Registers – Coded record sensors – Particular sensor structure
Reexamination Certificate
1998-03-06
2001-03-27
Tremblay, Mark (Department: 2876)
Registers
Coded record sensors
Particular sensor structure
C235S462320
Reexamination Certificate
active
06206290
ABSTRACT:
BACKGROUND AND OBJECTS OF THE INVENTION
1. Field of the Invention
The present invention relates to light scanning systems for reading data. In preferred embodiments the invention is useful in compact moving spot scanning systems for reading bar code symbols.
2. Description of Related Art
Various optical scanning systems have been developed for reading bar code symbols. In many such systems a laser spot is swept across the bar code. The bar code symbols reflect or absorb the incident light. A photo detector receives reflected light and produces a signal from which the data is obtained. Normally, in such systems the laser spot scans the bar code symbols in such a way that it crosses all of the bars and spaces which make up the code. These various optical scanning systems require apparatus for sweeping the spot across the bar code symbol.
For this purpose, it is known to use a stationary source of light, a scanning mirror and a driver to repetitively oscillate the mirror, so that an incident light beam from the source is repetitively swept through an angular distance at a rate, for example, of tens of oscillations per second. Such a system is shown, for example, in U.S. Pat. No. 4,816,660 to Swartz et al. An electric motor may be used to drive the mirror. Alternatively, a swept beam may be produced by a semi conductor laser whose output beam is directed by a piezoelectric driver. Such a system is shown in U.S. Pat. No. 5,625,483 to Swartz et al. Magnetic fields may also be used to drive small mirror elements.
In motor driven mirror scanning systems, conventional motor controls are used to insure the appropriate scanning. In these systems, the components, such as photo diodes, mirrors, motor parts and control circuits are separately manufactured and then assembled. The components must be accurately aligned for proper operation. These production steps are costly. Use of a micro machined permits partial or total integration of the scanner into a miniature package with components formed on one or a few substrates. However, in a system based on the use of a driven, micro machined scanner element, there is the need to insure the proper movement of the scanner in a way which is compatible with the micro machined parts in terms of size and structure, and in terms of the manufacturing steps used to make the micro machined parts.
Micro machined scan mirrors have been described in prior art literature. However, there are unique challenges in designing a scan mirror for bar code scanning. In particular, the mirror is advantageously several millimeters on each side to accommodate the scan beam. Handheld bar code scanners operate at very low frequencies, scan large angles, and need to survive large shock loads. The mirrors may be operated at resonance in order to reduce power consumption. Low resonant frequency dictates a large mass on relatively weak suspension, which makes it difficult to provide the required shock resistance. Another important requirement is low cost.
A micro machined mirror for scanning a light beam is disclosed in U.S. patent application Ser. No. 08/483,163 filed Jan. 7, 1995 to Swartz et al. entitled AN INTEGRATED SCANNER ON A COMMON SUBSTRATE, which is hereby incorporated by reference. In this system, the mirror may be driven by various techniques including electrostatic actuation, electromagnetic actuation, and heat actuation. However, such mirrors are difficult to operate due to the high Q of the mechanical system and the drive requirements for such a system.
OBJECTS OF THE INVENTION
Accordingly, it is an object of the present invention to provide a simply and inexpensively fabricated miniature light beam scanner having an accurately controlled, moving optical component, such as a mirror.
It is a further object of the present invention to provide a simple and accurate system for sensing the position of a moving, micro machined optical element in a light beam scanner.
It is a further object of the present invention to provide a system for controlling at least one of the amplitude and frequency of a moving optical element in a light beam scanner.
It is a further object of the present invention to provide a system for controlling a micro machined, resonant mirror for hand-held bar code readers.
These and other objects and features of the present invention will be apparent from this written description and drawings.
SUMMARY OF THE INVENTION
A light beam scanner is controlled to direct a light beam to move in a predetermined pattern such as a back and forth pattern traversing a symbol to be read. The scanner includes an optical element, such as a micro machined mirror, at least a portion of which is moveable in relation to a supporting substrate and/or a light source.
An electrically actuated driver applies a driving force to the optical element. In a preferred embodiment, the electrically actuated driver is a driving electrode located proximate to the mirror and a voltage controlled power supply, which together provide an electrostatic driving force.
A sensor detects movement of the optical element, for example by detecting variations in the capacitance between a pick-up electrode and the mirror caused by motion of the mirror. In preferred embodiments, a carrier signal is applied to the mirror, and a varying voltage signal is induced in the pick-up electrode containing information concerning the amplitude and phase of the movement of the optical element relative to the pick-up electrode.
Feed back circuitry controls the electrically actuated driver to drive the optical element at a resonant frequency and predetermined amplitude.
A related method is disclosed for controlling a moving optical element, which involves applying a periodically varying electrostatic force to the optical element to vary its position, sensing the position of the mirror, and modifying the applied electrostatic force in response to the sensed mirror position.
A scanner element of a preferred embodiment of the present invention includes an optical element, which provides a light beam having direction which varies as the element moves. In a preferred embodiment, the optical element is a micro machined mirror suspended for torsional oscillation on a pair of conductive hinges. One or more electrodes are formed on the substrate adjacent the optical element to apply an electrostatic driving force to the optical element and to sense the position of the element.
The subject matter of the invention is set out with particularity in the appended claims.
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Breng et al, Electrostatic Micromechanic Actuators, J. Micromech. Microeng. 2 (1992) pp. 256-261.
K.E. Peterson, Silicon Torsional Scanning Mirror, IBM J. Res. Develop. 24, pp. 631-637 (Sep., 1980).
DiFazio Constanzo
Giebel James
Goren David
Mazz Thomas
Stern Mik
Burns Doane , Swecker, Mathis LLP
Symbol Technologies Inc.
Tremblay Mark
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