JPS61212728A - Rotary encoder - Google Patents

Abstract

PURPOSE:To enable highly accurate measurement while reducing the load of a rotating object to be inspected, by introducing light to a light receiving means after overlapped by a specified order of reproduced diffraction lights among those from a radial grating. CONSTITUTION:A polarized beam splitter 3 a luminous flux from a laser 1 is divided into the reflected flux and the transmission flux almost equal in the quantity of light. These two luminous fluxes turn to circularly polarized lights after passing through respective 1/4 wavelength plates 41 and 42. The transmission luminous flux thereof is irradiated linearly at the position M1 on a radial grating 8 through a cylindrical lens 61 while the reflected flux is done so at the position M2 on the radial grating 8 through a reflecting mirror 5 and a cylindrical lens 61'. Reirradiation thereof is done at the positions M1 and M2 with reflecting mirrors 7 and 72' through cylindrical lenses 62 and 62'. In this manner, after overlapped by a specified order of diffraction light, these light are introduced to light receiving elements 12 and 12', output signals of which are shaped in the waveform to detect the direction of rotation which is integrated and displayed with a counter to determine the angle of rotation. This can reduce the load on an rotating object to be inspected thereby enabling accurate measurement.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a rotary encoder, and particularly 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 of a rotating object is used. A rotary encoder that is attached to the radiation grating, irradiates the radiation grating with a beam of light from a laser, and utilizes the diffracted light from the radiation grating to fully photoelectrically detect the rotational state of the radiation grating or rotating object, such as the rotation angle. It is.

(Prior art) Conventionally, computer equipment such as the drive of a floppy desk, office equipment such as a printer, some industrial machine tools, and even the rotational speed and rotational speed of rotating mechanisms such as the Yapsutten motor and rotating drum in a VTR are used. A photoelectric rotary encoder has been used as a means to detect the amount of variation in

The method using a photoelectric rotary encoder consists of a so-called main scale, which has light-transmitting parts and light-shielding parts arranged at equal intervals around a disc connected to a rotating shaft, and corresponding light-transmitting parts and light-shielding parts arranged at equal intervals to the main scale. The section and the light-shielding section are set at 9 so-called fixed index scales and both scales 11. Hand I
It adopts a so-called index scale structure in which the light receiving means and the light receiving means are arranged opposite to each other. In this method, as the main scale rotates, a signal synchronized with the interval between the light-transmitting part and the light-blocking part of both scales is obtained, and the full frequency of this signal is analyzed to detect fluctuations in the rotational speed of the rotating shaft. Therefore, the finer the scale interval between the light-transmitting part and the light-blocking part of both schools, the higher the detection accuracy can be. 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 diffracted light, resulting in a decrease in detection accuracy. For this reason, if the total number of gratings in the light-transmitting and light-blocking parts of the main scale is fixed and the distance between the light-transmitting and light-blocking parts is increased to the extent that it is not affected by diffracted light, the diameter of the main scale disc will increase. This increases the size and thickness of the device, resulting in an increase in the size of the entire device, which has the disadvantage of increasing the load on the rotating object to be tested.

(Objective of the present invention) The present invention reduces the load on the rotating object to be tested, and the installation of a radiation grating for detecting rotational speed formation on the rotating object to be tested is a compact and highly accurate rotary encoder that reduces the influence of eccentricity. For the purpose of providing.

(Main feature of the present invention) A light beam from a coherent light source is divided into i-polymerized beams by means of a beam splitting means. The diffracted light of a specific order among the diffracted lights from the radial grating is made to enter approximately the same position of the radial grating, and the re-diffracted light from the radial grating is After the diffracted lights of a specific order are superimposed, the light is guided through a light receiving means, and the rotational state of the rotating object is determined using an output signal from the light receiving means.

Other features of the invention are described in the examples.

(Example) In the figure, 1 is an interferometric light source such as a laser, and 2
is a collimator lens, and 3 is a polarizing beam splitter, whose polarization axis is 4 for linearly polarized light from laser l.
It is arranged so that it is close to each other. 4□, 4□, 43
are pure wavelength plates, and are arranged so that their respective polarization axes are at the 4th angle with respect to the linearly polarized light beams reflected and transmitted by the polarizing beam splitter 3. That is, the magnetic wave plate 4□ is arranged so that its polarization axis is at the 4th angle with respect to the linear polarization direction of the reflected light beam from the optical beam splitter 3, and the 1/Iv long plate 4□ is arranged as a polarizing beam splitter. The polarization axis is 4 for the linear polarization direction of the transmitted light beam of 3.
5'. In addition, the A wavelength plate 43
The polarization axis is 4 with respect to either the polarization direction of the transmitted or reflected light beam of the polarization beam splitter 3.
They are arranged at 5 degrees. 5 is a reflecting mirror.

6□, 62.6□', and 6□' are cylindrical lenses, and 7 and 7' are reflecting mirrors. 8 is a radiation grating in which, for example, a grid pattern of transparent parts and reflective parts is provided at equal angles on a disk; 9
is the rotation axis of the rotating object to be tested (not shown). IO is a beam splitter 111, and 11' is a polarizing plate, which are arranged so that the polarization directions are at 45 degrees to each other. 12, 1
2' is a light receiving element.

The light beam emitted from the laser 1 is turned into a substantially parallel light beam by the collimator lens 2, and is then sent to the polarizing beam splitter.
3. The polarizing beam splitter 3 is disposed so that its direction is at the fourth angle with respect to the linearly polarized direction of the laser 1, and splits the light beam from the laser 1 into a reflected light beam and a transmitted light beam of substantially equal amounts. The two divided beams become circularly polarized light after passing through the A wavelength plates 4□ and 4□, respectively. Of these, the transmitted light flux is the cylindrical lens 6□
A linear beam is irradiated onto the position M0 on the radiation grating 8 through the beam. On the other hand, the reflected light flux is linearly irradiated onto position M2 on the radiation grating 8 via the reflecting mirror 5 and the cylindrical lens 6□'. Here, silicate/trical lens 61
6□' are arranged as necessary so as to linearly irradiate the light beam in a direction perpendicular to the radiation direction of the radiation grating 8. By performing linear irradiation in this manner, it is possible to reduce the pitch error in the grid pattern between the transparent portion and the reflective portion corresponding to the irradiated portion of the luminous flux on the radiation grating 8. Furthermore, the irradiation positions M0 and M2 on the radiation grating 8 are set to have a positional relationship that is approximately symmetrical with respect to the rotation center of a rotating object to be detected (not shown).

The light beam incident on the radiation grating 8 is reflected and diffracted by the lattice pattern of the radiation grating 8. Now, if the pitch of the lattice pattern at the irradiation position of the light beam is 'tP, then the m-th order reflected diffraction light L
, L' diffraction angle - is expressed by the following equation (1).

Song □. -0λ/, ・・・・Song・
(1) Here, λ is the wavelength of the luminous flux.

Now, the radiation grating 8 is rotating with an angular velocity ω.
From the rotation center of the radiation grating, the irradiation position M, ,
If the distance to M2 is tr, the circumferential speed at the irradiation position M 9M2 will be MAR rat.

Here, the incident light flux to M□9M2 is expressed as 1 in wave number vector expression, the reflected diffracted light and L' are expressed as km and kk in wave number vector expression, and the position M, ,
The circumferential velocity of the radiation grating 80 at M2 is expressed as V in vector representation, and the relationship is shown in FIG. 2. The frequencies of the reflected diffracted light and L' undergo a so-called Doppler shift by amounts Δf and Δf' expressed by the following equations.

Here, . represents the inner product of vectors.

Then, through the cylindrical lenses 62 and 6, the reflecting mirrors 7 and 7' re-irradiate the area @M2t-. Then, it is diffracted again at position M 9M2, and the m-th reflected diffracted light beam returns to the original optical path, but upon re-diffraction, it returns to (
2) undergoes a Doppler shift of the amount expressed by Eq. Therefore, the light beam that is re-diffracted at the position M□ and returns to the original optical path is
After undergoing a Doppler shift with a frequency of 2Δf, the position M2
The light beam that is re-diffracted at , and returns to the original optical path undergoes a Doppler shift of frequency -2Δf.

The light beam that is re-diffracted at this point and returns to its original optical path is
When the light passes through the magnetic wave plate 4□ again, it is reflected by the polarization beam splitter 3 as a linearly polarized light whose orientation has been rotated by a number of degrees from that at the time of incidence.

In addition, when the light beam that is re-diffracted at position M2 and returns to the original optical path passes through the magnetic wave plate 4□ again, it becomes linearly polarized light that has been rotated by a number of degrees from the time of incidence, and is transmitted through the polarizing beam splitter -3ft. . The light beams re-diffracted at the position M□9M2 overlap, pass through the magnetic wave plate 43, and are split into two light beams by the beam splitter 10, and then the polarizers ti,
The light passes through u' and enters the light receiving elements 12 and 12'. In this way, when receiving the Doppler shift of frequency 2Δf and frequency -2Δf, the light receiving element 12 suffers from the overlapping force of the two light fluxes.

The frequency of the output signal of 12' is 2Δ/−(−2Δ/)−
4Δf. In other words, the frequency F of the output signal of the light receiving elements 12 and 12' is F-4Δf-4rω81-/λ
From the diffraction condition equation (1), F −4mrω
/p. If the total number of grid patterns of the radiation grating 8 is N1 and the equal angular pitch is Δψ, then p−rΔψ, Δψ−2π/
From N, F −2mNω/t =−−(3
). Now, the rotation angle to of the radiation grating 80 between the wave number ksΔt of the output signal of the light receiving element during the time Δt
Then, n-FΔt, θ-ωΔt, n-2mNθ
/π ...... (4), and by calculating the wave number of the output signal waveform of the light receiving element, the rotation angle of the radiation grating 8 can be calculated as (4).
) can be obtained using the formula.

By the way, when detecting the rotation angle, it is more preferable if the rotation direction can be detected. Therefore, in this embodiment, as is well known in conventional photoelectric rotary encoders, all of the plurality of light receiving elements are prepared and arranged so that the phases of their signals are shifted by 90 degrees, and the degree of rotation due to rotation is A method is used to extract a signal indicating the rotation direction from the phase difference signal.

In this embodiment, the 9σ phase shift between the output signals of the light receiving elements 12 and 12' is determined by the polarization beam splitter and the A
It is produced by combining a wavelength plate and a polarizing plate. That is, the light beams that are re-diffracted at the position M□9M2 and return to the original optical path are reflected and transmitted by the polarizing beam splitter 3, overlap each other, and become linearly polarized light by passing through the wavelength plate 43t. Polarization direction/radiation grating 80
Changes with rotation. And a light receiving element 12.

By shifting the polarization directions of the polarizing plates 11 and 11' provided on the front surface of the light receiving elements 12 and 12' from each other by iC4S'',
A phase difference of 90'' is provided between the output signals of 12'.

As shown in FIG. 1, for example, a light receiving element 12.

After shaping the output signal of 12' and detecting the rotation direction, the rotation angle t is calculated by integrating the output signal with color/tar.

In this embodiment, if the tachometer is used to simply measure the rotational speed, 3 in FIG. 1 may be a simple half mirror, and pure wave plates 4□, 42.43, polarizing plates 11 and 11', and a beam splitter may be used. -10, and the light receiving element 12 is unnecessary.

Figure 3 shows the radiation grating 8 of Figure 1 and the radiation grating 8 of the two beams.
FIG. 3 is an explanatory diagram of the upper irradiation positions M, , M2 and the rotation center of the rotating object to be tested.

In this embodiment, two points M1. By using M2 as the measurement point, the influence of eccentricity between the center of the radiation grating 8 and the rotation center of the rotating body to be tested is reduced. That is, it is mechanically difficult to completely align the center of the radiation grating 8 with the center of rotation, and eccentricity between the two is unavoidable.

For example, as shown in FIG. 3, when there is an amount of eccentricity a between the center 0 of the radiation grating 8 and the rotation center 0',
The Doppler frequency shift at the measurement point M□ located at a distance r from the rotation center is r
/(r+a), it changes by r/(ra)t.

On the other hand, at this time, the frequency shift at the measurement point M2, which is symmetrical to the position M1 with respect to the center of rotation, changes from r/ra to r/ra, contrary to the change at the position M0.
Since it changes up to r + m, the influence of eccentricity is reduced by measuring two points, M and M2, at the same time.

FIG. 4 is a schematic diagram of a portion of another embodiment of the invention, showing the vicinity of where the light beam is incident on the radiation grating 8 of FIG. In the figure, the number 9 attached to each element indicates the same element as shown in FIG. Position M of radiation grating 8
The transmitted diffracted light of order ±m of the luminous flux incident on M2 is made to enter the radiation grating 8 again through the cylindrical lens 6□ 66 and the reflecting mirrors 7 and 7'', and is returned to the original optical path, resulting in the result shown in Fig. 1. The same effect as the example shown is obtained.

FIG. 5 is a schematic diagram similar to FIG. 4 of yet another embodiment of the invention.

In FIG. 5, 13 and 13' are corner cube reflecting mirrors, respectively. Positions M and M2 of the radiation grating 8 The +/-m-order reflection of the light beam incident on the radiation grating 8 (or it may be transmitted as shown in Fig. 4) is applied to the diffracted light by a single IJ7 doric lens 6.
The light is returned to the original optical path by a corner cube reflector after 2.6 bits, and the same effect as in the embodiment shown in FIG. 1 is obtained. When the center of the radiation grating 8 and the center of rotation of the rotating object to be tested are eccentric, the distance between the transparent part and the reflective part of the radiation grating 8 changes depending on the location, so the diffracted light and the diffraction angle of L'It's going to change. In the embodiment shown in FIG. 1, a semiconductor laser is used as the light source 1 due to its small size.
Most desirable in terms of low price and high output.

However, it is known that the oscillation wavelength of a semiconductor laser changes depending on changes in the surrounding temperature. In the embodiment of FIG. 1, as the wavelength of the light source 10 changes, the diffracted light and the diffraction angle of L' change. At this time, if plane mirrors such as 7 and 7' in FIG. 1 are used as reflecting mirrors for the diffracted light and L', the reflecting mirrors will be in a so-called tilted state, and interference fringes will appear in front of the light receiving elements 12 and 12'. occurs in large numbers,
The S/N ratio of the output signals of the light receiving elements 12 and 12' may decrease. Therefore, as shown in FIG. 5, by using corner cup reflectors 13 and 13' as reflectors,
Even if the diffracted light diffracted by the radiation grating 8 and the diffraction angle of L' change for the above reasons, the light beams reflected by the corner cube reflections *13 and 13' can be returned to their original optical paths. This prevents the occurrence of a large number of interference fringes on the front surface of the light receiving elements 12, 12', and improves the S/N ratio of the output signals of the light receiving elements 12, 12'.

In each of the nine embodiments described above, two m-order diffracted lights are used, but ±m-order diffracted lights or two diffracted lights of different orders may be used. In this embodiment, the eccentricity error between the center of the radiation grating and the center of rotation of the rotating object to be tested can be ignored, and if used as a tachometer, the radiation grating will be irradiated at the t-1 location and one light receiving element will be provided. (Effect of the present invention) According to the present invention, a small and highly accurate rotary encoder that does not reduce the eccentricity error t between the center of the radiation grating with a small load on the rotating object to be tested and the center of rotation of the rotating object. can be achieved.

For example, the index scale type photoelectric rotary encoder that has been used in the past, the above-mentioned (4)
The relationship between the wave number n of the output signal from the light-receiving element, the total number N of main scales, and the rotation angle θ, which corresponds to the formula, is n - Nθ/2K...
...(5), so the rotation angle Δθ per wave number is
is Δθ−2π/N (radian)...
......(6). On the other hand, in the embodiment of the present invention, from equation (4), Δθ−π/2mN (radian)...
......(7).

Therefore, according to this embodiment, even if a scale with the same number of divisions is used, the rotation angle can be detected at f1 degrees, which is 4m times as large as the conventional fil.

In addition, in conventional photoelectric rotary encoders, the interval between the light-transmitting part and the light-blocking part is limited to about 10 μm, considering the influence of original diffraction. In order to obtain seconds, in the conventional example, the number of divisions of the main scale is N-360X60X 60/30-
Only 43,200 is required. Therefore, if the distance between the light-transmitting part and the light-blocking part at the outermost circumference of the main scale is t-10 μm, the diameter of the main scale is α01×43,2
00/π-137, 5th key is required.

However, according to the embodiment of the present invention, in order to obtain the same rotation angle detection of 81 degrees as in the conventional example, the number of divisions of the radiation grating is 1.
/4m is sufficient. In the case of m-1 using ±1st order diffracted light,
The number of grating divisions of the radiation grating 8 to obtain a rotation angle detection accuracy t of 30 seconds may be 43200/4-10,800. In the embodiment of the present invention, if laser diffraction light is used, the distance between the transparent part and the reflective part can be narrow, so for example, if the gold is 4 μm, the diameter of the radiation grating is 0.
(104m x 10,800/π-13.7511
1I11 would be fine. In other words, according to the embodiment of the present invention, the shape that can obtain rotational angle detection accuracy equivalent to that of a conventional index scale type photoelectric rotary encoder may be smaller than the size of a tow.

Therefore, the load on the rotating object to be tested is also lower than that of the conventional example.
(much smaller), allowing for more accurate measurements.

[BRIEF DESCRIPTION OF THE DRAWINGS] Fig. 1 is a schematic diagram of an embodiment of the present invention, Fig. 2 is an explanatory diagram of vector representation of the incident light flux and reflected diffracted light to the radiation grating according to the present invention, and Fig. 3 is a schematic diagram of an embodiment of the present invention. FIGS. 4 and 5 are explanatory diagrams illustrating eccentricity between the center of the radiation grating and the center of rotation of the present invention, and FIGS. 4 and 5 are explanatory diagrams of a part of other embodiments of the present invention, respectively. 1 in the figure is a light source,
2 is a collimator lens, 3 is a polarizing beam splitter
14□, 4□, 43 are barrel wave plates, 5, 7゜7' are reflectors, 6□, 6□, 6shi are cylindrical lenses, 8 is a radiation grating, 9 is the rotation axis of the rotating typeface to be tested, 10 Beam splitters 111 and 11' are polarizing plates, 12 and 12' are light receiving elements, and 13 and 13' are corner cube reflecting mirrors.

Claims (1)

[Claims] (1) After splitting the light flux from a coherent light source by a light flux splitting means, the split light fluxes are made to respectively enter positions of a radial grating arranged on a rotating object that are approximately point symmetrical to the center of rotation of the rotating object, and Among the diffracted lights from the grating, the diffracted light of a specific order is made to enter the radial grating at substantially the same position again, and after the diffracted lights of the specific order among the re-diffracted lights from the radial grating are superimposed, the light is guided to the light receiving means. , A rotary encoder characterized in that the rotational state of the rotating object is determined using an output signal from the light receiving means.