Abstract:
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.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
       [0001]    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 
       [0002]    Not applicable. 
       FIELD OF THE DISCLOSURE 
       [0003]    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 
       [0004]    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. 
         [0005]    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. 
         [0006]    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. 
         [0007]    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. 
         [0008]    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. 
         [0009]    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. 
         [0010]    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 
       [0011]    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. 
         [0012]    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. 
         [0013]    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. 
         [0014]    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. 
         [0015]    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. 
         [0016]    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. 
         [0017]    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. 
         [0018]    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. 
         [0019]    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. 
         [0020]    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. 
         [0021]    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. 
         [0022]    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. 
         [0023]    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. 
         [0024]    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. 
         [0025]    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. 
         [0026]    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. 
         [0027]    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. 
         [0028]    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. 
         [0029]    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. 
         [0030]    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. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0031]    Embodiments of the present disclosure may be better understood with reference to the following description and accompanying drawings, which are given by way of example only: 
           [0032]      FIG. 1  is a side view of an exemplary forestry work machine comprising an exemplary timber-working head according to one embodiment of the present disclosure; 
           [0033]      FIG. 2  is an end perspective view of a prior art feed arm system; 
           [0034]      FIG. 3  is an end perspective view of an exemplary feed arm system; 
           [0035]      FIG. 4  is a block diagram of an exemplary control system for controlling operation of an exemplary timber-working head; 
           [0036]      FIG. 5  is a front elevation view of an exemplary timber-working head, and 
           [0037]      FIG. 6  is a flow diagram illustrating an exemplary method of controlling an exemplary timber-working head. 
       
    
    
     DETAILED DESCRIPTION 
       [0038]      FIG. 1  illustrates an exemplary forestry work machine (generally indicated by arrow  1 ) comprising a carrier  2  supporting an articulated boom  3 . An exemplary timber working implement in the form of a harvester head  4  is connected to an end of the boom  3 , using a dog-bone joint  5  connected to a rotator  6 , which is in turn connected to a frame  7  of the head  4  by hanger  8 . In operation, the head  4  may swivel relative to the end of the boom  3  about the rotator  6 , and pivotally move about its connection to the hanger  8  between 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). 
         [0039]    The harvester head  4  comprises a pair of grapple or delimbing arms  9  pivotally connected to the frame  7  and configured to grasp the stem of the tree. The head  4  also comprises a pair of feed arms  10  pivotally connected to the frame  7  and comprising feed wheels configured to control the longitudinal position of the tree relative to the head  4 . The harvester head  4  also comprises a main chain saw at the end marked by arrow  11 , and a topping chain saw at the end marked by arrow  12 . 
         [0040]    The machine  1 , particularly harvester head  4 , 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 to  FIG. 4 ) controls operation of the harvester head  4  in response to data or signals received from various components of the harvester head  4  and in conjunction with the operator input devices. 
         [0041]      FIG. 2  illustrates a prior art feed arm system  200  for a harvester head (such as harvester head  4  illustrated in  FIG. 1 ). The system  200  comprises a left-hand (LH) feed arm  201  and a right-hand (RH) feed arm  202 . The feed arms  201 ,  202  are pivotally connected to the frame (not illustrated) by pins  203  and  204  respectively, such that the arms  201 ,  202  may be rotated to bring feed wheels  205  and  206  into contact with a tree stem  207 . 
         [0042]    Movement of the arms  201 ,  202  is driven by hydraulic cylinders  208  and  209  respectively. Each cylinder  208 ,  209  is connected to the frame by pins  210  and  211  respectively, and the arms  201 ,  202  by pins  212  and  213  respectively. 
         [0043]    The arms  201 ,  202  are mechanically connected by a timing link  214  between LH ear  215  and RH pin  216 . The arms  201 ,  202  cannot rotate about pins  203 ,  204  without affecting movement of the other arm due to the timing link  214 . The timing link  214  means that any movement by LH arm  201  towards or away from vertical centerline  217  will encourage the mirror movement by RH arm  202 . As such, where the stem  207  is irregular in profile, one feed wheel  205 ,  206  will have greater contact with the stem  207  than the other. This unequal application of force may shift the stem away from the feed axis (not illustrated, but perpendicular to vertical centerline  217 ) of the harvester head. 
         [0044]      FIG. 3  illustrates an exemplary feed arm system  300  according to one aspect of the present disclosure. The system  300  comprises a left-hand (LH) feed arm  301  and a right-hand (RH) feed arm  302 . The feed arms  301 ,  302  are pivotally connected to the frame (not illustrated) by pins  303  and  304  respectively, such that the arms  301 ,  302  may be rotated to bring feed wheels  305  and  306  into contact with a tree stem  307 . 
         [0045]    Movement of the arms  301 ,  302  is driven by LH and RH hydraulic cylinders  308  and  309  respectively. Each cylinder  308 ,  309  is connected to the frame by pins  310  and  311  respectively, and the arms  301 ,  302  by pins  312  and  313  respectively. Extension and retraction of the cylinders  308 ,  309  through the control of hydraulic pressure supplied to the respective cylinders  308 ,  309  pivots the arms  301 ,  302  about pins  312 ,  313 . The cylinders  308 ,  309  are each configured to output a signal indicating the position of each cylinder in terms of its extension. 
         [0046]    The pivotal movement of each of the arms  301 ,  302  is mechanically independent to that of the other arm  301 ,  302 . Unlike the prior art feed arm system  200 , there is no timing link connecting the arms  301 ,  302  to prevent independent rotation about pins  303 ,  304  without affecting movement of the other arm due to the timing link  214 . 
         [0047]      FIG. 4  illustrates an exemplary control system  400  for feed arm system  300 . The control system comprises a first position sensor  401  and a second position sensor  402  associated with hydraulic cylinders  308  and  309  respectively. These sensors  401 ,  402  are configured to output a signal indicative of the position, or extension of the cylinders  308 ,  309 . It should be appreciated that the sensors  401 ,  402  may be integrated into the structure of the cylinders  308 ,  309 , whether internally or externally. 
         [0048]    The signals are communicated to a controller  403 . The controller  403  comprises a data processor  404  which may access a look-up table, or apply an algorithm, to determine the respective positions of the cylinders  308 ,  309  from the signals. The controller  403  is also in communication with a data storage device  405  and manages the storage, retrieval or access of reference data  406  stored thereon. A pressure adjustment module  407  of the controller  403  may respond to position data received from the cylinders  308 ,  309  to control their operation, as will be described further below with reference to  FIG. 6 . It should be appreciated that reference to the controller  403  performing certain tasks may comprise those performed by the processor  404  and/or pressure adjustment module  407 . 
         [0049]    A hydraulic control module  409  is in communication with the controller  403 , and is configured to control the delivery of hydraulic fluid to the cylinders  308 ,  309 . It should be appreciated that the hydraulic control module  409  may 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 module  409  may be a centralized unit, or comprise components located at the cylinders  308 ,  309  themselves. It should be appreciated that reference to the controller  403  controlling operation of the cylinders  308 ,  309  may comprise operations performed by the hydraulic control module  409 , although explicit reference to this may not be made. 
         [0050]    The controller  403  is also in communication with a user interface  408 . The user interface  408  may 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 system  300 . It should be appreciated that while the exemplary controller  403  is 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. 
         [0051]    Referring to  FIG. 5 , the feed arm system  300  is illustrated in the context of an exemplary timber-working head in the form of harvester head  500 , having a frame  501  to which the feed arm system  300  is connected. The pressure of cylinders (not illustrated) may be independently controlled to have the feed wheels  305 ,  306  maintain contact with a stem (not illustrated) held between them, while maintaining a desired lateral position of the stem relative to feed axis  502  of the head  500 . Along the feed axis  502  the head  500  comprises a drive wheel  503  for use in feeding the stem along the feed axis  502 , and a toothed measuring wheel (not illustrated) used to measure the length of the stem and its position relative to the head  500  (in particular main chainsaw  504  and topping saw  505 ). 
         [0052]      FIG. 6  illustrates an exemplary method  600  by which operation of harvester head  500 , and in particular feed arm system  300 , may be controlled. 
         [0053]    In step  601 , the controller  403  receives a command from user interface  408  to activate the feed arm system  300  to cause a stem to be grasped by the feed arms  301 ,  302 . 
         [0054]    In step  602  the controller  403  causes equal hydraulic pressure to be applied to both cylinders  308 ,  309 , in turn causing the feed arms  301 ,  302  to pivot inwardly. 
         [0055]    In step  603  the controller  403  receives signals from the position sensors  401 ,  402  and processes these in combination with previously stored position data to determine whether either or both of the cylinders  308 ,  309  are currently moving. If there is movement, the method proceeds to step  604 , otherwise the method continues with step  612 . 
         [0056]    In step  604 , the controller  403  determines whether the position of the LH cylinder  301  is ahead of the position of the RH cylinder  302  by 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 head  500  comprising the saws  505  and  506 . 
         [0057]    If the LH cylinder  301  is ahead of the RH cylinder  302  beyond the predetermined distance, this indicates that the stem being processed is off centre from the feed axis  502  to an undesired extent, and the method proceeds to step  605 . If not, the method continues with step  608 . In step  605 , the controller  403  determines whether the pressure set point of the RH cylinder  309  is at a maximum. If so, the set point of the LH cylinder  308  is reduced in step  606 , and the resulting reduced pressure differential with the RH cylinder  309  causes the RH feed arm  302  to act against the stem to bring it closer to the feed axis  502 . If the pressure set point of the RH cylinder  309  is not at maximum, the set point of the RH cylinder  309  is increased in step  607  to 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. 
         [0058]    Once steps  606  or  607  have been performed, the method may return to step  603 —unless interrupted by a command received from the operator to release the stem. 
         [0059]    In step  608 , a similar routine is followed if the RH cylinder  309  is ahead of the LH cylinder  308  is beyond the predetermined distance, and the method proceeds to step  609 . If not, the method continues with step  612 . In step  609 , the controller  403  determines whether the pressure set point of the LH cylinder  308  is at a maximum. If so, the set point of the RH cylinder  309  is reduced in step  610 , and the resulting reduced pressure differential with the LH cylinder  308  causes the LH feed arm  301  to act against the stem to bring it closer to the feed axis  502 . If the pressure set point of the LH cylinder  308  is not at maximum, the set point of the LH cylinder  308  is increased in step  611  to achieve the same effect. Once steps  610  or  611  have been performed, the method may return to step  603 —unless interrupted by a command received from the operator to release the stem. 
         [0060]    If no movement is detected in step  603 , or if the RH cylinder  309  is not ahead of the LH cylinder  308  by the predetermined distance, the method continues in step  612  where the controller  403  determines whether the pressure set point of each cylinder  308 ,  309  is equal. If they are, the method returns to step  603 —unless interrupted by a command received from the operator to release the stem. 
         [0061]    If the set points are not the same, in step  613  the controller  403  determines whether the LH cylinder  308  set point is greater than the RH cylinder  309  set point. If it is the method proceeds to step  614 , where the LH cylinder  308  set point is adjusted to be the same as the RH cylinder  309  set point. Conversely, if the LH cylinder  308  set point is less than the RH cylinder  309  set point the method proceeds to step  615 , where the RH cylinder  309  set point is adjusted to be the same as the LH cylinder  308  set point. Once steps  614  or  615  have been performed, the method returns to step  603 —unless interrupted by a command received from the operator to release the stem. 
         [0062]    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.