JPS6166926A - Rotary encoder - Google Patents

Abstract

PURPOSE:To detect the angle of rotation of an encoder with high precision by irradiating a rotating body which has a radial grating cut at its periphery with laser light and obtaining two diffracted light beams and superposing those diffracted light beams on each other again through a quarter-wavelength plate for splitting and detection, and splitting and detecting the light. CONSTITUTION:Light transmission parts and reflective parts are cut in the disk 5 in a grating pattern and the disk is rotated through a rotating shaft 6. A reflection point M, is irradiated with the laser light 1 to obtain reflected and diffracted lights L1 and L2. Those reflected and diffracted light beams L1 and L2 are passed through cylindrical lenses 32 and 33, and 32' and 33', reflecting mirrors 41 and 42, and 41; and 42', and quarter-wavelength plates 7 and 7' to illuminate a position M2 which is point- symmetric about the center of rotation. Those two diffracted light beams are super posed at the position M2. Then, the light is split by beam splitters 81-83 and shifted in phase by polarizing plates 9-12; and a photodetection part detect the quantity of the Doppler shifting of the diffracted light to detect the angle of rotation. Thus, the two diffracted light beams are superposed again and split for the detection, so the angle of rotation of the rotary encoder is detected with high precision and the device is reduces is size.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a rotary encoder, in which a radiation grating in which a plurality of grid patterns of, for example, transparent parts and reflective parts are periodically carved on the circumference is attached to a rotating object, and the radiation grating is This relates to a rotary encoder that irradiates a grating K with a beam of light from, for example, a laser, and uses diffracted light from the radiation grating to photoelectrically detect the rotation angle of the radiation grating or a rotating object.

Rotary encoders have traditionally been used as a means to detect the rotation angle of rotating mechanisms such as computer equipment such as floppy desk drives, printer-specific office equipment, NC machine tools, and even VTR capsten motors and rotating drums. It is being used.

The method using a photoelectric front-tally encoder consists of a fold-out main scale with light-transmitting parts and light-shielding parts provided at equal intervals around a disc connected to the rotation axis, and correspondingly spaced at equal intervals to the main scale. The place where the light-transmitting part and the light-blocking part are provided is set to the fixed index scale, and both scales are arranged in the same manner with the light emitting means and the light receiving means (!, 167;
The composition of the i1 index school system is being changed. In this method, as the main scale rotates, an I/H signal is obtained which is rotated by the interval between the light-transmitting part and the light-blocking part of both scales, and after waveform shaping of this signal, the rotation angle is detected by calculating VT. are doing.

Use the rotary encoder to tri both sides (D scale-#
The finer the scale interval between the light-transmitting part and the light-blocking part, the higher the detection accuracy.

However, when the scale interval is made smaller, the S/N ratio of the output signal from the light receiving means decreases due to the influence of the diffracted light, resulting in a decrease in detection accuracy. Therefore, the total number of gratings in the light-transmitting part and the light-blocking part of the main scale is eti! Il determined,
It is conceivable to increase the distance between the light-transmitting part and the light-blocking part to such an extent that it is not affected by diffracted light. However, this has the disadvantage that the diameter and thickness of the main scale disc increases, making the entire device larger, and as a result, the load on the rotating object to be tested increases.

An object of the present invention is to provide a small rotary encoder that reduces the load on a rotating object to be tested, reduces the influence of eccentricity when attached to the rotating object, and is capable of detecting a rotation angle with high precision.

A further object of the present invention is to provide a highly accurate rotary encoder that reduces measurement errors due to errors in the grid pattern of the radiation grating and fluctuations in the output level from the light source.

The main features of the rotary encoder for achieving the object of the present invention are a radiation grating in which a plurality of grid patterns are arranged at equal angles around the circumference of a disk, a rotating object connected to the radiation grating, and a luminous flux incident on the radiation grating. and a first illumination means for causing two diffracted lights of specific orders from among the diffracted lights from the light beam incident on the radiation grating to be set relative to the incident position itK of the light beam by the first illumination means on the radiation grating. Superimposing two diffracted lights of a specific order diffracted again by the second illumination means and the radiation grating, each of which is incident on a position substantially symmetrical with respect to the center of rotation of the rotating object via a wave plate. After that, a light splitting means for splitting the light beams into the four light beams of the superimposed light flux tubes and four polarizing plates each having a polarization direction shifted by 145 degrees receive the four light beams split by the light splitting means. It has four light receiving means for
The rotation angle of the rotating object is determined using output signals from two light receiving means.

Next, one embodiment of the present invention will be described with reference to each drawing.

FIG. 1 is a schematic diagram of one embodiment of the present invention.

In the same figure] is a light source such as a laser, 2 is a collimator lens, 3~3.3'~3a is a cylindrical lens,
41, 42. 41', 4d are reflecting parts, 5 parts are radiation gratings in which, for example, a lattice pattern of transparent parts and reflective parts are provided at equal angles on a disc, 6 parts are the rotation axis of the rotating object to be tested, 7.7 ' is a flea wave plate whose axis is 451 for the linearly polarized light beam from laser 1.
It is arranged at an angle of 145 degrees with W.

8□-83 are beam splitters 19, 10, 11.

There are 12 polarizing plates, and the polarizing plates 9, 1 (1, 11, and 12) are arranged so that their polarization directions are shifted by 45 degrees from each other.

13, 1/1, 15, and 161- are light receiving elements.

The light beam emitted from laser 1 passes through collimator lens 2
As a result, the light beam becomes a substantially parallel light beam, and is irradiated linearly at the position MIK on the radiation grating 5 by the cylindrical lens 3□.

By performing linear irradiation in this manner, it is possible to reduce the pitch error in the grid pattern of the transparent part and the reflective part, which corresponds to the irradiation partial pressure of the light beam on the radiation grating 5.

Incidentally, instead of the cylindrical lens, a slit or a lens and a slit may be used for linear irradiation.

The light beam from the laser 1 is reflected and diffracted by the grating pattern of the radiation grating 5. Now, if the pitch of the lattice pattern at the irradiation part @M1 of the luminous flux is p, then the reflected diffraction light of ±m order,
, L20 diffraction angle θ□ is 81] θ1-±mλ/p ・・・・・・・・・
...is dressed in fl+. Here, λ is the wavelength of the luminous flux.

1. Assume that the radiation grating 5 is rotating at an angular velocity ω.

If the distance from the rotation center of the radiation grating to the irradiation position Ml is r, the circumferential velocity at the irradiation point M1 is v-rω. At this time, the frequency of the ±m-order reflected diffraction light undergoes a so-called Doppler shift by an amount expressed by the following equation.

Δf−±sin em/λ−±ro+sjn 19m/
λ... (2) And, via the cylindrical lenses 32 and 33t,
Reflector 4.4□ reflects the +m-th order reflected light at a position M2 that is approximately point symmetrical about the center of rotation. ′, 33′, linear irradiation is performed again. Here, 1/4 wavelength plate 7
and 7' are arranged such that their respective axes are 45' and -45' with respect to the linear polarization direction of the incident laser. In addition, the angle of incidence on the irradiation position tjLM2 is equal to the reflection diffraction angle θ□ at the irradiation position M for each diffracted light, and the angle with respect to the circumferential velocity direction of the radiation grating 5 is also equal. Reflecting mirrors 4□' and 4°' are arranged at. Then, at the irradiation position M2, the ±m-order reflected diffraction light overlaps, and the cylindrical lens 3□
', it becomes a parallel beam of light again, and is split into four beams by three beam splitters - 8□, 8°, and 83K.
After passing through the polarizing plates 9 to 12, the light receiving elements 13 to 16
incident on . The overlapping ±m-order diffracted light reflected at the irradiation position M2 undergoes the Doppler frequency shift Δff of equation (2) again as the radiation grating 5 rotates, so the frequency when reflected at the irradiation position M2 is Together with the shift, the amount of frequency shift of the ±m-order diffracted light reflected at the irradiation position M2 becomes ±2Δf. In this way, ±
Since the light that has undergone m-order diffraction twice overlaps, the frequency of the output signal from the light receiving elements 13 to 16 is 2Δf-C-2Δf
)-4Δf. In other words, the frequency F of the output signal of the light receiving elements 13 to 16 is F-4Δf -4rmSInθ/λ
From the diffraction condition equation (1), F −4mr
It becomes ω/p. Total number of grid patterns of the radiation grid 5 k N
If the % equiangular pitch is Δψ, then p”−rΔψ, Δψ
-2π/N from F -2mNω/π ・・・・・・・・・
(3) Come out. Now, the wave number e n % of the output of the light receiving element during the time Δt is the rotation angle of the radiation grating 5 during the time Δt 1! If to, n −FJt, θ−ωΔt, then n −2mNθ/π ・・・・・・・・・
(4), and by counting the wave number of the output signal waveform of the light receiving element, the rotation angle θ of the radiation grating 5 can be calculated as (4)
It can be found by 2.

By the way, it is more preferable if the rotation direction is detected when the rotation angle is detected. Therefore, in this embodiment, as is well known in conventional photoelectric rotary encoders, one or more light-receiving elements are prepared and arranged so that the phase of each signal is shifted by 9σ°. ``We use a method to extract a signal indicating the rotation direction from the phase difference signal.

The center level of the output signal of the light-receiving element may fluctuate due to f9, an error in the line width between the light transmitting portion and the reflective portion of the radiation grating 5, and fluctuations in the output of the laser beam. Therefore, in this embodiment, this variation is suppressed and the center level is kept at a constant KL.
In order to stabilize the signal processing at the subsequent stage, a so-called bush-pull method is used in which the difference between the two output signals from the 180° phase difference tube is taken and the DC component is removed.

In this way, in this embodiment, the direction of rotation is detected and at the same time
In order to keep the center level of the signal constant, the output signal of the light receiving element is O', 9σ.

Four phase difference signals of 180° and 270'' are used.

In the configuration of this embodiment, these four phase difference signals are transmitted by the linearly polarized light of the laser, two quarter-wave plates 7°7', and
It is produced by a combination of polarizing plates 9 to 12. In general, a laser is linearly polarized light, but with respect to this polarization direction, ±mm in each optical path of the next destination light, as mentioned above,
The VC3A wave plates 7, 7"i- are placed on the axis 1 so that the angles are 45' and -45'. Then, the 1/4 wavelength plates 7,
The light beams transmitted through 7' become circularly polarized light in opposite directions,
At the irradiation position M2, the reflected and diffracted light of order ±m reoccurs and overlaps, becoming linearly polarized light again, but its polarization direction is
It changes as the radiation grating 5 rotates. This light beam is divided into four light beams by the three beam splitters 8 to 83 as described above, and the polarization direction is shifted by 45', and the polarizing plates 9 to 83 are divided into four beams.
The light enters the light receiving elements 13 to 16 via the light receiving element 12 . From the light receiving elements 13 to 16, as the radiation grating 5 rotates,
This means that signals whose phases are shifted by K are obtained. For example, if the phase of the output signal of the light-receiving element 13 is gold O°, the phases of the output signals of the light-receiving elements 14, 15, and 16 are each
90°.

180°, 270'. These output signals are PoIP9o, P18o, P27o respectively.
As shown in the above, the output signal P. and P-engineer. , P9o and P
When inputting into the differential amplifiers 20 and 21 K, respectively,
There is a 90° phase difference between the output signals of the differential amplifiers 20 and 21, and each output signal has a direct current component removed.
The signal pressure is constant at the center level.

Then, after shaping the waveform of the stiffness signal and detecting the rotation direction, the rotation angle can be determined by putting it into a counter and integrating it.

By the way, in the conventionally used index scale type photoelectric rotary encoder, the wave number n of the output signal from the light receiving element, the total number N of the main scale, and the rotation angle 0 correspond to equation (4). The relationship is n-N672K (5
), the rotation angle Δ0 per wavenumber is Δθ−
2x/N (radian) ・・・・・・・・・(6
). On the other hand, in this example, from equation (4), Δθ−π/2mN (radian)
...(7). Therefore, according to this embodiment, when using nine scales with the same number of divisions, it is possible to obtain a rotation angle detection accuracy 4 m times higher than that of the conventional example.

Further, in a conventional photoelectric rotary encoder, the distance between the light-transmitting part and the light-blocking part is limited to about 10 μm, considering the influence of light diffraction.

Now, in order to obtain a rotation angle detection accuracy of, for example, 30 seconds, K is the number of divisions of the main scale in the conventional example.
From formula (6), N-360X60X60/30-43,
Only 200 are required. Therefore, if the interval between the light-transmitting part and the light-blocking part at the outermost circumference of the main school is 10 μm, the diameter of the main scale is 0.01 tm x 43.200
/π-137.5m is required. However, according to this embodiment, in order to obtain the same rotation angle detection accuracy as the conventional example,
The number of divisions of the radiation grating may be 1/4 m. In the case of m-1 using a ±1st-order diffraction light tube, the number of grating divisions of the radiation grating 5 to obtain a rotation angle detection accuracy of seconds is 43.200/4.
-10.800 1” Yon.

In this embodiment, if laser diffracted light is used, the distance between the transparent part and the reflective part can be narrow, so for example,
If this is 4 μm, the diameter of the radiation grating is 0.00
4 wm x 10,800/π-1 & 75 m would suffice. In other words, according to this embodiment, the shape that achieves the same rotation angle detection accuracy as the conventional index scale type photoelectric rotary encoder is 1/1.
If it's less than 0, then it's a good thing. Therefore, the load on the rotating object to be tested is much smaller than in the conventional example, and accurate measurements can be performed.

FIG. 2 is an explanatory diagram of the irradiation positions M, , M2 of the light beam on the radiation grating 5 of a part of FIG. 1, the eccentricity between the center of the radiation grating 5 and the rotation center of the rotating object to be detected.

In this embodiment, two points M1 and M2' on the radiation grating 5 that are symmetrical with respect to the rotation center are used as irradiation points, that is, measurement points, and the eccentricity between the center of the radiation grating 5 and the rotation center of the rotating body to be tested is The impact is being reduced. That is, it is difficult to make the center of the radiation grating 5 and the center of rotation completely coincide,
Eccentricity between the two is inevitable. For example, as shown in FIG. 2, between the center 0 of one radiation grating 5 and the rotation center O/,
When the number of eccentricities increases to 6 by a, the Doppler frequency shift at the measurement point M1 located at a distance r from the center of rotation is from Xr/(r0m) to r/ compared to when there is no eccentricity.
(r-a) Changes at t. On the other hand, at this time, the frequency shift at measurement point M2, which is symmetrical to position M with respect to the center of rotation, is r/(
rm) to r/(r+a), it is possible to reduce the influence of eccentricity by using two points, M and M2, as measurement points at the same time.

FIG. 3 is a schematic diagram of a portion of another embodiment of the present invention, showing the vicinity where the light beam is incident on the radiation grating 5 of FIG.

In the figure, the numbers assigned to each element indicate the same elements as shown in FIG. The position MIK of the radiation grating 5 transmits the ±m-order transmitted diffracted light of the incident light flux through the cylindrical lens 3
．． 3. 3', 3' Reflector 4□, 4□, 4□'.

2 3 2 3'4□' A position M2 that is approximately symmetrical to the center of the rotation axis 6
The same effect as that of the embodiment shown in FIG. 1 is obtained by making the light incident again.

In each of the above-described embodiments, two diffracted lights of the ±m order were used, but instead of the ±m order diffracted lights, two diffracted lights of different orders were used.
Two diffracted lights may be used.

Alternatively, the lattice pattern on the radiation grating may be made up of only transmitting portions or only reflecting portions, and only transmitted diffracted light or reflected diffracted light may be used.

Further, the light source in the present invention is not limited to the l/- laser, but any light source that emits all wavelengths of a single wavelength can be used.

As described above, according to the present invention, it is possible to create a small and highly accurate rotary encoder t-a that has a small load on the rotating object to be tested and reduces the eccentricity error between the center of the radiation grating and the center of rotation of the rotating object. can.

Furthermore, by introducing the bush-pull method, it is possible to completely eliminate DC fluctuations in the output of the light receiving element due to K, such as the undefined line width of the reference radiation grating, thereby creating a rotary encoder f-t4 that is capable of stable signal processing. I can do it.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an embodiment of the present invention, Fig. 2 is an explanatory diagram showing the eccentricity between the center of the radiation grating and the center of rotation, and Fig. 3 is a partial block diagram showing another embodiment of the present invention. It is. 1 is a laser, 2 is a collimator lens, 3□~33.
3□' to 33' are cylindrical lenses, 4□, 4□,
4□', 4□' are reflecting mirrors, 5 is a radiation grating, 6 is the rotation axis of the rotating object to be tested, 7, 7' are wave plates, 81 to 83 are beam splitters, 19 to 12 are polarizing plates, 13 -16 are light receiving elements.

Claims (1)

[Claims] (1) A radiation grating in which a plurality of grid patterns are arranged at equal angles around the periphery of a disk, a rotating object connected to the radiation grating, a first illumination means for making a luminous flux incident on the radiation grating, and the radiation grating. Two diffracted lights of a specific order among the diffracted lights from the light beam incident on the beam are placed at a position approximately symmetrical with the center of rotation of the rotating object with respect to the incident position of the light beam by the first illumination means on the radiation grating. After superimposing the two diffracted lights of a specific order that have been diffracted again by the second illumination means and the radiation grating, each of which is made to enter again through a quarter-wave plate, the superimposed luminous flux is divided into four It has a light splitting means for splitting into light beams, and four light receiving means for receiving the four light beams split by the light splitting means through four polarizing plates whose polarization directions are shifted by 45 degrees. , A rotary encoder characterized in that a rotation angle of the rotating object is determined using output signals from the four light receiving means.