Method and apparatus for detecting the three-dimensional structure of a log

A method for detecting the three-dimensional structure of a log comprises the operating steps of:

The present invention relates to a method and an apparatus for detecting the three-dimensional structure of a log.

In particular, the present invention is advantageously applied in log cutting lines (FIG. 1), where the logs T are fed in sequence, positioned transversally to their direction of extension, to a band saw S. In more detail, a line L feeds one log T at a time to a movable carriage C which then moves it against the band saw S.

In plants of that type, cutting must be carried out in such a way as to optimise the result based on the characteristics of the log. To do that, the precise structure of the log must therefore be known.

According to a first known technology (schematically illustrated inFIG. 1), the log T is subjected to a three-dimensional scan upstream of the feed line. Therefore, in the station X, the three-dimensional structure of the log is detected and the control system can identify the best cutting pattern which can be applied. Consequently, when the log T arrives on the carriage C, only its position in space needs to be identified to allow correct application of the best cutting pattern previously identified.

However, that solution is relatively complicated to produce, since it requires a suitable detection station X in which the log must be stopped and observed on each side with suitable three-dimensional scanners.

Alternatively, the most widespread solution involves examination of the log T when it is already on the band saw S carriage C using a detector R. This solution is schematically illustrated inFIG. 2, which shows the portion of the plant indicated by the arrow II inFIG. 1. Obviously, in the solution inFIG. 2, the cutting plant does not comprise the scanning station upstream which in contrast is present in the solution inFIG. 1.

However, this latter solution also has disadvantages. Although it is simpler to produce, it has the significant limitation that the presence of the carriage C only allows examination of one side of the log T (as illustrated inFIG. 2). Consequently, the structure of the other side must be assumed.

Apart from the disadvantages of the apparatuses used in cutting plants which use band saws, it should be noticed that all prior art apparatuses of this type have disadvantages.

Apparatuses for detecting the three-dimensional structure of logs may be divided into two large families, those in which the log remains stationary, and those in which the log is fed along its main direction of extension.

In the former type of apparatuses, the main disadvantage is linked to the need to provide a large number of detection devices in order to be able to simultaneously detect the entire lateral surface of the log. Consequently, that type of apparatus is relatively expensive.

In contrast, in the latter case, the lateral surface is usually detected using cross-sections one after another as the log gradually passes through a detection station where two or more radial detectors detect each cross-section. In this latter case, the disadvantages are linked both to the need to provide two or more detectors (although smaller) and, above all, the fact that it is impossible to apply the technique to compact, high productivity production lines in which the logs must be fed positioned perpendicularly to the feed direction (if not rotating each log).

In this situation, the technical purpose which forms the basis of the present invention is to provide a method and an apparatus for detecting the three-dimensional structure of a log which overcome the above-mentioned disadvantages.

In particular, the present invention has for a technical purpose to provide a method and an apparatus for detecting the three-dimensional structure of a log which may be used in lines in which the log is fed positioned perpendicularly to its own direction of extension.

The present invention also has for a technical purpose to provide a method and an apparatus for detecting the three-dimensional structure of a log which allows the use of even a single detection device for detecting the entire lateral surface of the log.

The technical purpose specified and the aims indicated are substantially achieved by a method and an apparatus for detecting the three-dimensional structure of a log as described in the appended claims.

With reference to the accompanying drawings, the numeral1denotes as a whole an apparatus for detecting the three-dimensional structure of a log2in accordance with the present invention.

The apparatus1comprises firstly supporting means3forming a holder4for a log2to be examined and means5for detecting the log2lateral surface structure which are pointing towards the holder4.

In more detail, the supporting means3also form means6for making the log2rotate about two or more axes of rotation (described in more detail below) which are substantially parallel with the log2main direction of extension D. In the preferred embodiment, this is achieved by making the supporting means3with at least one pair of motor-driven supporting chains7angled at the two sides of the holder4and converging below it (in front view).

As shown inFIG. 3, the pair of supporting chains7therefore form V-shaped supports. However, in other embodiments, the chains7which form each pair may also be spaced out, and they may or may not form a V shape when seen from the front. In the embodiment illustrated, the supporting means3comprise two pairs of chains7, but in general they may comprise a plurality of them distributed along the length of the holder4to support the log2at several points.

The supporting chains7are looped around respective feed/return rollers8and, as illustrated inFIG. 3, may be driven in a synchronised fashion and in the same direction to make the log2rotate. InFIG. 3the log2is schematically illustrated as a circle, therefore after rotation of the chains7it is rotated about an axis of rotation passing through the centre of the circle. In contrast, in real conditions, the log2has an irregular cross-section, meaning that depending on the portion of the section resting on each chain7, the instantaneous axis of rotation varies, although it always remains substantially parallel with the log2main axis of extension (except for small angles due to the different irregularity, such as irregularity or bump2ainFIG. 5, of the individual sections resting on the support means3at each moment).

It shall be understood that in other embodiments the supporting and rotating means3may be made differently to what is described above.

According to the present invention, the detection means5are positioned on only one side of the holder4(above it inFIG. 3) so that they can always see only one part of the lateral surface of the log2. Depending on requirements, the detection means5may have any structure. In particular, according to what is also described below, the detection means5may be means for detecting by laser triangulation, by detecting the texture of the surface of the log2, etc. Moreover, the control and processing means are operatively connected to the detection means5for controlling their activation, for receiving detection step results from them and for reconstructing the log2overall surface structure, according to the methods described below. The control and processing means are also operatively connected to the means6for making the log rotate, to control their operation.

In order to be able to detect the entire lateral surface of the log2, the control and processing means are programmed to carry out the operating steps of the method forming the subject matter of the present invention described in detail below. However, very briefly, the control and processing means are programmed to detect the entire lateral surface of the log2in a plurality of steps one after another, during each of which only a portion of the surface is detected. However, each portion detected is detected in such a way that it is at least partly superposed on at least one other portion detected, or to be detected, so that the overall surface may be reconstructed by superposing the individual portions which were individually detected.

In a more complete embodiment, the apparatus1may comprise one or more detectors14which are positioned in such a way that they can detect one or both of the log2end surfaces, and operatively connected to the control and processing means for operating according to the methods indicated in detail below. However, to summarise, it may be said that in this case the control and processing means are programmed to activate the detectors14simultaneously with the detection means5at least for a plurality of lateral surface detection steps, so as to provide an overall detection step result consisting of the portion of lateral surface and one or both end surfaces. If this is done for all of the lateral surface detection steps, it is not necessary for the lateral portions detected to be partly superposed, since the end surfaces always are. Consequently, the reconstructions can be performed entirely or partly based on the information relating to the end surfaces.

Before examining the method according to this invention in detail, it must be emphasised that the present invention also relates to a log2cutting plant9comprising a band saw10, a carriage11for supporting a log2to be cut and able to move between a first, pick up position where a log2can be loaded on the carriage, and a second, cutting position where the band saw10can cut a log2positioned on the carriage, and a line12for feeding logs2to be cut to the carriage11located in the pick up position. According to the present invention, the plant9also comprises an apparatus1for detecting the three-dimensional structure of the log2made according to what is described above and preferably positioned downstream of the feed line12. In particular, the apparatus1may either be positioned between the feed line12and the carriage11to form a kind of loader for the carriage11, or it may be mounted directly on the carriage11(or may even form the carriage11itself).

If the apparatus1is an integral part of a log cutting plant9, there may also advantageously be means for positioning the log2in the optimum cutting position (not illustrated). Said means are controlled by the control and processing means and are designed to position the log2on the carriage11in the optimum cutting position decided in the meantime, according to known methods, by the control and processing means, after the log2has been completely detected. In particular, when the apparatus1is mounted directly on the carriage11, or coincides with it, the apparatus also forms the positioning means. In contrast, when the apparatus1is located directly upstream of the carriage, the positioning means may be either devices able to transfer the log2from the apparatus1to the carriage11with a predetermined rigid motion (such as a robot), or, more simply means for applying on the log2a visual positioning reference (such as a diametral line on an end face of the log2). In the latter case, correct log cutting positioning is determined by the operator who rotates the log2to align the visual reference relative to a predetermined orientation (for example vertical). The method according to the present invention generally comprises firstly the operating step of making the log2rotate about two or more axes of rotation which are substantially parallel with the log main direction of extension D. In practice, that depends, as already indicated, on the methods used to carry out the step (for example, depending on the structure and operation of the apparatus1supporting means3as described above).

Secondly, during said rotation, the method involves detecting the relative surface structure of the log2at least at one lateral surface portion13. The term “relative” surface structure refers to a reference system outside the log2(in practice usually integral with the detection means5).

It should be noticed that if two reference systems are assigned, the first Y to the detection means5and the second X to the log2, after log2rotation the first reference system Y integral with it may, relative to the second system Y, be subject to not just a rotation, but also a series of translations, for example after the irregularity of its surface which gradually rests on the supporting means3described above.

Also, according to a first embodiment of this invention the detection step is repeated a plurality of times, thus detecting at least once the relative surface structure of substantially all of the points of the lateral surface of the log2, and, at the same time, so that, at the end of all of the repetitions, each surface portion13detected shares at least several points with at least one other surface portion13detected. It should be noticed that the term surface portion13refers to a set of real points of the surface of the log2, whilst the term relative surface structure refers to detection of the surface trend of a predetermined surface portion13.

The final basic step of the method disclosed involves combining the relative surface structures detected to reconstruct an overall surface structure for the log2, and in particular combining them so that the points shared by the various relative surface structures are made to coincide with each other.

In the preferred embodiment of the method according to the invention, the detection steps are repeated in such a way that during each detection step points of the lateral surface of the log2are detected which are adjacent to those detected during the previous detection step. In this way, the entire lateral surface of the log2can be detected during a single log2rotation over itself.

Any methods may be used for carrying out the detection steps and they are not described in detail here, being of the known type. However, in the preferred embodiments, the detection steps are generally carried out by projecting a beam of light (preferably laser) on the surface of the log2and practically instantly detecting the surface structure of the illuminated zone using the triangulation technique. In contrast, in other embodiments, detection is carried out by detecting the log2surface texture (that is to say, its outer appearance). It is known that the three-dimensional appearance of an irregular object can be reconstructed according to how the appearance of the same zone of the surface of the object varies with variations in the reciprocal positioning between the point of observation (detection) and the zone of the surface detected. In other embodiments, the log surface can also be detected using the “time of flight” technique, in which the position of the surface points is obtained by measuring the time taken by a light pulse to reach the log and return to a detection sensor (this technique is of the known type and therefore not described in detail). Advantageously, to check the entire surface of the log rotary mirrors may be used, combined with interferometric techniques.

FIGS. 6 to 10show five possible embodiments for each detection step (with reference to the positioning ofFIG. 3,FIGS. 6 to 11show a top view of the log2) according to the first embodiment of the method disclosed, described here. In general, each portion13detected consists of the set of linear intersections between the surface of the log2and a plurality of separate planes incident on it (in the accompanying drawings all of the planes are perpendicular to the drawing plane, but in general they could also be at an angle to it). In particular, in the case ofFIGS. 6 and 7the separate planes are parallel with each other and, respectively, substantially parallel with the log2main direction of extension D, and at an angle to it. Whilst in the former case each point of each portion13is detected a number of times equal to the number of parallel planes (four inFIG. 6), in the latter case the distance between the different planes and the relative angle relative to the axis of the log2must be such that for each intersection at least several points can be detected during a subsequent detection step. InFIG. 7that situation is shown by the dashed line which shows how each point at it is detected during three separate detection steps.

In contrast, in the case inFIG. 8, the portion13of the lateral surface of the log2detected consists of the linear intersection between the surface and a second plurality of separate planes which are at an angle both to the surface and to each other. The second plurality of planes may be divided into a first group and a second group of parallel planes, the planes of the first group being at an angle to the planes of the second group. In this way the portion13detected forms a grid and all of the surface points are detected more than once.

In the case inFIG. 9, the detection planes are positioned side by side so that each surface portion13is a longitudinal band of the log2surface.

Finally, in the case inFIG. 10, the portion13of the log2lateral surface detected consists of the linear intersection between the surface itself and one or more first planes substantially parallel with the main direction of extension (D) of the log (2) (or at least positioned in such a way that they cover the entire length of the log) and one or more second planes substantially perpendicular to the main direction of extension (D) of the log (2). In this way, each second plane always covers the same log circumference and, with each detection step, half of its is acquired, which can easily be superposed on the half detected during the next acquisition, from which it differs only by several points.

Returning to the step of making the log2rotate, it should also be noticed that this is preferably carried out with a substantially constant speed and in such a way that after a complete rotation the log2is substantially in the starting absolute position in space. As indicated, this may advantageously be achieved by supporting the log2using means6for making it rotate, such as those illustrated inFIGS. 3 and 4.

Moreover, advantageously, all of the detection steps are carried out by observing the log2from the same absolute position relative to the means6for making it rotate.

Finally, the step of combining the relative surface structures may be implemented by taking the results of one detection step as the starting point and referring all of the others to it. In particular, once the starting relative structure has been set (and therefore the corresponding starting surface portion13), it is possible to superpose on it the other relative structures corresponding to the surface portions13sharing points with the starting surface portion13, making the shared points coincide. In other words, a first reference system integral with the starting relative surface structure is set and the coordinates of all of the other relative surface structures are transformed into coordinates belonging to said first reference system. Experts in the field will not have any difficulty determining the transformation formulas to be applied by means of a comparison of the various relative surface structures detected.

In a more complex embodiment, the method according to the present invention may also comprise an additional operating step of observing at least one end face of the log2, as illustrated inFIGS. 4 and 11(where the face is observed by a suitable detector14).

Advantageously, the end surface detection steps are associated with at least several of the relative surface structure detection steps. Preferably, the method disclosed may involve, simultaneously with at least a plurality of log2relative surface structure detection steps (advantageously all of them), the operating step of detecting at least one log end surface (preferably both). Advantageously, to detect the end surfaces the technique linked to the texture described above is preferably used.

Since the appearance of the end surface is usually well defined, knowledge of it simplifies reconstruction of the log1overall lateral surface.

According to the method of implementation described here, the step of combining relative surface structures is also carried out based on a comparison of the end surfaces that were detected at all or several of the relative surface structures. This is because a comparison of the different orientations in space detected for the same end surface allows one to infer the movement performed by the log even between the two steps for detecting the corresponding relative surface structures.

In particular, since the whole of the end surface is advantageously detected, a comparison between two subsequent detection step results reveals both the rotation to which the end surface was subjected and any translation of the end surface transversally to the axis of rotation. This addition to the first embodiment is particularly advantageous in the case of lateral surfaces which are too regular and which therefore do not provide sufficient references for correctly superposing the various detection step results, or, in the opposite case of surfaces that are too ragged and irregular and so produce a lot of “noise” in the detection step results.

The second preferred embodiment of the method according to this invention differs from the first embodiment described above only in the fact that one or both of the end surfaces is detected for each relative surface structure detection step, and the fact that there is no need for each relative surface structure (referred to the log2lateral surface) to share parts with the others. The detection step is in fact repeated in such a way that at least several points are shared by the results of two detection steps of one or both end surfaces of the log which have been carried out simultaneously with two corresponding detection steps for the relative surface structures. The reconstruction is performed exclusively based on superposing the end surfaces gradually detected. However, preferably, for a more accurate assessment of the log2, it is preferable to observe both end surfaces, since the combination of their movements allows five of the six degrees of freedom of the log to be described. The only degree of freedom which cannot be obtained is the log movement along its main axis of extension (that is to say, perpendicularly to the end surfaces).

However, that information can be obtained by means of the detection steps on the lateral surface, by assessing where the log2ends. But in general, log movements in this direction are relatively rare.

The present invention brings important advantages. First, the method and the apparatus for detecting the three-dimensional structure of a log according to the present invention may be used in lines in which the log is fed positioned perpendicularly to its own direction of extension.

Secondly, they also allow the use of a single detection device for detecting the entire lateral surface of the log, during of a single rotation of the log.

Also, the present invention may be inserted in log cutting plants which use a band saw, in particular between the log feed line and the cutting carriage. It should also be noticed that the present invention is relatively easy to produce and even the cost linked to implementation of the invention is not very high.

The invention described above may be modified and adapted in several ways without thereby departing from the scope of the inventive concept.

All details of the invention may be substituted by other technically equivalent elements and, in practice, all of the materials used, as well as the shapes and dimensions of the various components, may vary according to requirements.