JPH0739931B2 - Grating interference displacement detector - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a grating interference type displacement detecting device. Specifically, a grating interference type displacement in which a light beam from a light source is split into two waves and is made incident on the same diffraction point on the scale diffraction grating, and a mixed wave of a plurality of light beams generated at the diffraction point is detected as an electric signal. The present invention relates to a detection device, and more particularly, to a device that prevents light returning to a light source.

[0002]

BACKGROUND ART As one of the ones aiming at higher resolution of a conventional photoelectric encoder, a scale having a fine pitch (usually about 1 μm) is formed on a scale by using a holographic technique, and the scale is used as a diffraction grating. There is known a grating interference type displacement detection device which utilizes the above to detect relative displacement with high accuracy. This is a method in which a light beam from a light source is split into two waves, made incident on one or two diffraction points on the diffraction grating of the scale, and a mixed wave of a plurality of light beams generated at the diffraction points is detected as an electric signal. Then, with the one using a reflection type diffraction grating,
It can be classified into one using a transmission type diffraction grating.

As the former grating interference type displacement detecting device using the reflection type diffraction grating, as shown in FIG. 4, a reflection type diffraction grating 2A is provided so as to be displaceable in the left and right directions in the figure and along the displacement direction. The reflective scale 1A, the laser light source 11, the half mirror 24 that splits the laser beam emitted from the laser light source 11 into two waves A and B, and the branched light fluxes A and B are reflected to diffract the scale 1A. A pair of mirrors 23A and 23B which are incident on the same diffraction point P on the grating 2A from symmetrical directions respectively, and a mirror 32 which reflects the first-order diffracted lights A1 and B1 emitted right above at the diffraction point P right below.
And the reflected light from the scale 1A and the mirrors 23A and 23B.
And a detector 41 for converting the mixed wave mixed through the half mirror 24 into an electric signal. Here, the half mirror 24 and the pair of mirrors 23
A luminous flux splitting means 21 is constituted by A and 23B, and a luminous flux mixing means 31 is constituted by the half mirror 24, a pair of mirrors 23A and 23B, and a mirror 32.

Therefore, the laser beam from the laser light source 11 is divided into two by the half mirror 24. After each of the branched light fluxes A and B is reflected by each of the mirrors 23A and 23B,
The light is incident on the same diffraction point P on the diffraction grating 2A of the scale 1A from symmetrical directions. Then, the first-order diffracted lights A1 and B1 of the respective branched light beams A and B are generated at the diffraction point P. The first-order diffracted lights A1 and B1 are sequentially reflected by the mirror 32, the scale 1A, and the pair of mirrors 23A and 23B, then mixed by the half mirror 24, and guided to the detector 41. In the detector 41, the polarization directions of the mixed waves mixed by the half mirror 24 are matched by the polarizing plates to cause interference, and then converted into electric signals by the light receiving element. As a result, the detector 4
From 1, when the scale 1A is displaced by one pitch of the diffraction grating 2A, a complete sine wave signal φA for two cycles is obtained.

As the latter grating interference type displacement detecting device using the transmission type diffraction grating, as shown in FIG. 5, a transmission type diffraction grating 2B is provided so as to be displaceable in the left and right direction in the figure and along the displacement direction. The transmission type scale 1B has, a laser light source 11, a polarization beam splitter 22 that splits a laser beam emitted from the laser light source 11 into two waves A and B according to the deflection direction thereof, and reflects each branched light flux A and B. And a pair of mirrors 23A and 23B which are incident on the same diffraction point P on the diffraction grating 2B of the scale 1B from symmetrical directions respectively.
, A mirror 32 for directly reflecting the first-order diffracted light A1, B1 generated at the diffraction point P, a beam splitter 34 for mixing the reflected light, and detectors 41A, 41B for converting the mixed wave into an electric signal. It consists of and. here,
The polarization beam splitter 22 and the pair of mirrors 23
A and 23B constitute a light beam splitting means 21, and the mirror 32 and the beam splitter 34 constitute a light beam mixing means 31, respectively.

Therefore, the laser beam from the laser light source 11 is divided into two beams according to the polarization direction of the polarization beam splitter 22.
Be divided. The respective branched light fluxes A and B are transmitted to the respective mirrors 23A and 23
After being reflected by B, they are respectively incident on the same diffraction point P on the diffraction grating 2B of the scale 1B from symmetrical directions. Then, at the diffraction point P, the first-order diffracted light A1, of each branched light flux A, B
B1 is generated. The first-order diffracted lights A1 and B1 are reflected by the mirror 3
It is reflected right above by 2 and then mixed by the beam splitter 34 and then guided to the detectors 41A and 41B. In the one detector 41A, the polarization directions of one of the mixed waves mixed in the beam splitter 34 are matched by the polarizing plates to cause interference, and then converted into an electric signal by the light receiving element. In the other detector 41B, the beam splitter 3
The other mixed wave mixed in 4 is delayed in phase by 90 degrees with respect to the mixed wave incident on the one detector 41A by the quarter wavelength plate, and then the polarization direction of the mixed wave is matched by the polarizing plate. After making them interfere with each other, they are converted into electric signals by the light receiving element. Thereby, each detector 41A, 41B
From the above, when the scale 1B is displaced by one pitch of the diffraction grating 2B, complete sine wave signals φA and φB for two periods having different 90 ° phase differences are obtained.

[0007]

However, in any of the above-mentioned grating interference type displacement detecting devices, the branched light beams A and B are obliquely incident on the scales 1A and 1B and are perpendicular to the scales 1A and 1B. Since it is an optical system that reflects and diffracts light in the direction, there is return light to the laser light source 11. In order to remove this, a polarizing element, a wave plate, etc. are required, and even if these are provided, it is difficult to completely remove the return light, so the output from the laser light source becomes unstable. There is a drawback that.

Further, since the light beams A and B are obliquely incident on the scales 1A and 1B and the first-order diffracted lights A1 and B1 are emitted in the right angle direction, the optical elements are arranged in these systems. Be constrained to. In particular, the latter transmission type diffraction grating 2
In the case of B, the laser light source 11, the light flux splitting means 21, the light flux mixing means 31, and the detector 41 are sandwiched across the scale 1B.
Since the mirror 32 must be arranged on the side opposite to the optical system such as A and 41B, there is a problem that it is difficult to incorporate it into the device.

The object of the present invention is to solve the above-mentioned drawbacks of the prior art, to completely eliminate the return light to the light source, and to provide an optical arrangement different from the conventional one, and to provide the device. It is to provide a grating interference type displacement detection device that can be easily incorporated.

[0010]

Therefore, the grating interference type displacement detecting apparatus of the present invention is configured such that a scale having a transmission type diffraction grating, a light source, and a light beam from this light source are branched into two waves, and each of the branched light beams. Light beam splitting means for making the light incident on the same diffraction point on the diffraction grating of the scale, a light beam mixing means for mixing a plurality of light beams generated at the diffraction points on the diffraction grating, and a mixture mixed by the light beam mixing means. In a grating interference type displacement detection device provided with a detector for converting a wave into an electric signal, the light source, the light beam splitting means, the light beam mixing means and the detector are respectively arranged on one side of the scale, and diffraction of the scale is performed. It is characterized in that a light reflecting surface for reflecting the light flux generated at the diffraction point is formed on the surface opposite to the incident surface of the branched light flux with respect to the grating.

[0011]

The luminous flux from the light source is first divided into two by the branching means.
After being split into waves, it is incident on the same point on the diffraction grating of the transmissive scale. Then, first-order diffracted light whose phases are shifted in opposite directions at the diffraction point is generated. At this time,
The optical paths of the 1st-order diffracted light generated at the diffraction point and the optical path of the transmitted light are set to be different from each other, and the 1st-order diffracted light is mixed by the light flux mixing means and then is incident on the detector. If the light is reflected by the light reflection surface of the scale at an angle different from that of the first-order diffracted light and at an angle at which the light is not incident on the light source, the return light to the light source can be removed.

Further, 1 generated at the same point on the diffraction grating
The second-order diffracted light is phase-shifted in the opposite directions, and then reflected in the incident direction of each branched light flux on the light reflecting surface of the scale, that is, the incident light flux and the reflected light flux are in the same direction. An optical arrangement different from that of the grating interferometric displacement detection device is possible. Besides, on one side of the scale, the light source,
Since all the optical systems such as the light beam splitting means, the light beam mixing means, and the detector are arranged, they can be easily incorporated into the apparatus.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the grating interference type displacement detector according to the present invention will be described below in detail with reference to the accompanying drawings. In the following description, the same components as those in FIGS. 4 and 5 described above will be designated by the same reference numerals, and the description thereof will be omitted or simplified.

FIG. 1 shows a grating interference type displacement detector of this embodiment. In the same grating interference type displacement detection device, the laser light source 11, the light beam splitting means 21, the light beam mixing means 31, and the detectors 41A and 41B are respectively arranged on one side of the transmission type scale 1B, that is, on the diffraction grating 2B side. , The diffraction point P on the side opposite to the incident surface of the branched light fluxes A and B with respect to the diffraction grating 2B of the transmissive scale 1B.
A light reflecting surface 4 that reflects the first-order diffracted lights A1 and B1 generated in 1. is formed.

Here, the light beam splitting means 21 and the light beam mixing means 31 are formed by an integral prism 51. At the center position inside the prism 51, the laser beam from the laser light source 11 is moved according to its deflection direction.
A polarization beam splitter 22 constituting a light beam splitting means 21 for splitting into the waves A and B and a beam splitter 34 constituting a light flux mixing means 31 are provided respectively.
Further, on both side surfaces, the branched light beams A and B branched by the polarization beam splitter 22 are made incident on the same diffraction point P on the diffraction grating 2B of the scale 1B, and the light beams are generated and reflected at the diffraction point P. Mirrors 23A, 23 for reflecting the light beam reflected on the surface 4 to the beam splitter 34
B is formed.

The light reflecting surface 4 is formed between the transmission type diffraction grating 2B and the scale substrate 3B-1 as shown in FIG. 2 (A). In this case, the material of the scale substrate 3B-1 is not limited to a translucent material such as glass, but may be a metal or the like. Alternatively, the light reflecting surface 4 is formed on the scale substrate 3B-2 as shown in FIG.
Is formed on the one surface side opposite to the transmissive scale 2B. In this case, the material of the scale substrate 3B-2 needs to be a translucent material such as glass.

Due to such a constitution, the laser light source 1
The laser beam emitted from No. 1 is split into two waves A and B by the polarization beam splitter 22. The branched light fluxes A and B are reflected by the mirrors 23A and 23B, respectively, and then are incident on the same diffraction point P on the diffraction grating 2B of the scale 1B. Then, the first-order diffracted lights A1 and B1 of the respective branched light beams A and B are generated at the diffraction point P. Each of the first-order diffracted lights A1 and B1 is reflected by the light reflecting surface 4 and subsequently by the mirrors 23A and 23B, and then the beam splitter 34.
Mixed in.

That is, the reflected light of one first-order diffracted light A1 and the transmitted light of the other first-order diffracted light B1 are mixed, and the transmitted light of one first-order diffracted light A1 and the reflected light of the other first-order diffracted light B1 are mixed. And are mixed. After that, the one mixed wave is guided to the one detector 41A, where it is converted into an electric signal and taken out as a sine wave signal φA. Further, the other mixed wave is guided to the other detector 41B, where the phase thereof is delayed by 90 degrees with respect to the one mixed wave, and then converted into an electric signal and taken out as a sine wave signal φB.

Therefore, according to the present embodiment, the laser beam is split into two waves and then made incident on the same diffraction point P on the diffraction grating 2B of the scale 1B. Then, first-order diffracted lights A1 and B1 whose phases are shifted in opposite directions at the diffraction point P are generated. At this time, the optical paths of the first-order diffracted lights A1 and B1 generated at the diffraction point P and the optical path of the transmitted light are set to be different from each other. Then, the first-order diffracted lights A1 and B1 are converted into the scale 1B.
After being reflected by the light-reflecting surface 4, the light flux is mixed by the light flux mixing means 21 and subsequently incident on the detectors 41A and 41B. On the other hand, the transmitted light is reflected by the light reflecting surface 4 of the scale 1B at an angle different from that of the first-order diffracted lights A1, B1, and then reflected by the mirrors 23A, 23B in different directions. The return light can be removed.

Further, the first-order diffracted lights A1 and B1 generated at the diffraction point P on the diffraction grating 2B are phase-shifted in opposite directions, and then, on the light reflecting surface 4 of the scale 1B. Since the light is reflected in the incident direction, that is, the incident light beam and the reflected light beam are in the same direction, an optical arrangement different from that of the conventional reflection type grating interference type displacement detection device can be achieved, and the degree of freedom in design can be expanded. You can Moreover, scale 1
Since all the optical systems such as the light source 11, the light beam splitting unit 21, the light beam mixing unit 31, and the detectors 41A and 41B are arranged on one side of B, they can be easily incorporated into the apparatus.

The beam splitting means 21 and the beam mixing means 3 are also provided.
1, the polarization beam splitter 22, the beam splitter 34, and the mirrors 23A and 23.
Since B and the like are configured by the integral prism 51, 1
The main detection system can be configured by two prisms. This leads to a reduction in the number of parts, which can also contribute to a reduction in the number of assembling steps.

Although the present invention has been described with reference to the preferred embodiment, the present invention is not limited to this embodiment, and various improvements and design changes can be made without departing from the gist of the present invention. Of course it is possible.

For example, in the above embodiment, the luminous flux splitting means 21 and the luminous flux mixing means 31 are constituted by the integral prism 51, but they may be constituted separately as shown in FIG. In this case, the light beam splitting means 21
Is a scale 25 that includes a mirror 25 having right-angled reflecting surfaces 25A and 25B that split the laser beam into two waves A and B in the horizontal direction, and each of the light beams A and B split by the mirror 25.
A pair of mirrors 26A and 26B which are incident on the same diffraction point P on the transmission diffraction grating 2B of B, and the respective mirrors 26A and 26A,
Polarizing plates 27A and 2A inserted in the optical path of the reflected light of 26B.
7B and. Also, the light flux mixing means 3
Reference numeral 1 denotes a pair of mirrors 35 for reflecting the first-order diffracted lights A1, B1 generated at the diffraction point P and reflected by the light reflecting surface 4.
A and 35B and a beam splitter 34 that mixes the light fluxes reflected by the mirrors 35A and 35B.

With such a structure, in addition to the effects described in the above embodiment, the right angle reflecting surfaces 25A, 25 of the mirror 25 are provided.
Since the laser beam itself from the laser light source 11 is split into two waves A and B by B, different optical arrangements can be made without using a semi-transmissive optical element (for example, a half mirror or a beam splitter). . Moreover, by selecting the angles of the reflecting surfaces 25A and 25B, there is an advantage that the distribution angle for branching into two waves can be freely selected. As a result, the detection system can be downsized as compared with the conventional one.

In the above embodiment, the laser light source 11,
Light flux splitting means 21, light flux mixing means 31, and detector 41
Although the scale 1B is provided so as to be displaceable with respect to the optical system such as A and 41B, the optical system may be displaced with respect to the scale 1B, or both may be displaced. The point is that it can be applied to all of those in which the scale 1B and the optical system are relatively displaced.

[0026]

As described above, according to the grating interference type displacement detecting device of the present invention, all the optical systems are arranged on one side of the scale, and the surface opposite to the incident surface of the branched light flux on the diffraction grating of the scale is arranged. Since a light reflecting surface that reflects the light flux generated at the diffraction point is formed on the side, the return light to the light source can be removed and the incident light flux and the reflected light flux can be in the same direction. It is possible to have an optical arrangement different from that of the displacement detection device, and moreover, since all optical systems such as the light source, the light beam splitting means, the light flux mixing means and the detector are arranged on one side of the scale, it can be incorporated into the device. It's easy.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of a grating interference type displacement detection device of the present invention.

FIG. 2 is a diagram showing a configuration of a scale 1B of FIG.

FIG. 3 is a view showing another embodiment of the grating interference type displacement detection device of the present invention.

FIG. 4 is a diagram showing a conventional grating interference type displacement detection device (using a reflection type diffraction grating).

FIG. 5 is a diagram showing a conventional grating interference type displacement detection device (using a transmission type diffraction grating).

[Explanation of symbols]

 1B Transmission type scale 2B Transmission type diffraction grating 4 Light reflecting surface 11 Laser light source (light source) 21 Light flux splitting means 31 Light flux mixing means 41A, 41B Detector

Claims (1)

[Claims] 1. A scale having a transmissive diffraction grating, a light source, and a light beam splitting means for splitting a light beam from the light source into two waves and making each of the split light beams enter the same diffraction point on the diffraction grating of the scale. Displacement of grating interference type including: a light flux mixing means for mixing a plurality of light fluxes generated at the diffraction points on the diffraction grating; and a detector for converting the mixed wave mixed by the light flux mixing means into an electric signal. In the detection device, the light source, the light beam splitting means, the light flux mixing means and the detector are respectively arranged on one side of the scale, and the diffraction point is on the side opposite to the incident surface of the branched light flux with respect to the diffraction grating of the scale. A grating interference type displacement detection device characterized in that a light reflection surface for reflecting the light flux generated in (3) is formed.