JP7520595B2 - Optical encoder and drive control device - Google Patents

Description

The present invention relates to optical encoders, etc.

Conventionally, rotary encoders are used to measure angles in machine tools, factory automation equipment, and the like. Optical encoders can improve light receiving efficiency by providing a radial light collecting effect, as described in Patent Document 1, for example.

Japanese Patent Application Publication No. 3-113316

In a rotary scale, the spatial frequency in the direction of movement changes depending on the detection radius. In particular, when the detection radius is small, the change in spatial frequency with respect to the deviation of the radius becomes more sensitive.
Even if the light beam from a grating pattern in an area that is significantly shifted from the reading center diameter and cannot substantially contribute to the detection signal is focused on the light receiving surface, the signal efficiency cannot be improved and may even increase the noise component.
An object of the present invention is to provide an optical encoder that has low noise and high resolution even when its diameter is reduced.

The optical encoder of the present invention comprises:
a rotary scale that rotates about a predetermined axis and has a grating pattern including a first periodic pattern arranged in a first radial area and a second periodic pattern arranged in a radial area different from the first radial area;
A light source that irradiates the grid pattern;
a light receiving element for detecting interference fringes formed by the grating pattern irradiated with light from the light source,
the light receiving element is configured to receive first interference fringes formed by the first periodic pattern and to receive second diffracted light diffracted by the second periodic pattern in a radial direction from the second periodic pattern to the first periodic pattern,
an optical path length from the light source to the first periodic pattern and an optical path length of the first diffracted light from the first periodic pattern to the light receiving element are equal,
The optical path length from the light source to the second periodic pattern and the optical path length of the second diffracted light from the second periodic pattern to the light receiving element are configured to be different .

The present invention makes it possible to realize a low-noise, high-resolution optical encoder even when the diameter is reduced.

1 is a diagram showing a configuration of an optical encoder according to a first embodiment of the present invention; 1 is a diagram showing a cross-sectional structure of an optical encoder according to a first embodiment. FIG. 2 is a diagram showing a grating pattern according to the first embodiment. FIG. 2 is a diagram showing an arrangement of light receiving elements according to the first embodiment. FIG. 2 is a development of optical paths of the encoder according to the first embodiment. FIG. 4 is a diagram showing the spatial frequency response characteristic of the detection unit of the first embodiment. 4 is a development diagram of optical paths in the encoder of the first embodiment as viewed from the X-axis side. FIG. 4 is a development diagram of optical paths in the encoder of the first embodiment as viewed from the X-axis side. FIG. 4 is a development diagram of optical paths in the encoder of the first embodiment as viewed from the X-axis side. FIG. FIG. 13 is a diagram showing an example of a grid pattern according to a second embodiment. FIG. 11 is a development of optical paths as viewed from the X-axis side in the encoder of the second embodiment. 13 is a diagram showing the relationship between the normalized spatial frequency 1/P(r)×Ppd on the light receiving element array 12 and the radial position r through which the light beam passes in the second embodiment. FIG. 13 is a diagram showing a cross-sectional structure of an optical encoder according to a third embodiment. FIG. FIG. 13 is a diagram showing an example of a grid pattern according to a third embodiment. FIG. 11 is a development of optical paths of an encoder according to a third embodiment. FIG. 13 is a view of the encoder of the third embodiment as viewed from the scale side. FIG. 13 is a diagram showing the spatial frequency response characteristics of a detection unit according to the third embodiment. FIG. 11 is a development of optical paths in the encoder of the third embodiment as viewed from the X-axis side. FIG. 11 is a development of optical paths in the encoder of the third embodiment as viewed from the X-axis side. FIG. 13 is a diagram showing an example of a lattice pattern according to a fourth embodiment. FIG. 13 is a diagram showing an example of a grid pattern according to a fifth embodiment. FIG. 13 is a diagram illustrating a configuration of an imaging apparatus according to a sixth embodiment. FIG. 13 is a diagram showing the configuration of a laser processing apparatus according to a seventh embodiment.

The following describes an embodiment of the present invention with reference to the drawings.

Fig. 1 shows the configuration of an optical encoder (hereinafter simply referred to as an encoder) according to a first embodiment of the present invention. Fig. 2 shows a cross-sectional structure of the optical encoder in this embodiment as viewed from the X-axis side of Fig. 1.
The encoder has a sensor unit 10 attached to a fixed part of a measuring device (not shown), and a (rotary) scale 20 attached to a movable part of the measuring device and rotatable about a predetermined axis relative to the sensor unit 10. Note that the scale 20 may be attached to the fixed part of the device, and the sensor unit 10 may be attached to the movable part.

In other words, it is sufficient that the sensor unit 10 and the scale 20 are capable of relative movement. In the following description, the direction of movement of the scale 20 relative to the sensor unit 10 (X direction in FIG. 2), i.e., the direction of relative movement between the scale 20 and the sensor unit 10, is referred to as the position detection direction. The sensor unit 10 is an integrated light receiving and emitting sensor unit in which a light emitting element 11 such as an LED and a light receiving IC 13 having a light receiving element array 12 are mounted in the same package. The light receiving element array 12 is configured by arranging multiple light receiving elements in the position detection direction (X direction, i.e., the circumferential direction of the scale or the direction perpendicular to the radius) for detecting the intensity distribution of light reflected by a grid pattern provided on the scale 20 (see FIG. 4).

On the other hand, the scale 20 is provided with a grating pattern 21 formed as a reflective diffraction grating by reflective and non-reflective sections arranged alternately in the circumferential direction. Figure 3 shows an example of the grating pattern 21, where the grey sections are non-reflective sections and the white sections are reflective sections. Note that although a reflective scale is used in this embodiment, the present invention is not limited to this and a transmissive scale may also be used. In that case, the grey sections are non-transmissive sections and the white sections are transmissive sections.

The rotary scale has a region (region A, first radial region) centered on the reading center radius r0 (first radial position) and having a radial width Wr0. In addition, a plurality of slit rows (first pattern, first periodic pattern) are provided in the circumferential direction, each row consisting of reflective and non-reflective sections arranged alternately at a predetermined angle Tp/2 with respect to the center of rotation of the rotary scale. Each slit row has a radial shape extending radially from the center of rotation of the rotary scale, and is arranged at a predetermined angle. The first pattern has a first period P1.
The region with a radius larger than r0+Wr0/2 includes a region B (third radius region) that includes a predetermined radius r1 (third radius position).

Area B has a concentric pattern consisting of non-reflective and reflective parts arranged periodically at a predetermined interval in the radial direction. A plurality of concentric patterns are arranged at a predetermined interval from the center of rotation of the rotary scale and extend along the circumferential direction of the center of rotation. In addition, a slit row (second pattern, second periodic pattern) consisting of reflective and non-reflective parts arranged alternately in the circumferential direction is provided, and the period P2 of the second pattern in area B is longer than the period P1 of the first pattern. In addition, a grating pattern is formed by the second pattern and the concentric pattern. The distance between the radial centers of adjacent gratings in the radial direction is Rp1, the radial width of the reflective parts is Rm1, and the width of the non-reflective parts is Rs1.

The region with a radius smaller than r0-Wr0/2 has a region C (second radius region) including a predetermined radius r2 (second radius position), and has a concentric pattern consisting of non-reflective and reflective parts arranged periodically at a predetermined interval in the radial direction. The concentric patterns are arranged at a predetermined interval from the center of rotation of the rotary scale and extend along the circumferential direction of the center of rotation. In addition, a slit row (second (periodic) pattern) consisting of reflective and non-reflective parts arranged alternately in the circumferential direction is provided, and a grid pattern is formed by the second pattern and the concentric pattern. The period P2 of the second pattern in region C is shorter than the period P1 of the first pattern. The distance between the centers of the radially adjacent grid patterns is Rp2, the radial width of the reflective part is Rm2, and the non-reflective part width is Rs2. In addition, the circumferential width of the reflective part is Tm and the width of the non-reflective part is Ts in all of regions A, B, and C.

In this embodiment, the following parameters are used:
Wr0=0.3 mm
Tp=2π/1885=0.0033333 rad
Ts = Tp / 2
Tm = Tp / 2
Rp1=6 μm
Rs1 = Rp1/2
Rm1=Rp1/2
Rp2=6 μm
Rs2 = Rp2/2
Rm2 = Rp2 / 2
r0=6 mm
r1=6.2 mm
r2=5.8 mm

The central wavelength of the light source is λ, and the distance from the radial position where the light emitting point of the light emitting element 11 is disposed to the reading center radius r0 is dr0 (see FIG. 7).
λ=650 nm
dr0=1 mm
The light emitting element 11 irradiates the grid pattern with light at a predetermined angle.

Figure 4 shows the light receiving element array 12 as a light receiving element that detects the interference fringes of the grid pattern illuminated by light from the light source. In this embodiment, the light receiving element array 12 is configured with 160 light receiving elements arranged in a row in the position detection direction. The center-to-center distance (adjacent element pitch) Xpd between two adjacent light receiving elements in the position detection direction is 10 μm. In addition, the size (width) Ypd of each light receiving element in the direction perpendicular to the position detection direction (Y direction) is 1000 μm.

The 160 light receiving elements are assigned to the A(+), B(+), A(-) and B(-) phases in this order and in a cyclical manner, and 40 (two or more) light receiving elements assigned to each of these four phases constitute one light receiving element group. In other words, in this embodiment, four light receiving element groups each consisting of 40 light receiving elements are provided. The 40 light receiving elements constituting each light receiving element group are electrically connected to each other, and their outputs (currents) are added together and input to an IV (current-voltage) conversion amplifier (not shown) provided for each phase in the subsequent stage. The center-to-center distance (intra-group element pitch) Ppd between the two light receiving elements closest to each other in the position detection direction among the 40 light receiving elements constituting the same light receiving element group arranged every four is 40 (10 x 4) μm.

The output of the IV amplifier for each phase is a voltage signal (sine wave signal) whose value changes sinusoidally in response to the movement of the scale 20. The outputs of the four IV amplifiers provided for the four phases correspond to signal phases of 0 degrees, 90 degrees, 180 degrees, and 270 degrees, respectively, and are converted into position information by calculation.
5 is a diagram showing the optical path of the encoder of this embodiment expanded, that is, expanded as if reflection were transmission. The distance L1 from the light-emitting element 11 to the grating pattern 21 is set in the range of 2 mm ± 0.3 mm. The distance L2 from the grating pattern 21 to the light-receiving element array 12 is set equal to L1 (or within a range that can be considered equal). In this embodiment, L1 = L2 = 2 mm. Note that L1 and L2 correspond to the effective optical path length, which is the value obtained by dividing the physical length by the refractive index.

A divergent light beam emitted from an LED serving as a light-emitting element 11 is incident on a grating pattern 21. The zeroth-order light, the +1st-order diffracted light, and the -1st-order diffracted light diffracted and reflected by the grating pattern 21 interfere with each other on the light-receiving element array 12, thereby forming interference fringes having a light intensity distribution with a period P.
FIG. 6 shows the response characteristics of the signal amplitude of the output of each of the four IV amplifiers provided for the four phases, with respect to the spatial frequency P of the interference fringes on the light receiving element array 12.

The spatial frequency on the horizontal axis is normalized by the inverse of the element pitch in the photodetector array 12, 1/Ppd, and the signal amplitude response peaks at 1. In this embodiment, the element pitch Ppd in the photodetector array 12 as the detection grid corresponds to the period P0 at which the detection sensitivity peaks.

When the period P of the interference fringes deviates from Ppd, the output signal amplitude attenuates, and when Ppd/P deviates to (N+1)/N=1.025 or (N-1)/N=0.975, where N is the number of interference fringes being read (40 in this embodiment), the signal disappears. In other words, the light receiving element array 12 has a detection period corresponding to the period of the first interference fringes, and is capable of detecting first interference fringes within a predetermined period range that includes P0 as the first period, and is substantially unable to detect interference fringes outside the predetermined period range.

Fig. 7 shows an optical path development as seen from the X-axis side. As in Fig. 5, the optical path of the encoder of this embodiment is developed, that is, reflection is developed as if it were transmission. Next, Fig. 7 shows the effect of diffraction for each scale radius.
A light beam passing through radius r0 of region A is projected onto the light-receiving element array 12 with a circumferential pattern period Tp×r0 at an optical magnification M0=(L1+L2)/L1, forming interference fringes with a spatial period of Tp×r0×M0. The distance dr1 of radius r1 within region B from the radial position where the light-emitting point of the light-emitting element 11 is located can be written as follows:

dr1=r1-r0+dr0
The optical path length Opl1A of the light beam 31 incident on the area B at a radius r1 from the light emitting point can be written as the following equation 1.

光束３１の入射角θ１ｉｎは以下の数２のように書ける。

The incident angle θ1in of the light beam 31 can be written as the following Equation 2.

The distance dr1_r from the radial position r1 at which the light beam 41b is incident on the light receiving element array 12 after being diffracted inward from the radius r1 can be written as the following Equation 3 and Equation 4 using the emission angle θ1out of the diffracted light.

半径ｒ１から内周方向に回折され受光素子アレイ１２上に入射する光束の光学倍率Ｍ１は以下の数６のように書ける。

The optical path length OplB of the light beam 41b can be expressed as the following equation 5.

The optical magnification M1 of the light beam that is diffracted from the radius r1 in the inner circumferential direction and enters the light receiving element array 12 can be written as the following equation 6.

正規化空間周波数１／Ｐ１×Ｐｐｄは、０．９９９となる。
同様に、内周側のｒ２を経由する光線の作用を、図８を用いて説明する。
発光素子１１の発光点を配置する半径位置から領域Ｃ内の半径ｒ２の距離ｄｒ２は以下の数８のように書ける。 The spatial period P1 of the circumferential interference fringes formed on the light receiving element array 12 by the light beam 41b can be written as the following equation 7.

The normalized spatial frequency 1/P1×Ppd is 0.999.
Similarly, the effect of the light passing through r2 on the inner periphery side will be described with reference to FIG.
The distance dr2 of radius r2 within region C from the radial position where the light emitting point of the light emitting element 11 is disposed can be written as the following equation 8.

発光点から領域Ｃ内の半径ｒ２に入射する光束３２の光路長Ｏｐｌ２Ａは以下の数９のように書ける。

光束３１の入射角θ２ｉｎは以下の数１０のように書ける。

The optical path length Opl2A of the light beam 32 incident on the area C at a radius r2 from the light emitting point can be written as the following equation 9.

The incident angle θ2in of the light beam 31 can be written as the following equation 10.

半径ｒ２から外周方向に回折され受光素子アレイ１２上に入射する光束４２ｃの、受光素子アレイ１２に入射する半径位置からｒ２の距離ｄｒ２＿ｒは、回折光の出射角θ２ｏｕｔを用い以下の数１１、数１２のように書ける。

The distance dr2_r from the radial position r2 at which the light beam 42c is diffracted from the radius r2 in the outer circumferential direction and incident on the light receiving element array 12 to the light receiving element array 12 can be written as the following Equation 11 and Equation 12 using the emission angle θ2out of the diffracted light.

光束４２ｃの光路長Ｏｐｌ２Ｂは以下の数１３のように書ける。

The optical path length Opl2B of the light beam 42c can be written as the following equation 13.

半径ｒ２から外周方向に回折され受光素子アレイ１２上に入射する光束の光学倍率Ｍ２は以下の数１４のように書ける。

The optical magnification M2 of the light beam diffracted from the radius r2 in the outer circumferential direction and incident on the light receiving element array 12 can be written as the following Equation 14.

光束４２ｃにより、受光素子アレイ１２上に形成される円周方向の干渉縞の空間周期Ｐ２は以下の数１５のように書ける。

The spatial period P2 of the circumferential interference fringes formed on the light receiving element array 12 by the light beam 42c can be written as follows:

正規化空間周波数１／Ｐ２×Ｐｐｄは、１．００５となる。
以上のように、光源から第２の半径領域の格子（周期）パターンまでの光路長より、前記第２の半径領域の格子（周期）パターンから前記受光素子までの回折光の光路長が長くなるように構成されている。また、光源から第３の半径領域の格子（周期）パターンまでの光路長より、前記第３の半径領域の格子（周期）パターンから前記受光素子までの回折光の光路長が短くなるように構成されている。

The normalized spatial frequency 1/P2×Ppd is 1.005.
As described above, the optical path length of the diffracted light from the grating (periodic) pattern of the second radial region to the light receiving element is longer than the optical path length from the light source to the grating (periodic) pattern of the second radial region, and the optical path length of the diffracted light from the grating (periodic) pattern of the third radial region to the light receiving element is shorter than the optical path length from the light source to the grating (periodic) pattern of the third radial region.

On the other hand, a light beam 41a that is incident on the light receiving element array 12 from the radius r1 without being diffracted in the radial direction is as follows.
The light beam 41a (zeroth-order light in the radial direction) is projected onto the light-receiving element array 12 with a circumferential pattern period Tp×r1 at an optical magnification M0=(L1+L2)/L1, forming interference fringes with a spatial period P1' of Tp×r1×M0. The spatial period P1' is expressed by the following equation 16.

The normalized spatial frequency 1/P1' x Ppd is 0.968, which is equal to r0/r1. On the other hand, the normalized spatial frequency at which the signal disappears is (N-1)/N = 0.975, and since the above is further deviated from this, it cannot substantially contribute to the detection signal. In other words, r1 > r0 x N/(N-1) is one condition for it to not substantially contribute to the detection signal when there is no diffraction structure in the radial direction. Note that N is the number of interference fringes being read by the light receiving element.

Similarly, the light beam 42a that is incident on the light receiving element array 12 from the radius r2 without being diffracted in the radial direction is as follows. The light beam 42a (radial direction zero-order light) is projected onto the light receiving element array 12 with a circumferential pattern period Tp×r2 at an optical magnification M0=(L1+L2)/L1, forming an interference fringe with a spatial period P2' of Tp×r2×M0. The spatial period P2' is expressed by the following equation 17.

正規化空間周波数１／Ｐ２′×Ｐｐｄは、１．０３４となる。これは、ｒ０／ｒ２に等しい。一方、信号が消失する正規化空間周波数は、（Ｎ－１）／Ｎ＝１．０２５であり、上記はこれよりさらにずれているため、検出信号に実質的に寄与することができない。

The normalized spatial frequency 1/P2'×Ppd is 1.034, which is equal to r0/r2. On the other hand, the normalized spatial frequency at which the signal disappears is (N−1)/N=1.025, which is further shifted from this frequency and therefore cannot substantially contribute to the detection signal.

In other words, r2 < r0 × N/(N + 1) is one condition under which the absence of a diffraction structure in the radial direction makes no substantial contribution to the detection signal.
As described above, if there is no radial diffraction structure, the light beams passing through the radii r1 and r2 that satisfy the above conditions cannot effectively contribute to the detection signal.

It is desirable that the radial size Ypd of the light receiving element array 12 covers the positions where the light beams that substantially contribute to the detection signal, i.e., the light beam 41b diffracted inward from the radius r1 and the light beam 42c diffracted outward from the radius r2, are incident. More desirably, as shown in FIG. 9, the width (for example, Ypd = 600 μm) is set so that the light beams that do not substantially contribute to the detection signal, the light beams 41a and 42a that are not diffracted in the radial direction from the radius r1 and the radius r2, are not incident, thereby improving the signal-to-noise ratio of the signal.

As described above, if the pattern at the radial position of r1 or r2 does not have a radial diffraction structure as in this embodiment, it will only have a radial zero-order light component, which will fall outside the specified periodic range that the light receiving element can detect, and will not contribute to the S/N ratio of the position detection signal. However, in this embodiment, in order to allow patterns outside the specified periodic range to efficiently contribute to the detection signal, the pattern at the radial position (radial region) of r1 or r2 has a radial diffraction structure.

Furthermore, the light from the light source is irradiated onto the grating pattern from a side closer to the center of the rotary scale than the grating pattern, and the light receiving element is disposed to receive the diffracted light from the grating pattern on a side farther from the center of the rotary scale than the grating pattern.
The first pattern may be arranged so that any one of the optical characteristics, i.e., transmittance, reflectance, and optical path difference, changes alternately at predetermined angles in the circumferential direction, and the concentric patterns may be arranged so that any one of the optical characteristics, i.e., transmittance, reflectance, and optical path difference, changes radially.

More preferably, the circumferential interference fringes formed by the radial diffraction are within a range of half or less of the spatial frequency shift at which the signal disappears. The spatial frequency at which the signal disappears is expressed as follows, where N is the number of interference fringes used for detection, and P0 is the period at which the detection sensitivity reaches its peak:
(N±1)/N/P0
When the light receiving element array is used as a detection grating as in this embodiment, P0=Ppd.

Preferably, the spatial period P (P1 or P2 in this embodiment) of the circumferential interference fringes formed on the detection grating by the light beam diffracted in the radial direction and incident on the light receiving element array 12 satisfies the following condition: To this end, the distance Rp (Rp1 or Rp2 in this embodiment), which is the radial grating structure period, is set to meet the following condition.
(N-0.5)/N/P0<1/P<(N+0.5)/N/P0

The light receiving element array is disposed to receive first interference fringes having a period Q1 formed by the first pattern, and to receive second interference fringes having a period Q2 diffracted by the second pattern and formed in the direction of the first interference fringes. The optical encoder then performs the following for the second pattern in the region C:
P2×Q1/P1<Q2<P1×Q1/P2
For the second pattern in region B,
P2×Q1/P1>Q2>P1×Q1/P2
More preferably, the second pattern in the region C is configured to satisfy the following condition:
P2×Q1/P1<Q2<Q1
For the second pattern in region B,
P2×Q1/P1>Q2>Q1
It is configured to satisfy the following conditions.

As described above, according to this embodiment, a diffraction structure with a predetermined period in the radial direction is provided for the region of radius r1 or r2, which is an area where the period in the circumferential direction is shifted and cannot substantially contribute to the detection signal. In addition, the light beam from the region of radius r1 or r2 is diffracted to form interference fringes with a detectable period on the detection grating. As a result, the light beam from the radial area that cannot substantially contribute to the detection signal in the conventional technology can be received as an effective light beam, improving the light utilization efficiency and the signal-to-noise ratio.

Figure 10 is a diagram showing an example of a grating pattern 21 in Example 2. The rest of the configuration is the same as in Example 1. The scale 20 in this example is provided with a grating pattern 21 formed as a reflective diffraction grating with a fully reflective film on phase steps arranged alternately in the circumferential direction. In Figure 10, the gray parts are recesses and the white parts are protrusions. The phase difference between the recesses and protrusions is designed to be approximately half the wavelength.

The grid pattern 21 has a plurality of slit rows arranged in the radial direction, each row being made up of concave and convex portions alternately arranged in the circumferential direction. The slit rows are arranged alternately adjacent to each other in the radial direction, with a circumferential grid phase difference of 180 degrees between a row having a convex portion width Tw1 and a row having a convex portion width Tw2.
The radial center-to-center distance Rp(r) between adjacent slit rows having the same circumferential grating phase is changed so as to gradually decrease as the radius r moves away from r0.

In this embodiment, the following parameters are used:
Tp=2π/864=0.007272 rad
Tw1=Tp/2
Tw2=Tp/2
r0=5.5 mm
λ=650 nm
dr0=1 mm
L1 = L2 = 2 mm

In this embodiment, a reflective scale is used, but the present embodiment is not limited to this, and a transmissive scale may be used. In this case, the reflective film is eliminated, a step structure is formed using a transparent base material, and the phase difference due to the refractive index difference between air and the transparent base material is set to λ/2.
Next, the effect of radial diffraction will be described with reference to FIG.
The +1st order diffracted light and -1st order diffracted light diffracted and reflected by the grating pattern 21 interfere with each other on the index grating 15 shown in FIG. 13, for example, to form interference fringes with a period P(r).

That is, it acts as a diffractive lens that has a radial focusing effect, and forms an approximate focus on the light receiving element array 12. In order to form a focus, for example, the distance Rp(r) between the centers of the slit rows may be determined so as to satisfy the following equations 18 to 22.

光束４１ｂの光路長ＯｐｌＢは以下の数２４のように書ける。 The optical path length Opl1A of the light beam 31 incident on the radius r from the light emitting point can be written as the following equation 23.

The optical path length OplB of the light beam 41b can be written as the following equation 24.

半径ｒから内周方向に回折され受光素子アレイ１２上に入射する光束の光学倍率Ｍ１は以下の数２５のように書ける。

The optical magnification M1 of the light beam diffracted from the radius r in the inner circumferential direction and incident on the light receiving element array 12 can be written as the following Equation 25.

上記条件において、受光素子アレイ１２上の正規化空間周波数１／Ｐ（ｒ）×Ｐｐｄと、光束が通過した半径位置ｒの関係を図１２の実線に示す。 The spatial period P1 of the circumferential interference fringes formed on the light receiving element array 12 by the light beam 41b can be written as follows:

Under the above conditions, the relationship between the normalized spatial frequency 1/P(r)×Ppd on the light receiving element array 12 and the radial position r through which the light beam passes is shown by a solid line in FIG.

On the other hand, the light beam 41a (radial zero-order light) that is incident on the light receiving element array 12 without being diffracted in the radial direction from the radius r is projected onto the light receiving element array 12 with a circumferential pattern period Tp×r at an optical magnification M0=(L1+L2)/L1. As a result, an interference fringe with a spatial period P(r)' expressed by the following equation 27 is formed.

径方向に回折されずに受光素子アレイ１２上に入射する成分の、正規化空間周波数１／Ｐ（ｒ）′×Ｐｐｄと、光束が通過した半径位置ｒの関係を図１２の破線で示す。

The relationship between the normalized spatial frequency 1/P(r)'×Ppd of the component that is not diffracted in the radial direction and is incident on the light receiving element array 12 and the radial position r through which the light beam passes is shown by the dashed line in FIG.

As shown in FIG. 12, when the period P of the interference fringes deviates from Ppd, the output signal amplitude attenuates. If the number of interference fringes being read is N (40 in this embodiment), and Ppd/P deviates to (N+1)/N=1.025 or (N-1)/N=0.975, the signal disappears. In other words, if there is no radial diffraction structure, the light beam passing through a position shifted by ±0.1 mm or more from the reading center radius r0 cannot effectively contribute to the detection signal. On the other hand, as shown by the solid line, by providing a radial diffraction structure, even the light beam passing through a position shifted by ±1 mm from the reading center radius r0 can effectively contribute to the detection signal.

In this way, it can be seen that by providing a diffraction structure in the radial direction, it is possible to substantially contribute to the detection signal over a wide radial area.
Furthermore, the conditions for widening the radial range that substantially contributes to the detection signal while providing a radial light collecting effect will be described. In Fig. 11, the distance L1 from the light emitting element 11 to the lattice pattern 21 and the distance L2 from the lattice pattern 21 to the light receiving element array 12 are set equal to L1 (or within a range that can be considered equal), and L1 = L2 = L. The light receiving unit is disposed on the outer periphery of the rotation axis with respect to the light emitting element. The radial distance from the radial center of the light receiving unit to the radial center of the light emitting element is d, and the scale radius at the radial midpoint between them is r0.
When the following formula 28 is satisfied, a light collecting effect and a wide detection range can be obtained.

特に、下記の数２９が１に近いと、理想的な集光状態になる。

In particular, when the following equation (29) is close to 1, an ideal light-collecting state is achieved.

As described above, by arranging the light source and the light receiving element in the radial direction and the distance from the scale according to the above conditions, it is possible to focus the light in a narrow radial range while still allowing it to contribute effectively to the detection signal. Focusing the light in the radial direction also has the effect of increasing the tolerance for in-plane rotation.

FIG. 13 shows another example of the configuration of the optical encoder according to this embodiment.
The sensor unit 10 is an integrated light receiving/emitting sensor unit in which a light emitting element 11 constituted by an LED and a light receiving IC 13 having a light receiving element array 12 are mounted in the same package. In the optical path from the light emitting element 11 toward the scale 20, a light source grating (light source pattern) 14 is provided as a first grating formed as a transmission type diffraction grating by transmission parts and light blocking parts arranged alternately in the position detection direction (see FIG. 16).

In addition, an index grating (intermediate pattern) 15 is provided as a third grating in the optical path from the scale 20 to the light receiving element array 12 (between the scale 20 and the light receiving element array 12). The index grating 15 is formed as a transmission type diffraction grating with transmission parts and light blocking parts arranged alternately in the position detection direction. The light source grating 14 and the index grating 15 are each provided by forming a chrome film that serves as the transmission part on one surface of the cover glass 16. The cover glass 16 provided with the light source grating 14 and the index grating 15 is bonded to the light-transmitting resin 17 in which the light-emitting element 11 and the light-receiving IC 13 are sealed, and is optically integrated with the light-emitting element 11 and the light-receiving IC 13.

Fig. 14 is a diagram showing an example of a grating pattern 21 on a scale 20 in Example 3. The scale 20 in this example is provided with a grating pattern 21 formed as a reflective diffraction grating with a fully reflective film at phase steps arranged alternately in the circumferential direction. In Fig. 14, the grey parts are recesses and the white parts are protrusions. The phase difference between the recesses and protrusions is designed to be approximately half the wavelength.
An area having a radial width Wr0 centered on the reading center radius r0 includes an area A, and is provided with a row of slits each made up of a projection and a recess alternately arranged in the circumferential direction.

A region with a radius larger than r0+Wr0/2 includes region B that includes a predetermined radius r1. Region B has multiple slit rows arranged in the radial direction, each row consisting of convex portions and concave portions arranged alternately in the circumferential direction. The slit rows are arranged alternately in the radial direction, with rows of convex portions with a width in the radial direction of Tw1 and rows of convex portions with a width in the radial direction of Tw2, with the circumferential grating phases differing by 180 degrees. In the circumferential grating phases arranged alternately in the radial direction, the distance between the radial centers of adjacent grating phases in the radial direction is Rp1, the radial convex portion width is Rs1, and the concave portion width is Rm1.

Similarly, the region with a radius smaller than r0-Wr0/2 includes region C with a predetermined radius r2, and multiple slit rows consisting of convex portions and concave portions arranged alternately in the circumferential direction are arranged in the radial direction. The slit rows are arranged alternately in the radial direction with circumferential convex portion widths of Tw1 and Tw2, with the circumferential grating phases differing by 180 degrees. In the circumferential grating phases arranged alternately in the radial direction, the distance between the radial centers of radially adjacent grating phases is Rp2, the radial convex portion width is Rs2, and the concave portion width is Rm2.

In this embodiment, the parameters are as follows:
Wr0=0.12mm
Tp=2π/1885=0.0033333 rad
Tw1=Tp/2
Tw2=Tp/2
Rp1=9 μm
Rs1 = Rp1/2
Rm1=Rp1/2
Rp2=9 μm
Rs2 = Rp2/2
Rm2 = Rp2 / 2
r0=6 mm
r1=6.1 mm
r2=5.9 mm

In this embodiment, a reflective scale is used, but the present invention is not limited to this, and a transmissive scale may be used. In this case, the reflective film is eliminated, a step structure is formed using a transparent base material, and the phase difference due to the refractive index difference between air and the transparent base material is set to wavelength/2.
In this embodiment, the light receiving element array 12 is configured with 32 light receiving elements arranged in a row in the position detection direction. The center-to-center distance (adjacent element pitch) Xpd between two adjacent light receiving elements in the position detection direction is 64 μm. Furthermore, the size (width) Ypd of each light receiving element in the direction perpendicular to the position detection direction (Y direction) is 450 μm.

The 32 light receiving elements are assigned to the A(+), B(+), A(-) and B(-) phases in this order and in a cyclical manner, and the eight (two or more) light receiving elements assigned to each of these four phases constitute one light receiving element group. In other words, in this embodiment, four light receiving element groups are provided, each consisting of eight light receiving elements. The eight light receiving elements that make up each light receiving element group are electrically connected to each other, and their outputs (currents) are added together and input to an IV conversion amplifier (not shown) that is provided for each phase in the subsequent stage. The center-to-center distance (intra-group element pitch P) Ppd between the two light receiving elements that are closest in the position detection direction among the eight light receiving elements that make up the same light receiving element group arranged every four is 256 (=64×4) μm.

Figure 15 shows the optical path of the encoder of this embodiment expanded, that is, expanded as if reflection were transmission. The distance L0 between the light-emitting element 11 and the light source grating 14 is 0.3 mm. The distance L1 from the light source grating 14 (a secondary point light source described later), which constitutes a light source together with the light-emitting element 11, to the grating pattern 21 is set to a range of 2.1 mm ± 0.3 mm. The distance L2 from the grating pattern 21 to the index grating 15 is set to be equal to L1 (or within a range that can be considered equal). In this embodiment, L1 = L2 = 2.1 mm. The distance L3, which is the effective optical path length from the index grating 15 to the light-receiving element array 12, is 0.3 mm. The effective optical path length is the value obtained by dividing the physical length by the refractive index.

16 shows the structure of the sensor unit 10 as viewed from the scale side. The grating pitch _P1 of the light source grating 14 is 20 μm, and the grating pitch P3 of the index grating 15 is 18.46154 μm.
Divergent light beams emitted from the LEDs serving as the light emitting elements 11 pass through the light source grating 14 to form a light source array including a plurality of mutually incoherent secondary point light sources.

The divergent light beam emitted from the light source lattice 14 is incident on the lattice pattern 21. In this embodiment, a secondary point light source is formed by combining an LED with the light source lattice 14, but instead, a current confinement type LED or a semiconductor laser may be arranged as an effective point light source. In this embodiment, the divergent light beam from the point light source on the light source lattice 14 is directly incident on the lattice pattern 21, but instead, a lens may be used to convert the position of the effective point light source and incident on the lattice pattern 21. In this case, L1 is replaced with the distance between the effective point light source and the lattice pattern 21.

The +1st order diffracted light and -1st order diffracted light diffracted and reflected by the grating pattern 21 interfere with each other on the index grating 15, forming interference fringes with a period P. Due to the difference between the grating pitches P3 and P of the index grating 15, a light intensity distribution (interference fringes) in which a coarse spatial period Pm is superimposed on the original interference fringes is transmitted through the index grating 15. The spatial period Pm can be expressed by the following equation, where ABS(x) is a function expressing the absolute value of x.
Pm=ABS(P・P3/(P−P3))

The light intensity distribution with a spatial period Pm that has passed through the index grating 15 propagates further and is projected onto the light-receiving element array 12 with an image magnification M. That is, a light intensity distribution with a spatial period M·Pm is formed on the light-receiving element array 12. The image magnification M at this time is expressed as follows:
M=(L0+L1+L2+L3)/(L0+L1+L2)
It is expressed as:

An intensity distribution having a period of M·Pm is formed on the light receiving element array 12,
M Pm = Ppd
The detected amplitude reaches its peak when
In other words, the spatial period P0 at which the detected amplitude reaches a peak on the index grating 15 can be expressed as follows:

P0=P3・Ppd/(Ppd−M・P3)=20μm
At that time, the number N of interference fringes read on the index grating 15 is calculated by dividing the total width of the light receiving element array 12, 2048 μm, by P0·M, giving N=96.

Figure 17 shows the response characteristics of the signal amplitude of the output of four IV amplifiers provided for four phases against the spatial frequency P of the interference fringes on the index grating 15. The spatial frequency on the horizontal axis is normalized by the reciprocal of P0, the detection peak frequency of the detection system consisting of the index grating and the light receiving element array, and the signal amplitude response has a peak at 1.

When the period P of the interference fringes deviates from P0, the output signal amplitude attenuates, and if the number of interference fringes being read is N (96 in this embodiment), the signal disappears when P0/P deviates to (N+1)/N=1.01 or (N-1)/N=0.99.

Next, the effect of diffraction will be shown for each scale radius using FIG.
The central wavelength of the light source is λ, and the distance from the radius where the light emitting point of the light emitting element 11 is arranged to the reading central radius r0 is dr0.
λ=650 nm
dr0=1 mm
Let us assume that.

A light beam passing through a radius r0 of region A has a circumferential pattern period Tp×r0 and is projected onto the light receiving element array 12 with an optical magnification M0=(L1+L2)/L1, forming interference fringes with a spatial period of Tp×r0×M0/2.
The distance dr1 from the radius where the light emitting point of the light emitting element 11 is arranged to the radius r1 within the region B can be written as the following Expression 30.

光束３１の入射角θ１ｉｎは以下の数３１のように書ける。

The incident angle θ1in of the light beam 31 can be written as the following equation 31.

The optical path length Opl1A of the light beam 31 incident on a radius r1 in the region B from the light source lattice can be written as the following Equation 32.

The distance dr1_r from the radial position r1 at which the light beam 41b is diffracted from radius r1 in the inner circumferential direction and incident on the light receiving element array 12 enters the index grating can be written as the following equations 33 and 34 using the emission angle θ1out of the diffracted light.

光束４１ｂの光路長ＯｐｌＢは以下の数３５のように書ける。

The optical path length OplB of the light beam 41b can be written as the following equation 35.

半径ｒ１から内周方向に回折され受光素子アレイ１２上に入射する光束の光学倍率Ｍ１は以下の数３６のように書ける。

The optical magnification M1 of the light beam diffracted from the radius r1 in the inner circumferential direction and incident on the light receiving element array 12 can be written as the following Equation 36.

正規化空間周波数１／Ｐ１×Ｐ０は、０．９９９となる。
同様に、内周側のｒ２を経由する光線の作用を、図１９を用いて説明する。
発光素子１１の発光点を配置する半径から領域Ｃ内の半径ｒ２の距離ｄｒ２は以下の数３８のように書ける。 The spatial period P1 of the circumferential interference fringes formed on the light receiving element array 12 by the light beam 41b can be written as in the following equation (37).

The normalized spatial frequency 1/P1×P0 is 0.999.
Similarly, the effect of the light passing through r2 on the inner periphery side will be described with reference to FIG.
The distance dr2 from the radius where the light emitting point of the light emitting element 11 is arranged to the radius r2 within the region C can be written as the following Expression 38.

光束３１の入射角θ２ｉｎは以下の数３９のように書ける。

発光点から領域Ｃ内の半径ｒ２に入射する光束３２の光路長Ｏｐｌ２Ａは以下の数４０のように書ける。

The incident angle θ2in of the light beam 31 can be written as the following equation 39.

The optical path length Opl2A of the light beam 32 incident on the area C at a radius r2 from the light emitting point can be written as the following equation 40.

The distance dr2_r from the radial position r2 at which the light beam 42c is diffracted from the radius r2 in the outer circumferential direction and incident on the light receiving element array 12 to the light receiving element array 12 can be written as the following Equation 41 and Equation 42 using the emission angle θ2out of the diffracted light.

半径ｒ２から外周方向に回折され受光素子アレイ１２上に入射する光束の光学倍率Ｍ２は以下の数４４のように書ける。 The optical path length Opl2B of the light beam 42c can be written as the following equation 43.

The optical magnification M2 of the light beam diffracted from the radius r2 in the outer circumferential direction and incident on the light receiving element array 12 can be written as the following equation 44.

光束４２ｃにより、受光素子アレイ１２上に形成される円周方向の干渉縞の空間周期Ｐ２は以下の数４５のように書ける。

The spatial period P2 of the circumferential interference fringes formed on the light receiving element array 12 by the light beam 42c can be written as the following equation 45.

正規化空間周波数１／Ｐ２×Ｐｐｄは、１．０００となる。

The normalized spatial frequency 1/P2×Ppd is 1.000.

On the other hand, the light beam 41a that is incident on the light receiving element array 12 without being diffracted in the radial direction from the radius r1 is expressed by the following equation 46. The light beam 41a (radial zero-order light) is projected onto the light receiving element array 12 with a circumferential pattern period Tp×r1 at an optical magnification M0=(L1+L2)/L1, forming an interference fringe with a spatial period P1' of Tp×r1×M0/2.

正規化空間周波数１／Ｐ１′×Ｐ０は、０．９８４となる。

The normalized spatial frequency 1/P1'×P0 is 0.984.

Similarly, the light beam 42a that is incident on the light receiving element array 12 without being diffracted in the radial direction from the radius r2 is expressed by the following formula 47. The light beam 42a (radial zero-order light) is projected onto the light receiving element array 12 with a circumferential pattern period Tp×r2 at an optical magnification M0=(L1+L2)/L1, forming an interference fringe with a spatial period P2' of Tp×r2×M0.

正規化空間周波数１／Ｐ２′×Ｐｐｄは、１．０１７となる。

The normalized spatial frequency 1/P2'×Ppd is 1.017.

The output response due to interference fringes caused by light beams that do not diffract in the radial direction from radii r1 and r2 has the opposite sign to the response at period P0 where the detection sensitivity is at its peak, and it can be seen from Figure 17 that this is a component that does not substantially contribute to the detection signal. In other words, if there is no radial diffraction structure, the light beams that pass through radii r1 and r2 cannot effectively contribute to the detection signal.

As described above, according to this embodiment, a diffraction structure with an appropriate period in the radial direction is provided, and light beams from a pattern at a radial position in an area where the period in the circumferential direction is shifted and the area cannot substantially contribute to the detection signal are diffracted, forming interference fringes with a detectable period on the detection grating.

Figure 20 is a diagram showing an example of a grating pattern 21 in Example 4. The scale 20 in this example has a grating pattern 21 formed as a reflective diffraction grating with a fully reflective film at phase steps arranged alternately in the circumferential direction. In Figure 20, the gray parts are recesses and the white parts are protrusions. The phase difference between the recesses and protrusions is designed to be approximately half the wavelength.

A region with a radial width rW0 centered on the reading center radius r0 has an area A, in which a row of slits consisting of convex and concave portions arranged alternately in the circumferential direction is provided. In area A, the boundary Tp/6 width between the concave slits and the convex slits forms a concave-convex grating with a period in the radial direction. The grating period in the radial direction is 4 μm.

A region with a radius larger than r0+Wr0/2 includes region B that includes a predetermined radius r1. Region B has multiple slit rows arranged in the radial direction, each row consisting of convex portions and concave portions arranged alternately in the circumferential direction. The slit rows are arranged alternately in the radial direction, with rows of convex portions with a width in the radial direction of Tw1 and rows of Tw2, with the circumferential grating phases differing by 180 degrees. In the grating phases arranged alternately in the radial direction, the distance between the radial centers of adjacent grating phases in the radial direction is Rp1, the radial convex portion width is Rs1, and the concave portion width is Rm1.

Similarly, the region with a radius smaller than r0-Wr0/2 includes region C with a predetermined radius r2, and multiple slit rows consisting of convex portions and concave portions arranged alternately in the circumferential direction are arranged in the radial direction. The slit rows are arranged alternately in the radial direction with convex portion widths of Tw1 and Tw2, with the circumferential grating phases differing by 180 degrees. In the grating phases arranged alternately in the radial direction, the distance between the radial centers of adjacent grating phases in the radial direction is Rp2, the radial convex portion width is Rs2, and the concave portion width is Rm2.

The difference from Example 3 is that the grating duty ratio (the ratio of the convex portion width to the concave portion width in the circumferential period) is 1:2, i.e., Tw1/Tp=Tw2/Tp=1/3.
In this embodiment, the parameters are as follows:

Wr0=0.12mm
Tp=2π/1885=0.0033333 rad
Tw1=Tp/3
Tw2=Tp/3
Rp1=9 μm
Rs1 = Rp1/2
Rm1=Rp1/2
Rp2=9 μm
Rs2 = Rp2/2
Rm2 = Rp2 / 2
r0=6 mm
r1=6.1 mm
r2=5.9 mm

In this embodiment, a reflective scale is used, but the present invention is not limited to this, and a transmissive scale may be used. In that case, the reflective film is eliminated, a step structure is formed using a transparent substrate, and the phase difference due to the refractive index difference between air and the transparent substrate is set to λ/2.

In this embodiment, by setting the grating duty to 1:2 in regions B and C, it is possible to reduce the ±3rd order diffracted light in the circumferential direction contained in the diffracted light in the radial direction. In addition, by using a concave-convex grating with a radial period at the boundary Tp/6 width between the concave slits and convex slits in region A, it is possible to reduce the ±3rd order diffracted light in the circumferential direction contained in the component that does not diffract in the radial direction. In this way, it is possible to suppress the fluctuation in signal amplitude due to changes in the gap.

Figure 21 is a diagram showing an example of a grating pattern 21 in Example 5. The scale 20 in this example has a grating pattern 21 formed as a reflective diffraction grating with a fully reflective film on phase steps arranged alternately in the circumferential direction. In Figure 20, the gray parts are recesses and the white parts are protrusions. The phase difference between the recesses and protrusions is designed to be approximately half the wavelength.

The area with the reading center radius r0 at its center and radial width rW0 has area A, which has a row of slits made of convex and concave portions arranged alternately in the circumferential direction. The row of slits in area A is the same as that in Example 4.

A region with a radius larger than r0+Wr0/2 includes region B that includes a predetermined radius r1. Region B has multiple slit rows arranged in the radial direction, each row consisting of convex portions and concave portions arranged alternately in the circumferential direction. The slit rows are arranged alternately in the radial direction, with rows of convex portions with a width in the radial direction of Tw1 and rows of Tw2, with the circumferential grating phase differing by 120 degrees (2π×dT/Tp rad). In the grating phases arranged alternately in the radial direction, the distance between the radial centers of adjacent grating phases in the radial direction is Rp1, the radial convex portion width is Rs1, and the concave portion width is Rm1.

Similarly, the region with a radius smaller than r0-Wr0/2 includes a region C including a predetermined radius r2. Region C is provided with a plurality of slit rows arranged in the radial direction, each row being made up of convex portions and concave portions alternately arranged in the circumferential direction. The slit rows are arranged alternately in the radial direction, with a convex portion width Tw1 in the circumferential direction and a convex portion width Tw2 in the radial direction, with the circumferential grating phase differing by 120 degrees (2π×dT/Tp rad). In the grating phases arranged alternately in the radial direction, the distance between the radial centers of the grating phases adjacent in the radial direction is Rp2, the convex portion width in the radial direction is Rs2, and the concave portion width is Rm2.
In this embodiment, the parameters are as follows:

Wr0=0.12mm
Tp=2π/1885=0.0033333 rad
Tw1=Tp/2
Tw2=Tp/2
dT = Tp / 3
Rp1=9 μm
Rs1 = Rp1/2
Rm1=Rp1/2
Rp2=9 μm
Rs2 = Rp2/2
Rm2 = Rp2 / 2
r0=6 mm
r1=6.1 mm
r2=5.9 mm

This embodiment is an imaging device in which an encoder is mounted on a lens barrel, and Fig. 22 is a schematic cross-sectional view of the imaging device. In Fig. 22, 53 is a sensor unit, and 54 is a CPU, which functions as a control unit that executes various operations of the entire device based on a computer program stored in memory 57. These constitute an encoder. Here, the sensor unit 53 functions as the sensor unit 10 in the first embodiment.
In addition, the imaging means is constituted by a lens group 51, a movable lens 52, an imaging element 55, and a cylinder 50. The movable lens 52 constituting the lens group 41 is, for example, a lens for autofocusing, and is displaceable in the Y direction, which is the optical axis direction.

The movable lens 52 is not limited to an autofocus lens, but may be any other lens that can be driven and displaced, such as a zoom adjustment lens. The cylinder 50 in the scale mounting configuration of this embodiment is connected to an actuator (not shown) that drives the movable lens 52.
The scale 20 is a rotary scale consisting of a radial pattern formed on a disk surface, and is connected to the cylindrical body 50 via a reduction gear 56 .

When the cylinder 50 is rotated around the optical axis of the lens group 51 by an actuator or manually, the scale 20 is rotationally displaced relative to the sensor unit 53, and the driven lens 52 is accordingly driven in the Y direction (arrow direction) which is the optical axis direction. A signal corresponding to the displacement of the driven lens 52 obtained from the encoder sensor unit 53 is output to the CPU 54. A drive signal for moving the driven lens 52 to the desired position is generated from the CPU 54, and the driven lens 52 is driven based on that signal.

FIG. 23 is a diagram showing an example of a laser processing device including a galvano scanning device.
A laser beam from a laser source 610 is deflected in two orthogonal axial directions by galvano scanning devices 620 and 630. The laser beam focused by a lens 640 is irradiated onto an object 650 to be processed.
The galvano scanning devices 620 and 630 are provided with a mirror at a rotating movable part and are driven by a motor. An optical encoder including the sensor unit 10 in the first embodiment is built into the galvano scanning devices 620 and 630. The output of the optical encoder is input to a control unit (not shown) that has a built-in CPU and the like, and the control unit controls the operation of the rotation angle control of the motor to control the rotation angle and the like.

In this way, according to the present invention, an optical encoder capable of high-resolution position detection can be obtained. It can also be applied to drive control devices using optical encoders such as those in Examples 6 and 7. The moving parts in the drive control devices are not limited to lenses, mirrors, etc. as in Examples 6 and 7, and can be anything that can be driven and displaced. In other words, it goes without saying that the present invention can be applied to all drive control devices that measure the amount of displacement of a moving part using the optical encoder and control the operation of the moving part based on the measured amount of displacement.

Although the preferred embodiments of the present invention have been described above, the present invention is not limited to these embodiments, and various modifications and changes are possible within the scope of the gist of the present invention.
Furthermore, a computer program for implementing all or part of the control in this embodiment may be supplied to an apparatus using an optical encoder via a network or various storage media. Then, a computer (or a CPU, MPU, etc.) in the apparatus using the optical encoder may read and execute the program. In this case, the program and the storage medium storing the program constitute the present invention.

REFERENCE SIGNS LIST 10 sensor unit 11 light emitting element 12 light receiving element array 14 light source grating 15 index grating 20 scale 21 grating pattern

Claims (17)

a rotary scale that rotates about a predetermined axis and has a grating pattern including a first periodic pattern arranged in a first radial area and a second periodic pattern arranged in a radial area different from the first radial area;
A light source that irradiates the grid pattern;
a light receiving element for detecting interference fringes formed by the grating pattern irradiated with light from the light source,
the light receiving element is configured to receive first interference fringes formed by the first periodic pattern and to receive second diffracted light diffracted by the second periodic pattern in a radial direction from the second periodic pattern to the first periodic pattern,
an optical path length from the light source to the first periodic pattern and an optical path length of the first diffracted light from the first periodic pattern to the light receiving element are equal,
An optical encoder characterized in that an optical path length from the light source to the second periodic pattern and an optical path length of the second diffracted light from the second periodic pattern to the light receiving element are configured to be different. the light receiving element is disposed to receive first interference fringes having a period Q1 formed by the first periodic pattern having a first period P1 in the circumferential direction of the first radial region, and to receive second interference fringes having a period Q2 diffracted by the second periodic pattern having a second period P2 different from the first period in the circumferential direction of a radial region different from the first radial region and formed in a direction of the first interference fringes;
When P2<P1, P2×Q1/P1<Q2<P1×Q1/P2
Or, when P1<P2, P2×Q1/P1＞Q2＞P1×Q1/P2
2. The optical encoder according to claim 1, wherein the optical encoder is configured such that: the light receiving element is disposed to receive first interference fringes having a period Q1 formed by the first periodic pattern having a first period P1 in the circumferential direction of the first radial region, and to receive second interference fringes having a period Q2 diffracted by the second periodic pattern having a second period P2 different from the first period in the circumferential direction of a radial region different from the first radial region and formed in a direction of the first interference fringes;
When P2<P1, P2×Q1/P1<Q2<Q1
Or, when P1<P2, P2×Q1/P1＞Q2＞Q1
2. The optical encoder according to claim 1, wherein the optical encoder is configured such that: The optical encoder according to any one of claims 1 to 3, characterized in that the light source is arranged to irradiate the grid pattern with light from a side closer to the center of the rotary scale than the grid pattern. An optical encoder according to any one of claims 1 to 4, characterized in that the light receiving element is arranged to receive diffracted light from the grating pattern on a side farther from the center of rotation of the rotary scale than the grating pattern. An optical encoder according to any one of claims 1 to 5, characterized in that the second periodic pattern includes a grating pattern in a second radial region that is closer to the center of rotation of the rotary scale than the first radial region, and a grating pattern in a third radial region that is farther from the center of rotation of the rotary scale than the first radial region. The optical encoder of claim 6, characterized in that the optical path length of the light diffracted from the grating pattern in the second radial region to the light receiving element is longer than the optical path length from the light source to the grating pattern in the second radial region. An optical encoder according to any one of claims 6 and 7, characterized in that the optical path length of light diffracted from the grating pattern in the third radial region to the light receiving element is shorter than the optical path length from the light source to the grating pattern in the third radial region. An optical encoder according to any one of claims 1 to 8, characterized in that the light receiving element has a detection period corresponding to the period of the first interference fringes. a rotary scale that rotates about a predetermined axis and has a radial first pattern extending in a radial direction from the rotation center and arranged at predetermined angle intervals;
a light source that irradiates light onto the first pattern;
a light-receiving element capable of detecting, by light from the light source, first interference fringes within a predetermined periodic range including a first period formed by the first pattern in a first radial region of the rotary scale, and unable to detect interference fringes outside the predetermined periodic range,
an optical encoder comprising : a radial pattern of a second radial region having a second pattern of a second period outside the predetermined periodic range of the rotary scale; a plurality of concentric patterns arranged at predetermined intervals from the center of rotation and extending along a circumferential direction of the second radial region ; and a light source is used to diffract the second pattern of the second period of the second radial region of the rotary scale by the concentric patterns in the direction of the first interference fringes, thereby causing second interference fringes within the predetermined periodic range to be incident on the light receiving element. The optical encoder according to claim 10, characterized in that in the concentric circular pattern, the radial pitch of adjacent gratings in the radial direction is gradually changed as the distance from the center of rotation of the rotary scale increases. The optical encoder according to claim 11, characterized in that in the concentric circular pattern, the radial pitch of adjacent gratings in the radial direction is gradually decreased as the distance from the center of rotation of the rotary scale increases. An optical encoder according to any one of claims 10 to 12, characterized in that the duty ratio of the first pattern in the circumferential direction is 1:2. An optical encoder according to any one of claims 10 to 13, characterized in that the first pattern is arranged so that any one of the optical characteristics, transmittance, reflectance, and optical path difference, alternates at predetermined angles in the circumferential direction. An optical encoder according to any one of claims 10 to 14, characterized in that rows of the first pattern, the phases of which are shifted by 180 degrees from each other in the circumferential direction, are alternately arranged in the radial direction. An optical encoder according to any one of claims 10 to 14, characterized in that rows of the first pattern, the phases of which are shifted from each other in the circumferential direction by 120 degrees, are alternately arranged in the radial direction. A drive control device comprising a movable part that can be driven and displaced, an optical encoder according to any one of claims 1 to 16, and a control unit that uses the optical encoder to control the operation of the movable part.

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