Passively self-aligned assembly of compact barrel hinges for high-performance, out-of-plane mems actuators

A passively self-aligned, assembly-based process for rapidly creating compact, micro-barrel hinges with unconstrained rotation from SU-8 epoxy is presented. The alignment process takes places in two stages: a coarse alignment stage guided by external dowel pins followed by a fine alignment stage driven by the hinges' features themselves. The assembly of pins into housings circumvents the design rules for minimum gap between features of given thickness in SU-8 processing, enabling reduced hinge clearance for minimization of “side play”. The present hinges' fabrication and function are demonstrated through the design, implementation, and characterization of a displacement-amplifying, out-of-plane, scissor-based actuator that is driven by an in-plane, piezoelectric extensional actuator. The micro-barrel hinge enabled motion amplifier comprises six functional SU-8 multilayer plates joined by three layers of adhesives. Each functional plate comprises two or three layers of SU-8 fabricated by multiple exposures and a single development step. Displacements of up to 11.5 μm and forces of up to 10.5 mN are measured for the 10 mm
²
actuator, corresponding to a displacement and force per unit area of up to 1.15 μm/mm
²
and 1.05 mN/mm
²
respectively and offering potential solutions for applications like haptic interfaces and micropumps.