Study Of High-precision Glass Stress Testing Technology

The theoretical analysis and engineering implementation issues of the highprecision detection system of the glass internal stress using magneto opticalmodulation were mainly discussed in this article.First of all, the forming reasons and the influences when existing of the internalstress in glass were briefly described in this paper, and the usage of stress testing wasdescribed, then the present situation of stress detection technology development athome and abroad was described, the gap of the stress testing technology of ourcountry and abroad was pointed out. The function of high precision and automationare the glass stresses in the high-end fields need to have. With the development ofChinese current situation of stress detection technology, it cannot meet the demandof the internal stress’s high precision measurement in glass. They adopt the foreignequipment to test in the field of high precision measuring in our county, and theseequipments are extremely expensive. Therefore, it is an urgent demand for the studyof a new type of high precision internal stress testing technology with ourindependent intellectual property rights.The Magneto-optic modulation method is a new way to test the internal stressof glass accurately. The basic principles of magneto-optical modulation technique,the composition and structure of the key technical aspects to measure the internalstress of the glass, were introduced in detail in this paper; its performance, featuresand technical improvement for the conventional measurement method were pointingout. The principle of the basic measuring principle and signal processing methodabout the system are deduced by using the matrix optics method in this paper, thekey components’ selection, the devices, signal processing method and other variousfactors lead to the accuracy of the system were introduced and analyzed in detail atthe same time. The experiments have been carried out to verify the measurementsystem, results show that the method has improved in the accuracy relative to the previous measurement system, and the discreteness of the measured results are in0.4nm/cm. However, this method requires to rotate glass under test and partialdetector for many times in the ranges of180°to obtain a sufficient number ofmeasurement data, which ensures the accuracy of results. The whole processing wascomplex, cumbersome and had a long measuring time, which needed about2hoursto complete a measurement operation, all of that caused the low practical value ofthe system.According to the change of optical drive voltage can control polarizationrotation angle, which can achieve the goal of changing the polarization rotation angleto avoid rotating the partial detector. Moreover, there are some certain relationsbetween the rotation angle of glass to be measured and rotator angle, which increasethe information to calculate the measured stress birefringence and direction. We cantake use of these angle relationships to accurate internal stress information directly,that can avoid rotating the measured glass and partial detector for many times. Basedon the above ideas, a method of magneto optical modulation with rotator to measurethe internal stress in glass was put forward in this paper, and the principle wasdeduced in detail. The calibration experiments of rotator were carried on in theprocessing of measurement at first to obtain the linear relationship between thedriving voltage and the rotation angle. According to the relationship, the glassinternal stress measurement experiment was completed by magneto-opticmodulation with rotator, and the problems existing in the experimental processingwas found, which was that when the voltage was bigger, the optical drive coil washeat, resistance was change, that effect the rotation angle. In addition, the precisionof the applied voltage was too low to accurate control rotation angle, there was acertain error found in the experiment, that caused the discreteness of the systemmeasurement results was0.5nm/cm, and we rotated the glass under test for a timewhen measuring. Although the measuring time was shortened to about5minutescompared to the magneto-optical modulation method, but it still cannot achieve afully automated measurement.The U.S. patent-dual photoelastic modulation measurement method was referred, and the research results of the institute on the dual magneto-opticalmodulation to achieve the spatial orientation angle measurement was learned in thispaper, the dual magneto-optical modulation method to measure the stress in the glasswas proposed. The optical measurement principle was described, and a square wavemodulation of the light source was added to improve the measurement accuracy ofthe system. By conducting experiments, it’s found that the system can be automatedmeasurement, which could greatly reduce the measurement time, a measurementprocess could be completed within15seconds, and the use of pan volume andsegmentation rotational stage multi-tooth indexing table were avoided, themeasuring equipment bulk can be reduced, but it’s required to solve the problem thatthe base frequency signal amplitude which was used to compute stress informationwas small, that resulted in the signal amplitude gap was great between the detectionDC component and the base frequency component, which brought greater difficultiesfor signal detection and process, it led to the final measurement results discrete poor.The stress birefringence measurement result discrete is in3.1nm/cm, which is far toreach the requirements.Use the characteristics of AC signal amplitude was bigger when usingphotoelastic modulator modulation, the method that changed dual magneto-opticalmodulation measurement system to the magneto-optical with photoelasticmodulation was proposed to improve the amplitude of the base frequency signal, andto realize the purpose of enhancing the measurement performance. The principle ofmagneto-optical added photoelastic modulation method for measuring stresses inthe glass was derivate theoretically in this paper, the gotten signals amplitude whichwere detected by the magneto-optical modulation added photoelastic modulation andby dual magneto-optical modulation measurement system was emulated andcompared, the results showed that the baseband signal normalized amplitude by themagneto-optical added photoelastic modulation was much larger than the dualmagneto-optical modulation under the same conditions of stress measurementinformation. Finally, the system was test and verified that it had high measurementaccuracy and stability by a lot of experiments, and it proved the correctness of theoretical analysis. The dispersion of the birefringence measurements of stress is in0.3nm/cm, in addition, the adaptability and practicality of the system are greatlyenhanced, system’s basic indicators can meet the needs of high-precision glass stressbirefringence measurement.Through a lot of system debugging and experiments, some problems existed inthe measurement system were found out, that is a certain reference for the latersystem improvement and it lays the foundation of further ascension of the systemmeasurement performance. In addition, the last chapter puts forward the systemimprovement program aiming at the deficiencies in the experiment.