A Novel Parallel-Kinematics Machine Tool Jorge Angeles, Alexei Morozov and Shaoping Bai McGill University, Mechanical Engineering Department & Centre for Intelligent Machines 817 Sherbrooke Str. West, Room 452, Montreal, QC, Canada H3A 2K6 angeles@cim.mcgill.ca alexvit@cim.mcgill.ca mspbai@cim.mcgill.ca Abstract In the paper a novel parallel-kinematics machine (PKM) tool is introduced, consisting of two innovative components. The first is a manipulator capable of producing a special class of motions, namely, those produced with manipulators termed SCARA, an acronym Selective-Compliance Assembly Robot Arm. We propose to integrate this manipulator with another device, a tool-orienting head producing pitch and roll of a cutting tool; the latter is a mechanism of the automotive-differential type, whereby the gears have been replaced with cams and rollers. The first module of the PKM, contrary to conventional SCARA systems, has its four motors fixed to a common base, either at the ceiling or on the floor. The kinematics of the new manipulator is outlined. The second module of the PKM, an innovative robotic pitch-roll wrist, was designed using multi-lobe cams. The two-degree-of-freedom wrist has a double-layer structure. The outer layer consists of two roller-carriers (RCs), which are connected to actuators by means of corresponding shafts of horizontal axes protruding from the wrist frame. The inner layer is a cam sub- assembly driven by RCs to rotate as a planetary train, the wrist functioning, as their bevel-gear counterparts, under the principle of spherical differential mechanisms. The novel parallel-kinematics machine offers significant advantages over existing systems: higher dexterity of the tool-head and higher operational speed with sufficient rigidity, which should lead to higher productivity. Keywords: PKM, Parallel, Robot, Manipulator, Machine Tool 1. Introduction In modern industry most robots used for industrial manufacturing have articulated structures of the serial type, where each link is coupled to the two other links, except for the end links, which are coupled to one single neighbour. However, these simple, open kinematic chains of multi-axis machines suffer from the disadvantage that each axis must carry all other axes located upstream in the chain. The history of the development of robots with a parallel structure can be traced back 18 years [1]. As a milestone in this regard, Karl-Erik Neumann designed and built a new type of robot, the parallel kinematic robot (PKR), in 1987 [2]. This type of robot had three or more linear axes, one end of each attached to the base, the opposite end used to support the end-platform. Thus, all axes in such a robot function in parallel to each other. In spite of the early invention of parallel robots, they were not used widely until the early 90's, since this kinematics demanded sophisticated control not affordable with the computational means available at that moment. After 1992, when Comau Pico launched the first multiprocessor controller, new control systems appeared on the market, able to run PKR a.k.a. parallel-kinematics machines (PKM). Most PKM are based on hexapods, also known as Stewart or Gough-Stewart platforms [3]. A sample of PKM currently used in industry is displayed in Figure 1. The most widespread operation is machining. These include milling, cutting, drilling and deburring of sheet and cast metal parts. For example, in 1999 more than two thirds of robotic applications of the inventors and manufacturers of Tricept technology, Neos Robotics AB (Sweden), were machining, where clients wanted to have 10 microns of repeatability, stiffer links, and higher power, while maintaining flexibility. The Tricept (Figure 1c) is also used to hold laser and saw cutting tools, as well as friction welders. The aerospace industry uses Tricept robots for fabricating propellers, turbine blades, impellers and other parts with intricate surfaces which require significant amount of contouring.