Welding robot mainly includes two parts: robot and welding equipment. The robot is composed of the robot body and the control cabinet (hardware and software). The welding equipment, taking arc welding and spot welding as examples, consists of welding power source (including its control system), wire feeder (arc welding), welding gun (pliers) and other parts. For intelligent robots, there should also be sensor systems, such as laser or camera sensors and their control devices. Figure 1a, b shows the basic composition of the arc welding robot and the spot welding robot.
　　The welding robots produced in all countries in the world are basically joint robots, and most of them have 6 axes. Among them, the 1, 2, and 3 axes can send the end tool to different spatial positions, while the 4, 5, and 6 axes solve the different requirements of the tool posture. The mechanical structure of the welding robot body mainly has two forms: one is a parallelogram structure, and the other is a side-mounted (pendulum) structure, as shown in Figure 2a and b. The main advantage of the side-mounted (pendulum) structure is that the upper and lower arms have a large range of motion, so that the working space of the robot can almost reach a sphere. Therefore, the robot can be hung upside down to work on the rack to save floor space and facilitate the movement of objects on the ground. However, this type of side-mounted robot has a cantilever structure on the 2nd and 3rd axis, which reduces the stiffness of the robot. It is generally suitable for robots with smaller loads for arc welding, cutting or spraying. The upper arm of the parallelogram robot is driven by a pull rod. The pull rod and the lower arm form two sides of a parallelogram. Hence the name. The parallelogram robot developed early has a relatively small working space (limited to the front of the robot) and it is difficult to work upside down. However, a new type of parallelogram robot (parallel robot) developed since the late 1980s has been able to expand the working space to the top, back and bottom of the robot without the stiffness problem of the measuring robot, which has gained widespread attention. This structure is not only suitable for light but also suitable for heavy robots. In recent years, robots for spot welding (loads of 100 to 150 kg) mostly use parallelogram structure robots.