Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
1998-01-23
2001-09-11
Phan, James (Department: 2872)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C359S213100, C359S214100, C359S223100, C359S224200
Reexamination Certificate
active
06288816
ABSTRACT:
TECHNICAL FIELD
The present invention is directed to a miniature optical scanner for a one or two axis scanning system and more particularly to a miniature optical scanner having stationary magnets and stationary drive coils to raise the resonant frequency of the system, the resonant frequency being manually tunable and automatically adjustable to compensate for variables causing frequency drift. The scanning system includes a multiplying mirror to substantially increase the optical scan angle of the optical scanner. Further, a second optical scanner may be used as the multiplying mirror to provide a two axis scan with substantially increased optical scan angles for both axes.
BACKGROUND OF THE INVENTION
Optical resonant scanners of various types are known but are in general not suitable for use in applications such as a head mounted display system that requires the scanners to be very small so that they may be comfortably supported on a user's head. Scanners used in such systems must also be operable at a high frequency of resonance such as 20 khz. One type of known optical resonant scanner includes moving magnets as part of an electro-magnetic circuit for oscillating a scanning mirror. However, because the magnets move, these scanners have a higher rotational inertia than desirable making it difficult to attain a sufficiently high resonant frequency for many applications.
SUMMARY OF THE INVENTION
In accordance with the present invention, the disadvantages of prior optical resonant scanners and multiple axis scanning systems have been overcome. The optical scanner of the present invention is a miniature optical resonant scanner capable of operating at very high frequencies. This miniature optical scanner is used with a multiplying mirror to provide a scanning system with an output optical scan angle that is substantially larger than the optical scan angle of the optical scanner itself. Further, a second optical scanner may be used as the multiplying mirror to provide a two axis scan with substantially increased optical scan angles for both axes while minimizing the size and weight of the overall system. The optical scanner and optical scanning system of the present invention have numerous uses such as in head mounted display systems, video displays in general, cameras, bar code readers, ophthalmological devices, etc.
More particularly, the miniature optical scanner of the present invention includes a ferromagnetic base with first and second stator poles formed thereon. The first and second stator poles are generally parallel to each other. Each stator pole includes a respective stator coil wound thereabout to produce magnetic fields in the stators of opposite polarity in response to a drive signal applied to each coil. First and second magnets are disposed on the base of the scanner on opposite sides of the first and second stators such that the magnets are equidistant to the first and second stators. The optical scanner also includes a thin metal spring plate having first and second support portions that rest respectively on the first and second magnets. The spring plate also includes a centrally located mirror mounting portion disposed above the stators, the mirror mounting portion having an axis of rotation that is equidistant to the stator poles. A mirror is formed on the mirror mounting portion of the spring plate so that when an alternating drive signal is applied to the first and second stator coils, magnetic fields are created that oscillate the mirror about the axis of rotation of the spring plate's mirror mounting portion. This oscillating mirror scans light incident thereto relative to a first axis.
This optical scanner may be made very small, having dimensions, for example, that are less than two centimeters in diameter or width and length, and less than one centimeter in height. Further, because the mass of the moving parts in the scanner is minimized and is as close to the axis of rotation as possible, the rotational inertia of the scanner is minimized. Thus, the optical scanner of the present invention has a high resonant frequency such as on the order of 24 khz.
The optical scanner of the present invention includes means for manually adjusting the resonant frequency of the scanner. Further, the scanner also includes means for automatically varying the amount of tension in the spring plate to maintain the resonant frequency constant. Thus, the tension in the spring plate can be automatically adjusted to accommodate for variations in temperature and other factors which if not compensated for would alter the resonant frequency of the scanner.
In accordance with another feature of the present invention the optical scanner may be disposed in a housing forming a vacuum chamber so as to minimize problems with loss of energy, air turbulence and noise when operating at high speeds. The housing may also be formed with a scanning window to allow light to enter the housing and be reflected out from the housing by the scanning mirror. The scanning window is disposed in the housing at an angle with respect to the mirror when the mirror is in its rest position to minimize the effect of reflections from the housing window.
These and other objects, advantages and novel features of the present invention, as well as details of an illustrated embodiment thereof, will be more fully understood from the following description and from the drawing.
REFERENCES:
patent: 3532408 (1970-10-01), Dostal
patent: 4187452 (1980-02-01), Knappe et al.
patent: 5009473 (1991-04-01), Hunter et al.
patent: 5268784 (1993-12-01), Chaya
patent: 5428473 (1995-06-01), Takizawa et al.
Furness, III Thomas A.
Johnston Richard S.
Kollin Joel S.
Melville Charles D.
Tidwell Michael R.
McAndrews Held & Malloy Ltd.
Phan James
University of Washington
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