Welding robots mainly include two parts: robots and welding equipment. The robot consists of the robot body and the control cabinet (hardware and software). Welding equipment, taking arc welding and spot welding as an example, is composed of welding power supply, (including its control system), wire feeder (arc welding), welding torch (pliers) and other parts. For intelligent robots, there should also be sensing systems, such as laser or camera sensors and their control devices. Figures 1a and b show the basic components of arc welding robots and spot welding robots.
Welding robots produced in countries around 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. There are two main forms of mechanical structure of the welding robot body: one is a parallelogram structure and the other is a side-mounted (pendulum) structure, as shown in Fig. 2a and b. The main advantage of the side-mounted (pendulum) structure is the large range of motion of the upper and lower arms, which makes the robot work
The schematic diagram of the welding robot can make a space almost up to a sphere. Therefore, the robot can be hung upside down on the rack to save floor space and facilitate the flow of objects on the floor. However, this kind of side-mounted robot, 2 and 3 axes for cantilever structure, reduce the rigidity of the robot, generally suitable for robots with small loads, for arc welding, cutting or spraying. The upper arm of the parallelogram robot is driven by a tie rod. The tie rod forms the two sides of a parallelogram with the lower arm. Hence the name. The parallelogram robot developed early had a relatively small working space (limited to the front of the robot) and made it difficult to work upside down. However, the new parallelogram robot (parallel robot) developed since the late 80s has been able to expand the working space to the top, back and bottom of the robot without the stiffness problem of the measurement robot, so it has received widespread attention. This structure is suitable not only for light but also heavy robots. In recent years, spot welding robots (load 100~150kg) mostly use parallelogram structure robots.
Each axis of the above two robots is for rotary motion, so the servo motor is driven by the cycloid pinwheel (RV) reducer (1~3 axis) and harmonic reducer (1~6 axis). Before the mid-80s, DC servo motors were used for electrically driven robots, and since the late 80s, countries have switched to AC servo motors. Since the AC motor has no carbon brush and good dynamic characteristics, the new robot not only has a low accident rate, but also greatly increases the maintenance-free time, and the speed of adding (decremating) is also fast. Some new light robots with loads below 16kg have a maximum movement speed of more than 3m/s at the center point of the tool (TCP), accurate positioning and low vibration. At the same time, the control cabinet of the robot also uses a 32-bit microcomputer and a new algorithm, so that it has the function of optimizing the path by itself, and the running trajectory is closer to the trajectory of teaching.
