Robust Design: Tolerance Design Method

Abstract

There are three phases involved in Robust Design — conceptual design, parameter design, and tolerance design. Parameter design aims to specify the variations of the design parameters in order to meet the design requirement, and the tolerance design further specifies the optimized parameters in order to reduce the performance variation near the design target. A robust design requires that tolerance design to be preceded by parameter design. In this paper, our effort will be focused on presenting an iterative method to perform the tolerance design phase. Two hypothetical examples (whose parameter designs have been completed) will be used to illustrate the tolerance design methodology. The first example involves the design of a pneumatic cylinder whose piston movement can be expressed by a theoretical equation containing five parameters. With the equation, it becomes a simple task for determining the tolerances of the optimized parameters to constrain the design target. The second example involves the production of a agrochemical by mixing two chemicals to achieve a specific yield. A set of test data is available but the equation relating the parameters is not. In this case, we shall adopt the linear regression technique to obtain an experimental equation to represent the test data. Based on this equation, we can proceed to determine the tolerances of different parameters in order to achieve a specific variation of the yield. The step-by-step procedure outlined in the hypothetical examples demonstrates that this iterative method is a simple and effective way to conduct the tolerance design.