Constant Velocity High Force Microactuator for Stick-Slip Testing of Micromachined Interfaces

A chevron thermal actuator has been implemented as a constant velocity puller in a multiasperity frictional test platform. This platform enables a wide variation of puller velocity (1-3100 μm/s, 3.5 decades), normal load (2-4500 μN, 3.4 decades), and spring constant (0.06-100 μN/μm, 3.2 decades). These characteristics are achieved by leveraging the actuator thermal time constant, which is long compared with the mechanical time constant, in combination with iterative learning control. Good thermal isolation between the actuator and the friction block is achieved by shunting heat to the substrate. Uncoated and FOTAS [tridecafluorotris(dimethylamino)silane, CF₃(CF₂)₅(CH₂)₂Si(N(CH₃)₂)₃]-coated devices were tested, and normal load induced a transition from steady sliding to stick-slip. This platform could have several important uses for mapping microscale kinetic friction phase diagrams, including determining the stick-slip to steady sliding bifurcation line, performing startstop tests and instantaneous velocity change tests, and inferring information on wear performance of coatings as a function of load and velocity.