1、 Structural design
Due to the fact that the designed welding robot operates in a quasi planar and narrow space environment, in order to ensure that the robot can track the weld seam automatically according to the deviation information of the arc sensor, it is required that the designed robot should have a compact structure, flexible movement, and stable operation. In response to the characteristics of narrow space, a small mobile welding robot has been developed in this paper. Based on the motion characteristics of each structure of the robot, a modular design method is used, The robot mechanism is divided into three parts: a wheeled mobile platform, a welding torch adjustment mechanism, and an arc sensor. Among them, the wheeled mobile platform, due to its high inertia and slow response, mainly tracks the weld seam roughly. The welding torch adjustment mechanism is responsible for precise tracking of the weld seam, and the arc sensor completes real-time recognition of weld seam deviation. In addition, the robot controller and motor driver are integrated and installed on the robot mobile platform, making its volume smaller. At the same time, in order to reduce the impact of dust on moving parts in harsh welding environments, a fully enclosed structure is adopted to improve the system reliability.
2、 Characteristics
Spot welding does not have high requirements for welding robots. Because spot welding only requires point position control, there are no strict requirements for the movement trajectory of the welding tongs between points, which is also the reason why robots were originally only used for spot welding. Spot welding robots not only need to have sufficient load capacity, but also need to have fast speed, smooth movement, and accurate positioning when moving between points to reduce displacement time and improve work efficiency. The amount of load capacity required for a spot welding robot depends on the type of welding clamp used. For welding tongs separated from transformers, a robot with a load of 30-45kg is sufficient. However, on the one hand, this type of welding clamp is not conducive to robots extending the welding clamp into the workpiece for welding due to the long secondary cable line and high electrical energy loss; On the other hand, the cable oscillates continuously with the robot's movement, resulting in faster cable damage. Therefore, the use of integrated welding tongs is gradually increasing. This type of welding clamp, along with the transformer, has a mass of about 70kg. Considering that robots need to have sufficient load capacity and be able to send welding tongs to spatial positions for welding at a high acceleration, heavy-duty robots with a load of 100-150kg are generally selected. In order to adapt to the requirements of rapid short distance displacement of welding tongs during continuous spot welding. The new heavy-duty robot has added the function of completing 50mm displacement within 0.3 seconds. This places higher demands on the performance of motors, the computational speed and algorithms of microcomputers.