Zongxing Lu

Automatic Method for Synchronizing Workpiece Frames in Twin-robot Nondestructive Testing System

The workpiece frames relative to each robot base frame should be known in advance for the proper operation of twin-robot nondestructive testing system. However, when two robots are separated from the workpieces, the twin robots cannot reach the same point to complete the process of workpiece frame positioning. Thus, a new method is proposed to solve the problem of coincidence between workpiece frames. Transformation between two robot base frames is initiated by measuring the coordinate values of three non-collinear calibration points. The relationship between the workpiece frame and that of the slave robot base frame is then determined according to the known transformation of two robot base frames, as well as the relationship between the workpiece frame and that of the master robot base frame. Only one robot is required to actually measure the coordinate values of the calibration points on the workpiece. This requirement is beneficial when one of the robots cannot reach and measure the calibration points. The coordinate values of the calibration points are derived by driving the robot hand to the points and recording the values of top center point(TCP) coordinates. The translation and rotation matrices relate either the two robot base frames or the workpiece and master robot. The coordinated are solved using the measured values of the calibration points according to the Cartesian transformation principle. An optimal method is developed based on exponential mapping of Lie algebra to ensure that the rotation matrix is orthogonal. Experimental results show that this method involves fewer steps, offers significant advantages in terms of operation and time-saving. A method used to synchronize workpiece frames in twin-robot system automatically is presented.

Kinematic constraint analysis in a twin-robot system for curved-surface nondestructive testing

Purpose – Nondestructive testing based on cooperative twin-robot technology is a significant issue for curved-surface inspection. To achieve this purpose, this paper aims to present a kinematic constraint relation method relative to two cooperative robots. Design/methodology/approach – The transformation relation of the twin-robot base frame can be determined by driving the two robots for a series of handclasp operations on three points that are noncollinear in space. The transformation relation is used to solve the cooperative motion problem of the twin-robot system. Cooperative motions are divided into coupled and combined synchronous motions on the basis of the testing tasks. The position and orientation constraints for the two motion modes are also explored. Findings – Representative experiments between two industrial robots are conducted to validate the theoretical developments in kinematic constraint analysis. Artificial defects are clearly visible in the C-scan results, thereby verifying the validi...

Inverse kinematic analysis and evaluation of a robot for nondestructive testing application

The robot system has been utilized in the nondestructive testing field in recent years. However, only a few studies have focused on the application of ultrasonic testing for complex work pieces with the robot system. The inverse kinematics problem of the 6-DOF robot should be resolved before the ultrasonic testing task. A new effective solution for curved-surface scanning with a 6-DOF robot system is proposed in this study. A new arm-wrist separateness method is adopted to solve the inverse problem of the robot system. Eight solutions of the joint angles can be acquired with the proposed inverse kinematics method. The shortest distance rule is adopted to optimize the inverse kinematics solutions. The best joint-angle solution is identified. Furthermore, a 3D-application software is developed to simulate ultrasonic trajectory planning for complex-shape work pieces with a 6-DOF robot. Finally, the validity of the scanning method is verified based on the C-scan results of a work piece with a curved surface. The developed robot ultrasonic testing system is validated. The proposed method provides an effective solution to this problem and would greatly benefit the development of industrial nondestructive testing.

Kinematic analysis and simulation of ultrasonic testing manipulator

Ultrasonic testing for these workpieces with complex shapes is still a challenge in NDT filed. In order to address this problem, this paper provide an effective solution for curved surface scanning using Staubli TX90XL manipulator with six freedom degrees. Here an arm-wrist separateness method is adopted to solve the inverse of manipulator and a shortest distance rule is used to optimize the inverse solutions. Furthermore, we have developed a 3D application software to simulate the ultrasonic trajectory planning for complex shape specimens. Finally, the validity of this scanning method is verified by the C-scan results of the specimen with a curved surface.

Ultrasoud detection based on confocal Fabry-Perot interferometer

Laser ultrasonic technology has been paid more and more attention in the NDT field due to its outstanding ability of non-contact measurements. As a good vibration measurement technology, CFPI (confocal Fabry-Perot interferometer) method is sensitive to the laser frequency shift caused by the ultrasonic wave propagation. In this paper, a laser ultrasonic receiver system based on the CFPI method is established, and the system parameters are analyzed in order to obtain an optimal resolution. Also some initial experiment results are presented to certify this system ability.

Prediction of side-drilled hole signals in anisotropic cladding component

Ultrasonic non-destructive inspections focus on detecting, locating, and eventually sizing defects in components. For quantitative characteristics of complex materials, good ultrasonic measurement models are more efficient than general experimental studies. In this paper, An efficient ultrasonic measurement model for a vessel component with anisotropic cladding layer is established by combining the multi-Gaussian beam model and the scattering model with the separation of variables method. The effects of anisotropic cladding and curved surface on beam propagation are investigated using the beam model. Also with the help of the measurement model, the system efficiency factor can be determined and the response from a side-drilled hole reflector can be predicted. Finally, the accuracy of the proposed model is verified by the comparisons of the model predictions to the experimental results.