Data processing: measuring – calibrating – or testing – Measurement system – Dimensional determination
Reexamination Certificate
1997-12-30
2001-07-10
Assouad, Patrick (Department: 2857)
Data processing: measuring, calibrating, or testing
Measurement system
Dimensional determination
C702S159000, C356S370000, C250S559210
Reexamination Certificate
active
06260001
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a process for measuring the volume of an object by means of a laser scanner, and to an apparatus implementing the process.
A problem shared by many segments of industry and trade is that of assessing the volume of an object. In particular, the supply and shipment of goods demand that the volume of packages be measured in an automated fashion to provide an element of information which is valuable to the conduction of both the storehouse premises and the carrier means.
Storehouse premises and carriers generally handle objects according to their weight, and to one or more of their linear dimensions regarded as most significant. This handling style is, therefore, approximative and surely less than fully satisfactory.
SUMMARY OF THE INVENTION
Accordingly, a first aspect of the invention concerns a process for measuring the volume of an object with at least a laser scanner, which process comprises the steps of:
a) placing the object onto a bearing surface;
b) defining a feed direction for the object on the bearing surface;
c) defining a scan plane, intersecting the plane of the bearing surface along a scan base line which lies transverse to the feed direction, with a laser beam from a scanner that overlies the bearing surface being arranged to act in the scan plane;
d) moving the object across the bearing surface along the feed direction, relative to the scan plane, until the scan plane will intersect the object;
e) obtaining the height, above the bearing surface, of n points of measurement contained in a top face of the object and on the scan plane;
f) defining a stipulated height as a function of the measured heights of two successive points of measurement;
g) obtaining the plane position on the bearing surface of the n points of measurement;
h) defining a stipulated base as a function of the plane positions on the bearing surface of each pair of adjacent points of measurement;
i) computing a stipulated area element, vertical to the bearing surface, for each pair of adjacent points of measurement, as by multiplying the stipulated base by the stipulated height;
j) computing a stipulated area as the combined sum of the stipulated area elements computed;
k) moving the object relative to the scan plane a predetermined feed distance along a feed direction across the bearing surface;
l) defining a stipulated thickness as a function of the feed distance;
m) computing a volume element by multiplying the stipulated area by the stipulated thickness;
n) repeating steps e) to m) above until the entire object is scanned;
o) computing the object volume as the combined sum of all the volume elements.
The term top face is here a generic one, it encompassing any surface seen by the laser scanner placed above the bearing surface. In particular, even a sloping side surface may be taken to be the top face, whose slope is an upward taper angle of the object as referred to its rest position on the bearing surface.
The movement of step d) above should be understood as a relative movement. Thus, it may either be a movement of the object relative to a fixed scan plane, or a movement of the scan plane relative to an object held stationary, or both.
This process provides a reasonably accurate assessment of the volume of an object. The measurement is an approximate one, as usual, for two basic reasons.
A first reason is that the volume considered would not be the true volume of the object, but rather that included between the top face of the object lying on the bearing surface and its orthogonal projection onto the bearing surface. In practice, only the top face of the object is picked up for measurement, the assumption being that the top face is planar and the side faces square to the underside; therefore, any dimples present in faces other than the top face are taken to be solid. However, this approximation suits well the practical requirements for volume measurement; in fact, the geometric volume of the object is of less concern than its overall hamper, and it is preferred if possible dimples are left out as actually unaffecting hamper.
The second reason is that the measurement is arrived at by a spot reckoning procedure (the points of measurement) carried out on the top face of the object, rather than over the whole surface of that face. Anyhow, this approximation can be improved upon as required by increasing the number of points of measurement.
The spatial positions of the points of measurement may be reckoned with the scanner in different ways. Preferably, this is done by taking a first measurement in polar coordinates (centered on the origin of the virtual scan source, i.e. on the imaginary point whence the scan rays appear to issue, which point may lie within or outside the scanner and be fixed or movable, according to the optics being used), and then converting it to Cartesian coordinates in accordance with a stipulated system which has two axes in the plane of the bearing surface, a first of such axes being parallel to the feed direction, and a third axis perpendicular to the plane of the bearing surface. This arrangement is preferred because the measurement is related to coordinates which suit well the measuring instrument (the scanner movement is a polar type), and the computed result is expressed in coordinates which suit well the quantities to be measured and the calculations later to be performed.
The quantities which have been indicated as stipulated may be selected in different ways, according to the degree of approximation sought. Suitably, the stipulated height is computed as equal to the height of one of the two points of measurement (any one, the first or the second, the smallest or the largest), or preferably equal to the average (suitably the arithmetical average) between the heights of the two points of measurement. The stipulated base is preferably computed as equal to the difference between the values of the coordinates of the two measurement points along the second axis (y), or as equal to the distance between the projections of the two measurement points onto the plane of the bearing surface (x-y). The stipulated thickness is preferably proportional to the feed distance. These choices enable the slope &agr; of the scan line with respect to the perpendicular to the feed direction (axis y) to be taken into account in a very simple manner.
Preferably, the scan plane is vertical to the bearing surface. This arrangement makes the computation easier; otherwise, it would be necessary to take account of the inclination of the scan plane from the vertical to the bearing surface.
A second aspect of the invention concerns an apparatus for measuring the volume of an object, comprising:
a bearing surface for the object, whereacross an object feed direction is defined;
at least a laser scanner overlying the bearing surface and arranged to act in a scan plane intersecting the plane of the bearing surface along a scan base line transverse to the feed direction;
a processing unit linked to the scanner;
a means of moving the object across the bearing surface relative too the scan plane along the feed direction;
a means of sending a signal to the processing unit each time that the object is moved a predetermined feed distance relative to the scan plane;
wherein the scanner and/or processing unit is operative to:
reckon the height above the bearing surface of n points of measurement contained in a top face of the object and in the scan plane;
define a stipulated height as a function of the reckoned heights of two successive points of measurement;
reckon the plan position of the n points of measurement on the bearing surface;
define a stipulated base as a function of the plan position on the bearing surface of each pair of adjacent points of measurement;
compute a stipulated area element, vertical to the bearing surface, for each pair of adjacent points of measurement, as by multiplying the stipulated base by the stipulated height;
compute a stipulated area as the combined sum of the computed stipulated area elements;
define a stipulated thicknes
Assouad Patrick
Datalogic S.p.A.
Sughrue Mion Zinn Macpeak & Seas, PLLC
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