Note: Descriptions are shown in the official language in which they were submitted.
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ROTARY ELECTROSTATIC MICROACTUATOR
The present invention relates generally to electrostatic actuators and more
particularly to rotary electrostatic
microactuators with comb drive assemblies.
Many early rotating electrostatic motors used a central bearing with various
arrangements of electrostatic
stators around the motors to effect rotation. Unfortunately, these motors
tended to have problems with friction at
the central bearing and have had lifetime issues related to wear of the
bearing. The motors typically acted as stepper
motors where the rotor rotates with an incremental motion as the stator
elements are attracted. Thus it was difficult
to precisely adjust a plate to a particular angle with such motors.
Other angular motors have been described which use flexural elements to
support a rotating element.
Comb drive forgers are arranged in concentric arcs around a central flexural
pivot, so that small angular motion is
provided around the pivot. See, for example, D.A. Horsley, et al., "Angular
Micropositioner for Disk Drives",
Proceedings of the Tenth International Workshop on Micro Electro Mechanical
Systems, 1997, pp 454-458; L.-S.
Fan, et al., "Batch-Fabricated Area-Efficient Milli-Actuators", Proceedings
1994 Solid State Sensor and Actuator
Workshop, Hilton Head, pp 38-42; T. Juneau, et al., "Dual Axis Operation of a
Micromachined Rate Gyroscope",
Proceedings 1997 International Conference on Solid State Sensors and
Actuators, V.2, pp 883-890; E.H. Klaassen,
et al., "Silicon Fusion Bonding and Deep Reactive Ion Etching; A New
Technology for Microstructures", The 8th
International Conference on Solid-State Sensors and Actuators, and Eurosensors
D~, Stockholm, Sweden, June 25-
29, 1995, pp 556-559; W.C. Tang, et al., "Laterally Driven Polysilicon
Resonant Microstructures", Sensors
Actuators 20, 1989, pp 25-31 (IEEE reprint pp. 53-59) and U.S. Patent No.
5,025,346 to Tang et al. Unfortunately,
all of these devices provide a limited angular range of motion.
In general, it is an object of the present invention to provide a rotary
electrostatic microactuator with an
improved range of angular motion.
Another object of the invention is to provide a rotary electrostatic
microactuator of the above character
in which side instability forces in the one or more comb drive assemblies of
the microactuator are minimized.
Another object of the invention is to provide a rotary electrostatic
microactuator of the above character
which permits rotation of a member extending out of the plane of the
microactuator.
Another object of the invention is to provide a rotary electrostatic
microactuator of the above character
which can be other than circular in shape.
Another object of the invention is to provide a rotary electrostatic
microactuator of the above character
in which the axis of rotation of the microactuator can be disposed adjacent a
side of the microactuator.
The accompanying drawings, which are somewhat schematic in many instances and
are incorporated in
and form a part of this specification, illustrate several embodiments of the
invention and, together with the
description, serve to explain the principles of the invention.
FIG. 1 is a plan view of a rotary electrostatic microactuator of the present
invention.
FIG. 2 is a cross-sectional view of the rotary electrostatic microactuator of
FIG. 1 taken along the line 2-2
of FIG. 1.
FIG. 3 is a plan view of another embodiment of the rotary electrostatic
microactuator of the present
invention.
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FIG. 4 is a plan view of a further embodiment of the rotary electrostatic
microactuator of the present
invention.
FIG. 5 is a plan view of yet another embodiment of the rotary electrostatic
microactuator of the present
invention.
Rotary electrostatic microactuator 101 of the present invention is formed on a
planar substrate 102 (see
FIGS. I and 2). A rotatable member or circular mirror holder 103 overlies the
substrate 102. A plurality of first
and second comb drive assemblies 106 and I07 are carried by substrate 102 for
rotating mirror holder 103 in first
and second opposite angular directions about an axis of rotation 108 extending
through the center of the circular
mirror holder 103 perpendicular to planar substrate 102 and thus FIG. 1. Each
of the first and second comb drive
assemblies 106 and 107 includes a first comb drive member or comb drive I 11
mounted on substrate 102 and a
second comb drive member or comb drive 112 overlying the substrate 102. First
and second spaced-apart springs
113 and 114 are included in microactuator 101 for supporting or suspending
second comb drives 112 and mirror
holder 103 above the substrate 102 and for providing radial stiffness to the
movable second comb drives 112 and
thus the mirror holder 103.
Substrate 102 is made from any suitable material such as silicon and is
preferably formed from a silicon
wafer. The substrate has a thickness ranging from 200 to 600 microns and
preferably approximately 400 microns.
Mirror holder 103, first and second comb drive assemblies 106 and 107 and
first and second springs 113 and 114
are formed atop the substrate 102 by a second or top layer 116 made from a
wafer of any suitable material such as
silicon. Top wafer 116 has a thickness ranging from 10 to 200 microns and
preferably approximately 85 microns
ZO and is secured to the substrate 102 by any suitable means. The top wafer I
16 is preferably fusion bonded to the
substrate 102 by means of a silicon dioxide. layer 117 having a thickness
ranging from 0.1 to two microns and
preferably approximately one micron. Top wafer 116 may be lapped and polished
to the desired thickness. The
mirror holder 103, the first and second comb drive assemblies 106 and 107 and
the first and second springs 113
and 114 are formed from the top wafer 116 by any suitable means. Preferably,
such structures are etched from
wafer 116 using deep reactive ion etching (DRIE) techniques. Mirror holder 103
is spaced above substrate 102 by
an air gap 118, that ranges from three to 30 microns and preferably
approximately 15 microns, so as to be
electrically isolated from the substrate.
At least one and preferably a plurality of first comb drive assemblies 106 are
included in rotary electrostatic
microactuator 101 and disposed about axis of rotation 108, shown as a point in
FIG. 1, for driving mirror holder
103 in a clockwise direction about axis 108. At least one second comb drive
assembly 107 and preferably a
plurality of second comb drive assemblies 107 can be included in microactuator
101 for driving the mirror holder
in a counterclockwise direction about the axis of rotation 108. Each of the
first and second comb drive assemblies
I06 and 107 extends substantially radially from axis of rotation 108 and, in
the aggregate, subtend an angle of
approximately 180° so as to provide rotary microactuator I01 with a
semicircular or fanlike shape when viewed
in plan (see FIG. 1 ). More specifically, microactuator 101 has three first
comb drive assemblies 106a, 106b and
106c and three second comb drive assemblies 107a, 107b and 107c. Rotary
microactuator 101 has a base 119
extending along a diameter of the semicircle formed by the microactuator 101
and has an outer radial extremity 121
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resembling the arc of a semicircle. Radial extremity 121 has first and second
ends which adjoin the first and second
opposite ends of base 119. The radial extremity 121 is defined by the outer
radial extremities of fast and second
comb drive assemblies 106 and 107. Mirror holder 103 and axis of rotation 108
are disposed at the center of the
semicircle adjacent base 119.
First and second comb drive assemblies 106 and 107 are interspersed between
each other, that is, a second
comb drive assembly 107 is disposed between each pair of adjacent first comb
drive assemblies 106. The first comb
drive assemblies 106 are symmetrically disposed relative to the second comb
drive assemblies I07 about the radial
centerline of rotary electrostatic microactuator 101, that is the imaginary
line extending in the plane of substrate
102 through axis of rotation 108 and perpendicular to base 119. Each of the
first and second comb drive assemblies
106 and 107 has a length ranging from 200 to 2,000 microns and more preferably
approximately 580 microns.
Rotary microactuator 101 has a length measured along base 119 ranging from 500
to 5,000 microns and more
preferably approximately 1,800 microns.
First comb drive I 1 I of each of first and second comb drive assemblies 106
and 107 is mounted to
substrate 102 by means of silicon dioxide layer 117. As such, the first comb
drives 111 are immovably secured to
substrate 102. Each of the first comb drives 111 has a radially-extending bar
122 provided with a first or inner
radial portion 122a and a second or outer radial portion 122b. Outer portion
122b extends to outer radial extremity
121 of microactuator 101. A plurality of comb drive fingers 123 are
longitudinally spaced apart along the length
of bar I 22 at a separation distance ranging from eight to 50 microns and
preferably approximately 24 microns. The
comb drive fingers 123 extend substantially perpendicularly from bar 122 and
are each arcuate in shape. More
specifically, each comb finger 123 has a substantially constant radial
dimension relative to axis of rotation 108 as
it extends outwardly from the bar 122. Fingers 123 have a length ranging from
approximately 22 to 102 microns
and increase substantially linearly in length from bar inner portion 122a to
bar outer portion 122b. Although the
comb fingers 123 can vary in width along their length, the comb fingers 123
are shown as having a constant width
ranging from two to 12 microns and preferably approximately six microns. Bar
inner portions 122a for first comb
drive assemblies 106a and 106b and second comb drive assemblies 107b and 107c
are joined to a base member 124
which serves to anchor such bars 122 to substrate 102 and permit such bar
inner portions 122a to have a smaller
width and the related comb drives 123 to thus have a corresponding longer
length.
Second comb drives 112 are spaced above substrate 102 by air gap 118 so as to
be movable relative to
substrate 102 and relative to first comb drives 11 I. The second comb drives
112 have a construction similar to the
first comb drives 111 discussed above and, more specifically, are formed with
a bar 126 that extends radially
outwardly from axis of rotation 108. The bar 126 has a first or inner radial
portion 126a in close proximity to axis
108 and a second or outer radial portion 126b that extends to radial extremity
121. A plurality of comb drive fingers
127 are longitudinally spaced apart along the length of bar 126 and are
substantially similar to comb forgers 123.
Arcuate comb fingers 127 are offset relative to comb fingers 123 so that the
comb fingers I27 on second comb drive
112 can interdigitate with comb fingers 123 on first comb drive 111 when the
second comb drives 112 are rotated
about axis 108 towards the stationary first comb drives 1 I 1. Each of first
and second comb drive assemblies 106
and 107 resembles a sector of the semicircular microactuator 101.
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Means including first and second spaced-apart springs 113 and 114 are included
within rotary electrostatic
microactuator 101 for movably supporting second comb drives 112 over substrate
102. First and second suspension
elements or springs 113 and 114 each have a length which preferably
approximates the length of first and second
comb drive assemblies 106 and 107, however springs having lengths less than
the length of the comb drive
assemblies can be provided. Although first and second springs 1 I3 and 114 can
each be formed from a single
spring member, the springs 113 and 114 are each preferably U-shaped or V-
shaped in conformation so as to be a
folded spring. As shown, springs 113 and 114 are substantially U-shaped. Each
of springs 113 and 114 is made
from first and second elongate spring members 131 and 132. First or linear
spring member 131 has first and second
end portions l3ia and 131b and second or linear spring member 132 has first
and second end portions 132a and
132b.
The first end portion 131 a of each folded spring 113 and 114 is secured at
its end to substrate 102 adjacent
axis of rotation 108 by means of silicon dioxide layer 117 (see FIG. 2). The
balance of the spring is spaced above
the substrate by air gap 118. Second end portion 131b of each spring 113 and
114 is secured to first end portion
132a of the second spring member 132. First and second beam-like spring
members 131 and 132 each extend
radially outwardly from axis of rotation 108 and preferably have a length
approximating the length of first and
second comb drive assemblies 106 and 107. The spring members 131 and 132 are
preferably approximately equal
in length and each have a length of approximately 500 microns. As such, spring
first end portions 131 a are secured
to substrate 102 adjacent spring second end portions 132b. Although first end
portion 131 a of each spring 113 and
114 can be secured to substrate 102 adjacent mirror holder 103 or adjacent
outer radial extremity 121, the first end
portion 131a is preferably secured to substrate 102 adjacent outer radial
extremity 12I. First and second spring
members 131 and 132 each have a width ranging from one to 10 microns and
preferably approximately four
microns. First and second thin, elongate sacrificial bars 133 and 134, of a
type described in U.S. Patent No.
5,998,906 and in copending U.S. patent application Serial No. 09/135,236 filed
August 17,1998, the entire contents
of each of which are incorporated herein by this reference, extend along each
side of each spring member 131 and
132 for ensuring even etching and thus the desired rectangular cross section
of the spring members. Sacrificial bars
133 and 134 are disposed along opposite sides of the spring members and extend
parallel to the respective spring
member.
Second end portion 132b of each spring I 13 and 114 is secured to at least one
of second comb drives 112.
In this regard, first and second movable frame members or frames 141 and 142,
spaced above substrate 102 by air
gap 118, are provided in rotary electrostatic microactuator 101. Each of the
frames 141 an 142 is substantially U-
shaped in conformation and includes as side members bars 126 of the adjoining
second comb drives 112. More
specifically, first movable frame 141 includes bar i 26 of second comb drive
assembly 107a, bar 126 of first comb
drive assembly 106a and an arcuate member 143 which interconnects such bar
outer portions 126b. Second
movable frame 142 is similar in construction and includes as side members bar
126 of second comb drive assembly
107c, bar 126 of first comb drive assembly 106c and an arcuate member 144
which interconnects such bar outer
portions 126b. Second end portion I32b of first spring 113 is secured to
arcuate member 143 adjacent to bar outer
portion 126b of second comb drive assembly 107a, while the second end portion
132b of second spring 114 is
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secured to arcuate member 144 adjacent bar outer portion 126b of first comb
drive assembly 106c. In this manner,
first folded spring 113 is disposed inside first movable frame 142 and second
folded spring 114 is disposed inside
second movable frame 142. Bar inner portion 126a of second comb drive assembly
107a is joined to mirror holder
103 and serves to secure first spring 113 to the mirror holder. Similarly, bar
inner portion 126a of first comb drive
assembly 106c is joined to mirror holder 103 for interconnecting second spring
114 to the mirror holder.
First and second movable frames 141 and 142 are symmetrically disposed about
the radial centerline of
rotary electrostatic microactuator 101. At least one comb drive assembly and
preferably at least one first comb drive
assembly 106 and at least one second comb drive assembly 107 are disposed
between first and second movable
frames 141 and 142 and thus first and second springs .113 and 114. More
specifically, first comb drive assemblies
106a and 106b and second comb drive assemblies 107b and 107c are disposed
between frames 141 and 142. Bar
126 of second comb drive assembly 107b and bar 126 of first comb drive
assembly 106b are joined back to back
to form a third movable frame 147 preferably extending along the centerline of
microactuator 1 Ol between movable
frames 141 and 142. An inner arcuate member or shuttle 148 is joined at
opposite ends to first and second movable
frames 141 and 14Z. One end of rigid shuttle 148 is secured to bar inner
portion 126a of first comb drive assembly
106a while the second end of the shuttle 148 is secured to bar inner portion
126a of second comb drive assembly
107c. Third movable frame 147 is joined to the middle of the shuttle 148 so as
to rotate in unison with first and
second movable frames 141 and 142 about axis 108. An additional arcuate member
151 is provided in
microactuator 1 O 1 for rigidly securing together second end portions 13 I b
of first and second springs 1 I 3 and 114.
The arcuate member 1 S 1 overlies substrate 102 and extends at least partially
around the axis of rotation 108.
Member 151 is disposed between shuttle 148 and mirror holder 103 and rotates
about axis 108 free of mirror holder
103. The suspended structures of microactuator 101, that is mirror holder 103,
second comb drives 112, first and
second springs 131 and 132 and first and second movable frames 141 and 142,
each have a thickness ranging from
10 to 200 microns and preferably approximately 85 microns.
Second comb drives 112 of first and second comb drive assemblies 106 and 107
are movable in a direction
of travel about axis of rotation 108 by means of movable frames 141, 142 and
147 between respective first
positions, as shown in FIG. 1, in which comb drive forgers 123 and 127 of the
first and second comb drives are not
substantially fully interdigitated and respective second positions, not shown,
in which the comb drive forgers 123
and 127 are substantially fully interdigitated. Although comb drive forgers
123 and 127 can be partially
interdigitated when second comb drives 112 are in their first positions, the
comb fingers 123 and 127 are shown
as being fully disengaged and thus are not interdigitated when second comb
drives 112 are in their first positions.
When in their second positions, comb fingers 127 of second comb drives 112
extend between respective comb drive
fingers 123 of the first comb drives 111. Comb fingers 127 approach but
preferably do not engage bar 122 of the
respective first comb drives I I 1 and similarly comb drive forgers 123
approach but preferably do not engage bar
126 of the respective second comb drives 112. Rigid movable frames 141, I42
and 147 are constructed as light
weight members to decrease the mass and moment of inertia of the movable
portions of microactuator 1 O 1 and thus
facilitate rotation of second comb drives 1 I 2 and mirror holder 103 about
axis of rotation I 08. Each of the movable
frames 141, 142 and 147 is substantially hollow and formed with a plurality of
internal beams or trusses 152 for
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providing rigidity to the movable frame.
Electrical means is included within microactuator 101 for driving second comb
drives 112 between their
first and second positions. Such electrical means includes a controller and
voltage generator 161 that is electrically
connected to a plurality of electrodes provided on substrate 102 by means of a
plurality of electrical leads 162.
Controller 161 is shown schematically in FIG. 1. A first ground electrode 166
and a second ground electrode 167
are formed on substrate 102 and are respectively joined to the first end
portion 131a of first and second springs 113
and 114 for electrically grounding second comb drives 112 and mirror holder
103. Electrodes 166 and 167 serve
as the attachment points for spring first end portions 131 a to the substrate
102. First comb drives 111 of first comb
drive assemblies 106 can be supplied a voltage potential from controller 161
by means of an electrode 171
electrically coupled to bar outer portion 122b of first comb drive assembly
106a and an additional electrode 172
electrically coupled to the first comb drive 111 of first comb drive assembly
106b and to first comb drive 111 of
first comb drive assembly 106c by lead 173. An electrode 176 is secured to the
first comb drive 111 of second
comb drive assembly 107a by means of lead 177 and to second comb drive
assembly 107b and an electrode 179
is joined to bar outer portion 122b of second comb drive assembly 107c for
providing a voltage potential to the first
comb drives of second comb drive assemblies 107. A metal layer 181 made from
aluminum or any other suitable
material is created on the top surface of top wafer 116 for creating
electrodes 166, 167, 171, 172, 176 and 179 and
for creating leads 173, 174, 177 and 178 (see FIG. 2). First and second
pointers 186 extend radially outwardly from
the outer end of third movable frame 147 for indicating the angular position
of mirror holder 103 about axis 108
on a scale 187 provided on substrate 102.
Means in the form of a closed loop servo control can be included in
microactuator 101 for monitoring the
position of second comb drives 112 and thus mirror holder 103. For example,
controller 161 can determine the
position of the movable comb drives 112 by means of a conventional algorithm
included in the controller for
measuring the capacitance between comb drive forgers 127 of the movable comb
drives 112 and the comb drive
fingers 123 of the stationary comb drives 111. A signal separate from the
drive signal to the comb drive members
can be transmitted by controller 161 to the microactuator for measuring such
capacitance. Such a method does not
require physical contact between the comb drive forgers. Alternatively, where
microactuator 101 is used in an
optical system, a portion of the output optical energy coupled into the output
fiber can be diverted and measured
and the drive signal from the controller 161 to the microactuator 101 adjusted
until the measured optical energy is
maximizea.
In an exemplary operation of rotary electrostatic microactuator 101, a
micromirror (not shown) can be
mounted to mirror holder 103 out of the plane of the microactuator, for
example by means of insertion into slot 188
provided in the mirror holder 103, for rotation about axis of rotation 108.
The mirror has a reflective face (not
shown) which extends perpendicularly from plane of substrate 102 and can serve
as part of an optical switch for
deflecting a laser beam. An optical switch utilizing a microactuator 101
having such a mirror is particularly suited
for use in a fiber-optic network of a telecommunications system.
Mirror holder 103 can be rotated in opposite first and second directions of
travel about axis of rotation 108
by means of controller 161. Whea it is desired to rotate the mirror holder in
a clockwise direction about axis 108,
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a voltage potential is supplied by the controller to first comb drives 111 of
first comb drive assemblies 106 so as
to cause comb fingers 127 of the second comb drives I I2 of first comb drive
assemblies 106 to be electrostatically
attracted to comb forgers 123 of such first comb drives 111. Such attraction
force causes comb drive fingers 127
to move towards and interdigitate with comb drive fingers 123. The amount of
such interdigitation, and thus the
amount of rotation of mirror holder 103 about axis 108, can be controlled by
the amount of voltage supplied to first
comb drives 111 of first comb drive assemblies 106. When and if it is desired
to rotate mirror holder 103 in a
counterclockwise direction about axis 108, a suitable voltage potential can be
supplied to first comb drives 111 of
second comb drive assemblies 107 to cause comb drive fingers 127 of the
respective second comb drives 112 to
move towards and interdigitate with comb drive fingers 123 of the second comb
drive assemblies 107. As can be
seen, the second comb drive members 112 of one ~of first comb drive assemblies
106 or second comb drive
assemblies 107 are in their second positions when second comb drive members I
12 of the other of second comb
drive assemblies 107 or fn~st comb drive assemblies 106 are in their first
positions.
Suitable voltage potentials to drive comb drive assemblies 106 and 107 can
range from 20 to 200 volts and
preferably range from 60 to 150 volts. Microactuator 1 O 1 is capable of +/_
six degrees angular rotation, that is a
rotation of six degrees in both the clockwise and counterclockwise directions
for an aggregate rotation of twelve
degrees, when drive voltages of 120 volts are utilized. The amount of angular
deflection is dependent on the
number of comb forgers 123 and 127, the gap between the comb forgers and the
length and width of the fn~st and
second folded springs 113 and 114.
The use of radially-extending springs 113 and 114 within electrostatic
microactuator 101 enhances the
stability of the microactuator and thus facilitates relatively large angular
rotation of mirror holder 103. Springs 113
and 114 provide a radial stiffness to microactuator 101 which limits sidewise
movement of comb forgers 127 as they
interdigitate with comb fingers 123. Such radial stiffness thus inhibits any
sidewise snap over which may otherwise
occur between comb forgers 123 an 127.
The folded nature of springs 113 and 114 further enhances the radial stiffness
of microactuator 101. In
this regard, folded springs 113 and 114 are each able to contract radially in
response to rotation of second comb
drives 112 and thus inhibit the formation of axial tension in the springs.
More specifically, radial contraction due
to bending of one spring member 131 or 132 during rotation, which can alone
cause misalignment of the
interdigitating comb drive fingers 123 and 127, is compensated by the radial
contraction of the other spring member.
Such compensation is permitted by the symmetrical design of each of the
springs 113 and 114; spring members 131
and 132 are approximately equal in length and spring member 131 is attached to
substrate 102 at approximately the
same radial distance that spring member 132 is attached to the respective
movable frame 141 or 142.
The joinder of spring second end portions 131b by arcuate member 151, which by
symmetry rotates
angularly about axis 108 at half the angular rotation of mirror holder 103,
further enhances the radial stiffness of
microactuator 101 by constraining rotation of the folded inner radial portion
of springs 113 and 114 as comb drives
112 rotate about axis of rotation 108. As discussed above, first comb drive
assemblies 106a and 106b and second
comb drive assemblies 107b and 107c are disposed between first and second
movable frames 141 and 142. Arcuate
151 particularly contributes to the radial stiffness of the second comb drives
112 of these comb drive assemblies.
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First and second springs 113 and 114 are advantageously secured to substrate
102 at outer radial extremity
121 and thus away from axis of rotation 1 O8. The relatively large electrodes
166 and 167 which additionally serve
to connect the springs to the substrate are more easily accommodated at
extremity 121 than close to axis 108. In
additional, comb drive bars 126 can further serve to connect the ends of
springs 113 and 114 to mirror holder 103.
The symmetrical disposition of springs 113 and 114 relative to the centerline
ofmicroactuator 101 and the
angular separation of the springs a distance of ranging from 30° to 1
SO° and as shown approximately 90° serve to
constrain microactuator 101 so that externally imposed linear accelerations do
not substantially affect the angular
deflection of the optical components. More specifically, each spring 113 and I
I4 opposes linear accelerations along
its respective axis and provides the required radial stiffness to resist the
tendency of comb drive assemblies 106 and
107 to snap over in any radial direction.
The thickness of the movable structures of microactuator 101 affects the
stiffness to off axis modes. Thus,
a high aspect ratio device is preferred and the movable structures have a
thickness substantially greater than the
width of the smallest features of microactuator 101. In this manner, out-of
plane stiffness of the structures is
relatively great, substantially constraining motion to that in the plane of
the microactuator 101.
First and second folded springs 113 and 114 permit relatively large rotational
travel of mirror holder 103
about rotation axis 108. First and second spring members 131 and 132 bend
towards each other during clockwise
rotation of mirror holder 103 about axis 108 and bend away from each other
during counterclockwise rotation of
the mirror holder 103. First and second movable frames 141 and 142 are
sufficiently sized and provided with
sufficient internal space to accommodate the deflection of first and second
springs 113 and I 14 therein. The
utilization of two bendable spring members 131 and 132 joined together to
create a folded spring increases the
amount of permitted rotational travel relative to a microactuator having one
or more springs having a radial length
approximating the radial length of folded springs 113 and 114 but formed from
only a single such spring member,
that is one or more nonfolded springs.
The semi-circular or fanlike shape of rotary electrostatic microactuator 101
permits axis of rotation 108,
and for example the mirror carried thereby, to be placed close to a GRIN lens
or other component of the fiber-optic
system.
Although microactuator 101 has been disclosed for use in a fiber-optic network
of a telecommunications
system, it should be appreciated that the microactuator 1 O 1, for use with or
without a mirror, has other applications.
For example, microactuator 101 can be used in an optical switch or other
component of an optical data storage
system of the type described in copending U.S. patent application Serial No.
09/135,236 filed August I7, 1998, in
optical scanners, optical spectrometers, optical phase compensators or in
other structures for rotating components
such as optical waveplates, mirrors or diffraction gratings.
Other fan-shaped electrostatic microactuators having comb drive forgers which
interdigitate in an angular
direction of travel about an axis of rotation can be provided. Rotary
electrostatic microactuator 201, shown in FIG.
3, has similarities to microactuator 101 and like reference numerals have been
used to describe like components
of microactuators 1 O 1 and 201. A rotatable member or mirror holder 202
overlies substrate 102. A plurality of first
and second comb drive assemblies 203 and 204 are carried by the substrate 102
for rotating the mirror holder 202
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in fast and second opposite direction about an axis of rotation 206 extending
perpendicular to planar substrate 102.
The axis of rotation is shown as a point in FIG. 3 and labeled by reference
line 206. Each of the first and second
comb drive assemblies 203 and 204 includes a first drive member or comb drive
211 mounted on substrate 102
and a second comb drive member or com>z drive 212 overlying the substrate.
First and second spaced-apart springs
213 and 214 are included in microactuator 201 for supporting or suspending
second comb drives 212 and mirror
holder 202 above the substrate 102 and for providing radial stiffness to the
second comb drives 212 and the mirror
holder 202. The mirror holder 202, first and second comb drive assemblies 203
and 204 and first and second
springs 2I 3 and 214 are formed from top layer 116 by any suitable means such
as discussed above for microactuator
101. Mirror holder 202, second comb drives 212 and first and second springs
213 and 214 are spaced above
substrate 102 by air gap 188 and have thicknesses similar to those discussed
above for the like components of
microactuator 101.
At least one and preferably a plurality of first comb drive assemblies 203 are
included in rotary electrostatic
microactuator 201 and disposed about axis of rotation 206 for driving mirror
holder 202 in a clockwise direction
about axis of rotation 206. At least one and preferably a plurality of second
comb drive assemblies 204 can be
included in microactuator 201 for driving the mirror holder in a
counterclockwise direction about the axis of rotation
206. Each of the first and second comb drive assemblies 203 and 204 extends
substantially radially from axis of
rotation 108 and the assemblies 203 and 204, in the aggregate, subtend an
angle of approximately 180° to provide
the senucircular or fanlike shape to microactuator 201. More particularly,
microactuator 201 has four first comb
drive assemblies 203a, 203b, 203c and 203d and four second comb drive
assemblies 204a, 204b, 204c and 204d.
The first comb drive assemblies 203 are interspersed between the second comb
drive assemblies 204. The rotary
microactuator 201 has a base 219 substantially similar to base 119 and an
outer radial extremity 221 substantially
similar to outer radial extremity 121. First comb drive assemblies 203 are
symmetrically disposed relative to second
comb drive assemblies 204 about the radial centerline of rotary electrostatic
microactuator 201, that is the imaginary
line extending in the plane of substrate 102 through axis of rotation 206
perpendicular to base 219. Mirror holder
202 and axis of rotation 206 are disposed at the center of microactuator 201
adjacent base 219. The rotary
microactuator has a length measured along base 219 ranging from 500 to 5,000
microns and preferably
approximately 2,000 microns.
First comb drive 211 of each of first and second comb drive assemblies 203 and
204 is mounted to
substrate 101 in the manner discussed above with respect to first comb drives
111. Each of the first comb drives
211 has a radial-extending bar 226 provided with a first or inner radial
portion 226a and a second or outer radial
portion 226b. The outer portion 226b of each first comb drive 211 extends to
outer radial extremity 221. A
plurality of comb drive fingers 227 are longitudinally spaced apart along the
length of bar 226 at a separation
distance ranging from eight to 50 microns and preferably approximately 35
microns. The comb drive fingers 227
extend substantially perpendicularly from bar 226 and, like comb drive forgers
123, are each arcuate in shape.
Fingers 227 have a length ranging from ZS to 190 microns and increase
substantially linearly in length from bar
inner portion 226a to bar outer portion 226b. Each of the comb drive fingers
227a has a proximal portion 227a and
a distal portion 227b. The proximal portion 227 has a width ranging from four
to 20 microns and preferably
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approximately 10 microns, and the distal portion 227b has a width less than
the width of proximal portion 227a and,
more specifically, ranging from two to 12 microns and preferably approximately
six microns.
Second comb drives 212 and mirror holder 202 are part of a movable or
rotatable frame 231 spaced above
substrate 102 by air gap 118 so as to be electrically isolated from the
substrate and movable relative to the substrate
and first comb drives 211. Frame 231 includes a first arm 232, a second arm
233, a third arm 236 and a fourth arm
Z37, each of which extend in a substantial radial direction from axis of
rotation 206. First and fourth arms 232 and
237 are symmetrically disposed relative to the centerline of microactuator 101
and second and third arms 233 and
236 are also symmetrically disposed relative to such centerline. First and
fourth arms 232 and 237 are each U-
shaped in conformation and formed from first and second bars 241 and 242. The
first bar 241 has a first or inner
radial portion 241 a in close proximity to axis 206 and a second or outer
radial portion 241b that extends to outer
radial extremity 221. Similarly, second bar 242 has a first or inner radial
portion 242a and a second or outer radial
portion 242b. Outer radial portions 241b and 242b are joined by a base member
243 at outer radial extremity 221.
Inner radial portion 241a of the first bar 241 is joined to mirror holder 202,
while inner radial portion 242a of
second bar 242 extends freely adjacent the mirror holder 202. Second and third
arms 233 and 236 are joined at their
inner portions to mirror holder 202.
First bar 241 of first amz 232 forms part of second comb drive 212 of first
comb drive assembly 203a,
while second bar 242 of first arm 232 serves as part of the second comb drive
212 of second comb drive assembly
204a. A plurality of comb drive forgers 251 are longitudinally spaced apart
along the length of such first bar 241
for forming the comb drive fingers of first comb drive assembly 203a, while a
plurality of comb drive fingers 251
are longitudinally spaced apart along the length of second bar 242 of such
first arm 232 for forming the comb drive
fingers of first comb drive assembly 204a. Comb drive fingers 251 are
substantially similar to comb drive fingers
227 and have a first or proximal portion 251 a joined to the respective bar
241 or 242 and a second or distal portion
251 b extending from such proximal portion 251 a. Distal portions 251b have a
width less than the width of proximal
portions 251a. Arcuate comb drive fingers 251 are offset relative to comb
drive fingers 227 so that comb drive
fingers 251 can interdigitate with comb drive fingers 227. First bar 241 of
fourth arm 237 similarly serves as part
of second comb drive 212 of second comb drive assembly 204d, while second bar
242 of the fourth arm 237 serves
as part of the second comb drive 212 for first comb drive assembly 203d. Comb
drive fingers 251 extend from first
and second bars 241 and 242 of fourth arm 237.
Second and third arms 233 and 236 are included in second comb drives 212 of
first comb drive assemblies
203b and 203c and second comb drive assemblies 204b and 204c. The second arm
233 has a first or inner radial
portion 233a joined to mirror holder 202 and a second or outer radial portion
233b adjacent outer radial extremity
221. Third arm 236 is similar in construction to second arm 233 and has a
first or inner radial portion 236a and a
second or outer radial portion 236b. A first plurality of comb drive forgers
251 are longitudinally spaced apart
along the length of one side of second arm 233 for forming the second comb
drive of second comb drive assembly
204b and a second plurality of comb drive forgers 251 are longitudinally
spaced apart along the length of the other
side of second arm 233 for forming the second comb drive of first comb drive
assembly 203b. Similarly, a first
plurality of comb drive forgers 251 are longitudinally spaced apart along one
side of third arm 236 for forming
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second comb drive 212 of first comb drive assembly 203c and a second plurality
of comb drive forgers 251 are
longitudinally spaced apart along the opposite side of the third arm 236 for
forming second comb drive 212 of
second comb drive assembly 204c. The second and third arms 233 and 236 can
optionally be joined by a link 252
at the respective inner radial portions 233 and 236a for enhancing the
rigidity of the arms 233 and 236.
Means including first and second spaced-apart springs 213 and 214 are included
within rotary electrostatic
microactuator 201 for movably supporting mirror holder 202 and second comb
drives 212 over substrate 102.
Springs 213 and 214 are symmetrically disposed about the centerline of
microactuator 201 and preferably have a
length which approximates the length of at least some of fu~st and second comb
drive assemblies 203 and 204. Base
219 of microactuator 201 includes an attachment or bracket member 253 which
has a portion intersecting axis of
rotation 206 and serves to secure first and second springs 213 and 214 to
substrate 102. Each of the springs 213
and 214 is formed from a single beam-like spring member 256 having a first or
inner radial end portion 256a joined
at its end to bracket member 253 and a second or outer radial end portion 256b
joined to base member 243 of the
respective fast arm 232 or fourth arm 237. More specifically, first spring 213
extends from bracket member 253
up the center of first arm 232 for joinder to the center of base member 243.
Second spring 214 extends from bracket
member 253 radially outwardly through the center of fourth arm 237 for joinder
to the center of base member 243.
Inner end portions 256a of spring members 256 are joined to the bracket member
253 at axis of rotation 206. The
spring members 256 have a width ranging from one to 10 microns and preferably
approximately four microns.
Respective first and fourth amps 232 and 237 serve to secure outer end
portions 256b of the first and second springs
213 and 214 to mirror holder 202.
At least one comb drive assembly and preferably at least one first comb drive
assembly 203 and at least
one second comb drive assembly 204 is disposed between first and second
springs 213 and 214. More specifically,
first comb drive assemblies 203b and 203c and second comb drive assemblies
204b and 204c, each of which is
formed in part by second and third arms 233 and 236, are angularly disposed
between first and second springs 213
and 214. Additionally, first comb drive assembly 203a and second comb drive
assembly 204d, symmetrically
disposed relative to each other about the centerline of microactuator 201, are
angularly disposed between first and
second springs 213 and 214.
Comb drive fingers 227 and 251 of first and second comb drives 211 and 212 are
not substantially fully
interdigitated when in their first or rest positions shown in FIG. 3. Although
the term not substantially fully
interdigitated is broad enough to cover comb drive fingers which are not
interdigitated when in their rest positions,
such as comb drive forgers 123 and 127 of microactuator 101 shown in FIGS. 1
and 2, such term also includes
comb drive forgers which are partially interdigitated when in their rest
positions. In microactuator 201, distal
portions 227b and 251b of the comb drive fingers are substantially
interdigitated when the comb drives 211 and
212 are in their at rest positions.
At least one and as shown all of first and second comb drive assemblies 203
and 204 are not centered along
a radial extending outwardly from axis of rotation 206. In this regard, distal
ends 261 of comb drive fingers 227
for each comb drive assembly 203 or 204 are aligned along an imaginary line
that does not intersect axis of rotation
206 and, as such, is spaced-apart from the axis 206. Similarly, distal ends
262 of comb fingers 251 extend along
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an imaginary line which does not intersect axis of rotation 206. Each of first
and second comb drive assemblies
203 and 204 thus resembles a sector of a semicircle that is offset relative to
a radial of such semicircle.
Second comb drives 212 of first and second comb drive assemblies 203 and 204
are each movable in a
direction of travel about axis of rotation 206 between a first or rest
position, as shown in FIG. 3, in which comb
drive fingers 227 and 251 are not substantially fully interdigitated and a
second position (not shown} in which comb
drive forgers 227 and 251 are substantially fully interdigitated such as
discussed above with respect to comb forgers
123 and 127 of microactuator 101. Second comb drives 212 of first comb drive
assemblies 203 are in their second
positions when second comb drives 212 of second comb drive assemblies 204 are
in their first position and,
similarly, the second comb drives 212 of assemblies 204 are in their second
positions when the second comb drives
212 of assemblies 203 are in their first positions.
Electrical means is included within microactuator 201 for driving second comb
drives 212 between their
first and second positions. Such electrical means can include a controller and
voltage generator 161 electrically
connected to a plurality of electrodes provided on the substrate 102 by means
of a plurality of electrical leads 162.
For simplicity, controller 161 and leads 162 are not shown in FIG. 3. Such
electrodes, each of which is substantially
similar to the electrodes discussed above with respective to microactuator
101, include a ground or common
electrode 266 electrically coupled by lead 267 to bracket member 253, at least
one drive electrode 271 coupled
directly or by means of lead 272 to first comb drive 211 of first comb drive
assemblies 203 and one or more drive
electrodes 273 coupled directly or by means of lead 274 to first comb drives
211 of second comb drive assemblies
204. Several leads 274 extending out of the plane of microactuator 201 are
shown in phantom lines in FIG. 3. The
position of mirror holder 202 can optionally be monitored in the manner
discussed above with respect to
microactuator 101.
In operation, rotary electrostatic microactuator 201 is used in substantially
the same manner as discussed
above with respect to rotary electrostatic microactuator 101. When used as
part of a fiber-optic network of a
telecommunications system, a micromirror (not shown) can be mounted to mirror
holder 202, for example by means
of insertion into a recess or slot 276 provided in the mirror holder 202, for
rotation about axis of rotation 206. The
mirror extends out of the plane of microactuator 201 and has a reflective face
(not shown) which preferably
intersects axis of rotation 206. The recess 276 for receiving mirror need not
be centered on axis of rotation 206.
As discussed above, controller 161 provides voltage potentials to comb drives
212 of one of first and
second comb assemblies 203 or 204 to drive.mirror holder 202 in opposite first
and second angular directions about
axis 206. Suitable voltage potentials to electrodes 271 and 273 for so
rotating mirror holder 202 can range from
20 to 250 volts and preferably range from 60 to 180 volts. Microactuator 201
is capable of +/- six degrees angular
rotation, that is a rotation of six degrees in both the clockwise and
counterclockwise directions for an aggregate
rotation of twelve degrees, when such drive voltages are utilized.
In an alternative electrical drive configuration for electrostatic
microactuator 201, controller 161 applies
a ground potential to electrode 271 coupled to first comb drives 211 of first
comb drive assemblies 203 and a fixed
maximum potential to electrode 273 coupled to first comb drives 211 of second
comb drive assemblies 204. A
variable potential between the ground potential and the fixed maximum
potential is applied by the controller to
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common electrode 266 coupled to bracket member 253 and hence second comb
drives 212. When the potential
applied to common electrode 266 is equal to half of the maximum potential, an
equal potential differences exist
between electrodes 273 and 266 and between electrodes 271 and 266 resulting in
approximately equal forces
tending to rotate mirror holder 202 in counterclockwise and clockwise
directions and thus resulting in no net
rotation of the mirror holder 202. As the drive voltage applied to common
electrode 266 is varied from this half
value, an increasing net force is provided which results in net rotation of
mirror holder 202 from its rest position.
When the applied potential to common electrode 266 is at either ground or the
fixed maximum value, a maximum
force substantially equal to the drive force that occurs when a similar
maximum drive voltage is applied to either
electrode 273 or 271 and common electrode 266 is grounded is then applied so
as to cause rotation of mirror holder
202. Similar voltages to those discussed above can be applied and similar
rotations can be achieved. This
alternative drive configuration requires only a single variable potential
source and smoothly varies the position of
mirror holder 202 around its rest position by varying only a single source.
The number of electrical components
in controller 161 and thus the cost of the actuator system can be reduced with
this drive configuration.
Itadially-extending first and second springs 213 and 214 provide radial
stiffness to rotatable frame 231 and
thus second comb drives 212. Inner end portions 256a of spring members 256
advantageously join to substrate 102
at the point of intersection of axis of rotation 206 with the substrate. Outer
end portions 256b of the springs 213
and 214 are secured to second comb drives 2I2 either directly or by means of
rotatable frame 231 adjacent outer
radial extremity 221. Springs 213 and 214 are spaced apart at an angle ranging
from approximately 30° to 90° to
constrain microactuator 201 against linear accelerations in the manner
discussed above with respect to microactuator
101. The nonfolded springs 213 and 214 require less surface area for
deflection than the folded springs discussed
above and thus permit more surface area to be allocated to comb drive
assemblies 203 and 204.
First and second comb drive assemblies 203 and 204 are relatively densely
packed within rotary
electrostatic microactuator 20I. Such packing is permitted, in part, by the
of~'set nature of the comb drive
assemblies 203 and 204. As discussed above, distal ends 261 and 262 of comb
drive fingers 227 and 251 and the
radial centerline of each of first and second comb drive assemblies 203 and
204 does not intersect axis of rotation
206. This offsetting of comb drive assemblies 203 and 204 also permits inner
radial portions 226a of bars 226 to
have a greater width, and thus have increased stability, and comb drive
forgers 227 and ZS 1 at the inner proximal
end portions of each comb drive assembly 203 and 204 to be larger in length
than would be permitted for a
microactuator of comparable comb drive density but having comb drive
assemblies 203 and 204 that are radially
aligned with axis of rotation 206. As such, relatively greater rotational
forces and torque are permitted by
electrostatic microactuator 201.
The configuration of comb drive forgers 227 and 251 also permits relatively
greater rotational forces in
microactuator 201. In this regard, comb drive fingers 227 and 251 are
partially interdigitated when in their at rest
positions shown in FIG. 3. Since the spacing between adjacent comb drive
fingers 227 and 251 can be limited by
available etching techniques, distal portions 227b and 251b of the comb drive
forgers 227 and 251 have been
narrowed in width. Upon movement of second comb drives 212 to their second
positions, distal portions 251b
interdigitate with proximal portions 227a of the comb drive forgers of first
comb drive 211 and the spacing or gap
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between adjacent comb drive forgers 227 and 251 is decreased so as to enhance
the electrostatic attraction forces
between first and second comb drives 211 and 212.
It should be appreciated that the invention hereof is broad enough to cover
any rotary electrostatic actuator
that is approximately fanlike in shape or approximately semicircular or that
has comb drive assemblies which
subtend an angle of 180° or less, for example 90°, about an axis
of rotation. Such configurations permit the axis
of rotation to be placed adjacent a base or end of the microactuator. Such a
rotary electrostatic microactuator
preferably includes arcuate comb drive fingers which extend in an angular
direction about the axis of rotation. The
invention is also broad enough to cover any rotary electrostatic microactuator
having beam-like springs which
secure to the substrate at the point at which the axis of rotation intersects
the substrate. Each of such beam-like
springs can consist of a single beam member or be folded so as to be U-shaped
or V-shaped in conformation.
Rotary electrostatic microactuators can be provided which are other than fan-
shaped or semicircular in
plan and be within the scope of the present invention. For example, a rotary
electrostatic microactuator 301 which
is circular in plan is shown in FIG. 4. Microacluator 301 has similarities to
microaetuators 101 and 201 and like
reference numerals have been used to describe like components of
microactuators 101, 201 and 301. A rotatable
member or ring 302 overlies substrate 102. A plurality of first and second
comb drive assemblies 303 and 304 are
carried by substrate 102 for rotating ring 302 in first and second opposite
angular directions about an axis of rotation
306 extending through the center of ring 302 perpendicular to planar
substrate: Each of the first and second comb
drive assemblies 303 and 304 includes a first comb drive member or comb drive
311 mounted on substrate 102 and
a second comb drive member or comb drive 312 overlying the substrate 102. A
plurality of spring assemblies 312
are circumferentially disposed about axis of rotation 306 for supporting or
suspending second comb drives 312 and
ring 302 above substrate 102 and for providing radial stiffness to the second
comb drives 312 and ring 302. The
spring assemblies 313, comb drive assemblies 303 and 304 and ring 302 are
formed from top layer 116, preferably
using DRIE techniques. The spring assemblies 313, second comb drives 312 and
ring 302 are spaced above
substrate 102 by air gap 118. Such structures have thicknesses similar to the
thicknesses discussed above with
respect to the similar structures of microactuator 101.
At least one and preferably a plurality of first comb drive assemblies 303 are
included in rotary electrostatic
microactuator 301 and disposed about axis of rotation 306 for driving ring 302
in a clockwise direction about axis
of rotation 306. At least one second comb drive assembly 304 and preferably a
plurality of second comb drive
assemblies 304 can be included in the microactuator 301 for driving the ring
302 in a counterclockwise direction
about the axis 306. Each of the first and second comb drive assemblies 303 and
304 extends substantially radially
from axis of rotation 306 and, in the aggregate, subtends an angle of
approximately 360° so as to provide rotary
microactuator 303 with its circular shape. More specifically, microactuator
301 has a plurality of three first comb
drive assemblies 303a and a plurality of six first comb drive assemblies 303b,
and has a plurality of three second
comb drive assemblies 304a and a plurality of six second comb drive assemblies
304b. First and second comb drive
assemblies 303 and 304 are interspersed relative to each other and are
symmetrically disposed about axis of rotation
306. Each of the first and second comb drive assemblies 303 and 304 has a
length ranging from 200 to 2,000
microns and preferably approximately 580 microns. Rotary electrostatic
microactuator can be of any suitable size
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and preferably has a diameter ranging from 500 to 5,000 microns and more
preferably approximately 2,800
microns. An outer radial extremity or periphery 314 resembling a circle
extends around the circumference of
electrostatic microactuator 301.
First comb drive 311 of each of fast and second comb drive assemblies 303 and
304 is rigidly mounted
to substrate 102 by means of silicon dioxide layer 117. Each of the first comb
drives 311 for first comb drive
assemblies 303a and second comb drive assemblies 304a has a radially-extending
bar 316 provided with a first or
inner radial portion 316a and a second or outer radial portion 316b. First
comb drives 311 for adjacent pairs of first
comb drive assemblies 303b and second drive assemblies 304b share a radially-
extending bar 317 provided with
a first or inner radial portion 317a and a second or outer radial portion 3
I7b. Outer portions 316b and 317b extend
to outer radial extremity 314 of microactuator 301. Bars 316 and 317 increase
in width as they extend radially
outwardly so as to increase the area of the bar secured to substrate 102 and
thus increase the rigidity of such bars.
A plurality of comb drive forgers 321 substantially similar to comb fingers
123 discussed above with respect to
microactuator 101 are longitudinally spaced apart the length of bar 316 at any
suitable separation distance such as
discussed above with respect to comb fingers 123. A plurality of comb fingers
321 are longitudinally spaced apart
on each side of bar 317 for comb drive assemblies 303b and 304b at similar
separation distances. Comb forgers
321 are sized and shaped similar to comb forgers 123 and increase
substantially linearly in length from the bar inner
portion to the bar outer portion. The sharing of bar 317 by adjacent first
comb drives 311 eliminates the space
which would otherwise be provided between separate bars for such adjacent comb
drives 311. This saved space
can be incorporated into the length of comb drive forgers 321.
Second comb drives 312 are spaced above substrate 102 by air gap I 18 so as to
be moveable relative to
the substrate and first comb drives 311. The second comb drives 312 have a
construction similar to the first comb
drives 311. More specifically, the second comb drives for fast comb drive
assemblies 303a and second comb drive
assemblies 304a are each formed with a bar 326 that extends radially outwardly
from axis of rotation 306. The bar
326 has a first or inner radial portion 326a in close proximity to axis 306
and a second or outer radial portion 326b
that extends to radial extremity 314. A plurality of comb drive fingers 327,
substantially similar to comb fingers
321, are longitudinally spaced apart along the length of bar 326 for each such
second comb drive 312. The second
comb drives 312 for first comb drive assemblies 303b and second comb drive
assemblies 304b each have a bar 328
that extends radially outwardly from axis 306 and has a first or inner radial
portion 328a joined to ring 302 and a
second or outer radial portion 328b that extends to radial extremity 314.
Second comb drives 312 of first and
second comb drive assemblies 303b and 304b, which are back to back, share a
single bar 328. A plurality of comb
drive fingers 327 are longitudinally spaced apart along the length of bar 328
for each such second comb drive 312.
Comb fingers 327 shorten in length near the outer radial portion of bars 326
and 328 to accommodate the increased
thickness at the outer radial portions of respective bars 316 and 317. Arcuate
comb fingers 327 of second comb
drives 312 are offset relative to arcuate comb fingers 321 of first comb
drives 311 so that comb forgers 327 can
interdigitate with comb forgers 321 when the second comb drives 312 are
rotated about axis 306 towards the
stationary first comb drives 311.
Means including spring assemblies 313 are included within rotary electrostatic
microactuator 301 for
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movably supporting ring 302 and second comb drives 3I2 over substrate 101. The
spring assemblies 313 are.
circumferentially spaced apart around axis 306 at approximately 120°
angular intervals so as to provide a
symmetrical spring configuration. Each assembly 313 is provided with first and
second spaced-apart folded springs
336 and 337 having a length which preferably approximates the length of first
and second comb drive assemblies
303 and 304. Folded springs 336 and 337 are substantially similar to first and
second springs 313 and 314 of
microactuator 101. Although springs 336 and 337 can be formed from a single
spring member, the springs 336 and
337 are preferably U-shaped or V-shaped in conformation and are shown as being
substantially U-shaped. Each
of springs 336 and 337 is made from first and second elongate spring members
338 and 339 which are each
substantially beam-like in shape. First or linear spring member 338 has first
and second end portions 338a and 338b
and second or linear spring member 339 has first and second end portions 339a
and 339b.
First end portion 338a of each spring 336 and 337 is secured at its end to an
attachment member 340
formed from layer 1 I 6 and joined to substrate 102 by means of silicon
dioxide layer 117. The second end portion
338b of each spring member 338 is secured to the first end portion 339a of
each spring member 339. Spring
members 338 and 339 each extend radially outwardly from axis of rotation 306
and preferably have a length
approximating the length of first and second comb drive assemblies 303 and
304. Although first end portion 338a
can be secured to substrate 102 adjacent ring 302, the first end portion 338a
is preferably secured to substrate 102
adjacent outer radial extremity 314. Spring members 338 and 339 are preferably
approximately equal in length and
each have a width similar to the width of first and second spring members 131
and 132 discussed above. First and
second sacrificial bars 133 and 134 extend along each side of each spring
member 338 and 339.
Second end portion 339b of each spring 336 and 337 is secured to at least one
of second comb drives 312.
In this regard, microactuator 301 is provided with first and second movable
frames 341 and 342 for each spring
assembly 3 I3. At least one comb drive assembly and preferably at least one
first comb drive assembly 303 and at
least one second comb drive assembly 304 is disposed between first and second
movable frames 341 and 342 and
thus between first and second springs 336 and 337. More specifically, one
first comb drive assembly 303a and one
second comb drive assembly 303b are disposed between first and second movable
frames 341 and 342 and, together
with fast and second frames 341 and 342, are symmetrically disposed about a
radial of microactuator 301.
First and second movable frames 341 and 342 are substantially similar to first
and second movable frames
141 and 142 of microactuator 101 and are each substantially U-shaped in
conformation. First movable frame 341
includes as side members the bar 328 of adjacent second comb drive assembly
304b and the bar 326 of adjacent
first comb drive assembly 303a. An arcuate member 343 substantially similarto
arcuate member 143 interconnects
such bar outer portions 328b and 326b. Second movable frame 342 is similar in
construction and includes as side
members the bar 326 of adjacent second comb drive assembly 304a and the bar
328 of adjacent first comb drive
assembly 303b. An arcuate member 334 substantially similar to arcuate member
144 interconnects such bar outer
portions 326b and 328b. Second end portion 339b of first spring 336 is secured
to arcuate member 343 adjacent
to bar outer portion 326b of first comb drive assembly 303a, while second end
portion 339b of second spring 337
is secured to arcuate member 344 adjacent bar outer portion 326b of second
comb drive assembly of 304a. In this
maimer, first folded spring 336 is disposed inside first movable frame 341 and
second folded spring 337 is disposed
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inside second movable frame 342. The bar inner portion 328a of the first
movable frame 341 is joined to ring 302
and so serves to secure the first spring 336 to the ring 302. Similarly, the
bar inner portion 328b of second movable
frame 342b is joined to ring 302 for interconnecting spring 337 to ring 302.
An inner arcuate member or shuttle 346 is joined at opposite ends to first and
second movable frames 341
and 342. One end of the shuttle 346 is secured to bar inner portion 326a of
first movable frame 341 and the other
end of the shuttle 346 is secured to bar inner portion 326a of second movable
frame 342. A further arcuate member
347 is provided in microactuator 301 for rigidly securing together second end
portions 338b of first and second
springs 336 and 337. The arcuate member 347 overlies substrate 102 and extends
at least partially around axis of
rotation 306 between shuttle 346 and ring 302.
Second comb drives 312 of first and second comb drive assemblies 303 and 304
are movable in a direction
of travel about axis of rotation 306 between first positions, shown in FIG. 4,
in which comb drive fingers 321 and
327 are not substantially fully interdigitated and second positions, not
shown, in which the comb drive fingers 321
and 327 are substantially fully interdigitated. Although comb drive fingers
321 and 327 can be partially
interdigitated when second comb drives 312 are in their first positions, the
comb drive fingers 321 and 327 are
shown as being fully disengaged and thus are not interdigitated when second
comb drives 312 are in their first
positions. When in their second positions, comb fingers 327 of second comb
drives 312 extend between respective
comb fingers 321 of the first comb drives 311 in the same manner as discussed
above with respect to microactuator
101.
Electrical means is included within microactuator 301 for driving second comb
drives 312 between their
first and second positions. Such electrical means includes controller and
voltage generator 161 electrically coupled
by means of electrical leads 162 to a plurality of electrodes provided on
substrate 102. For simplicity, controller
161 and leads 162 are not shown in FIG. 4. Each of such electrodes is
substantially similar in construction to
electrodes discussed above with respect to microactuator 101. A ground
electrode 356 electrically coupled to the
first end portion 338a of one of the second folded springs 337 is provided for
grounding second comb drives 312.
A first drive electrode 357 is joined to the outer radial end portion of each
first comb drive 311 of first comb drive
assembly 303a and a second drive electrode 358 is joined to the outer radial
end portion of each fast comb drive
311 of second comb drive assembly 304a. A common drive electrode 359 is joined
to the outer radial end portion
of each first comb drive 311 of second comb drive assemblies 303b and 304b.
The position of ring 302 can
optionally be monitored in the manner discussed above with respect to
microactuator 101.
In one particularly suited application, rotary electrostatic microactuator 301
can be used in a data storage
system such as in an optics module of a magneto-optical data storage system.
Electrostatic microactuator 301 can
be used to rotate the polarization launch angle of light into an optical
fiber. In this regard, a central aperture 361
is provided in ring 302 for receiving a circular half wave plate 362 which is
adhesively secured to ring 302.
The operation and use of electrostatic microactuator 301 is substantially
similar to the operation and use
described above with respect to microactuators 101 and 201. Ring 302 can be
rotated in opposite first and second
directions of angular travel about axis of rotation 306 by means of controller
161. When it is desired to rotate ring
302 in a clockwise direction about the axis 306, a voltage potential is
supplied by the controller to first comb drives
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311 of first comb drive assemblies 303. The amount of the resulting
interdigitation of comb forgers 321 and 327,
and thus the amount of rotation of ring 302, can be controlled by the amount
of voltage supplied to the first comb
drives 311. When it is desired rotate ring 302 in a counterclockwise direction
about axis 306, a suitable voltage
potential can be supplied to first comb drives 311 of second comb drive
assemblies 304 to cause the respective
comb forgers 321 and 327 to interdigitate. Second comb drive members 312 of
one of first comb drive assemblies
303 or second comb drive assemblies 304 are in their second positions when the
comb drive members 312 of the
other of second comb drive assemblies 304 or first comb drive assemblies 303
are in their first positions. Suitable
voltage potentials to drive comb drive assemblies 303 and 304 can range from
20 to 250 volts and preferably range
from 60 to 150 volts. The electrostatic microactuator 301 is capable of+/_ six
degrees angular rotation when drive
voltages of up to 130 volts are utilized.
Clockwise or counterclockwise rotation of ring 302 is initiated by initially
supplying the drive voltage to
either first drive electrode 357 relating to first comb drive assemblies 303a
or second drive electrode 358 relating
to second comb drive assemblies 304a. As discussed above, electrodes 357 and
358 are dedicated to specific first
comb drives 311 and are not shared by back-to-back comb drives 311. When
engagement of comb fingers 321 and
327 for first and second comb drive assemblies 303b and 304b begins, the drive
voltage can then be supplied to
common drive electrode 359. Such initial engagement of comb forgers 321 and
327 ensures that the proper second
comb drive 312 is attracted to comb forgers 321 of shared comb drive bar 317.
Electrostatic microactuator 301 utilizes a six spring design, that is three
spring assemblies 313 that each
having first and second folded springs 336 and 337. This spring configuration
permits a spring 336 or 337 to be
circumferentially disposed at approximately 60° intervals about axis of
rotation 306. As discussed above, springs
336 and 337 provide radial stiffness to second comb drives 312 to inhibit snap
over between comb forgers 321 and
327. A circular microactuator similar to microactuator 301 can be provided
with less than or more than six springs
336 and 337 and be within the scope of the present invention. A trade off
exists between allocating space to springs
to provide radial stiffness or to comb drives assemblies to provide rotational
force. An aggregate number of springs
336 and 337 ranging from three to six in number has been found to be
preferable.
The circular and thus symmetrical configuration of microactuator 301
facilitates providing the center of
mass of the microactuator along axis of rotation 306. Such balancing inhibits
undesired disturbances to ring 302
by shock, vibration or linear accelerations due to external influences.
The rotary electrostatic microactuators of the present invention can utilize
other than radially-extending
comb drive assemblies. An exemplary push-pull microactuator using coupled
linear electrostatic nucromotors is
shown in FIG. 5. Rotary electrostatic microactuator 401 therein is similar in
certain respects to microactuators 101,
201 and 301 and like reference numerals have been used to describe like
components of the microactuators 101,
201, 301 and 401. The microactuator 401 includes a rotatable member 402
comprising a mirror holder, for
mounting to the microactuator 401 a micromirror 403 extending out of the plane
of microactuator 401, and a T-
shaped bracket 404 secured to micromirror 403. The profile of micromirror 403
is shown in FIG. 5. The rotatable
member 402 rotates about an axis of rotation 406 extending perpendicular to
planar substrate 102. The axis of
rotation 406 intersects micromirror 403 at its reflective surface 403a and is
identified as a point by reference
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numeral 406 in FIG. 5. Microactuator 401 is provided with at least one side
407 and rotatable member 402 is
disposed adjacent the side 407. The microactuator 401 has first and second
linear micromotors 408 and 409 and
fwst and second couplers 411 and 412 for respectively securing first and
second micromotors 408 and 409 to bracket
404.
First and second micromotors 408 and 409 are substantially identical in
construction and are formed atop
the substrate 102 from upper layer 116. The micromotors each includes at least
one comb drive assembly and
preferably includes at least one first comb drive assembly 416 and at least
one second comb drive assembly 417.
As shown, each of the micromotors 408 and 409 includes a plurality of four
first comb drive assemblies 416 and
a plurality of four second comb drive assemblies 471 aligned in parallel.
First comb drive assemblies 416 are
disposed side-by-side in a group and second comb drive assemblies 417 are
similarly disposed side-by-side in a
group. The group of assemblies 416 are disposed in juxtaposition to the group
of assemblies 417.
Comb drive assemblies 416 and 417 can be of any suitable type. In one
preferred embodiment, the comb
drive assemblies are similar to the comb drive assemblies described in U.S.
Patent No. 5,998,906 issued December
7, 1999 and in copending U.S. patent application Serial No. 09/135,236 filed
August 17, 1998. The comb drive
assemblies 416 and 417 are each provided with a first comb drive member or
comb drive 421 mounted on substrate
102 and a second comb drive 422 overlying the substrate. First comb drives 421
are each formed from an elongate
bar 426 having first and second end portions 426a and 426b. A plurality of
linear comb drive forgers 427, shown
as being linear, are secured to one side of the bar in longitudinally spaced-
apart positions along the length of the
bar. Comb drive forgers or comb fingers 427 extend perpendicularly from bar
426 and, as shown, can be of equal
length and have a constant width along their length. Second comb drives 422
are similar in construction to first
comb drives 421 and are each formed from a bar 431 having first and second end
portions 431a and 431b. A
plurality of linear comb fingers 432, shown as being linear, extend from one
side of the bar 431 in longitudinally
spaced-apart positions. Comb fingers 432 are substantially identical to comb
forgers 427, but are offset relative to
the comb fingers 427. When comb drive assemblies 416 and 417 are in their home
or rest positions, comb fingers
427 and 432 are not substantially fully interdigitated and, preferably, are
partially interdigitated as shown in FIG.
5.
An elongate member or shuttle 436 is included in each of first and second
micromotors 408 and 409.
Shuttle 436 has first and second end portions 436a and 436b. First end portion
431 a of each of bars 431 is secured
to shuttle 436 so that bars 431 extend perpendicularly from one side of the
shuttle 436 between shuttle end portions
436a and 436b.
First and second spaced-apart spring members 437 and 438 are included in each
of micromotors 408 and
409. Springs 437 and 438 can be of any suitable type and are preferably formed
from at least one elongate beam-
like member. In one preferred embodiment, springs 437 and 438 each consist of
a single such beam-like member
similar to first spring member 131 and to second spring member 132 discussed
above. Springs 437 and 438 are
substantially identical in construction and each include first and second
sacrificial bars 133 and 134 disposed along
opposite sides of the springs for the purposes discussed above. First spring
437 has first and second end portions
437a and 437b and second spring 438 has first and second end portions 438a and
438b. The spring second end
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portion 437b is secured to shuttle first end portion 436a and the spring
second end portion 438b is secured to shuttle
second end portion 436b. As a result, at least one and as shown all of first
and second comb drive assemblies 416
and 417 are disposed between first and second springs 437 and 438. The springs
437 and 438 preferably extend
perpendicular to shuttle 436 when comb drive assemblies 416 and 417 are in
their home or rest positions. Each of
the first and second springs 437 and 438 preferably has a length approximating
the length of comb drive assemblies
416 and 417 so that first end portions 437a and 438a are disposed adjacent the
second end portions 426b and 431b
of the comb drive bars 426 and 431. An attachment block 439 is secured to
substrate 102 for each spring 437 and
438 and serves to attach the first end portions 437a and 438a of the first and
second springs to the substrate 102.
Second comb drives 422, shuttle 436 and first and second springs 437 and 438
are spaced above substrate
102 by air gap 118 so as to be electrically isolated from the substrate and
movable relative to the substrate. These
structures can have any suitable thickness and preferably each have a
thickness ranging from 10 to 200 microns
and more preferably approximately 85 microns. First and second springs 437 and
438 are included within the
means of microactuator 401 for suspending and movably supporting second comb
drives 422 over substrate 102.
The second comb drives 422 are movable in a linear direction of travel
relative to first comb drives 421
between first positions, as shown in FIG. 5, in which comb forgers 427 and 432
are not substantially fully
interdigitated and second positions in which the comb fingers 427 and 432 are
substantially fully interdigitated.
When in their second positions, comb fingers 432 extend between respective
comb forgers 427 and approach but
preferably do not engage first comb drive bar 426. Second comb drive members
422 of first comb drive assemblies
416 are in their second positions when second comb drives 422 of second comb
drive assemblies 417 are in their
first positions. Conversely, the second comb drives of first comb drive
assemblies 416 are in their first positions
when the second comb drives of second comb drive assemblies 417 are in their
second positions.
The movement of second comb drives 422 to their first and second positions
causes shuttle 436 to move
in opposite first and second linear directions relative to substrate 102. Such
directions of travel are substantially
perpendicular to the disposition of the elongate first and second comb drive
assemblies 416 and 417. A plurality
of first stops 441 are secured to substrate 102 for limiting the travel of
second comb drives 422 of first comb drive
assemblies 416 towards their respective first comb drives 421. A plurality of
similar second stops 442 are secured
to the substrate for limiting the travel of second comb drives 422 of second
comb drive assemblies 417 towards
their respective first comb drives 421. In one preferred embodiment, first and
second micromotors 408 and 409
are disposed in juxtaposition so that respective shuttles 436 are disposed
side-by-side in parallel with each other.
Second end portions 436b of the shuttles 436 each generally point towards
micromirror 403 and are centered
relative to axis of rotation 406.
First and second couplers 411 and 412 are suspended above substrate 102 by air
gap 118 and have a first
end secured to shuttle second end portion 436b and a second end secured to the
bracket 404. The couplers 411 and
412 are preferably symmetrically disposed relative to each other with respect
to axis of rotation 406. First coupler
411 secures shuttle 436 of the first micromotor 408 to one side of bracket 404
and second coupler 412 secures
second micromotor 409 to the other side of bracket 404. In one preferred
embodiment, each of the first and second
couplers has at least one spring member or coupling spring to provide a non-
rigid connection between the shuttle
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436 and the bracket 404. In a particular preferred embodiment, each of the
first and second couplers 411 and 412
includes a rigid strip 446 secured at one end to shuttle 436 by means of a
first coupling spring 437 and secured at
its other end to bracket 404 by a second coupling spring 448. .
Electrical means is included within microactuator 401 for driving second comb
drives 422 of the first and
second micromotors 408 and 409 between their first and second positions. Such
electrical means includes a suitable
controller and voltage generator such as controller and voltage generator 161
electrically coupled to a plurality of
electrodes by means of a plurality of electrical leads 162. For simplicity,
controller 161 and leads 162 are not shown
in FIG. 5. Such electrodes, each of which is substantially similar to the
electrodes described above with respect to
microactuator 101, include first and second ground electrodes 453 which are
electrically coupled by means of
respective leads 454 to attachment block 439 for first springs 437 so as to
electrically ground first and second
springs 437 and 438, shuttle 436 and second comb drives 422 of each of the
micromotors 408 and 409. A first drive
electrode 457 is electrically coupled, either directly or by means of leads
458, to first comb drives 421 of the first
comb drive assemblies 416 of each micromotor 409 and 409. A second drive
electrode 461 is electrically coupled,
either directly or by means of lead 462, to the first comb drives 421 of the
second comb drive assemblies 417 of
the micromotors 408 and 409. An additional stop 463 secured to substrate 102
can additionally be provided for
each micromotor 408 and 409 to limit the forward travel of shuttle 436 towards
rotatable member 402. The position
of rotatable member 402 can optionally be monitored in the manner discussed
above with respect to microactuator
101.
In operation and use, controller 161 can be utilized to drive the second comb
drives 422 of each of first
and second micromotors 408 and 409, in the manner described above with respect
to micromotors 101, 201 and
301, so that shuttles 436 of the micromotors 408 and 409 travel in opposite
directions relative to substrate I02 and
the axis of rotation 406. When, for example, equal voltages are supplied to
the drive electrode 457 of first
micromotor 408 and drive electrode 461 of micromotor 409, shuttle 436 of the
first micromotor 408 is caused to
move towards axis 406 and shuttle 436 of the second micromotor 409 is caused
to move away from axis 406 so
as to cause first and second couplers 411 and 412 to pivot the rotatable
member 402 in a counterclockwise direction
about axis 406. In a similar manner, the first and second micromotors 408 and
409 can be utilized to pivot the
rotatable member 402 in a clockwise direction about axis 406. Suitable voltage
potentials to electrodes 457 and
461 for so rotating micromirror 403 can raage from 20 to 200 volts and
preferably range from 60 to 150 volts.
Microactuator 401 is capable of +/- 10° ~~~. rotation, that is a
rotation of 10° in both the clockwise and
counterclockwise directions for an aggregate rotation of 20°, when such
drive voltages are utilized. Mirror surface
403a can be used to accurately and repeatedly reflect a laser light beam.
The linear deflection of the micromotors 408 and 409 closely matches the
circumferential motion of the
rotatable member. Thus, if the linear micromotors 408 and 409 are each capable
of+/_ 30 microns of linear motion,
the rotatable member 402 will rotate slightly less than the arctan (30/R),
where R is the effective radius of the
rotatable member 402. As can be seen, the angular range depends on the
effective circumference of the rotatable
member 402; larger angles can be obtained for rotatable members with smaller
effective circumferences and smaller
angles can be obtained for rotatable members with larger effective
circumferences. The flexible coupling springs
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447 and 448 enhance the translation of the longitudinal movement of shuttles
436 to rotational movement of
micromirror 403 and bracket 404.
The symmetrical structure of first and second micromotors 408 and 409 and
first and second couplers 411
and 412, as well as the symmetrical disposition of first micromotor 408 and
first coupler 411 relative to second
micromotor 409 and second coupler 412, ensure proper push-pull so that the
micromirror and bracket 404 pivot
about the axis of rotation 406. In this regard, first micromotor 408 and first
coupler 411 are symmetrical to second
.micromotor 409 and second coupler 412 relative to an imaginary line extending
between shuttles 436 and axis of
rotation 406. The first and second couplers 411 and 412 are joined to bracket
404, and the micromirror 403 and
bracket 404 are sized and shaped, so that reflective surface 403a of
micromirror 403 pivots at axis of rotation 406.
Nonfolded springs 437 and 438 can be utilized in micromotors 408 and 409
because the required stroke
length of comb drive assemblies 416 and 417, and hence the length of comb
fingers 427 and 432, are relatively
small in the microactuator 401. As a result, the sidewise movement of comb
forgers 427 and 432 resulting from
bending of springs 437 and 438 during interdigitation of the comb forgers is
not significant. The symmetrical
disposition of micromotors 408 and 409 compensates for any such sidewise
movement of the shuttle 436 of the first
micromotor 408 relative to the sidewise movement of the shuttle 436 of the
second mieromotor 409. Push-pull
microactuators with folded springs can be provided.
Other rotary electrostatic microactuators realizing linear electrostatic
micromotors can be provided and
be within the scope of the present invention. For example, a push-pull
microactuator utilizing more than two
micromotors 408 and 409 can be provided. It is preferable that the nucromotors
of any such rotary microactuator
be symmetrically disposed about the axis of rotation of the microactuator.
Such microactuators having the axis of
rotation at the center of the microactuator, as opposed to at one side of the
microactuator as in microactuator 401,
are contemplated.
It should be appreciated that a rotary electrostatic microactuator of the type
described herein can be
provided with prebent springs or suspensions of the type disclosed in U.S.
Patent No. 5,998,906 that issued
December 7, 1999 or in copending U.S. patent application Serial No. 09/135,236
filed August 17, 1998 and be
within the scope of the present invention. Such prebent springs are nonlinear
and thus in a "bent" condition when
at rest in a static undefleeted condition. The spring members of such springs
straighten towards a linear condition
as the comb drive forgers interdigitate and thus increase in axial stiffness
during interdigitation. Such an
embodiment of a rotary electrostatic microactuator can be provided with two or
more prebent springs, one or more
springs which straighten during interdigitation of comb drive forgers driving
the microactuator in a first direction
and one or more springs which straighten during interdigitation of comb drive
forgers driving the microactuator in
an opposite second direction. Linear or angular traveling comb drive
assemblies can be provided in such rotary
microactuators. Use of such prebent springs results in improved stiffness in
the springs at or near the maximum
travel of the comb drives and accompanying structure, which is particularly
important in microactuators having
large deflections.
Rotary electrostatic microactuators can be provided which incorporate various
features of the
microactuators herein. Rotary electrostatic microactuators that use arcuate
comb drive forgers can be circular in
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shape or have other noncircular shapes such as fanlike shapes or shapes
resembling the sector or segment of a circle.
Radially-extending folded or nonfolded springs can be provided. Such springs
can be prebent or linear when in
their rest positions. The comb drive assemblies of the microactuator can be
centered on a radial or offset from a
radial. The comb drive fingers can be spaced apart or partially interdigitated
when in their rest positions and can
have a variety of shapes.
As can be seen from the foregoing, a rotary electrostatic microactuator with
an improved range of angular
motion has been provided. Side instability forces in the one or more comb
drive assemblies of the microactuator
are minimized and rotation of a member extending out of the plane of the
microactuator is permitted. In one
embodiment, the rotary electrostatic microactuator is other than circular in
shape. The axis of rotation of the
microactuator can be disposed adjacent a side of the microactuator.
