JPH03296620A - Linear absolute encoder - Google Patents

Abstract

PURPOSE:To improve the resolution by making an absolute pattern to be a track pattern extending linearly, providing on the line a first and a second groups of areas reversing each other, and obtaining the difference between a first and a second detectors. CONSTITUTION:A code plate 1 is made of a transparent base plate, having many light shielding areas 4a-4h and transmitting areas 5a-5h along a linear direction of the base plate. The areas 4a-4h, 5a-5h are reading areas reversing each other. A linear absolute pattern is thus formed. The absolute pattern is comprised of a first and a second groups of areas A and B. There are four photodetecting elements 2a1-2a4, 2b1-2b4 in the detecting parts 2a, 2b, respectively. When the code plate 1 is moved linearly to eight light sources and eight photodetecting elements 2a1-2a4, 2b1-2b4, signals of different levels are obtained from the elements 2a1-2a4, 2b1-2b4 depending on whether there is the transparent area or shielding area. These signals are output from respective photodetecting elements to a signal processing circuit 3, thereby to obtain the difference.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a linear absolute encoder.

[Conventional technology]

As a conventional absolute encoder of this kind, for example, as shown in "Japanese Patent Application Laid-Open No. 1-152314",
The absolute pattern is formed as one track pattern on the code plate, and a plurality of detectors for reading each reading area of the absolute pattern are arranged in the longitudinal direction of the track. An optical absolute encoder that detects position is known. This encoder is shown as a rotary type encoder, but it goes without saying that a linear type encoder is also applicable.

[Problem to be solved by the invention]

In the absolute encoder of the above publication, it is necessary to read the binary bit 0.1 of the absolute pattern using the detector, but in order to increase the resolution of the encoder, it is necessary to form the absolute pattern of the code plate finely. , the rising edge of the detector output pulse
The falling time becomes a problem, and the readout results of the detection outputs at these rising and falling portions may not be accurate position codes, which may cause errors in the encoder output.

Therefore, it is an object of the present invention to solve this problem and to obtain a linear absolute encoder which is not only an optical type but also a magnetic type, and which prevents errors from occurring in the output of the encoder.

[Means for Solving the Problems] In order to solve the above-mentioned problems, the present invention arranges a large number of two types of mutually inverted reading areas along a straight line direction, and uses the large number of areas to a code plate that forms an absolute pattern and is movable in the linear direction; a detector that is movable relative to the rotary plate in the linear direction of the pattern and reads the area; In the linear absolute encoder, the absolute pattern is one track pattern extending in a linear direction, and includes a first region group in which each of the regions is arranged within a predetermined range on the straight line; a second region group in which each region of the region group and each region inverted are arranged within a range of a different position on a straight line, and one region located in the first region group serves as the detector. of the second region group;
The technical point is that a second detector is provided to read an area that is inverted from the two areas, and a differential circuit is further provided to take the difference between the detection outputs of both the detectors.

[Effect]

According to this invention, the absolute pattern provided on the code plate as one track pattern extending in the linear direction is composed of the first region group and the second region group inverted to each region as described above. The first detector reads one area located in the first area group, and the second detector reads an area in the second area group that is opposite to the - two areas. Therefore, both detectors output synchronized detection signals whose amplitudes change complementary to each other. These two detectors are differentially operated by a differential circuit, and a nearly rectangular waveform signal with sharp rises and falls is obtained at the output end of the differential circuit. For this purpose, the output signal of the differential circuit is shaped by a comparator or the like, and an accurate rectangular wave signal can be obtained as the encoder output.

〔Example〕

Embodiments of the present invention will be described based on the drawings.

FIG. 1 is a block diagram of a linear absolute encoder according to an embodiment of the present invention, and shows an optical embodiment.

In the figure, this absolute encoder includes a code plate (scale) 1, and first and second detection units 2a for reading absolute signals recorded on the code plate 1.
, 2b, and a signal processing circuit 3 which receives each detection output from both detectors 2a and 2b. The signal processing circuit 3 is used to process the differential detection outputs from the two detectors ia and 2b and convert them into 4-bit parallel data representing absolute position.

The code plate 1 is made of a transparent substrate, and on its surface there are two types of
A large number of light-shielding areas 4a to 4h and transparent areas 5a to 5h made of vapor-deposited metal or the like are arranged along the longitudinal direction of the substrate (value line direction) as respective reading areas that are inverted with respect to each other. A linear absolute pattern is formed by the light blocking and transmitting regions.

As shown in the diagram, this absolute pattern is
It consists of a first area group A consisting of 6 bits and a second area group B consisting of 16 bits on the right side, and the first area group A is arranged in order from left to right in the figure. , a light-shielding region 4a consisting of four "0" bits, a transmitting region 5a consisting of a single "1" bit, a light-shielding region 4b consisting of a single "0" bit, and two "1" bits. Transparent area 5b
, a light-shielding region 4c consisting of two "0" bits, a transmitting region 5c consisting of four "l" bits, and a single "0" bit.
It has a light blocking area 4d consisting of bits and a transparent area 5d consisting of a single "l" bit, and the absolute code of this area group A is rooQOlolloolllo
l".

Further, the second region group B includes four rl regions in order from the right in the figure.
A transmission region 5e consisting of j bits, a light-shielding region 4e consisting of a single rQJ bit, a transmission region 5f consisting of a single "lJ" bit, a light-shielding region 4f consisting of two "0" bits, and two " a transparent region 5g consisting of 1” bit;
A light-shielding area 4g consisting of four “0” bits and a single “0” bit
Transmissive regions 5h consisting of a single "1" bit and light shielding regions 4h consisting of a single "0" bit are arranged, and in relation to each region of the first region group A, the right transmissive region 5e is arranged on the left. The right light shielding region 4e is also reversed to the left light transmitting region 5a, and the transmitting region 5f is also reversed to the left light shielding region 4b, and each region of the region groups A and B is as follows. Since the absolute code of the second area group B is inverted from that of the first area group A, it becomes ``rlllllOlooollooooolo'' because the absolute code is inverted from the left to the right in the figure.

On the left side 2a of the rain detection sections 2a and 2b, there is a 4-piece array constituting an array of light-receiving elements as an absolute signal detector.
Similarly, the right detection section 2b is also provided with four light receiving elements 2b+ to 2b4.

These light-receiving elements are actually arranged below the transparent substrate 1 (below the plane of the paper), and the light-receiving elements 2a+ and 2b+ in the figure are arranged as a pair, and 2
For example, -
When one of the two light-receiving elements of a set faces the transmission area, the light-receiving elements of the set are reversed so that the other light-receiving element of the set faces the light-blocking area.

Above the plane of the paper, eight light sources (not shown) are arranged, which face each of the light receiving elements via each region of the substrate 1.

With the above structure, the code plate 1 for eight light sources and eight light receiving elements 2a+~2a4.2tl~2b<
When moving in the longitudinal direction (linear direction), the light receiving elements 2 a+ to 2 a4s 2 bs to 2 b4 will have different light depending on whether there is an absolute pattern transmitting area or a light blocking area between the corresponding light source. Signals with different levels are obtained, and these signals are output to the signal processing circuit 3 by the respective light receiving and receiving elements.

The internal structure of the signal processing circuit 3 is shown in FIG. 2, and the light receiving elements 2a+ and 2b+ in FIG. 1 are the operational amplifier $ in FIG.
It is connected to the respective inverting input terminals of a and 9b. The same applies to each set of light receiving elements 2a2 and 2bt, 2as and 2bs, and 2a4 and 2b4 in FIG. 1, so only the set of light receiving elements 2a+ and 2b+ will be described here.

Since the regions of the light receiving elements 2a+ and 2bt facing the light receiving elements are reversed, the detection outputs obtained are complementary. As the code plate 1 shown in FIG. 1 moves in the linear direction, the detection signal of the light receiving element 2a+ is as shown in FIG.
) is as follows. These detection signals are amplified by the respective operational amplifiers $a and Jb in FIG. 2, and a signal as shown in FIG. 3(e) appears at the output terminal of one operational amplifier 6a, and The output terminal of the operational amplifier 6b has a third
A signal as shown in figure (d) appears. When the signals appearing at both output terminals are input to the differential amplifier 7 in Fig. 2 and differentially amplified, the output terminal of the differential amplifier produces a substantially rectangular waveform signal as shown in Fig. 3(e). can get. Since the pulse rise and fall of this signal have a certain steepness regardless of the pulse width, this signal is converted into a rectangular wave at a certain comparison level by the comparator 8, and the signal is outputted from the signal processing circuit 3. A rectangular wave signal as shown in Fig. 3 is obtained at the terminal 9a. Similarly, the set of light receiving elements 2az and 2b, the set of 2aa and 2baO, and the set of 2a4 in FIG.
A rectangular wave signal based on the detection signal from each of the sets 2b+ and 2b+ is also obtained at the respective output terminals 9b, 9c, and 9d in FIG. 4-digit 2 with different combinations of "0.1"
It is possible to get a forward code signal.

The rectangular wave signals appearing at the output terminals 9a to 9d of the signal processing circuit 3 due to the detection signals from each of the four sets of light receiving elements are illustrated in FIG. 4 in correspondence with FIG. 1. In this case, the code plate 1 is connected to the first
It is assumed that the object is moving to the left in the figure. In this example, four sets of light receiving elements Eat 2b+, 2a22bz
, 2as 2bi and 2a42b+, the absolute pattern arrangement (absolute code function) on track 2 is arranged so that code signals of the same combination of "0, l" are not generated from the output terminals 9a to 9d.
and the code is ``rllllolooloolloooolo''.

Therefore, the output terminal 9a is r2''j, 9b is "21", 9
By assigning C to r22J and 9d to "28J, a 4-bit absolute signal with different contents for relative movement of each bit is obtained. In Figure 4, the child hole number corresponding to each absolute signal is appended at the bottom. As you can see, if the rectangular wave signal in Fig. 4 is digitized as it is, it will be a numeric value of 16, which is also the code plate 1.
When shifted to a 16-bit displacement, the values are not the same at any one location, which indicates that an absolute encoder is configured.

Although the above is an optical embodiment, it is not limited to this, and a magnetic embodiment can also be applied, so the magnetic embodiment will be explained with reference to FIGS. 5 to 7.

5th r! gJ is a schematic configuration diagram of a linear absolute encoder showing a magnetic type embodiment. In FIG. 5, an absolute pattern is formed as one track in the longitudinal direction of the longitudinal code plate 11, and this absolute pattern is similar to the optical embodiment described above. It consists of a first area group A consisting of 16 bits on the left side and a second area group B consisting of 16 bits on the right side.

In the first region group A, from the left to the right in the figure, there are magnetized bits 12a consisting of four rlJ bits,
an unmagnetized bit 13a consisting of a single rOJ bit;
A magnetized bit 12b consisting of a single "1" bit, an unmagnetized bit 13b consisting of two "0" bits, a magnetized bit 12C consisting of two "1" bits, and four "0" bits.
" unmagnetized bit 13C consisting of a single "1" bit
A magnetized bit 12d consisting of bits and an unmagnetized bit 13d consisting of a single "0" bit are arranged, and the absolute code of this area group A is rllllolooloollooooloJ.

Further, in the second region group B, toward the right in the figure, there are an unmagnetized bit 13e consisting of four "0" bits, a magnetized bit 12e consisting of a single "1" bit, and a magnetized bit 12e consisting of a single "1" bit. One “0”
” bit, and two “l” bits.
A magnetized bit 12f consisting of a bit, an unmagnetized bit 13g consisting of two "0" bits, a magnetized bit 12g consisting of four "1" bits, and an unmagnetized bit 13h consisting of a single rlJ bit. and magnetized bits 12h consisting of a single "0" bit are arranged in sequence, and in relation to the magnetized bits and non-magnetized bits of the first region group A, the non-magnetized bits on the right Magnetic bit) 13e is the left magnetized bit 12a
Similarly, the right magnetized bit 12e is also reversed to the left unmagnetized bit 13a, and the right unmagnetized bit 13f is also reversed to the left magnetized bit 12b. Since the unmagnetized and magnetized bits of each area group ASB are inverted from the left to the right in the figure, the absolute code of the second area group B is the same as that of the first area group A described above. Inverted to the above code, it becomes "rOooololloolllol".

Each of the magnetized bits 12a to 12h has (2n+1) magnetized sections (S . , the length of the intermediate magnetized section sandwiched between them in the track longitudinal direction is substantially equal to λ/2. For example, the magnetized bit 12a on the left side of the figure has four bits (n
= 4), so there are a total of 9 magnetized sections (NSMSN
SNSN) are arranged in a row, and the two magnetized sections (N, N) at the starting end and the ending end each have a length of λ/4 in the longitudinal direction of the track,
In addition, the middle seven magnetized sections (SNSSNS) are each λ
/2.

The detection unit 14 in the figure is actually disposed below the code plate 11 along the lower side of the page so as to be movable relative to the code plate 11. Each set of MR element sensors 15a to 18a and ISb to tab are provided. These sensors correspond to the light receiving elements 2a+ to 2a and 2b+ to 2b in FIG. 1, respectively, and the MR
The element sensors ISa and ISb are used as a pair, and
6a and 16b, 17a and 17b, and 1Ba and 18b each form a pair, and one of the two sensors of the pair is set, for example, so that the respective bits facing the pixel sensor of each pair are inverted with respect to each other. Each sensor is positioned so that when facing the magnetized bit, the other sensor is reversed and faces the magnetized bit.

In each set of left and right sensors, the arrangement interval between the respective MR element sensors may be λ or an integral multiple thereof, and in FIG. 5, this interval is set to exactly λ. Regarding the respective MR element sensors, the connection configuration of the left MR element sensor 15a and the right sensor 15b is shown as shown in the figure. Although abbreviated in the same figure, other MR element sensors IEia and 16b, 17a and 1ab, and lea
and 18b are also configured in the same manner as the connection of the element sensors 15a and 15b described above, and here, for convenience,
The configuration of the connection between the element sensor 15a and ISb will be explained.

The left MR element sensor ISa is λ in the longitudinal direction of the track.
Two fine parallel MR elements 15a spaced apart by /4
The right sensor 15b also consists of two fine parallel MR elements ISb+, 15b spaced apart by λ/4 in the longitudinal direction of the track. As shown in the figure, power terminals 19 and 20 are provided through contacts (black dots) between the connections between the MR elements 15a and 15b2, and between the connections between the MR elements 15a and 15b1, respectively. Between the connections between the MR elements 15a and 15b1 and between the connections between the MR elements 15a and 15b,
Output terminals 1 and 22 are provided through the contacts (black dots), respectively, and the power supply terminals are connected so that the direction of current is opposite to each other due to the connection bias between MR elements 15a1 and 15b2 and MR elements 15a and 15bl. , 20 to form a bridge circuit, and a detection output is generated between the output terminals 1 and 22.

When a horizontal magnetic field is applied to an MR element, its own electrical resistance value decreases in accordance with the strength of the magnetic field, regardless of the polarity of the magnetic field.

Therefore, due to the relative movement between the detection unit 14 and the code plate 11,
The signal appearing at the output terminal 4.22 of said sensor is as follows.

As the code plate 11 moves leftward as shown in the figure, when the magnetized bit of the code plate 11 is applied to the MR element 15a1, a magnetic field is generated in the MR element 15a1, and the right M
The R element 15b1 loses the magnetic field due to the unmagnetized bit, and the potential of the output terminal 1 rises, and the MR elements 15a,
When a magnetic field is generated at the other MR element 15b, the magnetic field disappears at the other MR element 15b, and the potential at the output terminal 22 decreases.

Furthermore, when an unmagnetized bit comes to the MR element 15a from the end of the magnetized bit, the magnetic field disappears in that element 15a, and a magnetic field is generated by the magnetized bit in the other MR element ISb+, so that the potential of the output terminal 4 decreases, and MR element 1
5a, when the magnetic field also disappears, the other MR element 15b2
A magnetic field is generated and the potential of the output terminal 22 increases.

In addition, since the distance between the pair of MR elements for both sensors ISa and ISb is λ/4 as described above, the amplitude waveforms at output terminals 1 and n are exactly vertically symmetrical, and the phase shift between the two outputs is λ360. When expressed in degrees, the phase difference is 90 degrees.

One output terminal 1 of the set of MR elements 15a and 15b is connected to the input terminal 23 of the signal processing circuit shown in FIG. 6, and the other output terminal 22 is connected to the input terminal. FIG. 6 shows an example of a signal processing circuit for processing the detection output of the detection section 14, in which the MR element 15a
Although the set of MR elements 15a and 15b is illustrated, the same applies to other sets of MR elements in FIG. 5, so only the set of MR elements 15a and ISb will be described here.

The magnetic field pattern located at the left MR element sensor 15a in FIG. 5 is as shown in FIG. 7(a), and the magnetic field pattern located at the other MR element sensor 15b is as shown in FIG. As shown in b).

When this is relatively scanned by the sensors ISa and 15b, each consisting of two MR elements spaced apart by λ/4, a pulsating current pulse-like signal as shown in FIG. 7(C) appears at the output terminal 1. , a complementary pulsating current pulse-like signal as shown in FIG. 7(d) appears at the other output terminal 22. The signals appearing at both output terminals 1 and 22 are sent to the differential amplifier 2 in Fig. 6.
5 and differentially amplified, a substantially rectangular waveform signal as shown in FIG. 7(e) is obtained at the output terminal 26 of the differential amplifier 25. The pulse rise and fall of this signal are constant and steep regardless of the pulse width. When this signal is converted into a rectangular waveform at a constant comparison level by the comparator 27 in FIG. 7, a rectangular wave signal as shown in FIG. 7(f) is obtained at the output terminal 28a of the signal processing circuit.

Other MR elements IGa and IGb, 1a and 1 shown in FIG.
Each set of 7b and 18a and 18b is also subjected to signal processing in the same manner as described above, and each output terminal 2nd a to 28d in FIG.
It goes without saying that it is possible to obtain four-digit binary code signals with different combinations of .

〔Effect of the invention〕

According to the present invention, in both the optical type and magnetic type embodiments, the absolute pattern provided on the code plate is one track pattern extending in a linear direction that covers the first area group and each of the first area groups. the first detector reads one area located in the first area group, and the second detector reads one area located in the first area group; In order to read the region inverted from the above-mentioned two regions, both detectors output synchronized detection signals whose amplitudes change complementary to each other. These two detectors are differentially connected by a differential circuit, and the output terminal of the differential circuit receives a signal with sharp rises and falls with an S/N ratio that is approximately twice that of the detection signal of each individual detector. A substantially rectangular wave signal is obtained, and this signal is shaped by a comparator or the like to obtain an accurate rectangular wave signal as the encoder output.

Therefore, a high-resolution absolute encoder with no error in output can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a schematic top view of a linear absolute encoder according to an embodiment (optical type) of the present invention. FIG. 2 is a circuit diagram showing the internal configuration of the signal processing circuit in FIG. 1. 3(a) to 3(f) are diagrams showing the photoelectric signals transmitted through the transparent area of the absolute pattern formed on the code plate 1 in FIG. 1 and the waveforms of each part of the signal processing circuit. It is. FIG. 4 is a diagram showing the final output waveform of the absolute pattern according to the embodiment shown in the first figure. FIG. 5 is a schematic top view showing the configuration of a linear absolute encoder according to another embodiment (magnetic type) of the present invention. FIG. 6 is a circuit diagram showing an example of a signal processing circuit for processing the detection output of the MR element sensor in FIG. FIGS. 7(a) to 7(g) are diagrams showing magnetic field patterns caused by the magnetized bits of the absolute pattern formed on the code plate shown in FIG. 5 and waveforms of various parts of the signal processing circuit. [Explanation of symbols of main parts] 1.11-.--1--code plates 2a, 2b, 14--.---1 detection section 2 a+~
2 a4.2 b 1 to 2 b 4-'------Light receiving element 3----- Signal processing circuit 4a to 4h...------ Light shielding area 5a to 5h
...-----Transparent areas 12a to 12h...
・-----Magnetized bits 13a to 13h-----
・Unmagnetized bit 15a to 1st a115b to 1st b --
--MR element sensor applicant Takao Watanabe, representative of Nikon Co., Ltd. Figure 5 Figure 7

Claims (1)

[Scope of Claims] A large number of two types of mutually inverted reading areas are arranged along a linear direction, a linear absolute pattern is formed by the large number of areas, and the reading area is movable in the linear direction. In the linear absolute encoder, the absolute pattern includes: a code plate provided; and a detector provided movably relative to the code plate in a linear direction of the pattern and for reading the area; A first region group in which each of the regions is arranged within a predetermined range on the straight line as one track pattern extending in a linear direction, and each region in the region group is arranged within a range of another position on the straight line. and a second region group in which inverted regions are arranged, and the detector is a first detector that reads one region located in the first region group, and a second region group in which the second region group is arranged. ,
A linear absolute encoder comprising: a second detector that reads an area that is inverted from the one area; and a differential circuit that takes a difference between detection outputs of both the detectors.