JP3068408B2 - Lattice 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 method for splitting a light beam from a light source into two waves and making the light beam incident on two different points on a diffraction grating of a scale. A grating interference type displacement detection device that detects a signal can be used when an optical system is configured using a reflection type diffraction grating as a scale.

[0002]

2. Description of the Related Art As one of the attempts to improve the resolution of a conventional photoelectric encoder, a graduation of a fine pitch (usually about 1 μm) is formed on a scale using holographic technology, and the graduation is used as a diffraction grating. There is known a grating interference type displacement detecting device which detects relative displacement with high accuracy by utilizing the same. In this method, a light beam from a light source is split into two waves and made incident on one or two points on a diffraction grating of a scale, and a mixed wave of a plurality of light beams generated at this point is detected as an electric signal. The scale can be classified into a scale using a reflection type diffraction grating and a scale using a transmission type diffraction grating.

As a device using the latter transmission type diffraction grating, for example, a grating interference type displacement detecting device described in Japanese Patent Application Laid-Open No. 5-1924 is known. As shown in FIG. 7, a grating interference type displacement detection device 600 is provided so as to be displaceable in the left-right direction in the figure and a transmission type diffraction grating 602 is formed along the displacement direction, and a laser light source 603. A prism 605 that splits the laser beam emitted from the laser light source 603 into two waves and causes each of the split light beams A and B to enter two different diffraction points P1 and P2 on the scale 601; Are arranged at the intersection (point K in the figure) of the two first-order diffracted lights A1 and B1 diffracted by the above, the respective first-order diffracted lights A1 and B1 are branched, and the diffracted light of one light flux and the transmitted light of the other light flux are separated. It is configured by a transmission type diffraction grating 607 that generates two mixed waves MA and MB by mixing, and detectors 608A and 608B that convert the mixed waves MA and MB into electric signals.

A transmission type diffraction grating 604 is provided on the hypotenuse of the prism 605 so that the laser beam emitted from the laser light source 603 is diffracted and transmitted at point R in the drawing to split into two waves. Polarizing elements 606A and 606 which make the polarization directions of the two waves orthogonal to each other are sandwiched between the other two sides.
06B is provided. The two transmission-type diffraction gratings 604 and 607 are both arranged in parallel with the scale 601.

Here, the prism 605 (transmission type diffraction grating 604, polarizing elements 606A and 606B) constitutes a light beam branching unit 609, and the transmission type diffraction grating 607 constitutes a light beam mixing unit 610. In addition, the detector 608A includes a polarizing plate 611A that causes one of the mixed waves MA mixed by the transmission type diffraction grating 607 to coincide with each other in the polarization direction and causes interference, and converts a light beam that is interfered by the polarizing plate 611A into an electric signal. And a light receiving element 612A for conversion. Then, the detector 608B passes through the quarter-wave plate 613 and a quarter-wave plate 613 for delaying the phase of only one polarization component of the other mixed wave MB mixed by the transmission type diffraction grating 607 by 90 degrees. And a polarizing plate 611B for causing the mixed wave MB to have the same polarization direction to cause interference.
And a light receiving element 612B for converting the light beam interfered by 11B into an electric signal.

[0006] Such a grating interference type displacement detecting device 600
In, the laser beam emitted from the laser light source 603 is split by the prism 605 into two waves whose polarization directions are orthogonal to each other. Each of the split luminous fluxes A and B is divided into diffraction points P1 and P2 on the diffraction grating 602 of the scale 601 respectively.
Is incident on. At this time, first-order diffracted light beams A1 and B1 of the respective branched light beams A and B are generated at the diffraction points P1 and P2. These first-order diffracted lights A1 and B1 are mixed by a transmission type diffraction grating 607 and then converted into electric signals by detectors 608A and 608B.

Accordingly, in the grating interference type displacement detecting device 600, when detecting the amount of movement of the scale 601 as the brightness of the interference light, the interference between the first-order diffracted lights A1 and B1, which are phase-shifted in opposite directions, is used. Therefore, assuming that the scale 601 is displaced by one pitch of the diffraction grating 602, two cycles of complete sine wave signals φA and φB are obtained from the detectors 608A and 608B (two light and dark periods are obtained). ). This means that one pitch of the diffraction grating 602 is optically divided into two, thereby improving the resolution. For example, one pitch of the diffraction grating 602 is 0.5 μm
Then, the sine wave signals φA and φB obtained from the detectors 608A and 608B have a period corresponding to a resolution of 0.25 μm.

Further, since the quarter wavelength plate 613 is provided in one of the detectors 608B, two detectors 608A and 608B are provided.
The sine wave signals φA and φB obtained from B have phases different from each other by 90 degrees, so that the displacement direction of the scale 601 can be grasped.

[0009] The mixed wave MA sent to the detector 608A on the left side in the figure mixes the light beam once diffracted from the laser light source 603 and reaches the detector 608A with the light beam diffracted three times. It has become. That is, the light beam once diffracted is the diffraction grating 60 of the scale 601.
2 is a light beam diffracted only at the diffraction point P2 (a branched light beam B and its first-order diffracted light beam B1). On the other hand, a light beam diffracted three times is a point R on the transmission type diffraction grating 604,
At the diffraction point P1 on the diffraction grating 602 of the scale 601 and the point K on the transmission type diffraction grating 607, the diffracted light flux (branched light flux A and its first-order diffracted light A
This is 1).

[0010]

However, in the case of the grating interference type displacement detecting device 600 using the transmission type diffraction grating 602 as the scale 601 as described above, the scale 601 is moved from both sides (up and down in FIG. 7). Since the detection system must be configured in a sandwiched state, there is a problem that the detection system becomes large or the degree of freedom in mounting the scale 601 is limited.

On the other hand, by using a reflection type diffraction grating as a scale, it is conceivable to reduce the size of the detection system and improve the degree of freedom in mounting the scale. That is,
It is conceivable to configure a detection system in a state where the above-described grating interference type displacement detection device 600 of FIG. 7 is simply folded back at the position of the scale 601. However, when an attempt is made to configure a detection system in a state where the grating interference type displacement detection device 600 is simply folded back by using a reflection type diffraction grating as a scale, the installation positions of the laser light source 603 and the detector 608A coincide. Therefore, a detection system cannot be established.

Also, if the diffraction point P on the scale 601 is
Even if the detection system in the state where the grating interference type displacement detection device 600 is folded back with the incident angle and the diffraction angle at 1 and P2 being different angles, the alignment between the scale 601 and other devices and its variation are insensitive. However, there is a problem that a complicated optical system cannot be formed. That is,
When the scale 601 is tilted or rotated with respect to other devices, the optical path difference and optical path length difference of the two light beams that are mixed and interfere with each other become large, which adversely affects the quality of the detection signal and the counting as an encoder. There is a problem.

It is an object of the present invention to reduce the size of the device and to match the incident angle and the diffraction angle at the diffraction point on the diffraction grating of the scale to improve the quality of the detection signal and improve the diffraction efficiency. An object of the present invention is to provide a grating interference type displacement detecting device which can be improved.

[0014]

According to the present invention, a transmission type diffraction grating is used as a light beam branching means and a light beam mixing means, and an optical system on a light emitting side (a side with a light source) and a light receiving side (a side with a light receiving element) are used. The above-mentioned object is achieved by arranging the optical system in a different plane. Specifically, the present invention provides:
A scale having a reflection type diffraction grating, a light source for emitting a light beam, and a light beam splitting means for splitting the light beam from the light source into two waves and making each of the split light beams incident on two different points on the diffraction grating of the scale A grating interference type displacement detecting device comprising: a light beam mixing means for mixing a plurality of light beams generated by the diffraction grating of the scale; and a detector for converting a mixed wave mixed by the light beam mixing means into an electric signal. Wherein the light beam splitting means splits the light beam from the light source into two waves by diffracting and transmitting the light beam, and transmits each of the split light beams to two different points on the diffraction grating of the scale. A light beam mixing means, which is disposed at the intersection of the two light beams diffracted on the diffraction grating of the scale, splits each light beam, and sets And a transmission type diffraction grating that generates two mixed waves by mixing the diffracted light of the light flux and the transmitted light of the other light flux. The light path of each light beam reaching the diffraction grating and the light path of each light beam diffracted on the diffraction grating of the scale and reaching the detector via the light beam mixing means are different from each other on the same side of the scale. It is characterized by being arranged in.

Further, in the grating interference type displacement detecting device according to the present invention, the light beam mixing means may convert the mixed wave generated by the transmission type diffraction grating toward the opposite side to the light source into two waves. It is characterized by including a non-polarizing beam splitter that branches.

Further, in the grating interference type displacement detecting device according to the present invention, a point on the transmission type diffraction grating of the light beam splitting means from which the light beam from the light source is split, and each of the split light beams split at this point. Either the middle of the optical path between a point on the scale diffraction grating where one of the split beams is incident, and a point on the scale grating where the one branch beam is incident is diffracted at this point. A quarter-wave plate is provided in the optical path between the point where the reflected light beam reaches the transmission type diffraction grating of the light beam mixing means and the phase of the polarization component having the same direction is delayed by 90 degrees. It is characterized by having been done. Here, 1/4 provided in the middle of the two optical paths
The wave plates may be separate quarter wave plates, respectively, or may be a single combined quarter wave plate. Further, the one of the branched light beams may be an arbitrary light beam of the two waves branched by the light beam branching means. In short, one of the two waves and the optical path of the first-order diffracted light thereof It is only necessary that a １ ／ wavelength plate be provided in the device.

In the above-described displacement detection apparatus of the present invention, the transmission type diffraction grating forming the light beam branching means and the transmission type diffraction grating forming the light beam mixing means are one sheet. Desirably, the transmission grating is constituted by a transmission type diffraction grating. Further, the transmission type diffraction grating (the transmission type diffraction grating forming the light beam splitting means and the transmission type diffraction grating forming the light beam mixing means) and the scale diffraction grating (reflection type diffraction grating) It is desirable that they have the same pitch.

Further, in constructing the grating interference type displacement detecting device of the present invention as described above, the incident angle of each branched light beam incident on the diffraction grating of the scale, and each of these branched light beams is determined by the diffraction grating of the scale. The diffraction angle of each of the first-order diffracted lights generated by the above diffraction may be made coincident or different. However, it is preferable that the incident angle and the diffraction angle be matched from the viewpoint of improving the quality of the detection signal and improving the diffraction efficiency.

[0019]

According to the present invention, the light beam from the light source is split into two waves by the light beam splitting means and made incident on two different points on the reflection type diffraction grating of the scale. The displacement of the scale is grasped by mixing the two light beams by the light beam mixing means, causing the mixed waves to interfere with each other with a detector and detecting the mixed waves as an electric signal. At this time, the optical path on the light-emitting side, that is, the optical path of each light beam emitted from the light source and reaching the diffraction grating of the scale via the light beam branching means, and the optical system on the light-receiving side, that is, diffracted on the diffraction grating of the scale Since the optical paths of the light beams reaching the detector via the light beam mixing means are arranged in different planes, each device constituting the light-emitting side optical system and each device constituting the light-receiving side optical system are arranged in different planes. The arrangement positions do not interfere, and the degree of freedom in the arrangement configuration of each device is improved.

For this reason, the incident angle of each branched light beam incident on the diffraction point on the diffraction grating of the scale and the diffraction angle of each first-order diffracted light generated by each of these branched light beams being diffracted at the diffraction point. It is possible to make them coincide. This makes it possible to configure an optical system that is insensitive to alignment between the scale and other devices and its fluctuation. In other words, if the angle of incidence and the angle of diffraction match, if the scale is tilted or rotated with respect to other devices, the optical path difference and optical path length difference of the two light beams that mix and interfere will almost occur. Since there is no change, the quality of the detection signal and the counting as an encoder are hardly affected, and even when the distance between the scale and other devices changes, no change in the optical path occurs at all. In addition, the coincidence between the incident angle and the diffraction angle maximizes the diffraction efficiency, thereby improving the diffraction efficiency. In the present invention, it is not always necessary to make these incident angles and diffraction angles coincide.

Also, since the reflection type diffraction grating is used as the scale, the light emitting side optical system and the light receiving side optical system are arranged on the same side of the scale. Compared with the case of the grating interference type displacement detection device 600 (see FIG. 7) used as the scale 601, the size of the device can be reduced and the degree of freedom in mounting the scale can be improved.

Then, the light beam from the light source is split into two waves by the transmission type diffraction grating, and each of the split light beams is made incident on two different points on the scale diffraction grating, and is diffracted on the scale diffraction grating. Since the two light fluxes are mixed, the distance from the scale to the light source and the detector is shorter than when a similar function is realized using a beam splitter, and the size of the apparatus is further reduced, These objects are achieved by these.

Further, if a non-polarizing beam splitter for splitting a mixed wave directed to the opposite side of the light source into two waves out of two mixed waves generated by the transmission type diffraction grating constituting the light beam mixing means is provided, The mixed wave split by the non-polarizing beam splitter and sent to the detector becomes a mixed wave of light beams diffracted by the same number of times, so that the mixed wave is diffracted once like the grating interference type displacement detection device 600 described above. The quality of the detection signal is improved as compared with the case where the mixed wave MA of the light beam and the light beam diffracted three times is sent to the detector 608A. That is, the mixed wave sent to the non-polarizing beam splitter is diffracted (first diffraction) by the transmission type diffraction grating constituting the light beam branching unit after being emitted from the light source, and further diffracted at the diffraction point on the scale diffraction grating. Diffraction (second diffraction)
The luminous flux that passes through the transmission type diffraction grating constituting the luminous flux mixing means and reaches the non-polarization beam splitter, and is transmitted from the transmission type diffraction grating constituting the luminous flux splitting means after being emitted from the light source, and is on the scale diffraction grating. (First diffraction) at the diffraction point, and further diffracted (second diffraction) by the transmission type diffraction grating constituting the light beam mixing means to become a mixed wave with the light beam reaching the non-polarizing beam splitter. Light beams diffracted the same number of times are mixed.

Further, in the middle of the optical path between a point on the transmission type diffraction grating of the light beam branching means and a point on the scale diffraction grating, and a point on the scale diffraction grating and the transmission type diffraction of the light beam mixing means. If a quarter-wave plate arranged so as to delay the phase of the polarization component of the same direction by 90 degrees is provided in the middle of the optical path between the points on the grating, the transmission type diffraction grating of the light beam mixing means is provided. The direction of polarization of the two light beams
It is possible to easily make the states orthogonal to each other.

In the case where the transmission type diffraction grating constituting the light beam branching means and the transmission type diffraction grating constituting the light beam mixing means are constituted by a single transmission type diffraction grating,
Since the apparatus is simplified, the size and cost of the apparatus can be further reduced. Furthermore, if the transmission type diffraction grating and the scale diffraction grating are set at the same pitch, when the wavelength of the light source fluctuates, the fluctuation of the diffraction angle due to the fluctuation of the wavelength becomes small. No longer occurs, and a mixed wave can be obtained reliably.

[0026]

Embodiments of the present invention will be described below with reference to the drawings. [First Embodiment] FIGS. 1 and 2 show a grating interference type displacement detecting apparatus 10 according to a first embodiment of the present invention.
1A is a configuration diagram on the light emission side of the grating interference type displacement detection device 10, FIG. 1B is a configuration diagram on the light reception side, and FIG. It is a schematic perspective view which shows the arrangement state of an optical path. FIGS. 1A and 1B both show a state viewed from the direction of arrow Y in FIG.

In FIG. 1 (A), a grating interference type displacement detecting device 10 is provided so as to be displaceable in the left-right direction in the figure and has a reflection type diffraction grating 12 formed along the direction of displacement. A laser light source 13 provided at the upper left in the figure for emitting a laser beam, and a transmission type diffraction grating 14 provided in parallel with the scale 11 above the scale 11 in the figure.
And

Each light path on the light emission side of the grating interference type displacement detecting device 10 formed by the laser light source 13 and the transmission type diffraction grating 14 is located within a first surface 20 located on the near side in FIG. Are located. This first surface 20
It is arranged along the displacement direction of the scale 11 (the X direction in FIG. 2) and at a predetermined angle φ with the surface N including the normal of the diffraction grating 12 of the scale 11.

In FIG. 1B, a grating interference type displacement detecting device 10 includes a transmission type diffraction grating 14 disposed substantially at the center of the figure and a scale 11 above the transmission type diffraction grating 14. A non-polarizing beam splitter 15 provided at a right angle, and the non-polarizing beam splitter 15
Are provided with two detectors 41A and 41B provided on both sides of the light source and the light amount monitor 16.

The transmission type diffraction grating 14, the non-polarization beam splitter 15, the light amount monitor 16, and the detector 4
Each optical path on the light receiving side of the grating interference type displacement detecting device 10 formed by 1A, 41B and the like is arranged in the second surface 30 located on the far side in FIG. This second surface 30
It is arranged so as to form a predetermined angle φ with the surface N including the normal line of the diffraction grating 12, and is symmetrical with the first surface 20 described above with respect to the surface N including the normal line of the diffraction grating 12. The laser light source 13, the transmission type diffraction grating 14, the non-polarization beam splitter 15, the light amount monitor 16, and the detectors 41A and 41B are all on the same side (upper side in the figure) with respect to the scale 11. Is provided.

The transmission type diffraction grating 14 extends in a direction perpendicular to the plane of FIG. 1 (A) and FIG. 1 (B) and is connected, and crosses both the first surface 20 and the second surface 30. Are arranged as follows. Then, as shown in FIG.
By diffracting and transmitting the laser beam from the laser light source 13 at the position of the point R in the figure, the two branched light beams A and B
As shown in FIG. 1B, the two first-order diffracted lights A1 generated by diffracting these branched light beams A and B on the diffraction grating 12 (diffraction points P1 and P2) of the scale 11 are generated. , B1 (at the point K in the figure) and diffracts and transmits each of these first-order diffracted lights A1, B1 to generate two mixed waves. The pitch of the transmission type diffraction grating 14 is the same as the pitch of the diffraction grating 12 of the scale 11. Further, since the transmission type diffraction grating 14 is fixed with respect to the laser light source 13, the light beam diffracted by the transmission type diffraction grating 14 does not change in phase.

The non-polarizing beam splitter 15 is similar to that shown in FIG.
As shown in (B), of the two mixed waves generated by the transmission type diffraction grating 14, the mixed wave directed to the opposite side (right side in the figure) to the laser light source 13 is changed into two waves without changing the polarization direction. It is arranged to branch and send to each of the detectors 41A and 41B. Here, the light beam splitting means 21 is constituted by the transmission type diffraction grating 14, and the light beam mixing means 31 is constituted by the transmission type diffraction grating 14 and the non-polarization beam splitter 15. That is, the transmission type diffraction grating 14 is also used as the light beam splitting means 21 and the light beam mixing means 31.

The detector 41A has a quarter-wave plate 42 for delaying the phase of only one polarization component of one of the mixed waves split by the non-polarization beam splitter 15 by 90 degrees, and has passed through the quarter-wave plate 42. It is composed of a polarizing plate 43A that makes the polarization directions of the mixed waves coincide with each other and causes interference, and a light receiving element 44A that converts a light beam that is interfered by the polarizing plate 43A into an electric signal. Then, the detector 41B includes a polarizing plate 43B that causes the other mixed wave split by the non-polarizing beam splitter 15 to coincide with the polarization direction of the other mixed wave to cause interference, and a polarizing plate 43B.
And a light receiving element 44B for converting the light beam interfered by B into an electric signal.

The light quantity monitor 16 is a transmission type diffraction grating 14.
Are arranged so that a mixed wave directed toward the laser light source 13 (left side in the drawing) out of the two mixed waves generated by the above is incident, and is provided to compensate for fluctuations in diffraction efficiency of the scale 11.

In FIG. 1A, a point R on a transmission type diffraction grating 14 from which a light beam from a laser light source 13 is branched, and a scale 11 on which one of the branched light beams B branched at this point R is incident. A 波長 wavelength plate 51 is provided in the middle of the optical path between the diffraction grating 12 and the diffraction point P2. Also,
In FIG. 1B, a diffraction point P2 on a diffraction grating 12 of a scale 11 and a first-order diffracted light B diffracted at the diffraction point P2.
A 波長 wavelength plate 52 is provided in the optical path between the point 1 and the point K on the transmission type diffraction grating 14. These quarter-wave plates 51 and 52 are each arranged with a phase delay of 45 degrees with respect to the polarization direction of the branched light beam B (linearly polarized light) and tilted by 90 degrees with respect to the polarization component of the same direction. The arrangement is the same to delay it.

Therefore, the split light beam B and its first-order diffracted light beam B1
Are two quarter-wave plates 51 and 52 arranged in the same manner.
, So that the phase of only one polarization component is 1
As a result, the split light beam B (linearly polarized light) before passing through the quarter-wave plate 51 and the quarter-wave plate 52
And the first-order diffracted light B1 (linearly polarized light) after passing through, the polarization direction is rotated by 90 degrees. On the other hand, since the split light beam A and its first-order diffracted light A1 do not pass through the quarter-wave plate, the polarization direction does not change. As a result, the first-order diffracted lights A1 and B1 collected at the point K of the transmission type diffraction grating 14 are in a state where their polarization directions are orthogonal to each other.

FIG. 3 shows an enlarged cross section of the scale 11. The scale 11 has a glass 11A disposed on the upper side in the drawing, a mirror surface 11B disposed on the lower side, and a volume phase type diffraction grating (hologram diffraction grating) 12 interposed therebetween. It has a structure.

When a gap D is formed between the diffraction grating 12 and the mirror surface 11B as shown in FIG. 4, the gap D is adjusted to an appropriate size as follows. . That is, in FIG. 4, there are the following four types of light beams generated by the diffraction grating 12 with respect to the incident light C, and (1)
A light flux C1 that is reflected by the mirror surface 11B after being diffracted by the diffraction grating 12 and passes through the diffraction grating 12, and (2) a light flux that is reflected by the mirror surface 11B after being transmitted through the diffraction grating 12 and is diffracted by the diffraction grating 12 C2 and (3) diffraction grating 12
, A light beam C3 reflected by the mirror surface 11B and transmitted again through the diffraction grating 12, and (4) a light beam C4 reflected by the mirror surface 11B after being diffracted by the diffraction grating 12 and diffracted by the diffraction grating 12 again. There is.

Of these, the light beams C1 and C2 are first-order diffracted lights that have been diffracted once by the diffraction grating 12, and are thus light beams that undergo a phase change due to the movement of the scale 11. Therefore, when the gap D is sufficiently small with respect to the width of the light flux, the gap D is adjusted so that the light fluxes C1 and C2 interfere with each other to enhance the light intensity, and the scale D is adjusted. The gap D is kept constant during the stroke 11. When the gap D is relatively large (for example, when the width of the light flux is about 1 mm and the gap D is about 3 mm), only one of the two light fluxes C1 and C2 is used. However, the other light beam may be blocked from being used after being emitted from the scale 11.

The remaining two light beams C3 and C4 are not diffracted at all by the diffraction grating 12 or are diffracted twice, and therefore do not cause a phase change due to the movement of the scale 11, and are both reflected. It can be handled as light (zero-order light). Further, as such a diffraction grating 12, for example, one having a grating pitch of about 500 nm and a wavelength of the laser light source 13 of about 780 nm can be adopted.

In the first embodiment, the movement of the scale 11 is detected as follows. First, the laser beam emitted from the laser light source 13 is diffracted and transmitted at a point R on the transmission type diffraction grating 14 and split into two waves. At this time, the diffraction angle and the transmission angle at the point R are the same angle (θ1). And the transmission type diffraction grating 1
The split light beam A diffracted at the point R on 4 enters the diffraction point P1 on the diffraction grating 12 of the scale 11, while the split light beam B transmitted at the point R passes through the 波長 wavelength plate 51. After that, the light is incident on the diffraction point P2 on the diffraction grating 12 of the scale 11.

At each of the diffraction points P1 and P2, each of the split light beams A and
B first-order diffracted light A1, B1 and reflected light (0-order light) A
0, B0 are generated. At each of the diffraction points P1 and P2, the angle of incidence θ1 of each of the branched luminous fluxes A and B at the diffraction points P1 and P2 is the same as the angle of diffraction θ2 of each of the first-order diffracted lights A1 and B1.

Next, the first-order diffracted light A1 reaches a point K on the transmission type diffraction grating 14, while the first-order diffracted light B1 is 1 /
After passing through the four-wavelength plate 52, the light reaches the point K on the transmission type diffraction grating 14. Further, the respective zero-order lights A0 and B0 are removed from the respective diffraction points P1 and P2 on the diffraction grating 12 of the scale 11 in the horizontal direction in the figure. At the point K on the transmission type diffraction grating 14, each of the first-order diffracted lights A1 and B1 is diffracted and transmitted to generate two mixed waves. In other words, the diffracted light of the first-order diffracted light A1 and the transmitted light of the first-order diffracted light B1 are mixed to generate a mixed wave directed toward the laser light source 13 (left side in the figure), and the transmitted light of the first-order diffracted light A1 and 1 The diffracted light of the next diffracted light B1 is mixed to generate a mixed wave directed toward the opposite side (right side in the figure) of the laser light source 13.

Thereafter, the mixed wave traveling from the point K on the transmission type diffraction grating 14 toward the laser light source 13 is transmitted to the light amount monitor 16.
, And on the other hand, the mixed wave traveling toward the side opposite to the laser light source 13 is branched by the non-polarizing beam splitter 15 and reaches the detectors 41A and 41B, where it is converted into an electric signal.
The mixed wave reaching each of the detectors 41A and 41B is combined with the luminous flux diffracted twice at the point R on the transmission type diffraction grating 14 and each diffraction point P1 on the diffraction grating 12 of the scale 11 and the scale 11 It is a mixed wave with the light flux totally twice diffracted at each diffraction point P2 on the diffraction grating 12 and a point K on the transmission type diffraction grating 14. On the other hand, the mixed wave reaching the light amount monitor 16 is three times in total at the point R on the transmission type diffraction grating 14, each diffraction point P1 on the diffraction grating 12 of the kale 11, and the point K on the transmission type diffraction grating 14. It is a mixed wave of the diffracted light beam and the light beam diffracted once only at each diffraction point P2 on the diffraction grating 12 of the scale 11.

According to the first embodiment, the following effects can be obtained. That is, the diffraction grating 1 of the scale 11 emitted from the laser light source 13 through the light beam branching means 21
2 that reach the diffraction points P1 and P2 (each branch light A,
The optical path B) is provided in the first surface 20 and the diffraction point P
Since the respective optical paths of the respective first-order diffracted lights A1 and B1 and the respective zero-order lights A0 and B0 generated in P1 and P2 are provided in the second plane 30, the diffraction points P1 and B1 of the respective branched luminous fluxes A and B are provided. The angle of incidence θ1 on P2 can be made to coincide with the diffraction angle θ2 of each of the branched light beams A1 and B1. For this reason, since the optical system can be made insensitive to the alignment between the scale 11 and other devices and the fluctuation thereof, it is possible to improve the quality of the detection signal and prevent a change in counting as an encoder. In addition, the diffraction efficiency can be improved.

Further, with the configuration in which the first surface 20 and the second surface 30 are provided, each device (the laser light source 13 and the light beam splitting means 21) constituting the optical system on the light emitting side and the optical system on the light receiving side are connected. The constituent devices (the light beam mixing means 31 and the detectors 41A and 41B) can be installed without being affected by the positions of the devices, and the degree of freedom in the arrangement of the devices can be improved.

Further, since the mixed wave traveling from the point K on the transmission type diffraction grating 14 to the side opposite to the laser light source 13 is split by the non-polarizing beam splitter 15, each of the detectors 41A and 41B is provided. Can be a mixed wave of light beams diffracted the same number of times (twice), so that the quality of the detection signal can be improved.

Also, since the reflection type diffraction grating 12 is used as the scale 11, each device (the laser light source 13 and the light beam branching means 21) constituting the optical system on the light emitting side and each device constituting the optical system on the light receiving side. Since the devices (the light beam mixing means 31 and the detectors 41A and 41B) can be arranged on the same side of the scale 11, the grating interference type displacement detection device 600 using the transmission type diffraction grating 602 as the scale 601 described above.
Compared with the case of (see FIG. 7), the size of the apparatus can be reduced and the degree of freedom in mounting the scale can be improved.

Further, since the quarter-wave plates 51 and 52 are provided, the polarization directions of the two light beams converging at the point K on the transmission type diffraction grating 14 can be easily made orthogonal to each other. it can. Further, since the transmission type diffraction grating 14 is also used as the light beam splitting means 21 and the light beam mixing means 31, the device can be simplified, so that the size and cost of the device can be further reduced.

Since the transmission type diffraction grating 14 and the diffraction grating 12 of the scale 11 have the same pitch, when the wavelength of the laser light source 13 changes, the diffraction angle fluctuation accompanying the wavelength fluctuation can be reduced. Therefore, it is possible to prevent the optical path of the two light beams to be mixed from being shifted, and to surely obtain the mixed wave.

Further, when detecting the amount of movement of the scale 11 as the brightness of the interference light, the interference between the first-order diffracted lights A1 and B1, which are phase-shifted in opposite directions, is utilized. If the sensor is displaced by one pitch, two cycles of complete sine wave signals φA and φB can be obtained from each of the detectors 41A and 41B (two light and dark periods can be obtained). For this reason, since one pitch of the diffraction grating 12 is optically divided into two, the resolution can be improved.

Further, since the 波長 wavelength plate 42 is provided in one of the detectors 41A, the sine wave signals φA and φB obtained from the two detectors 41A and 41B have a phase difference of 90 degrees from each other. Thus, the displacement direction of the scale 11 can be grasped.

[Second Embodiment] FIG. 5 shows a grating interference type displacement detecting device 60 according to a second embodiment of the present invention. FIG. 5A is a configuration diagram on the light emission side of the grating interference type displacement detection device 60 (within the first surface 20), and FIG. 5B is a configuration diagram on the light reception side (within the second surface 30). The grating interference type displacement detecting device 60 is the grating interference type displacement detecting device 1 of the first embodiment.
0 has substantially the same configuration as that of the non-polarizing beam splitter 15.
Since only the presence or absence of the light amount monitor 16 is different, the same portions are denoted by the same reference numerals and detailed description thereof will be omitted, and only different portions will be described below.

In the grating interference type displacement detecting apparatus 10 of the first embodiment, a non-polarizing beam splitter 15 for splitting a mixed wave traveling from the point K on the transmission type diffraction grating 14 to the side opposite to the laser light source 13, Although the light amount monitor 16 is provided to receive the mixed wave directed toward the laser light source 13 (see FIG. 1B), these are not provided in the second embodiment. That is, in the second embodiment, as shown in FIG. 5B, the mixed wave traveling from the point K on the transmission type diffraction grating 14 to the opposite side to the laser light source 13 is sent to the detector 41B. The mixed wave traveling toward the laser light source 13 is detected by the detector 41.
A.

In the second embodiment, the first-order diffracted lights A1 and B1 are collected at the point K on the transmission type diffraction grating 14 in the same manner as in the first embodiment. Then, at this point K, each of the first-order diffracted lights A1 and B1 is branched, and a mixed wave of the diffracted light of the first-order diffracted light A1 and the transmitted light of the first-order diffracted light B1 is sent to the detector 41A, and the first-order diffracted light A1 Transmitted light and 1
A mixed wave of the next-order diffracted light B1 and the diffracted light is sent to the detector 41B.

According to the second embodiment, the same effect as that of the first embodiment can be obtained except for the effect of improving the quality of the detection signal by installing the non-polarizing beam splitter 15 of the first embodiment. Can be. That is, by providing the first surface 20 and the second surface 30, the effect of improving the degree of freedom of the arrangement configuration of each device, the improvement of the quality of the detection signal due to the coincidence of the incident angle θ 1 and the diffraction angle θ 2 and the diffraction efficiency Effect of using the reflection type diffraction grating 12 as the scale 11 to reduce the size of the device and to improve the degree of freedom in mounting the scale;
The effect of orthogonalizing the polarization directions of the two light beams by installing the / 4 wavelength plates 51 and 52, the light beam splitting means 21 of the transmission type diffraction grating 14
In addition, the size of the apparatus can be reduced and the cost can be reduced by using the same as the light beam mixing means 31.
Of the optical path deviation due to the same pitch of the diffraction grating 12 and the resolution improvement effect by utilizing the interference between the first-order diffracted lights A1 and B1, and each sine wave signal φA by installing the quarter-wave plate 42. , ΦB by 90 degrees.

It should be noted that the present invention is not limited to the above embodiments, but includes other configurations that can achieve the object of the present invention. For example, the following modifications are also included in the present invention. . That is, the first surface 20 on which the light emitting side optical system is arranged and the second surface 30 on which the light receiving side optical system is arranged are not limited to the arrangement shown in FIG. By folding the first surface 20 and the second surface 30 using a prism 81 as shown in FIG. 6A, the first surface 20 and the second surface 30 are made parallel to each other at the upper part of the prism 81. May be arranged, or a cylindrical lens 82 as shown in FIG.
A similar arrangement may be made using a transmission type diffraction grating 83 as shown in FIG. 6C. In short, the first surface 20 and the second surface 30 are on the same side of the scale 11 and are different surfaces. It is sufficient if they are arranged inside.

In each of the above embodiments, the １ ／ wavelength plate 5
Reference numerals 1 and 52 are provided at positions where the branched light beam B and the first-order diffracted light B1 at the diffraction point P2 of the branched light beam B pass.
1 may be provided at a position through which the first-order diffracted light A1 passes. In short, any one of the branched light beams A and B passes through the quarter-wave plate twice. Good.

In each of the above embodiments, the １ ／ wavelength plate 5
1, 52 are optical paths in the first surface 20 and the second surface 30;
Although they are separately provided in the optical paths inside, one 波長 wavelength plate may be provided so as to straddle these two optical paths.
Further, in each of the above-described embodiments, the quarter-wave plates 51 and 52 are provided so that the polarization directions of the two light beams gathered at the point K on the transmission type diffraction grating 14 are orthogonal to each other. The means for making the polarization directions orthogonal to each other is not limited to the installation of such a quarter-wave plate. For example, each of the split luminous fluxes A and B after being split at a point R on the transmission type diffraction grating 14 is used. By passing B through polarizing elements (similar to the polarizing elements 606A and 606B in FIG. 7), the polarization directions of the two light beams may be made orthogonal.

In each of the above embodiments, the transmission type diffraction grating 14 is used also for the light beam splitting means 21 and the light beam mixing means 31. The transmission type diffraction grating constituting the means 31 may be provided separately. However, from the viewpoint of simplification, miniaturization, and cost reduction of the apparatus, it is preferable to use one transmissive diffraction grating as in the above embodiments. Further, in the first embodiment, the light amount monitor 16 is provided, but the light amount monitor 16 may be omitted.

In each of the above embodiments, the scale 11
Has a laminated structure of a glass 11A, a volume phase type diffraction grating (hologram diffraction grating) 12 and a mirror surface 11B as shown in FIG. 3 or FIG.
Is not limited to such a structure, for example,
A scale in which a diffraction grating is formed on the surface of a mirror may be used. In other words, a scale having a reflection type diffraction grating may be used.

The pitch of the diffraction grating 12 and the wavelength of the laser light source 13 are preferably about 500 nm and about 780 nm described in each of the above embodiments, but are not limited to such numerical values. Instead, appropriate numerical values may be selected as long as the configuration of the present invention can be implemented.

In the first embodiment, the non-polarizing beam splitter 15 is provided so as to be perpendicular to the scale 11, but the installation direction of the non-polarizing beam splitter 15 is arbitrary. Transmission type diffraction grating 1
It suffices if the mixed wave mixed by 4 can be branched into two waves.

In each of the above embodiments, the laser light source 1
3. The scale 11 is provided so as to be displaceable with respect to the optical systems such as the light beam branching means 21, the light beam mixing means 31, and the detectors 41A and 41B, but these optical systems are displaceable with respect to the scale 11. Or both may be displaced. In short, it is only necessary that the scale 11 and the optical system be displaced relative to each other.

[0065]

As described above, according to the present invention, the optical path of each light beam of the optical system on the light emitting side and the optical path of each light beam of the optical system on the light receiving side are arranged in different planes. Therefore, each device constituting the optical system on the light emitting side and each device constituting the optical system on the light receiving side can be installed without being affected by the mutual arrangement position, and the degree of freedom in the arrangement configuration of each device can be improved. In addition, the incident angle of each branched light beam and the diffraction angle of each first-order diffracted light can be matched to improve the quality of a detection signal and the diffraction efficiency, and use a reflection type diffraction grating as a scale. Since the optical system on the light emitting side and the optical system on the light receiving side can be arranged on the same side of the scale, there is an effect that the size of the apparatus can be reduced and the degree of freedom in mounting the scale can be improved.

In the case where a non-polarizing beam splitter for splitting a mixed wave directed toward the side opposite to the light source into two waves out of two mixed waves generated by the transmission type diffraction grating constituting the light beam mixing means is provided. Since it is possible to make the mixed wave sent to the detector a mixed wave of the light beams diffracted by the same number of times, there is an effect that the quality of the detection signal can be further improved.

Further, one of the two branched light beams branched on the transmission type diffraction grating of the light beam branching means and the polarization component having the same azimuth in each optical path of the first order diffracted light of this light beam. When a quarter-wave plate arranged so as to delay the phase of the light beam by 90 degrees is provided, the polarization directions of the two light beams collected on the transmission type diffraction grating of the light beam mixing means can be easily set to be orthogonal to each other. There is an effect that can be.

Further, when the transmission type diffraction grating constituting the light beam branching means and the transmission type diffraction grating constituting the light beam mixing means are constituted by a single transmission type diffraction grating, the apparatus can be simplified. Therefore, there is an effect that the size and cost of the apparatus can be further reduced. When the transmission diffraction grating and the scale diffraction grating have the same pitch, when the wavelength of the light source fluctuates, the optical path of the two light beams to be mixed can be prevented from being shifted. There is an effect that waves can be reliably obtained.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a first embodiment of the present invention.

FIG. 2 is a schematic perspective view illustrating an arrangement state of different surfaces (a first surface and a second surface) of the first embodiment.

FIG. 3 is a sectional view of the scale of the first embodiment.

FIG. 4 is another sectional view of the scale of the first embodiment.

FIG. 5 is a configuration diagram showing a second embodiment of the present invention.

FIG. 6 is a schematic configuration diagram showing a modification of the present invention.

FIG. 7 is a configuration diagram showing a conventional example.

[Explanation of symbols]

Reference Signs List 10, 60 Lattice interference type displacement detector 11 Scale 12 Reflection type diffraction grating 13 Laser light source 14 Transmission type diffraction grating also used as light beam splitting means and light beam mixing means 15 Non-polarizing beam splitter 21 Light beam splitting means 31 Light beam mixing means 41A, 41B Detector 51, 52 Quarter-wave plate A, B Branch light beam A1, B1 First-order diffracted light P1, P2 Diffraction point

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Tetsuro Baba 1-2-1 Sakado, Takatsu-ku, Kawasaki City, Kanagawa Prefecture Mitutoyo Co., Ltd. (56) References JP-A-4-130220 (JP, A) JP-A-2 −110319 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01B 11/00-11/30 102 G01D 5/38

Claims (6)

(57) [Claims] A scale having a reflective diffraction grating;
A light source that emits a light beam, a light beam branching unit that splits the light beam from the light source into two waves, and causes each of the branched light beams to enter two different points on the diffraction grating of the scale, and a light source that is generated by the diffraction grating of the scale. A light beam mixing means for mixing the plurality of light beams, and a grating interference type displacement detection device including a detector for converting a mixed wave mixed by the light beam mixing device into an electric signal, wherein the light beam branching means includes: A transmission type diffraction grating that splits a light beam from the light source into two waves by diffracting and transmitting the light beam, and causes each of the split light beams to enter two different points on the diffraction grating of the scale; The mixing means is disposed at the intersection of the two light beams diffracted on the diffraction grating of the scale, splits each light beam, and diffracts one light beam and the transmitted light of the other light beam. An optical path of each light beam emitted from the light source and reaching the diffraction grating of the scale via the light beam branching means; and And a light path of each light beam that is diffracted on the diffraction grating and reaches the detector via the light beam mixing means, and is arranged on the same side of the scale and in a different plane. Detection device. 2. The grating interference type displacement detecting device according to claim 1, wherein said light beam mixing means converts a mixed wave generated by said transmission type diffraction grating toward a side opposite to said light source. A grating interference type displacement detecting device comprising a non-polarizing beam splitter that splits into two waves. 3. The grating interference type displacement detecting device according to claim 1, wherein a point on the transmission type diffraction grating of the light beam splitting means for splitting a light beam from the light source and a light beam splitting at this point. In the middle of the optical path between a point on the diffraction grating of the scale where any one of the split light beams is incident, and on the diffraction grating of the scale where the one branch light beam is incident. In the middle of the optical path between the point and the point where the light beam diffracted at this point reaches the transmission type diffraction grating of the light beam mixing means, they are arranged so as to delay the phases of the polarization components of the same direction by 90 degrees. A grating interference type displacement detecting device provided with a １ ／ wavelength plate. 4. The grating interference type displacement detecting device according to claim 1, wherein the transmission type diffraction grating forming the light beam branching means and the transmission type diffraction grating forming the light beam mixing means. A grating interference type displacement detecting device, wherein the grating is constituted by one transmission type diffraction grating. 5. The grating interference type displacement detecting device according to claim 1, wherein the transmission type diffraction grating and the scale diffraction grating have the same pitch. Lattice interference displacement detector. 6. The grating interference type displacement detecting device according to claim 1, wherein an incident angle of each branched light beam incident on the diffraction grating of the scale, and each of these branched light beams is A grating interference type displacement detecting device, wherein a diffraction angle of each first-order diffracted light generated by being diffracted on a scale diffraction grating coincides with each other.