JP2007071634A - Photoelectric encoder - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a photoelectric encoder with high detection accuracy for surely shutting off stray light without complicating its manufacturing process. <P>SOLUTION: This photoelectric encoder is equipped with a main scale 1 with a scale grating 12 formed along a measurement axis X, and a sensor head 2 disposed movably in the direction of the measurement axis X with respect to the main scale 1 for reading the scale grating 12. The sensor head 2 is equipped with a light source 25 for applying measurement light to the scale grating 12, and a light-receiving element array 23 for receiving light from the scale grating 12 to output a displacement signal. The element array 23 is equipped with shading films 34, which are arranged at prescribed pitches with angles of their gaps with each of photodiodes PDi patterned so as to correspond to incident angles of light from the scale grating 12. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a photoelectric encoder for detecting the relative displacement amount and direction of an object.

  In various machine tools and measuring devices, photoelectric encoders that detect the displacement of two members that move relative to each other are used. This photoelectric encoder irradiates a light beam emitted from a light emitting element such as an LED toward a scale, receives a light beam transmitted, diffracted or reflected by the scale by a light receiving element such as a photodiode, and receives the light beam. The displacement amount and direction of the object are detected based on the state. Due to the demand for miniaturization of devices on which photoelectric encoders are mounted, there is a strong demand for miniaturization of photoelectric encoders.

  However, when the photoelectric encoder is miniaturized, it is difficult to prevent the incidence of light other than measurement light for detecting displacement (hereinafter referred to as “stray light”) such as diffusely reflected light and leaked light. Thus, there is a problem that the detection accuracy is deteriorated. For example, in a photoelectric encoder having an origin detection system, the origin detection system has a light source and a light receiving element that are different from the displacement detection system. When light from the light source for origin detection is incident on the light receiving element of the displacement detection system, it becomes noise or DC offset in the displacement detection system and causes deterioration in detection accuracy.

Patent Document 1 proposed by the applicant discloses a photoelectric encoder that blocks stray light by forming a light guide member oriented obliquely with respect to a detection surface of a light receiving element by a thin film technique or the like. However, the three-dimensional structure such as the light guide member of Patent Document 1 must be formed by a special process different from a semiconductor process for forming a normal light receiving element array, and the formation process becomes complicated. There was a problem of increasing the manufacturing cost.
JP 2001-41775 A (paragraphs 0020 to 0022, FIG. 5 and others)

  An object of the present invention is to provide a photoelectric encoder capable of reliably blocking stray light without complicating the manufacturing process and having high detection accuracy.

  In order to achieve the above object, a photoelectric encoder according to the present invention includes a main scale having a scale lattice formed along a measurement axis, and the scale is arranged to be movable in the measurement axis direction with respect to the main scale. A sensor head that reads a grating, and the sensor head includes a light source that irradiates the scale grating with measurement light, and a light receiving unit that receives light from the scale grating and outputs a displacement signal. Is a light receiving element array formed by forming light receiving elements on the substrate surface at a predetermined pitch, a transparent substrate formed on the substrate surface, and each of the light receiving elements arranged on the transparent substrate at a predetermined pitch and in the gap And a light shielding film formed by patterning the metal wiring layer so that the angle with respect to the angle corresponds to the incident angle of light from the scale grating. To.

  In this photoelectric encoder, the light shielding film is formed in a plurality of stages, and is patterned so that the gap in each of the stages is an angle corresponding to the incident angle of light from the scale grating. Can be configured. In this case, the stray light shielding effect can be further enhanced. The light shielding film may also serve as a signal wiring connected to the light receiving element array. In this case, the signal wirings that overlap in the same direction may be electrically connected to each other.

  According to the present invention, the angle of the gap of the light shielding film with respect to each of the light receiving elements is formed by a normal semiconductor manufacturing process so as to correspond to the incident angle of light from the scale grating, thereby complicating the manufacturing process. Therefore, it is possible to provide a photoelectric encoder that can reliably block stray light and has high detection accuracy.

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

  First Embodiment FIG. 1 shows the configuration of a photoelectric encoder according to a first embodiment of the present invention. FIG. 1A is a plan view of a reflective photoelectric encoder according to this embodiment, and FIG. 1B is a cross-sectional view in the measurement axis X direction. The photoelectric encoder includes a main scale 1 and a sensor head 2 configured to be relatively movable with respect to the main scale 1 in the measurement axis X direction. The main scale 1 includes a glass substrate 11, and a scale lattice 12 and an origin detection pattern 13 are formed on the glass substrate 11. The scale grating 12 is formed at a predetermined pitch corresponding to the resolution of the photoelectric encoder. The origin detection pattern 13 is arranged along another track shifted in the Y direction from the track of the scale lattice 12.

  The sensor head 2 is configured by forming an index grating 22 for detecting displacement, a light receiving element array 23 for detecting displacement, and a light receiving element 24 for detecting origin on a glass substrate 21. The sensor head 2 also includes a displacement detection LED 25 that irradiates the index grating 22 and an origin detection LED 26 that irradiates the track on which the origin detection pattern 13 exists through the slit S1.

  The light receiving element array 23 receives the measurement light from the displacement detection LED 25 that has passed through the index grating 22 and reflected by the scale grating 12 and detects the displacement amount and direction of the sensor head 2 relative to the main scale 1. is there. The light receiving elements constituting the light receiving element array 23 are preferably PIN photodiodes, but may be PN photodiodes or phototransistors.

  Details of the structure of the light receiving element array 23 are shown in FIG. The light receiving element array 23 includes photodiodes PDi formed on the surface of the silicon substrate 31 at a predetermined pitch, silicon oxide films 32 and 33 as transparent substrates formed on the silicon substrate 31, and predetermined on the silicon oxide film 32. The light shielding film 34 is formed with a pitch. The light shielding film 34 can be formed of, for example, an aluminum metal film. After the aluminum film is uniformly formed on the silicon oxide film 32 formed on the silicon substrate 31 by sputtering or the like, the light shielding film 34 can be formed by patterning by a known photolithography method and etching. 2B, the light shielding film 34 is not disposed so as to correspond to the gap of the photodiode PDi but is shifted by a predetermined amount of displacement in the lateral direction. Arranged in position. The amount of deviation corresponds to the incident angle of the signal light incident from the scale grating 12 by the angle θ between the line segment connecting the end of the gap of the light shielding film 34 and the end of the photodiode PDi and the silicon substrate 31. It is set to be an angle. By configuring the light shielding film 34 in this manner, signal light obliquely incident from, for example, the arrow direction of FIG. 2 from the scale grating 12 can be incident on the photodiode PDi, while causing noise and the like. Stray light incident from the direction is blocked. The light shielding film 34 can be formed by a normal semiconductor manufacturing process including photolithography and etching. Since this is the same process as the process of forming the photodiode PDi, the manufacturing process is simplified.

  The light shielding film 34 can be formed of a conductive film such as an aluminum film as described above, and can be used as a signal wiring for taking out a detection signal of the photodiode PDi, for example.

  [Second Embodiment] FIG. 3 shows a photoelectric encoder according to a second embodiment of the present invention. FIG. 3 is a cross-sectional view showing details of the structure of the light receiving element array 23 of the photoelectric encoder of this embodiment. Since the entire configuration of the photoelectric encoder is the same as that of the first embodiment, its detailed description is omitted.

  In this embodiment, the light shielding film 36 is further formed on the silicon oxide film 33, and this is covered with the silicon oxide film 35, whereby the light shielding films 34 and 36 are configured in two stages. The form is different. The light shielding films 34 and 36 are arranged so that the angle θ between the line connecting the end portions of the light shielding films 34 and 36 and the silicon substrate 31 corresponds to the incident angle of the signal light from the scale grating 12. The light shielding film 36 can also be used as a signal wiring in the same manner as the light shielding film 34.

  The light-shielding film can be formed not in two stages as shown in FIG. 3, but in three or more stages. In this way, by forming the light shielding film over a plurality of stages, the possibility of stray light entering the photodiode PDi can be further reduced.

  As shown in FIG. 4, the light shielding films 34 and 36 that overlap in the same direction in the vertical direction are connected by the contact V1, and the light shielding films connected to each other by the contact V1 are the same electrical signal (A phase signal of the photodiode PDi). , B phase signal, etc.). According to this configuration, interference between the light shielding films 34 and 36 stacked in the vertical direction, that is, between the signal lines is suppressed, and the stray light blocking effect can be enhanced by the presence of the contact V1.

  Further, as shown in FIG. 5, the light shielding film 36 in the upper layer (the lowest position in FIG. 5) can be formed thicker than the light shielding film 34 in the lower layer. As a result, stray light can be blocked more reliably, and the light shielding film 36 can be used as a wiring through which a large current flows, such as a power supply voltage wiring.

  [Third Embodiment] Next, a photoelectric encoder according to a third embodiment of the present invention will be described with reference to FIGS. 6 and 7. Constituent members that are the same as in the above embodiment are given the same reference numerals in the drawings, and detailed descriptions thereof are omitted. In this embodiment, the overall configuration of the photoelectric encoder is substantially the same as that of the first embodiment. However, in this embodiment, the index grating 22 is formed at a position displaced in the Y direction perpendicular to the measurement axis X, and the displacement detection LED 25 is inclined from the Y direction, that is, YZ in FIG. The index grating 22 is irradiated on a plane including a plane. Therefore, the signal light from the scale grating 12 also enters the light receiving element array 23 at an oblique incident angle along the YZ plane.

  FIG. 7 shows the configuration of the light receiving element array 23 of this photoelectric encoder. FIG. 4A is a plan view showing the positional relationship between the photodiode PD and the light shielding films 34 and 36, and FIG. 4B is a cross-sectional view in the Y direction of FIG.

  As shown in FIG. 7A, the light shielding films 34 and 36 are both arranged at a predetermined pitch in a direction perpendicular to the longitudinal direction of the photodiode PD, and the light shielding film 36 is formed of the light shielding film 34. However, it is arranged at a position slightly shifted in the Y direction. The amount of deviation is set so that the angle θ between the line connecting the ends of the two and the silicon substrate 31 corresponds to the incident angle of the signal light from the scale grating 12 (see FIG. 7B). By forming the light shielding films 34 and 36 as described above, the signal light from the scale grating 12 can be incident on the light receiving element array 23 even in the photoelectric encoder having the configuration shown in FIG. Can be effectively blocked.

  Although the embodiments of the invention have been described above, the present invention is not limited to these embodiments, and various modifications, substitutions, and the like are possible without departing from the spirit of the invention. For example, the main scale having a reflective scale grating has been described in the above embodiment, but the present invention can also be applied to those employing a transmissive scale grating. In the above embodiment, an encoder that detects a one-dimensional displacement amount has been described, but it goes without saying that the present invention is applicable to an encoder that detects a two-dimensional position.

  In the above embodiment, the origin detection LED 26 is provided separately from the displacement detection LED 25. However, as shown in FIGS. 8A and 8B, by guiding the light from the displacement detection LED 25 to the origin detection pattern 13 by the mirrors 27 and 28, the displacement detection LED 25 is also used as the origin detection LED. The origin detection LED 26 may be eliminated.

1 shows a configuration of a photoelectric encoder according to a first embodiment of the present invention. Details of the structure of the light receiving element array 23 of FIG. 1 are shown. The structure of the photoelectric encoder of the 2nd Embodiment of this invention is shown. The modification of the light receiving element array 23 in the photoelectric encoder of 2nd Embodiment is shown. Another modification of the light receiving element array 23 in the photoelectric encoder of the second embodiment is shown. The structure of the photoelectric encoder of the 3rd Embodiment of this invention is shown. The detail of the light receiving element array 23 of the photoelectric encoder of 3rd Embodiment is shown. The modification of embodiment of this invention is shown.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Main scale, 2 ... Sensor head, 11 ... Glass substrate, 12 ... Scale lattice, 13 ... Origin detection pattern, 21 ... Glass substrate, 22 ... Index lattice, 23 ... Light receiving element array, 24 ... Light receiving element, 25 ... Displacement detection LED, 26 ... Origin detection LED,
27, 28 ... mirror, 31 ... silicon substrate, PDi ... photodiode, 32, 33 ... silicon oxide film, 34, 35, 36 ... light shielding film, V1 ... contact.

Claims (6)

A main scale with a scale grid formed along the measurement axis;
A sensor head which is arranged so as to be movable in the measurement axis direction with respect to the main scale and reads the scale grid,
The sensor head is
A light source for irradiating the scale grating with measurement light;
A light receiving unit that receives light from the scale grating and outputs a displacement signal;
The light receiving unit is
A light receiving element array formed by forming light receiving elements on a substrate surface at a predetermined pitch;
A transparent substrate formed on the substrate surface;
A light-shielding film formed on the transparent substrate by patterning a metal wiring layer so that an angle of each gap with respect to each of the light-receiving elements corresponds to an incident angle of light from the scale grating; A photoelectric encoder characterized by comprising:   The light shielding film is formed in a plurality of stages, and the gaps in the plurality of stages are patterned so that the gaps are arranged at an angle corresponding to an incident angle of light from the scale grating. The photoelectric encoder according to claim 1. The main scale further includes an origin detection pattern indicating an origin position,
The photoelectric encoder according to claim 1, wherein the sensor head further includes an origin detection light receiving element for detecting the origin detection pattern.   The photoelectric encoder according to claim 3, wherein the sensor head further includes an origin detection light source for illuminating the origin detection pattern.   The photoelectric encoder according to claim 1, wherein the light shielding film also serves as a signal wiring connected to the light receiving element array.   6. The photoelectric encoder according to claim 5, wherein the signal wirings overlapping in the same direction are electrically connected to each other through a contact.

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