WO2024003451A1

WO2024003451A1 - Method and control system for controlling a boom of a harvester

Info

Publication number: WO2024003451A1
Application number: PCT/FI2023/050390
Authority: WO
Inventors: Aleksi KIVI
Original assignee: Ponsse Oyj
Priority date: 2022-07-01
Filing date: 2023-06-27
Publication date: 2024-01-04
Also published as: FI20225617A1

Abstract

A method and a control system for controlling a boom (9) of a harvester (1) by tip control. In the solution, at least one first target position (23) and at least one second target position (24) is determined for a harvester head (17) of the harvester (1), at least one control command is produced for performing a first and a second work stage alternately following each other of the harvester head (17) such that the first work stage of the harvester head (17) is performed in at least one first target position (23) and the second work stage of the harvester head (17) is performed in at least one second target position (24), and the position of at least one boom part of the boom (11) is changed automatically or semi-automatically for changing the location of the harvester head (17) alternately between at least one first target position (23) and at least one second (24) target position.

Description

Method and control system for controlling a boom of a harvester

Background of the invention

The invention relates to a method and a control system for controlling a boom of a harvester by utilizing the so-called tip control.

When processing trees by a harvester head being at the end of the boom of the harvester, particularly when delimbing and/or debarking a tree and when cutting its trunk into parts, i.e. logs, or in other words blocks, in accordance with one or more determined dimensions, a problem can be that branches end up in a pile to be collected of the logs. The branches or pieces of bark having ended up in the log pile must be removed either by the driver of the harvester with the harvester head or later by the driver of a separate forwarder used for collecting the logs or, at the latest, by the driver of the timber truck with a grabber of the forwarder or the timber truck. Picking up branches and pieces of bark from among the logs with a harvester head or a grabber intended for handling tree trunks is both slow and challenging but, above all, it is an unnecessary and nonproductive work stage which decreases work efficiency and causes unnecessary strain for the driver taking care of removing the branches or pieces of bark.

Usually, the branches and pieces of bark are prevented from ending up in the same pile with logs by transferring the harvester head clearly to the front side of the log pile in the tree feeding stage i.e. for the duration of the delimbing and/or debarking stage, whereby also the branches and/or pieces of bark will pile up on the front side of said log pile. After the feeding has stopped, the harvester head is transferred onto the log pile for the tree cutting, whereby a log cut from the tree falls into said pile. This to-and-fro transfer of the harvester head between the delimbing and/or debarking stage and the cutting stage of the tree also stresses the driver, even though not as much as the removing of branches and pieces of bark having ended up in the log pile after the processing of the tree.

Brief description of the invention

It is the object of the invention to provide a new type of a method and control system for controlling a boom of a harvester.

The solution according to the invention is characterised by what is disclosed in the independent claims.

In the solution according to the invention, at least one first target position and at least one second target position are determined for a harvester head of a harvester, at least one control command is produced for performing a first and a second work stage of the harvester head following each other alternately such that the first work stage of the harvester head is performed in at least one first target position and the second work stage of the harvester head is performed in at least one second target position, and the attitude of at least one boom part of a boom is changed automatically or semi-automatically for changing the location of the harvester head alternately between at least one first target position and at least one second target position.

An advantage of the arrangement according to the invention is that rou- tine-like work stages of the harvester head of the harvester that follow each other alternately in different locations can be transferred from the control of the operator of the harvester into measures that are performed automatically or semi-auto- matically. This increases the quality and efficiency of timber harvesting and, at the same time, decreases the mental and physical stress experienced by the operator of the harvester.

Some embodiments of the invention are presented in the dependent claims.

Brief description of the drawings

The invention will now be described in more detail in connection with preferred embodiments and with reference to the accompanying drawings, in which:

Figure 1 is a schematic view of a harvester,

Figure 2 is a schematic top view of a harvester in a work environment, Figure 3 is a schematic flow chart of a method for controlling the operation of a harvester, and

Figure 4 is a schematic view of a control method of a harvester for controlling the operation of the harvester.

For reasons of clarity, some embodiments of the invention are illustrated in the figures in a simplified form. In the figures, like reference numerals identify like elements.

Detailed description of the invention

Figure 1 is a schematic view of a harvester 1 which constitutes a mobile forest work machine in which the above-described solution can be applied. The mobile forest work machine, in which the above-described solution can also be applied, can also be a combination of a forwarding machine suitable for transporting loads, such as e.g. a forwarder, and a harvester. The harvester 1 shown in Figure 1 is a articulated steer forest work machine, but the above-described solution can also be applied in other ways, such as e.g. via steerable wheels controllable mobile harvesters. Next, as for characteristics or embodiments examined in this description, reference is particularly made to the harvester 1 of Figure 1, but the examined characteristics or embodiments are equivalently applicable in other forest work machines implementing the operations of a harvester.

The harvester 1 of Figure 1 comprises a chassis 2, which comprises a first frame part 3 and a second frame part 4, which are connected to each other via a link 5 such that the first frame part 3 and the second frame part 4 can rotate in relation to each other via the link 5, whereby the harvester 1 is a so-called articulated steer forest work machine. Into connection with the chassis 2 are arranged moving means 6, by means of which, the harvester 1 can move in relation to its work surface. Said moving means 6 are wheels in Figure 1, but generally said moving means can comprise at least one of the following: wheels arranged on an axle, wheels arranged on a bogie, a track system or some other means known as such to provide the movement of the harvester 1 and to possibly change the direction of the movement of the harvester in relation to its work surface or work environment.

If the harvester were a combination of e.g. a forwarder and a harvester, a load space would also be arranged to the harvester for taking a load to be transported by the harvester. In this case, said load space would be typically intended for transporting parts of a tree trunk typically cut to size, which are typically called logs or blocks but, in alternatives uses the load to be transported can also comprise harvesting or thinning waste produced in connection with timber harvesting or forest thinning. Because the harvester 1 of Figure 1 does not include said load space, the harvester 1 of Figure 1 is thus solely intended for implementing the felling, delimbing and/or debarking of the tree and its cutting into logs of desired length.

The harvester 1 of Figure 1 further comprises a power source 7 which is arranged to be supported by the second frame part 4. The power source 7 can comprise e.g. a combustion engine, one or more electric motors and sets of batteries, a generator or different combinations of these for generating the required power for providing the movement of the harvester 1 and for operating the devices arranged in the harvester 1.

The harvester 1 of Figure 1 further comprises a cab 8 which is arranged to be supported by the first frame part 3. The cab 8 comprises required control means 18, by means of which, the operator of the harvester 1 can control the drive of the harvester 1 and the devices arranged to it for performing control commands to be given via the control means 18. Said control means 18 are shown very schematically in Figure 1 and they can comprise one or more manually controllable control means, such as e.g. a control lever, and/or one or more foot-controllable control means, such as e.g. a pedal. Said control means 18 can also comprise a predesigned harvester work plan in the form of a runnable programme which is runnable by e.g. one or more harvester control units 19 very schematically shown in Figure 1 for controlling the drive of the harvester 1 and the devices arranged in it. Said control unit 19 can be e.g. a computer or some other device or means comprising a microprocessor or some other microcontroller that is obvious to those skilled in the art.

The harvester 1 of Figure 1 is a harvester operating based on the active control of the operator of the harvester 1. However, it is also possible to apply the presented solution in both semi-autonomously operating harvesters, whereby the harvester can operate at least part of the time without the active control of the operator, and in substantially totally autonomously operating harvester, whereby the operator does not actively contribute to the control of the harvester operations without a special reason. Said special reason could be e.g. such an exceptional operating situation of the harvester which the control unit 19 controlling the operations of the harvester cannot perform autonomously. In connection with said both semi-autonomously operating harvesters and totally autonomously operating harvesters, the control means used for controlling the harvester can be located separate from the harvester, whereby the harvester does not necessarily comprise an actual cab and the control of the harvester is implemented by remote control or automatically.

The harvester 1 of Figure 1 further comprises a boom 9. The boom 9 can be supported e.g. on the chassis 2 or a separate tilting base or some other part of the machine frame. The cab 8 and/or boom 9 can be arranged foldably and/or rotatably in relation to the chassis 2. The outmost end of the boom 9 includes a harvester head 17 of the harvester 1, whereby said outmost end of the boom 9 and the harvester head 17 arranged to it constitute a tip of the boom 9.

In the harvester 1 of Figure 1, the boom 9 is constituted such that a base 10 with a turntable or a reversal link 11 is attached to the harvester 1. The turntable or the reversal link 11 further includes a lower ring and an upper ring which is provided with a toothing and it is rotated by a motor which rotates a toothed gear against the toothing. The boom 9 further comprises a column 12 of the boom 9. The column 12 of the boom 9 in turn has a lifting boom 13 pivoted to it. The lifting boom 13 is moved by a lifting cylinder 14.

Furthermore, a luffing boom 15 is pivoted to the lifting boom 13. The luffing boom 15 is moved by a folding cylinder 16. The outmost end of the luffing boom 15 includes the above-mentioned harvester head 17 of the harvester 1. The luffing boom 15 can also include a telescopic extension movable by its own actuator, whereby said harvester head 17 of the harvester 1 is arranged to the outer end of said telescopic extension.

The boom 9 can also be described as having, as its successive boom parts, a ring base to be rigidly connected to the harvester, a foot section of the boom rotatably bearing-mounted to the ring base, a first boom pivoted to the foot section, a second boom pivoted to the first boom, and a possible telescopic arrangement in the second boom. Additionally, the boom 9 and the harvester head 17 arranged at its end comprise actuators, which are obvious to those skilled in the art, for using each successive boom part, i.e. for either rotating by means of said pivoting or for shortening or lengthening by means of the possible telescopic arrangement, or for using or rotating the harvester head and, further obvious to those skilled in the art, a sensor arrangement comprising one or more sensors for determining the attitude and/or state of motion of the boom parts of the boom 9 and for determining the attitude and/or state of motion of the harvester head 17, wherein the state of motion of the boom part or the tool describes the speed, acceleration and/or angular velocity of the movement of the boom part or tool in question. The attitude and/or state of motion of the boom parts and/or the harvester head can be determined independently or in relation to a part of the boom 11 or the forest work machine frame. Said actuators can in turn be e.g. above-mentioned cylinders or other cylinders or various motors, and said sensors can be e.g. various position sensors, motion speed sensors, sensors measuring acceleration or angular velocity, pressure sensors, sensors sensing the direction of a magnetic field, or radars based on e.g. radio waves or optics, or cameras.

The presented solution further applies tip control of the boom 9 for providing a desired placement and possibly also desired attitude of the tip of the boom 9, i.e. the outer end of the boom 9 and the harvester head 17 in it, for performing a work stage. In the tip control, a control command is given to the tip of the boom 9 by the control device of the harvester, in other words, a request to move to a particular direction at a particular speed. Said control commands are converted by means of one or more control units 19 included in the control system of the harvester to at least one control measure of at least one actuator affecting the attitude of the boom 9 and/or at least one control measure of at least one actuator affecting the attitude of the harvester head 17. For each said actuator of the boom 9 or the harvester head 17 is calculated by said one or more control units 19 the required motion speed such that the combined effect of the various actuators affecting the attitude of the boom 9 or the harvester head 17 provides the desired movement of the tip of the boom 9 and, as its result, further the end position and, if required, the desired direction of the tip of the boom 9. That is, by controlling the boom parts of the boom 9 and/or the harvester head 17 into a desired attitude, the desired position and direction of the tip of the boom 9 is provided.

In the tip control, the control command directed at the tip of the boom 9 by the control means for moving the tip of the boom 9 is implemented by dividing said control command to the movement of the individual boom parts of the boom 9 and/or the movement of the harvester head 17 for moving the tip of the boom 9 in accordance with the control command using the attitudes of the boom parts and/or the attitudes and states of motion of the harvester head measured by the sensors within degrees of freedom allowed by the boom parts and the harvester head and their actuators. The desired movement of the tip of the boom 9 is divided into parts for different boom parts and/or the harvester head by making use of e.g. the so-called Jacobian matrix. For implementing the tip control, guidance can be found e.g. in the following literature references: Bjorn Lofgren: Kinematic Control of Redundant Knuckle Booms, Licentiate thesis, Department of Machine Design, Royal Institute of Technology, Stockholm, 2004; Bjorn Lofgren: Kinematic Control of Redundant Knuckle Booms with Automatic Path-Following Functions, Doctoral thesis, Department of Machine Design, Royal Institute of Technology, Stockholm, 2009; Mikkel M. Pedersen, Michael R. Hansen, Morten Ballebye: Developing a Tool Point Control Scheme for a Hydraulic Crane Using Interactive Real-time Dynamic Simulation: Modelling, Identification and Control, Vol. 31, No. 4, 2010, pp. 133-143, ISSN 1890-1328.

Figure 2 is a schematic top view of a harvester 1 in a work environment 21. The work environment 21 includes at least one area 22 to be worked by the harvester 1, the purpose being to fell trees from the area 22. Said workable area 22 is shown in Figure 2 very schematically outlined with a dashed line. For performing work stages occurring after the felling of the tree, i.e. for delimbing branches of the tree and/or debarking the tree trunk and for cutting the tree trunk into logs, a first target position 23 and a second target position 24 of the harvester head 17 of the harvester 1 are further determined in the work environment 21. Said first target position 23 and second target position 24 are also shown in Figure 2 schematically outlined with a dashed line.

The first target position 23 of the harvester head 17 of the harvester 1 refers to an area where the purpose is to delimb the felled tree and/or debark the felled tree and the second target position 24 of the harvester head 17 of the harvester 1 refers to an area where the logs cut from the tree trunk or, alternately, the whole delimbed trunk is intended to be located. In this case, the branches delimbed and/or bark debarked from the tree are intended to remain in the area of said first target position 23 without essentially ending up in the area of the second target position 24, whereby there will be almost no harvesting waste formed by branches and/or bark in the pile where the cut logs or whole delimbed tree trunks are collected.

Different from Figure 2, there can be more than one of the first target positions 23, e.g. two of them, whereby mainly tree branches are collected into one of the first target positions 23, i.e. delimbing the tree is performed substantially in the area of the work environment 21 related to the target position in question, and whereby mainly tree bark debarked is collected into some other first target position 23, i.e. debarking the tree is substantially performed in the area of the work environment 21 related to the target position in question. Then, during the delimbing and debarking of the tree, the harvester head 17 of the harvester 1 is configured to transfer between said first target positions 23 as required.

Furthermore, different from Figure 2, there can be more than one of said second target positions 24, e.g. two of them, whereby e.g. parts of the felled tree suitable for logs are collected into one second target position 24 and e.g. parts of the felled tree suitable for pulp are collected into some other second target position 24. Then after a specific cut-to-size section of the felled tree trunk has been delimbed and/or debarked in the area of the corresponding target position 23, the harvester head 17 of the harvester 1 and the trunk of the felled tree still attached to it are transferred into the area of some other second target position 24 for cutting the section in question of the delimbed and/or debarked tree trunk into a pile being in the second target position 24 in question. When said section of the tree trunk has been cut in the second target position 24, the harvester head 17 of the harvester 1 and the felled tree trunk still attached to it are transferred back to one first target position 23 for delimbing and/or debarking the next section of the felled tree trunk. These work stages are implemented alternately to each other until the trunk of the felled tree has been totally processed in the desired way.

The locations of the target positions 23, 24 in the work environment 21 and data on the material comprised by the target positions 23, 24 can also be stored in a system being available to a forwarder or some other forwarding machine to be the basis of the design of the work of the forwarding machine.

Figure 3 schematically shows a flow chart of a method for controlling a boom 9 of a harvester 1, and Figure 4 schematically shows a control system of a harvester 1 for controlling a boom 9 of the harvester 1. The boom 9 is controlled by tip control for controlling an outer end of the boom 9 and the harvester head 17 in it, i.e. the tip of the boom 9, in a work environment 21 of the harvester 1 shown schematically in Figure 2 between at least one first target position 23 and one second target position 24.

In the method of Figure 3, in block 31, at least one first target position 23 and at least one second target position 24 for the harvester head 9 of the harvester 1 are determined. Said at least one first target position 23 can be determined e.g. by controlling the tip of the boom 9 in accordance with a control command CC produced by control means 18 into said first target position 23, whereby said control command CC is converted by a control unit 19 into at least one control measure CA-9/17 affecting the attitude of boom parts of the boom 9 and possibly the attitude of the harvester head 17 for controlling the tip of the boom 9 into said first target position 23. When the tip of the boom 9 has reached said first target position 23, the control means 18 can produce a control command CC, which sets the attitudes of the boom parts of the boom 9 corresponding the first target position 23 and possibly also the attitude of the harvester head 17 into the memory of the control unit 19, whereby said specific attitudes of the boom parts of the boom 9 and possibly the attitude of the harvester head 17 set into the memory of the control unit 18, whereby the attitude of the boom parts of the boom 9 and possibly the attitude of the harvester head 17 indicate the location of the first target position 23 of the harvester head 17 in the work environment 21 in relation to the harvester 1. It is also possible to allow a predetermined range of variation for said attitudes of the boom parts of the boom 9 and said attitude of the harvester head 17, said ranges of variation describing e.g. the areal dimension of the target position 23 in the work environment i.e. determining the areal limits of the target position 23 in the work environment 21. Said at least one second target position 24 can be determined correspondingly. Alternatively, the location of said target positions 23, 24 in the work environment 21 can be determined by controlling the tip of the boom 9 to the intended location of the target position 23, 24 in the work environment 21 and by performing the work stage of the harvester head 17 related to the target position 23, 24 in question in the location in question.

The attitudes of the boom parts of the boom 11 and the attitude of the harvester head 17 can be determined in the control unit 19 based on measurement information Ml received from the actuators and/or sensors of the boom 11. Designation CA-9/17 used in connection with the control measure refers to the fact that said control measure can, depending on the situation, affect either solely the actuators affecting the attitude of the boom parts of the boom 9, solely the actuators affecting the attitude of the tool 17, or them both.

In block 32, the control means 18 produce at least one control command CC for performing a first and a second work stage of the harvester head 17 following alternately each other such that the first work stage of the harvester head 1 is performed in at least one first target position 23 and the second work stage of the harvester head 17 is performed in at least one second target position 24 whereby, with reference to the above described, the delimbing and/or debarking of the felled tree trunk, i.e. the first work stage, is performed in said at least one first target position 23 and the cutting of a section of the delimbed and/or debarked tree trunk, i.e. the second work stage, is performed in at least one second target position 24. The control command CC produced in block 32 can be produced as a response to the felling of a standing tree.

In block 33, the attitude of at least one boom part of the boom 9 is changed automatically or semi-automatically for changing the location of the harvester head 17 alternately between at least one first target position 23 and at least one second target position 24 of the harvester head 17. The control command CC produced in block 32 is converted in block 33 by means of the control unit 19 into at least one control measure CA-9/17 of at least one actuator of the boom 9 for changing the position of the tip of the boom 9 alternately between at least one first target position 23 and at least one second target position 24 of the harvester head 17 until the whole trunk of the felled tree has been processed in the desired way. In addition to the attitude of the boom parts of the boom 9, it is also possible to affect the attitude of the harvester head 17 as required.

In the solution shown in Figures 3 and 4, the control command CC for controlling the tip of the boom 9 of the harvester 1 in the work environment 21 of the harvester 1 alternately between the two target positions is converted into one or more control measures occurring automatically or semi-automatically in relation to the harvester 1 affecting the attitude of the boom parts of the boom 9, and possibly additionally the attitude of the harvester head 17, such that the operator of the harvester 1 has no need to intervene with the processing of an already felled tree without a special reason. This decreases the stress directed to the operator of the harvester 1. Additionally, the arrangement also improves the quality and efficiency of timber harvesting by decreasing the ending up of branches or pieces of bark to log piles due to possible control errors of the operator of the harvester 1.

When changing the location of the harvester head 17 automatically between at least one first target position 23 and at least one second target position 24, the operator of the harvester 1 has no need to intervene with the processing of the already felled tree without a special reason before controlling the harvester head 17 to grab the next tree to be felled. When changing the location of the harvester head 17 semi-automatically between at least one first target position 23 and at least one second position 24, the operator of the harvester 1 can e.g, give a control command with the control means 18 for changing the location of the harvester head 17 from at least one first target position 23 to at least one second position 24, or vice versa, without the operator still not intervening with the control of the boom 9 or the harvester head 17, whereby the tip of the boom 9 is controlled into the desired direction to the intended target position automatically.

The presented solution can thus decrease or totally prevent branches and/or pieces of bark from ending up in logs piles, thus improving the quality and efficiency of timber harvesting. The presented solution can decrease the control measures performed by the operator of the harvester 1 and thus decrease the mental and physical stress experienced by the operator of the harvester 1, simultaneously freeing the harvester operator to focus on the next work stages, such as e.g. to the selection of the next tree to be processed.

The productivity of the harvester 1 can be further improved by utilizing e.g. computer vision or laser scanning for identifying the number and/or location of branches in the tree trunk. Then, it is e.g. possible to avoid the transfer of the harvester head 17 away from the log pile when the next cut-to-size section of the tree trunk does not include branches at all and there is no intention to bark the trunk but it is possible to perform at least two successive cuts of the cut-to-size section of the tree trunk without delimbing and/or debarking in between.

According to an embodiment, said first work stage is finalized in said at least one first target position 23 before starting to change the location of the harvester head 17 into said at least one second target position 24 and/or said second work stage is finalized in said at least one second target position 24 before starting to change the location of the harvester head 17 into said at least one first target position 23. In this embodiment, the work stage in question is finalized in the corresponding target position of the harvester head 17 without anticipating the change of the location of the harvester head 17 to the next target position, whereby the delimbed branches, the debarked pieces of bark and the sawn section of the tree trunk are arranged to end up accurately in the area of the corresponding target position 23, 24.

According to an embodiment, the change of the location of the harvester head 17 to said at least one second target position 24 is started before said first work stage has been finalized in said at least one first target position 23 and/or the change of the location of the harvester head 17 to said at least one first target position 23 is started before said second work stage has been finalized in said at least one second target position 24. In the embodiment, the transfer of the harvester head 17 to the next target position for performing the work stage is anticipated before the on-going work stage has been finalized in the target position corresponding it. The object of anticipation is to speed up the work cycle of the harvester 1 but it can cause e.g. delimbed branches and/or debarked bark ending up outside the area corresponding the first target position 23 in question.

When utilizing said anticipation, it is thus possible to speed up working but also use the forces directed to the boom 9 by the harvester head 17 particularly in the acceleration and deceleration stage of the feeding of the tree occurring through the harvester head 17. The starting and acceleration of said feeding occurs more lightly when the end of the boom 9 follows for a moment the natural movement of the harvester head 17. The starting of the movement of the end of the boom 9 can even be made a little predictive and/or overcontrolled, whereby the boom 9 tries to assist the feeding event even more. Equivalently, when the feeding approaches the target dimension of the part of the tree trunk, when deceleration starts, the transfer of the harvester head 17 back towards the log pile is also started using the change in force directed at the end of the boom 9 by the deceleration.

By using the forces directed to the boom at the right time, the transfer of the end of the boom 9 in the direction of the tree being fed can be done more lightly, which reduces energy consumption and decreases loading on the boom 9. In this way, the total efficiency of operations related to the boom 9 can be better controlled and the overloading of the boom 9 can be prevented. According to an embodiment, said at least one first target position 23 and said at least one second target position 24 are set at a predetermined distance away from each other. In this embodiment, the distance between the target positions 23, 24 is set as a standard distance of substantially predetermined size.

According to an embodiment, the performance of the first work stage and the second work stage following each other is paused as a response to the incomplete performance of the first work stage and/or the second work stage in the corresponding target position. The pausing comprises e.g. the removal of branches or pieces of bark having ended up in the log pile e.g. in the second target position 24 from the log pile or the transfer of a part of the tree trunk not having ended up in the log pile in the first place to the log pile. In order to minimize the pause time, said measures are tended to be done after the trunk of the felled tree has been totally processed in the first 23 and the second 24 target position. The pause can be detected e.g. by the control unit 19 based on control measures that differ from the common control measures of the first work stage or the second work stage. However, a temporary pause of said work stages for felling the next tree to be processed or a pause intended to be temporary of the use of the harvester 1 are not considered as a pause which can be detected e.g. as a lack of conventional control measures of the first work stage or the second work stage or from setting the harvester 1 running idle. Branches or pieces of bark having ended up in a log pile or a log having fallen outside the log pile can be detected based on observation means 20 based on e.g. computer vision and image recognition. Said means based on computer vision and image recognition can also be utilized for detecting where the branches or pieces of bark actually end up in relation to their target position.

According to an embodiment, the location of said at least one first target position 23 and said at least one second target position 24 is changed in relation to each other based on the substantially continuous realization of the first work stage and the second work stage following each other. In this embodiment, the substantially continuous realization of the first work stage performed by the harvester 1 in at least one first target position 23 and the second work stage performed in at least one second target position 24 is determined, that is, the time or duration that the harvester 1 performs the work stages in question without a pause. Said substantially continuous realization can be determined e.g. in the control unit 19 based on control commands CC received from the control means 18, whereby the control command CC for e.g. removing branches or pieces of bark having ended up in a log pile from the log pile or for transferring a log not having ended up in the log pile in the first place to the log pile determines that the substantially continuous realization of the first work stage and the second work stage has ended. Said substantially continuous realization can be determined e.g. in the control unit 19 and it is shown in Figures 4 and 6 very schematically by designation CR.

According to an embodiment, the distance of said at least one first target position 23 and said at least one second target position 24 from each other is increased when the substantially continuous realization of the first work stage and the second work stage following each other is smaller than the limit value set for said realization. In this embodiment, the distance of said at least one first target position 23 and said at least one second target position 24 from each other is increased as a response to the substantially continuous realization of the first work stage and the second work stage following each other being smaller than the limit value set for said realization, which is caused by said at least one first target position 23 and said at least one second target position 24 being too close to each other resulting in e.g. delimbed branches and/or debarked bark ending up in the log pile too often from the viewpoint of the efficient use of the harvester 1, thus causing too often the need to pause the work of the harvester 1 in order to remove branches and/or pieces a bark from the log pile. Said limit value of substantially continuous realization can be set e.g. in the control unit 19 and it is shown in Figures 4 and 6 very schematically by designation LIMITCR.

According to an embodiment, the distance of said at least one first target position 23 and said at least one second target position 24 from each other is decreased when the substantially continuous realization of the first work stage and the second work stage following each other is larger than the limit value set for said realization. In this embodiment, the distance of said at least one first target position 23 and said at least one second target position 24 from each other is decreased as a response to the substantially continuous realization of the first work stage and the second work stage following each other being larger than the limit value set for said realization, which is caused by said at least one first target position 23 and said at least one second target position 24 being too far from each other resulting in e.g. delimbed branches and/or debarked bark not ending up in the log pile at all or ending up very rarely in the log pile, which in turn can indicate that said at least one first target position 23 and said at least one second target position 24 are too far away from each other from the viewpoint of the efficient use of the harvester 1. Those skilled in the art will find it obvious that, as technology advances, the basic idea of the invention may be implemented in many different ways. The invention and its embodiments are thus not restricted to the examples described above but can vary within the scope of the claims.

Claims

1. A method for controlling a boom of a harvester by tip control, in which method determining at least one first target position and at least one second target position for a harvester head of the harvester, producing at least one control command for performing a first and a second work stage of the harvester head following each other alternately such that the first work stage of the harvester head is performed in at least one first target position and the second work stage of the harvester head is performed in at least one second target position, and changing the attitude of at least one boom part of the boom automatically or semi-automatically for changing the location of the harvester head alternately between at least one first target position and at least one second target position of the harvester head, wherein said first work stage of the harvester head comprises the feeding of a felled tree trunk through the harvester head for delimbing the tree and/or for debarking the tree trunk, and said second work stage of the harvester head comprises the cutting of the tree trunk, and wherein said at least one first target position of the harvester head comprises a piling site for branches delimbed and/or bark debarked from the tree trunk, and said at least one second target position comprises a piling site for logs cut of the tree trunk.

2. A method according to claim 1, c h a r a c t e r i z e d by starting the change of the location of the harvester head to said at least one second target position before said first work stage in finalized in said at least one first target position and/or starting the change of the location of the harvester head to said at least one first target position before said second work stage is finalized in said at least one second target position.

3. A method according to claim 1 or 2, c h a r a c t e r i z e d by pausing the performance of the first work stage and the second work stage following each other as a response to the incomplete performance of the first work stage and/or the second work stage in the corresponding target position.

4. A method according to any one of the previous claims, c h a r a c t e r i z e d by changing the location of said at least one first target position and said at least one second target position in relation to each other based on a substantially continuous realization of the first work stage and the second work stage following each other.

5. A method according to claim 4, c h a r a c t e r i z e d by increasing the distance of said at least one first target position and said at least one second target position from each other when said substantially continuous realization is smaller than the limit value set for it.

6. A method according to claim 4 or 5, c h a r a c t e r i z e d by decreasing the distance of said at least one first target position and said at least one second target position from each other when said substantially continuous realization is larger than the limit value set for it.

7. A control system for controlling a boom of a harvester by tip control, the control system comprising at least one control system for controlling at least the boom of the harvester by tip control, sensors for determining the attitude of the boom parts of the boom and the attitude of the harvester head at the end of the boom, actuators for changing the attitude of the boom parts of the boom and the attitude of the harvester head, and at least one control means for producing at least one control command for performing a first work stage and a second work stage of the harvester head following each other alternately such that the first work stage of the harvester head is performed in at least one first target position of the harvester head and the second work stage of the harvester head is performed in at least one second target position of the harvester head, and said at least one control unit is configured for: setting at least one first target position and at least one second target position as a response to at least one corresponding control command produced by at least one control means, and producing at least one control measure for changing the attitude of at least one boom part of the boom automatically or semi-automatically for changing the location of the harvester head alternately between at least one first target position and at least one second target position of the harvester head as a response to at least one corresponding control command produced by at least one control means, wherein said first work stage of the harvester head comprises the feeding of a felled tree trunk through the harvester head for delimbing the tree and/or for debarking the tree trunk, and said second work stage of the harvester head comprises the cutting of the tree trunk, and wherein said at least one first target position of the harvester head comprises a piling site for branches delimbed and/or bark debarked from the tree trunk, and said at least one second target position comprises a piling site for logs cut of the tree trunk.

8. A control system according to claim 7, characterized in that said at least one control unit is configured to start the changing of the location of the harvester head to said at least one second target position before said first work stage has been finalized in said at least one first target position and/or said at least one control unit is configured to control to start the changing of the location of the harvester head to said at least one first target position before the second work stage has been finalized in said at least one second target position.

9. A control system according to claim 7 or 8, characterized in that said at least one control unit is configured to pause the performance of the first work stage and the second work stage following each other as a response to the incomplete performance of the first work stage and/or the second work stage in the corresponding target position.

10. A control system according to any one of claims 7-9, characterized in that said at least one control unit is configured to change the location of said at least one first target position and said at least one second target position in relation to each other based on the substantially continuous realization of the first work stage and the second work stage following each other.

11. A control system according to claim 10, characterized in that said at least one control unit is configured to increase the distance of said at least one first target position and said at least one second target position from each other when said substantially continuous realization is smaller than the limit value set for it.

12. A control system according to claim 10 or 11, characterized in that said at least one control unit is configured to decrease the distance of said at least one first target position and said at least one second target position from each other when said substantially continuous realization is larger that the limit value set for it.