Classifications

• • G—PHYSICS
  • G06—COMPUTING; CALCULATING OR COUNTING
  • G06K—GRAPHICAL DATA READING; PRESENTATION OF DATA; RECORD CARRIERS; HANDLING RECORD CARRIERS
  • G06K7/00—Methods or arrangements for sensing record carriers, e.g. for reading patterns
  • G06K7/10—Methods or arrangements for sensing record carriers, e.g. for reading patterns by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation
  • G06K7/10544—Methods or arrangements for sensing record carriers, e.g. for reading patterns by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation by scanning of the records by radiation in the optical part of the electromagnetic spectrum
  • G06K7/10821—Methods or arrangements for sensing record carriers, e.g. for reading patterns by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation by scanning of the records by radiation in the optical part of the electromagnetic spectrum further details of bar or optical code scanning devices
  • G06K7/10881—Methods or arrangements for sensing record carriers, e.g. for reading patterns by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation by scanning of the records by radiation in the optical part of the electromagnetic spectrum further details of bar or optical code scanning devices constructional details of hand-held scanners
• • G—PHYSICS
  • G06—COMPUTING; CALCULATING OR COUNTING
  • G06K—GRAPHICAL DATA READING; PRESENTATION OF DATA; RECORD CARRIERS; HANDLING RECORD CARRIERS
  • G06K7/00—Methods or arrangements for sensing record carriers, e.g. for reading patterns
  • G06K7/10—Methods or arrangements for sensing record carriers, e.g. for reading patterns by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation
  • G06K7/10544—Methods or arrangements for sensing record carriers, e.g. for reading patterns by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation by scanning of the records by radiation in the optical part of the electromagnetic spectrum
  • G06K7/10792—Special measures in relation to the object to be scanned
  • G06K7/10801—Multidistance reading
  • G06K7/10811—Focalisation
• • G—PHYSICS
  • G06—COMPUTING; CALCULATING OR COUNTING
  • G06K—GRAPHICAL DATA READING; PRESENTATION OF DATA; RECORD CARRIERS; HANDLING RECORD CARRIERS
  • G06K7/00—Methods or arrangements for sensing record carriers, e.g. for reading patterns
  • G06K7/10—Methods or arrangements for sensing record carriers, e.g. for reading patterns by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation
  • G06K2007/10485—Arrangement of optical elements
• • G—PHYSICS
  • G06—COMPUTING; CALCULATING OR COUNTING
  • G06K—GRAPHICAL DATA READING; PRESENTATION OF DATA; RECORD CARRIERS; HANDLING RECORD CARRIERS
  • G06K2207/00—Other aspects
  • G06K2207/1013—Multi-focal

Definitions

• the present invention is directed to optical information readers and more particularly to portable optical reader systems for instantaneously reading optical information over a substantial range of distances.
• Portable instantaneous optical information readers are also known to the art, e.g., as represented by Danielson and DurbinU.S. Patent N a 4,877,949 assigned to the assignee herein.
• the present invention provides a novel system capable of instantaneously reading optically readable information over a substantial range of distances.
• a preferred embodiment comprises a hand-held data collection terminal with a combined reader and RF module which includes a casing having a Ught receiving opening for alignment with optical information.
• optical means housed within the casing are optical means which include light generating means and reflected light collecting means for forming a reflected light image.
• reading sensor means for converting a reflected light image of optical information into an information signal.
• the optical means is adjustable such that a reflected light image of optical information, located within a substantial range of distances, is focused onto the reading sensor means.
• Light beam generating means is provided for range finding.
• the light beam generating means is associated with the casing and directed relative to the optical means and the light receiving opening so that a light beam generated by the generating means ma be caused to impinge on the surface of an information carrier displaying optical information to be read and will then be reflected from the carrier into the light receiving opening through the collecting means to the reading sensor means.
• the system is so configured that the position of impingement of the reflected light beam on the reading sensor means is a function of the range of the information carrier. Accordingly, focal adjustments may be made based on position information from the reading sensor for focusing the image of optical information onto the reading sensor means.
• control means may be provided for accomplishing such adjustments according to the position of impingement of a pair of reflected light beams on the reading sensor means.
• Figure 1 is a top plan diagrammatic view of an embodiment of a portable optical reader system for reading optical information over a substantial range of distances;
• Figure 2A, 2B, and 2C are graphical representations of waveforms illustrating the output of a CCD image sensor under various conditions of focus adjustment and object distance, and with the distance measurement beams active;
• Figures 3A, 3B, and 3C are graphical representations of waveforms as a function of time illustrating the output of a CCD image sensor at zones A, B, and C, respectively, of Figure 1;
• Figures 4A and 4B are ray diagrams illustrating the viewed range of an object located at a given distance from the window of an embodiment of the present invention, Figure 4B is a side elevati ⁇ nal tracing, and Figure 4A is a top plan tracing;
• Figure 5 is a side elevational view of an optical system configuration for adjustably imaging optically readable information on a reading sensor
• Figures 6 and 7 are side elevational views of a preferred optical system illustrating the optical system of the present invention focused at zero inch and (twenty) inches respectively;
• Figure 8 is a graphical representation of a focus quality gradient
• Figures 9A and 9B are graphical representations of a family of overlapping focus quality functions for a number of equally spaced positions of a focusing mechanism
• Figures 10A and 10B are graphical representations of waveforms illustrating the output of a CCD image sensor
• Figure 11 is a graphical representation of a waveform wherein W is the pulse width at a threshold level, T is the pulse threshold level, and A is the pulse amplitude;
• Figure 12 is a graphical representation illustrating the separation of incident LED spot images on white paper in pixels versus object position in motor steps wherein: line (1) defines this function where the lens position is zero; line (2) defines this function where the lens position is located at 20 motor steps; and line (3) defines this function where the lens position is located at 40 motor steps;
• Figure 13 is a graphical representation of the waveform of the LED spots superimposed on a focused barcode, wherein LED spot centers were located at 285 and 652;
• Figure 14 is a graphical half -scale representation of the waveform of Figure 13 wherein the waveform has been processed
• Figure 15 is a graphical representation of a focus quality gradient wherein the focus quahty of an object located at a position 12 inches from the invention is shown at varying lens positions as determined by (1) a pulse modulation algorithm, (2) a maximum slew rate algorithm, and (3) a maximum slew rate algorithm wherein the signal of every 10 pixels is averaged;
• Figure 16 is a graphical representation of a focus quahty gradient utilizing a pulse modulation algorithm wherein the lens was focused at 9 inches, 13 inches, and 20 inches respectively;
• Figure 17 is a is a graphical representation of a focus quahty gradient wherein the focus quality of an object located at a position 20 inches from the invention is shown at varying lens positions as determined by (1) a pulse modulation algorithm, (2) a maximum slew rate algorithm, and (3) a maximum slew rate algorithm wherein the signal of every 10 pixels is averaged;
• Figure 18 is a graphical representation of a focus quahty gradient wherein the focus quahty of an object located at a position 2 inches from the invention is shown at varying lens positions as determined by (1) a pulse modulation algorithm, (2) a maximum slew rate algorithm, (3) a maximum slew rate algorithm wherein the signal of every 10 pixels is averaged, and (4) a relative length of curve algorithm;
• Figure 19 is a graphical representation of a focus quahty gradient wherein the focus quahty of an object located at a position 4 inches from the invention is shown at varying lens positions as determined by (1) a pulse modulation algorithm, (2) a maximum slew rate algorithm, and (3) a maximum slew rate algorithm wherein the signal of every 10 pixels is averaged;
• Figure 20 is a graphical representation illustrating the separation of incident LED spot images on a bar code label in pixels versus object position in motor steps wherein: line (1) defines this fimction where the lens position is zero; hne (2) defines this function where the lens position is located at 20 motor steps; and line (3) defines this fimction where the lens position is located at 40 motor steps;
• Figure 21 is a graphical representation of the waveform of two LED spot images superimposed, slightly out of focus, and incident on a dense bar code label wherein the lens was located at 40 steps and the label was located at 38 steps (illuminations was high with peaks detected at 326, 576);
• Figure 22 is a graphical representation of the waveform of two LED spot images superimposed, out of focus, and incident on a dense bar code label wherein the lens was located at 40 steps and the label was located at
• Figure 23 is a graphical representation of the waveform of two LED spot images superimposed, in focus, and incident on a dense bar code label wherein the lens was located at 30 steps and the label was located at 30 steps (illuminations was high with peaks detected at 288, 646);
• Figure 24 is the processed scan illustrated by Figure 23 showing the uneven illumination of the bar code label
• Figure 25 is a graphical representation of the waveform of two LED spot images superimposed, out of focus, and incident on a dense bar code label wherein the lens was located at 30 steps and the label was located at
• Figure 26 is a graphical representation of the waveform of two LED spot images superimposed, in focus, and incident on a dense bar code label wherein the lens was located at 20 steps and the label was located at 20 steps (peaks detected at 195, 738);
• Figure 27 is a graphical representation of the waveform of two LED spot images superimposed, out of focus, and incident on a dense bar code label wherein the lens was located at 20 steps and the label was located at 10 steps (peaks detected at 114, 813);
• Figure 28 is a graphical representation of the waveform of two LED spot images superimposed, in focus, and incident on a dense bar code label wherein the lens was located at 10 steps and the label was located at 10 steps (peaks detected at 107, 831);
• Figure 29 is a graphical representation of the waveform of two LED spot images superimposed, out of focus, and incident on a dense bar code label wherein the lens was located at 0 steps and the label was located at 10 steps (peaks detected at 84, 843);
• Figures 30 and 31 are side elevational views of a preferred optical system utilizing a moveable prism
• Figures 32, 33, and 34 are graphical representations of focus quahty gradients prepared using a pulse modulation algorithm wherein the lens was focused at 18 inches, 9 inches, and 13 inches respectively;
• Figures 35, 36 r 37, and 38 are graphical representations of the waveform of a reflected light image of a bar code label wherein illumination was constant and focus quahty was changed;
• Figure 39, 40, and 41 are graphical representations of the waveform of a reflected light image of a bar code label wherein focus quahty was constant and illumination was changed;
• Figure 42 is a graphical representation of a focus quahty gradient wherein the focus quahty of an object located at a position 20 inches from the invention is shown at varying lens positions as determined by (1) a pulse modulation algorithm, (2) a maximum slew rate algorithm, (3) a maximum slew rate algorithm wherein the signal of every 10 pixels is averaged, and (4) a relative length of curve algorithm;
• Figure 43 is a graphical representation of a focus quahty gradient wherein the focus quahty of an object located at a position 5 inches from the invention is shown at varying lens positions as determined by (1) a pulse modulation algorithm, (2) a maximum slew rate algorithm, (3) a maximum slew rate algorithm wherein the signal of every 10 pixels is averaged, and (4) a relative length of curve algorithm; and
• Figure 44 is a graphical representation of a focus quahty gradient wherein the focus quahty of an object located at a position 2 inches from the invention is shown at varying lens positions as determined by (1) a pulse modulation algorithm, (2) a maximum slew rate algorithm, (3) a maximum slew rate algorithm wherein the signal of every 10 pixels is averaged, and (4) a relative length of curve algorithm.
• Figures 45 - 48 depict a flow diagram of an exemplary instruction set to be used by the microprocessor to carry out the processes of the present invention.
• Fig. 1 is a diagrammatic illustration of a presently preferred embodiment of the instant invention. While the reading system of Fig. 1 could be contained within a housing such as indicated in the third figure of U.S. Patent N a 4,877,949, and as described in detail in U.S. Patent N a 4, 570,057, it is highly advantageous to be able to house the reader system of Fig. 1 within a compact modular casing such as generaUy indicated in the thirty- second figure of the international patent application pubhshed under the
• the module casing 10 may represent a module casing having a length of about eight centimeters, a width of about seven centimeters, and a depth of about six centimeters, constructed to interchangeably engage with a base housing such as utilized with the RT 1000 radio data terminal of Norand Corporation, and containing an RF transceiver in addition to the reader system of Fig. 1.
• the module casing 10 may have a frontal end 10a with a hght transmissive window 10b accommodating marginal hght rays, such as 11, 12.
• an elongated hght source 14 may be electrically energized from a lamp driver 16 to illuminate the region bounded by marginal rays 11, 12.
• the maximum length of bar codes which may be read depends on the distance of the bar code carrier from the reader frontal end. At a minimum distance, a bar code of a length corresponding to the width of the hght transmissive window (60mm) maybe successfully read, while at a distance of 1.5 inches, the bar code may have a length of ninety millimeters, and at a distance of three inches, the bar code may have a length of one hundred thirty millimeters.
• the reading sensor 20 e.g., a CCD type image sensor with a length of about thirty millimeters and between 2,000 and 5,000 elements
• the reading sensor 20 maybe driven via clock buffers 26 from a microprocessor 30, and that each pixel value in the output from the sensor 20 may be converted to digital form (e.g., a binary number) with a gray scale range of substantial extent for processing, either by a high speed external analog to digital converter 32, or by comparable on-chip means associated with microprocessor 30.
• the microprocessor is indicated as controlling focus via a stepper driver 34 and stepper motor 36.
• Visible hght beam generators 41, 42 are indicated as being electrically energized under the control of microprocessor 30 via a driver 44.
• the beams 51, 52 from beam generators 41, 2 preferably produce sharply defined spots on a bar code carrier within the operating range of the lens system.
• the microprocessor may flash the beam generators 41, 42 to generate beams 51, 52. These beams assist the user in aiming the reader toward a bar code.
• the reflected hght from the beams will in part foUow a path through the hght transmissive window 10b at frontal end 10a, and via optics system 22 to impinge on reading sensor 20.
• the reading sensor may be utilized to supply the output generated by the reflected beams (with hght source 14 inactive) and that such output may be processed by the microprocessor 30 to obtain an indication of the direction and amount to move the lens system to improve focus.
• a further flashing of beams 51, 52 may result in a more accurate measure of the positions at which the reflected beams impinge on the reading sensor.
• the microprocessor may quickly determine the distance to move lens system 22 so as to bring the bar code within the depth of field range of the lens system.
• Experimental Work Regarding Fig. 1 In testing the conception of the use of marker beams 51, 52 for obtaining a distance indication, an optical system was used having an F- number for infinity of four and requiring a change in the optical path distance from the lens to the sensor of about fourteen millimeters (14mm). Such a system was determined to be capable of focusing over distances from lens to an object between nil and 578 millimeters (578mm).
• Beam sources corresponding to sources 41, 42 were light emitting diodes that created hght spots at a distance of twenty inches which were about one inch square. At close up distances between zero and one inch, such hght spots were about one-quarter (%) inch square. Even with such light emitting diodes, it was found that distance measurements were feasible based on outputs from the
• FIG. 2A shows waveforms representing the output of a CCD image sensor using the beam sources just described.
• the sensor (20) output was digitized by a flash six bit A/D converter (32) and acquired by a personal computer (PC).
• the PC was programmed to store the image in memory, display the image on a monitor, and then print a graphical representation of the image on paper.
• These graphs show the images of the spots of light produced by the two pointing beams (51, 52) for various distances to an object.
• Fig. 2A was taken when the distance was twenty inches and the lens 22 was focused for zero inch object distance.
• Fig. 2C shows the image of the spots 57, 58 when the object is positioned at a five inch distance and the lens 22 is focused for zero inch object position.
• the distance between the spots is about 416 pixels indicating a smaller distance to the target.
• TCD1201 Pll size of a pixel image for sensors with 11 microns per pixel
• TCD1250 P8 size of a pixel image for sensors with 8 microns per pixel
• TCD1300 lp required lens resolution in line pairs per mm at 0 deg pitch and 5096 modulation to read corresponding bar width b lp@55 required resolution at 55 degree pitch and 5096 modulation to read corresponding bar of width b @ 55
• * b@201p is the width of a bar which can be resolved with 5096 modulation at distance D using a lens quahty of twenty line pairs per millimeter
• the microprocessor 30 may emit a pulse to the LED driver 44 of predetermined duration sufficient to create visible marker spots at a distance of twenty inches, but of brief duration to avoid detrimental blurring.
• the reflected hght due to beams 51, 52 is evaluated based on the output from the image sensor 20. If the output from the sensor 20 resembles Fig. 3C, where pulses 61, 62 have a relatively close spacing (in time) Pc relative to total sensor readout time T, computer 30 could conclude that the focus adjustment was proper without activating stepping motor driver 34. In this case, with the beam sources 41, 42 de-energized, the clock buffers 26 could be activated to clear the image sensor 20 and effect a readout therefrom.
• a lens condition register e.g., maintained by battery power while the reader remained in a standby mode.
• the microprocessor would then activate stepper driver 34 to effect focus adjustment.
• the microprocessor could take a reading from sensor 20 with the beam sources 41, 42 off. Normally at this time, the user might not yet have ahgned the reader with the bar code, but the output from converter 32 would provide information which could be used to determine whether the auxiliary hght source 14 should be pulsed via lamp driver 16.
• a next operation of the microcomputer might be either to again pulse beam sources 41, 42 to maintain the marker beam and distance monitor function, or to pulse the hght source 14 and make a further attempt at a bar code reading.
• the driving pulse supplied to the hght source 14 could have a time duration such as to provide for a vahd bar code reading even with stepper motor 36 operating at top speed.
• the microprocessor 30 could refine the target lens adjustment. As such target focus condition was approached, the microcomputer would follow an optimum deceleration program to bring the lens system to a stop at an optimum focus position.
• the microprocessor would maintain a current register for lens focus position as pulses were supphed to the driver 34, and, for use in a subsequent reading operation, this register could then show the final position of the lens system where a vahd bar code reading had been obtained.
• the microprocessor 30 is preferably programmed so as to provide periodic flashes of the beam sources 41, 42 while a reading operation is in progress so that the operator is adequately guided in aiming of the reader toward a bar code.
• the operation of auxiliary hght source 14, where indicated will be brief enough to avoid detrimental blur.
• the hght source 14 is preferably only flashed, as may be needed, to verify the microcomputer's evaluation of operating conditions until such time that the microcomputer determines that proximity to optimum focus has been reached, e.g., where the object is located within the depth of focus of the lens system for the current lens system adjusted position.
• the microprocessor may frequently examine the output of the image sensor 20 using ambient hght during focus adjustments since this does not require the use of lamp driving power, and since the readings can provide useful information concerning the need for the auxiliary hght source and/or supplemental information concerning the focus condition of the optical system. It is preferred, however, that bar code information only be sent to a host system where such information appears to represent vahd bar code information which could be decoded by the host. An alternative would be for the microprocessor to decode the incoming signal from converter 32 prior to sending bar code information to the host.
• microprocessor 30 would generate a binary (rectangular waveform) bar code signal to represent the decoded data, or of course, merely send the bar code number as decoded.
• microprocessor 30 may activate the stepper motor 36 to place the lens system 22 in such initial condition, e.g., focused at a distance where the next label is most likely to be found based on the experience of the last few reading operations.
• STEP (4) A comparison of the focusing mirror's existing position with the desired focusing mirror position is made and the computer calculates the amount and direction of corrective motion and sends the necessary control signals to the motor driver; STEP (5) An image of the object without the pointing beams is taken, processed and made available for decoding;
• STEP (6) The cycle may be repeated in order to correct the focusing mirror position by taking an image with the pointing beams "ON" for remeasuring the interval between the spots (the computer recognizes the spot images since they are substantially different from barcode pulses); and STEP (7) After successfully decoding label data, the reading system, including the microcontroller, goes into a power down mode for conserving the battery energy, leaving the focusing mirror in the latest position.
• the pointing beams may be generated by either bright visible LEDs or visible sohd state lasers.
• both LEDs and lasers may be of an infrared type if their purpose would be limited only to range measurement.
• a single beam (instead of the two beams used in the preferred embodiment) might also be used for the same purpose.
• the position of the center (of area of the image) of a single beam relative to a fixed point on the image sensor would then correspond with the distance to the target.
• a target surface pitch angle might produce an error since the point of impingement of a single beam might not represent the average distance of the label from the reader.
• Two pointing beams are preferred.
• Two beams provide the computer with the information necessary to determine the distance to the target independently in two points, i.e., the centers of the two pointing spots.
• the distance between spots provides knowledge pertaining to the distance to the middle point between the spots, but if necessary, the individual distance to each spot may be determined and used for reading long labels at significant pitch angles by sequentially focusing at both halves and reconstructing the full label data.
• visible LEDs may be utilized without additional lenses to distances of about 1 to 2 feet. If a longer range is desired, visible lasers or collimating lenses (external to LED) may be used. For cost reduction, two beams may be created with a single laser with a beam sphtter and mirror.
• the hght source 14 may be of the type disclosed in the aforementioned Laser et al. U.S. Patent 4,570,057, it is conceived that the hght source might comprise a tungsten wire 70 with an associated reflector 71 (as indicated in Fig. 5). Tension springs may act on the opposite ends of the wire in order to absorb the elongation of the wire when driven to emit a hght pulse. Microcomputer 30 may monitor the pulse excitation of the wire 70 so as to take into account wire temperature during a further electric current pulse, and may further limit the duration of the electric current pulse to only that time interval required to produce the desired hght output.
• auxiliary on-board hght source may be, for example, either: (1) an array of bright LEDs, (2) a long filament incandescent bulb powered in a supercharge mode, or (3) a strobe hght.
• a significantly bright pulse of hght may be regularly produced by applying a 2 ms pulse with a voltage eight times the nominal lamp voltage. The energy spent in such a pulse was determined to be 0.15 J. This approximates the same energy used by the strobe hght found in the product described in Laser, et al., U.S. Patent N a 4,570,057.
• data may be determined regarding: (1) the necessary voltage and power requirement per pulse, (2) energy storage devices, (3) filament modification, and (4) bulb life.
• Incandescent lamps are capable of producing pulses of hght with durations in milliseconds. Incandescent lamps provide the following advantages: (1) small size, (2) power efficiency, (3) utilization with a concentrated flux and small reflector (a thin filament presents an accurate hght source), (4) long life, (5) durability, (6) high energy flash output, and (7) the amount of hght per pulse may be controlled.
• Existing line filament lamps exhibit a typical life of between 1,000 to
• Strobe lights are also commonly utihzed as hght sources. Strobe hghts may be the best option where very fast label motion is required, hi order to achieve a 10 inch per second non-blurred image speed (with a label having
• the CCD integration time should not exceed 250 microseconds. However, such an integration time is not a problem if an electronic shutter is utihzed. In such a case, the required level of label ihumination will be very high.
• the strobe hght hardware described in the Laser, et al., U.S. Patent N a 4,570,057 might be utihzed for the instant apphcation. Where fast label motion is required a customized xenon tube with a significantly reduced diameter would produce a much more accurate hght beam that would be easy to form and direct efficiently. Such a customized xenon tube would reduce power. consumption, component size, and provide an increased firing rate.
• Exemplary Optical Systems Figs. 5, 6 and 7
• the lens 81 should be aspheric with an F-number of approximately five.
• the variable parameter for focusing is the distance between the sensor 82 and the lens 81.
• a light weight mirror 84 is inserted in the optical path between the sensor 82 and the lens 81 to serve two goals: (1) to shorten the required length of the housing, and (2) to alter the distance by moving a low mass component. The second goal is the most critical of the two. For fast acting focusing mechanisms the amount of moving mass is a crucial consideration.
• the mirror 84 and supporting bracket 85 may be made as a single metallized plastic part with a mass of less than 0.5 grams.
• this rotational movement is accomplished by pivotally mounting the mirror support bracket 85 to a drive quadrant 86.
• the drive quadrant is drivably connected to a stepper motor 87.
• a single photosensor array 82 mounted within a housing, is utihzed for both ranging and imaging purposes.
• the housing includes a hght receiving opening for alignment with optical information or the like.
• Optical means are associated with the array 82 such that the image of optical information may be focused on the array 82.
• the optical means includes a lens 81 associated with a primary mirror 83 (Fig. 5, 6, & 7). Light entering the housing through the opening is refracted by the lens 81 onto the primary mirror 83. Light refracted by the lens 81 onto the primary mirror 83 is then reflected back through the lens 81 onto the focusing mirror 84.
• the focusing mirror 84 may be adjusted such that both the angle of separation and distance between the mirrors may be changed (Fig. 6 & 7).
• the focusing mirror 84 is held by the bracket 85 which is pivotably connected to a drive quadrant 86. Rotation of a drive motor shaft causes the position of the focusing mirror 84 to change in relation to the array 82 (Fig. 6 & 7).
• the image of a bar code, or the like is focused from any distance, within a substantial range of distances, onto the array 82 by operation of the stepper motor 87.
• An ultra high brightness LED is preferably used for distance measurement.
• Such an LED is commercially available as part AND190CRP from AND Corporation of Burlingame, California.
• the AND190CRP may be utihzed in pulse mode.
• pulse mode current may be increased up to ten times in order to achieve a corresponding increase in brightness. Since available power is limited to five volts, a current increase of three to four times may be expected in pulse mode.
• Mirror positioning might be based on a number of approaches.
• the auto-focusing algorithm may have several branches with various priorities depending on the instant situation.
• Focusing data might be derived from the distance between the two red pointer spots. With a pair of "Kilobright” LEDs the narrow beams could be turned on and off during alternate scans so the image could be taken with or without the LED beams.
• Another source of focusing information might be derived from an analysis of sensor data.
• the steepness of slopes may be studied for deciding which direction to drive the focusing mirror.
• the modulation coefficient for different pulse widths could be measured and then compared with a similar measurement of a following scan.
• the processed data could be sorted statisticaUy in histograms, representing distribution of modulations in the pulse width domain. Then particular groups of pulse widths could be identified in different scans and their average modulations compared. This comparison would provide focusing quahty (FQ) criteria.
• the computer could trace the history of FQ and make decisions regarding the amount and direction of focusing movement.
• Automatic focusing of a barcode reading system may be accomplished by analyzing, in real time, certain quahties of an image signal produced by a CCD sensor. A numerical value may be calculated to provide the quantitative estimate of the focusing accuracy . This focus criterion may then be used to estimate the amount of adjustment necessary to achieve an optimum focus. The f ollowing three methods may be used for determining
• Slopes of pulses represent transitions from dark to bright and are steeper for sharp images.
• the microprocessor 30 may determine the sharpest slope in a scan and record its value in volts per pixel.
• the slope rate is a function of focus quahty.
• the slope rate function may be reshaped into a value by using a table.
• the degree of modulation of pulses present in a bar code image signal depends on the width of those pulses.
• A is an amphtude of a pulse, measured from its root to peak value
• E is an average of peak values for bright and dark pulses in the area of interest.
• modulations maybe stored temporarily along with values of corresponding widths.
• Wl is the largest width permitted for the narrow group
• W2 is the shortest pulse width in a scan
• k is an empirically adjusted coefficient equal to 2.5 ⁇ 0.5.
• focusing quahty Q m may be derived through modulation measurements as:
• Q a is a measure of focus quahty which represents a normahzed dispersion of the extreme values of a signal. Without loss of functionality the squaring of deviations may be omitted in order to increase processing speed.
• A is a current extreme value of a bright pulse
• a 0 is an average value of bright extremes ((l/n) ⁇ A j ), Bj is a current extreme value of a dark pulse, B 0 is an average value of dark extremes ((l/n) ⁇ Bi), and n is the number of pulse pairs.
• Fig. 8 shows a typical curve.
• this function exhibits duahty, it is still very useful for determining the position of the best focus by measuring its value at a current position, e.g., if it is possible to measure a current value q of the focus quahty function in the current position of the focusing mechanism (pi or p2) then the distance to the best position p may be found, and the duplicity problem could be resolved by tracing the direction and result of a previous move.
• Fig. 9A and Fig. 9B illustrate a family of overlapping focus quahty functions for a number of equally spaced positions of a focusing mechanism.
• bar code density must decrease as distance is increased.
• the further the target with a label the wider the minimum bar (or space) of a bar code. This corresponds with the function of a fixed focal length lens where the distance from the lens to the sensor is adjustable for focusing.
• Fig. 9A best illustrates focus quahty as the position of best focus moves towards longer ranges.
• the focusing mechanism would move an equal amount (for example 3 steps of a stepper motor) between each of the shown positions.
• the curves will be about the same and equahy spaced, as shown on the Fig. 9B. This adds to the simplicity of the focusing mechanism design.

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• 1992
  • 1992-07-23 CA CA 2121464 patent/CA2121464A1/en not_active Abandoned
  • 1992-07-23 EP EP92916874A patent/EP0621970A1/de not_active Withdrawn
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