Since the designed welding robot works in a quasi - planar and narrow - space environment, in order to ensure that the robot can track the weld seam and perform automatic welding according to the deviation information from the arc sensor, the designed robot is required to have a compact structure, flexible movement, and stable operation. In this paper, aiming at the characteristics of the narrow space, a small mobile welding robot is developed. According to the motion characteristics of each structure of the robot, the modular design method is used to divide the robot mechanism into three parts: the wheeled mobile platform, the torch adjustment mechanism, and the arc sensor. Among them, due to its large inertia and slow response, the wheeled mobile platform mainly performs rough tracking of the weld seam, the torch adjustment mechanism is responsible for accurate tracking of the weld seam, and the arc sensor completes real - time identification of the weld seam deviation. In addition, the robot controller and the motor driver are integrated and installed on the robot mobile platform to make its volume smaller. At the same time, in order to reduce the influence of dust on moving parts in the harsh welding environment, a fully enclosed structure is adopted to improve the reliability of the system.

Equipment

The welding equipment of the spot - welding robot uses an integrated welding gun, and the welding transformer is installed behind the welding gun, so the transformer must be miniaturized as much as possible. For transformers with smaller capacities, 50Hz power - frequency alternating current can be used. For transformers with larger capacities, inverter technology has begun to be used to convert 50Hz power - frequency alternating current into 600 - 700Hz alternating current, which reduces the volume and weight of the transformer. After transformation, 600 - 700Hz alternating current can be directly used for welding, or secondary rectification can be carried out for direct - current welding. The welding parameters are adjusted by a timer, as shown in Figure 1b. The new - type timer has been computerized, so the robot control cabinet can directly control the timer without an additional interface. The welding gun of the spot - welding robot is usually a pneumatic welding gun. The opening degree between the two electrodes of the pneumatic welding gun generally has only two - stage strokes. Moreover, once the electrode pressure is set, it cannot be changed at will. In recent years, a new type of electric servo spot - welding gun has emerged, as shown in Figure 4. The opening and closing of the welding gun are driven by a servo motor with encoder feedback, so that the opening degree of this welding gun can be arbitrarily selected and preset according to actual needs. Moreover, the pressing force between the electrodes can also be steplessly adjusted. This new type of electric servo spot - welding gun has the following advantages:

1) The welding cycle of each solder joint can be significantly reduced. Since the opening degree of the welding gun is precisely controlled by the robot, the welding gun can start to close during the movement of the robot between points. After welding a point, the robot can move while the welding gun is opening, without waiting for the robot to arrive before the welding gun closes or for the welding gun to fully open before the robot moves.

2) The opening degree of the welding gun can be arbitrarily adjusted according to the situation of the workpiece. As long as there is no collision or interference, the opening degree should be reduced as much as possible to save the time occupied by the opening and closing of the welding gun.

3) When the welding gun closes and applies pressure, not only can the pressure be adjusted, but also the two electrodes close gently when closing, reducing impact deformation and noise.