An Integrated Compact Unit for Wide Range Micro-Newton Force Measurement

Abstract

Wide range compact sensor is preferably sought for force sensing in testing of micro objects or local area of macro objects with the observation of high resolution microscope. This paper presents the design and development of an integrated passive cantilever type force sensing unit with the specificities of range variation, interchangeability of components and compact size by incorporating with cantilever, probe and a capacitive sensor for measurement of large range micro-newton forces in wide scope of application. In the design, the tactile force at the probe perpendicularly attached to the cantilever is converted as cantilever deflection, which is measured by the capacitive sensor. In connection to a tiny capacitive sensor a compatible cantilever with double-beam structure is considered. Cantilever length variation facility is incorporated in the unit for obtaining different force measurement ranges by using the same cantilever. Characterization of the cantilever is performed against a standard load cell. The force resolution with a typical cantilever is estimated as 10 nN. The elastic property of human hair is efficiently determined by testing with the combination of a digital microscope and the developed sensor system. The utility of the unit for different resolution/range by the interchangeability of cantilevers is also demonstrated. Experimental results show that this integrated force sensing unit achieves good sensitivity and linearity, and wide measurement range.