System and method of optical reading with enhanced depth of field collection

Optical systems and methods of data reading with collection systems having improved depth of field. One configuration is directed to an image-based optical reading system with a plurality of sensor arrays, such as a charge coupled device (CCD) arranged in a compact configuration to minimize the overall package size while providing extended read range. In an example configuration, two CCD arrays are placed back to back to minimize height and overall package size with fold mirrors providing the optical path to a backward facing array.

BACKGROUND

The field of the present invention relates to data capture devices, such as scanners and optical code reading devices. In particular, optical readers and methods of reading are described herein which employ imaging technology to capture optical codes.

A common type of optical code is a barcode such as the omnipresent UPC label. A barcode label comprises a series of parallel dark bars of varying widths with intervening light spaces, also of varying widths. The information encoded in the barcode is represented by the specific sequence of bar and space widths, the precise nature of this representation depending on which particular barcode symbology is in use. Typical methods for reading barcodes comprise generation of an electronic signal wherein a signal voltage alternates between two preset voltage levels, one representing a dark bar and the other representing a light space. The temporal widths of these alternating pulses of high and low voltage levels correspond to the spatial widths of the bars and spaces. It is this temporal sequence of alternating voltage pulses of varying widths which is presented to an electronic decoding apparatus for decoding.

In one method of reading, referred to as “scanning,” an illumination beam is moved (i.e., scanned) across the barcode while a photodetector monitors the reflected or backscattered light. For example, the photodetector may generate a high voltage when a large amount of light scattered from the barcode impinges on the detector, as from a light space, and likewise may produce a low voltage when a small amount of light scattered from the barcode impinges on the photodetector, as from a dark bar. The illumination source in spot scanners is a typically a laser, but may comprise a coherent light source (such as a laser or laser diode) or non-coherent light source (such as light emitting diode). A laser illumination source may offer advantages of higher intensity illumination which may allow barcodes to be read over a larger range of distances from the barcode scanner (large depth of field) and under a wider range of background illumination conditions.

Another method of reading is referred to as the “imaging” method whereby light reflecting off a surface is detected by an array of optical detectors, commonly a charge-coupled device (CCD) or CMOS. The scan surface is typically illuminated by some uniform light source, such as a light-emitting diode (LED), incandescent light, or laser illumination. Alternately, the illumination may be provided by ambient light such as disclosed in U.S. Pat. No. 5,814,803 hereby incorporated by reference. In such an imaging technique, as with a scanning laser, an electrical signal is generated having an amplitude determined by the intensity of the collected light.

In either the scanning laser or imaging technique, the amplitude of the electrical signal has one level for dark bars and a second level for light spaces. As the label is scanned, positive-going and negative-going transitions in the electrical signal occur, signifying transitions between bars and spaces. Techniques are known for detecting edges of bars and spaces by detecting the transitions of the electrical signal. Techniques are also known for determining the widths of bars and spaces based on the relative location of the detected edges and decoding the information represented by the bar code.

In data reading devices, a return light signal from the object or symbol being read is focused onto a detector or detector array. In the example of a data reader reading the bars and spaces of a typical bar code, there needs to be sufficient difference in signal intensity between the signal corresponding to the light space and the signal corresponding to the dark bar in order for the processor to differentiate therebetween. In either type of data reading system, depth of field plays an important role in effectively detecting the an image at the sensor. Thus in data reading applications there has been demand for increased depth of field, i.e., the range of distance over which the scanner can effectively scan.

There are several methods for improving depth of field, but there are essentially two areas which may be controlled, namely (1) outgoing beam generation and (2) collection. This application focuses on methods for improving depth of field and signal differentiation from the collection side.

SUMMARY OF THE INVENTION

The present invention is directed to data readers and methods of data reading with collection systems having improved depth of field.

A preferred embodiment is directed to an image-based optical reading system with a plurality of sensor arrays, such as a CCD or CMOS, arranged in a compact configuration to minimize the overall package size while providing extended read range. In one configuration, a data reader includes two separate CCD or CMOS arrays and optical paths produce the extended read range. In one arrangement, the CCD or CMOS arrays are placed back to back to minimize height and overall package size with fold mirrors providing the optical path to the backward facing array.

The foregoing and other objects, features, and advantages will become apparent from the following more detailed description set forth in conjunction with the accompanying drawings. It is intended that each of these disclosed embodiments may be implemented individually or in combination with other of the embodiments.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The preferred embodiments will now be described with reference to the drawings. For conciseness of description, the detector arrays are described as CCD arrays, but other suitable detectors may be implemented such as CMOS.

FIG. 1illustrates a typical imaging system100comprised of an optical collection system or lens103, a CCD detector104, a pre-amplification block105, a signal processing block106, and a decoding block107. The optical collection system103operates in the presence of ambient illumination101, gathering ambient light reflecting off a target (such as a bar code label102) and focusing the gathered light on the CCD detector104. Alternately, the system may be provided with an illumination system, such as one or more LED's (light emitting diodes). The CCD detector104interacts with the pre-amplification block105to obtain a CCD input signal comprised of imaging data. The CCD input signal may be processed by the signal processing block106and provided to the decoding block107for decoding.

Although the imaging region of the CCD detector13may be various shapes, a planar imaging surface is preferred. In contrast to a conventional retrodirective multi-line laser scanner having a laser and mirrors, the optical sensing portion of an area imaging system may be quite small because of the relatively small size of the CCD array.

FIG. 2is a cut-away view of a handheld data reader150of suitable configuration according to a preferred embodiment. The handheld data reader150comprises a head section151encasing most or all of the optical system and electronics, a digital board153on which is mounted an optics chassis156, and an analog board154connected to the back of the optics chassis156and also connected to the digital board153. The data reader150also includes a handle board155encased in a portion of the housing formed as a handle section152below the scan head section151.

The left sections of the housing head section151and handle section152are removed and thus not shown in the figure. The data reader150may also include a window disposed in a front portion of the head section151for sealing off the interior space of the data reader where the various components are disposed but allowing light to pass therethrough.

The data reader may also be provided with an aiming mechanism. For example two pointer LED assemblies157a,157bare mounted on or in the optical chassis156, each containing a pointer LED with suitable focusing/diffusing optics for projecting an aiming pattern into the read volume. The pointer LED projects an aiming pattern comprised of a spot, line segment, or image to assist the operator in aiming the reader so as to position the target being read at a desired location relative to the reader.

The data reader150preferably comprises an imaging system having a relatively large depth of field that can operate solely in ambient light. Alternately, the data reader150may employ illumination source(s) such as LED's158a,158bmounted on the PCB153. Alternately, the illumination LED's may be mounted to some other suitable location such as the chassis156or the housing.

The data reader includes inlets159a,159bfor the two CCD arrays that are arranged in a compact arrangement to minimize the overall package size. The two separate CCD arrays, arranged along separate optical paths produce the extended read range.

Preferably, each of the CCD arrays is two-dimensional array capable of acquiring a two-dimensional image. Such a imaging array is useful for reading one-dimensional codes such as UPC/EAN and Code 39, but is particularly useful for reading two-dimensional codes such as PDF-417, Maxicode, Datamatrix, Datastrip, RSS (Reduced Space Symbol), and Code 49.

FIG. 3illustrates a first embodiment of an optical system160having a first collection system, shown as a lens170, that focuses an image along first incoming optical path172and onto the first CCD array174. A second collection system, shown as a lens180, focuses an image along a second incoming optical path182and toward a first fold mirror184, then to second fold mirror186, and then onto a second CCD array188. The back-to-back arrangement of the first CCD array174and second CCD array188may minimize height and overall package size. The first and second CCD arrays174,188may be mounted on a common substrate such as a chassis, or on opposite sides of a common printed circuit board190simplifying both mechanical construction and electrical connection.

The two optical paths172,182and lens designs for the lens systems170,180provide for two overlapping read ranges with both a wide angle and narrow angle field of view. The back-to-back placement shortens the overall length and provides some height reduction. The height reduction also minimizes the optical path offset, which should enhance smooth overlap between the two read ranges.

The two incoming optical paths172,182are generally parallel, but offset from each other. The offset may be lateral, such as the configuration ofFIG. 2, or may be some other arrangement such as vertical or diagonal.

In the back-to-back arrangement illustrated inFIG. 3, the respective sensors arrays174,188face in opposite directions. In another configuration, the respective sensors arrays174,188may be arranged to face in the same direction. In such a system, the first fold mirror184would reflect the incoming light182between the sensors arrays174,188and second fold mirror186would be positioned between the sensors arrays174,188for reflecting the incoming light182onto the second sensor array188.

FIG. 4illustrates an alternate embodiment of an optical system200having a first collection system, shown as a lens210, that focuses an image along optical path212and onto the first CCD array214. A second collection system, shown as a lens220, focuses an image along optical path222and onto a second CCD array224. The first CCD array214and second CCD array224are constructed in a side-by-side or in a stacked arrangement to provide for common mounting such as on a common PCB230.

The back-to-back arrangement of two CCD arrays may be more compact than a stacked or side-by-side arrangement.

FIG. 5illustrates another embodiment of an optical system250having a first collection system, shown as a lens260, that focuses an image along first incoming optical path262and toward a first fold mirror264which in turn reflects the image onto the first CCD array266. A second collection system, shown as a lens270, focuses an image along a second incoming optical path272and toward a first fold mirror274, which in turn reflects the image onto a second CCD array276. The first CCD array266and second CCD array276are arranged facing in opposite directions perpendicular to the axes262,272of the lenses260,270to minimize height and overall package size. The first and second CCD arrays266,276may be mounted on a common substrate such as a chassis, or on opposite sides of a common printed circuit board280simplifying both mechanical construction and electrical connection. The CCD arrays266,276may aligned back-to-back or, as illustrated inFIG. 5, laterally offset. Further, the arrays may be disposed in offset, parallel planes as inFIG. 5, or may be configured in a common plane.

FIG. 6illustrates another embodiment of an optical system300having a first collection system, shown as a lens310, that focuses an image along first incoming optical path312and onto the first CCD array314. A second collection system, shown as a lens320, focuses an image along a second incoming optical path322and toward a first fold mirror324, then to second fold mirror326, and then onto a second CCD array328. The first CCD array314and second CCD array328are arranged front-to-back separated by a gap within which the second fold mirror326is disposed. Such a configuration may minimize height and overall package size. The first and second CCD arrays314,328may be mounted on a common substrate such as a chassis, or on a common printed circuit board330simplifying both mechanical construction and electrical connection.

FIG. 7illustrates another embodiment of an optical system350having a first collection system, shown as a lens360, that focuses an image along first incoming optical path362, and toward a fold mirror364which reflects the image and onto the first CCD array366. A second collection system, shown as a lens370, focuses an image along a second incoming optical path372and toward a fold mirror374, and then onto a second CCD array376. The first CCD array366and second CCD array376are arranged face-to-face, facing in opposite directions, separated by a gap within which the fold mirrors364,374are disposed. Such a configuration may minimize height and overall package size. The first and second CCD arrays366,376may be mounted on a common substrate such as a chassis, or on a common printed circuit board380simplifying both mechanical construction and electrical connection.

FIG. 8illustrates another embodiment of an optical system400having a first collection system, shown as a lens410, that focuses an image along first incoming optical path412, and toward a fold mirror414which reflects the image and onto the first CCD array416. A second collection system, shown as a lens420, focuses an image along a second incoming optical path422and toward a fold mirror424, and then onto a second CCD array426. The first CCD array416and second CCD array426are arranged facing in opposite directions, with offset axes providing different distances from the respective lenses410,420. The first and second CCD arrays416,426may be mounted on a common substrate such as a chassis, or on a common printed circuit board (not shown) for simplifying both mechanical construction and electrical connection.

FIG. 9illustrates another embodiment of an optical system450having a first collection system, shown as a lens460, that focuses an image passing through aperture462along first incoming optical path464and toward a first fold mirror466which in turn reflects the image onto the first CCD array468. A second collection system, shown as a lens470, that focuses an image passing through aperture472along first incoming optical path474and toward a first fold mirror476which in turn reflects the image onto the first CCD array478. The first CCD array468and second CCD array478are arranged facing in the same direction perpendicular to the axes464,474of the lenses460,470to minimize height and overall package size. The first and second CCD arrays468,478may be mounted on a common substrate such as a chassis, or on opposite sides of a common printed circuit board480simplifying both mechanical construction and electrical connection. The CCD arrays468,478may aligned side-by-side in a common plane.

Typically the arrays illustrated in the previous embodiments are linear in geometry such as the arrays516,526illustrated inFIGS. 10 and 11.

Another alternate multiple sensor imaging collection system500is illustrated inFIGS. 10-11. An incoming image of a barcode for example is passed through a slit or aperture512and is focused via a first collection system, shown as a lens510, along an incoming optical path toward a fold mirror514which reflects the image and onto the first CCD array516. Another image of that same barcode is passed though slit or aperture522and is collected by a second collection system, shown as a lens520, which focuses the image along an incoming optical path and toward a second fold mirror524, and then onto a second CCD array526. The lenses510,520are vertically offset (as shown inFIG. 11) and longitudinally offset (as shown inFIG. 10). The lenses510,520focus a linear image of the barcode toward the elongated fold mirrors514,524so that a section of an entire width of the bar code is imaged onto the detectors516,526. As in previous embodiments, the lens systems520,520focus to different fields due to differing axial position (e.g. lens510is nearer to the target) and/or different optical lens power. The lenses510,524may have the same optical power (and preferably are the same for ease of manufacture) but may provide different focal fields due to the differing axial location. The fold mirrors514and524are elongated corresponding to a section of a barcode being imaged onto the linear CCD arrays516,526. The mirrors514,524are arranged generally perpendicular and stacked vertically. The first CCD array516and second CCD array526are arranged facing in opposite directions, but may be offset vertically for alignment with respective fold mirrors514,524.

Yet another alternate multiple sensor imaging collection system550is illustrated inFIGS. 12-14. An incoming image of a barcode for example is first reflected off a common fold mirror560toward the multiple collection systems. The first collection system570comprises a wide field imager, including lens sections572and574, focusing an image reflecting off fold mirror560onto sensor array576. The second collection system comprised of lens580is a more standard field imager with a longer focal length, focusing an image reflecting off the fold mirror560and onto the sensor array586. As shown in the figures, the first collection system570produces a wide field of view578and579in the near fields. The second collection system580has a longer focal length and produces a more narrow field of view588for the near field reading and a more narrow field of view589for far field reading.

The collection lens systems570,580have axes which are offset but aligned as shown in the rear view ofFIG. 14. The axes of the lenses570,580are not necessarily parallel, each axis being oriented to achieve a desired overlapping image fields.

In each of the embodiments, the collection systems may comprise a lens system comprised of one or more optical elements such as lenses, prisms, mirrors, holographic elements, apertures, gratings. The lens elements may be single focal or multifocal such as described in U.S. Pat. No. 5,814,803 incorporated by reference, or may include active focusing mechanism such as a movable focusing lens element.

The data reading systems may be implemented for a handheld reader150as illustrated inFIG. 2for portable operation, or may comprise a fixed reader such as may be used for presentation scanning. Alternately, the reader may comprises a portable unit operable for multi-mode operation being operable in either a fixed mode and a handheld mode. The switch may comprise either a manually actuated switch on the housing or alternately a sensor which senses when the reader is moved (using a motion sensor or accelerometer) or is grasped by the operator (such as a contact sensor). Upon sensing that the reader has been moved or grasped, the reader may switch into handheld mode.

The aiming mechanism may apply to either handheld or fixed mode. When operating in handheld mode, the operator uses the aiming pattern to assist in moving the data reader to position the aiming pattern onto the optical code. In the fixed mode of operation, the operator moves the item to place the optical code into the scan region and thereby positions the aiming pattern onto the optical code.