Technical Field

The present disclosure relates to forestry machines. More particularly, the present disclosure relates to tree shears, and a method for regulating the speed and/or force applied by said tree shears.

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 force for every use, will excessive wear the blade(s) of the tree shears and thus shorten their operational life. The use of maximum 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 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 controlling tree shears having a pair of opposed jaws. The method may be computerized or carried out using hydraulic, pneumatic, or any other suitable means. As used herein, ‘computerized’ is intended to mean that the tree shears are adapted to be controlled at least partially by a computer device. According to an embodiment of the present disclosure, the method comprises moving the pair of opposed jaws towards each other with a cutting force to thereby perform a cutting action on a tree arranged between the jaws.

The tree shears may comprise driving means configured to apply a force to thereby move (e.g. push, drive, or actuate) the jaws towards each other, wherein the driving means may be able to vary the force and/or the speed with which the jaws are moved towards each other.

For example, the driving means may comprise a hydraulic system configured to apply a closing force using at least one hydraulic piston, such that the amount of force applied the jaws on the tree can be varied by changing the amount of hydraulic pressure in the cylinder of the hydraulic piston. The hydraulic system may additionally or alternatively comprise a speed valve for varying the speed of motion of the hydraulic piston.

In other examples, the driving means may comprise an electric system, a pneumatic system, or another system suitable for moving the jaws of the tree shears towards each other with a variable amount of speed or force. The driving means may comprise a plurality of driving means coupled to respective jaws of the pair of jaws, or the driving means may only be coupled to one jaw of the pair of opposed jaws such that one jaw is moved towards the other jaw by the driving means.

The presently described control method may work through a control of the force applied by the jaws, or through a control of the speed with which the jaws move. For ease of understanding, the force of motion of the jaws is referred to primarily herein, but it will be appreciated that ‘force’ is intended to allow for ‘speed or force’, with any necessary adaptation for such allowance.

The initial cutting force with which the jaws are controlled to move towards each other with may be predetermined, such as a maximum or a median force (where such terms are intended to mean ‘maximum/average force that the driving means are capable of providing’), or the initial cutting force may be dynamically determined. For example, qualities of the tree arranged between the jaws may be determined by sensors, cameras, or other sensing means with a view to informing the initial cutting force.

Once the blade(s) of the jaws makes contact with the tree, a substantial resistance (which may, for example, manifest as a reaction force) may be experienced as a result of the resistance put up by the tree against the blade(s). If the initial resistance experienced by the jaws exceeds the initial cutting force, the motion of the jaws may be momentarily retarded. The resistance may be determined as a reaction force, such as using a force sensor, or may be determined as a function of a reduction in speed (e.g. relative to requested speed), depending on the implementation.

According to the presently described embodiment of the present disclosure, the method may further comprise determining a resistance on the jaws during the cutting action. The resistance may be determined by a resistance sensor such as a force sensor, which may be part of or connected to the driving means, or may be separate therefrom. For example, a reaction force may be determined based on a hydraulic pressure in a cylinder of a hydraulic piston, or a reaction force may be determined by a crush sensor or a torsion sensor (if the jaws are rotatably moved) arranged on or in the tree shears.

In some examples, it may be preferred to calibrate a determined reaction force relative to a cutting force applied by the jaws, such that the jaws do not accelerate when the determined reaction force is equal to the cutting force that the jaws are being instructed to apply as part of the control thereof.

Furthermore, according to the presently described embodiment of the present disclosure, the method may further comprise controlling the cutting force applied by the jaws during the cutting action based on the determined resistance.

For example, the cutting force may be controlled so as to match a determined reaction force, or the cutting force applied by the jaws during the cutting action may be controlled based on a sum of the determined reaction force and an additional force. Such an additional force may be determined according to a fixed/predetermined amount, e.g. corresponding to 30 bars of additional pressure in a hydraulic cylinder, or a percentage such as 10% more force than the reaction force.

Accordingly, the force applied by the jaws in order to cut the tree is not excessive relative to the force required to cut through the tree. Thus, the blade(s) of the jaws is not excessively worn when cutting through the tree, hence providing a longer operation life of the blade(s). A similar operational scheme may be derived in respect of a speed of motion of the jaws.

The tree shears may be incorporated as part of a processing head of a working machine (e.g. installed on a boom of a harvester machine). By not using excessive force in cutting trees arranged between the jaws, and instead tailoring the speed or amount of force used to cut the trees based on a determined resistance during said cutting, a chassis of the processing head may be advantageously protected from excessive mechanical strain. Indeed, the reaction force experienced by the jaws may be transferred to the structure holding said jaws. Therefore, not only is the operational life of the blade(s) of the jaws improved, but also the surrounding structure of the tree shears.

Thus, according to the presently described embodiment, the (components of the) tree shears (and/or the surrounding structure(s)) may beneficially be operational for a longer time without requiring repair or replacement. This is particularly advantageous in the field of forestry, as working machines used for forestry may be located in remote areas, far from potential sourcing locations for replacement parts or servicing personnel.

According to a preferred example, the jaws may also 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 blade(s) resulting from an excessively firm or fast closing may be advantageously reduced. More particularly, the method may further comprise a step of determining that the jaws are at an intermediate position between an open position, for receiving the tree, and a closed position wherein the jaws are abutting. The intermediate position may be a predetermined position, such as 90% between open and closed, or it may be dynamically determined based on, e.g. the determined reaction force.

According to this example, the method may further comprise a step of controlling, in response to determining that the jaws are at the intermediate position, the pair of opposed jaws to move to the closed position with a closing force to thereby perform a closing action, determining a maximum closing speed or force (e.g. based on the determined resistance), and limiting said closing speed force applied by the jaws during the closing action to said maximum closing speed or force.

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 first example control scheme, employed during the cutting action, the jaws are controlled to move towards each other and thereby cut the tree with a cutting force based on the reaction force, experienced as a result of the resistance of the tree against the blade(s) of the jaws cutting therethrough. This first control scheme may be employed between the open position and the intermediate position.

According to a second example control scheme, employed during the closing action, the jaws may be controlled to move towards each other and thereby finish cutting a last portion of the tree and arrive in abutment with each other, using a closing force limited to a maximum closing force. That is, the jaws may move from the intermediate position to the closed position with a constant force or a varying force that is equal to or less than the determined maximum closing force. The method may further comprise determining that the jaws are in the closed position and, in response to determining that the jaws are in the closed position, controlling the jaws to open. The jaws may be determined as being in the closed position by detecting that the jaws are in the closed position, or detecting an increase in the resistance (i.e. indicating that the jaws are abutting). 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.

In some examples, the maximum closing speed or force may be predetermined (e.g. fixed at a set value) or may be dynamically determined. For example, the maximum closing speed or force may be determined based on the maximum resistance determined 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 to mitigate the wear on the blades 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 force corresponds to the maximum reaction force during the cutting action, it is likely that the final portion of the tree will not require a greater force to cut through than the maximum reaction force experienced during the cutting action, as there is likely less of the tree left to cut through than at the time said maximum reaction force was determined. Therefore, the maximum closing force can be set at an appropriate limit.

As mentioned above, the closing action may be initiated 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, the method may comprise determining a decrease in the determined resistance, indicating that most of the tree (or at least the portion of the tree requiring the most force to cut through) has been cut, and thus the remaining portion of the tree still to be cut will likely require no more than the peak or maximum resistance, e.g., measured as a reaction force (or the maximum cutting force used during the cutting action). Hence, the cutting speed/force and the closing speed/force can be calibrated for every use of the tree shears to reduce excessive application of force and thus reduce wear on the jaws and the blade(s) thereof.

In other examples, the jaws may be determined as being at the intermediate position by 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 (i.e. not 100% closed, i.e. <100% 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 force is adapted to the closing speed or force before the jaws are brought into abutment.

As well as the force applied by the jaws, the tree shears may also or alternatively be configured so that the speed of the movement of the jaws is controllable. For example, the speed with which the jaws move towards each other may be controlled according to a maximum possible speed during the cutting action. Thus, the amount of time taken to cut through the tree may be reduced, thus increasing potential throughput of the tree shears. It will be appreciated that the maximum possible speed may be limited by the resistance experienced by the jaws as they attempt to cut through the tree.

Moreover, in some examples, the speed with which the jaws move to the closed position (i.e. from the intermediate position) may be decreased and/or limited during the closing action. Thus, the limitation in closing speed or force may be allowed time to be completely effected, e.g. to accommodate for any latency in the control operations of the tree shears, thus improving the reliability of the ‘soft-close’ function described above.

If the closing speed can be known or predetermined, then 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 blades are brought into abutment.

Thus, according to such examples, the jaws may determined as being at the intermediate position by detecting (e.g. using a position sensor) an almost-closed positioning of the jaws, and then the closing action may have a predetermined duration configured to ensure that the jaws are brought into abutment in the closed position. 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 blades.

The reliability may be further improved using this technique as a position sensor may be implemented using reliable, structurally simple, and mechanically reliable means, which may not require additional complex electronics. For example, the predetermined duration may be pre-loaded into the control unit controlling the driving means.

According to an example of such mechanically reliable means, the almost-closed positioning of the jaws may be detected by a position sensor formed of a protrusion on at least one of the jaws, and a detector arranged on the tree shears. The detector may then be configured to detect the protrusion when the protrusion is proximal (e.g. immediately adjacent) to the detector. Accordingly, the detector may be configured to detect the protrusion when the protrusion is in close vicinity of the detector. The detector may detect the protrusion if the protrusion is next to the detector, such as arranged adjacently/oppositely/proximal to the detector. Thus, the detector may detect the protrusion when the jaws are in a position such that the protrusion is proximal to the detector. The detector may be arranged at a fixed position on the tree shears such that the protrusion is detected as being proximal to the detector when the jaws are in the intermediate position.

An example of such a detector may be an inductive sensor configured to generate a response when a metal (e.g. a metal protrusion on one or both of the jaws) is proximal thereto. The protrusion may be integrally formed as part of the jaws.

It will also be appreciated that such a technique can be applied to the detection of the jaws being in the closed position. That is, a further protrusion may be provided on the jaws, such that the detector detects proximity of this further protrusion when the jaws are in the closed position. It will also be appreciated that the functions described above may also be implemented without computerized control and may instead be implemented entirely mechanically. For example, the driving means may comprise a telescopic actuator having at least two actuating/driving phases, wherein the final actuating phase is configured to apply an equal or lesser force than a previous actuating phase (which may be configured to apply a greater force for cutting). The driving means may, in some examples, comprise a regenerative hydraulic system.

According to such examples, the stroke of the earlier phase(s) (which may themselves be computerized in their control) may be limited such that the jaws cannot be brought into abutment in the closed position during such phase(s). Thus, it can be reliably ensured that the closing action is performed with a closing force that is limited to a maximum closing speed or force, i.e. limited by the mechanical capabilities of the final actuating phase.

It will be appreciated that, if the presently described tree shears are implemented as a processing head on a working machine, e.g. part of a harvester, then the control module may be included in or on said working machine or a boom thereof, and connected to the driving means of the tree shears via wired or wireless means. The same may apply to the driving means or portions thereof, e.g. hydraulic systems and such.

Nonetheless, in any implementation, the control of the jaws of the tree shears to intelligently calibrate the speed or force during cutting (and closing, in some examples) may advantageously prolong the operational life of the jaws and any surrounding load-bearing components, as well as other advantages as described above and in relation to the below-summarized figures.

Brief Description of the Drawings

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 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.

The tree shears 200 may further comprise one or more force sensors 212 for determining 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 force sensor 212 may be in data communication with a control unit 220, configured to control the amount of force applied by 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. 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 control unit 220 may control the jaws 202 via the driving means 206 to move together with a cutting force FCUT, and to determ ine/measure the reaction force FR, e.g. using the 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.

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. The determined reaction force FR may then be used at step 108 to determine the cutting force based on the determined reaction force. This determination may take place every time a value of the reaction force FR is determined, or every predetermined period, or according to some other scheme. The cutting force FCUT may preferably change with as little delay as possible after a determined change in the reaction force FR.

The cutting force FCUT may be controlled so as to substantially match and track the reaction force FR, or the cutting force FCUT may be calculated as a sum of the reaction force FR and some additional force FADD.. It will be appreciated that this additional force FADD. may be high enough to ensure a rapid and effective cutting of the tree 204 without excessively increasing the cutting force FCUT, SO as to preserve the advantageous maintenance of the jaws 202 and other components.

For example, the reaction force FR may be measured by the force sensor 212 based on a hydraulic pressure of a hydraulic cylinder comprised in the driving means 206. The cutting force FCUT may then be controlled by the driving means 206 by adjusting the desired hydraulic pressure. To give an example, the cutting force Fc may be determined (by proxy) by measuring the hydraulic pressure of the hydraulic cylinder and controlling (i.e. requesting) a desired hydraulic pressure of the hydraulic cylinder that is 30 bars (or some other fixed or dynamic amount) greater than said measured hydraulic pressure.

The initial cutting force FCUT, i.e. before a reaction force FR has been measured based on the resistance of the tree 204, may be set as a fixed or dynamically determined value. For example, the initial cutting force FCUT may be a maximum or a median force that is capable of being applied by the driving means 206. Alternatively, the initial cutting force FCUT may be determined based on determined properties of the tree 204, such as diameter (which may be measured by separate holding or feeding means, not shown in the figures 2A to 2C), estimated hardness (which may be based on artificial intelligence or machine learning techniques and computer vision, for example), or other such properties.

The cutting of the tree 204 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 110.

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 reaction force FR determined by the 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 reaction force FR 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.

It will be appreciated that numerous factors may contribute to the behavior of the determined reaction force FR, 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 computational latency, may be considered in the determination of how best to define the intermediate position.

As shown in step 110 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 force FCLOSE to be used during a closing action, the closing action following the cutting action, preferably automatically.

The control of the driving means 206 may then be transitioned from a first control scheme, based on the determined reaction force FR, to a second control scheme, limited to a maximum closing force FCLOSE_MAX. The jaws 202 may then perform a closing action such that the driving means 206 are controlled to 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 at least the first control scheme, as defined above, i.e. during the cutting action, 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 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. 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 force.

It will be appreciated that the maximum closing force FCLOSE may not always be less than the cutting force FCUT. However, by adapting the force control scheme away from one based on the reaction force FR, it can be ensured that an excessive force spike/peak is not caused when the jaws 202 closed against each other. As is made clear in figure 3, if the first control scheme were maintained during the closing action, 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.

According to some examples, and as shown in step 114, 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 reaction force FR (indicative of the jaws 202 pushing against each other). Irrespective of how, 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 116, 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 reaction force FR 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.

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 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 possible, until the closing action is initiated, at which point the speed may be reduced, e.g. by a predetermined amount or to a fixed limit. In some examples, the 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 the cutting force FCUT to the closing force FCLOSE can be reliably enacted.

It will be appreciated that, 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 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.