JPH08304118A - Compound type rotary encoder - Google Patents

Abstract

PURPOSE: To detect rotation information from a small and stable optical system by constituting either one of an origin pattern and an absolute code pattern of a plurality of circular-arc diffraction gratings. CONSTITUTION: The light flux emitted from a light source LGT is converted into parallel light flux R by a collimator lens LNS. The light, among the light flux R, with which a diffraction grating GT is irradiated, generates ± first-order diffraction grating by a grid GT, and then these diffraction gratings are diffracted again by a first-order diffraction grating GBS1, then crossing at a point in a space, and then diffracted again by a second-order diffraction grating GBS2 disposed there, and overlapped each other to be emitted as interference light flux interfering each other. Transmitted modulation light of the light flux R with which a disk D is irradiated, is detected in a lump by each photo-detecting element on a photo-detecting element array SARY. Since an origin pattern Z and an absolute code pattern UVW are constituted of a circular-arc diffraction grid with a rotation axis as the center, the diffraction light is diffracted in the direction of radiation passing the rotation axis.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a composite rotary encoder, and more particularly to highly accurately detecting rotational information such as a rotational position of a rotating body, an amount of rotational displacement, a rotational displacement direction, rotational speed and rotational acceleration. In addition, the present invention is suitable for detecting the absolute position of the rotating body even when the rotating body is at rest, especially when driving an AC motor or the like.

[0002]

2. Description of the Related Art Conventionally, it has been popular to measure rotation information (rotational displacement amount, speed, acceleration, etc.) of an object with high accuracy by using an incremental rotary encoder. On the other hand, in a brushless motor typified by an AC motor, an absolute rotary encoder is used to detect the absolute rotation position of the rotor in the motor to control the rotation (starting) of the motor. When controlling the rotational position of an object using an AC motor or the like, a composite rotary encoder that can obtain both highly accurate relative displacement information and absolute position information is used.

A conventional example of the incremental encoder and the absolute encoder will be described. FIG. 11 is an explanatory view of the principle of the high-precision incremental encoder disclosed in Japanese Patent Publication No. 58-26002. In the figure,
LGT is a light source. D is a scale, which is fixed to the displacement object. A transmission type diffraction grating GT is formed on the scale D. Assuming that the light source LGT is below the scale D, the fixed first diffraction grating GBS1 is provided on the scale D. The grating pitch of the first diffraction grating GBS1 is half that of the diffraction grating GT. Further, a fixed second diffraction grating GBS2 is provided on the first diffraction grating GBS1. Second diffraction grating
The grating pitch of GBS2 is the same as that of the diffraction grating GT. A light receiving element (displacement amount detecting element) SA is provided on the second diffraction grating GBS2.

The operation of this conventional example will be described. The monochromatic light flux R emitted from the light source LGT illuminates the diffraction grating GT, and the ± first-order diffracted light fluxes R ₊ and R ₋ generated by the diffraction grating are the first diffraction grating.
It enters the GBS1, respectively ± 1-order diffracted light beam R _{+ -,} R _- generates _+. These diffracted light beams R _+- , R- ₊ intersect at the second diffraction grating GBS2, and are diffracted by the diffraction grating R _+-+ , R _-+-.
Occurs. The two diffracted light beams are emitted in the same direction, and their optical paths are overlapped with each other to interfere with each other to form an interference light beam, which is then incident on the light receiving element SA. Then, with the movement of the diffraction grating GT (scale), a periodic change in the light amount of the interfering light beam is created, and by detecting it with the photoelectric element SA, an incremental encoder signal is output and the displacement amount of the displacement object is detected with high accuracy. ing.

FIG. 12 is a diagram illustrating the principle of the high-precision incremental encoder disclosed in Japanese Patent Publication No. 58-45687. In the figure, LGT is a light source. D is a scale, which is fixed to the displacement object. A reflective diffraction grating GT is formed on the scale D. A fixed diffraction grating GBS3 is provided between the light source LGT and the scale D. The grating pitch of the diffraction grating GBS3 is twice that of the diffraction grating GT. A light receiving element (displacement amount detecting element) SA is provided next to the light source LGT.

The operation of this conventional example will be described. The monochromatic light beam R emitted from the light source LGT is obliquely incident on the fixed diffraction grating GBS3, and the ± first-order diffracted light beams R ₊ , R generated by the diffraction grating GBS3 are generated.
_- the diffraction grating enters the GT, respectively ± 1-order diffracted light beam R ₊ as well as reflected by the diffraction grating _-, R _- generates _+. These diffracted light beams R _+- , R- ₊ intersect at the fixed diffraction grating GBS3 and generate diffracted lights R _+-+ , R _-+- by the diffraction grating. The two diffracted light beams are emitted in the same direction, and their optical paths are overlapped with each other to interfere with each other to form an interference light beam, which is then incident on the light receiving element SA. Then, with the movement of the diffraction grating GT (scale), a periodic change in the light amount of the interfering light beam is created, and by detecting it with the photoelectric element SA, an incremental encoder signal is output and the displacement amount of the displacement object is detected with high accuracy. ing.

On the other hand, an absolute rotary encoder, as disclosed in, for example, US Pat. No. 3591841, has a plurality of transmission / non-transmission (or reflection / non-reflection) patterns ( For example, a gray code pattern) is formed so that only one code is combined in one rotation, and the absolute position in the rotation direction of the disk is detected by detecting the transmitted light or the reflected light (modulated light) of each. are doing.

Also, as an absolute encoder for a motor, a plurality of transmission / non-transmission (or reflection / non-reflection) patterns (for example, gray code patterns) are provided on the rotating disk on different circumferences, and the number of poles of the motor is M. In response to the
If it is formed so as to have only a combination of M codes, the position between the rotor and the stator of the motor is output by detecting transmitted light or reflected light (modulated light) in each circumference.

[0009]

As a recent trend, encoders have been miniaturized (for example, disks having an outer diameter of 10 mm). As described above, composite encoders that combine encoders based on different principles are not miniaturized. It was difficult.

To miniaturize such an encoder, it is sufficient to simply provide optical systems based on different detection principles and miniaturize each, but there is a limit to miniaturization of the optical system of the incremental encoder and the absolute encoder. In addition, in this case, there are problems that a plurality of light sources are required, current consumption increases and heat generation increases, and the number of parts increases and the structure becomes complicated.

Furthermore, when such a high precision rotary encoder is used as a high precision positioner by combining it with a motor, the motor heats up. Therefore, it is necessary to detect an interference signal by using a light emitting diode LED as a highly reliable light source. There is.

According to the present invention, a small-diameter disk and one light source having a high-density radial diffraction grating and an origin pattern forming one element of an incremental encoder and / or an absolute code pattern forming one element of an absolute encoder, and By reading the light intensities of multiple modulated lights at once using the light receiving element array, it is a small-sized, small-diameter, thin-type composite rotary encoder that can detect rotation information from a stable optical system at the same time. For the purpose of provision.

[0013]

The composite rotary encoder of the present invention comprises: (1-1) A rotatable disk-shaped disc having a radial phase diffraction grating, an origin pattern, and an absolute code pattern for a light beam emitted from a light source. The modulated light of the light irradiated onto a part of the disk and the absolute code pattern is received by the absolute position detection element to detect the absolute position of the disk, and the modulated light of the light irradiated onto the origin pattern is the origin position. The detection element detects the origin position of the disc, and the displacement detection element receives the interference light diffracted and synthesized by the phase diffraction grating and the fixed diffraction grating on the disc to detect the displacement information of the disc. In the rotary encoder of the composite type for obtaining the above, one or both of the origin pattern and the absolute code pattern are diffracted in a plurality of arcs. It is characterized in such that it is constituted by a child.

In particular, (1-1-1) the arc-shaped diffraction grating is a phase diffraction grating. (1-1-2) The origin pattern and the absolute code pattern are composed of a diffraction grating in which at least one of the shape parameters of the diffraction grating changes discontinuously. (1-1-3) The absolute position detection element, the origin position detection element, and the displacement amount detection element are formed on one substrate. (1-1-4) An opening member for limiting a light beam incident on the absolute position detection element, the origin position detection element, and the displacement amount detection element is provided near the disc. It is characterized by such things.

The composite rotary encoder of the present invention further comprises (1-2) a rotatable disc-shaped disc having a radial phase diffraction grating, an origin pattern, and an absolute code pattern for a light beam emitted from a light source, and Irradiate the fixed diffraction grating arranged in a superimposed manner, the modulated light of the light irradiated with the absolute code pattern is received by the absolute position detection element to detect the absolute position of the disk, and the light irradiated with the origin pattern is detected. The origin position detection element receives the modulated light to detect the origin position of the disk, and the displacement amount detection element receives the interference light obtained from the diffracted light that passes through the fixed diffraction grating and the phase diffraction grating on the disk. In a composite rotary encoder that obtains the displacement information of the disk, one or both of the origin pattern and the absolute code pattern are used. Is characterized such that it constitutes a by a plurality of arcuate diffraction grating.

In particular, (1-2-1) the arc-shaped diffraction grating is a phase diffraction grating. (1-2-2) The origin pattern and the absolute code pattern are composed of a diffraction grating in which at least one of the shape parameters of the diffraction grating changes discontinuously. (1-2-3) The absolute position detection element, the origin position detection element, and the displacement amount detection element are formed on one substrate. (1-2-4) An opening member is provided near the disk to limit a light beam incident on the absolute position detection element, the origin position detection element, and the displacement amount detection element. It is characterized by such things.

Further, in the composite rotary encoder of the present invention, (1-3) a disk-shaped disk is provided with a radial diffraction grating and an arc-shaped diffraction grating centered on the rotation axis, and a light irradiation means is provided. From the displacement amount detecting element while detecting the diffracted light generated when the luminous flux from is incident on the radial diffraction grating and detecting the absolute position detecting element or the origin position of the diffracted light generated when the luminous flux is incident on the arc-shaped diffraction grating. It is characterized in that the rotation information of the disk is detected by using a signal obtained by the element and obtained from the displacement amount detecting element and the absolute position detecting element or the origin position detecting element.

In particular, (1-3-1) the arc-shaped diffraction grating is a phase diffraction grating. (1-3-2) The arc-shaped diffraction grating is composed of a diffraction grating in which at least one of the shape parameters of the diffraction grating changes discontinuously. It is characterized by such things.

[0019]

Embodiment 1 FIG. 1 is a schematic view of the essential portions of Embodiment 1 of the present invention. FIG. 2 is an explanatory diagram of patterns on the disc of the first embodiment. 3 is an explanatory view of the principle of the interference optical system of the first embodiment, FIG. 4 is an enlarged view of each diffraction grating of the first embodiment, FIG. 5 is a perspective view of essential parts of the first embodiment, and FIG. 6 is an absolute code of the first embodiment. It is explanatory drawing of pattern UVW.

In FIG. 1, LGT is a light source, which is composed of an LED or the like and emits monochromatic light. LNS is a collimator lens, which converts the light beam from the light source LGT into a parallel light beam R. The light source LGT, the collimator lens LNS, etc. constitute one element of the light irradiation means.

D is a disk, which is a disk-shaped member formed of a transparent body, which is fixed to a rotating object to be measured and rotates. Therefore, disk D has an axis of rotation. As shown in FIG. 2, on the disk D, a radial phase diffraction grating GT centering on the rotation axis, an origin pattern Z composed of an arcuate phase diffraction grating, and an absolute code pattern UVW composed of an arcuate phase diffraction grating are provided. Are formed on different circumferences (tracks) of the disk. These will be described. (a1) The radial phase diffraction grating GT has N diffraction gratings formed on the GT track of the disk D in one revolution. Therefore, the lattice pitch P is P = 2π / N radian. (a2) Origin pattern Z is one of Z _a track and Z _b track.
Narrow arc-shaped phase diffraction gratings Z1 and Z2 are installed side by side so that their ends are in contact with each other at one location on the circumference. The portions without the diffraction grating Z1 or Z2 on the Z _a track and the Z _b track are transparent portions. The diffraction gratings Z1 and Z2 are formed by changing the duty among the shape parameters of the diffraction grating. (a3) Absolute code pattern UVW is formed by forming six types of arc-shaped phase diffraction gratings on the UVW track. As shown in FIG. 6, these diffraction gratings are a diffraction grating U that generates only the _0th- order diffracted light θ ₀ as a transmitted diffraction light, a diffraction grating W that generates only the _1st- order diffracted light θ ₁ , and a 0th-order diffracted light θ _0.
And the diffraction grating V that generates the _first- order diffracted light θ ₁ , the second-order diffracted light θ
Diffraction grating V for generating a ₂ only _-, 0-order diffracted light theta ₀ and second diffraction grating W to generate diffracted light theta _{2 -,} 1-order diffracted light theta ₁ and 2 to generate a diffracted light theta _second diffraction grating U _- six Is. The action of generating these specific diffracted lights is caused by configuring one diffraction grating with at least one of the shape parameters (duty, pitch, thickness) of the phase diffraction grating being discontinuously different. Absolute code pattern UVW these six diffraction grating U to W _- disk D
Are formed in the same order in each quadrant on one lap. (Note that
UVW track as shown in FIG. 2, GT track, Z _a, Z _b tracks the arrangement if I independently may be arbitrary).

In FIG. 1, assuming that the collimator lens LNS is on the lower side of the disc D, the fixed first diffraction grating GBS1 is installed on the upper side of the disc D. First diffraction grating GBS1
Is a radial phase diffraction grating, and its grating pitch P ₁ is P ₁
= Π / N radian.

Further, a fixed second diffraction grating GBS2 is installed on the first diffraction grating GBS1. Second diffraction grating GBS2
Is a radial phase diffraction grating, and the grating pitch is P ₁ =
It is 2π / N radian. Diffraction grating GBS2 is a boundary point P ₀ as shown in FIG. 4, an area GBS2-A, GBS2-B, GBS2-A -, GBS2
-B _- have been divided into four, the phase of the sequence of another grid
It is formed by shifting by 1/8 pitch.

The first and second diffraction gratings GBS1, GBS2 and the diffraction grating GT have a fine structure such that 0th-order diffracted light is not generated in the lamella phase grating.

A light receiving element array SARY is installed on the second diffraction grating GBS2 to detect various modulated light beams generated by the disk D. The light receiving element array SARY has the following three groups of light receiving elements. (b1) Incremental detector S _{A, B} , (displacement detector) This consists of four-division photo detectors SA, SB, SA-, SB-, and interference from each of the four divided regions of the second diffraction grating GBS2. The light intensity of light is detected. (b2) Origin position detector S _Z , (Origin position detector) This consists of two photo detectors SZ1 and SZ2, and Z _a track, Z
_It is placed on the _b track and receives the 0th order diffracted light from each track. (b3) Absolute position detector S _UVW , (Absolute position detector) This is the arrangement of three photo detectors SU, SV, SW on one straight line and each diffraction grating U, V, W, on the UVW track. Of the diffracted light generated by U ₋ , V ₋ , W ₋ , 0th-order diffracted light θ ₀ , 1st-order diffracted light θ ₁ , and 2nd-order diffracted light θ ₂ are received.

The light receiving element array SARY is formed by forming the above respective light receiving elements on one substrate.

The operation of this embodiment will be described. The light flux emitted from the light source LGT is converted into a parallel light flux R by the collimator lens LNS, and irradiates a part on the disk D that rotates in the opposite direction, and a part of the GT track, Z _a , Z _b track, and UVW track. Are illuminated all at once.

Of the light flux R, the light that illuminates the diffraction grating GT is
As shown in FIG. 3, the diffraction grating GT generates two ± 1st-order diffracted light beams R ₊ and R _−, and these diffracted light beams are diffracted again by the first diffraction grating GBS1 to produce a diffracted light beam R _{+ −} , R
_-+ Is generated, the optical path is bent, and it intersects at point P ₀ in space. Then the second diffraction grating GBS2 placed there
Diffracted light flux that is diffracted again by and is emitted in the same direction
R _+-+ and R _-+- are generated and emitted as an interference light beam that overlaps and interferes with each other.

Since the luminous flux R illuminating the disc D has a spread, it is diffracted by the diffraction grating GT and then the first diffraction grating GBS1.
Even when it reaches, the diffraction grating GB remains almost overlapping.
The light is guided through S1 and GBS2 to the light receiving elements SA, SB, SA-, SB-.

For example, the luminous flux diameter for illumination is 500 μm, the number of diffraction gratings GT is N = 2500, and the recording radius of the GT track is r = 5000.
μm, LED wavelength λ = 0.86 μm, first-order diffraction angle θ becomes θ = arcsin {λ · N / (2πr)} = 3.92 °, and the gap between the diffraction grating GT and the first diffraction grating GBS1
If h = 500 μm, the amount of separation of the two diffracted light beams R ₊ and R ₋ is 68.5 μm, which is extremely small.

Diffracted light flux emitted from the second diffraction grating GBS2
The light paths of R _+-+ and R _-+- are emitted in parallel with each other, and the symmetry of all the light paths from the light source LGT is maintained and interfere with each other.

At this time, when the diffraction grating GT moves by one pitch due to the rotation of the disk D, the diffracted light R _+-+ is shifted in phase by -2π, and the diffracted light R _-+- is diffracted by the rotation of the disk D. When the grating GT moves by one pitch, the wavefront phase becomes -2π.
It shifts. Therefore, when the diffraction grating GT moves by one pitch due to the rotation of the disk D, the interference light becomes bright and dark with a sine wave shape.
Change times.

Further, in the second diffraction grating GBS2, the points
The region is divided into four regions with P ₀ as the boundary, and the phase of the lattice arrangement is shifted by 1/8 pitch in each region, so the interference phase (bright and dark phase) in each region is 1 It changes twice in a sinusoidal manner with a shift of / 4 cycle.

The interference light from these four regions is received by the light receiving element S.
Since it is incident on A, SB, SA-, SB-, the light receiving element SA, SB, SA-, SB-
Generates a sinusoidal analog signal current with a 2N cycle in which the interference phase is deviated by 1/4 cycle per revolution of disk D.

On the other hand, of the parallel light flux R illuminating the disk D, the light illuminating the Z _a and Z _b tracks is transmitted through the direct light flux (0th order light), as shown in FIG. Two states of the diffracted light flux (first-order light) appear, and the respective lights are incident on the light receiving elements SZ1 and SZ2 according to their positions.

For example, as shown in FIG. 1, when the light flux R illuminates a portion of the origin pattern Z where the diffraction gratings Z1 and Z2 are not present (this portion is transparent), the light receiving element SZ1,
Directly transmitted light beams are incident on SZ2. If the area with the origin pattern Z is illuminated, the light receiving element SZ1
, SZ2 does not enter the light beam. During the process, a light beam is incident on the two light receiving elements SZ1 and SZ2 according to the position.

Therefore, when the origin pattern Z moves within the illumination area due to the rotation of the disk D, the light receiving elements SZ1 and SZ2
The amount of light incident on is changed, and the timings when the amounts of light change are deviated from each other. From the light receiving elements SZ1 and SZ2, valley-shaped waveform analog signal currents having peaks deviated from each other are generated. Therefore,
As the origin signal, for example, a pulse signal may be generated when the outputs of the light receiving elements SZ1 and SZ2 match.

Further, in FIG. 5, the light receiving elements SZ1-, SZ are indicated by dotted lines.
2- is added and placed, but the origin pattern is
In the part without Z, the light beam is incident on the light receiving elements SZ1 and SZ2,
The light beam may be incident on the light receiving element SZ1- or SZ2- in the portion where the diffraction grating Z1 or Z2 exists. In this case, in the middle of the process, the luminous flux is distributed and incident on each light receiving element according to the position. Therefore, the light receiving element SZ1,
SZ2, SZ1-, and SZ2- generate analog signal currents having a valley or peak waveform with their peaks deviated from each other. Light receiving element
Opposite phase signals from SZ1 and SZ1-
Since signals having opposite phases are generated from the above, the pulse signal may be generated when the signal levels of the difference signals match.

On the other hand, of the parallel light flux R illuminating the disk D, the light illuminating the UVW track generates only the _0th-order diffracted light θ ₀ (U), 1 as shown in FIG. 6 depending on the illuminated position.
Only the _first-order diffracted light θ ₁ is generated (W), the 0th-order diffracted light θ ₀ and the first-order diffracted light θ ₁ are generated (V), and only the _second-order diffracted light θ ₂ is generated (V ₋ ), 0
Six states of generation of the second-order diffracted light θ ₀ and the second-order diffracted light θ ₂ (W ₋ ) and generation of the first-order diffracted light θ ₁ and the second-order diffracted light θ ₂ (U ₋ ) appear, and the light receiving element SU, Light and diffracted light beams are directly incident on the SV and SW. Therefore, an absolute code signal group is output from the light receiving elements SU, SV, SW, and the absolute position of the disc D is determined by the combination of the binary information.

As described above, the luminous flux illuminating the disk D
The transmission modulated light of R is collectively detected by each light receiving element on the light receiving element array SARY. In the present embodiment, the origin pattern Z and the absolute code pattern UVW are composed of arc-shaped diffraction gratings centering on the rotation axis, so that the diffracted light is diffracted in the direction of the radiation passing through the rotation axis. Therefore, it is possible to arrange the incremental detectors S _{A and B} , the origin position detector S _Z , and the absolute position detector S _UVW in a substantially straight line, so that the light receiving element array SARY can be made compact.

Although not shown in FIG. 1 in this embodiment, the opening member shown in FIG.
BL is provided. This opening member BL is GT track, Z _a , Z _b
After irradiating the track and UVW track, the luminous flux incident on the displacement amount detection element, the origin detection element, and the absolute position detection element is limited. As a result, the S / N of the modulated light from each diffraction grating is
The ratio is improved, and the detection accuracy of each is increased.

The optical system of Example 1 is partially modified to
Incremental interference light, absolute code pattern
If the UVW and the origin pattern Z are projected onto the light receiving element array SARY by the imaging projection lens, the resolution of the edges of the absolute code pattern and the origin pattern is improved, and the detection accuracy is improved.

Further, the diffraction grating GT, the absolute code pattern UVW and the origin pattern Z may be arranged on both sides of the disk D.

In this embodiment, the radial phase diffraction grating GT, the origin pattern Z composed of the arcuate phase diffraction grating, and the absolute code pattern composed of the arcuate phase diffraction grating
Since the UVW is formed in a narrow area on the disk D, it is convenient to construct a small-sized composite rotary encoder.

Further, since the three diffraction gratings are irradiated with the light flux generated from one light source, it is advantageous for downsizing and generates less heat.

Further, since the light receiving element array formed on one substrate is used, it is advantageous for downsizing of the composite rotary encoder.

Further, the origin pattern Z and the absolute code pattern UVW are composed of diffraction gratings in which the shape parameters (duty, pitch, thickness) of the phase diffraction grating are discontinuously different, whereby the intensity of the diffracted light of a specific order is increased efficiently. I am raising it well. As a result, high detection reliability is obtained.

A stable optical system is realized by the structure of one power source and one light receiving element array.

The light-receiving element array SARY of this embodiment is 1
Although it is composed of one substrate, it may be divided into a plurality of substrates in some cases.

FIG. 8 is a schematic view of the essential portions of Embodiment 2 of the present invention. The major difference between this embodiment and Embodiment 1 is disc D.
The point is that all of the three diffraction gratings formed above are reflection type, and other optical components are set on one side of the disk D 1.

FIG. 9 is an explanatory view of the principle of the interference optical system of the second embodiment, and FIG. 10 is an enlarged view of each diffraction grating of the second embodiment.

In FIG. 8, LGT is a light source, which is composed of an LED or the like and emits monochromatic light. LNS is a collimator lens, which converts the light beam from the light source LGT into a parallel light beam R. BS
Is a beam splitter, which reflects a part of the reflected and diffracted light from the disk to the side. The light source LGT, the collimator lens LNS and the like form one element of the light irradiation means. D
Is a disk, which is fixed to a rotating object to be measured by a disk-shaped member and rotates. Similar to the first embodiment, three diffraction gratings of a radial phase diffraction grating GT, an origin pattern Z consisting of an arcuate phase diffraction grating, and an absolute code pattern UVW consisting of an arcuate phase diffraction grating are provided on the disk D. It is formed on different circumferences (tracks) of the disk, and a reflective film is formed on the disk. These will be described. (c1) The radial phase diffraction grating GT has N diffraction gratings formed on the GT track of the disk D in one revolution. Therefore, the lattice pitch P is P = 2π / N radian. (c2) Origin pattern Z is 1 of Z _a track and Z _b track.
Narrow arc-shaped phase diffraction gratings Z1 and Z2 are installed side by side so that their ends are in contact with each other at one location on the circumference. The portions without the diffraction grating Z1 or Z2 on the Z _a track and the Z _b track are plane portions. The diffraction gratings Z1 and Z2 are formed by changing the duty among the shape parameters of the diffraction grating. (c3) Absolute code pattern UVW is constructed by forming six types of arc-shaped phase diffraction gratings on the UVW track. These diffraction gratings are a diffraction grating U that generates only the 0th-order reflected diffracted light θ ₀ as the reflected diffracted light, a diffraction grating W that generates only the 1st-order reflected diffracted light θ ₁ , and a 0th-order reflected diffracted light θ.
₀ and 1-order reflected diffracted light theta ₁ the generated diffraction grating V, second-order diffraction grating V which generates only the reflected diffracted light theta _{2 -,} 0-order reflected diffracted light theta ₀ and second order reflected diffraction light theta ₂ Generating diffraction grating W
_- diffraction grating U generated first-order reflection diffraction light theta ₁ and second-order reflected diffracted light theta _{2 -} is a six. The action of generating these specific diffracted lights is caused by configuring one diffraction grating with at least one of the shape parameters (duty, pitch, thickness) of the phase diffraction grating being discontinuously different. Absolute code pattern UVW these six diffraction grating U to W _- a are formed in the same order in each quadrant on one rotation of the disc D.

A fixed diffraction grating GBS3 is installed between the beam splitter BS and the disc D. The diffraction grating GBS3 is a radial phase diffraction grating, and its grating pitch P ₁ is P ₁ =
It is 4π / N. The diffraction grating GBS3, as shown in FIG.
The P ₀ in the boundary, the area GBS3-A, GBS3-B, GBS3-A -, GBS3-B - Four to have split, by shifting the phase of the sequence of another grating by 1/8 pitch min Is forming.

The diffraction grating GT and the diffraction grating GBS3 are
The lamella phase grating has a stepped fine structure that does not generate zero-order diffracted light.

A light receiving element array SARY is installed on the side of the beam splitter BS to detect various modulated light beams generated by the disk D. The light receiving element array SARY has the following three groups of light receiving elements. (d1) Incremental detector S _{A, B} , (displacement detector) This consists of four-division photo detectors SA, SB, SA-, SB-, and the light of the interference light from each of the four divisions of the diffraction grating GBS3. Detect intensity. (d2) an origin position detecting unit S _Z, consists (origin position detection element) which two light-receiving elements SZ1, SZ2, Z _a track, Z
_It is placed on the _b track and receives the 0th order diffracted light from each track. (d3) Absolute position detector S _UVW , (Absolute position detector) This is three diffraction elements SU, SV, SW arranged on one straight line, and each diffraction grating U, V, W, on the UVW track. Of the diffracted light generated by U ₋ , V ₋ , W ₋ , 0th-order diffracted light θ ₀ , 1st-order diffracted light θ ₁ , and 2nd-order diffracted light θ ₂ are received.

The light receiving element array SARY is formed by forming the above respective light receiving elements on one substrate.

The operation of this embodiment will be described. The light beam emitted from the light source LGT is parallel light beam R becomes by the collimator lens LNS, passes through the beam splitter BS, the diffracted light beam is diffracted part of the light flux by the diffraction grating GBS3 of which R _+, R _- and generate , Irradiate the diffraction grating GT on the disk D rotating relative to each other. Of the parallel light flux R, the diffraction grating GB
A light beam that does not pass through the S3 area rotates as it is
Illuminate some of the other tracks on D.

Irradiation of a diffraction grating GT as shown in FIG.
The two diffracted light beams R ₊ and R ₋ generate two ± 1st-order reflected diffracted light beams R _{+ −} and R _{− +} by the diffraction grating GT, and these light beams are re-diffracted by the diffraction grating GBS3 and emitted in the same direction. Luminous flux
R _+-+ , R _-+- are formed, the optical paths are overlapped with each other, and interfere with each other to be emitted as an interference light beam, which is reflected laterally by the beam splitter BS and then enters the light receiving element.

Since the luminous flux R illuminating the disc D has a spread, even if it reaches the radial diffraction grating GT after being diffracted by the radial diffraction grating GBS3, it remains almost overlapped.
The light is guided to the light receiving element through the diffraction gratings GT and GBS3.

For example, the luminous flux diameter for illumination is 500 μm, the number of radial gratings N = 2500, the recording radius r of the disk D = 5000 μ
When m is the wavelength of the LED λ = 0.86 μm, the incident angle θ of the disc illumination light is θ = arcsin {λ · N / (4πr)} = 1.96 °, and the gap h between the radial diffraction grating GT and the diffraction grating GBS3 is If it is 500 μm, the separation amount of the two diffracted light beams is 3
It is very small, 4.2 μm.

The light beam R _+-+ re-diffracted from the diffraction grating GBS3,
R _-+- are emitted parallel to each other with overlapping optical paths, and the symmetry of all optical paths from the light source LGT is maintained,
Interfere with each other.

At this time, when the diffraction grating GT moves by one pitch due to the rotation of the disk D, the diffracted light R _+-+ shifts the phase of the wavefront by -2π, and the diffracted light R _-+- is diffracted by the rotation of the disk D. When the grating GT moves by one pitch, the wavefront phase becomes -2π.
It shifts. Therefore, when the diffraction grating GT moves by one pitch due to the rotation of the disk D, the interference light becomes bright and dark with a sine wave shape.
Change times.

Further, in the diffraction grating GBS3, the region is divided into four regions with the point P ₀ as a boundary, and the phase of the grating arrangement is shifted by 1/8 pitch in each region. The interference phase (brightness phase) in the area is
It changes twice in a sinusoidal manner with a shift of 1/4 cycle.

Interference light from these four areas is received by the light receiving element S.
Since it is incident on A, SB, SA-, SB-, the light receiving element SA, SB, SA-, SB-
Generates a sinusoidal analog signal current with a 2N cycle in which the interference phase is deviated by 1/4 cycle per revolution of disk D.

On the other hand, of the parallel light flux R illuminating the disk D, the reflected direct light flux (0th order diffracted light) and the reflected diffracted light flux (1st order diffracted light) depending on the position of the light origin pattern Z illuminating the Z _a and Z _b tracks. 2 light beams of (diffracted light) appear, and accordingly, the respective lights are incident on the light receiving elements SZ1 and SZ2.

For example, as shown in FIG. 8, when the light flux R illuminates a portion without the origin pattern Z, the light receiving element SZ1
, SZ2 are reflected and direct rays are incident respectively. If the portion where the diffraction grating Z1 or Z2 is present is illuminated, no light beam is incident on any of the light receiving elements SZ1 and SZ2. In the middle of the process, a light beam is incident on the two light receiving elements according to its position.

Therefore, when the origin pattern Z moves in the illumination area due to the rotation of the disk D, the light receiving elements SZ1, SZ2
The amount of light incident on is changed, and the timings when the amounts of light change are deviated from each other. From the light receiving elements SZ1 and SZ2, valley-shaped waveform analog signal currents having peaks deviated from each other are generated. Therefore,
As the origin signal, for example, a pulse signal may be generated when the outputs of the light receiving elements SZ1 and SZ2 match.

On the other hand, of the parallel light flux R illuminating the disc D, the light illuminating the UVW track is generated only by the 0th-order diffracted light θ ₀ (U) and only by the 1st-order diffracted light θ ₁ (W), depending on the illuminated position. Generates _0th-order diffracted light θ ₀ and 1st-order diffracted light θ ₁ (V)
Only the second-order diffracted light θ ₂ is generated (V ₋ ), the 0th-order diffracted light θ ₀ and the second-order diffracted light θ ₂ are generated (W ₋ ), the first-order diffracted light θ ₁ and the second-order diffracted light θ ₂ are generated (U ₋ ). A state appears, and the reflected light and the reflected diffracted light beam are directly incident on the light receiving elements SU, SV, SW according to the illumination position. Therefore, an absolute code signal group is output from the light receiving elements SU, SV, SW, and the absolute position of the disc D is determined by the combination of the binary information.

As described above, the luminous flux illuminating the disc D
The reflection modulated light of R is collectively detected by each light receiving element on the light receiving element array SARY. In the present embodiment, the origin pattern Z and the absolute code pattern UVW are composed of arc-shaped diffraction gratings centering on the rotation axis, so that the diffracted light is diffracted in the direction of the radiation passing through the rotation axis. Therefore, it is possible to arrange the incremental detectors S _{A and B} , the origin position detector S _Z , and the absolute position detector S _UVW in a substantially straight line, so that the light receiving element array SARY can be made compact.

In this embodiment, although not shown in FIG. 8, an opening member BL shown in FIG. 7 is provided above the disc D. This opening member BL is a GT track, Z _a , Z _b track,
After irradiating the UVW track, the luminous flux incident on the displacement amount detection element, the origin detection element, and the absolute position detection element is limited. This improves the S / N ratio of the modulated light from each diffraction grating,
The detection accuracy of each is improved.

A part of the optical system of the second embodiment is changed to
Incremental interference light, absolute code pattern
If the UVW and the origin pattern Z are projected onto the light receiving element array SARY by the imaging projection lens, the resolution of the edges of the absolute code pattern and the origin pattern is improved, and the detection accuracy is improved.

In this embodiment, a radial phase diffraction grating GT, an origin pattern Z composed of an arcuate phase diffraction grating, and an absolute code pattern composed of an arcuate phase diffraction grating.
Since the UVW is formed in a narrow area on the disk D, it is convenient to construct a small-sized composite rotary encoder.

Further, since the three diffraction gratings are irradiated with the light flux generated from one light source, it is advantageous for downsizing and generates less heat.

Further, since the light receiving element array constituted by one substrate is used, it is advantageous for downsizing of the composite rotary encoder.

The origin pattern Z and the absolute code pattern UVW are composed of diffraction gratings in which at least one of the shape parameters (duty, pitch, thickness) of the phase diffraction grating is discontinuously different. Efficiently increasing strength. As a result, high detection reliability is obtained.

A stable optical system is realized by the structure of one power source and one light receiving element array.

The light receiving element array SARY of this embodiment is 1
Although it is composed of one substrate, it may be divided into a plurality of substrates in some cases.

In addition, it is possible to add the following modifications to the first and second embodiments.

In Example 1, the number of diffraction gratings GT is N ₁ (pieces / circle), and the number of first diffraction gratings GBS 1 is N ₂ (pieces / circle).
Circumference), the number of second diffraction gratings GBS2 is N ₃ (pieces / circle), and n ₁ , n ₂ , and n ₃ are diffraction grating GT, first diffraction grating GBS1,
As a diffraction order by the second diffraction grating GBS2, it should be configured such that n ₁ · N ₁ + n ₂ · N ₂ + n ₃ · N ₃ = 0 is satisfied between them. (In the first embodiment, n ₁ = + 1
, N ₂ = -1, n ₃ = + 1, N ₁ = 2500, N ₂ = 5000, N ₃ = 2500. ) At this time, the number N of radial diffraction gratings that do not need to be recorded in the entire circumference does not have to be an integer, and may have a decimal point.

The absolute code pattern UVW is converted from a circular diffraction grating into a normal pure binary code,
Change to gray code, etc.

To reverse the relationship of transmission / non-transmission or reflection / non-reflection of the absolute code pattern UVW and the origin pattern Z.

Changing the number of divisions and the phase shift amount of the diffraction grating (the second diffraction grating GBS2 in the first embodiment) that generates the incremental phase difference signal. (For example, dividing into 2 and shifting the phase by 90 degrees, dividing into 6 and shifting the phase by 60 degrees, etc.) The origin pattern Z is divided into two as in Examples 1 and 2, and the difference between the two signals is divided. Change to a method that detects the peak of the correlation function by superposing two normal random pitch patterns instead of obtaining from the signal.

Changing the absolute code pattern UVW and / or the origin pattern Z to an arc-shaped diffraction grating with a light-dark pattern.

[0084]

As described above, the present invention has a small diameter with a high-density radial diffraction grating forming one element of an incremental encoder and an origin pattern or / and an absolute code pattern forming one element of an absolute encoder. By collectively reading the light intensities of a plurality of modulated lights using the disk, one light source, and the light receiving element array, it is possible to detect rotation information from a stable optical system while being compact, small in diameter, and thin. Achieved a combined rotary encoder.

[Brief description of drawings]

FIG. 1 is a schematic view of a main part of a first embodiment of the present invention.

FIG. 2 is an explanatory diagram of each pattern on the disc

FIG. 3 is an explanatory diagram of the principle of the interference optical system according to the first embodiment.

FIG. 4 is an enlarged view of each diffraction grating of Example 1.

FIG. 5 is a perspective view of a main part of the first embodiment.

FIG. 6 is an absolute code pattern UVW of the first embodiment.
Illustration of

FIG. 7: Opening member

FIG. 8 is a schematic view of the essential portions of Embodiment 2 of the present invention.

FIG. 9 is an explanatory diagram of the principle of the interference optical system of Example 2.

FIG. 10 is an enlarged view of each diffraction grating of Example 2.

FIG. 11 is an explanatory diagram of the principle of a conventional incremental encoder (transmission type).

FIG. 12 is an explanatory diagram of the principle of a conventional incremental encoder (reflection type).

[Explanation of symbols]

LGT Light source R Luminous flux LNS Collimator lens D Disc GBS1, GBS2 Fixed radial phase diffraction grating GBS3 Fixed radial phase diffraction grating GT Radial phase diffraction grating formed on disk P ₀ GBS2 or GBS3 Combined luminous flux position SARY Received light Element array S _{A, B} Displacement detection element SA, SA-, SB, SB- Light receiving element for interference light flux from radial diffraction grating S _Z Origin position detection element SZ1, SZ2 Light receiving element for light flux from origin pattern S _UVW Absolute position detecting elements SU, SV, the light receiving element of the light flux from the SW absolute code pattern UVW Z origin pattern Z1, Z2 arcuate phase grating UVW absolute code pattern _{U, V, W, U -} , V -, W - arcuate Phase diffraction grating

Claims (13)

[Claims] 1. A part of a rotatable disc-shaped disc having a radial phase diffraction grating, an origin pattern, and an absolute code pattern is irradiated with a light beam emitted from a light source, and the light irradiated with the absolute code pattern is modulated. The light is received by the absolute position detection element to detect the absolute position of the disc, and the modulated light of the light that illuminates the origin pattern is received by the origin position detection element to detect the origin position of the disc. In the composite rotary encoder for obtaining the displacement information of the disc by receiving the interference light diffracted and synthesized by the phase diffraction grating and the fixed diffraction grating by the displacement amount detection element, the origin pattern and the absolute code pattern A composite rotary encoder, characterized in that one or both of them is composed of a plurality of arc-shaped diffraction gratings. 2. The composite rotary encoder according to claim 1, wherein the arc-shaped diffraction grating is a phase diffraction grating. 3. The origin pattern and the absolute code pattern are at least one of the shape parameters of the diffraction grating.
3. A composite rotary encoder according to claim 1, wherein the rotary encoder is composed of a diffraction grating that changes discontinuously. 4. The composite rotary encoder according to claim 1, wherein the absolute position detecting element, the origin position detecting element and the displacement amount detecting element are formed on one substrate. . 5. An opening member for limiting a light beam incident on the absolute position detecting element, the origin position detecting element and the displacement amount detecting element is provided in the vicinity of the disc. (1) A composite rotary encoder according to item 1. 6. A rotatable disc-shaped disc having a radial phase diffraction grating, an origin pattern, and an absolute code pattern, and a fixed diffraction grating arranged so as to overlap the luminous flux emitted from a light source, The absolute position detection element receives the modulated light of the light irradiated with the absolute code pattern to detect the absolute position of the disk, and the modulated light of the light irradiated with the origin pattern is received by the origin position detection element to detect the absolute position of the disk. A composite rotary encoder that detects the origin position and receives the interference light obtained from the diffracted light that has passed through the fixed diffraction grating and the phase diffraction grating on the disc to the displacement amount detection element to obtain the displacement information of the disc. In either one of or both of the origin pattern and the absolute code pattern, a plurality of arc-shaped diffraction gratings are provided. Complex type rotary encoder that. 7. The composite rotary encoder according to claim 6, wherein the arc-shaped diffraction grating is a phase diffraction grating. 8. The origin pattern and the absolute code pattern are at least one of shape parameters of a diffraction grating.
8. The composite rotary encoder according to claim 6 or 7, characterized in that one is composed of a diffraction grating that changes discontinuously. 9. The composite rotary encoder according to claim 6, wherein the absolute position detecting element, the origin position detecting element and the displacement amount detecting element are formed on one substrate. . 10. An aperture member for limiting a light beam incident on the absolute position detection element, the origin position detection element and the displacement amount detection element is provided in the vicinity of the disk. (1) A composite rotary encoder according to item 1. 11. A radial diffraction grating and a circular arc diffraction grating are provided around a rotation axis on the circumference of a disc-shaped disk, and when a light beam from a light irradiating means is incident on the radial diffraction grating. The generated diffracted light is detected by the displacement amount detecting element and the diffracted light generated when the diffracted light is incident on the arc-shaped diffraction grating is detected by the absolute position detecting element or the origin position detecting element, and the displacement amount detecting element and the absolute position are detected. A composite rotary encoder characterized in that rotation information of the disk is detected using a signal obtained from a detection element or the origin position detection element. 12. The composite rotary encoder according to claim 11, wherein the arc-shaped diffraction grating is a phase diffraction grating. 13. The composite rotary encoder according to claim 11, wherein the arc-shaped diffraction grating is composed of a diffraction grating in which at least one shape parameter of the diffraction grating changes discontinuously.