JPH0331703A - Fixed position detector - Google Patents

Abstract

PURPOSE:To simplify the specific position of a relative mobile object and to stably and highly accurately detect the fixed position by utilizing a change in the optical length of interference light attended with the movement of the relative mobile object. CONSTITUTION:A luminous flux with weak interference projected from a light source is converted into an approximate parallel beam and bisected with demultiplexer 2. One of the luminous flux is made incident upon a reflector 4 on a fixed body 4a through an optical path L0 and the other is made incident upon a reflector 3 on the relative mobile object 8 through an optical path L1. The reflected luminous flux of respective reflectors 3, 4 are superposed by the demultiplexer 2 and optically modulated based upon a difference between the optical lengths of respective optical paths L0, L1 to form interference light and the interference light is made incident upon a photodetector 5. An output signal S from the photodetector 5 is compared with a previously set regulation level by a comparator 6, and when the mobile object 8 reaches a fixed position, a fixed position detecting signal SP is generated. Consequently, the fixed position can be highly accurately detected.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a fixed position detection device, and in particular, detects whether a moving object to be detected has passed a specific position by utilizing the coherence and polarization characteristics of light. 2, and when it passes, a fixed position detection signal is generated.

(Conventional technology) Highly accurate positioning and detection of objects has traditionally been used in NC machine tools, snail robots, and semiconductor manufacturing equipment.
There is a need for a fixed position sensing device that can This fixed position detection device includes, for example, a device that automatically reads the position of an object using light, magnetism, or the like.

If accuracy on the order of microns or nanometers is required, displacement can be achieved using a laser interferometer that uses light interference or an encoder that uses diffracted light interference! 11 is used.

Generally, in measurements in which the absolute position of an object is determined by integrating the amount of displacement of the object, it is necessary to accurately determine the origin position (or fixed position). 2. Description of the Related Art Conventionally, a number of fixed position detection devices have been proposed that detect the origin position of a moving object.

6 to 9 are schematic diagrams of main parts of conventional fixed position detection devices. FIG. 6(A) shows the presence or absence of light reflected by the reflective pattern 63 by focusing the light beam from the light source 61 onto the passage track of a minute reflective pattern 63 provided on an object 64 via a half mirror 62. By detecting the presence or absence of reflected light of -1-7 above the specified level vc as shown in (B) by the detection means 65, a constant (i7 position detection signal) is generated.

FIG. 7(A) shows a minute reflection pattern 6 provided on an object 64.
A half mirror transmits the light beam from the light source 61 to the passing track of 3.
62, and the timing of the occurrence of reflected light is determined by U.
Two types of reflected light A and No. 1 shifted by 1 and 2 are obtained by two light receiving means 71 and 72, and as shown in FIG. Detects the Z condition and obtains a fixed position detection signal.

FIG. 8(A) shows that the detecting means 65 detects a steep change in the light flux of the light beam from the light source 61 depending on the overlapping condition of two random grid array plates 81 and 82, that is, FIG. 8(B> As shown in , transmitted light 610) -Ij- below the specified level VC
Fixed position detection A and ζ are obtained by detecting nothing.

(Problems to be Solved by the Invention) In order to obtain a highly accurate and reproducible fixed position signal regarding the fixed position of an object in the apparatus shown in FIG. 6(A), a steep waveform is required. ], and the focused beam diameter must be set within the range of several microns to nanometers.

Generally, even when laser light is focused by a condensing lens, the diameter of the focused beam is limited to about 1 μm. Furthermore, even if a luminous flux of 1 μm or less is obtained, the optical system will have an extremely shallow depth of focus, so the configuration must be such that the distance between the reflection pattern and the condensing lens is always within the depth of focus. Such a configuration is difficult and has problems such as requiring a complicated mechanical mechanism and servo device.

The device shown in Fig. 7 (A) uses the coincidence of the two signal levels by shifting the generation timing of the reflected light, and does not require a steep wavelength as much as the device shown in Fig. 6 (A). In order to achieve reproducibility of object position with accuracy of
There is a problem similar to that of the device shown in FIG. 6(A).

The device shown in FIG.
There is a problem in that fine random pitch grating plates are arranged very close to each other in order to maintain the spacing, and a mechanism is required to maintain the spacing stably, which is very difficult to implement.

The present invention detects a specific position of a relatively moving object stably and with high precision by utilizing the change in the optical path length of the optical beam that accompanies the movement of a relatively moving object, and generates a fixed position detection signal. - It is an object of the present invention to provide a fixed position detection device that can perform

(Means for Solving the Problems) The fixed position detection device of the present invention splits a weak coherent beam into two beams using a beam splitter, and one of the beams is reflected by a relatively moving object. The other light beam is incident on a fixed object or a reflector RC different from the reflector RV provided on the relatively moving object, and the two reflected light beams from these reflectors RV and RC are transmitted to the light splitter. The signal level obtained from the light receiving element is compared with a predetermined level set in advance by the determining means, and the signal generating circuit generates a fixed position detection signal based on the determination result from the determining means. It is characterized by the fact that it has occurred.

In addition, when utilizing polarization characteristics in the present invention,
A light beam with weak coherence is made into a light beam with predetermined polarization characteristics, and the first light splitter splits it into two light beams. One of the light beams is fixed to a reflector RV provided on a relatively moving object, and the other light beam is fixed. The light is incident on a different reflector RC from the reflector RV provided on the object or the relatively moving object, and these reflectors RV
, the two reflected light beams from the RC are converted into linearly polarized light whose polarization planes are perpendicular to each other, and are superimposed by the first light splitter, and then passed through a phase plate to polarize the light beams according to the optical path length difference between the two reflected light beams. After converting into substantially linearly polarized light with a rotating surface, it is split into two light beams by a second light splitter, and the two light beams are passed through polarizing elements with different polarization azimuths, and are incident on corresponding light receiving elements. , the determining means determines whether or not the two signal levels obtained from the two light receiving elements match, and whether or not at least one of the two signal levels has reached a preset specified level. Based on the determination result by the determining means, a signal generating circuit generates a fixed position detection signal.

(Embodiment) FIG. 1(A) is a schematic diagram of a main part of a first embodiment of the present invention. In the figure, a weakly coherent light beam emitted from a light source 1, such as a light emitting diode, is made into substantially parallel light by a collimator lens 1a, and is incident on a light splitter 2, where it is split into two light beams. The negative beam of these is the optical path. The other light beam passes through the optical path L1 and is made to enter the reflector 3 provided on the relatively moving object 8. The two reflected light beams reflected by each reflector 3.4 are superimposed by the light splitter 2 to form two optical paths. , Ll, the light is modulated based on the optical path length difference, and interference light is formed to be incident on the light receiving element 5.

Then, the output signal S from the light receiving means 5 is compared with a preset standard level (judgment level) Z by the comparator 6 constituting the determining means, and it is determined whether it exceeds the standard level 2 or matches the standard level 2. Is going. When it is determined that the output signal S exceeds or matches the specified level Z, it is assumed that the object 8 has reached the home position, and the signal generating circuit 7 generates the home position detection signal sp.

Next, details of the discrimination method by the discrimination means in this embodiment will be explained.

The weakly coherent light beam emitted from the light source 1 according to this embodiment has an emission spectrum that is similar to the oscillation center wavelength (for example, λ=) of a GaP-based visible light emitting diode, as shown in FIG. 1(B). 700nm)λ. Wide wavelength band＠
(for example, Δλ=100 nm), and there are two optical paths at this time. .

This refers to a light beam in which an interference signal is obtained only when the optical path length difference X of L is around zero.

Figure 1(C) shows the two optical paths at this time.

FIG. 7 is an explanatory diagram when interference occurs only when the optical path length difference X of Ll is around zero. As shown in the figure, the optical path length difference X is the center wavelength λ of the radiation spectrum of the light source. A peak occurs at a position that is an integral multiple of , and the peak becomes smaller as the optical path length difference X becomes larger.

The present invention makes use of such optical properties, and for example, as shown in FIG. 1(D), the first peak value P1 and the second peak value P1 of the interference light are
The first peak value P2 is determined by the determining means, and the first peak value P2 is determined by the determining means.
The determination level (prescribed level) value Z is set between the values P1 and 22 so that only 1 is detected by the discriminating means.

When the signal level generated from the light receiving element 5 exceeds or matches the determination level (prescribed level) Z, it is assumed that the object 8 has reached the home position, and the signal generation circuit 7 generates the home position signal sp. There is. In this example, the position that matches the determination level Z is 2 as shown in FIG. 1(D).
There are several locations, so I try to use only one of them.

In this embodiment, the output signal from the light receiving element 5 shown in FIG. 1(A) is passed through the comparator 5, and only while the signal exceeds the determination level Z, the signal generation circuit 7 outputs a Hi level signal SP.

U of the rectangular pulse signal which is the output signal SP at this time)
By detecting only the rise or fall of x, the fixed position (original position) of an object moving in a specific direction is detected with high precision.

Incidentally, at this time, a circuit for extracting only the rising edge or rising edge of the rectangular pulse signal may be added to generate the fixed position detection signal.

In addition, in the actual R'6 example, the light source has a center wavelength λ=5
Half-value wavelength width Δλ = 80-150nm at 50-800nm
It is preferable to use a luminous flux of

FIG. 2 is a schematic diagram of main parts of a second embodiment of the present invention. In the figure, a coherent light beam emitted from a light source 1 such as a light emitting diode is converted into substantially parallel light by a collimator lens 1a, and then converted into linearly polarized light at a 45° orientation via a polarizing element 10 at a 45° orientation. The light is made incident on the splitter 11 and split into two linearly polarized lights p, , s, which are orthogonal to each other. Of these, the light beam P1 that has passed through the polarizing beam splitter 11 is turned into a circularly polarized light via a quarter-wave plate 13, and then the optical path is made. The light passes through and is incident on a reflector 4 provided on a fixed object 4a.

Then, the light beam reflected by the reflector 4 is returned to the 1/4 wavelength plate 13.
The light is passed through to become linearly polarized light S2 orthogonal to the initial light, reflected by the polarizing beam splitter 11, and guided to the quarter-wave plate 14.

Also, the luminous flux S reflected by the polarizing beam splitter 11 is 1
The light is made into circularly polarized light via the /4 wavelength plate 12, and is made to pass through the optical path L1 and enter the reflector 3 provided on the relatively moving object 8. Then, the light beam reflected by the reflector 3 is transferred to the 1/4 wavelength plate 12 again.
The polarized light P2 is converted into linearly polarized light P2 orthogonal to the initial polarized light, and the light is guided to the quarter-wave plate 14 through the polarizing beam splitter 11.

The above two luminous fluxes p2. s2 are linearly polarized lights whose polarization directions are orthogonal to each other, and the optical path length of the light beams changes with the movement of the relatively moving object 8, and as a result, their mutual phases are continuously shifted. Light path. When the optical path lengths of both P2 and P2.
The phase of S2 also matched, and the light beam that passed through the quarter-wave plate 14 became linearly polarized light with a 45° azimuth as shown in FIGS. When the light beam passes through a polarizing element (polarizing plate, etc.) oriented at 45°, a wave signal (periodic signal) with a peak at every even multiple of the phase difference φ1 - φ2 or π between the two beams is generated from the light receiving element. can get.

In the k embodiment, as shown in FIG. 2(C), the direction of the combined linearly polarized light wave changes depending on the phase difference φ1-φ2 between the two light beams, so adjusting the direction of the polarizing element 10 changes the polarization signal. It is possible to shift the timing of the peak.

Now, as the optical path length of the optical path L1 gradually increases and the phase φ2 shifts as shown in FIG. 2(C), the combined linearly polarized light waves rotate counterclockwise. Therefore, as shown in FIG. 1(D), a polarizing plate 16 is placed on one side of the light beam divided into two by the non-polarizing beam splitter 15 so that the polarization angle is 225 degrees, and a polarizing plate 17 is placed on the other side to polarize the beam. Arrange so that the orientation is 67.5°. Then, the peak of the interference signal generated by passing through the polarizing plate 16 is shifted in phase by 1/4 period from the peak of the interference signal generated by passing through the polarizing plate 17, and two types of combined signals are obtained. The peaks of these interference signals become lower as the optical path length difference increases, as shown in FIG. 2(B).

Therefore, in this embodiment, the interference signal of the light-receiving element 5b is generated d later than the interference signal of the light-receiving element 5a, and where the signal levels of both coincide, the phase shift of the two light beams is # (or an even multiple of π).
Or wavelength. Since it is an integral multiple of /2, only the intersection point where the phase shift of the two light beams becomes zero is detected, and at this time, the signal generating circuit 7 and the AND circuit 9 are used to generate a fixed position detection signal.

Therefore, in this embodiment, as shown in FIG. 2(B), the signal values Z and Z' are set so that the signal value Z at the intersection of the first peak and the signal value Z' at the intersection of the second peak can be distinguished. A determination level VC is provided between the two signals, and the AND circuit 9 is used to generate a fixed position detection signal only when the two signal levels match and the signal level 3 is equal to or higher than the signal value VC. I have to. In this embodiment, when the light receiving elements 5a and 5b pass through the comparators 6a and 6b, they are inverted at every intersection, so a pulse is generated at the moment when the sum signal of the light receiving elements 5a and 5b is equal to or greater than the signal value 2vc and an inverted signal is generated. A circuit arrangement is added to generate the home position detection signal.

In this embodiment, the fixed position detection signal is generated at exactly one location, and in principle it does not depend on the moving direction of the relatively moving object, so it is possible to generate a very highly accurate fixed position detection signal.

2nd (E), (F), and (G) are explanatory diagrams of interference signals obtained from the light receiving elements 5a and 5b when the polarization directions of the polarizing elements 16 and 17 are changed in this embodiment.

When the polarization direction between the two polarizing elements 16 and 17 is changed from 45' to 1350, the entire interference signal is reversed and the bottom becomes the bottom, as shown in FIG. Therefore, the determination level is set to signal value 2', the condition that the signal value is below Z' is given, and the signal value Z at the intersection at this time is detected.

Generally, when the polarization direction between the two polarizing elements 16 and 17 is changed, the optical path length difference is λ. It comes off from a position that is an integer multiple of . In that case, since the signal values Z and Z' are close to each other, it is necessary to set the range so that the signal values Z and Z' can be sufficiently distinguished.

Furthermore, when the angle difference between the two polarizing elements 16 and 17 is made smaller than 45 degrees, the waveforms of the two interference signals approach each other as shown in FIG. On the other hand, if it is larger than 45°, it becomes 2
The waveforms of the two interference signals are separated and the position of the signal value Z at the intersection is 0.
5, and it becomes difficult to distinguish it from the signal value Z'.

In this embodiment, in either case, the polarizing element 16.
The purpose of the present invention can be achieved by determining the mutual polarization angle difference and polarization direction such that the signal value 2 at the first intersection point and the signal value Z' at the second intersection point can be separated and distinguished. can be achieved.

Third. 4th. FIG. 5 shows the 3rd and 4th sections of the present invention, respectively. It is a principal part schematic diagram of a part of 5th Example.

In the third embodiment shown in FIG. 7J3, the reflector 4 provided on the fixed object 4a in the embodiment of FIG. .

The optical path lengths of L and L are configured to change in opposite directions as the moving object moves.

1st. Compared to the configuration of the embodiment shown in FIG. 2, this embodiment has the advantage that the amount of change in the optical path length difference per unit movement, that is, the sensitivity is doubled, and the fixed position detection accuracy is doubled. The other configurations are the same as those in the first or second embodiment.

A fourth embodiment shown in FIG. 4 differs from the embodiment shown in FIG. 3 in that the reflecting surfaces 3 and 4 are tilted at an angle θ with respect to the moving direction of the relatively moving object 8. This makes the entire device more compact.

In this embodiment, when the angle θ is set to 45', for example, both reflectors 3.4 as shown in FIGS.
is placed on the moving object 8, the first. Compared to the second embodiment, each sensitivity is 1/F7, so the sensitivity is 2/g=1'X times as a whole.

The fifth embodiment shown in FIG. 5 is a so-called "cat's eye" in which the directions of the incident optical path and the exit optical path are completely equal by combining convex lenses and mirrors as the reflectors 3 and 4 in the fourth embodiment shown in FIG. 4(A). (A) shows mirrors 5 at the focal positions of lenses 51 and 52.
3.54 is arranged, the same figure (B) shows a reflective film 57.54 on the bottom surface of an edge imaging type gradient index lens 55.56.
58 is placed as a reflector.

When these optical systems are used, stripes due to tilt caused by deviations in the reflection direction between the reflectors 3.4 do not occur, so the amplitude of the bright and dark signals of the interference light detected by the light receiving elements 5a and 5b can be maintained in a good condition. .

Further, even when the optical path length is long and the optical path length difference is close to zero, there is little risk that the beam will deviate from the light receiving elements 5a, 5b, and the interference between two beams can be easily and stably performed.

Incidentally, the optical reflector of this embodiment can be used as a reflector in other embodiments.

(Effects of the Invention) According to the present invention, a so-called Michelson interferometer is constructed using a light emitting diode or the like as a light source that emits a light beam having a weak interpolation, and the optical path length of the two light beams is changed as the moving object moves. The interference signals are arranged so that the difference changes, and it is determined that the intensity of the interference signal exceeds an appropriate specified level (discrimination level), or in addition, two types of interference signals that are out of phase with each other are generated, and the level of both signals is changed. By defining a coincidence as a fixed position (origin, zero point) and generating a fixed position detection signal, it is easier and more stable than conventional fixed position detection devices, that is, the positional relationship can be changed to some extent. It is possible to generate a fixed position detection signal even if there is a deviation, and it is possible to detect the fixed position with high accuracy.The simple task of attaching a reflector to the object to be detected is enough to form a fine pattern of micron size. Or, 2
It is possible to achieve a fixed position detection device that does not require much trouble such as preparing and accurately mounting two locks.

[Brief explanation of drawings]

FIG. 1(A) is a schematic diagram of a main part of a first embodiment of the present invention. FIG. 1(B) is an explanatory diagram of the radiation spectrum of the light source in FIG. 1, FIG. 1(Ill), (D) is an explanatory diagram of the interference signal, and FIG. A schematic diagram of the main parts of the example,
FIG. 2(B) is an explanatory diagram of the two interference signals in FIG. 2(A),
Figure 2 (C) is an explanatory diagram for synthesizing linearly polarized light polarized in a predetermined direction in Figure 2 (A), and Figure 2 (D) is
) is an explanatory diagram of generating two interference lights in Figure 2 (
E), (F), and (G) are explanatory diagrams of two interference lights, 3rd. 4th. FIG. 5 shows the third embodiment of the present invention. 4th. Fifth
A schematic diagram of a part of the main part of the embodiment, 6th. 7th. FIG. 8 is an explanatory diagram of each conventional fixed position detection device. In the figure, 1 is a light source, 1a is a collimator lens, 2.15
is a light splitter, 3 and 4 are reflectors, 4a is a fixed object, 5
．． 5b, 5b are light receiving elements, 8 is a relatively moving object, 6, 6a
, 6b, 6c are comparators, 7 is a signal generation circuit, 9 is an AND
In the circuit, 10.1617 is a polarizing element, 11 is a 1-optical beam splitter, and 2 13.14 is a 1/4 wavelength plate. Figure (C)

Claims (2)

[Claims] (1) A light beam with weak coherence is split into two light beams by a light splitter, one of which is placed on a reflector RV placed on a relatively moving object, and the other beam is placed on a fixed object or the relatively moving object. The two reflected light beams from the reflectors RV and RC are superimposed by the light splitter and are made to enter the light receiving element, and the signal obtained from the light receiving element is A fixed position detection device characterized in that a level is compared with a predetermined level set in advance by a discriminating means, and a fixed position detection signal is generated from a signal generating circuit based on the determination result from the discriminating means. (2) A light beam with weak coherence is made into a light beam having a predetermined polarization characteristic, is split into two light beams by the first light splitter, and one of the light beams is sent to a reflector RV provided on a relatively moving object, and the other is The light flux is made incident on a reflector RC different from the reflector RV provided on a fixed object or the relatively moving object, and the two reflected light fluxes from these reflectors RV and RC are converted into linearly polarized light whose polarization planes are orthogonal to each other. After being superimposed by the first beam splitter, the two reflected beams are passed through a phase plate and converted into substantially linearly polarized light whose plane of polarization rotates according to the optical path length difference between the two reflected beams. The two light beams are split into two light beams, passed through polarizing elements with different polarization azimuths, and made incident on the corresponding light receiving elements. Check whether the two signal levels obtained from the two light receiving elements match. and whether or not at least one of the two signal levels has reached a predetermined level is determined by a determining means, and the signal generating circuit detects the fixed position based on the determination result by the determining means. A fixed position detection device characterized by generating a signal.