Welding robots mainly consist of two parts: the robot and the welding equipment.
A robot consists of a robot body and a control cabinet (hardware and software). Welding equipment, taking arc welding and spot welding as examples, consists of a welding power source (including its control system), a wire feeder (for arc welding), and a welding torch (or clamp), among other components.
Intelligent robots should also have sensing systems, such as laser or camera sensors and their control devices. Welding robots produced worldwide are mostly articulated robots, with the vast majority having six axes. Axes 1, 2, and 3 can move the end effector to different spatial positions, while axes 4, 5, and 6 address different tool posture requirements.
There are two main types of mechanical structures for welding robot bodies: one is a parallelogram structure, and the other is a side-mounted (swinging) structure.
The parallelogram robot's upper arm is driven by a lever. The lever and the lower arm form two sides of a parallelogram, hence the name.
Early parallelogram robots had relatively small workspaces (limited to the front of the robot), making it difficult to work upside down. However, new parallelogram robots (parallel robots) developed since the late 1980s have been able to expand the workspace to the top, back, and bottom of the robot, and have not suffered from the rigidity problems of stationary robots, thus gaining widespread attention.
This structure is suitable for both light and heavy robots. In recent years, most spot welding robots (with a load capacity of 100-150kg) have adopted a parallelogram structure.
The main advantage of the side-mounted (swinging) structure is the large range of motion of the upper and lower arms, allowing the robot's workspace to almost reach the size of a sphere. Therefore, this type of robot can work upside down on the frame, saving floor space and facilitating the movement of objects on the ground.
However, this type of side-mounted robot has a cantilever structure for its 2nd and 3rd axes, which reduces the robot's rigidity. It is generally suitable for robots with smaller loads, used for arc welding, cutting, or spraying.
Both types of robots described above perform rotary motion on all axes, therefore they are driven by servo motors via cycloidal pinwheel (RV) reducers (axis 1-3) and harmonic reducers (axis 1-6). Before the mid-1980s, DC servo motors were used for electrically driven robots, but since the late 1980s, various countries have successively switched to AC servo motors.
Because AC motors have no carbon brushes, they have excellent dynamic characteristics, resulting in new robots with not only a low accident rate but also significantly increased maintenance-free time and faster acceleration and deceleration. Some new lightweight robots with a load capacity of less than 16kg can achieve a maximum tool center point (TCP) speed of over 3m/s, with accurate positioning and low vibration.
Meanwhile, the robot's control cabinet has been upgraded to use a 32-bit microcomputer and new algorithms, enabling it to optimize its own path and make its running trajectory closer to the taught trajectory.
Selection of degrees of freedom for welding robots
The arm and wrist of a welding robot are the basic moving parts. Any robot arm design has three degrees of freedom to ensure that the end of the arm can reach any point within its working range. The three degrees of freedom of the wrist are rotational movements about three mutually perpendicular coordinate axes X, Y, and Z in space, commonly referred to as roll, pitch, and yaw movements.
When customers purchase and use welding robots, they should consider the following aspects:
1. The production type of welded parts is characterized by multi-variety, small-batch production;
2. The structural dimensions of the welded parts are mainly small to medium-sized welded workpieces, and the material and thickness of the welded parts are conducive to the use of spot welding or gas shielded welding methods;
3. The blanks to be welded meet the welding robot's process requirements in terms of dimensional accuracy and assembly precision;
4. Equipment used in conjunction with welding robots, such as automated welding equipment and welding positioners, should be able to coordinate with the welding robots to ensure synchronized production rhythms;
Advantages of welding robots
With the development of electronic technology, computer technology, numerical control, and robotics, automatic welding robots have been used in production since the 1960s. Their technology has matured significantly, and their advantages are mainly as follows:
1) Stabilizes and improves welding quality, and can reflect welding quality in numerical form;
2) Improve labor productivity;
3) Improves the intensity of workers' labor, enabling them to work in hazardous environments;
4) Reduced the skill requirements for workers;
5) It shortens the preparation cycle for product upgrades and reduces corresponding equipment investment.
