Field of the Invention

This invention relates to a method for processing round logs of which at least some are curved, comprising the steps of feeding the logs one by one through a pro¬ cessing station including a cant-shaping device for pro¬ ducing at least one pair of opposing, horizontal, paral¬ lel and flat upper and lower surfaces on the log, thereby forming a cant or cant-like log portion, as well as at least one cutting device, e.g. a circular saw or a band saw, disposed after the cant-shaping device as seen in the feeding direction and cutting the thus-formed cant into separate pieces of wood; and feeding the logs by means of one or more sets of feed rollers which are laterally mov¬ able to follow the -rrved shape of the log without losing their driving engagement with the log. Description of the Prior Art

Logs which are to be split into boards or planks in a sawmill cannot normally be fed directly into the cutting device proper, but must first be shaped into cants or blocks which have two opposing and flat surfaces. This is done in a cant-shaping device which is arranged before the cutting device and which, in actual practice, may consist of an edge frame saw which comprises two vertical bands or blades between which the log is passed while slabs are cut off on both sides of the log, or a reducer which comprises two rotatable and vertically positioned cutter discs removing wood material on both sides of the log by a sort of milling operation resulting in the formation of two flat surfaces. Occasionally, one may also use a combina¬ tion of an edge frame saw and a canter.

Nature-grown trees are almost never absolutely straight, but are instead more or less curved, which is due to e.g. the wind conditions in their habitat. Thus, logs sawn from such trees are practically always inherent¬ ly curved to some extent. If a curved log were to be put

directly on a conveyor to be fed linearly through a con¬ ventional cant-shaping device, the yield of wood from the future cant would be poor, especially for logs of a markedly curved shape, since one edge-frame-saw blade or reducer would then cut away too much wood material at the top and root ends, but only a little or none at all at the middle of one side of the log, whereas the opposite blade or reducer would remove a lot of material at the middle of the log, but only a little or none at all at the ends. Therefore, the log has previously been positioned in a rotational position in which the log curve is facing sub¬ stantially upwards, i.e. vertically, when passing through the cant-shaping device. For this purpose, use has been made of a special turning device arranged before the σant- shaping device. When the cant shaped in the cant-shaping device is ready, it is turned through 90°, so that the curve plane is horizontally oriented, before being fed into the cutting device.

This method has, however, several drawbacks. Thus, the processing station requires a lot of space, since the cant, after passing through the cant-shaping device, has to be turned through 90° before being fed into the cutting device, thereby necessitating that the space between the cant-shaping device and the cutting device is able to accommodate the largest logs. If performed manually, the step of adjusting the turning of the log so that its curve plane is vertically oriented before fed into the cant- shaping device, is an exacting task. If performed automa¬ tically, this step requires expensive and complicated equipment.

Summary of the Invention

This invention aims at obviating the above drawbacks and providing a log-processing method which requires a minimum of space between the inlet and outlet ends of the processing station. Thus, a basic object of the invention is to provide a log-processing method which can be imple¬ mented in a compact and space-saving plant. Another

object of the invention is to provide a method in which the log is conveniently placed on a feeding conveyor before being fed into the cant-shaping device, i.e. there is no need for turning the log to a position in which the curve plane is vertically oriented. Yet another object of the invention is to provide a method in which the cant produced in the cant-shaping device can be split by ver¬ tical sectioning cuts without having to be turned during its passage from the cant-shaping device to the cutting device. A further object of the invention is to provide a processing method giving a maximum yield of boards or planks. An additional object of the invention is to enable the production of ready-to-use pieces of wood directly from round logs also when the pieces of wood have a special design and e.g. are profiled or formed with grooves and tongues. Further, the invention is to provide a processing station which not only is compact, but can be manufactured in easily assembled sections that are readily transported and handled. According to the invention, at least the basic object is achieved by a method having the distinctive features recited.in the characterising clause of appended claim 1.

Apart from the method, the invention concerns a plant for splitting logs. The distinctive features of this plant are recited in appended claims 2-7. Further Elucidation of the Prior Art

On the market, there is a log-cutting plant having a compact processing station in which the cant produced in a cant-shaping device need not be turned through 90° before being fed into the cutting device. In this prior-art plant, the curved log is, however, fed into the cant-shap¬ ing device with its curve plane vertically oriented. More specifically, the log is, when fed into the cant-shaping device, made to rest between two axially spaced-apart pairs of feed rollers, and the log is then automatically caused by its own weight to occupy a position in which its 'back' is facing downwards. In this position, the log is

first fed through the cant-shaping device and then, now in the form of a cant, is fed directly into the cutting device. The latter has to be equipped with cutting means making horizontal sectioning cuts in the cant. However, such cutting techniques give rise to serious problems when the individual, horizontally disposed boards in the cant later are to be separated from one another, since these boards will then lie stacked upon each other.

Contrary to this prior-art plant, the present inven- tion is based on the idea of splitting the cant by verti¬ cal sectioning cuts ensuring that the individual boards are easily and readily separated from one another at a later stage.

Further, EP 0,158,580, SE 9000604-0 and WO91/07260 disclose different plants for splitting logs. The last two deal exclusively with curve sawing of cants or blocks, i.e. pieces of wood which, in a station before the saw, have been processed into cants or blocks in one way or another. It is true that the introduction to W091/07260 contains an obscure statement that the plant relates to the processing -of 'a piece of timber, espe¬ cially a block*, but the following, more concrete description and the appended claims make it clear that the plant is restricted to the processing of previously shaped blocks and does not process unworked logs. Inter alia, the feed-roller means of the plant require a pro¬ cessed surface (see claim 1, line 11 and 12). Although the plant according to WO91/07260 comprises two canter discs arranged immediately before the cutting device, these discs (easily disposed with, to say the least) only serve to remove the rounded side edges of the incoming block whose upper side and under side have already been made horizontal and flat in a previous station not described in detail in this document. SE 9000604-0 only discloses curve sawing of square cants, i.e. logs which, in a previous station (not described in detail), have been given a pair of upper

and lower horizontal flat surfaces, as well as a pair of vertical flat lateral surfaces.

EP 0,158,580 discloses a plant which actually can be used for curve sawing of both logs and cants. This is per- formed according to two alternatives. The alternative of log sawing is illustrated in Figs 1 and 2, and the alter¬ native of cant sawing is illustrated in Figs 3-8. The alternative of log sawing illustrated in Figs 1 and 2 results in a number of individual boards of varying width, which have to be edged in an edging operation after the sawing. This is an extremely costly procedure, owing to the extensive and complicated subsequent finishing and handling of a multitude of individual boards and planks. In the second alternative, a cant is first sawed in a sta- tion (see p. 22, lines 14-26 and p. 23, lines 1-11, as well as p. 12, lines 1-21), the position of the cant being such that the back of the curved log is vertical. Then, the cant is, after being turned through 90°, transferred by conveyors to a subsequent sawing device in which it is split into boards or other pieces of wood. The plant employed according to EP 0,158,580 is extremely space- requiring compared with the plant according to the present invention.

Brief Description of the Drawings In the drawings,

FIG. 1 is a plan view of the plant according to the invention, part A illustrating a feeding-in con¬ veyor, part B illustrating the processing station of the plant, and part C illustrating a feeding- out conveyor (in actual practice, these parts are arranged in line after one another but are here shown spaced apart for reasons of drawing simpli¬ fication), FIG. 2 is a side view of the plant in Fig. 1, the con- veyors and the processing station being shown in parts A-C as in Fig. 1,

FIG. 3 is a slightly enlarged side view of part B in Fig. 2, the component parts being illustrated in more detail, FIG. 4 is an enlarged plan view of part B in Fig. 1, FIG. 5 is a plan view of but one feeding-in station of the part in Fig. 4, FIG. 6 is an exploaded plan view of three devices forming part of the feeding-in part in Fig. 5, FIGS 7 and 8 are schematic views of a log being longitudi- nally fed according to two different principles, and FIG. 9 is a cross-section of a cant shaped in the pro¬ cessing station of Figs 3 and 4 according to one of several conceivable alternatives. Description of the Preferred Embodiment.

Figs 1 and 2 show a first conveyor 1 for feeding logs 2 into a processing station 3. A feeding-out conveyor 4 is provided in the area after the processing station 3. A saw line or cutting line running through the entire plant is designated 5.

Before a more detailed description of the plant illu¬ strated,in Figs 1-6 is given, reference is made to Figs 7 and 8 which schematically illustrate a log 2' having a perfectly conical shape, i.e. tapers from the root to the top. In the drawing, the thickness of the log is exagge¬ rated in relation to its length, as is its conicity. Through the log runs a centre line 6, which in the follow¬ ing will be referred to as the volume centre of the log, by which is meant a line interconnecting all centres in optional cross-sections taken along the length of the log. In practice, the log is, of course, neither completely straight nor perfectly conical, and the volume centre line is consequently almost never completely straight.

In Fig. 7, the log 2' is placed on a horizontal underlying structure 7, e.g. a conveyor. If this log were to be set in motion parallel to the underlying structure, e.g. through a cant-shaping device or a cutting device,

every optional point P in the log would move parallel to the underlying structure 7, but not parallel to the volume centre line 6 which, depending on the conicity of the log, forms a certain angle with the underlying structure. In Fig. 8, on the other hand, the volume centre line 6 of the log 2' is horizontally oriented, which means that every optional point P in the log will move parallel to the volume centre line when the log is longitudinally fed in the horizontal plane. One object of the present invention is to provide a plant in which the logs can be fed as in Fig. 8, i.e. along a path determined by the volume centre line 6.

Fig. 9 illustrates one of several conceivable alter¬ natives for shaping a log into a cant 8. This cant com- prises a main portion 9, as well as two lateral portions 10, 10' which are separated from the main portion by sub¬ stantially vertical sectioning cuts 11. The main portion 9 may optionally be divided into separate boards or planks 12 by other substantially vertical sectioning cuts 13. In the areas above and below the lateral portions 10, 10', the wood has been milled off or otherwise removed, result¬ ing in the formation of four corner areas 14. This means that the lateral boards 10, 10' separated by the section¬ ing cuts 11 have less width than the boards 12 in the main portion of the cant. These comparatively narrow lateral boards can be made since the flat outsides 15 defining the lateral boards have been located relatively far out towards the periphery of the log, which is made possible by milling off the corner portions 14. Although the late- ral boards 10, 10' in Fig. 9 are shown with flat long-side edges (the narrow upper and lower edge surfaces), they may also be profiled, e.g. formed with grooves and tongues. This can be achieved by using suitable profile cutters together with the cutting device of the plant. In analo- gous manner, also the pieces of wood 12 in the main por¬ tion 9 can be given profiled instead of flat surfaces.

Reference is now made to Figs 1 and 2. The conveyor 1 serving to feed the incoming logs 2 into the processing station 3 comprises a table 16 on which is mounted an end¬ less chain 17 having suitable means for longitudinally feeding the log. The table 16 is vertically.adjustable at least at the end facing the processing station 3, e.g. by being connected to a lower supporting stand by a system of links 18. Above the table 16 is provided at least one press roller 19 serving to press the log against the con- veyor chain. Equipment (indicated at 20) for registering the shape and/or the dimensions of the log (primarily the diameter of the incoming front end) is associated with the conveyor. Upon arrival at the conveyor 1, the log 2 can simply be dropped onto the conveyor, where it is naturally oriented so that the curve plane is horizontal, as shown in Fig. 1. The end diameter of the individual log can be read by the equipment 20, and this information is regis¬ tered in a computer adapted to control different compo¬ nents in processing stations. The processing station 3 illustrated in Figs 3 and 4 is divided into three different sections 21, 22 and 23. The first section serves to feed and guide the log coming from the conveyor 1 into a cant-shaping device forming part of the following section 22. The section 23 includes a cutting device for splitting a cant produced in the cant-shaping device. In practice, the sections 21, 22, 23 are manufactured as separate units in the form of support¬ ing frameworks which are mounted adjacent to one another in the sawmill where the station is to operate. The feed- ing-in section 21 comprises two pairs of feed rollers 24, 25 and a means 26 for finally guiding the log into the cant-shaping device in the section 22. As appears from Figs 5 and 6, the first two feed rollers 24 are mounted on arms 27, 27' which are pivotable towards and away from one another about vertical shafts 28 by means of two cylinder units 29, 30. The first cylinder unit extends directly between the arms 27, 27', while the second cylinder unit

extends diagonally between one arm 27 and an extension piece 31 of the other arm 27' . The unit 29 is of single- cylinder type, while the unit 30 is of double-cylinder type and takes on the nature of a diagonal brace of variable length. When the cylinders in the unit 30 are pressurised, this unit thus has a given length and func¬ tions as a rigid diagonal brace. When the cylinder 29 is shortened in order to apply a pressure to a log between the feed rollers 24, the latter will move uniformly rela- tive to the saw line. By adjustment of the pressure in the cylinder 29, the feed rollers 24 can be made to apply a suitable pressure to the outside of the log. In analogous manner, the feed rollers 25 are arranged on arms 32 which are pivotable about the same vertical shafts 28 as the rollers 24, and are operated by the cylinder units 29',

30' . These cylinders are connected to a pivotable means 33 which is operable by a third cylinder 34 able to pivot this means about the associated shaft 28 while pivoting an arm 34' of a clamping jaw 37 forming part of the guide means 26. When the cylinder units 30, 30' are depressur- ised, the feed rollers 24,* 25 may freely follow the shape of a curved log without ceasing to be drivingly applied against the log. It should here be pointed out that each feed roller can be driven by stationary motors 35 (see Fig. 3) via universal joints 36.

The guide means 26 comprises two clamping jaws or clamping-jaw-like members 37, 37' which are interconnect¬ ed by a system of links 38 and a diagonal brace 39 and which are operated by a cylinder 40 at all times striving to apply the clamping jaws against a log passing there¬ between. The clamping jaws constantly strive to occupy a centered position in relation to the cutting line 5. By the control means 26, the front narrow end of the log will be laterally centered when guided into the following cant-shaping device, at the same time as the two pairs of longitudinal feed rollers 24, 25 adapt themselves to the curved shape of the log. This adaptation is performed by

depressurising the cylinder units 30, 30' functioning as diagonal braces. The cylinder unit 34, connecting the feed roller 25 to the clamping jaw 37 via the pivotable means 33 and the arm 34', ensures, together with the diagonal brace 39, that the two clamping jaws 37, 37! move outwards when the feed rollers 25 do so, and vice versa. It should be observed that each feed roller 24 in the first or front pair of rollers is formed with a peripheral, gradually tapering recess 49. Advantageously, this recess is defined by two truncatedly conical surfaces meeting in a plane which is horizontally oriented and located in the same horizontal plane as the saw line 5. Owing to this shape of the feed rollers 24, a log nipped therebetween will auto¬ matically be centered, so that the volume centre line 6 of the log is located in the same horizontal plane as the saw line 5 of the station, although the volume centre line 6 of curved logs may bend laterally outwards in relation to the central saw line 5. By the vertically centring effect of the feed rollers 24 and the vertically adjusting effect of the conveyor table 16, on the one hand, as well as the horizontally centring effect of the guide means 26, on the other hand, the log will be centered with respect to the saw line 5 in the area of the guide means.

The cant-shaping device in the section 22 comprises two pairs of canter plates 41, 42. The first pair 41 serves to produce flat, horizontal surfaces on the upper side and the under side of the log. It should be observed that the clamping jaws 37, 37' of the guide means 26 are arranged between the canter plates in the first pair. For this reason, the clamping jaws have a height which is less than the smallest height of the future cant. The second pair of canter plates 42 serve to produce flat, vertical surfaces on the two opposing long sides of the log, in this case the surfaces 15 in Fig. 9. All the canter plates may be of conventional type, i.e. have a truncatedly coni¬ cal surface equipped with a plurality of cutters serving

the remove wood material from the log in a sort of milling operation.

The cutting device forming part of the section 23 comprises two sets of saw blades 43 mounted on shafts 44, 44' which are slightly offset in relation to one another in the feeding direction, such that the peripheries of the blades may overlap somewhat in order to make a complete, throughgoing sectioning cut in the cant. In practice, several saw blades are mounted on each shaft in order to make several sectioning cuts in the cant, as illustrated in Fig. 9. Advantageously, the blades 43 are adjustable along the shafts 44, 44' to enable the making of different sectioning patterns in the cant. Further, special milling elements may be associated with the blades on each shaft and adapted to mill off the corner areas 14 in Fig. 9 and optionally profile the lateral boards or the boards in the main portion of the cant.

Ahead of the cutting device are arranged a set of press rollers 45, as well as a set of feed rollers 46 for feeding out the shaped and cut cant on the feeding-out conveyor 4.

Advantageously, the conveyor 4 is a central, endless conveyor chain 47 on whose two opposing sides are arranged a set of successive iπstal sheets 48 which are inclined relative to the horizontal plane and whose upper edges can be yieldably pressed against the main portion 9 of the cant in the lower corner areas 14 (see Fig. 9). The metal sheets 48 may thus guide and follow the main portion of the cant 9 while keeping together the individual boards 12 therein, at the same time as the lateral boards 10, 10' are separated by sliding downwards along the metal sheets onto a transverse conveyor below. In this way, the diffe¬ rent boards 10, 12 of the cant are easily and automati¬ cally separated from one another, which is made possible by the fact that the sectioning cuts in the cant, and con¬ sequently the boards themselves, are vertically oriented. The special conveyor 4 forming part of the plant is the

subject of SE Patent Application 9101197-3 having the same priority date as the present application.

It should also be pointed out that the canter plates 42 serving to shape the vertical lateral surfaces 15 of the cant are mounted in close vicinity to the following saw blades 43, at the same time as the guide means 26 is mounted immediately before the canter plates 42. Thus, the guide means 26, the canter plates 42 and the saw blades 43 are all mounted in a space of severely restricted axial extent, which means that also logs of markedly curved shape can be processed without any loss of yield, since the canter plates 42 and the saw blades 43 at the moment of processing substantially follow a tangent of the radius of curvature of the log. The plant operates as follows. The individual log 2 (see Fig. 1) is put on the feeding-in conveyor 1. Depend¬ ing on the dimensions of the log (read off by the equip¬ ment 20 and registered in the computer of the plant), the conveyor table is raised or lowered so that the volume centre line 6 at the front end of the log is positioned on a level with the centre of the first feed rollers 24 (the table is lowered for thick logs and raised for narrow ones). Then, the conveyor chain is set in motion so as to feed the log into the nip between the feed rollers 24 which grip the front end of the log and forward the log towards the second pair of feed rollers, the volume centre line of the log being situated in the same horizontal plane as the cutting line 5. Also the feed rollers 25 nip the log and push it through the first set of canter plates 41, the second set of canter plates 42 and the cutting device made up of the saw blades 43. Thus, the canter plates 41, 42 gradually shape the log into a cant which, by the cutting device, is split into the vertical boards 12 and 10. When the log is longitudinally fed, the feed rollers 24, 25 are laterally moved so as to adjust them¬ selves to the curved shape of the log, more precisely in such a manner that the feed rollers maintain their driving

engagement with the log but do not apply to the log any forces tending to pivot the log laterally in the area of the canter 42 and the cutting device 43. Thus, the saw blades of the cutting .device will be disposed substan- tially along a tangent of the radius of curvature of the log, at the same time as the rear thick end of the log moves laterally to such an extent that the saw blades keep their tangential orientation during the entire cutting procedure. Of course, this means that the front end of the log follows a curved path of motion after passing the cut¬ ting device, which is made possible by the feed rollers 46, like the feed rollers 24, 25, being mounted on pivot¬ able arms permitting lateral displacement of the rollers while pressed against the cant split into boards. It should here be pointed out that the term 'cant' used in the present application does not mean that the log in its entirety is shaped into a conventional cant before being cut. In the invention, the term 'cant' refers to the log portion extending rearwards from the cant-shaping device. This cant portion is then immediately cut in the cutting device in such a manner that the cant, after hav¬ ing passed through the cutting device in its entirety, in practice is composed of a number of boards separated by sectioning cuts and kept together in a unit when discharg- ed onto the feeding-out conveyor 4 (then, the lateral boards are immediately separated from the main portion of the cant, and the boards of the main portion are forwarded to be finally separated).

The advantages of the invention leap to the eye. Thus, the cutting techniques according to the invention enable the construction of a plant which is extremely space-saving, which means that the volume of the plant building can be considerably reduced, with ensuing savings in costs. Further, guiding the log into the processing station and removing the processed and cut cant are easily performed compared with the prior art. Since the section-

ing cuts in the cant are vertical, the individual boards are easily separated.

The expression 'substantially vertical sectioning cuts' used in the description and the appended claims is to be interpreted in the broad sense, and essentially means that the sectioning cuts are vertically oriented rather than horizontally. Thus, it is conceivable to make at least one sectioning cut which is inclined relative to the vertical line, e.g. by 1-15°. Such inclined sectioning cuts may be used e.g. in the production of weather board¬ ing.

It should be added that the logs can be fed through the processing station with the top end or the root end first. Finally, it should be pointed out that the clamping jaws of the guide means 26 may be designed in many diffe¬ rent ways. Thus, these jaws may each be equipped with at least one endless chain applied against the log, one chain being driven and the other being taken along.