In 1994 two American machine tool companies, Giddings & Lewis and Ingersoll surprised the world with the presentation of a new type of machine tool. Traditional machine tools used in machining or assembly systems are characterized by a typical serial structure while these new systems were based on the parallel link kinematics structure, first developed by Steward in England in1965.
The idea of making parallel CNC robot was made in the center in order to learn this recent innovation and to remove fear of using nonstandard robotic architectures. Also some features which are peculiar to parallel robots, such as good dynamic performance, high amount of flexibility and high structural stiffness, were attracting the attention of us to build one.
The project was fulfilled with a team containing five undergraduate students under supervision of two faculty members in about two years.
As a general rule, main hindrances of the Stewart platforms are: limited workspace (mobility bonds) and path singularities (dexterity bonds). These drawbacks are minimized, due to suitable setting of geometrical ratios and proper choice of the upper joints set-up. The basic platform is composed by a base and a platform connected by means of six legs; each leg characterizes by the joint sequence S-S (spherical -spherical).One spherical joint S is placed between the fixed base and the leg; while the other joint S connects the leg and the floating platform, with final setup having three degrees of freedom. To obtain modularity, aiming at compressing design and construction time and at simplifying maintenance, the plate with 120° symmetry shapes is considered for the moving platform. The moving platform is equipped with a spindle as a tool to add machining capability to the robot. Each leg is connected to a ball screw driven by a150W DC motor which is controlled by means of a computer through object oriented software. The movement of the can be done both continuous or from rest to rest.
The current setup for the laboratory enables us not only to demonstrate a sample of parallel kinematics architecture with demo predefined paths for students but also may be used for higher level education purposes for individuals to use their own control algorithm and evaluate its feasibility through experiment.