detection section 11.
When an abnormality detection signal is received from the abnormality detection circuit 18, the abnormality is displayed on the display 7 to notify the abnormality.

The causes of erroneous counting in the incremental encoder with the above configuration include an abnormal output value in which the first signal and/or the second signal deviate significantly from the normal state where the first signal and/or the second signal changes around the threshold level of the Schmitt trigger circuit. , a case of phase difference abnormality in which the phase difference between the first signal and the second signal deviates significantly from 90 degrees can be considered.

FIG. 3a shows the first amplifier output and the second amplifier output when the first signal and the second signal are in a normal state.

In FIG. 3b, the amplitude of the first signal is a, and the difference between the amplitude fluctuation center level _O1 and the threshold level TL is b. Furthermore, it is assumed that the amplitude of the second signal is c, and the difference between the amplitude fluctuation center level _O2 and the threshold level TL is d. Figure 3b
is the phase difference between the first signal and the second signal in this case.
The first amplifier output and the second amplifier output when the output value changes at 90 degrees are shown.

FIG. 3c shows that the amplitudes of the first signal and the second signal are a
2 shows the first amplifier output and the second amplifier output when the phase difference between the first signal and the second signal becomes significantly larger than 90 degrees.

FIG. 3d shows the first amplifier output and the second amplifier output at the time of an abnormal phase difference in which the phase difference between the first signal and the second signal becomes extremely small.

First and second Schmitt trigger circuits 14, 15
However, depending on the threshold level TL, Figure 3a
A signal obtained by converting the signal shown in FIG. 3 into a rectangular wave is shown in FIG. 4a, a signal obtained by converting the signal shown in FIG. The converted signal is shown in FIG. 4c, and the signal obtained by rectangular wave conversion of the signal shown in FIG. 3d is shown in FIG. 4d.

The pulse generator 17 generates pulses at the rise and fall of the first signal and the second signal,
The first signal and the second signal generate the pulse train shown in FIG. 5a by the rectangular wave signal at the normal time shown in FIG. 4a, and the pulse train shown in FIG. The pulse train shown in Fig. 5b is generated, and the pulse train shown in Fig. 4c is generated.
and the fifth rectangular wave signal at the time of phase difference abnormality shown in d.
The pulse trains shown in Figures c and d are generated.

The pulse train that the pulse generator 17 normally generates is a pulse train with equal pulse intervals as shown in FIG. 5a. On the other hand, the pulse train generated by the pulse generator 17 when the output value is abnormal or when the phase difference is abnormal includes portions where the pulse intervals are narrowed, as shown in FIGS. 5b, c, and d. If the pulse interval increases or decreases significantly due to such output value changes or phase changes, erroneous counting will occur and measurement accuracy will decrease.

When the output value is abnormal, as shown in FIG. 3b, if the first signal becomes a・sin wt+b and the second signal becomes c・cos wt+d, the pulse generator 1
The output of 7 becomes the pulse train shown in FIG. 5b. The portion where the pulse interval becomes narrow corresponds to the portion where both the first signal and the second signal approach the threshold level TL in FIG. 3b.

Therefore, the pulse generator 17 causes erroneous counting.
In order to know that the pulse interval of the output of It is only necessary to detect whether both of the second signals are simultaneously between the first reference level and the second reference level, that is, in a predetermined zone. When actually configuring the circuit, select a predetermined zone of ± levels around the threshold level TL, taking into consideration the width of the pulse generated by the pulse generator 17, the fluctuation width of the threshold level TL, etc. do.

Although the above explanation has been made with the aim of preventing erroneous counting of pulses, it is usually necessary to ensure the accuracy of measuring instruments, and if the amount of error becomes large even if it does not result in erroneous counting, an alarm will be issued. There may be times when it is necessary to do so.

In the case of an abnormal output value, that is, when the amplitude of the first signal or the second signal (a, c in Figure 3 b) fluctuates greatly, or when the DC bias component deviates significantly from the threshold level TL. As is clear from FIG. 3b, the points at which the first signal and the second signal cross the threshold level TL are close to each other,
The detection pulse interval becomes narrower. To detect this,
This is determined by detecting whether both the first signal and the second signal are simultaneously between the first reference level and the second reference level.

If the distance from the threshold level TL to the intersection point of the signal shown in FIG. 3b is L', then L' can be determined by the following equation.

L' _H = a sin α + b (upper intersection) - and L' _L = a sin (α + π) + b (lower intersection) - where becomes. When converted to a pulse signal, the phase change of the rise and fall of the first signal compared to the normal state is as follows:
From Figure 3b, sin ^-1 b/a.

The phase change of the rising and falling of the second signal is
cos ^-1 d/c. Since the pulse generator 17 generates pulses for counting at the rise and fall of the pulse, an error in the output values of the first signal and the second signal appears as a cause of measurement error.

Next, in the case of an abnormal phase difference, the first signal is a
Let sin wt and the second signal be a cos (wt+β).
The first and second signals when β≒45° are shown in Figure 3c.
and when β≈−45°, the first and second signals are shown in FIG. 3d.

The output of the pulse generator 17 based on the first signal and the second signal when β≒45° becomes the pulse train shown in FIG. 5c, and the portion where the pulse interval is narrowed is shown in FIG.
As is clear from the above, the points where the first signal and the second signal cross the threshold level TL are close to each other, and the first signal and the second signal cross the threshold level TL at the same time. It corresponds to the part in between.

On the other hand, when β≒-45°, the output of the pulse generator 17 based on the first signal and the second signal becomes the pulse train shown in FIG. 5d, and the part where the pulse interval is narrowed is
As is clear in FIG. 3d, the points where the first signal and the second signal cross the threshold level TL are close to each other, and the first signal and the second signal cross the threshold level TL at the same time. This corresponds to the area between the standard level and the standard level.

In the case of a phase difference abnormality, the points where the first signal and the second signal cross the threshold level TL are close to each other,
Conditions in which the interval between the detection pulses narrows are shown in FIGS. 3c and 3d, with cases in which the phase difference between the two signals becomes significantly smaller than 90° and cases in which it becomes significantly larger.
To detect this case, it is sufficient to determine whether both the first signal and the second signal are simultaneously between the first reference level and the second reference level. This can be determined by determining whether the absolute values of the intervals L' _L and L' _H between the intersection of the first signal and the second signal and the threshold level TL are smaller than a predetermined level.

The distances L′ _L and L′ _H are determined by the following formulas.

L' _H = a sin 1/2 (90°-β) L' _L = a sin 1/2 (270°-β) ｜L' _H ｜=｜L' _L ｜ =｜a sin 1/2 (90゜-β) | - Also, whether the first signal and second signal in Fig. 3 d exist simultaneously within a predetermined zone depends on the interval between the first signal and the threshold level TL, and the second signal. Similarly to FIG. 3c, it is necessary to judge whether or not the interval between the threshold level TL and the threshold level TL is equal, and whether this value is smaller than the level L of the predetermined zone.

The distances L'' _H and L'' _L can be determined from FIG. 3 d using the following formula.

L″ _H = a sin 1/2 (270+β) L″ _L = a cos 1/2 (270 − β) |L″ _H |= |L″ _L | = | a sin 1/2 (270+β) | − and Become. In this case, the maximum measurement error when compared with the normal signal is β.

Therefore, in order to ensure accuracy, allowable output value fluctuation and phase fluctuation ranges are defined using the above formulas or formulas, an appropriate abnormality detection zone level L is set, and the first signal and second signal are simultaneously detected in this range. If it is detected that the sensor is within the range, a measurement whose accuracy cannot be guaranteed can be notified. The abnormality detection circuit 18, which is configured to perform abnormality detection as described above, includes three resistors R ₁ , R ₂ , R ₃ and four comparators, as shown in FIG.
It consists of _OP1 to _OP4 and one NOR circuit NOR. Resistors _R1 to _R3 are connected in series from the +V terminal to the ground terminal, and their resistance values are
The selection is made so that a voltage at the TL+L level shown in FIG. 3B is formed at the connection between _R1 and _R2 , and a voltage at the TL-L level at the connection between the resistors _R2 and _R3 . This TL
The +L voltage is input to one end of comparators OP ₁ and OP ₃ , while the TL-L voltage is input to the + ends of comparators OP ₂ and OP ₄ . The first signal, which is the output of the first amplifier, is connected to the + terminal of the comparator OP ₁ and the - terminal of the comparator OP ₂ .
A second signal, which is the output of the second amplifier, is input to the + terminal of OP ₃ and the - terminal of OP. Comparator OP ₁ or
The output of OP ₄ is input to the NOR circuit, and the output of this NOR circuit is input to the microprocessor 21 of the calculation display section 10.
has been entered.

In the above configuration, the comparator OP ₁ receives the first signal, and the comparator OP ₃ receives the second signal TL.
A comparison is made to see if it exceeds the +L level. The comparator _OP2 and the comparator _OP4 respectively compare whether the first signal and the second signal are below the TL-L level.

As shown in FIG. 3a, when the first signal and the second signal are in a normal state, the output signals of the comparators OP ₁ to OP ₄ and the NOR circuit in FIG. 6 to which they are input are as shown in FIG. 7. Shown in a. Figure 3 a, 1st
For the second signal, the first signal and the second signal are never in the range TL±L at the same time, so the output of the NOR circuit is always L.

The first and second signals in Figure 3b, where the output value fluctuates significantly, or Figures 3c and d, where the phase difference is significantly more than 90°, may fall within the range of TL±L at the same time. .

The outputs of comparators OP ₁ to OP ₄ in FIG. 6 when the signal in FIG. 3 b is input to the abnormality detection circuit and
The output of the NOR circuit NOR is shown in Figure 7b and Figure 3c.
When the signal in Figure 7c is input, the signal in Figure 3d
When the signal is input, the comparator and
The output of the NOR circuit is shown. 1st signal and 2nd signal
The comparator only applies when the signal is in the range HL±L.
The outputs of OP ₁ to OP ₄ all become L, and the output of the NOR circuit becomes H. When the output of the NOR circuit becomes H, it indicates an abnormal output value or an abnormal phase difference. When the microprocessor 21 receives the H signal indicating this abnormality, it displays an abnormality indication on the display to prevent measurements exceeding the permissible range.

By configuring as described above, it is possible to provide an incremental encoder with improved reliability.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of a digital transit that performs an incremental encoder according to the present invention, FIG. 2 is a block diagram of a processing section of the digital transit shown in FIG. 1, and FIG. 3 is a diagram of the digital transit shown in FIG. Figure 4 is a rectangular wave diagram of the output signal shown in Figure 3.
Figure 5 is a pulse train diagram using the rectangular wave shown in Figure 4;
FIG. 6 is a circuit diagram of the above detection circuit, and FIG. 7 is an output waveform diagram of the above detection circuit shown in FIG. 1...Telescope, 4a...Main code plate, 4b...
Index code board, 18... Abnormality detection circuit,
20... Counting circuit, 21... Microprocessor.

Claims (1)

[Claims] 1. A main code part and an index code part that are formed at a predetermined pitch and move relative to each other; a detection part that detects a first signal and a second signal from the two code parts with different phase differences; A first reference level and a second reference level are set across the amplitude center of the second signal, and it is determined whether the first signal and the second signal are higher or lower than the first reference level and the second reference level, respectively. A comparator to compare,
the first signal by determining from the output of the comparator whether the first signal and the second signal are simultaneously between the first reference level and the second reference level;
An incremental encoder comprising: an abnormality detection unit that detects an output abnormality or a phase abnormality of the signal and the second signal.