Page 523 - Cam Design Handbook

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CAMS IN MICROELECTROMECHANICAL SYSTEMS 511

need to move or deform elastically in very simple ways. Thus, controlled and coordinated
movement of mechanical elements is not usually required. Even when such movement is
required, it is quite simple, such as holding a clamped-clamped beam in different deformed
configurations. In microfluidics, fluid is moved in a controlled manner through microchan-
nels for which valves and pumps are necessary. The mechanical structures in these are
also not subject to sophisticated mechanical movement. Manipulating light beams is one
application in MEMS that requires mechanical transmissions to a limited extent. A com-
mercially available MEMS-based projection display system from Texas Instruments uses
an array of micromirrors, each of which can be individually tilted between two angles
about an axis. This is an example of microoptomechanical systems where mechanical
movement is quite simple. There are some others, optical workbenches for example, where
reasonably sophisticated mechanical movements are necessary.
Many types of actuators use mechanical movements but those are usually quite simple,
such as rotation about an axis or sliding along an axis. Compliant mechanisms (i.e., elas-
tically flexible structures) are used widely in MEMS for achieving mechanical movements.
These are referred over rigid-link jointed mechanisms because of the ease of fabrication
as a unitized structure without assembly. An example of a compliant mechanism is shown
in Fig. 15.3. Several microgrippers are also demonstrated but the extent of mechanical
movement in them is also quite limited. Micromechanical locks developed by Sandia
National Laboratories for weapons-safety systems is a MEMS device that has substantive
mechanical complexity. Some devices developed for microassembly and manipulation of
micron-sized objects also exist. In the remainder of this section, generic joints, gears, and
some mechanisms are described. These serve as ancillary parts to the MEMS devices built
using cams. Specific applications involving cams and gears are described in detail in
Sec. 15.6.

15.5.1 In-Plane Revolute Joints

A revolute joint whose axis is perpendicular to the wafer surface is necessary for fabri-
cating micromechanisms with in-plane motion. Microfabricating such a joint without

FIGURE 15.3. A laser-micromachined displacement amplifying compliant
micromechanism made using an index-card.