JP2011043438A - Reflective photoelectric encoder - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve detection resolution, while improving the efficiency of using light, by improving resolution of a reflective photoelectric encoder using a concave reflecting grating. <P>SOLUTION: In the reflective photoelectric encoder for detecting reflected light from a reflection scale 10 by a light receiving element 40 through a detection optical system 30, and detecting relative displacement between a detector 20 including a detection optical system and the light receiving element and a measuring axis direction of the reflection scale, the reflecting grating 12 of the reflection scale is formed to have a concave shape whose axis is extended in the measuring axis direction, and whose height range of a detection range is equal to or below a focal depth of the detection optical system, and as the detection optical system, reflected light is imaged into the light receiving element, by using telecentric optical systems 32, 50 including cylindrical lenses 34, 52 arranged so that the reflected light from the reflection scale is imaged in the measuring axis direction, and having an axis in a direction perpendicular to the measuring axis, and a slit 38 disposed on the focal position thereof, and extending in the direction perpendicular to the measuring axis. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  In the present invention, the reflected light from the reflection scale is detected by the light receiving element through the detection optical system, and the reflection including the detection optical system and the detector including the light receiving element and the relative displacement in the measurement axis direction of the reflection scale is detected. In particular, the reflection type photoelectric encoder that can improve the resolution of the reflection type photoelectric encoder using the concave reflection grating and improve the light utilization efficiency and the detection resolution. It relates to the encoder.

  Patent Document 1 proposes a technique for detecting an absolute pattern or a grating pattern on a reflective scale with a detection optical system including a lens in a reflective photoelectric encoder.

  Here, when the light receiving element is made small for the purpose of improving the detection response frequency, there is a problem that the amount of light that can be detected is reduced.

  On the other hand, Patent Document 2 describes a technique of forming a scale lattice shape three-dimensionally and condensing an optical path at one point for the purpose of increasing the detected light amount.

  However, in this method, since the scale lattice must be three-dimensionally formed, there is a problem that the manufacturing cost increases.

  Patent Documents 3 and 4 describe a technique for condensing an optical path at one point by making the reflection surface of the reflection scale into an arc shape.

JP2003-307440 (FIG. 4) JP 2003-337052 (FIG. 1) JP-A-4-218720 (FIG. 3) JP 2006-250877 A (FIG. 8)

  In the techniques described in Patent Documents 3 and 4, a projection image of a reflection grating on a reflection scale is generated on the light receiving element surface. However, since there is no imaging means in the measurement axis direction, imaging on the light receiving element surface in the measurement axis direction cannot be obtained. Therefore, it is impossible to increase the resolution by making the grating pitch fine.

  In addition, since the reflection surface of the reflection scale has an arc shape, there is a problem that interference fringes generated by the light reflected by the reflection grating are not generated if it is a plane scale.

  The present invention has been made to solve the above-described conventional problems, and improves the resolution of a reflective photoelectric encoder using a concave reflection grating, thereby improving the light utilization efficiency in the reflective photoelectric encoder. However, it is an object to improve detection resolution.

  In the present invention, the reflected light from the reflection scale is detected by the light receiving element through the detection optical system, and the reflection including the detection optical system and the detector including the light receiving element and the relative displacement in the measurement axis direction of the reflection scale is detected. In the type photoelectric encoder, the reflection grating of the reflection scale is formed in a concave shape in which the axis extends in the measurement axis direction and the height range of the detection range is less than the focal depth of the detection optical system, and the detection optical system A cylindrical lens having an axis in a direction orthogonal to the measurement axis, which is arranged so as to form an image of reflected light from the reflection scale in the measurement axis direction, and a measurement axis disposed at the focal position thereof. By using a telecentric optical system including a slit extending in an orthogonal direction, the reflected light is imaged on a light receiving element to solve the above problem.

  Here, the telecentric optical system can be a double-sided telecentric optical system in which cylindrical lenses are provided before and after the slit.

  In addition, a beam splitter can be provided immediately above the reflection scale, and the optical axis of the illumination light and the optical axis of the detection optical system can be superimposed / separated immediately above the reflection scale.

  ADVANTAGE OF THE INVENTION According to this invention, the resolution of a reflective photoelectric encoder using a concave reflection grating can be improved, and the detection resolution can be improved while improving the light utilization efficiency in the reflective photoelectric encoder.

  In addition, since a cylindrical lens is used, adjustment in one direction is sufficient, and the optical axis is easily aligned. On the other hand, in the case of a round lens, adjustment in two directions is necessary, and adjustment with a microscope is necessary.

The perspective view which shows the whole structure of 1st Embodiment of this invention. The top view which looked at 1st Embodiment from the light source direction Side view of the first embodiment viewed from the measurement axis direction The top view which shows the optical path of the detection optical system of 1st Embodiment Same side view Optical path diagram showing the detection optical system deployed Side view showing an example of a method for forming a concave reflection grating The perspective view which shows the whole structure of 2nd Embodiment of this invention. The top view which looked at 2nd Embodiment from the light source direction Side view of the second embodiment viewed from the measurement axis direction

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

  As shown in FIG. 1 (perspective view), FIG. 2 (plan view seen from the light source direction), and FIG. 3 (side view seen from the measurement axis direction), the first embodiment of the present invention reflects from the reflective scale 10. Light is detected by the light receiving element 40 through the detection optical system 30, and the reflection type photoelectric type is configured to detect the relative displacement in the measurement axis direction between the detector 20 including the detection optical system 30 and the light receiving element 40 and the reflection scale 10. In the encoder, the reflection grating 12 of the reflection scale 10 is formed in a concave shape in which the axis extends in the measurement axis direction and the height range of the detection range is equal to or less than the focal depth of the detection optical system 30, and the detection optical system As shown in FIG. 2, a cylindrical lens 34 having an axis in a direction orthogonal to the measurement axis, which is arranged so as to form an image of reflected light from the reflection scale 10 in the measurement axis direction, as shown in FIG. Arranged in Was, by using the telecentric optical system 32 including the measuring axis and perpendicular slit plate 36 slits 38 are formed extending in a direction, the reflected light is obtained so as to formed on the light receiving element 40.

  In the present embodiment, a beam splitter 26 is provided in the detector 20 immediately above the reflection scale 10, and the illumination light emitted from the light source 22 in the detector 20 and converted into parallel rays by the collimator lens 24 is used. The axis (referred to as the light source optical axis) and the optical axis of the detection optical system 30 are superimposed / separated immediately above the reflection scale 10.

  In the figure, the light source 22 and the collimator lens 24 are provided above the reflection scale 10, and the detection optical system 30 is provided on the side of the reflection scale 10, but the arrangement of the light source and the detection optical system is reversed. Also good.

  As shown in FIG. 2, a detection grating 42 is disposed on the front surface of the light receiving element 40. The pitch of the detection grating 42 is set to the same pitch as the imaging grating image formed on the light receiving element 40 by the telecentric optical system 32 including the cylindrical lens 34 and the slit 38.

  Therefore, the imaging grating image interferes with the detection grating 42, and a light amount that changes according to the movement of the imaging grating image is incident on the light receiving element 40. Therefore, the light receiving element 40 can output a detection signal corresponding to the movement of the imaging grid image, and can detect the displacement of the detector 20 relative to the reflection scale 10 in the measurement axis direction.

  Thus, the light reflected by the reflection scale 10 can be condensed on the light receiving element 40 by making the reflection grating surface concave.

  The dimensions of the optical path from the reflective scale 10 to the light receiving element 40 are shown in FIG. 4 (plan view), FIG. 5 (side view), and FIG. A cylindrical lens 34 is disposed at an intermediate point between the reflection scale 10 and the light receiving element 40, and a slit 38 having a slit width Ws is disposed at an intermediate point between the cylindrical lens 34 and the light receiving element 40. Therefore, a one-side telecentric optical system having the reflection scale 10 as an object surface is configured.

Here, the NA (numerical aperture) of the one-side telecentric optical system is obtained from the focal length f of the cylindrical lens 34 and the slit width Ws by the following equation.

Further, the cutoff spatial frequency fc of the optical system having the numerical aperture NA can be obtained from the following equation, where λ is the wavelength of light from the light source 22.

Therefore, the detection limit pattern period Pc in this case is obtained by the following equation.

Here, when λ = 880 nm, f = 10 mm, and Ws = 0.88 mm, Pc is obtained by the following equation.

  Therefore, the detection limit pitch of this optical system is 10 μm, and a reflection grating with a very fine pitch can be detected as compared with the case where no imaging system exists between the reflection scale 10 and the light receiving element 40. .

The depth of focus DOF can be obtained from the following equation.

Accordingly, when Pc = 10 μm and λ = 880 nm, DOF is obtained by the following equation.

  That is, the depth of focus of this optical system is ± 0.23 mm, and even when the height of the detection range of the reflective scale 10 is changed by a concave curved surface (arc shape on the side of FIG. 6), the fine pitch is small. An image of the reflection grating can be formed on the light receiving element surface, and this can be detected by the light receiving element 40.

  With the above operation, it is possible to improve the resolution by making the reflection scale 10 concave to improve the light utilization efficiency and by reducing the grating pitch of the reflection grating 12 to be detected.

  For example, as shown in FIG. 7, the reflection grating 12 can be formed in a concave shape by placing a tape scale 14 in a frame 16.

  Next, a description will be given of a second embodiment of the present invention in which the detection optical system is changed from a one-side telecentric optical system to a two-side telecentric optical system. In this embodiment, as shown in FIG. 8 (perspective view), FIG. 9 (plan view seen from the light source direction), and FIG. 10 (side view seen from the measurement axis direction), the detection optical system is placed before and after the slit 38. This is a double-sided telecentric optical system 50 provided with cylindrical lenses 34 and 52.

  Here, the cylindrical lens 52 on the light receiving element 40 side is arranged so that the slit 38 comes to the focal position.

  In the present embodiment, it becomes difficult to be affected by fluctuations in the distance between the slit 38 and the light receiving element 40.

  In the above-described embodiments, the reflection grating 12 is an incremental pattern having an equal pitch. However, the type of the reflection grating is not limited to this, and an absolute pattern in which the absolute position can be detected at an unequal pitch. It may be. Further, the illumination is not limited to the combination of the light source 22 and the collimator lens 24. Further, the beam splitter 26 may be omitted to make the oblique incidence, and the light source optical axis and the detection optical system optical axis may be made independent. Also, the detection grid 42 and the light receiving element 40 can be separated. Furthermore, a rotary encoder may be used instead of the linear encoder.

DESCRIPTION OF SYMBOLS 10 ... Reflection scale 12 ... Reflection grating 20 ... Detector 22 ... Light source 24 ... Collimator lens 26 ... Beam splitter 30 ... Detection optical system 32 ... Telecentric optical system 34, 52 ... Cylindrical lens 38 ... Slit 40 ... Light receiving element 42 ... Detection grating 50 ... Both telecentric optical system

Claims (3)

A reflection type photoelectric encoder that detects reflected light from a reflection scale with a light receiving element through a detection optical system, and detects a relative displacement in the measurement axis direction between the detector including the detection optical system and the light receiving element and the reflection scale. In
The reflection grating of the reflection scale is formed in a concave shape in which the axis extends in the measurement axis direction and the height range of the detection range is equal to or less than the focal depth of the detection optical system,
As the detection optical system, a cylindrical lens having an axis in a direction orthogonal to the measurement axis, which is arranged so as to form an image of reflected light from the reflection scale in the direction of the measurement axis, is disposed at the focal position thereof. A reflective photoelectric encoder characterized in that the reflected light is imaged on a light receiving element using a telecentric optical system including a slit extending in a direction perpendicular to the measurement axis.   2. The reflective photoelectric encoder according to claim 1, wherein the telecentric optical system is a double-sided telecentric optical system in which cylindrical lenses are provided before and after the slit.   3. A beam splitter is provided immediately above the reflection scale, and the optical axis of illumination light and the optical axis of the detection optical system are superimposed / separated immediately above the reflection scale. Reflective photoelectric encoder described in 1.

Images