JP2003097975A - Origin detecting device for rotary encoder and measurement device for rotation information - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a small detection system for an origin position having high accuracy that enables origin detection at both sides of a rotary disk together with a detection optical system for incremental signal. SOLUTION: A monochromatic luminous flux is radiated from a light source to then be converted into a parallel luminous flux with a collimator lens and thereafter divided into two parallel luminous fluxes where an optical axis is parallelly shifted with a diffraction grating plate. This parallel luminous flux is individually divided into two parts and then taken out by each of polarized light components. Each of fluxes from the polarized light components is lighted to a point symmetrical position to the rotating axis of a diffraction grating track in a detection system for a rotation quantity, and then diffraction beams of mutually different orders generated in the diffraction grating track are taken out to be interfered by superimposing wave surfaces, and then a cycle signal accompanied with the rotation movement of a disk is generated. Each of other fluxes from polarized light components is lighted to a point symmetrical position to the rotating axis of a origin track, and then two fluxes modulated with a origin pattern are detected with each of photodetectors and then an origin signal is generated in a detection system for a origin position.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-precision rotary encoder origin position detecting device having a resolution of the order of submicron, and more particularly to an optical origin detecting device to which the detection of a fine pattern by light is applied and the origin detecting device. The present invention relates to a rotation information measuring device used. Further, the purpose of applying the present invention is to provide a specific origin position detecting means having detection reproducibility on the order of submicrons.

[0002]

2. Description of the Related Art Encoders of the so-called grating interference system, which are based on the principle of illuminating a laser on a diffraction grating to cause the diffracted lights to interfere with each other and detecting the relative movement of the diffraction grating, are used in various high-precision positioning devices and the like. Has been done. In general, an incremental type rotary encoder has 1 in 1 rotation.
A pattern for generating an origin signal indicating the origin position is provided, and the number of pulses generated by the rotation of the radial diffraction grating is counted to obtain the rotation position from the target origin position. In particular, the Japanese Patent Publication No. Sho-Kai by the present inventors discloses an optical system in which the grating interference system is constructed as a rotary encoder in a small size.

FIG. 8 shows this conventional rotary encoder. Now, in the rotary encoder shown in the same figure, in order to realize a small size and high accuracy, a prism having a dividing surface PBS is used, and a collimator lens CL collimates a collimated light flux from a light source LD into two, which are symmetrically divided. The luminous flux is illuminated at two symmetrical positions of the rotating disk on which the diffraction grating GT is recorded, and the diffracted light obtained from the luminous flux is separated by 1 each.
An interference signal is generated by reusing the prism through the quarter-wave plate QWP and the cat's eye CA1 and CA2.

With such a structure, it is unavoidable for the rotary disk to cancel the measurement error of the angle information due to the deviation (eccentricity) between the pattern center and the rotation center of the rotary disk, which is a problem peculiar to the rotary encoder. Even if the eccentricity error remains, highly accurate angle detection can be performed. That is, by detecting the angular displacement information at two points symmetrical with respect to the rotation axis and optically averaging the information,
Only the parallel-lateral displacement component of the disc is canceled.
The error due to the eccentricity of the disc is not only caused when the disc is mounted on the rotation shaft, but also when the disc rotation shaft position is laterally displaced on the submicron order due to an external force acting on the rotation shaft during rotation of the disc. This is especially important in the case of high resolution encoders, as it affects them.

Further, in the origin detection of the rotary encoder shown in FIG. 8, the parallel light flux from the collimator lens CL is split by the beam splitter HM, and the origin signal pattern OP is irradiated through the cylindrical lens LZ.
Light is received by the light receiving element PD (Z1, Z2).

[0006]

However, when the angular resolution of the encoder is on the order of submicrons on the circumference of the radial grating on the disk, it is said that the movement of the radial grating is detected only on one side of the disk. , The movement of the radial grating due to the parallel displacement of the disk is detected due to the influence of the external force. Therefore, in order to measure the angle information accurately, both the incremental signal detection and the origin signal detection are measured on both sides with respect to the rotation axis of the rotating disk,
There is a demand for averaging technology. Among them, Fig. 10
Even in the origin detection in the rotary encoder shown in (1), the index of the rotating disk is optically detected at a single place because of the restriction of the small outer shape.

An object of the present invention is to use a small and highly accurate origin position detecting device for a rotary encoder, which is capable of performing origin detection on both sides of a rotating disk together with an incremental signal detection optical system. It is to provide a rotation information measuring device.

[0008]

Therefore, the present inventors have
Incremental light flux and origin light flux are formed in parallel by using a prism of a unique shape, and the incremental signal detection light flux and the origin detection light flux can be illuminated at two locations symmetrically with respect to the rotation axis of the disc. It was done like this.

That is, the origin detecting device of the rotary encoder according to the present invention includes a collimator lens for converting a monochromatic light beam emitted from a light source into a substantially parallel light beam and at least two parallel light beams whose optical axes are displaced in parallel. A diffraction grating plate for generating a parallel light flux, and a polarization beam splitter for splitting each of the at least two parallel light fluxes into two and extracting the polarized light for each polarization component are provided. Is illuminated at a position that is substantially point-symmetric with respect to the rotation axis of the origin track provided with the origin pattern and provided on the rotating plate for detecting the rotation amount, and the two light fluxes modulated by the origin pattern are respectively illuminated. It is characterized in that it is detected by a light receiving element and an origin signal is generated.

Further, the rotation information measuring device of the present invention divides a substantially parallel light beam by a light source that irradiates a monochromatic light beam, a collimator lens that converts light emitted from the light source into a substantially parallel light beam, and optical axes are parallel to each other. Grating plate for generating at least two parallel light beams deviated from each other, a polarization beam splitter for splitting each of the at least two parallel light beams into two polarization components, and a diffraction grating track and origin pattern having a radial diffraction grating Generated on the diffraction grating track by illuminating a rotating plate having an origin track, which is equipped with, and one light flux from each of the two polarized light components, at a position point-symmetric with respect to the rotation axis of the diffraction grating track. A rotation amount detection system that takes out the diffracted lights of different orders and causes the wavefronts to overlap and interfere with each other to generate a periodic signal associated with the rotational movement of the disk. Each one by another first light flux from the polarized light component, to illuminate the substantially point symmetrical positions with respect to the axis of rotation of the origin track, which is modulated by the origin pattern 2
It is characterized by having an origin position detection system that detects one light flux by each light receiving element and generates an origin signal.

[0011]

In the preferred embodiment of the present invention, each light receiving element for detecting the origin position is a two-division photoelectric sensor, and a modulated light beam is illuminated near the division line of these light receiving elements. The deviation of the origin position is detected by utilizing the level change between the two divided photoelectric sensors.

Further, since the pair of origin patterns are provided at positions substantially point-symmetric with respect to the rotation axis of the origin track, they are detected twice each time the rotary plate makes one revolution. In order to avoid this, for example, a pair of slit-shaped reflection patterns is provided at a position slightly deviated from the position symmetrical with respect to the rotation axis of the origin track, and the position substantially symmetrical with respect to the rotation axis of the origin track is provided. Each of the light fluxes that illuminate at a point may be illuminated at a position that is slightly offset from the point-symmetrical position with respect to the rotation axis of the origin track so that a pair of slit-shaped reflection patterns are simultaneously illuminated. Further, even when the origin pattern is provided at a position which is just point-symmetrical, it can be avoided by providing a pair of diffractive lens patterns that converge or reflect only the illumination from one angle to the origin position detecting light receiving element.

(Embodiment 1) A first embodiment of the present invention will be described with reference to FIG. FIG. 1 is a schematic perspective view showing an embodiment of a rotation information measuring device in which the origin detecting device of the present invention is applied to a grating interference type rotary encoder, and a part of a light beam in the shadow of a member is also indicated by a solid line. ing. 2 is a top view of the rotary encoder shown in FIG. 1, and FIG. 3 is a side view.

In the figure, LD is a monochromatic light source, CL is a collimator lens, GT1 and GT2 are diffraction gratings for splitting and deflecting the light flux, PP is a polarization prism, PBS is a polarization splitting surface (polarization beam splitter), and M1 is , M2 is a mirror prism, DP is a disk plate that rotates relative to the detection optical system, GT is a radial diffraction grating recorded on the circumference of the disk, and SLIT1 and SLIT2 are disks D.
A slit-shaped reflection pattern recorded on the origin track OT on P, QWP1 to 3/4 wavelength plate, CA1 to CA2 optical element, NBS non-polarizing beam splitter, P45 45 ° azimuth polarizing plate, and P90. Is a 90-degree azimuth polarization plate, and PDA, PDB, and PDZ (Z1 to Z4) are light receiving elements.

In the present embodiment, the light beam emitted from the light source LD is converted into a substantially parallel light beam by the collimator lens CL, enters the diffraction grating GT1, and generates the 0th-order diffracted light R0 and the deflected 1st-order diffracted light R1. The first-order diffracted light R1 is further incident on the diffraction grating GT2 to generate −1st-order diffracted light R2.
As a result, these two light fluxes R0 and R2 are light fluxes whose positions are displaced from each other and travel in the same direction. Both of them enter the polarizing prism PP, are reflected by the reflecting surface inside thereof, and are transmitted P polarized light and reflected S by the internal polarization splitting surface PBS.
Split into polarized waves. As shown in FIG. 2, the polarization splitting surface PBS is located in an imaginary plane that passes through the center of rotation of the disc plate DP and is perpendicular to the disc plate DP.

The P-polarized light transmitted through the polarization splitting surface PBS passes through the mirror prism M1 and one P-polarized light beam is illuminated at the point P1 on the radial diffraction grating track GT of the disk DP at the angle of the first-order diffraction. Transmitted through the radial diffraction grating 1
Next-order diffracted light is generated almost perpendicular to the disc DP,
The light passes through the four-wave plate QWP1 to become circularly polarized light, reflected by the original optical path of the CAT'S EYE optical element CA1, and again ¼.
It is converted into S-polarized light by passing through the wave plate QWP1, travels again into the polarization prism PP, and the internal polarization splitting surface P
Since it acts as S-polarized light at the BS, it is reflected this time and emitted from the polarizing prism PP to the quarter-wave plate side QWP3. The other P-polarized light beam is illuminated on the origin pattern track OT of the disc DP, and when the slit-shaped reflection origin pattern SLIT1 is in the illumination area, the reflected light travels toward the light receiving elements PDΖ1 and PDΖ2. Light receiving element P
The light quantity of DΖ1 and PDΖ2 is determined by the slit-shaped origin pattern S
Since it is configured so as to continuously change according to the position of LIT1 (shadow and not shown in FIG. 1), the timing at which light is incident on both light receiving elements at the same light amount (rotation position of the disk: see FIG. 4). ) Exists.

On the other hand, one of the reflected S polarized waves is illuminated through the mirror prism M2 to the point P2 on the radial diffraction grating track GT of the disk DP at the angle of the -1st order diffraction and transmitted through the radial diffraction grating. The minus first-order diffracted light is generated substantially vertically, passes through the quarter-wave plate QWP2, becomes circularly polarized light, and is reflected by the CAT'S EYE optical element CA2 to the original optical path.
The light beam that traces the original optical path is again the quarter wave plate QWP2.
Is converted into P-polarized light by passing through, and then travels again into the polarization prism PP, and since it acts as P-polarized light on the internal polarization splitting surface PBS, this time it is transmitted, and the polarization prism PP transmits a quarter wave plate. It is injected to the QWP3 side. In addition, this P
The polarized light beam and the S-polarized light beam are respectively a quarter wavelength plate Q
One of them is transmitted through the WP3, converted into circularly polarized light beams of opposite directions, and combined with each other, whereby the polarization plane of the linearly polarized light beam is rotated by a change in phase difference (rotation of the disk) between the two light beams. It is converted into a linearly polarized light beam. This luminous flux is
It is divided into two equivalent light fluxes by the NBS, passes through the polarizing plates P45 and P90, respectively, and is further received by the light receiving elements PDB and PDB.
It is incident on DA. The linearly polarized light flux passing through the polarizing plates P45 and P90 has the maximum amount of transmitted light when the polarization azimuth coincides with the optical axis of the polarizing plate. Therefore, the signal changes sinusoidally, and further two received light beams are received. The timing of the change in the sinusoidal light-dark signal reaching the element is generated by the azimuth shift of the polarizing plates. In this embodiment, the phase shift is 90 degrees.

The other S-polarized light beam is illuminated on the origin pattern track OT of the disk DP, and when the slit-shaped reflection origin pattern SLIT2 is in the illumination area, the reflected light travels toward the light receiving elements PDΖ3 and PDΖ4. To do. The light amounts of the light receiving elements PDΙ3 and PDΖ4 are configured to continuously change according to the position of the slit-shaped origin pattern SLIT2, so that the timing (disc rotation position) at which light is incident on both light receiving elements is equal. Exists.

Therefore, as shown in FIG. 4, the light receiving element PD
The output of Z1 (Z1) and the output of PDZ3 (Z3) are added, the output of the light receiving element PDZ2 (Z2) and the output of PDZ4 (Z4) are added, and the change in both output levels is seen. The waveforms are averaged so as to remove the effects of eccentricity and the like. Then, the added signals are compared with each other, and at the moment when the levels of the two coincide with each other, that is, the difference signal {(Z1 + Z3)-(Z2 + Z4)} between the received light amount sum signals becomes 0, the origin signal pulse Z of a certain width is generated. Should occur.

In the present embodiment, the origin track OT
It is supposed that the upper slit-shaped origin pattern is recorded at two points symmetrical about the rotation axis of the disk DP.
Therefore, if the origin is detected in this state, 2
Two origin signals are obtained. Therefore, the first slit pattern SLIT1 and the second slit pattern SL
By slightly shifting IT2 from the symmetrical position, only when a specific origin pattern is detected by a specific light receiving element in one rotation, a reflected light flux of a sufficient level is incident on both light receiving elements, and the addition signal (light reception Light amount sum signal: Z1 + Z3 or Z2 + Z4, and total sum signal: Z1 + Z2 + Z3 + Z
The level of 4) is almost doubled. On the other hand, in the case of the reverse combination, the timing of detecting the origin slit pattern is deviated, and looking at the added levels, it is found that the respective detection signals deviate. Since it is observed, when monitoring the level coincidence between the added signals, the combination of the origin patterns can be specified depending on whether or not the overall level exceeds the specified value. For example, as shown in FIG. 4, a window signal (W) is transmitted in a state where the level of the total sum signal exceeds a specified value, and when the window signal is ON, a difference signal between the received light amount sum signals is 0
It may be monitored whether or not FIG. 2 shows a state in which the origin pattern is detected. As shown in the figure,
SLIT1 and SLIT2 are formed at positions slightly deviated in the same direction from a straight line that passes through the center of rotation of the disc plate DP and is perpendicular to the virtual plane.

(Second Embodiment) A second embodiment of the present invention will be described with reference to FIGS. FIG. 5 is a schematic perspective view showing an embodiment in which the origin detection device of the present invention is applied to a rotary encoder of the grating interference system, and a part of the light flux in the shadow of the member is also shown by a solid line. 6 is a top view of the rotary encoder shown in FIG. 5, and FIG. 7 is a side view.

In the figure, the members designated by the same reference numerals as those in FIGS. 1 to 3 indicate the same members. Further, the present embodiment is different from the first embodiment except that diffractive lenses DL1 and DL2 that are eccentrically recorded are formed on the origin pattern track OT instead of the slit-shaped origin patterns SLIT1 and SLIT2 described above. It has the same configuration and function.

With respect to one of the P-polarized light fluxes illuminated at the point P3 on the origin pattern track OT of the disc DP, when the reflection diffraction lens DL1 which is the origin pattern is in the illumination area, the reflected condensed light is a light receiving element. Proceed towards PDZ1 and PDZ2. Since the incident positions on the light receiving elements PDZ1 and PDZ2 are configured so as to continuously change according to the position of the reflective diffraction lens DL1, the timing at which both light receiving elements are incident with an equal amount of light (rotational position of the disk). Exists.

When the reflection diffraction lens DL2 is in the illumination area, one of the S-polarized light beams illuminating the point P4 on the origin pattern track on the disk has its reflected condensed light directed to the light receiving elements PDZ3 and PDZ4. And proceed. Light receiving element PD
The incident position on Z3 and PDZ4 is also the reflection diffractive lens DL2.
Since it is configured so as to continuously change depending on the position of (1), there is a timing (rotational position of the disk) at which light is incident on both light receiving elements.

Therefore, the output of the light receiving element PDZ1 and the PDZ
The output of PDZ2 and the output of PDZ2 are added.
Add the outputs of and see the change in the output level of both,
The waveforms are averaged to eliminate the effects of disc eccentricity and the like. Therefore, the added signals may be compared with each other and an origin signal pulse having a certain width may be generated at the moment when the levels of the two match.

In this embodiment, the diffractive lens patterns DL1 and DL2 on the origin track are recorded at two points symmetrical about the rotation axis of the disc. However, since the reflected and condensed light fluxes from the first diffractive lens DL1 and the second diffractive lens DL2 are recorded so as to be decentered so as to be emitted in a specific angle direction, in the case of the reverse combination, the diffraction for the origin is performed. The condensed light flux from the lens does not travel to the light receiving element side. Therefore, also in the present embodiment, the origin detection can be performed by the same method as the method of the first embodiment described with reference to FIG.

[0027]

As described above, according to the present invention,
The origin detection optical system (illumination system) can be installed in the optical path of the incremental signal detection optical system of the rotary encoder, and the rotation information measuring device can be downsized. Further, since the origin can be detected at two symmetrical positions, it is possible to correct the deterioration of the measurement accuracy due to the radial deviation of the rotating shaft due to the disturbance.

[Brief description of drawings]

FIG. 1 is a schematic perspective view showing the entire incremental signal detection optical system and origin detection optical system of a grating interference type encoder according to a first embodiment.

FIG. 2 is a top view showing a part of FIG.

FIG. 3 is a side view showing the origin pattern detection unit of FIG.

FIG. 4 is a graph for explaining output signals and signal processing when an origin pattern is detected by a light receiving element.

FIG. 5 is a schematic perspective view showing the entire incremental signal detection optical system and origin detection optical system of the grating interference encoder of the second embodiment.

FIG. 6 is a top view showing a part of FIG.

FIG. 7 is a side view showing the origin pattern detection unit of FIG.

FIG. 8 is a diagram showing the entire incremental signal detection optical system and origin detection optical system of a conventional grating interference encoder.

[Explanation of symbols]

LD: monochromatic light source, CL: collimator lens, GT1, G
T2: Diffraction grating for separation and deflection, PP: Polarizing prism, PB
S: polarization splitting surface, M1, M2: mirror prism, DP:
Disc plate, GT: radial diffraction grating, SLIT1, SL
IT2: slit-shaped reflection pattern, DL1, DL2: diffractive lens, QWP1 to 3: 1/4 wavelength plate, CA1 to 2:
Cat's eye optical element, NBS: non-polarizing beam splitter, P45: 45-degree azimuth polarization plate, P90: 90-degree azimuth polarization plate, PDA, PDB, PDZ (Z1 to Z4): light receiving element.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Shujiro Kadowaki             Kyano, 3-30-2 Shimomaruko, Ota-ku, Tokyo             Within the corporation (72) Inventor Takayuki Kadoshima             Kyano, 3-30-2 Shimomaruko, Ota-ku, Tokyo             Within the corporation (72) Inventor Yasushi Kaneda             Kyano, 3-30-2 Shimomaruko, Ota-ku, Tokyo             Within the corporation (72) Inventor Hori Takara             Kyano, 3-30-2 Shimomaruko, Ota-ku, Tokyo             Within the corporation F term (reference) 2F065 AA17 AA39 BB02 CC00 DD02                       FF48 FF49 FF51 GG22 HH05                       JJ05 LL00 LL35 LL36 LL37                       LL42 LL46 MM04 PP13 QQ14                       QQ25                 2F103 BA32 CA01 CA03 CA04 DA01                       DA13 EA07 EA12 EB02 EB03                       EB32 EC03 EC13 EC14 EC15

Claims (8)

[Claims] 1. A collimator lens for converting a monochromatic light beam emitted from a light source into a substantially parallel light beam, and a diffraction grating plate for splitting the parallel light beam to generate at least two parallel light beams whose optical axes are shifted in parallel. A polarization beam splitter for splitting each of the at least two parallel light beams into two and extracting each of the polarized light components, and detecting the amount of rotation for each one light beam from each of the two polarized light components. The origin track is provided on the rotary plate, and the origin track is illuminated at a position that is substantially point-symmetric with respect to the rotation axis of the origin track, and the two light beams modulated by the origin pattern are detected by the respective light receiving elements. An origin detection device for a rotary encoder, which is characterized by generating a signal. 2. Each of the light receiving elements is a two-division photoelectric sensor, the modulated light flux is illuminated near the dividing line of these light receiving elements, and the origin is obtained by utilizing the level change between the two divided photoelectric sensors. The origin detection device according to claim 1, wherein a position shift is detected. 3. The origin pattern is a pair of diffractive lens patterns provided at positions symmetrical with respect to a rotation axis of the origin track.
Origin detection device described in. 4. The origin pattern is a pair of slit-shaped reflection patterns provided at a position slightly deviated from a point-symmetrical position with respect to the rotation axis of the origin track, and is substantially parallel to the rotation axis of the origin track. Each of the luminous fluxes that illuminate the point-symmetrical position illuminates a position slightly deviated from the point-symmetrical position with respect to the rotation axis of the origin track so that the pair of slit-shaped reflection patterns are simultaneously irradiated. The origin detection device according to claim 1 or 2. 5. A light source that emits a monochromatic light beam, a collimator lens that converts light emitted from the light source into a substantially parallel light beam, and at least two parallel light beams that divide the substantially parallel light beam and have their optical axes shifted in parallel. A diffraction grating plate for generating a light beam, a polarization beam splitter for splitting each of the at least two parallel light beams into two and extracting each polarization component, a diffraction grating track having a radial diffraction grating, and an origin track having an origin pattern. A rotating plate having the above and one light flux from each of the two divided polarization components are illuminated at positions (P1, P2) which are point-symmetrical with respect to the rotation axis of the diffraction grating track, and are irradiated to the diffraction grating track. A rotation amount detection system that takes out the diffracted light of different orders generated by the above, causes the wavefronts to overlap and interfere with each other, and generates a periodic signal accompanying the rotational movement of the disk. The other one light flux from each of the two split polarization components is illuminated at a position (P3, P4) that is substantially point symmetric with respect to the rotation axis of the origin track, and is modulated by the origin pattern. Two light beams are detected by each light receiving element,
A rotation information measuring device having an origin position detection system for generating an origin signal. 6. Each of the light receiving elements is a two-division photoelectric sensor, the modulated light flux is illuminated near the dividing line of these light receiving elements, and the origin is obtained by utilizing the level change between the two divided photoelectric sensors. The rotation information measuring device according to claim 5, wherein a position shift is detected. 7. The origin pattern is a pair of diffractive lens patterns provided at positions symmetrical with respect to the rotation axis of the origin track.
The rotation information measuring device described in. 8. The origin pattern is a pair of slit-shaped reflection patterns provided at a position slightly deviated from a point-symmetrical position with respect to the rotation axis of the origin track, and is substantially parallel to the rotation axis of the origin track. Each of the luminous fluxes that illuminate the point-symmetrical position illuminates a position slightly deviated from the point-symmetrical position with respect to the rotation axis of the origin track so that the pair of slit-shaped reflection patterns are simultaneously irradiated. The rotation information measuring device according to claim 5 or 6.