Actuator with a flexure arrangement to accommodate a long...

Details Actuator with a flexure arrangement to accommodate a long... Actuator with a flexure arrangement to accommodate a long...

2001-01-16

2003-04-01

Tamai, Karl (Department: 2834)

Electrical generator or motor structure

Non-dynamoelectric

Charge accumulating

Reexamination Certificate

active

06541892

ABSTRACT:

TECHNICAL FIELD
The invention relates generally to actuators and more particularly to flexural arrangements for supporting a movable member for controlled long range motion relative to a stationary member.
BACKGROUND ART
In many micromachine applications that use actuators, design goals include providing a long range of translator motion along a particular axis, while retarding out-of-plane displacements and in-plane displacements that are perpendicular to the intended direction of travel. Electrostatic surface actuators for use in micromachine applications are known. Such actuators may be used in advanced data storage applications and optical telecommunications applications. U.S. Pat. No. 5,986,381 to Hoen et al., which is assigned to the assignee of the present invention, describes electrostatic actuators and voltage variation techniques for driving a translator relative to a stator. U.S. Pat. No. 5,378,954 to Higuchi et al. also describes electrostatic actuators.
All of the actuators displace one element (i.e., the translator) relative to another element (i.e., the stator) and require that the moving element be stabilized against motions in undesired directions. Rolling or sliding elements are most commonly used to directionally stabilize the translator. However, in micromachined actuators, bending flexures are preferred, since the surface contact associated with the rolling or sliding elements is particularly unpredictable and risky for extremely small devices. Nevertheless, bending flexures pose different problems, since their stiffness varies with displacement. For a unidirectional actuator, the bending flexures must stabilize the translator with respect to the out-of-plane motions and with respect to the in-plane motions perpendicular to the desired direction of travel. Supports that are rigid against out-of-plane displacements are particularly important for electrostatic surface actuators, because the force tending to attract the two surfaces is approximately the same as the force pushing the translator parallel to the stator.
FIG. 1
shows an example of one type of folded beam flexure
10
that is used in micromachined electrostatic actuator applications. The flexural device includes a rigid floating beam
12
having opposite sides connected to flexible beams
14
and
16
. The flexible beams
14
and
16
are anchored to supports
18
and
20
on a stationary member (not shown), such as a semiconductor substrate. In addition to the pair of flexible beams
14
and
16
, there is a second pair of flexible beams
22
and
24
connected to the rigid floating beam
12
. The second pair of flexible beams supports a second rigid beam
26
, which moves with the movable member of interest.
The folded beam flexure
10
of
FIG. 1
produces generally straight-line motion along an x axis. However, as the second rigid beam
26
is displaced along the x axis, the flexible beams
14
,
16
,
22
and
24
become increasingly compliant to forces along the y axis. For many electrostatic actuators, such as comb drives and surface drives, the applied force in the desired direction of motion (i.e., along the x axis) is accompanied by an instability in the y axis direction. The maximum stable travel of the second rigidly floating beam
26
is thus limited to when the y axis force gradient exceeds the y axis stiffness of the flexible beams.
A second known flexural device
28
is shown in FIG.
2
. Here, the translator is connected directly to the rigid floating beam
12
that is connected to the stator (not shown) via the two flexible beams
14
and
16
. This device is better suited for maintaining stiffness along the y axis as the rigid beam is displaced. Unfortunately, motion of the rigid floating beam does not follow a straight line as it is displaced. This is not suitable for use in actuators that require straight-line motion.
FIG. 3
shows a third known flexural device
30
which uses micromachine flexible beams. A series of pre-bent flexible beams
32
,
34
,
36
,
38
,
40
,
42
,
44
and
46
is used to provide increased stiffness to motion along the y axis. The flexible beams
32
,
34
,
36
and
38
are anchored to supports
50
at one end and are connected to either a first rigid floating beam
48
or a second rigid floating beam
52
at the opposite ends. The supports
50
are locations on a stationary member, such as a semiconductor wafer. The flexible beams
40
and
42
connect the first rigid floating beam
48
to a third floating member
54
, while the flexible beams
44
and
46
connect the second rigid floating beam to the third floating member.
The flexible beams
32
,
36
,
42
and
44
are pre-bent in such a way that the ends opposite to the rigid floating beams
48
and
52
are offset in a “negative direction” along the x axis with respect to the connections to the rigid floating beams. On the other hand, the flexible beams
34
,
38
,
40
and
46
are pre-bent in such a way that the ends opposite to the rigid floating beams
48
and
52
are offset in a “positive direction” along the x axis with respect to the connections to the rigid floating beams. Because of the difference in pre-bent conditions, as one set of flexible beams softens with increased bending, the other set is straightening, thereby maintaining the y axis stiffness. More particularly, as the third floating member
54
which is connected to the translator moves in the positive x direction, the flexible beam
44
will begin to straighten, while the flexible beam
46
will become increasingly bent. This has the effect of causing the third floating member
54
to rotate in a clockwise direction. However, for the same motion, the flexible beam
40
will become increasingly bent and the flexible beam
42
will straighten, causing the third floating member to be urged in a counterclockwise rotation. The two rigid floating beams
48
and
52
are linked at their centers by a bending flexure
56
that acts as a torsional joint. Because each side of the third floating beam
54
is acted upon by offsetting rotational forces, the third floating beam
54
moves in a straight-line motion.
There are some concerns with the flexural device
30
of FIG.
3
. First, it does not efficiently use semiconductor wafer area, which is often times at a premium. Second, the flexural device
30
requires contacts to rigid supports
50
which are sometimes fully surrounded by the various beams. Thus, it may be difficult to fabricate the device using a single material layer without external supports, as is often preferred with deep reactive ion etching.
A more complete flexural system
58
that utilizes folded beam arrangements
60
and
62
is shown in
FIGS. 4 and 5
. Each of the folded beam arrangements
60
and
62
is identical to the one described with reference to
FIG. 1
, but with a translator
64
taking the place of the second rigid beam
26
. The system
58
is shown in a relaxed state in FIG.
4
. In this state, the flexible beams
14
,
16
,
22
and
24
are generally perpendicular to the floating rigid beams
12
. As noted above, the flexible beams
14
and
16
are anchored to supports
18
and
20
, respectively, on the stationary substrate
65
, which is represented by dashed lines. The flexible beams
22
and
24
are connected between the rigid floating beams
12
and the translator
64
.
Before any motion takes place in the x direction, the system
58
is very stiff to forces in the y direction. This is because the flexing beams
14
,
16
,
22
and
24
are straight beams and must buckle in order to allow motion in the y direction. However, the system is more susceptible to forces in the y direction after some displacement of the translator
64
has occurred from the condition shown in
FIG. 4. A
displaced translator
64
is represented in FIG.
5
. Electrostatic forces that urge the translator
64
laterally cause the two rigid floating beams
12
to move more closely together, as indicated by the difference between the dotted lines and the solid lines representing the rigid floating beams. Becaus

Affiliated with

Also associated with

Rating

Actuator with a flexure arrangement to accommodate a long... does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Actuator with a flexure arrangement to accommodate a long..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Actuator with a flexure arrangement to accommodate a long... will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3021047