JP2006284421A - Encoder - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an encoder with a compact constitution of illumination optics. <P>SOLUTION: The encoder of this invention has a light source 11, a splitting optical system 13 for splitting the light from the light source 11 into two light fluxes, an irradiation means 14 for irradiating the two light fluxes c1 and c2 from the irradiation means 14 to the same position, a moving scale 15 which is arranged in the position that the two light fluxes c1 and c2 from the irradiation means 14 comes to the same position and relatively movable to the irradiation means 14 and on which a plurality of gratings 15' perpendicular to the moving direction are formed, and a reception element 16 for detecting the light fluxes (more specifically, interference of diffracted light) irradiated from the irradiation means 14 via the moving scale 15. The irradiation means 14 is constituted in a polyhedron including at least the first surface and the second surface wherein two light fluxes c1 and c2 from the splitting optical system 13 go respectively, the third surface arranged in non-parallel to the first surface opposite to it reflecting the light introduced to the first surface, and the fourth surface arranged in non-parallel to the second surface opposite to it reflecting the light introduced to the second surface. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an encoder.

  As one of conventional photoelectric encoders, a three-grating encoder using three sets of diffraction gratings is known (for example, see Patent Document 1). In this three-grating encoder, first, the first diffraction grating separates the light from the light source into two diffracted lights (that is, ± 1st-order diffracted lights) and makes them incident on the second diffraction grating. Next, the second diffraction grating diffracts these lights and makes them incident on the same position of the third diffraction grating. Then, the third diffraction grating diffracts the incident light and superimposes the light on each other to be emitted as one diffracted light. In general, another optical system is fixed, and only the third diffraction grating is attached to a movable object as a scale so as to be movable, and the displacement of the third diffraction grating is detected by detecting the diffracted light thereof. It is configured as follows.

  In the photoelectric encoder using the diffraction grating as described above, the resolution depends on the grating pitch of the third diffraction grating which is a moving scale. For example, in order to obtain high resolution, the grating pitch of the third diffraction grating is generally made fine. Here, when the incident angle of light incident on the diffraction grating is α, the wavelength is λ, and the grating pitch is P, the diffraction angle θ of the n-order light can be expressed by the following equation (1).

  sin θ = (nλ / P) −sin α (1)

From the above formula (1), it can be seen that the smaller the grating pitch of the third diffraction grating, the larger the diffraction angle θ in the third diffraction grating.
Japanese Patent Laid-Open No. 2002-81964

  By the way, in order to increase the diffraction angle θ in the third diffraction grating as described above, the incident angle of light incident on the third diffraction grating, that is, the third diffraction grating from the second diffraction grating which is an illumination optical system is used. Therefore, it is necessary to increase the incident angle of the light beam incident on the diffraction grating. As a result, the configuration of the optical system including the illumination optical system is increased in size, and may be unstable with respect to environmental changes and disturbances such as temperature and atmospheric pressure changes.

  The present invention has been made in view of such problems, and an object thereof is to provide an encoder having a compact illumination optical system.

  In order to achieve such an object, the encoder of the present invention irradiates a light source, a separation optical system that divides the light from the light source into two light beams, and the two light beams from the separation optical system at the same position. An irradiating means and the two light fluxes from the irradiating means are arranged at the same position, are movable relative to the irradiating means, and a plurality of gratings perpendicular to the moving direction are formed. A moving scale and a light receiving element that detects a light beam emitted from the irradiation unit via the moving scale, and the irradiation unit receives the two light beams from the separation optical system, respectively. A surface, a second surface, a third surface that is disposed non-parallel to the first surface and reflects light incident on the first surface, and a non-parallel surface disposed to the second surface. Reflects light incident on the second surface 4 surface and configured to at least include polyhedral shape.

  As described above, according to the present invention, an encoder having a compact illumination optical system can be realized.

  Hereinafter, an encoder of the present invention will be described with reference to the drawings.

  As shown in FIG. 1A, the encoder 1 of the present invention includes a light source 11, a (collimator) lens 12, a separating unit 13, an irradiating unit 14, a moving scale 15, and a light receiving element 16. Yes.

  The light source 11, the (collimator) lens 12, the separating unit 13, and the irradiating unit 14 are fixed side by side on the optical axis z. Further, the moving scale 15 is movable relative to these 11 to 14 in the x-axis direction of FIG.

  As the light source 11, a laser light source, a light emitting diode (LED), or the like is used, and the light a is emitted toward the (collimator) lens 12.

  The (collimator) lens 12 emits the light a from the light source 11 as a parallel light beam b.

  The separating means 13 divides the parallel light beam b from the (collimating) lens 12 into two light beams c1 and c2 and emits them.

  In the present embodiment, a grating 13 ′ is engraved on the separating means 13 at a pitch P3, and functions as an optical member that divides the parallel light beam b into two light beams c1 and c2. The pitch P3 is set to the same pitch as the pitch P5 of the lattice 15 'engraved on the moving scale 15 described later (however, the pitch P3 is not limited to this. That is, the pitch P3 and the pitch P5). May be at different pitches).

  That is, the two light beams c1 and c2 generated by the separating unit 13 are the + 1st order diffracted light c1 and the −1st order diffracted light c2 diffracted by the grating 13 ′. In practice, higher-order diffracted light is also generated, but since the intensity is extremely small compared to the first-order diffracted light, the first-order diffracted light is used as the measurement light. As shown in FIG. 1A, the + 1st-order diffracted light is emitted in the x-axis positive direction from the optical axis z in the xz plane at an angle θ, and the −1st-order diffracted light is angled from the optical axis z in the xz plane at an angle θ ′. Injected in the negative x-axis direction. Here, when the wavelength of the light beam is λ, the angle θ is calculated by the following equation (2), and the angle θ ′ is calculated by the following equation (3). However, θ ′ = − θ.

sin θ = λ / P3 (2)
sin θ ′ = − λ / P3 (3)

  The irradiating means 14 condenses the two light beams c1 and c2 from the second optical system 12 at the same position on the moving scale 15 after multiple reflection inside thereof. The irradiating means 14 is made of a light transmitting member (glass block), and the two light beams c1 and c2 emitted from the separating means 13 are incident on the incident surface 14A. The incident light includes an incident surface 14A (corresponding to the first surface and the second surface according to claim 1) and a surface 14B facing the incident surface 14A (corresponding to the third surface and the fourth surface according to claim 1). Multiple reflections between. In the irradiation unit 14 used in the present embodiment, the distance between the incident surface 14A and the surface 14B is symmetrically increased from the center of the irradiation unit 14 toward the outside. That is, the incident surface 14A is formed in a V shape. The incident surface 14A may be formed in a flat shape, and the surface 14B may be formed in an inverted V shape. Thus, the incident angle of light incident on the moving scale 15 can be changed by changing the angle of the incident surface 14A or the surface 14B.

  More specifically, since the two light beams c1 and c2 are incident obliquely on the surface 14A, they are refracted at the interface and enter the inside of the glass block. Of the two light beams incident on the glass block, the light beam c1 is multiple-reflected by the glass block surfaces 14A and 14B, propagates in the glass block in the positive x-axis direction, and reaches the end surface 14C, which is the final stage of the reflective surface. . The light beam c <b> 1 reflected by the end face 14 </ b> C is emitted from the face 14 </ b> B and collected on the grating 15 ′ of the moving scale 15. On the other hand, the light beam c2 incident on the glass block propagates in the negative direction of the x-axis through the glass block by multiple reflection, is reflected by the other end face 14D, is emitted from the face 14B, and is a grating 15 ′ of the moving scale 15. Focused on top.

  The irradiation means 14, specifically the glass block, is provided with a reflective coating on a part of the surfaces 14A and 14B, and the incident angles thereof are set so that the light beams c1 and c2 propagating inside are totally reflected. This makes it possible to perform multiple internal reflections.

  The moving scale 15 is movable relative to the irradiating means 14 (in the x-axis direction in FIG. 1A), and a plurality of lattices 15 'that are engraved perpendicular to the moving direction are formed. Yes. The lattice 15 'is engraved at a predetermined pitch P5, and is set to be the same as the pitch P3 of the separating means 13 as described above.

  The light beams c1 and c2 collected on the moving scale 15 are diffracted by the grating 15 ′, are subjected to ± 1st-order diffraction, and are superimposed again and condensed to become diffracted light d on the light receiving element 16. Incident.

  The light receiving element 16 detects the interference of the diffracted light d generated by transmitting the lights c1 and c2 from the irradiation unit 14 through the grating 15 ′ formed on the moving scale 15. More specifically, the intensity (interference fringes) of the diffracted light d is converted into an electric signal and output to the outside. Based on this electrical signal, the displacement in the moving direction (x-axis direction) of the moving scale 15 (relative to the irradiation means 14) can be detected.

  In summary, in the encoder 1 of the present invention, the light a emitted from the light source 11 is converted into a parallel light beam b by the (collimator) lens 12 and divided into two light beams c1 and c2 by the separating unit 13. After multiple reflection in the optical system 11, the light is condensed at the same position of the moving scale 15 that can move relative to the optical systems 11 to 14, passes through the grating 15 ′ of the moving scale 15, and enters the light receiving element 16. . Based on the intensity change of the diffracted light d detected by the light receiving element 16, the relative movement amount of the moving scale 15 with respect to the first to third optical systems 12 to 14 including the light source 11 is detected. In the present embodiment, in the irradiation unit 14, the surface 14A on which the two light beams c1 and c2 from the separation unit 13 are incident and the surface 14B facing the surface are orthogonal to the surface including the parallel light beam b. It is comprised from the light transmissive member (glass block) which has a cross-sectional shape.

  Here, as a comparative example, a three-lattice encoder that does not use a glass block for the irradiation means 14 is shown in FIG. The first diffraction grating 101, the second diffraction grating 102, and the third diffraction grating 103 are all transmissive diffraction gratings, and the first and third diffraction gratings 101 and 103 have the same grating pitch, and the second diffraction grating is the same. The grating pitch of the grating 102 is set to ½ of the pitch of the first and third diffraction gratings 101 and 103. When compared with FIG. 1, the first diffraction grating 101 corresponds to the separating means 13, and the third diffraction grating 103 corresponds to the moving scale 15.

  The beam 104 emitted from the light source 100 is diffracted by the first diffraction grating 101 to generate a beam 105 that is + 1st order diffracted light and a beam 106 that is -1st order diffracted light. The beams 105 and 106 are diffracted by the second diffraction grating 102 and are incident on the third diffraction grating 103. The beams 105 and 106 incident on the third diffraction grating 103 are subjected to ± 1st-order diffraction, overlapped and condensed again, and enter the light receiving element 108 as diffracted light 107.

  In FIG. 2, in order to increase the incident angle to the third diffraction grating 103, the interval between the first diffraction grating 101 and the second diffraction grating 102 is increased, or the second diffraction grating 102 itself is moved. It needs to be bigger. Therefore, since the illumination optical system including the first and second diffraction gratings 101 and 102 becomes large and the influence of thermal expansion increases, it is necessary to take measures such as using a low expansion coefficient material for the illumination optical system. .

  However, in the encoder 1 of the present invention, the two light beams c1, c2 from the separating means 13 are propagated to the left and right using the multiple reflection inside the glass block constituting the irradiating means 14, and thereby the two light beams c1, c2. The incident angle of c2 is increased. Therefore, the greater the number of multiple reflections, the smaller the glass block thickness (dimension in the optical axis z direction) can be made. Note that the dimension in the direction of the optical axis z can be reduced to a thickness that can secure the end faces 14C and 14D sufficient to reflect the two light beams c1 and c2. Therefore, instability factors with respect to environmental changes such as thermal expansion can be suppressed for the entire illumination optical system.

  Further, in the encoder 1 of the present embodiment, the incident angle of light incident on the moving scale 15 can be easily changed by changing the angle of the incident surface 14A or the surface 14B of the irradiation means 14.

  The present invention as described above is not limited to the above embodiment, and can be improved as appropriate without departing from the gist of the present invention.

  For example, in the above embodiment, as shown in FIG. 1A, the surface 14A of the glass block of the irradiating means 14 is formed in a substantially V shape. However, as shown in FIG. In this way, the light can be condensed at the same position on the moving scale 15.

  In the above embodiment, as shown in FIG. 1A, the grating 15 'formed on the moving scale 15 is a transmission type. For example, this grating is made a reflection type and receives light in the reflection direction of the grating. By arranging the element 16, it is possible to configure as a reflective photoelectric encoder.

  Further, the light source 11 may be disposed at a place other than the optical axis Z in FIG. 1A, and light may be guided onto the optical axis Z using a waveguide, an optical fiber, or the like. With this configuration, the light source 11 can be disposed outside the encoder 1, and a thinner encoder configuration can be obtained. In addition, by arranging the light source 11 outside the encoder 1, the encoder 1 is less susceptible to the heat generated from the light source 11, which contributes to stabilization of the optical system.

  Furthermore, as shown in FIG. 4, the inclination angles of the end faces 14 </ b> C and 14 </ b> D in the irradiation unit 14 may be set to different settings. With this configuration, the condensing position where the two light beams c1 and c2 that have passed through the irradiation unit 14 are superimposed can be set to a position other than on the optical axis z, and an optical path length difference is given to the two light beams c1 and c2. It becomes possible. In addition, since the incident angles of the light beams c1 and c2 from the irradiation unit 14 to the moving scale 15 can be freely set according to the diffraction angle of the grating 15 ′ formed on the moving scale 15, the incident angle is large. Even if it becomes, it can cope without enlarging the structure of an illumination optical system. The incident angles of the light c1 and c2 on the moving scale 15 need only secure the dimensional accuracy of the glass block of the irradiation means 14, and the processing accuracy around the illumination optical system does not need to be strict. In the example shown in FIG. 4, the angle of inclination of the end face 14D is set to α <0, the angle of inclination of the end face 14C is set to α = 0, and the superimposed light collection position is moved to the left side of the optical axis z.

  Moreover, as shown in FIG. 5, you may comprise at least 1 surface in a curved surface among the surfaces which comprise the light transmissive member (in the said embodiment, glass block) in the irradiation means 14. As shown in FIG. In particular, as shown in FIG. 5, by setting a curved surface at the final stage of reflection in the glass block of the irradiation means 14, a shaping effect such as condensing / diverging of the light c1 and c2 irradiated to the moving scale 15 is given. be able to.

  Specifically, in the example shown in FIG. 5, the end surfaces 14C and 14D of the irradiation means 14 are curved. The lights c1 and c2 reflected by the end faces 14C and 14D are collected with respect to the y-axis direction, and become elongated and linear light beams extending in the x-axis direction on the moving scale 15. The diffracted light d obtained by superimposing the lights c1 and c2 travels in the direction of the light receiving element 16 while once condensed, spreads in the y-axis direction again. In this way, the cross-sectional shape of the light c1 and c2 after being emitted from the glass block is linear, and the width of the light beam is very large with respect to the direction (y-axis direction) in which the engraving lines of the grating 15 ′ of the moving scale 15 extend. If it is narrow, it is possible to reduce the deterioration of the received light signal due to the positional deviation of the separating means 13.

  Here, compared with the conventional example shown in FIG. 2, in this example, in order to condense the beams 105 and 106, it is necessary to add a condensing lens, and the optical system becomes large. However, in the example shown in FIG. 5, it is only necessary to change the shape of the end faces 14C and 14D of the irradiation means 14, preventing an increase in the size of the optical system, and being resistant to environmental changes and disturbances such as temperature and pressure changes. A system can be realized. In addition, although light c1, c2 was condensed only by end surface 14C, 14D, you may condense using several surfaces of a multiple reflection surface.

  In addition, at least one of the surfaces constituting the light transmitting member (glass block) in the irradiating means 14 is separated by the separating means 13 (specifically, the incident light is converted into two light beams as in the diffraction grating 13 'of the present embodiment). A separation element that divides and injects may be incorporated. In order to divide the light beam into two, in the example shown in FIG. 1A, the separating unit 13 is provided separately from the irradiation unit 14, but in the example shown in FIG. 6, the upper surface 14A of the glass block of the irradiation unit 14 is provided. A separation element 17 was formed. This separation element 17 is engraved on the upper surface 14A of the glass block to form a diffraction grating, and has the functions of the separation means 13 and the irradiation means 14 described above. With this configuration, the separation unit 13 and the irradiation unit 14 can be integrated, and a thinner optical system can be constructed. Further, since the number of parts is reduced, the adjustment elements of the optical system are reduced, which contributes to the stabilization of the optical system. In the example shown in FIG. 6, the separation element 17 is formed on the upper surface 14A of the glass block, but may be formed on the lower surface 14B.

It is a figure which shows embodiment of the photoelectric encoder which concerns on this invention, (a) is a whole block diagram, (b) is a figure which shows the shape in the Ib-Ib cross section in a 3rd optical system. It is a figure which shows the 3 grating | lattice type encoder as a comparative example. It is a figure which shows other embodiment of the photoelectric encoder which concerns on this invention. It is a figure which shows other embodiment of the photoelectric encoder which concerns on this invention. It is a figure which shows other embodiment of the photoelectric encoder which concerns on this invention. It is a figure which shows other embodiment of the photoelectric encoder which concerns on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Encoder 11 Light source 12 (Collimate) lens 13 Separation means 14 Irradiation means 15 Moving scale 16 Light receiving element

Claims (7)

A light source;
A separation optical system that divides light from the light source into two light beams;
Irradiating means for irradiating the two light beams from the separation optical system at the same position;
A moving scale in which the two light fluxes from the irradiating means are arranged at the same position, are movable relative to the irradiating means, and are formed with a plurality of gratings orthogonal to the moving direction; ,
A light receiving element for detecting a light beam irradiated from the irradiation means via the moving scale;
The irradiating means is arranged so that the first surface and the second surface on which the two light beams from the separation optical system are incident respectively, and the light incident on the first surface that is arranged non-parallel to the first surface. An encoder having a polyhedral shape including at least a third surface that reflects and a fourth surface that is arranged non-parallel to the second surface and reflects light incident on the second surface.   The encoder according to claim 1, wherein the first surface and the second surface are on the same plane.   The encoder according to claim 1, wherein the third surface and the fourth surface are on the same plane.   The irradiation means has a symmetrical shape with respect to the moving direction of the scale with reference to a perpendicular bisector connecting a line segment connecting the first surface and the incident position on the second surface of the two light beams. The encoder according to any one of claims 1 to 3.   The distance between the first surface and the third surface and the distance between the second surface and the fourth surface become wider or narrower as the distance between the incident positions of the two light beams on the first surface and the second surface increases. The encoder according to any one of claims 1 to 4, wherein   The encoder according to any one of claims 1 to 5, wherein at least one of the surfaces constituting the irradiating unit excluding the first surface and the second surface is a curved surface.   The encoder according to claim 1, wherein the separation optical system is formed on the first surface and the second surface, or the third surface and the fourth surface.

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