A laser interference displacement measurement device and its usage method

Abstract

The present invention relates to a laser interference displacement measurement device and a method for using the same, including a reading head and a triangular wave mirror. The reading head includes a laser source, a first beam splitter, a second beam splitter, a beam splitting prism, a first photodetector, a condenser lens, a second photodetector, and a processor. The present invention adds a beam splitting prism and a first photodetector to avoid deviation of the final measurement result caused by changes in the wavelength of the laser beam due to environmental factors or the like during the measurement process, and compensates for changes in the wavelength of the laser beam. This solution uses simple optical devices and utilizes the principle of laser interference to complete the measurement of the displacement of the object to be measured. While ensuring the measurement accuracy, the complexity of the device is also simplified.

Description

Technical Field

[0001] The present invention relates to the technical field of wavelength measurement, and particularly relates to a laser interference displacement measurement device and a method for using the same. Background Art

[0002] Precise measurement is crucial for the field of optical precision measurement. Taking a laser interferometer as an example, its measurement accuracy is directly related to the accuracy of the laser wavelength. How to improve the measurement accuracy, reduce the influence of the laser wavelength on the measurement accuracy, and reduce the complexity and cost of the measurement device has become an important research content in the related field. Summary of the Invention

[0003] The purpose of the present invention is to improve the measurement accuracy of a laser interferometer and simplify the complexity of the measurement device, and to provide a laser interference displacement measurement device and a method for using the same.

[0004] In order to achieve the above-mentioned invention purpose, the embodiments of the present invention provide the following technical solutions:

[0005] A laser interference displacement measurement device includes a reading head and a triangular wave mirror, which is used to receive the laser beam transmitted by the first beam splitter and reflect the received laser beam.

[0006] The reading head includes:

[0007] A laser source, which is used to emit a laser beam;

[0008] A first beam splitter, which is used to transmit the laser beam emitted by the laser source to the triangular wave mirror and reflect it to a condenser lens;

[0009] A second beam splitter, which is used to receive the laser beam reflected by the triangular wave mirror, reflect the received laser beam to the triangular wave mirror again, and transmit it to a beam splitting prism;

[0010] A beam splitting prism, which is used to receive the laser beam transmitted by the second beam splitter and transmit the laser beam to a first photodetector;

[0011] A first photodetector, which is used to receive the laser beam transmitted by the beam splitting prism;

[0012] A condenser lens, which is used to receive the laser beam reflected by the first beam splitter and the triangular wave mirror, and transmit the received and condensed laser beam to a second photodetector;

[0013] A second photodetector, which is used to receive the laser beam transmitted by the condenser lens;

[0014] A processor, which is used to record the displacement amount of the laser beam on the first photodetector, detect the interference phenomenon generated on the second photodetector, and calculate the displacement amount of the reading head or the triangular wave mirror.

[0015] In this solution, a beam splitter prism and a first photodetector are added to avoid the deviation of the final measurement result caused by the change of the wavelength of the laser beam due to environmental factors during the measurement process, and a compensation calculation for the change of the wavelength of the laser beam is performed. This solution uses simple optical devices and utilizes the laser interference principle to complete the measurement of the displacement of the object to be measured. While ensuring the measurement accuracy, the complexity of the device is also simplified.

[0016] To describe the setting method of the measurement device in more detail, the first beam splitter is inclined above the triangular wave mirror and has an angle of 30 degrees with the horizontal direction; the second beam splitter is parallel to the first beam splitter.

[0017] To describe the structure of the measurement device in more detail, the triangular wave mirror includes N reflection structures with the same structure. Each reflection structure includes a first reflection surface and a second reflection surface. The first reflection surface or the second reflection surface is parallel to the mirror, and there is an angle of 120 degrees between the first reflection surface and the second reflection surface.

[0018] To describe the structure of the optical device selected in the measurement device and its setting method in more detail, the condenser lens is a convex lens and is set parallel to the horizontal direction.

[0019] Preferably, the condenser lens is an aspherical lens.

[0020] Preferably, the first photodetector is a position sensitive detector.

[0021] To improve the measurement device, the reading head is set on the object to be measured and moves with the object to be measured, and the triangular wave mirror is fixedly set; or the triangular wave mirror is set on the object to be measured and moves with the object to be measured, and the reading head is fixedly set.

[0022] Furthermore, there are multiple reading heads, and multiple reading heads alternately participate in the interference fringe counting.

[0023] A method for using a laser interference displacement measurement device includes the following steps:

[0024] Step S1: Fix the triangular wave mirror / read head, and set the read head / triangular wave mirror on the object to be measured, so that the read head / triangular wave mirror moves with the object to be measured. Set the angle of the laser source so that the angle between the laser beam emitted by the laser source and the horizontal direction is 150 degrees; Set the first beam splitter and the second beam splitter parallel to each other, and the angle between the first beam splitter and the second beam splitter and the horizontal direction is 30 degrees; Set the condenser lens on the side of the first beam splitter away from the triangular wave mirror, and make sure that the condenser lens can receive the laser beams reflected by the first beam splitter and the triangular wave mirror; Set the second photodetector at the focal point of the condenser lens, so that the second photodetector can receive the two laser beams transmitted by the condenser lens and generate an interference phenomenon; Set the beam splitting prism between the second beam splitter and the condenser lens, so that the beam splitting prism can receive the laser beam transmitted by the second beam splitter; Set the first photodetector between the beam splitting prism and the condenser lens, so that the first photodetector can receive the laser beam transmitted by the beam splitting prism;

[0025] Step S2: Turn on the laser source, use the processor to detect the interference phenomenon generated on the second photodetector. The read head / triangular wave mirror moves horizontally with the object to be measured, so that the interference phenomenon generated on the second photodetector is constructive interference / destructive interference, and record the number of interference times at this time as 0 times;

[0026] Step S3: Move the object to be measured horizontally again within time t. The read head / triangular wave mirror moves with the object to be measured, and record the number of constructive interference / destructive interference times generated on the second photodetector as M;

[0027] Step S4: Calculate the average laser beam wavelength λ within time t through the change of the incident position point of the laser beam on the first photodetector;

[0028] Step S5: According to the number of constructive interference / destructive interference times M generated on the second photodetector and the average laser wavelength λ, calculate the displacement of the object to be measured horizontally for the second time

[0029] Step S6: Repeat Step S3 to Step S5 to calculate the cumulative displacement of the object to be measured.

[0030] As another implementable way, a method for using a laser interference displacement measurement device includes the following steps:

[0031] Step S1: Fix the triangular wave mirror / read head, and set the read head / triangular wave mirror on the object to be measured, so that the read head / triangular wave mirror moves with the object to be measured;

[0032] Step S2: Turn on the laser source. Use the processor to detect the interference phenomenon generated on the second photodetector. The reading head / triangular wave mirror moves vertically with the object to be measured, so that the interference phenomenon generated on the second photodetector is constructive interference / destructive interference, and record the laser interference times as 0 at this time;

[0033] Step S3: Move the object to be measured vertically again within time t. The reading head / triangular wave mirror moves with the object to be measured, and record the number of constructive interference / destructive interference generated on the second photodetector as M;

[0034] Step S4: Calculate the average laser wavelength λ within time t through the change of the incident position point of the laser beam on the first photodetector;

[0035] Step S5: Calculate the displacement of the reading head / triangular wave mirror in the vertical direction for the second time according to the number of constructive interference / destructive interference M generated on the second photodetector and the average wavelength λ of the laser beam

[0036] Step S6: Repeat Step S3 to Step S5 to calculate the cumulative displacement of the object to be measured.

[0037] Compared with the prior art, the beneficial effects of the present invention are:

[0038] The present invention compensates for the change of the laser beam wavelength due to environmental factors during the measurement process through the beam splitter prism and the first photodetector, and uses the average wavelength of the laser beam within the measurement time period to calculate the cumulative displacement of the object to be measured, which greatly improves the measurement accuracy.

[0039] During the displacement measurement process of this solution, since the maximum interference optical path is greatly shortened and does not increase linearly with the increase of the displacement amount, the influence of the laser wavelength on the interference counting is also greatly reduced.

[0040] This solution uses simple optical devices and utilizes the laser interference principle to complete the displacement measurement of the object to be measured. While ensuring the measurement accuracy, it also simplifies the complexity of the device.

[0041] When the present invention performs measurement in the vertical direction, it can also avoid the influence of gravity on the measurement result and further ensure the measurement accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required for the embodiments. It should be understood that the following drawings only show some embodiments of the present invention, and therefore should not be regarded as limiting the scope. For those of ordinary skill in the art, other related drawings can also be obtained based on these drawings without creative efforts.

[0043] Figure 1 Schematic diagram of the device structure provided by the embodiment of the present invention;

[0044] Figure 2 Schematic diagram of the device working in the horizontal direction provided by the embodiment of the present invention;

[0045] Figure 3 For the present invention Figure 2 Partial enlarged schematic diagram of the device working;

[0046] Figure 4 Schematic diagram of the device working in the vertical direction provided by the embodiment of the present invention;

[0047] Figure 5 Schematic diagram for calculating the displacement of the reading head when the device provided by the embodiment of the present invention works in the horizontal direction;

[0048] Figure 6 For the present invention Figure 5 Partial enlarged schematic diagram.

[0049] Description of main component symbols

[0050] Reading head 1, laser source 100, first beam splitter 200, second beam splitter 300, beam splitting prism 400, first photodetector 500, condenser lens 600, second photodetector 700, triangular wave mirror 2, first reflecting surface 21, second reflecting surface 22. Detailed implementation manners

[0051] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Usually, the components of the embodiments of the present invention described and shown in the drawings here can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed present invention, but merely represents the selected embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative efforts belong to the scope of protection of the present invention.

[0052] It should be noted that: similar reference numerals and letters denote similar items in the following drawings. Therefore, once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings. At the same time, in the description of the present invention, terms such as "first", "second", etc. are only used for distinguishing descriptions, and cannot be understood as indicating or implying relative importance, or implying any such actual relationship or order between these entities or operations.

[0053] Example 1:

[0054] The present invention is implemented by the following technical solutions. As Figure 1 shown, a laser interference displacement measurement device includes a reading head and a triangular wave mirror. The reading head includes a laser source, two beam splitters, a beam splitting prism, a condenser lens, and two photodetectors, where:

[0055] The laser source is used to emit a laser beam to the first beam splitter.

[0056] The first beam splitter is disposed above the triangular wave mirror. As Figure 3 shown, it has a 30-degree angle with the horizontal direction. It is used to receive the laser beam emitted by the laser source, transmit the received laser beam to the triangular wave mirror, and reflect it to the condenser lens. For the convenience of distinction, the laser beam reflected by the first beam splitter to the condenser lens is defined as the reflected laser beam, and the laser beam transmitted by the first beam splitter to the triangular wave mirror is defined as the transmitted laser.

[0057] The second beam splitter is disposed above the triangular wave mirror and is parallel to the first beam splitter. It is used to receive the transmitted laser beam reflected by the triangular wave mirror, transmit the received transmitted laser beam to the beam splitting prism, and reflect it to the triangular wave mirror again.

[0058] The beam splitting prism is disposed between the second beam splitter and the condenser lens. It is used to receive the transmitted laser beam transmitted by the second beam splitter and transmit the received transmitted laser beam to the first photodetector.

[0059] The first photodetector is disposed between the beam splitting prism and the condenser lens and is used to receive the transmitted laser beam transmitted by the beam splitting prism.

[0060] The condenser lens is used to receive the reflected laser beam reflected by the first beam splitter and the transmitted laser beam reflected by the triangular wave mirror, and transmit the two laser beams to the second photodetector.

[0061] The second photodetector is disposed at the focal point of the condenser lens and is used to receive the laser beam transmitted by the condenser lens.

[0062] The processor is used to record the change in the incident position point of the laser beam on the first photodetector, detect the interference phenomenon generated on the second photodetector, calculate the displacement of the reading head or the triangular wave mirror, and thus the displacement of the measured object.

[0063] The present invention moves the reading head or the triangular wave mirror in the horizontal or vertical direction, so that the transmitted laser beam generates a change in the optical path difference. A processor is used to detect the light interference phenomenon generated on the second photodetector, and records the number M of constructive interference / destructive interference generated on the second photodetector during the movement; the wavelength of the laser beam may change due to environmental reasons. For example, changes in temperature, humidity, etc. in the environment will cause changes in the wavelength of the laser beam. Therefore, in the present invention, a beam splitting prism and a first photodetector are provided to record the change in the incident position of the laser beam on the first photodetector during the movement of the reading head or the triangular wave mirror, calculate the average wavelength of the changed laser beam, and use this average wavelength to calculate the displacement of the reading head or the triangular wave mirror; Given the wavelength of the laser beam and the number M of constructive interference / destructive interference generated on the second photodetector, the change in the optical path difference of the laser beam during the movement of the reading head or the triangular wave mirror can be calculated, thereby obtaining the displacement X of the reading head or the triangular wave mirror, that is, the displacement of the measured object, and completing the measurement work. It can not only complete the measurement work well, but also avoid the problem of low measurement accuracy caused by the change of the laser beam wavelength due to environmental factors. While improving the measurement accuracy, the measurement device is simple and the device complexity is reduced.

[0064] Further, the triangular wave mirror includes N reflection structures with the same structure. Each reflection structure includes a first reflection surface and a second reflection surface. As Figure 3 shown, the first reflection surface or the second reflection surface is parallel to the mirror, and there is an included angle of 120 degrees between the first reflection surface and the second reflection surface. For example, as Figure 1 shown, the triangular wave mirror includes eight reflection structures, and the first beam splitter transmits the transmitted laser beam to the second reflection surface of the first reflection structure.

[0065] To illustrate the working principle of the present invention in more detail, in this embodiment, the reading head is moved in the horizontal direction, the triangular wave mirror is fixedly arranged, and the number of constructive interference generated on the second photodetector is detected. As Figure 1As shown, after the laser source emits a laser beam to the first beam splitter, the first beam splitter transmits the transmitted laser beam to the second reflecting surface of the first reflecting structure of the triangular wave mirror. Since there is a 120-degree angle between the first reflecting surface and the second reflecting surface, the transmitted laser beam transmitted from the first beam splitter is parallel to the first reflecting surface. Therefore, after the transmitted laser beam reaches the second reflecting surface, it perpendicularly enters the second beam splitter, and the first beam splitter directly reflects the reflected laser beam to the condenser lens. After the second beam splitter receives the transmitted laser beam reflected by the triangular wave mirror, it transmits the transmitted laser beam to the spectroscope prism and reflects the transmitted laser beam to the triangular wave mirror again. The spectroscope prism transmits the received transmitted laser beam to the first photodetector. The triangular wave mirror reflects the transmitted laser beam reflected by the second beam splitter to the condenser lens, and the condenser lens transmits the received transmitted laser beam and the reflected laser beam to the second photodetector. Before the measurement starts, horizontally move the reading head so that constructive interference occurs on the second photodetector. At this time, record that the number of interference times generated on the second photodetector is 0 times, and at the same time, the processor records the landing position of the laser beam on the first photodetector.

[0066] As Figure 2 shown, after the measurement starts, the measured object moves horizontally, driving the reading head to move together. Set that there are M constructive interferences generated on the second photodetector within the time t, and at the same time, the processor records the landing position of the laser beam on the first photodetector. If during the measurement process, the wavelength of the laser beam changes due to environmental factors, then the landing point of the laser beam on the first photodetector will change. At this time, calculate the average laser beam wavelength λ within the time t through the change in the incident position point of the laser beam on the first photodetector.

[0067] Combined with Figure 2 、 Figure 3 shown, it can be seen that during the second movement of the reading head, the optical path of the reflected laser beam reflected from the first beam splitter does not change, but the optical path of the transmitted laser beam transmitted from the first beam splitter changes. According to the laser interference principle, the change in the optical path difference is equal to an integer multiple of the wavelength. Then, in this embodiment, the processor has obtained the changed laser beam wavelength and the number M of constructive interferences generated on the second photodetector, and can calculate the change in the optical path difference.

[0068] Continuing as Figure 5 shown, it can be seen that the change in the optical path difference is h + L. Then, magnify the change in the optical path difference of the laser beam in Figure 5 as shown in 6. Given the angles between the first beam splitter, the first reflecting surface, and the second reflecting surface, Therefore, the change in the optical path difference of the transmitted laser beam of the first beam splitter is The change in the optical path difference of the laser beam reflected by the second beam splitter is also Then the optical path difference of the overall interference optical path is Thus, according to the interference displacement measurement principle, the displacement X of the reading head is obtained, and the measurement work is completed.

[0069] Furthermore, the condenser lens is selected as a convex lens. When two parallel beams of light are perpendicularly incident on the convex lens, both beams of light will pass through the focal point of the convex lens after passing through the convex lens. Therefore, a convex lens with a condensing effect is used, and the second photodetector is arranged at the focal point of the condenser lens so that the two laser beams passing through the condenser lens can be incident on the second photodetector and an interference phenomenon occurs on the second photodetector.

[0070] Furthermore, the first photodetector is a position-sensitive detector.

[0071] Based on the above device, the present invention also proposes a usage method of a laser interference displacement measurement device, including the following steps:

[0072] Step S1: Fix the triangular wave mirror / reading head, and set the reading head / triangular wave mirror on the object to be measured so that the reading head / triangular wave mirror moves with the object to be measured. Set the angle of the laser source so that the angle between the laser beam emitted by the laser source and the horizontal direction is 150 degrees; set the first beam splitter and the second beam splitter parallel to each other, and the angles between the first beam splitter and the second beam splitter and the horizontal direction are 30 degrees; set the condenser lens on the side of the first beam splitter away from the triangular wave mirror so that the condenser lens can receive the laser beams reflected by the first beam splitter and the triangular wave mirror; set the second photodetector at the focal point of the condenser lens so that the second photodetector can receive the two laser beams transmitted by the condenser lens and an interference phenomenon occurs; set the beam splitting prism between the second beam splitter and the condenser lens so that the beam splitting prism can receive the laser beam transmitted by the second beam splitter; set the first photodetector between the beam splitting prism and the condenser lens so that the first photodetector can receive the laser beam transmitted by the beam splitting prism;

[0073] Step S2: Turn on the laser source, use the processor to detect the interference phenomenon generated on the second photodetector, and the reading head / triangular wave mirror moves horizontally with the object to be measured so that the interference phenomenon generated on the second photodetector is constructive interference / destructive interference, and record the interference times as 0 times at this time;

[0074] Step S3: Move the object to be measured horizontally again within the time t, and the reading head / triangular wave mirror moves with the object to be measured, and record the number of constructive interference / destructive interference times generated on the second photodetector as M;

[0075] Step S4: Calculate the average laser beam wavelength λ within the time t through the change of the laser beam incident position point on the first photodetector;

[0076] Step S5: Calculate the displacement of the object to be measured in the horizontal direction for the second time based on the number of constructive / destructive interferences M generated on the second photodetector and the average laser wavelength λ.

[0077] Step S6: Repeat Steps S3 to S5 to calculate the cumulative displacement of the object to be measured.

[0078] As another implementable manner, a method for using a laser interference displacement measurement device includes the following steps:

[0079] Step S1: Fix the triangular wave mirror / read head, and set the read head / triangular wave mirror on the object to be measured so that the read head / triangular wave mirror moves with the object to be measured.

[0080] Step S2: Turn on the laser source, use the processor to detect the interference phenomenon generated on the second photodetector, and the read head / triangular wave mirror moves with the object to be measured in the vertical direction so that the interference phenomenon generated on the second photodetector is constructive / destructive interference, and record the laser interference count as 0 at this time.

[0081] Step S3: Move the object to be measured in the vertical direction again within time t, and the read head / triangular wave mirror moves with the object to be measured, and record the number of constructive / destructive interferences generated on the second photodetector as M.

[0082] Step S4: Calculate the average laser wavelength λ within time t through the change in the incident position point of the laser beam on the first photodetector.

[0083] Step S5: Calculate the displacement of the read head / triangular wave mirror in the vertical direction for the second time based on the number of constructive / destructive interferences M generated on the second photodetector and the average wavelength λ of the laser beam.

[0084] Step S6: Repeat Steps S3 to S5 to calculate the cumulative displacement of the object to be measured.

[0085] As described above, the above is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art can easily think of changes or substitutions within the technical scope disclosed by the present invention, and all should be covered by the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims

1. A method of using a laser interferometric displacement measurement device, which is implemented based on a laser interferometric displacement measurement device, and is characterized in that: The device includes: a reading head; It further includes a triangular wave mirror, which is used to receive the laser beam transmitted by the first beam splitter and reflect the received laser beam; The reading head includes: A laser source, which is used to emit a laser beam; A first beam splitter, which is used to transmit the laser beam emitted by the laser source to the triangular wave mirror and reflect it to the condenser lens; A second beam splitter, which is used to receive the laser beam reflected by the triangular wave mirror, reflect the received laser beam to the triangular wave mirror again, and transmit it to the beam splitting prism; A beam splitting prism, which is used to receive the laser beam transmitted by the second beam splitter and transmit the laser beam to the first photodetector; A first photodetector, which is used to receive the laser beam transmitted by the beam splitting prism; A condenser lens, which is used to receive the laser beams reflected by the first beam splitter and the triangular wave mirror, and transmit the received laser beams to the second photodetector after focusing; A second photodetector, which is used to receive the laser beam transmitted by the condenser lens; A processor, which is used to record the change in the incident position point of the laser beam on the first photodetector, detect the interference phenomenon generated on the second photodetector, and calculate the displacement of the reading head or the triangular wave mirror; The reading head is arranged on the object to be measured and moves with the object to be measured, and the triangular wave mirror is fixedly arranged; or the triangular wave mirror is arranged on the object to be measured and moves with the object to be measured, and the reading head is fixedly arranged; The method includes the following steps: Step S1: Fix the triangular wave mirror / reading head, and arrange the reading head / triangular wave mirror on the object to be measured so that the reading head / triangular wave mirror moves with the object to be measured. Set the angle of the laser source so that the angle between the laser beam emitted by the laser source and the horizontal direction is 150 degrees; Set the first beam splitter and the second beam splitter to be parallel to each other, and the angles between the first beam splitter and the second beam splitter and the horizontal direction are 30 degrees; Arrange the condenser lens on the side of the first beam splitter away from the triangular wave mirror so that the condenser lens can receive the laser beams reflected by the first beam splitter and the triangular wave mirror; Arrange the second photodetector at the focal point of the condenser lens so that the second photodetector can receive the two laser beams transmitted by the condenser lens and generate an interference phenomenon; Arrange the beam splitting prism between the second beam splitter and the condenser lens so that the beam splitting prism can receive the laser beam transmitted by the second beam splitter; Arrange the first photodetector between the beam splitting prism and the condenser lens so that the first photodetector can receive the laser beam transmitted by the beam splitting prism; Step S2: Turn on the laser source, use the processor to detect the interference phenomenon generated on the second photodetector, and the reading head / triangular wave mirror moves with the object to be measured in the horizontal direction so that the interference phenomenon generated on the second photodetector is constructive interference / destructive interference, and record the interference count as 0 times at this time; Step S3: Move the object to be measured in the horizontal direction again within time t, and the reading head / triangular wave mirror moves with the object to be measured, and record the number of constructive interference / destructive interference times generated on the second photodetector as M; Step S4: Calculate the average laser beam wavelength within time t based on the change in the incident position point of the laser beam on the first photodetector ; Step S5: Calculate the displacement of the object to be measured in the horizontal direction for the second time based on the number of constructive / destructive interference times M generated on the second photodetector and the average laser wavelength , ; Step S6: Repeat steps S3 to S5 to calculate the cumulative displacement of the object under test.

2. A method for using a laser interference displacement measurement device, implemented based on a laser interference displacement measurement device, characterized in that: The device includes: a reading head; It further includes a triangular wave mirror for receiving the laser beam transmitted by the first beam splitter and reflecting the received laser beam; The reading head includes: A laser source for emitting a laser beam; A first beam splitter for transmitting the laser beam emitted by the laser source to the triangular wave mirror and reflecting it to the condenser lens; A second beam splitter for receiving the laser beam reflected by the triangular wave mirror, reflecting the received laser beam back to the triangular wave mirror again, and transmitting it to the spectroscope prism; A spectroscope prism for receiving the laser beam transmitted by the second beam splitter and transmitting the laser beam to the first photodetector; A first photodetector for receiving the laser beam transmitted by the spectroscope prism; A condenser lens for receiving the laser beams reflected by the first beam splitter and the triangular wave mirror, condensing the received laser beams and transmitting them to the second photodetector; A second photodetector for receiving the laser beam transmitted by the condenser lens; A processor for recording the change in the incident position point of the laser beam on the first photodetector, detecting the interference phenomenon generated on the second photodetector, and calculating the displacement of the reading head or the triangular wave mirror; The reading head is disposed on the object under test and moves with the object under test, and the triangular wave mirror is fixedly disposed; or the triangular wave mirror is disposed on the object under test and moves with the object under test, and the reading head is fixedly disposed; The method includes the following steps: Step S1: Fix the triangular wave mirror / reading head and dispose the reading head / triangular wave mirror on the object under test so that the reading head / triangular wave mirror moves with the object under test; Step S2: Turn on the laser source, use the processor to detect the interference phenomenon generated on the second photodetector, and the reading head / triangular wave mirror moves with the object under test in the vertical direction so that the interference phenomenon generated on the second photodetector is constructive interference / destructive interference, and record the laser interference count as 0 at this time; Step S3: Move the object under test in the vertical direction again within time t, and the reading head / triangular wave mirror moves with the object under test, and record the number of constructive interference / destructive interference generated on the second photodetector as M; Step S4: Calculate the average laser beam wavelength within time t based on the change in the incident position point of the laser beam on the first photodetector ; Step S5: Calculate the displacement of the read head / triangular mirror in the vertical direction for the second time according to the number of constructive / destructive interference times M generated on the second photodetector and the average wavelength of the laser beam , ; Step S6: Repeat steps S3 to S5 to calculate the cumulative displacement of the object under test.

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