Registers – Coded record sensors – Particular sensor structure
Reexamination Certificate
2001-04-13
2003-11-25
Lee, Michael G. (Department: 2876)
Registers
Coded record sensors
Particular sensor structure
C235S462330, C235S462340, C235S462350
Reexamination Certificate
active
06651886
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to optical code readers using holographic optical elements, especially optical code readers having input or output optical paths which include one or more electrically switchable systems including holographic optical elements for modifying the optical characteristics of the code reader, for example, to modify the field of view of the code reader.
BACKGROUND AND OBJECTS
Optical Code Readers
Optical code readers are known in the prior art for reading various symbologies such as UPC bar code symbols appearing on a label or on the surfaces of an article. The optical code symbol itself maybe a bar code pattern of indicia comprised of a series of bars of various widths spaced apart from one another to bound spaces of various widths, the bars and spaces having different light reflecting characteristics. The readers in scanning or imaging systems electro-optically transform the graphic indicia of a target symbol into electrical signals, which are decoded into information, typically descriptive of the article or some characteristic thereof. Such information is conventionally represented in digital form and used as an input to a data processing system for applications in point-of-sale processing, inventory control and the like. Optical code readers are of two general types: scanning laser beam code readers and imaging code readers.
In the laser beam scanning systems known in the art, the laser light beam is directed by a lens or other optical components along the light path toward a target that includes a bar code symbol on the surface. The moving-beam scanner operates by repetitively scanning the light beam in a line, pattern or series of lines across the symbol by means of motion of a scanning component, such as the light source itself or a mirror disposed in the path of the light beam. The scanning component may either sweep the beam spot across the symbol and trace a scan line across the pattern of the symbol, or scan the field of view of the scanner, or both.
Optical code reading systems also include a sensor or photo detector which detects light reflected or scattered from the symbol. The photo detector or sensor is positioned in the scanner in an optical path so that it has a field of view which ensures the capture of a portion of the light which is reflected or scattered off the symbol. This light is detected and converted into an electrical signal.
Some optical code reading systems are “retro-reflective.” In a retro-reflective system, a moving mirror is used to transmit the outgoing beam and receive reflected light. Non-retro-reflective systems typically employ a moving mirror to transmit the outgoing beam and a separate detection system with a wide, static field of view.
Optical codes can also be read employing imaging devices. For example an image sensor may be employed which has a two dimensional array of photo sensor cells which correspond to image elements or pixels in a field of view of the device. Such an image sensor may be a one dimensional (linear) sensor or a two dimensional area sensor such as a charge coupled device (CCD), CMOS device, charge modulated device (CMD) or charge injection device (CID). Associated circuitry produces electronic signals corresponding to a one or two-dimensional array of pixel information for a field of view.
It is known in the art to use a photo detector and objective lens assembly in an imaging optical code reader. In the past, such systems have employed complex objective lenses assemblies originally designed for use in relatively expensive video imaging systems. Such systems may have a single sharp focus and a limited depth of field, which along with conventional aiming, illumination and signal processing and decoding algorithms, limits the versatility and working range of the system.
Other known imaging systems are designed primarily for reading optical code. Such reading systems involve the assembly and alignment of several small parts. These parts may include a lens, an aperture and a 2D optical detector array such as a CCD chip. Such a structure is illustrated, for example, in U.S. patent application Ser. No. 09/096,578 to Correa et al. entitled “Imaging Engine and Method for Code Readers” filed Jun. 12, 1998 and assigned to Symbol Technologies, Inc. The Correa et al. application is hereby incorporated by reference herein.
Electrically Switchable Holographic Optical Elements
Electrically switchable holographic optical elements (ESHOEs) are known in the art. Such devices may consist of a pair of plates which may be transparent or reflective. A polymer-dispersed liquid crystal material may be located between the plates. One or more interference patterns are formed in the material and define a volume hologram. The ESHOE has optical properties that changes in response to an electrical field applied to the plates. The composition and fabrication of such devices are discussed, for example, in U.S. Pat. No. 5,942,157 to Sutherland et al. entitled “Switchable Volume Hologram Materials and Devices.”
The volume hologram is angle and wavelength selective, which makes a wide variety of applications possible. The hologram can be recorded as a reflection or transmission hologram. The volume hologram may be created by exposing a mix of monomers and liquid crystal located between the plates to intersecting laser beams, giving rise to an interference pattern. Photo-polymerization is selectively initiated by the light to form a matrix of polymer and liquid crystal droplets. When an electric field is applied to the plates the orientation of the liquid crystal molecules changes, resulting in erasing the hologram. When the field is removed, the hologram returns. Application-specific ESHOEs are offered by DigiLens, Inc., of Sunnyvale, Calif.
It has been proposed to use ESHOEs, for example, for projecting images on a projection screen, or providing displays in which the ESHOEs perform simple optical functions commonly associated with traditional optical devices, such as those performed by lenses, prisms and mirrors. It has also been proposed to use ESHOEs in sophisticated optical manipulations such as varying the light intensity with respect to a specific direction. The construction and application of such devices are discussed, for example, in U.S. Pat. No. 6,040,928 to Popovich entitled “Holographic Desktop Monitor.” It has been suggested that the DigiLens ESHOEs be used for applications including beam steering, diffractive correction or wavelength selective filtering.
It is an object of the present invention to provide novel applications for volume holograms in optical code readers.
It is another object of the present invention to provide novel applications for ESHOEs in optical code readers.
These and other objects and features of the invention will be apparent from this written description and drawings.
SUMMARY OF THE INVENTION
The present disclosure includes various systems and methods employing diffractive or holographic optical elements for improving the performance of optical code readers or providing new functions in such devices.
In one embodiment of the present invention an optical code reading system employs a photo sensor with an array of cells for producing electrical signals responsive to an image directed to said sensor. An optical system sequentially focuses images on the sensor corresponding to at least two different fields of view which may be partially overlapping or completely non-overlapping. The optical system which performs this function includes at least one electrically switchable holographic optical element (ESHOE) for switching between the fields of view. Electronic control circuitry switches the ESHOE to change fields of view. Image data from one or more of the fields of view is selected for decoding in the conventional fashion to extract information from an optical code symbol located in the selected field(s) of view. The system may include processing hardware and/or software for stitching together image portions from at least two of the fields of view to form a composite
Bianculli Thomas D.
Blasczak Matthew
Gurevich Vladimir
Krichever Mark
Nagano Shinji
Carter, Deluca, Farrell & Schmidt LLP
Lee Michael G.
Nguyen Kimberly
Symbol Technologies Inc.
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