WO2001020324A1

WO2001020324A1 - Method for quality determination and handling of elongate wood items

Info

Publication number: WO2001020324A1
Application number: PCT/DK2000/000511
Authority: WO
Inventors: Niels Peter Pretzmann
Original assignee: Opti-Wood Aps
Priority date: 1999-09-14
Filing date: 2000-09-14
Publication date: 2001-03-22
Also published as: AU7270200A; EP1212614A1

Abstract

There is disclosed a method making possible an unequivocal and effective registration of features of wood items, including location of heartwood and share of heartwood in a wooden item (1). Cameras (2) are used by the method, taking pictures of the end faces which are preferentially treated with heartwood reactant. Subsequently, image processing is performed in a central control unit (3). Hereby heartwood share and the location of the heartwood in the wooden item (1) are determined whereby the item may optionally be turned by means of a turning means (8) for correct orientation for subsequent shaping. The control unit may likewise use registration for sifting out wooden items in different categories, for example by sifting out to a separate receiving unit (11).

Description

METHOD FOR QUALITY DETERMINATION AND HANDLING OF ELONGATE WOOD ITEMS

Background of the invention

The present invention concerns a method for quality determination and handling of wood items with lateral faces and end faces, comprising optical registration of surface features and digital processing for controlling the handling of the wood items as a central control unit is used for processing registered data and for controlling process steps in the handling of the items.

Within the wood industry, and preferably when producing items that are to have great durability, as in the case of casings, frames and similar in wall openings, it is desirable to have wood which is as durable as possible. It is also desirable to make such building elements of wood or planks which are handled and processed in such a way that the planks have been freed from knots etc.

For many years it has thus been a problem for makers of wooden items to be used subsequently for windows, doors, furniture, stairways, etc. to have a quality that may vary. Many attempts have been made to produce a quality which is uniform and at the same time has a high share of heartwood. It is commonly recognised that a high share of heartwood is particularly suited for frames in wall openings due to its high content of resin, making the wood very weatherproof.

Through many years it has been commonly known, in spite of this knowledge, that sapwood, which the outermost part of the stem, has been used as raw material in the production of wood items for aesthetic reasons. Hereby it has become possible to avoid knots on the visible surfaces in, for example, windows and doors. Even though the immediate result was aesthetically pleasing due to the uniformity of the sapwood without knots, there have been problems with the durability due to a low content of resin. Therefore, it has appeared that glued sapwood could be separated in glue joints as well as the durability has been very limited. Through several years it has been known to use optical registration of the surface for registering knots or other unwanted features in an attempt to improve the quality and the aesthetical appearance. With digital processing of these images it has been possible to use collected data for controlling by means of process steps and machines to remove such unwanted wooden parts. In order to obtain an elongate item it has also been known that the two ends at each side of a part cut off are then glued together.

Furthermore, it has been known to use an optical registration of surface features for sifting out wooden items which, for example, do not have full edges or which may have cracks making them unsuited for subsequent use.

Another problem recognised in usual wooden items is known particularly in connection with boards and planks with limited thickness in relation to their width. Here is the risk that the plank profile is curved which can make difficult shaping in a satisfac- tory way. Furthermore, asymmetrical location of the heartwood in an elongate wood item may cause that this can not only curve but also twist during subsequent processing.

Even though it has been known to register the surface on such wooden items, until now it has only been possible to estimate the location of the heartwood and the total share of heartwood in a plank by subjective estimates which are very uncertain. As no actual measurement of the location or share of heartwood is performed, this has been a process which may be connected with disadvantages due to failing quality in the finished items and/or sifting out of wood items which could have been used.

Until now a measuring method has been known for assessing whether the share of heartwood has been disposed upward or downward and for seeing whether the heart- wood centre is oriented upward or downward in relation to a wood item by using three mechanical sensors. These sensors may register a curvature. Then it is assumed that there is an unequivocal relation between curvature and location of centre of the heart- wood. This is not always the case, and the curvature measurement is therefore uncertain. This uncertainty is especially a problem with narrow wood items. The method has therefore significant uncertainty and may only be used to a small extent in connection with an effective registration in connection with automatic handling of wood items through shaping processes.

It is the purpose of the present invention to relieve the drawbacks by the known techniques and to provide a method enabling an unequivocal and effective registering of surface features, including location of heartwood and share of heartwood in an item, and to use these registrations for controlling subsequent shaping which preferentially may be performed in automatic machines. In particular it is a purpose of the invention to ensure a method enabling overcoming the disadvantages which have been connected with the manual registration of location of heartwood or share of heartwood in a wooden item.

According to the present invention this is achieved with a method of the kind men- tioned in the introduction which is peculiar in that the end faces of the item are registered as one or more pictures are taken of one or both ends of the item, that the picture is processed in the control unit as registration of the heartwood share and the location of the heartwood in the wood item is performed, that heartwood shares are used for sorting the items into categories as the control unit transmits signals to selection units guiding the items into different paths, and that data concerning location of the heart- wood is used for orienting the item as desired in accordance with the intended use and later processing.

In the present application, end face of the item means the surface of an item oriented largely perpendicularly to the longitudinal direction of the wood. The wood item may be elongate and will then usually have a longitudinal axis which parallel with an axis in the longitudinal direction of the wood. However, wood items which are handled by a method according to the invention may also be provided as items where the dimension in the longitudinal direction is very small or less than the than the dimension of the item perpendicular to the longitudinal direction of the wood. With such a method, the end face of the item will be registered by means of camera taking single pictures or by means of a video camera taking pictures continually. The pictures are processed in a control unit comprising a computer in which is stored programs for digital image processing. From the optical registrations taken, by this digital image processing it may be possible to find the parameters enabling registering of the location of the heartwood. Furthermore, the program may contain algorithms giving indication of a location of the pith of the wood item so that this may be used as reference point for a subsequent orientation of the item.

As a result of registering/calculating such data it will be possible to introduce these in a control circuit, for example via a PLC controlling subsequent selection units which may be provided in the form of gates, conveyor belts or other equipment being well- known per se within the wood industry for directing/transporting wood item in one or the other direction. Furthermore, registration data may be used in a control unit for controlling turning units orienting the wood items with correctly oriented heartwood relative to subsequent handling and/or shaping machines. Furthermore, the control unit may set these shaping machines by means of these data so that shaping may be performed which is correct in relation to the intended use of the wood.

Thus with the system it becomes possible automatically to register and to use these date for an automatic sifting out and subsequent controlling of shaping machines with a precision hitherto not attainable. Hereby not only achieved technically correct products are obtained where the risk of twisting is avoided and where the risk of decomposition of the wood occurs due to low share of heartwood resulting in surfaces that are exposed to weather. Furthermore, a final product may be achieved where the high precision by registering surface features results in an aesthetically pleasing product. It is thus possible to achieve a product with an aesthetically pleasing exterior and simultaneously applying the wood items with heartwood disposed correctly providing for weather-resistance etc.

The method will, for example, be suited for handling wood items which subsequently are to be used for orienting staves in laminated wood for providing maximum strength and least possible settlement due to moisture and temperature conditions. Furthermore, it may be used for orienting wood staves correctly for providing optimal appearance of the finished product. As mentioned, there may also be achieved a correct orientation of the heartwood/sapwood in the finished constructions, for example so that heartwood only appears externally in a frame placed in wall openings.

Furthermore, the automatic handling of each single item with great precision will enable achieving a very uniform quality and establishing a quality marking and quality sorting of the wooden items.

In order to achieve the greatest possible security by registering heartwood shares and location, it is preferred that the end faces of the items are treated with heartwood reagent before the taking of pictures. This may, for example, occur by they being treated together in a pallet which immediately after is inserted in a registration unit in an ap- paratus or which is stored a number of hours before the subsequent registration/handling. As heartwood reactant may be used liquids or other agents producing an image within the visible range which thus enables detection by means of traditional cameras. Alternatively, it is possible to use heartwood reactant producing accentuation of the grain geometry within a spectrum which is not visible with traditional technique but instead, for example, uses ultraviolet light. With such kind of heartwood reactant visible colouring of the wood items is avoided which may be unfavourable in some situations.

For correctly orienting the boards and for performing calculation of heartwood shares, by the method it is preferred that a registration of the centre of the pith of the item is performed, and that this centre is used as reference point by orienting the item. Alternatively, it is possible to use sapwood or a surface on the wood item as reference point if this is suitable with regard to subsequent handling/shaping. However, it is preferred to use the centre of the pith of the wood item as reference point when allowance is to be made for correct orientation of the items when providing for subsequent use, for example for enabling orientation of items with the pith center correctly oriented for subsequent glueing together of several wood items. The orientation of the item will preferably be a rotation about an axis in the longitudinal direction of the wood, where it preferentially may be placed on one of its lateral faces. It may be any polygonal cross-section but for traditional planks/boards it may be four lateral faces, and therefore the orientation will occur by rotation through an- gles of 90°, 180° or 270°. Hereby the item may be placed optimally for a subsequent passage through shaping machines. Alternatively, it is also possible to turn the item about an axis perpendicular to the length of the wood for orienting it with this or the other end first through a subsequent process.

The data achieved by the digital image processing are used for controlling selection units and subsequent shaping units. Thus it will be possible to perform an individual sifting out of single items/board in a stack of boards and possible to perform an individual shaping of each single item. By registering data it may thus be localised whether a shaping unit is to grind/trim plane a curving item as well as it is possible to perform shaping in the form of milling with different sections with regard to heart- wood share in the actual item. Thus it will be possible to remove a larger or lesser part of a wooden item if this is optimal with respect to the subsequent use of the wood item.

According to an advantageous embodiment, the method is peculiar in that subsequently an optical registration of surface features on the longitudinal sides is performed, and that signal herefrom is registered and processed in the control unit which uses data about it for controlling a transverse cutting up for removing lengths with unwanted features, and that the ends of the items thus shortened are provided with tenons for subsequent assembly to form an elongate item with the desired length.

Hereby it becomes possible to achieve optimal technical working out of the wooden items. Not only registration of the heartwood will thus be performed but in addition registration and removal of knots with a subsequent joining of the shortened items. It will thus be possible to make finished elongate items which are free from knots and which have a desired length. The mortise joints used will preferably be a finger mortise joint which is well-known in the art. By the method it becomes possible to handle wood items with different cross-sectional area. According to a special embodiment, the method will be peculiar in that in the image processing determination of the cross-section of the item is performed, and that these data are used for sorting into categories as further selection units are controlled from these data, and that these data are also used for controlling the subsequent processing. Even though automatic processes are preferentially used for handling wood items with uniform cross-section, the present process will be suited for handling items with non-uniform cross-section. This may be the case not with planks but with converting logs where a subsequent shaping machine is provided in the form of cutting units which convert a log into boards/planks being optimal with regard to heart wood location and heartwood shares in each of the planks produced.

By performing the method it is possible to use mechanical handling units which are known per se. Thus it is possible to use mechanical turning means where the wood items are turned by engagement between mechanical fingers or the like which are controlled via a program contained in the control unit.

By combining registration of surface features on the end faces of the item and registering features along the surface it becomes possible to get a complete registration ena- bling an automatic handling/shaping. Thus the program used may establish calculation of heartwood share measured in percent and compare this with previously stored data after which the result may be used for controlling selection units so that the wood items may be sorted according to categories of quality based on the relative share of heartwood. Such data may be stored and used by the subsequent documentation for the quality of the wood items. Hereby is achieved classification of the quality of the products produced by using the wood items.

Description of the Drawing

The invention will then be explained in more detail with reference to the accompany- ing drawing where: Fig. 1 shows schematically the structure of a plant for use in performing the method according to the invention, Fig. 2 shows different examples of end faces in a wood item according to the invention.

The plant illustrated in Fig. 1 is intended for handling wood items 1 in the shape of elongate boards which are supplied to the process in the shape of palletised stacks. For illustration reasons only a single elongate wood item 1 is shown in the plant in a position between two cameras 2 which are intended for taking pictures of the ends of the wood item having a plane surface which is oriented largely perpendicular to the longitudinal direction of the wood. The cameras are connected with a central control unit 3 provided with a display, printing facility and programs for registering and processing data via digital image processing and programs for controlling the single apparatuses of the plant.

The plant comprises a floor roller conveyor 4 on which palletised wood stacks are placed as they have been previously treated with heartwood reactant. In immediate extension of the floor roller conveyor 4 there is provided a floor roller conveyor 5 with a built-on lifting table, and over this is disposed a feeder 6 which may advance whole layers on a chain conveyor 7 disposed between the two cameras 2. In association with the chain conveyor 7 there is provided an item turning means 8 used for rotating the wood items 1 through an angle that may be 90°, 180° or 270° depending on control signal from the control unit 3.

The items 1 are passed from the chain conveyor 7 onto a conveyor 9 which is oriented perpendicularly thereto for displacing the items 1 in the direction of the arrow 10. By displacing from a first section 9' of the conveyor 9 to a second section 9" of the conveyor there is provided a selection device 10 pushing the wood items away from the conveyor into a unit 11 as a result of signals from the control unit 3. In the plant shown there is only shown one unit 11. However, it is possible to provide plural units where items 1 are introduced in different quality categories which, for example, are determined from the calculated relative content of heartwood in the item 1 concerned. Items 1 going on to further shaping and which may have different qualities to be handled in different ways are transferred to a chain conveyor 12. Immediately associated with the chain conveyor or before this a further turning device (not shown) may be freely provided, rotating the items 1 about an axis perpendicularly to the longitudinal direction of the wood so that a desired end of the wood items is oriented to the right or to the left depending on the subsequent treatment.

The chain conveyor 12 introduces the items into a feeder 13 to a plane 14 which planes/trims the lateral faces on the wood items. The items 1 are moved from the plane 14 to a buffer store 15 wherefrom they are introduced into a conveyor 16. The conveyor 16 moves the items through a registering unit 17 comprising cameras and where registration of the surface features on the longitudinal side of the items is performed. This occurs with the purpose of registering knots, cracks or other irregularities which are undesired in the finished product. The unit 17 is also connected with the central control unit 3, and thus digital processing of the pictures taken is performed, and the result is used for controlling succeeding shaping machines.

The items are moved from the unit 17 into a buffer store 18 which moves the items into a saw 19 controlled by the control unit 3 and where cuts are performed trans- versely of the longitudinal direction for removing unwanted parts. In the saw 19, finger tenons are simultaneously established at the ends of the shortened wood items. Waste is moved by a conveyor 21 to a container 22 according to the arrow 20 for further use or disposal.

The shortened wood items are conveyed on a belt conveyor 23 further on to a stacking device 24. The stacked items are moved via a conveyor 25 further on to a sorting unit 26,27 for subsequent correct placing in a feeder 28 to an apparatus establishing finger joints by glueing together the shortened items in position end-to-end. Hereby are established elongate items which are conveyed out from the apparatus 29 via a conveyor 30 to a transfer conveyor 31 which conveys the glued wood items with the desired lengths to a stacking unit 32. Then the wood items are ready for subsequent shaping in millers, planers or other shaping machines which also may be controlled by the central control unit 3. Alternatively, the plant may comprise a printing unit 33 imparting identification on the wood items, indicating orientation of heartwood, heartwood share etc. in a form which can be registered in a scanner and which may be used as control signal for subsequent shaping machines.

Fig. 2 shows three different types of wood items 1 ', 1 " and 1 "' as seen from the end in direction along the longitudinal axis of the wood. The wood item 1 ' is oriented with the heartwood 34 placed symmetrically and with centre 35 for pith located at a lateral face of the item 1 '.

The wood item 1 " corresponds in principle to the left half of the wood item 1 '. Here it is seen that the wood will have centre 35 for pith located at one corner and have sap- wood 36 located at an opposite corner contrary to the location of sapwood 36 at opposite sides in the wood item 1 ' .

The wood item 1 " ' illustrates an item where an upward directed curvature of the corner areas 37 causes the cross-section not to be rectangular. In such a construction it may be desired to remove part of the material by plane grinding/shaping for establishing a rectangular cross-section for a subsequent use. The curvature of the wood may be registered by the processing of the pictures taken by the cameras 2. Thus it becomes possible to make allowance for the curved wood item 1 " ' by the subsequent adjusting of tools in the shaping machines.

The invention is explained in the above in connection with a specific plant. However, other embodiments of plant as well as method will be possible. Thus it will be possible to use a different feeding for not handling other types of wood items, e.g. wood trunks. Also, here will be a subsequent shaping comprising cutting units controlled by the central control unit 3.

Claims

1. A method for quality determination and handling of wood items with lateral faces and end faces, comprising optical registration of surface features and digital process- ing for controlling the handling of the wood items as a central control unit is used for processing registered data and for controlling process steps in the handling of the items, characterised in that the end faces of the items are registered as one or more pictures are taken of one or both ends of the item, that the picture is processed in the control unit as registration of the heartwood share and the location of the heart- wood in the wood item is performed, that heartwood shares are used for sorting the items into categories as the control unit transmits signals to selection units guiding the items into different paths, and that data concerning location of the heartwood is used for orienting the item as desired in accordance with the intended use and later processing.

2. A method according to claim 1, characterised in that end faces of the items are treated with heartwood reagent before the taking of pictures.

3. A method according to claim 1 or 2, characterised in that the location of the pith is used as reference point when the item is oriented.

4. A method according to any preceding claim, characterised in that the orienting of the item comprises rotation about an axis in the longitudinal direction of the wood as the item is preferably oriented for lying on one of its lateral faces.

5. A method according to claim 4, characterised in that rotation occurs through angles of 90°, 180° or 270°.

6. A method according to any preceding claim, characterised in that the image processing is used for determining curvature in the item, and that data about it is used for controlling selection units and subsequent processing units.

7. A method according to any preceding claim, characterised in that subsequently an optical registration of surface features on the longitudinal sides is performed, and that signal herefrom is registered and processed in the control unit which uses data about it for controlling a transverse cutting up for removing lengths with unwanted features, and that the ends of the items thus shortened are provided with tenons for subsequent assembly to form an elongate item with the desired length.

8. A method according to claim 7, characterised in that the items are provided in the shape of unplaned planks/boards, and that before registration of surface features on the longitudinal sides there is performed a planing/trimming of the longitudinal sides, and that during this provision is made for possible curvature by adjusting the tool used so that the longitudinal side is planed.

9. A method according to any preceding claim, characterised in that in the image processing determination of the cross-section of the item is performed, and that these data are used for sorting into categories as further selection units are controlled from these data, and that these data are also used for controlling the subsequent processing.

10. A method according to any preceding claim, characterised in that the processing comprises milling/planing or similar cutting processes for imparting a desired cross-sectional profile to the items for subsequent use, preferably for making casings, frames and the like in wall openings in buildings.