Design and modeling of a series–parallel compliant device for reliable assembly during a position or angle deviation

Abstract

Automatic assembly using manipulators has lately attracted increased attention due to its low cost and high quality. Since a manipulator is entirely rigid, position or angle deviations often cause assembly failure or even cause damage to the manipulator. A series–parallel compliant device that did not produce a significant contact force was developed during this study to achieve reliable assembly when position or angle deviations occurred. The primary objective for this device was for it to be compliant enough to effectively counteract contact forces and move in a specific direction. The device allowed for a relatively significant misalignment during assembly, and it produced a small force, which protected parts and manipulators. It had two compliant components that were connected using a rigid block. Each compliant component consisted of a rigid frame, four elastic limbs with similar “n” shapes, and a square block. Because an elastic material was used, each elastic limb was equivalent to a compliant hinge (or spring), essentially making the device a series–parallel compliant structure. In this way, the device became compliant and could move in a particular direction when the contact force exceeded a specific value. On this basis, the desired compliance of the device was obtained in all directions depending on the compliant deformation, and an optimization method was proposed to determine the parameters of this device based on the kinematic model and a stiffness analysis. Experiments were performed at different working conditions, and their results demonstrate that this device performed reliably during assembly even when a position deviation or an angle deviation occurred.