Electricity: measuring and testing – Measuring – testing – or sensing electricity – per se – Using radiant energy
Patent
1995-09-26
1998-06-16
Karlsen, Ernest F.
Electricity: measuring and testing
Measuring, testing, or sensing electricity, per se
Using radiant energy
359198, G01R 1338, G02B 2610
Patent
active
057676666
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a mirror galvanometer suitable for example for laser beam scanning systems and the like, and in particular to an ultra small planar type mirror galvanometer with the capability of detecting the displacement of a reflecting mirror for scanning a laser beam, and its method of manufacture.
BACKGROUND ART
Mirror galvanometers are used for example in laser scanners which deflection scan a laser beam, operating on the theory that when an electrical current is passed through a movable coil arranged in a magnetic field, an electromagnetic force is generated due to the interaction between the electrical current and the magnetic flux, producing a rotational force (torque) proportional to the electrical current. The construction involves a device using galvanometer theory where a movable coil rotates to an angle where the torque and a spring force are in equilibrium, the presence or absence and size of a current being detected by an indicator needle swung by the movable coil. However instead of the indicator needle a reflecting mirror is provided on a member which rotates with the movable coil.
In practice mirror galvanometers use for example a movable piece of iron instead of the movable coil arranged in a magnetic field , with a magnetic path formed around the periphery by means of a magnetic body involving two permanent magnets and four magnetic poles. The magnetic flux between the poles is altered by changing the size and direction of a current flowing in a drive coil wound around the magnetic body, so that a reflecting mirror is swung by the movable piece of iron, to thus deflection scan a laser beam (see for example "Practical Laser Technics", Kyoritsu Publishing Company, Dec. 20 1987, p. 210-212).
With the mirror galvanometer of this construction however, miniaturization is difficult due for example to the drive coil being mechanically wound.
A technique for miniaturization of a mirror galvanometer is disclosed for example in Japanese Unexamined Patent Publication No. 4-211218.
With this technique, a frame portion, a reflecting mirror portion and a beam portion for axially supporting the reflecting mirror portion on the frame portion, are formed integrally together by means of a semiconductor manufacturing process using a silicon substrate. The portions formed on the silicon substrate are arranged on a glass substrate which is provided with an electrode for rotating the reflecting mirror portion, the construction being such that the reflecting mirror is rotated by electrostatic attraction acting between the reflecting mirror and the electrode. The beam portion is formed in an S shape enabling a long beam having a small torsional rigidity to be formed in a small space, the purpose being to enable drive of the planar portion with a small drive force without detracting from miniaturization of the mirror galvanometer.
With the mirror galvanometer, the mirror displacement angle is usually controlled by an open loop, however high accuracy control of the mirror displacement angle is possible by detecting the mirror displacement angle and feeding back the displacement signal to the mirror drive system. Methods which have been considered for detecting the displacement angle of the mirror in the abovementioned planar type mirror galvanometer involve for example an optical method as shown in FIG. 1 or a capacitance type method as shown in FIG. 2.
With the optical method of FIG. 1, a light beam, for example from an optical fibre 53, is impinged centrally onto the rear face of a reflecting mirror 52 which rotates about a shaft 51, and the reflected light is received by a PSD 55 provided on a glass substrate 54. The displacement angle .phi. of the reflecting mirror 52 is detected by detecting a change in an incident location X of the reflected light on the PSD 55 with angular displacement of the reflecting mirror 52. The incident location X can be expressed as X=L/tan (.theta.+.phi.) where L is the distance from the glass substrate 54 to the reflecting mirror 52 in a leve
REFERENCES:
T. Hirai, "Deflection by a Galvano-Scanner", Practical Laser Techniques, pp. 210-213 (1987).
Asada Norihiro
Esashi Masayoshi
Karlsen Ernest F.
The Nippon Signal Co., Ltd
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