Measuring and testing – Speed – velocity – or acceleration – Acceleration determination utilizing inertial element
Reexamination Certificate
2001-04-23
2003-04-15
Kwok, Helen (Department: 2856)
Measuring and testing
Speed, velocity, or acceleration
Acceleration determination utilizing inertial element
C073S514290
Reexamination Certificate
active
06546801
ABSTRACT:
DESCRIPTION
1. Field of the Invention
The field of the invention is mechanical structures and particularly micro-machined mechanical structures, comprising a moving mass connected by at least one beam with two ends at an anchor point, one of the ends of the beam being connected to the moving mass and the other end being connected to the anchor point. It is also related to a device and particularly a sensor incorporating the structure.
2. State of the Art
Mechanical oscillators exist in which the force applied to a moving mass and the movement of this moving mass are related by a non-linear relation, and in this case the stiffness of a beam coupling the moving mass to a fixed structure of the oscillator is variable as a function of the displacement amplitude of the moving mass. This effect of the variation in the stiffness of the beam is more sensitive when the movement amplitude of the moving mass increases. The induced effect may be sub-linear or supra-linear. The non-linear relation between the force applied to the moving mass and the movement amplitude of the moving mass means that there can be two possible amplitudes of the movement at frequencies close to resonance for a given frequency. Therefore the movement becomes unstable. When a structure is excited close to its resonant frequency, the movement amplitude of the moving mass with respect to the static position of the moving mass is amplified by a factor called the “Q quality factor”. This factor is higher when energy losses in the mechanical structure are low. This amplification is used to obtain large oscillation amplitudes with low excitation forces. The mechanical transfer function (movement as a function of the excitation frequency) becomes asymmetric close to the resonant frequency and then becomes unstable. The non-linearity phenomenon of the relation between the force applied to the moving mass and the movement amplitude of the moving mass limits the amplitude of the movement that can be accepted if the movement is to be remain stable. For example, silicon micro-structures are observed with built in-built in type beams with a length of a few hundred &mgr;m, for which the oscillation becomes unstable for movement amplitudes of a few &mgr;m. This limits important performances for some systems, for example the sensitivity of a measurement device in which such a structure is used. In order to limit the non-linearity phenomenon, attempts have been made to limit the oscillation amplitude of the moving mass. Thus, the system remains within the linear range and a stable movement is possible. Thus, patent DE-202 445 2 B granted to IBM Corp. describes a monolithic electromechanical oscillator comprising a semi-conducting part for which the mechanical resonant frequency determines the oscillation frequency. An oscillation amplitude control circuit is integrated in the oscillator. The oscillation amplitude control circuit controls the excitation energy, in other words the current flux through a heating resistance as a function of a threshold value and the amplitudes of the observed real oscillation. Another example in which the oscillation amplitude is limited is described in patent SU 493 770 A awarded to KAUN POLY. In this patent, the vibration amplitude is captured. When the vibration amplitude exceeds a predetermined threshold, a means changes the stiffness of an elastic system such that the resonant frequency is changed and therefore the vibration amplitude is limited. Known examples of mechanical structures comprising an oscillating moving mass will now be described with reference to
FIGS. 1A
to
1
D. Identical reference numbers in these figures denote elements with the same functions.
FIG. 1A
represents a mechanical structure
1
incorporating a fixed frame
2
within which a moving mass
3
oscillates. The moving mass
3
is connected to the fixed frame
2
through beams
4
and
5
. The movement direction represented by a double arrow
10
is perpendicular to beams
4
,
5
and is located in the XOY plane in the figure. The movement of the moving mass is parallel to the OY direction. End
11
of the beam
4
is connected to the moving mass
3
, and end
12
is connected to an anchor point
8
fixed in the OY direction of the movement of the moving mass. Similarly, end
13
of beam
5
is connected to the moving mass and end
14
is connected to an anchor point
9
fixed in the OY direction.
FIG. 1B
shows a mechanical structure
1
comprising a moving mass
3
as shown in
FIG. 1A
, but in the case in
FIG. 1B
, the moving mass
3
is connected through a set of four beams to the anchors
8
and
9
respectively, therefore there are two additional beams
6
,
7
with ends
15
,
16
;
17
,
18
respectively, these beams coupling the moving mass
3
to anchors
8
and
9
respectively.
FIGS. 1C and 1D
also show a mechanical structure
1
incorporating a moving mass
3
in which the beams connecting the moving mass
3
to anchor points
8
,
9
respectively are not straight beams. The shape of the beams
4
,
5
or
6
,
7
shown in
FIGS. 1C and 1D
enables deformation of the beam in the XOY plane and consequently larger vibration amplitudes of the moving mass
3
. This larger vibration amplitude of the moving mass
3
is made without non-linear phenomena occurring, precisely due to the shape of beams
4
,
5
,
6
or
7
. This type of deformable beam, that for example can be found in patent application WO 95/34798 assigned to BOSCH, has the disadvantage that it has a moving mass
3
that oscillates not only in the Y direction in the XOY plane, but also in the X direction of the XOY plane. The result is parasite phenomena that disturb the signal that can be produced by such a device, and particularly a sensor with this type of mechanical structure. For example, these parasite phenomena can produce a shift in the resonant frequency by the occurrence of mechanical deformation modes that can be combined with the required excitation mode in the Y direction and finally by increased sensitivity to accelerations along several axes. In the latter case, the result is a reduced control over the directivity of the movement.
The problem of dependence between the vibration amplitude of the oscillating mass and the vibration frequency of this mass is discussed in patent U.S. Pat. No. 5,902,012 awarded to BOEING NORTH AMERICAN.
This patent (column 1, lines 44-48) describes that the vibration amplitude may be as high as 20% of the length of the suspension beams supporting the oscillating mass, and that the elongation of the beams in their axial direction can no longer be ignored under these conditions. To overcome this fact, this patent (column 1, line 63-column 2, line 2) proposes to make the suspension beam more easily extendible, and to do this by modifying the beam or the configuration of the frame or the mass at the location at which this suspension beam is attached.
This better extendibility is obtained either by:
forming each suspension beam with a curved shape in the plane of vibration of the oscillating mass as shown in
FIG. 1
in this patent; or
by providing parts to enable relaxation of the elongation stress, for example in the form of cut-outs made at the connections between the beam and the fixed frame and/or the oscillating mass, or in the form of cut-outs made on the elongation beam as shown in
FIGS. 2
to
5
in this patent.
Note that in all the examples given, the elongation means are symmetrical with respect to the stiffness. This means that the value of the resistance to elongation is the same for the same value of the tension applied along each direction of the axial line of the suspension beam. In other words, the deformation of the elongation means is the same regardless of whether the tension is made in one direction or in the opposite direction.
BRIEF DESCRIPTION OF THE INVENTION
The invention is intended to provide a mechanical structure in which the oscillating moving mass moves along a known axis without moving in other directions, and according to a linear movement without any of the instabiliti
Diem Bernard
Lefort Olivier
Orsier Elisabeth
Wehbe-Alause Hélène
Commissariat a l'Energie Atomique
Kwok Helen
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
LandOfFree
Micro-machined mechanical structure and device incorporating... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Micro-machined mechanical structure and device incorporating..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Micro-machined mechanical structure and device incorporating... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3047393