HK1169504B - Integrated illumination assembly for symbology reader - Google Patents

Description

Integrated illumination assembly for symbology reader

This application is a divisional application filed on application No. 200680048666.8(PCT/US2006/041041) on a date of 2006, 10/19, 10/2006 entitled "integrated illumination assembly for symbology reader".

Technical Field

The present invention relates to machine vision systems and symbology readers employing machine vision, and more particularly to illuminators for such symbology readers.

Background

Machine vision systems utilize image acquisition devices that include a camera sensor to provide information about the object being viewed. The system then interprets the information in accordance with various algorithms to perform programming decision-making and/or recognition functions. In order to most effectively acquire an image in the visible and near visible range by the sensor, the subject should be properly illuminated.

In the paradigm of symbology reading (also commonly referred to as "bar code" scanning) with an image sensor, proper illumination is highly desirable. Symbology reading requires aiming an image acquisition sensor (CMOS camera, CCD, etc.) at a target location containing a symbol ("bar code") and acquiring an image of the symbol. The symbol comprises a set of predetermined patterns representing an ordered set of characters or shapes from which an attached data processor (e.g., a microcomputer) can derive useful information about the object (e.g., its serial number, type, model number, price, etc.). Various shapes and sizes of symbols/barcodes may be used. The two most common types of symbols in identifying and recognizing objects are the so-called one-dimensional barcodes, which are made up of vertical lines of varying width and spacing, and the so-called two-dimensional barcodes, which are made up of two-dimensional arrays of dots or rectangles.

By way of background, FIG. 1 illustrates an exemplary scanning system 100 suitable for handheld operation. An exemplary hand-held scanning appliance or handpiece 102 is provided. Which includes a grip portion 104 and a body portion 106. The imaging system 151, shown in phantom, may be controlled and may direct image data to the on-board embedded processor 109. The processor may include a scanning software application 113 through which application 113 controls lighting, acquires images, and interprets image data into usable information (e.g., alphanumeric strings derived from symbols (e.g., the illustrated two-dimensional barcode image 195)). The decoded information may be directed via cable 111 to a PC or other data storage device 112 having, for example, a display 114, a keyboard 116, and a mouse 118, where it may be stored and further manipulated using a suitable application 121. Alternatively, the cable 111 may be connected directly to an interface in the scanning appliance and an appropriate interface in the computer 112. In this case, the computer-based application 121 performs various image interpretation/decoding and illumination control functions as needed. The precise placement of the handheld scanning appliance is highly variable relative to an embedded processor, computer or other processor. For example, a wireless interconnect may be provided without the cable 111 therein. Similarly, the illustrated microcomputer may be replaced with another processing device, including an on-board processor or a miniaturized processing unit such as a personal digital assistant or other small computing device.

The scanning application 113 may be adapted to respond to input from the scanning appliance 102. For example, when the operator toggles the trigger 122 on the handheld scanning appliance 102, the internal camera image sensor (part of the imaging system 151) acquires an image of the region of interest 131 on the target 105. An exemplary region of interest includes a two-dimensional symbol 195 that can be used to identify the target 105. Identification and other processing functions are implemented by the scanning application 113 based on image data transmitted from the handheld scanning appliance 102 to the processor 109. The visual indicator 141 may be illuminated by a signal from the processor 109 to indicate a successful reading and decoding of the symbol 195.

The type of illumination employed is a point of interest when reading symbologies or other objects of interest. Where symbologies and/or other viewed objects are printed on a flat surface with highly contrasting inks or pigments, diffuse high angle "bright field" illumination may best highlight these features of the sensor. With high angles, it is generally meant that the light impinges on the target almost perpendicularly (orthogonally) or at an angle that differs from perpendicular (orthogonally) to the surface of the object being scanned by no more than about 45 degrees. Such illumination tends to reflect back to the sensor in large amounts. For example, barcodes and other targets that require predominantly bright field illumination may be provided on printed labels attached to objects or containers, or in printed areas in relatively smooth areas of objects or containers.

Conversely, when symbols or other targets are formed on more irregular surfaces, or generated by directly etching or peening a pattern on the surface, it may not be appropriate to use highly reflective bright field illumination. The peened/etched surface has a two-dimensional nature that tends to scatter the bright field illumination, thereby obscuring the acquired image. When the object under observation has such a well-defined two-dimensional surface structure, it can be optimally illuminated with dark-field illumination. This is an illumination that utilizes a characteristic small angle (e.g., about 45 degrees or less) relative to the target surface (i.e., an angle greater than about 45 degrees relative to normal). With this low angle dark field illumination, two dimensional surface structures (indentations appear as bright spots and the surroundings as shadows) can be more effectively contrasted to obtain a better image.

In the case of other applied symbols, diffuse type direct illumination may be preferred. Such illumination is typically produced using a directly projected illumination source, such as a Light Emitting Diode (LED), which passes through a diffuser to produce the desired illumination effect.

To take full advantage of the versatility of the camera image sensor, bright field, dark field, and diffuse illumination are preferably provided. However, it is necessary to provide dark field illumination close to the target to obtain low angles of incidence. Instead, bright field illumination is better generated at relative distances to ensure overall area illumination.

Commonly assigned U.S. patent application No.11/014478 entitled "HAND HELDSYMBOLOGY ILLUMINATION DIFFUSER", and U.S. patent application No.11/019763 entitled "LOW PROFILE ILLUMINATION source PART MARK READERS", both to Laurens w. These techniques include providing a particular geometric arrangement of direct bright field LEDs and a conical and/or flat diffuser, which are disposed between the bright field illuminator and the target to better diffuse the bright field light. The introduction of "HAND heldsymbolloy real ILLUMINATION DIFFUSER" above also teaches the use of specific colors to improve the ILLUMINATION suitable for a specific type of surface. For many types of surfaces and/or specific angles at which the reader is directed at the surface, the choice of bright field, dark field, direct or diffuse light is often not intuitive for the user. In other words, a surface may appear to be best read with dark field illumination, but in practice, especially at certain viewing angles, it is preferable to pick up the required details with bright field. Similarly, for handheld readers, the viewing angle between the surface and the surface (part and part) is never very the same, some viewing angles are better with bright fields, and others may be better with dark fields. The above-mentioned patent application contemplates the use of multiple illumination types to obtain optimal images for a particular surface and viewing angle.

It has been recognized that handheld readers present a number of unique problems. At least some of these problems are common with stationary readers. For example, the material from which most light guides are made is acrylic (commonly known as "plexiglass"). Acrylic exhibits a high refractive index (about 1.58), which is most suitable for transmitting light along the interior of the light guide. However, acrylic resin is easily broken in response to impact. This may limit the life and durability of the handheld reader (especially of the cordless/wireless type), which is expected to occasionally fall and strike a hard floor, perhaps a light pipe. Although the light pipe may be armored with shock absorbing materials and an outer jacket, this may disadvantageously increase production costs, weight, protrusion, and may optically obscure the pipe.

Further, the light pipes described in the above patents may include a chamfered end to project dark field illumination via internal reflection. Direct bright field illumination is also produced by refraction of the polished beveled tip. The optical clarity of the light guide and tip tends to produce a spotlight effect in which each individual illumination source (e.g., red LED) is clearly visible on certain surfaces (see fig. 7 below). This is contrary to the typical goal of providing a uniform illumination spread.

Furthermore, prior art devices are limited in their ability to provide a total source of direct diffuse illumination using a conical diffuser: light from several individual illumination sources (e.g., LEDs) is spread across the diffusing surface and then onto the target as diffuse light. Thus, diffuse light tends to exhibit a characteristic, namely localized speckle and dark spot effects. Adding additional illumination sources to the diffuse portion may be limited by the relative cost of space and illumination sources, especially when using the more costly blue LEDs.

Furthermore, prior art readers often include visual indicators on their back, top, or another surface that indicate the current status of the reader (e.g., power on/off, read good, error, read bad, ready, not ready, etc.). Various information may be provided to the user by different colors of light (e.g., red/green) and/or via a blinking pattern. However, in a production environment, small back-mounted or top-mounted indicators may be overlooked or otherwise interfere with a user attempting to focus on the surface being read. It would be highly desirable to have a technique for more conveniently associating indicators with the user's primary focus.

Disclosure of Invention

The present invention overcomes the deficiencies of the prior art by providing a variety of novel features that can be applied to readers in a variety of ways to improve illumination performance in dark field/direct bright field and direct diffuse type illumination. Other features enable enhanced light pipe durability without increasing weight or size and provide an easier to read status indicator by placing the status indicator close to the target and significantly enlarging the overall size of the indicator.

In one embodiment, the light pipe is made of durable polycarbonate for enhanced impact resistance. The beveled end of the light pipe is textured or frosted to further diffuse the refracted light passing through the end, thereby providing a more uniform effect. A tapered/wedge (tapered) diffuser within the light pipe is illuminated by a reflector having a white textured surface that reflects multiple backward (opposite to the illumination and viewing directions) illumination sources back to the diffuser. The reflector may define a predetermined cross-section that directs more light to the forwardmost, remote regions of the diffuser to produce better overall light spread and mitigate the effects of bright and dark spots. A textured surface on the chamfered light pipe end may be employed to better project the indicator light. Alternatively (or additionally), a textured surface may be applied to the exposed portion of the inner wall adjacent the distal (forward) end of the catheter.

The illumination sources, which may be multi-colored sources, are arranged in a ring at the inner end of the light pipe and flash in an appropriate pattern in response to the controller projecting the appropriate color and/or pattern to indicate various conditions, such as a read success or failure. The controller is typically adapted to provide these specific indications between actual image acquisitions in order to appropriately illuminate the image acquisitions. The controller may operate portions of the ring such that only a corresponding portion (e.g., quadrant) of the light pipe perimeter is illuminated at a particular color at a given time. In one example, different quadrants may be illuminated simultaneously with different colors.

In an exemplary embodiment, the light pipe defines a polygonal (e.g., rectangular) cross-section (the polygon is generally defined as at least four linear or non-linear sides, the four sides being connected at corners (which may be rounded) to form a (typical) inequilateral shape). The chamfered edge of each side is at a fixed angle, so that the north-south side is of a different length (in the case of a rectangle) than the east-west side, resulting in two different distances for dark field light to converge, which increases the depth of field. In other words, the polygon (rectangle) includes at least two pairs of opposing sides, the first pair of opposing sides having a different length than the second pair of opposing sides to create two different distances of dark field ray convergence points.

Drawings

The following description of the invention refers to the accompanying drawings, in which:

FIG. 1, already introduced, is a perspective view of a handheld scanning system with integrated illumination according to the prior art;

FIG. 2 is a side cross-sectional view of a handheld scanning system that can be used in conjunction with the teachings of the present invention;

FIG. 3 is a front view of the scanning system of FIG. 2;

FIG. 4 is an exploded view of an illumination assembly and image sensor for the scanning system of FIG. 2;

FIG. 5 is a somewhat schematic side cross-sectional view of a sensor and illumination assembly used in conjunction with the scanning system of FIG. 2, illustrating in detail the paths taken by the various illumination types;

FIG. 6 is a somewhat schematic side cross-sectional view of the light pipe of the illumination assembly of FIG. 5, showing the projection of direct bright field illumination in greater detail;

FIG. 7 is a diagram showing the illumination effect of projecting various illumination sources onto a surface through a polished beveled light pipe end;

FIG. 8 is a partial perspective view of a viewing end of a reader featuring an illumination assembly and having a textured surface on a chamfered light pipe end;

FIG. 9 is a diagram illustrating the illumination effect achieved with a textured chamfered light pipe end according to an embodiment of the present invention;

FIG. 10 is a block diagram of an image processor and illumination control circuit interacting with a sensor, trigger and illumination ring featuring respective quadrant controls and a multi-color illumination source;

FIG. 11 is a partial perspective view of the viewing end of the reader showing the textured chamfered light pipe end being illuminated by red light for use as an indicator;

FIG. 12 is a partial perspective view of the viewing end of the reader showing a textured chamfered light pipe end illuminated by green light for use as an indicator;

FIG. 13 is a partial perspective view of the viewing end of the reader showing a textured chamfered light pipe end illuminated red in predetermined quadrants and green in other predetermined quadrants to serve as an indicator;

FIG. 14 is a schematic side cross-sectional view of a light pipe, diffuser, illumination source and reflector showing a predetermined reflector geometry to enhance the projection of light along the remote region of the diffuser;

FIG. 15 is a somewhat schematic, side cross-sectional view of a light pipe of the lighting assembly, showing in detail the draft angle (r) provided for molding the light pipe, and showing an alternative placement of the diffusing surface at the distal end of the light pipe;

FIG. 16 is a schematic view of the general shape of a rectangular cross-section light pipe showing representations of the north, south, east and west edges;

FIG. 17 is a schematic representation of the convergence of dark field rays from the north and south edges of the light pipe of FIG. 16, showing a first distance thereto;

FIG. 18 is a schematic representation of the convergence of dark field rays from the east and west edges of the light pipe of FIG. 16, showing a first distance thereto; and

FIG. 19 is an exploded perspective view of a light pipe defining an elliptical cross-section in accordance with an alternative embodiment of the present invention.

Detailed Description

Fig. 2 shows a cross-sectional side view of an exemplary embodiment of a reader 200 according to the present invention. The imager 212 and the illumination panel 214 are located on an impact resistant mount (not shown) within the housing 206. In the exemplary embodiment, the processor module and associated functional electronics are mounted on a processor board 215. The grip portion 202 and the trigger 204 functionally cooperate with the housing 206 and components of the processor board 215. The grip portion 206 includes a conveniently located trigger 204 that can be actuated by a user's fingers to initiate image acquisition and decoding functions. More specifically, pressing the trigger causes illumination of all types and colors (as described further below) to be projected onto the target of interest simultaneously, and causes the imager to acquire images accordingly.

Referring briefly to the illuminator, the illumination board 214 supports a plurality of LEDs 310, which in this embodiment are red (multiple colors may be used). The LED 310 is directed forward, toward the opening of the reader. These LEDs are located behind a passive optical conduit 244, the passive optical conduit 244 transmitting light from the ring of LEDs 310 towards the interior of the front end 230. In this embodiment, the leading end 230 includes a chamfered surface 232. Various examples of lightpipes for use in readers or similar applications are shown and described in U.S. patent application No.10/693626, entitled "LIGHT piping SYSTEM AND METHOD," to William h.

Briefly, light propagates through the body of the conduit 244 from the inner end adjacent the LED 310. The body is formed of a transmissive/transparent substance. As mentioned above, one concern with light pipes is durability and impact resistance. In the examples of the present invention, a transparent polycarbonate (commercially available from BASF of Germany under the trade name Makrolon, or alternatively from general electric Company andcommercially available) to manufacture the light pipe. Can utilize the followingThe liquid resin formed into the desired shape injection molds the substance. The transmitted light is internally reflected by the angled/chamfered surface 232 of the light pipe 244 to exit at a low angle toward the central optical axis 270. Although acrylic exhibits a good refractive index (about 1.58), it has been found that the refractive index of polycarbonate (about 1.49) is also sufficient to achieve the degree of light transmission and internal reflection employed for dark field illumination according to embodiments of the present invention. The inner and/or outer wall surfaces of the light pipe 244 can be coated with an opaque paint or another mixture to prevent light from leaking into or out of the pipe. In this example, a shield 250 is also provided along the inner surface of the light pipe. One function of the shield 250 is to prevent the transmission of stray light (as described below) into the light pipe. Another function is to redirect light transmitted from the reflector (see below) back into the diffuser.

In this example, the ring of LEDs 310 is used to produce the red direct bright field effect along with the dark field effect by refraction of some of the light from the LEDs through the chamfered surface 232. Typically, at short read distances from the surface (< 25mm between the light pipe distal (front) end 230 and the surface), bright field illumination from the light pipe 230 tends not to interfere with dark field illumination. However, for larger reading distances (> 25mm between the tip 230 and the surface), the bright field illumination is also available. This is useful for easy-to-read codes such as black and white printed marks. In an alternative embodiment, a separate brightfield illuminator may be provided, as described below. In fact, many available imagers include an integrated red bright field illuminator. In an alternative embodiment, a separate bright field illuminator of a discrete (discrete) color (e.g. green) may be provided.

Note that a pair of aiming LEDs 220 (typically emitting green light) are provided. However, these are optional. Such aiming LEDs may be integrated with commercially available imagers employed herein.

The cable 260 provides power to the reader 200 and a communication transmission path for the decoded string of encoded information, although it is contemplated that the reader 200 may be configured for battery power and wireless communication for full portable flexibility.

Referring also to fig. 3, a front view of reader 200 is shown. The distribution and placement of the LEDs (or other suitable light elements) 310 emitting light to the light pipe 244 is represented by a series of adjacent xs positioned around the perimeter of the light pipe 244 in line with the distal end 230. The exemplary LED placement produces a substantially uniform lighting effect. The placement of these optical and other elements as used herein is highly variable. In addition, the addressing of the light elements can be controlled such that only particular elements are activated at a particular time to produce a desired overall dark field illumination intensity and/or bias of the dark field illumination effect on the target (e.g., one side is brighter than the other). This variable addressing feature is described further below and in more detail in the above-incorporated U.S. patent applications and other commonly assigned U.S. patent applications referenced therein.

Reference is now also made to the exploded view of fig. 4, which shows the components of the overall illumination assembly in more detail with respect to the imager 212. As shown, the various lighting assembly components described above have been separated to reveal various structural details. The imager 212 is located on the left side of the view. The lighting panel assembly 214 is positioned in front thereof. Positioned in front of the lighting panel 214 and the LEDs 310 is a proximal (or base) end 410 of the light pipe 244 that receives light emitted from the LEDs 310 and transmits it internally to the beveled distal end 230. A wedge-shaped (also referred to strictly as a "cone-shaped") diffuser 280 (see also fig. 2) is nested within the light pipe 244, with a narrow proximal opening 420 provided adjacent the imager 212 and a widened distal opening 422 at the opposite end. In an exemplary embodiment, the diffuser 280 may be fabricated from an internally frosted/textured thin (1-3 mm) polymer material. As described above, a thin shield 250 is provided against the interior of the light pipe to block the transmitted light of the diffuser from entering the light pipe 244. In this way, the light emitted from the diffuser is not mixed with the transmission of the light guide.

Space may be limited in the region between the shield 250 and the inner surface of the diffuser 280. Furthermore, it is contemplated in many embodiments that the use of high output blue LEDs to provide blue for diffuse illumination may be more costly than red or green LEDs. Thus, it is highly desirable to use a smaller number of such LEDs. The fewer individual illumination sources employed, the greater the need to spread the light around the diffuser to avoid the effects of bright and dark spots on the surface of interest. To achieve the desired spread of diffuse illumination with a minimum number of individual illumination sources, the light projected by the diffuser is provided by a set (four) of rear-projecting LEDs 282 mounted on the illumination board 214 on the side opposite the ring of light pipe LEDs 310. These LEDs 282 project back into a conical, spherical, parabolic (or other shaped) reflector 290 that spreads the reflected light throughout the inner surface of the diffuser 280 so that the light exits as substantially uniformly spread, direct diffused light onto the surface of interest. As described further below, the shape of the reflector may be optimized to improve the spread of light along the conical diffuser. In this embodiment, reflector 290 is fabricated from a polymer having a white textured surface to further diffuse the light reflected therefrom. Such indirect projection of light with a diffusive reflective surface greatly helps to reduce the number of diffuse illumination LEDs 282 used to project diffuse illumination, thereby reducing production costs and power consumption. As described above, in the present embodiment, the diffuse illumination LED 282 is a high-output blue LED. However, the specific colors used for each illumination are highly variable. However, it is highly desirable that the diffuse illumination be sufficiently spectrally spaced from the dark field illumination to achieve sufficient resolution of the two wavelengths of light.

A translucent "cone" filter 292 is provided. Filter 292 is adapted to filter out light of larger wavelengths, allowing the smaller wavelengths of blue light to pass through the diffuser and onto the surface, but preventing any red light reflected from the surface from being retransmitted, which would otherwise tend to be retransmitted as diffuse red light along with the red dark field illumination. The dispersion of wavelengths between red and blue is sufficient to achieve this filtering without affecting the performance of any type of illumination (dark field/direct bright field versus direct diffuse). The filter 292 conforms to the shape of the outer (exposed) surface of the diffuser and may be affixed or affixed to the diffuser surface using various fastening techniques as will be apparent to those of ordinary skill in the art. Note that a similar effect can also be obtained by using a color diffuser (see fig. 6 below) instead of the separate filter (292). The color should be chosen such that the diffuser transmits diffuse light (blue light in this embodiment) but does not reflect dark field light (red light in this embodiment) transmitted from the light guide.

Thus, in summary, at least two separate sets of illumination emitters (e.g., LEDs) are provided according to an exemplary embodiment, namely a direct diffuse emitter 282 and a dark field emitter 310. According to an exemplary embodiment, each set of discrete emitters 282 and 310 produces a corresponding discrete illumination color. For example, direct diffuse illumination may be produced by a blue LED, and a dark field (and direct bright field) may be produced by a red LED. The use of two discrete colors allows each illumination to be limited to its specific application without mixing using filtering in the illumination assembly. In this embodiment, each illumination produces an image that is received by the imager 212. The imager in this embodiment includes a conventional monochrome sensor that produces a gray scale image from colored light. Note that in alternative embodiments a color sensor may be employed. One such implementation is shown and described in commonly assigned U.S. patent application entitled "SYSTEMAND METHOD FOR EMPLOYING COLOR ILLUMINATION ANDCOLOR FILTRATION IN A SYMBOLOGY READER", filed on even date herewith and made by Laurens w.

Referring now to fig. 5 and 6, the illumination pattern achieved by the light pipe 244 and the diffuser 280 of the illumination assembly is generally depicted. Referring first to FIG. 5, a cross-section of one implementation of diffuser 280 is shown with respect to imager assembly 212 (and associated lens structure 240) having a light pipe 244 as generally described above. Dark field illumination (light rays 510) is directed into light pipe 244, which is internally reflected at beveled distal (front) end 230, directing it at low angle to target surface 520. More information on the basic design and implementation of a passive optical conduit utilizing selectively activated ILLUMINATION to provide dark field ILLUMINATION can be found in U.S. patent application No.10/693626, entitled "LIGHT PIPE ILLUMINATION SYSTEM AND METHOD," by William h. Direct illumination (light rays 532) from blue LEDs 282 is converted to overall diffuse direct illumination by reflection off reflector 290 and into and through diffuser 280 of the present embodiment. Whereby the diffuser 280 projects diffuse illumination onto the target surface 520 within the field of view, shown as the area bounded by dashed lines 540. In this embodiment, the diffuser 280 itself is translucent, with no color tone or color filtering effect. In alternative embodiments, the diffuser may be tinted to produce a desired color and/or act as a color filter (with a colored or white illumination source (282)). It should be noted that the diffuser 280 according to this and other embodiments described herein can be constructed and arranged to be removably attached to a handheld scanning appliance. In one example, the diffuser may be eliminated to allow emitter 282 to operate as non-diffuse direct bright field illumination. Alternatively, the diffuser may be provided with a movable baffle that selectively exposes a transparent (non-frosted/non-diffusing) window in the entire diffuser. The removability of the diffuser 280 may be achieved by incorporating snap-fit apertures and/or features in the diffuser and light pipe 242 that allow for removable components (not shown).

In this embodiment, direct non-diffuse bright field illumination (see rays 620 in FIG. 6) is provided by refraction of light through the chamfered end 230 of the light pipe 244. As particularly shown in fig. 6, a portion of the light reflected along the interior of the conduit 244 exits directly from the chamfered end 230 as higher angle (typically greater than 45 degrees relative to the axial surface 520) bright field light (rays 620). The remaining light is internally reflected by the chamfered end 230 and exits adjacent to the interior corner 630 of the conduit 244, as generally described above. Note that in an alternative embodiment, the light pipe may be modified to include a flat ring (lying in a plane perpendicular to the axis 270). This will allow additional bright field light to be transmitted directly onto surface 520. Similarly, an embedded light pipe with a flat (not chamfered) ring formed at its distal end can be used in alternative embodiments for direct transmission of bright field light along a waveguide separate from the dark field light pipe 244 shown. This may be useful in case the illuminator with discrete colors is used for direct bright field light. Alternatively, where optional direct bright field emitters are employed, they may be positioned so as to project light through clear/transparent portions (not shown) of diffuser 280.

Although not shown in this figure for simplicity, it is contemplated that a filter (292 above) may be employed above the diffuser to prevent reflected dark field (and bright field) light from moving into the diffuser 280.

As described in the background above, illuminator light pipes according to various prior implementations of indicia readers include polished distal ends. Referring briefly to FIG. 7, an image 710 of a reflective surface acquired using a light pipe having a polished tip is shown. This image 710 clearly shows the contour blob 720 produced by a single illumination source in the illumination ring. These spots result in a slightly damaged illumination pattern, which may affect the acquisition of the mark 730.

Referring to fig. 8, the reader 200 is provided with an illumination assembly 800 that includes a light pipe 810 according to an embodiment of the present invention. The light pipe 810 includes a chamfered end 820 near its forward periphery that is generally sized and shaped as described above. Notably, the illustrated outer surface 830 of the beveled tip 820 is finely frosted or textured. This provides a soft diffusion effect for light exiting as direct bright field illumination (see fig. 6) and internally reflected light exiting as dark field illumination. The resulting diffusion produces an image as shown in fig. 9. Note that the ring of light 920 surrounding the mark 930 is more uniform and the mark itself exhibits better contrast than the result of the polished end version shown in fig. 7.

The frosted or textured surface 830 provided along the chamfered end facilitates a novel and desirable display of the status of a reader according to embodiments of the present invention. Before describing the status display in detail, reference is made to fig. 10, which schematically shows the basic components of the illumination and image processing system of the reader. The circuit board (215 in fig. 2) of the reader includes a processor and an illumination controller, which are schematically represented as a processor/control block 1010. The processor/control 1010 may employ conventional image processing and tag identification/decoding processes. The processor/control 1010 receives a signal from the trigger (block 1012) for operating the illumination assembly and obtaining image data via the imager (block 1014). Under the control of processor 1010, the aiming LEDs are operated before and during image acquisition (block 1016 and see 220 in FIG. 2). These operations are used to keep the user aligned with the mark during the acquisition process, especially when scanning is performed at an offset distance from the target surface. For this reason, it is noted that acquiring images according to the present embodiment involves stepping through a plurality of illumination types (dark field and diffuse) in timed sequence, with the acquisition of the relevant images of the markers being performed during each illumination. Typically, the best image (or combination of images) is selected to decode the data represented by the mark. Before or after the fetch, the reader may indicate various status codes, such as read ready, read successful, read failed, and the like. These indicators are described below.

During the stepping process, the processor 1010 instructs the illumination ring (block 1020) to illuminate. The processor then instructs the diffuse illuminator (block 1018) to illuminate. As described in the various patent applications incorporated by reference above, the ring 1020 may include separate sets of LEDs (or other illumination sources), in this example, formed as quadrants, i.e., top/north 1022, bottom/south 1024, right/east 1026, and left/west 1028 (looking toward the reader front from the outside). The quadrants may be addressed individually by the processor. This allows the output of each quadrant to be varied to produce the desired effect on the target. This is particularly useful when the reader is positioned at a non-perpendicular angle to the target surface or the target surface is not flat. Various automatic adjustment processes may be included to effectively cycle through various lighting settings between quadrants to determine the arrangement/profile (profile) that achieves the best image. In this embodiment, the individual illumination sources (LEDs 1030) are commercially available multi-color LEDs (red and green in this embodiment, schematically represented by the split line in the middle of each LED 1030) that are capable of projecting either of two colors in response to the processor 1010. From an imaging perspective, this may be useful in providing different colors for dark field and direct bright field. More notably, the multi-color capability of the illumination ring allows the light pipe (and particularly the frosted tip 820) to project highly visible indicator light adjacent the target in multiple colors.

Fig. 11 generally shows in detail the illumination of light pipe 810 in order to provide an indicator to a user. In this example, the four quadrants 1110, 1120, 1130, and 1140 of the textured chamfered edge 820 are illuminated in red (represented by the circled R) by the appropriate set of LEDs in the ring. The frosted surface actually creates a bright, diffuse color band that enhances the viewing performance of the indicator. The indicator may be illuminated before, during or after image acquisition as a continuous or flashing signal. The flashes may be timed in a Morse (Morse) code to achieve the desired status message. It will be appreciated that providing a large clearly visible indicator light at the distal end of the lightpipe (near the indicia where the user will focus his or her attention) can provide a highly effective indicator that does not distract the user's attention from the target and that is visible whether the reader is placed close to or spaced from the target surface. Indeed, at offset distances, the indicator itself projects a colored light onto the surface, further focusing the user's attention on the task at hand.

As shown in FIG. 12, all light pipe end quadrants 1110, 1120, 1130, 1140 are illuminated with green light (represented by the circled G). This may be an uninterrupted (continuous green) or flashing indicator. The red (or another color) may also be alternately flashed according to any predetermined pattern to provide a particular message.

As shown in fig. 13, the indicator is characterized by two (or more) colors being simultaneously displayed by different quadrants (or other portions) of the light pipe edge. In this example, the top quadrant 1110 is red and the left quadrant 1140 is green. The opposing bottom and left quadrants 1120 and 1130, respectively, may also be red and green. The pattern may flash or alternate (e.g., red and green switching). Similarly, a unique color rotation may be made in which each quadrant changes to a different color in turn, such that the color change appears to move around the perimeter. Any visual and desirable color shift is contemplated as an indicator according to the present invention.

Reference is now made to fig. 14, which illustrates a variation of the shape of the reflector described above. As described above, the length and angle (a) of the conical diffuser 280 (typically less than 45 degrees relative to the axis 270 in each quadrant) defines a remote distal region 1410 between the inner wall of the diffuser 280 and the shield 250 that is small in volume and difficult for light from the reflector 1420 to fill adequately. The gap between the inner periphery of the illumination plate 214 and the inner wall of the diffuser further blocks the transmission of light into these remote areas 1410. Thus, the reflective surface 1422 of the reflector 1420 of this embodiment includes a plurality of steps 1424, 1426, 1428, 1429 that are designed to direct particular portions of the reflected light (rays 1430) from the LEDs 282 toward various portions of the diffuser, including the remote regions 1410. Note that adjacent to the central window 1450 in the reflector through which the imager views the object, a plurality of small angled steps 1429 formed in the cross-section are particularly suitable for transmitting light rays 1430 from the light source 282 to various points along the remote regions 1410 for optimal light spreading along the entire diffuser surface. The reflector 1420 in this embodiment also includes a textured surface and white surface coloration to achieve maximum diffusion. In alternative embodiments, different surface colors and surface finishes may be used. In this way, a more uniform illumination of the entire diffuser surface is achieved and the presence of bright and dark spots on the target is minimized.

While stepped reflector 1420 is shown and described in accordance with an embodiment of the present invention, it is expressly contemplated that reflectors having various surface cross-sectional profiles may be employed in alternative embodiments. Such a reflector should be suitable for distributing light along the length of a wedge-shaped or cone-shaped diffuser having a shape as broadly contemplated herein using optical focusing techniques in order to avoid undesirable speckle on localized areas of the surface of interest.

It is contemplated that light pipes having textured or frosted chamfered ends according to embodiments of the present invention may be produced by various techniques including grit blasting or peening of the polished surface, i.e., the desired construction techniques required to mold the light pipe from the poured resin. The chamfered end is located near the bottom of the mold and the back end (adjacent the illumination ring) is located at the top of the mold where the polished catheter is ejected from the mold. The bottom of the mold is provided with a frosted or textured pattern to create the surface effect on the beveled end of the polished catheter. Referring to FIG. 15, a cross-section of the light pipe 244 is shown. The mold is configured to have a slight draft angle that is tapered such that the resulting light pipe 244 defines a pair of interior walls (each side being 1 degree relative to the axis 270) having a draft angle AD of approximately at least 2 degrees therebetween. Because the mold includes a frosted/textured surface, the draft angle is set to about 2 degrees, rather than the typical 1 degree for smooth molded parts. This 2 degree draft angle better overcomes possible sticking effects that can occur between the polished conduit and the textured mold surface. Such draft angles are used when applying texture to the chamfered end 230. Note that each chamfered end 230 defines an angle of about 70 degrees therebetween (each end being about 35 degrees relative to the axis 270). It should be appreciated, however, that the techniques used to form the light pipes and other components herein may vary within the purview of the ordinary artisan.

With further reference to FIG. 15, according to an alternative embodiment, a frosted or textured finish may be applied to the inner wall of the light pipe 244 at the end location 1520. This location 1520 is exposed at the distal end of the diffuser 280 and beyond the shield 250 described above to allow the dark field light (ray 510) to propagate unimpeded. This results in the reflected dark field light passing through the diffusive structures before impinging on the marking surface. Note that a textured surface may also be applied to the outside (location 820) in embodiments of the present invention. Alternatively, the textured surface may be selectively applied to only one of the interior locations (1520) or the exterior locations (820), as appropriate. It should be noted that the actual draft angle AD (FIG. 14) will typically be greater than 2 degrees when texturing the interior wall at location 1520. The appropriate draft angle can be determined by one skilled in the art of molding plastic parts.

According to the above-described embodiment, the light pipe has a generally cross-sectional perimeter shape that is rectangular (as viewed in a plane passing through the axis 270). For the purposes of this specification, the term "rectangular" shall include the case where the sides of the rectangle deviate somewhat from the straight shape. In other words, the rectangular shape herein may include, for example, a curvilinear arc as shown and described. In general, the term rectangle should be generally defined as a set of linear or non-linear edges that intersect at each of four corners (which may be substantially rounded corners) such that the general direction of two adjacent edges changes by approximately ninety degrees. A generalized representation of the height of the rectangular light pipe 1610 is shown in fig. 16. As described above, the sides 1620, 1622, 1624, and 1626 of the rectangular light pipe 1610 may be defined in terms of north (arrow N), south (arrow S), east (arrow E), and west (arrow W). Similarly, each edge of the distal beveled tip can be represented as EN (north edge), ES (south edge), EE (east edge), and EW (west edge) accordingly. The length LNS between the north edge EN and the south edge ES (in this embodiment) is shorter than the length LEW between the east edge EE and the west edge EW (LNS < LEW). Note that in alternative embodiments, the opposite case may be (LNS > LEW), or the measures may be approximately equal.

Referring to fig. 17 and 18, the chamfered edges along each edge are set to the same fixed angle (about 55 degrees in this embodiment) to produce dark field rays that converge at point 1710 at an average fixed angle θ of about 32 degrees (representing half of the chamfer angle with a resulting draft angle of 1 degree and further refraction of the light as it exits the inner wall of the conduit). Since distance LNS is less than distance LEW, the convergence distance DNS for light from a pair of opposing edges EN and ES is less than the convergence distance DEW for light from a pair of opposing edges EE and EW. This arrangement then provides a wider depth of field for the reader by providing two different illumination distance ranges for the indicia. In an embodiment of the present invention, the length NS is approximately 3cm and the length EW is approximately 4.5 cm. DNS is approximately.92 cm, and DEW is approximately 1.23 cm. Thus providing a suitable difference of more than 0.31cm for a greater depth of field.

In addition to providing a greater depth of field with two throw distances, the rectangular light pipe shape described above provides several advantages over circular light pipes and other generally equilateral shaped light pipes. The rectangular shape more closely conforms to the conventional 4: 3 horizontal to vertical ratio exhibited by commercially available sensors. The rectangular cross section achieves a larger dark field range than that provided by a circular catheter. It also allows for a lower profile reader in terms of overall height. Furthermore, as described above, the use of separate "edges" on the catheter enables easier control of the individual quadrants.

Note that while the embodiments described herein are generally contemplated as somewhat polygonal shapes with corners connecting adjacent sides, it is expressly contemplated that a continuously curved connection between "sides" may be provided. As such, the terms "edge" and a pair of opposing edges should be understood to include ellipses in which the opposing edges spanned by the major axis are greater in length than the opposing edges spanned by the minor axis. In this way, each set of edges produces a different dark field average convergence distance, thereby producing the desired increased depth of field. To this end, FIG. 19 details an elliptical cross-section light pipe 1910 (with appropriate redesign of the illumination ring and diffuser shapes where applicable) that can be adapted for use with embodiments of the present invention. The distal end of light pipe 1910 terminates at an angled, beveled end 1920 and operates as generally described herein. The edges of the beveled ends generally define a pair of opposing north and south edges (1930 and 1932, respectively) and east and west edges (1940 and 1942, respectively) that are spaced at different distances. In this case, these distances are (respectively) the minor axis MIA and the major axis MAA of the ellipse. In this embodiment, the "edge" may be characterized as: continuously merge into one another with arbitrary boundaries or with "continuously curved corners". Variations of this basic oval shape are expressly contemplated. In any case, for a given fixed chamfer angle, the edges produce at least two discrete ray convergence distances.

It should be clear from the above embodiments that a reader with excellent illumination and indicia reading capabilities is described herein. Such a reader alleviates many of the disadvantages encountered with prior art readers and provides improved target illumination, status indication and overall robustness.

The foregoing is a detailed description of exemplary embodiments of the invention. Various modifications and additions may be made without departing from the spirit and scope thereof. For example, any of the various features described herein may be combined with some or all of the other features described herein in accordance with alternative embodiments. Furthermore, although a plurality of multicolored LEDs are provided, individual single-color LEDs, each of a plurality of colors, may also be provided adjacent to each other on the illumination ring in alternative embodiments. Similarly, although a quadrant-divided ring is shown, any acceptable division of the entire ring may be provided according to alternative embodiments. Some parts of the whole ring can be made to work together with other parts according to embodiments thereof. For example, the top and right portions may work together in total, or the top and bottom portions may work together in total. Similarly, other ring colors, such as yellow, may be used to provide more types of indicators. A multi-color illumination source or a plurality of adjacent individual illumination sources (or a combination of individual and multi-color sources) may be used to produce the desired set of ring colors. Further, although a rectangular light pipe is shown and described, a greater range of depth of field may be obtained by providing a non-equilateral shape (e.g., a slanted hexagon) with more than four sides connected by corners. The present invention contemplates polygonal light pipe sections having four or more sides (straight or curved) joined at corners (which may be rounded). Finally, it is expressly contemplated that any of the processes or steps described herein can be implemented as hardware, software, including program instructions executing on a computer, or a combination of hardware and software. Accordingly, this description is to be construed as illustrative only and is not intended to limit the scope of the invention in any way.

Claims (7)

1. An illumination assembly for an indicia reader disposed along an optical viewing axis, comprising:

a light pipe bounded by at least four adjacent sides, including a first pair of opposing sides and a second pair of opposing sides, the light pipe including a beveled edge at a distal end that directs light from a ring light source at a proximal end onto a surface as a dark field; and is

Wherein a length of a first spacing between the first pair of opposing sides is different than a length of a second spacing between the second pair of opposing sides.

2. The illumination assembly as set forth in claim 1 wherein the light pipe includes a diffuser positioned within an interior defined by the light pipe, the diffuser projecting direct diffuse illumination.

3. The lighting assembly of claim 1, wherein at least one of the chamfered edge and an inner edge of the light pipe opposite the chamfered edge includes a diffusive surface thereon.

4. The lighting assembly of claim 3, further comprising a lighting controller adapted to project lighting in at least a first color from the ring light source to provide a first status signal at the chamfered edge.

5. The lighting assembly of claim 4, wherein the controller is adapted to project illumination from the ring light source in a second color different from the first color to provide a second status signal at the chamfered edge.

6. The lighting assembly of claim 1, wherein the first pair of opposing sides and the second pair of opposing sides collectively define an approximately elliptical shape.

7. The lighting assembly of claim 1, wherein the first and second pairs of opposing sides collectively define a rectangle having corners between adjacent sides.