A Design Of A Compliant Constant-force Mechanism Based On Sarrus Considering The Hinge’s Nonlinearity

Compliant mechanism is a kind of mechanism that utilizes its partial or all of its parts to obtain the mechanical motion. Thanks to its unique construction, It has much more advantages than the traditional rigid mechanisms. Such as it needs no rigid links. That means when we want to complete some special motion, we just need a little parts and because the rigid parts’ connection has no gap, we don’t need the lubricating oil any more. All the characters make the compliant mechanism has no friction, no wear, no backlash and simply assembling, conveniently maintenance, reliably and cleanly using. Therefore, it attracts wide attention from both academia and industry fields. Now compliant mechanisms have been widely used to implement specific movement in some places such as in MEMS. While the energy stemmed from its deformation make it difficult to ensure the movement’s precision. But that problem can’t hinder its development. People has designed like bistable and other multistable compliant mechanisms when they make full use of the energy resulted from their deformation. So we should not divide the kinematics and the potential energy from each other. But take them together to consider may be a wonderful researching direction. This paper tries to connect them together to design a compliant constant-force mechanism.As an important part of compliant mechanism, the flexible hinge, naturally becomes the object of study. Now kinds of hinges have been designed such as vertical, parabolic, elliptic and many other forms. Because of their own matters, they can’t be used in larger deformation mechanisms. This paper choose a special kind pivot, cross-axis flexural pivots as the study objective, because it can used in large deformation, what is more,it can stand larger load. While it also has its disadvantage, its stiffness would appear nonlinear phenomenon. In order to find its internal change law this paper chose one of its important structural parameters and a shape parameter as the key research objects, and then find an empirical formula that can describe its stiffness in large deformation by a lot of experiments.This paper also describes a spatial 6R mechanism-Sarrus mechanism which can realize the transformation between the rotary motion and straight-line motion without reference guide rail, and spends a lot of time to analyze its statics and kinematics’ characters.Then the paper focused on the compliant style of Sarrus mechanism and get the expression of the force on the straight-line linkage with the pseudo-rigid-body-model method and virtual work principle. At last the paper uses the particle swarm optimization to optimize the structure and then obtain a special compliant Sarrus mechanism which has a constant-force character in a large movement scope.