Design and control of multibody mechanical systems

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Productivity-enhancement has called for fast, efficient robotic mechanical systems capable of moving a payload with motions of a special kind, that exclude some rigid-body motions, which has given rise to what is known as lower-mobility robots or mechanisms. These entail kinematic loops, as they bear a parallel architecture. As a consequence, these systems are inherently overconstrained, in that any manufacturing and assembly errors either make loop-closure impossible or limit their degree of freedom. Expert designers use extra joints to cope with this feature, the downside being that stiffness, and hence, precision, are compromised. In the research program proposed here for the next five years we will investigate the design and control of lower-mobility robots. On the design side, we will introduce complexity as a main design criterion, for it can handle the limited amount of information available at the conceptual stage of the design process. By assigning a complexity measure to each of the machine performance aspects, precision, stiffness and assemblability, we will be able to face the current challenges of industry. The main idea here is to distribute the load as uniformly as possible among all actuators, while aiming at a mechanical structure with geometric, kinematic and mechanical symmetries. The outcome should be a mechanical system with the same precision and stiffness properties in any direction of motion, and the same natural frequencies. However, functional requirements may make it impossible to meet the foregoing ideal conditions. In this case, a compromise should be reached in aiming at machines whose performance lies as closely as possible to the foregoing ideal. On the control side, we will also use complexity as a major design criterion, which will allow us to produce the simplest control-system architecture, one approaching a parallel array of identical single-input, single-output control subsystems, one for each motion direction of the payload.