JPS62163925A - Rotary encoder - Google Patents

Abstract

PURPOSE:To facilitate the miniaturization of the equipment as a whole while smaller load of a rotating object to be inspected, by providing a reflecting means in which a reflecting surface is arranged to reflect specified order of diffraction light alone near a focal plane. CONSTITUTION:A convex lens 141, a reflecting mirror 151 and a mask 161 forms an optical system as a part of reflecting means and a luminous flux projected in parallel to the concave lens 141 is focused on the reflecting mirror 151 through the mask 161. The luminous flux thus focused is reflected to return to the original light path and irradiate the position M1 on the radiation grating 6 again. The optical system of the reflecting means thus arranged allows the removal of this diffraction lights other than specified order of diffraction light L1 such as zero order of one incident into the convex lens 141. Thus, this can reduce the distance between the radiation grating 6 and the reflecting means 141, 151 and 161.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a rotary encoder, and in particular to a rotary encoder, in particular a radiant grating fully rotating object in which a plurality of lattice patterns of, for example, transparent parts and reflective parts are periodically carved on the circumference. For installation, the radiation grating is irradiated with the entire beam from a laser, for example, and the diffracted light from the radiation grating is used to photoelectrically measure the rotational state of the radiation grating or rotating object, such as the rotational speed or the amount of variation in rotational speed. This is about a rotary encoder that detects.

(Prior art) Conventionally, it has been used to measure the rotational speed and the amount of variation in rotational speed of computer equipment such as floppy desk drives, office equipment such as printers, NC machine tools, and rotating mechanisms such as VTR capsten motors and rotating drums. A photoelectric rotary encoder has been used as a means for detection.

The photoelectric rotary encoder connects to the rotating shaft and has light-transmitting parts and light-shielding parts spaced at equal intervals around the periphery of the nine-circle plate, i.e., a so-called main scale, and corresponding light-shielding parts and light-shielding parts spaced at equal intervals to the main scale. The rhAf4 index scale system has a so-called fixed index scale with a section and a so-called fixed index scale, and both scales are placed facing each other with a light emitting means and a light receiving means sandwiched therebetween. In this method, as the main scale rotates, a good signal is obtained by synchronizing the interval between the light-transmitting part and the light-blocking part of both scales, and this signal is frequency-analyzed to detect fluctuations in the rotational speed of the rotating shaft. There is. For this reason, the finer the scale interval between the light-transmitting part and the light-blocking part of both scales, the better the detection accuracy. can be increased. However, when the scale interval 1a is used, the S/N ratio of the output signal from the light receiving means decreases due to the influence of the diffracted light, and the detection area decreases, resulting in five drawbacks. For this reason, if you fix the total number of gratings in the light-transmitting part and the light-shielding part of the main scale, and try to increase the distance between the light-transmitting part and the light-shielding part to such an extent that the influence of diffracted light cannot be overcome, the diameter of the main scale disc will increase. This increases the thickness and increases the overall size of the device, which has the disadvantage of increasing the load on the rotating object being tested.

(Problems to be Solved by the Invention) An object of the present invention is to provide a rotary encoder that has a small load on a rotating object to be inspected, is easy to miniaturize the entire device, and is capable of detecting a rotational state with high precision.

(Rounding means to solve the problem) A beam from a coherent light source is made incident on a part of a disc-shaped radiation grating connected to a rotating object, and the diffracted light of a specific order from the radiation grating is totally reflected. In a rotary encoder that determines the rotational state of the rotating object by making it incident on the radiation grating again and receiving all of the re-diffracted light of a specific order from the radiation grating, It has an optical system in which a reflecting surface is arranged to reflect only the diffracted light of the number of people.

The features of this pond water invention are described in the Examples.

(Implementation row) FIG. 1 shows glRI of an optical system according to an embodiment of the present invention.

I'll go.

In the same figure, l is a coherent light source such as a laser, 2 is a collimator lens X3, and 32 is a polarizing beam splitter, so that the polarization axis is 45' for the linearly polarized light from laser l. It is located. 4□ to 45 are A wavelength plates, and 51 to 54 are each a silicon/trical lens 16, which 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. 7 is not shown. This is the rotation axis of the rotating object to be tested. 91.9□ is a reflecting mirror, 10 is a W wavelength plate, 1
1 is a beam splitter, 12 and 122 are polarizing plates, 13
．． 13□ is a light receiving element. 14□.

14 is a convex lens with condensing properties, and 15.15□ is a reflective boundary placed near the focal point of the convex lens 14.14□, and in front of it is a mask 16□ that limits the light flux.

16□ is provided.

In this implementation, the convex lens 14 and the reflecting mirror 15□SM
The r frame 16□ constitutes an optical system which is a part of the reflecting means.

The entire operation of the rotary encoder shown in FIG. 1 will be briefly explained. The luminous flux emitted from the V-zer 1 is turned into a substantially parallel luminous flux by a collimator V lens 2, and enters a polarizing beam splinter 3□, where it is transmitted and reflected in substantially equal amounts. Of these, the transmitted light beam passes through the intense wavelength plate 4□ and becomes circularly polarized light, and irradiates the entire position M1 on the radial frame 16 in a linear manner via the cylindrical lens 5□.

Here, the cylindrical lens 51 has a luminous flux total radiation grating 6
They are arranged as necessary to emit linear radiation in a direction perpendicular to the radiation direction. By irradiating in a linear manner in this way, it is possible to reduce the pitch error of the grid pattern of the transparent part and the reflective part corresponding to the irradiated part of the luminous flux on the radiation grating 6.0 Position M on the radiation grating 6 The nine specific orders of diffracted light that are linearly irradiated and diffracted are turned into a substantially parallel light beam by a cylindrical lens 5□ and enter a convex lens 14□ which is a part of the optical system. FIG. 2 shows the approximate distance between an optical system which is a part of one reflecting means in this embodiment, and a reflecting mirror 15□ is arranged substantially at the focal plane of a convex lens 14□. For this reason, the light beam incident parallel to the convex lens 14□ is condensed onto the reflecting mirror 15□ via the mask 16□. The condensed light traveling flux is reflected and returns to the original optical path to the top of the radiation grating 6! Re-irradiate Mlk. The light beam diffracted by the M-technique is 1, and the V4 wavelength plate 4
zV passes through □ and is reflected by polarizing beam splitter 3□
It is reflected by the reflecting mirror 9□ via the 4-wavelength plate 4□, and is transmitted through the polarizing beam splitter 3□ again via the A-wavelength plate 4□. Then, the polarization direction is rotated by 9σ by the A wavelength plate 10 and reflected by the polarization beam splinter 3□ S1/!
Via the wavelength plate 45, it is exposed by the beam splitter 11, and the light receiving element 13.13 is exposed through the polarizing plates 12□, 12□.
Light is received at □.

On the other hand, the beam emitted from the laser l and reflected by the polarizing beam splitter 3□ passes through the A-wave plate tot- and passes through the polarizing beam splitter 32.
It is reflected by the reflecting mirror 9□, reflected by the polarizing beam splitter 3□, and transmitted through the A wavelength plate 4S and the cylindrical lens 53 to the position tiLM2 on the group 1 grating 〇.
irradiate linearly.

Here, the positions M and M2 have a positional relationship that is substantially symmetrical by one point with respect to the rotation center of the rotating object to be tested.

Among the light beams diffracted by the position fit M2, the diffracted light L2 of a specific order becomes a substantially parallel beam by the cylindrical lens 54 in the same manner as the diffracted light L process, and enters the convex lens 14□, and passes through the light flux limiting mask 16□. The light is focused onto the reflecting mirror 15□. The condensed light flux is reflected and returns along the original optical path to re-irradiate the point M2t on the radiation grating 6. and point M
The second beam is re-diffracted at 2, returns to its original optical path, completely passes through the polarizing beam splitter 3 degrees, overlaps with the diffracted light beam L at position M, and is received by light receiving elements 13□, 13□.

When the rotating object to be tested rotates, the frequency of the diffracted light beam L at the first position M shifts by Δf-rω51n-/λ. Here, r is the distance from l to M during rotation, ω is the angular velocity, θrn is the diffraction angle of the Sm-order diffracted light L, and λ is the 10 wavelength of the laser.

Since the diffracted light L is reflected by the reflecting means and re-diffracted at the position M, the frequency is shifted by 2△f when it enters the light receiving elements 13□ and 13□. On the other hand, tM2
When the diffracted light L2 enters the light receiving elements 13□, 13□, the frequency is similarly shifted by −2Δf.

Therefore, the frequency of the output signal from one light receiving element 13.13□ is 4Δf. If is the pip t-p of the checkered pattern at the 91st position M-9M2, then from the diffraction conditions, S1nθ, -
mλ/P Therefore, the frequency of the output signal of the light receiving element is F-
4Δf −4mrω/P.

The total number of grid patterns of the radiation grid 6 is N1, and the equal angular pitch is Δ
If ψ, then -, F from P-rΔψ, Δψ-2π/N
-2mNω/π. Now, if the wave number '1ris of the output signal of the light-receiving element during the time Δt is the rotational radius θ of the radiation grating 6 during the time Δt, then from n - FΔt, θ-ωΔL, z n -2mNθ/π...・(1), the wave number n of the output signal of one light receiving element? From counting K, the rotation angle θ of the radiation grating 6 can be determined by equation 11. In the embodiment of FIG. It is possible to use a fine grating with a small diameter, and therefore, the diameter of the entire device is small, and the load on the rotating object to be tested is also small.In addition, in this example, the diffraction light L process is used. ,L2
By using the -6 lens 14.14□ and the reflector 15.15□ as a reflection means to re-irradiate the t-position M-work 9M2, it achieves the same function as the field using a corner cube reflector. .

In other words, the wavelength of the light beam incident on the radiation grating 6 has changed due to the change in the surrounding temperature.In addition, the rotation center of the rotating object to be tested and the rotation center of the radiation grating 6 do not match, and the wavelength of the light beam incident on the radiation grating 6 has changed. When the pitch of the grating structure at the light flux incident position [M 1 M2 changes as the radiation grating 6 rotates, the diffraction angle of the diffracted light beams L and L2 changes.

However, according to this embodiment, by configuring the optical system of the reflecting means as described above, the light beam incident on the convex lens 14. The original light M can be returned by being emitted from the convex lens 14.14□. Furthermore, the light flux limiting mask 16.16□ provided on the front surface of the reflecting mirror removes diffracted light other than the diffracted lights L□ and L2 of specific orders, such as the zero-order diffracted light that enters the convex lens 14.14□. I can do it. This allows the radiation grating 6 and the reflecting means 1 to
4□, 14°, 15□, 15□.

It becomes possible to shorten the distance from 16.16□.

For example, if the pitch of the grid pattern at the position M□1M2 of the radiation grating 6 is 10 μm, the wavelength of the human radiation beam is 0.83 μm.
In the case of m, when trying to re-irradiate the radiation grating 6 with the first-order diffracted light using a plano-convex microlens with an A radius of 31 as the convex lenses 14, 142, the 0th-order diffracted light (d11th-order diffracted light) Since it enters the microlens 14, 142 at an angle of 4.8° and 1f, the light flux control mask 1
If an aperture of 6.16 □ is provided with a radius of less than (focal length of microlens -6 tea) At this time, the reflection from the first radiation grating 6 d 15t , 152
A distance Fm of about 15w is sufficient. Also 1
Convex lens 141°14°, anti! Boundary 15□, 15□1 luminous flux limiting mask 16□.

Both angles of 16° can be easily manufactured, and therefore have the advantage of being lower in cost than, for example, using a corner cube reflector.

In this embodiment, instead of the reflecting mirrors 15 and 15° full plane mirrors, concave mirrors having the center of curvature at the nodes of the convex lenses 14 and 14° may be used. Furthermore, it is preferable to construct the optical system of the reflecting means by integrating a convex lens, a mask, and a reflecting mirror as shown in FIG. 3, since this simplifies the entire apparatus.

In the same figure, 18 is a condenser lens and 18° is a reflective lens. The surface 183 is a mask.

Furthermore, as shown in Fig. 4, a reflective mirror is deposited only at the center of the planar end surface of the lens shown in Fig. 3, which is a total refractive index gradient lens, such as the product name SELFOC Micro Lens (manufactured by Nippon Sheet Glass Co., Ltd.). If this is done, manufacturing will be easier and the equipment will be smaller and simpler.

In FIG. 4, 19□ is a gradient index lens, and 19° is a reflecting portion (back mirror).

The diffraction grating used in the present invention may be a so-called amplitude type diffraction grating consisting of a light blocking part and a light transmitting part, a phase type diffraction grating consisting of parts having mutually different refractive indexes, or the like. In particular, a phase grating (phase grating) can be obtained, for example, by forming a relief-type uneven pattern on the circumference of a transparent disk, and is effective because it can be mass-produced using a stamper, embossing, etc. Further, a single-reflection type phase grating can be easily formed by forming a reflection film such as vapor deposition on a concavo-convex pattern.

In this embodiment, a case has been described in which transmitted diffraction light is used, but the object of the present invention can be achieved in the same way even if reflected diffraction light is used.

(Effects of the Invention) As described above, according to the present invention, the load on the rotating object to be inspected is small, and the overall size of the apparatus can be reduced by using a reflecting means that has a reflecting section on the focal plane and a secondary optical system. High precision rotary encoder? can be achieved.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of an optical system according to one embodiment of the present invention, and is an explanatory diagram of a part of another embodiment of the invention. In the figure, 1 is a light source, 2 is a collimator lens, and 3□. 3 is a polarizing beam splitter, 4□~45 are A wavelength plates, 51~54 are cylindrical lenses, 6 is a radiation grating,
7 is the rotation axis, 9□, 9° is a reflecting mirror, 12.12° is a polarizing plate, 13□, 13° is a light receiving element, 14.14 is a convex lens, 15, 15° is a reflecting mirror, 16.16□ is a This is a light flux limiting mask.

Claims (1)

[Claims] A light beam from a coherent light source is made incident on a part of a disc-shaped radiation grating connected to a rotating object, and diffracted light of a specific order from the radiation grating is made to be incident on the radiation grating again by a reflecting means. , in a rotary encoder that determines the rotational state of the rotating object by receiving re-diffracted light of a specific order from the radiation grating, the reflecting means has a reflecting surface near the focal plane that reflects only the diffracted light of the specific order. A rotary encoder characterized by having an optical system arranged.