JPH04130220A - Encoder - Google Patents

Abstract

PURPOSE:To make it possible to detect the moving state stably and highly accurately without wavelength dependency of laser light by splitting coherent luminous flux into a plurality of diffracted lights at the specified orders, and irradiating the diffracted lights into a plurality of regions of the diffraction grating on the surface of a moving scale. CONSTITUTION:The laser light emitted from a laser light source 1 is made to be the parallel luminous flux through a collimator lens 2 and vertically irradiates into a diffraction grating 101. Diffracted lights 1a1 and 1b1 at the specified orders are emitted from the diffraction grating 101 at a diffraction angle theta0. The diffracted lights 1a1 and 1b1 are irradiated on two places 102a and 102b of the diffraction grating on a moving scale 3 at an angle theta0' respectively. Two diffracted lights 1a2 and 1b2 at the specified orders which undergo doppler shift in response to the moving speed V of the moving scale 3 in the direction of each center are irradiated into a transmitting type diffraction grating 103 at an incident angle theta0' respectively. After the diffraction and overlapping, the lights are irradiated into a light receiving means 8. In the light receiving means 8, the output signal corresponding to the moving state of the moving scale 3 is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to an encoder, and more particularly, to an encoder, in which a coherent light beam is incident on a diffraction grating on a moving scale surface attached to a moving object, and a Doppler shift from the diffraction grating is detected. Rotary encoders, linear encoders, etc. that measure the movement state of a diffraction grating, that is, the movement state of a moving object, by making the received diffracted lights of specific orders interfere with each other to form interference fringes, and counting the bright and dark fringes of the interference fringes. This is related to the encoder.

(Prior Art) In recent years, precision machines such as NC machine tools and semiconductor printing equipment have required precision measuring instruments that can measure in units of 1 gm or less (submicron). Traditionally, measuring instruments capable of measuring in submicron units use a laser-specific coherent light beam to form interference fringes from the diffracted light from a moving object, and use rotary encoders and linear encoders that utilize these interference fringes. Encoders are well known.

FIG. 7 is a block diagram of an example of a conventional linear encoder proposed in, for example, Japanese Patent Laid-Open No. 63-311121. In the same figure, a coherent light beam from a laser 1 is made into a substantially parallel light beam by a collimator lens 2, and is incident on a polarizing beam splitter 9, where it is split into two light beams: a linearly polarized transmitted beam and a linearly polarized reflected beam. There is. At this time, the mounting position of the laser 1 is adjusted so that the linear polarization direction of the emitted light beam of the laser 1 is 45 degrees with respect to the polarizing beam splitter 9. As a result, the intensity ratio of the transmitted luminous flux and the reflected luminous flux from the polarizing beam splitter 9 is approximately l.
:1.

Then, the reflected light flux and the transmitted light flux from the polarizing beam splitter 9 are made into circularly polarized light through a 1/4 wavelength plate 51.5 m, and when they are reflected by reflectors 101 and 101 and incident on the diffraction grating 30, the target diffraction The m-th order diffracted light from the grating 30 is reflected from the diffraction grating 30 substantially perpendicularly.

That is, when the grating pitch of the diffraction grating 30 is P, the wavelength of the coherent light beam is λ, m is an integer, and the angle of incidence of the coherent light beam on the diffraction grating 30 is θ, then θ, 4sin-'(mλ/
P).

The m-th order diffracted light emitted substantially perpendicularly from the diffraction grating 30 is made incident on an optical member 11 comprising a so-called cat's eye optical system. Since a reflective film 12 is provided near the focal plane of the optical member 11, the incident light beam is reflected by the reflective film 12 as shown in FIG. 8, returns to its original optical path, and exits from the optical member 11. The light enters the diffraction grating 30 again.

Then, the m-th order reflected diffracted light that is diffracted again by the diffraction grating 30 returns to the original optical path and is reflected by the reflecting mirrors 10+ and 10.
74 wavelength plates 5I and 5O and polarized beam splitter.
9.

At this time, the re-diffracted light goes back and forth between the 1/4 wavelength plates 5+ and 5+, so when the light beam first reflected by the polarizing beam splitter 9 re-enters, the polarization direction is 90 degrees with respect to the polarizing beam splitter 9. Since it is becoming popular, it becomes transparent. Conversely, the light beam that first passes through the polarizing beam splitter 9 is reflected when it enters the beam again.

In this way, the two diffracted lights are superimposed by the polarizing beam splitter 9, passed through the 1/4 wavelength plate 5I, and then converted into circularly polarized light.
The beam splitter 6 splits the beam into two beams, each passes through a polarizing plate 7+, 7m, and then becomes linearly polarized light through a light receiving element 8+,
The light is incident on each of the eight beams.

The signals detected by the light receiving elements 8+ and 8m as two-phase periodic signals having a phase difference of 90 degrees are subjected to interpolation processing in the pulse output circuit 15 in order to increase the detection resolution. Then, a divided pulse is obtained by detecting the zero-crossing point of the waveform of each output signal, and this is output as a detection pulse corresponding to the displacement of the diffraction grating 30. That is, the pulse output circuit 15 outputs a number of detection pulses corresponding to the relative change amount (movement amount) of the diffraction grating 30 with respect to the incident light beam. The linear encoder shown in the figure uses the detection pulses to determine the moving speed of the moving object.
The state of movement, such as the direction of movement, is detected.

(Problems to be Solved by the Invention) In the encoder shown in FIG. 7, when a semiconductor laser is used as the laser 1, wavelength fluctuations occur in the laser light due to, for example, temperature changes. Along with this, the diffraction angle from the diffraction grating 30 changes, and the light beam incident on the condensing system 20 deviates from the original optical path. In this figure, a cat's eye optical system as shown in FIG. 8 is used in order to return the incident light beam that is deviated from the original optical path due to the wavelength modulation to the optical path in the same direction as when it was incident.

Note that the same effect can be obtained in avoiding the wavelength dependence at this time by using a corner cube instead of the cat's eye optical system.

However, in general, if a cat's eye optical system or a corner cube is provided in a part of the device, the above-mentioned effects can be obtained, but the device as a whole tends to become complicated.

The present invention improves the encoder shown in Fig. 7 and provides an encoder that is capable of detecting a moving state with a stable and high precision without wavelength dependence of laser light with a simple configuration without using a cat's eye optical system or a corner cube. With the goal.

(Means for solving the problem) The encoder of the present invention splits a coherent light beam into a plurality of diffracted lights of a predetermined order via a first diffraction grating, and connects each of the plurality of diffracted lights to a moving object. A plurality of diffracted lights of specific orders generated from the diffraction grating on the moving scale surface are incident on a plurality of regions of a diffraction grating provided on the moving scale surface.
The feature is that the light is superimposed through a diffraction grating and then guided to a light receiving means, and the moving state of the moving object is detected using an output signal obtained from the light receiving means.

In this other invention, a coherent light beam is divided into a plurality of diffracted lights of a predetermined order through a first diffraction grating, and each of the plurality of diffracted lights is connected to a moving object. A plurality of diffracted lights of specific orders generated perpendicularly from the diffraction grating on the moving scale surface are made incident on multiple regions of a diffraction grating having the same grating pitch as the grating, and are returned to the original optical path via a mirror. After being diffracted by a diffraction grating on the moving scale surface and superimposed via the first diffraction grating, the light is guided to a light receiving means, and the moving state of the moving object is detected using the output signal obtained from the light receiving means. It is characterized by the fact that it is made to do so.

(Embodiment) FIGS. 1A and 1B are a perspective view and a sectional view of a main part of a first embodiment when the present invention is applied to a linear encoder.

1 in the figure is a laser light source, which consists of a semiconductor laser and has a wavelength λ (
=780nm) laser beam is emitted. A collimator lens 2 converts the laser beam from the laser light source 1 into a parallel beam.

101% First and second diffraction gratings 103 are transmission type diffraction gratings with a grating pitch of 2d, and are provided on substrate surfaces having the same coefficient of thermal expansion.

This prevents detection errors due to temperature changes.

3 is a transparent moving scale connected to a moving object (not shown), and is provided with a transmission type diffraction grating 102 having a grating pitch d. The moving scale 3 is sandwiched between the first and second diffraction gratings 101 and 103, and moves at a speed V in the grating arrangement direction as shown by the arrow.

8 is a light receiving means.

In this embodiment, the laser light emitted from the laser light source 1 is converted into a parallel beam by the collimator lens 2, and the first diffraction grating 10
It is perpendicularly incident on 1. At this time, from the first diffraction grating 101, two diffracted lights 1al and lbl of a predetermined order (±1st order in this embodiment, but 2nd order or more may also exist) are transmitted at a diffraction angle θ0.
．． That is, it is ejected at 0o-sun-' (input/2d)---(1).

The diffraction angle θ at the first diffraction grating 101. The two diffracted lights 1al and lbl are respectively incident on two locations 102m and 102b of the diffraction grating on the three surfaces of the moving scale at an angle θ0.

Then, each of the diffraction gratings 102m and 102bll has two specific orders (in this example, ±1
The second diffraction grating 1 transmits the diffracted light 1a2.1b2 of
03 is the incident angle θ.

After being diffracted and superimposed, the light is made incident on the light receiving means 8.

The light receiving means 8 obtains an output signal corresponding to the moving state of the moving scale 3.

In this embodiment, the moving scale 3 is moving at a speed V,
Diffraction gratings 102a and 102b on the three surfaces of the moving scale
The angle of incidence θ is from the direction in which it appears on the surface. The two diffracted lights 1a1.
lbl is incident.

At this time, the frequencies of the diffracted lights from the diffraction gratings 102a and 102b undergo a Doppler shift of +Δf and −Δf, respectively, in proportion to the moving speed V. Here, if λ is the wavelength of the laser beam, then the frequency position Δf can be expressed by the following equation (2), where θ is the incident angle.

Δf=v-5in (θ)/λ−−−(2)+Δf,−
The two diffracted lights that have undergone a Doppler shift of Δf interfere with each other and cause a change in brightness on the light receiving surface of the light receiving means, and the frequency F thereof is given by the following equation (3).

F=2 ・Δf=2 ・V-sin(θ)/λ-...
(3) From equation (3), the moving speed V of the moving scale 3 can be found by measuring the frequency F (hereinafter referred to as "Doppler frequency") of the light receiving means.

In this embodiment, the diffraction gratings 102a and 10 of the moving scale 3
Since the light is incident on portion 2b at an incident angle θ0 from each direction, F: 2 · v−S in θ from equations (1) and (3). /λ=V/d・・
・ ・ ・ (4) It is possible to detect the Doppler frequency F, which is 1wJ and is inversely proportional to the grating of the diffraction grating and the width d of the diffraction grating, independent of the wavelength λ of the laser beam, and proportional to the speed ■ of the moving scale 3.

At this time, when the moving scale 3 is displaced by one grating pitch d of the diffraction grating 102 in the grating arrangement direction as shown by the arrow, four bright and dark signals (sine wave signals) are obtained from the light receiving means 8. That is, a signal of 1 nosrus is detected from the light receiving means 8 for a displacement amount of d/4 of the moving scale 3.

In this embodiment, using the output signal from the light receiving means 8 at this time, the moving scale 3. That is, the moving state of the moving object is detected.

Furthermore, in this embodiment, the wavelength λ of the laser light emitted from the laser light source 1 changes, resulting in the diffraction angle θ of equation (1). Even if s changes
Inθ·/λ is kept constant. That is, since the position of incidence of the ±1st-order diffracted light toward the center, which has undergone a Doppler shift generated from the moving scale 3, on the second diffraction grating 103 remains unchanged, one advantage is that a stable signal can always be obtained. .

FIG. 2 is a sectional view of a main part of a second embodiment when the present invention is applied to a linear encoder.

In this embodiment, compared to the first embodiment shown in FIG.
．． 5I, beam splitter 17, polarization direction to each other 4
Two polarizing plates 71.7 m arranged at an angle of 5 degrees, and 2
one light receiving means 8+.

8, is provided. By providing these elements, a phase difference of 90 degrees is imparted to the output signals obtained from the light receiving means 81, 81, so that the moving direction of the moving scale 3 can also be determined.

The other configurations are the same as in FIG. 1.

In this embodiment, the laser beam emitted from the laser light source 1 is made into a parallel beam by the collimator lens 2, and the first diffraction grating 10
1, and the first diffraction grating 101 has a predetermined order (
±1st order) two diffracted lights la1. It is separated into lbl. Then, the two diffracted lights 1aL and lbl are each transferred to a λ/4 plate 5.
+, circularly polarized light at 5 m and diffraction grating 1 on the 3 planes of the moving scale
02a and 102b, and the diffraction grating 102a,
Two diffracted lights of a specific order (±1st order) from the section 102b are made incident on the second diffraction grating 103 and superimposed. Then, the diffracted light from the second diffraction grating 103 is separated into two beams, a reflected beam and a transmitted beam, by a beam splitter 17, and each is converted into a sine wave signal whose phase is shifted by 90 degrees from each other through a polarizing plate TI. 0 detected by the light receiving means 81.8m
In this embodiment, the moving speed and moving direction of the moving scale 3 are simultaneously detected using the output signals from these two light receiving means 81.8.

FIGS. 3(A) and 3(B) are a perspective view and a sectional view of a main part of a third embodiment when the present invention is applied to a linear encoder.

The advantage of this embodiment is that, compared to the first embodiment shown in FIG. , the other configurations are substantially the same.

In this embodiment, the laser beam emitted from the laser light source 1 is made into a parallel beam by the collimator lens 2, and is passed through the polarizing beam splitter 17 whose polarization direction is adjusted to 45.
The 1/4 wavelength plate 5 tilted at a degree converts the light into circularly polarized light and makes it perpendicularly enter the transmission type first diffraction grating 101 . First diffraction grating 101
The two diffracted lights 1a and lb of a predetermined order are (1
) is emitted at a diffraction angle θ0 shown by the formula, enters the reflection type diffraction gratings 102a and 102b provided on the three surfaces of the moving scale, undergoes a Doppler shift, is reflected, and returns to the original optical path.
The light enters the first diffraction grating 101 again and is superimposed.

Then, the two superimposed diffracted lights are passed through the 1/4 wavelength plate 5 as linearly polarized light whose polarization direction is perpendicular to that at the time of incidence, reflected by the polarizing beam splitter 17, and then made incident on the light receiving means 8. There is. The light receiving means 8 obtains a pulse signal corresponding to the moving state of the moving scale 3.

In this embodiment, the movable scale 3 is provided with a reflective diffraction grating, and each element is arranged on the same side, making it possible to arrange the movable scale 3 independently, thereby facilitating assembly of the entire device.

FIGS. 4(A) and 4(B) are a perspective view and a sectional view of a main part of a fourth embodiment when the present invention is applied to a linear encoder.

Compared to the third embodiment shown in FIG. 3, this embodiment uses diffraction gratings of a specific order generated in the vertical direction from the diffraction gratings 102a and 102b with a grating pitch d on the three surfaces of the moving scale. 1 The grating pitch of the diffraction grating 101 is
The advantages are that the grating pitch d is the same as in 02 and that a mirror 104 is used, but the other configurations are the same.

In this example, the above equation (1) becomes θ,=sin-'(λ/d)--(1°),
Further, the formula (4) becomes F = 2 V/d (4°).

In this embodiment, the laser beam emitted from the laser light source 1 is made into a parallel beam by the collimator lens 2, and is passed through the polarizing beam splitter 17 whose polarization direction is adjusted to 45.
The 1/4 wavelength plate 5 tilted at a degree converts the light into circularly polarized light and makes it perpendicularly enter the transmission type first diffraction grating lot. First diffraction grating 101
The two diffracted lights 1a and lb of a predetermined order are (l
o) Diffraction angle θ shown by the formula. It emits light, enters the reflective diffraction gratings 102a and 102bs provided on the three surfaces of the moving scale, undergoes a Doppler shift, is reflected and diffracted in the vertical direction, is reflected by the mirror 104, and returns to the original optical path to the moving scale. 3
The light re-enters the diffraction gratings 102a and 102b on the surface, is diffracted, re-enters the first diffraction grating lot, and is superimposed.

Then, the two superimposed diffracted lights are passed through the 1/4 wavelength plate 5 as linearly polarized light whose polarization direction is perpendicular to that at the time of incidence, reflected by the polarizing beam splitter 17, and then made incident on the light receiving means 8. . The light receiving means 8 obtains a pulse signal corresponding to the moving state of the moving scale 3.

In this embodiment, four light and dark signals (sine wave signals) are obtained from the light receiving means 8 for each displacement of one grating pitch d of the diffraction grating 102 of the moving scale 3.

That is, one pulse output signal is obtained for every d/4 displacement amount.

Then, the wavelength λ of the laser light from the laser light source 1 changes, resulting in the diffraction angle θ of the above-mentioned equation (lo). Even if the diffraction grating changes, the two diffracted lights generated from the diffraction gratings 102a and 102b of the moving scale 3 that have undergone Doppler shift enter the first diffraction grating lot on the same path and are superimposed, so the output signal is always stable. is obtained.

Another advantage is that even if the distance between the first diffraction grating 101 and the moving scale 3 changes, a stable output signal can be obtained as long as they are parallel to each other.

FIGS. 5A and 5B are a perspective view and a sectional view of a main part of a fifth embodiment when the present invention is applied to a linear encoder.

In this embodiment, compared to the fourth embodiment shown in FIG. 4, the moving scale 3 is made of a transmission type glass material, and the diffraction grating 102
is a transmission type diffraction grating, and the diffraction grating 1 of the moving scale 3 is
The difference is that the surface opposite to the surface on which 02 is provided is a mirror surface 12, and the other configurations are the same.

That is, the diffraction gratings 102a and 102b on the three surfaces of the moving scale
Among the light beams incident on the diffraction gratings 102a and 102b, the diffracted light of a specific order (±1st order) that is transmitted and diffracted in the vertical direction is reflected by the mirror surface 12, returns to its original optical path, and enters the diffraction gratings 102a and 102b again. , and the subsequent optical path and configuration are the same as in the fourth embodiment shown in FIG.

Although each of the above embodiments shows the case where the present invention is applied to a linear encoder, the present invention can be similarly applied to a rotary encoder. In this case, a rotary scale may be used instead of a linear scale.

In addition, in the 6-dimensional system, the ±1st-order diffracted light is used as the diffracted light generated from the diffraction grating, but it may also be ±nn-th order (where n is a natural number), or two diffracted lights of different orders, for example, the 0th order. The light and the n-th order light may be used.

FIG. 6 is a system configuration diagram of the encoder drive system of the present invention.

In the figure, an encoder 111 is connected to the drive output part of a drive means 110 having a drive source such as a motor, actuator, or internal combustion engine, or to the moving part of a driven object, and encodes the amount of rotation, rotation speed, amount of movement, etc. Detects driving conditions such as speed.

The detection output of the encoder 111 is fed back to the control means 112, and the control means 112 transmits a drive signal to the drive means 110 so that the state set by the setting means 113 is achieved. By configuring such a feedback system, the setting means 11 can be operated without being affected by disturbances.
The driving state set in step 3 can be maintained. Such a drive system can be widely applied to, for example, machine tools, manufacturing machines, measuring instruments, recording instruments, and not only these, but also general devices having drive means.

(Effects of the Invention) According to the present invention, by setting each element as described above, the moving state of a moving object can be determined without using the cat's eye optical system even if the wavelength of the laser light emitted from the laser light source changes. , it is possible to achieve an encoder that can perform stable and highly accurate detection without wavelength dependence.

[Brief explanation of drawings]

1(A) and (B) are a perspective view and a sectional view of a main part of a first embodiment of the present invention, FIG. 2 is a sectional view of a main part of a second embodiment of the present invention, and FIG. A), (B) to FIG. 5 (A), (B) are perspective views and cross-sectional views of the main parts of the third to fifth embodiments of the present invention, respectively, and FIG. 6 is a diagram of the drive system of the present invention. system configuration diagram,
Figure 7 is a schematic diagram of the main parts of a conventional encoder, and Figure 8 is a schematic diagram of the main parts of a conventional encoder.
It is an explanatory view of a part of a figure. In the figure, 1 is a laser light source, 2 is a collimator lens, 3 is a moving scale, 5.5+, 5@ is a 1/4 wavelength plate, 6 is a beam splitter, 7, 71, 7 is a polarizing plate, 8.8+,
8m is a light receiving means, 9 is a polarizing beam splitter 110,
, 101, 12 are mirrors 101 is the first diffraction grating, 10
3 is a second diffraction grating, and 102a and 102b are diffraction gratings.

Claims (5)

[Claims] (1) A plurality of diffraction gratings are provided on a moving scale surface that divides a coherent light beam into a plurality of diffracted lights of a predetermined order via a first diffraction grating, and each of the plurality of diffracted lights is connected to a moving object. A plurality of diffracted lights of specific orders generated from the diffraction grating on the moving scale surface are superimposed via a second diffraction grating, and then guided to a light receiving means, and an output obtained from the light receiving means. An encoder characterized in that the moving state of the moving object is detected using signals. (2) The first diffraction grating on the moving scale surface splits the coherent light beam into a plurality of diffracted lights of a predetermined order through a first diffraction grating, and connects each of the plurality of diffracted lights to a moving object. The diffraction lights are incident on a plurality of regions of a diffraction grating having the same grating pitch, and a plurality of diffracted lights of a specific order generated in the vertical direction from the diffraction grating on the moving scale surface are returned to the original optical path via a mirror,
After being diffracted by the diffraction grating on the moving scale surface and superimposed via the first diffraction grating, the light is guided to a light receiving means, and an output signal obtained from the light receiving means is used to determine the moving state of the moving object. An encoder characterized by detecting. (3) The encoder according to claim 1, wherein the first diffraction grating and the second diffraction grating have the same grating pitch and are provided on substrate surfaces having the same coefficient of thermal expansion. (4) The encoder according to claim 1 or 2, wherein the diffraction grating on the moving scale surface is a reflection type, and the first diffraction grating and the second diffraction grating are made of the same material. (5) The diffraction grating on the moving scale surface is of a transmission type, and the mirror is provided on a surface of the moving scale opposite to the surface on which the diffraction grating is provided. Encoder according to item 2.