Registers – Coded record sensors – Particular sensor structure
Reexamination Certificate
2003-06-24
2004-11-09
Le, Thien M. (Department: 2876)
Registers
Coded record sensors
Particular sensor structure
C372S032000, C372S033000, C359S819000, C359S820000
Reexamination Certificate
active
06814288
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to optical scanning devices such as bar code scanners, and more particularly to beam-shaping systems for generating a scanning laser beam adapted for use with a selected broad range of working distances and symbol densities.
BACKGROUND AND OBJECTS
Bar 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 bar code symbol itself is a coded 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 systems electro-optically transform the graphic indicia 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. Scanning systems of this general type have been disclosed, for example, in U.S. Pat. No. 5,600,121, assigned to the same assignee as the instant application. Such systems may employ a portable laser scanning device held by a user, which is configured to allow the user to aim the device, and more particularly, a scanning laser light beam, at a targeted symbol to be read.
The light source in a laser scanner bar code reader is typically a semiconductor laser. The use of semiconductor devices as the light source is especially desirable because of their small size, low cost and low voltage requirements. The laser beam is optically modified typically by an optical assembly, to form a beam spot of a certain size at the target distance. It is preferred that the cross section of the beam spot at the target distance be approximately the same as the minimum width between regions of different light reflectivity, i.e., the bars and spaces of the symbol.
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 a moving mirror placed 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.
Bar 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. The light is detected and converted into an electrical signal.
Some bar code reading systems are “retro-reflective”. In a retro-reflective system, a moving optical element such as a 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.
Electronic circuitry and software decode the electrical signal in a digital representation of the data represented by the symbol that has been scanned. For example, the analog electrical signal generated by the photo detector is converted by a digitizer into a pulse or modulated digitized signal, with the widths corresponding to the physical widths of the bars and spaces. Such a digitized signal is then decoded, based on the specific symbology used by the symbol, into a binary representation of the data encoded in the symbol, and subsequently to the information or alphanumeric characters so represented. Such signal processors are disclosed in U.S. Pat. No. 5,734,152 assigned to Symbol Technologies, Inc. which patent is hereby incorporated by reference.
Different bar codes have different information densities and contain a different number of elements in a given area representing different amounts of encoded data. The denser the code, the smaller the elements and spacings. Printing of the denser symbols on an appropriate medium is exacting and thus is more expensive than printing symbols with larger elements. The density of a bar code symbol can be expressed in terms of the minimum bar/space width, also called “module size”, or as a “spatial frequency” of the code, which is in the inverse of twice the bar/space width.
A bar code reader typically will have a specified resolution, often expressed by the module size that is detectable by its effective sensing spot. For optical scanners, for example, the beam spot size may be somewhat larger than the minimum width between regions of different light reflectivities, i.e., the bars and spaces of the symbol. The resolution of the reader is established by parameters of the beam source or the detector, by lenses or apertures associated with either the beam source or the detector, by the angle of beam inclination with respect to the plane of the symbol, by the threshold level of the digitizer, by the programming in the decoder, or by a combination of two or more of these elements. The photo detector will effectively average the light scattered from the area of the projected spot which reaches the detector aperture.
The region within which the bar code scanner is able to decode a bar code is called the effective working range of the scanner. Within this range, the spot size is such as to produce accurate readings of bar codes for a given bar code density. The working range is dependent on the focal characteristics of the scanner components and on the module size of the bar code.
Many known scanning systems collimate or focus the laser beam using a lens system to create a beam spot of a given diameter at a prescribed distance. The intensity of the laser beam at this point, in a plane normal to the beam (ideally approximately parallel to the scanned symbol), is ordinarily characterized by a “Gaussian” distribution with a high central peak. Gaussian beams typically have a profile along their axis of propagation exhibiting a waist (collimated) zone with limited divergence followed by a divergence zone thereafter. The collimated zone determines a depth of field (focusing range) for maximum bar code density. The working range is defined as the region within which the scanned beam spot is sufficiently well formed that its detected scattered radiation can be decoded by the scanner. But as the distance between the scanner and the symbol moves out of the working range of the scanner, which is typically only a few inches in length, the Gaussian distribution of the beam spot greatly widens, preventing accurate reading of a bar code. Such scanning systems, accordingly, must be positioned within a relatively narrow range of distances from a symbol in order to properly read the symbol.
It has been proposed to create a laser scan beam by directing a collimated beam of laser light onto a linear axicon optical element, for example, a conical lens, to produce a beam of light which exhibits a consistent spot size over a substantial distance along the axis of the beam. Such an optical system is disclosed in U.S. Pat. No. 5,331,143 to Marom et al. and assigned to Symbol Technologies, Inc., which patent is hereby incorporated by reference.
The aforementioned axicon system produces a nearly diffraction free beam. The use of such a beam has been proposed to maximize the focusing limited working range of the scanning beam. Such a beam exhibits substantially no divergence over a relatively long distance range and then breaks into a donut like spot pattern of intensity distribution. Such a non-diverging beam can provide two to three times the range of a conventional Gaussian beam for a particular bar-code densit
Barkan Edward
Breytman Alexander
Gurevich Vladimir
Krichever Mark
Li Yajun
Hess Daniel A.
Kirschstein et al.
Le Thien M.
Symbol Technologies Inc.
LandOfFree
Beam shaping system and diverging laser beam for scanning... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Beam shaping system and diverging laser beam for scanning..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Beam shaping system and diverging laser beam for scanning... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3358375