Patent Publication Number: US-9903100-B2

Title: Excavation system providing automated tool linkage calibration

Description:
TECHNICAL FIELD 
     The present disclosure is directed to an excavation system and, more particularly, to an excavation system providing automated tool linkage calibration. 
     BACKGROUND 
     Heavy equipment, such as load-haul-dump machines (LHDs), wheel loaders, carry dozers, etc., are used during an excavation process to scoop up loose material from a pile at a first location (e.g., within a mine tunnel), to haul the material to a second location (e.g., to a crusher), and to dump the material. A productivity of the excavation process can be affected by an efficiency of each machine during every excavation cycle. In particular, the efficiency of each machine increases when the machine&#39;s tool (e.g., a bucket) is fully loaded with material at the pile within a short amount of time, hauled via a direct path to the second location, and quickly dumped. 
     The efficiency of a machine can be affected by accuracy in movements of the machine&#39;s tool linkage system. In particular, when a machine has full movement capacity, and the movements precisely correspond with operator and/or autonomous control commands, the machine may perform at a higher level. The movement capacity and precision may be ensured by periodic calibration of the tool linkage system. 
     An exemplary calibration system is disclosed in U.S. Pat. No. 6,615,114 of Skiba et al. that issued on Sep. 2, 2003 (“the &#39;114 patent”). The calibration system includes a position sensor coupled to a lift cylinder of a front-end loader, and an electronic control module (ECM) operatively coupled to the position sensor. The position sensor senses the position of a piston inside the lift cylinder, and generates a corresponding position signal directed to the ECM. During a calibration process, the ECM generates and transmits a command signal to fully extend the lift cylinder. As the lift cylinder is extending, the movement of the piston is monitored by the position sensor. The ECM differentiates the signals generated by the position sensor during cylinder extension to detect when a velocity of the cylinder is zero. Once a signal representative of the cylinder being in a fully extended position is generated by the position sensor (i.e., when the cylinder velocity is zero), the ECM stores the value of the position signal in memory. The ECM then uses this value as a fully extended calibration factor. The ECM also performs a similar calibration process with respect to moving the lift cylinder to its fully retracted position. 
     Although the calibration system of the &#39;114 patent may be helpful in calibrating a position sensor associated with a lift cylinder, it may lack applicability to more complicated machines, where multiple actuators interact with each other in a dependent manner. 
     The disclosed excavation system is directed to overcoming one or more of the problems set forth above and/or other problems of the prior art. 
     SUMMARY 
     One aspect of the present disclosure is directed to an excavation system for a machine having a work tool. The excavation system may include a first actuator configured to move the work tool in a first direction, and a second actuator configured to move the work tool in a second direction. The second actuator may only be capable of full range second actuator movement when the first actuator is positioned within a sub-range of first actuator movement. The excavation system may also include a first sensor configured to generate a first signal indicative of movement of the first actuator, a second sensor configured to generate a second signal indicative of movement of the second actuator, and a controller in communication with the first and second sensors. The controller may be configured to command movement of the first actuator to the sub-range, and to confirm that the first actuator has moved to the sub-range based on the first signal. The controller may also be configured to command movement of the second actuator to an end-of-stroke position after the first actuator is confirmed to be within the sub-range, and to selectively record a current position of the second actuator as the end-of-stroke position based on the second signal. 
     Another aspect of the present disclosure is directed to a method of controlling a machine having a work tool and first and second actuators connected to move the work tool in different directions. The method may include commanding movement of the first actuator to a sub-range of first actuator movements that allows full range movement of the second actuator, and sensing movement of the first actuator. The method may also include commanding movement of the second actuator to an end-of-stroke position after the first actuator is within the sub-range, and sensing movement of the second actuator. The method may further include selectively recording a current position of the second actuator as the end-of-stroke position. 
     Another aspect of the present disclosure is directed to a machine. The machine may include a frame, a work tool, lift arms pivotally connected at a first end to the frame and at a second end to the work tool, lift cylinders connected between the frame and the lift arms, and a tilt cylinder operatively connected between the frame and the lift arms. The tilt cylinder may only be capable of full range tilting movement when the lift cylinders are positioned within a sub-range of lifting movement. The machine may further include a lift sensor configured to generate a first signal indicative of movement of the lift cylinders, a tilt sensor configured to generate a second signal indicative of movement of the tilt cylinder, and a controller in communication with the lift and tilt sensors. The controller may be configured to command movement of the lift cylinders to a maximum lift position, to confirm that the lift cylinders have been moved to the maximum lift position when a change in the first signal indicates a lift speed less than a threshold value, and to responsively record the current lift position as the maximum lift position. The controller may also be configured to command movement of the lift cylinders to a minimum lift position, to confirm that the lift cylinders have been moved to the minimum lift position when the change in the first signal indicates the lift speed less than the threshold value, and to responsively record the current lift position as the minimum lift position. After recording the maximum and minimum lift positions, the controller may additionally be configured to command movement of the lift cylinders to the sub-range, to confirm that the lift cylinders have moved to the sub-range based on a position value of the first signal, to command movement of the tilt cylinder to an end-of-stroke position after the lift cylinders are confirmed to be within the sub-range, and to selectively record a current position of the tilt cylinder as the end-of-stroke position when a change in the second signal indicates a tilt speed less than a threshold value. The controller may be further configured to selectively create a position-to-sensor reading map based on recordation of the maximum lift position, the minimum lift position, and the end-of-stroke position. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1 and 2  are side and top-view diagrammatic illustrations, respectively, of an exemplary disclosed machine operating at a worksite; 
         FIG. 3  is a diagrammatic illustration of an exemplary disclosed excavation system that may be used in conjunction with the machine of  FIGS. 1 and 2 ; and 
         FIG. 4  is a flowchart depicting an exemplary disclosed method that may be performed by the excavation system of  FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION 
       FIGS. 1 and 2  illustrate an exemplary machine  10  having multiple systems and components that cooperate to move material such as ore, overburden, waste, etc. In the disclosed example, machine  10  is a load-haul-dump machine (LHD). It is contemplated, however, that machine  10  could embody another type of excavation machine (e.g., a wheel loader or a carry dozer), if desired. Machine  10  may include, among other things, a linkage arrangement  12  configured to move a work tool  14 , an operator station  16  for manual control of linkage arrangement  12 , and a power source  18  (e.g., an engine) that provides electrical, hydraulic, and/or mechanical power to linkage arrangement  12  and operator station  16 . 
     Linkage arrangement  12  may include fluid actuators that exert forces on structural components of machine  10  to cause lifting and tilting movements of work tool  14 . Specifically, linkage arrangement  12  may include, among other things, a pair of spaced apart generally plate-like lift arms  20 , and a bell crank  22  centered between and operatively connected to lift arms  20 . Lift arms  20  may be pivotally connected at a proximal end to a frame  24  of machine  10  and at a distal end to work tool  14 . Bell crank  22  may be pivotally connected to work tool  14  directly, or indirectly via a tilt link  26 . A pair of substantially identical lift cylinders  28  (shown only in  FIG. 2 ) may be pivotally connected at a first end to frame  24  and at an opposing second end to lift arms  20 . A tilt cylinder  30  may be located between lift arms  20  and pivotally connected at a first end to frame  24  and at an opposing second end to bell crank  22 . With this arrangement, extensions and retractions of lift cylinders  28  may function to raise and lower lift arms  20 , respectively, along with connected work tool  14 , bell crank  22 , and tilt link  26 . Similarly, extensions and retractions of tilt cylinder  30  may function to rack and dump work tool  14 , respectively. This arrangement may be recognized as similar to a commonly known Z-bar linkage. It is contemplated, however, that machine  10  could have another linkage arrangement, if desired. 
     Numerous different work tools  14  may be attachable to a single machine  10  and controllable via operator station  16 . Work tool  14  may include any device used to perform a particular task such as, for example, a bucket (shown in  FIGS. 1 and 2 ), a fork arrangement, a blade, a shovel, a crusher, a shear, a grapple, a grapple bucket, a magnet, or any other task-performing device known in the art. Although connected in the embodiment of  FIGS. 1 and 2  to lift and tilt relative to machine  10 , work tool  14  may alternatively or additionally rotate, swing, slide, extend, open and close, or move in another manner known in the art. 
     Operator station  16  may be configured to receive input from a machine operator indicative of a desired work tool movement. Specifically, operator station  16  may include one or more input devices  32  (shown only in  FIG. 3 ) embodied, for example, as single or multi-axis joysticks located proximal an operator seat (not shown). Input devices  32  may be proportional-type controllers configured to position and/or orient work tool  14  by producing a work tool position signal that is indicative of a desired work tool speed and/or force in a particular direction. The position signal may be used to actuate any one or more of lift and tilt cylinders  28 ,  30 . It is contemplated that different input devices may additionally or alternatively be included within operator station  16  such as, for example, wheels, knobs, push-pull devices, switches, pedals, and other operator input devices known in the art. It is contemplated that operator station  16  could be omitted in applications where machine  10  is remotely or autonomously controlled, if desired. 
     Power source  18  may be supported by frame  24  of machine  10 , and configured to generate the electrical, hydraulic, and/or mechanical power discussed above. In the disclosed embodiment, power source  18  is an engine, for example a diesel engine, that combusts a mixture of fuel and air to produce the power. In other embodiments, however, power source  18  could include a fuel cell, a battery, a tethered motor, or another source known in the art. 
     Lift and tilt cylinders  28 ,  30  may each be a linear type of actuator consisting of a tube and a piston assembly arranged within the tube to form opposing control chambers. The control chambers may each be selectively supplied with pressurized fluid and drained of the pressurized fluid to cause the piston assembly to displace within the tube, thereby changing an effective length of lift and tilt cylinders  28 ,  30  and moving work tool  14 . A flow rate of fluid into and out of the control chambers may relate to a translational speed of the cylinders, while a pressure differential between the control chambers may relate to a force imparted by the cylinders on the associated structure of linkage arrangement  12 . It is contemplated that lift and/or tilt cylinders  28 ,  30  could be replaced with another type of actuator (e.g., a rotary actuator), if desired. 
     As illustrated in  FIG. 3 , lift and tilt cylinders  28 ,  30  and input device  32  may form portions of an excavation system (“system”)  34 . System  34  may include one or more fluid circuits that distribute pressurized oil used to drive the cylinders described above in response to received input. In particular, system  34  may include, among other things, a common pump  36  connected via a suction passage  38  to a common low-pressure reservoir  40 , and one or more control valves (e.g., one or more lift control valves  42  and one or more tilt control valves  44 ). Pump  36  may be configured to draw fluid from reservoir  40  via suction passage  38  and to pressurize the fluid. Valves  42 ,  44  may be connected to pump  36  via a supply passage  46  to receive the pressurized fluid, and also to reservoir  40  via a drain passage  48 . In addition, valves  42 ,  44  may be connected to the corresponding lift cylinders  28  and tilt cylinder  30  via one or more conduits  50  and  52 , respectively. Each control valve  42 ,  44  may be responsible for connecting supply passage  46  and drain passage  48  to particular control chambers inside the corresponding actuators to cause commanded extensions or retractions of the actuators between opposing end-of-stroke (i.e., maximum and minimum) displacement positions. 
     In manually controlled applications, the commands to extend or retract lift and tilt cylinders  28 ,  30  may be generated via input device  32  and processed by an on-board controller  54 . That is, on-board controller  54  may receive the input from the operator via device  32 , and convert the input into commands directed to valves  42 ,  44 . In remotely or autonomously controlled applications, however, the commands may be directly generated by on-board controller  54  or by another off-board controller (not shown) that is in remote communication with on-board controller  54 . Regardless of the application, controller  54  may additionally be configured to monitor the movements of lift and tilt cylinders  28 ,  30  achieved as a result of the commands. In particular, excavation system  34  may include one or more sensors (e.g., a lift sensor  58  and a tilt sensor  60 ) configured to provide feedback to controller  54  regarding commanded movements. 
     Controller  54  may embody a single microprocessor or multiple microprocessors that include a means for monitoring operations of machine  10 . For example, controller  54  may include a memory, a secondary storage device, a clock, and a processor, such as a central processing unit or any other means for accomplishing a task consistent with the present disclosure. Numerous commercially available microprocessors can be configured to perform the functions of controller  54 . It should be appreciated that controller  54  could readily embody a general machine controller capable of controlling numerous other machine functions. Various other known circuits may be associated with controller  54 , including signal-conditioning circuitry, communication circuitry, and other appropriate circuitry. 
     Sensors  58  and  60  may each embody an extension sensor located internally or externally of cylinders  28 ,  30 ; a rotational position sensor associated with the pivoting motions of linkage arrangement  12 ; a local or global coordinate position sensor associated with work tool  14 ; or any other type of sensor known in the art that generates a signal indicative of extending or retracting movements of cylinders  28 ,  30 . Signals generated by these sensors  58 ,  60  may be sent to controller  54  for further processing. It is contemplated that controller  54  may derive any number of different parameters based on the signals from sensors  58 ,  60  and, for example, an elapsed period of time (e.g., a time period tracked by an internal or external timer—not shown). In particular, controller  54  could determine position values, orientation values, speed values, acceleration values, etc. Controller  54  may then use this information to confirm a status of a commanded movement. That is, based on the signals generated by sensors  58 ,  60 , controller  54  may determine if a desired speed is being achieved, if a desired position or orientation has been attained, etc. And from this feedback, controller  54  may selectively adjust the commands directed to valves  40 ,  42 . 
     In order for controller  54  to make the necessary command adjustments described above, the information received from sensors  58 ,  60  should be accurate. As shown in  FIG. 4 , controller  54  may be configured to selectively implement a calibration process involving sensors  58 ,  60  to help ensure the accuracy of sensors  58 ,  60 .  FIG. 4  will be discussed in more detail in the following section to further illustrate the disclosed concepts. 
     INDUSTRIAL APPLICABILITY 
     The disclosed excavation system finds potential application within any machine at any worksite where it is desirable to provide tool loading assistance and/or automated control. The excavation system finds particular application within an LHD, wheel loader, or carry dozer that has multiple actuators, which interact to cooperatively move a work tool. The excavation system may help to ensure precise and efficient work tool movements through the use of a unique sensor calibration process. Operation of excavation system  34  will now be described in detail with reference to  FIG. 4 . 
     Controller  54  may be triggered to initiate the calibration process in many different ways. In one example, controller  54  may receive a request for calibration initiation (Step  405 ). This request may be received manually from a local or remote operator (e.g., via input device  32 ). In another example, controller  54  may determine a need to recalibrate sensors  58 ,  60 , such as when work tool  14  does not reach an expected position or does not move with an expected speed or acceleration. In yet another example, controller  54  may initiate the calibration process based on a time elapsed since a previous calibration event. Other ways to initiate the calibration process may also be implemented. 
     After the request for calibration initiation is received, controller  54  may check to see if conditions are appropriate for start of the process. For example, controller  54  may check to see if work tool  14  is within a pre-defined calibration range of positions (Step  410 ). This pre-defined calibration range of positions may correspond with linkage arrangement  12  being in a low-energy state. In one specific example, the low-energy state may correspond with lift arms  20  being lowered below a particular elevation and/or with a bottom surface of work tool  14  resting generally parallel to (e.g., on) a ground surface. It is contemplated that the operator may perform this function and then indicate to controller  54  that work tool  14  is in the correct position. Alternatively, the operator may perform this function while controller  54  monitors and confirms that work tool  14  is in the calibration start position (Step  415 ). If controller  54  is programmed to monitor and confirm the calibration start position of work tool  14 , controller  54  may selectively inform the operator when work tool  14  is in an improper position (Step  415 ). Control may cycle through steps  405 - 415  until work tool  14  has moved to within the range of acceptable start positions. 
     Once work tool  14  is within the range of acceptable start positions, controller  54  may assume calibration control and command work tool movement to a minimum lift position (i.e., to a full lower position) and to a maximum tilt position (i.e., to a full rack position) (Step  420 ). These movements may be commanded and achieved sequentially or simultaneously, as desired. During the movements, controller  54  may monitor the speeds of lift and tilt cylinders  28 ,  30  (e.g., sensors  58 ,  60 ) to determine when the corresponding changes in piston assembly displacements fall below a threshold value for a given period of time (Step  425 ). This threshold value for both lift and tilt may be about 0.3 m/s, and corresponds with lift and tilt cylinders  28 ,  30  reaching their end-of-stroke positions. It is contemplated that, in some embodiments, the lift and tilt speed thresholds may be different, if desired. Controller  54  may continue commanding minimum lift and maximum tilt positions until step  425  is satisfied (i.e., control may cycle through steps  420  and  425  until both of the corresponding end-of-stroke positions are attained). Thereafter, controller  54  may record the corresponding current positions in memory as the minimum lift and maximum tilt positions (Step  430 ). 
     After calibration of the minimum lift and maximum tilt positions, controller  54  may command work tool  14  to move to its maximum lift position (Step  435 ), while monitoring the movement. Controller  54  may compare the displacement speed of lift cylinders  28  to a threshold value (Step  440 ). This threshold value for lift may again be about 0.3 m/s, and corresponds with lift cylinders  28  reaching their end-of-stroke positions. It is contemplated that, in some embodiments, the maximum and minimum lift speed thresholds may be different, if desired. Controller  54  may continue commanding maximum lift position until step  435  is satisfied (i.e., control may cycle through steps  435  and  440  until the corresponding end-of-stroke position is attained). Thereafter, controller  54  may record the corresponding current position in memory as the maximum lift position (Step  445 ). 
     The linkage configuration of machine  10  may allow for work tool  14  to be tilted to its minimum position only when work tool  14  is lifted to within a particular sub-range of its entire lift range. For example, work tool  14  may only be tilted to its maximum position when it has been lifted to about 55-65% (e.g., to about 60%) of the distance from its minimum lift position to its maximum lift position. Accordingly, after calibration of the maximum lift position, controller  54  may command work tool  14  to move to the particular sub-range described above that corresponds with the minimum tilt capability (Step  450 ). 
     During the lifting movement of work tool  14  to the minimum tilt sub-range, controller  54  may not be able to rely on monitored speed to determine that work tool  14  has reached the sub-range, as lift cylinders  28  would not reach an end-stop that causes the speed to fall below a threshold. Instead, since controller  54  has already calibrated the minimum and maximum lift positions, controller  54  can now accurately monitor just the displacement positions (regardless of speed) of lift cylinders  28  to determine when work tool  14  has reached the sub-range (Step  455 ). Control may cycle through steps  450  and  455  until the sub-range has been reached. 
     After work tool  14  has been lifted to the minimum tilt sub-range, controller  54  may command work tool  14  to move to its minimum tilt position (Step  460 ), while monitoring the movement. Controller  54  may compare the displacement speed of tilt cylinder  30  to a threshold value (Step  465 ). This threshold value for tilt may again be about 0.3 m/s, and corresponds with tilt cylinder  30  reaching its end-of-stroke position. It is contemplated that, in some embodiments, the maximum and minimum tilt speed thresholds may be different, if desired. Controller  54  may continue commanding minimum tilt position until step  465  is satisfied (i.e., control may cycle through steps  460  and  465  until the corresponding end-of-stroke position is attained). Thereafter, controller  54  may record the corresponding current position in memory as the minimum tilt position (Step  470 ). 
     After the maximum and minimum lift and tilt positions have been recorded into the memory of controller  54 , controller  54  may create a linkage position-to-sensor reading map from the position values (Step  475 ). This map may then be used to generate future work tool movement commands. Controller  54  may then command return of work tool  14  to the original calibration start position (Step  480 ), while monitoring the movement. When controller  54  determines that work tool  14  is in the original calibration start position (Step  485 : Y), control may return to step  405 . 
     This disclosed excavation system may provide for enhanced machine movement accuracy and efficiency by way of a unique calibration process. The calibration process may be enhance machine movement accuracy and efficiency by calibrating multiple interacting actuators in a manner that allows full movement of individual actuators during the calibration process, even when the movement of some of the actuators depend on prior calibration and movements of other actuators. 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the excavation system of the present disclosure. Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice of the excavation system disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope being indicated by the following claims and their equivalents.