JP2006153597A - Optical encoder - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reconcile detection stability on a reference position with detection accuracy as to an optical encoder using an equal-magnification inverting optical system. <P>SOLUTION: By a projection means 4 comprising an equal-magnification inverting optical system, one reference slit pattern 25a cast to a first domain A by a light source 2 is converted with an equal magnification into an inverted real image of the slit pattern and projected onto a second domain B. A light receiving element 3 receives the real image of the slit pattern 25a moving in the opposite direction with the other reference slit pattern 25b passing through the second domain B used as a mask to detect the reference position of a moving plate 1. The slit pattern comprises slits 5 severally arranged with irregular pitches. The slit pattern 25a is disposed in a previously inverted relation to the slit pattern 25b. An entire slit real image included in the real image of the slit pattern 25a overlaps with all the slits 5 included in the slit pattern 25b in the second domain B only when the moving plate 1 comes to the reference position. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical encoder including a light emitting element (light source), a light receiving element, and a moving plate having a slit. In particular, the present invention relates to an optical encoder in which an equal magnification inversion optical system is disposed between a light emitting element and a light receiving element to double the resolution. More specifically, the present invention relates to a technique for detecting a reference position of a moving plate in such an optical encoder.

An optical encoder using the equal magnification reversal optical system is described in Patent Document 1 below. Further, a reference position detection technique for a normal optical encoder is described in Patent Document 2 below.
JP-A-10-122905 Japanese Patent Laid-Open No. 53-097862

  FIG. 9 is a schematic perspective view showing the optical encoder described in Patent Document 1. As shown in FIG. As shown in the figure, the optical encoder includes a moving plate 1, a light source 2 composed of a light emitting element such as an LED, a light receiving element 3 composed of a phototransistor array and the like, and a projection means 4. In this example, the moving plate 1 is a disk that is rotationally displaced, and is incorporated so as to pass through the first region A and the second region B. The light source 2 is disposed facing the first region A on the lower surface side of the moving plate 1. The light receiving element 3 is also arranged facing the second region B on the lower surface side of the moving plate 1. The projection means 4 is interposed between the first area A and the second area B on the upper surface side of the moving plate 1. The moving plate 1 has slits 5 arranged at a constant pitch P along the moving direction (in this example, the circumferential direction of the disk) connecting the first region A and the second region B. The light source 2 illuminates the slit 5 passing through the first area A to form a slit object image. The projecting means 4 projects the slit object image projected onto the first area A into the inverted real slit image at the same magnification and projects it onto the second area B. The light receiving element 3 receives the slit real image moving in the opposite direction with the slit 5 passing through the second region B as a mask, and detects the rotational displacement of the moving plate 1. The projection means 4 described above is an equal magnification reversal optical system, which rotates the image by bending the optical path of the collimator lens 6 facing the first area A, the imaging lens 7 facing the second area B, and both the lenses 6 and 7. Including two mirrors M1 and M2. The pair of mirrors M1 and M2 are perpendicular to each other. The projection unit 4 includes an integrated prism 8 and includes a total reflection surface constituting two mirrors M1 and M2, an incident surface on which a collimator lens 6 is disposed, and an exit surface on which an imaging lens 7 is disposed. ing.

  FIG. 10 explains the principle of image formation in the optical encoder shown in FIG. (A) is the top view which looked at the integrated prism 8 from right above, (b) is the side view which looked at the integrated prism 8 from the circumferential direction of the rotary disk, (c) is also the integrated prism 8 It is the side view seen from the diameter direction of the rotating disk. All the rays shown in each figure are meridian luminous fluxes. As shown in the figure, the light source 2 and the light receiving element 3 are arranged on the same surface side of the moving plate 1, and the projection means 4 is arranged on the opposite surface side of the moving plate 1. As described above, the projection unit 4 includes the collimator lens 6 facing the first region A and the imaging lens 7 facing the second region B, and is a 1 × magnification inversion optical system. The projection means 4 is composed of an integrated prism 8 and is integrally formed with an optical plastic together with a collimator lens 6 and an imaging lens 7. The collimator lens 6 is disposed on the incident surface 10 of the integrated prism 8, and the imaging lens 7 is disposed on the output surface 12 of the integrated prism 8.

  A light source 2 composed of a light emitting element such as an LED irradiates a slit 5 formed on the moving plate 1 and projects a slit object image 9 to the first area A. The slit object image 9 is transferred to the imaging lens 7 side through the collimator lens 6 by two mirrors M1 and M2 formed by total reflection surfaces of the integrated prism 8 and perpendicular to each other. Thereafter, the slit real image 13 is projected onto the second region B through the imaging lens 7. The optical axis 14a of the collimator lens 6 and the optical axis 14b of the imaging lens 7 are coaxial via an integrated prism 8, and image transfer mirrors M1 and M2 are interposed between the two lenses. As shown in (c), the slit object image 9 is formed once by the collimator lens 6 and the imaging lens 7 to generate a slit object image 13. When viewed from the radial direction, the light beam emitted from the light source 2 is reflected by the mirrors M1 and M2 and reaches the light receiving element 3. Since the normal vectors of the mirrors M1 and M2 have no component in the slit moving direction (circumferential direction), the real slit image 9 is inverted to become a slit object image 13 when viewed from the radial direction. On the other hand, as shown in FIG. 5B, when viewed from the circumferential direction, the light beam emitted from the light source 2 is reflected twice by mirrors M1 and M2 orthogonal to each other and then reaches the light receiving element side. In this way, the slit object image undergoes image reversal by the two mirrors M1 and M2 orthogonal to each other. As a result, the slit real image becomes an erect image when viewed from the circumferential direction. Therefore, as schematically shown in (a), the object image R is converted into a real image that is inverted at the same magnification with the radial direction as the axis of symmetry.

  As shown in (c), the slit object image 9 projected onto the first area A by the light source 2 is projected as a slit object image 13 onto the second area B via the projection means 4. The light receiving element 3 receives the slit real image 13 using the slit 5 itself formed in the movable plate 1 as a mask. At this time, the slit real image 13 is inverted with respect to the slit object image 9 at the same magnification. Therefore, the slit real image 13 overlaps the slit 5 itself in the second region B in the reverse direction. Further, the moving direction of the slit real image 13 is opposite to the moving direction of the slit 5 itself as indicated by an arrow. Accordingly, the amount of light incident on the light receiving element 3 periodically increases and decreases with the rotational displacement of the movable plate 1 because the slit 5 itself becomes a mask with respect to the actual slit image 13. Moreover, since the slit 5 itself and the slit real image 13 move in the opposite directions at half the pitch P of the slit 5, an encoder output having a resolution twice the slit pitch can be obtained.

  In an optical encoder, in addition to the displacement amount of the moving plate described above, it is often desirable to detect the reference position. FIG. 11 shows a slit configuration that enables reference position detection. As shown in the figure, the moving plate 1 includes a pair of reference slit patterns 25a arranged at intervals corresponding to the distance between the first region A and the second region B in addition to the main track formed of a row of slits 5 arranged at a constant pitch. , 25b. Correspondingly, the light receiving element has light receiving areas respectively assigned to the main track and the sub track, and detects the reference position in addition to the displacement of the movable plate 1. Specifically, each of the pair of reference slit patterns 25a and 25b is composed of a single slit, and is disposed on the inner side with respect to the row of slits 5 on the main track side. The angle interval α between the slit patterns 25a and 25b is equal to the angle interval between the first region A and the second region B. If the moving plate 1 is rotationally displaced in the clockwise direction now, when one reference slit pattern 25a reaches the second area B, the other slit pattern 25b reaches the first area A, and its real image becomes the second area. B is projected. Therefore, the light receiving element outputs a detection signal indicating the reference position of the movable plate 1 when the real image of the reference slit pattern 25b overlaps the reference slit pattern 25a itself.

  As described above, the reference slit patterns 25a and 25b are generally formed of a single slit, and are basically the same as the slit 5 formed in the main track. In order to improve the detection accuracy of the reference position, the narrower the reference slit pattern, the better. In order to make it equal to the detection accuracy of the displacement amount, it is necessary to narrow the width of the reference slit pattern as much as the width of the slit 5 formed in the main track. However, when the resolution of the optical encoder is increased, the slit width is inevitably narrowed, so that there is a problem that a sufficient amount of received light cannot be obtained. In particular, since the reference slit pattern is a single slit, the amount of received light is extremely small compared to the row of slits 5 formed on the main track side. For this reason, the level of the light reception signal (detection signal) is lowered, and there is a problem that the operation of the optical encoder becomes unstable due to erroneous detection of the reference position due to the influence of disturbance noise or the like.

  In order to cope with this, it is conceivable to increase the width of the single slit constituting the reference slit pattern as compared with the width of the slit formed on the main track side. Increasing the slit width increases the amount of received light. As a result, the amplitude level of the detection signal increases, so that it is less susceptible to disturbance noise. However, when the slit width is increased, there is a problem that the detection accuracy of the reference position is inevitably deteriorated compared with the detection accuracy of the displacement amount, and the performance of the apparatus is hindered.

  As described above, it is difficult for the conventional optical encoder using the equal magnification reversal optical system to achieve both the reference position detection stability and the reference position detection accuracy. In this regard, Patent Document 2 discloses a technique that achieves both reference position detection stability and detection accuracy with a general optical encoder that does not use a 1 × inversion optical system. In this optical encoder, a movable plate and a fixed plate are arranged so as to overlap each other between a light emitting element and a light receiving element which are arranged to face each other. A reference slit pattern including a plurality of slits is formed on the moving plate. The plurality of slits are arranged at unequal intervals. For example, seven slits are arranged in a ratio of 1: 2: 3: 5: 7: 10. A reference slit pattern including a plurality of slits arranged in the same order and at the same interval is also formed on the fixed plate side. When the moving plate has just reached the reference position, all the slits overlap the reference slit pattern on the moving plate side and the reference slit pattern on the fixed plate side. At the moving plate position other than the reference position, two or more slits do not overlap at the same time. As a result, even if the widths of the individual slits are narrowed, the plurality of slits all overlap at the reference position, so that a sufficient amount of received light can be obtained and is less susceptible to disturbance noise. On the other hand, the width of each slit of the reference slit pattern can be made the same as the width of a normal slit formed for detecting the displacement, so that necessary reference position detection accuracy can be ensured.

  However, the reference position detection technique disclosed in Patent Document 2 is applied to a general optical encoder provided with a moving plate and a fixed plate, and as disclosed in Patent Document 1, Instead, it cannot be applied as it is to an optical encoder using a 1 × inversion optical system.

  In view of the above-described problems of the conventional technology, an object of the present invention is to achieve both the detection stability and the detection accuracy of the reference position in an optical encoder using a 1 × inversion optical system. In order to achieve this purpose, the following measures were taken. That is, according to the present invention, the moving slope passing through the first area and the second area, the light source arranged facing the first area on one side of the moving plate, and the second area facing the second area on the one side of the moving plate A light receiving element; and a projection unit interposed between the first region and the second region on the other surface side of the moving plate, the moving plate being constant along a moving direction connecting the first region and the second region. A main track composed of a row of slits arranged at a pitch, and a sub-track composed of a pair of reference slit patterns arranged at intervals corresponding to the distance between the first region and the second region, wherein the light source includes the first region Illuminating a row of slits and a reference slit pattern that pass through, the projection means is composed of an equal magnification reversal optical system, and the light source is projected to the first area by the light source, and the same size as a row of slit real images obtained by inverting the row of slits. Convert and project to the second area, Thus, one of the reference slit patterns projected to the first region is converted into a real image of the inverted reference slit pattern and projected onto the second region, and the light receiving element is a slit that passes through the second region. One reference line moving in the opposite direction using the other reference slit pattern passing through the second region as a mask while detecting the displacement of the moving plate by receiving the row of the slit real image moving in the opposite direction using the line as a mask In the optical encoder that receives a real image of the slit pattern and detects the reference position of the moving plate, the pair of reference slit patterns each include a plurality of slits arranged at unequal pitches along the moving direction. The reference slit pattern is arranged in an inverted relationship with respect to the other reference slit pattern in advance, and the one reference slit pattern that has been inverted at the same magnification by the equal magnification inversion optical system. All slit real image included in the real image of Topatan, when the mobile plate comes to a reference position only, characterized in that the overlap with all slits included in said other reference slit pattern in the second region.

  Preferably, the slits arranged at an unequal pitch in the sub-track to constitute the reference slit pattern have a slit opening width comparable to the slits arranged at a constant pitch in the main track. The equal-magnification reversing optical system includes a collimator lens facing the first region, an imaging lens facing the second region, and two optical elements that rotate at right angles by bending the optical path between both lenses. It consists of a mirror.

  A slit row for detecting the amount of movement is formed on the main track, while a pair of reference slit patterns are formed on the sub track for detecting the reference position. Each reference slit pattern is composed of a plurality of slits arranged at unequal pitches. However, one reference slit pattern is formed in advance so as to have an inverted relationship with respect to the other slit pattern. In other words, the pair of reference slit patterns are arranged symmetrically with respect to a plane passing through the rotation axis of the moving plate and the intermediate point between the light source and the light receiving element. Therefore, an image of one reference slit pattern illuminated by the light source is inverted and formed on the light receiving element side by the equal magnification inversion optical system. In the present invention, one reference slit pattern formed in a reversal relationship in advance is inverted again by the equal magnification inversion optical system and then overlaps the other reference slit pattern. Therefore, the reverse image of one reference slit pattern coincides with the other reference slit pattern at the reference position, and all slits arranged at unequal pitches overlap. Thereby, a sufficient amount of received light can be obtained at the reference position. On the other hand, when the moving plate deviates from the reference position due to the rotation of the moving plate, two or more slits do not overlap at the same time because they are arranged at unequal pitches. Therefore, at the reference position, a sufficient amplitude can be obtained to obtain a detection signal by shaping the received light signal. On the other hand, the individual slit width of the reference slit pattern can be formed to the same extent as the width of the slit formed in the main track, so that the required reference position accuracy can be obtained.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic plan view showing an embodiment of an optical encoder according to the present invention. As shown in the figure, the optical encoder includes a moving plate 1, a light source 2, a light receiving element 3, and a projection unit 4. The moving plate 1 rotates around the rotation axis and passes through the first area A and the second area B. The light source 2 is disposed facing the first region A on the lower surface side of the moving plate 1. The light receiving element 3 is also arranged facing the second region B on the lower surface side of the moving plate 1. The projection means 4 is interposed between the first area A and the second area B on the upper surface side of the moving plate 1.

  The moving plate 1 includes a main track 20 and a sub track 25 concentrically. The main track 20 is formed with rows of slits 5 arranged at a constant pitch along the moving direction (circumferential direction) connecting the first region A and the second region B. The sub-track 25 is formed with a pair of reference slit patterns 25a and 25b arranged at intervals corresponding to the distance between the first area A and the second area B. The light source 2 illuminates the row of slits 5 passing through the first region A and the reference slit patterns 25a and 25b. The projecting means 4 comprises an equal magnification reversal optical system, converts the row of slits 5 projected in the first area A by the light source 2 into a row of inverted slit real images, projects the same onto the second region B, and projects the light source. 2, one reference slit pattern 25a projected in the first area A is converted into a real image of the inverted reference slit pattern and projected onto the second area B.

  The light receiving element 3 detects the displacement of the moving plate 1 by receiving the real image row of the slits 5 moving in the opposite direction with the row of the slits 5 of the main track 20 passing through the second region B as a mask. Using the other reference slit pattern 25b passing through the region B as a mask, a real image of one reference slit pattern 25a moving in the opposite direction is received and the reference position of the moving plate 1 is detected.

  As a feature of the present invention, each of the pair of reference slit patterns 25a and 25b includes a plurality of slits 5 arranged at unequal pitches along the moving direction (circumferential direction), and one reference slit pattern 25a is the other. The reference slit pattern 25b is arranged so as to be inverted in advance. The entire slit real image included in the real image of the one reference slit pattern 25a that has been inverted by the same magnification by the 1 × magnification inversion optical system is the second reference slit pattern 25b in the second region B only when the movable plate 1 comes to the reference position. It overlaps with all the slits 5 included in. Preferably, the slits 5 arranged at unequal pitches on the sub-track 25 to form the reference slit patterns 25a and 25b have the same slit opening width as the slits 5 arranged at a constant pitch on the main track 20. Note that, for example, the configuration shown in FIG. 9 can be adopted for the equal magnification reversal optical system constituting the projection unit 4. That is, the projecting means 4 includes a collimator lens facing the first area A, an imaging lens facing the second area B, and two mirrors that form a right angle with each other to fold the optical path between both lenses and rotate the image. It consists of. However, the present invention is not limited to this, and an equal magnification inversion optical system having another configuration can be adopted.

  As is clear from the above description, the pair of reference slit patterns 25a and 25b are arranged on the sub track 25 of the movable plate 1 so as to be separated from each other in the circumferential direction. When one reference slit pattern 25 a is on the optical axis of the light source 2, the other reference slit pattern 25 b is positioned at the center of the light receiving element 3. Each reference slit pattern 25a, 25b is composed of a set of a plurality of slits 5, respectively. Each of the slits 5 included in the reference slit patterns 25a and 25b has an opening width that is approximately the same as the width of the displacement detection slit 5 carved in the circumferential track 20 of the moving plate 1 at an equal pitch. In the present embodiment, each reference slit pattern is composed of four slits 5 and is arranged at an unequal pitch, for example, an interval of 1: 1.5: 2. The layout of the unequal pitch slits 5 arranged in the pair of reference slit patterns 25 a and 25 b is symmetric with respect to a symmetry plane 30 that passes through the rotation axis of the moving plate 1 and the intermediate point between the light source 2 and the light receiving element 3. The image of the unequal pitch slit obtained from the projection means 4 overlaps with the other unequal pitch slit on the light receiving element 3. As for the overlap, all of the plurality of slits overlap when the moving plate 1 just reaches the reference position, but two or more slits do not overlap at another position shifted from the reference position.

  FIG. 2A is an enlarged view of one reference slit pattern 25a. As shown in the figure, the reference slit pattern 25a is formed by arranging a plurality of slits 5 radially at different pitches P1, P2, and P3 in the counterclockwise order.

  FIG. 2B is an enlarged view of the other reference slit pattern 25b. A plurality of slits 5 are arranged radially at different pitches P1, P2, and P3, similarly to the reference slit pattern 25a. However, the order is clockwise as opposed to the reference slit pattern 25a.

  As described above, in the present invention, the image of the reference slit pattern 25a is inverted at the same magnification and inverted by the equal-magnification reversal optical system including the lens and the reflecting surface so as to overlap the reference slit pattern 25b. For this reason, the reference slit pattern 25a is formed so as to have a reverse relationship with respect to the reference slit pattern 25b in advance. This inversion reference plane is a symmetry plane 30 that passes through the rotation axis of the movable plate 1 and the intermediate point between the light source 2 and the light receiving element 3 as shown in FIG. The different pitches P1, P2, and P3 are, for example, 1 to 1.5 to 2. The opening width of the slit 5 is 0.5 times the minimum pitch P1. However, the setting of the unequal pitch is not limited to the illustrated example. In general, in order to prevent two or more slits from overlapping each other between the pair of reference slit patterns 25a and 25b at positions other than the reference position, it is necessary to set the interval between the slits to be equal to or greater than the width and to arrange them at unequal pitches. is there. The ratio of the slit intervals can be, for example, 1: 2, 3: 3, 5,7: 10. As shown in FIGS. 2A and 2B, the pair of reference slit patterns 25a and 25b are arranged symmetrically with respect to a plane passing through the rotation axis of the moving plate and the intermediate point between the light source and the light receiving element. Yes. Therefore, when the image of the reference slit pattern 25a illuminated by the light source is inverted and formed on the light receiving element side by the projection means, the inverted image of the reference slit pattern 25a and the slit of the reference slit pattern 25b overlap each other, and the light receiving element An optical signal reaches 3. The reverse image and the slit all overlap at the reference position, but when the moving plate 1 is deviated from the reference position by the rotation of the movable plate 1, two or more slits 5 do not overlap at the same time. Therefore, a reference pulse signal having a sufficient amplitude and a narrow width for shaping the waveform only at the reference position is obtained, and the reference position detection accuracy is improved.

  FIG. 3 is an enlarged view showing a reference example of the reference slit pattern. In order to facilitate understanding, portions corresponding to the reference slit pattern of the present invention shown in FIG. In the illustrated reference example, a single slit (single slit) 5 is used as each of the pair of reference slit patterns 25a and 25b. Moreover, the opening width of the single slit 5 is equal to the opening width of the displacement detection slit 5 formed in the main track 20. As a result, the detection accuracy of the reference position can be the same level as the detection accuracy of the displacement amount, but the received light amount for detecting the reference position is very small. Therefore, since it is strongly influenced by disturbance noise or the like as it is, stable reference position detection cannot be performed.

  FIG. 4 is an enlarged view showing another reference example of the reference slit pattern. In order to facilitate understanding, portions corresponding to the reference slit pattern of the present invention shown in FIG. In this reference example, the reference slit patterns 25a and 25b are both formed by the single slit 5, but the opening width is enlarged to increase the amount of received light. As a result, the amplitude level of the received light signal at the reference position increases, and the structure is strong against disturbance noise. However, since the opening width of the single slit 5 formed in the reference slit patterns 25a and 25b is wider than that of the displacement detection slit 5 formed in the main track 20 of the movable plate 1, the reference position detection accuracy is improved. bad.

  FIG. 5 is a waveform diagram showing output waveforms of the optical encoder according to the present invention shown in FIG. 1 and FIG. A waveform X is an output waveform indicating the amount of displacement, and a waveform Z is an output waveform indicating the reference position. The displacement detection signal X consists of a pulse train that appears every time the slit train and its inverted real image overlap periodically on the main track side. Since the plurality of slits and their inverted real images simultaneously overlap within the light receiving area of the light receiving element, the pulse amplitude of the displacement detection signal X is at a sufficient level. On the other hand, the reference position detection signal Z consists of a single pulse that appears when the inverted real image of one reference slit pattern and the other reference slit pattern overlap at the reference position. In the present invention, since a plurality of slits and their inverted real images simultaneously overlap at the reference position, the amplitude of the single pulse included in the reference position detection signal is also at a sufficient level and is not affected by disturbance noise. Moreover, the opening width of each slit constituting the reference slit pattern is set to be substantially the same as the opening width of the displacement detection slit. Therefore, the width of the single pulse included in the reference position detection signal Z is sharp, as is the width of each pulse of the pulse train included in the displacement amount detection signal X. Therefore, the reference position detection accuracy of the same level as the displacement amount detection can be obtained.

  FIG. 6 is a waveform diagram showing an output waveform of the optical encoder according to the reference example shown in FIG. In order to facilitate understanding, the same notation as the output waveform of the present invention shown in FIG. 5 is adopted. Although there is no change in the displacement detection signal X, the level of the single pulse included in the reference position detection signal Z is extremely lowered. This is because the reference slit pattern is composed of a single slit and its opening width is narrow. Since the light receiving element cannot obtain a sufficient amount of received light at the reference position, the amplitude of the reference position detection signal Z is reduced, and the influence of disturbance noise is increased.

  FIG. 7 shows an output waveform of the optical encoder according to the reference example shown in FIG. Although the displacement amount detection signal X is not changed, the width of the single pulse included in the reference position detection signal Z is expanded. This is because the opening width of the single slit constituting the reference slit pattern is widened. Although the light receiving element can obtain a sufficient amount of received light at the reference position, the reference position detection accuracy deteriorates because the pulse width increases.

  In an optical encoder, it is often desirable to detect the displacement direction in addition to the displacement amount and the reference position of the moving plate. At this time, a pair of encoder outputs whose phases are shifted from each other by 90 ° are required. The displacement direction can be detected according to the relative phase relationship between the two outputs. FIG. 8 shows two examples of the slit structure and the light receiving element structure that enable detection of the displacement direction. In the example of (a), the movable plate 1 has a pair of parallel tracks 21 and 22 along a row of slits 5 arranged at a constant pitch P. The portion of the slit 5 belonging to the radially outer track 21 is effectively shifted in spatial phase by 1/8 pitch with respect to the portion of the slit 5 belonging to the inner track 22. Therefore, when the slit 5 itself and the slit real image 13 are overlapped on the outer track 21, the slit 5 itself and the slit real image 13 are shifted by ¼ pitch on the inner track 22. Correspondingly, the light receiving element 3 includes an outer light receiving region 23 and an inner light receiving region 24. As a result, the light receiving element 3 outputs a pair of electrical signals whose phases are shifted from each other by 90 °, and the displacement direction of the movable plate 1 can be detected.

  In the example of (b), the slit 5 is formed in a slightly inclined state with respect to the radial direction of the movable plate 1, and the portion of the slit 5 belonging to the inner track is the portion of the slit 5 belonging to the outer track. On the other hand, the spatial phase is effectively shifted by 1/8 pitch. As a result, when the slit 5 itself and the slit real image 13 coincide with each other in the outer track, the slit 5 itself and the slit real image 13 are effectively shifted by ¼ pitch in the inner track.

1 is a schematic plan view showing an embodiment of an optical encoder according to the present invention. It is an enlarged view which shows the principal part of the optical encoder shown in FIG. It is a typical top view which shows the reference example of an optical encoder. It is a typical top view which shows the other reference example of an optical encoder. It is a wave form diagram which shows the output signal of the optical encoder concerning this invention shown in FIG.1 and FIG.2. It is a wave form diagram which shows the output signal of the optical encoder concerning the reference example shown in FIG. It is a wave form diagram which shows the output signal of the optical encoder concerning the other reference example shown in FIG. It is a schematic diagram which shows other embodiment of the optical encoder concerning this invention. It is a typical perspective view which shows the conventional optical encoder. It is a schematic diagram with which it uses for operation | movement description of the conventional optical encoder shown in FIG. It is a typical top view which shows another example of the conventional optical encoder.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Moving plate, 2 ... Light source, 3 ... Light receiving element, 4 ... Projection means, 5 ... Slit, 20 ... Main track, 25 ... Sub track, 25a ... Reference slit pattern, 25b ... reference slit pattern, 30 ... symmetric plane

Claims (3)

A moving hill passing through the first region and the second region, a light source disposed facing the first region on one surface side of the moving plate, a light receiving element disposed facing the second region on one surface side of the moving plate, A projection means interposed between the first region and the second region on the other surface side of the moving plate,
The moving plate includes a main track composed of a row of slits arranged at a constant pitch along a moving direction connecting the first region and the second region, and a pair arranged at intervals corresponding to the distance between the first region and the second region. A sub-track consisting of a reference slit pattern of
The light source illuminates a row of slits and a reference slit pattern that pass through the first region,
The projection means comprises an equal-magnification reversal optical system. The projection of the slits projected to the first area by the light source is converted into a real-slit-reversed slit image and projected onto the second area. Is converted into a real image of the reference slit pattern inverted from one of the reference slit patterns projected to the first area, and projected to the second area,
The light receiving element receives the row of slit real images moving in the opposite direction using the row of slits passing through the second region as a mask, detects the displacement of the moving plate, and detects the other reference passing through the second region. In an optical encoder that receives a real image of one reference slit pattern that moves in the opposite direction using the slit pattern as a mask and detects the reference position of the moving plate,
The pair of reference slit patterns are each composed of a plurality of slits arranged at unequal pitches along the moving direction, and one reference slit pattern is arranged in a previously inverted relationship with respect to the other reference slit pattern,
The entire slit real image included in the real image of the one reference slit pattern that has been inverted at the same magnification by the equal magnification inversion optical system is the second reference slit pattern in the second region only when the movable plate comes to the reference position. An optical encoder that overlaps with all the slits included in.   2. The optical system according to claim 1, wherein the slits arranged at unequal pitches in the sub-tracks to form the reference slit pattern have a slit opening width that is about the same as the slits arranged at a constant pitch in the main track. Type encoder.   The equal-magnification reversing optical system includes a collimator lens facing the first region, an imaging lens facing the second region, and two mirrors that form a right angle with each other to fold the optical path between both lenses and rotate the image. The optical encoder according to claim 1, comprising:

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