Optics: measuring and testing – Inspection of flaws or impurities – Surface condition
Reexamination Certificate
2001-10-25
2004-06-29
Stafira, Michael P. (Department: 2877)
Optics: measuring and testing
Inspection of flaws or impurities
Surface condition
Reexamination Certificate
active
06757058
ABSTRACT:
TECHNICAL FIELD
The invention relates to an illumination system employed in an inspection process and, in particular, to a blinded fiber-optic light line to illuminate lumber and facilitate the detection of tracheid, color, and geometric characteristics of the lumber during an automated grading process.
BACKGROUND OF THE INVENTION
Until recently, wood processing required human visual inspection. Automation of the inspection process provides more consistent inspection criteria, provides more thorough inspection with faster decision making, permits market-influenced selection of resources, and allows better tracking of the resource pre- and post-processing. To date, however, this type of machine-based optical inspection has been somewhat limited by feature, cost, and safety issues, most of which are derived from difficulties of the available light sources to enhance the optical characteristics of the wood fiber. Moreover, detection and image processing techniques are restricted by the optical characteristics of the image source.
Typically unblinded white light and lasers have dominated attempts to automate the optical inspection process, although other methods have included x-ray and ultraviolet light technologies. Some aspects that are considered when choosing a light source type for lumber inspection include: 1) cost, 2) wood fiber characteristic enhancement ability, and 3) safety.
The initial cost of the light source affects the overall cost of an automated inspection system and thus affects the marketability of the system. Long term replacement costs, including costs of replacement of the light sources and labor-intensive difficulties experienced in performing the replacement, also drive a customer's management decisions for purchase criteria.
Currently, three types of wood fiber detection characteristic enhancements are possible: color spectra response, tracheid effect, and geometric projection. The color spectra response occurs when light (white or specific wavelengths) impinges a board that scatters the incident light. When the scattered light is detected and processed, the reflectance and absorption characteristics of the incident wavelengths by the wood fiber indicate information about the orientation, density, and composition of the wood fiber.
The tracheid effect examines the transmission of incident light through the hollow tracheid tubes that the tree used for transferring water from the root to the leaves. The transmission pattern can provide useful information about the natural fiber structure of the wood by detecting the emitted light at a given distance. This information is particularly useful when an exact location of the origin of the light source is known.
Information about the contour of the surface of wood can be gathered by observing the change in position of a hard-edged light as viewed from a given angle to the source. This geometric projection technique similarly employs a fixed point of origin, as well as a fixed angle of origin for the light source.
Unblinded white light as a light source is inexpensive and has few safety problems. While capable of highlighting color spectra responses, unblinded white light limits the field of information available due to its unspecific glow.
While laser technology becomes less expensive, the intensity needed for generating and inspecting the tracheid effect increases the safety problems inherent to laser use. Lasers are also limited in the color spectra area, but can produce a tracheid effect and allow geometric contouring. Lasers possess their own unique problems in quality of light as well. For instance, when used over a large field of view, many laser line generating techniques yield a Gaussian or other non-uniform response, limiting the amount of area one laser usefully illuminates. Also, lasers tend to provide a speckled image, introducing noise into the detection process, and are sensitive to vibration, a common problem in the industrial environment.
Accordingly, an inexpensive light source that can perform these and other inspection techniques well in an industrial environment and overcome the aforementioned problems would be greatly desirable.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a system and method for illuminating with a line of light a product for optical inspection.
Another object of the invention is to provide such a method and system that facilitate the inspection of the product by enhancing its optical characteristics detectable in at least two and, preferably three, modes.
A further object of the invention is to provide such a method and system for inspecting a wood product.
In a preferred embodiment, the present invention employs a blinded fiber-optic light line to illuminate a wood board with a sharp projected light edge to detect the tracheid, color, and geometric characteristics of lumber during an automated grading process. The light line employs thousands of fibers from a glass-fiber cable that are spread into a light line subunit of desired length and thickness. The fibers are randomized such that fibers neighboring each other in the cable do not necessarily neighbor each other in the light line so that the emitted light has substantially uniform intensity over its spatial range. Multiple light line subunits are positioned adjacent to one other to achieve a desired light line length.
A set of cameras in predetermined positions obtain three types of data from the light incident to the board. A computer analyzes the data to interpret the physical characteristics of the board and determine how to grade or cut the board. Sequentially with respect to the direction of travel of the wood board, in front and at a 45° angle to the board, a fast camera obtains geometric data of the wood board. A color camera, having a row of pixels for each wavelength of interest, is positioned in front of the light line and nearly perpendicularly to the wood board to obtain color data concerning the grain and defect structures illuminated. A black and white camera is positioned behind a blinder connected to the light line and nearly perpendicularly to the wood board to obtain tracheid data.
Additional objects and advantages of this invention will be apparent from the following detailed description of preferred embodiments thereof, which proceeds with reference to the accompanying drawings.
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IBM Technical Disclosure Bulletin, NB85036225, vol. 27, #10B, pp. 6225-6226, Mar. 1985.
Carman George M.
Freeman Patrick S.
Lucidyne Technologies, Inc.
Stafira Michael P.
Stoel Rives LLP
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