Abstract:
The present invention concerns a method for the indication of the sharpness of the teeth at a harvesting head at a forestry machine, an arrangement for the execution of the method, and a forestry machine for the use of the arrangement during execution of the method.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is a U.S. National Stage patent application of PCT/SE2013/051611 filed on Dec. 20, 2013, the entire contents of which are incorporated herein by reference. 
     
    
     TECHNICAL AREA 
       [0002]    The present invention concerns a tree-felling working head at a forestry machine, to be more precise, an arrangement and a method for indicating when the teeth of the working head are too blunt and therefore need to be sharpened or exchanged. 
       BACKGROUND 
       [0003]    In large forestry plantations in, for example, South America and Australia, forestry stands grow in which the trees demonstrate a relatively uniform size and with equivalent properties such as density and moisture content. The trees grow rapidly and are planted in rows such that they grow with equal spaces at a separation from each other and on relatively level ground. These conditions make efficient forestry possible in which one or several forestry machines can work along the outer edge of the stand and process the trees at a rapid pace. 
         [0004]    The processing often takes place with the aid of accumulating working heads arranged at an arm of a tool carrier in the form of a forestry machine, excavator or similar that is driven by wheels or tracks. The head is attached to the arm by a tool fixture of known type in a manner that allows it to be removed. The term “accumulating working head” is here used to denote a timber working head that is manoeuvred by the arm of the tool carrier to a first tree, the tree is clamped against it by one or several holder arms, and cut by a rotating toothed blade or disc. The working head is subsequently moved to the next tree, which also is clamped against the working head and cut. This continues until the working head is full. When the working head is full, the arm is pivoted away from the working area and deposits the collected bundle of cut trees, after which the procedure is repeated. 
         [0005]    The blade or disc of the working head comprises a flywheel with a large mass and with teeth arranged along the periphery of the disc. The disc is accelerated by a motor up to a pre-determined speed before the cutting, after which the cutting is started. It is indicated that the correct speed has been reached by a gauge of the rate of revolution or by a pressure gauge arranged in connection with the disc or the motor. This gauge of the rate of revolution is used also to indicate when the speed of rotation is too low for it to be possible to carry out efficient cutting. As a consequence of the uniform properties and sizes of the trees, it is possible to cut a tree in a very short time, approximately one second or less. When a number of trees have been cut, a waiting period occurs in order for the disc to be able to reach again the correct speed. 
         [0006]    The disadvantage of the prior art technology is that when the teeth of the disc loose their sharpness and become blunt after a number of cuttings, the consumption of time for each cutting becomes longer. This means that the working head cannot be filled with trees before the disc must be accelerated up to the correct speed again, whereby the efficiency becomes lower. 
         [0007]    Monitoring of the sharpness of the teeth is currently carried out by the driver, who sits in the forestry machine. Not only does production of heat take place when the teeth are blunt and must wear their way through the trunk, but also the driver discovers that the speed of the disc becomes too low before the working head is filled. 
       SUMMARY OF THE INVENTION 
       [0008]    The disadvantages described above are solved through an arrangement and a method for the indication of when the teeth of the disc are too blunt and must be exchanged or sharpened, without it being necessary for the driver to observe the consumption of time during cutting and the degree of filling of the accumulating working head. 
     
    
     
       DESCRIPTION OF DRAWINGS 
         [0009]      FIG. 1  shows schematically a forestry machine with an accumulating working head, 
           [0010]      FIG. 2  shows a block diagram of signal pathways, and 
           [0011]      FIG. 3  shows a diagram of an accumulation sequence with sharp and blunt teeth, and it shows when indication takes place and the teeth need to be exchanged or sharpened. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0012]      FIG. 1  shows a forestry machine  1  in the form of a tracked tool carrier. It comprises a chassis  2  with tracks  3  on each side. A driver&#39;s cabin  4  is located such that it can be rotated on a slewing ring  5  and can be rotated through 360 degrees. A folding arm  6  is mounted jointed at the chassis  2  and it comprises in known manner a boom  7  and a stick  8 , which are mounted jointed relative to each other. A hydraulic system with hydraulic cylinders, lines, valves and pumps drives in known manner the driving of the tracks  3 , regulation of the driver&#39;s cabin  4  and manoeuvring of the arm  6 . At the farthest end of the arm  6  a tree harvesting head  9  is attached at a tool fixture  10 , advantageously in a manner that allows it to be removed. The tree harvesting head may in another embodiment be directly attached to the arm. 
         [0013]    The tree harvesting head  9  comprises an extended frame  11  with at least one holder arm  12  and one grip arm  13 . An accumulation compartment  14  that extends in the longitudinal direction of the frame has been made in the frame for the accumulation of cut trees. The term “holder arm”  12  is here used to denote an arm that can be regulated in a manner that can hold a sawn tree  15  fixed against the frame  11 . The term “grip arm”  13  is here used to denote a similar arm, although this arm is jointed. When the arm  13  grips a tree  15 , it is clamped against the frame  11 , after which the tree  15  is cut. The subsequent tree is clamped against the grip arm  13 , and the grip arm is able, due to the fact that it is jointed, to slide out between the two trees such that both of the trees are held fixed by the holder arm  12 . A certain number of trees can be gripped and held fixed in the manner that is described above, until the accumulation compartment  14  is full. The filling of an accumulation compartment  14  with cut trees will be denoted below by the term “accumulation sequence A”. 
         [0014]    The end of the frame  11  that faces the ground is arranged with a cutting arrangement  16 . The cutting arrangement comprises a rotating disc  17  or a flywheel with a large mass. The disc  17  is provided with fixed or removable teeth  18  along the periphery  19  of the disc  17 . The large mass of the disc  17  ensures that the speed of rotation of the disc is influenced to a lesser degree than if, for example, a saw blade had been used. 
         [0015]    The disc  17  is driven by a motor  20 , and it is an advantage if this is carried out by direct driving through a hydraulic motor. It is an advantage if the motor  20  is driven by the hydraulic system of the forestry machine  1 . The motor  20  is arranged inside the frame  11  of the working head  9  and is in this way protected from external influence by tree trunks that are held against the frame  11 . The motor  20  is provided with a speed sensor  21  for the direct measurement and registration of the speed of rotation of the motor. The speed sensor  21  may in another embodiment be located in connection with the periphery  19  of the disc  17  for the measurement of the speed of rotation. The speed sensor  21  is so arranged that it measures and registers the speed of rotation of the disc  17 . Since the mass of the disc  17  is so great, the inertia of the disc can be used during the cutting of trees. Before each accumulation sequence A, the speed of rotation of the disc is increased to a pre-determined value  22 . Such an increase in the speed will be denoted below by the term “recovery phase B”. 
         [0016]    At each cutting, the disc  17  is exposed to a resistance that leads to a reduction in the speed of rotation of the disc. Even though the motor  20  and the hydraulic system strive to maintain the speed of rotation of the disc  17  at a pre-determined value  22  by imparting a small increase in speed after each cutting, this increase is less than the reduction in the speed of rotation that the disc  17  experiences during each cutting. 
         [0017]    The resistance is equal at each tree, due to the uniform properties of the stand of trees. This allows statistical results of the number of cuttings to be used in order to discover when the resistance at each tree has become too large. A diagram of an accumulation sequence A is shown in  FIG. 3 , where the cutting is initiated when the disc  17  has achieved a pre-determined speed  22 , which has been measured and registered. Each tree that is cut leads to blunter teeth and gives a reduction in the speed of rotation. This reduction in the speed of rotation becomes greater as the teeth become blunter, and it is measured and registered, as is illustrated in  FIG. 3  with the reference numbers  23   a,    23   b  and  23   c,  where  23   a  is the reduction in the speed of rotation when the teeth are sharp,  23   b  is the reduction in the speed of rotation when the teeth are blunt, and  23   c  is the reduction in the speed of rotation that leads to insufficient time being available in which to fill the accumulation compartment  14 . When a number of cuttings, which in this embodiment is six cuttings, has been carried out, the reductions  23   a - 23   c  in the speed of rotation of the disc have been added and registered in order finally to become so large that a lowest permissible speed of rotation  24  has been registered, whereby a recovery phase B is initiated during a period of time that is denoted in  FIG. 3  with the reference numbers  25   a - 25   c.  The speed of rotation  22  that the disc has before an accumulation sequence A is initiated must be sufficient to carry out the number of cuttings that is required to fill the accumulation compartment  14 , i.e. the speed of the disc must be higher than the lowest permissible speed of rotation  24  when all reductions in the speed of rotation have been subtracted from the original speed  22 . If the recovery phase B must be initiated before the accumulation compartment has been filled, in this embodiment after four cuttings as is shown in  FIG. 3  with the reference symbol P, this means that the reduction in speed of rotation  23   c  is too high, and this in turn indicates that the teeth  18  of the disc  17  are too blunt, whereby a signal  27  is transmitted to the driver. This is illustrated in  FIG. 3  with the reference number  25   c.  The recovery phase B can be described as the working head  9  being held at a distance greater than the cutting distance from the tree  15  after the final tree in an accumulation sequence has been cut, while the motor  20  is allowed to work in order to increase the speed of rotation to the pre-determined speed  22 , and it is an advantage if this takes place during the period  25   a - 25   c  during which the working head  9  is being emptied. The speed of rotation  22  is determined by the diameter of the disc in such a manner that a disc with a lower diameter can be given a higher pre-determined speed of rotation and a disc with a larger diameter can be given a lower pre-determined speed of rotation. 
         [0018]    If the working head  9  can be filled without the need for a recovery phase B arising, it may however be the case that the recovery phase will be too long, i.e. that the time  25   b  from the final cutting having been carried out until the working head has again been returned to a tree and the speed of rotation  22  has been registered. This means that the speed of rotation has been reduced by too great an amount and that the teeth have reached their maximal capacity and are on the verge of needing sharpening or being exchanged, whereby a signal  27  is transmitted to the driver. 
         [0019]    When the resistance at each tree becomes too great, for example at the point P in  FIG. 3 , and the accumulation compartment  14  of the working head  9  cannot be filled between two recovery phases B, this indicates that the teeth  18  of the disc  17  are blunt. This means that the driver must allow a recovery phase B to take place, without having filled the accumulation compartment  14 . This leads to a large loss of time and an inefficient working procedure. In order to avoid this, statistics are retrieved for each tree  15  that is cut during the initial work cycle C. The term “work cycle” is here used to denote the time from the first cutting until the last of a pre-determined number of bundles has been placed on the ground, i.e. a number of accumulation sequences A carried out as shown in  FIG. 3 . The values that are registered and collected are the speed of rotation after each cut tree, the consumption of time and the resistance in the form of an increase in pressure in the hydraulic system, which leads to a reduction  23  in the speed of rotation. These collected values are stored in a memory of a calculation computer  26  to which the speed sensor  21  is connected. Also data concerning the properties of the working head  9  are stored in the memory, for example the number of trees that can be accommodated in the accumulation compartment  14 , the sizes and the capacities of the motor  20  and the hydraulic pump, when the teeth  18  of the disc  17  were sharpened or exchanged, and data concerning the relevant forestry stand that is being processed such as the estimated mean diameter and density. 
         [0020]    Signals  27  that indicate that the teeth are blunt or need to be exchanged are sent through the calculation computer  26  to a display  28  inside the driver&#39;s cabin, which makes it possible for the driver to plan maintenance, such as sharpening or the exchange and teeth. 
         [0021]    The present invention is not limited to what has been described above and shown in the drawings: it can be changed and modified in several different ways within the scope of the innovative concept defined by the attached patent claims.