WO2023242018A1

WO2023242018A1 - Tree shears and control method therefor

Info

Publication number: WO2023242018A1
Application number: PCT/EP2023/065235
Authority: WO
Inventors: Johannes SVEGBO; Daniel LINDER
Original assignee: Komatsu Forest AB
Current assignee: Komatsu Forest AB
Priority date: 2022-06-13
Filing date: 2023-06-07
Publication date: 2023-12-21
Anticipated expiration: 2024-12-13
Also published as: SE546521C2; FI20246472A1; AU2023293543A1; SE2250708A1

Abstract

There is disclosed herein a method for cutting tree (204) with tree shears (200) having a pair of opposed jaws (202), and tree shears (200) adapted to carry out said method. The method comprises moving the jaws (202) towards each other from an open position to an intermediate position, between the open position and a closed position, to thereby perform a cutting action on a tree (204) arranged between the jaws (202), and moving the jaws (202) towards each other from the intermediate position to the closed position to thereby perform a closing action. The movement of the jaws (202) during the cutting action is controlled according to a cutting control scheme and the movement of the jaws (202) during the closing action is controlled according to a closing control scheme, wherein at least the closing control scheme comprises limiting a speed or force of the jaws (202) to a maximum closing speed or force.

Description

TREE SHEARS AND CONTROL METHOD THEREFOR

Technical Field

The present disclosure relates to forestry machines. More particularly, the present disclosure relates to tree shears, and a method for closing the jaws of said tree shears with a limited closing speed and/or force.

Background

Forestry machines are used in forests for harvesting logs from trees. Trees may be felled and processed into logs in situ in the forest, for example as part of a ‘cut-to-length’ processing. As such, forestry machines may be expected to function reliably in remote locations and in harsh conditions.

Conventional harvesters (forestry machines for harvesting logs) may use saws such as bar saws or disc saws in their felling heads to fell trees. However, saws may be left running throughout a harvesting operation even when they are not being used to cut trees, which may excessively consume power and create excessive noise.

Tree shears are an alternative to saws for felling trees which may overcome one or all of these disadvantages. Tree shears comprise bladed jaws that close around a tree to thereby cut and fell the tree, similar to the action of garden shears or a guillotine. The closing of the jaws may be assisted by powered means, under the control of an operator, to assist with the cutting of even larger trees, which may have a diameter of up to 750 mm or more.

It is preferred for forestry operations to be carried out as quickly and efficiently as possible, such that a maximum number of logs can be harvested during the operations. Therefore, tree shears may be operated with a maximum cutting speed or force to fell trees as quickly as possible. Summary

It is an object of the present disclosure to provide tree shears for use in forestry operations that have a longer operational life, are easier to operate, and are more easily adaptable for different tree types or sizes.

For example, it is appreciated as part of the present disclosure that prior art tree shears, which are operated with a maximum cutting speed and/or force for every use, will excessive wear the blade(s) of the tree shears and thus shorten their operational life. The use of maximum speed and/or force for every use, i.e. irrespective of tree type (different types of trees having different hardness, for example) or size, may also excessively consume power, and/or may also cause excessive mechanical stress on the surrounding structure of the tree shears, e.g. the chassis of a processing head of a working machine comprising said tree shears.

It is further appreciated as part of the present disclosure that prior art tree shears are difficult to operate because an operator may be required to manually activate the closing of the jaws, and continue instructing the jaws to close until the operator deems the jaws to be sufficiently closed, at which point the operator may be required to manually instruct the jaws to open.

The blade(s) of the jaws may thus be closed against each other with a maximum speed and/or force, thereby causing additional wear on said blade(s). Such a closing with maximum force may also risk damage to the powered means closing the jaws (e.g. hydraulics, pneumatics, or similar). Therefore, in order to address at least these problems, which may not yet have been considered in relation to the prior art systems, there is provided a method for cutting tree with tree shears having a pair of opposed jaws, wherein the closing of the jaws is performed with a limited speed or force.

In particular, according to an aspect of the present disclosure, the method may comprise moving the jaws towards each other from an open position to an intermediate position between the open position and a closed position to thereby perform a cutting action on a tree arranged between the jaws.

The method may then comprise moving the jaws towards each other from the intermediate position to the closed position to thereby perform a closing action. The movement of the jaws during the cutting action may be controlled according to a cutting control scheme, while the movement of the jaws during the closing action is controlled according to a closing control scheme. In some examples, the cutting control scheme may not involve detailed control but may instead be crudely controlled, e.g. according to a maximum possible speed or force for closing the jaws.

According to the presently described aspect of the present disclosure, at least the closing control scheme may comprise limiting a speed or force of the jaws to a maximum closing speed or force. Put another way, the jaws may be controlled to perform a ‘soft-close’ function such that the jaws are not closed against each other with excessive speed or force. Thus, wear on the jaws (include any blade(s)) or surrounding structure of the jaws resulting from an excessively firm or fast closing thereof may be advantageously reduced.

Thus, viewed from one perspective, the movement of the jaws from the open position to the closed position may be realized in two stages, each stage having different control schemes.

According to a cutting control scheme, employed during the cutting action, the jaws are move towards each other according to a cutting control scheme. In some examples, the cutting control scheme may comprise determining a cutting force based on a determined resistance, experienced as a result of the resistance of the tree against the blade(s) of the jaws cutting therethrough. This cutting control scheme may be employed between the open position and the intermediate position.

In some examples, the cutting control scheme may be less ‘intelligent’, and the jaws may merely be controlled to close in a typical fashion, i.e. with a maximum possible speed or force. In other examples, the cutting control scheme may comprise determining a limit for a cutting speed or force, which may be based on, e.g., properties of the tree such as a diameter or type of tree determined by the tree shears or some external device. According to a closing control scheme, employed during the closing action, the jaws may be moved towards each other to thereby finish cutting a last portion of the tree and arrive in a closed position (e.g. in abutment with each other), using a closing speed or force limited to a maximum closing speed or force. That is, the jaws may move from the intermediate position to the closed position with a constant/fixed speed or force or a varying (e.g. decreasing) speed or force that remains equal to or less than the determined maximum closing speed or force.

In some examples, the maximum closing speed or force may be determined based on a maximum determined resistance during the cutting action. Thus, the speed or force with which the jaws are moved towards each other during the closing action can be limited, e.g., to mitigate the wear on the blades if/when they are brought into abutment. The maximum closing speed or force may nonetheless be at least enough to cut through the final portion of the tree.

For example, if the maximum closing speed or force corresponds to the maximum resistance determined during the cutting action, it is likely that the final portion of the tree will not require a greater speed or force to cut through than that corresponding to a maximum resistance experienced during the cutting action, as there is likely less of the tree left to cut through than at the time said maximum resistance was determined. Therefore, the maximum closing speed or force can be set at an appropriate limit.

As mentioned above, the closing action may be initiated (e.g. automatically) when the jaws reach the intermediate position between the open position and the closed position, and this intermediate position may be fixed or may be dynamically determined.

In some examples, determining that the jaws have reached the intermediate position may comprise detecting an almost-closed positioning of the jaws (e.g. using a position sensor), which may be 50% closed, 75% closed, 90% closed or some other position, depending on the implementation. The term almost-closed positioning may be interpreted to mean a positioning/state of the jaws where they are almost closed, but not fully closed. Depending on implementation this may be e.g. 50%, 75% or 90% closed. The term “an almost-closed positioning” may mean a positioning of the jaws wherein a degree of closure, DoC, fulfils 50% < DoC < 100%, i.e. the positioning of the jaws may be between 50% closed and 100% closed. Oppositely, almost fully open could be between 0% closed and 50% closed. In an example, the jaws may be determined as being at the intermediate position by detecting an almost-closed positioning of the jaws, wherein the jaws are between 50% and 100% closed. In further examples, the almost- closed positioning of the jaws may mean between 75% and 100% closed, or between 90% and 100% closed.

The almost-closed position may be predetermined based on an anticipated amount of time to change the closing speed or force, e.g. if the control of the driving means has some latency. Thus, the almost-closed position may be determined to allow enough time to ensure that the cutting speed or force is adapted to the closing speed or force before the jaws are brought into the closed position (e.g. abutment).

According to such examples, the closing action may have a predetermined duration configured to ensure that the jaws are brought into abutment in the closed position. Therefore, in some examples, the almost- closed position may be determined based on an estimated time required for the instruction to initiate the closing action to take effect, and the known closing speed, such that the distance allows for the closing action to take effect before the jaws are brought into abutment. Such an approach may advantageously provide an upper limit on the intermediate position, thus improving the reliability of the control method to reduce wear on the tree shears.

In other examples, determining that the jaws have reached the intermediate position may comprise detecting a decrease in a resistance on the movement of the jaws. The resistance may be measured as a reaction force, and a decrease in the resistance may indicate that a portion of the tree constituting the most difficult portion to cut has been cut. It may thus be assumed thereafter that the closing action can take place with a limited closing speed or force whilst having enough speed or force to finish cutting the remaining portion of the tree. In still further examples, the intermediate position may be defined as an extreme or near-extreme of a stroke for a cylinder which may form part of a telescopic or regenerative hydraulic arrangement, or a similar arrangement.

The method may further comprise moving the jaws from the closed position to the open position to thereby perform an opening action. For example, the opening action may be performed in response to determining that the jaws are in the closed position.

Determining that the jaws are in the closed position may be performed in a similar fashion as how the jaws are determined as being at the intermediate position. That is, determining that the jaws are in the closed position may comprise detecting that the jaws are in the closed position, such as using a position sensor, or detecting an increase in the resistance (caused by the jaws attempting to close against each other), for example.

Therefore, the jaws may be opened as soon as they are detected as being closed, thus allowing for a quick reset of the tree shears and an increased operational throughput, meaning that more logs can be harvested in less time.

In an optional adaptation, the jaws may be controlled to open a predetermined time after being determined as being in the closed position, and/or in response to detecting a threshold increase in the resistance (e.g. measured as a reaction force). Therefore, the likelihood of a reliable closing and cutting of the final section of the tree can be advantageously increased, as some trees may break off during the cutting action or closing action to leave thin and difficult-to-cut strands. Hence, the operational throughput can be further enhanced, as the likelihood of improperly-cut trees is reduced.

The tree shears may take any suitable form, as the presently disclosed method is widely applicable to a variety of tree shears, and may be employed by any suitable means such as a computerized control, a hydraulic control, or some other type of control.

Brief Description of the Figures

One or more embodiments will be described, by way of example only, and with reference to the following figures, in which: Figure 1 schematically shows a method for controlling tree shears having a pair of opposed jaws, according to an embodiment of the present disclosure;

Figures 2A to 2C schematically show an example of tree shears, wherein the jaws are in the open, intermediate, and closed positions, respectively;

Figure 3 shows an example force diagram showing the determined resistance (as reaction force) and the applied cutting force and closing force during various stages of a cutting action and a closing action; and

Figures 4A and 4B show an example implementation of tree shears as a processing head for a working machine, with and without a mounting chassis, respectively.

Detailed Description

The present disclosure is described in the following by way of a number of illustrative examples. It will be appreciated that these examples are provided for illustration and explanation only and are not intended to be limiting on the scope of the disclosure.

Furthermore, although the examples may be presented in the form of individual embodiments, it will be recognized that the present disclosure also covers combinations of the embodiments described herein.

Figure 1 schematically shows a method 100 for controlling tree shears having a pair of opposed jaws, such as the tree shears 200 illustrated in figures 2A to 2C. Figures 1 and 2A to 2C are discussed together below for ease of understanding.

The tree shears 200 shown in figures 2A to 2C may comprise a pair of opposed jaws 202 (also referred to herein as simply ‘jaws 202’), wherein at least one of the jaws 202 may comprise a cutting blade for cutting a tree 204 arranged between the jaws 202.

In the illustrated example, the jaws 202 may be rotatably coupled to a hub 214, which may be part of a fixed structure (e.g. a chassis) of the tree shears 200. Each of the jaws 202 may then be configured to move towards each other in a rotatable fashion, for example similar to standard garden shears or scissors. However, in some alternative embodiments, only one of the jaws 202 may be configured to move relative to the other, which may be fixed. Furthermore, in some embodiments, the relative movement of the jaws 202 may be translational, e.g. in a clamping or guillotine motion, where the surfaces of the jaws 202 remain parallel during their relative motion.

The jaws 202 may be moved towards each other with a force FCUT applied by driving means 206, which may comprise an actuator 208 such as a hydraulic cylinder, an electronic actuator, etc., each actuator 208 being coupled to a respective jaw 202 via a coupling 210. Therefore, the jaws 202 may cut the tree 204 with a force FCUT according to the force applied by the driving means 206.

Viewed from another perspective, the jaws may be moved towards each other with a cutting speed VCUT, which may be controllable or fixed by the driving means 206.

The tree shears 200 may further comprise one or more sensors 212, which may be force sensors or speed sensors, for determining a resistance (in this example, a reaction force FR) experienced by the jaws 202, as illustrated in figures 2B and 2C. In figure 2B, the main source of the reaction force FR may be the resistance of the tree 204 against the jaws 202 as they attempt to cut through the tree 204. In figure 2C, the main source of the reaction force FR may be the abutment of the jaws 202 against each other, whilst driving means 206 may still be attempting to move the jaws 202 further together.

The driving means 206 and the sensor 212 may be in data communication with a control unit 220, configured to control the speed and/or force of the jaws 202 via control of the driving means 206.

The control unit 220 may be a computing device arranged in a chassis of the tree shears 200 or in a working machine such as a harvester, having the tree shears 200 attached thereto, e.g. as a processing head. In another example, the control unit 220 may be a hydraulic control module, a pneumatic control module, or the like. In the example where the control unit 220 is a computing device, the control unit 220 may comprise a processor and/or memory, wherein the memory may have stored therein computer-executable instructions which, when executed, cause the control unit 220 to carry out, via the processor, the method 100 illustrated in figure 1 , or at least a portion thereof.

According to the illustrated example, the method 100 may begin in an ‘idle state’ of the tree shears 200, wherein at step 102, the tree shears 200 await an instruction to cut the tree 204. An instruction may be generated, for example, by an operator of the tree shears 200, for example as a simple button push, level pull, touch screen, or any other suitable mechanism. In some examples, the instruction may be automatically generated internally to the tree shears 200, e.g. upon detection of the tree 204 between the jaws 202.

Once the instruction is received, the method 100 may progress to step 104, wherein the jaws may be moved 202 towards each other via the driving means 206 (e.g. under control of the control unit 220) according to a cutting control scheme.

In the illustrated example of figure 2B, the cutting control scheme may comprise moving the jaws 202 towards each other with a cutting force FCUT, and to determine/measure the resistance as a reaction force FR, e.g. using a force sensor 212.

The reaction force FR may be measured constantly or as constantly as allowed for by a refresh rate of the data communication between the force sensor 212 and the control unit 220. The reaction force FR may instead be measured at predetermined internals (e.g. every millisecond), or a value for the reaction force FR may be output in response to a threshold detected change in the reaction force FR, SO as to reduce the amount of data communication required between the force sensor 212 and the control unit 220.

Although the force sensor 212 is shown as being a separate unit to the driving means 206, it will be appreciated that it may take any form, including integrated with said driving means 206. For example, the driving means 206 may comprise a hydraulic cylinder, and the force sensor 212 may be a pressure sensor arranged for sensing a hydraulic pressure of said hydraulic cylinder. Alternatively, the sensor 212 may be a speed sensor, configured to determine resistance based on a speed of motion of the jaws 202.

The cutting of the tree 204 according to the cutting control scheme (e.g. using a cutting force FCUT that is based on the determined reaction force FR) may continue until the jaws 202 reach an intermediate position, as shown in step 106 of the method and illustrated in figure 2B, at which point the method 100 may progress to step 108.

As shown in figure 2B, the tree shears 200 may further comprise a position sensor 216 arranged to detect the proximity of a protrusion 218 on one of the jaws 202, when the jaws are at the intermediate position. For example, the position sensor 216 may include an electro-inductive detector configured to detect the proximity of metals, and the protrusion 218 may be a metal block or strip attached to or formed as part of the jaw 202. Such an arrangement may advantageously be mechanically resilient (e.g. in the event of impact to the tree shears 200) and inexpensive to implement.

In some examples, the intermediate position may not be a fixed position but may be defined in respect of the determined resistance (e.g. a reaction force FR determined by a force sensor 212). For example, the intermediate position may be defined as being the point, during the movement of the jaws 202 towards each other, at which the determined resistance begins to decrease.

It may be expected for the reaction force FR to begin lower (as the jaws 202 only just enter the outer section of the tree 204) and then increase as, e.g., a greater surface area of the jaws 202 (which may have one or more cutting blades arranged or formed thereon) is in contact with the tree 204. The reaction force FR may then peak and being to decrease as a lesser amount of the tree 204 is left uncut, and the torsional contribution from the weight of the tree 204 being cut contributes to the separation/cutting of the final section (i.e. cross-section) of the tree 204.

It will be appreciated that numerous factors may contribute to the behavior of the determined resistance, such as the angle at which the actuator(s) 208 of the driving means 206 are arranged relative to the jaws 202, the tensional strength of the wood fibers in the tree 204, etc. These factors, as well as others such as control latency, may be considered in the determination of how best to define the intermediate position.

As shown in step 108 of the method 100, in response to the determination that the jaws 202 are in the intermediate position (however that may be defined in the particular implementation), the control unit 220 may determine the closing speed or force (e.g. VCLOSE or FCLOSE) to be used during a closing action, the closing action following the cutting action, preferably automatically, and being performed according to a closing control scheme.

The movement of the jaws 202 by the driving means 206 may then be transitioned from the cutting control scheme, (wherein this may be based on the determined reaction force FR or may be simply a maximum speed or force) to a closing control scheme, which may be limited to a maximum closing speed or force (e.g. VCLOSE_MAX or FCLOSE_MAX). AS shown in step 110, the jaws 202 may move together according to the closing control scheme. The jaws 202 may then perform a closing action such that the driving means 206 move the jaws 206 together until they are in a closed position (e.g. abutting, overlapping, etc. depending on the construction of the tree shears 200), as shown in figure 2C.

It will be appreciated that the closed position is not limited to abutment, as the advantages of the present disclosure obtained in respect of the cutting and closing control schemes, as defined above, i.e. during the cutting and closing actions, may be realized irrespective of whether the jaws 202 abut, overlap, or are otherwise positioned in the closed position.

According to the illustrated example in figures 2A to 2C, the intermediate position may be a predefined positioning of the jaws 202, wherein the jaws 202 are almost closed. This may be referred to as an ‘almost-closed’ position, characterized in that a time taken for the jaws 202 to move from said almost-closed position to the closed position is at least enough to transition from the cutting force FCUT to the closing force FCLOSE, as indicated in figure 2B.

The jaws 202 may be identified as being in the intermediate position by using a position sensor 216, configured to detect the proximity of a protrusion 218 on one of the jaws 202. It can be seen in figure 2B that, when the jaws 202 are in the intermediate position, the protrusion 218 on one of the jaws 202 is immediately proximate the position sensor 216, thereby causing the position sensor 216 to provide an indication to the control unit 220 (by some data communication, e.g. wired or wireless) that the jaws 202 are in the intermediate position. In response to such an indication, the control unit 220 may control the driving means 206 to transition from the cutting force FCUT to the closing force FCLOSE.

It will be appreciated that data communications between the control unit and sensors (e.g. speed or force sensor 212 and/or position sensor 216) may involve some latency. Therefore, the intermediate position may be particularly configured to allow for such latency, e.g. to ensure that the jaws 202 do not close with an excessive speed or force.

It will be appreciated that the maximum closing speed or force V/FCLOSE may not always be less than the cutting speed or force V/FCUT. However, by adapting the control scheme to a cutting control scheme whereby the speed or force is limited to some maximum closing speed or force, it can be ensured that excessive damage to the jaws or blades thereon is not caused when the jaws 202 are closed against each other.

As is made clear in figure 3, if a cutting control scheme were maintained during the closing action, whereby a cutting force FCUT were based on a maximum closing force or on a determined resistance FR, the jaws 202 closing against each other may cause an increase in reaction force FR, which may in turn cause an increase in the applied force, which may unnecessarily strain the jaws 202 and/or the surrounding structure and thus reduce the operational life thereof.

As shown in step 112, it may be determined that the jaws 202 are in the closed position, as shown in figure 2C. This determination may be carried out using the position sensor 216, e.g. using a second protrusion 218 arranged at a position that aligns proximate with the position sensor 216 when the jaws 202 are in the closed position. Additionally or alternatively, it may be determined that the jaws 202 are in the closed position by detecting an increase in the resistance (e.g. reaction force FR), indicative of the jaws 202 pushing against each other.

Irrespective of how it is done, when it is determined that the jaws 202 are in the closed position, the driving means 216 may be controlled to open the jaws 202 again, as shown in step 114, so as to be ready to receive another tree 214.

This control to open the jaws 202 may be performed immediately after the jaws 202 are determined as being in the closed position or after some delay. In some examples, a threshold increase in resistance may trigger the opening of the jaws 202. Therefore, it can be advantageously ensured that the final section of the tree 214 has been thoroughly severed.

After step 116 when the jaws 202 are in the open position, the method 100 may return to step 102 to await any further instructions to cut a tree 214.

Figure 3 shows an example force diagram 300 showing the determined reaction force FR and the applied cutting force FCUT and closing force FCLOSE during various stages A through G of a cutting action and a closing action. In this illustrated example, the control schemes are based on force instead of speed, although in other examples, the control schemes may be based on speed instead of, or in addition to, force.

The horizontal axis is time, and the vertical axis is force, which may be in arbitrary units for illustration. It will be appreciated that the same diagram may be presented with hydraulic pressure as the vertical axis, in a case where force is applied by a hydraulic cylinder as a driving means, as hydraulic pressure is proportional to force applied by the hydraulic cylinder on the jaws 202.

The initially upper line in figure 3 represents a controlled force applied by the jaws 202, which is initially an initial cutting force FCUT at stage A. It may be determined that the initial cutting force FCUT is excessive relative to the determined reaction force FR, shown as the initially lower line. The cutting force FCUT may be controlled so as to equal the reaction force FR plus some additional force FADD.

Therefore, if the determined reaction force FR is less than the applied cutting force FCUT (e.g. by more than the additional force FADD), the cutting force FCUT may be controlled to decrease to match or track said decrease in reaction force FR.

As shown at stage B, the reaction force FR may then increase, and may increase to more than the currently applied cutting force FCUT, which may slow or retard motion of the jaws 202. Therefore, in accordance with the above described control scheme, the cutting force FCUT may be increased based on this determined increase in the reaction force FR.

In stage C, the tracking or following of the reaction force FR can be seen in the step-wise control of the cutting force FCUT. The steps of the step- wise control may be at regular or irregular intervals, depending on the implementation, or the steps may be smoothed into a curve in some examples, e.g. using a PID control algorithm with a smoothing function.

As mentioned above, the cutting force FCUT may be controlled to be equal to the determined reaction force FR plus some additional force FADD, which may be a fixed or proportional offset. In the illustrated example, the additional force FADD is 30 scale units of force.

However, as the force sensor measuring the reaction force FR may have latency in reporting its measurements to the control unit, and the control unit may have some latency in sending control instructions to the driving means, there may be a delay or latency At such that a cutting force FCUT may correspond to a reaction force FR that was determined a time At ago.

The cutting action may terminate when the jaws reach the intermediate position, at stage D, at which point the force regulation scheme may change from a cutting control scheme to a closing control scheme, to perform a closing action with the jaws, using a closing force FCLOSE, which is limited to a maximum closing force FCLOSE.

In some examples, including the example illustrated in figure 3, the maximum closing force FCLOSE may be limited to the maximum cutting force FCUT used during the cutting action (which incidentally was used immediately before stage D).

The closing force FCLOSE may then be maintained throughout the closing action, or it may be decreased according to the determined reaction force FR. In any event, the closing force FCLOSE is not increased beyond the maximum closing force FCLOSE SO as not to excessively put wear on the jaws and/or the surrounding structure.

As can be seen in the determined reaction force FR during the closing action, the reaction force FR may briefly increase and then rapidly decrease until a local minimum at stage E. This may correspond to the final section of the tree breaking or cutting off, thus removing resistance from the jaws.

In some examples, stage D (i.e. the transition from the cutting action to the closing action) may be initiated by detection of this local minimum, i.e. in response to detecting a decrease in the reaction force FR, which may ensure that an appropriate amount of cutting force FCUT is used throughout the cutting action, if possible.

The determined reaction force FR may then increase until peaking at stage F, corresponding to the jaws being firmly in the closed position, at which point the motion of the jaws towards each other may be stopped (causing the reaction force to reduce again, see stage G).

During stages A until D, the jaws may be moved towards each other with a maximum speed and/or force possible, until the closing action is initiated, at which point the speed or force may be limited or reduced, e.g. by a predetermined amount or to a fixed limit. In some examples, a closing speed may be related to the latency At and/or the position of the intermediate position relative to the closed position. Therefore, the closing speed can be maintained such that the multiple of the closing speed and the latency can be less than the distance from the intermediate position to the closed position. Therefore, it can be ensured that any desired change or limitation from a cutting speed or force V/FCUT to a closing speed or force V/FCLOSE can be reliably enacted.

As mentioned above, while a force regulation scheme is described above, having cutting force FCUT, closing force FCLOSE, and a determined reaction force FR serving as a metric for resistance, it will be appreciated that a speed regulation scheme may also be employed according to the same principles. For example, the jaws may be first moved towards each other with a cutting speed VCUT, and may then change to a closing speed VCLOSE, and the resistance may be measured as a function of the actual speed of the jaws, such as a differential between requested and actual speed of the jaws, which may be determined by a module analogous to the force sensor described above.

Figure 4A shows a processing head 400 for mounting, e.g., onto a boom of a working machine such as a forestry harvester. The processing head 400 may comprise tree shears 410 similar to or the same as those described above. Figure 4B shows the cutting parts of the tree shears 410 on their own, without the rest of the processing head 400.

The processing head 400 may comprise a chassis 402 for mounting and shielding the cutting parts of the tree shears 410, and a mounting bracket 404 for mounting the processing head 400 onto a working machine. The chassis 402 and the mounting bracket 404 may be manufactured by any suitable means, such as cast as a single piece, welded from various plates, etc., depending on the implementation.

The chassis 402 may serve multiple purposes in the processing head 400. For example, the chassis 402 may protect the workings of the cutting parts of the tree shears 410 from falling debris (e.g. branches), as well as serving as a rigid structure for absorbing the reaction force from the cutting parts of the tree shears 410.

The mounting bracket 404 may comprise various through-holes and/or conduits for routing lines/hoses, e.g. for transporting data, power, hydraulic fluid, etc., which may connect to other parts of the working machine. For example, the working machine may house the control unit of the tree shears so as to provide a safer location for the electronics therein, for example.

Figure 4B shows the cutting parts of the tree shears 410 in more detail, with some reference numerals corresponding to those used in figures 2A to 2C for ease of understanding where components may be the same or similar in function.

As illustrated, the cutting parts of the tree shears 410 may comprise jaws 202, each jaw 202 having a corresponding blade 202a. The outermost portion of the jaws 202, where the blade 202a terminates, there may be provided an abutment damper 202b for damping the motion of the jaws 202 as they are brought into abutment in the closed position. This damper 202b may further assist in limiting the wear on the jaws 202, in particular in respect of the blades 202a thereon.

The jaws 202 may be mounted on holding plates 222, which couple the jaws 202 via a coupling 210 to the driving means 206, which in this illustrated example are hydraulic cylinders 206a being fed by hydraulic hoses 206b. The hydraulic cylinders 206a may be telescopic or regenerative hydraulic cylinders, in some examples. The jaws 202 may be arranged to mutually pivot around a central bearing 224.

The holding plates 222 or the jaws 202 themselves may comprise one or more protrusions 218a, 218b. When the jaws 202 are pivoted around the central bearing 224, the protrusions 218a, 218b may move relative to one or more position sensors 216, which are fixed relative to the surrounding structure of the processing head 400.

Each jaw 202 may have two corresponding protrusions 218a, 218b. The first protrusions 218a may align proximate to the position sensors 216 when the jaws 202 are in the intermediate position, and the second protrusions may align proximate to the sensors 216 when the jaws 202 are in the closed position.

The position sensors 216 may be inductive sensors such that the protrusions 218a, 218b, being simply formed of metal, for example, may induce a signal to be generated by said position sensors 216 when they are immediately proximate to the position sensors 216. This may advantageously provide a contactless but reliable mechanical system for detecting the position of the jaws 202.

It will be appreciated that the implementation of tree shears shown in figures 4A and 4B is but one example of many which may fall within the scope of the present disclosure, and this illustrated example has been provided merely to assist in understanding particular aspects of the present disclosure.

Any reference to prior art documents or comparative examples in this specification is not to be considered an admission that such prior art is widely known or forms part of the common general knowledge in the field.

Furthermore, whilst the present disclosure is susceptible to various modifications and alternative forms, specific embodiments are shown and described by way of example in relation to the drawings, with a view to clearly explaining the various advantageous aspects of the present disclosure. It should be understood, however, that the detailed description herein and the drawings attached hereto are not intended to limit the disclosure to the particular form disclosed. Rather, the intention is to cover all modifications, equivalents, and alternatives falling within the scope of the following claims.

Claims

1 . A method for cutting tree with tree shears having a pair of opposed jaws, the method comprising: moving the jaws towards each other from an open position to an intermediate position between the open position and a closed position to thereby perform a cutting action on a tree arranged between the jaws; and moving the jaws towards each other from the intermediate position to the closed position to thereby perform a closing action; wherein: the movement of the jaws during the cutting action is controlled according to a cutting control scheme; the movement of the jaws during the closing action is controlled according to a closing control scheme; and at least the closing control scheme comprises limiting a speed or force of the jaws to a maximum closing speed or force.

2. The method according to claim 1 , wherein the cutting control scheme also comprises limiting a speed or force of the jaws to a maximum cutting speed or force.

3. The method according to any claim 1 or claim 2, wherein the cutting control scheme comprises: controlling the jaws to move towards each other with a maximum possible speed or force.

4. The method according to claim 1 or claim 2, wherein the cutting control scheme comprises: determining a resistance on the movement of the jaws during the cutting action; and controlling the speed or force of the jaws during the cutting action based on the determined resistance.

5. The method according to claim 4, wherein: the maximum closing speed or force is determined based on a maximum determined resistance during the cutting action.

6. The method according to any preceding claim, wherein: the maximum cutting speed or force and/or the maximum closing speed or force is based on properties of the tree.

7. The method according to any preceding claim, wherein the closing control scheme comprises: moving the jaws towards each other with a fixed closing speed or force.

8. The method according to any preceding claim, wherein: the closing action is performed in response to a determination that the jaws have reached the intermediate position.

9. The method according to claim 8, wherein: determining that the jaws have reached the intermediate position comprises: detecting an almost-closed positioning of the jaws, or detecting a decrease in a resistance on the movement of the jaws.

10. The method according to claim 9, wherein: the jaws are determined to have reached the intermediate position by detecting an almost-closed positioning of the jaws; and the closing action has a predetermined duration configured to ensure that the jaws are brought into abutment in the closed position.

11 . The method according to any preceding claim, further comprising: moving the jaws from the closed position to the open position to thereby perform an opening action.

12. The method according to claim 11 , wherein: the opening action is performed in response to determining that the jaws are in the closed position, wherein determining that the jaws are in the closed position comprises: detecting that the jaws are in the closed position, or detecting an increase in the reaction force.

13. The method according to claim 12, wherein: the jaws are controlled to open a predetermined time after being determined as having reached the closed position, and/or in response to detecting a threshold increase in a resistance on the movement of the jaws.

14. The method according to any preceding claim, wherein the control of the speed and/or force of the jaws is carried out using hydraulic and/or computerized means.

15. Tree shears adapted to carry out the method according to any of claims 1 to 14.