The design and the fabrication of a magnetically actuated microgripper are described. The device is designed to have an out-of-plane motion; a novel concept among the microfabricated grippers. The gripper consists of three metallic fingers, radially directed and equally spaced on a circle; each finger composed by two beams, whose motion is driven by a magnetic field. The microgripper is modeled as an elastic system of two rectilinear beams, using Euler- Bernoulli theory for small deflections. The boundary value problem is solved and the deflection of the structure is calculated as a function of the magnetic force. The microgripper is fabricated using a UV-lithography based 3D electroforming technique. Each layer of the structure is made by metal electrodeposition into a polyimide mold. Several layers are stacked by repeated deposition and the final structure is obtained by dissolving the mold. Details about the fabrication techniques are presented and discussed. Properties and problems related to the photosensitive polyimide used (such as moisture absorption, loss of adhesion, etc.) are addressed. Electroforming of nickel, copper and permalloy are performed and optimized. In particular, a nickel activating solution is applied successfully for electroforming of microstructures. A shadow mask technique for seed-layer patterning is presented and discussed. A planar electromagnetic coil is fabricated by micromolding of thick photoresist and copper electroforming into the mold. The magnetic circuit is made by electrodeposition of permalloy.
James G. Boyd,
"Magnetically actuated metallic microgripper", Proc. SPIE 3519, Microrobotics and Micromanipulation, (5 October 1998); doi: 10.1117/12.325739; https://doi.org/10.1117/12.325739