Illumination – Light fiber – rod – or pipe – With optical fiber bundle
Reexamination Certificate
1998-08-17
2001-09-18
O'Shea, Sandra (Department: 2875)
Illumination
Light fiber, rod, or pipe
With optical fiber bundle
C362S551000, C362S555000, C362S558000, C362S297000, C362S294000, C362S580000
Reexamination Certificate
active
06290382
ABSTRACT:
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 emission head or fixture 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 fixture surrounding the lens. It is usually desirable that the light fixture 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 (such as a halogen lamp) is used for providing light into fiber-optic-based ring head or fixture. Such systems, however, are costly, very large, inefficient, 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. Further, xenon flashtube light sources also tend to exhibit tip to about a five per cent (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 fixtures 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 fixture 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 fixtures 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 fixture.
Thus, what is needed is a fiber-optic-based illumination system and method which is compact, well controlled, adaptable to various lighting needs, and modular 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 fixture, preferably one that is monochromatic. Another need is to provide a compact monochromatic LED (light-emitting diode) illumination fixture that can be quickly configured to a number of different illumination patterns remote from the LEDs. Another need is to have such an LED illumination fixture be pulsed with a relatively high-power, low duty-cycle power source.
SUMMARY OF THE INVENTION
The present invention takes advantage of the efficiency and flash controllability of high-brightness LEDs in one or more of a variety of colors, preferably arranged in a row or array, and then concentrated into a fiber-optic bundle and the properties inherent to a fiber-optic configuration to produce an illumination fixture for machine-vision systems. The present invention, in some embodiments, provides the advantages of providing monochromiiatic, efficient, stable light into a fiber-optic bundle. In some embodiments, the light is strobed in order to “stop” the movement and to concentrate the light into the time in which the shutter of the camera or the light-acquisition time of the imaging device is obtaining light.
In one embodiment, an illumination fixture for illuminating an object at a machine-vision station is provided. The fixture includes a plurality of light-emitting diode (LED) light sources, and a fiber-optic assembly having a common first bundle end and plurality of second ends. Each one of the second ends is optically coupled to receive light from one of the plurality of LEDs. The fibers transmit light from the second ends to the common first end such that light from the LEDs is output at the first end. In one Such embodiment, the common first end comprises a bundled arrangement of first ends of individual optical fibers, and wherein the second ends of each of the fibers is optically coupled to receive light from one of the plurality of LEDs. In another embodiment, each fiber at the first end terminates at a common plane. In yet another embodiment, each fiber is randomly located within the bundle at the first end.
One embodiment further includes a plurality of pipe cells, wherein each LED is associated with a respective pipe cell that serves to focus light from the LED into one or more of the fibers. In one such embodiment, each of the pipe cells includes a focussing reflective surface. In another such embodiment, each of the pipe cells includes a concave substantially spherical focussing reflective surface. In yet another such embodiment, each of the pipe cells includes a focussing lens that focusses light emitted from its LED on a fiber end.
One embodiment further includes a coupling unit attached to the first bundle end adapted to receive one of a plurality of interchanageably connected fiber-bundle head fixtures, and a fiber-bundle head fixture. Another embodiment includes a heat sink thermally coupled to the plurality of LEDs.
Another aspect of the present invention provides a method for illuminating an object at a machine-vision station. The method includes (a) emitting light from a plurality of LEDs onto individual ones of a first plurality of optical fibers; (b) forming the first plurality of optical fibers into a compact bundle having a first bundle end; and (c) coupling light from the first bundle end of the first plurality of optical fibers into a first end of a separate second plurality of optical fibers.
The method optionally includes optically coupling light from each one of the plurality of LEDs into second ends of corresponding one of the fibers is optically coupled to receive light from one of the plurality of LEDs. In other embodiments, the method includes terminating each fiber at the first end at a common plane; locating each fiber randomly within the bundle at the first end; or focussing light from each LED into one or more of the fibers using a plurality of pipe cells, wherein each LED
Bourn Charles T.
Lemaire Charles A.
Alavi Ali
O'Shea Sandra
PPT Vision, Inc.
Schwegman Lundberg Woessner & Kluth P.A.
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