Aspherical optical center deviation error measurement device and its measurement method

Abstract

The present invention relates to the field of aspherical optical measurement technology, and particularly relates to an aspherical optical center deviation error measurement device and a measurement method thereof. The aspherical mirror optical center deviation error measurement device includes a base, on which a high-precision turntable is arranged. A measured part fixing table is arranged on the high-precision turntable, and the measured part fixing table is coaxially arranged with the base and the high-precision turntable. A laser micro-displacement probe is arranged at the upper end of the center of the top of the measured aspherical mirror. A probe moving support is arranged on the base outside the high-precision turntable, and the laser micro-displacement probe is movably arranged on a slide rail. The present invention can effectively guarantee the measurement accuracy of the center deviation error of the measured aspherical mirror, and can directly obtain the angular deviation amount of the measured aspherical mirror. During the movement of the probe, the center deviation errors of each annulus of the measured aspherical mirror can be measured. The device has a simple structure, and the components are all conventional standardized products without the need for special design. The measurement method has a short measurement time, high efficiency and convenient operation.

Description

Technical Field

[0001] The present invention relates to the technical field of aspherical optical measurement, and particularly relates to an aspherical optical center deviation error measurement device and a measurement method thereof. Background Art

[0002] Aspherical mirrors are widely used due to their superior optical performance, especially in endoscopy and nanoscale fluorescence microscopy. High-precision laser projection is also based on focused aspherical lenses, which can achieve perfect images.

[0003] The application of aspherical mirrors in optical systems greatly improves the imaging quality of optical systems. At the same time, the optical path can be shortened, the volume of the optical system can be reduced, and the system can be miniaturized and lightened. However, the curvature radii of each point on the aspherical lens are different, and there is only one axis of symmetry. The optical center deviation destroys this coaxial symmetry, which will cause astigmatism and other problems in the lens, reducing the imaging quality.

[0004] An aspherical optical center deviation error measurement device can detect the center deviation error under different curvatures of an aspherical mirror. Currently, there are the following two detection methods for aspherical mirrors:

[0005] One method is to measure the height information of each point on the surface by scanning the reflected light of the laser on the surface of the measured lens with a laser centering measuring instrument, and obtain the eccentricity of the lens by reconstructing the height information. However, this device needs to add an autocollimator to center the spherical center of the aspherical vertex, resulting in a large cost, long scanning time, and low measurement efficiency.

[0006] Another high-precision aspherical centering method is based on the interference principle. By detecting the change of the interference pattern during the rotation of the aspherical mirror with the turntable, the eccentricity and tilt of the aspherical mirror relative to the turntable axis are judged. However, this method requires adding additional measurement devices, resulting in a large cost, and also requires adjusting the interferometer and the aspherical compensating mirror, which is troublesome to operate and has low measurement efficiency. Summary of the Invention

[0007] In view of this, in order to solve the problems of complex measurement, high cost, and long measurement time in the prior art, the present invention provides an aspherical optical center deviation error measurement device and a measurement method thereof.

[0008] To achieve the above object, the technical solution adopted by the present invention is: an aspherical mirror optical center deviation error measurement device, including a base, a high-precision turntable is arranged on the base, a measured part fixing table is arranged on the high-precision turntable, the measured part fixing table is coaxially arranged with the base and the high-precision turntable, and a laser micro-displacement probe is arranged at the upper end of the center of the top of the measured aspherical mirror; a probe moving bracket is arranged on the base outside the high-precision turntable, the probe moving bracket is composed of a fixed connection section and an arc-shaped slide rail, one end of the fixed connection section is fixed on the base, and the laser micro-displacement probe is movably arranged on the slide rail.

[0009] Further, the above fixed connection section is "L"-shaped, with both ends of the slide rail located at the top of the aspherical mirror to be measured and the bottom side of the aspherical mirror to be measured respectively. The curvature of the slide rail is larger than the spherical radius of the aspherical mirror to be measured.

[0010] Further, the reference axis of the above laser micro-displacement probe is perpendicular to the tangent plane of the measurement point of the aspherical mirror to be measured.

[0011] Further, the above workpiece fixing table is a threaded screw clamping mechanism.

[0012] Further, the above laser micro-displacement probe is a non-contact fiber laser type laser micro-displacement probe.

[0013] Further, the method for measuring the center offset error of the aspherical mirror using the above device is to fix the aspherical mirror to be measured on the workpiece fixing table. The laser micro-displacement probe moves on the probe moving bracket, and the radial displacement values of n annuli on the aspherical surface can be measured. During the measurement process, first, the center offset error of one annulus is detected. By rotating the workpiece to be measured forward and backward, the radial displacements of the two reflected light spot images are obtained. The radial displacement is the linear offset of the annulus eccentricity. The angular offset of the annulus is related to its linear offset, chord length, and the asphericity of the aspherical mirror to be measured. The center offset error is obtained using the angular offset of the annulus. The relational expression is:

[0014]

[0015] where, Δ i is the linear offset detected on the i-th annulus, R i is the radius of curvature on the i-th annulus, k i is the coefficient related to the asphericity and chord length; then, the center offset error detection of n annuli is carried out, and the overall center offset of the aspherical surface takes the largest angular offset among each annulus as the center offset error of the aspherical surface.

[0016] Compared with the prior art, the present invention has the following advantages and effects:

[0017] 1) The present invention directly measures the aspherical mirror to be measured by adjusting the position of the probe head, and simply realizes the measurement of the center offset error of the aspherical surface of the aspherical mirror to be measured by using the displacement on the slide rail. During this process, in order to ensure the measurement accuracy, we select a high-precision turntable as the reference rotation axis for the aspherical mirror to be measured. The axis of the workpiece fixing table is coaxial with this reference axis, which can effectively guarantee the measurement accuracy of the center offset error of the aspherical mirror. This method has a simple structure and is practical and convenient;

[0018] 2) The method of the present invention can directly obtain the angular deviation of the aspheric surface to be measured, greatly improving the practicability. During the movement of the probe, the center deviation error of each annulus of the aspheric mirror can be measured. The probe utilizes the reflective micrometer principle, and the measurement principle is simple.

[0019] 3) The device of the present invention has a simple structure, and the components are all conventional standardized products, without the need for special design.

[0020] 4) Using this method for measurement has a short measurement time, high efficiency, and is convenient to operate and use. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is a schematic structural diagram of the present invention;

[0022] Figure 2 is a schematic structural diagram of a specific embodiment of the aspheric optical center deviation error measurement device;

[0023] Figure 3 is a schematic structural diagram of the measurement principle of the aspheric optical center deviation error measurement device;

[0024] Figure 4 is a flowchart of an embodiment of the eccentric measurement method of the aspheric mirror of the present invention;

[0025] In the figure, 1, base; 2, high-precision turntable; 3, fixed table for the workpiece to be measured; 4, tightening nut for the fixed table of the workpiece to be measured; 5, laser micro-displacement probe; 6, probe moving bracket; 7, aspheric mirror to be measured; 8, moving direction; 9, normal direction. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0026] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0027] The present invention uses a high-precision turntable as the reference rotation axis for the aspheric mirror to be measured. The aspheric mirror to be measured is placed on the fixed table for the workpiece to be measured and rotates with the high-precision turntable. The laser micro-displacement probe is used to measure the symmetry error of each annulus of the aspheric mirror surface relative to the reference rotation axis of the high-precision turntable. This error is the eccentric error of the annulus after conversion. At this time, the light of the laser micro-displacement probe is coaxial with the normal of the surface of the measured annulus. Then, the laser micro-displacement probe is moved to perform multi-point measurement on the entire aspheric mirror to be measured, and the eccentric error of the entire aspheric mirror to be measured can be obtained.

[0028] A device for measuring the optical center deviation error of an aspheric mirror provided by the present invention, as Figure 1As shown in the figure, it includes a base 1, a high-precision turntable 2, a workpiece fixing table 3, a workpiece fixing table tightening nut 4, a laser micro-displacement probe 5, a probe moving bracket 6, and a measured aspherical mirror 7 fixed on the workpiece fixing table 3. The workpiece fixing table 3 is coaxially arranged with the base 1 and the high-precision turntable 2.

[0029] The workpiece fixing table 3 is a threaded screw clamping mechanism. By screwing the screw into the thread of the mechanism, the distance between the clamping parts is adjusted until the measured aspherical mirror 7 is clamped.

[0030] A probe moving bracket 6 is arranged on the base 1 outside the high-precision turntable 2. The probe moving bracket 6 is composed of a fixed connection section and an arc-shaped slide rail. One end of the fixed connection section is fixed on the base 1, and the laser micro-displacement probe 5 is movably arranged on the slide rail. The fixed connection section is in an "L" shape. The two ends of the slide rail are respectively located at the top of the measured aspherical mirror 7 and the bottom of the side of the measured aspherical mirror 7. The radian of the slide rail is larger than the spherical radius of the measured aspherical mirror 7, which is convenient for installing the laser micro-displacement probe 5. The laser micro-displacement probe 5 can be moved and measured on the probe moving bracket 6 according to the size of the measured aspherical mirror 7 and actual needs; the direction of the incident light emitted by the laser micro-displacement probe 5 is adjustable, so that the laser is normally incident on the measurement point. During the moving measurement process, the laser micro-displacement probe 5 can be adjusted to make the reference axis of the laser micro-displacement probe 5 coaxial with the normal line of the measurement point of the measured aspherical mirror 7.

[0031] The high-precision turntable 2 is placed on the base 1, and the to-be-measured aspherical surface 7 is placed on the workpiece fixing table 3. The measured aspherical mirror 7 rotates on the high-precision turntable 2, and the displacement information of a ring zone on the measured aspherical mirror 7 can be measured. If there is no center deviation error on the ring zone, the reflected light finally forms a light spot at the same position, and the measurement value of the laser micro-displacement probe 5 remains unchanged; if there is a center deviation error on the ring zone, the reflected light finally forms two or more light spots at different positions, and light spots are formed during the rotation measurement process. The workpiece fixing table 3 can adjust the distance by rotating the workpiece fixing table tightening nut 4, and aspherical mirrors of different sizes can be placed; a slide rail is arranged on the probe moving bracket 6, and the laser micro-displacement probe 5 moves on the slide rail of the probe moving bracket 6, that is, the center deviation errors of n ring zones on the measured aspherical mirror 7 are measured.

[0032] Embodiment:

[0033] As Figure 2 shown, during the measurement process of the aspherical mirror optical center deviation error measuring device, the laser micro-displacement probe 5 moves at a certain curvature in the moving direction 8. As Figure 2 shown by the dotted line box, the center deviation of the measured aspherical mirror 7 can be measured at the position where measurement is required.

[0034] In a specific implementation, the aspherical mirror 7 to be measured is placed on the workpiece fixing table 3. The nut 4 of the workpiece fixing table is used to tighten and clamp the workpiece to be measured. The base 1, the high-precision turntable 2, the workpiece fixing table 3, and the aspherical mirror 7 to be measured are placed along the same reference axis, so that the aspherical mirror 7 to be measured is symmetric about the reference axis during the rotation measurement, ensuring the symmetry of the aspherical mirror 7 to be measured during the measurement process. This symmetry is reflected in that when the laser emitted by the laser micro-displacement probe 5 irradiates the surface of the aspherical mirror 7 to be measured during measurement, the aspherical mirror 7 to be measured rotates around the reference axis. Theoretically, the aspherical mirror 7 is symmetric, and the light reflected from a ring belt on the aspherical mirror 7 to be measured irradiated by the incident laser should be imaged at the same position on the image plane (non-contact laser micro-displacement probe 5) during the rotation process. If the imaging positions are not the same, it can indicate that there is a centering deviation error in the aspherical mirror 7 to be measured.

[0035] In order to measure the centering deviation of the entire aspherical mirror 7 to be measured, the laser micro-displacement probe 5 can move on the slide rail section of the probe moving bracket 6, and the non-contact laser micro-displacement probe 5 can adjust its direction. As Figure 2 shown in the dashed box, the non-contact laser micro-displacement probe 5 can move to the position to be measured for measurement. The non-contact laser micro-displacement probe 5 scans and measures along the probe moving bracket with a certain curvature, and the centering deviations of n ring belts on the aspherical mirror 7 to be measured can be measured, ensuring that the centering deviations of all ring belts of the entire aspherical surface can be measured.

[0036] The measurement principle of this embodiment is as Figure 3 shown. The non-contact laser micro-displacement probe 5 adopts a reflection measurement principle and is composed of a transmitting optical fiber, a receiving optical fiber, and a laser light source. The light source emits laser light that is incident on the aspherical mirror 7 to be measured along the normal direction 9 of the transmitting optical fiber. Incidence along the normal direction 9 can ensure that the reflected light returns to the non-contact laser micro-displacement probe 5 along the original path. After the reflected light is reflected by the surface to be measured, the imaging light information is received by the receiving optical fiber, and the imaging light information is finally subjected to corresponding detection and processing and transmitted to a computer for analysis.

[0037] In a specific implementation, the centering deviation of the final aspherical mirror 7 to be measured is obtained using the following formula: where, Δ i is the linear deviation detected on the i-th ring belt, R i is the radius of curvature of the i-th ring belt, and k i is a coefficient related to the asphericity and chord length.

[0038] In specific implementation, the final evaluation method is as follows: The laser micro-displacement probe 5 receives the radial displacement of the annulus generated due to the central deviation of the measured aspherical mirror 7 on an annulus, and this displacement represents the eccentricity error of the annulus. The laser micro-displacement probe 5 can detect the eccentricity error of each or multiple annuli. The central deviation angle (i.e., angular deviation) of the annulus is related to its radial eccentricity error, chord length, and the asphericity of the measured aspherical mirror 7. The central deviation is described by the angular deviation of the annulus. After detecting the central deviation errors of n annuli, the overall central deviation of the measured aspherical mirror 7 takes the maximum angular deviation among all the annuli as the evaluation result of the measured aspherical mirror 7.

[0039] A measuring method for the optical center deviation error of an aspherical mirror measuring device is as Figure 4 shown, and the method steps are as follows:

[0040] Step S41: The base 1 is used to hold the high-precision turntable 2 and the probe moving bracket 6. The high-precision turntable 2 and the base 1 are coaxial, and the measured part fixing table 3 is placed coaxially with the high-precision turntable 2. A suction pad is installed at the bottom of the base 1 to stably place the entire device on the workbench.

[0041] Step S42: Place the measured aspherical mirror 7 on the measured part fixing table 3 and tighten the nut. The measured part fixing table tightens the nut 4 to clamp the measured aspherical mirror 7.

[0042] Step S43: Adjust the laser micro-displacement probe 5 so that the incident laser normal direction 9 irradiates the aspherical surface to be measured.

[0043] Step S44: The measured aspherical mirror 7 rotates stably at the center of the high-precision turntable 2, and the rotation of the high-precision turntable 2 is used to achieve the purpose of measuring the central deviation error of a certain aspherical annulus.

[0044] Step S45: The laser micro-displacement probe 5 moves on the probe moving bracket 6, and can quickly obtain the relative shaft radial displacement information of n annuli on the measured aspherical mirror 7.

[0045] Step S46: If there is no central deviation error on the annulus, the reflected light finally forms a light spot at the same position and does not generate radial displacement; if there is a central deviation error on the annulus, then the position of the returned light spot image will generate radial displacement before and after rotation, and the magnitude of the radial displacement is proportional to the eccentricity of the corresponding annulus. Then the reflected light finally forms two or more light spots at different positions, and forms an annulus radial displacement during the rotation measurement process. This reflects the radial eccentricity error of the corresponding annulus.

[0046] The above is only a preferred embodiment of the present invention, and is not used to limit the protection scope of the present invention.

Claims

1. Measuring method of aspherical mirror optical center deviation error measuring device, characterized in that: The device adopted by the measuring method includes a base (1), on which a high-precision turntable (2) is arranged. On the high-precision turntable (2), a measured part fixing table (3) is arranged. The measured part fixing table (3) is coaxially arranged with the base (1) and the high-precision turntable (2). At the upper end of the top center of the measured aspherical mirror (7), a laser micro-displacement probe (5) is arranged; on the base (1) outside the high-precision turntable (2), a probe moving bracket (6) is arranged. The probe moving bracket (6) is composed of a fixed connection section and an arc-shaped slide rail. One end of the fixed connection section is fixed on the base (1), and the laser micro-displacement probe (5) is movably arranged on the slide rail; The fixed connection section is "L"-shaped. The two ends of the slide rail are respectively located at the top of the measured aspherical mirror (7) and the bottom of the side surface of the measured aspherical mirror (7). The radian of the slide rail is larger than the spherical radius of the measured aspherical mirror (7); The reference axis of the laser micro-displacement probe (5) is perpendicular to the tangent plane of the measured point of the measured aspherical mirror (7); The measured part fixing table (3) is a threaded screw clamping mechanism; The laser micro-displacement probe (5) is a non-contact optical fiber laser type laser micro-displacement probe; Fix the measured aspherical mirror (7) on the measured part fixing table (3), and move the laser micro-displacement probe (5) on the probe moving bracket (6), and the radial displacement values of n annular zones on the aspherical surface can be measured; During the measurement process, first detect the center deviation error of an annular zone. Rotate the part to be measured forward and backward to obtain the radial displacements of the two reflected light spot images. The radial displacement is the linear deviation of the annular eccentricity. The angular deviation of the annular zone is related to its linear deviation, chord length and the asphericity of the measured aspherical mirror. Use the angular deviation of the annular zone to obtain the center deviation error. The relationship formula is: where, Δ i is the line offset detected on the i-th annular zone, R i is the radius of curvature of the i-th annular zone, and k i is the coefficient related to the asphericity and chord length; Then, detect the center deviation errors of n annular zones. The overall center deviation of the aspherical surface takes the largest angular deviation among each annular zone as the center deviation error of the aspherical surface.

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