Welding robots mainly include two parts: the robot and the welding equipment. The robot consists of the robot body and the control cabinet (hardware and software). Taking arc welding and spot welding as examples, the welding equipment consists of the welding power source (including its control system), the wire feeder (for arc welding), the welding gun (or electrode holder), etc. For intelligent robots, there should also be a sensing system, such as a laser or camera sensor and its control device. Figures 1a and 1b show the basic composition of arc welding robots and spot welding robots.

With the development of electronic technology, computer technology, numerical control, and robot technology, since automatic welding robots were introduced into production in the 1960s, their technology has become increasingly mature, with the following main advantages:

1) Stabilize and improve the welding quality, which can be reflected in numerical form.

2) Improve labor productivity.

3) Reduce the labor intensity of workers and allow them to work in harmful environments.

4) Lower the requirements for workers' operation skills.

5) Shorten the preparation cycle for product model changes and reduce the corresponding equipment investment.

Therefore, they have been widely used in various industries.

The requirements for spot - welding robots are not very high. Since spot welding only requires point - to - point control, there are no strict requirements for the movement trajectory of the electrode holder between points. This is also the reason why robots could only be used for spot welding at first. Spot - welding robots not only need to have sufficient load - carrying capacity but also need to move quickly, smoothly, and accurately between points to reduce the shifting time and improve

work efficiency. The required load - carrying capacity of a spot - welding robot depends on the type of electrode holder used. For electrode holders separated from the transformer, a robot with a load capacity of 30 - 45 kg is sufficient. However, on the one hand, due to the long secondary cable, there is a large power loss, and it is also difficult for the robot to insert the electrode holder into the workpiece for welding; on the other hand, the cable swings constantly as the robot moves, so the cable is damaged more quickly. Therefore, integrated electrode holders are increasingly used at present. The mass of this kind of electrode holder together with the transformer is about 70 kg. Considering that the robot needs to have sufficient load - carrying capacity to send the electrode holder to the spatial position for welding with a large acceleration, heavy - duty robots with a load capacity of 100 - 150 kg are generally selected. To meet the requirement of short - distance and rapid shifting of the electrode holder during continuous spot welding, new heavy - duty robots have added the function of completing a 50 - mm displacement within 0.3 s. This puts forward higher requirements for the performance of the motor, the computing speed of the microcomputer, and the algorithm.