Fanwu Meng

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...

A method of optical non-contact measurement to rotary part's profile

The research on the technology of non-contact measurement of rotary parts profile has important academic significance and practicability for improving the rotary parts manufacture precision. In this paper, a method of non-contact measurement to rotary parts profile is studied. This method can be used to measure rotary parts more efficiently and accurately. In order to measure the rotary parts profile continuously, a laser beam-blocking method is presented. One or two laser beam-blocking sensors are used. The part that be measured is placed between the sensors emitter and receiver. The part will block some laser beam. From the sensor, the diameter in a certain section of the part can be got directly. In order to eliminate the influence brought by the parts position error, we should obtain the axes equation and contour line equations through curve fitting. Then we get the real surface size through coordinate transformation. In this paper, genetic algorithm is used to fit the contour line equations and the axes equation in order to improve the speed and precision of data processing. The experiments results show that the scheme presented in the paper is feasible, and the data processing method is correct.

Research on the ultrasonic test system for the complex curved surface based on robot

Only keep the tracing points of the robot a one-to-one match to the inspected points on the tested part can the detected ultrasonic signals collect the defect information of the tested part correctly during the ultrasonic testing for the complex curved surface. To solve this problem, in this paper, the 6R robot and the ultrasonic sensor are applied to the automatic detection system for the complex curved surface. First, the frame of system is presented, and then the synchronous acquisition between ultrasonic echo signal and the position of robot is described in detail. Taking for example Staubli TX90XL robot with six freedom degrees, this paper uses mixed synchronous trigger based on time-position to detect the aeronautic engine blade. The ultrasonic signal is acquired and then analysed briefly to test the synchronism of the system.

Ultrasonic automatic scanning for arbitrary rotator

The normal tracking of curved surface contour is a key technology of ultrasonic automatic scanning for arbitrary rotator. This paper presents a method of contour normal tracking used in detecting the arbitrary rotator with thick-casting wall. It uses the cubic spline curve interpolation to reconstruct the complex generatrix of rotator based on its CAD model data and deduce the normal tracking trajectory algorithm of the probe. This method can guarantee the fixed water path and vertical incidence. The ultrasonic automatic detection software system of rotator was compiled using MFC programming language and used in testing wheel hub of vehicle. Experiments showed that this method can get clear images and realize ultrasonic automatic scanning and imaging test.

A quick algorithm for circularity error evaluation based on minimum circumscribed circle method

The evaluation of circularity based on the minimum circumscribed circle method is an important method suitable for the circle with the maximum material condition of a convex like a shaft. The minimum circumscribed circle is determined by a small number data points according to the criteria of the minimum circumscribed circle. This article points out the minimum circumscribed circle can be obtained only at vertices of convex hull. Based on three theorems developed, a strategy is proposed to identify the critical data points. The validated results show that the method gives an efficient approach to solve the circularity problems on the minimum circumscribed circle, especially when the number of data points is large.