The Art and Signs of a Few Good Mechanical Designs in MEMS
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range of motion. This design is commonly found in micromachined accelerometers,
electrostatic comb drive actuators, and other MEMS devices.
3 Ease of Making of a Compliant Two-Axis Gimbal
When Micro-Opto-Electro-Mechanical Systems (MOEMS) started to emerge,
researchers needed an array of tiny mirrors to reflect and steer light beams. Texas
Instruments (TI) pioneered a tilting mirror, which could rotate about a single axis
parallel to the silicon wafer. It used a short beam segment that twists to provide
rotation. It was a simple design and served its purpose then. When it came to mirrors
that needed to rotate about two orthogonal axes, more ingenuity was required. Such
a need is depicted in Fig. 3. A light ray from any single input optical fiber in an input
bundle needs to the directed to any fiber in an output bundle. For this, two arrays of
mirrors were used by Agere Systems [4]. Each mirror was expected to tilt about two
in-plane orthogonal axes. And the mirrors should almost fill the space in a plane,
which means that the suspension of the mirror should be as compact as possible. The
design question was this: How do we obtain a two-axis gimbal design that has a large
range of rotation about both axes and one that can be compactly microfabricated in
a single releasable layer? The answer can be seen in Fig. 4a–c.
A short beam of the kind used in the TI mirror does not give much rotation; it
is severely limiting because the stress in a beam that twists a lot is very high. The
alternative is to use bending using slender beams, which embody the concept of
distributed compliance [18]. This concept is shown in Fig. 4d where a serpentine
beam that is anchored at both the ends can be seen. When one end is fixed to a frame
Fig. 3 The schematic of Optical Cross-Connect (OXC) developed at Agere Systems in early 2000s
[4]. Each mirror in the two planar arrays should be tiltable about two axes in order to steer light
from any fiber in the input bundle to any fiber in the output bundle
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range of motion. This design is commonly found in micromachined accelerometers,
electrostatic comb drive actuators, and other MEMS devices.
3 Ease of Making of a Compliant Two-Axis Gimbal
When Micro-Opto-Electro-Mechanical Systems (MOEMS) started to emerge,
researchers needed an array of tiny mirrors to reflect and steer light beams. Texas
Instruments (TI) pioneered a tilting mirror, which could rotate about a single axis
parallel to the silicon wafer. It used a short beam segment that twists to provide
rotation. It was a simple design and served its purpose then. When it came to mirrors
that needed to rotate about two orthogonal axes, more ingenuity was required. Such
a need is depicted in Fig. 3. A light ray from any single input optical fiber in an input
bundle needs to the directed to any fiber in an output bundle. For this, two arrays of
mirrors were used by Agere Systems [4]. Each mirror was expected to tilt about two
in-plane orthogonal axes. And the mirrors should almost fill the space in a plane,
which means that the suspension of the mirror should be as compact as possible. The
design question was this: How do we obtain a two-axis gimbal design that has a large
range of rotation about both axes and one that can be compactly microfabricated in
a single releasable layer? The answer can be seen in Fig. 4a–c.
A short beam of the kind used in the TI mirror does not give much rotation; it
is severely limiting because the stress in a beam that twists a lot is very high. The
alternative is to use bending using slender beams, which embody the concept of
distributed compliance [18]. This concept is shown in Fig. 4d where a serpentine
beam that is anchored at both the ends can be seen. When one end is fixed to a frame
Fig. 3 The schematic of Optical Cross-Connect (OXC) developed at Agere Systems in early 2000s
[4]. Each mirror in the two planar arrays should be tiltable about two axes in order to steer light
from any fiber in the input bundle to any fiber in the output bundle