Analysis of the joint clearance effects on a compliant spatial mechanism

• Articulated and compliant mechanisms with clearance joint are investigated.
• The PRBM is used to simplify the analysis of compliant mechanism.
• Different geometries and materials of pseudo joint are studied.
• Suspension effects of flexural pivot are analyzed upon the impact force in joints.
• Pseudo joint leads to a force-closed kinematic pair in compliant mechanism.

This study investigates the dynamics of a partly compliant mechanism with joint clearance. A spatial slider–crank mechanism is used as a numerical example. The kinematic and dynamic performances of articulated and compliant mechanisms are compared to each other. As a pseudo joint, a multi-axis small-length flexural pivot is used to ensure the necessary mobility between the connecting rod and piston links. In order to simplify the analysis, pseudo-rigid-body model is transferred to the analytic equations of compliant mechanism. The results show that clearance in joints leads to chaotic behaviour on the kinematic and dynamic outputs of the mechanisms. Due to the flexibility effect of small pivot and the relation of force-closed kinematic pair between the ball and socket in a clearance joint, compliant mechanism offers a good solution to decrease the chaotic phenomenon arising from clearance in mechanism's outputs. Also, for minimizing the partly resistive behaviour of pseudo joint relative to the mechanism motion, material and geometric features of small flexural pivot can be used as design variables.