Method and apparatus for defining illumination field of view of barcode reader

A method and apparatus for defining the illumination field of view of a barcode reader. The method includes (1) generating an illumination with an illumination source; (2) directing the illumination with an illumination lens to pass through an aperture to generate an illumination pattern directed toward a target object and to define an illumination field of view with the aperture; and (3) focusing light reflected from the target object onto a photosensor array with an imaging lens in an imaging system.

FIELD OF THE DISCLOSURE

The present disclosure relates generally to imaging-based bar code readers.

BACKGROUND

Various electro-optical systems have been developed for reading optical indicia, such as bar codes. A bar code is a coded pattern of graphical indicia comprised of a series of bars and spaces of varying widths, the bars and spaces having differing light reflecting characteristics. Some of the more popular bar code symbologies include: Uniform Product Code (UPC), typically used in retail stores sales; Code 39, primarily used in inventory tracking; and Postnet, which is used for encoding zip codes for U.S. mail. Bar codes may be one dimensional (1D), i.e., a single row of graphical indicia such as a UPC bar code or two dimensional (2D), i.e., multiple rows of graphical indicia comprising a single bar code.

Systems that read bar codes (bar code readers) electro-optically transform the graphic indicia into electrical signals, which are decoded into alphanumerical characters that are intended to be descriptive of the article or some characteristic thereof. The characters are then typically represented in digital form and utilized as an input to a data processing system for various end-user applications such as point-of-sale processing, inventory control and the like.

Bar code readers that read and decode bar codes employing imaging systems are typically referred to as imaging-based bar code readers or bar code scanners. Imaging systems include charge coupled device (CCD) arrays, complementary metal oxide semiconductor (CMOS) arrays, or other imaging pixel arrays having a plurality of photosensitive elements (photosensors) or pixels. An illumination apparatus or system comprising light emitting diodes (LEDs) or other light source directs illumination toward a target object, e.g., a target bar code. Light reflected from the target bar code is focused through a system of one or more lens of the imaging system onto the pixel array. Thus, the target bar code within a field of view (FV) of the imaging lens system is focused on the pixel array.

Periodically, the pixels of the array are sequentially read out generating an analog signal representative of a captured image frame. The analog signal is amplified by a gain factor and the amplified analog signal is digitized by an analog-to-digital converter. Decoding circuitry of the imaging system processes the digitized signals representative of the captured image frame and attempts to decode the imaged bar code.

As mentioned above, imaging-based bar code readers typically employ an illumination apparatus to flood a target object with illumination from a light source such as a light emitting diode (LED) in the reader. Light from the light source or LED is reflected from the target object. The reflected light is then focused through the imaging lens system onto the pixel array, the target object being within a field of view of the imaging lens system.

The illumination system is designed to direct a pattern of illumination toward a target object such that the illumination pattern approximately matches the field of view (FV) of the imaging system. In some of the illumination systems, however, illumination intensity of the illumination pattern may not be very uniform, especially near the edges of the illumination pattern. It is desirable to have an illumination pattern that has substantially uniform illumination intensity within the entire illumination pattern. It is also desirable to have an illumination pattern with sharply defined edges.

Accordingly, there is a need for improved methods and apparatus for defining the illumination field of view of the barcode readers.

SUMMARY

In one aspect, the invention is directed to a barcode reader. The barcode reader includes an illumination source for generating an illumination and an aperture for defining an illumination field of view. The barcode reader also includes an illumination lens and an imaging system. The illumination lens is deposited between the illumination source and the aperture for directing the illumination from the illumination source through the aperture to generate an illumination pattern directed toward a target object. The imaging system includes a photosensor array and an imaging lens for focusing light reflected from the target object onto the photosensor array.

In another aspect, the invention is directed to a method. The method includes (1) generating an illumination with an illumination source; (2) directing the illumination with an illumination lens to pass through an aperture to generate an illumination pattern directed toward a target object and to define an illumination field of view with the aperture; and (3) focusing light reflected from the target object onto a photosensor array with an imaging lens in an imaging system.

Implementations of the invention can include one or more of the following advantages. The illumination pattern generated by the aperture can have sharply defined edges that can be used to let the user know where the field of view of the imaging system is located.

These and other advantages of the present invention will become apparent to those skilled in the art upon a reading of the following specification of the invention and a study of the several figures of the drawings.

DETAILED DESCRIPTION

An exemplary embodiment of an imaging-based bar code reader of the present invention is shown schematically at10inFIGS. 1-5. The bar code reader10includes an imaging system12and a decoding system14mounted in a housing16. The reader10is capable of reading, that is, imaging and decoding bar codes. The imaging system12is adapted to capture image frames of a field of view FV of the imaging system12arid the decoding system14is adapted to decode encoded indicia within a captured image frame. The housing16supports circuitry11of the reader10including the imaging and decoding systems12,14within an interior region17of the housing16.

The imaging system12comprises a scan engine or imaging camera assembly20and associated imaging circuitry22. The imaging camera assembly20includes a housing24supporting focusing optics including one or more imaging lens26and a photosensor or pixel array28. The sensor array28is enabled during an exposure period to capture an image of a target object32within a field of view FV of the imaging system12. The field of view FV of the imaging system12is a function of both the configuration of the sensor array28and the optical characteristics of the imaging lens26and the distance and orientation between the array28and the imaging lens26. In one exemplary embodiment, the imaging system12is a linear or one dimensional imaging system and the sensor array28is a linear or 1D sensor array.

The imaging system12field of view FV (shown schematically inFIG. 5) includes both a horizontal and a vertical field of view, the horizontal field of view being shown schematically as FVH inFIG. 3and the vertical field of view being shown schematically as FVV inFIGS. 1 and 4. The linear sensor array28is primarily adapted to image ID bar codes, for example, a UPC bar code as shown inFIG. 1which extends along a horizontal axis HBC and includes one row of indicia, an array of dark bars and white spaces. However, one of skill in the art would recognize that the present invention is also applicable to imaging systems utilizing a 2D photosensor array to image 2D bar codes, postal codes, signatures, etc.

The housing16includes a gripping portion16aadapted to be grasped by an operator's hand and a forward or scanning head portion16bextending from an upper part16cof the gripping portion16a. A lower part16dof the gripping portion16ais adapted to be received in a docking station30positioned on a substrate such as a table or sales counter. The scanning head16bsupports the imaging system12within an interior region17a(FIG. 4) of the scanning head16b. As can best be seen inFIG. 2, looking from the front of the housing16, the scanning head16bis generally rectangular in shape and defines a horizontal axis H and a vertical axis V. The vertical axis V being aligned with a general extent of the gripping portion16a.

Advantageously, the reader10of the present invention is adapted to be used in both a hand-held mode and a fixed position mode. In the fixed position mode, the housing16is received in the docking station30and a target object32having a target bar code34(FIG. 1) is brought within the field of view FV of the reader's imaging system12in order to have the reader10read the target bar code34. The imaging system12is typically always on or operational in the fixed position mode to image and decode any target bar code presented to the reader10within the field of view FV. The docking station30is plugged into an AC power source and provides regulated DC power to circuitry11of the reader10. Thus, when the reader10is in the docking station30power is available to keep the imaging system12on continuously.

In the hand-held mode, the housing14is removed from the docking station30so the reader10can be carried by an operator and positioned such that the target bar code34is within the field of view FV of the imaging system12. In the hand-held mode, imaging and decoding of the target bar code34is instituted by the operator depressing a trigger16eextending through an opening near the upper part16cof the gripping portion16a.

The imaging system12is part of the bar code reader circuitry11which operates under the control of a microprocessor11a. When removed from the docking station30, power is supplied to the imaging and decoding systems12,14by a power supply11b. The imaging and decoding systems12,14of the present invention may be embodied in hardware, software, electrical circuitry, firmware embedded within the microprocessor11aor the scan engine20, on flash read only memory (ROM), on an application specific integrated circuit (ASIC), or any combination thereof.

The bar code reader10includes an illumination apparatus or system40, described more fully below, to illuminate the target bar code34and an aiming system60which generates a visible aiming pattern62(FIG. 5) to aid the operator in aiming the reader10at the target bar code34when using the reader in the hand-held mode. The aiming system60generates the visible aiming pattern62comprising a single dot of illumination, a plurality of dots and/or lines of illumination or overlapping groups of dots/lines of illumination. The aiming system60typically includes a laser diode64, a focusing lens66and a pattern generator68for generating the desired aiming pattern62.

The camera housing24is supported within the scanning head interior region17ain proximity to a transparent window70defining a portion of a front wall16fof the scanning head16b. The window70is oriented such that its horizontal axis is substantially parallel to the scanning head horizontal axis H and its vertical axis is substantially parallel to the scanning head vertical axis V. Reflected light from the target bar code34passes through the transparent window70, is received by the focusing lens26and focused onto the imaging system sensor array28. In one embodiment, the illumination apparatus40and the aiming assembly60may be positioned behind the window70. Illumination from the illumination apparatus40and the aiming pattern62generated by the aiming assembly60also pass through the window70.

The imaging circuitry22may be disposed within, partially within, or external to the camera assembly housing24. The imaging lens26(which may be a single lens or series of lenses) are supported by a lens holder26a. The camera housing24defines a front opening24athat supports and seals against the lens holder26aso that the only light incident upon the sensor array28is illumination passing through the imaging lens26.

Depending on the specifics of the camera assembly20, the lens holder26amay slide in and out within the camera housing front opening24ato allow dual focusing under the control of the imaging circuitry22or the lens holder26amay be fixed with respect to the camera housing25in a fixed focus camera assembly. The lens holder26ais typically made of metal. A back end of the housing24may be comprised of a printed circuit board24b, which forms part of the imaging circuitry22and extends vertically to also support the illumination apparatus40and the aiming apparatus60(best seen inFIG. 4).

The imaging system12includes the linear sensor array28of the imaging camera assembly20. The sensor array28comprises a charged coupled device (CCD), a complementary metal oxide semiconductor (CMOS), or other imaging pixel array, operating under the control of the imaging circuitry22. In one exemplary embodiment, the sensor array28comprises a linear pixel CCD or CMOS array with a one row of pixels. The number of pixels in the row typically would be 512, 1024, 2048 or 4096 pixels. The typical size of a pixel in the pixel array would be on the order of 7 microns in horizontal width .times.120 microns in vertical height.

The illumination-receiving pixels of the pixel array define a sensor array surface28a(best seen inFIG. 4). The pixel array28is secured to the printed circuit board24b, in parallel direction for stability. The sensor array surface28ais substantially perpendicular to an optical axis OA of the focusing lens26, that is, a z axis (labeled ZSA inFIG. 4) that is perpendicular to the sensor array surface28awould be substantially parallel to the optical axis OA of the focusing lens26. The pixels of the sensor array surface28aare disposed substantially parallel to the horizontal axis H of the scanning head16b.

As is best seen inFIG. 4, the focusing lens26focuses light reflected and scattered from the target bar code34through an aperture26bonto the sensor array surface28aof the pixel/photosensor array28. Thus, the focusing lens26focuses an image of the target bar code34(assuming it is within the field of view FV) onto the array of pixels comprising the pixel array28. When actuated to read the target bar code34, the imaging system12captures a series of image frames74which are stored in a memory84. Each image frame74includes an image34aof the target bar code34(shown schematically inFIG. 5). The decoding system14decodes a digitized version of the image bar code34a.

Electrical signals are generated by reading out of some or all of the pixels of the pixel array28after an exposure period. After the exposure time has elapsed, some or all of the pixels of pixel array28are successively read out thereby generating an analog signal76(FIG. 4). In some sensors, particularly CMOS sensors, all pixels of the pixel array28are not exposed at the same time, thus, reading out of some pixels may coincide in time with an exposure period for some other pixels.

The analog image signal76represents a sequence of photosensor voltage values, the magnitude of each value representing an intensity of the reflected light received by a photosensor/pixel during an exposure period. The analog signal76is amplified by a gain factor, generating an amplified analog signal78. The imaging circuitry22further includes an analog-to-digital (A/D) converter80. The amplified analog signal78is digitized by the A/D converter80generating a digitized signal82. The digitized signal82comprises a sequence of digital gray scale values83typically ranging from 0-255 (for an eight bit processor, i.e., 2.sup.8=256), where a 0 gray scale value would represent an absence of any reflected light received by a pixel during an exposure or integration period (characterized as low pixel brightness) and a 255 gray scale value would represent a very high intensity of reflected light received by a pixel during an exposure period (characterized as high pixel brightness).

The digitized gray scale values83of the digitized signal82are stored in the memory84. The digital values83corresponding to a read out of the pixel array28constitute the image frame74, which is representative of the image projected by the focusing lens26onto the pixel array28during an exposure period. If the field of view FV of the focusing lens26includes the target bar code34, then a digital gray scale value image34aof the target bar code34would be present in the image frame74.

The decoding circuitry14then operates on the digitized gray scale values83of the image frame74and attempts to decode any decodable image within the image frame, e.g., the imaged target bar code34′. If the decoding is successful, decoded data86, representative of the data/information coded in the bar code34is then output via a data output port87and/or displayed to a user of the reader10via a display88. Upon achieving a good “read” of the bar code34, that is, the bar code34was successfully imaged and decoded, a speaker90and/or an indicator LED92is activated by the bar code reader circuitry13to indicate to the user that the target bar code34has successfully read, that is, the target bar code34has been successfully imaged and the imaged bar code34ahas been successfully decoded. If decoding is unsuccessful, a successive image frame74is selected and the decoding process is repeated until a successful decode is achieved.

InFIGS. 6 and 7, the illumination system40includes an illumination source42for generating an illumination and an aperture46having a generally rectangular opening46afor defining an illumination field of view. The illumination source42can include one or more LEDs. The illumination source42can also be other kinds of light source, such as, a cold cathode lamp (CFL). The illumination system40also includes an illumination lens44deposited between the illumination source42and the aperture44. The illumination lens44directs the illumination from the illumination source42through the aperture46to generate an illumination pattern IP that fills or substantially coincides with the field of view FV of the imaging system12. In the exemplary embodiment shown inFIG. 6 and 7, the illumination pattern IP and field of view FV are generally rectangular in shape.

InFIGS. 6 and 7, when the aperture46is used to limit the light projected onto the object space by the illumination lens44, the end effect is an illumination pattern IP with sharply defined edges that may be used to illuminate the object space in addition to functioning as the aiming system letting the user know where the imaging field of view FV is located.

FIGS. 8A and 8Bdepict a barcode reader that has the illumination source placed on a circuit board and the aperture formed on a chassis. As shown inFIGS. 8A and 8B, the illumination source42including two LEDs are placed on a circuit board24b. The photosensor array28for the imaging camera assembly and a diode64for the aiming system are also placed on the circuit board24b. The aperture46having the rectangular opening46ais formed on the chassis90. In some implementations, the aperture46and the chassis90can be formed as a single piece during an injecting mold process. In other implementations, the aperture46and the chassis90can be formed separately, and the separately constructed aperture46can be inserted into an opening on the chassis90.

InFIGS. 8A and 8B, the imaging lens26is deposited within the chassis90for focusing light reflected from the target object onto the photosensor array28. InFIGS. 8A and 8B, a focusing lens66and a pattern generator68for the aiming system are also deposited within the chassis90. The desired aiming pattern can be generated by the light from the diode64passing through the focusing lens66and the pattern generator68. In other implementations, the desired aiming pattern can be generated by a laser diode, and the light from the laser diode can pass through other reflective optical element or diffractive optical element for the aiming system.