Brent L. Weight and Dr. Larry L. Howell, Mechanical Engineering
A compliant mechanism is one in which the mechanism’s motion comes from deflection of one or more of its members. Compliant mechanisms offer several advantages over rigid-body mechanisms. The member deflection characteristic of compliant mechanisms results in the ability to store energy directly within the member, eliminating the need for additional energy storage devices (i.e. springs) found in rigid-body mechanisms. The member deflection also allows for the replacement of pin joints with small length flexural pivots, or living hinges, thereby reducing part count and assembly time. In fact, one of the most significant advantages of compliant mechanisms is their ability to be fabricated from one piece of material providing savings in both production time and manufacturing cost. Due to these advantages, better, less expensive compliant mechanisms have replaced many rigid-body mechanisms.
The constant-force mechanism is one type of special purpose compliant mechanisms. In many applications it is desirable to have a steady output regardless of the displacement. Using various tools such as the pseudo-rigid-body model, optimization, and type synthesis, specific traditional compliant slider crank parameters can be defined resulting in a mechanism with a constant output force. Previous research has defined 15 configurations for the constant-force mechanism.
The ORCA project was focused around improving the understanding of constant-force mechanisms in general and preparing tools to aid in the implementation of these mechanisms into real applications. These tools would include new types of mechanisms, design methodologies, and optimization programs. Most recently, work has been done to implement these mechanisms into electrical contacts. These constant-force electrical contacts (CFEC) would provide a constant contact force helping to improve the reliability of contacts.
The following was accomplished:
Developed A new set of parameters was developed to show the relative amount of stress and force of a specific mechanism. This has been a major part of the work and has resulted in the ability to compare existing and new configurations of mechanisms with each other to identify the best mechanisms. These parameters can also be added to optimization models to help find the best mechanisms.
A portion of a design methodology for constant-force mechanisms was developed using these new parameters. Since these parameters allow for quick checking of stress and force feasibility of any design problem, the design time and process are quickly reduced and optimized.
An optimization model was developed that allows for the output of the mechanism to be optimized to obtain a constant-force. The model is robust and can handle a variety of initial conditions and configurations. The model, in correlation with the parameters mentioned above, was first used to refine one of the 15 original configurations. The outcome was a mechanism that was 15% shorter in length, but had the same maximum deflection. This configuration is being considered for the CFEC project.
Constant Force Electrical Contact
Using the new parameters, configurations, and other ideas generated as part of this ORCA research, several promising electrical contact concepts have been developed. The project is following traditional design procedures and the new design methodology. Currently, the ideas are still in the concept phase and final iterations on the concepts are being done to produce the best possible solutions.
The work done for this ORCA project is the beginning of a Masters Thesis. In fact, the ORCA work has already been written forming several chapters of the thesis. Additionally, the CFEC project is currently being worked on by two graduate students (including myself) and an Industrial Designer. The results of the ORCA project are being used to help open new avenues for the CFEC project.
This ORCA project only touched the surface of the vast amount of work needed to be done in the area of constant-force mechanisms. The project did result in valuable and useful work. It has resulted in the development of a critical set of parameters for the mechanisms, an optimization model that will be utilized in thesis work, several new configurations, and several excellent concepts for CFECs. The ORCA experience has been valuable and has helped me make the transition into graduate research.