Novel design for an ultra high precision 3D micro probe for CMM applications

Abstract

The paper reports on the design and testing of several new piezoresistive ultra high precision 3D microprobes for the use in coordinate measuring machines (CMM). The microprobes are all composed of three primary components a piezoresitive sensing element and stylus with probing sphere. The sensing element consists of a bossed KOH-etched silicon membrane with diffused piezoresistors. Several designs were investigated to increase sensor sensitivity while improving the anisotropy of stiffness. The initial design used a Wheatstone bridge piezoresistor configuration with a solid sensing membrane. Additionally, apertures where added to the solid silicon membrane to increase stress within the piezoresistors which untimely led to higher probe tip sensitivity. To improve the stiffness in the xy direction of the probe tip a double triangle design was tested that bonded two sensor chips back to back. This was found reduce the ratio between the stiffness in xy- and z-direction from 32 initially to 2.