JP2849697B2 - 2-DOF vibration microactuator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a two-degree-of-freedom vibration type microactuator using electrostatic force or electromagnetic force, and more particularly to a mirror driving mechanism of an optical scanner, a vibration type atmosphere sensor, and an optical shutter of a display. The present invention relates to a two-degree-of-freedom vibration type micro-actuator that can be effectively used for example.

[0002]

2. Description of the Related Art As shown in FIG. 6, a one-degree-of-freedom torsional vibrator having electrodes arranged in a parallel plate shape has been proposed since the early days of microactuator research because of its simple structure. KEPetersen: "Silicon Torsi
onal Scanning Mirror ", IBM J. Res.Develop., vol. 24 (19
80) See page 631). In addition, a one-degree-of-freedom electrostatic drive type vibrator using the above-mentioned torsional vibrator as a cantilever type has been proposed (Kawamura et al .: “Study of micromechanics using Si”). Proceedings, p.753).

[0003] The one-degree-of-freedom electrostatic drive type torsional vibrator shown in FIG. 6 has fixed ends 3 of a movable electrode plate 3 made of a silicon single crystal plate at both ends on a glass substrate 1 via spacers 2.
a between the fixed portions 3a at both ends of the movable electrode plate 3.
A fixed electrode 4 supporting the movable electrode portion 3c via the narrow torsion bar 3b and facing the movable electrode portion 3c at an electrode interval is provided in parallel with the movable electrode portion 3c on the glass substrate 1. Have been placed. Movable electrode plate 3
A power supply 5 is connected between the power supply 5 and the fixed electrode 4 via a switch 6.

In the torsional vibrator having the above structure, when a voltage is applied between the movable electrode portion 3c and the fixed electrode 4, the movable electrode portion 3 is rotated about the torsion bar 3b by electrostatic attraction.
c rotates. However, since the electrostatic attractive force is inversely proportional to the square of the electrode interval, it is desired to reduce the electrode interval in this type of electrostatic actuator. However, in the above-described structure having one degree of freedom, the movable electrode portion 3c serves as both an electrode and a movable portion. Therefore, if the electrode interval is reduced, the displacement (rotation angle) is restricted. Need to be larger. Therefore, there is a problem that it is difficult to achieve both low voltage driving and large amplitude.

[0005]

The technical problem of the present invention is to separate a driving part and a movable part which are driven by applying a voltage or the like to form a two-degree-of-freedom vibration system so that the electrode spacing (electromagnetic force) can be reduced. Another object of the present invention is to provide a two-degree-of-freedom vibrating microactuator that has a small transmission interval and enables low-voltage driving, and at the same time secures a movable range of a movable part to obtain a large amplitude.

[0006]

The two-degree-of-freedom vibration type microactuator of the present invention for solving the above-mentioned problems is provided by:
The drive plate periodic electrostatic force is applied as an external force, first
The movable plate is elastically connected to the driving plate via a second elastic connecting member, and the driving plate and the movable plate are elastically supported by the respective elastic connecting members. A vibration system driven by an anti-resonance frequency of a two-degree-of-freedom vibration system by forming a two-degree-of-freedom vibration system that is displaced in a dynamic manner, and setting an excitation frequency of the external force equal to a natural frequency of the drive plate system. Is formed.

[0007]

In the two-degree-of-freedom vibrating microactuator having the above-described structure, the driving plate and the movable plate constitute a vibration system, and the frequency of the periodic electrostatic force or electromagnetic force applied to the driving plate from the outside is appropriately adjusted. When set, the amplitude of the driving plate can be set to approximately 0, and the amplitude of the movable plate can be set to a finite value. Here, the electrostatic force or electromagnetic force for driving the driving plate is inversely proportional to the square of the distance transmitting the driving plate. Therefore, the smaller the amplitude of the driving plate, the shorter the distance and the lower the voltage (low power). The movable range of the plate is secured, and a large amplitude can be obtained.

[0008]

1 and 2 show an embodiment of a microactuator according to the present invention. The two-degree-of-freedom electrostatic drive type microactuator shown in FIG. 1 has a fixed electrode 18 provided on a glass substrate 10 whose surface has been subjected to required processing by etching, and has a required shape formed by anisotropic etching from a single crystal silicon wafer. It is configured by attaching the formed movable electrode plate 20.

The glass substrate 10 has a substantially rectangular shape, and a spacer 11 for supporting the fixed portions 21 of the movable electrode plate 20 at both ends in the longitudinal direction on the surface thereof is formed by the etching. In addition, along the longitudinal center line L, the blade-shaped edge 12 clearly shown in FIG.
In addition, the other portions are excavated and thinned, and in particular, the portion 14 of the movable electrode plate 20 facing the later-described movable plate 25 is further deepened, whereby the movable electrode plate 20 is entirely formed on the glass substrate. In a state of being separated from the surface of 10, both end fixing portions 21 are supported on the spacer 11.

On the other hand, the movable electrode plate 20 is provided between the fixed portions 21 provided at both ends thereof via a narrow first torsion bar 22 along the center line L on both sides thereof.
And the electrode plate 23 is partially cut away to form a second torsion bar 24 along the center line L and a movable plate 25 through the second torsion bar 24. Are connected. This movable electrode plate 20
Are symmetrical on both sides of the center line L.

The movable electrode plate 20 has fixed portions 21 at both ends thereof adhered and supported on the spacer 11 on the glass substrate 10 with hot wax or the like, and torsion bars 22 and 24 along the center line L thereof. Blade type edge 1 on glass substrate 10
2 is fixed to the glass substrate 10 by being placed in a contact state (FIG. 2). Further, on the glass substrate 10, the fixed electrode 18 is disposed on one side of the center line L at an electrode interval with respect to the electrode plate 23. This fixed electrode 18 can be formed by means such as evaporating Ti on the glass substrate 10. Although not shown, the fixed electrode 18 and the electrode plate 23 are connected to a power supply.

In the two-degree-of-freedom vibrating microactuator having the above configuration, the electrode plate 23 and the movable plate 25 constitute a vibration system, and a periodic voltage is applied between the fixed electrode 18 and the electrode plate 23. When the electrode plate 23 is driven by the electrostatic force and the torsion bars 22 and 24 are torsionally oscillated, and the frequency of the periodic electrostatic force is appropriately set, the amplitude of the electrode plate 23 is reduced to almost zero, and the amplitude of the movable plate 25 is reduced. Can be set to a finite value. Here, the electrode plate 2
Since the electrostatic force for driving 3 is inversely proportional to the square of the electrode interval, the smaller the amplitude of the drive plate, the shorter the electrode interval,
The movable range of the movable plate 25 can be secured at a lower voltage, and a large amplitude can be obtained.

FIG. 3 shows the structure of the two-degree-of-freedom vibration type microactuator using a dynamic model, and the same reference numerals are assigned to parts corresponding to those in the above embodiment. In this dynamic model, the electrode plate 23 is elastically supported by the first torsion bar 22 with respect to the fixed portion 21, and the movable plate 25 is elastically connected to the electrode plate 23 by the second torsion bar 24. Therefore, the electrode plate 23 and the movable plate 25 rotate around the torsion bars 22 and 24, respectively, and form a two-degree-of-freedom torsional vibration system.

In this dynamic model, I ₁ and θ ₁ are the moment of inertia and displacement of the electrode plate 23, respectively.
₂ , θ ₂ are the moment of inertia and displacement of the movable plate 25,
Further, k ₁ and k ₂ are changed to the first torsion bar 22 and the second torsion bar 22.
Is the torsion spring constant of the torsion bar 24, the equation of motion when a periodic external force T · sinωt acts on the electrode plate 23 is given by the following equation.

[0015]

(Equation 1)

Further, the natural frequency omega ₂ of the natural frequency omega ₁ and the movable plate type electrode plate system, respectively,

(Equation 2) Given by

Here, if θ _st is the static displacement of the electrode plate, the amplitude due to the periodic external force is given by the following equation for each of the electrode plate and the movable plate.

(Equation 3)

[0018] From the above equation, the amplitude of the electrode plate 23 by the periodic external force in omega = omega ₁ becomes zero. At this time, the movable plate 2
The amplitude of 5 is a finite value represented by the equation (4). The amplitude of the movable plate 25 can be set to a predetermined value by appropriately designing the electrode plate 23, the movable plate 25, and the two torsion bars.

In the prototype of the present inventor, the movable electrode plate 20 was formed to have a thickness of 0.3 mm and an outer dimension of about 20 mm ×
It was integrally formed from a 20 mm single crystal silicon wafer by anisotropic etching. The fixed electrode 18 and the electrode plate 2
3 was 8 μm, and the distance between the movable plate 25 and the glass substrate 10 was 38 μm.

The displacement (torsion angle) of the electrode plate 23 and the movable plate 25 was measured by the optical lever method in the prototype two-degree-of-freedom torsional vibration type actuator. First, when a voltage of 100 V was applied statically, the electrode plate 23 and the movable plate 2
The displacements of No. 5 coincided with each other, and θ _st = 0.02 °. Next, excitation was performed by applying a voltage that fluctuates periodically. FIG.
The resonance curve of the electrode plate 23 and the movable plate 25 when a sinusoidal voltage (100 Vp-p) is applied is shown. The vertical axis indicates the displacement, which is divided by the static displacement θ _st measured in advance.

From this resonance curve, the prototype torsional vibration type actuator has resonance points at 241 Hz and 580 Hz.
Is zero, indicating that the object of obtaining a large displacement of the movable plate 25 without displacing the electrode plate 23 almost can be achieved. Therefore, by optimizing the electrode plate 23, the movable plate 25, and the torsion bars 22, 24,
Only the displacement of the movable plate 25 can be enlarged. As a result, since the displacement of the electrode plate 23 is reduced, an efficient microactuator in which the displacement of the movable plate 25 is increased even if the distance between the electrode plate 23 and the fixed electrode 18 is reduced and the power supply voltage is set lower than the conventional one. Obtainable.

FIG. 5 shows the configuration of another embodiment of the two-degree-of-freedom vibration type microactuator by using a dynamic model. Uses the bending vibration of an elastic connecting member having substantially the same structure as the torsion bar. That is, the electrode plate 33 is elastically supported by the first elastic connecting member 32 with respect to the fixed portion 31, and the movable plate 35 is elastically connected to the electrode plate 33 by the second elastic connecting member 34. Therefore, the electrode plate 33 and the movable plate 35 are tilted by the bending of the elastic connecting members 32 and 34, respectively, and form a bending vibration system having two degrees of freedom.
The operation in this vibration system is substantially the same as that in the case of the dynamic model shown in FIG. 3, and a description thereof will be omitted.

In both of the above embodiments, a case has been described in which a voltage is applied between the electrode plates 23 and 33 and the fixed electrode to apply an electrostatic force to the electrode plates. By forming a fixed electrode side on the glass substrate 10 with a coil as a plate, a means such as driving a driving plate corresponding to the electrode plate with an electromagnetic force may be employed to apply a periodic external force. .

[0024]

As described above in detail, according to the two-degree-of-freedom vibration type microactuator of the present invention, the driving part driven by voltage application and the movable part are separated to form a two-degree-of-freedom vibration system. With the anti-resonance frequency of the two-degree-of-freedom vibration system
Since the driving plate is driven, the displacement of the driving plate can be made sufficiently small to enable low-voltage driving, and at the same time, the displacement of the movable plate can be increased. That is, in a two-degree-of-freedom vibration system, the magnitude of the amplitude displacement of the movable part is not restricted by the driving part, and the amplitude displacement of the movable part can be increased as compared with the one-degree-of-freedom vibration system. A microactuator with a large range can be obtained.

[Brief description of the drawings]

FIG. 1 is an exploded perspective view showing an embodiment of a two-degree-of-freedom vibration type microactuator according to the present invention.

FIG. 2 is a cross-sectional view of a main part of the embodiment.

FIG. 3 is a perspective view showing a dynamic model of the embodiment.

FIG. 4 is a graph showing a resonance curve of an electrode plate and a movable plate in the same example.

FIG. 5 is a perspective view showing a dynamic model according to another embodiment of the present invention.

FIG. 6 is a perspective view showing a configuration of a conventional one-degree-of-freedom torsional vibrator.

[Explanation of symbols]

 18 fixed electrode, 21, 31 fixed part, 22, 24 torsion bar, 23, 33 electrode plate, 25, 35 movable plate, 32, 34 elastic connecting member.

Claims (1)

(57) [Claims] The method according to claim 1] periodic electrostatic force is applied as an external force drive plate, it is elastically supported by the fixed portion through the first elastic coupling member, via a second elastic coupling member to the drive plate movable plate elastically coupled to, elastically displaced in each of the elastic coupling member to the drive plate and the movable plate 2 to form the freedom of the vibration system, the natural frequency of the drive plate system the number of excitation vibration by the external force Anti-resonance vibration of two-degree-of-freedom vibration system
2. A vibration system driven by the number of rotations is formed.
Freedom vibration type micro actuator.