Engineering system co-design with limited plant redesign

Modern engineering systems often are impractical to design from the ground up. New designs typically are modifications of earlier systems (and frequently only small perturbations of them). This limited redesign approach is becoming increasingly important as the scale and complexity of engineering systems increases. One significant application of limited redesign is the repurposing of mechatronic systems. Often engineers seek to meet the needs of a new application by redesigning only the control system for a mechatronic device. While in many cases this approach is successful, control design changes alone may not always be sufficient. If control redesign alone is inadequate, physical system (plant) design changes should be investigated. Complete plant redesign cost may be prohibitive, and usually is unnecessary. A limited set of plant design changes should be identified that enable system requirement satisfaction at the lowest cost. Here we present a formal integrated approach for limited redesign of mechatronic systems. Candidate plant modifications are identified using sensitivity analysis, and then an optimization problem is solved that minimizes the cost of system redesign while satisfying requirements. This formal methodology for plant limited co-design (PLCD) is demonstrated using a robotic manipulator design problem. First the manipulator is designed in a way that exploits passive dynamics to minimize energy consumption for a specific task. Afterward a new task is introduced that cannot be performed successfully through control changes alone. Limited plant changes are identified, and the PLCD result for this new task is compared to a full system redesign. The PLCD result costs significantly less than the full redesign with a small performance penalty. Parametric studies illustrate the tradeo? between redesign cost and performance, and it is shown that the proposed sensitivity analysis results in the lowest cost limited redesign.