Papers by Author: Guang Jun Zhang

Abstract: This paper presents a new method to improve the estimation of the positions for serial robots using power-activated feed-forward neural network. In the paper, a six-input three-output neural network is created with robot joint angle sine values as inputs and positions in the world frame as outputs. The neuron is activated with an orthogonal polynomial sequence,and the neural weights can be calculated directly without involving iterative and convergent problem. It is found that, the RMS error is less than 0.25 mm for the whole work space. And the absolute and relative errors of this method are smaller than those of built in kinematics model and the traditional back propagation (BP) neural network method. Experimental results show that the proposed method can effectively predict the positioning of the given joint angles.

Abstract: The active droplet oscillation is a method previously proposed to detach the droplet at currents below the transition current. In this method, a droplet oscillation is actively excited when the current is switched from the exciting peak level to base level. The downward momentum of the droplet is utilized to enhance the droplet detachment. In this work, the current waveform is modified to achieve stronger droplet oscillation with lower average current. The critical change is to separate the droplet growing and exciting processes such that the two processes can be controlled independently. The heat input can thus be reduced, and stronger droplet oscillation is obtained. A further optimized current waveform is proposed to maximize the droplet oscillation energy despite the growing current level.

Abstract: A low-current GMAW experimental system is established using a constant current power supply and a controlled wire feed system. The metal transfer behavior and the droplet growing process in low-current GMAW are investigated by using a high-speed camera, and the welding current and voltage are monitored by a data acquisition set. The metal transfer in low-current GMAW can be classified into three modes: short-circuiting transfer, long-arc short-circuiting transfer and large globular transfer. The arc voltage is the primary factor that affects the metal transfer mode. The droplets growing in low-current GMAW are observed and analyzed. The maximum detaching size of the droplet and the corresponding growing time with different welding current are calculated from the recorded image sequences of metal transfer. Based on such results, a prediction model of the droplet size is thus established, which will be used in the future research on pulsed laser-enhanced GMAW.

Abstract: This paper describes a novel rapid manufacturing and remanufacturing system based on robotic gas metal arc welding. If worn parts are maintainable, this system play a repairer role; if worn parts are unfit to remain in service, this system play a manufacturer role. This system works in ‘modeling - slicing - stacking’ principle. First, Detecting and building three-dimensional models of damaged zone by structured light. Second, Slicing established three-dimensional model in layers with some thickness. Third, planning robotic tool path to get optimumwelding path and parameters. Finally, executing remanufacturing task with robotic GMAW stacking layer by layer. This system remanufactures parts in human - robot interactive way. Take a half cylinder shell as worn part, experiments are conducted. Results show the mean error of surface smoothness is less than 0.5mm.

Abstract: This paper presents a generic design and implementation of a telerobotic system application for the remote welding of unstructured and hazardous environment. The objective is to establish a remote welding telerobotic system that is flexibility to carry out welding seam tracing and welding remotely. According to the difference of welding task and environment, this paper presents human machine cooperative control strategies that integrate sensor and model-based computer assistance. The human operator decision and control commands participate into every control level of the teleoperation system. The specific control modes have been presented to integrate into human machine interface (HMI).

Abstract: In the near twenty years, with the rapid increase of Chinese economy, Chinese welding technology developed very fast. In 2003, the annual output of steel in China has reached 230 megatons and above 40 percent was manufactured by welding process. The main welding engineering projects include: the Three Gorges power station, bridges over the Changjiang River, high pressure heavy-duty chemical container, pipeline project of transferring natural gas from West to East and manned spacecraft etc. Meanwhile, Chinese annual output of welding materials exceeds 1,200 kilotons, welding equipments exceed 200,000 sets and the welding automation rate reached 40 percent. The State Key Laboratory of Advanced Welding Production Technology in Harbin Institute of Technology is the only welding laboratory of national level in China. It is the base of applied fundamental research and high quality welding technicians training. It has completed many projects of welding technology development and some significant applied engineering tasks. Every year, about 15-20 Doctors, 40-50 Masters and 70-100 Bachelors graduate from the Laboratory. Also, it is opened to the whole world.