JP6732487B2 - Encoder having linear scale and origin determination method thereof - Google Patents

Description

The present invention relates to an encoder having an optical scale and a method for determining the origin thereof, and more particularly to an encoder having a linear scale and a method for determining the origin thereof, which is suitable when the optical scale is linear or arcuate.

In order to measure the shape such as the length, thickness, inner and outer diameter of the object to be measured and the displacement amount such as rotation angle or movement amount with high accuracy, the optical scale and the reading/moving device that is movable relative to this optical scale. An optical encoder with a head is used. There are two types of optical encoders: a transmissive type that detects transmitted light that has passed through the optical scale and a reflective type that detects reflected light that is reflected by the optical scale. It is used.

The optical encoder reads a pattern in which reflective portions and transmissive portions are alternately formed on the optical scale, and measures the relative movement amount of the optical scale and the reading head. At that time, in the incremental optical encoder, only the relative displacement of the optical scale is measured, and the absolute position is not measured. On the other hand, if an event such as a shock, dirt on the optical scale, or stop of the power supply occurs in a device having an optical encoder, there is a risk of erroneous measurement at that time. When such an event occurs, the encoder having the origin can start the remeasurement by the origin return operation. However, when the encoder does not have an origin, the entire device has to be reset, and it is desired that the origin can be determined by adding a simple device even in an incremental optical encoder. ..

In Patent Document 1, two optical scales are used to enable highly accurate origin detection with a simple arithmetic circuit. Therefore, in the first optical scale, the transmissive portion and the reflective portion are regularly arranged. Then, the second optical scale is provided close to the first scale, and the arrangement of a part of the transmissive portion and the reflective portion of the second optical scale breaks the regularity. Also, the first and second light receiving sensors for detecting the reflected light of the first and second scales are arranged corresponding to the respective scales, and the first light receiving sensor for detecting the first optical scale is used to detect the optical scale. The second light receiving sensor that detects the movement amount and the second optical scale detects the position where the regularity is broken as the origin.

Further, in Patent Document 2, in an optical encoder, an origin track including an origin measurement slit is formed on a scale fixed to a measurement target so that an accurate origin signal can be obtained. Then, the spot of the beam emitted from the light source is extended to the direction perpendicular to the moving direction of the scale on the origin track to enable irradiation to the origin detection slit, and the light receiving element that detects the moving direction of the scale is the origin. The light transmitted through the measuring slit is also collected.

Further, in Patent Document 3, the encoder emits light emitted from the light emitting unit in order to obtain an encoder that has a small dependence on the operation direction and can stably perform origin detection in synchronization with the A-phase or B-phase signal. The detector is provided with a detector for projecting on the scale and detecting the diffraction pattern of the reflected light, and a signal processing circuit for processing the signal of the detector as an encoder signal. Then, a solid pattern consisting of two regions, a light reflection region and a light transmission region, is used for the Z phase scale forming the Z phase signal for detecting the origin position, and the Z phase of the pulse signal which is detected and digitized. The signal is obtained, and the displacement of the object is detected from the relative movement amount between the Z-phase signal and the scale.

JP, 2005-161595, A JP, 2007-127539, A JP2012-103230A

In each of the above-mentioned Patent Documents 1 to 3, in the incremental optical encoder, by providing the origin determining means in addition to the displacement amount measuring means, accurate measurement can be repeated. In particular, in Patent Document 1, two substantially similar optical scales are arranged side by side, and the transmissive portion and the reflective portion of one optical scale only partially break the regular arrangement. There is no need to use a special method in the fabrication or the fabrication of the light-receiving sensor, and it is only necessary to add a simple arithmetic circuit to the general circuit used to detect the amount of movement, and it is possible to detect the origin with high accuracy. have.

However, although it is remarkable when it is used for measurement and processing of a minute portion or the like, the encoder is also required to be downsized in accordance with the demand for downsizing of the measuring instrument and the entire processing portion. For example, in a linear encoder used for a micro processing sensor, the size of the sensor portion is required to be a size corresponding to the pushing amount of the processing spindle. Therefore, arranging the two scales in parallel, that is, the optical scale for measuring the amount of movement or displacement and the optical scale for detecting the origin, causes an increase in the size of the optical scale portion, and improvement is required.

In the optical encoder described in Patent Document 2, since the Z-phase slit is provided in parallel with the distance measuring scale, the scale width is almost doubled even if the scale lengths are the same. There is. As a result, the area occupied by the scale as a whole is increased, which leads to an increase in the scale. Further, it is necessary to spread the beam from the light source to the Z-phase slit, which may increase the size of the lens system. Further, also in Patent Document 3, since a Z-phase detecting scale is provided in addition to the A-phase and B-phase detecting scales, there is a possibility that the scale is enlarged and the space for the light-receiving sensor is increased accordingly. There is.

The present invention has been made in view of the above-mentioned problems of the prior art, and an object thereof is to increase the size of the optical scale in the incremental type optical linear encoder by simply adding a simple configuration. The point is to be able to determine the origin. In addition to the above, it is another object of the present invention to realize an optical encoder capable of making the speed characteristics of the leading head for length measurement and the origin determination the same when an arc type optical scale is used.

The features of the present invention for achieving the above-mentioned object are a linear scale in which a large number of patterns of pairs of transmissive portions and reflective portions are regularly arranged, a light source that emits light to the linear scale, and A linear sensor having a light receiving sensor that detects either transmitted light or reflected light of the emitted light, and a reading head that moves relative to the linear scale in the pattern arrangement direction of the linear scale. In the incremental encoder having a scale, a cycle changing portion having a width of the transmissive portion or the reflective portion different from other portions is provided near an end of the linear scale, and the reading head is substantially Has two identical light receiving sensors, and these two light receiving sensors are arranged side by side in the pattern arrangement direction of the linear scale.

Further, in this feature, it is preferable that one of the two light receiving sensors is provided with a stopper that restricts movement of the linear scale or the one light receiving sensor so as not to detect the period changing portion. Is formed in an arc shape, and one light receiving sensor that cannot detect the cycle changing portion and the other light receiving sensor that can detect the cycle changing portion are arranged on the same arc at the pattern arrangement position. May be.

Further, in the above-mentioned feature, each of the two light receiving sensors may be formed by combining only one set of photodiodes for detecting A phase, B phase, A ⁻ phase, and B ⁻ phase. Of course, the linear scale may be provided on the moving side in the absolute space, and the reading head may be provided on the fixed side in the absolute space. Here, "to the moving side in the absolute space" means to the side that actually moves, not to the relative, and "to the fixed side in the absolute space" means to the fixed side that does not actually move. Is the meaning.

Another feature of the present invention that achieves the above object is that a linear scale in which a large number of pairs of patterns of a transmissive portion and a reflective portion are regularly arranged is emitted from a light source, and transmitted light or reflection of light emitted from the light source is performed. An encoder having a linear scale in which one of the lights is detected by a reading head having a light receiving sensor that moves relative to the linear scale, and the origin of the linear scale is determined based on the output of the light receiving sensor. In the method of determining the origin, the light receiving sensor is two substantially the same light receiving sensors that are arranged side by side in the pattern arrangement direction, and the light transmitting section or the light transmitting section that is provided near an end of the linear scale is used. The width of the reflecting portion does not exceed the period changing portion having a width different from that of the other portion, and the one light receiving sensor that cannot detect the period changing portion and the period changing portion can be moved to move the period changing portion. It is the other light-receiving sensor that can be detected, and the difference between the outputs of these two light-receiving sensors is compared with a predetermined threshold value to be the origin of the linear scale.

Further, in this feature, when the count number in which the output difference of the two light receiving sensors exceeds a predetermined threshold value has passed a predetermined count, the other light receiving sensor traced back by a predetermined count after the predetermined count has elapsed is detected. The position is preferably the origin, and the width of the transmissive part or the reflective part forming the period changing part is preferably about 1.3 to 1.5 times the width of the other pattern.

According to the present invention, in the incremental type optical linear encoder, a reflective portion or a transmissive portion having a different interval is provided in a part of the linear scale, the linear scale is opposed to the linear scale, and the linear scale is opposed to the linear scale. Since a substantially identical light receiving sensor that can be moved, is used for distance measurement and origin determination respectively, a simple configuration can be achieved without increasing the optical scale of the optical linear encoder. The origin can be determined simply by adding it. Even if the optical scale is an arc-shaped optical scale, the speed characteristics of the reading head for length measurement and the origin determination can be made the same.

It is a schematic diagram of one Example of the optical encoder which concerns on this invention, (a) is a front view, (b) is a top view. It is a figure explaining the operation range of the optical encoder shown in FIG. It is a figure explaining the structure of a light receiving sensor. It is a figure explaining the relationship between a light receiving sensor and a linear scale, (a) shows a ranging position, (b) shows a shift boundary position. It is a figure explaining the gain of a light receiving sensor. It is a graph explaining the principle of origin detection. It is a simulation result of origin detection. It is a schematic diagram which shows the example of an arc-shaped scale. It is a figure explaining setting of an origin position.

Several embodiments of the optical linear encoder according to the present invention will be described with reference to the drawings. In the following description, not only a linear optical scale but also an arc-shaped optical scale excluding infinite rotation is referred to as a linear encoder. Further, in the following description, the case where the optical scale moves is described, but the same applies when the optical scale stands still and the reading head moves. That is, it suffices if the optical scale and the reading head can move relative to each other.

1A and 1B are diagrams showing a main part of an optical linear encoder 100 according to the present invention. FIG. 1A is a front view thereof, and FIG. 1B is a top view thereof. In the longitudinal direction of the scale substrate 1 made of transparent glass or the like, a reflection pattern 2 is repeatedly formed regularly at a pitch p2 by a pair of a reflection portion 2a and a transmission portion 2b that reflects light for a predetermined length. There is. The reflection pattern 2 formed on the scale substrate 1 has a period changing portion 2c in a part thereof, as will be described later in detail. The sensor substrate 10 is disposed on the scale substrate 1, and the two reading heads 41a and 41b are disposed on the same axis on the lower surface of the sensor substrate 10 in close proximity or at intervals. Has been done. It should be noted that in order to facilitate understanding, the leading heads 41a and 41b are indicated by alternate long and short dash lines in FIG.

As described above, in the present embodiment, the reading heads 41a and 41b are stationary while the linear encoder 100 is in use, and the scale substrate 1 reciprocates in the direction indicated by the arrow 51 in FIG. Therefore, the two reading heads 41a and 41b are provided on the same axis in the moving direction 51 of the scale substrate 1. The reading heads 41a and 41b have exactly the same specifications and have LED light sources 11a and 11b and light receiving portions 14a and 14b, respectively. For miniaturization, light sources may be independently provided, and the leading heads 41a and 41b may have only the light receiving portions 14a and 14b.

FIG. 2 is a schematic top view showing a specific example of an apparatus using the optical linear encoder 100 having the relationship of FIG. This is the case of the length measuring device 80, and the portion of the linear encoder 100 is formed in an arc shape. The scale substrate 1 is formed in an arc shape, and the reflection pattern 2 is formed in the vicinity of the outer periphery thereof so as to be perpendicular to the arc. A cycle changing portion 2c having a different cycle of the reflection pattern 2 is formed at one end of the repeated reflection pattern 2, that is, in the vicinity of the right end in the figure. The period changing unit 2c is also called an origin scale shift point or shift boundary. At the center of the arc-shaped scale substrate 1, there is a scale rotation shaft 22a extending in the radial direction inside the arc, and a rotation center 21 is provided at the middle of the scale rotation shaft 22a in the longitudinal direction. A probe shaft 22b is provided at the other end of the scale rotation shaft 22a, and the probe 22 is attached to the tip of the probe shaft 22b.

Stoppers 17a and 17b are provided on both sides of the scale rotation shaft 22a and between the rotation center 21 and the scale substrate 1. Corresponding to the stoppers 17a and 17b, a stopper (not shown) is provided in a casing (not shown). The attached stoppers 18a and 18b are arranged. On the other hand, the casing is also provided with reading heads 41a and 41b, which are located on an arc formed by the reflection pattern 2 on the scale substrate 1. In FIG. 2, the leading heads 41a and 41b are arranged near the line perpendicular to the midpoint of the line connecting the stoppers 18a and 18b.

In the length measuring device 80 configured as described above, the detection position of the scale substrate 1 and the relative positions of the leading heads 41a and 41b change as the probe 22 moves. That is, when the probe 22 is pushed in the most, the scale substrate 1 rotates (1a) around the rotation center 21, and the stopper 17b of the scale substrate 1 contacts the stopper 18b on the housing side. At that time, the two reading heads 41 a and 41 b detect the reflection pattern 2 near the left end of the scale substrate 1.

On the other hand, when the pushing amount of the probe 22 is the smallest, the scale substrate 1 rotates about the rotation center 21 in the opposite direction (1b), and the stopper 17a of the scale substrate 1 moves toward the housing side stopper 18a. Abut. In this state, the two reading heads 41a and 41b detect the reflection pattern 2 near the right end of the scale substrate 1. However, the right reading head 41b detects the cycle changing portion 2c during the movement of the scale substrate 1, but the left reading head 41a cannot reach the cycle changing portion 2c. As a result, the left leading head 41a can be used for distance measurement (movement distance measurement) and the right leading head 41b can be used for origin measurement. The details will be described below together with the principle.

FIG. 3 shows an example of the configuration of the light receiving units 14a and 14b. As shown in the drawing, four sensor parts PS1 to PS4 having the same width are formed at the sensor part pitch sp in the array axis direction of the reflection pattern 2, and these four sensor parts PS1 to PS4 are set as one set and a plurality of sets are formed. The light receiving portions 14a and 14b are arranged in an array. In this embodiment, there are 13 sets of sensor unit groups Gr, and a total of 52 sensor units are provided. The sensor units PS1 to PS4 are formed of, for example, photodiodes and operate as independent light receiving elements. The 13 sensor sets PS1 to PS4 have the same sensor parts, for example, the outputs of PS1 connected in common. To the A-phase signal obtained by connecting the PS1 each other, it is obtained by connecting to each other PS2, the different B-phase signals 90 ° phase with the A-phase, obtained by connecting the PS3 to each other in opposite phase to the A phase A ^- A signal in which PS4s are connected to each other is output as a B ^- phase signal which is a reverse phase of the B phase.

Here, the light from the light sources 11a and 11b is reflected by the reflecting portion 2a and is incident on the light receiving portions 14a and 14b. As described above, each light receiving portion 14a and 14b includes the set of 13 sensor units PS1 to PS4. Since the width of each sensor unit PS1 to PS4 is 10 μm, L ₀ =13×40=520 μm is required. The length of the sensor unit PS1 is disclosed in the applicant's prior application (Japanese Patent Application Laid-Open No. 2015-161595).

FIG. 4 is a front view showing the relationship between the light receiving portions 14a and 14b and the scale substrate 1. The figure (a) shows the relationship in the distance measuring range, and the figure (b) shows the relationship at the position including the cycle changing portion 2c. The start position of the cycle changing unit 2c is referred to as a shift boundary 2d. In the distance measuring range, the reflection patterns 2 of the reflecting portion 2a and the transmitting portion 2b are regular, so that the sensor portions PS1 (PS2, PS3, PS4) of the same phase of each of the groups Gr1 to Gr13 forming the light receiving portions 14a and 14b are provided. Output is almost the same. On the other hand, at the position including the cycle changing unit 2c, an output difference occurs even in the in-phase sensor units among the sensor units of the 13 sets Gr1 to Gr13.

This state is shown in FIG. The vertical axis of FIG. 5 is the normalized output of each phase detected by the light receiving units 14a and 14b, for example, the A phase, and the horizontal axis represents the movement distance X of the scale substrate 1. As shown by the solid line in FIG. 5, the output signals of each phase (A phase, B phase, A ⁻ phase, B ⁻ phase) are as long as the reflection pattern 2 of the scale substrate 1 detects a regular range. It is a sinusoidal signal having a cycle of 20 μm, and although not shown in the figure, the phases are 90° out of phase with each other. However, when the shift boundary 2d of the scale substrate 1 passes through the leading head 41b, as shown by the broken line in the drawing, the cycle of 20 μm slightly increases as the output decreases. The change in the cycle and the output is restored when the shift boundary 2d of the scale substrate 1 completely exceeds the reading head 41b.

Since the two reading heads 41a and 41b are substantially the same, as long as the reading heads 41a and 41b detect the distance measuring range in which the reflection pattern 2 is regularly arranged on the scale substrate 1, The count number of the reflection pattern 2 between the two reading heads 41a and 41b based on the detection signal of FIG. 5 does not change and should be the same as the initial state. On the other hand, if one of the leading heads 41a detects the distance measuring range on the scale substrate 1 and the other of the leading heads 41b detects the cycle changing portion 2c on the scale substrate 1, the sensor units PS1 to PS4. The output and the cycle change. This cycle change disappears when the cycle changing unit 2c completely moves out of the detection range of the reading head 41b, so that there is no change in the cycle of the two reading heads 41a and 41b in the subsequent detection.

This state is schematically shown in FIG. Assuming that the two reading heads 41a and 41b are both within the distance measuring range, consider a case where the scale substrate 1 starts to move so that the cycle changing unit 2c approaches the reading head. The light receiving portions 14a and 14b of each reading head start counting based on the reflection pattern 2 formed on the scale substrate 1. In FIG. 6, the difference Δ in the number of counts detected by the two light receiving units 14a and 14b is shown based on the difference at the start of movement of the scale substrate 1. Therefore, Δ at the start of movement is Δ=0. is there. The horizontal axis represents the moving distance X of the scale substrate 1. In FIG. 6, it is described that the count number changes only when the cycle changing unit 2c passes the one reading head 41b, but in reality, the light receiving unit is composed of 13×4 sensor units PS1 to PS4. Therefore, the longer time count number changes and then becomes constant.

Therefore, by setting the changing position of the reflection pattern 2 on the scale substrate 1, that is, the shift boundary 2d as the origin from the change of the count number, even in the incremental encoder, the track for exclusive use of the origin detection is not provided. The origin can be easily detected with just the track. At that time, it is sufficient to use two substantially the same reading heads 41a and 41b, and to provide the pattern 2 having the cycle changing portions 2c with different cycles on a part of the scale substrate 1 to increase the size of the apparatus. It is possible to detect and detect the origin with a simple structure.

Further, the two substantially the same reading heads 41a and 41b, more precisely the two substantially same light receiving portions 14a and 14b need to be coaxial with the moving direction of the scale substrate 1, but as described above. In addition, the reflection pattern 2 formed on the scale substrate 1 does not necessarily have to be in phase with each other, and although two pieces are arranged, the number of steps for assembling the leading heads 41a and 41b and the light receiving portions 14a and 14b is reduced. Can be avoided.

FIG. 7 shows the simulation result of the distance measuring system using the optical linear encoder having the above configuration. The encoder has a pattern pitch of 20 μm and an interpolation bit number of 4096. The width of the cycle changing portion 2c is 14 μm, and the pattern pitch p2m is 24 μm. The leading head 41b on the origin detection side reciprocates the cycle changing unit 2c.

It can be seen from FIG. 7 that the difference in the width of the period changing portion 2c from other portions, that is, the point where the difference between the pattern pitch p2m and the pattern pitch p2 is 4 μm can be clearly set as the origin. In this simulation result, it is determined that the movement distance X of the scale substrate 1 is between about 800 μm and 1100 μm, and there is a difference of a period width of 4 μm, so the starting point of this change is set to 800 μm. Alternatively, the origin can be set easily and with good reproducibility by setting the origin as a point that is traced back by a predetermined count number from 1100 μm where the change has stopped.
In the example of FIG. 7, the length of the period changing portion 2c is set to 14 μm, but the pitch of the original reflection pattern 2 is 20 μm and the pitch of the reflecting portion 2a (or the transmitting portion 2b) is p2/2. Is set to be 10 μm. If the length of the cycle changing portion 2c is, for example, 20 μm, the slope of Δ in FIG. 7 becomes steep, and it is considered that the origin position can be determined more surely. In that case, however, the A phase and the B phase can be distinguished. Difficult to attach and measurement becomes difficult. On the other hand, if the length of the cycle changing portion 2c is further shortened, as can be seen from FIG. 7, it is difficult to distinguish whether the change of the difference Δ is due to the change of the cycle or other factors such as disturbance, Also, since the slope becomes gentle, it becomes difficult to find the critical point. Therefore, in the case of the present embodiment, it is preferable to make the length about 3 to 5 μm longer than that of the reflecting portion 2a (or the transmitting portion 2b) having no periodic change. If this is divided by the pitch p2/2 of the reflecting portion 2a (or the transmitting portion 2b), the optimum value is 1.3 to 1.5 times.

Next, FIG. 8 shows an example of an arc-shaped optical linear encoder 100 similar to that shown in FIG. By providing the cycle changing portion 2c on one end side of the semi-circular scale substrate 1, it is possible to perform distance measurement with high accuracy over substantially a semicircle. In this case also, the scale substrate 1 is moved without the one of the leading heads 41a being exceeded by the cycle changing portion 2c. Conventionally, it was necessary to provide a track for origin on the inside of the scale substrate 1, but according to the present embodiment, only one track is required, and the scale substrate 1 can be miniaturized.

FIG. 9 shows a modification of the present invention. The use of two substantially identical reading heads 41a and 41b is the same as each of the above-mentioned embodiments, but the above-mentioned each embodiment is different in that the cycle changing portions 2c and 2f are provided at both ends of the scale substrate 1. It differs from the example. It is supposed to be applied to a spindle 23b or the like to which the processing tool 23 is attached. Since the cycle changing portions 2c and 2f are provided on both ends of the scale substrate 1, the effective length of the scale substrate 1 is reduced by about the length of the leading heads 41a and 41b. Can also be used for origin detection and can be used according to the suitability of the device, increasing the operational margin. For example, in the same figure (b), in combination with the same figure (a), the spindle release end is used for origin detection, and in the same figure (c) the arrangement of the reading head opposite to that of the same figure (a) is used. Use the spindle push-in end to detect the origin. The other period changing unit 2f may be used for a safety device such as a detection limit. Needless to say, the provision of the period changing portions 2c and 2f on both ends of the scale substrate 1 is not limited to the spindle but may be a length measuring device or the like.

According to the above-mentioned embodiment and each modification, since the optical linear encoder has substantially the same two light receiving portions, when an error occurs in the distance measurement data, an error occurs on the scale substrate side. There is also an effect that it is possible to easily determine whether there is an abnormality on the side of the reading head or not by comparing the data of the two reading heads.

1, 1a, 1b... Scale substrate, 2... Reflection pattern, 2a... Reflecting part, 2b... Transmissive part, 2c... Period changing part, 2d... Shift boundary, 2f... Period changing part, 10... Sensor substrate, 11a, 11b... Light source, 14a, 14b... Light receiving part, 17a, 17b... (scale substrate side) stopper, 18a, 18b... (housing side) stopper, 21... Rotation center, 22... Probe, 22a... Scale rotation axis, 22b... Probe Axis, 23... Processing tool, 23b... Spindle, 41a... (distance measuring) reading head, 41b... (origin detection) reading head, 51... Moving direction, 80... Length measuring device, 100... (Optical linear ·) ^{encoder, a, B, a -,} B - ... ( detection) _phase, Gr 1 _{~Gr 13} ... (photosensor) set, p2 ... pattern pitch, p2m ... (cycle changing unit) pattern pitch, p3 ... (photo sensor set) pitch, PS1 to PS4... sensor part (photo sensor), sp... (sensor part) pitch, X... distance, Δ... difference

Claims (8)

A linear scale in which a large number of pairs of patterns of transmissive parts and reflective parts are regularly arranged, a light source that emits light to this linear scale, and either transmitted light or reflected light of the light emitted from this light source Incremental encoder having a linear scale, which has a light-receiving sensor for detecting, and is provided with a reading head that moves relative to the linear scale in the pattern arrangement direction of the linear scale,
In the vicinity of the end portion of the linear scale, a period changing portion having a width of the transmitting portion or the reflecting portion different from other portions is provided,
The reading head has two light receiving sensors that are substantially the same,
These two light receiving sensors are arranged side by side in the pattern arrangement direction of the linear scale ,
One of the light receiving sensor does not exceed the cycle changing portion, cannot detect the cycle changing portion,
The other light-receiving sensor is movable beyond the period changing unit and is capable of detecting the period changing unit,
An encoder having a linear scale, characterized in that the origin of the linear scale is determined by comparing the difference between the outputs of these two light receiving sensors with a predetermined threshold value . The linear scale according to claim 1, wherein one of the two light receiving sensors is provided with a stopper that restricts movement of the linear scale or one of the light receiving sensors so as not to detect the period changing portion. An encoder with a scale. The linear scale is formed in an arc shape, and the one light receiving sensor that cannot detect the cycle changing portion and the other light receiving sensor that can detect the cycle changing portion are on the same arc and have the pattern. An encoder having a linear scale according to claim 2, wherein the encoder is arranged in the array position. The two light-receiving sensors are each formed by combining a plurality of sets of one set of photodiodes for detecting A-phase, B-phase, A-phase and B-phase. An encoder having a linear scale according to any one of 1 to 3. An encoder having a linear scale according to any one of claims 1 to 4, wherein the linear scale is provided on a moving side in absolute space, and the reading head is provided on a fixed side in absolute space. Relative to the linear scale, either the transmitted light or the reflected light of the light emitted from the light source is emitted to the linear scale in which a large number of pairs of patterns of the transmission portion and the reflection portion are regularly arranged. In a method of determining the origin of an encoder having a linear scale, which is detected by a reading head having a light receiving sensor that moves to, and determines the origin of the linear scale based on the output of the light receiving sensor,
The light receiving sensors are two substantially the same light receiving sensors arranged side by side in the pattern arrangement direction, and the width of the transmissive portion or the reflective portion provided near the end of the linear scale is One of the light receiving sensors that cannot detect the cycle changing portion and does not exceed the cycle changing portion having a width different from that of the other portion, and the other that can move beyond the cycle changing portion and can detect the cycle changing portion A method for determining an origin of an encoder having a linear scale, which is the light receiving sensor, wherein a difference between outputs of the two light receiving sensors is compared with a predetermined threshold value to set the origin of the linear scale. .. When the number of counts in which the output difference of the two light receiving sensors exceeds a predetermined threshold value has passed a predetermined count, the position detected by the other light receiving sensor traced back by a predetermined count after the predetermined count has elapsed is the origin. The method for determining the origin of an encoder having a linear scale according to claim 6, wherein: 8. The linear device according to claim 6, wherein the width of the transmissive portion or the reflective portion forming the period changing portion is about 1.3 to 1.5 times the width of another pattern. Origin determination method for encoder having scale.