Optical scanner

Details Optical scanner Optical scanner

1998-12-16

2001-02-13

Phan, James (Department: 2872)

Optical: systems and elements

Deflection using a moving element

By moving a reflective element

C359S198100, C359S199200, C359S223100

Reexamination Certificate

active

06188504

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to an optical scanner which reflects light from a light source and scans the reflected light.
<First Prior Art>
As a conventional optical scanner, Jpn. Pat. Appln. KOKAI Publication No. 63-82165 discloses an optical scanner having an arrangement like the one shown in
FIGS. 45A and 45B
, i.e., a deflector
300
.
As shown in
FIG. 45B
, the deflector
300
includes a large york
328
, a coil
329
wound around the york
328
, and an optical deflecting element
310
placed in the space inside the york
328
.
As shown in
FIG. 45A
, the optical deflecting element
310
includes a mirror
312
, a driving coil
311
, and ligaments
313
and
314
. These components are integrally formed and supported by a support frame
315
.
In the deflector
300
, the ligaments
313
and
314
are twisted by the force exerted on the driving coil
311
owing to the interaction between a current flowing in the driving coil
311
and a magnetic field generated by the york
328
and the coil
329
. As a result, the mirror
312
is vibrated at a predetermined frequency.
Light is irradiated on the mirror
312
, and the reflected light is scanned one-dimensionally.
<Second Prior Art>
As another conventional optical scanner, Jpn. Pat. Appln. KOKAI Publication No. 6-46207 discloses an optical scanner designed to vibrate its reflecting surface by using a piezoelectric element.
As shown in
FIG. 46
, in this optical scanner, a cantilever constituted by a carrier material
2
and an electrode
3
is supported on a silicon substrate
1
.
This cantilever constitutes a unimorph piezoelectric actuator
6
. The unimorph piezoelectric actuator
6
is manufactured by sequentially forming the carrier material
2
and the electrode
3
on the upper surface of the silicon substrate
1
, and forming a space
7
by etching.
A strain gage
9
is placed on the cantilever. Another strain gage
10
is placed at the fixed end of the cantilever.
The strain gage
9
is used to measure the deformation amount of the unimorph piezoelectric actuator
6
. The strain gage
10
is used to obtain a reference signal for the measuring operation.
According to this optical scanner, the deformation-free distal end portion of the cantilever functions as a reflecting surface, on which light is irradiated.
The cantilever is vibrated by the unimorph piezoelectric actuator
6
. As a result, light reflected by the distal end portion of the cantilever is scanned one-dimensionally.
The optical scanner as the first prior art disclosed in Jpn. Pat. Appln. KOKAI Publication No. 63-82165 requires the large york
328
and the coil
329
to obtain a sufficient driving force. The overall structure of this device is large.
Recently, demands have arisen for compact optical scanners. However, as the overall size of a scanner is reduced to meet such demands, the driving force is reduced, and hence the deflection angle of a scan beam becomes insufficient. In addition, this scanner requires a cumbersome mechanical assembly process.
The optical scanner as the second prior art disclosed in Jpn. Pat. Appln. KOKAI Publication No. 6-46207 is smaller in size than the above optical scanner. However, the deflection angle of a scan beam is not large enough to meet the future demands.
In addition, as the electric elements of this optical scanner, e.g., the electrode
3
and the electrodes of the strain gages
9
and
10
are exposed, no countermeasures are taken against aging. That is, a problem is posed in terms of maintenance of stable performance.
<Third Prior Art>
Still another known compact optical scanner includes a vibration input portion formed by bonding a scan portion for reflecting light, an elongated elastic deformation portion, and a piezoelectric actuator. The reflecting portion is vibrated two-dimensionally by the piezoelectric actuator to scan light.
Such an optical scanner is disclosed, for example, in Jpn. Pat. Appln. KOKAI Publication No. 5-100175.
FIGS. 47A and 47B
show the structure of a silicon substrate
1
disclosed in Jpn. Pat. Appln. KOKAI Publication No. 5-100175.
This optical scanner
1
comprises a thin plate
6
and a piezoelectric actuator
21
.
On the plate
6
, a vibration input portion
5
, an elastic deformation portion
2
, a scan portion
3
, and a weight portion
3
W are integrally formed.
The piezoelectric actuator
21
is formed by bonding a strain conversion element
23
to a multilayered piezoelectric element
22
.
The scan portion
3
has a mirror surface
4
for reflecting a light beam.
In the optical scanner
1
having the above structure, when a voltage is applied to the piezoelectric actuator
21
bonded to the vibration input portion
5
to vibrate the vibration input portion
5
, the elastic deformation portion
2
resonates, and the scan portion
3
pivots about an axial center P in
FIG. 47A
within the range of an angle &thgr;
T
. At the same time, the scan portion
3
pivots about an axial center Q in
FIG. 47B
within the range of an angle &thgr;
B
.
In this case, the piezoelectric actuator
21
vibrates the vibration input portion
5
in a vibration mode in which vibrations having a resonant frequency of a torsional deformation mode are superimposed on vibrations having a resonant frequency of a bending deformation mode. As a result, the torsional deformation mode and the bending deformation mode are amplified by the elastic deformation portion
2
, and the torsional vibrations and the bending vibrations are synthesized at the scan portion
3
.
In the optical scanner
1
having the above structure, two-dimensional optical scanning is realized by controlling the voltage applied to the piezoelectric actuator
21
using a driving circuit (not shown).
<Fourth Prior Art>
Still another known compact optical scanner uses a silicon semiconductor substrate and a helical torsion spring. This optical scanner uses an optical deflecting element for scanning light by swinging a reflector using an electromagnetic force.
Such an optical scanner is disclosed, for example, in “TECHNICAL DIGEST OF THE SENSOR SYMPOSIUM”, 1995, pp. 17-20.
FIGS. 48A and 48B
show the structure of the optical scanner disclosed in this reference.
This optical scanner has a reflector
34
and helical torsion springs
33
, formed on a silicon semiconductor substrate
31
, together with a fixing frame
50
for supporting them. These components are integrated into an optical deflecting element.
Flat coils
35
are arranged around the peripheral portion of the reflector
34
. The flat coils
35
are electrically connected to electrodes
36
on the fixing frame
50
through the helical torsion springs
33
.
In addition, circular permanent magnets
38
are located through a spacer insulating substrate
40
such that the direction of magnetization of each permanent magnet
38
is parallel to the reflector
34
and makes an angle of about 45° with the axial direction of the helical torsion spring
33
.
When an AC current is applied to the flat coil
35
, a Lorentz force is generated therein owing to the interaction between the current and the magnetic field generated by the permanent magnet
38
.
This Lorentz force causes the reflector
34
to swing in the twisting direction of the helical torsion spring
33
.
When a current having the same frequency as the resonant frequency defined by the elastic properties of the helical torsion spring
33
and the mass and center of gravity of the reflector
34
is applied to the flat coil
35
, the maximum amplitude at the current value can be obtained.
In this case, the reflector
34
is vacuum-sealed to reduce the damping coefficient.
Referring to
FIGS. 48A and 48B
, reference numeral
39
denotes a gas absorbent;
41
, a front cover insulating substrate;
42
, a lower surface insulating substrate and
32
, a movable plate.
In the third and fourth prior-art techniques, there is no description concerning the durability of electric elements such as wiring layers for the optical scanner which vibrates at large deflection angles. Moreover, in the

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