FI95415B - Optical process for determining the three-dimensional shape of an object - Google Patents

Description

95415

OPTICAL METHOD OF DETERMINING THE THREE DIMENSIONAL SHAPE OF A BODY

The invention relates to an optical method for determining the three-dimensional shape of a body.

Today, many methods utilize imaging in which the shape of the body, in the plane of the camera image, is obtained directly by measurement, and the height of the body is often obtained with different cameras from the length of the side lighting shadow. The cameras can be line cameras, in which objects are moved to obtain a planar image, or matrix cameras, in which a three-dimensional image is obtained directly. To measure the dimensions of wood and especially logs, a technique has been used in which a moving object is photographed from the side with a matrix camera 15. When, for example, a laser beam is subjected to line illumination at an angle of e.g. When images are taken from two or three directions, the cross-sectional area of 20 objects, e.g. a log, can be determined. When the subject is moved longitudinally past the cameras, a three-dimensional image is formed.

The methods described above are often relatively expensive and often require very efficient data processing systems, i.e. the main weakness of known commercial methods is their cost.

It is an object of the invention to provide a method for determining the three-dimensional shape of a body 30 by which method eliminates the drawbacks associated with current methods. In particular, it is an object of the invention to provide a method which is inexpensive, simple and reliable.

The object of the invention is achieved by a method characterized by what is stated in the claims.

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In the method according to the invention, a light-diffusing material is placed on one side of the measuring point of the cross-sectional profile of the body, a light source 5 moving in the direction of the cross-section to be measured the end or re-detection of detection means a tangential cross-sectional point of 10 pieces, where when the position of the light source is known as a function of time, the cross-sectional points are constructed with cross-profile points, and The method is simple, inexpensive and works reliably. The invented method is best suited for measuring the cross-sectional profile of simple smaller bodies very rapidly when the body is moved in a direction perpendicular to the cross-sectional profile to be measured. In this way, for example, a three-dimensional image of the dimension of the part is obtained by means of a movement on a conveyor belt. There are several areas of application, such as the control of the dimensions of boards and planks in the wood industry, the control of the size of chips and the measurement of averages in the pulp industry, and the control of the integrity of pieces produced in general with a conveyor belt.

The invention will now be explained in more detail with reference to the accompanying drawing, which shows the principle of a method according to the invention and a solution applied in practice.

♦ · «··" The apparatus shown in the figure comprises an opal glass 1 on which the object 3 to be measured is moved, a laser 4, a rotatable polygonal mirror 5 and measuring devices 6, 7, 8, 35 placed on the opposite side of the object from the glass surface 1. The principle of the method is , that by scanning the laser beam 10 with a light diffusing glass plate 1

II

3 95415 provides a fast moving light source 9 which illuminates in all directions. In this embodiment, the light source 9 is made so that the light beam from the laser to be April 10 controlled by the rotary polyhedral mirror 5 to the wipe 2 5 indicate the direction of the arrow over the opal glass. In other words, a moving light source is formed on the surface of the opal glass. The deflection can be made in several ways, for example with an acousto-optical grating without moving parts or in another known way.

10

When a moving light source 9 is provided, a body 3 to be measured is placed on the direction of travel of the light source. In this case, the body to be examined is a planing board moving from the plane of the image perpendicular to the viewer.

15 The purpose of dimensional control is to ensure that the board is wide enough and that it is full-beam, ie sufficiently high on both sides.

Consider a situation where a light source is shifted from 20 right edges to the left edge. Initially, all three light intensity meters, photodiodes 6, 7, 8, detect light. When the light source travels some distance, the photodiode 6 no longer detects the light source. The time is measured, and when the photodiode 7 no longer detects the light source, the time measurement is stopped and the time tx is obtained. At the same time, a new time measurement is started, which is stopped when the photodiode 7 again detects the light source and the time t2 is obtained (corresponds to the situation drawn in the figure). A third timing is then started, which is stopped when the photodiode 8 detects light. In this case, the time measurement 30 is stopped and the time t3 is obtained. The photodiodes are far away, i.e. their distances from the board are considerably greater than the width of the board, and the scanning speed of the light source is constant. The sweep speed can be measured by placing photodiodes on the edges of the opal glass, and the speed can be e.g. 1 cm / ms. If the photo-35 of the diodes 6 and 8, the viewing angles are 451, from the right side of the board height is directly given by hx = tx xv board width formula 1 = t2, XV and a left-side elevation gas 4 95415 counter h2 = t3x v. When the speed of 1 cm / ms, are times measured in milliseconds directly in centimeters. Rough edge orientation is shown as follows: if for example the underside of the left edge is missing, a photodiode 6 detects the light source 5 too early compared with the photodiode 7. If the upper corners of the missing edge, appears in the course of the heights hi and h2 decrease.

In the above application, three photodiodes 10 were used and three cross-sectional dimensions of the object were considered, whereby a three-dimensional image of a moving object is obtained on the basis of the cross-sections. Measuring photodiodes can of course be added. In this case, the cross-sectional direction of the body becomes more accurately measured, because in principle each time the photodiode is added, one lateral limit is added to determine the cross-sectional area of the body. Of course, the method does not measure the concavity of the concave surfaces of the body, but always the lateral points, i.e. the extremes, in the cross-sectional inspections. The laser scanning plane is folded aside from the imaging plane of the light intensity meters 20 so that the jet through the diffuser does not hit the light intensity measuring devices.

The invention is not limited to the above example, but can be modified within the scope of the claims. In general, * «it is suitable for any view of part dimensions, as only the part can be set to the required view geometry.

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Claims (4)

5,95415 An optical method for determining the three-dimensional shape of a body, characterized in that a light-diffusing material (1) is placed on one side of the cross-sectional measurement point of the body (3), a light source (9) moving in the direction of the cross-section to be measured by the scanning laser beam (10), a plurality of measuring devices (6, 7, 10 8) are placed on the side in the desired cross-sectional plane, respectively, with which measuring devices detect a moving light source (9), whereby the end or rediscovery of the light source in the measuring device (6, 7, 8) always means tangential cross-sectional profile 15, where when the position of the light source as a function of time is known, the cross-section of the body (3) is constructed by means of cross-sectional points, and when the body is moved relative to the devices in the opposite direction to the devices and successive cross-sections are obtained a three-dimensional extreme image of the body. A method according to claim 1, characterized in that the scanning laser beam is formed by directing the light beam coming from the laser (4) to a rotating multifaceted mirror. 25 through (5) to the diffusing material (1). Method according to Claim 1, characterized in that the point of light is formed on the opal surface (1) of the light-diffusing glass, which is placed directly below the object (3) to be measured. • s Method according to claim 3, characterized in that the laser scanning plane is folded aside from the imaging plane of the light intensity meters (6, 7, 8), 35 where the jet passed through the diffuser (1) does not hit the light intensity measuring devices (6, 7). , 8). 95415