NZ705265B - A timber-working device and method of locating at least one stem relative to a feed axis of a timber-working device - Google Patents

Abstract

When processing a stem of a felled tree using a timber-working device, it is useful to centralise the stem relative to the drive mechanism of the device in order to improve effectiveness and accuracy of the device’s operation. Existing devices rely on manual control by an operator to achieve this. An automated method is provided for locating at least one stem relative to a feed axis of a frame of a timber-working device having a first pair of arms and a second pair of arms, each pivotally attached to the frame. The method includes receiving, at a controller, a signal indicating initiation of closure of the second pair of arms to grasp at least one stem currently grasped by the first pair of arms. In response to the signal indicating initiation of closure of the second pair of arms, and during closure of the second pair of arms, the first pair of arms are opened in accordance with at least one predetermined control parameter. The first pair of arms are closed once the opening of the first pair of arms has met the at least one predetermined control parameter. n automated method is provided for locating at least one stem relative to a feed axis of a frame of a timber-working device having a first pair of arms and a second pair of arms, each pivotally attached to the frame. The method includes receiving, at a controller, a signal indicating initiation of closure of the second pair of arms to grasp at least one stem currently grasped by the first pair of arms. In response to the signal indicating initiation of closure of the second pair of arms, and during closure of the second pair of arms, the first pair of arms are opened in accordance with at least one predetermined control parameter. The first pair of arms are closed once the opening of the first pair of arms has met the at least one predetermined control parameter.

Description

James & Wells Ref: 300357/73 P23051-NZ-PRI A TIMBER-WORKING DEVICE AND METHOD OF LOCATING AT LEAST ONE STEM RELATIVE TO A FEED AXIS OF A TIMBER-WORKING DEVICE FIELD OF THE DISCLOSURE The present invention relates to a timber-working device and method of operation.

BACKGROUND It is well-known to mount timber-working devices, commonly referred to as forestry or harvester heads, to a carrier vehicle in order to perform a number of operations in connection with timber processing. These operations may include one, or a combination of, grappling and felling a standing tree, and processing one or more resulting stems by delimbing, debarking, and cutting those stems into logs.

Feeding the stem along its length relative to the head is typically achieved using arm mounted rotary drives, for example having a drive wheel at the end of opposing drive arms which may be pivoted to open and close. These drive arms are often used to hold the stem(s) against one or more frame mounted driven wheels which assist in the feeding action.

There are occasions, particularly when picking up one or more stems, where the stem does not sit centrally in the head relative to the drives. This can impact on the effectiveness and accuracy of the head’s operation. One such undesirable effect may be loss of traction of the driven wheels, which in addition to inefficiencies may damage the stem.

While an experienced operator may be capable of centralising a stem or stems manually by manipulation of head and carrier functions, this may distract from core tasks and contribute to increased levels of stress and fatigue – which may in turn lead to poor decision making with regard to control of the head and lost value to the forest owner.

It is an object of the present invention to address the foregoing problems or at least to provide the public with a useful choice.

All references, including any patents or patent applications cited in this specification are hereby incorporated by reference. No admission is made that any reference constitutes prior art. The discussion of the references states what their authors assert, and the applicants reserve the right to challenge the accuracy and pertinency of the cited documents. It will be clearly understood that, although a number of prior art publications are referred to herein, this reference does not constitute an admission that any of these documents form part of the common general knowledge in the art, in New Zealand or in any other country.

James & Wells Ref: 300357/73 P23051-NZ-PRI Throughout this specification, the word "comprise" or “include”, or variations thereof such as "comprises", “includes”, "comprising" or “including” will be understood to imply the inclusion of a stated element, integer or step, or group of elements integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.

Further aspects and advantages of the present invention will become apparent from the ensuing description which is given by way of example only.

SUMMARY In an exemplary embodiment there is provided a method of locating at least one stem relative to a feed axis of a frame of a timber-working device having a first pair of arms and a second pair of arms, each pivotally attached to the frame, the method including the steps of: receiving, at a controller, a signal indicating initiation of closure of the second pair of arms to grasp at least one stem currently grasped by the first pair of arms; in response to the signal indicating initiation of closure of the second pair of arms, and during closure of the second pair of arms, opening the first pair of arms in accordance with at least one predetermined control parameter; and closing the first pair of arms once the opening of the first pair of arms has met the at least one predetermined control parameter.

In an exemplary embodiment there is provided a timber-working device, including: a frame; a first pair of arms, each pivotally attached to the frame; a second pair of arms, each pivotally attached to the frame; at least one controller, configured to: receive a signal indicating initiation of closure of the second pair of arms to grasp at least one stem currently grasped by the first pair of arms; in response to the signal indicating initiation of closure of the second pair of arms, and during closure of the second pair of arms, control opening of the first pair of arms in accordance with at least one predetermined control parameter; and control closure of the first pair of arms once the opening of the first pair of arms has met the at least one predetermined control parameter.

James & Wells Ref: 300357/73 P23051-NZ-PRI According to another aspect of the present invention there is provided an article of manufacture having computer storage medium storing computer readable program code executable by a computer to implement a method of operating a timber-working device including a cutting device, the code including: computer readable program code receiving a signal indicating initiation of closure of a second pair of arms to grasp at least one stem currently grasped by a first pair of arms; computer readable program code opening the first pair of arms in accordance with at least one predetermined control parameter in response to the signal indicating initiation of closure of the second pair of arms, and during closure of the second pair of arms; and computer readable program code closing the first pair of arms once the opening of the first pair of arms has met the at least one predetermined control parameter.

The timber-working device may be a forestry or harvester head, and may be referred to as such throughout the specification. Forestry heads typically have the capacity to grapple and fell a standing tree, delimb and/or debark a felled stem, and cut the stem into logs. However, a person skilled in the art should appreciate that the present invention may be used with other timber-working devices, and that reference to the timber-working device being a forestry head is not intended to be limiting.

In an exemplary embodiment, at least one of the pairs of arms may include a first drive arm and a second drive arm.

The use of opposing drive arms, one on each side of a feed axis of the frame of the head, is well known in the art. Each drive arm may include a drive mechanism at the end of the arm distal from its pivotal connection to the frame – for example a rotary drive coupled with a feed wheel configured to be brought in contact with stem. The drive arms may be actuated, for example by hydraulic cylinders, to pivot relative to the frame in order to grapple the stem with the feed wheels. Rotation of the feed wheels may then drive or feed the stems along the feed axis of the head.

In an exemplary embodiment the timber-working device may further include one or more frame mounted drive mechanisms. For example, a frame mounted feed wheel may be positioned on either side of the feed axis, which may be controlled independently to each other. Where two stems are grasped by the drive arms, these frame mounted wheels may be controlled together with those of the respective drive arms to independently control the relative positions of the two stems along the feed axis.

It should be appreciated that this is not intended to be limiting, and the timber-working device may include only a single frame mounted feed wheel, for example aligned with the feed axis. If James & Wells Ref: 300357/73 P23051-NZ-PRI the timber-working device were to process two stems and it was desirable to feed the stems independently, the frame mounted wheel may be locked or permitted to spin freely, with the arm mounted feed wheels used to control feeding.

In an exemplary embodiment, at least one of the pairs of arms may include a first delimb arm and a second delimb arm.

Pivoting delimb arms are also known in the art, having sharpened edges to cut limbs from the stem as it is driven by the feed wheels. Such delimb arms may be substantially narrower in thickness at the distal ends from the frame in comparison with the drive arms, and so more readily used to select and pick up one or more stems from a deck (a stack of felled stems).

The drive arms may then be closed to grasp the stem(s) to carry out further processing.

In an exemplary embodiment, the first pair of arms may be a first delimb arm and a second delimb arm, and the second pair of arms may be a first drive arm and a second drive arm. For clarity, throughout the remainder of the specification the first pair of arms may be described as being the first delimb arm and the second delimb arm, and the second pair of arms described as being the first drive arm and the second drive arm. However, it should be appreciated that this is not intended to be limiting.

In exemplary embodiments, the timber-working device may be attached to a carrier vehicle by way of a tilt bracket – enabling transition between a standing position (in which the device may grasp a standing tree), and a prone position (in which the device may grasp a stem in a horizontal orientation). It is envisaged that embodiments of the method described herein may be performed while the device is in the prone position, in which gravity may assist with operation.

The value of the predetermined control parameter may be such that the delimb arms are opened to an extent that the one or more stems are permitted to move within the space between the delimb arms, but retained therein.

During this time in which they are not held against the frame or frame mounted feed wheel(s), the one or more stems may settle towards the lowest point of that space. The angle of the arms relative to the frame means that this settling may result in the stems being funnelled towards the centre by the arms.

This effect also occurs between the feed wheels of the drive arms as they close, so that the one of more stems have an opportunity to settle into a central position between the feed wheels of those arms. Because the respective pairs of delimb arms and drive arms are longitudinally offset from each other along the feed axis of the frame, the stems settle at two longitudinally offset points, aligning them along their length with the centre of the timber-working device.

James & Wells Ref: 300357/73 P23051-NZ-PRI This increases the likelihood of the stems being held against the frame, or one or more feed wheels, centrally relative to the feed axis on completion of closure of the drive arms. This in turn increases the likelihood of the feed wheels acting evenly against the one or more stems, without requiring operator intervention to make adjustments to achieve this.

In order to retain the one or more stems, and prevent them from falling from the control of the timber-working device, the control parameter may be such that the delimb arms do not open to an extent that the one or more stems can pass between them – at least until the drive arms have closed.

In an exemplary embodiment, the value of the predetermined control parameter may be such that the delimb arms remain overlapping during opening of the delimb arms. Reference to the delimb arms overlapping should be understood to mean an intersection of the delimb arms when viewed along the feed axis of the frame.

In an exemplary embodiment, the value of the control parameter may be such that the distance between the delimb arms does not exceed the diameter of the at least one stem.

In an exemplary embodiment, the timber-working device may include at least one angular position sensor configured to output a signal indicative of an associated arm relative to the frame.

The angular position sensor may be any suitable means known to a person skilled in the art for determining rotation of the arm or arms – whether absolute or incremental. For example, the angular position sensor may be a rotary encoder.

It should be appreciated that the angular position sensor may not directly measure rotation of the arm. For example, the angular position sensor may be configured to output a signal indicative of the position of a linear actuator driving the pivoting arm. Reference to the position of the linear actuator should be understood to mean the position of a point on the actuator which may be used to determine the degree to which the actuator is extended. For example, the linear actuator may be a hydraulic cylinder including a linear position sensor. Various technologies are known in the art for achieving this – for example operating using magnetostrictive principles, or Hall-Effect. Given known geometries of the head, the position of the actuator may be used to derive the angular position of the arm, or arms.

The angular position of at least one of the arms may be used in conjunction with the known geometry of the frame to determine the relative position of various points on the device, and thereby geometry of the stem(s) being grasped by the arms – particularly diameter.

James & Wells Ref: 300357/73 P23051-NZ-PRI It should be appreciated that reference to obtaining the diameter of a stem using the angular position of an arm is not intended to be limiting. For example, acoustic and optical diameter sensing systems have been proposed in the art.

In an exemplary embodiment, the steps of opening the delimb arms in accordance with the control parameter and subsequently closing the delimb arms may not be initiated where a measured diameter of the one or more stems exceeds a threshold diameter value. It is envisaged that stems having a diameter beyond this threshold may be less prone to misalignment and therefore not require the process to be performed. It should be appreciated that such a threshold may vary between timber-working devices of different capacities and configurations.

In an exemplary embodiment, the predetermined control parameter may be a time period.

It should be appreciated that the value of the time period for the control parameter may be influenced by a number of factors associated with the timber-working device such as geometry of the frame and arms, and/or rate of movement of the arms. Further influences may include the extent to which the arms are to be opened, as discussed previously.

In an exemplary embodiment the value of the time period may be determined, at least in part, by a measured characteristic of the stem. For example, where the delimb arms are not to be opened beyond the measured diameter of the stem, the time period may be set accordingly.

In an exemplary embodiment, the predetermined control parameter may be an arm angle relative to the frame. As discussed above, given known geometry of components of the frame, arm angle may be correlated with aspects of operation such as distance between the arms.

In an exemplary embodiment, closure of the first delimb arm and the second delimb arm may be controlled in accordance with a second predetermined control parameter.

For example, the second control parameter may be a time period. The time period may the same as the time period set for the first control parameter, although this is not intended to be limiting.

In an exemplary embodiment, the second control parameter may be force applied by an actuator of the arm. For example, it is known in the art to control pressure of hydraulic actuators of the pivoting arms to close the arms to achieve a desired clamping pressure against the stems. When the pressure of the cylinder is determined to be such that it is indicative of the stem being grasped against the frame, or frame mounted wheels, the first and second delimb arms may be determined to be sufficiently closed.

In an exemplary embodiment, closure of the first delimb arm and the second delimb arm may James & Wells Ref: 300357/73 P23051-NZ-PRI be interrupted by a signal indicating a user input. For example, the operator may input a command to feed the one or more stems, at which time the delimb arms may be controlled to close (or open) to a position suitable for that operation.

In an exemplary embodiment, the automated process of opening the delimb arms in accordance with the control parameter and subsequently closing the delimb arms may be prevented until a particular operating state of the timber-working device is achieved.

In an exemplary embodiment, this state may be one by which the controller may determine that processing of a previous stem has been completed – for example after the drive arms have opened to reach a pre-defined diameter reading.

In an exemplary embodiment, the predetermined control parameter may be selected from a plurality of control parameters based at least in part on an indication of the number of stems currently being processed by the head.

For example, a control parameter may be set for each of single stem processing, or multiple stem processing. The appropriate control parameter could then be selected based on the indicated number of stems. The indication of the number of stems may be initiated by an operator of the timber-working device. For example, the operator may manually select a single or multiple stem processing mode on an operator input device, generating a signal indicative of the input for transmission to the controller. As the operator is continuously observing the timber-working device and its operation, selection of the number of stems being processed is envisaged as being a straightforward and intuitive step.

However, it should be appreciated that this is not intended to be limiting, and that embodiments may be implemented with automated detection or determination of the number of stems. In some embodiments the stem count device may be a general purpose controller, having other functions within the context of operating the timber-working device.

By way of example, a first angular position sensor may be provided to output a signal indicating an angular position of at least one of the delimb arms, and a second angular position sensor may be provided to output a signal indicating an angular position of at least one of the drive arms. The controller may be configured to receive the signals indicating the respective angular positions of the delimb arm and the drive arm, and correlate the angular position of the delimb arm with the angular position of the drive arm to determine the number of stems currently grasped by the timber-working device.

As the collective profile of the stems varies from the generally circular shape as in the case of a single stem, the relationship between the angular positions of the drive and delimb arms may also change. This may enable correlation of these angles to determine the number of stems held by the arms.

James & Wells Ref: 300357/73 P23051-NZ-PRI In an exemplary embodiment, determination of the number of stems may be performed using pressure plates with associated pressure switches disposed laterally across the feed axis of the frame. Pressure applied to the plates due to one or more stems bearing against them when grasped by the drive or delimb arms may trigger the pressure switches. The number of stems held may be inferred by the pattern or lateral spread of the triggered switches.

For example, where three pressure plates are positioned across the frame – one centred on the feed axis and one laterally offset from the feed axis on either side – triggering of the switch associated with the central plate, but not the others, may be indicative of a single stem being processed. In contrast, triggering of the switches associated with the lateral plates, but not the central plate, may be indicative of two stems being processed.

In an exemplary embodiment there is provided a method of locating at least one stem relative to a feed axis of a frame of a timber-working device having a first pair of arms, and a second pair of arms, each arm pivotally attached to the frame, the method including the steps of: receiving, at a controller, a signal indicating a request from the operator to centre at least one stem currently grasped by the second pair of arms; controlling the position of the first pair of arms such that the distance between ends of the first pair of arms distal from the frame does not exceed a predetermined distance; and opening the second pair of arms in accordance with a predetermined control parameter; closing the second pair of arms once the opening of the second pair of arms has met the predetermined control parameter.

In an exemplary embodiment the first pair of arms may be a first drive arm and a second drive arm, and the second pair of arms may be a first delimb arm and a second delimb arm. In another exemplary embodiment the first pair of arms may be a first delimb arm and a second delimb arm, and the second pair of arms may be a first drive arm and a second drive arm.

In an exemplary embodiment, the predetermined distance may be less than a stem thickness measurement of the at least one stem.

In an exemplary embodiment in which the first pair of arms is a first delimb arm and a second delimb arm, the predetermined distance may be such that the delimb arms remain overlapping.

The various illustrative logical blocks, modules, circuits, and algorithm steps described in connection with the embodiments disclosed herein may be implemented as electronic hardware, computer software, or combinations of both. In particular, they may be implemented or performed with one or more controllers having one or more processors, such as a James & Wells Ref: 300357/73 P23051-NZ-PRI microprocessor, or any other suitable means known in the art designed to perform the functions described.

The steps of a method, process, or algorithm and functions described in connection with the embodiments disclosed herein may be embodied directly in hardware, in a software module executed by a processor, or in a combination of the two. If implemented in software, the functions may be stored as processor readable instructions or code on a tangible, non-transitory processor-readable medium – for example Random Access Memory (RAM), flash memory, Read Only Memory (ROM), hard disks, a removable disk such as a CD ROM, or any other suitable storage medium known to a person skilled in the art. A storage medium may be connected to the processor such that the processor can read information from, and write information to, the storage medium.

BRIEF DESCRIPTION OF DRAWINGS Further aspects of the present invention will become apparent from the following description which is given by way of example only and with reference to the accompanying drawings in which: is a side view of an exemplary timber-working system including, for example, a forestry head; is an elevated view of the forestry head; is a diagrammatic view of an exemplary control system for the timber-working system; is a flowchart illustrating an exemplary method for operating a timber-working device; -4C are end views of the forestry head in various stages of operating in accordance with the exemplary method; is a flowchart illustrating an exemplary method for determining the number of stems grasped by a forestry head, and is a line graph showing an exemplary relationship between the angular position of a delimb arm relative to the angular position of a drive arm of a forestry head.

James & Wells Ref: 300357/73 P23051-NZ-PRI DETAILED DESCRIPTION illustrates a timber-working system including a carrier 10 for use in forest harvesting.

The carrier 10 includes an operator cab 12 from which an operator (not shown) controls the carrier 10. The carrier 10 further includes a boom assembly 14, to which a timber-working device in the form of a forestry head 16 is connected.

Connection of the head 16 to the boom assembly 14 includes a rotator 18, configured to rotate the head 16 about the generally vertical axis of rotation marked by dashed line 20. A tilt bracket 22 further allows rotation of the head 16 between a prone position (as illustrated) and a standing position.

Referring to , the head 16 includes a frame 24 to which the tilt bracket 22 of is pivotally attached. Right hand (RH) and left hand (LH) delimb arms 26a and 26b are pivotally attached to the frame 24, as are opposing RH and LH feed arms 28a and 28b. RH and LH feed wheels 30a and 30b are attached to RH and LH feed arms 28a and 28b respectively, which together with RH and LH frame-mounted feed wheels 32a and 32b may be controlled to feed one or more stems (not illustrated) along feed axis 34 of the head 16. Feed wheels 30a, 30b, 32a and 32b may collectively be referred to as the ‘feed mechanism.’ A measuring wheel 36 may be used to measure the length of the stem as it passes.

A main chainsaw 38, and a topping chainsaw 40, are attached to the frame 24. The main saw 38 is typically used to fell a tree when the head 16 is in a harvesting position, and to buck stems into logs in the processing position of the head 16 (as seen in . The topping saw 40 may be used to cut off a small-diameter top portion of the stem(s) to maximize the value recovery of the trees.

The various operations of the head 16 may be controlled by the operator using hand and foot controls as known in the art. Further, certain automated functions of the harvester head 16 may be controlled by an electronic control system 200 as shown by The control system 200 includes one or more electronic controllers, each controller including a processor and memory having stored therein instructions which, when executed by the processor, causes the processor to perform the various operations of the controller.

For example, the control system 200 includes a first controller 202 on board the carrier 10 and a second controller 204 on board the head 16. The controllers 202, 204 are connected to one another via a communications bus 206 (e.g., a CAN bus, or a wireless link).

A human operator operates an operator input device 208, for example hand and foot controls, located at the operator’s cab 12 of the carrier 10 to control the head 16. Details of operation James & Wells Ref: 300357/73 P23051-NZ-PRI are output to an output device 210 – for example a monitor. Certain automated functions may be controlled by first controller 202 and/or second controller 204.

The system 200 includes angular position sensors – for example at least one delimb rotation sensor 212a mounted to one or both of delimb arms 26a or 26b, and at least one feed rotation sensor 212b mounted to one or both of feed arms 28a or 28b – each configured to output a signal indicative of the angular position of the associated arm for transmission to first controller 202 via second controller 204 and bus 206.

The head 16 has a number of valves 214 arranged, for example, in a valve block and coupled electrically to the second controller 204 so as to be under its control. The valves 214 include, for example, delimb arm valves 216 configured to control pivotal movement of the delimb arms 26a and 26b, and feed arm valves 218 configured to control pivotal movement of the feed arms 28a and 28b.

The control system 200 is configured to implement method 300 of , which will be described with reference to FIGS. 1A, 1B, and 2, together with through 4C showing the head 16 in use.

In step 302, a human operator operates the operator input device 208 to grasp one or more stems (for example stem 400) with the delimb arms 26a and 26b, such that the stem(s) is held against the frame-mounted feed wheels 32a and 32b – as illustrated in .

In step 304, delimb rotation sensors 212a transmits a signal indicating the angular position of the associated delimb arms 26a and 26b to the first controller 202 via second controller 204 over bus 206. This angular position measurement is used to determine the diameter(s) of the one or more stems 400.

In step 306, if the diameter measurement is greater than a predetermined threshold, the first controller 202 exits the remainder of the control routine of method 300. If the diameter measurement is below the threshold, the controller 202 awaits further input by the operator.

In step 308, on receiving an indication of initiation of closure of the feed arms 28a and 28b – for example by way of a signal from the operator input device 208 – the first controller 202 transmits instructions to the second controller 204 to close the feed arms 28a and 28b. The first controller 202 also transmits instructions to open the delimb arms 26a and 26b in accordance with a first predetermined control parameter – for example a time period.

In step 310 the second controller 204 operates the various valves 116 and 118 to close the feed arms 28a and 28b, and open the delimb arms 26a and 26b. During this step, the stem 400 falls towards a lowest within the space between the delimb arms 26a and 26b – as James & Wells Ref: 300357/73 P23051-NZ-PRI illustrated in – to centralise the stem 400 between the delimb arms 26a and 26b.

As the feed arms 28a and 28b continue to close, the feed wheels 30a and 30b are brought into contact with the stem 400 at a position longitudinally offset from the delimb arms 26a and 26b.

This also serves to centralise the stem 400 at that point, with the combination of the two sets of arms serving to align the stem 400 relative to the feed axis 34 (illustrated in ).

In step 312, once the predetermined threshold has been reached the second controller 204 controls the delimb arm valves 116 to close the delimb arms 26a and 26b – for example for a closing time period equivalent to that used during opening of the delimb arms 26a and 26b – until the stem 400 is held against the frame mounted feed wheels 32a and 32b by both the feed wheels 30a and 30b, and delimb arms 26a and 26b, as illustrated in .

In an exemplary embodiment, performance of steps 304 to 312 may be influenced by the number of stems grasped by the delimb arms 26a and 26b in step 302.

In an embodiment, an indication of the number of stems may be transmitted to first controller 202 following input into the operator input device 208 from the operator. In another embodiment an automated method 500 for determining the number of stems may be performed – described herein with reference to In step 502, rotation sensors 212a and 212b transmits signals indicating the angular positions of the respective associated arms to the first controller 202 via second controller 204.

In step 504 the first controller 202 correlates the angular position of the delimb arm 26a or 26b with the angular position of the drive arm 28a or 28b to determine the number of stems currently grasped by the head 16. illustrates an exemplary relationship between the angular position of RH delimb arm 26a and the angular position of RH feed arm 28a. The line designated at 600 represents the relationship in the case of grasping a single stem, and the line designated at 602 represents the relationship in the case of grasping two stems.

It may be seen that there is the relationship between the RH delimb arm 26a and RH drive arm 28a may be distinguished between the two cases (single stem 600 and two stems 602). It should be appreciated that exact angular position values may vary between head configurations and geometries, but that the general principle applies.

Determination of the number of stems may thus be achieved, for example, by referencing the angular position of the RH drive arm 28a and comparing the angular position of the RH delimb arm 26a with a threshold delineating the two cases (see line designated at 604).

James & Wells Ref: 300357/73 P23051-NZ-PRI As an example, where the angular position of the RH drive arm 28a is 25 degrees, if the angle of the RH delimb arm 26a is less than 64 degrees the first controller 202 determines that a single stem is currently grasped by the head 16. If the angle of the RH delimb arm 26a is greater than 64 degrees the first controller 202 determines that two stems are currently grasped by the head 16.

The entire disclosures of all applications, patents and publications cited above and below, if any, are herein incorporated by reference.

Reference to any prior art in this specification is not, and should not be taken as, an acknowledgement or any form of suggestion that that prior art forms part of the common general knowledge in the field of endeavour in any country in the world.

Embodiments described herein may also be said broadly to consist in the parts, elements and features referred to or indicated in the specification of the application, individually or collectively, in any or all combinations of two or more of said parts, elements or features.

Where in the foregoing description reference has been made to integers or components having known equivalents thereof, those integers are herein incorporated as if individually set forth.

It should be noted that various changes and modifications to the presently preferred embodiments described herein will be apparent to those skilled in the art. Such changes and modifications may be made without departing from the spirit and scope of the disclosure and without diminishing its attendant advantages. It is therefore intended that such changes and modifications be included within the present invention.

Embodiments have been described by way of example only and it should be appreciated that modifications and additions may be made thereto without departing from the scope thereof as defined in the appended claims.

James & Wells Ref: 300357/73 P23051-NZ-PRI

Claims (9)

CLAIMS 1.:

1. A method of locating at least one stem relative to a feed axis of a frame of a timber- working device having a first pair of arms and a second pair of arms, each pivotally attached to the frame, the method including the steps of: receiving, at a controller, a signal indicating initiation of closure of the second pair of arms to grasp at least one stem currently grasped by the first pair of arms; in response to the signal indicating initiation of closure of the second pair of arms, and during closure of the second pair of arms, opening the first pair of arms in accordance with at least one predetermined control parameter; and closing the first pair of arms once the opening of the first pair of arms has met the at least one predetermined control parameter.

2. A method as claimed in claim 1, wherein the value of the predetermined control parameter is such that the first pair of arms remain overlapping during opening of the first pair of arms.

3. A method as claimed in claim 1, wherein the value of the predetermined control parameter is such that the distance between the first pair of arms does not exceed the diameter of the at least one stem.

4. A method as claimed in any one of claims 1 to 3, wherein the steps of opening the first pair of arms in accordance with the control parameter and subsequently closing the first pair of arms are not initiated where a measured diameter of the one or more stems exceeds a threshold diameter value.

5. A method as claimed in any one of claims 1 to 4, wherein the predetermined control parameter is a time period.

6. A method as claimed in any one of claims 1 to 4, wherein the predetermined control parameter is an arm angle of at least one of the first pair of arms relative to the frame.

7. A method as claimed in any one of claims 1 to 6, wherein the value of the predetermined control parameter is determined, at least in part, by a measured characteristic of the stem.

8. A method as claimed in claim 7, wherein the measured characteristic of the stem is diameter.

9. A method as claimed in any one of claims 1 to 8, wherein closure of the first pair of arms is controlled in accordance with a second predetermined control parameter. James & Wells Ref: