Optical scanning head

Description “Optical Scanning Head”

Field of the invention

The invention relates generally to a scanning system for reading and / or analyzing bar code symbols and more particularly to a portable scanning code bar reader.

Background of the invention

Many industries, including assembly processing, grocery and food processing industries, use an identification system in which products are marked with a bar code symbol consisting of a series of lines and spaces with widths. variables. A number of barcode scanners and scanners have been developed to decode the symbol pattern, to obtain a multi-digit representation, for inventory, production tracking and for verification or sales purposes. Optical scanning devices are available in a number of configurations, some of which are integrated into a fixed scanning station and other portable devices. The portability of an optical scanning head provides a number of advantages, including the ability to inventory products on shelves and track portable items such as files or light equipment. A number of these portable scanning heads incorporate laser diodes, which allow the user to scan the bar code symbols at any time.

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varying distances from the surface where barcodes are printed. A drawback of scanners is that they are. in. Expensive manufacturing.

Another type of barcode scanners that can be incorporated into the portable system uses light emitting diodes. (LED). as a light source, and charge coupled devices (CCD) as detectors. This class of barcode scanners is commonly known as “CCD scanners”. While CCD scanners have the advantage of being more economical to manufacture, they limit the user to scanning by barcode scanning, or by making contact with the surface on which the barcode is printed, or maintaining a no more than about 1.5 cm (1.5 cm) from the bar code, which creates another limitation, because a barcode longer than the window or width of the scanning head housing cannot be read. Thus, the CCD scanning scanner does not provide the comfort or versatility of the laser scanning scanner, which allows variable distance scanning of bar code symbols, which may be wider than the window or width of the housing.

Recently, considerable attention has been paid to two-way barcodes, which can store about 100 times more information in the same space as a one-dimensional barcode. In two-dimensional bar coding, they stack on top of other rows of lines and spaces. The codes are. scanned by laser through each line successively in a zigzag pattern. This scanning scanning technique introduces the risk of loss of vertical sync. There is also the

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The inconvenience of requiring a barcode illumination laser, which makes the scanner more expensive to scan.

US 4,331,245 relates to an optical reader device. with an array of light-emitting diodes. A sensor transmits the received data signals to a pattern identification circuit. The signals are also transmitted to a light control circuit to vary the illumination of the array to provide uniform illumination of the characters to be read.

US 4,818,886 relates to a method and apparatus for self-referencing and autofocusing a barcode reader. The apparatus utilizes a plurality of LEDs arranged at varying distances from a lens to provide radiation that is substantially focused or out of focus on the barcode surface. A full reading requires a relative scanning motion, either under manual control or. ^ to traverse the bar code pattern.

Summary of the Invention

An advantage of the present invention is that it provides a scanning optical head for reading bar code symbols at varying distances from the symbol using light sources. LED and detectors

CCD

According to the invention there is provided an optical scan explorer according to claim 1.

In one embodiment, as an example, the scanning optical head comprises a plurality of light emitting diodes arranged in the immediate vicinity of each other, each of the LEDs being oriented towards each other.

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emit light from different angles so as to create a range of light. Generally, the LEDs are also oriented so that all LEDs are oriented at a certain non-zero angle from a line perpendicular to the window through which light is emitted. The number of LEDs may vary according to the intensity of. desired light and application. For example, scanning a two-dimensional barcode will require more LEDs, usually a dual light array, while a one-dimensional barcode needs only one row. A single scanning head can be made with the ability to select one-dimensional or two-dimensional scanning, including a trigger or other switching means that activates the appropriate LED number. LEDs can be arranged in a number of clusters, such as those in the form of a V or a U. or in single or parallel lines. In a form. Alternatively, the LED array may be replaced by a photographic flash lamp, which provides more intense light for scanning at greater distances.

An optical module includes an optical shield or “darkroom” and a lens / filter assembly providing scanning depth control of the scanner. The optical module is located behind the light source and the detector, consisting of a CCD array, is mounted behind the optical module to detect the light intensity in the reflected beam in the field of view through the bar code symbol. The CCD array may consist of a single linear array, a dual linear array or a matrix array. The CCD array generates an electrical signal indicative of the detected light intensity. This signal is carried to a signal converter consisting of an analog filter and analog-to-digital conversation circuitry to filter out noise and digitize the analog signal to generate data describing the bar code symbol. Gain control, which may or may not be automatic, highly adaptive margin detection, or threshold creation, is provided to adjust the received signal magnitude to a predetermined level, regardless of the distance between the barcode and the explorer. scanning and ambient lighting. Each of these techniques is aimed at the inclination of the waveform produced when the barcode is scanned (whereas the ideal signal would be a set of rectangular pulses, the actual signal has a rounded shape because of the distortion of convolution).

In front of the LEDs, a light-transmitting window is positioned for manipulating and focusing the light. The window may include a filter and / or an anti-reflection coating. The window can be configured to have a double focusing radius with two different focal lengths and can be “jagged” or trimmed to homogenize the light. For optimal performance, the window is located at a distance in front of the LEDs that coincides with the highest light concentration.

The scanning optical head is powered by a direct current source, or preferably rechargeable battery, which provides direct voltage to the LEDs and CCDs in response to clock signals to provide a sequencer module. drive and synchronization clock. The timing signal can control serial LED illumination and coordinate CCD activation to minimize power consumption during scanning operations. Alternatively, the voltage supplied to the LEDs may be modulated in response to the signal level produced by the CCD. If a barcode is scanned over a short distance, a lower light level provides an intense signal. However at longer distances from the barcode, the light intensity is higher to get a good quality signal on the CCD. In this latest version, energy is saved by not supplying full power to LEDs only when necessary.

The timing signal can also be used to control an optional electronic shutter that periodically closes to create bar code “snapshots”. This preserves the signal integrity of the barcode drawing while the barcode scanner is in motion.

Brief Description of Drawings

The understanding of the present invention will be facilitated by considering the following detailed description of a preferred embodiment of the present invention, with reference to the accompanying drawings, in which the same numerals refer to like parts and whose figures represent:

Fig. 1 is a schematic view of the relative arrangement of the LEDs, optical module and detector on a printed circuit board;

Figs. 2a, 2b and 2c are schematic views of the relative positions of the LEDs, respectively one three, two three or three LED three;

Fig. 3 is a view, with the separate parts, of the lens assembly,

Fig. 4 is a perspective view of an optical scanning head including a housing;

Fig. 5 is a cross-sectional view taken along line 5-5 of FIG. 4;

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Fig. 6 is a schematic of the LED card for the 12 LED configuration of FIG. 1,

As. 7a to 7g, clock pulse graphs for different timing configurations, relating to scanning activation of the scanner (fig. 7a); alternating illumination cycles (fig. 7b, 7c and 7d) according to the present invention, analog reset of the detector (fig. 7e) and illumination patterns according to prior art processes 1 and 2 (fig. 7f and 7g).

Fig. Figure 8 is a block diagram of the scan scan head operating sequence according to the present invention;

Fig. 9 is a schematic view of an alternative arrangement of the LEDs and the corresponding distribution thereof. light;

Fig. 10 is a schematic view of a second alternative arrangement of the LEDs and their corresponding light distribution.

Fig. 11 is a schematic view of a third alternative arrangement of LEDs and corresponding light distribution;

Fig. 12 is a block diagram of the scanning device

Figs. 13a and 13b, air gap front views, for one-way and two-way applications, respectively;

Figs. 14a and 14b are schematic views of a serrated cylindrical lens with concave and convex exit edge respectively;

Fig. 15, a schematic view of a double-radius cylindrical lens,

Fig. 16 is a block diagram of the CCD module;

Fig. 17 is a partial start side elevation of the invention using

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a double radius cylindrical lens;

Figs. 18a to 18f, schematic LED orientation views for two-dimensional scanning scanning, fig. 18a parallel and fig. 18b perpendicular to the front of the printed circuit board, fig. 18c an arrangement of the LEDs in two rows, fig. 18d, two vertical LED rows, fig. 18e and fig. 18f, a combination of horizontal and vertical arrangements;

Fig. 19 is a schematic view of a simple light source with a parabolic reflector;

Figs. 20a to 20d, intensity graphs, with the number of pixels for a current image (20a), a dark frame (20b), a flat field (20c), and. a correct image (20d); and

Fig. 21 is a graph of a filter transfer function.

Detailed Description of Preferred Embodiment

The scanning head module shown in FIG. 1 comprises the printed circuit board (PCB) (2), having the generic configuration of a U or a Y, in which a plurality of LEDs (from 3 to 24 individual LEDs), with the configuration of a pattern in shape, are mounted. of V, U-shaped or linear, in an orientation leading to the projection of a beam of light by an LED in a direction different from that of another LED in the trio. The configuration illustrated in fig. 1 It has 12 LEDs mounted on the V-shaped PCB (2). These are identified as LEDs 4 to 15 which emit light rays (104) through (l 15). The portion of the printed circuit board (2) from which LED light is emitted will be considered the front of the card. A reference line for defining LED orientation angles runs perpendicular to the front of the PCB (2). In the center of the

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behind the LEDs is an optical module (17) consisting of an optical shield (darkroom (16)) in which is contained the lens assembly (18) which filters and focuses the light reflected from a scanned barcode on the CCD detector 20 arranged behind the optical module. back of the PCB (2). A signal generated by the activation of the reflected light CCDs is conveyed to the signal converter (22), the one-dimensional scan explorer consisting of an analog filter and an analog-to-digital converter circuit, or by the signal converter (22 ') , for the two-dimensional scanning explorer. In front of the LEDs, fixed to the PCB (2) or mounted inside a housing containing the PCB (2), is the light-transmitting window (24) that provides filtering, focusing, and positioning of the PCB (2). path of light from the illuminating beam affecting the bar code to be scanned. The reflected light carrying the intensity-modulated bar code signal is returned to the lens assembly and detector.

The scan head may also include a decoder module 26 which decodes a multi-digit representation of bar code symbols such as UPC, EAN, JAN, Code 39, Code 2/51, Code 2/5. , Code 128, Codabar, Plessey and other barcode systems. In the two-dimensional barcode reader, a buffer (88). 1.2, will store the two-dimensional image prior to decoding by the decoder module. (26).

The first embodiment of the light source illustrated in fig. 1 consists of 12 LEDs mounted in a generally V-shaped configuration relative to other LEDs so that they point outwards at such angles.

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which groups of three on one leg, for example LEDs (4, 5 and 6) or (13,14, 15), form substantially a single beam of light that expands as depth of field increases. The actual grouping of the LEDs is best illustrated in FIGS. 2a, b, c. Here, the 12 LEDs are divided into groups of three, or three, of LEDs. From this we can see that a given LED trio is not determined by serially progressing the location of the LEDs in the V configuration, but rather that the combined lighting of the trio completely fills the window (24) and expands from it. ,, to form a range of light, to facilitate detection of barcodes that are wider than the window itself.

In fig. 2a ,. LEDs (6, 10, 13) constitute the first triplet. The light rays 106, 110, 113) shown in fig. 1 fill a substantial portion of the window 24. The second LED trio comprises LEDs 5, 10, 14 which are added to the first trio as shown in FIG. 2b. The beams emanating therefrom, the rays (.105, 110, 114), shown in fig. 1, supplement the rays coming from the first triplet to fill the window (24) and expand from it. Fig. 2c illustrates the location of the third LED trio (7,11,12). The rays (107, 111, 112) emanate from there to supplement the light from the first two triplets. The fourth trio consists of the LEDs (4, 8, 15) with their respective rays (.104, 108, 115). The specific LEDs included in a given trio are variable while the resulting light range substantially fills the window (24). As will be described below, the grouping of the designated LEDs, either in a trio or in a number greater than 2, can be sequentially illuminated to save energy from the power source. For example, the twelve LED configuration can also be divided into two sextets or three quartets. Similarly, if 24 LEDs are used. the

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groupings may consist of three, four, six, eight or twelve LEDs. LED grouping is important when using sequential or graded lighting.

Alternative configurations for the arrangement of the LEDs may be a U-shape or a generally straight line across the front of the card, as shown in Fig. 11. For two-dimensional barcode scanning, variants may include two rows. LED lines parallel to the front of the PCB 2 or two linear LED lines perpendicular to the front of the card as illustrated in FIGS. 18a and 18b, respectively. Combinations of parallel and perpendicular rows may also be used. A multi-row arrangement may also be used for positioning the LEDs, for example with one row over the other, as in FIG. 1.8c, .or two upwardly extending vertical rows from PCB 2 as in FIG. 18d or any combination thereof. In fig. 18e, a possible combination is an LED strip extending through the upper row and a single LED on one side and FIG. 18f, a single LED is placed on each of the four sides in a vertical plane. In each case, the light range is created by orienting the LEDs from different angles. In the straight line configuration of fig. 11, the most central LEDs 209 and 210 are turned to point at an angle of 1.625 ° with a line perpendicular to the front of the card. Advancing outward, each LED is 3.25 ° from its adjacent interior LED.

The LEDs are chosen so that they emit light at a wavelength of 660 nm, red within the visible spectrum. These wavelengths provide optimum contrast for barcode scanning applications where dark bars have to be distinguished from bar

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clear. Infrared light also provides better contrast, so LEDs that emit light outside the visible spectrum can be used.

An alternative light source is a photographic flash lamp 130 or any other bright light source illustrated in FIG. 19. Available photographic lightning lamps can emit light of a number of different wavelengths. The wavelength at which the chosen photographic lightning lamp emits light will be determined by the color of the barcode and its background so that the best contrast possible is obtained. A parabolic reflector (132) is included within the optical scanning head assembly. with the photographic lightning lamp (130) in its center. This allows you to direct the maximum amount of light forward for bar code illumination. The higher light intensity will allow scanning by distances greater than about 89 cm (34 inches).

The optical module (17) consists of three lenses mounted within a slidable lens holder (30), all contained within the darkroom (16). The choice of the three lenses, which comprise the lenses. (.1.8) depends on the desired reference plane, that is, the desired depth of field, which is the distance between the detector (20) and the barcode to be scanned, so that the reflected light is properly focused in the aggregate of. detectors. The lens assembly 18 consists of a flat convex lens. (32), followed by a band filter (34), a biconcave lens (36), followed by an optical diffuser (28) and a biconvex lens (40). focusing and receiving. Lens 40 is important for the success of the present invention as it determines the diameter of the beam incident on the detector array and concentrates the beam to provide the

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maximum light available on the detector. In a two-dimensional scanning explorer, the image is focused on the detector array without distortion by a flat-convex lens instead of the focusing lens. The lenses may be coated with an anti-reflective coating and / or a bandpass coating to minimize reflectance at the interface between adjacent lenses and the ends of the lens assembly.

The optimum depth of field can be adjusted by moving the lens assembly forward or backward in its mounting device 21 relative to the detector. This will modify the focal point on the detector so that it can be finely adjusted to a desired scan scanning height.

This may include one. spatial filter inside the optical module disposed next to or even integrated with the lens assembly (18). The space filter (42) is. an air gap with an orientation and configuration corresponding to the shape of the barcode being scanned. For a one-dimensional barcode, a single slot, illustrated in FIG. 13a. The slot is oriented horizontally so that it is parallel to the direction in which the barcode scan is performed. For two-dimensional barcodes, a cross-slot pattern is used to provide a two-dimensional spatial filter 42 'as shown in Fig. 13b. The space filter (42) or (42 ') may be positioned in front of or behind the lens (32). The space filter (42). or (42 ') and the web filter (34) may also be formed as a unit with the slit pattern formed directly on the filter (34). The spatial filter 42 'can also be used for one-dimensional barcode applications. The horizontal and vertical slots may each have the same dimensions as the single slot, or the vertical and horizontal slots may differ from each other. The light absorber / diffuser 28 is shaped like a funnel with an aperture with its widest end facing the detector end of the lens assembly. The funnel allows absorption and concentration of diffracted light from the lens edges. The band filter 34 serves to block any radiation outside the 660 nm centered wavelength range (or wavelengths around infrared light for the infrared scanning explorer). For the visible light system, it is particularly desirable to filter out infrared portions and other visible portions of the light spectrum that can reach the window from the sensitive zone to provide optimal contrast. This improves the bar code reading resolution, a. less than depth of field.

The window (24). have one. Generically Z-shaped profile. one of. whose legs extend in front of the optical assembly (18) and support or consist of a web filter (25) centered approximately 660 nm (for the explorer by visible light filter scanning) and an equalizer / diffuser of the light, the other leg supporting a cylindrical lens (38). which focuses light along an axis to form a light plane and a light line is created at its focal point. When the barcode is scanned precisely at the focal point of the cylindrical lens 38, as much light as possible will be reflected by the detector. The function of the components of. The window consists of suppressing the radiation noise from the LEDs to form a homogeneous incident beam for bar code illumination, collimating the beam and filtering reflected light by removing extraneous light falling outside the 660 frequency range. predetermined acceptable nm.

The cylindrical lens 38 may be modified to provide a

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uniform light distribution at the focal point. This "homogenization" is provided by knurling or cropping the inlet side 90 of the lens as shown in FIG. 14. Each of the steps (92) on the serrated edge (90) acts as a "minilent" which. scatters light that enters the cylindrical lens at this point. A. Light scattered or diffused from each mini-lens overlaps with other diffused light to homogenize the light at the focal point of the cylindrical lens. The focal point of the cylindrical lens is determined by the outer side (94). Ideally, the positioning of the cylindrical lens 38 relative to the LEDs is determined by the point at which. LEDs combine to produce maximum concentrated light. In fig. 9, this point is along the line (75).

In conjunction with the serrated entry edge, the exit edge of the. Cylindrical lens can be concave or convex. The concave edge 94 'is shown in FIG. 1.4a and the convex edge (94). is shown in fig. 14b. The concave edge 94 is chosen for scanning by two-dimensional barcodes at contact distances up to 7,62 cm (3 inches). The convex edge 94 is used for remote scanning. greater than about 7.62 cm (3 ”).

Another modification of the cylindrical lens is illustrated in FIG. .15. The double ray actually creates two cylindrical sub-lenses 96 and 98, each with a different focal length. The light emitted by the LEDs will be focused by the two sub-lenses 96 and 98 so that two different lines of focused light are created at different angles to the lens as shown in FIG. 17 This lens provides greater variability in the distance at which barcodes can be accurately read without requiring a cylindrical lens change or compromise.

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on signal strength.

The detector module (20). It consists of an array of charge coupled devices (CCDs) arranged in equidistant imaging elements and may include additional processing elements shown in FIG. 16. The spacing of the pixels determines the limit of the detector definition, so it is necessary to adapt the CCD definition to the desired spatial definition in the image plane where the detector is located. The lens system magnification should be chosen so that at least two image elements in the CCD cover the minimum width of the bar to be defined in the image plane. This is particularly important for barcodes printed with a dot matrix printer.

The arrangement of the CCD aggregate will depend on the application. For a unidirectional barcode, a single linear CCD aggregate is acceptable. For two-way barcodes, a single linear array can be used by moving the scan head from the top to the barcode fluid. However, for better definition, two parallel CCD lines or an area CCD array can be used. The use of multiple CCD rows makes it possible to use a self-correcting technique in which the signal read by a CCD row can be double-checked by a second row.

Dual line portions of the CCD array or area array may be selectively switched on and off by connecting the CCD module controller to an external trigger or switch having multiple selections. This will allow a unidirectional barcode to be read by a two-dimensional scanning explorer while saving energy using only the number of aggregates.

CCD required.

Three types of CCD can be used. known in the art for the two-dimensional barcode reader area aggregate. The first type is the full frame CCD, which. has a single parallel recorder for photon exposure, charge integration and load transport. A shutter is used to control exposure and block light so as not to focus on CCDs during output reading.

The second type, the frame transfer CCD, has a parallel register consisting of two tandem CCDs. One such recorder is the storage aggregate, which is covered with an opaque mask and provides temporary storage of the collected load during output reading. The other CCD recorder, the image aggregate, is identical in capacity to the storage aggregate and is used to collect the image. After. As the image aggregate is exposed, the electronic image it generates is shifted to the storage aggregate for reading. As the storage aggregate is read, the image aggregate may collect load for the next image.

The third type of CCD is the interline transfer CCD. This CCD has a parallel register that is subdivided such that the opaque storage register is between the pixel columns. The electronic image accumulates in the exposed area of ​​the recorder in parallel. For output reading, the entire image is shifted under the leading mask. The CCD shift register is also located below the leading masks. The reading of. output is the same as in the frame transfer CCD.

The area aggregate (102), which is included in the CCD module (20) illustrated

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in fig. 16, operates in an interlaced mode. This mode consists of displacing half-pixel potential sources in alternating fields, with the term "fields" referring to the scanning head field of view. This displacement is possible, due to the arrangement in. multiple phases of the CCD gate structures, which allow sequential propagation of loads collected at potential sources, as is known in these techniques. This results in two successive fields that contain different information, given a number of line images with reduced random errors. During the exposure period, or integration, charge accumulates on each pixel in proportion to the incident lighting. Each line includes a number of image elements. A transfer pulse will “read out” the load at each lmha to gear an analog signal. The combined output readings of each line represent the two-dimensional barcode. The information will be conditioned and stored in the buffer (88). to be decoded by the decoder (25). After the transfer is verified, the area aggregate (102) will return to its state of. integration to accumulate charge for the next field.

For optimum effectiveness, dark levels must be calibrated and shadows corrected. It is stored. a plot. dark and subtracted from an image to produce a zero reference.

A frame, shadow correction, or smooth field is required to correct for variations in system response. Because CCDs have excellent linearity, only a smooth field is required to correct an image somewhere within the dynamic range at a specific wavelength (660 nm). Shadow varies with wavelength, yielding smooth fields often at many wavelengths. A calibration sequence requires taking the image of interest I_R, a dark plot, lj>. and a smooth field Ip. An arithmetic calculation, element by element, provides a corrected image with photometric integrity Ic. (Ir-Id) / (If-Id).

The drive sequencer clock module 106 utilizes a single quartz crystal or an exterior clock to provide all the necessary logic and synchronization signals. A TTL / MOS buffer (.104), as known in the art, is included as an interface between the area aggregate (102) and the sequencer module (106).

The detector module 20 may also include an anti-glare anti-blur device. This device, acting on each image element, consists of a diode that is separated from the image site by a potential barrier. This potential barrier is controlled by a dedicated gate, which is fed with clock pulses by a clock pulse gate control. As a result, the overcharge gives rise to a very weak current, so that the efficiency of said anti-blur device is virtually unlimited.

Other side effects that limit resistance to overlighting are: 1) flicker due to the passage of each column imaging element along the over-illuminated element during image transfer to memory and 2) carrier diffusion on the substrate, which is linked to the probability of collecting an electron generated under a pixel at the neighboring source. Although this effect is hardly noticeable on a “soft” image, it gains significant importance when there is a brightly lit zone, as might

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occur when reading in sunlight.

The CCD module includes a pixel defect corrector 108 for managing the correction of such defects. The pixel corrector works in association with the buffer (88). It works by replacing the signal of the element or of the pixels in a line with the signal produced by the last non-defective pixel. This data substitution is effected by a sampling and holding circuit with a mibid input located downstream of the CCD output and prior to conditioning and / or processing the video signal.

The positions of the defective pixels are mapped to the buffer 88 in terms of their x, y coordinates. These are quantified by the number of lines in the CCD's memory zone and the number of lines of clock pulses in which the defects appear. Similarly, the first defective image element is captured relative to the frame synchronization pulses. Defective pixels may be captured by one or two sync pulses and clock pulses.

In applying two-dimensional barcodes, the horizontal definition on the x axis is much more important than on the y axis. Therefore, CCD “combining” can be used to significantly increase depth of field. This “combination” is the process of combining element loading. adjacent images to obtain “super elements” during output reading. This combination process improves the signal to noise ratio and allows the dynamic range of the CCD to be expanded at the expense of spatial definition.

Electrical power is supplied to the CCD array by a current source.

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or a battery (46). In a first embodiment of the invention, the power supply to the CCD array is coordinated by a clock signal with sequential or graded LED illumination. Specifically, as shown in fig. 7e a clock signal (from clock 50) is provided to the CCD array to clear it in coordination with the activation of the LEDs. The CCD array can be scanned at a variable frequency of 36 to 200 scans per second, this frequency being determined by the density of the scanned barcodes. The scanning frequency is adjusted by the system clock which then modifies the LED illumination sequence so that the coordination illustrated in FIGS. 7a-7e. Scanning frequency determination can be programmed and can be initiated by scanning a barcode with the adjusted scanning frequency information or other relevant information prior to measuring the barcodes of interest.

The processing sequences are shown in FIGS. 8 and 12. For one-dimensional operation (following the first path in Fig. 8), the signal provided by the CCD array will be amplified and then processed by a bipolar low-pass filter and a pentamolar high-pass filter (shown combined ,, as filter (52).). that will extract from the signal any noise generated by the incident light or by the CCD itself. The automatic gain control (AGC) (54) will adjust the smal level to a predetermined value. The input smal level in the AGC is a function of the distance scanned by the barcode. . The longer the scan scanner is held above the scanned code, the weaker the signal. A filtered smal

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will then provide a voltage to a circuit that determines the center reference level ("zero crossing") in real time to a comparator that will convert the output analog video signal to a digital signal representing the barcode . The use of automatic comparator control (AGC) (56). will avoid the hysteresis noise and will prevent the loss of the white guard and the first commutation representing a. first bar of the video signal. The signal is then converted from analog to digital by the A / D converter (58) and output to the decoder (26). (Decoder 26 is shown to be "optional" because it can be combined with or be external to the scanning optical head.)

In the two-dimensional scanning explorer, a. The output of component CC.Q is directed through the signal converter (22 '). Here, the signal is amplified and filtered, as in the one-dimensional path, by filter 52 '. The filter 52 'may be one. active or programmable multipolar active amplifier filter. When a barcode is scanned, the waveform produced has a rounded shape with a continuously varying component due to alternating black and white bars, with amplitude being an indication of pulse width. To amplify the amplitude according to the width of the bars and spaces, the filter (.52 '), which is a (active) band filter, will amplify the small amplitude portion of the signal and keep the large amplitude portion in the same level. The "transfer function" of filter 52 'is shown in FIG. 2.1 .. The segments “BC.” And “CD” indicate amplification according to the high frequency (low level), or the small black and white bars to be magnified. The segment “” AB ”corresponds to the wide black and white bars to maintain the same amplitude. The inclinations of

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“FA”, “BC”, “CD” or “EG” segments may vary, to adjust the relative amplitude, of narrow black and white bar widths with. the wide bars. This filtration can be achieved by means of a fixed filter, an automatic filter or a programmable function, activated by a menu.

The gain command (54 '), which can be automatic, margin detection or adaptive thresholding (described below) are provided to adjust the magnitude of the received signal to a predetermined level, regardless of the distance between the code bar scanning and scanning and ambient lighting. (These techniques can also be used in the one-dimensional scan explorer). The dark reference (55). provides the means by which calibration can be performed to correct for variations in system responsiveness. The comparator and threshold control 56 'may include highly adaptive thresholding to retrieve the precise shape of the barcode signal with elimination of convolution distortion.

Convolution distortion refers to the calculation of the smal average due to the finite dimensions of the C CD definition and delays in the electronic circuits. The distortion results in a rounding of the signal slope, which causes a significant error. The process of adaptive thresholding is to follow the signal slope and to switch the digital output level from the final comparator shape to a level on the upward slope of the analog signal and to zero on the downward slope of the analog signal, using the analog signal zero crossing (mean value) as the reference level.

A video signal processing module, as known in these techniques, can also be used to process the analog signal to

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providing a digital data stream at the output and / or decoding and providing a signal representing the decoded information within a two-dimensional barcode.

In an alternative embodiment, instead of lighting the LEDs sequentially, the LED voltage is adjusted in response to the signal level at the detector. The stronger the received signal, the lower the required light intensity of the LEDs. The signal strength depends on the distance between the scanner and the barcode, so that at the maximum scanning distance, the LEDs receive all the energy. This saves energy by only asking for power when it is needed. It also prevents saturation or distortion of the detected signal if the barcode is read at close range from the scanner by high light intensity scanning.

The scanning optical head of the present invention provides energy saving by utilizing a system clock to control a progressive scan illumination of LEDs in coordination with CCD array cleaning. The scheme of FIG. 6 illustrates the sequential command of the four different LEDs illustrated in the embodiment of FIG. 1. For example, the clock trigger provides a signal to activate the amplifier (U2A), which then provides a signal to the first triplet, identified as TRIO 1, to illuminate LEDs 5, 6 and 12. TRIO 1 is switched on. mode is on whenever the scanner is activated, regardless of which other triplets are on (note the base-collector short circuit in the transistor (Q8)).

Fig. 7 provides samples of pulse patterns for activation of the

LED of the embodiment illustrated in fig. 1. Fig. 7a illustrates scanning activation of the scanner at the start of a first clock pulse, that is, when the power is turned on. According to the pulse pattern illustrated in fig. 7b when the “on” signal is applied, the first LED trio (TRIO 1) is illuminated. At the beginning of the second clock cycle, a second trio (TRIO 2) is illuminated. Also at this time, a signal is provided to the CCD array to reset it to initiate its detection function shown in FIG. 7e. At the beginning of the third clock cycle, a third LED trio (TRIO 3) is connected, and. During a fourth clock cycle, a fourth LED set (TRIO 4) is switched on. During the fifth clock cycle, the (TRIO 2, TRIO 3, TRIO 4) will turn off, only the TRIO will be turned on. This on / off sequence continues until the shutter is turned off at the time shown in Fig. 7a. In fig. 7c, a second possible pulse pattern is illustrated in which the first LED trio is on during the first clock cycle and a second LED trio is on in the second clock cycle, turning off in the third clock cycle, so that the first triplet stays on until the seventh clock cycle, when the second and third triplets are turned on, for a single clock cycle. The first LED type stays on throughout the process and, in clock cycle twelve, all four LED triplets turn on during one cycle. After a single clock cycle, in which only the first set of LEDs stay on, the sequence is repeated. In Fig. 7d, the pulse pattern alternates between two connected LED triplets and the connection of four LED triplets, with one trio always connected. For comparison of the process of the invention with prior art practices, FIGS. 7f and 7g. In fig. 7f. only a simple toggle occurs on and off. In fig. 7g ,. any of the LED combinations stay on for as long as the shutter button is activated.

In an alternative embodiment, energy savings are achieved by regulating the voltage supplied to the LEDs. in response to the signal level generated by the detector array. As before, the signal level in the detector depends on the distance to be scanned by the barcode. For longer distances, the signal level will be lower. In response to this lower signal, the voltage supplied to the LEDs will be increased. When the signal level exceeds a predetermined limit, the voltage supplied to the LEDs will be lower as less light is required to provide an acceptable signal. As an example, if the barcode is read a. Within a short distance, the LEDs will be powered up to 25% of the maximum current, which is 5 mA, on the prototype device. If the barcode is read at half the full depth of field, the LEDs receive 50%. ie 10 mA. At the outer limits of the depth of field, the current supplied will be 20 mA. The percentage of energy applied to the LEDs may vary with the color of the barcode as needed to obtain the optimum light intensity for scanning scanning. This power management technique will use the output video signal level to control and control the current in the LEDs through an appropriate clock pulse function.

The path of light from the incident beam in the scanning front will produce a light beam at an angular distance in a field of view through the bar code symbol in the vicinity of the reference plane. The width of the light transmitting window 24 represents a factor limiting the incident beam width. For this reason, the LEDs are mounted the

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as close as possible to window 24 to optimize the field of view and the energy of the incident beam. Despite this limitation, the field of. incident beam view is generally independent of the width of the PCB (2) or housing. This allows the field of view, that is, the transverse dimension of the incident beam to be greater than the width of the window (24). This is because the LEDs emit the incident beam in different directions from each side of the device inside the scanning head. The LEDs are oriented to provide parallel beams in pairs. For example, a first pair of LEDs consisting of LEDs (4) and (7) are oriented at an angle of 7.5 ° to the y axis (a line perpendicular to the front of the PCB (2)), the LEDs 5 and 8 are oriented at 15 ° and LEDs 6 and 7 at 22.5 ° as shown in FIG. 9. The LEDs on the other leg of the V are analogously oriented in the opposite direction. As can be seen from the figure, the light fan resulting from this orientation provides a higher intensity distribution within a narrow zone in the center of the fan as determined at a distance of about 17.78 cm ( 7 ”) of the explorer by sweep.

The alternative arrangement of the LEDs shown in fig. 10 places the LEDs more centrally at an angle of 3.75 ° from the perpendicular line in front of the scanner, the other LEDs being oriented with 3.75 ° increments as they progress outward along the legs. This LED configuration leads to a slightly larger zone of higher intensity compared to the embodiment described above. It should be noted that the cylindrical lens (38) must be positioned at a distance from the LEDs corresponding to the point where the beams intersect to provide the highest intensity, for example.

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example at point 120 in fig. 10

In fig. 11 ,. A third configuration of the. LED, which shows an LED line with various orientations. This configuration is described above.

Other electrical sub-circuits may also be provided on the PCB card (2), including an analog filter (50) and an A / D converter (52). However, in order to set the scan explorer housing to the desired position, it may be necessary to provide a second printed circuit board oriented at a certain angle with respect to the first printed circuit board on which additional sub-circuits may be placed. , which include a decoder chip and a memory device. Per. For example, two or more printed circuit boards can be configured so that they abut each other approximately perpendicularly, to create an L-shaped or U-shaped arrangement. This arrangement would allow the placement of one of the cards in the barrel of a scanning cannon, the other card extending partially within the handle portion.

The decoder module 26 may be inside or outside the scan head housing and process the digitized signal generated on the scan head to calculate the desired data, for example the representation or code with multiple digits, represented by the bar code symbol according to the algorithm contained in the program system. The decoder module includes a random access memory (RAM). for temporary data storage, and EPROM or PAL for storing the control program and a microprocessor that controls RAM and EPROM memories or PAL programmable matrix logic. The module

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The decoder will also include circuitry for controlling the scanning head and communication circuits for communicating with different functions of the scanning head or with a host system to which the scanning head may be connected, such as , a personal computer with manual data display terminal for a computer network.

The housing includes a battery detector (.60) below with an indicator LED (61) to provide an indication of insufficient power to continue scanning operations. This will provide advance warning for the operator to become aware of the problem before having scanned a number of items without giving. not, an appropriate registration would be possible for insufficient power.

An electromechanical shutter 116 shown in FIG. 1.6. is. activated by the clock signal from the clock (50) to periodically prevent the integration of charge from the light falling on the detector (20). This gives the barcode image 'snapshots' to preserve the signal integrity of the barcode pattern when the scan head and / or barcode is moving relative to each other.

The. circuits, with or without power supply, with a bearable configuration, the optical scanning explorer are protected within a housing (30). what. It has a contour to fit easily into the user's hand. The user picks up the housing (30) by its handle portion (32). illustrated in figs. 4 and 5, with the window portion (34). pointing the barcode symbols to read. The trigger (36) is incorporated into the handle (32) for easy one-handed operation of the explorer, the trigger being placed a short distance from the user's fingers, so that activation is simply the pressure on the trigger. A dual trigger, a multi-position trigger or an additional switch is provided to select between one-dimensional or two-dimensional scan scanning, so that only the amount of power needed to ensure a high quality signal is used. The window portion may be placed anywhere from 0 to about 60 cm (0 to 22 ”) above or in front of the barcode to be scanned. With a scan distance of less than about 17.78 cm (7 ”), it is desirable to focus the light range on the barcode, as some portions of the barcode may be illuminated at different intensities due to limitation. LED sequence, brighter than others, and due to the higher density of. light in the center of the fan. For explorations larger than about 60 cm (22 ”), LEDs can be replaced by photographic lightning lamps.

The scanning optical head of the present invention provides a device for constituting a small or portable, standalone device, a portable component of a multi-component scanning scanner or the optical part of a built-in scanning unit for barcode scanning using LED and CCD technology, making it a cost-effective device. The scanning head is capable of scanning barcodes up to 60 cm (22 ”) distances from the LED-illuminated detector, and even more with a photographic flash lamp, so it is versatile both in fixed as in portable implementation. The variable pulsed activation of the LEDs and the

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CCD aggregates, or graduated LED illumination, make the device capable of operating at low wattages with minimal power consumption during illumination, an important factor in portable explorers. The lens system and the range of light produced by the LED array allows the reading of a wide, range of densities and widths of barcodes. For point-of-sale or industrial applications, where the scanning scanner is fixed and the bar code printed object moves past it, a number of scanning optical heads of the present invention may be used. , in combination and mounted at different angles so that, regardless of the orientation or position of the barcode, the barcode can be read. For example, a star-crossed cross pattern can be made, combining two or four scanning heads respectively. The signal generated by each individual scanning head will be compared to signals from other scanning heads and the signal with the smallest error will be used. Signals from each scan scan head can also be used to double check the signals provided by other scan scan heads.

Another combination in which the scanning optical head of the present invention can be incorporated is a "non-contact" barcode "tunnel" consisting of mounting on one side of a rectangular passage tunnel on each side one or more heads. scanners formed on each wall of the tunnel, ie above and on both sides. The tunnel can be, but not necessarily, included in a conveyor belt system used in point of sale or industrial applications. The result is that, regardless of the position or side of the barcode object, at least one of the scanners is able to automatically read the barcode, one or two-dimensional, and transmit the decoded data to computer or to the cash register. This process will simplify handling and reduce item verification time. Such a possibility would be largely advantageous in a grocery check situation.

The foregoing description and drawings are intended to be exemplary only, the scope of the invention being limited only by the appended claims.

Lisbon, February 7, 2000

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