Patent Publication Number: US-2019182413-A1

Title: Imaging module and reader for, and method of, expeditiously setting imaging parameters of imagers for imaging targets to be read over a range of working distances

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation of U.S. patent application Ser. No. 15/083,493, filed on Mar. 29, 2016, and incorporated herein by reference in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates generally to an imaging module and an imaging reader for, and a method of, expeditiously setting one or more imaging parameters, such as exposure and/or gain values, of at least one imager for imaging targets to be electro-optically read by image capture over a range of working distances. 
     Solid-state imaging systems or imaging readers have been used, in both handheld and/or hands-free modes of operation, to electro-optically read targets, such as one- and two-dimensional bar code symbol targets, and/or non-symbol targets, such as documents. A handheld imaging reader includes a housing having a handle held by an operator, and an imaging module, also known as a scan engine, supported by the housing and aimed by the operator at a target during reading. The imaging module includes an imaging assembly having a solid-state imager or imaging sensor with an imaging array of photocells or light sensors, which correspond to image elements or pixels in an imaging field of view of the imager, and an imaging lens assembly for capturing return light scattered and/or reflected from the target being imaged, and for projecting the return light onto the array to initiate capture of an image of the target. Such an imager may include a one- or two-dimensional charge coupled device (CCD) or a complementary metal oxide semiconductor (CMOS) device and associated circuits for producing and processing electronic signals corresponding to a one- or two-dimensional array of pixel data over the imaging field of view. In order to increase the amount of the return light captured by the array, for example, in dimly lit environments, the imaging module generally also includes an illuminating light assembly for illuminating the target with illumination light in an illumination pattern for reflection and scattering from the target. 
     In some applications, for example, in warehouses, it is sometimes necessary for the same reader to read not only far-out targets, e.g., on products located on high overhead shelves, which are located at a far-out range of working distances on the order of thirty to fifty feet away from the reader, but also close-in targets, e.g., on products located at floor level or close to the operator, which are located at a close-in range of working distances on the order of less than two feet away from the reader. The reader may illuminate the far-out targets by emitting an illumination light at an intense, bright level, and capturing the return light from the illuminated far-out targets by employing a far-out imager having a relatively narrow field of view, and may illuminate the close-in targets by emitting the illumination light at a less intense, dimmer level, and capturing the return light from the illuminated close-in targets by employing a close-in imager having a relatively wide field of view. This variable illumination light level enables each such target to be more reliably imaged and successfully read. 
     However, the use of more than one imager and the variable illumination level presents a challenge to reader performance. For optimum reader performance, each target must be read by the correct imager; the correct imager should be set with one or more optimum imaging parameters, such as exposure values and/or gain values; and the illumination light should be set at an optimum illumination light level or value. These values are different for each imager, and vary, among other things, as a function of the working distance and of the illumination light level. Increasing the exposure and/or the gain values of the imager, as well as increasing the illumination light level, will increase the captured image brightness of the image of the target, and vice versa. 
     In order to set an imager with one or more optimum imaging parameters, it is known for the imager to capture an entire image from the target, to analyze the brightness of the entire image, to change the imaging parameters based on the analysis of the entire image, to capture another entire image from the target, and to repeat all the steps of this process for as many times as it takes until the brightness of the entire image is within an acceptable level. An automatic exposure controller (AEC) is typically used to control the imager&#39;s exposure, and an automatic gain controller (AGC) is typically used to control the imager&#39;s gain. A typical known strategy is to use exposure priority, in which the exposure is increased first until a maximum exposure time or threshold (typically around 4-8 ms in order to reduce hand-jitter motion effects for a handheld reader) is reached. If the image brightness is still too low, then the gain is increased. This strategy maximizes the signal-to-noise ratio (SNR) of the imager, because the gain is only increased when necessary. Although generally satisfactory for its intended purpose, this known process is very slow and inefficient in practice, especially when more than one imager is involved, and when the entire known process has to be repeated for each additional imager. Reader performance can be deemed sluggish, and is unacceptable in many applications. 
     Accordingly, there is a need to expeditiously select the correct imager in such readers, to expeditiously set the selected imager with one or more optimum imaging parameters, and to expeditiously set the illuminating light assembly to illuminate the target with illumination light at an optimum illumination light level, in order to more rapidly, efficiently, reliably, and successfully read both far-out targets and close-in targets with the same reader. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       The accompanying figures, where like reference numerals refer to identical or functionally similar elements throughout the separate views, together with the detailed description below, are incorporated in and form part of the specification, and serve to further illustrate embodiments of concepts that include the claimed invention, and explain various principles and advantages of those embodiments. 
         FIG. 1  is a side elevational view of a portable imaging reader operative for reading targets by image capture over an extended range of working distances in accordance with this disclosure. 
         FIG. 2  is a schematic diagram of various components, including imaging, illuminating, and range finding assemblies supported on an imaging module that is mounted inside the reader of  FIG. 1 . 
         FIG. 3  is a perspective view of the imaging module of  FIG. 2  in isolation. 
         FIG. 4  is a cross-sectional view taken on line  4 - 4  of  FIG. 3 . 
         FIG. 5  is a cross-sectional view taken on line  5 - 5  of  FIG. 3 . 
         FIG. 6  is a vertical sectional view taken on line  6 - 6  of  FIG. 3 . 
         FIG. 7  is a flow chart depicting steps performed in accordance with a method of this disclosure. 
     
    
    
     Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions and locations of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention. 
     The system and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein. 
     DETAILED DESCRIPTION OF THE INVENTION 
     One aspect of the present disclosure relates to an imaging module, also known as a scan engine, for setting one or more imaging parameters, e.g., exposure and/or gain values, of at least one imager for imaging targets to be electro-optically read over a range of working distances away from the module. Another aspect of the present disclosure relates to an imaging reader having a housing for supporting the imaging module, and a light-transmissive window on the housing. 
     In both aspects, the imaging module comprises an imaging assembly including a near imager for imaging targets over a relatively wider imaging field of view, and a far imager for imaging targets over a relatively narrower imaging field of view. An illuminating light assembly illuminates targets with illumination light. A range finder determines a distance to a target. A main controller or programmed microprocessor controls a default one of the imagers, for example, the far imager, to capture a minor portion of an image of the target, determines a light intensity level of the captured minor portion of the image, selects at least one of the imagers based on the determined distance and/or the determined light intensity level, and controls the illuminating light assembly to illuminate the target with illumination light at an illumination light level based on the determined distance and/or the determined light intensity level. In addition, the main controller sets at least one of the imaging parameters of the selected at least one imager to a predetermined value based on the determined light intensity level and/or the determined distance, and controls the selected at least one imager, which has been set with the predetermined value, to capture an image of the target, which has been illuminated at the illumination light level. 
     A memory is accessible to the main controller and stores a plurality of predetermined values, e.g., exposure values and/or gain values, of the at least one imaging parameter for retrieval by the main controller from a look-up table. These predetermined values are different based on the determined light intensity level and/or the determined distance. Advantageously, the default imager is controlled by the main controller to operate at a predetermined frame rate, e.g., 60 frames per second (fps). The main controller determines the light intensity level from the minor portion of the image at a rate faster than the predetermined frame rate. By way of numerical example, if the image is subdivided into four quadrants, then the minor portion of the image can be one of these quadrants, in which case, the main controller can determine the light intensity level from the minor portion of the image at a rate that is four times faster, e.g., 240 fps, than the predetermined frame rate. Thus, the selected imager is more rapidly and efficiently set with optimum exposure values and/or gain values than heretofore. 
     Still another aspect of the present disclosure relates to a method of setting one or more imaging parameters of at least one imager for imaging targets to be electro-optically read over a range of working distances. The method is performed by providing a near imager to image targets over a relatively wider imaging field of view, by providing a far imager to image targets over a relatively narrower imaging field of view, by providing an illuminator to illuminate targets with illumination light, and by determining a distance to a target. The method is further performed by controlling a default one of the imagers, e.g., the far imager, to capture a minor portion of an image of the target, by determining a light intensity level of the captured minor portion of the image, by selecting at least one of the imagers based on the determined distance and/or the determined light intensity level, by controlling the illuminating light assembly to illuminate the target with illumination light at an illumination light level based on the determined distance and/or the determined light intensity level, and by setting the at least one imaging parameter of the selected at least one imager to a predetermined value based on the determined light intensity level and/or the determined distance. The method is still further performed by controlling the selected at least one imager, which has been set with the predetermined value, to capture an image of the target, which has been illuminated at the illumination light level. 
     Reference numeral  30  in  FIG. 1  generally identifies an ergonomic imaging reader configured as a gun-shaped housing having an upper barrel or body  32  and a lower handle  28  tilted rearwardly away from the body  32  at an angle of inclination, for example, fifteen degrees, relative to the vertical. A light-transmissive window  26  is located adjacent the front or nose of the body  32  and is preferably also tilted at an angle of inclination, for example, fifteen degrees, relative to the vertical. The imaging reader  30  is held in an operator&#39;s hand and used in a handheld mode in which a trigger  34  is manually depressed to initiate imaging of targets, especially bar code symbols, to be read in an extended range of working distances, for example, on the order of thirty to fifty feet, away from the window  26 . Housings of other configurations, as well as readers operated in the hands-free mode, could also be employed. 
     As schematically shown in  FIG. 2 , and as more realistically shown in  FIGS. 3-6 , an imaging module  10  is mounted in the reader  30  behind the window  26  and is operative, as described below, for expeditiously setting one or more imaging parameters, e.g., exposure and/or gain values, of an imager for imaging targets to be electro-optically read by image capture through the window  26  over an extended range of working distances away from the module  10 . A target may be located anywhere in a working range of distances between a close-in working distance (WD 1 ) and a far-out working distance (WD 2 ). In a preferred embodiment, WD 1  is either at, or about eighteen inches away, from the window  26 , and WD 2  is much further away, for example, over about sixty inches away from the window  26 . An intermediate working distance between WD 1  and WD 2  is about eighteen to about sixty inches away from the window  26 . The module  10  includes an imaging assembly that has a near imaging sensor or imager  12 , and a near imaging lens assembly  16  for capturing return light over a relatively wide imaging field of view  20 , e.g., about thirty degrees, from a near target located in a close-in region of the range, e.g., from about zero inches to about eighteen inches away from the window  26 , and for projecting the captured return light onto the near imager  12 , as well as a far imaging sensor or imager  14 , and a far imaging lens assembly  18  for capturing return light over a relatively narrow imaging field of view  22 , e.g., about sixteen degrees, from a far target located in a far-out region of the range, e.g., greater than about sixty inches away from the window  26 , and for projecting the captured return light onto the far imager  14 . Although only two imagers  12 ,  14  and two imaging lens assemblies  16 ,  18  have been illustrated in  FIG. 2 , it will be understood that more than two could be provided in the module  10 . 
     Each imager  12 ,  14  is a solid-state device, for example, a CCD or a CMOS imager having a one-dimensional array of addressable image sensors or pixels arranged in a single, linear row, or preferably a two-dimensional array of such sensors arranged in mutually orthogonal rows and columns, and operative for detecting return light captured by the respective imaging lens assemblies  16 ,  18  along respective imaging axes  24 ,  36  through the window  26 . Each imaging lens assembly is advantageously a Cooke triplet, although other fixed focus and variable focus lens combinations can also be employed. 
     As also shown in  FIGS. 2 and 4 , an illuminating light assembly is also supported by the imaging module  10  and includes an illumination light source, e.g., at least one light emitting diode (LED)  40 , stationarily mounted on an optical axis  42 , and an illuminating lens assembly that includes an illuminating lens  44  also centered on the optical axis  42 . The illuminating light assembly is shared by both imagers  12 ,  14 . As further shown in  FIGS. 2, 5 and 6 , an aiming light assembly is also supported by the imaging module  10  and includes an aiming light source  46 , e.g., a laser, stationarily mounted on an optical axis  48 , and an aiming lens  50  centered on the optical axis  48 . The aiming lens  50  may be a diffractive or a refractive optical element, and is operative for projecting a visible aiming light pattern on the target prior to reading. 
     As further shown in  FIG. 2 , the imagers  12 ,  14 , the LED  40  and the laser  46  are operatively connected to a main controller or programmed microprocessor  52  operative for controlling the operation of these components. A memory  54  is connected and accessible to the controller  52 . Preferably, the controller  52  is the same as the one used for processing the return light from the targets and for decoding the captured target images. 
     The aforementioned aiming light assembly also serves as a range finder to determine the distance to a target. The aiming axis  48  is offset from the imaging axes  24 ,  36  so that the resulting parallax provides target distance information. More particularly, the parallax between the aiming axis  48  and either one of the imaging axes  24 ,  36  provides range information from the pixel position of the aiming beam on one of the imaging sensor arrays. It is preferred to use the imaging axis  36  of the far imager  14 , because the parallax error will be greater for the far imager  14  than for the near imager  12 . It will be understood that other types of range finders, e.g., acoustic devices, can be employed to determine the target distance. Thus, the range finder locates the target to determine whether the target is in a close-in region, or an intermediate region, or a far-out region, of the range. 
     In operation, the main controller  52  controls a default one of the imagers, for example, the far imager  14 , to capture a minor or fractional portion of an image of the target. For example, if the image is comprised of a two-dimensional array of pixels arranged in a predetermined row number (M) of rows and a predetermined column number (N) of columns, then the minor portion of the image is comprised of a subarray of pixels arranged in a number of rows less than M and in a number of columns less than N. The subarray can be located anywhere on the image; for example, it can be in a corner or central area of the image, or it can be the area of the image covered by the aiming light pattern. 
     The main controller  52  then determines a light intensity level of the captured minor portion of the image. This is performed much faster than in the known art where the light intensity level had to be determined from the entire image. For example, if the default far imager  14  operates at a predetermined frame rate, e.g., 60 frames per second (fps), and if the image is subdivided into four quadrants, then the main controller  52  can determine the light intensity level from the minor portion or quadrant at a rate that is four times faster, e.g., 240 fps, than the predetermined frame rate. 
     The main controller  52  then selects either the near imager  12  or the far imager  14  based on the determined distance and/or the determined light intensity level. Once the correct imager has been selected, the main controller  52  then sets the one or more imaging parameters, e.g., exposure and/or gain values, of the selected imager to a predetermined or optimum value based on the determined light intensity level and/or the determined distance. The aforementioned memory  54  stores a set of exposure values and/or a set of gain values in a look-up table  60 . The main controller  52  has a gain controller  56  that can access the look-up table  60  and retrieve the correct gain value that corresponds to the determined distance and/or the determined light intensity level. The main controller  52  also has an exposure controller  58  that can access the look-up table  60  and retrieve the correct exposure value that corresponds to the determined distance and/or the determined light intensity level. Each set of exposure and gain values includes a range of different values, and is determined in advance by knowledge of the F-stop and responsivity of each imager as a function of distance away from the respective imager and/or the light intensity level. 
     The main controller  52  also controls the illuminating light assembly to illuminate the target with illumination light at an illumination light level based on the determined distance and/or the determined light intensity level. The main controller  52  energizes the illuminating light assembly to illuminate the target with illumination light of a relatively lesser intensity when the range finder determines that the target to be imaged and read is located in a close-in region of the range; or energizes the illuminating light assembly to illuminate the target with illumination light of a relatively greater intensity when the range finder determines that the target to be imaged and read is located in a far-out region of the range; or energizes the illuminating light assembly to illuminate the target with illumination light of a relatively intermediate intensity that is between the lesser intensity and the greater intensity when the range finder determines that the target to be imaged and read is located in an intermediate region that is between the close-in region and the far-out region of the range. 
     More particularly, the main controller  52  energizes the LED  40  with a variable electrical current to vary the intensity or level of the illumination light. By way of non-limiting numerical example, the electrical current is on the order of 30 milliamperes when the close-in region lies between about 0.0 inches and about eighteen inches from the window  26 , is on the order of 150 milliamperes when the intermediate region lies between about eighteen inches and about sixty inches from the window  26 , and is on the order of 600 milliamperes when the far-out region lies between about sixty inches and infinity from the window  26 . The main controller  52  varies the intensity of the illumination light either as a continuous analog function, or as a stepwise, multi-level function, of the distance determined by the range finder. 
     Once the correct imager has been selected by the main controller  52 , and once the gain and/or exposure values for the selected imager have been set by the gain and exposure controllers  56 ,  58 , and once the illumination light level has been determined by the main controller  52 , then the selected imager is operated by the main controller  52  to capture an image of the target to be read. Reader performance is rapid and aggressive. 
     The flow chart of  FIG. 7  depicts the method disclosed herein. In step  100 , the minor portion of the image of the target is captured by one of the imagers by default, e.g., the far imager  14 . In step  102 , the light intensity level of the captured minor portion of the image is determined, and the distance to the target is also determined. Either the far imager  14  or the near imager  12  may be selected based on the determined distance and/or the determined light intensity level in step  104 . The target is illuminated with illumination light whose illumination level is also based on the determined distance and/or the determined light intensity level in step  106 . Then, optimum exposure and/or gain values are set for the selected imager in step  108  by referral to the look-up table  60 . In step  110 , the selected imager, whose exposure and/or gain has already been set, captures an image of the target, which has been illuminated at the illumination light level. 
     In the foregoing specification, specific embodiments have been described. However, one of ordinary skill in the art appreciates that various modifications and changes can be made without departing from the scope of the invention as set forth in the claims below. Accordingly, the specification and figures are to be regarded in an illustrative rather than a restrictive sense, and all such modifications are intended to be included within the scope of present teachings. 
     The benefits, advantages, solutions to problems, and any element(s) that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as a critical, required, or essential features or elements of any or all the claims. The invention is defined solely by the appended claims including any amendments made during the pendency of this application and all equivalents of those claims as issued. 
     Moreover in this document, relational terms such as first and second, top and bottom, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. The terms “comprises,” “comprising,” “has,” “having,” “includes,” “including,” “contains,” “containing,” or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises, has, includes, contains a list of elements does not include only those elements, but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. An element proceeded by “comprises . . . a,” “has . . . a,” “includes . . . a,” or “contains . . . a,” does not, without more constraints, preclude the existence of additional identical elements in the process, method, article, or apparatus that comprises, has, includes, or contains the element. The terms “a” and “an” are defined as one or more unless explicitly stated otherwise herein. The terms “substantially,” “essentially,” “approximately,” “about,” or any other version thereof, are defined as being close to as understood by one of ordinary skill in the art, and in one non-limiting embodiment the term is defined to be within 10%, in another embodiment within 5%, in another embodiment within 1%, and in another embodiment within 0.5%. The term “coupled” as used herein is defined as connected, although not necessarily directly and not necessarily mechanically. A device or structure that is “configured” in a certain way is configured in at least that way, but may also be configured in ways that are not listed. 
     It will be appreciated that some embodiments may be comprised of one or more generic or specialized processors (or “processing devices”) such as microprocessors, digital signal processors, customized processors, and field programmable gate arrays (FPGAs), and unique stored program instructions (including both software and firmware) that control the one or more processors to implement, in conjunction with certain non-processor circuits, some, most, or all of the functions of the method and/or apparatus described herein. Alternatively, some or all functions could be implemented by a state machine that has no stored program instructions, or in one or more application specific integrated circuits (ASICs), in which each function or some combinations of certain of the functions are implemented as custom logic. Of course, a combination of the two approaches could be used. 
     Moreover, an embodiment can be implemented as a computer-readable storage medium having computer readable code stored thereon for programming a computer (e.g., comprising a processor) to perform a method as described and claimed herein. Examples of such computer-readable storage mediums include, but are not limited to, a hard disk, a CD-ROM, an optical storage device, a magnetic storage device, a ROM (Read Only Memory), a PROM (Programmable Read Only Memory), an EPROM (Erasable Programmable Read Only Memory), an EEPROM (Electrically Erasable Programmable Read Only Memory) and a Flash memory. Further, it is expected that one of ordinary skill, notwithstanding possibly significant effort and many design choices motivated by, for example, available time, current technology, and economic considerations, when guided by the concepts and principles disclosed herein, will be readily capable of generating such software instructions and programs and ICs with minimal experimentation. 
     The Abstract of the Disclosure is provided to allow the reader to quickly ascertain the nature of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. In addition, in the foregoing Detailed Description, it can be seen that various features are grouped together in various embodiments for the purpose of streamlining the disclosure. This method of disclosure is not to be interpreted as reflecting an intention that the claimed embodiments require more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive subject matter lies in less than all features of a single disclosed embodiment. Thus, the following claims are hereby incorporated into the Detailed Description, with each claim standing on its own as a separately claimed subject matter.