JP2011059055A - Photoelectric encoder - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To increase, a quantity of light received by a light-receiving element by widening a width between a light source and an aperture in a direction where the resolution is not necessary (a direction perpendicular to the direction of the measurement axis) by means of imaging optics while keeping accuracy and characteristics in a direction (a direction of a measurement axis) where resolution of an optical grid on a scale is necessary. <P>SOLUTION: A photoelectric encoder 100 for modulating light emitted from a light source 102 by an optical grid 110 provided on the scale 106 and for detecting the modulated light by the light-receiving element 122 includes a both-side telecentric optical system 114 for forming an image of the light modulated by the optical grid 110. Both-side telecentric optical system 114 includes an aperture 118A for transmitting part of the light modulated by the optical grid 110 and also having a width b wider in a direction Y than a width (a) of the aperture 118A in a direction X. The number of light-source-side apertures NA<SB>lighty</SB>by a width dy of the light source 102 in the direction Y is larger than the number of detecting-side apertures NA<SB>optx</SB>by the width (a) of the aperture 118A in the direction X. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a photoelectric encoder that modulates light emitted from a light source with an optical grating provided on a scale and detects the modulated light with a light receiving element, and particularly uses an imaging optical system. While maintaining the accuracy and characteristics of the direction in which the optical grating on the scale needs to be resolved (measurement axis direction), the light source and the aperture in the direction where the resolution is not needed (direction perpendicular to the measurement axis direction) The present invention relates to a photoelectric encoder that can increase the amount of light received by a light receiving element by widening the width.

  Conventionally, a photoelectric encoder that modulates light emitted from a light source with an optical grating provided on a scale and detects the modulated light with a light receiving element has been used in various machine tools and measuring devices. It was.

  For example, in the photoelectric encoder disclosed in Patent Document 1, an image of an optical grating is formed on a light receiving surface of a light receiving element using a telecentric optical system in which an aperture plate is disposed at a focal position of an imaging lens as an imaging optical system. Thus, the relative position change of the scale with respect to the light receiving element is obtained.

JP 2004-264295 A

  However, in a telecentric optical system as disclosed in Patent Document 1, much of the light emitted from the light source is blocked by the aperture of the aperture plate provided in the imaging optical system. Taking the double-sided telecentric optical system 14 as shown in FIG. 17 as an example, much light Rl is blocked by the aperture plate 18 even if the light passes through the imaging lens 16. For this reason, the illumination efficiency (wattage incident on the light receiving element 22 / lighting illumination wattage of the light source) is poor, and the amount of light incident on the light receiving element 22 is small. At the same time, the light Rl blocked by the aperture plate 18 is reflected, or even light that has passed through the aperture of the aperture plate 18 is repeatedly reflected between the light receiving element 22 and the aperture plate 18, and finally. There is also a possibility that image quality on the light receiving surface of the light receiving element 22 is deteriorated.

  The present invention has been made to solve the above-mentioned problems, and using an imaging optical system, while maintaining the accuracy and characteristics of the direction (measurement axis direction) in which the optical grating on the scale needs to be resolved, It is an object to provide a photoelectric encoder capable of increasing the amount of light received by a light receiving element by widening the width of a light source and an opening in a direction that does not require resolution (a direction orthogonal to a measurement axis direction). And

  The invention according to claim 1 of the present application is a photoelectric encoder that modulates light emitted from a light source with an optical grating provided on a scale and detects the modulated light with a light receiving element. An imaging optical system that forms an image of the modulated light, wherein the imaging optical system transmits a part of the light modulated by the optical grating, and in the measurement axis direction that is the relative movement direction of the scale. An aperture having a width wider than the width of the aperture in a direction orthogonal to the measurement axis direction, and the light source side numerical aperture according to the width of the light source in the direction orthogonal to the measurement axis direction is determined by the measurement axis in the imaging optical system. This problem is solved by making the detection side numerical aperture larger than the opening width in the direction.

  The invention according to claim 2 of the present application further includes an illumination optical system that irradiates the scale with light emitted from the light source, and a diffusion plate that diffuses the light emitted from the light source in the illumination optical system. It is what I did.

  The invention according to claim 3 of the present application further includes an illumination optical system that irradiates the scale with the light emitted from the light source, and the former stage that transmits a part of the light emitted from the light source to the illumination optical system. A front stage opening plate provided with an opening is provided.

  The invention according to claim 4 of the present application further includes an illumination optical system that irradiates the scale with the light emitted from the light source, and the illumination optical system further includes an illumination lens that refracts the light emitted from the light source. It is what I did.

  In the invention according to claim 5 of the present application, the illumination optical system is configured such that one illumination lens is arranged on the illumination optical axis from the light source to the optical grating so that the light source is at a focal position of the illumination lens. This is a one-side telecentric optical system.

  In the invention according to claim 6 of the present application, the illumination optical system is configured such that an opening of one front aperture plate is disposed at a focal position between two illumination lenses on an illumination optical axis from the light source to the optical grating. This is a double-sided telecentric optical system.

  The invention according to claim 7 of the present application is such that the illumination lens is a cylindrical lens having a curvature only in the measurement axis direction.

  In the invention according to claim 8 of the present application, the light source is disposed on the same side as the imaging optical system with respect to the scale, and the light reflected from the scale is imaged by the imaging optical system. Is.

  In the invention according to claim 9 of the present application, the illumination optical axis from the light source to the optical grating and the detection optical axis from the optical grating to the light receiving element are orthogonal to the measurement axis direction, and the illumination optical axis The detection optical axis is arranged so as not to coincide with each other in all paths.

  According to a tenth aspect of the present invention, the imaging optical system includes an aperture plate provided with the aperture.

  According to an eleventh aspect of the present invention, the imaging optical system is provided with an imaging lens that refracts the light modulated by the optical grating.

  The invention according to claim 12 of the present application is such that the imaging lens is a cylindrical lens having a curvature only in the measurement axis direction.

  In the invention according to claim 13 of the present application, the light source is arranged on the same side as the imaging optical system with respect to the scale, the light reflected by the scale is imaged by the imaging optical system, and the light source The optical axis of illumination from the optical grating to the optical axis of detection from the optical grating to the light receiving element is orthogonal to the direction of the measurement axis, and the optical axis of illumination and the optical axis of detection are inconsistent in all paths. The imaging optical system includes an imaging lens that refracts the light modulated by the optical grating, and the imaging lens is a cylindrical lens having a curvature only in the measurement axis direction. And the illumination lens.

  The invention according to claim 14 of the present application further irradiates the optical grating with light emitted from the light source by combining the illumination lens with a cylindrical lens having a curvature only in a direction orthogonal to the measurement axis direction. It is what I did.

  In the invention according to claim 15 of the present application, the imaging optical system is configured such that an aperture of one aperture plate is arranged at a focal position of one imaging lens on a detection optical axis from the optical grating to a detection element. This is a one-side telecentric optical system.

  In the invention according to claim 16 of the present application, the imaging optical system is provided with an aperture of one aperture plate at a focal position between two imaging lenses on a detection optical axis from the optical grating to a detection element. This is a double-sided telecentric optical system to be arranged.

  In the invention according to claim 17 of the present application, a non-light-emitting region that does not emit light by the light source is arranged in the measurement axis direction from the illumination optical axis from the light source to the optical grating.

  According to the present invention, an imaging optical system is used to maintain the accuracy and characteristics of the direction (measurement axis direction) in which the resolution of the optical grating on the scale is required, while maintaining the direction (measurement in which the resolution is not required). By increasing the width of the light source and the opening in the direction orthogonal to the axial direction, the amount of light received by the light receiving element can be increased.

1 is an overall perspective view of a photoelectric encoder according to a first embodiment of the present invention. The whole schematic diagram Schematic diagram showing the illumination optical system Schematic diagram of aperture plate according to first embodiment and conventional aperture plate The schematic diagram which shows the effect of the aperture plate which concerns on 1st Embodiment. Schematic diagram explaining the relationship between the size of the light source and the opening width of the aperture plate The whole perspective view of the photoelectric encoder concerning a 2nd embodiment of the present invention. Overall perspective view of a photoelectric encoder according to a third embodiment of the present invention. Overall perspective view of a photoelectric encoder according to a fourth embodiment of the present invention. Overall perspective view of a photoelectric encoder according to a fifth embodiment of the present invention. The schematic diagram which shows an example of the light source which concerns on 6th Embodiment of this invention. Overall perspective view of a photoelectric encoder according to a seventh embodiment of the present invention Overall perspective view of a photoelectric encoder according to an eighth embodiment of the present invention. Overall perspective view of photoelectric encoder according to ninth embodiment of the present invention Overall perspective view of a photoelectric encoder according to a tenth embodiment of the present invention. Overall perspective view of a photoelectric encoder according to an eleventh embodiment of the present invention. Schematic diagram showing the state of light shielding in the aperture plate of a conventional telecentric optical system

  Hereinafter, an example of an embodiment of the present invention will be described in detail with reference to the drawings.

  First, the configuration of the photoelectric encoder according to the first embodiment will be described with reference to FIGS.

  As shown in FIGS. 1 and 2, the photoelectric encoder 100 includes a light source 102, a collimator lens 104 as an illumination optical system, a scale 106, a bilateral telecentric optical system 114 as an imaging optical system, and a light receiving element 122. . That is, the photoelectric encoder 100 can modulate the light emitted from the light source 102 with the optical grating 110 provided on the scale 106 and detect the modulated light with the light receiving element 122.

  As shown in FIGS. 1 to 3, the light source 102 has a long rectangular shape in the Y direction orthogonal to the measurement axis direction X, which is the relative movement direction of the scale 106 with respect to the light receiving element 122. As shown in FIGS. 2 and 3, the light source 102 has a short width dx in the measurement axis direction (longitudinal direction of the scale 106 necessary for resolution) X and a direction Y (direction in which resolution is not required). (Also referred to as a lateral direction) with a long width dy (dx <dy). As the specific light source 102, for example, a surface-emitting LED having a rectangular shape or a light source having a rectangular portion as a light source can be used.

  The collimator lens 104 (illumination lens) is a lens (referred to as a round lens) having a curvature in both directions X and Y on the optical axis O as shown in FIGS. The collimator lens 104 refracts the light emitted from the light source 102 disposed at the focal distance f and irradiates the scale 106 (one-side telecentric optical system).

Here, as shown in FIGS. 2 and 3, the numerical aperture NA _light (referred to as the _light source side numerical aperture) based on the distance f from the light source 102 to the collimator lens 104 and the size of the light source 102 is expressed by the equations (1) and (1). Defined in (2). NA _lightx represents the light source side numerical aperture in the direction X, and NA _lighty in the direction Y.

NA _lightx = dx / (2 * f) (1)
NA _lighty = dy / (2 * f) (2)

  Here, since dx <dy, Expression (3) is obtained.

NA _lightx <NA _lighty (3)

  As shown in FIGS. 1 to 3, the scale 106 includes optical gratings 110 provided at regular intervals in a direction X on a scale substrate (not shown) (not necessarily at regular intervals). The scale substrate is made of an optically transparent material such as glass. The optical grating 110 is formed, for example, by lithographic processing of a light-opaque metal thin film such as chromium formed on a scale substrate. For this reason, when light is irradiated onto the scale 106, the light travels through the scale substrate and passes through the gaps of the optical grating 110 (the light is modulated by the optical grating 110). The optical axis O from the light source 102 to the optical grating 110 is referred to as an illumination optical axis Ol.

  The two-sided telecentric optical system 114 includes imaging lenses 116 and 120 and an aperture plate 118, as shown in FIGS. The imaging lenses 116 and 120 are both round lenses having curvatures in the directions X and Y. The imaging lens 116 refracts the light modulated by the optical grating 110. The opening plate 118 includes a rectangular opening 118A having a width a narrow in the direction X and a width b wide in the direction Y (FIG. 4A). The opening 118 </ b> A transmits a portion of the light modulated by the optical grating 110 and refracted by the imaging lens 116. The imaging lens 120 refracts the light that has passed through the opening 118 </ b> A and forms an image on the light receiving surface of the light receiving element 122. The opening 118A is disposed at the focal length F of the imaging lenses 116 and 120 on the optical axis O. For this reason, in the double-sided telecentric optical system 114, the magnification of the image formed by the imaging lenses 116 and 120 does not vary even if the distance between the imaging lens 116 and the optical grating 110 varies somewhat. At the same time, even if the distance between the imaging lens 120 and the light receiving surface of the light receiving element 122 varies somewhat, the magnification of the image formed by the imaging lenses 116 and 120 does not vary. In other words, even when the distance between the imaging lens 116 and the scale 106 is slightly changed during attachment, and the attachment between the light receiving element 122 and the imaging lens 120 is slightly changed, highly accurate position measurement is maintained. Can do. The optical axis O from the optical grating 110 to the light receiving element 122 is referred to as a detection optical axis Oo.

Here, as shown in FIG. 2, the numerical aperture NA _opt (referred to as the detection-side numerical aperture) based on the distance F from the optical grating 110 to the imaging lens 116 and the widths a and b of the opening 118A is expressed by equation (4). Is shown in equation (5). NA _optx represents the detection side numerical aperture in the direction X, and NA _opty represents the direction Y.

NA _optx = a / (2 * F) (4)
_NAopty = b / (2 * F) (5)

  That is, the aperture plate 118 employed in the present embodiment shown in FIG. 4A has a wider width b of the aperture 118A in the direction Y, and therefore, compared to the conventional aperture plate 18 shown in FIG. As shown in FIG. 8, it is possible to transmit more light and guide it to the light receiving element 122.

  The light receiving element 122 is an array sensor having a plurality of light receiving regions arranged at least in the direction X. As the light receiving element 122, for example, a photodiode array can be used. Therefore, by sweeping the light receiving region of the light receiving element 122 in the direction X, the image of the optical grating 110 formed on the light receiving surface of the light receiving element 122 can be recognized as an image in at least the direction X. As a result, the position of the scale 106 with respect to the light receiving element 122 in the direction X can be measured with high accuracy. The light receiving element 122 may include a long light receiving region in the direction Y, or may include a plurality of light receiving regions in the direction Y (in this case, a processing circuit (not shown) The obtained signals are integrated to increase the signal intensity in the direction X).

  Next, the relationship between the size of the light source 102 and the size of the opening 118A of the aperture plate 118 will be described.

  As shown in FIG. 5, by increasing the width of the opening 118A of the opening plate 118 in the direction Y, the amount of light can be increased in a direction that does not require resolution. However, the light reaching the aperture plate 118 is greatly affected by the state of the light source 102.

For example, as shown in FIG. 6, when the light source 2 has a width d in both directions X and Y, the light source side aperture is used to efficiently propagate the light amount irradiated to the scale 106 to the light receiving element 122 in the direction X. It is desirable that the numerical aperture NA _lightx and the detection-side numerical aperture NA _optx be substantially the same (if the light source-side numerical aperture NA _lightx is extremely larger than the detection-side numerical aperture NA _optx , most of the light emitted from the light source is an aperture plate) This is because the propagation efficiency (efficiency inherited from the _light source side numerical aperture NA _light to the detection side numerical aperture NA _opt ) is poor. That is, the relationship of the following formula (6) is established.

NA _lightx = NA _lighty = NA _optx (6)

  At this time, as shown in FIG. 6 (B), even if the width b of the opening 118A of the opening plate 118 in the direction Y is a <b, the amount of light hardly changes from when b = a. That is, in this embodiment, in order to increase the amount of light, it is necessary to satisfy the requirement of the following formula (7).

NA _lighty > NA _optx (7)

In other words, in consideration of the propagation efficiency in the direction Y, the light source side numerical aperture NA _lighty by the width dy of the light source 102 in the direction Y is _set as the detection side numerical aperture NA by the width a of the opening 118A in the direction X in the double telecentric optical system 114. _{It needs} to be larger than _optx .

  Next, the operation of the photoelectric encoder 100 according to this embodiment will be described with reference to FIG.

  First, light emitted from the light source 102 is refracted by the collimator lens 104 and becomes light (diffuse light source) having a divergence angle according to the sizes dx and dy of the light source 102. Then, the light enters the scale 106 and is modulated by the optical grating 110. The modulated light is incident on the imaging lens 116 of the bilateral telecentric optical system 114 and is refracted. The refracted light passes through the opening 118A of the aperture plate 118. The passed light further enters the imaging lens 120 and is refracted to form an image on the light receiving surface of the light receiving element 122. On the light receiving surface, in the direction X, an image is formed with sufficient resolution by the width a of the opening 118A necessary for resolution. In the direction Y, since the width dy of the light source 102 and the width b of the opening 118A are made wider than the width dx and the width a, respectively, the amount of light can be increased. That is, by increasing the width dy and the width b, even if the DC component that does not contribute to the contrast expansion of the light / dark pattern that is the image of the optical grating 110 increases, the light / dark pattern signal (PP component) that contributes to the contrast expansion also increases. can do. For this reason, the position of the scale 106 is calculated with high accuracy due to an increase in the light / dark pattern signal (PP component) detected by the light receiving element 122.

  That is, the light source in the direction Y, which is a direction that does not need to be resolved, while maintaining the accuracy such as the resolution in the direction X of the optical grating 110 on the scale 106 and the characteristics such as the contrast using the double-sided telecentric optical system 114. By increasing the width dy of 102 and the width b of the opening 118, the amount of light received by the light receiving element 122 can be increased. For this reason, the position of the scale 106 can be stably measured with high accuracy.

  In this embodiment, since the one-side telecentric optical system is used as the illumination optical system, the illumination light to the scale 106 is uniformly controlled even if the distance between the collimator lens 104 and the scale 106 varies slightly during installation. be able to.

  In the present embodiment, since the imaging optical system is the double-sided telecentric optical system 114, the distance between the imaging lens 116 and the scale 106 varies slightly during attachment, and further, the light receiving element 122 and the imaging lens. Even if the attachment with 120 is slightly changed, highly accurate position measurement can be maintained.

  In this embodiment, since the collimator lens 104 and the imaging lenses 116 and 120 are round lenses, the amount of light that contributes to the illumination of the optical grating 110 in the direction Y is increased and the light modulated by the optical grating 110 is used. Can be concentrated on the light receiving surface of the light receiving element 122, so that the amount of light received by the light receiving element 122 can be greatly increased.

  In this embodiment, the photoelectric encoder 100 is a transmissive type, and the utilization efficiency of the light emitted from the light source 102 is high, so that more stable position measurement is possible.

  Next, a second embodiment of the present invention will be described with reference to FIG.

  In the photoelectric encoder 100 of the first embodiment, the imaging lenses 116 and 120 are round lenses having curvatures in the directions X and Y, respectively, whereas in the photoelectric encoder 200 of the present embodiment, the imaging lenses 216, The difference is that 220 is a cylindrical lens having a curvature only in the measurement axis direction X. For this reason, the optical axis alignment of the both-side telecentric optical system 214 that is an imaging optical system is facilitated. Further, since it is easy to make the imaging lenses 216 and 220 have higher shape accuracy, it is possible to measure the position with high accuracy while appropriately increasing the amount of light to the light receiving element 222.

  Next, a third embodiment of the present invention will be described with reference to FIG.

  The photoelectric encoder 200 of the second embodiment is a transmissive type, whereas the photoelectric encoder 300 of the present embodiment is a reflective type. That is, the light source 302 is disposed on the same side as the double-sided telecentric optical system 314 with respect to the scale 306, and the double-sided telecentric optical system 314 forms an image of light reflected by the scale 306.

  In the present embodiment, the illumination optical axis Ol from the light source 302 to the optical grating 306 and the detection optical axis Oo from the optical grating 306 to the light receiving element 322 are further orthogonal to the measurement axis direction X, and the illumination optical axis Ol and detection are detected. The arrangement is such that the optical axis Oo is inconsistent in all the paths. In other words, the scale 306 is irradiated obliquely from the direction Y that does not resolve.

  Note that the scale 306 includes a scale base material and an optical grating provided in the direction X. The scale substrate is made of an optically opaque material such as metal. The optical grating is formed, for example, by lithography processing a metal thin film that is opaque to light, such as chromium, formed on a scale substrate and has high light reflectance. For this reason, when light is irradiated onto the scale 306, it is reflected by the surface (ie, the scale) of the optical grating (becomes light modulated by the optical grating).

  In the present embodiment, as described above, the illumination optical axis Ol and the detection optical axis Oo are inconsistent in all the paths, so that a half mirror for irradiating the scale 306 can be eliminated. For this reason, although this embodiment is a reflection type, reduction of a number of parts and increase of a light quantity can be aimed at. In addition, since the illumination optical axis Ol and the detection optical axis Oo are orthogonal to the scale 306 with respect to the direction X, the resolution characteristics of the optical grating on the scale 306 are prevented from being impaired. is doing.

  Moreover, since the photoelectric encoder 300 of this embodiment is a reflection type, there is a large degree of freedom in attachment to a counterpart machine. Furthermore, since the double telecentric optical system 314 is employed in the present embodiment, there is an advantage that no strictness is required for attaching the scale 306 to the counterpart machine.

  Next, a fourth embodiment of the present invention will be described with reference to FIG.

  In the photoelectric encoder 300 of the third embodiment, the collimator lens 304 is a round lens and the imaging lens 316 is a cylindrical lens, whereas in the photoelectric encoder 400 of the present embodiment, the collimator lens 404 is also a cylindrical lens. The difference is that the imaging lens 416 and the collimator lens 404 are also used.

  For this reason, in the present embodiment, by adopting the rectangular light source 402 and the aperture plate 418 having a rectangular opening, the amount of light reaching the light receiving element 422 is correspondingly increased, and the collimator lens 404 is further shared. The number of parts can be reduced. At the same time, since the illumination optical axis Ol and the detection optical axis Oo can be easily matched in the direction Y, it is possible to reduce the number of assembling steps and provide a lower-cost photoelectric encoder 400.

  Next, a fifth embodiment of the present invention will be described with reference to FIG.

  In the photoelectric encoder 400 of the fourth embodiment, the imaging lens 416 and the collimator lens 404 are used as a cylindrical lens and also as a cylindrical lens. On the other hand, in the photoelectric encoder 500 of the present embodiment, the collimator lens 504 is different from the cylindrical lens 504A combined with the imaging lens 516 and the cylindrical lens 504A having a curvature in the direction Y.

  For this reason, the collimator lens 504 has a curvature also in the direction Y, so that the light can be made uniform in the direction Y and the light applied to the scale 506 can be increased. That is, in the present embodiment, the amount of light received by the light receiving element 522 can be increased by uniformizing and increasing the light applied to the scale 506. That is, it is possible to perform position measurement with higher accuracy than in the fourth embodiment. In the present embodiment, since the cylindrical lens 504A is directly attached to the imaging lens 516, jigs for mounting the cylindrical lens 504A can be minimized, and optical axis alignment is facilitated. Can do. Although the half mirror is not used in the third to fifth embodiments, a part of the path between the illumination optical axis Ol and the detection optical axis Oo may be matched by using the half mirror.

  Although the present invention has been described with reference to the above embodiment, the present invention is not limited to the above embodiment. That is, it goes without saying that improvements and design changes can be made without departing from the scope of the present invention.

  For example, in the above embodiment, a rectangular shape having a wide width in the direction Y is used as the light source, but the present invention is not limited to this. For example, as in the light source 602 of the sixth embodiment shown in FIG. 11, when the light source 602 has the width M in the direction Y equal to or larger than the width L in the direction X, the width is sufficiently large in any direction. It may be a case with a light emitting surface. The width L of the light source 602 in the direction X is limited in principle by the width of the aperture of the imaging optical system determined from the accuracy required in the direction X. For this reason, the substantial size of the light source is a rectangular shape that is narrow in the direction X (wide in the direction Y). That is, in principle, it is not necessary to limit the light emitting region at the light emitting position at the position of the light source 602. In the present embodiment, a chip LED is assumed as the light source 602. Here, a bonding area BA for operating the chip LED is provided at the center Op of the light source 602, which is a non-light emitting area (diameter B) where light is not emitted. For this reason, the illumination optical axis Ol is arranged so as to be removed from the center Op of the light source 602 in the direction X by the offset value OF so as to avoid the non-light emitting region. In this case, if the width of the light source required to maximize the propagation efficiency from the width of the aperture of the imaging optical system in the direction X that requires resolution is S, Equations (8) and (9) It is more desirable to satisfy.

(LB) / 2 ≧ S (8)
(B + S) / 2 ≦ OF ≦ (LS) / 2 (9)

  That is, the amount of light incident on the light receiving element can be maximized by arranging the light source 602 on the illumination optical axis Ol so as to satisfy the expressions (8) and (9).

In the above embodiment, the double-sided telecentric optical system is used as the imaging optical system, but the present invention is not limited to this. For example, the imaging optical system may be a one-side telecentric optical system in which the aperture of one aperture plate is arranged at the focal position of one imaging lens on the detection optical axis Oo. In that case, since there is only one imaging lens, the optical axis can be easily aligned, and the cost can be reduced. In this case, if the distance from the imaging lens to the aperture plate is F, and the aperture width of the aperture plate is D, the detection-side numerical aperture NA _opt can be obtained by Expression (10). Note that the numerical aperture in the direction X is obtained by substituting the width in the direction X (the same applies to the following).

NA _opt = D / (2 * F) (10)

  In the above embodiment, the aperture plate is disposed at the focal position. However, the aperture plate is not necessarily disposed at the focal position, and the aperture plate is not necessarily required. Even if there is no aperture plate, since the aperture is limited by using the imaging lens, the size of the aperture is substantially determined.

Further, it is possible to use only the aperture plate as the imaging optical system without using the imaging lens. Even with only the aperture plate, an imaging effect is obtained by the aperture, and an image of the optical grating can be formed on the light receiving surface of the light receiving element. In this case, the cost can be reduced more than any of the above, and the man-hours for optical axis alignment can be further reduced. In this case, if the distance from the optical grating to the aperture plate is F, and the aperture width of the aperture plate is D, the detection-side numerical aperture NA _opt can also be obtained from Equation (10).

In the above embodiment, the one-side telecentric optical system is used as the illumination optical system, but the present invention is not limited to this. For example, there may be a case where there is no illumination optical system and a light source is simply arranged on the illumination optical axis Ol. In this case, the arrangement of the light source and the scale can be easily determined (the tolerance can be large), the number of parts can be reduced, and the cost can be further reduced. In this case, if the distance from the light source to the scale is f and the size of the light source is d, the light source-side numerical aperture NA _light can be obtained by Expression (11).

NA _light = d / (2 * f) (11)

  Even when an illumination optical system is used, the functions of the illumination optical system are to reduce the light that is reflected by the aperture plate of the imaging optical system and becomes stray light, and the quality of light that irradiates the scale (diffuse light, It is only necessary to control the parallel light) or to define the light source side numerical aperture in order to mitigate uneven brightness of the light source.

  For example, as the illumination optical system, a diffusion plate that diffuses light emitted from the light source may be provided between the light source and the scale. In this case, it is possible to uniformly irradiate the scale with the diffusion plate (in the case of using only the diffusion plate, the numerical aperture on the light source side can be obtained by using the above-described equation (11) as it is. it can).

Alternatively, as the illumination optical system, a front aperture plate in which a front aperture that transmits part of the light emitted from the light source is provided between the light source and the scale may be used. Also in this case, the number of parts is small, the illumination optical system can be made at lower cost, and the optical axis can be easily aligned. In this case, if the distance from the light source to the preceding stage aperture plate is f and the size of the light source is d, the light source side numerical aperture NA _light can be similarly obtained from the equation (11).

Alternatively, as the illumination optical system, a double-sided telecentric optical system in which an aperture of one front aperture plate is disposed at a focal position between two illumination lenses on the illumination optical axis Ol from the light source to the optical grating may be used. In that case, even if the mounting of the light source is somewhat varied (even if there is some positional error), uniform illumination can be realized. In this case, assuming that the distance from the light source to the illumination lens is f and the size of the light source is d, the light source-side numerical aperture NA _light can be similarly obtained from Equation (11).

  In the above embodiment, the photoelectric encoder is a linear encoder, but the present invention is not limited to this. For example, a rotary encoder or a circular encoder may be used. An example of the configuration in that case is shown by the rotary encoders of the seventh to tenth embodiments shown in FIGS. 12 to 15 instead of the linear encoders shown in the second to fifth embodiments. The measurement axis direction of the rotary encoder is the circumferential direction of each disk-like scale (since the circular encoder uses a part of the disk-like scale, it is the same as the rotary encoder). In addition, even if it is a rotary encoder or a circular arc encoder, unlike the scale of the said embodiment, the cylindrical scale which provided the optical grating on the side surface may be sufficient. For example, instead of the disk-shaped scale 806 of the eighth embodiment of FIG. 13, the cylindrical scale 1106 of the eleventh embodiment shown in FIG. 16 may be used (the cylindrical scale is a figure). 12, can be used instead of the scale shown in FIG. 14, FIG. 15). In this case, the measurement axis direction is a circumferential direction along the side surface of the scale 1106.

  Moreover, in the said embodiment, although each demonstrated as separate invention, this invention is not limited to this, Any component can be combined suitably.

  In the above embodiment, the focal lengths f and F are common to all the embodiments, but may be changed for each embodiment.

2, 102 to 1102 ... Light source 6, 106 to 506, 716 to 1106 ... Scale 14, 114 to 514, 714 to 1114 ... Both sides telecentric optical system 16, 20, 116 to 516, 120 to 520, 716 to 1116, 720 DESCRIPTION OF SYMBOLS 1120 ... Imaging lens 18, 118-518, 718-1118 ... Aperture plate 22, 122-522, 722-1122 ... Light receiving element 100-500, 700-1100 ... Photoelectric encoder 104-504, 704-1104 ... Collimator lens 110, 710, 1110 ... optical grating 118A ... aperture

Claims (17)

In a photoelectric encoder that modulates light emitted from a light source with an optical grating provided in a scale and detects the modulated light with a light receiving element,
An imaging optical system that images light modulated by the optical grating;
The imaging optical system transmits a part of the light modulated by the optical grating and is wider in a direction perpendicular to the measurement axis direction than the width of the opening in the measurement axis direction, which is the relative movement direction of the scale. With a wide opening,
A photoelectric encoder, wherein a light source side numerical aperture due to a width of the light source in a direction orthogonal to the measurement axis direction is larger than a detection side numerical aperture due to the width of the aperture in the measurement axis direction in the imaging optical system . And an illumination optical system for irradiating the scale with light emitted from the light source,
The photoelectric encoder according to claim 1, wherein the illumination optical system includes a diffusion plate that diffuses light emitted from the light source. And an illumination optical system for irradiating the scale with light emitted from the light source,
3. The photoelectric encoder according to claim 1, wherein the illumination optical system includes a front-stage aperture plate provided with a front-stage aperture that transmits a part of the light emitted from the light source. And an illumination optical system for irradiating the scale with light emitted from the light source,
4. The photoelectric encoder according to claim 1, wherein the illumination optical system includes an illumination lens that refracts light emitted from the light source.   The illumination optical system is a one-side telecentric optical system in which one illumination lens is arranged on the illumination optical axis from the light source to the optical grating so that the light source is at a focal position of the illumination lens. The photoelectric encoder according to claim 4, wherein   The illumination optical system is a double-sided telecentric optical system in which an opening of one front aperture plate is disposed at a focal position between two illumination lenses on an illumination optical axis from the light source to the optical grating. The photoelectric encoder according to claim 4, wherein   The photoelectric encoder according to claim 5 or 6, wherein the illumination lens is a cylindrical lens having a curvature only in the measurement axis direction.   The light source is disposed on the same side as the imaging optical system with respect to the scale, and the imaging optical system images light reflected from the scale. The photoelectric encoder described in 1.   The illumination optical axis from the light source to the optical grating and the detection optical axis from the optical grating to the light receiving element are orthogonal to the measurement axis direction, and the illumination optical axis and the detection optical axis are all in each path. The photoelectric encoder according to claim 8, wherein the arrangement is inconsistent.   The photoelectric encoder according to claim 1, wherein the imaging optical system includes an aperture plate provided with the aperture.   The photoelectric encoder according to claim 1, wherein the imaging optical system includes an imaging lens that refracts light modulated by the optical grating.   The photoelectric encoder according to claim 11, wherein the imaging lens is a cylindrical lens having a curvature only in the measurement axis direction. The light source is disposed on the same side as the imaging optical system with respect to the scale, and the imaging optical system forms an image of light reflected by the scale,
The illumination optical axis from the light source to the optical grating and the detection optical axis from the optical grating to the light receiving element are orthogonal to the measurement axis direction, and the illumination optical axis and the detection optical axis are all in each path. Disagreement, and
The imaging optical system includes an imaging lens that refracts light modulated by the optical grating, and the imaging lens is a cylindrical lens having a curvature only in the measurement axis direction;
The photoelectric encoder according to claim 7, wherein the imaging lens and the illumination lens are combined.   Furthermore, the optical lens is irradiated with light emitted from the light source by combining the illumination lens with a cylindrical lens having a curvature only in a direction orthogonal to the measurement axis direction. Photoelectric encoder.   The imaging optical system is a one-side telecentric optical system in which an aperture of one aperture plate is arranged at a focal position of one imaging lens on a detection optical axis from the optical grating to a detection element. The photoelectric encoder according to any one of claims 11 to 14, wherein the photoelectric encoder is characterized in that:   The imaging optical system is a double-sided telecentric optical system in which an aperture of one aperture plate is arranged at a focal position between two imaging lenses on a detection optical axis from the optical grating to a detection element. The photoelectric encoder according to claim 11, wherein the photoelectric encoder is a photoelectric encoder.   17. The photoelectric device according to claim 1, wherein a non-light-emitting region that does not emit light from the light source is arranged so as to be removed from the illumination optical axis from the light source to the optical grating in the measurement axis direction. Type encoder.

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