KR20010097143A - Apparatus and its method for displacement measurement by optical process - Google Patents

Abstract

The present invention relates to a displacement measuring apparatus and method by an optical method, and more particularly, to a laser beam generated from an optical head connected to move according to the movement of an object on a substrate, and detecting a reflected laser beam with a photodetector, followed by signal processing. Apparatus and method for measuring a moving distance through

An optical head bundle 20 composed of an optical device including a substrate 7 composed of pits 1 and lands 2 having different reflectances, and a laser generator 8 for generating a laser beam on the substrate 7; Characterized in that it consists of a Michelson interferometer including a photo detector 16 for sensing the laser beam reflected from the substrate (7),

Measurements can also be made when metal objects interfere with the magnetic field and the measuring site. The measuring range is 0.1mm to several meters and the same measurement accuracy is measured over the entire measuring range regardless of the long and short measuring distance. In addition, if a mechanical device is supported, the measuring range can be extended without any deterioration.

Description

Apparatus and its method for displacement measurement by optical process

The present invention relates to an apparatus and method for measuring displacement by an optical method, and more particularly, by detecting a laser beam reflected by a photodetector by irradiating a laser beam generated from an optical head connected to move according to an object movement. An apparatus and method for measuring a moving distance through post-signal processing are disclosed.

Conventionally, a technique for measuring the position of a stationary or moving object using a linear variable differential transducer (LVDT) (US Pat. No. 5,708,298, US Pat. No. 4,982,156, US Pat. No. 4,514,689, US Pat. No. 4,467,320, US Pat. 5,767,670, etc.) have been widely used. However, the LVDT measuring device is excellent within the measuring range, but when the measuring range is out of range, the measuring accuracy is notably reduced, and when the metallic object is interfered in the vicinity after the LVDT measuring device is installed, the measuring is difficult and severe. Measurement becomes impossible. In addition, LVDT is difficult to use in the place of severe temperature change because the measurement accuracy changes severely when the surrounding temperature changes, and if there is an electromagnetic field around it, it should be effectively blocked.

Another conventional technology is a device for measuring the position of the object in accordance with the position of the core connected to a stationary or moving object in the center of the substrate after connecting a plurality of substrates having a measuring or transmitting coil in parallel (US Patent No. 4,253,079). Call, etc.) has too many signal lines to connect several boards with measuring or transmitting coils in parallel, and there is a difficulty in making a complicated connection. If there is an electromagnetic field, it must be effectively blocked.

In addition, the code track transducer (Code Track Transducer) (U.S. Patent No. 5,841,244, U.S. Patent No. 5,886,513) is composed of a Code Track Transmitter and at least one Code Track Receiver. Precise measurement is possible within the measurement range, but the measurement accuracy is degraded under the influence of surrounding electromagnetic fields.

Inductosyns (Sensors, A comprehensive Survey, Vol. 5, pp. 275-276) consists of a scale and a slider, and the slider detects movement on the scale to measure the position of a stationary or moving object. In the case of irregular mechanical movement and a lot of dust, the measurement accuracy is reduced.

The present invention has been invented to solve the above problems in the prior art, an optical method that solves the problem that measurement accuracy decreases as the measurement range increases, and the measurement is disturbed by the influence of electromagnetic fields and dust or foreign matter. It is an object of the present invention to provide a displacement measuring apparatus and method.

1 is a structural diagram of a displacement measuring apparatus according to the present invention,

2 is a cross-sectional view A-A of the substrate shown in FIG. 1;

3 is a block diagram of a Michelson interferometer,

4 is a reflectance of the laser beam on the substrate,

5A and 5B are signal diagrams detected by a photodetector,

6 is a signal processing circuit diagram for correcting mechanical error;

7 is a signal processing circuit diagram for displacement measurement;

8A and 8B are schematic views of a displacement measuring device using a Segnac interferometer,

9A and 9B illustrate an embodiment of a sensor head of a Segneck interferometer,

10 is a surface view of a rotating substrate for measuring the rotational speed and angle.

<Description of the symbols for the main parts of the drawings>

1,1a: Pit 2,2a: Land

3: polycarbonate 4: aluminum reflective layer

5: protective layer 6: laser beam

7 substrate 8 laser diode

9: diffraction grating

10: Polarizing Beam Splitter

11: polarizer lens

12: 1/4 Collimator Lens 13: Objective Lens

14: Concave Singlet Lens

15: cylindrical lens 16: photodetector

17: mechanical connecting means 18: direction of movement

19: Guide

20: Optical Head Assembly

21: detected laser beam 22: substrate protector

23, 23a: Sensor Head

24: Optical Isolator

25, 25a, 25b, 25c, 25d, 25e, 25f: Optical Fiber

26, 26a, 26b: Optical Fiber Coupler

27, 27a, 27b: Phase Modulator / Phase Delay Unit

28: Digital Signal Processing Unit

29 cylinder 30 piston

31,32: reflector 33: rotating substrate

Displacement measuring device and method according to the optical method of the present invention for achieving the above object is a substrate (7) consisting of a pit (1) and land (2) having different reflectivity, and a laser beam on the substrate (7) And a Michelson interferometer including an optical head bundle 20 composed of an optical device including a laser generating device 8 for generating the photodetector 16 for detecting a laser beam reflected from the substrate 7. do.

In addition, the present invention is an interferometer, the laser generator 8, the optical isolator 24, the optical fiber 25, the optical fiber coupler 26, the phase shifter / phase delay 27, the digital signal processor 28 and the sensor head Characterized in that it uses a Segneck interferometer consisting of (23).

In addition, the present invention is a laser generator (8), diffraction grating (9), spectrometer (10), polarizing lens (11), quarter wave plate (12), objective lens (13), concave singlet lens (14). ), A Michelson interferometer including a cylindrical lens 15 and a photo detector 16 is used.

The present invention also provides three optical fiber couplers 26, 26a and 26b, two phase shifters / phase delays 27a and 27b and two laser beams in the Segneck interferometer. The Segneck interferometer consisting of a sensor head (23a) irradiated to) is used.

In addition, according to the present invention, the sensor heads 23 and 23a are fixed to the cylinder 29, and the reflector 32 and the piston 30 to which the pit 1a and the land 2a are attached measure the movement of an object. It is characterized by.

In addition, the present invention is characterized by using a rotary substrate 32 instead of the substrate (7).

In addition, according to the present invention, the laser beam generated by the laser generator 8 passes through the diffraction grating 9, the spectrometer 10, the polarizing lens 11, the quarter-wave plate 12, and the objective lens 13. After irradiating onto the substrate 7, the laser beam reflected from the substrate 7 again returns the objective lens 13, the quarter-wave plate 12, the polarizing lens 11, and the spectroscope 10. The reflected laser beam forms an image of the laser beam on the photodetector 16 by using a Michelson interferometer passing through the concave lens 14 and the cylindrical lens 15, respectively, which is detected by the photodetector 16. After passing through the signal processor for focusing the laser beam 21, the signal processor for displacement measurement is characterized by calculating the output value with the calculator (33a), (33b), (33c).

In addition, in the present invention, the laser beam emitted from the laser generator 8 passes through the optical isolator 24, the optical fiber coupler 26, the phase shifter / phase delay 27 connected to the optical fiber 25, and the sensor head 23. After being transmitted to the substrate 1 and irradiated onto the substrate 1, the reflected laser beam is again reflected using the Segneck interferometer which exits the sensor head 23, the phase shifter 27, and the optical fiber coupler 26. A beam is detected by the photodetector 16.

Hereinafter, with reference to the accompanying drawings will be described in detail with respect to the present invention.

1 is a structural diagram of a displacement measuring apparatus according to the present invention, by connecting the optical head assembly (20, Optical Head Assembly) with the object to move together with the object to measure the displacement to the linear motion When you move along the guide (19).

In addition, the optical head bundle 20 includes a plurality of laser generators capable of generating a laser beam, and the pits 1 and Pit in which the laser beam 6 generated from the laser generator is recorded on the substrate 7. ) And land (2, Land).

FIG. 2 is a sectional view taken along line A-A of the substrate 7 shown in FIG. 1, and the fabrication method thereof is as follows.

First, a master tape containing the pit 1 is made, and the surface of the glass is flattened and dried in a clean state using soda glass. The disc of glass is defined in length according to the size of the substrate 7, that is, the measurement range to be measured, and the width w is made much larger than the wavelength of the laser beam 6.

In order to make the pit 1, a photoresist is covered by the glass plate by 110 to 120 nm. The light is modulated to fit the pit (1) in the master tape made by premastering, and the light is transmitted to the glass plate, where the lighted part is not dissolved in water, and the lighted part is dissolved in water. A glass master for making the pit 1 is manufactured.

Since the glass master is an insulator, nickel is coated on the surface to form a conductor, which is a conductor, and after the nickel plating is applied to the father, the glass master is a mother. Nickel-plated on the mother again, the separated is a stamper (Stamper), it is used to melt the polycarbonate (3, Polycarbonate) to make a liquid and then dip the substrate. An aluminum reflective layer 4 is coated on the polycarbonate 3 and a protective layer 5 which protects the aluminum reflective layer 4 is coated. Copper, gold or other metals may also be used instead of the aluminum.

Finally, after inspecting the defective article, it is completed by attaching to the substrate protector 22.

The laser beam 6 is irradiated to the pit 1 and the land 2 engraved in the completed substrate 7 so that the polycarbonate 3 in the substrate 7 acts as a kind of optical system. When the reflectance in air is 1.0, the reflectance of light of the polycarbonate 3 is 1.55. In addition, when the laser beam 6 projects from the polycarbonate 3, the laser beam 6 is reflected at a large angle from the surface. For example, an initial incident spot of the laser beam 6 reaching about 800 μm is incident. The silver shrinks to about 1.7 μm in the aluminum reflective layer, causing focus to become less susceptible to dust and scratches.

The laser beam used in the present invention may be various, but for the sake of convenience in connection with the present invention, the laser beam uses an AlGaAs laser diode having a wavelength of 780 nm close to the infrared region, wherein a polycarbonate The wavelength of the laser beam at is about 500 nm.

3 shows a schematic diagram of a Michelson interferometer.

The laser beam generated by the laser generator 8 is converted into one of the middle beams and two other small beams through a diffraction grating 9. In the present invention, not only the diffraction grating 9 but also a beam expander may be used, so that the laser beam reads the pit 1 and the land 2 engraved in the substrate 7 so as not to leave the track. It is because the width of 1) and w1 were made large.

The laser beam passing through the diffraction grating 9 passes through a polarizing beam splitter 10 and is converted into parallel light while passing through a collimator lens 11. The parallel light is converted into circularly polarized light while passing through a 1/4 wavelength plate 12 and focused on the substrate 7 through the objective lens 13.

The reflected laser beam passes through the quarter wave plate 12 again and the direction is reversed. The spectrometer 10, the concave singlet lens 14 and the cylindrical lens 15 ) Is captured by the photodetector 16 in sequence.

In FIG. 4, a path of a wavelength at which the laser beam is irradiated and reflected on the pit 1 and the land 2 of the substrate 7, respectively, and the height h2 of the pit 2 located in the substrate 1 is illustrated. Is produced so that it becomes 1/4 of the wavelength of the laser beam 6. This means that the path of the laser beam 6 irradiated to the land 2 in the substrate 7 is 1/2 of the wavelength of the laser beam 6, which is twice the height h 2 of the pit 1, so that the land ( The laser beam 6 reflected in 2) is delayed by 1/2 of the wavelength of the laser beam. Since the laser beam reflected from the land 2 is in a state in which the laser beam reflected from the pit 1 is exactly out of phase and the two lights cancel each other, the laser beam is not reflected from the pit 1. .

FIG. 5A shows the reaction in the photodetector 16 according to the distance between the objective lens 13 and the substrate 7 in three cases. When the light irradiated from the objective lens 13 to the substrate 7 is focused, the laser beam 21 sensed by the photodetector 16 becomes a circular image, and the objective lens 13 and As the distance between the substrates 7 approaches, vertically elongated images are formed. In addition, when the distance increases, a long image is formed horizontally.

FIG. 5B shows a photo according to the case where the laser beam is irradiated across the land and the pit (a), only the land is irradiated (b), the pit and the land is irradiated (c), and only the pit is irradiated (d) The sensed response at detector 16 is shown. In conclusion, the laser beam reflected from the pit 1 and the land 2 engraved in the substrate 7 is not reflected from the pit 1 but is reflected from the land 2, so that the pit 1 and the land 2 are reflected. ) Is easy to distinguish, and the displacement can be measured using three different signals illustrated in FIG. 5B.

In addition, the width t of the pit 1 causes the diameter d of the laser beam 6 to have the same size when the laser beam 6 is accurately focused between the objective lens 13 and the substrate 7, and the pit and the pit The substrate 7 is manufactured so that the interval between them is equal to the width t of the pit.

By examining the changing state of the signal, it is possible to know whether the optical head bundle 20 moves from the bottom to the top of the substrate 7 or from the top to the bottom. More specifically, the photodetector 16 of FIG. When the pattern of the detected signal changes from (a) → (b) → (c) → (d), it moves from the bottom to the top of the substrate 7 shown in FIG. 5b, and vice versa. C) → (b) → (a) is to move from the top to the bottom of the substrate (7).

Displacement measuring apparatus according to the optical method of the present invention is a signal processing unit composed of the adder and the subtractor shown in Figure 6 when the focus between the objective lens 13 and the substrate 7 is out of focus due to some errors in manufacturing To adjust the focus of the laser beam due to mechanical errors. In addition, the signal processor shown in FIG. 7 may be used to increase the measurement accuracy.

8A and 8B show a displacement measuring apparatus and a method using a Sagnac interferometer. FIG. 8A uses one optical fiber coupler and one laser beam irradiated onto a substrate, while FIG. 8B shows three optical fibers. It is a device that uses a coupler and measures displacement with two laser beams.

First, referring to FIG. 8A, the laser beam generated by the laser generator 8 is split into two laser beams while passing through the optical fiber 25 through the optical fiber 25 through the optical isolator 24. The optical isolator 24 may not be used if necessary. In addition, the amount of light to be diverted may vary depending on the need, and mainly split to 50:50 using the 3dB optical fiber coupler 26. The laser beam that is moved along the branched optical fiber is reflected by the reflector 31 and passes through the optical fiber coupler 26 to be sent to the photodetector 16. On the other hand, the laser beam branched to the other optical fiber is irradiated to the pit (1) or land (2) engraved on the substrate 7 through the sensor head 23 through the phase shifter / phase delay unit 27, and then reflected And is sent to the photodetector 16 through the optical fiber coupler 26.

The phase shifter / phase delay unit 27 is irrelevant in the case where the phase shifter / phase delay unit 27 is installed at another position as necessary or for convenience of manufacture.

Three optical fiber couplers are used to measure the accuracy more precisely. As shown in FIG. 8B, the laser beam emitted from the laser generator 8 passes through the optical isolator 24 and through the optical fiber 25 through the optical fiber coupler 26. Is delivered. Through the two optical fibers 25a and 25b branched through the optical fiber coupler 26, the two optical fibers coupler 26a and 26b respectively branch back to two optical fibers. One of the optical fibers branched from the optical fiber coupler 26a is connected to the reflector 31a and the other optical fiber is connected to the phase shifter / phase delay 27a. In addition, the optical fiber branched from the optical fiber coupler 26b is also connected to the reflector 31b, and the other optical fiber is connected to the phase shifter / phase delay 27b, and then the phase shifters 27a and 27b. ) Is connected to the sensor head 23a by the optical fibers 25a and 25d. When two laser beams irradiated through the sensor head 23a are reflected on the substrate 7 and reach the optical fiber couplers 26a and 26b through the connected optical fibers, the optical fibers 25e and 25f The reflected laser beam containing the information of the substrate 7 is sent to the photo detector 16 to be sensed, and then the displacement is measured through the digital signal processor 28. In the method using the three optical fiber couplers 26, 26a, and 26b, two different photodetectors are used to sense the movement of the sensor head and to process them in the digital signal processor 28. can do.

Also, in the above method, when the laser beam is irradiated to the substrate 7 through the sensor head with the optical fibers 25c and 25d, the two laser beams are arranged so as not to be parallel to each other, thereby improving the measurement accuracy by about 2 times. have.

The displacement measuring method using the Segneck interferometer shown in FIGS. 8A and 8B is a method of measuring displacement of a stationary or moving object while moving the sensor heads 23 and 23a in parallel with the substrate 7. Similar or equivalent to the method using a kelson interferometer. Therefore, the laser beam detected by the photodetector 16 is the same as that of FIG. 5B, and a method of measuring displacement using the signals will be described.

As illustrated in FIG. 7, three different values are output as a-b, a-d, and c-b from the photodetector 16 through the calculators 33a, 33b, and 33c. If the value output from the calculator 33a is zero and a or b is greater than zero, the laser beam is placed on the land (Fig. 5B (b)). If a or b is zero, the laser beam is applied to the pit. (D) of FIG. 5B).

In other words, if the output value in the calculator 33a is five zeros and a or b is greater than zero at the start of the measurement and the fifth output value is also greater than zero, the optical head bundle 20 of the Michelson interferometer Since the sensor head 23 of the Segneck interferometer has passed through the land 2 three times and the pit 1 twice, the distance that the optical head bundle 20 or the sensor head 23 has moved is the pit 1 5t, which is five times the thickness of t). If t is 5 μm, the object has moved 25 μm.

In addition, if the value output from the operator 33a is five times zero and a or b was zero at the beginning, and the fifth is also a or b zero, the optical head bundle 20 or the sensor head 23 is filled with feet ( Beginning at 1), the pit 1 has been passed through three times and the land 2 has been passed through twice. Accordingly, if t is 5 μm, which is 5 times the thickness t of the pit 1, that is, 5 t, the optical head bundle 20 or the sensor head 23 has moved 25 μm.

If the value output from the operator 33a is five times zero, a or b was zero at the start, and a or b is zero at the fifth time, and then the optical head bundle 20 or the sensor head 23 is stopped. In this case, if the output signal of the calculator 33b is negative and a is zero, the laser beam lies in the center of the pit 1 and the land 2 as shown in Fig. 5B. And the distance moved was 5t, which is five times the thickness t of the pit 1, so that the laser beam was placed in the middle of the pit and the land, so that 0.5t was added and moved by 5.5t.

In order to increase the measurement accuracy, the output values of the calculators 33a, 33b, and 33c of FIG. 7 may be used in combination. Based on the three output values, it is possible to precisely measure the desired signal and the linear moving distance of the stationary or moving object, and the precise degree is determined between the wavelength of the laser beam and the width t of the pit 1 and between the pit and the pit. It depends on the distance. If a blue laser beam having a wavelength of 0.5 μm is used, the width of the pit 1 and the distance between the pit and the pit can be manufactured to 0.5 μm, and the measurement accuracy will be 0.25 μm or less. This represents a precision of 0.25m for a billion.

The method using the Michelson interferometer has the disadvantage that the whole optical system is mounted on the optical head bundle 20 and moves together, whereas the method using the Segneck interferometer connects several optical fibers to the sensor heads 23 and 23a. Since the sensor heads 23 and 23a are freely moved, they can be mounted at the convenience of the measurer. Therefore, the length of the optical fiber needs to have sufficient margin.

Next, as another embodiment of the Segneck interferometer in FIGS. 9A and 9B, the piston 30 with the reflector plate 32 or the piston with the pit and land in the state in which the sensor head is fixed to the cylinder 29 is shown. 30 shows a device for measuring a small displacement as it moves.

9A shows the displacement of the sensor head fixed to the cylinder 29 with one optical fiber, while FIG. 9B shows that the sensor head fixed to the cylinder 29 has two optical fibers 25c and 25d. ) And the displacement is measured, where the method shown in FIG. 9B can increase the measurement accuracy by about twice as compared to the method using FIG. 9A since the height of the pit is made 1/4 of the laser beam wavelength. have. That is, in the method of measuring displacement by connecting one optical fiber, the measurement accuracy of 1/2 of the laser light wavelength can be obtained, while in the method of measuring displacement by connecting two optical fibers, measuring up to 1/4 of the laser beam wavelength You can get a degree.

Fig. 10 is a surface view of the rotating substrate for measuring the rotational speed and the angle, which is formed in the compact disk-type rotating substrate 33 after making a compact disk-type rotating substrate 33 and connecting it with one side of the rotating body. By reading the signal reflected by the laser beam 6 on the pit 33a and the land 33b, the rotation speed and rotation angle of the rotating body can be precisely measured by the method described above.

As described in detail above, if the displacement measuring apparatus and method according to the optical method of the present invention is applied, it is possible to measure even when the metal object interferes in the place and the measurement site where the magnetic field is generated, the measuring range is 0.1mm The same measurement accuracy is achieved over the entire measurement range up to several meters and regardless of the long and short measuring distances. In addition, if a mechanical device is supported, the measuring range can be extended without any deterioration.

Claims (8)

In a device for measuring displacement of a stationary or moving object, An optical head bundle 20 composed of an optical device including a substrate 7 composed of pits 1 and lands 2 having different reflectances, and a laser generator 8 for generating a laser beam on the substrate 7; Displacement measuring device by an optical method, characterized in that it comprises an interference means including a photo detector (16) for detecting the laser beam reflected from the substrate (7). The method of claim 1, wherein the interference means comprises: a laser generator (8), an optical isolator (24), an optical fiber (25), an optical fiber coupler (26), a phase shifter / phase delay (27), and a digital signal processor (28). Displacement measuring device by the optical method, characterized in that using a segment neck interferometer consisting of a sensor head (23). The method according to claim 1, wherein the interference means includes a laser generator (8), a diffraction grating (9), a spectrometer (10), a polarization lens (11), a quarter-wave plate (12), an objective lens (13), and a concave. An apparatus for measuring displacement by an optical method, characterized by using a Michelson interferometer including a type singlet lens (14), a cylindrical lens (15), and a photodetector (16). 3. The Segneck interferometer according to claim 2, wherein three optical fiber couplers 26, 26a, 26b, two phase shifters / phase delays 27a, 27b, and two laser beams An apparatus for measuring displacement by an optical method, characterized in that the segment neck interferometer composed of the sensor head (23a) irradiated to (7) is used. The method according to claim 2 or 4, wherein the sensor heads (23) and (23a) are fixed to the cylinder (29) and the reflector (32) and the piston (30) to which the pit (1a) and the land (2a) are attached are moved. Displacement measuring device by an optical method, characterized in that for measuring the movement of the object. The rotation displacement measuring apparatus according to any one of claims 1 to 5, wherein a rotating substrate (33) is used as the substrate (7). In measuring the displacement of a stationary or moving object, The laser beam generated by the laser generator 8 passes through the diffraction grating 9, the spectrometer 10, the polarizing lens 11, the quarter-wave plate 12, and the objective lens 13 in order, and then the substrate 7. And the laser beam reflected from the substrate 7 passes through the objective lens 13, the quarter-wave plate 12, the polarizing lens 11, and the spectroscope 10, respectively. 14) and a signal processing unit for focusing the laser beam 21 detected by the photodetector 16 by the Michelson interferometer passing through the cylindrical lens 15, and detected by the photodetector 16. After passing through, the displacement measuring method by the optical method, characterized in that for calculating the output value by the calculator (33a), (33b), (33c) in the signal processing unit for displacement measurement. The laser beam of claim 7, wherein the laser beam emitted from the laser generator (8) passes through an optical isolator (24), an optical fiber coupler (26), and a phase shifter / phase delay (27) connected to the optical fiber (25). After being transmitted to the head 23 and irradiated onto the substrate 1, the reflected laser beam is again returned from the sensor head 23, the phase shifter / phase delay device 27, and the optical fiber coupler 26. Using the optical method, characterized in that the reflected laser beam is detected by the photodetector (16).