Patent Application
20090140049
Various electro-optical readers have previously been developed for reading both one- and two- dimensional bar code symbols appearing on a label or surface of a product or target. The symbol itself is a coded pattern of indicia. An example of a one-dimensional bar code symbol is a Universal Product Code (UPC) symbol. Examples of two-dimensional symbols are Code 49, as described in U.S. Pat. No. 4,794,239, and PDF417, as described in U.S. Pat. No. 5,304,786. Generally, the readers electro-optically transform graphic indicia of the symbols into electrical signals, which are decoded into alphanumeric characters. The resulting characters describe the target and/or some characteristic of the target with which the symbol is associated. Such characters typically comprise input data to a data processing system for applications in point-of-sale processing, inventory control, article tracking and the like.
A moving laser beam electro-optical reader has been disclosed for reading both one- and two-dimensional symbols, for example, in U.S. Pat. No. 4,251,798; U.S. Pat. No. 4,369,361; U.S. Pat. No. 4,387,297; U.S. Pat. No. 4,409,470; U.S. Pat. No. 4,760,248; and U.S. Pat. No. 4,896,026. Both one- and two-dimensional symbols can also be read by employing an imaging reader containing a solid-state imager that includes a one- or two-dimensional array of cells or photosensors that correspond to image elements or pixels in a field of view of the imager. In a workstation, hands-free mode of operation, an operator of the imaging reader slides or swipes a symbol across a window of the reader in a “swipe” mode, or merely presents the symbol to the window by holding the symbol momentarily steady in a “presentation” mode. In a portable handheld mode of operation, the operator may pick up the reader to scan large and/or heavy objects that cannot be easily positioned in front of the reader. The choice depends on operator preference or on the layout of the environment. The symbol must be located within a range of working distances relative to the window in order to be successfully read.
An optical assembly comprised of one or more lenses in the imaging reader captures either indoor or outdoor ambient light reflected or scattered from the symbol especially in the case of a brightly lit environment, as well as either internal or external illumination light directed at the symbol for reflection and scattering therefrom especially in the case of a dimly lit environment in response to actuation of a trigger. The captured light passes through the window to the imager, which may advantageously be a one- or two-dimensional charge coupled device (CCD) or a complementary metal oxide semiconductor (CMOS) device and includes associated circuits for producing electronic signals indicative of the captured light and corresponding to a one- or two-dimensional array of pixel information over the field of view. The electronic signals may be processed by a microprocessor either locally or sent to, and processed in, a remote host to read the symbol from the captured light.
As advantageous as such imaging readers are in capturing data as stand-alone or portable data capture systems, such a reader is usually very sensitive to stray or unwanted light from the above-described ambient and illumination light. Stray light often causes ghost images, as well as lowering the contrast of the image of the symbol being read. Such stray light degrades reader performance. In an effort to reduce stray light effects, it is known to anodize, or to apply a black coating on, holders for optical components in the readers. However, most black coatings are not completely light absorptive and, in many cases, exhibit wide variations in their diffuse and specular reflection characteristics.
One feature of the present invention resides, briefly stated, in a reader for electro-optically reading indicia, such as one- or two-dimensional symbols, located in a range of working distances relative to the reader. The reader includes a housing having a window and could be operated in a workstation mode in which the reader rests directly on a support surface such as a countertop, or in a stand resting on the support surface, and is stationary during reading, and/or in a handheld mode in which the reader is held in an operator's hand during reading. During reading, in the case of the workstation mode, the symbol is swiped past, or presented to, the window and, in the case of the handheld mode, the reader itself is moved relative to, and aimed at, the symbol. In the preferred embodiment, the reader is used in a retail establishment.
An optical assembly is mounted in the housing for capturing light from the indicia through the window over the field of view during the reading. The optical assembly includes a one- or two-dimensional, solid-state imager having an array of image sensors, preferably a CCD or a CMOS array. The optical assembly further includes one or more optical elements, such as an imaging lens and an aperture stop, spaced away from the imager along an optical axis, and a holder for holding the imaging lens.
The imager is preferably associated with an illuminator for illuminating the indicia with illumination light to enable an image of the indicia to be acquired, preferably in a very short period of time, for example, on the order of 500 microseconds, so that the indicia image is not blurred even if there is relative motion between the imager and the indicia. The illumination light is preferably brighter in intensity than that of ambient illumination, especially close to the window. The illuminator preferably includes a single light source or light emitting diode (LED), but may include a plurality of light sources or LEDs, and a lightpipe constituted of an optical material and operative for optically guiding the illumination light from the light source(s) toward the indicia. The imager is operative for sensing the illumination light scattered or reflected from the indicia.
In accordance with this invention, a baffle is provided for reducing an amount of stray light directed to the imager. The stray or unwanted light arises from the above-described ambient and illumination light. The baffle effectively rejects any ambient and/or illumination light incident on the lens holder at an angle that would otherwise scatter and/or reflect towards the imager and create ghost images and low contrast images of the indicia being read. The baffle reduces the formation of such ghost images and low contrast images, thereby improving reader performance.
The baffle is advantageously integrated into the lens holder, thereby making for a compact design. A light-absorptive coating is applied on the baffle and the holder. The integral baffle reduces assembly and manufacturing costs and promotes the use of the reader as a miniature component or subsystem in a non-stand-alone apparatus, or a myriad of other apparatuses, such as a telephone, a mobile computer, or the like, where space is at a premium.
In a preferred construction, the holder is a generally cylindrical barrel having a diameter and opposite axial end regions, and the baffle is located at one of the end regions of the barrel. The baffle is advantageously annular and has a diameter greater than the diameter of the barrel. In one embodiment, the baffle has a plurality of surfaces for reflecting and scattering the stray light incident thereon away from the imager. One of the surfaces is inclined relative to the optical axis, and another of the surfaces is generally orthogonal to the optical axis. In another embodiment, the baffle has a plurality of stepped elements of different dimensions as considered in a direction generally orthogonal to the optical axis, and the different dimensions of the stepped elements increase in a direction along the optical axis toward the imager.
Another feature of the present invention resides, briefly stated, in a method of electro-optically reading indicia, the method being performed by capturing light from the indicia over a field of view during the reading with a solid-state imager having an array of image sensors, by spacing an optical lens away from the imager along an optical axis, by holding the optical lens with a holder, and by reducing an amount of stray light directed to the imager by integrating a baffle with the holder.
The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.
Reference numeral 10 in
Reference numeral 30 in
Each reader 20, 30 includes, as shown for representative reader 20 in
As shown in
In operation, the microprocessor 36 sends a command signal to the illuminator 42 to pulse the LEDs for a short time period of 500 microseconds or less, and energizes the imager 40 to collect light from a target symbol substantially only during said time period. A typical array needs about 33 milliseconds to read the entire target image and operates at a frame rate of about 30 frames per second. The array may have on the order of one million addressable image sensors.
The imager 40 itself should have a global electronic shutter in which all the sensors are simultaneously exposed for light capture. Most CCD arrays are designed with a global electronic shutter. A typical CMOS array is designed with a rolling electronic shutter in which different sensors are exposed at different times. If a CMOS array is used, then it must be designed to allow a global electronic shutter.
Optical assemblies for capturing light from the indicia are shown in more detail in
In accordance with this invention, a baffle 54 is integrated with the holder 43, for reducing stray light directed, either directly or indirectly, to the imager 40. The baffle 54 is located at the end region of the barrel 43 furthest from the imager 40. The barrel 43 has a diameter, and the baffle 54 is annular and has a diameter greater than the diameter of the barrel.
In the embodiment of
In the embodiment of
The baffle 54 and the holder.43 may be anodized or a black or other light-absorptive coating 68 may be applied especially on the surfaces 56, 58, 60 or the stepped elements 62, 64, 66 in order to still further reduce the image degrading effects of the stray light.
The baffle 54 is integrated into the lens holder 43, thereby making for a compact design. The integral baffle 54 reduces assembly and manufacturing costs and promotes the use of the reader as a miniature component or subsystem in a non-stand-alone apparatus, or a myriad of other apparatuses, such as a telephone, a mobile computer, or the like, where space is at a premium.
It will be understood that each of the elements described above, or two or more together, also may find a useful application in other types of constructions differing from the types described above. Thus, readers having different configurations can be used.
While the invention has been illustrated and described as reducing the stray light in an imaging reader, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.
Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.
