Abstract:
An illumination method and apparatus for machine-vision systems, including a ring-light source (e.g., LEDs arranged in one or more circular rows), and a reflective-ring focusing element. The illumination source exhibits multi-directional ring-illumination properties which are useful for illumination of small components (which are being inspected or measured) without unwanted shadows. One embodiment provides a darkfield illumination system. One embodiment of the present invention uses a strobed (or pulsed) power supply to drive the LEDs. Yet another embodiment of the present invention uses a xenon strobe ring-light source and a backplane slit in place of the row of LEDs  25.  In one such xenon strobe embodiment, a color filter, is also placed in series with the light path in order to obtain a monochromatic light. While xenon flashtube light sources tend to exhibit a five percent (5%) flash-to-flash variation in intensity which makes accurate measurements of certain characteristics difficult, they are useful in certain cases where intense white, or especially ultraviolet, light is desired. Strobed LEDs provide very little flash-to-flash variation in intensity. The compact ring-light generator has little, if any, shadowing. The present invention also provides an inexpensive apparatus and method for changing the light-source-to-optical-axis angle.

Description:
This application is a divisional of U.S. patent application Ser. No. 08/914,441, filed Aug. 19, 1997, now U.S. Pat. No. 6,022,124 which application is incorporated by reference. 
    
    
     TECHNICAL FIELD OF THE INVENTION 
     The present invention pertains generally to illumination optics, and more particularly systems and methods for illumination of objects in machine-vision systems. 
     BACKGROUND OF THE INVENTION 
     During the manufacture of certain products, such as electrical components, it is necessary to be able to provide high-intensity illumination so that components can be thoroughly inspected with a machine-vision system. Often, the light source needed includes one or more light sources, for example a ring-shaped flashtube or a number of light-emitting diodes arranged along a circle or a remote light source that drives light into a number of optical fibers arranged along a circle, surrounding the lens of a video camera such that the object being imaged by the video camera is illuminated with light angled in towards the optical axis of the camera from the light source surrounding the lens. It is desirable that the light source or sources are arranged such that no light shines directly from the light sources into the lens. 
     Typically, a xenon flashtube or laser-based single-point source or other high-intensity light source is used for providing light into fiber-optic-based ring source. Such systems, however, are costly, very, large and bulky, and can interfere with the placement of other components in the machine-vision system. This is particularly troublesome when the components being measured or inspected are extremely small. Xenon flashtube light sources also tend to exhibit up to about a five percent (5%) flash-to-flash variation in intensity which makes accurate measurements of certain characteristics difficult. Single-point source systems are also generally limited to emitting light radially from only one single point, which is of limited value when shadows are problematic, such as, when inspecting a grid of electrical connectors. Specifically, light from only one or just a few point sources only illuminates the first over-sized or over-height electrical connector and, due to shadows from the first object encountered, does not provide proper illumination which would determine if other objects behind this particular first object are missing, of the incorrect size or height, or perhaps in the wrong position. 
     Conventional illumination systems produce a light which can be too bright in certain areas and too dim in other areas. Often, the end-result is “bloom”, especially when viewing white, lightly colored, or very reflective objects which are near other objects which need to be viewed by a machine-vision camera. In order to get enough light on the other objects which need to be viewed, the aperture on the camera cannot be “stopped down” in order to prevent overexposure of the bright objects. Specifically, the area is illuminated to such an extent that the entire image appears to be the same bright saturated white color (or, if a monochromatic light source is used, saturated at whatever color is used) as viewed by the machine-vision camera and system. Such extreme brightness also poses a danger of blinding, at least temporarily, human workers nearby. 
     Quite often, illumination sources either leave certain portions of the scene in shadows, or provide too much light in certain areas, while leaving other areas with too little light. In other cases, the illumination source is too bulky and gets in the way of other components of the machine-vision system, associated robots, manipulators, and/or human workers. 
     The optimal light-source-to-optical-axis angle can vary depending on the object being inspected. One shortcoming of conventional ring light sources is the cost and difficulty in changing the angle between the light sources relative to the optical axis, and in changing the spread and/or focus of the light from ring-light source. 
     Thus, what is needed is an ring-light illumination system and method which is compact, provides control over both the angle between the light source and the optical axis of the camera, as well as the spread and/or focus of the light from ring light source, so that even extremely small parts can be quickly and adequately inspected and accurately viewed or measured with a machine-vision system. Another need is to provide a compact illumination source, preferably monochromatic, which can be focused to provide uniform multi-directional light onto objects from all sides while avoiding light going directly from the light sources to the lens of the camera. Another need is to provide a compact monochromatic LED (light-emitting diode) illumination source, which can be changeably focused to provide uniform multi-directional light onto objects. Another need is to have such an LED illumination source be pulsed with a relatively high-power, low duty-cycle power source. 
     SUMMARY OF THE INVENTION 
     The present invention takes, advantage of the efficiency of high-brightness red, infra-red, blue, white, or other color LEDs arranged in one or more circular rows, and the properties inherent to a reflective focusing element such as a turned angled reflective ring to produce an illumination source for machine-vision systems. The illumination source exhibits multidirectional ring-illumination properties which are useful for illumination of small components (which are being inspected or measured) without unwanted shadows. One embodiment provides a darkfield illumination system. One embodiment of the present invention uses a strobed (or pulsed) power supply to drive the LEDs. Yet another embodiment of the present invention uses a xenon strobe ring-light source and a backplane slit in place of the row of LEDs  25 . In one such xenon strobe embodiment, a color filter is also placed in series with the light path in order to obtain a monochromatic light. While xenon flashtube light sources tend to exhibit a five percent (5%) flash-to-flash variation in intensity which makes accurate measurements of certain characteristics difficult, they are useful in certain cases where intense white, or especially ultraviolet, light is desired. 
     The present invention provides a compact ring-light generator which has little, if any, shadowing. The present invention also provides an inexpensive method for changing the light-source-to-optical-axis angle. The present invention also provides an inexpensive method for changing the spread and/or focus of the light from ring light source. 
     The present invention provides a method and apparatus which provide an illumination source for illuminating an object in a machine-vision system having a machine-vision camera, the camera having an optical axis. One embodiment of the illumination source includes a ring-light source emitting light from a plurality of points, the points being along one or more circles, a focusing element, the focusing element including an angled ring reflector to direct rays from the ring light source at an angle generally towards the optical axis. One embodiment provides a replaceable ring reflector for changing the light-source-to-optical-axis and/or changing the spread and/or focus of the light from ring light source. One embodiment provides light from multiple directions in order to reduce shadowing. One embodiment provides light to illuminate the inside of, for example, an aluminum beverage can before it is filled and sealed. 
     One embodiment uses a ring-reflector focusing element which includes a first conical section reflective surface at a first conical angle to the optical axis. Another embodiment further includes a second conical section reflective surface at a second conical angle to the optical axis. 
     One embodiment includes an illumination source for illuminating an object in a machine-vision system, the system having an optical axis. The illumination source includes a ring light source and a ring reflector. The ring light source emits light from a plurality of points or from a line, the points or line being substantially in a plane that intersects the optical axis, each of the points or the line disposed at least a first distance from the optical axis and less than a second distance from the optical axis. The ring reflector has an exit opening through which the optical axis passes, the emitted light from the ring light source being generally directed centered on lines that intersect a reflecting surface of the ring reflector, the ring reflector reflecting the emitted light from the light source through the exit opening inwards and generally toward the optical axis or an area around the optical axis. 
     In one such embodiment, the ring light source includes a plurality of light-emitting diodes (LEDs) arranged substantially along a circle disposed perpendicular to and centered on the optical axis. In another such embodiment, each LED has an focal centerline emission axis along which emission is centered, and each LED&#39;s emission axis is parallel to the optical axis. In yet another such embodiment, each LED has an focal centerline emission axis along which emission is centered, and each LED&#39;s emission axis is perpendicular to the optical axis. 
     In one embodiment, the light emitted from the LEDs is two or more selected from the following: infra-red, red, amber, yellow, green, blue, violet, ultraviolet, or white in color. In another such embodiment, the light emitted from the LEDs is primarily within an angle of about 5° from a focal centerline of each individual LED. 
     One embodiment further includes a focusing element that includes a cylindrical ring lens having at least one convex face. 
     In one embodiment, the ring light source includes a ring-shaped flashtube located substantially along a circle disposed perpendicular to and centered on the optical axis, and further includes an enclosure having a slit located between the ring-shaped flashtube and the ring reflector, wherein the slit allows light from the flashtube to fall on a reflecting surface of the ring reflector. 
     In one embodiment, the ring reflector has a surface that enhances its reflectivity at one or more selected wavelengths of the ring light source. 
     In one embodiment, the ring reflector and ring light source are configured to produce a darkfield illumination. 
     Another aspect of the present invention is a method for illuminating an object located along anoptical axis. The method includes the steps of (a) emitting light from a plurality of points or from a line, the points or line being substantially in a plane that intersects the optical axis, each of the points or the line disposed at least a first distance from the optical axis and less than a second distance from the optical axis; and (b) reflecting the emitted light from the light source inwards and generally towards the object at the optical axis or in an area around the optical axis. 
     In one such embodiment, the object is an electrical connector, and the method further includes the step of acquiring a machine-vision image of the electrical connector. One application for such a method is inspecting ball-grid arrays. 
     Another aspect of the present invention provides a machine-vision illumination system. The system includes an imaging device, an image processor coupled to the imaging device, and an illumination source coupled to the image processor. The illumination source includes a ring light source and a ring reflector. Other aspects of such a system are described above. 
     Another aspect of the present invention provides a ring reflector for use in reflecting light from a ring light source The ring reflector includes a substantially circular exit opening though which the optical axis passes and a reflective surface surrounding the exit opening. The reflective surface extends from approximately a first circle having a first radius, to approximately a second circle and having a second radius, the second radius being larger than the first radius, the first radius being larger than the difference between the second radius and the first radius. 
     In one such embodiment, the reflective surface includes a conical section. In another such embodiment, the reflective surface includes a plurality of adjoining conical sections. In yet another such embodiment, the reflective surface includes a circularly-rotated parabolic section. In still another such embodiment, the reflective surface includes a plurality of reflective facets. In one such embodiment, for a plurality of the facets, a line normal to the facet surface passes through the optical axis. Another aspect of the present invention provides a reflective surface that is configurable to change the angle at which it reflects light. 
     These and other features, aspects, and advantages of the present invention will become better understood with regard to the following description, appended claims and accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1A is a side-view schematic diagram of one embodiment of machine-vision illumination system  100 . 
     FIG. 1B is a circuit schematic diagram of a portion of one embodiment of machine-vision illumination system  100 . 
     FIG. 2A is an exploded isometric view of ring-reflector illumination source  200  according to one embodiment of the present invention. 
     FIG. 2B is a cut-away side view of ring-reflector illumination source  200  according to one embodiment of the present invention. 
     FIG. 2C is a cut-away side view of one ring-light source  230  using LEDs according to one embodiment of the present invention. 
     FIG. 2D is a cut-away side view of another ring-light source  230  using LEDs according to one embodiment of the present invention. 
     FIG. 2E is a cut-away side view of yet another ring-light source  230  using LEDs according to one embodiment of the present invention. 
     FIG. 2F is a cut-away side view of ring-light source  236  using a xenon flashtube according to one embodiment of the present invention. 
     FIG. 2G is an exploded isometric view of a flash-tube light source  2361  according to one embodiment of the present invention. 
     FIG. 2H is an exploded isometric view of a flash-tube light source  2362  according to one embodiment of the present invention. 
     FIG. 2I is a cut-away side view of two stacked ring-reflector illumination sources  200 A and  200 B according to one embodiment of the present invention. 
     FIG. 2J is a cut-away side view of an alternative ring-reflector illumination source  200  according,to one embodiment of the present invention. 
     FIG. 3A is a cut-away side view of one ring reflector  220  according to one embodiment of the present invention. 
     FIG. 3B is a cut-away side view of another ring reflector  220  according to one embodiment of the present invention. 
     FIG. 3C is a cut-away side view of yet another ring reflector  220  according to one embodiment of the present invention. 
     FIG. 3D is a cut-away side view of still another ring reflector  220  according to one embodiment of the present invention. 
     FIG. 3E is a cut-away side view of a facetted ring reflector  226  according to one embodiment of the present invention. 
     FIG. 3F is a cut-away side view of a configurable ring reflector  227  according to one embodiment of the present invention. 
     FIG. 3G is an enlarged cut-away side view of a configurable ring reflector  2273  having overlapped facets  2271  each pointing towards the optical axis  299 . 
     FIG. 3H is an enlarged cut-away, side view of a configurable ring reflector  2283  having overlapped facets  2281  each pointing off to the side of the optical axis  299 . 
     FIG. 3I is an enlarged cut-away side view of a configurable ring reflector  2283  having a stretchable reflective membrane  2281 . 
     FIG. 4A is a cut-away side schematic of the ring reflector  220  of FIG. 3A showing the light pattern generated. 
     FIG. 4B is a cut-away side schematic of the ring reflector  220  of FIG. 3B showing the light pattern generated. 
     FIG. 5A is an enlarged cut-away side schematic of the ring reflector  220  of FIG.  3 A. 
     FIG. 5B is an enlarged cut-away side schematic of the ring reflector  220  of FIG.  3 B. 
     FIG. 6 is a schematic diagram of the LED drive electronics for one exemplary system  100 . 
     FIG. 7 is a schematic diagram of one exemplary power supply  20 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In the following detailed description of the preferred embodiments, reference is made to the accompanying drawings which form a part hereof, and in which are shown, by way of illustration, specific embodiments in which the invention may be practiced. It is to be understood that other embodiments may be utilized and structural changes may be made without departing from the scope of the present invention. 
     The present invention provides a method and system for generating rays of light with suitable brightness and evenness from a source surrounding, for example, the lens of a machine-vision camera. The rays are directed generally towards the optical axis of the camera. One embodiment provides a diffuse source circumferentially such that even extremely small objects can be adequately inspected and accurately measured by a machine-vision system  100 . 
     The unique ability of the method and apparatus of the LED illumination system of the present invention to provide an inexpensive and changeable light source within these constraints distinguishes this system from other illumination systems purporting to provide suitable high-intensity illumination for machine-vision inspecting or measuring purposes. 
     An illumination system is described in MACHINE-VISION ILLUMINATION SYSTEM AND METHOD, U.S. patent application Ser. No. 08/532,213, filed Oct. 12, 1995, now U.S. Pat. No. 5,745,176 by Gary A. Lebens and assigned to PPT Vision, Inc., the assignee of the present invention, and which is hereby incorporated by reference. 
     A serial machine-vision interconnection system is described in HIGH-SPEED DIGITAL VIDEO SERIAL LINK, U.S. patent application Ser. No. 08/825,774, filed Apr. 2, 1997, now U.S. Pat. No. 6,084,631) which is a file-wrapper continuation of Ser. No. 08/410,119, filed Mar. 24, 1995 by Joseph C. Christianson and Larry G. Paulson and assigned to PPT Vision, Inc., the assignee of the present invention, and which is hereby incorporated by reference. 
     FIG. 1A is a side-view schematic diagram of an embodiment of machine-vision illumination system  100  according to the present invention. In FIG. 1, an object  160  (for example, a beverage can or other food or drink container, or an electronics assembly or other manufactured item) is illuminated for inspection by a machine-vision camera (or other imaging device)  140  which is coupled to computer/image processor  150 . In this embodiment, camera  140  is disposed to view object  160  through an opening in ring-reflector illumination source  200  which directs light downward and inward. In the exemplary system shown, it is desired to illuminate the top edge, inside walls and inside bottom surface of object  160  for viewing by camera  140  with even, high intensity, short-duration illumination of a fixed intensity. In one embodiment camera  140  is a video camera, such as a Panasonic model GPMF702, having a telemetric lens, such as an Invaritar-brand lens made by Melles-Griot. In one such embodiment, the telecentric lens, which has uniform magnification across the field of view, of camera  140  is made larger in diameter than the diameter of object  160  being viewed (e.g., one embodiment uses a 6-inch diameter lens for 3-inch diameter objects) in order to reduce lens distortion, such as pin-cushioning and barrel distortion. Camera  140  is coupled to image processor  150  with suitable cables, for example, a digital-serial link such as described in patent application Ser. No. 08/825,774 cited above, or other suitable electrical or fiber-optical signal cables. In one embodiment, camera  140  is positioned above and facing objects  160  moving by action of conveyor mechanism  170  across the camera field of view, so that camera  140  can obtain and send a captured image of object  160  to image-processing computer  150 . In one embodiment, computer  150  analyzes the captured image and activates selection mechanism  175  to accept or reject each successive object (e.g., diverting rejected items into a reject bin) based on predetermined criteria, all using methods and apparatus well known to those skilled in the art of machine vision. 
     Camera  140  is implemented as any one of a number of device technologies including vidicon, CCD (charge-coupled device) line- or array-imaging devices, metal-oxide semiconductor (MOS) video cameras, and so forth. In one embodiment, camera  140  is a solid state MOS camera having a peak wavelength sensitivity of about 550 nanometers (nm), and range of approximately 500 to 600 nm at about 97% of peak. In one embodiment, the aperture on the lens of camera  140  is suitably small in order that a relatively large depth-of-field is obtained. The type and size of lens is chosen to match the field-of-view to the size/depth of object  160 . 
     In one embodiment, shown; in FIG. 1B (FIG. 1B is a circuit schematic diagram of a portion of one embodiment of machine-vision illumination system  100 ), each ring-reflector illumination source  200  is connected to a capacitor box  19 , which is connected to a power supply  20 , which is connected to image processor  150 . The charge on capacitor box  19  is discharged through LEDs  231  in ring-reflector illumination source  200  when computer  150  drives a pulse on signal cable  202  to amplifier  201  which in turn drives power MOSFET (metal-oxide-semiconductor field-effect transistor)  211  to substantially short to ground. In one embodiment, a short-duration pulse (approximately 10 microseconds to 100 microseconds long) to provide a short, intense pulse of light. Further details of power supply  20  and capacitor box  19  are found on Ser. No. 08/532,213 cited above. In one such embodiment, a photodetector  21  is used to detect the light output and provides feedback to computer  150  which is used to control the duration or frequency of the light pulses. 
     In the embodiment shown in FIG. 1, ring-reflector illumination source  200  is enclosed to light except for the lens opening  245  through back plate  240  and opening  225  in ring reflector  220 . 
     FIG. 2A is an exploded isometric view of ring-reflector illumination source  200  according to one embodiment of the present invention. Ring-reflector illumination source  200  includes bottom enclosure  210 , replaceable/changeable ring reflector  220 , ring illumination source  230  (in this embodiment, this is an LED light source  230  having a single row of LEDs arranged in a circle that is centered on optical axis  299  of camera  140 , the focal centerlines  298  of each LED is directed along a line parallel to optical axis  299 ), and top cover  240  that is attached to bottom enclosure  210 , for example by four screws  242 . In the embodiment shown, bottom enclosure  210  has an opening  215  having a lip or collar into which reflector ring  220  fits. 
     It is contemplated that a user will have more than one reflector ring  220 , each having a different reflective angle or reflective configuration/focus, so that the ring reflector  220  in ring reflector illumination source  200  may be changed according to the needs of the object being inspected, the particular camera or lens being used, etc., without replacing other parts in ring-reflector illumination source  200 . Alternatively, a configurable ring reflector  2205 , such as described on FIGS. 3F,  3 G,  3 H, and  3 I, can be used in place of multiple replaceable/changeable ring reflectors  220 , thus allowing the user to change the reflective angle or reflective configuration/focus by changing the configuration of reflector  2205  (explained further below). It is further contemplated that a user may have more than one ring-light source  230 , each having a different configuration of LEDs, dispersion angle, color or wavelength configuration, intensity or pulse response, so that the ring-light source  230  in ring-reflector illumination source  200  may be changed according to the needs of the object being, inspected, the camera being used, etc., without replacing other parts in ring-reflector illumination source  200 . FIG. 2A shows one configuration that makes possible the exchange of ring reflector  220  and/or ring-light source  230 , however other configurations are contemplated that make changing of the ring reflector  220  and/or ring-light source  230  easier and faster, such as by threading with matching complementary threads the outer circumference of ring-light source  230  and the inner circumference of opening  215 , such that ring reflector  220  can be exchanged without otherwise disassembling ring-reflector illumination source  200 . 
     FIG. 2B is a cut-away side view of ring-reflector illumination source  200  according to one embodiment of the present invention. In the embodiment shown, ring-reflector illumination source  200  includes bottom enclosure  210 , replaceable/changeable ring reflector  220  (designed to fit into a complementary opening  215  in bottom enclosure  210 ), ring illumination source  230  (in this embodiment, this is an LED light source  230  having a single row of LEDs  231  closely spaced in a circle that is centered on optical axis  299  of camera  140 , the focal centerlines  298  of each LED directed along a line parallel to optical axis  299 ), and top cover  240  that is attached to bottom enclosure  210 , for example by four screws  242  that pass through spacers  241  used to maintain the desired spacing and placement of the LED light source  230  within ring-reflector illumination source  200 . In one embodiment (see FIG.  2 C), LED light source  230  includes a printed circuit board  2300  onto which are soldered (or otherwise mechanically and electrically connected) a plurality of individual LEDs  231  (e.g., in one embodiment, high-brightness red LEDs 1200 millicandles (mcd) at a peak wavelength of approximately 621 nm, for example, HLMA-KH00-type T1-sized lights having a half-angle of approximately 22.5° available from Hewlett-Packard; In another embodiment, a Toshiba part number TLRH160 emitting red light (644 nm at 1800 typical mcd) with a 5-degree half angle is used), spaced as closely as possible in a single row, the row centered on a circle that is perpendicular to and has a center on the optical axis  299 . (In other embodiments, other LEDs having different colors/wavelengths, half-angles, intensity, or power capabilities are used. In one such embodiment, LED light source  230  is configures to be replaced/changed in order to let the user choose a suitable combination of colors/wavelengths, half-angles, intensity, or power capabilities for a particular application.) 
     In the following discussion, ring reflector  220  refers generally to any ring reflector (e.g., ring reflector  221  of FIG. 3A, ring reflector  222  of FIG. 3B, ring reflector  223  of FIG. 3C, or ring reflector  224  of FIG. 3D, or other similar ring reflector). Similarly, ring light source  230  refers generally to any ring light source (e.g., ring light source  230 . 0  of FIG. 2C, ring light source  230 . 1  of FIG. 2D, ring light source  230 . 2  of FIG. 2E, ring light source  236  of FIG. 2F, or other similar ring light source). 
     In the embodiments shown in FIGS. 2A-2F, printed circuit board (PCB)  2300  has a circular opening  235  also having a center on the, optical axis  299 . Signal wire  202  passes through insulating strain relief  2021  which is mounted to bottom enclosure  210 . Signal wire  202  is soldered to PCB  2300 , which then distributes the electrical power from signal wire  202  to each of the LEDs  231 . 
     FIG. 2C is a cut-away side view of one ring-light source  230  using a single circular row of LEDs  231  according to one embodiment of the present invention. In one embodiment, all LEDs  231  are of the same color and type. In another such embodiment, a mix of LED colors are used in order to get a polychromatic light. In yet another such embodiment, white phosphor/LED devices, such as a blue LED having a broad-spectrum phosphor that absorbs the blue light and re-emits a broad-spectrum centered at yellow to achieve a compact, very-long-life, efficient white light source (e.g., white LEDs such as manufactured by Nichia Chemical Industries, Ltd. of Japan; for example Part No. NLPB 510; see internet address http://www 1 a.meshnet.or.jp/nichia/wled-e.htm) are used in order to get a polychromatic, white-appearing light. In one embodiment, a pulsed electrical drive current is used (described in further detail below) in order to increase light efficiency (particularly during the time that the camera  140  is and/or to strobe the light pulse thereby reducing any blurring due to motion of the object being observed. In another embodiment, a direct-current (DC) electrical drive is used. 
     In the embodiments shown in FIGS. 2C-2E, each individual LED  231  and  232  has a built in focussing arrangement, typically including a cone-shaped reflector holding an LED chip, and a convex plastic lens package, that together direct and “focus” the light emitted from the LED chip in a direction centered about a focal centerlines  298  along an axis of the package. Such LED packages can be purchased at a number of dispersion angles (generally specified as the “half-angle” for the LED package), and at a variety of intensity capabilities (generally specified as millicandles (mcd) or milliwatts (mw) of light output). Conventionally, this arrangement has required that the axis of each LED package be pointed in the direction that light is wanted, i.e., at one or another angle pointed obliquely towards the optical axis of camera  140 . It has been expensive to fabricate such a ring of LEDs, each pointed obliquely towards the optical axis of camera  140 . Further, it is cumbersome and expensive to change the angle at which the LEDs point towards the optical axis (i.e., to move the angle of all of the LEDs, or to replace the ring with another having the desired angle. 
     The present invention provides an inexpensive and elegant solution to these problems. By providing an LED ring-light source having all the LEDs with the axes of their packages (i.e., the LED&#39;s individual focal centerlines  298 ) aligned parallel to the optical axis  299  (i.e., perpendicular to PCB  238 ), the cost of manufacture is minimized. In order to direct the light obliquely towards the/optical axis  299 , one or more inexpensive and easily changeable reflective rings  220  are provided. In order to change the intensity of light provided, a variable pulse-width and/or variable pulse-frequency LED power supply is provided. 
     FIG. 2D is a cut-away side view of another ring-light source  230  using a circular double row of LEDs  231  and  232  according to another embodiment of the present invention. In this embodiment, PCB  2301  is configured to mechanically and electrically connect to two rows of LEDs (outer circular row  231  and inner circular row  232 ). In one such embodiment, a two-angle reflector (e.g.,  222  or  224  of FIG. 3B or FIG. 3D) is used, and the outer row  231  of LEDs is reflected at a shallow angle (e.g., by a face  2222  (See FIG. 3B) that is at an angle of approximately 53 degrees from the plane of exit opening  225 ) in order to achieve a deep area of illumination (i.e., further from exit opening  225 ), and the inner row  232  of LEDs is reflected at a less-shallow angle (e.g., by a face  2221  (See FIG. 3B) that is at an angle of approximately 47 degrees from the plane of exit opening  225 ) in order to achieve a shallower area of illumination (i.e., closer to exit opening  225 ). In one embodiment, both rows of LEDs ( 231  and  232 ) are simultaneously illuminated, in order to simultaneously get both deep and shallow illumination. In another embodiment, each row is flashed at different times, in order to get either deep or shallow illumination. 
     FIG. 2E is a cut-away side view of yet another ring-light source  230  using a circular double row of LEDs  231  and  232 , wherein row of LEDs  232  is mounted at a small distance from PCB  2301 , for example, by inserting spacers  233  between each LED and the PCB  2301 , according to another embodiment of the present invention. In this embodiment, PCB  2301  is configured the same as for FIG. 2D, however, spacers  233  or other means, are used to drop the position of LEDs  232  relative to the PCB  2301 , thus moving the plane of the circle for those LEDs closer to ring reflector  220  (e.g., ring reflector  222 ,  223  or  224 ). 
     FIG. 2F is a cut-away side view of ring-light source  236  using a xenon flashtube according to one embodiment of the present invention. In one embodiment, a xenon strobe light source  237 , e.g., any suitable circular short-arc flashlamp bulb, and a diaphragm  238  having backplane slit  239 , are used in place of the row of LEDs  25  (see FIG.  2 A). In one such embodiment, raised collar  2351  is fabricated to be bolted to top cover  240  through screw holes  2352 , then inner slit ring  2353  (having opening  235 ) is fastened to the lower edge of collar  2351 , in order that only light passing through slit  239  is used (i.e., reflected and directed by ring reflector  220 ). The gap between the outer circumference of slit ring  2353  and the inner edge of the hole  2381  in diaphragm  238  defines a continuous (e.g., circular) slit  239  having no breaks. In another embodiment (see FIG. 2G which shows four struts holding the inner ring to the diaphragm  238 ), such breaks are due to, for example, support struts that are needed to hold inner slit ring  2382  to diaphragm  238 . In one such xenon strobe embodiment, an optional color filter  2371  is also placed in series with the light path in order to obtain a monochromatic light, which can be more sharply focused by the lens of camera  140  than white light. 
     In one such xenon strobe embodiment, an optional circular cylindrical ring lens  2391  (i.e., equivalent or similar to the cross-section of a convex-convex cylindrical lens as shown, that is rotated in a circle centered on optical axis  299 ; another embodiment uses a plano-convex) is also placed in series with the light path in order to focus light from the circular xenon source (i.e., focusing the emitted light to a circular line). In another embodiment, such a cylindrical ring lens  2391  is placed in series with light emitted from a ring-LED source such as ring light source  230 . 0  of FIG.  2 C. 
     Ring-light source  236  refers generally to a flashtube-slit assembly such as flash-tube light source  2361  of FIG. 2G or flash-tube light source  2362  of FIG.  2 H. In some embodiments, flashtube  237  is replaced by a similarly shaped enclosed incandescent filament circular tube, or a fluorescent circular tube, or linear LED chips arranged in a polyhedron, or other continuous circular light source. 
     FIG. 2G is an exploded isometric view of a flash-tube light source  2361  according to one embodiment of the present invention. Struts  2384  hold inner slit ring  2382  to diaphragm  238 . Raised collar  2351  is fabricated to be bolted to top cover  240  through screw holes  2352 , and for its lower edge to be light-tight against inner slit ring  2382  when assembled in ring-reflector illumination source  200 . 
     FIG. 2H is an exploded isometric view of a flash-tube light source  2362  according to another embodiment of the present invention. In this embodiment, as described above, raised collar  2351  is fabricated to be bolted to top cover  240  through screw holes  2352 , then inner slit ring  2353  (having opening  235 ) is fastened to the lower edge of collar  2351 , in order that only light passing through slit  239  is used (i.e., reflected and directed by ring reflector  220 ). The gap between the outer circumference of slit ring  2353  and the inner edge of the hole  2381  in diaphragm  238  defines a continuous (e.g., circular) slit  239  having no breaks. 
     FIG. 2I is a cut-away side view of two stacked ring-reflector illumination sources  200 A and  200 B according to one embodiment of the present invention. In this embodiment, ring-reflector illumination source  200 A is configured to have the light from its LEDs  231  reflected at a shallow angle (e.g., by a face  2211 A that is at an angle of approximately 53 degrees from the plane of exit opening  225 ) in order to achieve a deep area of illumination (i.e., further from its exit opening  225 ). Ring-reflector illumination source  200 A is configured to have the light from its LEDs  231  reflected at a less-shallow angle (e.g., by a face  2211 B that is at an angle of approximately 47 degrees from the plane of its exit opening  225 ) in order to achieve a shallower area of illumination (i.e., closer to exit opening  225 ). 
     In one embodiment, ring reflector  220  is fabricated by turning on a lathe a blank of aluminum, stainless steel, plastic, glass or other suitable material to generate a circularly symmetric reflective face (e.g., conical-section face  2211 ) (i.e., the surface of the cross section shown is a straight line at an angle of 52 degrees from the plane of exit opening, i.e., 38 degrees from the optical axis  299 ), which is then polished and/or chrome plated to enhance its reflectivity at a wavelength of ring-light source  230 . In another embodiment, ring reflector  221  is cast, e.g., by injection molding, from a suitable plastic, and then coated by well known methods with a reflective coating of chrome, gold or other metal, alloy, or multiple optical coating layers to enhance its reflectivity at one or more selected wavelengths of ring-light source  230 . (These manufacturing methods can apply to any of the ring reflectors described below.) 
     FIG. 2J is a cut-away side view of an alternative ring-reflector illumination source  200  according to one embodiment of the present invention. In this embodiment, each LED  234  is mounted on PCB  2300  in a circle around PCB opening  235  such that its light-emission focal centerline  298  is directed along a line radially perpendicular to optical axis  299  (i.e., the light is directed radially outward, centered on an emission plane that is perpendicular to optical axis  299 ). Ring reflector  229  is configured so that the emission plane intersects its operative reflective surface  2291 , which redirects the light to a darkfield pattern (such as pattern  2218  as shown in FIG.  4 A). 
     Darkfield illumination patterns, often used in microscopy applications, involve illumination in which light approaches the object (i.e., object  160 ) at an angle oblique or perpendicular to the optical axis, in order to minimize or eliminate light from the illumination source entering the camera (or microscope) lens either directly, or by reflection off some background object behind the object of interest. Thus, one application of the present invention is to provide darkfield illumination within, for example, a food container or beverage can  160 , without illuminating the bottom of the can, e.g., in order to check for foreign objects within a clear beverage. One embodiment of darkfield illumination of the present invention is thus particularly useful for spotting foreign objects within open opaque aluminum cans, while minimizing light reflecting off the bottom of the can towards the camera. In one such embodiment, a pattern  2218  is designed so as to illuminate as deep as possible within a can  160  while minimizing illumination of the bottom of the can  160 . The embodiments  221 ,  222 ,  223  of ring reflector  220  are particularly useful for generating such darkfield illumination patterns, since these ring reflectors  220  block the light from LEDs  231  that travels generally in the direction of the optical axis and that otherwise could illuminate background below the object of interest. 
     In contrast, other applications benefit from a deep illumination pattern which also illuminates the bottom of the can or food container. In one such embodiment, a pattern  2218  is designed so as to illuminate as deep as possible within a can  160  including illumination of the bottom of the can  160 . The embodiments  229  (FIG. 2J) of ring reflector  220  is particularly useful for generating such darkfield illumination patterns, since these ring reflectors  220  block the light from LEDs  231  that otherwise could illuminate below the object of interest. 
     All of the embodiments shown are useful for inspecting electrical components, and in particular, components or substrates having ball-grid arrays of connector pads. Ball-grid arrays, such as IBM Corporation&#39;s C4 controlled-collapse connectors, generally include rectangular grids of spherical connector balls (i.e., tiny solder balls), that are used to simultaneously connect multiple signals from chips to modules, or modules to boards. 
     In the embodiment shown in FIG. 2J, the reflective surface  2291  is a single conical section; in other embodiments, this reflective surface is replaced by two conical sections (in a manner similar to that shown in FIG. 3B below); a circularly symmetric parabolic or other curved section (in a manner similar to that shown in FIG. 3C below); a series of facets (in a manner similar to that shown in FIG. 3E below), or a configurable reflective surface (in a manner similar to that shown in FIG. 3F,  3 G, or  3 H below). 
     FIG. 3A is a cut-away side view of one ring reflector  220  according to one embodiment of the present invention. In this embodiment, ring reflector  221  is a circularly symmetric conical-section reflective face  2211  (i.e., the surface of the cross section shown is a single straight line at an angle of approximately 52 degrees from the plane of exit opening, i.e., approximately 38 degrees from the optical axis  299 ). In this embodiment, the spread half-angle of light emission from the LEDs  231  is not significantly changed by reflecting off of surface  2211 , and continues to diverge at approximately the same half-angle as before reflection (although now directed along a cone converging towards optical axis  299 ) thus providing a relatively broad spread of light below exit opening  225 , as shown in FIG.  5 A. Since the angle of incidence (approximately 38 degrees) is equal to the angle of reflection (also approximately 38 degrees), the cone of the centerlines of the LEDs approached the optical axis  299  at an angle of approximately 76 degrees. In other embodiments, the angle of face  2211  is set to other values to achieve the lighting pattern desired. In one embodiment, the lower edge of face  2211  is given a small chamfer (e.g., 0.02 inches) to reduced the danger to a user of otherwise sharp edges. In one embodiment, the length of face  2211 , the distance from face  2211  to LEDs  231  (e.g., in one embodiment, this is made as close as possible), and the half-angle of light emission of the LEDs  231  (e.g., in one embodiment, LEDs are specified to have a small half-angle), are together configured such that most or all of the light emitted from LEDs  231  is reflected by face  2211  (rather than passing directly through exit opening  225 ). FIG. 5A is an enlarged cut-away side schematic of the ring reflector  220  of FIG.  3 A. 
     In one such embodiment, particularly useful for darkfield microscopy, ring reflector  221  is a circularly symmetric conical-section reflective face  2211  having an angle of approximately 45 degrees from the plane of exit opening, i.e., approximately 45 degrees from the optical axis  299 ). In this embodiment, the spread half-angle of light emission from the LEDs  231  is not significantly changed by reflecting off of surface  2211 , and continues to diverge at approximately the same half-angle as before reflection (although now directed along a cone diverging towards optical axis  299 ) thus providing a relatively broad spread of light within ring reflector  221  within exit opening  225 . Since the angle of incidence (approximately 45 degrees) is equal to the angle of reflection (also approximately 45 degrees), the cone of the centerlines of the LEDs approached the optical axis  299  at an angle of approximately 90 degrees (perpendicular). For example, a glass slide could be placed flush against exit opening  225 , with the specimen suspended in water above the slide and within such a ring reflector  221 , whereby only light impinging on the specimen is visible through the lens of the camera or microscope. 
     In another such embodiment, the arrangement of FIG. 2B is inverted (i.e., with cover  240  further from the lens of camera  140  (or the microscope) and exit opening  225  closer to camera  140  (or the microscope)), such that the lens of the camera  140  (or microscope) is above, and on the same side of ring-reflector illumination source  200  as, exit opening  225 . In this case, the glass slide is placed on top of exit opening  225  (towards the lens) with the specimen in a liquid above the slide, an opening  245  (now at the bottom) is covered with a non-reflective black surface such as black felt. In this way, the specimen is illuminated at oblique angles from below, with a darkfield illumination. 
     FIG. 3B is a cut-away side view of another ring reflector  220  according to one embodiment of the present invention. In this embodiment, ring reflector  222  is a circularly symmetric reflective face having two adjacent conical-sections  2221  and  2222  (i.e., the surface of the cross section shown is two straight-line chords at angles of approximately 47 and 53 degrees respectively from the plane of exit opening, i.e., approximately 37 and 43 degrees from the optical axis  299 , the chords meeting at a concave intersection). In this embodiment, the spread half-angle of light emission from the LEDs  231  is narrowed by reflecting off of surfaces  2221  and  2222 , and continues to diverge at a smaller half-angle than before reflection (although now redirected along a cone converging towards optical axis  299 ) thus providing a relatively smaller spread of light below exit opening  225 , as shown in FIG.  5 B. Since the two conical-section surfaces  2221  and  2222  form a somewhat concave surface having an average angle of incidence and reflection of 40 degrees, the cone of the centerlines of the LEDs approached the optical axis  299  at an angle of approximately 80 degrees. In other embodiments, the angles of faces  2221  and  2222  are set to other values to achieve the lighting pattern desired. In one embodiment, the angles of faces  2221  and  2222  are approximately 53 and 47 degrees respectively from the plane of exit opening (i.e., the reverse of the above case), thus forming a convex reflecting cross-section, and thus increasing the half-angle of dispersion of the emitted light. 
     FIG. 5B is an enlarged cut-away side schematic of the ring reflector  220  of FIG.  3 B. 
     FIG. 3C is a cut-away side view of yet another ring reflector  220  according to one embodiment of the present invention. In this embodiment, ring reflector  223  is a circularly symmetric reflective face having a cross section that is concave circular or concave parabolic  2231  (i.e., the surface of the cross section shown is a curved-concave section of a circle or parabola at continuously varying angles from the plane of exit opening). In this embodiment, the spread half-angle of light emission from the LEDs  231  is narrowed by reflecting off of surface  2231 , and continues to converge at a smaller half-angle than before reflection (although now redirected along a cone converging towards optical axis  299 ) thus providing a relatively smaller spread of light below exit opening  225 , similar to as shown in FIG.  5 B. By choosing an appropriate curved concave section, the focus provided by reflector ring  223  can be determined to the degree desired. By extension, by choosing an appropriate curved convex section, the additional divergence provided by reflector ring  223  can alternatively be determined to the degree desired. 
     FIG. 3D is a cut-away side view of still another ring reflector  220  according to one embodiment of the present invention. In this embodiment, ring reflector  224  is a circularly symmetric reflective face having two adjacent conical-sections  2241  and  2242 , and is otherwise identical to ring reflector  222  of FIG.  3 B. Ring reflector  224  is configured to have the light from an outer row of LEDs  231  reflected by surface  2242 , and to have the light from an inner row of LEDs  232  reflected by surface  2241 . In one such embodiment, outer row of LEDs  231  emits light of a first color, and inner row of LEDs  232  of a second color, and are lit alternatively or simultaneously to achieve lighting effects as desired. In another such embodiment, outer row of LEDs  231  and inner row of LEDs  232  both emit light of the same color, and are lit alternatively or simultaneously to achieve lighting effects as desired (i.e., shallow lighting, deep lighting, or both. 
     FIG. 3E is a cut-away side view of a facetted ring reflector  226  according to one embodiment of the present invention. In one such embodiment, for every facet  2261 , a line  2269  drawn from the center of the facet perpendicular to the plane of the facet will intersect the optical axis  299  on order that the most amount of light will be centered on the optical axis. In another such embodiment, for every facet  2261 , a line  2269  drawn from the center of the facet perpendicular to the plane of the facet will pass to the side of the optical axis  299  (e.g., approximately 1 or 2 centimeters (cm) to the side) in order that the light is spread onto a wider volume (still centered around the optical axis) than in the just-before described example. In a third such embodiment, for every facet  2261 , a line  2269  drawn from the center of the facet perpendicular to the plane of the facet will pass through or pass to the side of the optical axis  299  by successively different amounts (e.g., a first facet perpendicular passes through the optical axis  299 , the next adjacent facet perpendicular passes approximately 1 cm to the clockwise side, the next adjacent facet perpendicular passes approximately 2 cm to the clockwise side, and then the pattern repeats for, each successive three facets) in order that the light is spread onto a wide volume, but now slightly more centered around the optical axis, than in the just-before described example. 
     FIG. 3F is a cut-away side view of a configurable ring reflector  227  according to one embodiment of the present invention. In this embodiment, each facet  2271  is made of a thin reflective material such as a small trapezoid of aluminum, aluminized silicon, aluminized mylar, or other reflective chip, and is fastened to pliable focusing gasket  2272  preferably made of rubber or pliable plastic. Outside ring  2273 , preferably made of metal such as aluminum, is permanently attached to pliable focusing gasket  2272  at their junction (e.g., by adhesive), and is threaded at the bottom of its inside circumference to accept threaded, tapered compression ring  2274 . As compression ring  2274  is rotated into the threads of the inner bottom of outside ring  2272 , it first contacts the inner diameter edge of pliable, focusing gasket  2272 , thus deflecting each facet  2271  upward at their bottom edges, while the top edges of each facet  2271  remains at the junction of pliable focusing gasket  2272  and outside ring  2273 . This changes the angle of each facet  2271  (e.g., from a nominal undeflected angle of approximately 38 degrees to a larger angle). In one such embodiment, for every facet  2271 , a line  2269  drawn from the center of the facet perpendicular to the plane of the facet will intersect the optical axis  299  on order that the most amount of light will be centered on the optical axis. In one such embodiment, every other facet has edges that overlay above the edges of each of its closest neighbors, as shown in FIG.  3 G. In another such embodiment, every facet  2271  has its, e.g., left edge overlaying above the right edge of each of its closest left-hand neighbor, as shown in FIG. 3H, in order that, for every facet  2271 , a line  2279  drawn from the center of the facet perpendicular to the plane of the facet will pass to the side of the optical axis  299  (e.g., approximately 1 or 2 centimeters (cm) to the right side in the example FIG. 3H) in order that the light is spread onto a wider volume (still centered around the optical axis), than in the just-before described example. 
     FIG. 3I is a cut-away side view of a configurable ring reflector  228  according to one embodiment of the present invention. In this embodiment, thin reflective surface  2281  is fastened to (or deposited on the surface of) stretchable focusing membrane  2282  preferably made of rubber or pliable plastic. Outside ring  2283 , preferably made of metal such as aluminum, is permanently attached to stretchable focusing membrane  2282  at their junction (e.g., by adhesive or a dovetail joint), and is threaded at the bottom of its inside circumference to accept threaded, tapered stretching ring  2284 . As stretching ring  2284  is rotated into the threads of the inner bottom of outside ring  2282 , it releases some of the stretch of stretchable focusing membrane  2282 , thus deflecting reflective surface  2281  upward at its bottom edge, while the top edge of reflective surface  2281  remains at the junction of stretchable focusing membrane  2282  and outside ring  2283 . This changes the angle of reflective surface  2281  (e.g., from a nominal undeflected angle of approximately 38 degrees to a larger angle). 
     FIG. 4A is a cut-away side schematic of the single-conical-section ring reflector  221  of FIG. 3A showing the light pattern generated (having highest intensity within the dotted line volume  2218 ), which is sometimes called a darkfield-illumination pattern. In such a darkfield-illumination pattern, an object  160  located within A deeper pattern is generated by a shallower angle in reflector  221 , and/or a wider half-angle of LEDs  231 . 
     FIG. 4B is a cut-away side schematic of the concave dual-conical-section ring reflector  222  of FIG. 3B showing the light pattern generated (having highest intensity within the dotted line volume  2228 ). A deeper pattern is generated by a shallower angles in reflector  222 , and/or a wider half-angle of LEDs  231 . 
     FIG. 5A is an enlarged cut-away side schematic of the ring reflector  220  of FIG.  3 A. 
     FIG. 5B is an enlarged cut-away side schematic of the ring reflector  220  of FIG.  3 B. 
     FIG. 6 is a block diagram of the electrical connections for one embodiment of machine-vision illumination system  100 . Image processor  150  sends a reset signal to camera  140 , then shortly thereafter (or simultaneously) sends a trigger signal to power supply  20 . Within power supply  20 , the trigger signal activates pulse generator  20 . 1  to generate a control pulse of a predetermined length. The control pulse is used to turn on transistor Q 1  to generate a flash on LEDs  231 , which is current-limited (if desired) by resistor R 30 . The control pulse also activates the maximum-rate-limit circuit  20 . 2 , which inhibits any further control pulses from pulse generator  20 . 1  for a predetermined amount of time. The 12-volt signal from power supply  20  is filtered by the low-pass filter comprising C 1 , L 1 , D 1 , and R 10 , and charges capacitors C 2  through C N  (in one embodiment, N is 12). In one such embodiment, C 1  through C 12  are each 2200 μF, L 1  is 40 μH iron-core, D 1  as a 1N4001 diode, and R 10  is a 0 ohm conductor (i.e., a short). C 2  through C N  are discharged through, e.g., fifteen LEDs  231  as shown in the circuit diagram, which in this embodiment are wired in a parallel-series manner as shown, (in another embodiment, sixty LEDs arranged in a single row are used; in another embodiment, 150 LEDs are used, each in a similar serial-parallel-wired connection circuit), and R 30  and Q 1 , as activated by the above-described control pulse. In one such embodiment, R 30  is replaced by a zero-ohm conductor, and the voltage drop across the LEDs  231  and Q 1  is used to self-limit the current through the LEDs  231 . The control pulse is fed across resistor R 20 , which in one embodiment is 100 KΩ, to develop the necessary voltage for driving transistor Q 1 , which in this embodiment is a MTP75N05HD MOSFET. 
     FIG. 7 is a more-detailed schematic diagram of power supply  20 . The input trigger is fed through resistor R 21  to drive the input of opto-isolator OI 1 . The output of opto-isolator OI 1  is coupled through capacitor C 12  (and the associated circuit R 4 , R 6  and D 2 ) to the TRG input of timer circuit  1 C 1   A . (In one embodiment, timers  1 C 1   A  and  1 C 1   B  are each ½ of a 556-type dual timer.) The timing constant of timer  1 C 1   A  is set by C 14  and R 1 -x, (where x is selected from 1 through N), and determines the pulse width of the control pulse driving Q 1 , and thus the LEDs  231 . In one embodiment, five selectable pulse widths are predetermined and selected by SW 1 , which is a five-way exclusive dual-pole-single-throw switch, wherein one resistor of the set R 1 - 1  through R 1 -N is selected for connection to the DIS input pin of  1 C 1   A , and a corresponding one resistor of the set R 2 - 1  through R 2 -N is selected for connection to the DIS input pin of  1 C 1   B . The timing constant of timer  1 C 1   B  is set by C 17  and R 2 -x, (where x is selected from 1 through N), and determines the minimum time between control pulses driving Q 1 , and thus the LEDs  231 . In one embodiment, the five selectable predetermined pulse widths are 25 microseconds (μs), 50 μs, 100 μs, 200 μs and 500 μs; the corresponding maximum pulse rates controlled by maximum rate limit circuit  20 . 2  are 200 Hz, 120 Hz, 60 Hz, 30 Hz, and 10 Hz, respectively, and are predetermined and selected by SW 1 . Thus, in the embodiment which uses a 60 Hz camera image rate, 100 μs-long control pulses are used to activate LEDs  231 . In one embodiment, it is desired to have an average LED illumination intensity of at least ten times the ambient light; thus, when camera  140  is taking one frames every 16.7 milliseconds, a 100 microsecond pulse should be at least 1670 times as intense as the ambient light. In one such an embodiment, a shroud is used to reduce the ambient light, and a red filter (substantially transparent to the peak wavelength of ring-reflector illumination source  200 ) is placed over the lens of camera  140  in order to reduce ambient light and pass the light of ring-reflector illumination source  200 . The control pulse output signal is driven through resistor R 31 . 
     In one embodiment, opto-isolator OI 1  is a 4N37-type part, resistor R 2  is 100Ω, resistor R 3  is 100Ω, resistor R 7  is 1 MΩ, resistor R 8  is 1 KΩ and visible-color LED D 3  indicates when the circuit is active, resistor R 4  is 4700Ω, resistor R 5  is 10Ω, resistor R 6  is 10 KΩ diode D 2  is a 1N914, resistor R 1 - 1  is 2.26 KΩ, resistor R 1 - 2  is 4.53 KΩ, resistor R 1 - 3  is 9.1 KΩ, resistor R 1 - 4  is 18.2 KΩ, resistor R 1 - 5  is 45.3 KΩ, resistor R 2 - 1  is 37.4 KΩ, resistor R 2 - 2  is 75 KΩ, resistor R 2 - 3  is 150 KΩ, resistor R 2 - 4  is 301 KΩ, resistor R 2 - 5  is 909 KΩ, C 14  is 0.01 μF, C 17  is 0.1 μF, C 12  is 0.001 μF, C 10  is 100 μF, C 11  is 0.1 μF, C 13 , C 15 , and C 16  are each 0.01 μF, Q 2  and Q 3  are each 2N3904 NPN transistors, and RP 1  is a 10 KΩ resistor pack. 
     “Chromatic aberration” is where a lens focuses different wavelengths of light at different focal points. “Spherical aberration” occurs when light from the edges of a circularly-curved lens are focused at different distances that light through the center of the lens. Circularly curved lenses are used since they are cheaper to produce a lens with a spherical curved surface than one in which the curvature changes. The problem, however, is that spherical aberration can occur, where the edges of the lens focus the light waves at a different point from the center of the lens, causing lack of sharpness. Regarding the oblique rays passing through the lens, these fall on different parts ofthe “image plane,” in a blur rather than being superimposed. This slightly different aspect-of spherical aberration is called coma. To overcome this can be costly, but mirror-type ring-reflector focusing elements  220  do not suffer from these aberrations. 
     The process of the present invention is unlike conventional illumination sources since it is compact, generates a light source from more than one point source with suitable brightness in order to reduce shadows, focuses the light source into a broad, deep, multidirectional source illuminating a volume with lght rays that approach generally the optical axis of the machine-vision system at oblique angles from a ring that surrounds the optical axis, so that even extremely small parts can be adequately inspected and accurately viewed or measured with machine-vision system  100 . Another aspect of the present invention is to provide a compact illumination source, preferably monochromatic, which can be focused to provide uniform multi-directional light onto all surfaces that are viewable by the machine vision camera. Yet another aspect of the present invention is to have such an LED illumination source be pulsed with a relatively high-power, low duty-cycle power source. 
     In one embodiment, most or all interior surfaces of ring-reflector illumination source  200  except the operative reflecting surface (e.g., surfaces  2211 ,  2221 ,  2222 , or  2231 ) have an anti-reflective (e.g., flat black) surface to prevent stray reflections. In one embodiment, the flat black surface is obtained by applying flat black paint. In another embodiment, the flat black surface is obtained through use of a standard black anodization process. 
     It is to be understood that the above description is intended to be illustrative, and not restrictive. Many other embodiments will be apparent to those of skill in the art upon reviewing the above description. The scope of the invention should, therefore, be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled.