Optical: systems and elements – Deflection using a moving element – By moving a reflective element
Reexamination Certificate
2000-04-27
2001-07-17
Phan, James (Department: 2872)
Optical: systems and elements
Deflection using a moving element
By moving a reflective element
C359S223100, C359S198100, C359S199200
Reexamination Certificate
active
06262827
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electrostatically driven galvano-mirror used in e.g. an optical disk apparatus for controlling the direction of light emission.
2. Description of the Related Art
A typical electrostatically driven galvano-mirror is disclosed in e.g. “Silicon Torsional Scanning Mirror (IBM J. RES. and DEVELOP., Vol. 24, No. 5, September 1980)”. As shown in
FIGS. 12 and 13
of the accompanying drawings, the conventional galvano-mirror is provided with a lower substrate
100
and an upper substrate
102
bonded to the lower substrate
100
. The upper substrate
102
includes a frame
104
, a mirror element
106
(formed with a mirror surface
106
a
), and two torsion bars
108
connecting the mirror element
106
to the frame
104
.
With such an arrangement, the mirror element
106
is deflected in a torsional movement about the torsion bars
108
upon application of external forces to the mirror element
106
. The mirror element
106
has a bottom surface on which a pair of first electrodes
110
a,
110
b
are formed. Correspondingly, the lower substrate
100
is provided with a pair of second electrodes
112
a
and
112
b
facing the first electrodes
110
a
and
110
b,
respectively. The lower substrate
100
is formed integrally with a ridge
100
a
contacting with the mirror element
106
. The ridge
100
a
extends along the aligned axes of the torsion bars
108
.
When voltage is applied across the first electrode
110
a
and the second electrode
112
a,
the mirror element
106
is rotated counterclockwise in
FIG. 13
by electrostatic force. When voltage is applied across the other first electrode
110
b
and the other second electrode
112
b,
the mirror element
106
is rotated clockwise. Such electrostatic force is proportional to the area of the respective electrodes. Thus, for actuating the mirror element
106
with a low voltage, the area of the first electrodes
110
a,
110
b
needs to be large, which may cause the electrodes
110
a,
110
b
to cover almost the entirety of the lower surface of the mirror element
106
. The size of the second electrodes
112
a,
112
b
is determined in correspondence to the size of the first electrodes
110
a,
110
b.
In the conventional galvano-mirror described above, the mirror element
106
in motion tends to be subject to unfavorable damping due to the viscosity of the air present between the mirror element
106
and the lower substrate
100
. Consequently, it is difficult to properly control the movement of the mirror element
106
.
For reducing such viscous air-damping, the lower substrate
100
may be formed with a plurality of grooves facing the mirror element
106
, as taught in JP-A-9(1997)-146034 for example. However, the additional processing of such grooves may make the fabrication procedures of the galvano-mirror disadvantageously complex. As a result, the production efficiency is lowered, while the cost is unduly increased.
Another problem of the conventional galvano-mirror of
FIGS. 12 and 13
is that the mirror element
106
may be displaced sideways upon application of voltage across the first electrode
110
a
and the second electrode
112
a
(or across the other first electrode
110
b
and the other second electrode
112
b
). The mirror element
106
is moved in this manner since the electrostatic force generated by the voltage application has a horizontal component acting on the mirror element
106
. Such sideways displacement may render the posture of the mirror element
106
unpredictable. Thus, desired control accuracy in operating the mirror element
106
may be unobtainable.
The above-described sideways displacement of the mirror element
106
may be reduced by attaching the mirror element
106
to the ridge
100
a
in a deflectable manner, as taught by JP-A-5(1993)-119280. Specifically, the bottom surface of the mirror element
106
may be formed with a groove into which the top of the ridge
100
a
is received. The drawback of this arrangement is that the production cost tends to be increased because it is necessary to precisely form the groove in the mirror element
106
at the right position. The ridge
100
a
also needs to be formed and positioned accurately.
SUMMARY OF THE INVENTION
The present invention has been proposed under the circumstances described above, and its object is to provide a galvano-mirror in which the occurrence of viscous air-damping is reliably prevented. The galvano-mirror is also advantageous in minimizing an increase in production cost.
Another object of the present invention is to provide a galvano-mirror in which the sideways displacement of the mirror element is reliably prevented by taking inexpensive countermeasures.
According to a first aspect of the present invention, there is provided a galvano-mirror comprising:
a mirror substrate including a frame, a mirror element and torsion bars rotatably connecting the mirror element to the frame, the mirror element being provided with a body having an obverse surface and a reverse surface, the mirror element being also provided with a mirror surface formed on the obverse surface and first electrodes formed on the reverse surface; and
an electrode substrate provided with second electrodes arranged in facing relation to the first electrodes;
wherein the electrode substrate is formed with a through-hole extending through a thickness thereof and facing the mirror element.
With such an arrangement, the through-hole of the electrode substrate permits freer flow of the air which would otherwise be trapped between the mirror element and the electrode substrate. Thus, the problem of the air-damping is advantageously overcome.
In a preferred embodiment, the second electrodes are arranged adjacent to the through-hole.
Preferably, the galvano-mirror may further comprise stoppers for preventing the first electrodes from contacting with the second electrodes.
According to a second aspect of the present invention, there is provided a galvano-mirror comprising:
a mirror substrate including a frame, a mirror element and torsion bars rotatably connecting the mirror element to the frame, the mirror element being provided with a body having an obverse surface and a reverse surface, the mirror element being also provided with a mirror surface formed on the obverse surface and first electrodes formed on the reverse surface;
an electrode substrate formed with second electrodes facing the first electrodes;
third electrodes formed on the obverse surface of the mirror element; and
a supporting structure provided with fourth electrodes facing the third electrodes.
With such an arrangement, unfavorable sideways displacement of the mirror element is effectively prevented by canceling out the opposite components of the electrostatic forces acting on the mirror element. In this manner, there is no need to accurately process and position a ridge member to be formed in the electrode substrate for holding the mirror element in place.
In the galvano-mirror of the second aspect again, the electrode substrate may be formed with a through-hole extending through a thickness thereof and facing the mirror element.
The above-mentioned through-hole may be generally symmetrical with respect to axes of the torsion bars. Further, the second electrodes may comprise two conductive layers which are arranged close to the through-hole and symmetrical with respect to the axes of the torsion bars.
Specifically, the through-hole may be rectangular, elliptic, circular or the like.
Preferably, the first electrodes, the second electrodes, the third electrodes and the fourth electrodes may comprise two conductive layers, respectively, which are arranged symmetrically with respect to axes of the torsion bars. This means that the first electrodes may comprise two conductive layers symmetrical with respect to the axes of the torsion bars, the second electrodes may also comprise other two conductive layer symmetrical with respect to the axes of the torsion bars, and so on.
In a preferred embodiment, the two conductiv
Okuda Hisao
Ueda Satoshi
Armstrong Westerman Hattori McLeland & Naughton LLP
Fujitsu Limited
Phan James
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