Design and modeling of a six DOF's MEMS-based precision manipulators

In this paper a design is presented for a precision MEMS-based six degrees-of-freedom (DOFs) manipulator. The purpose of the manipulator is to position a small sample (10 μm × 20 μm × 0.2 μm) in a transmission electron microscope. A parallel kinematic mechanism with slanted leaf-springs is used to convert the motion of six in-plane electrostatic comb-drives into six DOFs at the end-effector. The manipulator design is based on the principles of exact constraint design, resulting in a high actuation compliance (flexibility) combined with a relatively high suspension stiffness. However, due to fabrication limitations overconstrained design has been applied to increase the stiffness in the out-of-plane direction. The result is a relatively large manipulator stroke of 20 μm in all directions combined with a high first vibration mode frequency of 3.8 kHz in relation to the used area of 4.9 mm × 5.2 mm. The motion of the manipulator is guided by elastic elements to avoid backlash, friction, hysteresis and wear, resulting in nanometer resolution position control. The fabrication of the slanted leaf-springs is based on the deposition of silicon nitride (SixNy) on a silicon pyramid, which in turn is obtained by selective crystal plane etching by potassium hydroxide (KOH). The design has been analyzed and optimized with a multibody program using flexible beam theory. A previously developed flexible beam element has been used for modeling the typical relatively large deflections and the resulting position-dependent behavior of compliant mechanisms in MEMS. The multibody modeling has been verified by FEM modeling. Presently only parts of the manipulator have been fabricated. Therefore, a scaled-up version of the manipulator has been fabricated to obtain experimental data and to verify the design and modeling.