Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
2000-06-28
2001-09-04
Schuberg, Darren (Department: 2872)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C359S196100, C359S224200, C310S036000
Reexamination Certificate
active
06285485
ABSTRACT:
TECHNICAL FIELD
This invention pertains to scanners for controlling the direction of propagation of a light beam, particularly to micro-mechanical scanners for controlling the direction of propagation of a light beam.
BACKGROUND ART
Scanners are used to control the direction of propagation of a light beam. Scanners are frequently found in devices such as laser printers and bar-code readers. The three general categories of previous scanner devices are mechanical, electro-optical, and ultrasonic devices. The most commonly used devices have been mechanical scanners, which are based upon a mirror or set of mirrors attached to the turning axis of an electromagnetic actuator such as a galvanometer or electric motor. Limitations of prior mechanical scanners include their relatively large size, high power consumption, and limited scanning frequencies. Prior galvanic scanners are typically 20×20×50 mm or larger, with a mass exceeding 50 grams (excluding control electronics), a typical power consumption of 1 Watt, and a scanning frequency below 8 kHz. Prior rotating polygon scanners (a type of mechanical scanner employing mirror-faced polygons attached to the rotating axis of an electric motor) are typically 100×100×90 mm or larger (excluding control electronics), with a typical power consumption of 5 Watts or more, and a scanning frequency below 10 kHz.
Prior electro-optical and ultrasonic devices are expensive, have limited deflection angles, and experience high attenuation of reflected light beams. Their scanning frequencies can be higher, however, in the MHz range.
Micro-electromechanical scanners based on electrostatic actuation of a moving mirror have been reported, but these devices have achieved only small deflection angles and low efficiencies as compared to electromagnetic devices of approximately the same resonance frequency and size. See K. Petersen, “Silicon Torsional Scanning Mirror,”
IBM J. Res. Develop.
, vol. 24, pp. 631-637 (1980); and K. Gustafsson et al., “A Silicon Light Modulator,”
J. Phys. E: Sci. Instrum.
, vol. 21, pp. 680-685 (1988). These references demonstrated that, while silicon is an excellent structural material for manufacturing a monolithic resonant scanning mirror with very good fatigue resistance (i.e., with a long working lifetime), electrostatic actuation was inefficient for millimeter-scale devices, producing mechanical deflection angles of only about 2°.
The present inventor has previously reported micro-mechanical scanners using electromagnetic actuation via a coil attached to a rotor, where the coil was electrically connected to an external power supply. The interaction between a constant external magnetic field and the electric current flowing in the coil generated a torque that deflected the rotor of millimeter-scale devices to mechanical deflection angles of 10°. These prior devices experienced mechanical fatigue in the conductive tracks used to supply electric power to the moving coil after 100 hours of operation at 1 kHz and 10° peak-to-peak mechanical deflection of the mirror. These fatigue problems limited the utility of these devices. L. Ferreira, “Microscanner de Silício” (in Portuguese), doctorate thesis presented at Universidade Estadual de Campinas, Campinas, São Paulo, Brazil (1994); L. Ferreira et al., “Micromechanical Galvanometric Light Beam Scanner,”
Proc.
1996
Science and Technology Workshop, Center for Advanced Microstructures and Devices
, Baton Rouge, La. (April 1996); laid-open Brazilian patent application number 9500860-8 (in Portuguese), filed Feb. 21, 1995.
DISCLOSURE OF INVENTION
A micro-electromechanical scanner has now been discovered for the efficient, controlled deflection of light beams. The novel device may be built on a micro-mechanical scale, and comprises a moving rotor, a suspension system, and a stator. The rotor comprises a closed-circuit coil and a mirror. Mechanical deflection angles of 10° or more may be achieved, corresponding to optical deflection angles (i.e., the deflection angle of the scanned light beam) of 20° or more. The suspension system may be, for example, a set of torsion bars on which the rotor is mounted. The stator may be, for example, a rectangular frame holding the suspension system. When placed in a constant magnetic field and excited by a magnetic field that causes a change in the magnetic flux through the rotor's coil, the rotor oscillates at the frequency of the exciting magnetic field. The exciting magnetic field may be a constant direction, amplitude-modulated magnetic field generated, for example, from an inductor; or the exciting magnetic field may be generated, for example, by a magnetic circuit such as is shown in
FIG. 3
(discussed below). Mechanical scanning oscillation frequencies of 10 kHz, 12 kHz, 15 kHz, 20 kHz, or higher may be achieved.
All else being equal, the highest deflection angles occur at the natural mechanical resonance frequency of the rotor-suspension combination. A light beam reflected from the rotor's mirror is deflected at twice the deflection angle of the rotor. A prototype device has been constructed, measuring 12×25×9 mm, with a power consumption less than 1 Watt, and exhibiting a mechanical deflection angle of 0.4 degrees peak-to-peak at an oscillation frequency of 1606 Hz when excited by an external coil carrying a sinusoidal current of 100 mA and immersed in a static magnetic field of 550 gauss. The deflection angle may be increased, for example, by increasing the strength of the constant magnetic field, or by increasing the strength of the alternating magnetic field, or both. Compared to conventional devices, the novel device can be smaller, can be less expensive, can consume less power, and may exhibit higher deflection angles over a given time scale than other micromechanical devices operating on different actuation principles. The novel device may be used, for example, to replace the scanning devices currently used in laser printers, laser bar-code readers, and laser image projectors (e.g., large screen televisions). The control electronics may optionally be manufactured on the same chip as the device, eliminating the need for a separate controller and further reducing costs.
The novel inductive microscanner overcomes the fatigue problem of the inventory's prior micro-mechanical scanner by eliminating the power supply tracks entirely, while still maintaining the strong deflection torque desirable in millimeter-scale devices. Electric power is delivered to the moving coil by electromagnetic induction generated by an external coil or other magnetic circuit.
Less preferably, the closed coil could be replaced by a continuous area of a conductive material (such as the interior of a rectangle), as an alternating magnetic field will still induce a current in such a continuous area, albeit less efficiently.
Another alternative is to replace the alternating magnetic field with a magnetic field that rotates through a limited angle around the rotor, producing a change in the magnetic flux through the rotor's coil and inducing a current in the coil.
In another alternative, the electric circuits and magnetic fields may be eliminated, and the rotational driving force may be provided by acoustic waves.
REFERENCES:
patent: 5606447 (1997-02-01), Asada et al.
patent: 9500860-P (1995-02-01), None
Bassous, E., “Fabrication of Novel Three-Dimensional Microstructures by the Anisotropic Etching of (100) and (110) Silicon,” IEEE Trans. on Electron. Devices, vol. ED-25, pp. 1178-1185 (1978).
Bean, K., “Anisotropic Etching of Silicon,” IEEE Trans. on Electron. Devices, vol. ED-25, pp. 1185-1193 (1978).
Ferreira, L., “Microscanner de Silício,” (in Portuguese), doctoral thesis presented at Universidade Estadual de Campinas, Campinas, São Paulo, Brazil (1994) (with partial translation).
Ferreira, L. et al., “Micromechanical Galvanometric Light Beam Scanner,” Proc. 1996 Science and Technology Workshop, Center for Advanced Microstructures and Devices, Baton Rouge, Louisiana (Apr. 1996).
Gustafsson, K. et al., “A
Board of Supervisors of Louisiana State University and Agricultu
Runnels John H.
Schuberg Darren
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