Research On Lens Center Thickness Measurement System

As the most important component of the optical system,the processing error of the central thickness of the lens directly affects the imaging quality of the optical system.With the rapid development of optoelectronic products,the requirements for the quality of optical lenses are coming stringent.At present,the probe contact is still the typical method of measuring the center thickness of the lens,which cannot guarantee the measurement accuracy and the quality of the device under test..Therefore,high-precision and non-destructive measurement of the center thickness of the lens has become a domestic and overseas hotspot.The laser triangulation method opens a new dimension for the measurement of the center thickness of the lens,due to its high measurement accuracy,fast speed,and no damage to the surface to be measured.In this paper,the measurement of the lens center thickness based on the laser triangulation method is studied.Firstly,based on the principle of laser triangular thickness measurement,the overall plan of the center thickness measurement of the direct-type double CCD laser triangulation lens is determined,and the theoretical measurement accuracy analysis of the measurement system is completed in combination with the Scheimplug Condition.Secondly,combining theoretical precision analysis and beam shaping design,the laser beam of the semiconductor laser is shaped into a Gaussian laser beam with a focus spot diameter of 2 mm by Zemax software,the design of the self-collimation module is completed according to the characteristics of the system structure to ensure the accuracy of the measuring device;Trough the analysis of the system structural parameters,the structural design of the mechanical is completed with the five major parts including the laser light source,the auto-collimation module,the lens to be tested,the receiving CCD,and the L-shaped skeleton.Then,the laser triangulation lens center thickness measurement device is set up,and the entire measurement device is debugged in combination with the system's optical-mechanical structure,measurement range and measurement accuracy.In this paper,the detailed calibration process and test process of the measurement system are formulated.Calibration is carried out through Harris corner detection and checkerboard to complete the accurate calibration of the measurement system.The gray-scale centroid method is used to accurately extract the laser spot center.By the analysis of the influence of the laser spot area on the accuracy of the spot center extraction,the optimal measurement area range is given,and an effective lens thickness measurement model is obtained to establish the lens center thickness measurement process of the measurement system.Finally,four different types of lenses including plano-convex,bi-convex,plano-concave,and bi-concave are selected as the measurement objects.According to the lens center thicknessmeasurement process,the measurement of the center thickness is completed.The measurement range of the system is 1?20mm,the repeatability is less than 0.05,which meets the tolerance requirements of the center thickness of the lens.At the same time,the error factors such as laser intensity,laser spot size,system setup,lens curvature radius,tilt angle,surface roughness,and speckle are analyzed in detail.