Timber-working head and method of operation

A timber-working head and method of operation are provided. The head has a frame to which first and second arms are pivotally connected. Respective linear drive actuators pivot the respective arms relative to the frame to open and close them. At least one processor controls application of pressure by the linear drive actuators such that the arms grasp timber to be processed by the head. The position of the linear actuators is used to determine whether the timber is offset from a feed axis of the frame beyond a predetermined distance, and the application of pressure by one of the linear actuators to reduce the offset to be within the predetermined distance.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application claims priority under 35 U.S.C. § 119 to New Zealand Patent Application No. 607713, filed Feb. 28, 2013, the entire contents of which are incorporated herein by reference.

STATEMENT OF FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

FIELD OF THE DISCLOSURE

The present disclosure relates to a timber-working head, and more particularly to a system and method for controlling pivoting arms of a timber-working head.

BACKGROUND OF THE DISCLOSURE

It is well-known to mount a timber-working head, for example in the form of a harvesting head, to a forestry work machine to perform a number of functions in connection with timber. Such heads may be used to grapple and fell a standing tree and process the felled tree by delimbing, possibly debarking (depending on the configuration of the head), and cutting the stem of the tree into logs of predetermined length.

Processing the felled tree typically involves feeding the resulting stem along its length relative to the head using a feed mechanism. One well known system uses arm mounted hydraulic rotary drives having a feed wheel at the end of each arm. The arms may be driven by hydraulic cylinders to pivot relative to the frame of the head in order to grapple the stem with the feed wheels, which may then be driven in the desired direction. In order to ensure that the stem is firmly grasped in the desired centre position, a mechanical link between the arms is used so they open and close together.

However, the stems processed by the harvester head may be ill-formed, for example having sweep (i.e. variation in the axial linearity of the stem) or other contour irregularities (e.g. bulges, depressions, lack of circularity). In such cases the fixed relationship of the arms relative to each other means that one feed wheel may have a different degree of contact with the stem surface than the other, impacting on traction. This can cause hydraulic oil to bypass, leading to one wheel slipping and spinning—causing less than optimal feed performance and potentially damage to the stem by the slipping wheel ripping into the surface. There can also be further ramifications in terms of damage to the motors themselves as the result of this slipping and motor cavitation.

The mechanical link also adds weight and complexity to the harvester—particularly in the steel support frame and pins required for pivotal connection—which in turns adds to the cost of manufacture. These also create potential points of mechanical failure, particularly where ill-formed stems lead to an imbalance of forces being applied to the two arms—essentially attempting to rip them apart. As the operation of the feed arms is a crucial component of many, if not all, of the functions of a harvester head, time required to repair the link may reduce the productivity of the forestry work machine.

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 reference states what their authors assert, and the applicants reserve the right to challenge the accuracy and pertinence 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 forms parts of the common general knowledge in the art, in New Zealand or in any other country.

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 disclosure will become apparent from the ensuing description which is given by way of example only.

SUMMARY OF THE DISCLOSURE

According to an embodiment of the present disclosure there is provided a timber-working head. The head may comprise a frame. A first arm and a second arm may be pivotally connected to the frame, wherein pivotal movement of the first arm is mechanically independent to pivotal movement of the second arm. A first linear drive actuator may be connected to the first arm, and a second linear drive actuator may be connected to the second arm. The linear actuators may be configured to pivot the respective arms relative to the frame to open and close them.

According to another embodiment of the present disclosure there is provided a timber-working head. The head may comprise a frame. A first arm and a second arm may be pivotally connected to the frame. A first linear drive actuator may be connected to the first arm, and a second linear drive actuator may be connected to the second arm. The linear actuators may be configured to pivot the respective arms relative to the frame to open and close them. At least one processor may be configured to control application of pressure by the first and second linear drive actuators such that the arms grasp timber to be processed by the head. The at least one processor may determine whether the position of the linear actuators indicates that the timber is offset from a feed axis of the frame beyond a predetermined distance. The at least one processor may control application of pressure by either the first linear actuator or the second linear actuator to reduce the offset to be within the predetermined distance.

According to another embodiment of the present disclosure there is provided a method of operating a timber-working head comprising a frame, a first arm and a second arm pivotally connected to the frame, and a first linear drive actuator connected to the first arm, and a second linear drive actuator connected to the second arm. The method may comprise applying pressure by the first and second linear drive actuators such that the arms grasp timber to be processed by the head. It may be determined whether the position of the linear actuators indicates that the timber is offset from a feed axis of the frame beyond a predetermined distance. Pressure applied by either the first linear actuator or the second linear actuator may be controlled to reduce the offset to be within the predetermined distance.

According to an exemplary embodiment of the disclosure there is provided an electronic control device for a timber-working head comprising a frame, a first arm and a second arm pivotally connected to the frame, and a first linear drive actuator connected to the first arm, and a second linear drive actuator connected to the second arm. The control device may comprise at least one processor configured to control application of pressure by the first and second linear drive actuators such that the arms grasp timber to be processed by the head. The at least one processor may determine whether the position of the linear actuators indicates that the timber is offset from a feed axis of the frame beyond a predetermined distance. The at least one processor may control application of pressure by either the first linear actuator or the second linear actuator to reduce the offset to be within the predetermined distance.

According to another exemplary embodiment there is provided an article of manufacture having computer storage medium storing computer readable program code executable by a computer to implement a method for operating a timber-working head comprising a frame, a first arm and a second arm pivotally connected to the frame, and a first linear drive actuator connected to the first arm, and a second linear drive actuator connected to the second arm. The code may comprise computer readable program code applying pressure to the first and second linear drive actuators such that the arms grasp timber to be processed by the head. The code may comprise computer readable program code determining whether the position of the linear actuators indicates that the timber is offset from a feed axis of the frame beyond a predetermined distance. The code may comprise computer readable program code controlling pressure applied to either the first linear actuator or the second linear actuator to reduce the offset to be within the predetermined distance.

In an exemplary embodiment the timber-working head may a harvester head, and may be referred to as such throughout the specification. Harvester 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 disclosure may be used with other timber-working heads, for example a feller buncher, debarking and/or delimbing head, disc saw head, saw grapple, and so on—and that reference to the timber-working head being a harvester head is not intended to be limiting.

As such, in an exemplary embodiment the arms may be feed arms, each comprising a feed wheel configured to be brought in contact with timber. The feed wheels may each be connected to a rotary drive such that they may be used to feed the timber along a feed axis of the head. However, it should be appreciated that the present disclosure may be applied to other arms of the timber-working head, for example delimb arms.

In an exemplary embodiment, pivotal movement of the first arm may be mechanically independent to pivotal movement of the second arm. Reference to the pivotal movement of the arms being mechanically independent should be understood to mean the absence of a physical link causing one arm to pivot relative to the frame when corresponding pivotal movement of the other arm occurs. It may be said that the arms can pivot independent of one another, although it should be appreciated that control of each arm may be influenced by movement of the other.

In an exemplary embodiment the linear drive actuators may be hydraulically driven. Reference will herein be made throughout the specification to the linear actuator being a hydraulic cylinder, however is should be appreciated that other actuator types—for example electric or pneumatic—may be used in embodiments of the disclosure.

In an exemplary embodiment each of the first and second drive cylinders may be configured to output a signal indicative of the position of the cylinder. Reference to the position of the cylinder should be understood to mean the position of a point on the cylinder which may be used to determine the degree to which the cylinder is extended. For example, the cylinder may comprise a linear position sensor. Various technologies for sensing linear position are known in the art—for example operating using magnetostrictive principles, or Hall-Effect.

In an exemplary embodiment the timber-working head may comprise a controller configured to control operation of the first and second cylinders. In particular, it is envisaged that the controller may be configured to control pressure applied by the first and second linear actuators.

The controller may be configured to initially control pressure applied by the first and second linear actuators to be equal on receiving a command signal from an operator to close the arms. In doing so, it is envisaged that the arms may “float”—pressing against the surface of the timber, but being permitted to independently move inwardly or outwardly to maintain contact with the surface to account for irregularities which may be unequal between the sides of the timber.

The controller may be configured to control operation of the cylinders based on their respective positions. In an exemplary embodiment it is envisaged that the controller may be configured to control the pressure applied by one of the cylinders based on the position of the linear actuators indicating that a stem held between the arms is offset from a feed axis of the frame beyond a predetermined distance.

While it may be useful to allow independent movement of the arms to allow for irregularities in the profile of the timber, it may also be desirable to maintain the lateral position of the stem within certain limits relative to the feed axis of the timber-working head. In particular, it may be desirable for the stem to be held roughly centre in order to align it with delimbing blades, and maintain maximum traction by the feed wheels. Further, it may be desirable for the stem to be held such the saw may perform a cut at a substantially 90 degree angle. As the length measurement is taken from the shortest side of a cut log, achieving a square cut may assist in maximizing the value of the log cut.

It should be appreciated that the predetermined distance may vary between different configurations of timber-working heads, particularly with regard to the dimensions of the heads themselves and the diameter of timber expected to be processed. Movement of the stem may generally limited by the harvester body itself. Control of the travel within this may account for maintaining a minimum gap between the harvester and the stem to reduce the likelihood of the stem grating against the side and potentially causing damage to the stem and/or harvester. Variation in the stem due to sweep or other contour irregularities may also be taken into consideration.

In an exemplary embodiment the controller may be that used to control other functions of the timber-working head. However, it should be appreciated that the controller may be one dedicated to performance of the present disclosure and in communication with a control module configured to control general operation of the head.

The various steps or acts in a method or process may be performed in the order shown, or may be performed in another order. Additionally, one or more process or method steps may be omitted or one or more process or method steps may be added to the methods and processes. An additional step, block, or action may be added in the beginning, end, or intervening existing elements of the methods and processes.

The various illustrative logical blocks, modules, circuits, and algorithm steps described in connection with the embodiments disclosed herein may be implemented by a programmed processor executing instructions stored in memory. The functions, acts or tasks are independent of the particular type of instructions set, storage media, processor or processing strategy and may be performed by software, hardware, integrated circuits, firm-ware, micro-code and the like, operating alone or in combination.

The memory may comprise computer-readable media. The term “computer-readable medium” may comprise a single medium or multiple media, such as a centralized or distributed database, and/or associated caches and servers that store one or more sets of instructions. The term “computer-readable medium” may also comprise any medium that is capable of storing, encoding or carrying a set of instructions for execution by a processor or that cause a computer system to perform any one or more of the methods or operations disclosed herein. The “computer-readable medium” may be non-transitory, and may be tangible.

It should be appreciated that in exemplary embodiments one or more dedicated hardware implementations, such as application specific integrated circuits, programmable logic arrays and other hardware devices, can be constructed to implement one or more of the methods described herein. One or more embodiments described herein may implement functions using two or more specific interconnected hardware modules or devices with related control and data signals that can be communicated between and through the modules, or as portions of an application-specific integrated circuit.

DETAILED DESCRIPTION

FIG. 1illustrates an exemplary forestry work machine (generally indicated by arrow1) comprising a carrier2supporting an articulated boom3. An exemplary timber working implement in the form of a harvester head4is connected to an end of the boom3, using a dog-bone joint5connected to a rotator6, which is in turn connected to a frame7of the head4by hanger8. In operation, the head4may swivel relative to the end of the boom3about the rotator6, and pivotally move about its connection to the hanger8between a generally upright, harvesting position for felling a tree (not illustrated) and a generally prone, processing position (as illustrated) for processing the felled tree (e.g., delimbing, debarking, cutting to length).

The harvester head4comprises a pair of grapple or delimbing arms9pivotally connected to the frame7and configured to grasp the stem of the tree. The head4also comprises a pair of feed arms10pivotally connected to the frame7and comprising feed wheels configured to control the longitudinal position of the tree relative to the head4. The harvester head4also comprises a main chain saw at the end marked by arrow11, and a topping chain saw at the end marked by arrow12.

The machine1, particularly harvester head4, may be controlled by an operator (not illustrated) using hand and foot controls as known in the art. A controller (such as that described with reference toFIG. 4) controls operation of the harvester head4in response to data or signals received from various components of the harvester head4and in conjunction with the operator input devices.

FIG. 2illustrates a prior art feed arm system200for a harvester head (such as harvester head4illustrated inFIG. 1). The system200comprises a left-hand (LH) feed arm201and a right-hand (RH) feed arm202. The feed arms201,202are pivotally connected to the frame (not illustrated) by pins203and204respectively, such that the arms201,202may be rotated to bring feed wheels205and206into contact with a tree stem207.

Movement of the arms201,202is driven by hydraulic cylinders208and209respectively. Each cylinder208,209is connected to the frame by pins210and211respectively, and the arms201,202by pins212and213respectively.

The arms201,202are mechanically connected by a timing link214between LH ear215and RH pin216. The arms201,202cannot rotate about pins203,204without affecting movement of the other arm due to the timing link214. The timing link214means that any movement by LH arm201towards or away from vertical centerline217will encourage the mirror movement by RH arm202. As such, where the stem207is irregular in profile, one feed wheel205,206will have greater contact with the stem207than the other. This unequal application of force may shift the stem away from the feed axis (not illustrated, but perpendicular to vertical centerline217) of the harvester head.

FIG. 3illustrates an exemplary feed arm system300according to one aspect of the present disclosure. The system300comprises a left-hand (LH) feed arm301and a right-hand (RH) feed arm302. The feed arms301,302are pivotally connected to the frame (not illustrated) by pins303and304respectively, such that the arms301,302may be rotated to bring feed wheels305and306into contact with a tree stem307.

Movement of the arms301,302is driven by LH and RH hydraulic cylinders308and309respectively. Each cylinder308,309is connected to the frame by pins310and311respectively, and the arms301,302by pins312and313respectively. Extension and retraction of the cylinders308,309through the control of hydraulic pressure supplied to the respective cylinders308,309pivots the arms301,302about pins312,313. The cylinders308,309are each configured to output a signal indicating the position of each cylinder in terms of its extension.

The pivotal movement of each of the arms301,302is mechanically independent to that of the other arm301,302. Unlike the prior art feed arm system200, there is no timing link connecting the arms301,302to prevent independent rotation about pins303,304without affecting movement of the other arm due to the timing link214.

FIG. 4illustrates an exemplary control system400for feed arm system300. The control system comprises a first position sensor401and a second position sensor402associated with hydraulic cylinders308and309respectively. These sensors401,402are configured to output a signal indicative of the position, or extension of the cylinders308,309. It should be appreciated that the sensors401,402may be integrated into the structure of the cylinders308,309, whether internally or externally.

The signals are communicated to a controller403. The controller403comprises a data processor404which may access a look-up table, or apply an algorithm, to determine the respective positions of the cylinders308,309from the signals. The controller403is also in communication with a data storage device405and manages the storage, retrieval or access of reference data406stored thereon. A pressure adjustment module407of the controller403may respond to position data received from the cylinders308,309to control their operation, as will be described further below with reference toFIG. 6. It should be appreciated that reference to the controller403performing certain tasks may comprise those performed by the processor404and/or pressure adjustment module407.

A hydraulic control module409is in communication with the controller403, and is configured to control the delivery of hydraulic fluid to the cylinders308,309. It should be appreciated that the hydraulic control module409may comprise any suitable means known in the art for controlling hydraulic fluid flow, for example solenoids, relays, servo-motors in combination with some form of valve. The hydraulic control module409may be a centralized unit, or comprise components located at the cylinders308,309themselves. It should be appreciated that reference to the controller403controlling operation of the cylinders308,309may comprise operations performed by the hydraulic control module409, although explicit reference to this may not be made.

The controller403is also in communication with a user interface408. The user interface408may comprise a number of user input devices such as hand and foot controls and a touch screen as known in the art for controlling operation of a timber-working head comprising the feed arm system300. It should be appreciated that while the exemplary controller403is illustrated as a single device, this is not intended to be limiting and the functions described may be shared over multiple devices—for example, a first controller associated with the vehicle to which the head is connected, communicating with a second controller associated with the head over a communications bus.

Referring toFIG. 5, the feed arm system300is illustrated in the context of an exemplary timber-working head in the form of harvester head500, having a frame501to which the feed arm system300is connected. The pressure of cylinders (not illustrated) may be independently controlled to have the feed wheels305,306maintain contact with a stem (not illustrated) held between them, while maintaining a desired lateral position of the stem relative to feed axis502of the head500. Along the feed axis502the head500comprises a drive wheel503for use in feeding the stem along the feed axis502, and a toothed measuring wheel (not illustrated) used to measure the length of the stem and its position relative to the head500(in particular main chainsaw504and topping saw505).

FIG. 6illustrates an exemplary method600by which operation of harvester head500, and in particular feed arm system300, may be controlled.

In step601, the controller403receives a command from user interface408to activate the feed arm system300to cause a stem to be grasped by the feed arms301,302.

In step602the controller403causes equal hydraulic pressure to be applied to both cylinders308,309, in turn causing the feed arms301,302to pivot inwardly.

In step603the controller403receives signals from the position sensors401,402and processes these in combination with previously stored position data to determine whether either or both of the cylinders308,309are currently moving. If there is movement, the method proceeds to step604, otherwise the method continues with step612.

In step604, the controller403determines whether the position of the LH cylinder301is ahead of the position of the RH cylinder302by a distance greater than a predetermined value, for example 10 mm. It should be appreciated that this value may be dependent on a number of factors, for example the dimensions of various components of the head500comprising the saws505and506.

If the LH cylinder301is ahead of the RH cylinder302beyond the predetermined distance, this indicates that the stem being processed is off centre from the feed axis502to an undesired extent, and the method proceeds to step605. If not, the method continues with step608. In step605, the controller403determines whether the pressure set point of the RH cylinder309is at a maximum. If so, the set point of the LH cylinder308is reduced in step606, and the resulting reduced pressure differential with the RH cylinder309causes the RH feed arm302to act against the stem to bring it closer to the feed axis502. If the pressure set point of the RH cylinder309is not at maximum, the set point of the RH cylinder309is increased in step607to achieve the same effect. It should be appreciated that control loop feedback, such as PID control, may be used to ramp the accelerations or decelerations for each arm.

Once steps606or607have been performed, the method may return to step603—unless interrupted by a command received from the operator to release the stem.

In step608, a similar routine is followed if the RH cylinder309is ahead of the LH cylinder308is beyond the predetermined distance, and the method proceeds to step609. If not, the method continues with step612. In step609, the controller403determines whether the pressure set point of the LH cylinder308is at a maximum. If so, the set point of the RH cylinder309is reduced in step610, and the resulting reduced pressure differential with the LH cylinder308causes the LH feed arm301to act against the stem to bring it closer to the feed axis502. If the pressure set point of the LH cylinder308is not at maximum, the set point of the LH cylinder308is increased in step611to achieve the same effect. Once steps610or611have been performed, the method may return to step603—unless interrupted by a command received from the operator to release the stem.

If no movement is detected in step603, or if the RH cylinder309is not ahead of the LH cylinder308by the predetermined distance, the method continues in step612where the controller403determines whether the pressure set point of each cylinder308,309is equal. If they are, the method returns to step603—unless interrupted by a command received from the operator to release the stem.

If the set points are not the same, in step613the controller403determines whether the LH cylinder308set point is greater than the RH cylinder309set point. If it is the method proceeds to step614, where the LH cylinder308set point is adjusted to be the same as the RH cylinder309set point. Conversely, if the LH cylinder308set point is less than the RH cylinder309set point the method proceeds to step615, where the RH cylinder309set point is adjusted to be the same as the LH cylinder308set point. Once steps614or615have been performed, the method returns to step603—unless interrupted by a command received from the operator to release the stem.

Aspects of the present disclosure 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.