MEMS-based clamp with a passive hold function for precision position retaining of micro manipulators
The goal was to design, model and fabricate a precision MEMS-based clamp with a relatively large clamping force. The purpose of the clamp is to mechanically fix a six degrees of freedom (DOFs) MEMS-based sample manipulator once the sample has been positioned in all DOFs. The clamping force is generated by a rotational electrostatic comb-drive actuator and can be latched passively by a parallel plate type electrostatically driven locking device. The clamp design is based on the principles of exact constraint design, resulting in a high actuation compliance (flexibility) combined with a high suspension stiffness. Therefore, a relatively large blocking force of 1.4 mN in relation to the used area of 1.8 mm2, is obtained. The fabrication is based on silicon bulk micromachining technology and combines a high aspect ratio deep reactive ion etching (DRIE), conformal deposition of low pressure chemical vapor deposition (LPCVD) silicon nitride and an anisotropic potassium hydroxide (KOH) backside etching technology. Special attention is given to void-reduction in SixNy trench isolation and reduction of heating phenomena during front side release etching. Guidelines are given for the applied process. Measurements showed that the clamp was able to fix, hold and release a test actuator. The dynamic behavior was in good agreement with the modal analysis.
3 DOFs motion recorded using a microscope: http://www.youtube.com/watch?v=mh-3E5xURSQ
Figure 1. The six DOFs MEMS-based precision manipulator design including the clamps. The overall dimensions are ca. 6 x 6 x 0.5 mm3.
Figure 2. Half the clamp. The two rigid bodies, ‘Jaw’ and ‘Comb-shuttle 1’ rotate around a common pivot point when actuated.
Figure 3. Top view of the total clamp with part of the manipulator comb-drive actuator. The Rack and Pin locking mechanism is shown in more detail in figures 8 and 9.
(a) (b)
(c) (d)
Figure 4. Top view microscope photographs of the rack and pin locking mechanism (material shown in white). Close-ups are presented at the lower right corner. a) The initial fabricated situation of the clamp. b) The parallel plate actuator is activated. Electrostatic actuator forces are shown by arrows. c) The rotational comb-drive is activated. d) The parallel plate actuator is switched off, locking the pin in the rack. The comb-drive is switched off subsequently.
Figure 5. SEM photo showing an overview of the clamp and test actuator.
For more information:
D.M. Brouwer, B.R. de Jong, M.J. de Boer, H.V. Jansen, J. van Dijk, G.J.M. Krijnen and H.M.J.R. Soemers, Design, modeling and fabrication of a MEMS-based clamp with a passive hold function for precision position retaining of micro manipulators, Journal of Micromechanics and Microengineering, Vol.19 No.6, 2009, 065027, pp. 1-20. doi: 10.1088/0960-1317/19/6/065027