JPS60190812A - Position detector - Google Patents

Abstract

PURPOSE:To make it possible to perform highly sensitive detection of a position, by interfering light beams having the same positive and negative degrees, which are inputted to a diffraction grating vertically, thereby using an extremely small grating constant. CONSTITUTION:Light from a point light source 1 in monochrome is made to be parallel light by a collimate lens 2 and veritcally inputted to the flat surface of the grating groove of a reflecting type diffraction grating 10. Diffracted light beams R1 and R2 having positive and negative degrees, respectively, are reflecteed in the directions determined by the incident wavelengths and a grating constant (d). In this case, there are the diffracted light beams having various degrees. But herein only a set of the light beams having the same degree is noted. The diffracted light beams R1 and R2 are reflected by parallel reflecting surfaces M1 and M2 and then inputted to a beam splitter 11. The transmitted diffracted light R1 and the reflected diffracted light R2 advance in the same direction and are interfered. Then the light beams are inputted to a photoelectric element 6. By reducing the grating constant (d) to the extremely small value, the highly sensitive detection of the position can be performed.

Description

[Detailed description of the invention] [Field of application of the invention] The present invention relates to a position detector using a diffraction grating.

[Background of the invention]

Conventionally, a so-called moiré scale, which consists of two overlapping transmission gratings, has been widely used as a means of measuring linear displacement in micrometers (μm).
For example, Journal of Ph-physics
E:5 scientific instrument
972VOL5p-193-). An example of this is shown in FIG.

Light from a light source I is made into parallel light by a collimator lens 2, and is irradiated onto a main scale 3 in which grating grooves with a pitch of about 8 μm are formed. An Intex scale 4 having grating grooves with the same period as the main scale 3 is arranged to face the main scale 3, and depending on the geometric relationship between both scale grating grooves, the irradiated light can pass through or be blocked. Sometimes it happens.

The passing light is collected by a condensing lens 5, enters a photoelectric conversion element 6, and is converted into an electrical signal corresponding to the light intensity. When using a scale with a grating groove period of about 8 μm,
As the main scale 3 moves, a sinusoidal signal with one cycle of 8 μm is generated, and by counting the number of peaks of this signal, the amount of movement wJ of the king scale can be measured.

Figure @2 is an example of a case where a reflection type diffraction grating is used instead of the transmission type scale 3. The light from the light source 1 is made into parallel light by the collimator lens 2, and the light from the reflective scale 7
incident at an angle to the As a result, the light that hits the reflective part of the grating groove of the reflective scale 7 is reflected, but the light that hits the transparent part is either transmitted or absorbed, so the cross section of the reflected light beam is a stripe of light and dark. The situation is as follows. This stripe moves as the reflective scale 7 moves.

This striped reflected light travels back along the optical path it came from by combining the condensing lens 5 and the reflecting mirror 8. This backward striped reflected light moves with the movement of the reflection scale 7,
The direction of movement is reversed by the reflecting mirror 8. This light is reflected again by the reflection groove part of the reflection scale 7, and is reflected by the lens 2.
, enters the photoelectric element 6 via the half mirror 9. The intensity of light incident on the photoelectric element 6 becomes bright and dark in a sinusoidal manner as the reflection scale 7 moves, but as mentioned above, the light reflected by the reflection mirror 8 moves in the opposite direction to the reflection scale 7. The period is the pitch before the grating (7) l/
It becomes 2. In other words, the displacement sensitivity is 2 compared to that in Figure 1.
Double.

In the above-mentioned two types of moire scales, the grating groove scale is simply used as a row of bright and dark slits, and the diffraction phenomenon of the grating is not utilized. Therefore, while white light with a distance of 1 m can be used as a light source,
If the grating pitch of the scale is made smaller in order to improve the displacement sensitivity, the light diffraction phenomenon becomes impossible to ignore, and at most 5
There is a drawback that the grating pitch can only be reduced to about μIn.

Different from the above-mentioned type of moiré scale, one that utilizes the interference of diffracted light from grating groove scales is being considered (
0ptics &; 5pectroscopy Vo
L.

L3p-295-). FIG. 3 shows an example. Light from a monochromatic point light source 1 is made into parallel light by a collimator lens 2, and then obliquely enters a beam splitter 11, where it is split into two parts, a transmitted light a and a reflected light, at its splitting surface.

Each light beam obliquely enters the reflection type diffraction grating 10 and is diffracted. The direction of the reflected diffracted light is determined by the incident angle of the grating constant 41 of the diffraction grating 10 and the incident wavelength λ, and by appropriately selecting them, it is possible to diffract the reflected diffracted light in the direction of incidence. In this case, the diffracted light has a negative order.

Now, the two lights a' that have been diffracted and traced the optical path of the incident light in opposite directions
, b' are each again 2 by beam splitter 1
be divided. a' and b transmitted through the beam splitter 11
'The light passes through the lens 2 and half mirror 9 to the photoelectric element 6.
incident on . These two lights are coherent, so they interfere,
Produces brightness and darkness in light intensity. When the electric signal is displaced by a distance d/2 corresponding to 1/2 of the grating grooves of the diffraction grating 10, the electric signal generates a sine wave with one period. Since this type of device uses diffraction phenomenon, it requires a coherent light source, but the stock constant can be made small.
It is possible to obtain a highly sensitive 1a detector.

However, there are the following drawbacks in implementing the type shown in FIG. In other words, ■) working distance (the distance between the diffraction grating 10 and the beam splitter 1 in the space where objects do not collide)
If you want to take a relatively large distance (for example, about 10 mm), the distance between the two light beams irradiated onto the diffraction grating will inevitably become large, and it will be difficult to detect a fixed distance of movement. requires a longer diffraction grating.

2) The incident light from the light source is split by a beam splitter, and the transmitted light is not affected by the tilt angle of the beam splitter, but the reflected light depends on the tilt angle, so there are two reflections and diffraction from the diffraction grating lO. It is necessary to strictly align the optical axes of the beam splitter 11 and the light source luns 2, etc., so that the light interferes well, and conversely, this diffraction grating lO
If the lens moves, the optical system is likely to go awry. and,
3) The light to be interfered with each other is caused by two different diffraction gratings 10.
Since the light is diffracted by two parts, a diffraction grating with particularly uniform grating groove performance is required to obtain good coherence, and it is easily affected by dust and scratches on the grating. .

[Purpose of the invention]

The present invention provides a position detector that eliminates the above-mentioned conventional drawbacks.

explain.

The light from the monochromatic black light 'm, 1 is made into parallel light by the collimating lens 2, and is made to be incident perpendicularly to the grating groove plane of the reflection type diffraction grating 10. Then, the diffracted lights of the positive and negative orders of R1 and R2 are reflected in directions determined by the incident wavelength and the grating constant d. In this case, there are diffracted lights of many orders, but here we will focus only on the set of lights of the same order. Now, the diffracted beams ill and R2 are reflected by a reflective surface M parallel to each other.
, L, after being reflected by M2 beam splitter 1
The diffracted light L that enters and passes through j and the diffracted light R that is reflected
2 travel in the same direction, interfere with each other, and enter the optical heavy element 6. The interference is combined again by the bending point on the diffraction grating 10 and the beam splitter 11 to obtain a sinusoidal signal.

As explained above, the present invention is characterized by causing the same number of beams of light vertically incident on the diffraction grating to interfere with each other, and as a result, it is possible to eliminate the above-mentioned conventional drawbacks. Become. Zunawaji utilizes the diffraction phenomenon, so the lattice constant d is extremely small, for example d = 0.
．． It is also possible to use a material with a diameter of about 8 μm, which allows highly sensitive position detection. Further, alignment of the optical system is easy because the light is incident perpendicularly to the diffraction grating, and furthermore, by using a diffraction grating in which orthogonal grating grooves are formed, XY two-dimensional position detection becomes possible. This will be described in detail later. In FIG. 4, the basic structure of the present invention is explained using an example of a reflection type diffraction grating, but it is of course possible to use this as a transmission type diffraction grating.

FIG. 5 is a diagram illustrating an embodiment of the present invention. The light source 13 uses a laser diode with a wavelength of 830 nm, and its light is made into a parallel beam by the collimator lens 2 and enters the reflection type diffraction grating 10 perpendicularly. The lattice constant d is 1
．． 6μr71 (in the case of d, each of the positive and negative first-order diffraction lights is reflected and diffracted at an angle of about 40°, and the Porro prism l is 1%
2. Both diffracted lights are reflected in the horizontal direction by their respective Porro prisms, and are again focused on a point X2 on the diffraction grating.
and is diffracted again. Here, since polarized light 11 (polarized light &P1°P2 with 1+) which are perpendicular to each other are provided in each optical path, the 0th order diffracted light at the point X2 is blocked, while the The two diffracted lights enter the beam splitter 11 with their polarization planes orthogonal to each other.The two linearly polarized lights that have passed through this beam splitter are
The light passes through a polarizing plate P3 having a polarization angle of 50 degrees, becomes mutually coherent light, and enters the light receiving element 1]1. On the other hand, the linearly polarized light reflected by the beam splitter 1 passes through a polarizing plate P4 having a plane of polarization rotated by 90 degrees from the polarizing plate P3, and enters the light receiving element D2.

Signal SL obtained from each light receiving element 1)l, D2
, 82 are sinusoidal signals whose period is the amount of movement of the diffraction grating d/4 (20.4 μm) and whose phases are shifted by 90° from each other, as shown in FIG. 6(a). . After comparing the magnitude of this sine signal's amplitude of 11 yen to 11 cores of 100, and converting the signal into a technical signal as shown in Figure 6 (1)), the rising and falling edges of the signal are The Y-shaped pulse signal shown in FIG. 6(C) is generated. These signal processes can be performed using known methods.

Through the above processing, the pulse is shifted by the amount of movement of the diffraction grating d/16 (
This occurs every 20.1 μm), and by counting this, the amount of movement can be determined. In this embodiment, a Porro prism is used to cause the diffraction to occur twice, but this allows the traveling directions of the two diffracted lights to always match even if the diffraction grating is slightly tilted due to movement of the diffraction grating 10.
The purpose is to obtain elegant interference. Furthermore, since the beam is diffracted twice, the sensitivity is twice as high as that of the one shown in FIG. This sensitivity can be increased by causing multiple orders to interfere with each other as diffracted light. It is also obvious that the same effect can be obtained by using a keep corner or the like instead of the Porro prism.

FIG. 7 is a diagram showing an embodiment in which two-dimensional digit 1d detection is performed according to the present invention. As the diffraction grating 10', X,
A diffraction grating 10' having grooves formed perpendicularly to the Y direction (a right-angled grating) is used, and a laser beam is incident perpendicularly onto the diffraction grating 10', as in FIG. As a result, the light is reflected and diffracted in four directions perpendicular to the grating grooves, and the porroprism Rλ+,
Rx-, y+.

It is incident on Ry- and reflected. Porro prism Rx+ and RX
The light reflected by - is collected at one point X2 on the diffraction grating and is diffracted vertically again. On the other hand, the lights in the Y-axis direction coincide at point Y2.

With such an optical system, movement of the diffraction grating in the X-axis and Y-axis directions can be obtained as interference of independent diffracted lights, and two-dimensional position detection can be performed.

In addition, in the figure, 2', 11'.

13', S,', D,', S2', D2',
P3' and P4' are 2, 11, and 11, respectively, shown in Figure 5.
13. S,,Dl.

S2 + D2 + ``3 +'' 4 shows the same thing, and Px+ and Pχ- are polarizing plates arranged in the X direction, p
y+.

PY- indicates a polarizing plate arranged in the Y direction.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, it is possible to detect the position in units of 041 μm even though the distance from the moving grating is about 1 Om m, and there is no need to worry about focusing.

In addition, since two-dimensional position detection is easy, it can be combined with an XY moving table, etc., to create a measuring instrument that detects coordinates, or a system that requires precision positioning. ! It has various advantages such as being applicable to r-maki manufacturing machinery, and its effects are significant when put into practical use. Note that the present invention is not limited to the specific numerical values used in the above embodiments, and it goes without saying that they can be set as appropriate.

[Brief explanation of drawings]

Figures 1 to 3 are diagrams showing conventional position detectors, Figure 4 is a diagram explaining the basic principle of the present invention, and Figure 5 is a diagram showing the basic principle of the present invention.
6 is a diagram showing an example of the present invention, FIG. 6 is a signal waveform diagram showing an example of the signal processing, and FIG. 7 is a diagram showing an example of performing two-dimensional position detection according to the present invention. It is. In the figure, ■... point light source, 2... collimating lens,
6...Photoelectric element, lO...Diffraction grating, 11...Beams ■1 Figure F32 Figure 5 Name 11 "1'" 4.Relationship with supplementary consideration "1f" Patent applicant's name fho (510) chair, ceremony ceremony [-1ki Zifv creator agent person) 11:) ㅅ[Publication oo Tokyo Chiyo 11'' Ward Marunouchi--''
Kawa"5' (! 'j No. 1 Co., Ltd. 1" Tate Manufacturing Telephone: Tokyo 212-1111 (Major Representative) Amendment Order No. 1
Ko1i□I' It! f 4'll 60 years 3JJ26
1” Target of correction Akira 5 ill ;! ``Details of the invention 31''
11 Explanation” column/-7〉＼ Contents of correction (1) Ming #m i! The description from page 1, line 20 +41 to page 2, line 2 of x is corrected as follows. [Widely used. Public companies disclosing such technology
For example, Journal Off Fujisogsui: Scientific Inc. Instrument h197
2 Volume 5] page 93 (, 1 Journal of Phys.
j, cs tE: 5cientifj, c Ins
trument 1 972 Vol, 5. pi9
3). An example of this is shown in FIG. (2) Page 4, line 9, L1 and lines 1-0, dedicated to details]
1st generation is corrected as follows. [It is being done. For example, Optisotas and Spec 1
- Rothkopi Volume 13, Page 295 (0ptics & 5p
electronoscopy Vol, 1.3, p29
5). Figure 3 shows an example of this.

Claims (1)

[Claims] a diffraction grating having grating grooves perpendicular to the direction of movement of the diffraction grating, means for making monochromatic parallel light perpendicularly incident on the diffraction grating, and a set of diffracted lights of the same order among the diffracted lights generated by the diffraction grating. means to extract and interfere with these,
A position detector comprising means for detecting the moving position of the diffraction grating based on an electric signal obtained by photoelectrically converting the interference light.