Optical encoder

Abstract

An optical encoder 10 comprising: a light source 11; a splitter 12 splits a light from the light source 11, a light receiving unit 16; a scale 13 is arranged on a light path and movable in a measurement direction, a grating being arranged on a main surface of the scale; and an offset diffraction grating 14 includes a plurality of diffraction gratings arranged in the optical path from the splitter 12 to the light receiving unit 16, the plurality of diffraction gratings diffracting the split lights with different phases, wherein, the plurality of diffraction gratings 13 in the offset diffraction grating 14 are arranged in one plane parallel to the main surface of the scale and are offset each other in an offset direction orthogonal to the measurement direction, the light receiving unit 16 includes a plurality of light-receiving elements 16-11 to 16-23 arranged in the offset direction.

Claims

1. An optical encoder comprising: a light source; a splitter that splits a light from the light source, a light receiving unit; a scale that is arranged on a light path and movable in a measurement direction, a grating being arranged on a main surface of the scale; and an offset diffraction grating that includes a plurality of diffraction grating patterns arranged in the optical path from the splitter to the light receiving unit, each of the plurality of diffraction grating patterns comprising a plurality of diffraction gratings diffracting the split lights with different phases, wherein, the plurality of diffraction gratings in the offset diffraction grating patterns are arranged in one plane parallel to the main surface of the scale, and the plurality of diffraction grating patterns are offset each other in an offset direction orthogonal to the measurement direction, and the light receiving unit includes a plurality of light-receiving elements arranged in the offset direction.

2. The optical encoder according to claim 1, wherein the splitter is a first non-polarization beam splitter, and the optical encoder comprises a second non-polarization beam splitter that is arranged in an optical path from the scale to the light receiving unit.

3. The optical encoder according to claim 2, wherein the offset diffraction grating is arranged in an optical path from the scale to the second non-polarization beam splitter.

4. The optical encoder according to claim 2, wherein the offset diffraction grating is arranged in an optical path from the first non-polarization beam splitter to the scale.

5. The optical encoder according to claim 1, wherein the splitter is an index grating.

6. The optical encoder according to claim 5, wherein the offset diffraction grating is arranged in an optical path from the scale to a site of the index grating that emits a light to the light receiving unit.

7. The optical encoder according to claim 5, wherein the offset diffraction grating is arranged in an optical path from a site of the index grating on which the light from the light source is incident to the scale.

8. The optical encoder according to claim 5, wherein the scale reflects a light.

9. The optical encoder according to claim 1, wherein the light receiving unit includes a plurality of rows in which the plurality of the light receiving elements are arranged in the offset direction; and the plurality of diffraction gratings in the offset diffraction grating are offset each other in the offset direction parallel to the main surface of the scale.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a top view showing an outline of an optical portion of the optical encoder according to the first embodiment;

(2) FIG. 2 is a diagram showing the configuration of an offset diffraction grating according to the first embodiment;

(3) FIG. 3 is a perspective view showing the outline of a portion of the optical encoder according to the first embodiment;

(4) FIG. 4 is a top view schematically showing the optical portion of the optical encoder according to the first embodiment;

(5) FIG. 5 is a top view schematically showing the optical portion of the optical encoder according to the second embodiment;

(6) FIG. 6 is a perspective view showing the outline of a portion of the optical encoder according to the second embodiment;

(7) FIG. 7 is a top view showing an outline of an optical portion of the optical encoder according to the second embodiment;

(8) FIG. 8 is a perspective view showing an outline of an optical portion of the optical encoder according to the third embodiment;

(9) FIG. 9 is a diagram showing the configuration of a conventional optical encoder;

(10) FIG. 10 is a diagram showing the configuration of a conventional optical encoder;

(11) FIG. 11 is a diagram showing a configuration of a conventional optical encoder;

(12) FIG. 12 is a diagram showing the configuration of a conventional optical encoder; and

(13) FIG. 13 is a diagram showing the configuration of a conventional optical encoder.

DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

First Embodiment

(14) The following describes an optical encoder according to a first embodiment of the present invention with reference to the drawings. FIG. 1 is a top view showing an outline of an optical portion of the optical encoder according to the first embodiment.

(15) In FIG. 1, an optical encoder 10 includes a light source 11, a non-polarization beam splitter 12 (also referred to as a splitter 12), a scale 13, an offset diffraction grating 14, a non-polarization beam splitter 15, and light receiving units 16-1 and 16-2. In the optical encoder 10, a detection head 17 includes the light source 11, the non-polarization beam splitter 12, the offset diffraction grating 14, the non-polarization beam splitter 15, and the light receiving units 16-1 and 16-2, and measures the amount of displacement of the detection head 17 relatively moving in an X-axis direction along the scale 13.

(16) The light source 11 is configured to emit a light in the direction of the non-polarization beam splitter 12. Specifically, the light source 11 which is configured to emit a light beam, for example, a LED (Light Emitting Diode), a semiconductor laser, an SLED (Self-Scanning Light Emitting Device), or an OLED (Organic light-emitting diode), can be used.

(17) The non-polarization beam splitter 12 is a splitting means (splitter) for splitting the light beam emitted from the light source 11 into two light beams. Generally, the non-polarization beam splitter 12 causes two light beams to reach the scale 13 in phase. For example, the non-polarization beam splitter 12 is arranged in a plane perpendicular to the scale 13 and the light source 11 is arranged so that the light beam from the light source 11 is incident on the main surface of the non-polarization beam splitter 12 from an oblique direction, and thereby two light beams reach the scale 13 thorough equal distances.

(18) One or more diffraction gratings are arranged in parallel on the main surface of the scale 13. The scale 13 can be moved parallel to the measurement direction. The pattern of the diffraction grating of the scale 13 is preferably linear projections and depressions that are configured side by side in parallel with pitches of micrometer size. Moreover, any material capable of forming a grating-like light transparent portion which transmits light and a grating-like light nontransparent portion that does not transmit light can be applied to the scale 13.

(19) The offset diffraction grating 14 in which a plurality of diffraction grating patterns are arranged in parallel on one side of the main surface of the scale 13 diffracts each of the split lights by the plurality of diffraction grating patterns. In the offset diffraction grating 14, since the plurality of diffraction grating patterns are arranged on the same plane and it has an offset in a direction orthogonal to the measurement direction between the diffraction grating patterns, the light beams diffracted in the respective diffraction grating patterns have different phases from each other.

(20) The-polarization beam splitter 15 synthesizes the lights diffracted in the offset diffraction grating 14 and emits the synthesized light to the light receiving units 16-1 and 16-2. For example, the non-polarization beam splitter 15 is arranged on the symmetry plane to which diffracted light diffracted by a grating area 14-1 and the diffracted light diffracted by a grating area 14-2 are plane-symmetrical as shown in FIG. 2.

(21) As shown in FIG. 3, the light receiving unit 16-1 has a configuration in which a plurality of light receiving elements 16-11, 16-12 and 16-13 are arranged in the offset direction. Also, the light receiving unit 16-2 has a configuration in which a plurality of light receiving elements 16-21, 16-22 and 16-23 are arranged in the offset direction as well as the light receiving unit 16-1.

(22) That is to say, the receiving units 16-1 and 16-2 can obtain a plurality of interfering signals having phase differences as electric signals by converting the intensity of light obtained by synthesizing the light beams that are diffracted by each of the diffraction gratings of the offset diffraction grating 14 and have the different phases into the electrical signals.

(23) The light receiving units 16-1 and 16-2 preferably include a photodiode array. Further, any of a phototransistor, a photoresistor, and so on can be applied as far as the unit can receive the light and convert it into the electrical signal.

(24) Now, the offset diffraction grating as a feature of the present embodiment will be described. FIG. 2 is a diagram showing the configuration of an offset diffraction grating according to the first embodiment. In FIG. 2, the offset diffraction grating 14 has a grating area 14-1 and a grating area 14-2.

(25) The grating area 14-1 and the grating area 14-2 have diffraction gratings formed in a direction perpendicular to the diffraction grating of the scale 13. There are an offset in a direction orthogonal to the measurement direction, i.e. in a Y-axis direction, between the grating pattern of the grating area 14-1 and the grating pattern of the grating area 14-2. The offset amount may be any amount which causes the phase difference between the light beams diffracted in each grating area.

(26) For example, when the grating pitch is p and the offset amount y is p/4, the phase difference between the light beams is 90. Since the phase difference between the light beams may not be 0, the phase difference between the light beams occurs when the offset amount is not equal to an integral multiple of the grating pitch.

(27) The present embodiment is characterized in that the phase difference is generated between light beams by the offset diffraction grating, and further a plurality of interfering signals are generated by using a three-dimensional optical path. Next, the generation of the interfering signal will be described.

(28) FIG. 3 is a perspective view showing an outline of a portion of the optical encoder according to the first embodiment. The same configurations as those of FIG. 1 will be indicated by the same numbers and description of those will be omitted.

(29) FIG. 3 shows a portion of a subsequent stage of the offset diffraction grating 14 in the optical encoder 10 of FIG. 1. The light beam of the light source 11 is split into two beams in the non-polarization beam splitter 12.

(30) Then, the two light beams are diffracted +1 order or 1 order in the scale 13, respectively, and are incident on the offset diffraction grating 14. Specifically, +1 order diffracted light is incident on the grating area 14-1 of the offset diffraction grating 14, and 1 order diffracted light is incident on the grating area 14-2 of the offset diffraction grating 14.

(31) Here, the +1 order diffracted light after diffraction at the scale 13 is expressed by a following equation (1), and the 1 order diffracted light after diffraction at the scale 13 is expressed by a following equation (2).

(32) $\begin{array}{cc}{U}_{X+1}=\exp \left(i.Math.2\frac{x}{g}\right)& \left(1\right)\\ U_{X-1}=\exp \left(-i.Math.2\frac{x}{g}\right)& \left(2\right)\end{array}$

(33) g represents the grating pitch of the scale 13, and x represents a position of the scale. In addition, the subscript of U represents diffraction. For example, U.sub.x+1 means the +1 order diffracted light of the X-axis (measurement) direction in FIGS. 1 to 3, and U.sub.x1 means the 1 order diffracted light of the X-axis (measurement) direction in FIGS. 1 to 3.

(34) The +1 order diffracted light is turned into zero-order, +1 order, and 1 order diffracted lights by the grid pattern of the grating area 14-1. Similarly, the 1 order diffracted light is turned into zero-order, order +1, and 1 order diffracted lights by the grid pattern of the grating area 14-2.

(35) The resulting diffracted lights are expressed by equations (3) to (8).

(36) $\begin{array}{cc}{U}_{X+1,Y+1}=\exp \left(i.Math.2\frac{x}{g}+i.Math.2\frac{y+y}{p}\right)& \left(3\right)\\ U_{X-1,Y+1}=\exp \left(-i.Math.2\frac{x}{g}+i.Math.2\frac{y}{p}\right)& \left(4\right)\\ U_{X+1,Y0}=\exp \left(i.Math.2\frac{x}{g}\right)& \left(5\right)\\ U_{X-1,Y0}=\exp \left(-i.Math.2\frac{x}{g}\right)& \left(6\right)\\ U_{X+1,Y-1}=\exp \left(i.Math.2\frac{x}{g}-i.Math.2\frac{y+y}{p}\right)& \left(7\right)\\ U_{X+1,Y-1}=\exp \left(-i.Math.2\frac{x}{g}-i.Math.2\frac{y}{p}\right)& \left(8\right)\end{array}$

(37) g represents the grating pitch of the scale, p represents the grating pitch of the diffraction grating offset, and y represents the position of the offset diffraction grating. In addition, the subscript of U represents diffraction. For example, U.sub.y+1 means the +1 order diffracted light in the Y-axis direction in FIGS. 1 to 3, and U.sub.y1 means the 1 order diffracted light in the Y-axis direction in FIGS. 1 to 3.

(38) For example, U.sub.x+1, y+1 means +1 order diffraction at the scale 13 and +1 order diffraction at the offset diffraction grating 14.

(39) Also, y represents the offset amount in the Y-axis direction between the grating areas in the offset diffraction grating 14 as described above. That is to say, when the grating area 14-1 has an offset of y in the Y-axis direction on the basis of the grating area 14-2, as shown in the equation (3), (7), the phase shift is caused by the offset amount y in the +1 order diffraction and 1 order diffraction light at the grating area 14-1. Note that the zero order diffracted light of the grating area 14-1 is not a diffractive light but instead a straight light, and the phase shift is not generated by the offset amount y as shown in Equation (5).

(40) Then, as shown in equations (4), (6), (8), in the 1 order diffracted light, the 0 order diffracted light, and +1 order diffraction light, the phase shift is not caused by the offset amount y at the grating area 14-2.

(41) Thus, in the encoder of the present embodiment, since the phase shift among the grating areas having an offset in the direction orthogonal to the measurement direction is caused by the offset amount y in the diffracted light, there is no need to use a wave plate or a polarizing plate.

(42) Moreover, only the offset amount y is important in principle for the offset diffraction grating, and there is no need to design the grating parameter for providing the predetermined phase difference in the interfering signal.

(43) Further, in this configuration, a plurality of interfering signals having the phase differences are obtained from the interference wave as a synthetic wave of UX+1 and the UX1 at the offset diffraction grating 14. Therefore, since the effect of scale defects is generated similarly in all of the signals, change in the particular interfering signal never occurs.

(44) Next, the interfering light synthesized by the non-polarization beam splitter after being diffracted by the offset diffraction grating will be described.

(45) The respective diffracted light diffracted by the grating areas 14-1 and the respective diffracted light diffracted by the grating area 14-2 are synthesized into the interfering light at the non-polarization beam splitter 15. Specifically, the light that is +1-order-diffracted by the grating area 14-1, and the light that is +1-order diffracted by the grating area 14-2 are synthesized. Then, the light which is zero-order-diffracted by the grating area 14-1, and the light which is zero-order-diffracted by the grating area 14-2 are synthesized. Also the light id 1-order diffracted by the grating area 14-1 and a light that is 1-order diffracted by the grating area 14-2 are synthesized.

(46) The intensities of the synthesized light are respectively converted to an electric signal at the light receiving elements of the light receiving units 16-1 and 16-2. Specifically, in FIG. 3, the light receiving elements 16-11 and 16-21 receive the interfering light generated by that synthesizing the lights +1-order-diffracted in the grating area 14-1 and grating area 14-2. Then, the light receiving elements 16-12 and 16-22 receives the interfering light generated by synthesizing the lights zero-order diffracted in the grating areas 14-1 and grating area 14-2. In addition, the light-receiving elements 16-13 and 16-23 receive the interfering light generated by synthesizing the lights 1-order-diffractedin the grating area 14-1 and grating area 14-2.

(47) Here, the intensity of the interfering light received at the light receiving elements 16-11 is defined as I.sub.A1, the intensity of the interfering light received at the light-receiving elements 16-12 is defined as I.sub.A2, the intensity of the interfering light received at light receiving elements 16-13 is defined as I.sub.A3, similarly the intensity of the interfering light received at the light receiving elements 16-21 is defined as I.sub.B1, the intensity of the interfering light received at the light receiving elements 16-22 is defined as I.sub.B2, and the intensity of the interfering light received at light receiving elements 16-23 is defined as I.sub.B3. The intensities of the interfering lights are expressed by the following Equations (9), (10), and (11), respectively.

(48) $\begin{array}{cc}{I}_{A1}=I_{B1}=.Math.U_{X+1,Y+1}+U_{X-1,Y+1}.Math.=2\left[1+\cos \left\{2\left(\frac{2x}{g}+\frac{y}{p}\right)\right\}\right]& \left(9\right)\\ I_{A2}=I_{B2}=.Math.U_{X+1,Y0}+U_{X-1,Y0}.Math.=2\left[1+\cos \left(2.Math.\frac{2x}{g}\right)\right]& \left(10\right)\\ I_{A3}=I_{B3}=.Math.U_{X+1,Y+1}+U_{X-1,Y+1}.Math.=2\left[1+\cos \left\{2\left(\frac{2x}{g}-\frac{y}{p}\right)\right\}\right]& \left(11\right)\end{array}$

(49) As shown in Equation (10), the interfering light of the 0 order diffracted light has no phase shift due to the offset amount y of offset diffraction grating. Meanwhile, as shown in Equations (9) and (11), the interfering lights of the first order diffracted light have the phase shift due to the offset amount y of offset diffraction grating.

(50) Thus, the optical encoder of the present embodiment can obtained the interfering light having no phase shift and the interfering light having the phase shift.

(51) The amount of the phase shift can be determined by the offset amount y between the diffraction gratings in the offset diffraction grating.

(52) For example, when the y=p/8, since the difference of 90 between the I.sub.A1 and I.sub.A3 is caused, it is possible to output a phase A and a phase B as in the prior art. In this case, I.sub.A2 is not needed. Also, when the y=p/4, since the difference of 90 between the I.sub.A1 and I.sub.A2 is caused, and it is possible to output the phase A and the phase B phase as in the prior art. In this case, I.sub.A3 is not needed.

(53) Also, a suitable signal processing method may also cause the phase difference of 120 between the interfering signals I.sub.A1, I.sub.A2, and I.sub.A3 by establishing y=p/3 and may convert into a differential signal having the phase difference of 90 with a known method.

(54) Then, the amount of change in the displacement x associated with the movement of the scale 13 is obtained from these interfering signals. The processing of these interfering signals can be implemented by calculation processing of analog or digital electrical signals.

(55) Arithmetic processing after converting the interfering signals into the electrical signals can be implemented by CPU (Central Processing Unit) or ASIC (Application Specific Integrated Circuit) internal or external to the encoder and executing a predetermined arithmetic processing. Also, it may be implemented by connecting to the external computer and processing the arithmetic processing as software.

(56) Thus, the optical encoder of the first embodiment can obtain a plurality of interfering signals having the phase difference by offsetting a plurality of diffraction gratings in the direction orthogonal to the measurement direction from each other and by individually measuring diffraction light in the offset direction without using the wave plate and a polarizing plate.

(57) Moreover, the optical encoder of the first embodiment can be easily miniaturized because the diffraction grating has no limitation other than setting an offset in a direction orthogonal to the measurement direction. Also the optical encoder of the first embodiment has no variation among the interfering signals due to the effect of scale defects because the defects of the scale affect all the plurality of interfering signals.

(58) The position in which the offset diffraction grating is arranged may be any position where the optical path of each beam is split. In the present embodiment, the splitter 15 is arranged in the optical path between the non-polarization beam splitter 12 and the non-polarization beam.

(59) In the optical encoder of FIG. 1, although the offset diffraction grating 14 is arranged in the optical path between the scale 13 and the non-polarization beam splitter 15, as shown in FIG. 4, the offset diffraction grating 14 may be arranged in the optical path between the non-polarization beam splitter 12 and the scale 13.

Second Embodiment

(60) In a second embodiment, an example of using an index grating to split light is described. FIG. 5 is a top view schematically showing the optical portion of the optical encoder according to the second embodiment. In FIG. 5, the same configuration as that of FIG. 1 are indicated the same numerical sign and the description of that will be omitted.

(61) In FIG. 5, an optical encoder 20 includes the light source 11, an index grating 21 (also referred to as a splitter), the scale 13, the offset diffraction grating 14, an index grating 22, and the light receiving unit 16-1 and 16-2.

(62) The index grating 21 splits the light beam emitted from the light source 11 into two light beams. Generally, the index grating 21 causes the split two light beams to reach the scale 13 in phase. For example, the main surface of the index grating 21 is arranged in parallel on the main surface of the scale 13, the light source 11 is arranged so that the light beam from the light source 11 is incident on the main surface of the index grating 21 from an oblique direction, and thereby the split two light beams reach the scale 13 thorough equal distances.

(63) Index grating 22 synthesizes between diffracted lights in the offset diffraction grating 14, and emits the synthesized light to receiving unit 16-1 and 16-2. For example, the main surface of the index grating 22 is arranged in parallel to the main surface of the scale 13.

(64) Processing of the optical and electrical signals is same processing in the first embodiment processing except that non-polarization beam splitter 12 of the first embodiment is replaced with the index grating 21 and that the non-polarization beam splitter 15 is replaced by the index grating 22.

(65) In optical encoder 20 described in FIG. 5, the light receiving units 16-1 and 16-2 include a plurality of light receiving elements similarly to the optical encoder of the first embodiment. FIG. 6 is a perspective view showing the outline of a portion of the optical encoder according to the second embodiment.

(66) The light receiving unit 16-1 has a configuration in which a plurality of light receiving elements 16-11, 16-12 and 16-13 are arranged in the offset direction. Also the light receiving unit 16-2 has a configuration in which a plurality of light receiving elements 16-21, 16-22 and 16-23 in the offset direction similarly to the light receiving unit 16-1.

(67) As shown in FIG. 6, in the index grating 22, the light receiving elements 16-11 and 16-21 receive the interfering light synthesized between +1 order diffraction lights. Similarly, in the index grating 22, the light receiving elements 16-12 and 16-22 receive the interfering light synthesized between zero-order diffraction lights. In the index grating 22, the light receiving elements 16-13 and 16-23 receives the interfering light synthesized between 1 order diffracted lights.

(68) Then, the light receiving elements 16-11 to 16-23 converts the intensity of each light into an electrical signal. Similarly to the first embodiment, the interfering light of the 0 order diffracted light has no phase shift due to the offset amount y of offset diffraction grating. Meanwhile, the interfering lights of the first order diffracted light have the phase shift due to the offset amount y of offset diffraction grating.

(69) Thus, according to the optical encoder of the second embodiment, since the phase shift caused by the offset amount y in the diffracted light between the grating areas having an offset in the direction orthogonal to the measurement direction, there is no need to be limited the index grating the phase grating, and it is not necessary to design the grating parameters for providing the predetermined phase difference, so there is no constraints on designing the diffraction grating.

(70) Further, the index gratings 21 and 22 are applicable either if the configuration capable of splitting light, amplitude grating such slits formed grating are also applicable.

(71) The position to be arranged the offset diffraction grating may be any position where the optical path of each beam is split. In the present embodiment, the optical path between the index grating 21 to the index grating 22 corresponds to position where be arranged the offset diffraction grating. In the optical encoder of FIG. 5, although offset diffraction grating 14 are arranged in the optical path between the scale 13 and the index grating 22, also offset diffraction grating 14 may be arranged in the optical path between the index grating 21 and scale 13 as shown in FIG. 7.

Embodiment 3

(72) Also, in the optical encoder 20 of the second embodiment, the index grating 21 and the index grating 22 may have a common configuration. FIG. 8 is a perspective view showing an outline of an optical portion of the reflective optical encoder according to the third embodiment. In FIG. 8, the optical encoder 30 includes the light source 11, the glass substrate 31, the index grating 32, the scale 33, the offset diffraction grating 14-1, and receiving units 16-11 to 16-23.

(73) Glass substrate 31 is a glass substrate having two parallel surfaces, the index grating 32 is formed on one side, and the offset diffraction grating 14-1 and 14-2 is formed on the other side. Further, the glass substrate 31 is made of a material for transmitting light incident from the light source 11.

(74) Index grating 32 has a configuration corresponding to the index grating 21 and the index grating 22 in FIG. 5, and split the light beam emitted from the light source 11 into two light beams, and synthesizes between diffracted lights diffracted in the offset index grating that includes grating areas 14-1 and 14-2, and emits the synthesized light to receiving unit 16-1 and 16-2.

(75) Scale 33 is the scale of the reflective type, and the scale 33 is obtained by forming a grating pattern on the material surface that reflects light such as steel. Scale 33 is displaced in the X-axis direction, the optical encoder 30 measures the displacement amount in the X-axis direction.

(76) Offset diffraction grating 14-1 and 14-2 have a configuration corresponding to offset diffraction grating 14 of FIG. 1 or FIG. 5

(77) In the optical encoder 30, light incident from the light source 11 is split into two beams in the index grating 32, and the light is transmitted through the glass substrate 31, and the light is reflected by the scale 33. Then, a reflected light is diffracted in the diffraction grating offset 14-1 and 14-2, and the reflected light is transmitted through the glass substrate 31, and the reflected light reaches to the index grating 32 again. And in the index grating 32, an interfering light that is synthesized between each other the diffracted light is measured in the light receiving units 16-11 to 16-23.

(78) Thus, according to the optical encoder of the third embodiment, the index grating is formed on one surface of a glass substrate, the diffraction grating having an offset in the direction orthogonal to the measurement direction by forming the back surface of the glass substrate, a simple detection site can be implemented by a more small number of parts.

(79) In the above embodiment, the offset diffraction grating has been described a configuration in which an offset between the two gratings may be configured to be offset between more than three gratings. In this case, it may be located on the main surface of the offset diffraction grating, and may be with the configuration to be offset in a direction orthogonal to the measurement direction. For example, it is also possible to form the optical system of the three-phase shifting the 2/3 each phase between the three grids. In other words, it will offset in a direction perpendicular to the measurement direction only of the grating width between the grids. It is offset of the grid width between the gratings in a direction perpendicular to the positioning direction.

(80) Also, each gratings and the scale can be any as long as it is a combination of a material comprising the opaque portions and light transmitting portions applications. In other words, may be used as the light transmitting portion to form a hole of the grid-shaped opaque glass, it may be formed an opaque portion to shield a portion of the transparent glass. Also it can be similarly applied to materials except of glass.

(81) The present invention is not intended to limited to the above embodiments, and it is possible to appropriately be changed without departing from the scope. For example, the optical encoder of the present invention is not limited to the linear encoder, it can be applied to a rotary encoder.

(82) From the invention thus described, it will be obvious that the embodiments of the invention may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended for inclusion within the scope of the following claims.