Digital Speckle correlation method (DSCM) is a computer-vision- based, non-contact, whole-field surface strain measuring method. It is becoming increasingly important as experimental mechanics tool. Its working principle is to compare one digital image of the displaced/deformed surface with the original one using a mathematically well-defined correlation function based on some subset of pixels. In the evolution of DSCM, several methods and techniques have been developed to raise the search speed and precision of DSCM. Typical methods include the coarse-fine search, Newton-Raphson and quasi-Newton method based on optimization theory. However, the coarse-fine search method considers only the rigid body translation displacement, New-Raphson and quasi-Newton is sensitive to the initial values and local extremum. It is possible for Quasi-Newton method to find a local extremum instead of global extremum, even impossible to obtain the extremum because bad initial estimate in iterative computation leads to divergence. The genetic algorithm can be used to optimize the subset correlation globally. But it has large computational workload if it is applied to complete all search procedures for whole speckle pattern. Its convergence velocity becomes the slower and slower along with searching near optimum solution. We present an improved DSCM by hybrid method, which combines the genetic algorithm, quasi-Newton with adjacent point initial estimate. Genetic algorithm is used to obtain the initial estimate for Quasi-Newton iterative method, which be performed only in preliminary search window. Initial estimate for the succedent search subset is obtained by corresponding adjacent point. The simulation experiments have proved the efficiency of the new method.
A optical measurement system of Micro-electro-mechanical system (MEMS) motion is demonstrated to increase the efficiency of MEMS design and manufacturing. The system is developed based on the heterodyne laser Doppler technology, and frequency shift of 40MHz is introduced by a Bragg cell. The paper introduced MEMS vibration theory, designed optical structure and electronic circuit, and obtained the linear relation between the Doppler shift and the target velocity. Experiments on driving and measuring double-ended tuning fork resonator were carried out. The resonator is driven by using electrostatic force at its natural frequency 2.4KHz. Experimental results indicate that the measure system can be used to measure MEMS motion with high accuracy.
The phase shifter is necessary in the optical phase-shifting measurement. At present the phase shifter commonly used is approximately divided into the penetrance-type and the reflection-type. In this paper, a reflection-type phase shifter made of piezoelectric ceramic stackup assemble is developed. The assemble are constituted of the flat piezoelectric ceramic with parallel connection circuit and inline structure. The communication between the computer and MCU is by RS232. The D/A converter controlled by the MCU outputs 0~10V voltage. Then the voltage is amplified to 0~400V DC voltage by the designed linear DC amplifier. When this voltage loads on the piezoelectric ceramic stackup assemble, the assemble will axially extend 0~5mm. In this paper, the connecting types for the mechanical construction and circuit of the piezoelectric ceramic stackup assemble, the driving power and the DC amplifier with high linearity are all introduced. The whole system developed is standardized by using phase-interfering Michelson. The standardization and the practical application indicates that this system has excellent linearity and precision repeatability.
For describing the micro-topography of a measured surface reasonably, this paper puts forward a parameter named minimal area of average height of the surface micro-topography based on the least square method, which is different from the qualitative uniformity surface parameters such as correlation theory, power spectral analysis, profile matrix spectrum and surface matrix spectrum. That means to look for the minimal size square which could represent the average height value of the sample area. If the deviation between the mean height values in this area and in the sample area is ±5% which is ±2σ of Gaussian distribution, and at the same time the ratio between the minimal area and the sample area is less than 0.8, then the measurement data from the sample area is considered as the characteristic of the measured surface micro-topography. Some standard samples finished by lapping grinding, surface grinding, planning, and end milling and plain milling are measured by using phase-shift Michelson and micro-grating-projection method in this paper. The two measurement principles are given in this paper. The Ra value of the standard samples measured and the measurement results of the minimal area of average height are given. The results shown that the parameter of minimal area of average height exist good consistency with the parameter of Ra.
In order to realize the coupling of the crystal spectrum line, the wavelength output by the laser-diode must be adjusted to be accordant with the peak value absorbed by laser crystal in the solid laser of the laser-diode pump. In this paper, the finite element analysis (FEA) of the heat emission of the to-3 encapsulated laser-diode was researched and an accurate PI+Fuzzy temperature control system was developed. The refrigeration and the accurate temperature control of the high-power laser-diode was realized by the semiconductor refrigerator. Combined with fussy control and PI control, a full solid refrigerator of the laser-diode was developed. AT89C51 MCU and CRI fussy control arithmetic were used in this system. So the system has high temperature control precision and little chatting. The rate of change of the optical power peak value output by the laser-diode was less than 1%.
In this paper, an automatic fillet weld pre-tracking system for welding the work piece of lorry back boards with several bend in haul automobile is developed basing on laser trigonometry. The optical measuring head based on laser-PSD trigonometry is used as position sensor. It is placed in front of the traveling direction of welding wire to get the distances from welding wire to the two side boards of the welding lines, upper board and bottom board of the fillet weld respectively. A chip of AT89S52 is used as the micro controller in this system. The AC servomotors, ball-screws and straight guide rails constitute the sliding table to take welding wire move. The laser-PSD sensors pass through the vertical board, upper board and bottom board of the fillet weld when welding wire moves and then get the distance. The laser-PSD sensors output the analog signals. After A/D conversion, the digital signal is input into AT89S52 and calculated. Then the information of the position and lateral deviation of the welding wire when welding a certain position are gotten to control welding wires. So the weld pre-tracking for welding the work piece with long distance and large bend in haul automobile is realized. The position information is input into EEPROM to be saved for short time after handled by AT89S52. The information is as the welding position information as well as the speed adjusting data of the welding wire when it welds the several bend of the work piece. The practice indicates that this system has high pre-tracking precision, good anti-disturb ability, excellent reliability, easy operating ability and good adaptability to the field of production.
To provide useful insight into the reliability of silicon micromachined resonator, a measurement system of resonator vibration is presented to check the dynamic characteristics of resonator. The system utilizes heterodyne laser Doppler techniques and acquires the relation between resonator motion and Doppler shift of scatter beam. The vibration principle of resonator was expatiated detailedly and a special driving control circuit was also designed. Experiments on driving and measuring double-ended tuning fork vibration were carried out. The frequency of driving signal is 2.4 kHz and the peak-to-peak value of driving voltage is 140 V. Experimental results indicate that the system can measure dynamic characteristics of Micro-electro-mechanical system (MEMS) well.