An Inverted Differential Mechanism Capable of Achieving Very Large Amplification Ratio: Design and Control

Abstract

A multitude of flexure-based displacement amplifiers have been developed to amplify piezoelectric actuators for achieving both high-precision motion and large output stroke. Single-stage amplifiers are compact but provide only amplification of several times, while multi-stage amplifiers are able to achieve amplification of dozens of times but are generally bulky in structure. In this work, a displacement amplifier with only a single stage displacement amplifier, which shows the capability of obtaining a very large amplification ratio, is proposed. The displacement amplifier contains two semi-bridge mechanisms with a slight geometric difference between them. This slight difference makes the amplifier require a very small input while achieving a large displacement at the output, leading to a very large amplification ratio. A kinetostatic model considering the nonlinearities in the deflections of both the flexure hinges and the links for the amplifier is developed, based on which the parameters of the amplifier are optimized to maximize the amplification ratio, resulting in an amplifier exhibiting an amplification ratio of 107. The optimization results were validated by those of a finite element model, proving the effectiveness and correctness of the proposed amplifier and the kinetostatic model. The finalized design was prototyped and the measured amplification ratios in a bilateral output mode and a unilateral output mode are 98.10 and 88.42, respectively. A neural network PID controller was designed for the displacement amplifier, with a maximum trajectory tracking error less than 4.7% of the displacement amplifier was achieved. Note to Practitioners—This paper was motivated by the need to extend the actuation stroke of piezoelectric actuators, which are crucial in automation systems requiring high-precision displacement and large motion range. Traditional single-stage amplifiers are compact but provide limited extension. Multi-stage amplifiers offer greater extension, but their bulkiness limits the practical use. We have developed an innovative single-stage amplifier with very large amplification ratio that incorporates a unique arrangement of semi-bridge mechanisms. This design significantly extend the actuation stroke of piezoelectric actuators with a compact structure. The integration of a neural network-based PID controller improves the accuracy and efficiency of the positioning control of the amplifiers system. The principles and design approach we used could also be applied to fields where high precision and large displacement are needed, for example, micro/nano manufacturing and aerospace applications. This could open up new avenues for enhancing the efficiency and capability of devices in these sectors.