JP2007315919A - Encoder - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To miniaturize an encoder capable of optically detecting the absolute positional information of a mobile body. <P>SOLUTION: The interval of incident position of the -first order diffraction light, zero-th order diffraction light, and +first order diffraction light, is set such that it is made triple pitches (3p) of the bit pattern of a track 31. By the rotational oscillation of oscillation mirror 14 by the driving device 16, the incident position of the zero order diffraction light, and ±first order diffraction light becomes oscillating to X-axis direction while keeping mutual interval. The amplitude (semi-amplitude) of this oscillation is set equal to the pitch p of the bit pattern. The incident position of the zero order diffraction light, and ±first order diffraction light moves with same interval as it is in the three-bit equivalent region respectively. Thereby, the incident position of the three diffraction light moves with 9 bit equivalent width. Therefore, the absolute positional information of 9 bit equivalent information can be read out using the three diffraction light. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an encoder, and more particularly to an encoder capable of optically detecting absolute position information of a moving body.

  Conventionally, an encoder capable of detecting absolute position information of a moving body without performing an origin return operation has been used. Such an encoder is generally called an absolute value encoder (absolute encoder). In the pattern formed on the code plate (scale) of the absolute encoder, the detection unit pattern corresponding to one detection unit needs to be different from the detection unit patterns at other positions.

As such a pattern, a pattern in which a plurality of parallel tracks corresponding to each bit is provided on a scale (for example, if 16 bits are provided, 16 parallel tracks corresponding to each bit are provided) is used. It is common that However, in order to obtain a resolution of 2 ^N with this type, at least N tracks are required. Therefore, the higher the resolution, the larger the scale and the higher the cost. Therefore, recently, a serial bit string pattern (for example, a single-line pattern representing an M-sequence (Maximum length code)) formed on a single track has been used (for example, Patent Document 1). reference).

  However, in the absolute encoder, it is necessary to prepare sensors for reading the value of each bit by the number of bits in the detection unit. Therefore, if the resolution is increased, the number of parts increases, the size of the device increases, and the cost increases. Become high.

Patent No. 2,699,542

  According to a first aspect of the present invention, there is provided a scale substrate having a first track in which a pattern associated with absolute position information is formed along a predetermined direction; and relative to the scale substrate in the predetermined direction. A beam irradiation device that moves and irradiates a part of the first track with illumination light; and a fluctuation device that periodically varies the irradiation position of the illumination light with respect to a part of the first track in the predetermined direction; An encoder.

  According to this, since the irradiation position of the illumination light irradiated to the first track is periodically changed in a predetermined direction, it is possible to increase the number of read bits per illumination light. As a result, even if the resolution is increased, the size and cost of the apparatus can be reduced.

  Hereinafter, an embodiment of the present invention will be described with reference to FIGS.

FIG. 1 shows a schematic configuration of a main part of an encoder 10 according to an embodiment of the present invention. As shown in FIG. 1, the encoder 10 includes a light source 12, a vibrating mirror 14, a driving device 16, a collimator lens 18, a beam generator 20, a beam splitter 22, an objective lens 23, and a moving scale 24. When, and a light receiving element 26 _{1-26 3} 27 _{1-27 3} 28 _{1-28 3.} The components other than the moving scale 24 have a fixed positional relationship with each other. Hereinafter, components other than the moving scale 24 are collectively referred to as a beam irradiation device. In the present embodiment, for convenience of explanation, the description will be made assuming that the position coordinates of the beam irradiation device are invariant in the XYZ coordinate system.

  The moving scale 24 constituting the encoder 10 is attached to a moving body (not shown) and moves in the X-axis direction as the moving body moves. The moving scale 24 is a reflective scale in which a reflective layer made of, for example, glass and chromium (Cr) is formed thereon. As shown in FIG. 2, on the moving scale 24, three parallel tracks 31, 32, 33 extending in the X-axis direction that is the measurement direction are provided. The track 33 is sandwiched between the tracks 31 and 32.

  The tracks 31 and 32 are provided with elongated patterns extending in the X-axis direction. The tracks 31 and 32 are delimited at a constant pitch in the X-axis direction, and a pattern indicating a value of “0” or “1” is formed in each area (bit area) delimited by the pitch. ing. That is, the pattern of the tracks 31 and 32 is a serial bit string pattern extending in the X-axis direction. Such a pattern can be realized, for example, by making the reflectance different between the “0” pattern and the “1” pattern. In FIG. 2, the pattern indicating the value “0” is shown in white, and the pattern showing the value “1” is shown in black. In tracks 31 and 32, a pattern is formed with the detection unit of the number of bits detected simultaneously being 9 bits. In the bit strings of the tracks 31 and 32, even if 9 consecutive bits are extracted at any point, the bit string has a unique numerical value at that position. Therefore, it is possible to recognize which position of the moving scale 24 the bit string pattern is read by reading the 9-bit value of the continuous bit strings in the tracks 31 and 32.

As such a pattern, for example, an M-sequence bit string pattern can be adopted. The M-sequence bit string pattern is formed by 2 ⁿ −1 (n = 9) “0” or “1” codes, and combinations of n consecutive codes are all different code strings. It is a pattern.

  In this embodiment, the bits corresponding to the same X position of the tracks 31 and 32 are inverted. That is, if the value of the bit of the track 31 at a certain X position is “0”, the value of the bit of the track 32 at that X position is “1”, and the value of the bit of the track 31 at the other X position is If “1” is “1”, the value of the bit of the track 32 at the X position is “0”.

  The track 33 is provided with a periodic pattern whose periodic direction is the X-axis direction. The periodic pattern is, for example, a sinusoidal phase grating, and the grating pitch is set to be the same as the pitch of the tracks 31 and 32, for example.

  FIG. 3 shows an optical path diagram of light irradiated on the track 31. As shown in FIG. 3, the light source 12 emits, for example, coherent light, for example, laser light having a wavelength λ (= 850 nm) in the + X direction.

  The vibration mirror 14 reflects the laser light from the light source 12 toward the collimator lens 18. The oscillating mirror 14 periodically oscillates in the rotational direction around the Y axis by a driving device 16 having an actuator such as a piezo element or a crystal resonator. Due to this rotational vibration, the reflection direction of the laser light incident on the oscillating mirror 14 varies according to the direction of the varying reflecting surface, and the angle of the laser light incident on the collimator lens 18 changes periodically due to this variation. .

  The collimator lens 18 converts the laser light reflected by the vibrating mirror 14 into parallel light. This parallel light is incident on the beam generator 20. On the beam generator 20, as shown in FIG. 1, three diffraction gratings 41, 42, and 43 whose periodic direction is the X-axis direction are arranged at equal intervals in the Y-axis direction. Among these diffraction gratings, the diffraction grating 41 is provided on the most + Y side, and the diffraction grating 43 is disposed so as to be sandwiched between the diffraction gratings 41 and 42. Although the grating pitches of the diffraction gratings 41 and 42 are the same, the grating pitch of the diffraction grating 43 may be the same as or different from the grating pitch of the diffraction gratings 41 and 42.

  The diffraction gratings 41, 42, and 43 are transmissive phase gratings. The parallel light transmitted through the diffraction gratings 41, 42, and 43 is diffracted to generate a plurality of diffracted lights. In FIG. 3, among the diffracted light generated by the diffraction grating 41, the 0th order light and the ± 1st order diffracted light (in FIG. The diffracted light is defined as -1st order diffracted light). In the following description, it is assumed that only 0th order light and ± 1st order diffracted light are generated.

  The 0th-order light and the ± 1st-order diffracted light are incident on the beam splitter 22, and part of them are transmitted. Each diffracted light transmitted through the beam splitter 22 enters the objective lens 23, is converted into light parallel to the Z axis, and then enters the moving scale 24.

  The 0th-order light and ± 1st-order diffracted light that have passed through the objective lens 23 enter the track 31. 4A to 4E show the movement of the incident positions of the three diffracted lights incident on the track 31. FIG. 4A to 4E, the incident position of the −1st order diffracted light is shown in white, the incident position of the 0th order diffracted light is shown in black, and the incident position of the + 1st order diffracted light is shown as x. Yes.

  As shown in FIG. 4A, the intervals between the incident positions of the −1st order diffracted light, the 0th order light, and the + 1st order diffracted light are set to be three times (3p) the pitch of the bit pattern of the track 31. Yes.

  Due to the rotational vibration of the oscillating mirror 14 by the driving device 16, the incident positions of the 0th-order light and the ± 1st-order diffracted light vibrate in the X-axis direction while maintaining the mutual distance. The amplitude (half amplitude) of this vibration is set to be the same as the pitch p of the bit pattern. Therefore, the incident positions of the three diffracted lights, which were at the position shown in FIG. 4A, sequentially move to the positions shown in FIGS. 4B to 4E. In other words, the incident positions of the 0th-order light and the ± 1st-order diffracted light reciprocate in an area corresponding to 3 bits, respectively, at equal intervals. As a result, the incident positions of the three diffracted lights move with a width corresponding to 9 bits as a whole.

Each diffracted light reflected by the track 31 of the moving scale 24 is bent by the beam splitter 22 through the objective lens 23 and proceeds in the −X direction. Among these diffraction lights, -1 order diffracted light, and reaches the light receiving element 27 _1, 0 order light reaches the light receiving element 27 _2, the + first-order diffracted light, reaches the light receiving element 27 _3. From the light receiving elements 27 ₁ , 27 ₂ , 27 ₃ , photoelectric conversion signals corresponding to the intensity of the received light are output. Each of these photoelectric conversion signals includes information on the value of a bit in the track 31 on which the −1st order diffracted light, 0th order light, and + 1st order diffracted light are incident.

The optical path of the light incident on the track 32 is also substantially the same as that shown in FIG. 3, and the −1st order diffracted light, 0th order light, and + 1st order diffracted light incident on the track 32 are light receiving elements 28 ₁ , 28 ₂ , 28. _Light is received at ₃ . Therefore, the photoelectric conversion signals output from the light receiving elements 28 ₁ , 28 ₂ , and 28 ₃ include a signal corresponding to a continuous 9-bit value in the track 32.

The photoelectric conversion signals output from the light receiving elements 27 _{1 to} 27 ₃ and 28 _{1 to} 28 ₃ are sent to the detection device 80. FIG. 5 shows a schematic configuration of the detection device 80. As shown in FIG. 5, the detection device 80 includes differential amplifier circuits 51, 52, 53, demultiplexers 55, 56, 57, a latch circuit 60, and a parallel-serial conversion circuit 70.

The photoelectric conversion signal (current signal) from the light receiving element 27 ₁ and the photoelectric conversion signal (current signal) from the light receiving element 28 ₁ are converted into a voltage signal by a current-voltage conversion circuit (not shown), and then the difference is obtained. Input to the dynamic amplifier circuit 51. The differential amplifier circuit 51 amplifies and outputs the difference value between the photoelectric conversion signal (voltage signal) from the light receiving element 27 ₁ and the photoelectric conversion signal (voltage signal) from the light receiving element 28 ₁ . When one of them indicates “1”, the other always indicates “0”, and when one indicates “0”, the other always indicates “1”. . When the value is “1”, the signal level of the photoelectric conversion signal is positive, and when the value is “0”, the signal level of the photoelectric conversion signal is negative. The difference in signal level will widen.

Similarly, the photoelectric conversion signal (current signal) from the light receiving element 27 ₂ and the photoelectric conversion signal (current signal) from the light receiving element 28 ₂ are converted into voltage signals by a current-voltage conversion circuit (not shown). Thereafter, the signal is input to the differential amplifier circuit 52. The differential amplifier circuit 52 amplifies and outputs a difference value between the photoelectric conversion signal (voltage signal) from the light receiving element 27 ₂ and the photoelectric conversion signal (voltage signal) from the light receiving element 28 ₂ . Furthermore, photoelectric conversion signals from the light receiving element 27 ₃ (current signal), the photoelectric conversion signals from the light receiving element 28 ₃ (current signal) is not shown in the current - the voltage conversion circuit is converted into a voltage signal Are input to the differential amplifier circuit 53. In the differential amplifier circuit 53, the photoelectric conversion signals from the light receiving element 27 ₃ and the (voltage signal), and amplifies and outputs the difference value between the photoelectric conversion signal from the light receiving element 28 ₃ (voltage signal).

  The demultiplexer 55 switches the output destination of the signal input from the differential amplifier circuit 51 at a predetermined interval. This switching timing is synchronized with the drive signal of the oscillating mirror 14 issued from the drive device 16. The drive signal of the oscillating mirror 14 is a sine wave signal, and the output destination of the signal is switched every time the phase of the sine wave changes by 60 degrees. In this way, the latch circuit 60 latches values corresponding to the values indicated by the bit patterns of the track 31 irradiated with the −1st order diffracted light. Similarly, the demultiplexers 56 and 57 are also synchronized with the drive signal of the drive mirror 14, and the latch circuit 60 receives the values of the bits of the tracks 31 and 32 irradiated with the 0th-order light and the + 1st-order diffracted light, respectively. It becomes latched. The latch timing is set to be the same as the period of the vibrating mirror 14.

  A signal corresponding to the value of each bit latched by the latch circuit 60 is input to the parallel-serial conversion circuit 70. The parallel-serial conversion circuit 70 converts the total 9-bit parallel data input from each bit of the latch circuit 60 into 9-bit serial data according to the 9-bit bit string pattern read by the track 31, and the serial data Data is output as absolute position information of the moving scale 24. For example, if the 9-bit pattern of the track 31 is as shown in FIG. 6 (A), the 9-bit serial data output from the parallel-serial conversion circuit 70 is as shown in FIG. 6 (B). Become.

  FIG. 7 shows an optical path diagram of light irradiated on the track 33. As shown in FIG. 7, the laser light emitted from the light source 12 is reflected by the vibration mirror 14, converted into parallel light by the collimator lens 18, and enters the diffraction grating 43. The −1st order diffracted light, 0th order light, and + 1st order diffracted light emitted from the diffraction grating 43 are incident on the track 33 on the moving scale 24 via the beam splitter 22 and the objective lens 23.

As described above, the track 33 is provided with the periodic pattern having the X-axis direction as the periodic direction. Therefore, the reflected light of the incident light on the track 33 relates to the phase of the periodic pattern at the incident position of the incident light. The light contains information. This reflected light passes through the objective lens 23 and is reflected by the beam splitter 22. Of the reflected light, -1 light reflected diffracted light incident on the light receiving element 26 _1, 0 order light is incident on the light receiving element 26 _2, + 1 light reflected diffracted light incident on the light-receiving element 26 ₃ To do.

  Due to the vibration of the oscillating mirror 14, the incident positions of the −1st order diffracted light, 0th order light, and + 1st order diffracted light on the track 33 also periodically vary in the X-axis direction. Due to this variation, the phase information of the incident position included in each reflected light in the periodic pattern of the track 33 is modulated.

The photoelectric conversion signals output from the light receiving elements 26 ₁ , 26 ₂ , and 26 ₃ are sent to the detection device 80. The detection device 80 demodulates the phase information of the periodic pattern included in these photoelectric conversion signals, and outputs the demodulated phase information as position information of the moving scale 24. The configuration and operation of the detection circuit 80 that demodulates the phase information and outputs the position information of the moving scale 24 are described in, for example, Japanese Patent Publication No. 2000-511634 or US Pat. No. 6,639,686. Since it is disclosed, detailed description is omitted.

  The detection device 80 generates final absolute position information of the moving scale 24 based on the absolute position information obtained from the tracks 31 and 32 and the phase information of the periodic pattern obtained from the track 33. As a result, the minimum reading unit of the absolute position information obtained from the tracks 31 and 32 is further interpolated by setting the period of the period pattern of the track 33 as one period, so that the final absolute position with improved detection resolution can be obtained. Information can be detected.

  Next, the operation of the encoder 10 will be described. Here, it is assumed that the encoder 10 is incorporated in a part of a device manufacturing processing apparatus that manufactures a device such as a semiconductor device. The device manufacturing processing apparatus is provided with a fixed part (not shown) whose position is fixed and a movable part (not shown) movable with respect to the fixed part. It is assumed that the part (beam irradiation apparatus) other than the moving scale 24 of the encoder 10 in FIG. 1 is attached to the fixed part, and the moving scale 24 is attached to the movable part. That is, the encoder 10 detects the relative displacement in the X-axis direction of the movable part with respect to the fixed part of the device manufacturing processing apparatus.

  After the device manufacturing processing apparatus is turned on, power supply to the encoder 10 is also started, and laser light emission from the light source 12 is started. At this stage, the encoder 10 first generates and outputs final absolute position information based on the absolute position information obtained from the tracks 31 and 32 and the phase information of the periodic pattern of the track 33. Therefore, in the device manufacturing processing apparatus, it is possible to obtain the absolute position information of the movable part with respect to the subsequent fixed part without performing the origin return operation of the movable part. From then on, the encoder 10 may detect the displacement of the movable part based on the phase information of the periodic pattern obtained from the track 32.

  As described above in detail, the irradiation position of the laser light applied to the tracks 31 and 32 is periodically changed in the X-axis direction, so that the number of read bits per illumination light can be increased. As a result, even when the number of bits of the tracks 31 and 32 is increased and the resolution is set high, the apparatus can be increased in size and cost.

  Moreover, according to this embodiment, the diffraction gratings 41 and 42 which diffract the laser beam emitted from the light source 12 and generate a plurality of diffracted beams as a plurality of beams are provided. Then, −1st order diffracted light, 0th order light, and + 1st order diffracted light generated by the diffraction gratings 41 and 42 are irradiated onto a part of the tracks 31 and 32. In this way, since it is not necessary to provide a plurality of light sources in order to generate a plurality of beams, it is possible to further reduce the size and cost of the apparatus.

  In this embodiment, the diffraction gratings 41 and 42 are used as optical elements that generate a plurality of beams, but other optical elements may be used. For example, a beam splitter (including a polarizing beam splitter), a half mirror, a birefringent prism, a split prism, and the like are examples. Further, by arranging an acousto-optic element (AOM) or an electro-optic element (EOM) as the beam generation unit, the interval between the beams irradiated to the track may be adjustable.

  According to the present embodiment, the irradiation positions of a plurality of beams are periodically changed in the X axis direction. In this way, more information can be acquired with a smaller number of beams, so that the encoder can be further increased in size and cost.

  In the present embodiment, the incident position of each diffracted light is periodically changed in the X-axis direction by the rotation of the vibrating mirror 14 around the Y-axis, but the present invention is not limited to this. For example, instead of the vibrating mirror, a crystal, a tuning fork type crystal, or the like may be used. Since such a crystal has a low resonance frequency, there is an advantage that less power is consumed. Alternatively, the drive device that drives the oscillating mirror may be replaced with a simple reflecting mirror, and the position of the light source 12 may be periodically changed to the Z axis. Further, the position of the collimator lens 18 may be periodically changed in the X-axis direction without changing the position of the light source 12.

  In the encoder 10 according to the present embodiment, the pattern of the track 31 of the moving scale 24 is formed according to a code bit sequence (M sequence) associated with the absolute position information. The moving scale 24 further includes a track 32 in which a line pattern representing a bit series in which the value of each bit of the M series is inverted is formed in the X-axis direction. Then, the encoder 10 is based on the difference between the signal corresponding to the light reception result through a part of the pattern of the track 31 and the signal corresponding to the light reception result through a part of the pattern of the track 32. The relative movement between the moving scale 24 and the beam irradiation device is detected. In this way, since the signal corresponding to the light reception result via the bit string pattern of the track 31 can be differentially amplified, the absolute position information can be detected with higher accuracy.

  Note that it is not necessary to invert the bit strings of the track 31 and the track 32, and the same bit string may be used. In this case, the detection device 80 may calculate the sum of the signal obtained from the track 31 and the signal obtained from the track 32 and detect the absolute position information based on the sum signal.

  In this embodiment, the moving scale 24 further includes a track 33 that is sandwiched between the track 31 and the track 32 and has a periodic pattern formed along the X-axis direction. If the periodic pattern track 33 is sandwiched between the two absolute pattern tracks 31 and 32 as described above, the movement scale 24 can be obtained from the tracks 31 and 32 by rotation around the Z axis (ie, yawing). The deviation between the absolute position information obtained and the relative position information obtained from the track 32 can be reduced.

  In the above embodiment, the intensity of the reflected light (the intensity level of the reflected light) is made different depending on the value of the bit in the bit area including the information of each bit of the bit string pattern of one line. However, the present invention is not limited to this, and various patterns can be applied to the bit area. You may make it provide the optical element from which the emission direction of reflected light differs according to the value which the bit area | region shows. For example, mirrors having different inclination amounts of the reflecting surface between the bit pattern “0” and the bit pattern “1” may be formed in each bit region. Furthermore, the laser beam may be transmitted through only one of the “0” and “1” patterns.

  Furthermore, a diffraction grating can be adopted as an optical element provided on the bit region. As the diffraction grating, a blazed diffraction grating as shown in FIG. 8A can be employed. As shown in FIG. 8A, a blazed diffraction grating is provided in each bit region of the track 31 '. The blazed diffraction grating is a diffraction grating in which the cross-sectional shape of the groove is a saw-tooth shape, and is a diffraction grating in which the spectrum intensity of the diffracted light is concentrated in a certain range. The periodic direction of the blazed diffraction grating is the Y-axis direction. For example, the blazed diffraction grating corresponding to a value of “0” is set so that the diffraction direction of incident light is inclined to the + Y side, and “1”. The blazed diffraction grating corresponding to this value is set so that the diffraction direction of the incident light is inclined to the -Y side.

  As shown in FIG. 8B, two light receiving elements 127 and 128 are provided in the traveling direction of the diffracted light by the blazed diffraction grating. In this way, the light receiving element that receives the diffracted light including the information “0” and the light receiving element that receives the diffracted light including the information “1” can be separated. It becomes possible to read accurately.

  Note that the periodic direction of the blazed diffraction grating is not limited to the Y-axis direction as shown in FIG. The periodic direction may be, for example, the X-axis direction, and when + Y is the direction of 0 o'clock, the period direction of the blazed diffraction grating in the bit region of “0” is the direction of 1:30, The periodic direction of the blazed diffraction grating in the bit region “1” may be set to the 7:30 direction. In short, it is only necessary that the emission direction of the reflected light is different between the bit region of “0” and the bit region of “1”.

  In the above embodiment, the amplitude of the incident position of each diffracted light is set to a width corresponding to three times the pitch of the bit patterns of the tracks 31 and 32, ie, 3 bits, and the interval between the incident positions of each diffracted light is 3 Although the bit interval is used, it is not limited to this. For example, the amplitude of the incident position of each diffracted light may be 2 bits or 4 bits or more, and the interval between the incident positions of each diffracted light may be 2 bits or 4 bits or more. The amplitude and interval of the incident position of each diffracted light is determined by the number of bits to be read at a time.

  In the above embodiment, the continuous 9 bits on the tracks 31 and 32 are used as the reading unit. However, the bit pattern read at a time may not be continuous. In particular, when the bit pattern interval is small, information of a plurality of bits separated according to the interval of the diffracted light may be read.

  In the above embodiment, three diffracted lights of −1st order diffracted light, 0th order light, and + 1st order diffracted light are used as detection light. However, higher order diffracted light may be used as detection light. Further, the diffraction gratings 41 and 42 are sine wave gratings, and only −1st order diffracted light and + 1st order diffracted light may be used as detection light. Furthermore, the number of beams may be only one without providing the beam generation unit 20.

  In the above embodiment, the pattern formed on the tracks 31 and 32 is an M-sequence serial bit string pattern. However, the present invention is not limited to this, and the serial bit string pattern capable of detecting the absolute position information of the moving scale 24 is not limited thereto. Any pattern may be used as long as it is (for example, a binary cyclic random number sequence).

  In the above embodiment, the number of tracks on which the absolute pattern is formed is two. However, the number of tracks may be one, or three or more. The same applies to tracks on which a periodic pattern (incremental pattern) is formed.

  Further, the configuration of the absolute position information detection device 80 is not limited to that shown in FIG. 5, and the design can be changed as appropriate. In short, any circuit configuration that can accurately detect the absolute position information of the moving scale 24 from the bit string read by the periodic variation of the illumination light by the detection device 80 may be used.

  In addition, the configuration of the optical system for detecting the phase information of the periodic pattern of the track 33 is not limited to the three-beam system as in the above-described embodiment, and may be any configuration. For example, a configuration in which the diffraction grating 43 is not provided and parallel light incident on the track 33 is allowed to pass through and the objective lens 23 forms one beam spot on the periodic pattern of the track 33 may be used. Further, on the periodic pattern of the track 33, the + 1st order diffracted light and the −1st order diffracted light from the diffraction grating 43 are caused to interfere to generate an interference fringe, and the interference fringe and the periodic pattern of the track 33 are relative to each other. The configuration may be such that phase information of the periodic pattern of the track 33 is detected based on the positional deviation.

  In the above embodiment, the moving scale 24 is attached to the moving body, and the movement displacement thereof is detected. Conversely, the scale is fixed and the beam irradiation device is attached to the moving body, and the beam irradiation device for the scale is fixed. Of course, the displacement may be detected.

  Moreover, in the said embodiment, although the encoder 10 was a linear encoder, it is also possible to apply this invention to the rotary encoder which detects the rotation amount of a rotary body. In this case, the absolute pattern similar to that on the tracks 31 and 32 and the periodic pattern of the track 33 are concentrically arranged on the scale substrate.

  In the above embodiment, the position information of the moving scale 24 is detected based on the absolute position information of the M-sequence bit string pattern formed on the tracks 31 and 32 and the phase information of the periodic pattern of the track 33. Instead of providing the track 33, only the tracks 31 and 32 may be provided, and the position information of the moving scale 24 may be detected from these M-sequence bit string patterns. Further, only the track 31 may be provided, and the position information of the moving scale 24 may be detected from only the M-sequence bit string pattern. In this case, the scale is not limited to a one-dimensional scale, and may be a two-dimensional scale.

  Moreover, although the said embodiment demonstrated the example which attached the encoder 10 to the device manufacturing processing apparatus, the encoder 10 can also be attached to NC machine tools etc.

  The wavelength of the laser beam and the value of the pitch in the track in the above embodiment are merely examples, and are appropriately determined according to the resolution required for the encoder. In general, the smaller the pattern pitch in a track, the higher the resolution of the encoder.

  As described above, the encoder of the present invention is suitable for accurately detecting the position information of the moving body.

It is a figure which shows schematic structure of the encoder which concerns on one Embodiment of this invention. It is a top view of a movement scale. It is an optical path figure of the encoder of FIG. FIGS. 4A to 4E are diagrams showing fluctuations in the incident position of the diffracted light on the track. 2 is a diagram illustrating a schematic configuration of a detection device 80. FIG. 6A is a diagram illustrating an example of a 9-bit pattern of the track 31, and FIG. 6B is output from the parallel-serial conversion circuit 70 when the pattern of FIG. 6A is read. It is a figure which shows the serial data of 9 bits. 3 is an optical path diagram of light irradiated on a track 33. FIG. FIG. 8A is a diagram of each bit region as viewed from above, and FIG. 8B is a diagram illustrating an example of detection of reflected light.

Explanation of symbols

10 ... encoder, 12 ... light source, 14 ... oscillation mirror, 16 ... drive unit, 18 ... collimator lens, 20 ... beam generating unit, 22 ... beam splitter, 23 ... objective lens, 24 ... moving scale, 26 _{1-26 3,} 27 _{1 to} 27 ₃ , 28 _{1 to} 28 ₃ ... Light receiving element, 31, 32, 33, 31 ′ ... track, 41, 42, 43 ... diffraction grating, 51, 52, 53 ... differential amplifier circuit, 55, 56, 57 ... Demultiplexer, 60 ... Latch circuit, 70 ... Parallel-serial conversion circuit, 71 ... Position detection circuit, 80 ... Detection device, 127, 128 ... Light receiving element.

Claims (9)

A scale substrate having a first track in which a pattern associated with absolute position information is formed along a predetermined direction;
A beam irradiation device that moves relative to the scale substrate in the predetermined direction and irradiates a part of the first track with illumination light;
An encoder comprising: a changing device that periodically changes the irradiation position of the illumination light with respect to a part of the first track in the predetermined direction. The beam irradiation device includes:
A beam generating member that generates a plurality of beams from the illumination light;
The encoder according to claim 1, wherein the plurality of beams are irradiated to a part of the first track. The variation device is:
The encoder according to claim 2, wherein irradiation positions of the plurality of beams are periodically changed in the predetermined direction. The beam generating member is
4. The encoder according to claim 2, further comprising a diffraction grating that diffracts the illumination light emitted from a light source to generate a plurality of diffracted lights as a plurality of beams. The pattern is
Formed with a predetermined code bit sequence associated with the absolute position information,
The scale substrate is
A second track in which a line pattern representing a bit sequence obtained by inverting each bit of the predetermined code bit sequence is formed in the predetermined direction;
Based on a difference between a signal corresponding to a light reception result through a part of the first track pattern and a signal corresponding to a light reception result through a part of the second track pattern. The encoder according to claim 1, further comprising: a detection device that detects relative movement between the scale substrate and the beam irradiation device. The scale substrate is
The encoder according to claim 5, further comprising a third track having a periodic pattern sandwiched between the first track and the second track and formed along the predetermined direction.   7. An optical element having a different emission direction of incident light for each value of the area is provided in an area including information on each bit of the line pattern. The encoder according to item.   The encoder according to claim 7, wherein the optical element is a diffraction grating.   The encoder according to claim 8, wherein the optical element is a blazed diffraction grating.

Images