JPH05133773A - Optical tape reference position sensing device - Google Patents

Abstract

PURPOSE:To make always constant the width of rectangular pulses included in the reference signal in an optical type encoder. CONSTITUTION:An encoder is equipped with a light source 1 and a displacement member 2 where a pair of reference slits 21, 22 separated from each other in the displacement direction, as specified so as to intersect the light source 1, are formed in the reference positions specified. A photo-receiving part 3 is arranged fast opposed to this displacement member 2. A pair of photo- reception regions RZ1, RZ2 are provided being split in the displacement direction to receive the projected light generated when the slits 21, 22 intersect the light source 1 and to emit a pair of reference sensing signals Z1, Z2 corresponding to the respective amounts of light reception. A processing circuit 4 performs comparative processing of the sensing signals Z1, Z2 on the basis of the reference signal (Z1+Z2)/K acquired by subjecting the sensing signals Z1, Z2 to an adding and a subtracting process, produces a rise signal Z2C and a fall signal Z1C, performs a logical processing, and emits a reference signal Z having a certain rectangular pulse width.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical encoder including a light source, an encoder plate, a light receiving element and the like, and more particularly to a device for detecting a reference position of the encoder plate.

[0002]

2. Description of the Related Art The basic principle of a reference position detecting method for an encoder plate will be briefly described with reference to FIG. The illustrated linear encoder plate 101 is arranged so as to be linearly displaced between the fixed light source and the fixed light receiving element. The encoder plate 101 has a periodic slit array 10 for detecting a displacement amount.
2 and the reference slit 103 are formed. The reference slit 103 has an opening size equal to one cycle of the slit row 102. The light passing through the moving encoder plate 101 is received by the light receiving element through a predetermined mask and outputs a detection signal according to the amount of received light. Reference slit 103
The pulse-shaped reference detection signal ZS is obtained from the light transmitted through, and the displacement detection signal AS having a sinusoidal waveform is obtained from the light transmitted through the periodic slit array 102. These detection signals are subjected to waveform shaping processing to obtain a reference signal ZP consisting of a single pulse and a displacement signal AP consisting of a periodic pulse train. The reference signal Z is synchronized with each rising or falling of the displacement signal AP.
The presence or absence of P is detected to accurately specify the reference position of the encoder plate 101. Therefore, it is necessary to shape the rectangular pulse width of the reference signal ZP so as to accurately correspond to the cycle of the displacement signal AP. However, even if the reference detection signal ZS consisting of a single peak is subjected to waveform processing, the peak height always fluctuates, so that a rectangular pulse having a constant width cannot always be obtained.

Therefore, various measures have been conventionally made in order to obtain a reference signal having a pulse width matching the cycle of the displacement signal. An example thereof is shown in FIG. Encoder plate 20
A pair of complementary reference slits 202 and 203 are formed at 1 to represent the reference position. The illustration of the periodic slit array is omitted. By receiving the light component that has passed through one of the reference slits 202, a reference detection signal Z1S having a positive peak is obtained, and by receiving the light component that has passed through the other reference slit 203 via a predetermined mask, a negative value is obtained. The reference detection signal Z2S having a peak is obtained. These pair of reference detection signals Z1S and Z2S
Are compared with each other to obtain a reference signal ZP consisting of a rectangular single-shot pulse having a predetermined pulse width.

FIG. 11 shows another conventional example. On the encoder plate 301, continuous slits 302 in a strip shape and code slit rows 303 arranged irregularly at the reference position are formed. The slit row for obtaining the displacement information of the encoder plate is not shown. An opening 402 corresponding to the band-shaped slit 302 and a mask slit row 403 corresponding to the code slit row 303 are formed on the mask plate 401 arranged immediately before the light receiving element. The constant voltage signal ZOS is obtained by receiving the light component that has passed through the opening 402, and the reference detection signal ZS is obtained by receiving the light component that has passed through the mask slit array 403. By thresholding this reference detection signal ZS with the constant voltage signal ZOS, the reference signal ZP consisting of rectangular pulses can be obtained.

[0005]

In the conventional example shown in FIG. 10, in order to match the pulse width of the reference signal ZP with the period of the displacement signal, the extraction width of the reference slit 202 and the remaining width of the reference slit 203 are accurately measured. Must match.
However, since the slit is usually formed by using photolithography and etching, it is difficult to match the punched width and the remaining width. Especially, when the slit width is reduced to several μm in order to increase the resolution, such a problem becomes remarkable. Also, reference detection signals Z1S and Z2S which are complementary to each other.
And a difference in response time occurs. That is, due to the influence of the junction capacitance of the photodiode constituting the light receiving element, the rising characteristic of the peak included in the reference detection signal tends to be delayed as compared with the falling characteristic. Therefore, it is difficult to make the rectangular pulse width of the reference signal ZP constant. In addition, although the illustrated example is a linear encoder plate, if this is applied to a rotary encoder plate, the pair of reference slits 202 and 203 will be aligned in the radial direction of the rotary encoder plate, and a difference will occur in the amount of transmitted light. Reference detection signal Z1S
, And the peak output of Z2S cannot be made equal.

On the other hand, in the conventional example shown in FIG. 11, a code slit array 303 formed on the encoder plate 301.
And the mask slit row 4 formed on the fixed mask plate 401
It is necessary to exactly match the shape and arrangement of 03. However, if the slit row is miniaturized for high resolution, accurate slit processing becomes difficult. Therefore, it is not always possible to obtain the reference signal ZP that coincides with and is synchronized with the period of the displacement signal.

In view of the above-mentioned problems of the prior art, the present invention provides an optical encoder reference position detecting device that can always output a reference signal having a pulse width that exactly matches one cycle of a displacement signal. The purpose is to do.

[0008]

The means employed to achieve the objects of the present invention will be briefly and clearly described with reference to FIG. The reference position detecting device includes a light source 1.
A displacement member 2 that can be displaced so as to cross the optical axis of the light source 1 is mounted. In the illustrated example, the displacement member 2 constitutes a linear encoder plate, but a rotary encoder plate may be used. The displacement member 2 is formed with a pair of reference slits 21 and 22 separated from each other along the displacement direction. In addition to this, a periodic slit array 23 is also formed. The separation distance between the pair of reference slits 21 and 22 is formed at equal intervals for one period of the periodic slit array 23. A fixed light receiving portion 3 is arranged below the displacement member 2. The light receiving unit 3 has a pair of light receiving regions RZ1 and RZ2 divided in the displacement direction, receives the projection light generated when the pair of reference slits 21 and 22 cross the optical axis of the fixed light source 1, and respectively receives the light. A pair of detection signals Z1 and Z2 corresponding to the amount are output.

The pair of detection signals Z1 and Z2 are processed by the processing circuit 4
Processed by. The preceding reference detection signal Z1 output from the preceding light receiving region RZ1 has a stepwise trapezoidal waveform shape. That is, it rises one step as the first reference slit 21 passes, and then further rises as the second reference slit 22 passes. After a predetermined level is maintained while the pair of slits 21 and 22 are passing, when the first reference slit 21 leaves, it falls one step and then the second reference slit 22 leaves to fall to 0 level. The subsequent reference detection signal Z2 output from the light receiving region RZ2 in the subsequent stage also has a similar stepped trapezoidal waveform shape with a predetermined delay. Now, the processing circuit 4 first performs addition processing and discount processing on the pair of detection signals Z1 and Z2 to obtain a reference signal (Z1 + Z).
2) Generate / K. The constant K represents a predetermined discount rate.
Then, based on this reference signal, the individual detection signals Z1 and Z
2 is compared and the falling signal Z1C and the rising signal Z2C are processed.
To form. These falling signals and rising signals are logically ORed to obtain the reference signal Z having a constant pulse width. On the other hand, the displacement signal A consisting of a rectangular pulse train is also obtained by electrically processing the light that has passed through the periodic slit train 23 formed in the displacement member 2. The rectangular pulse width of the reference signal Z exactly corresponds to one cycle of the displacement signal A, and the synchronization is maintained.

Preferably, the processing circuit 4 performs the window processing of the reference signal Z by using the window signal generated by performing the threshold processing of the reference signal (Z1 + Z2) / K based on a constant threshold signal. Including means.
It also includes means for performing a discount process at a constant rate of 1/4 to generate a reference signal. Alternatively, instead of this, means for performing a discount process at a fixed rate of 3/4 to generate a reference signal may be used.

[0011]

According to the present invention, the first reference slit 21 and the second reference slit 21
Since the reference slits 22 have the same shape, they can be formed with high precision by using photolithography and etching without causing a relative error. Further, unlike the prior art, the pair of reference slits 21 and 22 are separated along the displacement direction, so that the amount of transmitted light can be made equal to each other particularly when applied to a rotary encoder. Further, in the processing circuit 4, when the comparison processing of the individual detection signals Z1 and Z2 is performed, a discounted sum signal of the both is used as the reference signal. Therefore, even when the absolute amount of received light changes, there is no change in the relative ratio between the detection signal and the reference signal, and the rising signal and the falling signal can always be formed at a constant timing.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 2 is a schematic perspective view showing an embodiment in which the present invention is applied to a rotary encoder. Light source 1
The rotary encoder plate 2 is arranged at a position close to the upper part of. The light source 1 is composed of, for example, an LED. On the lower side surface of the rotary encoder plate 2, slit rows 23 arranged at a predetermined cycle along the circumferential direction are formed by photolithography and etching. Similarly, a pair of reference slits 21 and 22 are also formed on the inner side in the radial direction. The arrangement relationship of these is the same as that of the linear encoder plate shown in FIG. A light receiving portion 3 is fixedly arranged at a position separated from above the encoder plate 2. This light receiving part 3
Is composed of, for example, a photodiode array. A lens 5 is interposed between the encoder plate 2 and the light receiving section 3. The lens 5 magnifies and projects a primary image of the slit formed by the illumination of the light source 1 and forms a magnified secondary image on the front surface of the light receiving unit 3. Therefore, the secondary image has a similar relationship to the primary image, and moves as the rotary encoder plate 2 rotates.

The present invention is not necessarily limited to an encoder having a magnifying optical system, but can also be applied to a geometrical optical system encoder in which the encoder plate 2 and the light receiving portion 3 are arranged close to each other. Furthermore, the present invention can be applied to a wave optical system encoder that uses a coherent light source instead of an incoherent light source such as an LED and utilizes interference or diffraction of light.

FIG. 3 shows a planar shape of the light receiving portion 3 shown in FIG. On the left side of the light receiving surface, a pair of light receiving regions RZ1 and RZ2 divided in the displacement direction are formed. The pair of light receiving regions are the first and second reference slits 21 and 2 shown in FIG.
It is formed at a position where the second enlarged secondary image 5Z can be received. The magnified secondary image 5Z is the first reference slit 21.
The first peak 51Z and the second reference slit 22 accompanying the passage of the
It includes the second peak 52Z associated with the passage of, and moves in the direction of the arrow shown in the figure.

A pair of comb-shaped light receiving regions RA1 and RA2 are formed on the right side of the light receiving portion 3. This comb-teeth light receiving region is formed so that the peak of the enlarged bright-dark secondary image 50 of the periodic slit array 23 shown in FIG. 2 can be received. In addition,
The peak period of the enlarged bright-dark secondary image 50 matches the interval between the pair of reference peaks 51Z and 52Z described above. One comb-teeth light receiving area RA1 and the other comb-teeth light receiving area RA2 are aligned with each other and have a phase difference of 180 degrees. That is, RA1
When RA2 receives the bright part of the secondary image, RA2 receives the dark part, and when RA1 receives the dark part, RA2 receives the bright part. Therefore, the detection signals output from RA1 and RA2 have opposite phases. Further, another pair of comb-teeth light receiving regions RB1 and RB2 are formed in the central portion of the light receiving portion 3. The comb-teeth receiving area pairs RB1 and RB2 have the same shape arrangement as the comb-teeth receiving area pairs RA1 and RA2 described above, but their phases are deviated by 90 degrees. This phase difference is used to detect the displacement direction of the encoder plate. That is, when the magnified bright / dark secondary image 50 moves upward as shown in the figure, the pair of RA1 and RA2 becomes a phase advance and RB1
And the pair of RB2 are delayed. This relationship is reversed when the magnified bright-dark secondary image 50 moves in the opposite direction.

Next, FIG. 4 shows a pair of light receiving regions RZ1 and RZ.
2 shows an example of a circuit configuration for processing a pair of reference detection signals output from No. 2. The photocurrent output from one of the divided light receiving regions RZ1 is amplified by the corresponding amplifier AMP to obtain the preceding reference detection signal Z1. Further, the photocurrent output from the other divided light receiving region RZ2 is also amplified by the corresponding amplifier AMP to obtain the reference detection signal Z2 in the subsequent line. The pair of reference detection signals Z1 and Z2 are calculated by the arithmetic unit O.
The reference signal (Z1
+ Z2) / 4 is obtained. In this case, the discount processing is 1/4
It will be done at a fixed rate. Leading reference detection signal Z1
Is compared with the reference signal by the corresponding comparator CMP and outputs the falling signal Z1C. Similarly, the subsequent reference detection signal Z2 is also compared with the reference signal by the corresponding comparator CMP, and the rising signal Z2C is output. In addition, the reference signal also has a constant threshold voltage signal Vr by the corresponding comparator CMP.
And the window signal Z0 is output. Finally,
These signals Z1C, Z2C and Z0 are logically ORed by an AND gate circuit AND, and the final reference signal Z is output.

Next, the operation of the reference signal processing circuit shown in FIG. 4 will be described in detail with reference to the waveform chart of FIG. The preceding reference detection signal Z1 rises one step in response to the reception of the first peak 51Z and then further rises in response to the reception of the second peak 52Z. The preceding reference detection signal Z1 maintains a predetermined high level while passing the pair of peaks 51Z and 52Z. When the first peak 51Z has finished passing, it falls one step further, and when the second peak has finished passing, it falls to 0 level. Similarly, the subsequent reference detection signal Z2 also has a two-step rising shape and a two-step falling shape. However, the magnified image 5Z of the reference slit first passes through one divided light receiving region RZ1 and then the other divided light receiving region RZ.
Corresponding to advancing to 2, a predetermined delay time appears.

The reference signal (Z1 + Z2) / 4 is obtained by adding and discounting a pair of detection signals Z1 and Z2 as described above, and is a two-stage rising part, a two-stage falling part and a predetermined value between them. It has a level part. Window signal Z0
Is a reference signal that has been thresholded at a constant voltage level Vr. The constant voltage Vr is set to 3/4 of the maximum voltage of the reference signal, for example. Furthermore, the falling signal Z
Reference numeral 1C is obtained by comparing the preceding standard detection signal Z1 with the reference signal, and falls at the end of passage of the second peak 52Z. Further, the rising signal Z2C is obtained by comparing the reference detection signal Z2 of the subsequent line with the same reference signal, and rises when the first peak 51Z enters the divided light receiving region RZ2 of the subsequent stage. .. Finally, the reference signal Z consisting of rectangular pulses is the falling signals Z1C and Z2.
C is logically processed and windowed with the window signal Z0. That is, the reference signal Z is output only during the high level period of the window signal Z0 to prevent erroneous detection of the reference position. Further, the width of the rectangular pulse of the reference signal Z is always defined because it is accurately defined by the rising signal and the falling signal.

FIG. 6 is a waveform diagram showing the operation of another embodiment of the reference signal processing circuit. In the present example, the reference signal 3 (Z1 + Z2) / 4 is obtained by adding the pair of reference detection signals Z1 and Z2 and then discounting at a constant rate of 3/4. The reference detection signals Z1 and Z2 are respectively compared using this reference signal to obtain corresponding falling signals Z1C and rising signals Z2C. In this case, the subsequent reference detection signal Z
For No. 2, since the comparison processing is performed not in the first rising portion but in the second rising portion, a more accurate rising signal Z2C can be obtained. That is, since the comparison process is performed in a state where it has already risen to some extent, it is possible to eliminate the problem caused by the delay of the response characteristic of the light receiving element described in the conventional example. Finally, by logically processing the falling signal Z1C and the rising signal Z2C, it is possible to obtain the reference signal Z consisting of rectangular pulses.

FIG. 7 shows the four comb-teeth receiving regions RA shown in FIG.
1, a processing circuit for processing displacement detection signals output from RA2, RB1 and RB2 to obtain displacement signals. As shown in the figure, the photocurrent output from the comb-teeth receiving region RA1 is amplified by the corresponding amplifier AMP to obtain the detection signal A1. Similarly, the detection signal A2 is obtained from RA2, the detection signal B1 is obtained from RB1, and R
A detection signal B2 is obtained from B2. The detection signals A1 and A2 having different phases by 180 degrees are subjected to comparison processing by the corresponding comparators CMP to obtain the A-phase displacement signal. Further, the displacement detection signals B1 and B2 which are 180 degrees out of phase with each other are compared with each other by the corresponding comparators CMP to obtain the B-phase displacement signals.

FIG. 8 is a waveform diagram for explaining the operation of the displacement signal processing circuit shown in FIG. The displacement detection signal A1 has a pseudo sine waveform in response to the intermittent light reception of the peak of the enlarged bright-dark secondary image 50. Similarly, the displacement detection signal A2 also has a pseudo sine waveform. However, the phase is 1 for A1
It has been flipped 80 degrees. Further, the displacement detection signals B1 and B2 also have a pseudo sine waveform and their phases are shifted from each other by 180 degrees. Further, when the enlarged bright-dark secondary image 50 moves in the direction of the arrow in FIG. 3, a pair of displacement detection signals A1, A
2 is advanced by 90 degrees compared with the other pair of displacement detection signals B1 and B2. On the contrary, when moving, it becomes a lag.
The phase A displacement signal A consists of a periodic pulse train, A1 and A
It is obtained by comparing 2 with each other. The B-phase displacement signal also consists of a pulse train and is obtained by comparing B1 and B2 with each other. The pulse train of the A-phase displacement signal is 90 degrees advanced in phase compared to the pulse train of the B-phase displacement signal. By detecting this phase relationship, the rotation direction of the rotary encoder plate can be known. Further, the displacement speed of the encoder plate can be known from the pulse train rate, and the displacement amount can be known by counting the number of output pulses. By processing the displacement amount based on the previously detected reference position, the absolute displacement amount of the encoder plate can be measured.

[0022]

As described above, according to the present invention, in order to detect the reference position of the encoder plate, a pair of reference slits which are separated from each other along the displacement direction are provided. The light transmitted through the reference slit is detected by a pair of light receiving regions divided in the displacement direction and subjected to electrical processing to obtain a reference signal. Therefore, the width of the rectangular pulse included in the reference signal can be made constant at all times, and the reference position detection accuracy is significantly improved as compared with the conventional case.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a basic configuration of an optical reference position detection device according to the present invention.

FIG. 2 is a schematic perspective view showing an embodiment in which the present invention is applied to a geometrical optical rotary encoder.

FIG. 3 is a schematic plan view showing a planar shape of a light receiving element array that constitutes a light receiving section.

FIG. 4 is a circuit diagram showing an example of a reference signal processing circuit connected to a light receiving unit.

FIG. 5 is a waveform diagram for explaining the operation of the reference signal processing circuit.

FIG. 6 is a waveform diagram for explaining the operation of another embodiment of the reference signal processing circuit.

FIG. 7 is a circuit diagram showing a configuration example of a displacement signal processing circuit connected to a light receiving section.

FIG. 8 is a waveform diagram for explaining the operation of the displacement signal processing circuit.

FIG. 9 is a schematic diagram for explaining a general principle of reference position detection.

FIG. 10 is a schematic diagram showing an example of a conventional reference position detection method.

FIG. 11 is a schematic diagram showing another example of a conventional reference position detection method.

[Explanation of symbols]

 1 Light Source 2 Displacement Member 21 First Reference Slit 22 Second Reference Slit 23 Periodic Slit Array 3 Light-Receiving Section 4 Processing Circuit RZ1 Split Light-Receiving Area RZ2 Split Light-Receiving Area Z1 Preceding Reference Detection Signal Z2 Subsequent Reference Detection Signal (Z1 + Z2) / K Reference signal Z1C Fall signal Z2C Rise signal Z Reference signal A Displacement signal

Claims (4)

[Claims] 1. A light source, a displacement member in which a pair of slits separated from each other along a displacement direction defined so as to cross the light source are formed at predetermined reference positions, and a pair of light receiving members divided in the displacement direction. A light receiving section for receiving projection light generated when the pair of slits crosses the light source and outputting a pair of detection signals corresponding to the respective received light amounts; and an addition process for the pair of detection signals. An optical system including a processing circuit for comparing the individual detection signals based on the reference signal obtained by performing the discount processing to generate the rising signal and the falling signal, and then performing the logical processing and outputting the reference signal. Reference position detection device. 2. The processing circuit includes means for windowing the reference signal using a window signal generated by thresholding the reference signal based on a constant threshold signal. The optical reference position detecting device described in 1. 3. The optical reference position detecting device according to claim 1, wherein the processing circuit includes means for performing a discount process at a constant rate of 1/4 to generate a reference signal. 4. The optical reference position detecting device according to claim 1, wherein the processing circuit includes means for performing a discount process at a constant rate of 3/4 to generate a reference signal.