Non-contact detection sensor integrated differential optical path capable of reducing influence of environmental fluctuation

Abstract

The invention belongs to the technical field of non-contact high-precision component detection, and provides a non-contact detection sensor integrated differential optical path capable of reducing the influence of environmental fluctuation in order to meet the requirement for the surface measurement precision of a non-contact high-precision component and further reduce the influence of the environmental fluctuation. A two-stage system design is adopted: the first stage adopts a double-frequency heterodyne interference light path, the resolution can reach 0.3 nm under the subdivision of a quadruple light path, a measurement reflector c and a reference reflector c are symmetrically arranged, so that the interference light path is geometrically symmetric, and the phase drift caused by environmental disturbance can be reduced by performing differential subtraction on delta phi caused by environmental disturbance; a differential optical path is designed on the basis of a double-frequency heterodyne interference optical path and is integrated with a second-stage differential confocal optical path, so that the surface of an element to be measured can be tracked with high precision.

Description

Technical Field

[0001] The invention belongs to the technical field of non-contact high-precision component detection. Background Art

[0002] The use of complex free-form surface optical elements can increase the freedom of optical system design, greatly improve system performance, and reduce the number of components required for the system. They are widely used in remote sensing optics, semiconductor systems, head-mounted displays and other technical fields. However, complex free-form surface optical elements have high requirements for surface accuracy, which will inevitably increase the accuracy requirements and detection efficiency of detection equipment. High-precision measurement equipment is easily affected by temperature, humidity and air pressure in the environment. The Edlen formula is used to estimate the impact of environmental fluctuations on surface accuracy measurement. The air refractive index is a function of temperature, air pressure, humidity and CO2 content in the air. The differential formula near the normal state is derived:

[0003] δn=(0.00268δp-0.929δt-0.00042δf)×10 -6 ,

[0004] In the formula, δp, δt, and δf are the changes in air pressure, temperature, and humidity relative to the normal state. For example, when the dead distance of the measurement branch is 20 mm, the sensitivity to air pressure, temperature, and humidity are 0.054 nm / Pa, 18.58 nm / ℃, and 0.0084 nm / Pa, respectively, which is enough to show the negative impact of environmental fluctuations on surface accuracy measurement. Therefore, designing a non-contact detection sensor with environmental fluctuation resistance is of great significance to the accuracy of surface accuracy measurement of complex free-form surface optical elements.

[0005] There are two principles used in the sensor integrated differential optical path of the present invention: differential confocal principle and dual-frequency heterodyne interference principle.

[0006] like Figure 1 As shown, the optical path of the differential confocal principle consists of a differential laser beam passing through polarization beam splitter prism a and 1 / 4 wave plate a in sequence, and being focused on the surface of the component to be measured by objective lens a, and then reflected by it, passing through 1 / 4 wave plate a and returning to polarization beam splitter prism a. After being reflected by polarization beam splitter prism a, it reaches semi-transparent and semi-reflective mirror a located in the reflection direction of polarization beam splitter prism a. The reflected and transmitted light beams are converged by converging mirror a. Two pinholes a are respectively located at the Rayleigh distance from the focal plane in front of the converging mirror focus. Photodetector a is placed behind the pinhole. By differentially processing the two signals, the differential confocal measurement curve I is obtained. diff =I A -I B ,

[0007] Among them, I A ,I BRepresents the light intensity signal detected by the two photodetectors, I diff By determining the zero point of the curve, the precise focus position is obtained, ensuring that the sensor can be accurately focused.

[0008] like Figure 2 As shown, the optical path of the dual-frequency heterodyne interference principle consists of a dual-frequency laser emitting linearly polarized light with frequencies f0 and f1 that vibrate in perpendicular directions to each other. After passing through a beam splitter prism, the reflected light is used as a reference signal for the heterodyne interferometer. The transmitted light is divided into p light and s light by the polarization beam splitter prism b. The p light with a frequency of f1 is transmitted through the 1 / 4 wave plate b, incident on the reference reflector, reflected from b, and then passes through the 1 / 4 wave plate b and the polarization beam splitter prism b in sequence. After being reflected from the polarization beam splitter prism b, it reaches the corner cube prism b and enters the polarization beam splitter prism b again. After being reflected from the reference reflector b, it passes through the 1 / 4 wave plate b in sequence, and then passes through the polarization beam splitter prism b before being transmitted and collected by the heterodyne detector. The other s light with a frequency of f0 is reflected from the measuring reflector b, passes through the 1 / 4 wave plate b in sequence, is incident on the polarization beam splitter prism b, is transmitted to the corner cube prism b, and then enters the polarization beam splitter prism b again. After being transmitted from the polarization beam splitter prism b, it passes through the 1 / 4 wave plate b and the reference reflector b, and then passes through the 1 / 4 wave plate b and the polarization beam splitter prism b again before being reflected and collected by the heterodyne detector. That is, the two beams of light are combined into one beam through the polarization beam splitter prism b to form a measurement signal with a frequency of f. m =f2-f0±Δf, where

[0009] Where c is the speed of light, v is the speed of the measuring reflector b, and using binomial expansion, when the ratio 2v / c is very small, the higher-order terms can be ignored, and the Doppler frequency difference can be obtained as

[0010]

[0011] Then the classic formula for dual-frequency heterodyne interferometry length measurement is

[0012]

[0013] Among them, λ is the laser wavelength of the dual-frequency laser, and N is the number of interference fringes change cycles, that is, the frequency is f0 and the frequency is f m The two beams of light are transformed from the photoelectric detection signal to the interference beam to form the measurement signal I M When the measuring reflector b moves, the length of the measuring arm in the interferometer will change. At this time, the measuring signal I M There will be a phase change of ΔΦ.

[0014] Although the above differential confocal and dual-frequency heterodyne interference optical path can alleviate the impact of environmental fluctuations to a certain extent, it still cannot meet the requirements of non-contact high-precision component surface measurement accuracy. Summary of the invention

[0015] In order to meet the requirements of non-contact high-precision component surface measurement accuracy and further reduce the impact of environmental fluctuations, the present invention proposes a "non-contact detection sensor integrated differential optical path that can reduce the impact of environmental fluctuations."

[0016] The non-contact detection sensor integrates a differential optical path to mitigate the impact of environmental fluctuations, such as Figure 3 As shown, the laser 31 is located on the right side of the optical path and vertically enters the first right-angle prism 32 on the same horizontal line with the laser 31. The differential confocal light beam is deflected 90 degrees and propagates downward, and sequentially passes through the corner cube prism c33, the polarization beam splitter c34, the first 1 / 4 wave plate c35 at the bottom thereof, and the objective lens c36, and converges on the surface of the component to be measured. Among them, the bottom of the first right-angle prism 32, the corner cube prism c33, the first 1 / 4 wave plate c35, and the center of the objective lens c36 coincide with the differential confocal optical axis; the light beam converged on the surface of the component to be measured returns along the original path and passes through After being reflected by the polarization beam splitter prism c34, it is vertically incident on the second 1 / 4 wave plate c37 located on its left side; a semi-transparent and semi-reflective mirror c38 is arranged on the left side of the polarization beam splitter prism c34, and its central spatial position coincides with the horizontal center of the polarization beam splitter prism c34; a reflector 39 is located directly above the semi-transparent and semi-reflective mirror c38; two-way converging mirrors c315, a pinhole c and a photodetector c (not marked in the figure) are coaxial with the semi-transparent and semi-reflective mirror c38 and the reflector 39 from right to left in sequence; the pinhole c is respectively located at the Rayleigh distance from the focal plane in front of the focus of the two converging mirrors c315;

[0017] The dual-frequency heterodyne laser interferometer 316 emits linear polarized light with frequencies f0 and f1 and vibration directions perpendicular to each other. The light first passes through the second 1 / 4 wave plate c37 and is split by the polarization beam splitter prism c34. One beam is the transmitted light p and the other is the reflected light s. The transmitted light p passes through the third 1 / 4 wave plate c310 on the right side of the polarization beam splitter prism c34, which coincides with the horizontal center of the polarization beam splitter prism c34. The transmitted light p then passes through the second right-angle prism 311 on the right side of the third 1 / 4 wave plate c310. The transmitted light is folded 90° and vertically incident on the reference reflector c312 at the same horizontal position as the objective lens c36. After reflection, the light passes through the second right-angle prism 311, the third 1 / 4 wave plate c310, and the polarization beam splitter prism c34 in turn, and is reflected by the corner cube prism c33. After that, it is reflected by the polarization beam splitter prism and enters the third 1 / 4 wave plate c310 again, and is reflected by the second right-angle prism 311 and then vertically enters the reference reflector c312 and returns to the original path and is transmitted through the polarization beam splitter prism c34; the reflected light s passes through the first 1 / 4 wave plate c35 and vertically enters the measuring reflector c313 at the same horizontal position as the objective lens c36. The measuring reflector c313 and the objective lens c36 are fixed on the servo device together, and after being reflected by the measuring reflector c313, it enters the first 1 / 4 wave plate c35, the polarization beam splitter prism c34, and the corner cube prism c33, and then is projected through the polarization beam splitter prism c34, enters the first 1 / 4 wave plate c35 again and vertically enters the measuring reflector c313 again, returns to the polarization beam splitter prism c34, and is emitted to form a beat frequency with the transmitted light p.

[0018] Technical effects:

[0019] The invention adopts a two-stage system design: the first stage adopts a dual-frequency heterodyne interference optical path, and its resolution can reach 0.3nm under the condition of four-times optical path subdivision; a cut is made on the top of a corner cube prism c to add a new optical quality surface; a measuring reflector c and a reference reflector c are symmetrically placed, so that the interference optical path presents geometric symmetry; ΔΦ caused by environmental interference makes the reference arm and the measuring arm approximately equal because of the symmetry of the optical path; and the phase drift caused by environmental disturbance can be reduced through differential subtraction; a differential optical path is designed on the basis of the dual-frequency heterodyne interference optical path and is integrated with a differential confocal optical path of the second stage, so that high-precision tracking of the surface of the component to be measured can be achieved; in order to achieve the purpose of differential between the reference optical path and the measuring optical path, the second right-angle prism folds the transmitted light p by 90 degrees, so that the environmental fluctuations suffered by the transmitted light p and the reflected light s in the optical path traversed are approximately equal, thereby greatly reducing environmental interference; and the measuring reflector c is connected with the objective lens c, and the objective lens c and the measuring reflector c are driven by a servo device at the same time to achieve measurement of the precision component.

[0020] The non-contact detection sensor integrates a differential optical path to ensure that the non-contact detection sensor has a nm-level resolution and sub-nm-level measurement accuracy, and greatly reduces the impact of environmental fluctuations on the measurement accuracy, and has strong anti-interference and stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a schematic diagram of the optical path structure of the differential confocal principle.

[0022] Among them: differential laser 11, polarization beam splitter prism a12, 1 / 4 wave plate a13, objective lens a14, semi-transparent and semi-reflective mirror a15, converging mirror a16, photodetector a17, pinhole a18.

[0023] Figure 2 This is a schematic diagram of the optical path structure of the dual-frequency heterodyne interference principle.

[0024] Among them: dual-frequency laser 21, beam splitter prism 22, 1 / 4 wave plate b23, polarization beam splitter prism b24, corner cube prism b25, reference reflector b26, measurement reflector b27, dual-frequency signal acquisition data processing card 28.

[0025] Figure 3 Schematic diagram of the optical path structure of the present invention,

[0026] Among them: laser 31, first right-angle prism 32, corner cone prism c33, polarization beam splitter prism c34, first 1 / 4 wave plate c35, objective lens c36, second 1 / 4 wave plate c37, semi-transparent and semi-reflective mirror c38, reflector 39, third 1 / 4 wave plate c310, second right-angle prism 311, reference reflector c312, measurement reflector c313, integrated signal acquisition data processing card 314, converging mirror c315, dual-frequency heterodyne laser interferometer 316. DETAILED DESCRIPTION

[0027] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by ordinary technicians in this field without making creative work by adopting the embodiments of the present invention are within the scope of protection of the present invention.

[0028] Optical component selection and parameter requirements:

[0029] The light source may be a laser 31, and a laser with high power stability, such as a He-Ne laser with a wavelength of 633 nm, is selected.

[0030] The first right-angle prism 32 and the second right-angle prism 311 have their inclined surfaces coated with aluminum, and their right-angle surfaces coated with anti-reflection films.

[0031] The c33 angled surface of the corner cube prism is aluminum-plated for polarization maintenance, and its bottom surface and the optical quality surface formed after cutting are coated with anti-reflection coating.

[0032] The polarizing beam splitter c34 is anti-reflection coated on the through surface, and the extinction ratio is at least 1000:1.

[0033] The light-transmitting surfaces of the first 1 / 4 wave plate c35, the second 1 / 4 wave plate c37 and the third 1 / 4 wave plate c310 are all coated with anti-reflection coatings.

[0034] The splitting ratio of the semi-transparent and semi-reflective mirror c38 is 50:50±2%, the reflecting surface of the reflector 39 is coated with a high-reflection film at 45°, and the semi-transparent and semi-reflective mirror c38 and the reflector 39 meet 45°±30".

[0035] The reference reflector c312 and the measuring reflector c313 are coated with a high-reflection film at 0°.

[0036] The objective lens c36 has a magnification of 100×, a focal length of 2 mm, and a working distance of 3 to 6 mm. The specific model may be Mitutoyo Mplan Apo 100x.

[0037] The focal length of the converging lens 315 is 50 mm.

[0038] The noise equivalent sensitivity of the two photodetectors is better than The saturation optical power is greater than 30μW.

[0039] The dual-frequency heterodyne laser interferometer 316 can be selected to have a resolution better than 1 nm, an accuracy better than 0.4 ppm, and a beam diameter of 3 mm.

[0040] The sizes of the light-transmitting surfaces of the above-mentioned optical components need to match each other, and in order to ensure the size of the probe after integration, the components are selected as standard sizes as possible such as 12.7mm, 20mm, and 25.4mm to facilitate subsequent replacement or matching of the mounting bracket, and can be fixed together by epoxy resin bonding or the like, to achieve the integration and folding of the differential confocal and dual-frequency heterodyne optical paths, and to help improve stability and heat transfer.

[0041] Optical component reference dimensions:

[0042] The first right angle prism 32 has a size of 5 mm×5 mm×5 mm, and the second right angle prism 311 has a size of 25.4 mm×25.4 mm×25.4 mm.

[0043] The diameter of the corner cube prism c33 is 25.4 mm, and the height of the top of the corner cube prism c33 is 3 mm after the top angle is cut off.

[0044] The size of polarizing beam splitter prism c34 is 25.4mm.

[0045] The diameter of the first 1 / 4 wave plate c35 is 25.4 mm, the diameter of the second 1 / 4 wave plate c37 is 12.7 mm, and the diameter of the third 1 / 4 wave plate c310 is 25.4 mm.

[0046] The size of the semi-transparent and semi-reflective mirror c38 and the reflecting mirror 39 is 9×12 mm and the thickness is 2 mm.

[0047] The reference reflector c312 has a size of 25.4 mm, a central aperture diameter of 4 mm, and a thickness of 3 mm; the measurement reflector c313 has a size of 28 mm, a central aperture diameter of 4 mm, and a thickness of 5 mm.

[0048] The diameter of the converging mirror 315 is 8 mm.

[0049] The diameter of the two pinhole apertures is 30 μm.

[0050] The servo device uses a voice coil motor drive device based on the principle of electromagnetics as the driving mode of the probe motion system. It is a special form of single-phase two-pole direct drive motor. When current flows through the coil, it can generate a proportional force, so that the coil moves axially in the air gap. It has the characteristics of simple structure, small size, high acceleration and fast response. Furthermore, a piezoelectric ceramic drive device based on the principle of inverse piezoelectric effect can also be used. It can produce precise displacement and positioning accuracy of nm level, but the response speed is slow. In summary, a piezoelectric ceramic drive device is selected in the case of a small motion range, and a voice coil motor drive device is selected in the case of a large motion range.

[0051] The He-Ne laser beam is emitted horizontally, and mechanical parts are first used to ensure that the position of each optical component meets the tolerance requirements. The subsequent adjustment process is carried out in three steps: first, the focal plane position is determined by an interferometer; then the two pinholes are fixed at 0.5mm before and after the focus, and the beam quality analyzer is used to determine the axis of the light beam and the lens; finally, a waist hole with two degrees of freedom adjustment is set at the fixed position of the pinhole, and the pinhole is adjusted to detect the maximum light intensity as the judgment standard by the photoelectric detection module. At this time, the pinhole is fixed to complete the final adjustment process.

[0052] The preferred embodiments of the present invention are described in detail above in conjunction with the accompanying drawings. However, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, a variety of simple modifications can be made to the technical solution of the present invention, and these simple modifications all belong to the protection scope of the present invention.

Claims

1. A non-contact detection sensor integrated with a differential optical path that can mitigate the impact of environmental fluctuations, characterized in that: The laser (31) is located on the right side of the optical path and vertically irradiates the first right-angle prism (32) on the same horizontal line with the laser. The differential confocal light beam is deflected by 90 degrees and propagates downward, and sequentially passes through the corner cube prism c (33) located directly below, the polarization beam splitter prism c (34), the first 1 / 4 wave plate c (35) at the bottom thereof, and the objective lens c (36) to converge on the surface of the component to be measured, wherein the bottom of the first right-angle prism (32), the corner cube prism c (33), the first 1 / 4 wave plate c (35), and the center of the objective lens c (36) coincide with the differential confocal optical axis; the light beam converged on the surface of the component to be measured returns along the original path. After being reflected by the polarization beam splitter prism c (34), the light is vertically incident on a second 1 / 4 wave plate c (37) located on the left side thereof; a semi-transparent and semi-reflective mirror c (38) is arranged on the left side of the polarization beam splitter prism c (34), and its central spatial position coincides with the horizontal center of the polarization beam splitter prism c (34); a reflector (39) is located directly above the semi-transparent and semi-reflective mirror c (38); two converging mirrors c (315), a pinhole c and a photoelectric detector c are coaxial with the semi-transparent and semi-reflective mirror c (38) and the reflector (39) from right to left in sequence; and the pinholes c are respectively located at the Rayleigh distance from the focal plane in front of the focus of the converging mirror c (315); A dual-frequency heterodyne laser interferometer (316) emits linear polarized light with frequencies f0 and f1 and vibration directions perpendicular to each other. The light first passes through a second quarter wave plate c (37) and is split by a polarization beam splitter prism c (34). One beam is a transmitted light p and the other is a reflected light s. The transmitted light p passes through a third quarter wave plate c (310) on the right side of the polarization beam splitter prism c (34), which coincides with the horizontal center of the polarization beam splitter prism c (34). The transmitted light p then passes through a second right-angle prism (311) on the right side of the third quarter wave plate c (310). The transmitted light p is folded 90 degrees and vertically incident on a reference reflector c (312) at the same horizontal position as the objective lens c (36). After reflection, the transmitted light p passes through the second right-angle prism (311), the third quarter wave plate c (310), and the polarization beam splitter prism c (34) in sequence, and is reflected by a corner cube prism c (33). The polarization beam splitter prism c is reflected and enters the third 1 / 4 wave plate c (310) again, and after being reflected by the second right-angle prism (311), it is vertically incident on the reference reflector c (312) and returns to the original path and is transmitted through the polarization beam splitter prism c (34); the reflected light s passes through the first 1 / 4 wave plate c (35) and is vertically incident on the measuring reflector c (313) at the same horizontal position as the objective lens c (36); the measuring reflector c (313) and the objective lens c (36) are fixed on the servo device together, and after being reflected by the measuring reflector c (313), it is incident on the first 1 / 4 wave plate c (35), the polarization beam splitter prism c (34), and the corner cube prism c (33), and after being reflected back, it is projected through the polarization beam splitter prism c (34), enters the first 1 / 4 wave plate c (35) again, and is vertically incident on the measuring reflector c (313) again, returns to the polarization beam splitter prism c (34), and is emitted to form a beat frequency with the transmitted light p.

2. The non-contact detection sensor integrated differential optical path capable of alleviating the influence of environmental fluctuations according to claim 1, characterized in that: The first right-angle prism (32) and the second right-angle prism (311) have their inclined surfaces coated with aluminum, and their right-angle surfaces coated with anti-reflection films; The inclined surface of the corner cube prism c (33) is coated with aluminum, and the bottom surface and the optical quality surface formed after cutting are coated with an anti-reflection film; The polarization beam splitter prism c (34) is coated with an anti-reflection film on its surface, and has an extinction ratio of at least 1000:1; The light-transmitting surfaces of the first quarter wave plate c (35), the second quarter wave plate c (37), and the third quarter wave plate c (310) are all coated with an anti-reflection coating; The splitting ratio of the semi-transparent and semi-reflective mirror c (38) is 50:50±2%, the reflective surface of the reflector (39) is coated with a high-reflection film at 45°, and the semi-transparent and semi-reflective mirror c (38) and the reflector (39) meet 45°±30”; The reference reflector c (312) and the measuring reflector c (313) have reflective surfaces coated with a high-reflection film at 0°; Objective lens c (36) has a magnification of 100×, a focal length of 2 mm, and a working distance of 3 to 6 mm. The specific model is Mitutoyo MplanApo100x; The focal length of the converging lens (315) is 50 mm.

3. The non-contact detection sensor integrated differential optical path capable of alleviating the influence of environmental fluctuations according to claim 2, characterized in that: The first right angle prism (32) has a size of 5 mm×5 mm×5 mm, and the second right angle prism (311) has a size of 25.4 mm×25.4 mm×25.4 mm; The diameter of the corner cube prism c(33) is 25.4 mm, and the top of the corner cube prism c(33) is cut off to a height of 3 mm; The size of polarization beam splitter prism c (34) is 25.4 mm; The diameter of the first quarter wave plate c (35) is 25.4 mm, the diameter of the second quarter wave plate c (37) is 12.7 mm, and the diameter of the third quarter wave plate c (310) is 25.4 mm; The size of the semi-transparent and semi-reflective mirror c (38) and the reflective mirror (39) is 9×12 mm and the thickness is 2 mm; The reference reflector c (312) has a size of 25.4 mm, a central aperture diameter of 4 mm, and a thickness of 3 mm; the measurement reflector c (313) has a size of 28 mm, a central aperture diameter of 4 mm, and a thickness of 5 mm; The converging mirror (315) has a diameter of 8 mm; The diameter of the two pinhole apertures is 30 μm.

4. The non-contact detection sensor integrated differential optical path capable of alleviating the influence of environmental fluctuations according to claim 1, characterized in that: The servo device is a voice coil motor driving device.

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