Abstract:
A method for controlling the raise/extend function of a work machine is provided. The method comprises sensing the position of a frame and the position of a telescopic boom of the work machine, comparing the sensed positions to a desired position and controlling the raise/extend operation in response to the actual verses the desired positions.

Description:
TECHNICAL FIELD  
         [0001]    The invention relates to a method of controlling the function of a work machine and more particularly to a method of controlling the raise/extend function of a telescopic material handler.  
         BACKGROUND  
         [0002]    Material handling machines, such as telescopic material handlers are faced with stability problems during operation. These machines have these problems because of their high lifting capability, especially when heavy loads are being transported. These problems are even more troublesome when the material handlers are operated on work sites that have uneven terrain and are littered with debris. Many material handlers are provided with high ground clearance involving maintaining as much of the machine as possible elevated from the terrain, especially those elements which extend across the width of the vehicle, such as the axles. While high ground clearance facilitates maneuverability of the material handler it compounds the stability problem because of the elevated center of gravity. The stability problem is particularly acute when the material handlers are required to elevate substantial loads to considerable heights and move about on uneven terrain while balancing the load.  
           [0003]    Heretofore in utilizing material handlers on or over uneven terrain or work surfaces, load spilling and machine stability have sometimes been major operational problems. Various attempts have been made to stabilize material handlers in such situations one example is disclosed in U.S. Pat. No. 3,937,339 issued Feb. 10, 1976 to Geis et al. and assigned to Koehring Company of Milwaukee, Wis. This stabilizing system uses two pair of mercury switches, mounted to the body of the machine, one of the pair being actuated at a time to select between coarse and fine adjustment settings. The system automatically, through the use of a solenoid valve, supplies pressurized fluid to a pair of cylinders to level the body of the machine during operation. This system allows for adjustments to counter act uneven terrain while traversing a work sight and during a load lifting operation. However, this system can cause a load to be dumped due to rapid adjustments, inadvertent contact with an obstacle during lifting, let alone the uneasiness in the ride felt by an operator during an adjustment while traversing a work site.  
           [0004]    The present invention is directed to overcoming one or more of the following problems as set forth above.  
         SUMMARY OF THE INVENTION  
         [0005]    In one aspect of the present invention a method for controlling a boom raise/extend function of a work machine is provided. The work machine has a longitudinal frame and a support member. The method includes sensing the pressure at both ends of at least one hydraulic cylinder positioned between the frame and the support member. Comparing the sensed force reacted by the at least one hydraulic cylinder to a desired predetermined limit and controlling the boom raise/extend in response to the sensed force being within a predetermined limit. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]    [0006]FIG. 1 is a side elevation view of a work machine embodying the present invention;  
         [0007]    [0007]FIG. 2 is a front elevation view of a work machine embodying the present invention;  
         [0008]    [0008]FIG. 3 is a schematic diagram illustrating a portion of a hydraulic circuit of the present invention; and  
         [0009]    [0009]FIG. 4 is a flowchart illustrating the various operational steps. 
     
    
     DETAILED DESCRIPTION  
       [0010]    Referring to FIGS. 1 and 2, a work machine such as a telescopic handler  10  is shown. It will be understood that this invention is equally applicable to other work machines, such as forestry machinery and other non-construction related machinery. In general, the work machine  10  comprises a frame  12 , and a telescopic boom  14  that is pivotally mounted to the rear of the frame  12  for elevation to various angles relative to the frame  12 . The telescopic boom  12  is extended and retracted by a hydraulic cylinder (not shown) and is raised and lowered by cylinders  15  (only one shown in FIG. 1). In addition, an operator cab  16  is provided on one side of the frame  12 , and an engine enclosure  18  is provided opposite the boom  14 , so that the boom  14 , when lowered, extends between the cab  14  and the engine enclosure  18 .  
         [0011]    Front and rear support members such as axles  20 , 22  are pivotally mounted on the frame  12  for oscillating motion about a pivot point  24  parallel to the center-line of the frame  12 . The axles  20 , 22  carry front and rear wheels  26  of equal size, steered by means of hydraulic cylinders in a known manner. At least one hydraulic cylinder  28  is pivotally connected between the frame  12  and the front axle  20  and used to level the frame  12  relative to the ground, one cylinder may be used on either side of pivot point  24  may be used as well, when the machine  10  is operating on uneven terrain. As an alternative, some work machines include a support member  21  attached to the frame  12 . As shown in phantom in FIG. 2, support member  21  is an outrigger arrangement that includes a pair of legs  23  that are each controlled by cylinders  27 . Graphically represented on the cab  14  in FIGS. 1 and 2 is an electronic control module  30 . A first inclinometer  32  is shown attached to the cab  16  in FIG. 2 and a second inclinometer  34  is attached to the telescopic boom  15  in FIG. 1. Both inclinometers  32 , 34  are connected to the electronic control module  30  as by wire and receive signals therefrom related to the angular position of the frame  12  and the boom  15  respectively.  
         [0012]    Referring now to FIG. 3 a portion of a lateral stabilization circuit  36  is shown. Lateral stabilization circuit  36  includes a supply conduit  38  that connects a source of pressurized fluid (not shown) to a control valve  40 . A return conduit  42  drains the pressurized fluid back from the control valve  40  to a reservoir (not shown). Control valve  40  is a three position, four-way solenoid valve of any of a number of given configurations that is connected to hydraulic cylinder  28  via a conduit  44  and a conduit  46 . It should be understood that at least one of hydraulic cylinders  27  may be used in the representative circuit as an alternative without departing from the gist of this disclosure. Positioned in each of the conduits  44 , 46  is a counter balance valve  48 . In this example the counter balance valve  48  is used as a safety device that includes a pilot input  50  and a relief setting arrangement  52 . The counter balance valve  48  positioned in conduit  46  includes a pilot line  54  connecting the pilot input  50  to conduit  44 , while the counter balance valve  48  positioned in conduit  44  includes a pilot line  54  connecting the pilot input  50  to conduit  46 . A check valve  56  is positioned in parallel to each of the counter balance valves  48  so that fluid flow from the cylinder  28  is blocked. Additionally, connected to conduits  44 , 46  between the counter balance valves  48  and the control valve  40  is a resolver  58  that drains to a signal line  60 . Signal line  60  sends a fluid signal representative of load to a controller (not shown) such as a pump controller as is commonly known.  
         [0013]    Referring now to FIG. 4 a method for controlling the lateral stability of work machine  10  is illustrated. The controller  30  receives signals from various operator inputs such as a joystick, control lever or similar input device (not shown) requesting a desired raise/extend operation of the telescopic boom  14  and from the first and second inclinometers  32 , 34 . A calculation block  62  compares the actual position of the frame  12  and the telescopic boom  14  and compares the angular readings from the inclinometers  32 , 34  to stored data such as maps look up tables and the like in decision block  64 . If the frame  12  is within a predetermined limit or the raise/extend request does not put the work machine  10  in an unstable position a control block  66  of the controller  30  allows signals from the operator controls (not shown) providing full functionality of the telescopic boom  14 . Additionally, the level function is locked at this point in a control block  68 . If the frame  12  is not within the predetermined limit the controller  30  compares the frame  12  position and the telescopic boom  14  position signals from inclinometers  32 , 34  respectively, in a decision block  70  to see if any movement of the telescopic boom  14  will place the machine in an unstable position. If the frame  12  is not within the predetermined limit and any raise/extend request places the work machine  10  in an unstable position, from block  70 , a control block  72  of the controller  30  disables operator controls for raise/extend function. However, lower/retract functionality is still provided. At this point the operators options are provided in a control block  74  and allow the operator to send a signal through an operator input (not shown) to request the controller  30  to send a signal to control valve  34  to shift, allowing pressurized fluid to flow to either hydraulic cylinder  28  or at least one of hydraulic cylinders  27  to provide an automatic leveling function. If the frame  12  is not within the predetermined limit and a raise/extend request will not place the work machine  10  in an unstable position (i.e. the extend/raise is within a predetermined range) in block  70 , a control block  76  always operator control to provide limited raise/extend function until the controller  30  receives signals from inclinometer  34  representative of an unstable position, the controller  30  then disables operator controls for raise/extend function in control block  72 .  
       Industrial Applicability  
       [0014]    In operation a raise/extend input command is provided to controller  30  from the operator to raise/extend the telescopic boom  14 . To raise/extend the telescopic boom  14 , the controller  30  receives signals from the first and second inclinometers  32 , 34 . The controller  30  compares these signals to stored data related to the lateral orientation of the work machine  10  and position of the telescopic boom  14  in calculation block  62 . The controller  30  then makes a determination of the work machine being in an unstable position in decision block  64 . If the work machine  10  is found to be in a safe lateral orientation control block  66  allows for a load to be raised/extended (i.e. the cylinders  15  to raise telescopic boom  14  or the cylinder to extend telescopic boom  14 ) and the level function is blocked out in control block  68 . The controller  30  determines if a raise/extend request will place the work machine  10  in an unsafe position in decision block  70 . If the work machine  10  is not in a safe lateral orientation control block  72  disables the load raise/extend capability of the work machine  10 . Control block  74  then allows the operator to maneuver the frame  12  by supplying a command to the hydraulic cylinder  27 , 28  to laterally position the work machine  10  in a safe position so that a load can be raised/extended. Or the operator can lower/retract the telescopic boom  14  and reposition the work machine  10  in a laterally stable position. If a raise/extend request will not place the work machine  10  in an un-safe lateral orientation control block  76  allows a limited amount of raise/extend capability of the work machine  10  until just before an un-safe condition then control block  72  disables the load raise/extend capability of the work machine  10 . Control block  74  then allows the operator to maneuver the frame  12  by supplying a command to the hydraulic cylinder  27 , 28  to laterally position the work machine  10  in a safe position so that a load can be raised/extended.  
         [0015]    In view of the foregoing it is readily apparent that the method provides a process for controlling the raise/extend function of a work machine  10 . The method is for the most part automatic but does allow operator intervention so as to level the frame  12  of the machine  10  relative to the horizontal so as not to put the load or machine in an unstable situation.