CN114577125A - Non-contact optical lens center thickness measuring method and measuring device - Google Patents
Non-contact optical lens center thickness measuring method and measuring device Download PDFInfo
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- CN114577125A CN114577125A CN202210369397.6A CN202210369397A CN114577125A CN 114577125 A CN114577125 A CN 114577125A CN 202210369397 A CN202210369397 A CN 202210369397A CN 114577125 A CN114577125 A CN 114577125A
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- 230000003287 optical effect Effects 0.000 title claims abstract description 164
- 238000000034 method Methods 0.000 title claims abstract description 29
- 238000005259 measurement Methods 0.000 claims abstract description 84
- 230000001427 coherent effect Effects 0.000 claims description 10
- 230000004075 alteration Effects 0.000 claims description 9
- 239000000463 material Substances 0.000 abstract description 12
- 238000010586 diagram Methods 0.000 description 8
- 238000000691 measurement method Methods 0.000 description 6
- 238000013461 design Methods 0.000 description 3
- 238000002310 reflectometry Methods 0.000 description 3
- 238000000926 separation method Methods 0.000 description 3
- 238000001514 detection method Methods 0.000 description 2
- 239000011521 glass Substances 0.000 description 2
- 238000003384 imaging method Methods 0.000 description 2
- 239000011241 protective layer Substances 0.000 description 2
- 238000007796 conventional method Methods 0.000 description 1
- 238000005305 interferometry Methods 0.000 description 1
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B11/00—Measuring arrangements characterised by the use of optical techniques
- G01B11/02—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness
- G01B11/06—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness for measuring thickness ; e.g. of sheet material
Abstract
The invention provides a non-contact optical lens center thickness measuring method and a measuring device, wherein the measuring device comprises an interval measuring module and a measuring tool module, wherein the interval measuring module comprises a Michelson interferometer and is used for measuring an interval distance; the measurement tool module comprises a first parallel flat plate, a to-be-measured lens clamping and adjusting device and a second parallel flat plate, wherein the to-be-measured lens clamping and adjusting device is arranged between the first parallel flat plate and the second parallel flat plate and used for clamping the to-be-measured lens and adjusting the position of the to-be-measured lens, so that the optical axis of the to-be-measured lens is coaxial with the measuring beam. When the device is used for measuring the thickness, the central thickness of the optical lens is directly measured without knowing the refractive index of the optical lens to be measured, the device is not limited by the influence of material factors, the central thickness of any optical lens can be measured, and the measurement precision is improved.
Description
Technical Field
The invention relates to the technical field of optical precision measurement, in particular to a method and a device for measuring the central thickness of a non-contact optical lens.
Background
In optical systems, an optical lens is one of the most basic and important optical elements, and the measurement of the center thickness of an optical lens is of paramount importance. The measurement accuracy of the central thickness of the optical lens directly affects the imaging quality of the whole optical system, and particularly for lenses in high-performance optical systems such as an objective lens of a lithography machine and an aerospace camera, the aberration of the final objective lens can be caused by the deviation of the central thickness measurement of each single lens, and the imaging quality of the objective lens is affected. Therefore, a high-precision measurement method and a measurement apparatus are required to measure the center thickness of the optical lens.
There are two common methods for measuring the center of an optical lens, i.e., contact measurement and non-contact measurement. In the contact measurement, a handheld dial gauge, a micrometer or a height gauge is generally used for measurement, and in the measurement process, the accuracy of the position of the central point of the lens directly affects the detection precision, so that an inspector moves the measured lens back and forth during measurement to find the highest point (convex mirror) or the lowest point (concave mirror), so that the measurement speed is slow and the error is large, the existing lens material is a high-light-transmission optical material, the material is soft, and when a detection head moves on the surface of the lens during measurement, the surface of the lens is easily scratched. Sometimes, a protective layer is padded on the lens during measurement, but the existence of the protective layer affects the direct measurement of the thickness, and further brings extra errors. Therefore, the contact measurement has been eliminated in the application fields with high requirements for lenses because of the disadvantages of low measurement accuracy, low measurement efficiency, poor stability, etc.
In order to solve the problems of contact measurement, some non-contact measurement methods exist at present. Common non-contact measurement methods include image measurement, coplanar capacitance, white light confocal, and interferometry, but these non-contact measurement methods have the following problems: (1) before measurement, parameters of an optical lens material, particularly the refractive index of the optical lens, must be known, and for some unknown materials, a standard block made of the material needs to be introduced to measure the refractive index of the optical lens first, and then the thickness of the optical lens can be measured, so that the operation steps are complicated and extra errors are brought to influence the measurement accuracy; standard blocks are required to be manufactured for each unknown material, so that the measurement cost is high and the practicability is not high; (2) for gradient index lenses (GRIN lenses), since their refractive index is not a constant, previous non-contact measurements cannot enable thickness measurements on gradient index lenses; (3) in order to reduce the measurement deviation in the non-contact measurement, it is necessary to ensure that the optical axis of the lens coincides with the optical axis of the measurement beam, but in the current test method, the optical axis coincidence is not confirmed in the system, and therefore, additional deviation may be caused.
Therefore, it is desirable to design a non-contact optical lens thickness measuring method, which can realize non-contact measurement of the thickness of an optical lens made of any material, does not require the refractive index of the known optical lens, and has small measurement error and high measurement accuracy.
Disclosure of Invention
In order to solve the technical problem, the invention provides a non-contact optical lens center thickness measuring device, which is characterized by comprising an interval measuring module and a measuring tool module, wherein the interval measuring module comprises a michelson interferometer and is used for measuring an interval distance; the measurement tool module comprises a first parallel flat plate, a to-be-measured lens clamping and adjusting device and a second parallel flat plate, wherein the to-be-measured lens clamping and adjusting device is arranged between the first parallel flat plate and the second parallel flat plate, and the to-be-measured lens clamping and adjusting device is used for clamping the to-be-measured lens and adjusting the position of the to-be-measured lens, so that the optical axis of the to-be-measured lens is coaxial with the measurement beam; before the central thickness of the optical lens is measured, the interval measuring module measures the interval distance from the lower surface of the first parallel flat plate to the upper surface of the second parallel flat plate, and the interval distance is marked as L1; when the central thickness of the optical lens is measured, the distance between the lower surface of the first parallel flat plate and the top point of the upper surface of the lens to be measured is measured by the interval measuring module and is marked as L2; and the distance between the top point of the lower surface of the lens to be measured and the upper surface of the second parallel flat plate is measured by the interval measuring module and is marked as L3, and the central thickness d of the lens to be measured is L1-L2-L3.
The non-contact optical lens center thickness measuring device has the following advantages: (1) the thickness is measured in a non-contact mode, and in the measuring process, the measuring device is not in contact with the surface of the optical lens to be measured, so that the surface of the optical lens to be measured cannot be damaged, and the damage to the optical lens to be measured can be effectively avoided; (2) when the device is used for measuring the thickness, the central thickness of the optical lens is directly measured without knowing the refractive index of the optical lens to be measured, the device is not limited by the influence of material factors, the central thickness of any optical lens can be measured, and the measurement precision is improved.
Preferably, the interval measuring device includes a short coherent light source, a first objective lens, a beam splitter prism, a photomultiplier and a reference mirror, light emitted by the short coherent light source becomes a beam of parallel light after passing through the first objective lens, and then is divided into two beams by the beam splitter prism, which are a reference beam and a measuring beam respectively, the reference beam is reflected by the reference mirror, the measuring beam is reflected by a surface to be measured, during measurement, the position of the reference mirror is moved along the optical axis of the reference beam, and when the photomultiplier observes interference fringes, the measuring beam and the reference beam have equal optical path. When a short coherent light source is adopted, interference can occur only when the reference light beam and the measuring light beam are completely in equal optical path, so that the position of the reference mirror and the position of the reflecting vertex of the measuring light beam have one-to-one correspondence, and the optical path difference between the two reflecting vertices is equal to the relative distance of the movement of the reference mirror.
Preferably, the moving distance of the reference mirror is measured by using a grating ruler.
Preferably, the flatness and parallelism of the first parallel flat plate and the second parallel flat plate reach a submicron level, and the measurement accuracy of the grating ruler reaches the submicron level. The measurement precision of the measurement device is improved by improving the flatness and parallelism of the first parallel flat plate and the second parallel flat plate and the measurement precision of the grating ruler, so that the device can be used for measuring the thickness of the submicron optical lens.
Preferably, the interval measuring device further comprises a second objective lens, and the second objective lens is used for converging the measuring light beam to the middle position of the top point of the upper surface and the lower surface of the optical lens to be measured. The second objective is used for realizing the convergence of the measuring beam so as to reduce the facula possibly formed by the reflection of the parallel beam.
Preferably, the second objective lens and the first parallel plate are designed in combination, and are used for correcting spherical aberration brought by the first parallel plate.
Preferably, the splitting ratio of the splitting prism is adjusted so that the energy of the measuring beam is greater than the energy of the reference beam. Because the reflectivity of the lens to be measured is relatively low, the energy of the reflected measuring beam is small, and therefore, the energy of the measuring beam can be increased, and the interval measuring module can observe a good interference pattern.
Preferably, the non-contact optical lens center thickness measuring device further comprises a center deviation measuring module, the to-be-measured lens clamping and adjusting device comprises a turntable, and the center deviation measuring module is used for adjusting the position of the interval measuring module so that the optical axis of the measuring light beam is coaxial with the rotating shaft of the turntable; the central deviation measuring module is also used for adjusting the position of the optical lens to be measured, so that the optical axis of the optical lens to be measured is coaxial with the rotating shaft of the turntable. When the center thickness of the traditional non-contact optical lens is measured, the optical axis of the optical lens may not be consistent with the optical axis of the measuring beam.
Preferably, the central deviation measurement module includes a third objective lens, a fourth objective lens, a beam splitter, a target plate, a narrow-band light source and a CMOS camera, when the central deviation measurement module is in use, a light beam emitted by the narrow-band light source illuminates the target plate, the target plate is reflected by the beam splitter to the fourth objective lens and then becomes parallel light to be output, the parallel light is converged on one surface of the optical lens to be measured by the third objective lens, and a curvature image reflected by the surface of the optical lens to be measured can be clearly imaged in the CMOS camera.
Preferably, the third objective lens and the second parallel plate are designed in combination, and are used for correcting spherical aberration brought by the second parallel plate.
The invention also provides a method for measuring the central thickness of the non-contact optical lens, which is characterized by comprising the following steps: s1: adjusting the measuring device to enable the first parallel flat plate and the second parallel flat plate to be perpendicular to the measuring beam; s2: moving the position of the reference mirror, and measuring the distance L1 between the lower surface of the first parallel flat plate and the second parallel flat plate; s3: placing the lens to be measured on the lens clamping and adjusting device to be measured, and adjusting the position of the lens to be measured to enable the lens to be measured and the measuring light beam to be coaxial; s4: moving the position of the reference mirror, and measuring the distance L2 between the lower surface of the first parallel flat plate and the upper surface of the lens to be measured and the distance L3 between the lower surface of the lens to be measured and the upper surface of the second parallel flat plate; s5: from the measured distances L1, L2 and L3, the central thickness d of the optical lens is calculated, where d ═ L1-L2-L3.
Preferably, after the step S1, the method further comprises the step S1-1 of adjusting the interval measuring module to enable the optical axis of the measuring beam to be coaxial with the rotating shaft of the turntable on the device for clamping and adjusting the lens to be measured; the step S3 further includes: and placing the lens to be measured on the lens clamping and adjusting device to be measured, and adjusting the position of the lens to be measured to enable the optical axis of the lens to be measured to be coaxial with the rotating shaft of the objective lens clamping tool to be measured and the rotating shaft of the upper rotating table of the adjuster, so that the lens to be measured is coaxial with the measuring light beam.
Drawings
FIG. 1 is a schematic diagram of a first embodiment of a central thickness measuring apparatus for a non-contact optical lens according to the present invention.
FIG. 2 is a flowchart illustrating a method for measuring a center thickness of a non-contact optical lens according to a first embodiment of the present invention.
FIG. 3 is a schematic diagram of interference intensity during a measurement process of a non-contact optical lens center thickness measuring apparatus according to the present invention.
FIG. 4 is a schematic diagram of a second embodiment of a central thickness measuring apparatus for a non-contact optical lens according to the present invention.
FIG. 5 is a schematic diagram of a display interface in the decentration measurement module.
FIG. 6 is a measurement method corresponding to the device for measuring the central thickness of the non-contact optical lens in FIG. 4
Detailed Description
As shown in fig. 1, fig. 1 is a schematic diagram of a first embodiment of a non-contact optical lens center thickness measuring device according to the present invention, which includes a separation measuring module 11 and a measuring tool module 12, wherein the separation measuring module 11 is a michelson interferometer, and is used for measuring a separation distance; the measurement tool module 12 is used for clamping and adjusting the optical lens to be measured, and the central thickness of the optical lens to be measured is obtained by measuring the spacing distance of the surfaces of the components in the measurement tool module 12.
Specifically, the interval measurement module 11 includes a short coherent light source 111, a first objective lens 112, a beam splitter prism 113, a photomultiplier tube 114, a reference mirror 115, and a second objective lens 116. The light emitted from the short coherent light source 111 passes through the first objective lens 112 and then becomes a parallel light beam with a small aperture and a small divergence angle. The parallel beam is split into two beams by the beam splitter prism 113, one beam being a reference beam and the other beam being a measurement beam. The reference beam is reflected by the reference mirror 115, the measuring beam is converged by the second objective lens 116, and the measuring beam is converged to the middle position of the top point of the upper surface and the lower surface of the optical lens to be measured by the second objective lens 116. In this embodiment, the second objective lens 116 is used to converge the measuring beam to reduce the spot that may be formed by the reflection of the parallel beam. In the measurement process, the reference mirror 115 moves along the optical axis direction, and the moving distance of the reference mirror 115 may be measured by using a grating ruler, or the reference mirror 115 may be driven by a stepping motor to move, and the moving distance of the reference mirror 115 may be measured by using the stepping motor. When interference fringes are observed at the photomultiplier tube 114 at some positions while the reference mirror 115 is moving, it is considered that the reflected light of the measuring beam passing through the object and the reflected light of the reference beam passing through the reference mirror 115 interfere. Because the short coherent light source 111 emits the short coherent light beam, interference occurs only when the reference light beam and the measuring light beam are completely in equal path, so that the position of the reference mirror 115 and the position of the reflection vertex of the measuring light beam have a one-to-one correspondence, and the optical path difference between the two reflection vertices is equal to the relative distance moved by the reference mirror 115. As can be known from the above description of the principle of the interval measuring module 11, the optical path difference between two reflective vertices of the measuring beam in the optical path thereof is equal to the relative distance of the reference mirror 115 moving between the two reflective vertices, and the optical path difference between the two reflective vertices can be obtained by measuring the moving distance of the reference mirror 115. In order to improve the measurement accuracy of the interval measurement module 11, the accuracy of the grating ruler or the stepping motor reaches the submicron level.
In order to enable the above-mentioned interval measuring module 11 to observe a better interference pattern, because the reflectivity of the lens to be measured is relatively low and the energy of the reflected measuring beam is small, the splitting ratio of the splitting prism 112 can be adjusted so that the energy of the measuring beam is larger than that of the reference beam. Since the lens to be measured is made of glass, the reflectivity of the glass surface is generally 4%, therefore, the ratio of the energy of the measuring beam to the energy of the reference beam is preferably 96:4 to 96:3.5, so that the energy of the reflected measuring beam is equivalent to the energy of the reference beam.
The measurement tool module 12 includes a first parallel plate 121, a lens clamping and adjusting device 122 to be measured, and a second parallel plate 124. The first parallel plate 121 and the second parallel plate 122 are both perpendicular to the optical axis of the measuring beam, the to-be-measured lens clamping and adjusting device 122 is disposed between the first parallel plate 121 and the second parallel plate 122, and the to-be-measured lens clamping and adjusting device 122 is configured to clamp the to-be-measured lens 123 and adjust the position of the to-be-measured lens 123, so that the optical axis of the to-be-measured lens 123 is coaxial with the measuring beam. Before the central thickness measurement of the lens 123 to be measured, the distance between the lower surface of the first parallel plate 121 and the upper surface of the second parallel plate 124 is measured by the distance measuring module 11, and is denoted as L1. When measuring the central thickness of the lens 123 to be measured, first, the lens holding and adjusting device 122 holds the lens 123 to be measured and adjusts the position thereof, so that the optical axis of the lens 123 to be measured is coaxial with the measuring beam. Then, the position of the reference mirror 115 is moved, and the distance from the lower surface of the first parallel flat plate 121 to the top point of the upper surface of the lens 123 to be measured is measured and recorded as L2; measuring the distance from the top of the lower surface of the lens 123 to be measured to the upper surface of the second parallel flat lens 124, and recording as L3; the center thickness d of the lens 123 to be measured is L1-L2-L3. In order to improve the measurement efficiency, the device 122 for clamping and adjusting the lens to be measured of the present invention further includes a manipulator for automatically grabbing the lens to be measured 123 and adjusting the position of the lens to be measured 123 to make it coaxial with the measuring beam, when the measurement is completed, the lens to be measured 123 is taken down, and the above-mentioned steps are repeated to realize the automatic test.
In order to improve the measurement accuracy of the measurement apparatus, the first parallel plate 121 and the second objective 116 may be designed in combination to correct the spherical aberration caused by the first parallel plate 121, and the positions of the first parallel plate 121 and the second objective 116 are not limited to the positions in fig. 1, and may also be exchanged, and the measurement beam first passes through the first parallel plate 121 and then is converged by the second objective 116. In order to further improve the measurement accuracy of the measurement device, the flatness and parallelism of the first parallel plate 121 and the second parallel plate 124 reach the submicron level.
The non-contact optical lens center thickness measuring device provided by the invention is adopted for thickness measurement, and has the following advantages: (1) the thickness is measured in a non-contact mode, and in the measuring process, the measuring device is not in contact with the surface of the optical lens to be measured, so that the surface of the optical lens to be measured cannot be damaged, and the damage to the optical lens to be measured can be effectively avoided; (2) when the device is used for measuring the thickness, the central thickness of the optical lens is directly measured without knowing the refractive index of the optical lens to be measured, the device is not limited by the influence of material factors, the central thickness of any optical lens can be measured, and the measurement precision is improved; (3) the measurement error can be reduced by some optical designs, such as the combined design of the second objective lens and the first parallel flat plate, and the spherical aberration brought by the first parallel flat plate is reduced; converging the measuring light beams by using a second objective lens, and reducing light spots and the like generated by reflecting parallel light beams; (4) the measurement accuracy of the measurement device can be improved by improving the flatness and parallelism of the first parallel plate and the second parallel plate and the accuracy of the grating ruler or the stepping motor.
Fig. 2 is a flowchart illustrating a method for measuring a center thickness of a non-contact optical lens according to a first embodiment of the method for measuring a center thickness of a non-contact optical lens according to the present invention. The non-contact optical lens center thickness measuring method comprises the following steps: s11: adjusting the measuring device to enable the first parallel flat plate and the second parallel flat plate to be perpendicular to the measuring beam; s12: moving the position of the reference mirror to measure a distance L1 between the lower surface of the first parallel plate and the second parallel plate; s13: placing the lens to be measured on the lens clamping and adjusting device to be measured, and adjusting the position of the lens to be measured to enable the lens to be measured and the measuring light beam to be coaxial; s14: moving the position of the reference mirror, and measuring the distance L2 between the lower surface of the first parallel flat plate and the upper surface of the lens to be measured and the distance L3 between the lower surface of the lens to be measured and the upper surface of the second parallel flat plate; s15: from the measured distances L1, L2 and L3, the central thickness d of the optical lens is calculated, where d ═ L1-L2-L3.
FIG. 3 is a schematic diagram showing interference intensity during measurement by the non-contact optical lens center thickness measuring apparatus according to the present invention. The graph mainly corresponds to step S14, where the distance L2 between the lower surface of the first parallel plate and the upper surface of the lens to be measured and the distance L3 between the lower surface of the lens to be measured and the upper surface of the second parallel plate are measured, and it can be seen that a clear interference intensity peak can be seen on the photomultiplier tube every time when the reflected light reflected from the surface of the lens is encountered. Between two adjacent peaks, the moving distance of the reference mirror is the distance between the two surfaces.
The method for measuring the central thickness of the non-contact optical lens provided by the invention has the following advantages: (1) the thickness is measured by adopting a non-contact method, and in the measuring process, the measuring device does not contact with the surface of the optical lens to be measured, so that the surface of the optical lens to be measured cannot be damaged, and the damage to the optical lens to be measured can be effectively avoided; (2) when the thickness is measured, the refractive index of the optical lens to be measured does not need to be known, the central thickness of the optical lens is directly measured, the influence of material factors is not limited, the central thickness of any optical lens can be measured, and the measurement precision is improved.
In order to accurately measure the center thickness of the optical lens, the optical axis of the optical lens must coincide with the optical axis of the measuring beam. In a conventional method for measuring the center thickness of a non-contact optical lens, the position of the optical lens is generally adjusted by the energy intensity of reflected light so that the optical axis of the optical lens coincides with the optical axis of a measuring beam. Because the reflection of the measuring beam at the vertex position of the curved surface of the optical lens is strongest, the energy intensity of the reflected light of the measuring beam is strongest by adjusting the position of the optical lens, and the optical axis of the optical lens is consistent with the optical axis of the measuring beam at the position. However, the method has certain disadvantages that the judgment of the position with the strongest energy intensity of the reflected light is subjective, subtle differences among the energy intensities cannot be perceived, the judgment of the position with the strongest energy intensity of the reflected light lacks accuracy, and the strongest position which can be found is only the local strongest position rather than the strongest position of the whole optical lens curved surface, so that the accuracy of a measurement result is influenced.
In order to solve the problem that the optical axis of the optical lens may not coincide with the optical axis of the measuring beam in the conventional measuring method, the present invention provides a non-contact optical measuring device, as shown in fig. 4, which is a schematic diagram of a second embodiment of the non-contact optical lens center thickness measuring device in the present invention. The non-contact optical lens center thickness measuring device in fig. 4 is added with an off-center measuring module 23 on the basis of the measuring device in fig. 1. The other module structures and functions are the same as in fig. 1, wherein the interval measurement module 21 includes a short coherent light source 211, a first objective lens 212, a beam splitting prism 213, a photomultiplier tube 214, a reference mirror 215, and a second objective lens 216. The measurement tool module 22 includes a first parallel plate 221, a lens clamping and adjusting device 222 to be measured, and a second parallel plate 224. The first parallel plate 221 and the second parallel plate 224 are perpendicular to the optical axis of the measuring beam, and the lens to be measured clamping and adjusting device 222 is used for clamping the lens to be measured 223 and adjusting the position of the lens to be measured 223, so that the optical axis of the lens to be measured 223 is coaxial with the measuring beam.
The decentration measuring module 23 includes a third objective 231, a fourth objective 232, a beam splitter 233, a target plate 234, a narrow band light source 235, and a CMOS camera 236. When the central deviation measuring module 23 is in use, a light beam emitted by the narrow-band light source 235 illuminates the target plate 234, and is reflected to the fourth objective 232 by the beam splitter 233 to become parallel light, and then the parallel light is output, at this time, a curvature image reflected by the surface of the lens 223 to be measured is clearly imaged in the CMOS camera 236, and the CMOS camera 236 is a display interface of the central deviation measuring module 23. In order to reduce the light spots that may be generated by the parallel light reflection, a third objective 231 is further included in the decentration measuring module, and the third objective 231 is used for converging the parallel light output by the fourth objective 232 to the curvature center position of the lower surface or the upper surface of the lens 223 to be measured. The device 222 for holding and adjusting a lens to be measured includes a turntable along which the lens to be measured 223 can be rotated. When the parallel light converges on one surface of the lens 223 to be measured, when the lens 223 to be measured rotates along the turntable, the curvature image will draw a circle on the display interface of the central deviation measurement module, the radius of the circle represents the deviation of the lens 223 to be measured relative to the rotating shaft of the turntable, and the position of the lens 223 to be measured is adjusted according to the radius of the curvature image circle. The decentration measuring module 23 is moved up and down to converge the parallel light to the other surface of the lens 223 to be measured, so that the curvature image of the other surface of the lens 223 to be measured can be found, and the position of the lens 223 to be measured can be adjusted according to the radius of the curvature image circle. So reciprocating, finally, by adjusting the position of the lens to be measured 223, the optical axis of the lens to be measured 223 coincides with the axis of the turntable. When adjusting the position of the lens 223 to be measured, the horizontal position and the inclination angle of the lens 223 to be measured are mainly adjusted, specifically, the horizontal position of the lens 223 to be measured is adjusted by the curvature image of one surface of the lens to be measured, and the inclination angle of the lens 223 to be measured is adjusted by the curvature image of the other surface of the lens to be measured.
In order to improve the measurement accuracy of the measurement device, the second parallel plate 224 and the third objective 231 may be combined to correct the spherical aberration caused by the second parallel plate 224, and the positions of the second parallel plate 224 and the third objective 231 are not limited to the positions shown in fig. 4, and may be switched, and the light beam first passes through the second parallel plate 224 and then is converged by the third objective 231.
As shown in fig. 5, a schematic diagram of a display interface in the decentration measurement module is shown. When the optical axis of the lens 223 to be measured is superposed with the rotating shaft of the turntable, when the lens 223 to be measured rotates along the turntable, no curvature image can be generated on the display interface of the center deviation measuring module to draw a circle; when the optical axis of the lens 223 to be measured does not coincide with the rotating shaft of the turntable, when the lens 223 to be measured rotates along the turntable, a curvature image circle will appear on the display interface of the center deviation measurement module, and the radius of the curvature image circle represents the deviation of the curvature center of the lens surface relative to the rotating shaft of the turntable.
And taking the rotating shaft of the rotary table as a reference shaft, and adjusting the optical axis of the measuring beam before measurement to enable the optical axis of the measuring beam to be consistent with the rotating shaft of the rotary table. When adjusting, a ball lens with the radius not larger than 5mm is placed on the turntable, and the ball lens is adjusted according to the method for adjusting the lens to be measured, so that the optical axis of the ball lens is coaxial with the rotating shaft of the turntable. Adjusting the focal length of the second objective lens 216 to focus the measuring beam to infinity, then rotating the turntable, if the optical axis of the measuring beam does not coincide with the rotation axis of the turntable, the light spot will be seen to rotate on the display interface of the decentration measuring module, adjusting the positions of the components in the interval measuring module 21 to make the light spot not rotate, and then the optical axis of the measuring beam coincides with the rotation axis of the turntable.
Therefore, in the non-contact optical measuring device as shown in fig. 4, a decentration measuring module is added in the measuring device, and the rotating shaft of the turntable in the lens to be measured clamping and adjusting device is used as a reference shaft, the measuring beam is made to be coaxial with the rotating shaft of the turntable by adjustment, and the optical axis of the lens to be measured is made to be coaxial with the rotating shaft of the turntable, so that the beam of the lens to be measured is coaxial with the measuring beam, thereby realizing accurate measurement of the central thickness of the optical lens and reducing the measuring error.
As shown in fig. 6, a corresponding measurement method of the non-contact optical lens center thickness measurement apparatus in fig. 4 is shown. The measuring method comprises the following steps: s21: adjusting the measuring device to enable the first parallel flat plate and the second parallel flat plate to be perpendicular to the measuring beam; s22: adjusting the interval measuring module to enable the optical axis of the measuring beam to be coaxial with the rotating shaft of the upper rotating table of the clamping and adjusting device of the lens to be measured; s23: moving the position of the reference mirror to measure a distance L1 between the lower surface of the first parallel plate and the second parallel plate; s24: placing the lens to be measured on the lens clamping and adjusting device to be measured, and adjusting the position of the lens to be measured to enable the optical axis of the lens to be measured to be coaxial with the rotating shaft of the objective lens clamping tool to be measured and the rotating shaft of the turntable on the adjuster; s25: moving the position of the reference mirror, and measuring the distance L2 between the lower surface of the first parallel flat plate and the upper surface of the lens to be measured and the distance L3 between the lower surface of the lens to be measured and the upper surface of the second parallel flat plate; s26: from the measured distances L1, L2 and L3, the central thickness d of the optical lens is calculated, where d ═ L1-L2-L3.
In step S22, when the distance measuring module is adjusted so that the optical axis of the measuring beam is coaxial with the rotating shaft of the objective lens clamping tool to be measured and the upper turntable of the adjuster, the method includes the following steps: placing a ball lens with the radius not larger than 5mm on the rotary table, enabling the optical axis of the ball lens to be coaxial with the rotary shaft of the rotary table, adjusting the focal length of the second objective lens, enabling the measuring beam to be focused to infinity, then rotating the rotary table, if the optical axis of the measuring beam is not coincident with the rotary shaft of the rotary table, seeing that the light spot rotates on the display interface of the center deviation measuring module, adjusting the positions of all components in the interval measuring module, enabling the light spot not to rotate, and enabling the optical axis of the measuring beam to coincide with the rotary shaft of the rotary table at the moment.
In step S24, when adjusting the position of the lens to be measured so that the optical axis of the lens to be measured is coaxial with the rotating shaft of the objective lens clamping tool to be measured and the upper turntable of the adjuster, the method includes the following steps: when the parallel light is converged on one surface of the lens to be measured, when the lens to be measured rotates along the turntable, the curvature image draws a circle on the display interface of the central deviation measurement module, the radius of the circle represents the deviation of the lens to be measured relative to the rotating shaft of the turntable, and the position of the lens to be measured is adjusted according to the radius of the curvature image circle; moving the central deviation measuring module up and down, converging the parallel light to the other surface of the lens to be measured, finding out a curvature image of the other surface of the lens to be measured, and adjusting the position of the lens to be measured according to the radius of a curvature image circle; and finally, the optical axis of the lens to be measured is superposed with the axis of the turntable by adjusting the position of the lens to be measured.
Although the present invention has been described with reference to the preferred embodiments, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims.
Claims (12)
1. A non-contact optical lens center thickness measuring device is characterized by comprising an interval measuring module and a measuring tool module, wherein the interval measuring module comprises a Michelson interferometer and is used for measuring an interval distance;
the measurement tool module comprises a first parallel flat plate, a to-be-measured lens clamping and adjusting device and a second parallel flat plate, wherein the to-be-measured lens clamping and adjusting device is arranged between the first parallel flat plate and the second parallel flat plate, and the to-be-measured lens clamping and adjusting device is used for clamping the to-be-measured lens and adjusting the position of the to-be-measured lens, so that the optical axis of the to-be-measured lens is coaxial with the measurement beam;
before the central thickness of the optical lens is measured, the interval measuring module measures the interval distance from the lower surface of the first parallel flat plate to the upper surface of the second parallel flat plate, and the interval distance is marked as L1;
when the central thickness of the optical lens is measured, the distance between the lower surface of the first parallel flat plate and the top point of the upper surface of the lens to be measured is measured by the interval measuring module and is marked as L2; and the distance between the top point of the lower surface of the lens to be measured and the upper surface of the second parallel flat plate is measured by the interval measuring module and is marked as L3, and the central thickness d of the lens to be measured is L1-L2-L3.
2. The device for measuring the central thickness of a non-contact optical lens as claimed in claim 1, wherein the interval measuring device comprises a short coherent light source, a first objective lens, a beam splitter prism, a photomultiplier tube and a reference mirror, light emitted from the short coherent light source passes through the first objective lens and then is converted into a beam of parallel light, the beam of parallel light is then split into two beams of reference light and measuring light, the reference light is reflected by the reference light, the measuring light is reflected by the surface to be measured, during measurement, the position of the reference mirror is moved along the optical axis of the reference light, and when interference fringes are observed by the photomultiplier tube, the optical distances between the measuring light and the reference light are equal.
3. The apparatus of claim 2, wherein the distance of movement of the reference mirror is measured using a grating scale.
4. The apparatus of claim 3, wherein the flatness and parallelism of the first and second parallel plates are in the sub-micron order, and the measurement accuracy of the grating scale is in the sub-micron order.
5. The apparatus for measuring the center thickness of a non-contact optical lens according to claim 2, wherein the distance measuring apparatus further comprises a second objective lens for converging the measuring beam to an intermediate position of the vertexes of the upper and lower surfaces of the optical lens to be measured.
6. The apparatus of claim 5, wherein the second objective lens is combined with the first plate to correct spherical aberration caused by the first plate.
7. The apparatus of claim 2, wherein the beam splitting ratio of the beam splitting prism is adjusted so that the energy of the measuring beam is larger than the energy of the reference beam.
8. The apparatus of claim 1, further comprising a center deviation measuring module, wherein the apparatus for clamping and adjusting the lens to be measured comprises a turntable, and the center deviation measuring module is configured to adjust a position of the interval measuring module such that an optical axis of the measuring beam is coaxial with a rotation axis of the turntable; the central deviation measuring module is also used for adjusting the position of the optical lens to be measured, so that the optical axis of the optical lens to be measured is coaxial with the rotating shaft of the turntable.
9. The apparatus of claim 8, wherein the module for measuring center thickness of a non-contact optical lens includes a third objective lens, a fourth objective lens, a beam splitter, a target plate, a narrow-band light source and a CMOS camera, when the module for measuring center deviation is used, a light beam emitted from the narrow-band light source illuminates the target plate, the target plate is reflected by the beam splitter to the fourth objective lens and then becomes a parallel light, the parallel light is converged onto one surface of the optical lens to be measured by the third objective lens, and a curvature image reflected by the surface of the optical lens to be measured is clearly imaged in the CMOS camera.
10. The non-contact optical lens center thickness measuring device of claim 9, wherein the third objective lens and the second parallel plate are designed in combination to correct spherical aberration introduced by the second parallel plate.
11. A method for measuring the center thickness of a non-contact optical lens, comprising the steps of:
s1: adjusting the measuring device to enable the first parallel flat plate and the second parallel flat plate to be perpendicular to the measuring beam;
s2: moving the position of the reference mirror to measure a distance L1 between the lower surface of the first parallel plate and the second parallel plate;
s3: placing the lens to be measured on the lens clamping and adjusting device to be measured, and adjusting the position of the lens to be measured to enable the lens to be measured and the measuring light beam to be coaxial;
s4: moving the position of the reference mirror, and measuring the distance L2 between the lower surface of the first parallel flat plate and the upper surface of the lens to be measured and the distance L3 between the lower surface of the lens to be measured and the upper surface of the second parallel flat plate;
s5: from the measured distances L1, L2 and L3, the central thickness d of the optical lens is calculated, where d ═ L1-L2-L3.
12. The method for measuring the central thickness of a non-contact optical lens as claimed in claim 11, wherein after the step S1, the method further comprises the steps of S1-1, adjusting the interval measuring module such that the optical axis of the measuring beam is coaxial with the rotation axis of the turntable on the device for holding and adjusting the lens to be measured; the step S3 further includes: and placing the lens to be measured on the lens clamping and adjusting device to be measured, and adjusting the position of the lens to be measured to enable the optical axis of the lens to be measured to be coaxial with the rotating shaft of the objective lens clamping tool to be measured and the rotating shaft of the upper rotating table of the adjuster, so that the lens to be measured is coaxial with the measuring light beam.
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