With the increasingly higher requirements of automotive manufacturing on indicators such as welding accuracy and speed, as well as the increasing demand for individualized users, in order to meet the needs of multi-models and multi-batch markets, and to improve flexibility and elasticity of the production capacity of the body shop, Industrial robots have been widely used in body welding. This article describes the application of spot welding robots and arc welding robot systems in car body welding with examples.

The structure and craft of the car body largely determine the safety factor of the car. The body of the vehicle is a complex thin-plate structural part connected by more than a dozen large assemblies and hundreds of sheet metal stamping, which are connected by spot welding, arc welding, laser welding, brazing, riveting, mechanical joining and glue bonding. Due to the large number of parts involved in the bodywork, the complexity of the process and the variety of types of equipment. The body planning has high requirements for welding processes, welding fixtures, quality control and maintenance. This article focuses on the application of spot welding robot system and arc welding robot system in vehicle body welding.

When the two-armed coordinated motion control of the robot system is performed, there are mainly three kinds of control schemes, namely, position-position control, position-force control and dynamic control. Position-position control is a control method first developed in the dual-arm coordination research of robots. It controls the active robot moving according to a pre-planned trajectory. then the slave robot output the trajectory along the trajectory of active robot. Which achieves the Coordination movements of active and slave robots. The position-position control, due to the poor compliance of each robot, the internal position stress will be generated under rigid connection conditions. Therefore, this method is only suitable for low-speed or non-rigid connection motion.

In order to overcome the above insufficiency, the position-force control was proposed. That is, the active robot is for position control. It moves along a pre-planned trajectory. The slave robot is for force control. It provide feedback motion controlling through force information obtained by the wrist force sensor follows the active robot. . Based on the definition of workspace coordinates and the introduction of joint space vectors, M.Uchiyama deduced the kinematics and statics formulas of dual-arm robots and successfully applied hybrid position-force control.
In order to ensure the accuracy of the robot movement and good dynamic response, the researchers proposed a dynamic control scheme in the study of the two-arm coordination movement of the robot. It uses the nonlinear transformation method to study hybrid control algorithm of two robots to manipulate a single object when two arms were coordinated. And eliminating the internal forces between objects as a control quantity, only consider the inverse dynamics redundancy problem when the object is positioned, and achieved better control effect.

The system adopts distributed control, double-sided double robot adopts master-slave coordinated control strategy. Motoman robot is the main force (front), KUKA robot is slave force (back), establishes the algorithm model of coordinated motion of the system, according to the position and situation of the main force torch tip, regarding the plane of symmetry of the workpiece as reference path. By kinematic coordinate transformation, the movement path point of the backside hand robot tool end is deduced, so that the coordinated follow movement of the main force is controlled and the welding of the double-sided double arc welding robot is realized.