Design and control of mechanical systems with reduced mobility

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The quest for faster production machinery has called for the design and development of mechanical systems capable of moving a payload with motions of a special kind, short of some degrees of freedom of the total six of rigid bodies. Work in this area has given rise to what is known as low-mobility robots (LMR). Typical machines of this kind are what is known as SCARA (Selective-Compliance Assembly Robot Arm) systems, for the transfer of flat workpieces, as those appearing in modern electronic products (cell phones, iPods, etc.) that are displaced between two poses in which their two largest dimensions lie in parallel planes. This feature calls for a suppression of tilting about two independent horizontal axes, thereby leading to motions with four degrees of freedom, known to entail displacements endowed with the algebraic property of a group, what is called the Schoenflies subgroup of the rigid-body displacement group. These displacements are those undergone by the tray of a waiter: translations along three independent directions, but one single rotation, namely, about an axis of fixed direction, usually vertical. Conventional SCARA systems, featuring three pin joints of parallel axes and one sliding joint of direction parallel to the foregoing axes, in a serial array, have been around for about 25 years. Their technology has reached maturity, their performance having reached its physical limits, which has prompted, since the turn of the century, the development of alternative morphologies, namely, parallel, with up to four limbs connecting a fixed base with a moving platform. The latter carries the gripper. This is but one example of LMR; there are many more. The design and control of these systems pose interesting challenges because of the extreme demands in the accuracy of their machining and assembly. Robust means to face these challenges are proposed here. The philosophy adopted in the proposed work lies in the theoretical design work conducted by the applicant in the last six years.