WO2015122619A1

WO2015122619A1 - Distance measurement system using tunable laser and distance modulation and distance measurement method using same

Info

Publication number: WO2015122619A1
Application number: PCT/KR2014/012836
Authority: WO
Inventors: 김병기
Original assignee: 한국기술교육대학교 산학협력단
Priority date: 2014-02-13
Filing date: 2014-12-24
Publication date: 2015-08-20
Also published as: CN106164699A; KR20150095388A; CN106164699B; KR101606838B1

Abstract

Disclosed are a distance measurement system using a tunable laser and distance modulation and a distance measurement method using the same, wherein the distance measurement system comprises a laser oscillation part, a diffraction guide, a measurement unit, and a measurement part. The laser oscillation part generates continuous light having different wavelengths. The diffraction guide is disposed to be spaced a predetermined distance apart from the laser oscillation part. The measurement unit includes a measured object reciprocating between a first location spaced a first distance apart from the diffraction guide and a second location spaced a second distance apart from the diffraction guide. The measurement part receives coherent light between the measurement unit and the diffraction guide according to the occurrence of the continuous light.

Description

Distance measuring system using tunable laser and distance modulation and distance measuring method using same

The present invention relates to a distance measuring system using a laser and a distance modulation and a distance measuring method using the same, and more particularly to a distance measuring system using a tunable laser and a sensor distance modulation to improve the accuracy and a distance measuring method using the same It is about.

In general, a number of techniques have been disclosed for measuring the distance using a coherent light source by making an interferometer using a diffraction grating, a beam splitter, and a reference mirror. For example, a conventional Michelson interferometer may be mentioned. In this case, the half-wave precision of the light source is related to the measurement error because the magnitude of the light due to the interference between the reference and the two light beams transmitted from the measurement object is changed to the half-wave periodic function.

Therefore, in the conventional measuring method, when the moving distance of the workpiece is shortened, the measurement error is relatively increased, which causes a large number of problems in the accuracy of the measurement.

On the other hand, in relation to distance measurement using a tunable laser, Korean Patent Application No. 2012-0003401 discloses a technique using a tunable laser and applying a frequency scanning method while controlling a wavelength plate of an interferometer in an interferometer and an optical device using the same. Doing. In addition, Korean Patent Application No. 10-2006-0035199 discloses a technology in which the distance to be measured is easily calculated based on only the starting point and the target point to be measured when measuring the electronic distance using a laser at any position. Doing.

As described above, various techniques have been developed regarding a method for measuring a distance to a target using a tunable laser. However, when the measured object is repeatedly moved in a predetermined section, the tunable laser can measure the measurement more precisely. The technology has not been developed so far, and the need for technology to improve the accuracy of the measurement is required.

Accordingly, the technical problem of the present invention was conceived in this respect, and an object of the present invention relates to a distance measuring system capable of measuring the moving distance of a workpiece more precisely by using a tunable laser and sensor distance modulation.

In addition, another object of the present invention relates to a distance measuring method using a tunable laser and sensor distance modulation.

Distance measuring system using a laser according to an embodiment for realizing the object of the present invention includes a laser oscillator, a diffraction guide, a measuring unit and a measuring unit. The laser oscillator generates continuous light having different wavelengths. The diffraction guide is disposed to be spaced apart from the laser oscillation part by a predetermined distance. The measuring unit includes a measuring object reciprocating between a first position spaced by a first distance from the diffraction guide and a second position spaced by a second distance from the diffraction guide. The measuring unit receives light interfering between the measuring unit and the diffraction guide according to the generation of the continuous light.

In one embodiment, the laser oscillator may generate a continuous tunable laser.

In one embodiment, the laser oscillator may change the wavelength of the generated light so that the start of the optical signal received by the measuring unit is located at the maximum value of the wavelength of the received light.

In an embodiment, the laser oscillator may change the position of the reference guide when the reference guide is a state in which a workpiece reciprocating between the first position and the second position is located closest to the diffraction guide. The wavelength of the generated light may be changed such that an end portion of the optical signal received by the measurement unit is positioned at a maximum value of the wavelength of the received light.

In example embodiments, the laser oscillator may select the generated light such that a distance between the first distance and the second distance is an integer multiple of a half wavelength of the wavelength of the generated light.

The display device may further include a converting unit converting the interference light received by the measuring unit into a square wave signal, and a display unit displaying the interference light converted into the square wave.

In one embodiment, the measuring unit may be a photo detector.

According to another aspect of the present invention, there is provided a distance measuring method using a laser, the first position spaced by a first distance from a diffraction guide, and the second spaced apart by a second distance from the diffraction guide. Reciprocate the workpiece within the range of position. In the laser oscillator, light of different wavelengths is continuously generated by the diffraction guide and the measurement object. The wavelength of the light generated by the laser oscillation unit is changed based on the signal of the light interfered between the measurement object and the diffraction guide. The measurement object is moved between the first position and the second position and the wavelength of the light generated by the laser oscillator is changed based on the signal of the interference light. Measure the reciprocating distance of the workpiece.

In one embodiment, the wavelength of the generated light may be increased or decreased such that the beginning of the interfered optical signal is located at the maximum value of the wavelength of the interfered light.

In one embodiment, when the reference guide is a state in which a workpiece reciprocating between the first position and the second position is located closest to the diffraction guide, the position of the reference guide is increased or decreased so as to interfere with the interference. The wavelength of the generated light may be increased or decreased such that an end portion of the optical signal is located at a maximum value of the wavelength of the interfering light.

In one embodiment, the generated light may be selected such that the interval between the first distance and the second distance is an integer multiple of a half wavelength of the wavelength of the generated light.

In one embodiment, measuring the reciprocating distance of the workpiece, converting the interference light into a square wave signal to determine the moving distance of the workpiece, and displaying the interference light converted into the square wave signal It may further include.

According to the embodiments of the present invention, since the moving distance of the workpiece is measured by generating continuous light and receiving interference light, the accuracy is improved compared to measuring the moving distance of the workpiece by one light or discontinuous light. You can.

In particular, in the case of continuous light, since the wavelength of the light generated using the tunable laser is continuously varied, it is possible to easily select the light whose moving distance is an integer multiple of the half wavelength of the wavelength, and thus the moving distance of the measuring object from the wavelength of the light. Can be measured very precisely.

In addition, by changing the position of the reference guide to be an integer multiple of the half wavelength of the optical wavelength, it is possible to measure the moving distance of the workpiece more accurately.

1 is a schematic diagram showing a distance measuring system using a laser according to an embodiment of the present invention.

FIG. 2 is a schematic diagram showing the reflection and diffraction states of the irradiated light according to the position of the workpiece in the distance measuring system of FIG. 1.

3A is a graph illustrating the results measured by the measuring unit according to diffraction of the irradiated light of FIG. 2.

FIG. 3B is a graph repeatedly showing a measurement signal regarding a moving distance d of a workpiece among the results measured according to diffraction of the irradiated light of FIG. 2.

4A and 4B are flowcharts illustrating a distance measuring method using the distance measuring system using the laser of FIG. 1.

5A and 5B are graphs showing examples of results of distance measurement through the distance measuring method using the laser of FIGS. 4A and 4B.

6A and 6B are graphs illustrating another example of results of distance measurement through the distance measuring method using the laser of FIGS. 4A and 4B.

7 is a graph showing the results of experiments using the distance measuring method using the laser of FIGS. 4A and 4B.

* Explanation of the sign

10: distance measuring system 100: laser oscillator

200: base portion 300; Diffraction guide

400: measuring unit 401: reference guide

401, 402: change in position of the workpiece 500: measuring unit

510: converter 520: display unit

As the inventive concept allows for various changes and numerous modifications, the embodiments will be described in detail in the text. However, this is not intended to limit the present invention to a specific disclosed form, it should be understood to include all modifications, equivalents, and substitutes included in the spirit and scope of the present invention. In describing the drawings, similar reference numerals are used for similar elements. Terms such as first and second may be used to describe various components, but the components should not be limited by the terms.

The terms are used only for the purpose of distinguishing one component from another. The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting of the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise.

In this application, the terms "comprise" or "consist of" are intended to indicate that there is a feature, number, step, operation, component, part, or combination thereof described in the specification, and one or more other features. It is to be understood that the present invention does not exclude the possibility of the presence or the addition of numbers, steps, operations, components, parts, or combinations thereof.

Unless defined otherwise, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art. Terms such as those defined in the commonly used dictionaries should be construed as having meanings consistent with the meanings in the context of the related art and shall not be construed in ideal or excessively formal meanings unless expressly defined in this application. Do not.

Hereinafter, with reference to the accompanying drawings, it will be described in detail a preferred embodiment of the present invention.

Referring to FIG. 1, the distance measuring system 10 using the laser according to the present embodiment includes a laser oscillation unit 100, a base unit 200, a diffraction guide 300, a measurement unit 400, and a measurement unit 500. And a converting unit 510 and a display unit 520, and the measuring unit 400 includes a measuring object reciprocating between predetermined positions.

The laser oscillator 100 generates a tunable laser, that is, a continuous tunable laser, and irradiates the diffraction guide 300 and the measurement object 400. In this case, the tunable laser generated by the laser oscillator 100 means laser light of which the wavelength is continuously variable, and the laser light of which the wavelength is continuously variable is continuously generated under the control of a controller (not shown). Done. Hereinafter, the light generated by the laser oscillator 100 is referred to as generated light.

That is, the laser oscillator 100 continuously generates light having a continuously changing wavelength and irradiates the diffraction guide 300 and the measuring unit 400.

In this case, the measurement unit 500 to be described later with respect to the light of the continuous wavelength generated by the laser oscillator 100 also receives the interference light, the conversion unit 510 and the display unit 520 also Interference light received continuously is continuously converted and displayed.

That is, the interference light hereinafter refers to light that is interfered as the measurement object moves at a predetermined position, and means that the measurement unit 500 receives the interference light (received light).

The base portion 200 is a space between the laser oscillation portion 100 and the diffraction guide 300, the light generated from the laser oscillation portion 100 through the base portion 200 is the diffraction guide 300. And the interference light irradiated to the measuring unit 400 and interfered between the diffraction guide 300 and the measuring unit 400 passes through the base part 200 and is provided to the measuring unit 500.

In this case, since the measuring unit 400 includes a measurement object, the interference light corresponds to light interfering between the diffraction guide 300 and the measurement object.

The diffraction guide 300 is disposed at the end of the base portion 200, the plurality of slits (slit) are arranged at a predetermined distance apart.

Thus, part of the light generated by the laser oscillator 100 is primarily reflected by the slits of the diffraction guide 300 and passes through the base part 200, and the remaining light is slit of the diffraction guide 300. Passing between the two is provided to the measuring unit 400, each of which is reflected by the second object to pass through the base portion 200.

The measuring unit 400 includes a measuring object.

In the present embodiment, the measurement object is a first position spaced apart from the diffraction guide 300 by a first distance L, and a second position spaced apart from the diffraction guide 300 by a second distance L + d. It will be located to and from each other. That is, the measurement object is reciprocated by the movement distance d.

In this case, as will be described later, the measured object is positioned differently from the diffraction guide 300 according to the wavelength of the light generated by the laser oscillator 100. That is, the first distance L may also be variable.

Meanwhile, in the present embodiment, the reference guide 401 may be defined as a state in which the measured object reciprocating between the first position and the second position is located closest to the diffraction guide 300. Of course, the reference guide 401 also varies as the first distance L is variable.

In this embodiment, the moving distance (d) in which the measured object is moved is measured.

Meanwhile, the light passing between the slits of the diffraction guide 300 among the light generated by the laser oscillator 100 is reflected by the measurement object and provided to the base 200. Thus, in the base part 200, the light reflected from the diffraction guide 300 and the light reflected from the measurement object interfere with each other to generate interference light.

The measurement unit 500 receives interference light in which the light reflected by the diffraction guide 300 and the light reflected by the measurement object 402 interfere with each other.

In this case, the measuring unit 500 may be, for example, a photo detector.

The interference light received by the measurement unit 500 is provided to the conversion unit 510, and the conversion unit 510 converts the interference light into square wave signals, respectively. In this case, since the conversion unit 510 converts the interference light into the square wave signal, a detailed description thereof will be omitted.

The display unit 520 displays a result of converting the square wave signal by the conversion unit 510, and accordingly, determines the reciprocating distance d of the measurement object. In this case, a specific judgment method will be described later.

FIG. 2 is a schematic diagram showing the reflection and diffraction states of the irradiated light according to the position of the workpiece in the distance measuring system of FIG. 1. 3A is a graph illustrating the results measured by the measuring unit according to diffraction of the irradiated light of FIG. 2. FIG. 3B is a graph repeatedly showing a measurement signal regarding a moving distance d of a workpiece among the results measured according to diffraction of the irradiated light of FIG. 2.

Referring to FIG. 2, a portion of the light generated by the laser oscillator 100 is provided to the base 200 as the first reflected light ① reflected from the diffraction guide 300, and the diffraction guide 300 is provided. The second reflected light (②) reflected from the reference guide 401 (that is, the measured object at the first position) through the second part is also provided to the base part 200, and passes through the diffraction guide 300 to the second reflected light (②). The third reflected light ③ reflected from the measurement object 402 at the position is also provided to the base part 200.

In the following description, the measurement object reciprocates between the first position and the second position, and thus, for convenience of description, two kinds of cases in which the measurement object is positioned in the first position and in the second position will be described in detail.

In this case, referring to FIG. 2A, if the separation distance L between the diffraction guide 300 and the measurement object 401 is the same as the half wavelength of the light generated by the laser oscillator 100 ( L = λ / 2), and the interference light interfering with the first reflected light ① and the second reflected light ② forms a reflection.

Similarly, if the moving distance d of the measurement object is equal to the half wavelength of the light generated by the laser oscillator 100 (L = λ / 2), the first reflected light ① and the third reflected light ③ are Interfered interference light forms reflection.

On the other hand, referring to FIG. 2B, if the moving distance d of the measurement object is equal to 1/4 wavelength of the light generated by the laser oscillator 100 (L = λ / 4), the first reflected light (1) and the interference light interfering with the third reflected light (③) form a diffraction light (diffraction).

In this case, when the moving distance d of the measurement object is not n times (n is an integer) of 1/2 wavelength of the light generated by the laser oscillator 100, the first reflected light ① and the third reflected light All interference light interfered with (③) forms diffraction light.

On the other hand, the interference light interfered with the first reflected light (①) and the second reflected light (②) received by the measuring unit 500, or the first reflected light (①) and the third reflected light (③) interference When the interfering light is converted into a square wave signal by the conversion unit 510, it is shown as a graph of the square wave as shown in FIG. 3A.

That is, in the square wave shown in FIG. 3A, the peak value of the wavelength corresponds to one-half wavelength of the light generated by the laser oscillator 100, and from the diffraction guide 300 to the measurement object located at the first position. The first distance L may be determined through the number of peaks of the square wave. Similarly, the moving distance d of the workpiece in the reference guide 401 can also be determined through the number of peaks of the square wave.

However, in FIG. 3A, since the peak value of the light generated by the laser oscillator 100 and the first distance L and the moving distance d do not coincide with each other, the first distance L and the moving distance d ) Is difficult to measure accurately.

That is, referring to FIG. 3B, since the measurement result regarding the movement distance d of the measurement object is not located at the peak value as well as the start signal, the first distance L and the movement distance do not coincide with each other. Accurate measurement of (d) is difficult.

Accordingly, as in the present embodiment, while changing the wavelength of the light by continuously changing the light generated by the laser oscillator 100, the peak value of the wavelength of the generated light and the first distance (L) and the moving distance When the wavelength of the light (d) coincides with each other, the first distance L and the movement distance d can be accurately measured from the wavelength of the light.

The distance measuring method according to the present embodiment will be described in detail below.

4A and 4B are flowcharts illustrating a distance measuring method using the distance measuring system using the laser of FIG. 1. 5A and 5B are graphs showing examples of results of distance measurement through the distance measuring method using the laser of FIGS. 4A and 4B. 6A and 6B are graphs illustrating another example of results of distance measurement through the distance measuring method using the laser of FIGS. 4A and 4B.

4A and 4B, in the distance measuring method using the laser, first, the measurement object is reciprocated while maintaining the moving distance d between the first position 401 and the second position 402. (Step S10).

Thereafter, the wavelength of the light irradiated from the laser oscillator 100 is changed to continuously generate light having different wavelengths from the diffraction guide and the measurement object (step S20).

Thereafter, the laser oscillator 100 changes the wavelength of the light generated by the laser oscillator 100 based on the signal of the light interfered between the diffraction guide 300 and the measurement object (step S30).

The signal of the interference light is represented by a waveform having a constant period, the laser oscillator 100 increases the wavelength of the generated light so that the beginning of the waveform of the signal of the interference light is located at the maximum value of the wavelength of the interference light; Decrease.

That is, the laser oscillator 100 continuously generates light having different wavelengths and irradiates the diffraction guide 300 and the measurement unit 400.

Referring to FIG. 5A, while the wavelength of the generated light is changed, the beginning of the waveform of the interference light (waveform corresponding to the moving distance d in FIG. 5A) as shown in FIG. 5A is applied to the maximum value of the wavelength of the interference light. Increase or decrease the wavelength of the generated light to locate.

Thereafter, the measurement object is moved between the first position and the second position, and the wavelength of the light generated by the laser oscillator is further changed based on the signal of the interfered light (step S40).

That is, the wavelength of the generated light generated by the laser oscillator 100 is increased or decreased by increasing or decreasing the position of the reference guide 401 so that the end of the interfering optical signal is also located at the maximum value of the wavelength of the interfering light. Let's do it.

Referring again to FIGS. 5A and 5B, the generated light at which the beginning of the waveform of the interference light corresponds to the maximum value of the wavelength of the interference light is selected, but the end of the waveform of the interference light is not located at the maximum value of the wavelength of the interference light. Do not.

Accordingly, as shown in FIGS. 6A and 6B, while increasing or decreasing the position of the reference guide 401, not only the beginning of the interfering optical signal but also the end of the interfering optical signal may be The wavelength of the generated light generated by the laser oscillator 100 is increased or decreased to be located at the maximum value of the wavelength.

Thus, the movement distance d of the workpiece, that is, the distance between the first distance and the second distance, is an integer multiple of the half wavelength of the wavelength of generated light generated by the laser oscillator 100 (d = (λ / 2) n) the light generated by the laser oscillator 100 is selected.

6A and 6B show an example in which the wavelength of light is selected (tuned) so that the moving distance is three times the half wavelength (d = (λ / 2) * 3).

More specifically, the wavelength of the tuning light can be increased or decreased (step S41), and when the wavelength of the tuning light is increased, the position of the reference guide 401 is increased (step S42). In contrast, when the wavelength of the tuning light is reduced, the position of the reference guide 401 is also reduced (step S43). Thus, the end of the interfering light signal as well as the start of the interfering light signal can select the generated light located at the maximum value of the wavelength of the interfering light.

In this way, while increasing or decreasing the position of the reference guide according to the increase or decrease of the wavelength of the tuning light, it is determined whether the interval between the first distance and the second distance is an integer multiple of the half wavelength of the wavelength of the generated light ( Step S34).

Thus, as shown in Fig. 6B, a square wave is formed in which the peak value of the selected light is located at both the start and the end of the moving distance d, so that the moving distance d is several times the half wavelength of the selected light. It will be able to measure more accurately.

Thereafter, when the generated light satisfying the above conditions is selected, the moving distance d of the measurement object 402 can be measured directly from the wavelength of the generated light (step S50).

For example, referring back to FIGS. 5A and 5B, the wavelength of the tunable laser is increased very finely so that the wavelength when the signal at the end of the first distance L comes to the peak of the interference signal is λ ₁ . do. At this time, even if the generated light wavelength increases by Δλ according to the length of the first distance L, the end signal of the first distance L is changed by an integer multiple of Δλ. That is, when the first distance L is in the range of (100 to 101) * λ / 2 and the generated light wavelength is increased by Δλ, the first distance L is moved by 100 * Δλ / 2 and eventually the first One distance L is 100 * λ _1/2 .

Thereafter, while keeping the start signal of the moving distance d section as the peak of the interference signal, the end signal of the moving distance d section is positioned at the peak of the interference signal. The first distance L must also be changed. In this case, referring to FIG. 5B, since the moving distance d is three repetitive sections, the moving distance d may be reciprocated between 2.5 and 3 cycles of the generated light wavelength. have.

Therefore, the wavelength of the generated light must be reduced to adjust the moving distance d section to three periods of the generated light wavelength, and the wavelength of the generated light must be increased to adjust the period of the generated light wavelength to 2.5 periods. As it is close, it is recommended to reduce the generated light wavelength.

However, if the wavelength of the generated light is reduced as described above, the end signal of the first distance L is out of the peak of the interference signal as inferred in FIG. 5A. Therefore, when the period of the generated light wavelength is reduced, the first distance L must be simultaneously reduced so that the end signal of the first distance L does not deviate from the peak of the interference signal.

That is, as described above, when the generated light wavelength is reduced by λ ₁ to Δλ _1, the first distance L should be reduced by L ₁ = L-100 * Δλ ₁ so as not to deviate from the peak of the interference signal. As described above, as the first distance L is continuously reduced, the first distance L is the generated light wavelength when the movement distance d is located at the peak of the interference signal, as shown in FIGS. 6A and 6B. It becomes an integer multiple of the half wavelength of (3 times in Fig. 5b), at which time the moving distance (d) can be measured.

In FIG. 7, the wavelength of the generated light and the signal measured by the measurement unit 500 according to the wavelength of the generated light and the change of the first distance through the distance measuring method using the laser described in detail above are the moving distance. The starting point of (d) is located at the top peak of the wavelength, and the ending point of the moving distance d shows an example of the result located at the bottom peak of the wavelength.

According to the embodiments of the present invention as described above, since the moving distance of the workpiece is measured by generating continuous light and receiving the interference light, compared with measuring the moving distance of the workpiece by one light or discontinuous light. The precision can be improved.

While the foregoing has been described with reference to preferred embodiments of the present invention, those skilled in the art will be able to variously modify and change the present invention without departing from the spirit and scope of the invention as set forth in the claims below. It will be appreciated.

The distance measuring system using the laser and the distance measuring method using the same according to the present invention have industrial applicability that can be used to measure the distance of a workpiece.

Claims

A laser oscillator for generating continuous light having different wavelengths;

A diffraction guide arranged to be spaced apart from the laser oscillation part by a predetermined distance;

A measuring unit including a measurement object reciprocating between a first position spaced apart from the diffraction guide by a first distance and a second position spaced apart from the diffraction guide by a second distance; And

According to the generation of the continuous light, the distance measuring system using a laser including a measuring unit for receiving the interference light between the measuring unit and the diffraction guide.
The method of claim 1,

The laser oscillator is a distance measuring system using a laser, characterized in that for generating a continuous tunable (tunable) laser.
The laser oscillator of claim 2, wherein the laser oscillator

And the wavelength of the generated light is changed so that the start of the optical signal received by the measuring unit is located at the maximum value of the wavelength of the received light.
The method of claim 3, wherein the laser oscillator,

When the reference guide is a state in which the workpiece reciprocating between the first position and the second position is located closest to the diffraction guide,

And changing the wavelength of the generated light such that the end of the optical signal received by the measuring unit is positioned at the maximum value of the wavelength of the received light by changing the position of the reference guide.
The method of claim 4, wherein the laser oscillator,

And the generated light is selected such that the interval between the first distance and the second distance is an integer multiple of a half wavelength of the wavelength of the generated light.
The method of claim 1,

A converting unit converting the interference light received by the measuring unit into a square wave signal; And

And a display unit for displaying the interference light converted into the square wave.
The method of claim 6,

The measuring unit is a distance measuring system using a laser, characterized in that the photo detector (photo detector).
Reciprocating (1) the workpiece within a range of a first position spaced apart from the diffraction guide by a first distance and a second position spaced apart from the diffraction guide by a second distance;

In the laser oscillator, continuously generating (2) light having a different wavelength to the diffraction guide and the measurement object;

Changing (3) the wavelength of light generated by the laser oscillator based on the signal of the light interfered between the measurement object and the diffraction guide;

Moving (4) the measurement object between the first position and the second position and changing a wavelength of light generated by the laser oscillator based on the signal of the interfered light; And

Distance measuring method using a laser comprising the step (5) of measuring the reciprocating distance of the workpiece.
The method according to claim 8, wherein in the step (3),

And increasing or decreasing the wavelength of the generated light such that a start of the interfering optical signal is located at a maximum value of the wavelength of the interfering light.
The method of claim 9, wherein in step (4),

When the reference guide is a state in which the workpiece reciprocating between the first position and the second position is located closest to the diffraction guide,

And increasing or decreasing the position of the reference guide to increase or decrease the wavelength of the generated light such that an end portion of the interfering optical signal is positioned at a maximum value of the wavelength of the interfering light.
The method of claim 10, wherein in step (4),

And the generated light is selected such that the interval between the first distance and the second distance is an integer multiple of a half wavelength of the wavelength of the generated light.
The method of claim 11, wherein the measuring the reciprocating distance of the workpiece,

Converting the interfered light into a square wave signal to determine a moving distance of a workpiece; And

And displaying the interfered light converted into the square wave signal.