JP3728310B2 - Encoder - Google Patents

Description

  The present invention relates to an encoder. In particular, the present invention makes a coherent light beam such as a laser beam incident on a fine grating array such as a diffraction grating attached to a moving object (scale), and interferes with a predetermined order of diffracted light from the diffraction grating to form interference fringes. By forming and counting the bright and dark fringes of the interference fringes, it can be favorably applied to encoders such as rotary encoders and linear encoders that measure movement information of the diffraction grating, such as movement amount, movement direction, acceleration, and angular acceleration. .

  Conventionally, there is a rotary encoder as a measuring instrument that can measure rotation information such as the rotation amount and rotation direction of a rotating object in an NC machine tool or the like with high accuracy, for example, in submicron units, and is used in various directions. .

  In particular, as a high-precision and high-resolution rotary encoder, a coherent light beam such as a laser is made incident on a diffraction grating provided on a moving object, and diffracted lights of a predetermined order generated from the diffraction grating are caused to interfere with each other. 2. Description of the Related Art A diffracted light interference type rotary encoder that obtains a moving state such as a moving amount and a moving direction of a moving object by counting light and dark is well known.

  In addition, an accelerometer that detects acceleration by measuring elastic deformation of an elastic body is known (for example, Patent Document 1). In particular, an acceleration detector using a diffracted light interference type encoder has been proposed as an accelerometer for the purpose of highly accurate acceleration detection. Further, as an angular accelerometer for detecting angular acceleration, an angular accelerometer such as a piezoelectric vibrator type or an optical fiber type gyroscope has been proposed.

  FIG. 9 is a schematic view of a main part of a part of a conventional rotary encoder using a diffracted light interference method.

In the figure, a monochromatic light beam emitted from a light source 101 is incident on a fine grating array 105 having a grating pitch P (the number of diffraction grating arrays is N) consisting of diffraction gratings on a scale (disc) 105a. Diffracted light beams are generated. At this time, the order of the light beam traveling straight is set to 0, and diffracted lights of orders such as ± 1, ± 2, ± 3,... Are defined on both sides thereof, and the rotation direction of the scale 105a is + and the reverse direction is −. It distinguishes by attaching | subjecting the code | symbol. Then, the phase of the wavefront of the nth-order diffracted light is 2π · n · N · θ / 360 when the rotation angle of the scale 105a is θ (deg) with respect to the wavefront of the 0th-order light.
It has the property of shifting.

  Accordingly, the diffracted lights of different orders are out of phase with each other, so that when the optical paths of the two diffracted lights are overlapped and interfered with each other by an appropriate optical system, a bright / dark signal is obtained.

  For example, if the + 1st order diffracted light and the −1st order diffracted light are overlapped and interfered with each other using the mirrors 109a and 109b and the beam splitter 103, the scale 105a rotates with one pitch (360 / N degrees) of each other while rotating. Since the phase is shifted by 4π, the light quantity change of light and dark in two periods occurs. Therefore, the amount of rotation of the scale 105a can be obtained by detecting a change in light intensity between dark and dark at this time.

  FIG. 10 is a schematic view of a part of a conventional diffracted light interference type rotary encoder that detects not only the rotation amount of the scale 105a but also the rotation direction.

  In the figure, compared to the rotary encoder of FIG. 9, at least two types of light / dark signals obtained from two diffracted lights accompanying the rotation of the scale 105a are prepared, and the rotation direction of the scale 105a is shifted by shifting the light / dark timing of each other. Is detected.

  That is, in the same figure, before superimposing the n-th order diffracted light and the m-th order diffracted light generated from the fine grating array 105, the polarizing plates 108a, 108b, etc. are used to form linearly polarized light beams whose polarization planes are orthogonal to each other. . Then, the optical paths are overlapped via the mirrors 109a and 109b and the beam splitter 103a, then transmitted through the quarter-wave plate 107a, and converted into linearly polarized light whose orientation of the plane of polarization is determined by the phase difference between the two light beams.

  Further, the light beam is split into two light beams by the non-polarizing beam splitter 103b, and the light beams are transmitted through polarizing plates (analyzers) 108c and 108d arranged so that detection directions (directions of linearly polarized light that can be transmitted) are shifted from each other. The detectors 110a and 110b detect two types of light and dark signals with different light and dark timing due to interference between two light beams.

For example, if the detection directions of the two polarizing plates are shifted from each other by 45 °, the brightness timing is shifted by 90 ° (π / 2) in terms of phase. The rotary encoder shown in the figure detects rotation information including the rotation direction of the scale 105a using signals from the two detectors 110a and 110b at this time.
JP-A-4-264264

  In a conventional encoder, if a plurality of movement information, for example, rotation information and linear movement information, are detected with respect to an object to be measured, two detection systems must be provided respectively, so that the entire apparatus tends to be large and complicated. there were.

  A first object of the present invention is to provide an encoder capable of simultaneously and independently detecting a plurality of movement information of an object to be measured, for example, movement information in one direction and rotation information about one axis at the same time. Another object of the present invention is to provide an encoder that can detect the acceleration in one direction and the angular acceleration in one direction with high accuracy using this. Still other objects of the present invention will become apparent in the following description.

According to the first aspect of the present invention, the first and second light beams having coherence from the light source means to the object to be measured provided with the first diffraction grating and the second diffraction grating. Incident on the diffraction grating,
A first optical system configured to cause interference between two light beams that are relatively out of phase when the object to be measured linearly moves among a plurality of diffracted light beams diffracted, and to detect the linear motion of the object to be measured by a detection system; A first detection system;
Two movement information of the second optical system and the second detection system, in which two light fluxes that are relatively out of phase are caused to interfere when the measured object rotates, and the detection system detects the rotational movement of the measured object. It is characterized by having a detection system.

  According to a second aspect of the present invention, in the first aspect of the invention, the object to be measured is composed of a rotating object, and the first and second diffraction gratings are composed of a radiation grating centered on the rotational axis of the rotating object. It is characterized by that.

  According to a third aspect of the present invention, in the first or second aspect of the present invention, the object to be measured is a rotating object, and the first and second diffraction gratings are in a scale plane and orthogonal to the rotation axis of the rotating object. It is characterized by a linear grid parallel to the straight line.

  According to a fourth aspect of the present invention, in the first, second, or third aspect of the invention, the object to be measured includes an elastic body and a casing provided in the casing, and the first detection system and the second detection system are A variation of the elastic body with respect to the housing is detected, and acceleration and angular acceleration applied to the housing are detected.

  According to the present invention, movement information of an object to be measured, for example, movement information in one direction and rotation information about one axis can be independently detected with high accuracy.

  FIG. 1 is a schematic view of the essential portions of Embodiment 1 of the present invention. This embodiment shows a case where two reflection type diffraction gratings are provided on an object to be measured (also referred to as a rigid body or a scale) 5 to detect movement information and rotation information of the object to be measured.

  In FIG. 1, reference numeral 1 denotes a light source that emits coherent light beams of both P-polarized light and S-polarized light (for example, a semiconductor laser whose polarization plane is inclined 45 degrees). After the light beam from the light source 1 is shaped by the collimator lens 2, it is separated into S-polarized light LS and P-polarized light LP by the first polarizing beam splitter 3a in which the polarization plane is arranged at an angle of 45 degrees with respect to the optical axis. . Here, the polarization beam splitter 3a transmits P-polarized light and reflects S-polarized light.

  Among these, the P-polarized light LP is reflected by the mirror 4b and is incident on the region 5aP of the diffraction grating (first diffraction grating) 5a. The S-polarized light LS is reflected by the mirror 4a and is incident on the region 5aP of the diffraction grating 5a. At this time, the two light beams incident on the diffraction grating 5a are obliquely incident on the same point from two directions so that the incident angle is the same as the first-order diffraction angle. The S-polarized + 1st-order diffracted light S + and the P-polarized -1st-order diffracted light P- are reflected and diffracted in the same direction perpendicular to the surface of the diffraction grating 5a.

  Then, the first-order diffracted light S + and the −1st-order diffracted light P− are symmetric with respect to the first diffraction grating 5a with respect to the rotational axis (axis) 10 of the torsion of the measured object (elastic body) by the deflecting means 6a and 6b such as mirrors. Is incident perpendicularly to a diffraction grating (second diffraction grating) 5b.

  FIG. 2 is a schematic view when the scale 5 is moved in the A direction at this time, and FIG. 4 is a block explanatory diagram of each element of FIG.

  2 and 4, the P-polarized light P-- and the S-polarized light S +--1st order diffracted by the second diffraction grating 5b are reflected by the mirror 7b and guided to the polarizing beam splitter 3b. Further, P-polarized light P-++ and S-polarized light S ++ + 1st order diffracted by the diffraction grating 5b are reflected by the mirror 7a and guided to the polarizing beam splitter 3b, and these polarized lights are superposed by the polarizing beam splitter 3b. Yes.

  Of these luminous fluxes, S-polarized light S ++ and P-polarized light P-- having a relative phase difference of 8π are guided to the polarizing plate 13a and detected by the first photodetector 9a, and the relative phase difference is 0. S-polarized light S + 1 and P-polarized light P- + are guided to the polarizing plate 13b and detected by the second photodetector 9b. At this time, the movement information is detected by the photodetector 9a, but the movement information is not detected by the photodetector 9b.

  3 is a schematic diagram when the scale 5 is moved in the B direction in FIG. 1, and FIG. 5 is a block explanatory diagram of each element of FIG.

  3 and 5, the P-polarized light P-- and the S-polarized light S + -1 -1st order diffracted by the diffraction grating 5b are reflected by the mirror 7a and guided to the polarizing beam splitter 3b. Further, the P-polarized light P-++ and the S-polarized light S ++ + 1st order diffracted by the diffraction grating 5b are reflected by the mirror 7b and guided to the polarizing beam splitter 3b. Then, the polarization beamsplitter 3b superimposes these polarized lights.

  Then, P-polarized light P− + and S-polarized light S + − having a relative phase difference of 0 among these light beams are detected by the first photodetector 9a through the polarizing plate 13a, and the relative phase difference is detected. 8π P-polarized light P-- and S-polarized light S ++ are detected by the second photodetector 9b through the polarizing plate 13b. At this time, the movement information is detected by the photodetector 9b, but the movement information is not detected by the photodetector 9a.

  In this embodiment, the movement information of the moving object is detected by a signal processing system (not shown) using signals from the photodetectors 9a and 9b. Next, the detection principle of the moving information of the moving object in this embodiment will be described. This will be described with reference to FIGS. In FIGS. 4 and 5, the order m of the m-th order diffracted light is set to m = 1.

FIG. 6 is an explanatory diagram showing the relationship between the grating moving direction and the diffraction order. As shown in FIG. 6, when coherent light having a wavelength λ is incident on the diffraction grating 51 in which slits having a constant pitch P are formed, in the direction of the angle θ,
Psin θ = mλ (m = 0, ± 1,...)
Diffracted light is generated.

  Here, m-order diffracted light diffracted in the moving direction of the grating is defined as + m-order diffracted light, and m-order diffracted light diffracted in the opposite direction is defined as -m-order diffracted light. When the diffraction grating 51 moves X, the phase of the m-th order diffracted light before and after the movement is

Only changes. Therefore, in the first-order diffracted light (m = 1), when the diffraction grating moves by one pitch, the phase changes by 2π.

  In a diffracted light interference type encoder, in a diffraction grating provided on a scale, light that has been subjected to + 1st order diffraction twice and light that has been subjected to -1st order diffraction are overlapped so that the phase shifts by 8π relative to one pitch of the grating. It is configured. Therefore, a phase change of four periods occurs with respect to the scale movement of one pitch of the grating.

  In this embodiment, + m-order diffracted light diffracted from the diffraction grating is light diffracted in the moving direction of the diffraction grating out of m-th order diffracted light, and -m-order diffracted light is opposite to the moving direction of the diffraction grating in m-th order diffracted light. Is diffracted light.

  For example, in a diffracted light interference type rotary encoder, the relative phase of light that has been subjected to + m-order diffraction twice and light that has been subjected to -m-order diffraction twice is 1 of the diffraction grating due to the rotation of the scale by a radial diffraction grating. It changes by 8 mπ with respect to the angle change corresponding to the pitch. In this embodiment, the rotation information of the rotating object (diffraction grating) is detected by detecting the interference light of both at this time.

  Also, in the state where two parallel diffraction gratings on the scale are both moved by the same amount in the direction perpendicular to the grating, attention is paid to the m-th order diffracted light, and the light beam from the light source coherent to the first diffraction grating. The + m-order diffracted light Lm and the -m-order diffracted light L-m are transmitted by an optical transmission means such as a lens, a prism, a mirror, or an optical fiber, and are incident on the second diffraction grating. At this time, the + m-order diffracted light Lm, m, + m-order diffracted light -m-order diffracted light Lm, -m, -m-order diffracted light + m-order diffracted light L-m, m, -m Folded -m-order diffracted light Lm, -m, and above four kinds of m-order diffracted light are obtained.

  When the scale 5 moves in the A direction, as shown in FIG. 2 and FIG. 4 (reference), the + m-order diffracted light Lm of the + m-order diffracted light, and the −m-order diffracted light L-m, −m of the −m-order diffracted light. To interfere with. Since the phase between them is relatively shifted by 8 mπ per movement of one pitch of the diffraction grating, the interference light is detected by a first detection system having a device (photodetector) such as a photodiode or CCD. The movement information of the diffraction grating is detected.

  Further, the -m-order diffracted light Lm, -m of + m-order diffracted light and the + m-order diffracted light L-m, m of -m-order diffracted light are also detected by the second detection system similar to the first detection system. When the two diffraction gratings are both moving in the direction perpendicular to the grating, the two two-time diffracted beams Lm, -m, Lm, and m that reach the second detection system are in phase, so that the interference signal Does not change. For this reason, movement information cannot be obtained.

  Next, when the scale 5 changes in the B direction, that is, the two diffraction gratings are perpendicular to the grating, one diffraction grating is in the same direction as the above, and the other diffraction grating is in the opposite direction to the above direction. Consider the case of moving (in the case of moving in directions opposite to each other perpendicular to the lattice) (see FIGS. 3 and 5).

  This corresponds to a state in which the scale rotates in the plane. At this time, there is no phase difference between the two diffracted lights Lm, -m, Lm, and m that reach the first detection system. However, the two diffracted lights Lm, m, Lm, and -m that reach the second detection system are the same as the first diffraction grating and the second diffraction, as in the case where the above-described grating is moving in the same direction. The grating has a relative phase difference of 8 mπ when the difference in the amount of movement of the diffraction grating is two pitches.

  For example, if two diffraction gratings are provided in parallel to the direction connecting two irradiation points on the same rigid body (object to be measured), the signal of the first detection system is irradiated by two diffraction gratings. This is a signal for movement in the direction perpendicular to the grating on the diffraction grating plane at the midpoint of the point. Also, consider the case where the rigid body rotates in a plane including the diffraction grating. If the rotation angle is small, each diffraction grating can be regarded as linearly moving in the opposite direction, and the second detection system can detect an in-plane rotation angle including two gratings. it can.

  In addition, the detection range in the rotational direction can be expanded by using two diffractive gratings as radial diffractive gratings as in the conventional diffracted light interference type rotary encoder. At this time, since the direction of the grating changes with the linear movement, the detection range of the linear displacement becomes smaller than that of the parallel diffraction grating.

  In this embodiment, the movement information of the moving object is obtained using the above detection principle. Next, a specific detection method of this embodiment will be described.

  First, as shown in FIG. 2, when the two diffraction gratings are both displaced in the direction of arrow A (the diffraction grating scale moves linearly in the direction perpendicular to the grating).

  At this time, the light that passes through the polarizing beam splitter 3b and reaches the photodetector 9a (first detection system) through the polarizing plate 13a undergoes + 1st order diffraction with P polarized light P-- that has been subjected to -1st order diffraction twice. The S-polarized light S ++ is rotated twice, and the relative phase of each is 8π per displacement of one pitch of the grating. These lights pass through a polarizing plate (not shown) whose polarization axis is set to 45 degrees with respect to each linearly polarized light, thereby becoming linearly polarized light defined by the polarization axis, and accompanying the movement of the grating in the photodetector 9a. This is detected as the movement of interference fringes. Then, the movement information of the lattice, that is, the movement information of the torsion shaft 10 of the elastic body is obtained by calculation means (not shown) using the signal from the photodetector 9a.

  On the other hand, the light that is reflected by the polarization beam splitter 3b and reaches the photodetector 9b (second detection system) through the polarizing plate 13b is P-polarized P- + that has undergone -1st order diffraction and + 1st order diffraction, and + 1st order. This is S-polarized S + − that has been subjected to −1st order diffraction. At this time, there is no phase difference due to the movement of the grating. For this reason, the photodetector 9b does not change the interference state, and a signal cannot be obtained.

  As shown in FIG. 3, when two diffraction gratings rotate in the direction of arrow B (a state in which a scale provided with a grating rotates).

  That is, when the object to be measured is rotating around the rotation axis 10, the light passing through the polarizing beam splitter 3b and reaching the photodetector 9a through the polarizing plate 13a at this time is −1st order diffraction and + 1st order. Folded P-polarized light P- + and + 1st-order and -1st-order diffracted S-polarized light S +-, and no phase difference is caused by the rotation of the grating. For this reason, rotation information cannot be obtained.

  The light reflected by the polarizing beam splitter 3b and reaching the photodetector 9b via the polarizing plate 13b is P-polarized light P-- that has been subjected to -1st order diffraction twice and S-polarized light S ++ that has been subjected to + 1st order diffraction twice. There is a relative phase difference of 8π due to one pitch rotation in the plane including the grating. The P and S polarizations become linearly polarized light defined by the polarization axis by a polarizing plate (not shown) whose polarization axis is inclined by 45 degrees with respect to the P and S polarizations, and the movement of the interference fringes is detected by the photodetector 9b. Is used to detect the rotation information in the plane of the lattice.

In this embodiment, the photodetector 9a in FIG. 2 obtains a signal corresponding to the deviation in the A direction of the grating, and the photodetector 9b in FIG. 3 obtains a signal corresponding to the in-plane rotation of the grating. . In particular, the acceleration and angular acceleration applied to the beam 10 are detected by simultaneously detecting the deflection and torsion of the beam (roller) 10 provided with the diffraction grating by the detection signals from the photodetectors 9a and 9b. Since the method of detecting the acceleration and angular acceleration from the displacement and angular displacement is well known, the description thereof is omitted.

  In the configuration of FIG. 1, the tilt of the grating is shifted with the in-plane rotation, and the polarization direction is shifted. Therefore, the rotation angle is limited to a very small amount, but according to this configuration, the center of rotation is at two incident points of light. Without being limited, the rotation angle of the scale can be measured.

  In this embodiment, a mirror is used as a means for deflecting and transmitting light. However, if this is a means for deflecting the traveling direction of light, for example, a prism, an optical fiber, an optical waveguide, etc. using refraction are the same. Is possible. Further, in this embodiment, in order to make the optical paths of the S-polarized light and the P-polarized light between the first diffraction grating 5a and the second diffraction grating 5b the same, the incident angle to the first diffraction grating 5a is changed. Although it is the same as the first-order diffraction angle generated, it is possible to adopt a configuration in which the light is incident at another angle and transmitted through another optical path.

  Furthermore, when detecting the direction of movement, it is necessary to detect the moving direction of the interference fringes. At this time, as a method realized by a diffracted light interference type encoder, interference fringes in the light beam of interference light are brought close to zero. At this time, the interference light becomes a light / dark repetitive pattern accompanying the movement of the scale, but the optical system as shown in FIG. 7 is replaced with the λ / 4 plate 8a (8b) and the photodetector 9a (9b) in FIG. You may do it.

  In FIG. 7, reference numeral 8c denotes a λ / 4 wavelength plate having a fast axis set at 45 degrees with respect to the P-polarized light and the S-polarized light. The P-polarized light and the S-polarized light are circularly polarized light that are opposed to each other in the rotational direction. The interference light becomes linearly polarized light that rotates as the scale moves. This is divided into two by a non-polarizing beam splitter 12, and each rotating linearly polarized light is sine wave having a phase difference of 90 degrees by photodetectors 9c and 9d by polarizing plates 13a and 13b having different polarization directions by 45 degrees. The light is detected as light and dark.

  Then, the light detectors 9c and 9d detect the light and darkness of the two-phase light that is 90 degrees out of phase with each other, thereby obtaining information on the moving direction of the object to be measured. For example, if the object to be measured is displaced in both the directions of the arrow A and the arrow B in FIG. 1, movement information can be obtained from the photodetectors 9a and 9b, respectively.

  FIG. 8 is a schematic view of the essential portions of Embodiment 2 of the present invention. In this embodiment, a transmission type diffraction grating is used instead of the reflection type diffraction grating as compared with the first embodiment shown in FIG. 1, and the light beam from the light source 1 is incident perpendicularly on the first diffraction grating. Further, the difference is that the diffracted light of a predetermined order is obliquely incident on the second diffraction grating, and the other configurations are the same.

  In FIG. 8, a light beam emitted from the light source 1 and shaped by the collimator lens 2 is vertically incident on the first diffraction grating 5a. Then, the + 1st order diffracted light and the −1st order diffracted light diffracted by the diffraction grating 5a are made incident on the second diffraction grating 5b through the mirrors 6a and 6b and the mirrors 6c and 6d at the same angle as the first order diffraction angle. The first-order diffracted light and the −1st-order diffracted light diffracted by the diffraction grating 5 b are superimposed and detected by the photodetector 9 b via the photodetector 9 a, mirrors 7 a and 7 b, and the half mirror 11.

  The two diffraction gratings both move in the direction of arrow A in FIG.

  At this time, similarly to FIG. 2, the light having been subjected to the + 1st order diffraction twice and the light having been subjected to the −1st order diffraction are incident on the photodetector 9a in an overlapping state. As a result, when the diffraction grating moves by one pitch as in the first embodiment, the phase of each diffracted light is relatively shifted by 8π.

  In this embodiment, the displacement information of the diffraction grating is detected by counting the interference fringes based on this deviation. In addition, since the phase difference due to the movement of the diffraction grating does not occur in the light detected by the photodetector 9b, there is no change in the interference state in the signal obtained by the photodetector 9b, so that a movement signal is obtained. Absent.

  When two diffraction gratings rotate in the direction of arrow B in FIG.

  That is, when two diffraction gratings rotate about a rotation axis (not shown) as in FIG. 3, at this time, they are diffracted by the diffraction grating 5b, reflected by the mirrors 7a and 7b, superimposed by the beam splitter 11, and light The detector 9b becomes interference light between the light that has been subjected to the + 1st order diffraction twice and the light that has been subjected to the −1st order diffraction twice. At this time, interference fringes based on the superposition of the two lights from the signal obtained by the photodetector 9b. The rotation information of the diffraction grating is detected by counting.

  At this time, since the phase difference does not occur in the light detected by the photodetector 9a, a signal relating to the rotation information cannot be obtained by the photodetector 9a.

  In addition, the encoder capable of detecting movement information in two directions according to the present invention is applied to, for example, a diffraction grating provided in a part of the casing and the elastic body, and the twist due to the angular acceleration of the elastic body is used as the rotation of the scale. If detected, angular acceleration can be detected. At the same time, if the deflection of the elastic body is detected as the parallel movement of the scale, the acceleration can be detected. As a result, acceleration and angular acceleration can be simultaneously measured with the same optical system.

  FIG. 11 is a schematic view of the main part of a modified embodiment of the present invention. In the embodiment described above, one light beam is first incident on one grating, but in this modification, two light beams are incident and diffracted independently on each grating, and the optical transmission indicated by the dotted line in the figure. The same detection is possible even if they are combined by means. In the figure, LG indicates an optical transmission means, and HM indicates an optical splitting means. The subscript indicates the sign of the diffraction order. or,

X is when the L ₂ incident grating moves in the same direction as the L ₁ incident grating (linear motion), and Y moves in the opposite direction (rotational motion).

  Two light beams L1 and L2 having coherence are incident on two places of the grating provided on the object to be measured, and respective + m-order diffracted light and -m-order diffracted light are obtained. If these four beams are overlapped by two as shown in the figure, and an interference signal detection system is configured for each of them as in the embodiment described above, the rotational motion and linear motion of a rigid body provided with a grating can be detected independently. Can do.

Schematic diagram of essential parts of Embodiment 1 of the present invention Schematic diagram of the main part when the scale changes in the A direction in FIG. Schematic diagram of the main part when the scale changes in the B direction in FIG. Block explanatory diagram when the scale fluctuates in the A direction in FIG. Block explanatory diagram when the scale fluctuates in the B direction in FIG. Explanatory drawing which shows the relationship between the moving direction of the diffraction grating which concerns on this invention, and diffracted light Explanatory drawing when a part of FIG. 1 is changed Schematic diagram of essential parts of Embodiment 2 of the present invention Schematic diagram of a part of a conventional rotary encoder Schematic diagram of a part of a conventional rotary encoder The principal part schematic of the modification of this invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Light source 2 Collimator lens 3a, 3b, 11 Polarization beam splitter 4a, 4b, 6a, 6b, 6c, 6d, 7a, 7b Mirror 5a, 5b Diffraction grating 8a, 8b (lambda) / 4
9a, 9b photodetector 10 rotation axis

Claims (4)

First and second light beams having coherence from the light source means are incident on the first and second diffraction gratings on the object to be measured provided with the first diffraction grating and the second diffraction grating,
A first optical system that interferes with two light beams that are relatively out of phase when the object to be measured linearly moves among the plurality of diffracted light beams diffracted, and detects the linear motion of the object to be measured by a detection system; A first detection system;
Two movement information of the second optical system and the second detection system, in which two light fluxes that are relatively out of phase are caused to interfere when the measured object rotates, and the detection system detects the rotational movement of the measured object. An encoder characterized by having a detection system. 2. The encoder according to claim 1, wherein the object to be measured is composed of a rotating object, and the first and second diffraction gratings are composed of a radiation grating centered on the rotation axis of the rotating object. The object to be measured includes a rotating object, and the first and second diffraction gratings are linear gratings in a scale plane and parallel to a straight line orthogonal to a rotation axis of the rotating object. 1 or 2 encoders. The object to be measured includes an elastic body and a housing provided in the housing, and the first detection system and the second detection system detect a change of the elastic body with respect to the housing and add to the housing. 4. The encoder according to claim 1, wherein acceleration and angular acceleration are detected.