Nanometer / picometer displacement measuring instrument

Abstract

A nanometer / picometer displacement measuring instrument comprises a laser light source and a grating perpendicular to an emergent light beam, a symmetrical reflector group is arranged on a diffraction path, an interference field is located on a front focal plane of a first lens of a coding imaging system, the coding imaging system and an image sensor are arranged on a subsequent propagation path, and the image sensor is connected with a computer. The nanometer / picometer displacement measuring instrument disclosed by the invention adopts a displacement measuring technology of light field complex amplitude recovery, and the instrument has strong anti-interference capability. The working stability is high; the stable initial phase to be solved is directly solved from the fringe complex amplitude and corresponds to the change value of the displacement, high-stability numerical subdivision is realized, and the resolution of the instrument is improved; the measurement range depends on the length of the measured stripe grating, and wide-range displacement measurement can be realized.

Description

Technical Field

[0001] The invention relates to a nanometer / picometer displacement measuring instrument, belonging to the field of micro displacement measurement. Background Art

[0002] Manufacturing is an important foundation of industry and an important symbol of the level of industrial development. High-precision displacement measurement technology is the basis of high-end manufacturing and precision machining. In the fields of manufacturing, processing and measurement, the measurement accuracy of micro-displacement directly affects the performance of the device. Therefore, it is particularly important to develop high-precision and high-stability displacement measurement technology.

[0003] At present, the high-precision micro-displacement measurement methods that have been developed are mainly capacitive displacement measurement technology and grating measurement technology.

[0004] Among them, as one of the fastest-growing micro-displacement measurement technologies, the capacitive displacement measurement system is mainly composed of a movable plate and a static plate. When displacement occurs, the movable plate will move relative to the static plate, and the capacitance in the capacitor will change with the movement. The change in capacitance can be used to measure displacement. Capacitive displacement measurement technology has the advantages of non-contact measurement, simple structure, and small size. However, this technology is limited by nonlinear output, pull-down effect, parasitic capacitance, and electromagnetic interference, and cannot meet the application scenario requirements of high precision and a large range.

[0005] At present, most of the existing grating displacement measurement technologies are based on the principles of moiré fringe detection and multi-path interference. According to different application requirements, these technologies can generally achieve displacement detection of the order of 0.1nm-1μm. Moiré fringes are interference images produced by the overlapping of fence fringes with a certain angle. When the grating used as a scale moves in a direction perpendicular to the grating line, the moiré fringes also move a fixed distance. Measuring the movement of the moiré fringes can indirectly measure the movement of the scale grating. The grating displacement measurement technology based on the moiré fringe principle is limited by the principle. When the grating density increases, the diffraction phenomenon intensifies, and the moiré fringe signal will be affected by high-order harmonics, which cannot meet the requirements of high-precision nano-measurement. The principle based on multi-path interference is to use the light emitted by the light source as the reference light and the object light after the light is diffracted and split by the grating. When displacement occurs, the interference fringes will move, and thus the measurement is performed. However, the optical path is complex, the miniaturization design is difficult, and the stability is poor. Summary of the invention

[0006] In view of the shortcomings of the existing displacement measuring instrument technology, the present invention proposes a nanometer / picometer displacement measuring instrument, whose maximum range can reach 100mm or higher, and the measurement resolution is better than 1nm. At the same time, the instrument has strong anti-interference ability and high measurement stability.

[0007] The technical solution of the present invention is as follows:

[0008] A nanometer / picometer displacement measuring instrument, comprising a laser light source, a grating, a symmetrical reflector group, a coding imaging system, an image sensor and a computer;

[0009] The laser beam is incident vertically on the grating and diffracted. The reflector set on the diffracted light path reflects the diffracted light to the interference field, which coincides with the front focal plane of the first lens of the encoding imaging system. The light beam becomes parallel light after passing through the first lens of the encoding imaging system. The optical phase plate with known distribution modulates the parallel light beam, and then forms an image on the image sensor after passing through the second lens of the encoding imaging system. The image sensor is connected to the computer, and the complex amplitude of the interference field is obtained by the complex amplitude recovery algorithm of the collected image, and then the phase difference of the diffracted light beam is obtained by the phase solution method, which finally corresponds to the displacement.

[0010] Optionally, the grating is arranged on the displacement plane to be measured, and a symmetrical reflector group is provided in the diffraction direction of the light beam to reflect the diffracted light into the interference field.

[0011] Optionally, the interference field of the diffracted light beam coincides with the front focal plane of the first lens of the encoding imaging system.

[0012] Optionally, the coded imaging system consists of two lenses and an optical phase plate with a known distribution, wherein the optical phase plate is placed between the two lenses.

[0013] Compared with the prior art, the present invention has the following beneficial effects:

[0014] 1) The complex amplitude of the interference field of the grating diffraction beam is obtained by using the grating displacement detection principle and the light field complex amplitude recovery technology, which makes the instrument have strong anti-interference ability and high working stability.

[0015] 2) The phase demodulation algorithm is used to directly solve the stable initial phase to be sought from the fringe complex amplitude, corresponding to the change value of the displacement, to achieve highly stable numerical subdivision and improve the resolution of the instrument.

[0016] 3) The measurement range depends on the length of the measured fringe grating, and can achieve a large-range displacement measurement of 100mm. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0018] Figure 1 This is a schematic diagram of the structure of Embodiment 1 of the present invention;

[0019] Figure 2 This is a schematic diagram of the structure of Embodiment 2 of the present invention;

[0020] In the figure, 1. laser light source; 2. one-dimensional grating; 3. first reflector; 4. second reflector; 5. first lens; 6. optical phase plate; 7. second lens; 8. image sensor; 9. two-dimensional grating; 10. third reflector; 11. fourth reflector; 12. computer. DETAILED DESCRIPTION

[0021] In order to make the objectives, technical solutions and advantages of the present invention more clear, the embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0022] Embodiment 1:

[0023] like Figure 1 As shown, a one-dimensional nanometer / picometer displacement measuring instrument includes a laser light source 1 emitting a light beam and incident perpendicularly on a one-dimensional grating 2, diffraction occurs, and the displacement to be measured is one-dimensional, which is perpendicular to the incident light direction in the plane. A pair of symmetrical reflector groups, namely a first reflector 3 and a second reflector 4, are arranged on the two propagation paths of the diffracted light. The reflector group reflects the two diffracted light beams to the front focal plane of the first lens 5 of the encoding imaging system, causing interference to form an interference field.

[0024] The subsequent propagation path of the light beam is provided with a coding imaging system, an image sensor 8 and a computer 12. The first lens 5 of the coding imaging system modulates the interference field of the front focal plane into a parallel light beam, which is vertically incident on an optical phase plate 6 with a known distribution for coding. The encoded parallel light beam is imaged onto the target surface of the image sensor 8 through the second lens 7 of the coding imaging system. The image sensor 8 and the computer 12 are connected.

[0025] For the image calculation recorded by the computer 12, the image expression recorded by the image sensor 8 can be written as

[0026]

[0027] Wherein, I is the intensity image collected by the image sensor 8 , U is the complex amplitude of the light beam incident on the phase plate 6 , and P is the complex amplitude transmittance of the phase plate 6 . Stands for Fourier Transform.

[0028] The interference field to be determined is located in front of the first lens 5, so the complex amplitude U can be written as

[0029]

[0030] Where H is the complex amplitude distribution of the interference field. The complex amplitude H of the interference field can be obtained from the data image I recorded by the image sensor 8 through an iterative complex amplitude recovery algorithm. Then the phase difference of the diffracted light beam is obtained through a phase resolution method, and finally corresponds to the displacement amount.

[0031] Embodiment 2:

[0032] like Figure 2 As shown, this embodiment discloses a two-dimensional nanometer / picometer displacement measuring instrument, including a laser light source 1 emitting a light beam and incident perpendicularly to a two-dimensional grating 9, diffraction occurs, the grating is a two-dimensional grating, and the displacement to be measured is two-dimensional, which is the movement in a plane perpendicular to the incident light. Two pairs of symmetrical reflector groups 3 and 4, 10 and 11 are arranged on the four propagation paths of the diffracted light, and the reflector groups reflect the four diffracted light beams to the front focal plane of the first lens 5 of the encoding imaging system, causing interference to form an interference field.

[0033] The subsequent propagation path of the light beam is provided with coding imaging systems 5, 6 and 7, an image sensor 8 and a computer 12. The first lens 5 of the coding imaging system modulates the interference field of the front focal plane into a parallel light beam, which is vertically incident on an optical phase plate 6 with a known distribution for encoding. The outgoing parallel light beam passes through the second lens 7 of the coding imaging system to image the modulated light beam onto the target surface of the image sensor 8. The image sensor 8 is connected to the computer 12.

[0034] Finally, the recorded image is calculated by adopting the data processing method of Example 1, and the complex amplitude of the interference field is obtained by the complex amplitude recovery algorithm, and then the phase difference of the diffracted light beam is obtained by the phase solution method, and finally corresponds to the displacement.

Claims

1. A nanometer / picometer displacement measuring instrument, comprising a laser light source, a grating, a reflector group, a coded imaging system consisting of a first lens (5), an optical phase plate (6) and a second lens (7), an image sensor and a computer; It is characterized in that The laser light source is vertically incident on the grating, and after diffraction by the grating, it is reflected by the reflector group and interferes on the front focal plane of the first lens (5) to form an interference field; the interference field forms a parallel light beam after passing through the first lens (5), which is encoded by an optical phase plate (6) with a known distribution, and then imaged onto the target surface of the image sensor (8) through the second lens (7); the image sensor (8) is connected to a computer (12); the computer (12) uses a complex amplitude recovery algorithm to obtain the complex amplitude of the interference field from the collected image, and then obtains the phase difference of the diffracted light beam through a phase resolution method, which finally corresponds to the displacement.

2. The nanometer / picometer displacement measuring instrument according to claim 1, It is characterized in that The grating is perpendicular to the outgoing light beam.

3. The nanometer / picometer displacement measuring instrument according to claim 1, It is characterized in that The grating is a one-dimensional grating (2), and the reflector group is composed of a first reflector (3) and a second reflector (4) which are opposite to each other.

4. The nanometer / picometer displacement measuring instrument according to claim 1, It is characterized in that The grating is a two-dimensional grating (9), and two pairs of symmetrical reflecting mirror groups are arranged in the direction of the diffracted light beam.

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