Design and Analysis of Novel Millimetre-level Compliant Constant-force Mechanism

Abstract

This paper introduces the design method of a novel constant force mechanism (CFM), which can provide specific constant force for large-stroke. The oblique trapezoidal mechanism with straight beam provides negative stiffness, and the oblique trapezoidal mechanism provides positive stiffness. The negative and positive stiffness mechanisms are paralleled to obtain the constant force mechanism. One uniqueness of the CFM lies in that it can produce a large-stroke stable constant output force through input displacement. The CFM has a simple structure and occupies little space. The mathematical model is established by using pseudo-rigid body model (PRB) for positive stiffness mechanism and chain beam constraint model (CBCM) for negative stiffness mechanism, and it is verified by conducting simulation study with finite-element analysis (FEA). The results show that the mechanism can provide a constant output force of about 15N in a motion range of 5 mm. The constant force mechanism can be used in micro-operation tasks requiring constant force to effectively avoid damage to objects caused by excessive output force.