A method and a device for determination of desired middle line of a cylindrical object such as a log.

METHOD AND APPARATUS FOR DETERMINING THE DESIRED CENTER LINE OF A CYLINDRICAL BODY SUCH AS A WOODEN BOLT - FOR A DIFFERENT CENTER OF A CYLINDER BODY

The present invention relates to a method and apparatus for determining a desired cylindrical body, such as a desired centerline of a wood log, in which the diameter of a body and its longitudinal variation are recorded from its projections by at least one camera or other known imaging device from various angles.

In the plywood industry, plywood veneer is turned from a wooden log with a veneer lathe intended for that purpose. The lathe includes not only a blade assembly and spindles but also a hub that brings the log to be turned for attachment between the spindles. Due to the very vague shapes of the logs, it is important for the utilization of the raw material that the concentrator brings the log between the spindles in such a fastening position that the veneer obtained from the log is intact and flawless for as long as possible.

Hubs are most often three-point concentrators that compress a log between three jaws or blades at both ends of the log simultaneously, with the attachment points forming three points on the same circle. After all, this arrangement works properly only in the case of a faultless cylinder, and in the case of a wooden log, it is possible to distinguish e.g. the following sources of error:

- the log has an indeterminate cross-section, with only said three points coinciding with the center of rotation given to the log by the hub.

- the log is also somewhat incorrect in the longitudinal direction, so that the central axes given by the centering of the different ends may not coincide.

- the wood is always deformed somewhat when the hub is compressed, which affects the centering of the log.

- branches, pits and other irregularities at the jaws of the hubs cause a really large loss of raw material for such a log.

To solve these problems, ultrasonic devices based on the measurement of the thickness of the log are known, which help to center. However, these disadvantages are the inaccuracy of the sound of the float when measuring both inhomogeneous material and wood, and the fact that no information is available on the longitudinal misalignment of the wood.

It is an object of the present invention to provide a new type of automatic concentrator which is suitable for installation in existing mechanical concentrators and which does not slow down turning because the centering takes place separately from the lathe during the previous log turning. In order to achieve this effect, the method according to the invention, in which the workpiece is fixed at the time of registration to a hub known per se, the center line of the fastening members being parallel to the machine tool spindles, the desired center line being calculated by computer based on rectangles that the registration results are stored in the memory from the shadow images projected on a suitable background of the body, and on the basis of the images thus recorded, said computer is used to form rectangles parallel to the center line of the hub, substantially indicating the useful cross-sections of said body projections, and that the line of intersection between the lines of the smallest rectangle thus obtained and the second measured rectangle at an angle to it is considered to be the center line of the largest substantially intact cylinder intersected by the workpiece, calculating the

01 3 to move the actuator by means of the actuators so that its center line becomes the optimum center line.

Light-based imaging is fast and reliable even in the toughest conditions. Creating and recording an image of a piece from several different directions creates the basic conditions for perceiving the shapes of an arbitrary piece on a computer in three dimensions. The shadow image is sufficient information in this context, which has the advantages of simplicity of the necessary equipment and good resolution thanks to the two modes (black or white). The location of the retrieved centerline can be calculated because its distance from the normal centerline of the hub is known from two different directions. The calculation itself is trivial and can be performed in many different ways and using different coordinate systems, so it will not be described in more detail here.

A preferred embodiment of the invention is characterized in that the useful diameter of the body is determined by measuring in pairs the distances from the centerline of the hub to the contours of the body image, the useful diameter being the result of the smallest sum of these value pairs and dividing said sum by two. The position of the rectangles formed in this way and selected as a starting point in the viewing angle plane is thus registered with respect to the known center line of the hub, whereby the rectangles' own center lines and their distances to the center line of the hub can be determined.

A preferred embodiment of the invention is characterized in that, in addition to the projection containing the smallest inserted rectangle, a rectangle is selected whose image viewing angle is straight relative to the previous one. In this way, the center line is positioned with high precision so that as much veneer as possible can be turned from the log to its entire width.

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A preferred embodiment of the invention is characterized in that, when forming rectangles drawn in the images, minor local irregularities on the surface of the body, which would unreasonably reduce the size of the rectangle, are disregarded in accordance with a predetermined rule. The maximum height of the drawn rectangle is equal to the smallest radius of the body. If there is a small incision, possibly at the end of the log, a pit, etc. decisively reducing the smallest radius of the log projection would give a misleading picture of the size of the log's turnable wood surface in this projection and thus hamper the determination of the optimum centerline in the future.

A preferred embodiment of the invention is characterized in that the body is rotated from one viewing angle to another at a desired angular density with the imaging devices remaining in place. This embodiment is the simplest, because otherwise very sensitive imaging devices usually have to be moved.

A preferred embodiment of the invention is characterized in that the two imaging devices are mounted at an angle of 90 degrees to each other. In this way, the piece only needs to be rotated 90 ° to achieve an overall mapping.

A preferred embodiment of the invention is characterized in that the imaging device is at least one raster diode camera. The raster diode camera is simple and, thanks to the easy palpability of the pixels, is well suited for such applications.

The device applying the method according to the invention, which comprises a concentrator known per se and imaging devices, is mainly characterized in that the concentrator known per se is attached to rotatable arcs arranged to rotate the concentrator about its center line.

01 3 and that the concentrator can be moved vertically and laterally from its normal position by means of actuators. The actuators can be, at least when moving forwards and backwards, the devices belonging to the concentrator itself, for example a hydraulic cylinder.

A preferred embodiment of the device according to the invention is characterized in that there are two imaging devices, such as raster diode cameras, mounted at an angle of 90 degrees to each other and that the hub can also be rotated by arcs 90 °. In this embodiment, the advantages of easily controllable cross-diodes cameras are combined with their number of pieces, which in turn simplifies the structure of the device.

A preferred embodiment of the device according to the invention is characterized in that the rotational movement of the arcs is monitored by an angle sensor which gives impulses for performing the imaging at the desired angular intervals.

The invention will now be described in more detail by way of example with reference to the accompanying drawings, in which

Fig. 1. shows a concentrator according to the invention seen from the side, a) in the initial position for receiving and measuring the log, b) in the final position for handing over and measuring the log,

Fig. 2 shows a cross-section of a wooden log in which the previously known and claimed quantities and patterns necessary for carrying out the method according to the invention are drawn,

Fig. 3 illustrates the importance of the method in the correct centering of a log in a case.

The log 3 is introduced into the hub 4 when it is in the position shown in Fig. 1a, fixed at both ends from the circumference at three points, the center line of which is parallel to the center line of the lathes of the lathe. The centering actuators 5 and 6 of the center line of the log are in their middle position.

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The raster diode cameras 1 and 2 are oriented so that the point of intersection of their center lines is the queen line of the lathe, moved horizontally at a distance of the operating distance of the actuator 7 from the actual queen line of the lathe.

In this situation, the concentrator 4 and the log 3 therein are rotated 90 ° by arcs 8 until the position according to Fig. Ib is reached. During the rotation, the rotation angles are measured by a sensor 9, which gives a measurement command at 5 ° intervals to the cameras 1 and 2, which together measure the so-called log 3 at an angle of 90 ° to each other. the payload section so that the entire log is measured in its direction of rotation from a range of 180 °, which corresponds to the measurement of the diameters of the entire log at 5 ° intervals.

The diameters of the log are measured at several points in the longitudinal direction of the log. By measuring, the worst, most unfavorable utility beam section of the log 3 is retrieved and it is determined at which turning angle it was found.

The angle of rotation, the diameter of the worst utility section, the diameter of the corresponding section at 90 ° and the resulting center line position information of the largest intact cylinder from the wood relative to the lathe queen are given by control logic (e.g. process computer) that they merge between the spindles when the log is moved. The transfer takes place with the actuator 7.

Figure 2 shows how the smallest useful beam section of a log 3 is used to find the optimum center line of the log. The log is attached at its ends to the hub at points A, B and C, which are therefore not necessarily in the plane of the image. In the figure, the dashed lines D and E are the center lines (not drawn) of the respective cameras 2 and 1, which intersect with the normal center line of the hub, which

7101 3 in this direction appears as a point Q, placed in the rectangular origin of the xy coordinate system. Assume that the cross-section of the log 3 shown in the figure contains the most unfavorable diameter of the whole log, which is detected when the log is rotated by a raster diode camera 2 (not drawn) by measuring the distances a and b The position of the center line F of the smallest diameter in relation to D is obtained simply by calculating (a + b) / 2.

When the smallest diameter a + b is found, the measurement results made by the camera 1 are retrieved from the computer memory at the corresponding log angle, which are the distances c and d measured from its center line E to the log 3 outlines and the position of the image centerline G (c + d) / 2. Here, for the sake of clarity, both measurements are shown to occur in the same plane, but in the general case this is of course not the case, but the smallest diameters that determine the useful cross sections of certain projections may be located at different locations along the log.

The centerlines F and G of the diameters intersect at P. At the same time, this is the desired optimum centerline for the log, and its position relative to the normal centerline of the hub can be easily calculated and represented in the rectangular coordinate system as deviations Δx and Ay. These are given to the actuators to make corresponding displacements so that the optimum center line is made to coalesce with its spindle line when attached to the lathe.

Figure 2 also shows the cross section of the largest drawn cylinder H given by the concentrator itself and the cross section of the cylinder I obtained by optimization.

Another example of the benefit of the method, now seen from the side, is shown in Figure 3, where the centerline correction in this plane is denoted by £ xz.

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Note that the centerline correction varies at different points in the log. This is due to variations in the shapes of the log and the resulting abnormal attachment in the hub.

It will be clear to a person skilled in the art that the various embodiments of the invention are not limited only to the example given above, but may vary within the scope of the claims set out below.