copyright May, 1998, Michael Berglund
All rights reserved
THESIS
Visitors, welcome to my thesis introduction page! My thesis deals with the exciting world of compliant mechanisms and the design decision process. If you don't know what a compliant mechanism is, please visit the compliant mechanisms home-page before continuing!
MECHANICAL ENGINEERING
BRIGHAM YOUNG UNIVERSITY
242 CB
1.0 PROPOSED TITLE
A Methodology for the Evaluation and Selection of Acceptable Design Concept Alternatives for Compliant Mechanisms
2.0 STATEMENT OF THE PROBLEM
In order to be competitive in the marketplace, companies need to employ successful and rapid product development cycles. Companies need to reduce product development cycle time and costs as well as produce more reliable products.
Compliant mechanisms can offer better solutions to many motion design problems and can help companies achieve a competitive advantage. These mechanisms can reduce costs as well as provide increased reliability in products.
Compliant mechanisms are devices that transfer motion, energy, or force through the deflection of flexible members(1). Some of the advantages of compliant mechanisms include:
1. Reduction of parts compared to rigid-body designs.
2. Reduction in manufacturing and assembly time and costs.
3. Reduction in wear and lubrication.
4. Increase in precision (no backlash).
5. Reduction in weight.
6. Reduction in shipping costs.
7. Shortened lead times in product delivery.
The theory describing the behavior of compliant mechanisms is new, and little literature is available to aid engineers in compliant mechanism design. The theory is excellent in providing many possible solutions to design problems, but it is generally less effective in selecting among solutions, or deciding if a compliant mechanism is even feasible for a given application.
Dr. Michael French, from Lancaster University, an acknowledged expert on the engineering design process, agrees that engineers need design methods to help and encourage them in choosing compliant mechanism designs. In a recent e-mail, he writes,
"The chief need is for studies of how to design commonly-used flexible elements. As it is, designers don't try them because it is too laborious homing in on a design, and then it might be unacceptable (usually too bulky). Moreover, they don't know all the ways of improving performance, e.g. increasing stiffness ratios."(2)
Clearly the absence of applicable literature inhibits engineers from using flexible elements in their designs. This explains why there is little experience in industry in compliant mechanism design. Many engineers feel that a compliant mechanism is synonymous with unreliability and poor quality.
Even those engineers that do have experience in designing compliant mechanisms currently work on more of a "gut feel," than a specific design methodology and a screening criteria for competing designs in solving motion problems. These experienced engineers might "feel good" about a specific design and choose it over others, but they do not know why. Design is more based on intuition, iteration, and trial and error.
A process or methodology for the design of compliant mechanisms will help engineers avoid the occurrence of oversights and/or overlooked factors in design problems. It will also encourage engineers to use this new technology more often and to overcome any psychological barriers that may inhibit them from using compliant mechanisms in their design solutions.
The thesis outlined in this proposal will create a more rational method for selecting designs than the existing intuitive approach engineers now take. The primary objective of the thesis is to bring a logical procedure into the design and development of compliant mechanisms.
The thesis will provide the designer with the ability to better address the following two questions:
1. What motion problems are good candidates for a compliant mechanism, either in re-design or in new product development?
2. What criteria determines a "good" design and what criteria determines a "bad" design for a compliant mechanism?
By answering these two questions, the designer will be encouraged to develop more competitive designs to motion problems using compliant mechanisms.
ENDNOTES
1. Howell, Larry L., Midha, Ashok. Class Notes, ME 538 Compliant Mechanisms, BYU. 1997.
2. French, Michael J. Lancaster University, U.K. Engineering Department. Email sent Oct 20, 1997.