Optical System Design Of Ultraviolet LED Exposure Machine

Traditional ultraviolet exposure machine use high pressure mercury lamp as light source,which makes ultraviolet exposure machine have some disadvantages,such as poor quality of exposure results,low exposure accuracy,big volume,and radiate lots of heat.Because the technology of GaN growth has developed and the quality of ultraviolet LED chip has improved,now ultraviolet LED chip has substituted for high pressure mercury lamp.When ultraviolet LED chip used as light source,optical system can be designed according to the luminous intensity of LED chip to make emergent light collimated and make illumination uniform.Ultraviolet exposure machine can get high precision and quality of exposure results through this way.At the same time,ultraviolet LED chip radiate less heat and save more energy than high pressure mercury lamp.It also good for environmental protection.The main research content of this paper is to design a ultraviolet LED optical system,which can make divergence angle of emergent light less than 1 degree.So precision of exposure results can be improved.Meanwhile,illumination uniformity on receiver should be greater than 90%.Good illumination uniformity will enhance exposure quality of ultraviolet exposure machine.In addition to the divergence angle of emergent light and illumination uniformity,radiant illumination is required to be higher than 1 mW/cm~2,and the diameter of light spot on the receiving screen need to be not less than 10 cm.Nonimaging optics is the basic theory in this paper.Based on nonimaging optics theory,optical system was designed according to the luminous intensity of LED chip to meet the requirements of optical design.The design work mainly includes the following four steps:1.To design the optical system,the overall framework should be constructed.Optical elements which will be used in the optical system of ultraviolet exposure machine need be confirmed.And the function of every optical element played in optical system should be determined.2.According to the function of each optical element which is determined in the first step,the parameters of lens is computed.And the calculation is based on the luminous intensity of LED chip to satisfy the design requirements.3.After the parameters of lens is calculated,optical system model is constructed in the LightTools optical software.Then the optical system model is run to get simulation results.Output of radiation intensity and radiant illumination can be seen in the form of image and data.The divergence angle of emergent light can be got through radiation intensity.Illumination uniformity can be calculated according to the radiant illumination.4.On the basis of simulation results in LightTools optical software,the optical system model is recalculated.Recalculation will optimize optical model.Build a new model in the LightTools optical software using the optimized parameters of free-form surface,then simulate the optical model.Compared with the simulation results to see if the optical system is optimized.According to the design requirements,four different optical systems are designed.That the size of the light source has important influence on the divergence Angle of emergent light is found during the process of design.To improve collimation of emergent light,the size of the light source need decrease the size of the light source as much as possible.In the case of light radiant exitance remain unchanged,the decrease of the light source size will make radiant energy flux decrease.The energy get into optical system will also reduce,which can minish irradiance on receiving surface.Expressions about the relationship between the irradiance,the size of the light source and radiant exitance is deduced in this paper.The final model designed in this paper uses a set of light source array.The corresponding lens array is put at twice of the focal length away from light source array.The imaging will be formed at twice of the focal length away from lens array.The size of the imaging is the same as light source.An aperture is put at the position of imaging.The size of imaging can be controlled through the aperture.Another lens array is put at the once of the focal length away from aperture.The center of each microlens is aligned to the hole on aperture.Through this model,design requirements can be met.Divergence angle is less than 1 degree,radiant illumination is higher than 1 mW/cm~2,and illumination uniformity is greater than 90%.The final model meet the design requirements.