JP2004245634A - Rotation angle measuring device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an accurate rotation angle measuring device capable of easily measuring the angle of a rotary table at any angle. <P>SOLUTION: This rotation angle measuring device comprises a polygon mirror 14 fixed to a rotating object 12 and a detection part 16 having a light emitting part 18 and a light receiving part 20 fixed to a structural body separate from the rotating object which radiates laser beam from the light emitting part to the polygon mirror, receives the reflected laser beam by the light receiving part, and measures the rotating angle of the rotated object. The detection part 16 further comprises a light dividing means 24 dividing laser beam received by the light receiving part into a primary light 50 and a negative primary light 52 and a beam interference synthetic unit 30 allowing the divided primary light to be interfered with the negative primary light. The error of the rotating angle of the rotating object can be obtained by the beam interference synthetic unit. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a rotation angle measurement device, and more particularly to a rotation angle measurement device that can be suitably used in a technical field where a precise rotation angle is required to be detected, such as a machine tool or a semiconductor manufacturing device.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, in technical fields such as machine tools and semiconductor manufacturing apparatuses, it has been required to detect a rotation angle of a rotary table or the like with high accuracy. That is, since the rotation angle of the table on which the workpiece is placed in the machine tool or the like directly affects the processing accuracy, a high rotation angle of the table is required. As a configuration corresponding to this, for example, a rotary encoder, a comb-shaped index table (common name: Carbic), and the like were generally used.
[0003]
As a technique for measuring the rotation accuracy of these tables, a rotation angle measurement method by the present applicant has been proposed (see Patent Document 1). This technique includes a beam interference combining unit, and first and second laser beams emitted from the beam interference combining unit, which are incident thereon and reflect the incident first and second laser beams in opposite directions. This is an initial incident angle measuring method in rotation angle measurement using a laser interferometer composed of an angle detecting reflecting means provided with a second reflecting means.
[0004]
According to this technique, when the rotation amount is measured using the laser interferometer, the angle of incidence of the reflection unit of the laser beam is measured, and the effect of improving the accuracy of the angle measurement can be obtained.
[0005]
[Patent Document 1]
JP 2000-11325 A
[Problems to be solved by the invention]
However, in the proposal of the above-mentioned conventional Patent Document 1, when the stage returns by one rotation, the rotation accuracy is measured to determine the rotation accuracy of the stage. There is a problem that the angle cannot be measured at an angle, and this improvement has been demanded.
[0007]
SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and has as its object to provide a high-accuracy rotation angle measuring device that can easily measure an angle at an arbitrary angle such as a rotary table.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides a detecting unit including a plane mirror fixed to a rotating object, and a light projecting unit and a light receiving unit fixed to a body separate from the rotating object. Irradiating the plane mirror with laser light from the light projecting unit, receiving the laser light reflected by the plane mirror at the light receiving unit, and measuring a rotation angle of the rotating object, a rotation angle comprising: In the measurement device, the detection unit may include a light splitting unit that splits the laser light received by the light receiving unit into a primary light and a minus primary light, and a beam interference combination that causes the split primary light and the minus primary light to interfere with each other. A beam angle synthesizing unit for determining an error in the rotation angle of the rotating object.
[0009]
According to the present invention, a laser beam is emitted from the light projecting unit to the plane mirror, and the laser beam reflected by the plane mirror is received by the light receiving unit. The laser light received by the light receiving section is split by the light splitting means. The two split beams are diffracted by the diffraction scale, and the primary light of one beam and the minus primary light of the other beam are interfered by the beam interference combining unit, and as a result, the error of the rotation angle of the rotating object is obtained. Can be Therefore, according to this rotation angle measuring device, high-precision measurement is possible, and angle measurement at an arbitrary angle such as a rotary table is facilitated.
[0010]
In the present invention, it is preferable that the plane mirror is one surface of a polygon mirror. If a polygon mirror constituted by combining a plurality of plane mirrors is used as described above, the same measurement can be performed without interruption at every predetermined rotation angle, which is desirable as a rotation angle measurement device. For example, when a polygon mirror having 36 surfaces is used, the rotation angle of the entire circumference (360 degrees) can be measured by sharing the rotation angle of 10 degrees on each surface of the polygon mirror.
[0011]
In the present invention, the diffraction grating scale further includes a plurality of photodetectors, and the divided primary light and the minus primary light are irradiated on the diffraction grating scale, and the irradiated primary light is irradiated. It is preferable that the reflected light of the first and second primary lights at the position of the diffraction grating scale be read by the light detection element via the beam interference synthesizing unit.
[0012]
As described above, if the diffraction grating scale is provided and the positions of the primary light and the minus primary light applied to the diffraction grating scale are read, high-precision measurement is possible, and an arbitrary angle such as a rotary table can be obtained. This is because the angle measurement can be performed more effectively.
[0013]
Further, in the present invention, the runout of the rotation center of the rotating object is detected by a non-contact type position sensor, and the error of the rotation angle of the rotating object is corrected by the detected value of the runout. Preferably. When the rotary table or the like is set eccentrically, even with the rotation angle measuring device of the present invention, an error occurs due to this effect. Even in this case, the above-described problem can be solved by detecting the runout of the rotation center of the object with the non-contact type position sensor and feeding back the result as described above. is there.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, preferred embodiments of a rotation angle measuring device according to the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a front view showing an outline of a rotary table in which a rotation angle measuring device of the present invention is used.
[0015]
A polygon mirror 14 is concentrically fixed to a shaft 13 provided at the center of rotation of a rotating table 12 such as a machine tool, which is a rotating object. A detection unit 16 fixed to a frame (not shown) separate from the turntable 12 is arranged close to the polygon mirror 14. The polygon mirror 14 is irradiated with laser light from the light projecting unit 18 of the detection unit 16, and the laser light reflected by the polygon mirror 14 can be received by the light receiving unit 20.
[0016]
A position sensor 56 is fixed to the detection unit 16 via a sensor holding arm 58. The position sensor 56 is a capacitance-type sensor, and is disposed such that the tip end faces the shaft 13 of the turntable 12 at a predetermined distance. Thus, the runout of the rotation center of the shaft 13 (that is, the rotary table 12) can be detected with high accuracy. As the position sensor 56, a sensor other than the capacitance sensor, such as an eddy current sensor, can be used.
[0017]
FIG. 2 is a conceptual diagram showing the configuration of the rotation angle measuring device 10 of the present invention, which is shown by a plan view. The polygon mirror 14 fixed to the turntable 12 is composed of six polygons, and adopts a configuration in which each polygon shares a rotation angle of 60 degrees. Note that various values can be adopted as the number of surfaces of the polygon mirror 14. For example, in the case of a 36-sided polygon mirror, each polygon has a rotation angle of 10 degrees.
[0018]
A laser light source 18A is disposed in the light projecting unit 18 of the detection unit 16, and a collimating lens 18B is disposed in front of the laser light source 18A so that the optical axis of the collimating lens 18B coincides with that of the laser light source 18A. The position of the laser light emitted from the light projecting unit 18 is adjusted so as to irradiate the front surface (the lower surface in the figure) of the polygon mirror 14. As the laser light source 18A, for example, a semiconductor laser can be used.
[0019]
The light receiving unit 20 of the detecting unit 16 is provided with an FΘ lens 22 that receives the laser beam reflected by the polygon mirror 14 and converts the laser beam into a parallel beam. Behind the FΘ lens 22, there is provided a light dividing means 24 for dividing the laser light received by the light receiving section 20 into two optical paths, that is, a beam 50 and a beam 52. The light splitting means 24 is configured by combining a plurality of prisms.
[0020]
More specifically, the laser light that has entered the light receiving unit 20 and has passed through the FΘ lens 22 is reflected by the light splitting unit 24 through the half mirror surface 24A to become a beam 50 and the half mirror surface 24A. The beam 52 is split into a beam 52 that is further reflected by the mirror surface 24B. The beam 50 and the beam 52 are parallel to each other, and differ in optical path length by M.
[0021]
A diffraction grating scale 32 (commonly called an absolute scale) is fixed at a position where the beams 50 and 52 are irradiated. The beam 50 and the beam 52 enter the diffraction grating scale 32 and are diffracted, and are reflected by the reflection coating on the back surface of the diffraction grating scale 32. The beam interference combining unit 30 is arranged so that the first-order diffracted light of the diffracted reflected light of the beam 50 enters the beam interference combining unit 30 (hereinafter, referred to as an interference unit). Further, the beam interference synthesizing unit 30 is arranged so that the minus first order diffracted light of the diffracted reflected light of the beam 52 enters the beam interference synthesizing unit 30.
[0022]
The diffraction grating scale 32 has a configuration as shown in the conceptual diagram of FIG. 4, and has a grating pattern surface on the front surface and a mirror surface on the back surface. The illustrated diffraction grating scale 32 is irradiated with the primary light 50 and the minus primary light 52 so as to scan from left to right as the polygon mirror 14 rotates (counterclockwise). An origin Z is marked on the diffraction grating scale 32 at a position to the left of the center C in the left-right direction (Z phase). When the primary light 50 to be scanned passes through the position of the origin Z, it will be described later. The counter to be executed can be incremented.
[0023]
Between the light splitting means 24 and the diffraction grating scale 32, the above-described beam interference combining unit 30 for causing the split primary light 50 and the minus primary light 52 to interfere with each other is arranged. That is, the beam interference synthesizing unit 30 takes in the primary light 50 and the minus primary light 52 applied to the diffraction grating scale 32, causes them to interfere, and outputs the interfered light to the photodetector (photodiode PD).
[0024]
Hereinafter, the configuration of the beam interference combining unit 30 will be described with reference to FIG. The beam interference combining unit 30 includes a first polarizing beam splitter 34, a second polarizing beam splitter 36, a non-polarizing beam splitter 38, half-wave plates 40 and 42, and a quarter-wave plate 44. Be composed.
[0025]
Each of the first polarization beam splitter 34, the second polarization beam splitter 36, and the non-polarization beam splitter 38 has a rectangular cross section, and the diagonal of the rectangle is a bonding surface (non-polarization beam splitter surface). It is composed of prisms having a triangular cross section. In FIG. 3, the first polarizing beam splitter 34 and the second polarizing beam splitter 36 are arranged such that the joint surface (polarizing beam splitter surface) is horizontal, while the non-polarizing beam splitter 38 is The non-polarizing beam splitter surface is arranged vertically. The joint surface of each beam splitter plays a role of splitting the incident light beam into transmitted light and reflected light.
[0026]
In FIGS. 3A and 3B, ４０ wavelength plates 40 and 42 are attached to two adjacent lower surfaces of the non-polarization beam splitter 38, respectively. One surface of the first polarizing beam splitter 34 and one surface of the second polarizing beam splitter 36 are arranged on two adjacent surfaces on the upper side of the non-polarizing beam splitter 38, respectively. However, a quarter-wave plate 44 is inserted between the non-polarization beam splitter 38 and the second polarization beam splitter 36 on the left side.
[0027]
The surfaces from which the output of the beam interference synthesizing unit 30 is taken out are four surfaces, and four photodiodes PD, which are photodetectors, are arranged at positions corresponding to these surfaces. Is detected.
[0028]
Hereinafter, the primary light 50 and the minus primary light 52 radiated and emitted to the diffraction grating scale 32 are taken into the beam interference synthesizing unit 30 and follow the flow of light from the beam interference synthesizing unit 30 to the photodiode PD. The configuration of the beam interference synthesizing unit 30 will be reinforced.
[0029]
In FIG. 3, the primary light 50 irradiated and reflected on the diffraction grating scale 32 is incident on the half-wave plate 40 almost vertically from a position approximately 45 degrees below and to the left. Next, the light enters the non-polarizing beam splitter 38, passes through the non-polarizing beam splitter surface 38A, exits from the non-polarizing beam splitter 38, and then enters the first polarizing beam splitter 34 and transmits through the polarizing beam splitter surface 34A. Then, the light exits from the first polarization beam splitter 34 and enters the photodiode PD1.
[0030]
At the same time, the minus primary light 52 applied to and reflected by the diffraction grating scale 32 is incident on the half-wave plate 42 almost perpendicularly from a position approximately 45 degrees below and to the right. Next, the light enters the non-polarization beam splitter 38, is reflected by the non-polarization beam splitter surface 38A, exits from the non-polarization beam splitter 38, and then enters the first polarization beam splitter 34 and transmits through the polarization beam splitter surface 34A. Then, the light exits from the first polarization beam splitter 34 and enters the photodiode PD1.
[0031]
The photodiode PD1 simultaneously receives the primary light 50 and the minus primary light 52 that have been made to interfere with each other, and receives the interference light having a light intensity change (phase) shift of 0 degrees. The output signal of the photodiode PD1 due to the received light has a waveform as shown in FIG.
[0032]
Similarly, in FIG. 3, the primary light 50 irradiated and reflected on the diffraction grating scale 32 is incident on the half-wave plate 40 almost perpendicularly from a position approximately 45 degrees below and to the left of the left. Next, the light enters the non-polarization beam splitter 38, passes through the non-polarization beam splitter surface 38A, exits from the non-polarization beam splitter 38, and then enters the first polarization beam splitter 34 and is reflected by the polarization beam splitter surface 34A. Then, the light exits from the first polarization beam splitter 34 and enters the photodiode PD2.
[0033]
At the same time, the minus primary light 52 applied to and reflected by the diffraction grating scale 32 is incident on the half-wave plate 42 almost perpendicularly from a position approximately 45 degrees below and to the right. Next, the light enters the non-polarization beam splitter 38, is reflected by the non-polarization beam splitter surface 38A and exits from the non-polarization beam splitter 38, and then enters the first polarization beam splitter 34 and is reflected by the polarization beam splitter surface 34A. Then, the light exits from the first polarization beam splitter 34 and enters the photodiode PD2.
[0034]
The photodiode PD2 simultaneously receives the primary light 50 and the minus primary light 52 that have been made to interfere with each other, and receives the interference light whose light intensity change (phase) shifts by 180 degrees. The output signal of the photodiode PD2 due to the received light has a waveform as shown in FIG.
[0035]
Similarly, in FIG. 3, the primary light 50 irradiated and reflected on the diffraction grating scale 32 is incident on the half-wave plate 40 almost perpendicularly from a position approximately 45 degrees below and to the left of the left. Next, the light enters the non-polarization beam splitter 38, is reflected by the non-polarization beam splitter surface 38A, exits from the non-polarization beam splitter 38, and then passes through the quarter-wave plate 44 to the second polarization beam splitter 36. The light enters, passes through the polarization beam splitter surface 36A, exits from the second polarization beam splitter 36, and enters the photodiode PD3.
[0036]
At the same time, the minus primary light 52 applied to and reflected by the diffraction grating scale 32 is incident on the half-wave plate 42 almost perpendicularly from a position approximately 45 degrees below and to the right. Next, the light enters the non-polarization beam splitter 38, passes through the non-polarization beam splitter surface 38A, exits from the non-polarization beam splitter 38, and then passes through the quarter-wave plate 44 to the second polarization beam splitter 36. The light enters, passes through the polarization beam splitter surface 36A, exits from the second polarization beam splitter 36, and enters the photodiode PD3.
[0037]
The photodiode PD3 simultaneously receives the primary light 50 and the minus primary light 52 that have been interfered in this manner, and receives interference light having a light intensity change (phase) shift of 90 degrees. The output signal of the photodiode PD3 due to the received light has a waveform as shown in FIG.
[0038]
Similarly, in FIG. 3, the primary light 50 irradiated and reflected on the diffraction grating scale 32 is incident on the half-wave plate 40 almost perpendicularly from a position approximately 45 degrees below and to the left of the left. Next, the light enters the non-polarization beam splitter 38, is reflected by the non-polarization beam splitter surface 38A, exits from the non-polarization beam splitter 38, and then passes through the quarter-wave plate 44 to the second polarization beam splitter 36. The light enters, is reflected by the polarization beam splitter surface 36A, exits from the second polarization beam splitter 36, and enters the photodiode PD4.
[0039]
At the same time, the minus primary light 52 applied to and reflected by the diffraction grating scale 32 is incident on the half-wave plate 42 almost perpendicularly from a position approximately 45 degrees below and to the right. Next, the light enters the non-polarization beam splitter 38, passes through the non-polarization beam splitter surface 38A, exits from the non-polarization beam splitter 38, and then passes through the quarter-wave plate 44 to the second polarization beam splitter 36. The light enters, is reflected by the polarization beam splitter surface 36A, exits from the second polarization beam splitter 36, and enters the photodiode PD4.
[0040]
The photodiode PD4 simultaneously takes in the primary light 50 and the minus primary light 52 that have interfered in this way, and receives the interference light having a light intensity change (phase) shift of 270 degrees. The output signal of the photodiode PD4 due to the received light has a waveform as shown in FIG.
[0041]
The four types of signal waveforms detected by the photodiodes PD1 to PD4 shown in FIG. 5 are summed so as to be able to cancel fluctuations in the amount of light, etc., and arranged into two types of waveforms as shown in FIG. . The signal waveform of FIG. 6A is obtained by subtracting the signal waveform of FIG. 5B from the signal waveform of FIG. 5A. Is shown. The signal waveform of FIG. 6B is obtained by subtracting the signal waveform of FIG. 5D from the signal waveform of FIG. 5C. Is shown.
[0042]
The reason why the signal waveform having the light intensity change (phase) shift of 0 degree and the signal waveform of 90 degree is obtained is to count the frequency division and to determine the scanning direction of the light. The scanning distance of the light is obtained from the signal waveform obtained in FIG. 6, whereby the error of the rotation angle of the turntable 12 can be calculated.
[0043]
Hereinafter, the details of the signal processing will be described. FIG. 7 is a graph showing the relationship between the displacement of the diffraction grating and the output signal phase, and FIG. 8 is a block diagram showing the configuration of a length measuring machine using a diffraction grating scale. The four-phase moiré signals detected by the photodiodes PD1 to PD4 are each subjected to voltage amplification by a preamplifier 70 and then input to an operational amplifier 72 as a subtraction circuit. In the operational amplifier 72, subtraction is performed using a combination of signals having a phase difference of π, a DC component is removed, and the following signals Y ₁ and Y ₂ are output.
[0044]
(Equation 1)
Y ₁ = A · sin (2πx / P)
[0045]
(Equation 2)
Y ₂ = A · cos (2πx / P)
With this method, it is possible to remove an error or the like due to a change in light amount.
[0046]
The direction discriminating circuit 74 determines the moving direction of the diffraction grating from the relative relationship between the two-phase signals, and sends a signal for switching between Up and Down to the Up / Down counter 80. More specifically, the signal is sent from the direction discriminating circuit 74 to the Up / Down counter 80 via the dividing circuit 76 and the pulsating circuit 78, and also to the Up / Down switch 84. Further, the Up / Down counter 80 is provided with a loop returning through the zero detecting means 82 and the Up / Down switch 84. Since the Up / Down direction of the Up / Down counter 80 is reversed in the + and-regions, the passage of the counter through the zero point is detected and switched.
[0047]
The output from the Up / Down counter 80 is sent to the output buffer 90 and the display 92 via the data latch 88. The Up / Down counter 80 is connected to zero set means 86 so that zero can be set.
[0048]
Next, the operation of the rotation angle measuring device 10 will be described with reference to FIG. FIG. 2 shows a state in which the polygon mirror 14 concentrically fixed to the turntable 12 is rotated counterclockwise by θ from the state shown by the broken line in FIG. 2 to the state shown by the solid line. The reflected light, the primary light 50, and the minus primary light 52 before the rotation of the polygon mirror 14 are indicated by broken lines. On the other hand, the reflected light, the primary light 50, and the minus primary light 52 after the polygon mirror 14 is rotated by θ are shown by solid lines. The angle difference between the dashed reflected light and the solid reflected light is 2θ.
[0049]
If the distance between the reflection surface of the polygon mirror 14 and the light receiving section 20 (FΘ lens 22) is L, the shift amount d of the primary light 50 (minus primary light 52) due to the rotation of the polygon mirror 14 by θ is L × tan2θ. Therefore, the displacement output S detected by the diffraction grating scale 32 due to the rotation θ of the rotary table 12 (polygon mirror 14) is S = 2d.
[0050]
For example, when the distance L is 500 mm and the rotation angle deviation is 1 second, S = 0.97 μm. If the resolution of the diffraction grating scale 32 is 0.01 μm, this corresponds to 97 counts. Therefore, it can be said that sufficient measurement accuracy has been obtained.
[0051]
Incidentally, the error level of a conventionally used rotary encoder, a comb-shaped index table (common name: Carbic) or the like is 2 to 3 seconds in one rotation (360 degrees). Greatly inferior to precision.
[0052]
The rotation table 12 is rotated for each angle (60 degrees in this example) per surface of the polygon mirror 14, and the angle deviation is sequentially measured within the measurement range of the diffraction grating scale 32. At this time, when the scanned primary light 50 passes through the position of the origin Z of the diffraction grating scale 32 shown in FIG. 4, the incremental counter can be reset.
[0053]
As described above, the example of the embodiment of the rotation angle measuring device according to the present invention has been described. However, the present invention is not limited to the example of the above embodiment, and various aspects can be adopted.
[0054]
For example, in the example of the embodiment (FIGS. 3 and 5), a configuration using four-phase signal waveforms is adopted, but a configuration using two-phase signal waveforms of 0 degrees and 90 degrees is also used. Substantially the same effects can be obtained. In this case, the configuration of the beam interference combining unit 30 can be simplified.
[0055]
Further, in the example of the embodiment, the present invention is applied to the rotary table 12 that rotates in the horizontal direction as a rotating object. Instead, a configuration for measuring the tilt (Tilt) of the table with respect to the horizontal direction is used. Can also be applied. Even in this case, similarly excellent effects can be obtained.
[0056]
【The invention's effect】
As described above, according to the present invention, a laser beam is emitted from a light projecting unit to a plane mirror, and the laser beam reflected by the plane mirror is received by a light receiving unit. The laser light received by the light receiving section is split by the light splitting means. The two split beams are diffracted by the diffraction scale, and the primary light of one beam and the minus primary light of the other beam are interfered by the beam interference combining unit, and as a result, the error of the rotation angle of the rotating object is obtained. Can be Therefore, according to this rotation angle measuring device, high-precision measurement is possible, and angle measurement at an arbitrary angle such as a rotary table is facilitated.
[0057]
Further, according to the configuration including the diffraction grating scale, the laser beam received by the light receiving unit is split by the light splitting unit, and the two split beams are diffracted by the diffraction grating scale. And the minus primary light of the beam are interfered by the beam interference combining unit, and as a result, the error of the rotation angle of the rotating object is obtained. Therefore, according to this rotation angle measuring device, high-precision measurement is possible, and angle measurement at an arbitrary angle such as a rotary table is facilitated.
[Brief description of the drawings]
FIG. 1 is a front view showing an outline of a rotary table in which a rotation angle measuring device of the present invention is used. FIG. 2 is a conceptual diagram showing a configuration of a rotation angle measuring device of the present invention. FIG. FIG. 4 is a conceptual diagram showing the configuration of a diffraction grating scale. FIG. 5 is a graph showing a signal waveform detected by each photodiode. FIG. 6 is a graph showing a waveform obtained by synthesizing signals having phases different by 180 degrees. FIG. 7 is a graph showing the relationship between the displacement of the diffraction grating and the output signal phase. FIG. 8 is a block diagram showing the configuration of a length measuring machine using a diffraction grating scale.
DESCRIPTION OF SYMBOLS 10 ... Rotation angle measuring device, 12 ... Rotating table (rotating object), 14 ... Polygon mirror, 16 ... Detection part, 18 ... Light projection part, 20 ... Light receiving part, 22 ... F lens, 24 ... Light dividing means, 30 ... Beam interference synthesizing unit, 32 diffraction grating scale, 34 first polarizing beam splitter, 36 second polarizing beam splitter, 38 non-polarizing beam splitter, 40, 42 half-wave plate, 44 1 / 4 wavelength plate, 50: primary light, 52: minus primary light, PD: photodiode (photodetector)

Claims (4)

A plane mirror fixed to a rotating object,
The rotating object is fixed to a separate body, a detecting unit including a light projecting unit and a light receiving unit, and irradiates the plane mirror with laser light from the light projecting unit, and is reflected by the plane mirror. A detection unit that receives laser light at the light receiving unit and measures a rotation angle of the rotating object,
In a rotation angle measuring device comprising:
The detection unit includes a light splitting unit that splits the laser light received by the light receiving unit into primary light and minus primary light, and a beam interference combining unit that causes the split primary light and minus primary light to interfere with each other. And
A rotation angle measuring device, wherein an error of a rotation angle of the rotating object is obtained by the beam interference synthesis unit. The rotation angle measuring device according to claim 1, wherein the plane mirror is one surface of a polygon mirror. Furthermore, a diffraction grating scale and a plurality of photodetectors are provided,
The divided primary light and the minus primary light are irradiated on the diffraction grating scale, and the reflected light of the irradiated primary light and the minus primary light at the position of the diffraction grating scale is caused by the beam interference. The rotation angle measurement device according to claim 1, wherein the rotation angle is read by the light detection element via a synthesis unit. 3. A non-contact type position sensor for detecting a runout of a center of rotation of the rotating object, and correcting a rotation angle error of the rotating object based on the detected runout value. Or the rotation angle measuring device according to any one of 3.

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