Study On Key Problems In Twin-robot Scanning Techniques For Ultrasonic Nondestructive Testing

With the development of aerospace,automotive,energy and other fields,the application proportion of composite material has been continuously improved.Composite materials in the process of manufacturing and service need to be comprehensive and reliable detection to ensure the quality of the structure and application security,including the ultrasonic testing technology plays an important role.For the complex surface composite workpiece,improve precision,efficiency and the degree of automation is a new challenge to ultrasonic testing technology in modern industry.Combined with ultrasonic inspection scheme and the actual needs,this paper mainly studies on some key technology of ultrasonic testing for free-form surface composite workpiece.The beam modeling on composite,free-form surface automatic ultrasonic testing,two-robots base frame calibration and two-robot coopertive motion are systematically and deeply studied in this dissertation.In chapter 1,the purpose and significance of the research work were discussed.The research status at home and abroad,such as the beam modeling on composite,free-form surface automatic ultrasonic testing,two-robots base frame calibration and two-robot coopertive motion,were reviewed and analysis.Finally,the chapter structure were introduced.In chapter 2,the multi-Gaussian beam model for the acoustic field of the ultrasonic transducer has been enstablished.The theory of beam propagation in anisotropic media was discussed based on the single medium.The multi-Gaussian beam model calculation method in composite was derived,and introduces the solving method of fitting coefficient for the slowness surface.Finally,the experiments have verified the validity and effectiveness of the proposed method.In chapter 3,the kinematics model of the manipulator was studied,the positive solution model of the manipulator is established according to D-H method,the inverse solution model of manipulator was solved with an arm-wrist separateness method.For the trajectory planning of free surfaces in space by fitting NURBS curve and surface,and analysis the generation strategy of scanning trajectory,the orentation vector of the transducer was obtained according to the constraint of ultrasonic testing.to enable the smooth movement of the joint movement and eliminate the impact,fifth-degree polynomial function,sine function and combined sine function for joint trajectory planning were detail studied.The results of the three methods were compared,and the advantages and disadvantages of several characteristic indexes of different planning methods were analysed.In chapter 4,calculation method of two manipulators base frame transformation relation was studied.It proposed a method require only three non-collinear ponits in space to solve the trasonformation relation,two manipulators need to hand clasp operation in these points.A rotation matrix normalization and orthogonal method base on Lie algebra exponential mapping is proposed.The experimental results verified the validity and effectiveness of the proposed method,the calibration results were used to synchronize the workpiece frame of two manipulators.In chapter 5,the position and orentation constraints of the end-effectors under the different testing tasks was studied.The constraint relation of cupled synchronous motion in thickness workpiece ultrasonic testing was obtained from the constraints of ultrasonic testing task.The constraint relation of combined synchronous motion in the detection of unequalthickness workpieces was given.These constraints provided the theoretical basis for the slave manipulator trajectory planning.Finally,the experiments verified correctness of the two motion constraint relations.In chapter 6,the construction of two-robo automatic ultrasonic testing system platform was established based on the theoretical research.The system was mainly divided into hardware part and software part,the software part includesd the upper and lower machine software.The system structure,hardware configuration and software model were described.The automatic ultrasonic testing results for equal-and unequal-thickness workpieces were obtained,and analysis the experimental results.Artificial defects were clearly visible in the C-scan images,thereby verifying the validity and the effectiveness of the proposed method.The results shown the transducers based on the beam propagation method can obtained an better effectiveness.