The Mems Hammer, a Tool to Study Microfracture

Abstract

A MEMS actuator, dubbed the MEMS hammer, capable of storing and rapidly releasing mechanical energy has been designed, built and tested. The hammer is fabricated using a single mask silicon-on-insulator (SOI) process. These devices have been used to study fracture in both lateral and vertical regimes. The lateral tests have shown excellent agreement with shear fracture theory. Using either a mechanical or an electrostatic latching mechanism, the hammers are capable of storing energies up to 3.3µJ. The hammers have been shown to displace up to 36µm, exert a maximum force of 240 mN, move at speeds exceeding 50m/s, and deliver at least 330 mW of mechanical power.

Robots as Energy Systems: Advances in Robotics across Scales and Technologies

“…While millirobots can typically be assembled via laminate fabrication methods, [ 15 ] further reduction in scale requires either microfabrication with microelectromechanical system (MEMS) approaches [ 16 ] or wet chemistry techniques. [ 17 ] Recent work by Greenspun [ 18 ] shows robot made completely via MEMS techniques capable of leaping, as a mode of locomotion. The article carefully documents how electrostatic actuators convert an electrical input into mechanical work, which can be stored in submillimeter serpentine springs.…”

First Leaps of an Electrostatic Inchworm Motor-Driven Jumping Microrobot

“…A previously developed energy storage device, the MEMS Hammer, used beams in axial tension. This maximizes the stored energy in a given area by operating the beams in the cubic region of their force deflection curves [11]. Although this is an attractive option from an energy storage standpoint, the nonlinear nature of these beams requires much larger forces than those required for a linear serpentine spring to store the same amount of energy.…”

“…R3 is bounded by the shear limit of the buried oxide that anchors the central pin to the substrate. Previous work has shown the fracture stress of this oxide is 54 MPa [11], so R3 was chosen to be 47 μm to ensure this anchor remains fixed to the substrate.…”