High speed camera based sensors

Details High speed camera based sensors High speed camera based sensors

2001-08-17

2004-11-30

Smith, Zandra V. (Department: 2877)

Optics: measuring and testing

Shape or surface configuration

Triangulation

C250S2140RC, C250S559260, C382S154000

Reexamination Certificate

active

06825936

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to TV Camera based and other electro-optical sensors and systems, providing affordable methods and apparatus for high speed scanning of dimensions and other features of objects.
The invention uses one or more light sources combined with TV cameras which may be randomly scanned in some form, and whose output is used as input to a computer, such as a PC. This data is analyzed to typically provide data concerning the location or dimension of objects or parts of objects and/or the presence or characteristics of certain features of objects.
The invention is particularly useful for applications in which high measurement speed is needed, such as determining the shape of boards moving at high speed on conveyor lines in sawmills. Data taken with such sensors is used to control sophisticated sawing operations aimed at maximizing yield from boards of variant shape, particularly in their edge regions. Utmost accuracy, and high data density are both required, which in turn demands very fast sensing devices, particularly of the triangulation type.
BACKGROUND OF THE INVENTION
Triangulation based sensors have found favor in industry, particularly to date in the Wood processing, Automotive and Electronics industries, and for programmable contouring and robotic guidance in general.
Historic sensor devices employing image scanning based cameras with photodetector arrays to address these industries are typified by Pryor et al: U.S. Pat. No. 5,734,172 entitled Method and apparatus for electro optically determining the dimension, location and attitude of objects (the disclosure of which is incorporated by reference), and other patents by the same inventors. Typically such devices are built with laser light sources, generally semi-conducting diode lasers, which provide cost effective delivery of concentrated optical energy. However, projection of suitable zones onto parts using standard projection optics can also be used, particularly where grid or other two dimensional patterns of zones are employed. Grids can be projected for example by creating same electronically in an LCD or DLP projector, commonly available for power point presentations. Alternatively, a standard slide projector with a Ronchi ruling in place of a slide can be used in some cases.
Further references disclosing triangulation measurements with photo-detector arrays are; U.S. Pat. No. 4,891,772 Case, et al. entitled Point and line range sensors; and Liptay-Wagner et al, U.S. Pat. No. 4,394,683 entitled New photodetector array based optical measurement systems.
In the specific area wood measurement, examples of laser triangulation based sensor units specifically designed for this are Leong et al: U.S. Pat. No. 4,937,445, entitled Apparatus for determining the distances of points on a surface from a reference axis and Cielo et al, U.S. Pat. No. 5,056,922 entitled Method and apparatus for monitoring the surface profile of a moving workpiece, and Chasson, U.S. Pat. No. 4,188,544 entitled Method and Apparatus for Automatically Processing a workpiece employing calibrated scanning.
Speed of data acquisition is critical to many industrial applications. However the sensors described above which are capable of scanning an image in order to determine information concerning the object at high speed, use linear photodetector arrays to achieve the desired speed. This allows only one scan line of potential data to be interrogated, limiting the versatility of the sensor considerably, and increasingly adding extra cost (due to the relative expense of the lower volume linear array devices).
To-date the only known effort to achieve high speed triangulation with matrix arrays has been by IVP corporation, whose commercial literature today addresses a particular method of scanning individual lines of an array and processing onboard . A U.S. Pat. No. 5,982,393 by Forchheimer et al of IVP describes methods by which computing can be done directly on pixel data using processors located on the same image chip, but discloses little about the methods for sensing and processing the data desired. To our knowledge, no other IVP information available to the public exists.
We do not believe the IVP camera is a totally random access camera, but rather a “smart” camera that can select one line (column) and parallel process (thresholding etc.) on every pixel in the line. But it cannot randomly read out a single pixel, which is desirable in many embodiments of our invention.
U.S. Pat. No. 5,717,199 by Carbone et al. discloses methods and apparatus by which data can be read randomly from pixels of a camera, in a manner different than IVP. However, this patent does not disclose methods by which such devices can actually be used to make practical triangulation or other measurements required in industry in an apparatus such as disclosed herein.
SUMMARY OF THE INVENTION
This invention relates to a significant advance over the state of the art in for example, the sensors used in the wood processing business, such as disclosed in Leong et al, Cielo et al, and others for measuring boards moving transversely at the high speeds needed to provide information to real time sawing and other operations in lumber mills.
A preferred embodiment utilizes laser triangulation with one or more points or lines, and specialized camera scanning methods and apparatus to provide meaningful answers as rapidly as possible of the line or point image locations in the field of view of the camera.
The invention particularly concerns the use of random access photo-detector arrays, combined with detection and computational algorithms to increase the speed of triangulation devices 10 to 100 times.
It is noted that in the following discussion, the word “laser” is meant to connote not only the laser device itself of whatever kind (typically a semi-conducting diode laser), but also any associated optics and power sources needed to assure that reliable optical energy can be delivered to a zone on the surface of the object to be measured. Typically, but not necessarily, such a zone is produced by focusing the radiation emanating from the laser to a small zone at the mean point of object location in the laser projection direction. In other cases cylindrical optics are used to create line projections. Optics may be either refractive, reflective or diffractive/holographic in nature.
It should also be noted that light sources other than lasers can be used, such as LEDs. However, laser sources are generally preferable in all applications except where large areas are to be illuminated, such as with structured light grids or other patterns.
The application is particularly, but not exclusively, concerned with sensors using photo-detector arrays with randomly programmable addressing of pixel elements. Increasingly these arrays are made by the CMOS process, but any suitable array with similar random addressing capability such as CCD or CID types can be used. CMOS types are especially attractive as they permit random addressing, and are inexpensive.
GOALS OF THE INVENTION
It is a goal of the invention to provide a sensory device, employing at least one photo-detector array camera operating at the highest possible operational speed, with acceptable accuracy and at reasonable cost.
It is another goal of the invention to provide method and apparatus for selectively analyzing certain portions of an image in order to improve sensor response speed, and for predicting the portions to analyze in the future.
It is another goal of the invention to provide method and apparatus for improving sensor response speed by using low resolution A-D conversion, with a subsequent re-reading of pixel intensity values in the areas of interest.
It is another goal of the invention to provide method and apparatus for selectively on a pixel basis, controlling laser power or integration time.
It is also a goal of the invention to provide a method for increasing the reliability of detection of projected zones on objects with variant reflectance characteristics at different portions of their surface.
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