A Case Study on the Selection of Performance Index for Design Optimization of New Controllers

Product development is a difficult task when all of the design objectives, constraints, and options available to engineers are considered. Several decisions must be made during the design process such as product cost, reliability, volume, functions, options, packaging, the use of new technology, development time/cost, and available manpower. The engineer must factor these items to meet product objectives and achieve an optimal design. One problem in product development, of course, is determining what is an optimal design. A method of measurement must be established to quantitatively define the performance index for optimum design. Typically, designs are judged subjectively rather than by analytical techniques in which the engineer is trained. To alleviate this problem, the concept of the Merit Index is introduced to quantify the way in which new designs are measured. This analytical technique is used as a method in selecting the optimal design. The Merit Index is a unit of measure that is a function of the design adequacy, producibility, compatibility, reliability, and cost effectiveness. The design objectives are expressed as indexes and assigned individual weights to represent the relative importance in the performance index. This paper provides a design methodology to simplify the design process by utilizing analytical rather than subjective approaches to optimize product development. The development of a variable reluctance servomotor controller is used as a case study to illustrate the technique.