Parallelism error analysis and compensation for micro-force measurement

Abstract

The null balance method for micro- and nano-force measurement is widely used in various precision industries. A parallel spring and a lever mechanism are designed and analysed for an electrostatic force balance by the null balance method. Various design parameters are required to obtain high resolution, a large measurement range, and fast response. The corner loading error is one of the most dominant error sources that should be removed. A parallel spring known as the Roberval mechanism, used in the micro-weighing device, can be used for one-axis force measurement since it is very sensitive to the vertical direction force, but insensitive to other force components. However, precise control of parallelism to below a micrometre is required not only to compensate for but also to remove the corner loading error. In this paper, the effects of the parallelism error have been analysed using the Lagrange method and verified by the FEA method. It was found that parallelism control by the proposed precise compensation mechanism enables the simultaneous elimination of and compensation for the corner loading error.