Assembly robot is the core equipment of flexible automated assembly system, which consists of robot operator, controller, end-effector and sensing system. The controller generally adopts multi-CPU or multi-stage computer system to realize motion control and motion programming; the end-effector is designed as various hand claws and wrists to adapt to different assembly objects; the sensing system is used to obtain information about the interaction between the assembly robot, the environment and the assembly objects.
The two main types of commonly used assembly robots are the Programmable Universal Manipula-tor forAssembly (PUMA) robot (first appeared in 1978, the ancestor of industrial robots) and the planar double-articulated robot, the SCARA robot. Compared with general industrial robots, assembly robots have high precision, good flexibility, small working range, and the ability to be used with other systems, and are mainly used in the manufacturing industry of various electrical appliances.
Basic types and structures of assembly robots
1、PUMA robot
PUMA, developed by Unimation in 1977, is a computer-controlled multi-joint assembly robot. Generally there are 5 or 6 degrees of freedom, i.e. waist, shoulder, elbow rotation and wrist bending, rotation and twisting functions (Figure 1). Its control system consists of a microcomputer, servo system, input/output system and external devices. VAL II is used as the programming language, for example, the statement "APPRO PART, 50" means that the hand moves to 50 mm above PART, and the position of PART can be keyed or taught, and VAL has the functions of continuous trajectory motion and matrix transformation.
2、SCARA robot
A large amount of assembly work is vertical downward, which requires a large flexibility of horizontal (X, Y) movement of the hand claw to compensate the position error. The vertical (Z) movement and rotation around the horizontal axis have greater rigidity for accurate and powerful assembly. It is also required that the rotation around Z-axis has greater flexibility for key or spline fit. The University of Yamanashi in Japan has developed a SCARA robot, whose structural features meet the above requirements. Its control system is also relatively simple, such as the SR-3000 robot uses a microprocessor to achieve semi-closed-loop control of the θ1, θ2, and Z axes (DC servo motors) and open-loop control of the s axis (stepper motors). The programming language is SERF, which is similar to BASIC, and the latest version, Level4, has functions such as coordinate transformation, linear and circular interpolation, arbitrary speed setting, text-based subroutines, and error checking, etc. SCARA robots are one of the most used types at present.
Assembly robots are mainly used in the manufacture of various electrical appliances (including household appliances, such as TV sets, tape recorders, washing machines, refrigerators, vacuum cleaners), small motors, automobiles and their components, computers, toys, and the assembly of electromechanical products and their components.
