This paper examines the use of a trispiral hinge in compliant mechanisms generated by low cost, ABS-based, rapid prototyping machines. Hinges are examined to establish relationships between hinge geometry parameters (core radius, spiral angle, spiral pitch, and spiral thickness) and hinge performance (in-plane rotation, off-axis stability). A number of joint parameter combinations are found that provide good joint rotation characteristics with minimal off-axis instability. These joints allow for joint rotations up to ±90 degrees from a neutral position with little parasitic motion during the rotation. The implementation of these joints is further examined through the building and testing of fully compliant mechanisms based on the Roberts and Hoeken approximate straight-line mechanism geometries. The fully compliant mechanisms are shown to have the ability to closely recreate the approximate straight-line motion of the equivalent 4-bar chains. As such, the trispiral joint provides promise as a joint type that can be used effectively in conjunction with fused deposition modeling (FDM) machines that use ABS as the build material.

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