Radiant energy – Photocells; circuits and apparatus – With circuit for evaluating a web – strand – strip – or sheet
Patent
1997-10-28
1999-09-07
Allen, Stephone
Radiant energy
Photocells; circuits and apparatus
With circuit for evaluating a web, strand, strip, or sheet
250223R, 356385, 144357, G01N 2130
Patent
active
059490861
DESCRIPTION:
BRIEF SUMMARY
The object of the invention is a method and apparatus for measuring the characteristic quantities, such as e.g. the length, diameter, volume, and defects, of a log or similar, in which method the log is moved at a known speed past a photographing station, which photographing station consists of at least one plane of light that transects the direction of travel of the log and a video camera set at a fixed angle to this, and computer apparatus, which is arranged to calculate and collect sequential images of a group of surface points of a three-dimensional model depicting the surface of the log as the log moves through the plane of light, in which the coordinates of each point are calculated with the aid of the geometry of the photography, according to which the each point formed by the plane of light on the surface of the log is at the intersection of the angle of viewing and the plane of light.
Finnish Patent 64300 describes a method and apparatus for determining the length of logs. In it, the logs are moved through a photo-electric trip device. The photography takes place from the opposite side, when the log cuts the device. The protruding parts of the log remain in view, and by this means it is possible to calculate the length of the log. With the aid of this method the overall length of the log is obtained, which is also inaccurate if there are defects in the log. The apparatus is generally not able to recognise a situation in which two logs have come into the same section of the conveyor.
In addition to the length of the log, it is wished to know a great number of other characteristic quantities, which include the diameter at various points in the log, the total volume of the log and the amount and location of defective parts. For example, the end of the log may be too thin in length, or the log may be from a crooked-grown tree, i.e. it may be considerably warped, which is also essential to know for further processing.
U.S. Pat. No. 4,705,401 describes a general method for digitalizing the surface of a three-dimensional object. According to the publication, the object is rotated and lit by two light sources, which form two light planes lying on either side of the line of photography, being limited at the object by its surface. Each plane of light forms an observable line on the surface of the object. The location of each point on the line of light can be seen in the angle of view in the camera of each point, when the coordinates can be calculated with the aid of the geometry of the photography. As the object is rotated, a series of points is created from a series of pictures, which can be combined, once the speed of rotation of the object is known.
The intention of this invention is to create a new kind of method and apparatus for measuring the characteristic quantities of a log or similar longitudinal object. The characteristic features of the method in accordance with the invention are described in the accompanying Patent claim 1, and the characteristic features of an apparatus in accordance with the invention are described in Patent claim 7. The measurement method in accordance with the invention is extremely precise, when suitable filters are used, i.e. when the points remaining outside tolerance areas according to certain criteria are removed. Points of this kind outside the trunk are produced by such things as branches, loose pieces of bark, and possible interference. In addition, the position of the supports is known exactly and their influence can easily be removed from the image. Points that clearly cause discontinuity can also be removed from the group of points. A considerable number of points depicting the surface remains in any event, to which curve elements corresponding to the cross-sectional circle can be fitted. The remaining points in each subgroup define the cross-sectional circle and its centre point, when the entire log can be depicted as a series of cylinders, which are formed by the calculated cross-sectional circles. The total volume of the log is simply the sum of the volumes of
REFERENCES:
patent: 4300836 (1981-11-01), Holmes et al.
patent: 4301373 (1981-11-01), Sjodin
patent: 4500203 (1985-02-01), Bieringer
patent: 5544757 (1996-08-01), Geiger et al.
Kauppinen Mauno
Reponen Jorma
Allen Stephone
Vision Systems Oy
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