JP3392898B2 - Lattice interference displacement measuring device - 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 measuring device for optically measuring displacement using a scale having a diffraction grating.

[0002]

2. Description of the Related Art A grating interference type displacement measuring device is a type of photoelectric encoder which has a high resolution by using a diffraction grating as a scale. A light beam from one light source is divided into two and irradiated on the diffraction grating. The two diffracted light beams obtained from the scale by the incidence of the two light beams are condensed, and further, the two diffracted light beams are divided into halves and mixed by a beam splitter or the like.
This mixed wave is received by the light receiving element.

With such a configuration, when the scale is displaced relative to the light irradiation system and the light detection system, a detection signal that periodically changes according to the light and shade due to interference is obtained in the light detection system. The displacement amount can be measured by this detection signal period. A quarter wave plate or the like is inserted in one of the optical paths of the mixed waves of the two systems, which are divided into two by the beam splitter of the ordinary photodetection system and mixed to obtain detection signals of the two systems whose phases are shifted from each other. The moving direction of the scale can be detected by the phase difference between the detection signals of these two systems.

[0004]

In the displacement measuring device of the interference grating type, it is necessary to make two light beams having the same wavelength incident on the scale on which the diffraction grating is formed at the same incident angle. For this reason, light from a light source such as a semiconductor laser is divided into two by a beam splitter. However, in order to make the light beam divided into two parts by using the beam splitter enter the scale at the same incident angle, it is necessary to perform alignment of each optical element with extremely high accuracy. That is, it is necessary that the light source light be incident on the beam splitter in an oblique direction and the divided light beam be symmetrically incident on the scale. Therefore, the optical system becomes asymmetric and alignment of optical elements is not easy.

Further, it is desired that the light beam split into two has a constant light quantity ratio, but in the beam splitter, the split ratio of the light beam is determined by the characteristics of the semipermeable membrane, and the split ratio can be kept constant. There is a difficulty that it is difficult. A beam splitter is also commonly used to mix and interfere two light beams obtained from the scale. Therefore, this photodetection system also has the same problem as the above-mentioned light irradiation system. These problems cause deterioration of output signal characteristics of the grating interference type displacement measuring device using the diffraction grating.
That is, it is important to mix and interfere the two output diffracted light beams obtained from the scale by equal amounts in order to obtain high resolution characteristics. However, in the above-described conventional configuration, good output signal characteristics cannot be obtained. Therefore, it is difficult to obtain a sufficiently high resolution characteristic.

The present invention has been made in consideration of the above circumstances, and makes it possible to easily align the optical elements and to equalize the light amounts of the two light beams used.
It is an object of the present invention to provide a grating interference type displacement measuring device capable of obtaining high resolution characteristics.

[0007]

The first grating according to the present invention
The interferometric displacement measuring device includes a scale on which a diffraction grating is formed, a light irradiation system that irradiates the scale with two light beams, and two diffracted light beams obtained from the scale by the two light beams. And a photodetection system that mixes and receives the mixed wave, and outputs a detection signal that periodically changes according to a relative change of the scale with respect to the light irradiation system and the photodetection system. In the apparatus, the light irradiation system includes a light source arranged such that an output light beam is perpendicular to the scale, and two light sources for injecting the light beam output from the light source into the scale.
And a diffraction grating for splitting the light beam of diffracted light, two diffracted light beams obtained from the scale 1 wherein the wavelength of the light source as a diffracted light becomes perpendicular to the scale The grating constant of the diffraction grating and the scale is adjusted, and the photodetection system is
Drop two diffracted light beams from the light source onto the scale.
Light collecting means for collecting light on the perpendicular line and the two diffracted lights
It is placed perpendicular to the scale at the focal point of the beam.
The two condensed first-order diffracted lights having a semi-transmissive surface
A light beam consisting of a semi-transmissive surface that transmits and reflects respectively
A light mixing means for mixing transmitted light and reflected light by interfering them
And receive the light mixed by this light mixing means.
And a light receiving element . Of one aspect of the present invention
In an embodiment, the condensing means is
It is characterized in that it has a diffraction grating arranged in parallel with the scale for collecting two obtained diffracted light beams . In this case, the scale is a reflective diffraction grating.
The diffraction grating of the light irradiation system and the diffraction grating of the condensing means
May be formed on the same plane.

A second grating interference type displacement according to the present invention is also provided.
The measuring device consists of a scale with a diffraction grating and this scale.
A light irradiation system for irradiating the kale with two light beams;
Two times obtained from the scale by one light beam
An optical detector that collects and mixes a folded beam and receives the mixed wave.
And a light output system of the scale and a light detector.
Detection signal that changes periodically according to relative changes to the system
In the displacement measuring device of the grating interference type which outputs
The output system makes the output light beam perpendicular to the scale.
And the light output from this light source
Split the beam into two light beams consisting of the first-order diffracted light
First diffraction grating arranged parallel to said scale for
And two optical beams split by this first diffraction grating
From the first-order diffracted light that is vertically incident on the scale from the
And the scale for generating two light beams
A second diffraction grating arranged in rows, and the scale
The two diffracted light beams obtained from the
The scale collects the two diffracted light beams
It is characterized in that it also serves as a light collecting means. In the specification, “condensing” is used to mean that two light beams are collected at one point, and includes cases where the beam diameter of each light beam itself is narrowed and where it is not narrowed.

[0009]

In the present invention, the diffraction grating is used as a means for dividing the light beam from the light source into two. If a diffraction grating for beam splitting is arranged parallel to the scale and the light beam from the light source is perpendicularly incident on it, the + 1st-order diffracted light beam and the -1st-order diffracted light beam are incident on the scale. It can be used as a beam. That is, the diffraction grating for dividing the light beam from the light source and the scale can be arranged in parallel, and the light beam from the light source can be arranged so as to be perpendicularly incident on the diffraction grating. Being symmetrical, the alignment of the optical elements is therefore easy. Further, since the incident light beams on the scale are the + 1st-order diffracted light and the -1st-order diffracted light of the diffraction grating, the light amounts are equal. From the above, an extremely high resolution grating interference type displacement measuring device can be obtained.

Even when a diffraction grating is used as the focusing means for the diffracted light beam in the photodetection system, the resolution of the grating interference type displacement measuring device can be improved for the same reason.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows the configuration of a grating interference type displacement measuring device according to an embodiment of the present invention. The scale 10 is composed of a transmission type diffraction grating in this embodiment. A light irradiation system 20 is arranged on one side of the scale, and a light detection system 30 for detecting a light beam obtained by transmitting and diffracting the scale is arranged on the other side.

The light irradiation system 20 includes a semiconductor laser 21 as a light source, a collimator 22 for collimating an output light beam of the semiconductor laser 21, and a diffraction grating 23 for splitting the light beam passing through the collimator 22. It is configured. The diffraction grating 23 is arranged in parallel with the scale 10, and the semiconductor laser 21 is arranged so as to output a light beam perpendicular to these. The light beam B which is divided into two by the diffraction grating 23 and is incident on the scale 10.
01 and Bo2 are specifically + 1st-order diffracted light and -1st-order diffracted light. There is naturally the 0th-order diffracted light, but this is not shown in the figure because it is not related to the measurement operation.

The photodetection system 30 includes incident light beams B01 and B02.
A convex lens 31 for condensing the diffracted light beams B11, B12 respectively obtained from the scale 10, a half mirror for transmitting and reflecting the two converging light beams by half and interfering the transmitted light with the reflected light to mix them. 32, and photodiodes 33 and 35 for receiving the two mixed waves B21 and B22 obtained thereby. A quarter-wave plate 34 is inserted on one photodiode 35 side. In this embodiment, the diffracted light beam B obtained from the scale 10 is
11 and B12 are perpendicular to the scale 10, that is, the diffraction angle 90
It has become °. This diffraction angle is determined by the light source light wavelength used, the beam splitting diffraction grating 23, and the lattice constant of the scale 10.

With such a structure, the scale 10 is moved relative to the light irradiation system 20 and the light detection system 30 as indicated by an arrow A in the figure, so that the scale 10 is removed from the photodiodes 33 and 35. A sinusoidal detection signal whose frequency is determined by the grating pitch of is obtained, and the displacement amount can be measured from the period. Further, the detection signal obtained from the two photodiodes 33 and 35 is 1/4.
The wave plates 34 are 90 ° out of phase with each other, and the displacement direction of the scale can be determined by comparing the two.

According to this embodiment, as is apparent from the drawing, the light beam from the semiconductor laser 21 is perpendicular to the scale 10, and the optical system except the quarter wave plate 34 is perpendicular to the scale 10. It is symmetrical.
Therefore, alignment of the optical element is easy. Further, beam division is performed by the diffraction grating 23, and the ± first-order light is used as two incident light beams to the scale,
The amounts of light of the two incident light beams are completely equal. As described above, high resolution characteristics can be obtained.

Further, in this embodiment, the two light beams B11 and B12 obtained from the scale 10 are designed to be perpendicular to the scale 10, and thus the two light beams B11 and B12 are parallel to each other. This facilitates the design of the photodetection system 30 that collects and interferes with these light beams. Further, in this embodiment, the two light beams B11 and B12 obtained in the vertical direction from the scale 10 are condensed by the convex lens 31, and the half mirror 32 is arranged at the condensing point position to perform the light mixing. Therefore, the photodiode 3
Since the photodiodes 3 and 35 are arranged near the half mirror 32, the photodiodes 33 and 35 having a small light receiving area can be used.

2 and 3 show an embodiment in which the photodetection system 30 side of the embodiment of FIG. 1 is modified. The light irradiation system is the same as that of the embodiment of FIG. 1, and therefore the light irradiation system is omitted in these drawings. In the embodiment shown in FIG. 2, a diffraction grating 36 is used instead of the convex lens as a condensing means for the light beams B11 and B12 obtained from the scale 10. The diffraction grating 36 is arranged parallel to the scale 10. In the embodiment shown in FIG. 3, the diffraction grating 36 and the prism 3 serving as the half mirror 38 on the joint surface serve as means for collecting and interfering the light beams.
7 is used. The same effects as those of the previous embodiment can be obtained by these embodiments.

FIG. 4 shows an embodiment in which the scale 10 is a reflection type and the light irradiation system 20 and the light detection system 30 are arranged on one side of the scale 10. The parts corresponding to those in the embodiment of FIG. 1 are designated by the same reference numerals as those in FIG. In this embodiment, the surface 11 of the scale 10 opposite to the surface on which the diffraction grating is formed is a reflecting surface. Diffracted light beams B11 and B12 diffracted by the scale 10 and reflected by the surface 11
Are designed to extend above the scale 10 and perpendicular to the scale 10. According to this embodiment, the optical system is arranged only on one side of the scale 10, resulting in a more compact optical system.

FIG. 5 shows a modification of the embodiment shown in FIG.
Although the scale 10 itself is a transmissive type, a mirror 12 is arranged separately from the scale 10 to form a reflective type structure substantially the same as in FIG. 4 is the same as that of FIG. 4 except the part shown in FIG.

FIG. 6 shows an embodiment in which a beam splitting diffraction grating 23 is used as it is as a light converging means instead of the light converging convex lens 31 in the embodiment of FIG. As a result, the optical system can be made more compact.
FIG. 7 is an example in which a diffraction grating 39 is used in the portion of the half mirror 32 for mixing the light beams in the example of FIG. In this case, the lattice constant is selected so that the diffracted light beams from the two light beams by the diffraction grating 39 are obtained as a mixed wave B20 that is superposed on one another. Therefore, in order to output two light beams whose phases are shifted to detect the displacement direction, it is necessary to divide this mixed wave B20 into two. This can be done easily.

FIG. 8 shows an embodiment in which a condensing diffraction grating 40 is used separately from the beam splitting diffraction grating 23 in place of the converging convex lens 31 in the embodiment of FIG. FIG. 9 shows an embodiment in which the half mirror 32 for performing light mixing is replaced with a diffraction grating 39 in the embodiment of FIG. 8 as in the embodiment of FIG.

FIG. 10 is a diffraction grating 39 for mixing light in the embodiment of FIG. 9 so that one of the 0th-order diffracted light and the other 1st-order diffracted light are overlapped so that two mixed waves B21 and B22 are obtained. This is an example. This is also possible by selecting the grating constant of the diffraction grating 39 depending on the relationship between the wavelength of the light source used and the angle of incidence on the diffraction grating 39.

In the above, the embodiment using the convex lens as the light condensing means of the light detection system and the embodiment using the diffraction grating in place of the convex lens have been described, but the light converging means can be modified in various ways. . Examples in which the scale is a reflection type are shown in FIGS. 11 to 15.
FIG. 11 shows an embodiment in which the concave mirror 41 is used as a light collecting means.
FIG. 12 shows an embodiment in which the special prism 42 is used as a light collecting means and a light mixing means. The prism 42 is a laminated prism whose upper surface is a reflecting surface 43 having a spherical surface or a cylindrical surface,
The bonding surface is a half mirror 44. The two light beams B11 and B12 from the scale 10 are reflected by the upper surface of the prism 44, collected, and mixed by the internal half mirror 44.

FIG. 13 shows mirrors 45 and 4 as the light collecting means.
6 is an example using 6. In this case, two light beams B
Although 11 and B12 are condensed at one point, the beam diameter itself is not narrowed, unlike the previous embodiments. 14 is shown in FIG.
In the second embodiment, the reflecting surface 43 of the prism 42 is a flat surface. FIG. 15 shows a reflection type diffraction grating 47.
In this embodiment, the light collecting means is used. These FIG. 14 and FIG.
Also in this embodiment, the diameters of the two light beams focused as in the embodiment of FIG. 13 cannot be reduced.

FIG. 16 shows the diffraction grating 2 in the light irradiation system.
In this embodiment, the light beams B01 and B02 split by 3 are further made into light beams B01 'and B02' which are vertically incident on the scale 10 through the diffraction grating 24 arranged in parallel with the scale 10. In this embodiment, the scale 10 is a reflection type, but the vertical relationship between the light irradiation system 20 and the light detection system 30 is as follows.
This is the reverse of the embodiment shown in FIG. In the case of this embodiment, the diffracted light beams B11 and B12 obtained from the scale 10 are
Is condensed without using a lens or the like.

In each of the above embodiments, if a reflection type diffraction grating 23 is used for beam splitting, the arrangement of the semiconductor laser 21, the collimator 22 and the diffraction grating 23 of the light irradiation system 20 is reversed as shown in FIG. You can also do it. Further, in this case, the light irradiation system 20 is arranged on one side of the scale 10, but as shown in FIG.
0, the semiconductor laser 21 and the collimator 22 are arranged on one side, and the beam splitting diffraction grating 23 is arranged on the opposite side of the scale 10.
Can also be placed.

[0027]

As described above, according to the present invention, by using a diffraction grating as a means for splitting a light beam from a light source into two, alignment of optical elements is facilitated, and two split light beams are used. Since the light quantities of the beams are equalized, it is possible to obtain a grating interference type displacement measuring device having high resolution characteristics.

[Brief description of drawings]

FIG. 1 is a diagram showing a main configuration of a grating interference type displacement measuring device according to an embodiment of the present invention.

FIG. 2 is a diagram showing a configuration of a main part of a grating interference type displacement measuring device according to another embodiment.

FIG. 3 is a diagram showing a configuration of a main part of a grating interference type displacement measuring device according to another embodiment.

FIG. 4 is a diagram showing a configuration of a main part of a grating interference type displacement measuring device according to another embodiment.

FIG. 5 is a diagram showing a configuration of a main part of a grating interference type displacement measuring device according to another embodiment.

FIG. 6 is a diagram showing a configuration of a main part of a grating interference type displacement measuring device according to another embodiment.

FIG. 7 is a diagram showing a main configuration of a grating interference type displacement measuring device according to another embodiment.

FIG. 8 is a diagram showing a main configuration of a grating interference type displacement measuring device according to another embodiment.

FIG. 9 is a diagram showing a configuration of a main part of a grating interference type displacement measuring device according to another embodiment.

FIG. 10 is a diagram showing a main configuration of a grating interference type displacement measuring device according to another embodiment.

FIG. 11 is a diagram showing a configuration of a main part of a grating interference type displacement measuring device according to another embodiment.

FIG. 12 is a diagram showing a main configuration of a grating interference type displacement measuring device according to another embodiment.

FIG. 13 is a diagram showing a main configuration of a grating interference type displacement measuring device according to another embodiment.

FIG. 14 is a diagram showing a configuration of a main part of a grating interference type displacement measuring device according to another embodiment.

FIG. 15 is a diagram showing a main configuration of a grating interference type displacement measuring device according to another embodiment.

FIG. 16 is a diagram showing a configuration of a main part of a grating interference type displacement measuring device according to another embodiment.

FIG. 17 is a diagram showing a configuration of a main part of a grating interference type displacement measuring device according to another embodiment.

FIG. 18 is a diagram showing a main configuration of a grating interference type displacement measuring device according to another embodiment.

[Explanation of symbols]

10 ... Scale, 20 ... Light irradiation system, 30 ... Photo detection system, 2
1 ... Semiconductor laser, 22 ... Collimator, 23 ... Diffraction grating, 31 ... Convex lens, 32 ... Half mirror, 33, 35
... photodiode, 34 ... quarter wave plate, 36 ... diffraction grating, 37 ... prism, 11 ... reflective surface, 12 ... mirror,
39, 40 ... Diffraction grating, 42 ... Prism, 43 ... Spherical reflecting surface, 44 ... Half mirror, 45, 46 ... Mirror, 47
…Diffraction grating.

─────────────────────────────────────────────────── --- Continuation of the front page (56) References JP-A-5-1924 (JP, A) JP-A-51923 (JP, A) JP-A 60-260813 (JP, A) JP-A 62- 25212 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G01B 11/00 G01D 5/38

Claims (4)

(57) [Claims] 1. A scale on which a diffraction grating is formed, a light irradiation system for irradiating the scale with two light beams, and two diffracted light beams obtained from the scale are condensed and mixed by the two light beams. And a grating detection type displacement measuring apparatus having a photodetection system for receiving the mixed wave and outputting a detection signal that periodically changes according to a relative change of the scale with respect to the light irradiation system and the photodetection system. The light irradiation system includes a light source arranged so that an output light beam is perpendicular to the scale, and a light beam composed of two first-order diffracted lights that are incident on the scale. and a diffraction grating for splitting the two diffracted light beams obtained from the scale, 1 the diffraction wavelength of the light source as a diffracted light becomes perpendicular to the scale And the lattice constant of Kooyobi scale is adjusted, the light detection system, two diffracted light Bee from the scale
Light beam from the light source to the scale on the vertical line
Focusing means and focusing position of the two diffracted light beams
Has a semi-transmissive surface arranged perpendicular to the scale
Then, a light beam composed of the two condensed first-order diffracted lights is
The semi-transmissive surface transmits and reflects respectively to reflect the transmitted light.
A light mixing means for interfering with the incident light and mixing, and this light mixing hand.
It has a light receiving element that receives the light mixed in each stage.
Grating interferometric displacement measuring apparatus characterized by that. 2. The grating interference according to claim 1, wherein the condensing unit has a diffraction grating arranged in parallel with the scale for converging two diffracted light beams obtained from the scale. Mold displacement measuring device. 3. The scale is a reflection type diffraction grating.
The diffraction grating of the light irradiation system and the diffraction grating of the condensing means
Is a contract characterized by being formed on the same plane.
The grating interference type displacement measuring device according to claim 2. 4. A scale on which a diffraction grating is formed, a light irradiation system for irradiating the scale with two light beams, and two diffracted light beams obtained from the scale are condensed and mixed by the two light beams. And a grating detection type displacement measuring apparatus having a photodetection system for receiving the mixed wave and outputting a detection signal that periodically changes according to a relative change of the scale with respect to the light irradiation system and the photodetection system. The light irradiation system includes a light source arranged so that an output light beam is perpendicular to the scale, and a light beam output from the light source is divided into two light beams including first-order diffracted light. A first diffraction grating arranged in parallel with the scale, and two optical beams composed of a first-order diffracted light which is perpendicularly incident on the scale from the two light beams divided by the first diffraction grating. And a second diffraction grating arranged in parallel with the scale for generating the two diffracted light beams obtained from the scale are first-order diffracted light, and the scale is the two diffracted light beams. Displacement measuring device of grating interference type, which also functions as a light collecting means for collecting light.