A constant torque compliant mechanism has its output torque invariant in a large scope of input rotation. Different from conventional constant torque compliant mechanisms in which the input shaft can only rotate in one direction, the input shaft of a bidirectional constant torque compliant mechanism can rotate either clockwise or counter-clockwise. The direction of the output or resisting torque changes with the input rotation direction. A common problem in the current bidirectional constant torque compliant mechanisms is that they require a preloading range that is a certain starting range of the input rotation. Within the preloading range, the output torque does not have the desired torque, and it increases from zero to a value. The preloading range weakens the performance of bidirectional constant torque compliant mechanisms. In this paper, precompressed beams are used as building blocks for bidirectional constant torque compliant mechanisms to surmount the preloading problem. Bidirectional constant torque compliant mechanisms are synthesized through optimizing the design parameters of the composed precompressed beams. The introduced synthesis approach is demonstrated by synthesizing bidirectional constant torque compliant mechanisms that have different numbers of precompressed beams.

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