James D. Baker and Dr. Larry L. Howell, Mechanical Engineering
Contemporary engineering has received the benefits of computer-aided engineering (CAE) tools that automate and simplify the design of mechanical systems. However, such tools do not provide direct support for the specific field of compliant mechanisms, whose behavior can require difficult techniques for design and synthesis. Compliant mechanisms utilize flexible segments instead of joints, to achieve their motion. It was proposed that two CAE tools, namely Pro/ENGINEER and ADAMS/View, along with a method for analyzing compliant mechanisms known as the pseudo-rigid-body model, could greatly reduce the time and effort required to generate accurate results in the analysis of a compliant centrifugal clutch. This type of clutch holds significant advantages over conventional clutches due to the reduction in costs of assembly and tolerance allocation, so any tool to simplify its design and analysis is very desirable.
First, a solid model of the clutch mechanism was created using the Pro/ENGINEER solid modeling software package. Since this clutch consists of only one part, it is interpreted by the solid modeler program to be fully rigid, which precludes defining it as a mechanism within the modeler. However, it was possible to define the model such that the modeler could interpret the mechanical characteristics of the clutch correctly, using the techniques of the pseudo-rigid body model method of analysis. This method of analysis considers the behavior of compliant mechanisms as if they were conventional rigidbody mechanisms, thus allowing the designer to use classical kinematic analysis methods, as well as computer-based kinematics tools like ADAMS/View.
In defining a pseudo-rigid-body model of the mechanism, two copies of the clutch model were made, then some features of each copy were deleted, making one copy the main body of the clutch; the other one became one of the clutch’s arms. These parts were then assembled so that the resulting model comprised the clutch body and its two arms. The assembly model was then given constraints that defined its characteristics as a mechanism, and its geometry and constraints were transferred to the ADAMS/View environment, where the kinematic behavior of the mechanism could be analyzed.
Using computer-driven simulations of the mechanism offered the advantages of changing the key parameters of the clutch model, like the torsional stiffness of the flexible segments of the arms, or the speed of the clutch’s rotation. However, any significant changes to the model’s geometry would have to be executed in Pro/ENGINEER, and then the geometry would have to be exported to a format compatible with ADAMS/View.
The above procedure for analysis resulted in useful information about the kinematic and dynamic behavior of the clutch. The results included graphical representations of both angular and linear displacements of the arms, as well as the dynamic forces. Graphical animations were also simple to generate. However, generating purely numerical results for the same phenomena mentioned above is not supported by the software.
The use of the pseudo-rigid-body model to define the physical characteristics of this clutch has provided a simple way to construct the model and perform analyses on it. The user interfaces for both Pro/ENGINEER and ADAMS/View provide a fast and easy means for producing kinematic models that give accurate visually-oriented results. While this method has been productive in this case, the CAE tools can still benefit from tighter integration with each other, and more intuitive user interfaces.