System for improving the utilization of the capacity of a wood working line

Abstract

 System for improving the utilization of the capacity of a wood working line, the wood working line comprises a preceding wood working machine (9) though which wood pieces (16) are fed longitudinally into and a subsequent wood working machine (11), through which the wood pieces are fed transverse, wherein the speed of the preceding working station (9) on a regular basis is adapted to the length of the wood pieces (16), so that the number of wood pieces (16) which is delivered from the station per time unit is sought to be adapted to the speed of the subsequent wood working machine (11).

Description

[0001] The present invention relates to a system for improving the utilization of the capacity of a wood working line in accordance with the preamble of the subsequent claim 1,

[0002] In working pieces of wood, which are present as elongate planks or boards, a substantial part of the transport of the pieces takes place through the different working machines with the direction of transport transverse to the length of the pieces. The pieces often have different lengths. The different lengths do not have any significance on the transport speed through the various working machines as long as the transport is transverse to the lengths.

[0003] However, there exist needs to transport the pieces lengthwise through some working stations. In these stations the length of the single pieces, or rather, the total length of these, will determine how many wood pieces that may be fed through the station per time unit. The different working stations in a wood working factory are in general coupled together so that the transfer of wood pieces from one station to the next takes place practically automatically. Thus, the total production capacity will depend on the fact that the individual station can keep up with the deliveries from the previous station or deliver quickly enough to the next station. Thus, the production speed will never be higher than what the station with the lowest speed can deliver. If the preceding station has a larger production capacity than the subsequent station, the production speed of the preceding station must be reduced until the subsequent station can keep up with the wood pieces supplied.

[0004] To a certain degree disproportion in the production capacity can be compensated for by introducing buffers between stations. However, such a buffer presupposes that the average production speed for two stations is the same over time. If this is not the case, the buffer will either be completely filled of emptied after some time. In the first case, the preceding station must stop until the buffer is sufficiently reduced in size. In the second case the subsequent station will have to be stopped or run idle every time the buffer runs empty, pending new wood pieces entering the buffer,

[0005] It is therefore important to adapt the production speeds between the different stations.

[0006] A particular problem of disproportion between different stations exists in the case where the production speed for one station is depending on the length of the wood pieces, while the production speed of another station is not depending on the length. One such case is for example where a preceding station is a planing machine, which is set to plane the wood pieces in the longitudinal direction, and the subsequent station is a cross-cutting and sorting table, on which the wood pieces are placed in a slot defined between carriers on the cross-cutting and sorting table conveyor. The wood pieces are conveyed transverse to the longitudinal direction on this table and the capacity is thus independent of the length of the wood pieces.

[0007] The wood pieces are conveyed virtually end to end through the planning machine. Therefore, an accumulation of short wood pieces will result in a relatively frequent delivery of wood pieces from the machine. These pieces each have to have one slot in the cross-cutting and sorting table. As a consequence the planning machine cannot work any faster than the rate at which the cross-cutting and sorting table can receive the wood pieces in an individual slot.

[0008] From time to time an accumulation of long wood pieces will occur. In this case it will take some time between each time a wood piece is delivered and has to be transferred to the cross-cutting and sorting table. All the slots in the cross-cutting and sorting table will therefore not be filled. As a consequence the capacity of the cross-cutting and sorting table will not be utilized optimally.

[0009] One obvious solution to this is to provide for wood pieces which have the same length. This is in fact done when interior panel and some types of floorboard is produced. In these cases the wood pieces are cut to a certain length, for example 240 cm. However, this results in a substantial amount of wood spillage as stub ends, and as a result the finished panel of floorboards becomes more expensive.

[0010] The present invention has as an object to achieve a better utilization of the production capacity of stations where the capacity is depending on the number of wood pieces and which are subsequent to a station where the production capacity is depending on the length of the wood pieces. This achieved by on a regular basis adapting the speed of the preceding working station to the length of the wood pieces, so that the number of wood pieces which is delivered from the station per time unit is sought to be adapted to the speed of the subsequent wood working machine. Preferably, the number of wood pieces delivered from the station per time unit is kept relatively constant.

[0011] By relatively constant number of wood pieces is meant a rate which lies within a narrower range than what is the case if the speed of the preceding working station is substantially constant measured in length of wood per time unit.

[0012] This way the rate of wood pieces can be set close to the capacity of the subsequent station measured in wood pieces per time unit,

[0013] The adaptation of the speed of the preceding station relative to the length of the wood pieces takes preferably place based on measurements of the length of wood pieces before they enter the preceding working station.

[0014] The measurements of the length may be done in various ways, for example:

• Photocells, mechanical transducers, laser, video or other types of measuring equipment measuring the length of each wood piece or in intervals of, e.g., 30 cm.
• Calculation of the area of a plurality of wood pieces lying on a collection table upstream of the preceding working station,
• Running measurements of length done as the wood pieces are led lengthwise through a measuring station upstream of the working station.

By wood working in the foregoing and the subsequent is meant all types of machines that a wood piece is run through, no matter if an actual removal of wood mass is performed or not, Consequently, also a mere sorting table and a packing machine is included in this term.

[0015] The invention will now be explained in more detail referring to an embodiment shown in the accompanying drawings, in which:

Figure 1 shows a production plant for panels or floor boards,

Figure 2 shows a section of the production plant of figure 1,

Figure 3 shows a cross-section through the collection table of figure 2, and

Figure 4 shows the collection table with the measuring equipment.

[0016] Figure 1 shows a production plant with all stations necessary for production of panels or floor boards from sawn planks to finished and packed materials. The majority of the stations shown are constructed according to well known technology and works in a conventional way. Therefore, these stations will be explained very briefly.

[0017] Sawn planks enter as a timber package 1. The planks are separated in a plank separator 2 and are fed individually through a single piece feeder 3 to a jigsaw 4, which splits the plank longitudinally into two or three boards. The split planks/boards are then transferred to an intermediate storage 5 and from there to a further single piece feeder 6. Further from this the boards are put with their ends flush with each other by an end leveller 7. Thereafter, the boards are collected on a collecting table 8. From this tey are fed singularly through a planing machine 9, After the planing machine 9 the boards are delivered to a small buffer 10. From this the boards are picked up and put on a cross-cutting and sorting table 11. The cross-cutting and sorting table 11 has a slot for each board. The slot is defined between two rows of carriers (not shown), which extend transverse to the cross-cutting and sorting table 11. Such a cross-cutting and sorting table is described in Norwegian Patent No. 177046. In the cross-cutting and sorting table the boards are cross-cut at both their ends and at the same time a quality control is performed.

[0018] Downstream of the cross-cutting and sorting table the panel or floor boards are bundled in a sorting and bundling machine 12, Thereafter the bundles are wrapped in a foiling machine 13, labelled and fed to packaging in a packaging machine 14 before the packages are conveyed out of the production plant for further transport,

[0019] As far as the description above, this is well known technology,

[0020] During the travel through the production plant the planks and the boards will change their direction of travel from transverse travel to longitudinal travel and back to transverse travel many times. In the example shown, this takes place at three stations: at the jigsaw 4, at the planing machine 9 and at the foiling machine 13. The most critical of these machines is the planing machine 9. This is because of the fact that after the jigsaw there is a reasonably large buffer represented by the intermediate storage 5 and the fact that after the foiling machine there are no other critical working machines. However, the cross-cutting and sorting table is a critical station that easily becomes a bottle neck in the process.

[0021] Figure 2 shows in greater detail the process equipment upstream of the planing machine. Here is shown the intermediate storage 5, in which a substantial amount of boards can be collected, usually partly on top of each other. The single piece feeder 6 picks boards one by one from the intermediate storage 5. By an end leveller 7 the board is displaced longitudinally so that one of the ends (in the case shown, the end 17 facing left in the figure) lies against a stop 18. Thereby all the boards will lie with one of their ends flush with each other, Through a transverse conveyor 19 the boards are then conveyed to the collecting table 8. Here the boards will lie side by side against each other. A planing feeder 20 provides for feeding of the boards one by one longitudinally into the planing machine 9. This takes place so that when the trailing end 21 of the board 16 has passed the leading end 17 of the next board, this board will be displaced transversely until it is in line with the preceding board. Then the planing feeder will grip this subsequent board and push it in after the preceding board. This way all the boards 16 will be pushed into the planing machine 9 end-to-end.

[0022] The measurement of the length of the boards 16 before they are pushed into the planing machine 9 can take place in many ways. In figures 3 and 4 is shown an example where a simple system with a measuring boom 22 arranged above the collecting table 8 is used. The measuring boom 22 is equipped with a photo cell 23 which registers if the table 16 below the photo cell is above or below a certain length. Consequently, the boards are categorized into two classes of length only: short and long. When a long board 16a passes, this will be registered and the position of this will be supervised. When the turn comes to this board 16a to be fed into the planing machine, a control unit coupled to the measuring boom will give a signal to the speed regulator of the planing machine 9 and possibly also to the speed regulator of the planing feeder 20 and the through-put speed/tool speed of the planing machine will increase. Consequently, the time that the board 16a uses to travel through the planing machine 9 will be reduced compared to what would have happened if the planing machine 9 did not receive any message indicating that the board 16a was of the long type. Instead of logging the position of the board at any time, several photo cells may also be arranged along the boom 22 so that the length of all the boards 16 on the collecting table 8 is registered at any time.

[0023] To avoid a very frequent adjustment up and down of the feeding speed of the planing machine, which could happen if by accident every other board is long and short, it is convenient to demand that at least three subsequent long boards must be present before the speed is increased, or, e.g., that three of the five next boards must be long for the speed to be increased, and that the speed is kept at this level until all of the boards have passed. This results in a smoother running of the planing machine 9 and thereby reduced wear.

[0024] Instead of only two categories of length and two corresponding speeds, the boards may also be classified into several lengths and the speed of the planing machine 9 adjusted in several steps. The finer the subdivision is, the more even the rate will be, at which the boards 16 will exit the planing machine 9.

[0025] An even exiting rate from the planing machine 9 makes the cross-cutting and sorting table capable to receive the planed boards at the same speed each slot has in the transverse direction, and more slots can therefore be filled.

[0026] It is also possible to perform a calculation of average length of the boards that lies on the collecting table. This may, e.g., be done by measuring the area which is covered by boards. Since the width of the boards is known, a figure for of the average length will also be achieved. The planing machine 9 can then be run at a speed adapted to this average length until all these boards have been run through.

[0027] A precise measurement of the length and an accurate adaptation of the planing speed to this is also possible. However, this will result in very frequent changes in the speed of the planer and it is thereby more subject to wear.

[0028] It is also possible to provide for a feedback from the cross-cutting and sorting table, so that the speed of the planer can be adapted to the actual speed of the cross-cutting and sorting table, Thus, it is possible to set the cross-cutting and sorting table to a certain number of (wood) pieces per minute, The feeding into the planing machine can then follow this by adapting the planing speed to the number of pieces per minute. If the speed of the sorting table is reduced, this will (automatically) limit the planing speed. As a consequence, the number of pieces per minute at the sorting table is set and the rest will adapt to this according to the length of the pieces.

[0029] In practice the lowest capacity in the plant will be the sorting station and the foiling machine downstream of the cross-cutting and sorting table. The cross-cutting and sorting table consequently, although it may run at a higher speed, adapt to these subsequent stations.

[0030] Tests have been performed with a simple method of measurement upstream of a planing machine and adaptation of the speed to the length of the wood pieces, In this test the machines had the following capacities:

The planing machine could operate at a feeding speed between 40 and 200 m/min.

The cross-cutting and sorting table had, due to subsequent station, the possibility to run at a capacity of max. 32 wood pieces per minute.

In a test run over time it was found that the speed of production of the planing machine could be increased by 15% in the cases where a lot of long wood pieces occurred in a row. In total this constituted about 4% of the total production.

[0031] An increase of 4% is very substantial in a large production facility as shown in figure 1 and will constitute more than 500 boards per day. By optimizing the invention further, the increase in production is expected to be larger.

Claims

1. System for improving the utilization of the capacity of a wood working line, the wood working line comprises a preceding wood working machine though which wood pieces are fed longitudinally into and a subsequent wood working machine, through which the wood pieces are fed transverse, wherein the speed of the preceding working station on a regular basis is adapted to the length of the wood pieces, so that the number of wood pieces which is delivered from the station per time unit is sought to be adapted to the speed of the subsequent wood working machine.

2. System according to claim 1, wherein the number of wood pieces exiting the station per time unit is kept relatively constant.

3. System according to claim 2, wherein the length of the wood pieces is determined before they are run through the preceding working station.

4. System according to claim 3, wherein the length is determined by an interval measurement, which places the wood piece within certain length measurements.

5. System according to claim 4, wherein the length measurements is a determination of the fact if the wood piece is above or below a certain length.

6. System according to claim 3, wherein the length is determined by a measurement of the area of a plurality of wood pieces lying on a table upstream of the preceding working station.

7. System according to one of the preceding claims, wherein a minimum number of wood pieces among those which are to be fed through the preceding wood working machine must be above a certain length before the speed of the preceding wood working machine is increased.

8. System according to one of the preceding claims, wherein the preceding wood working machine is a planing machine.

9. System according to one od the preceding claims, wherein the subsequent wood working machine is a cross-cutting and sorting table.

10. System according to one of the preceding claims, wherein the wood working machines are included in a production line of several wood working and handling stations.

Drawing