Assembly robot is the core equipment of flexible automatic assembly system, which is composed of robot manipulator, controller, end effector and sensor system. The structure types of the manipulator include horizontal joint type, rectangular coordinate type, multi-joint type and cylindrical coordinate type; The controller generally adopts multi-cPU or multi-level computer system to realize motion control and motion programming; The end effector is designed into various grippers and wrists to adapt to different assembly objects; The sensor system is used to obtain the information of the interaction between the assembly robot and the environment and the assembly object.
Commonly used assembly robots mainly include two types: programmable universal manipulator for assembly, namely PUMA robot (first appeared in 1978, the ancestor of industrial robots) and planar two-joint robot, namely SCARA robot. Compared with general industrial robots, assembly robots have the characteristics of high accuracy, good flexibility, small working range, and can be used together with other systems. They are mainly used in the manufacturing industry of various electrical appliances.
Basic types and structures of assembly robots
1. PUMA robot
The PUMA developed by the United States in 1977 is a computer-controlled multi-joint assembly robot. Generally, it has 5 or 6 degrees of freedom, that is, the rotation of waist, shoulder and elbow, and the bending, rotation and torsion of wrist (Figure 1). Its control system consists of microcomputer, servo system, input and output system and external equipment. VAL II is used as the programming language. For example, the statement "APPRO PART, 50" means that the hand moves to 50mm above the PART. The position of PART can be typed or taught. VAL has the function of continuous track motion and matrix transformation.
2. SCARA robot
A large number of assembly operations are vertical and downward, which requires greater flexibility in the horizontal (X, Y) movement of the gripper to compensate for the position error. The vertical (Z) movement and rotation around the horizontal axis have greater rigidity for accurate and powerful assembly. In addition, it is also required to have greater flexibility when rotating around the Z axis to facilitate the fitting of keys or splines. The SCARA robot has been developed by Yamanashi University in Japan, and its structural characteristics meet the above requirements. Its control system is also relatively simple. For example, the SR-3000 robot uses a microprocessor to control θ 1、 θ 2. The Z-axis (DC servo motor) realizes semi-closed loop control, and the s-axis (stepper motor) carries out open-loop control. The programming language is SERF similar to BASIC. The latest version of Level4 has the functions of coordinate transformation, line and arc interpolation, arbitrary speed setting, subroutine named by text and error detection. SCARA robot is one of the most widely used types at present.
Assembly robots are mainly used in the manufacturing of various electrical appliances (including household appliances, such as television sets, tape recorders, washing machines, refrigerators, vacuum cleaners), small motors, automobiles and their components, computers, toys, electromechanical products and their components assembly, etc.