JPH0285717A - Encoder - Google Patents

Abstract

PURPOSE:To effectively incorporate an absolute type detection mechanism in a high-resolution increment type detection mechanism without lowering the accuracy of incremental signals by specifying the shape of slits on a diffraction grating. CONSTITUTION:Diffracted rays of light of a specific number of order of the transmissive diffracted rays of light which are made incident on and diffracted at a position M1 of a radiated grating are reflected 42 and transmitted to a beam splitter through a 1/4 wave plate 101. The transmitted luminous flux of the two luminous fluxes divided by a beam splitter 31 is reflected 41 and made incident on the position M2 which is center-symmetrical to the position M1 with respect to a rotary shaft 6. Then the diffracted rays of light of a specific number of order of the transmissive diffracted rays of light which are made incident on and diffracted at the position M2 are led to the beam splitter through a 1/4 wave plate 102. The wave plates 101 and 102 are set in directions which are deflected from the linearly polarized rays of light of a laser 1 by + or -45 deg.. Moreover, diffracted rays of light 71 and 72 are divided into two luminous fluxes after they are superimposed with each other and made incident on light receiving means 122 and 122 after a phase difference of 90 deg. is produced between the divided luminous fluxes through polarizing plates 111 and 112 provided with polarizing azimuths inclined by 45 deg.. At the light receiving means 122 and 122, intensities of interference fringes are detected.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to an encoder, and in particular to an encoder, in which a diffraction grating having a plurality of slits in a transmitting section or a reflecting section is attached to an object to be measured, and a coherent The present invention relates to an encoder that allows a beam of light to enter and simultaneously obtains an absolute signal and an incremental signal regarding the object to be inspected using diffracted light generated from the diffraction grating.

<Prior Art> Encoders have been widely used in the fields of machine tools, robots, etc. as devices for measuring the speed and displacement of objects under test with high precision.

In particular, recently there has been an increasing demand for high-precision encoders that combine an absolute type that can detect the absolute position of displacement and an incremental type that has high resolution.

Conventionally, a device configured by combining, for example, an incremental encoder and a potentiometer has been used. However, this device has the drawbacks of a complicated structure and an increase in size.

Also, if high-resolution displacement detection is to be performed using an absolute encoder, the shape of the encoder itself will become larger.
Furthermore, there is a problem in that the internal configuration of the encoder becomes complicated.

(Problems to be Solved by the Invention) The present invention is achieved by appropriately setting the slit shape of a diffraction grating provided on a test object and effectively incorporating an absolute detection mechanism into a high-resolution incremental detection mechanism. The purpose of the present invention is to provide an encoder that is small and has a simple configuration, in which two functions can be easily obtained from the same detection mechanism.

(Means for solving the problem) A coherent light beam is made incident on a diffraction grating provided on the circumference with multiple slits connected to the object to be tested, and a specific number of characters of diffracted light from the diffraction grating are superimposed. When determining the displacement state of the rotating object to be detected by forming interference fringes and detecting changes in the intensity of the interference fringes, the transmittance or reflectance of the plurality of slits of the diffraction grating is changed in a sinusoidal manner. This is what we have configured.

(Example) FIG. 1 is a schematic diagram of an optical system according to an embodiment of the present invention.

In this embodiment, the light beam emitted from the laser 1 is made into a parallel light beam by the collimator lens 2, and is made incident on the beam splitter 31, where it is split into two light beams, an anti-column incident light beam and a transmitted light beam, each having approximately the same amount of light.

Among these, the reflected light beam is transmitted through slits with the same angular pitch (lattice pitch) in the radial transmitting part and the reflecting part on a disc connected to the rotating object to be tested (not shown). The light is incident on a position M on the radial diffraction grating 5.

At this time, the transmittance of the transmitting portion is set so as to vary sinusoidally on the circumference of the radiation grating 5 as shown in FIG.

Of the transmitted diffracted light that enters the position M1 on the radiation grating 5 and is diffracted, the diffracted light of a specific order, for example, the first-order diffracted light 7I, is reflected by the reflecting mirror 42 and sent to the beam splitter 3 via the 1/4 wavelength plate 101. Light is guided to □.

In addition, the transmitted light beam out of the two light beams split by the beam splitter 31 is reflected by four reflecting mirrors, and then transferred to a position M on the radiation grating 5 and a position M2 that is approximately symmetrical with respect to the rotation axis 6.
It is input to. Of the transmitted diffracted light incident on the position M2 of the radiation grating 5 and diffracted, diffracted light of a specific order, for example, the first-order diffracted light 72, is guided to the beam splitter 32 via the 1/4 wavelength plate 102.

Two (7) quarter wave plates10. ．． 10. are set at azimuths of ±45° relative to the linearly polarized light of the laser 1.

Then, the beam splitter 32 splits the two diffracted lights 71.7
A polarizing plate 111 that divides the light beams into two light beams and arranges the polarization direction of each light beam at an angle of 45 degrees.
, 112 to each light receiving means 12., as linearly polarized light with a phase difference of 90 degrees. ．． 122.

and light receiving means 12. ．． 122 detects the intensity of the interference fringes of the two beams.

This measures the rotation angle of the rotating object to be tested. and quarter wavelength plates 101, 102 and polarizing plates 1.1.
．． 112, the rotational direction of the rotating object to be tested can be detected at the same time.

In this embodiment, the diffracted lights from the positions M, , M2 that are symmetrical to the center of rotation of the radiation grating 5 are caused to interfere with each other. Angle detection errors due to eccentricity are removed.

Next, a method for detecting the rotation angle of the rotating object to be tested in this embodiment will be explained.

1st order diffracted light flux7. ．． The phase of 72 increases or decreases by 2π when the radiation grating 5 rotates by one pitch.

Therefore, the output I(θ) from the light receiving elements 121 and 122 is expressed by the following equation.

T(θ)・1 mark (6?)・-i (<6　o-Ne　).

1 ``1 piece.-1(φ・-90)1・/2・[T(θ)
÷ T (θ + π) ÷ 2 FT 100 - ■] 47 shoulders cos 2 N θ] / 2 - A + f engineering allows 1 - " e cos 2 N θ ...... - (1
) In equation (1), I(θn is 360”/2 as shown in Figure 3.
Is it a sine waveform with one period of N, or its amplitude is A'
-B'cos' changes with e. However, the radiation grating 5
The light receiving element 12I interferes with the diffracted light from the two symmetrical points M, , M2.

The DC component A of the output ■(θ) of 12□ has no angle dependence and does not change. This facilitates processing when binarizing in a subsequent signal processing circuit or when improving the angular resolution of the encoder by electrically dividing the signal, resulting in a stable output.

In this embodiment, the rotational state of the rotating object to be tested is detected using the output signals (θ), that is, the incremental signals from the light receiving elements 121 and 122.

On the other hand, the 0th order diffracted light 8 of the diffracted light from the position M1 is made incident on the light receiving element 9. An output signal T(θ) as shown in FIG. 2 is obtained from the light receiving element 9 as the radiation grating 5 rotates.

In this embodiment, the absolute position θ of the rotation angle of the radiation grating 5 is determined using the output signal T(θ), that is, the absolute signal at this time.

In this embodiment, a method of obtaining an absolute signal by changing the transmittance of the transmitting part of the radiation grating 5 in a sinusoidal manner was shown. It may be obtained from a radiation grating having a variable length, or it may be obtained from a radiation grating having a variable slit width in a transparent or non-transparent portion as shown in FIG.

In addition, the incremental signal I (θ) and the absolute signal T (θ) are processed by the subsequent processing circuit, and the interpolation of the absolute signal T (θ) is performed using the incremental signal No. 13 (θ).
By doing so, a high-resolution absolute signal can be generated.

In the embodiment shown in FIG. 1, the light transmitted through the radiation grating 5 is used. It goes without saying that the same effect can be obtained even if reflected light is used.

In FIG. 1, the 0th-order destination beam 8 is used for absolute position detection, or is this the 1st-order diffracted beam 7 for incremental use?
Diffracted light of any order may be used as long as it is a light beam other than 1,7□. For example, a first-order diffracted light beam 8' that is symmetrical to the first-order diffracted light beam 7□ in FIG. 1 may be used.

FIG. 6 shows yet another embodiment of the present invention, which is an example applied to a linear encoder. In FIG. 6, 13 is a diffraction grating connected to a moving object to be detected (not shown). Diffraction grating 13
is set so that its transmittance varies sinusoidally with respect to the amount of movement X, similar to the radiation grating 5 in FIG.

The light beam emitted from the laser 1 is split into a transmitted light beam and a reflected light beam by a beam splitter 3, and then sent to a reflecting mirror 4. .

The diffraction grating 13 is irradiated via 42. At this time, assuming the incident angle θ, θffi~s i n-' (mλ/p)
(m: integer, λ: wavelength of laser 1, p: diffraction grating 13
If the reflecting mirrors 43 and 4 degrees are set so as to have a pitch of .±.m, the diffracted light of order ±m is emitted almost perpendicularly. Then, the diffraction grating 1 is
3, a ±m-order diffracted beam is generated again, and these ±mm-order diffracted beams return to the original optical path and are reflected at tJ14.
+, 42, interfere with each other and enter the light receiving element 12 via the beam splitter 3. This results in an incremental signal. In the embodiment shown in FIG. 6, since the light that has undergone ±m-order diffraction twice is caused to interfere,
When the diffraction grating 13 moves by one grating pitch p, a 4 m period sine wave signal, that is, an incremental signal, is obtained from the light receiving element 12.

On the other hand, in FIG. 6, the 0th order diffracted light transmitted through the diffraction grating 13 enters the light receiving element 9, and an absolute signal is obtained from the output signal of the light receiving element 9, as in the embodiment shown in FIG.

(Effects of the Invention) According to the present invention, by specifying the slit shape on the diffraction grating as described above, it is possible to effectively add an absolute type detection mechanism to a high-resolution incremental type detection mechanism without reducing the accuracy of the incremental signal. It is possible to achieve an encoder with a simple configuration in which two signals, an incremental signal and an absolute signal, can be easily obtained from the same device at the same time.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram of an optical system according to an embodiment of the present invention, Fig. 2 is an explanatory diagram of the transmittance of the radiation grating shown in Fig. 1 and the output signal obtained from the absolute light receiving element, and Fig. FIG. 1 is an explanatory diagram of an output signal obtained from an incremental light receiving element, and FIGS. 4 and 5 are explanatory diagrams of another embodiment of the radiation grating according to the present invention. FIG. 6 shows an embodiment in which the present invention is applied to a linear encoder. In the figure, 1 is the laser, 2 is the collimator lens, 31.3
□ is a beam splitter 141, 4□ is a reflecting mirror, 5 is a radiation grating, 6 is a rotation axis, 7. ．． 7° is 1st order diffracted light, 8 is 0
Next diffraction light, 9, 12. . 12□ is a light receiving element; 10. ．． 102 is a quarter wavelength plate, 1
1.1.112 is a polarizing plate. Patent applicant: Canon Co., Ltd. Rabbit 1st 2nd interview 3rd drawing 4th drawing 5th

Claims (2)

[Claims] (1) A coherent light beam is made incident on a diffraction grating with multiple slits connected to the object to be measured, and the diffracted light of a specific order from the diffraction grating is superimposed to form interference fringes. 1. An encoder characterized in that the transmittance or reflectance of a plurality of slits of the diffraction grating is changed in a sinusoidal manner when determining the displacement amount of the object to be tested by detecting a change in intensity of the encoder. (2) The diffraction grating is formed along the rotation direction of the rotating object to be tested, and the coherent light beam is divided into a plurality of points of the diffraction grating that are substantially point symmetrical with respect to the rotation center of the rotating object to be tested. 2. The encoder according to claim 1, wherein the rotational state of the object to be inspected is determined using diffracted light from these positions.