Integrated Design of Mechanical Structure and Control Algorithm for Closed-Chain Five-Bar Mechanism

In the traditional mechatronic systems, the controller designs are usually separated from the mechanical structure designs. Consequently, the controller algorithms become more and more complex, i.e., from the PD controller, to the computed-torque controller, and to all sorts of the adaptive controller. These complex control algorithms encounter many difficulties in implementation of the control algorithms to closed-chain mechanisms. The main reason for these difficulties is the so-called computational overhead with the dynamic model of the closed-chain mechanisms. The computational overhead is even experienced in a parallel manipulator system (one of the closed-chain types). One of the solutions to this problem is to seek a smart design of mechanical structures based on the methodology called Design For Control (DFC). DFC specifically proposes the procedure, i.e., design of a mechanical structure, simplification of the dynamic model of the mechanical structure, and design of a simple control algorithm (such as PD controller). In this paper, a 2-dof five-bar closed-chain mechanism (called Delta mechanism for short) is studied. It is shown that the smart design of the mechanical structure of the Delta mechanism can lead to some configuration invariants in the dynamic model. Therefore, the design of PD controllers, incorporating these invariants, can achieve excellent system performance. Keyword: DFC, five-bar mechanism, control algorithm, tracking performance