A statically balanced fully compliant power transmission mechanism between parallel rotational axes

This paper presents a fully compliant, potentially monolithic, power transmission mechanism which can rectify a large lateral offset between two parallel rotational axes. The planar nature of the design makes it ideal for manufacturing-limited applications such as micro/meso-scale power transmissions. The proposed compliant transmission is generated based on the Oldham Coupling and its equivalent Pseudo-Rigid-Body Model (PRBM). Normally, a compliant transmission mechanism cannot achieve a high efficiency due to the internal stiffness, i.e. actuation stiffness is not zero. However, in the proposed design, the internal stiffness is removed by static balancing and results in a statically balanced compliant transmission mechanism, i.e. with zero actuation stiffness. Therefore, the monolithic embodiment and static balancing features compensate for backlash, friction, assembly errors and poor mechanical efficiency inherent in conventional Oldham coupling, resulting in a transmission mechanism with high mechanical efficiency. Possible compliant design configurations based on the importance of different design criteria are discussed. Further, a compliant device based on the Paired Double Parallelogram (DP-DP) linear flexure bearing is designed and dimensioned. Moreover, the transmission stiffness, i.e. input-output rotational stiffness within the maximum allowable stress, and the actuation stiffness, i.e. minimum required actuation torque for certain angular displacement, of the designed device are predicted by the theoretical model and finite element modeling. Besides, the result shows the device is providing a constant transmission stiffness through a full cycle rotation. To prove the concept, a macro scale prototype is constructed and evaluated experimentally. It is shown that the results from the experiment are in agreement with the theoretical and finite element models.