Abstract:
An industrial reader is provided with an image formation system that is particularly adapted to read bar codes and two-dimensional symbols marked directly on objects. The image formation system includes illumination sources and illumination transmissive components that produce a combination of bright field and dark field illumination.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to the field of symbology readers used to read symbols marked directly on objects. Symbology readers of this type, commonly known as direct part mark readers, are an extension of hand-held and fixed-mount image-based symbology readers. A direct part mark reader requires a unique image formation system to produce an image of a symbol that can be successfully and consistently decoded. 
     2. Description of the Related Art 
     Two-dimensional symbols are used for most direct part marking applications because such symbols can encode a sufficient number of characters while maintaining a relatively compact size. Error correction schemes are typically included in most two-dimensional symbologies, to improve the readability. The two-dimensional symbols are marked directly on the part or component using various methods, depending upon the material composition, part application, and environmental conditions. Common methods include dot peening, laser, and electro-chemical etch. 
     Symbols marked directly on a part or component are often difficult to read in comparison to symbols printed on labels. An image of a dot-peened, or etched mark often exhibits very low contrast using illumination or image formation systems of most image-based symbology readers. When a symbol is printed on an adhesive label, and applied to a part or component, or the part packaging, a typical image-based symbology reader can provide sufficient read rate. Industry trends, however, suggest that applications of direct part marking are nevertheless increasing. 
     Illumination of a symbol or mark is a primary concern when acquiring an image of the symbol to be read and decoded by an image-based symbology reader. Where symbols are printed on labels, or when marked directly on a part with a flat surface, high-angle “bright field” illumination is the type of illumination often used. Bright field illumination is a term of art for a type of illumination that produces a dark object in a bright background. Under bright field illumination, high-angle illumination strikes the object nearly perpendicularly, or at an angle not greater than 45 degrees from perpendicular. This type of illumination results in substantial illumination reflecting back toward the reader. 
     When a symbol or mark is etched or peened onto the surface of part or component, and the surface is rough or irregular, high-angle bright field illumination may not be appropriate. The irregular surface of the mark features will scatter as much light back to the reader as the surface of the background, resulting in indistinguishable features in the image. Low angle, “dark field” illumination has been shown to be suitable for certain direct part marking applications. 
     Under dark field illumination, low-angle illumination strikes the object at a low angle from the surface of the object, i.e., at an angle between 45 degrees and 90 degrees from perpendicular. Dark field illumination reflects away from the reader, with only random, irregular features of the mark or symbol on the surface of the object reflecting a portion of the illumination back into the reader. Further, certain reading applications may yield higher successful read rates when a combination of bright field and dark field illumination is used. 
     Industrial symbology readers are typically designed to provide bright field illumination from lighting sources integrated into the reader. When these readers are adapted to read direct part mark symbols, the use of removable light pipes and other adapters are used to redirect bright field illumination into a dark field mode. Accordingly, hand held readers known in the art that are used for direct part mark reading applications are configured exclusively for either bright field mode or dark field mode. 
     Accordingly, there is a need for a direct part mark reader with integrated illumination that provides variable and controllable illumination in both bright field and dark field modes. 
     BRIEF SUMMARY OF THE INVENTION 
     An illustrative embodiment of the present invention provides an industrial identification mark reader with integrated illumination for both bright field and dark field modes. The reader has a housing with an imaging module that captures an image of a mark on an object placed before the reader. Within the housing, an illumination module has an array of selectively actuated illuminators for illuminating the mark or object. An integrated optical transmitter, supported by the housing, is aligned with, i.e., in optical cooperation with, the selectively actuated illuminators. The integrated optical transmitter has a dark field transmitter for transmitting dark field illumination, and bright field transmitters, for transmitting bright field illumination. 
     The integrated optical transmitter has a transparent window to provide a path for reflected illumination into the imager module, and to provide protection from the elements to the imager module, the illuminator module, and other internal components of the reader. 
     In an alternate illustrative embodiment, the integrated optical transmitter has a light pipe for the dark field transmitter, with a base having the bright field transmitter positioned within the light pipe. The alternate illustrative embodiment can be a removable component of the reader to permit field replacement for maintenance and repair and/or to permit the use of alternate light pipe designs for further varied illumination properties. 
     A third illustrative embodiment of the reader has a viewing port through which a user can view the field of view to which is visible to the imager. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       The invention description below refers to the accompanying drawings, of which: 
         FIG. 1  is a perspective view of a hand held industrial mark reader with an embodiment of the present invention; 
         FIG. 2  is a perspective view of an illumination transmitter according to an embodiment of this invention; 
         FIG. 3  is an exploded perspective view of the components of an industrial mark reader according to an embodiment of the present invention; 
         FIG. 4  is a side view of the components of an industrial mark reader according to an embodiment of the present invention; 
         FIG. 5   a  is a front plan view of a hand held industrial mark reader with an alternate illustrative embodiment of the present invention; 
         FIG. 5   b  is a left side plan view of a hand held industrial mark reader with an alternate illustrative embodiment of the present invention; 
         FIG. 5   c  is a top plan view of a hand held industrial mark reader with an alternate illustrative embodiment of the present invention; 
         FIG. 6  is a cross section diagram of the components of an industrial mark reader according to an alternate illustrative embodiment of the present invention; 
         FIG. 7  is an exploded perspective view of the components of an industrial mark reader according to an alternate illustrative embodiment of the present invention; 
         FIG. 8  is an exploded perspective view of the components of an industrial mark reader according to an alternate illustrative embodiment of the present invention; 
         FIG. 9  is an exploded perspective view of the components of an industrial mark reader according to an alternate illustrative embodiment of the present invention; 
         FIG. 10  is a cross section diagram of light pipe component of an industrial mark reader according to an alternate illustrative embodiment of the present invention, showing dark field illumination; 
         FIG. 11  is a cross section diagram of light pipe component of an industrial mark reader according to an alternate illustrative embodiment of the present invention, showing dark field illumination; and 
         FIG. 12  is a cross section diagram of the components of an industrial mark reader according to a third illustrative embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows an illustrative industrial mark reader  100  adapted for handheld operation, of the type that acquires an image of a mark or symbol, such as a one-dimensional or two-dimensional bar code, or data matrix symbol. An internal processor (not shown) performs an analysis of the acquired image, and decodes the mark or symbol to provide a character string of the encoded information. 
     The reader  100  shown in  FIG. 1  has a grip portion  102  and a trigger  104  that can be actuated by a finger of the user to initiate the image acquisition and decoding function. A housing  106  contains an imager  112  (shown in phantom) that is connected to a processor (not shown). A status illuminator  108  provides visual indication of the status of the reader, such as to indicate a successful decode of an acquired image of a mark. A tether cord  110  provides electrical power to the reader  100 , as well as a communication transmission path for the decoded character string of the encoded information, though it is contemplated that the reader  100  can be configured with battery power and wireless communication for complete portable flexibility. 
     The reader  100  provides illumination of the mark during the acquisition of an image of the mark through the emission of light from an illumination board  114  (shown in phantom). The reader  100  of the present invention includes an integrated optical transmitter  120 , as shown in further detail in  FIG. 2 , to provide various types of illumination. 
     Referring to  FIG. 2 , the integrated optical transmitter  120  is shown according to an illustrative embodiment of the present invention. The transmitter  120  is a molded plastic part that has a structural frame  210  that provides structural support by engaging in recessed channel of the housing  106  (not shown). One skilled in the art can appreciate a number of assembly techniques that can be used to assemble the various components of an opto-electronic device such as the exemplary reader  100 . The transmitter  120  also includes a plurality of bright field illumination transmitters  220  that transmit bright field illumination from within the housing  106 . The bright field transmitters  220  can be molded or fabricated to provide a lens capability and/or have diffusion properties to modify the angle and orientation of bright field illumination. The optical properties of the bright field transmitters  220  can be applied to either the front or the rear of the integrated transmitter  120  during fabrication, or both sides, as necessary to provide the lens capability. 
     The optical transmitter  120  also includes a dark field illumination transmitter  230  that transmits low angle dark field illumination from within the housing  106 . The dark field illumination transmitter  230  consists of an extended barrel of light transmissive material terminating (in this embodiment) in an angled tip  235 . As described further below, this tip is designed to cause internal reflection that projects a low-angle dark field illumination in the area directly in front of the reader  100 . As noted above, such dark field illumination is typically provided at an angle greater than approximately 45 degrees from perpendicular. 
     The transmitter  120  also includes a window  240  that provides a transmission path for the reflected illumination into the housing  106  in the optical path of a field of view for the sensor module  112 . The window  240  of the integrated optical transmitter  120  also provides physical protection from the elements for the several components of the reader that reside within the housing  106 . Additionally, the window  240  can provide other optical functions, including filtering (for example, to reduce the effects of ambient illumination), and providing a telecentric view at the object by restricting the size of the opening. 
       FIG. 3  shows a perspective exploded view of the integrated optical transmitter  120 , illumination board  114  and imager module  112 . The illumination board  114  has shown four bright field illuminators  320 , each aligned with a bright field transmitter  220 . The bright field illuminator  320  can be a surface mount LED that can be individually actuated by a processor controlling the illumination (not shown) concurrent to the acquisition of an image of a mark, if bright field illumination is desired during acquisition. 
     The illumination board  114  has shown an array of dark field illuminators  330  that are generally aligned with the dark field transmitter  230 . Each of the dark field illuminators  330  can be surface mounted LEDs that can be individually actuated by a processor controlling the illumination (not shown) to provide dark field illumination in a variety of modes concurrent to the acquisition of an image of a mark, if dark field illumination is desired during acquisition. For example, various modes of illumination can be provided by the array of dark field illuminators  330  that are actuated in quadrants, as disclosed in co-pending U.S. patent application Ser. No. 10/911,989 filed Aug. 5, 2004, herein incorporated by reference. Control of various modes of illumination, and the synchronization of illumination to a specific acquisition, can be performed by a processor module (not shown) within the reader  100 . 
     The illumination board  114  of the illustrative embodiment has a hole  340  that is aligned with the window  240  and the imaging module  112  to permit the transmission of reflected illumination from the mark into the imaging module  112  during image acquisition. Note that the size and shape of the hole  340  is sufficiently sized to not obscure reflected illumination from entering the imaging module  112 . 
     The imaging module  112  is positioned behind the illumination board  112  in the exemplary embodiment, to receive reflected illumination to produce an image of the mark or symbol. The imaging module  112  has an area sensitive imaging array and an imaging lens. The imaging array can be a charge coupled device (CCD) or a complimentary metal oxide semiconductor (CMOS) device, or other imaging sensor known in the art. The imaging module  112  can also include focus adjustment mechanism to optimize the focus of an image projected onto the imaging array. Additionally, the imaging module can also include illumination to project on-axis bright field illumination toward the field of view, and/or to project an aiming illumination beam onto the field of view to provide the user with guidance for positioning the reader  100  during acquisition. 
     Coupled to the imaging module  112  is a processor unit (not shown) for receiving an acquired image from the imager module  112  to process and ultimately decode the image of the mark or symbol presented to the reader  100 . The imager  112  can receive configuration instructions from the processing unit to set acquisition parameters, such as exposure duration, gain, offset, etc., in a manner commonly known in the art. The processor unit is coupled to the trigger  104  to initiate the illumination and image acquisition process when the trigger is actuated by the user. 
       FIG. 4  is a side view representation of the arrangement of the several components of the reader  100 . The integrated optical transmitter  120  directs bright field and dark field illumination onto the mark or symbol  410 . The illumination board  114  is positioned behind the integrated illumination transmitter  120 , and the imaging module  112  is positioned behind both the integrated transmitter  120  and the illumination board  114 . 
     When bright field illumination is used to illuminate a mark or symbol, the illumination projected onto the field of view has a high angle of incidence, e.g., less than 45 degrees from normal, as depicted as bright field illumination rays  430  in  FIG. 4 . Accordingly, bright field illumination mode  460  is attained when the reader  100  is positioned in the range of approximately 3 to 8 inches from the mark or symbol  410 . 
     When dark field illumination is used to illuminate a mark or symbol, the illumination projected onto the field of view has a low angle of incidence, e.g., greater than 45 degrees from normal, as depicted as dark field illumination rays  420  in  FIG. 4 . Due to internal reflection caused by the angled portion  425  of the angled tip  235 , low angle dark field illumination  420  exits from the transmitter  120 . Accordingly, dark field illumination mode  450  is attained when the reader  100  is positioned in the range of approximately 0 to 3 inches from the mark or symbol  410 . 
       FIGS. 5   a ,  5   b , and  5   c  depict an alternate illustrative embodiment of the reader  100  according to the present invention. Referring to  FIGS. 5   a - 5   c , the reader  100  has a grip portion  102  and a trigger  104  that can be actuated by a finger of the user to initiate the image acquisition and decoding function. A tether cord  110  provides electrical power to the reader  100 , as well as a communication transmission path for the decoded character string of the encoded information, though it is contemplated that the reader  100  can be configured with battery power and wireless communication for complete portable flexibility. In the alternate illustrative embodiment shown in  FIGS. 5   a - 5   c , the integrated optical transmitter  120  is partially shown in the reader  100 . The front view depicted in  FIG. 5   a  shows the bright field transmitters  220  and the window  240 . The dark field transmitter  230 , and additional description of the alternate illustrative embodiment of the integrated transmitter  120 , is shown in the cross sectional view depicted in  FIG. 6  and the following description. 
       FIG. 6  shows a cross sectional side view of the alternate illustrative embodiment of the reader  100  according to the present invention. The housing  106  supports the positioning of the imager  112  and the illumination board  114 . The processor module and related functional electronic components are mounted on the processor board  115 . The grip portion  102  and the trigger  104  are functionally cooperative with the housing  106  and components of the processor board  115 . The integrated optical transmitter  120 , and particularly, the dark field transmitter  230 , are elongated in this alternative illustrative embodiment so that the dark field transmitter  230  operates as a light pipe for dark field illumination. The bright field transmitter  220  and the window  240  are shown at the base of the light pipe portion of the transmitter  120 , and positioned within the light pipe. 
       FIG. 7  shows an exploded view of the integrated optical transmitter  120  according to the alternate embodiment of the present invention. The transmitter  120  can be fabricated from injection molded plastic components that are epoxied or thermosonically welded into a single, integrated optical component. The dark field transmitter  230  is attached to the structural frame  210 , that has the bright field transmitters  220  molded therein. The window  240  is attached to the structural frame as shown, though optionally, the window  240  can be molded as an integrated component to the structural frame  210 . 
     Also shown in  FIG. 7  is the imager  112  mounted to a frame  570 . Rubber grommets  580  are inserted into receptacles  585  that can receive protrusions from the housing (not shown) to provide vibration and mechanical shock isolation in the assembled reader. 
     The frame  570  receives the distal end member  575  of the optical transmitter  120  according to the alternate embodiment. A screw  590  can be used to secure the transmitter  120  into the frame  570 . One skilled in the art will appreciate that various methods can be used to mechanically secure the described assembly in place to permit the operation of an industrial mark reader. The skilled artisan will also appreciate that a transmitter  120  described herein can be removable in the field by way of such methods of attachment. 
       FIG. 8  depicts the alternate illustrative embodiment of the reader  100  in a partially assembled exploded view from a rear perspective, and  FIG. 9  shows the same embodiment from a front perspective.  FIGS. 8 and 9  illustrate how the frame  570  is attached to the processor board. The optical transmitter  120  is shown in its fabricated, integrated form, depicting the bright field transmitters  220 , the dark field transmitter  230 , and the window  240 .  FIGS. 8 and 9  illustrate how the distal member  575  of the transmitter  120  is aligned for insertion into the frame  570 . Further shown is the illumination board  114  with the array of dark field illuminators  330 , and the bright field illuminators  320 . The bright field illuminators  320  and the dark field illuminators  330  are surface mount LEDs that illuminate on the board side of the LED body as mounted on the board. The illumination board  114  is fabricated with holes at each LED location so that when the LED is energized, the illumination projects through the board. When the transmitter  120  is inserted into place, the bright field illuminators  320  align with the bright field transmitter  220 , and the array of dark field illuminators  330  are aligned with the dark field transmitter  230 . 
     The integrated optical transmitter  120  according to the illustrative embodiment is molded or fabricated with polymethyl methacrylate (PMMA) or polycarbonate. The optical properties of the transmitter  120  can be obtained through polished mold surfaces and/or post fabrication polishing of the transmitter  120 . 
     The integrated optical transmitter  120  of the alternate embodiment can produce illumination in both bright field and dark field modes, as described above.  FIG. 10  is a cross sectional view of the dark field transmitter  230  according to the alternate illustrative embodiment. Illumination enters the transmitter at the face end  630  from the dark field illuminators  330  (not shown). The transmitter is a elongated light pipe  600  about the optical axis  635 , with a tapered end  625 . Dark field illumination rays  640  reflect from the tapered end  625  to project a dark field mode of illumination  450  when the reader is positioned in the range of approximately 0 to 3 inches from the mark or symbol  410 . Additionally, by virtue of the elongated light pipe design, the dark field transmitter  230  will contribute to bright field illumination when the reader  100  is positioned in the bright field illumination mode  460 , as shown in  FIG. 11 . Illumination from the dark field illuminators  330  (not shown) will enter the transmitter at the face end  630  at an angle that results in internal reflection over the length of the elongated light pipe  600 . Some of the illumination will emit from the tapered end  625  as high angle bright field illumination rays  650 . 
     An inherent difficulty with dark field illumination in most industrial mark readers is that the it is difficult to ensure that the mark or symbol  410  is in the field of view. The reader body obscures the mark or symbol when it is in dark field mode  450  from the user&#39;s view, and therefore, aiming and alignment of the reader is difficult. In an alternate embodiment of the present invention, a low profile reader is provided that permits direct observation of the mark or symbol by the user in dark field mode. 
       FIG. 12  depicts the reader  100  in a third alternate embodiment with an observation port  500 . The reader  100  has an integrated illumination transmitter  120  and an illumination board  114  as previously described. The user  510  can view the mark or symbol  410  directly through the observation port  500 , depicted as the line of sight  550  in  FIG. 12 . The reflected illumination  560  projects into the imaging module  112  by reflecting the illumination through a first mirror  520  and a second mirror  530 . 
     The foregoing has been a detailed description of various embodiments of the invention. It is expressly contemplated that a wide range of modifications and additions can be made hereto without departing from the spirit and scope of this invention. For example, the number, position and relative placement of the bright field transmitters on the integrated optical transmitter is exemplary and a variety of such transmitters can be employed to perform bright field illumination on hand held image-based decoding methods herein. Further, additional functionality can be added to the optical transmitter  120 , such as aiming optics to direct aiming illumination onto the field of view to provide guidance to a user during operation of the reader  100 . Further still, sensor optics can be incorporated into the integrated transmitter  120  to permit the transmission and reception of electromagnetic signals to be used in conjunction with an auto-focus mechanism in the reader  100 . Thus, improved or differing components can be employed within the teachings of this invention. Accordingly, this description is meant to be taken only by way of example, and not to otherwise limit the scope of this invention.