Design and analysis of compliant mechanism for EMFC weighing cell with axis-symmetric structure

Abstract

In high-precision mass or force measurement, the electromagnetic force compensation (EMFC) weighing cell is utilized to achieve accuracy of sub-mg level. Conventional EMFC weighing cell consists of compliant flexure-based Roberval mechanism and lever amplification mechanism. In our previous work, we proposed a new type of EMFC weighing cell with an axis symmetric structure that three double parallelograms and lever mechanisms are arranged radially around the center of gravity axis. To investigate structural characteristics and design a proposed weighing cell, modelling and analysis of compliant mechanism was performed in this paper. The multi-body matrix method, which sets a mechanism as a multi-body mass-spring system and predicts static or dynamic characteristics through Lagrange equation, is adopted to model the proposed mechanism. We focused on the following three characteristics. First, we evaluated the stiffness in the weighing direction according to the dimensions of compliant mechanism, which should be minimized for high weighing sensitivity. Next, mode shapes and frequencies are evaluated depending on flexure dimensions to achieve control stability. Lastly, compensation force change from tilting of ground was observed to confirm the tilt sensitivity of the weighing cell.