Patent Application
20170022686
The present disclosure is directed to a control system and, more particularly, to a system that provides load-based automated tool control.
Mobile machines such as dozers, scrapers, motor-graders, and wheel loaders often include one or more material engaging implements utilized to dig into, scrape, scoop, or otherwise push against a ground surface. The ground surface can include non-homogenous loose soil or compacted material that can be easy or difficult for a machine to process. As a machine traverses a site that has changing terrain and/or varying ground surface conditions, the magnitude of resistance applied by the material to the implements and to traction devices of the machine also varies. If not accounted for properly by an operator of the machine, the machine can quickly be overloaded or underloaded.
When a machine is overloaded, the traction devices of the machine can be caused to slip (i.e., to spin faster than a travel speed of the machine), thereby reducing a forward momentum of the machine and possibly damaging the machine. The loss in momentum can result in lost productivity and/or efficiency. When the machine is underloaded, although the traction devices may not slip, the machine will still lose productivity and efficiency due to a reduced volume of material being moved. In order to help ensure that high productivity and efficiency of the machine are attained without damaging the machine, the operator of the machine must continuously alter settings of the machine and implement to accommodate the changing terrain and ground surface conditions. This continuous altering can be tiring for even a skilled operator and difficult, if not impossible, for a novice operator to achieve optimally.
One attempt to improve machine efficiency and productivity is disclosed in U.S. Pat. No. 8,726,543 of Kelly that issued on May 20, 2014 (“the '543 patent”). In particular, the '543 patent discloses an excavation machine having a blade that is autonomously controlled in order to maximize an amount of earth moved by the machine. Specifically, a controller signals automated height adjustment of the blade so that wheel-slip does not occur or occurs only within a maximum limit. Algorithms of the controller determine wheel-slip from a comparison of changes in GPS position that are less than a maximum distance expected from measured wheel rotation. When wheel-slip occurs, the controller redirects electro-hydraulic cylinders to raise the blade by a programmed increment. If the controller determines that additional work can be accomplished by the machine's engine within an optimized performance range, and that wheel-slip is not occurring, then the controller may direct the blade to be lowered by a programmed increment to increase the volume of earth being moved.
Although the system of the '543 patent may improve machine efficiencies and productivity by limiting wheel slip through blade height adjustment, the system may be complex and expensive. In particular, the controller may require complex algorithms in order to interface with GPS receivers and process the associated data. In addition, the GPS receivers can be cost-prohibitive in some applications.
The disclosed control system is directed to overcoming one or more of the problems set forth above and/or other problems of the prior art.
One aspect of the present disclosure is directed to a control system for a machine having a work tool and a traction device. The control system may include an actuator configured to adjust a depth of the work tool relative to a ground surface, a tool sensor configured to generate a first signal indicative of a performance parameter of the work tool, a speed sensor configured to generate a second signal indicative of an actual speed of the traction device, and a controller in communication with the actuator, the tool sensor, and the speed sensor. The controller may be configured to determine whether the work tool is engaged with the ground surface and, when the work tool is determined to be engaged with the ground surface, to make a comparison of the actual speed of the traction device with a rotational speed threshold. The controller may then be configured to selectively cause the actuator to adjust the depth of the work tool based on the comparison.
Another aspect of the present disclosure is directed to a method of controlling a machine having a work tool and a traction device. The method may include sensing a performance parameter of the work tool, sensing an actual speed of the traction device, and determining that the work tool is engaged with a ground surface. When the work tool is determined to be engaged with the ground surface, the method may also include making a comparison of the actual speed of the traction device with a rotational speed threshold, and selectively adjusting a depth of the work tool relative the ground surface based on the comparison.
Another aspect of the present disclosure is directed to a machine. The machine may include a frame, a work tool, and lift arms pivotally connected at a first end to the frame and at a second end to the work tool. The machine may also include a lift cylinder connected between the frame and the lift arms, at least one lift valve configured to regulate fluid flow through the lift cylinder, and a pressure sensor associated with the lift cylinder and configured to generate a first signal indicative of a current load on the work tool. The machine may further include a traction device connected to the frame and configured to propel the machine, a speed sensor configured to generate a second signal indicative of a speed of the traction device, and a powertrain supported by the frame and operable to power the lift cylinder and the traction device. The machine may additionally include a controller in communication with the at least one lift valve, the pressure sensor, and the speed sensor. The controller may be configured to determine whether the work tool is engaged with the ground surface based on the first signal and, when the work tool is determined to be engaged with the ground surface, to make a comparison of the actual speed of the traction device with a rotational speed threshold at which the traction device is known to slip for the current load. The controller may then be configured to selectively cause the lift cylinder to raise the work tool based on the comparison.
Linkage arrangement 12 may include fluid actuators that exert forces on structural components of machine 10 to cause lifting movements of work tool 14. Specifically, linkage arrangement 12 may include, among other things, a pair of spaced apart lift arms 22. Lift arms 22 may be pivotally connected at a proximal end to a frame 24 of machine 10 and at a distal end to work tool 14. One or more lift cylinders 26 may be pivotally connected at a first end to frame 24 and at an opposing second end to work tool 14 or to lift arms 22. With this arrangement, extensions and retractions of lift cylinders 26 may function to raise and lower lift arms 22, respectively, along with connected work tool 14. It is contemplated 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 blade (shown in
Operator station 16 may be configured to receive input from a machine operator indicative of a desired work tool and/or machine movement. Specifically, operator station 16 may include one or more input devices 30 (e.g., a first input device 30a and a second input device 30b—shown only in
Powertrain 18 may be supported by frame 24 of machine 10 and configured to generate the electrical, hydraulic, and/or mechanical power discussed above. Powertrain 18 may include any combination of an engine (e.g., a diesel engine), a torque converter (not shown), a transmission (e.g., a mechanical step-change, continuously variable, or hybrid transmission—not shown), a differential (not shown), one or more motors (e.g., electric or hydraulic motors—not shown), axles (not shown), a final drive (not shown), and/or any other known component that functions to transmit a torque through traction devices 20. When powertrain 18 is engaged, traction devices 20 may exert a torque on a ground surface below machine 10 that propels machine 10. Powertrain 18 may be manually and/or electronically controlled to drive traction devices 20 at the desired speed and/or up to the maximum speed selected via input device 30b. The engine of powertrain 18 may additionally drive lift cylinders 26 to move work tool 14 in accordance with manual and/or autonomous commands.
Lift cylinders 26 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 cylinders 26 and moving work tool 14. A flow rate of fluid into and out of the control chambers may relate to a translational speed of lift cylinders 26, while a pressure differential between the control chambers may relate to a force imparted by lift cylinders 26 on the associated structure of linkage arrangement 12. It is contemplated that lift cylinders 26 could be replaced with another type of actuator (e.g., a rotary actuator), if desired.
As illustrated in
In manually controlled applications, the commands to extend or retract lift cylinders 26 may be generated via input device 30a and processed by an onboard controller 48. That is, controller 48 may receive the input from operator via device 30a, and convert the input into electronic commands directed to valve 40. In remotely or autonomously controlled applications, however, the electronic commands may be directly generated by on-board controller 48 or by another off-board controller (not shown) that is in remote communication with on-board controller 48. Regardless of the application, controller 48 may additionally be configured to monitor the performance of lift cylinders 26 during commanded operations. For example, system 32 may include one or more sensors (e.g., a pressure sensor 50, a speed sensor 52, and an accelerometer 54) configured to provide feedback to controller 48 regarding commanded movements. Controller 48 may then selectively adjust lift cylinder operation based on the feedback.
Controller 48 may embody a single microprocessor or multiple microprocessors that include a means for monitoring operations of machine 10. For example, controller 48 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 48. It should be appreciated that controller 48 could readily embody a general machine controller capable of controlling numerous other machine functions. Various other known circuits may be associated with controller 48, including signal-conditioning circuitry, communication circuitry, and other appropriate circuitry.
Pressure sensor 50 may be associated with one or both of lift cylinders 26, and configured to generate signals indicative of a pressure of fluid therein. In one embodiment, sensor 50 is associated with one of the pressure chambers (e.g., the rod-end pressure chamber) inside one of lift cylinders 26. In another embodiment, pressure sensor 50 is associated with supply passage 42 that leads to both of lift cylinders 26 (and, in some embodiments, to other actuators of machine 10). In either embodiment, signals from pressure sensor 50 may be directed to controller 48 for use in regulating operation of valve 40.
Speed sensor 52 may embody a conventional rotational speed detector having a stationary element rigidly connected to frame 24 (referring to
Accelerometer 54 may embody a conventional acceleration detector rigidly connected to frame 24 in an orientation that allows sensing of fore/aft changes in speed of machine 10. It is contemplated that accelerometer 54 may include additional acceleration detectors (e.g., accelerometer 54 could embody a 3-way detector), if desired, to sense changes in speed of machine 10 in additional directions. Signals generated by accelerometer 54 may be directed to controller 48 for further processing.
The disclosed control system finds potential application within any machine at any worksite where it is desirable to provide tool loading assistance and/or automated control. The control system finds particular application within a dozer, motor-grader, wheel loader, or skid-steer that has one or more lift cylinders that raise and lower a work tool (particularly a blade or bucket). The control system may help to load the work tool in a productive and efficient manner, while avoiding excessive slipping of an associated traction device. Operation of system 32 will now be described in detail with reference to
During operation of machine 10, the loading of work tool 14 may affect forward momentum of machine 10 and/or operation of traction devices 20. For example, as work tool 14 is more heavily loaded, machine 10 may slow down due to an increasing resistance to forward travel. At this same time, a torque output of traction devices 20 may increase by an amount proportional to the loading. At some point, the loading could reach a point at which forward travel of machine 10 slows or stops, and traction devices 20 spin inefficiently (i.e., rotate at a speed much slower than a travel speed of machine 10). Controller 48 may be configured to selectively adjust loading of work tool 14 (e.g., by raising or lowering work tool 14 into the ground surface) to increase productivity and efficiency. Controller 48 may do this in several different ways, depending on how machine 10 is equipped.
In a first example shown in
When controller 48 determines at step 310 that machine 10 is traveling (and traveling in a forward direction) (step 310: Y), controller 48 may begin monitoring an actual speed of traction device 20 (Step 320). Controller 48 may determine a difference between the actual speed and the desired travel speed, and compare the difference to a speed threshold (Step 330). When loading of work tool 14 is an appropriate amount, the actual speed should be relatively close to the desired travel speed (e.g., within about 10-15%). However, as loading of work tool 14 becomes excessive, the actual speed may fall away from the desired travel speed by a greater amount. Therefore, as long as the difference between the actual speed and the desired travel speed remains less than the threshold speed (step 330: N), control may cycle back to step 300.
However, when controller 48 determines at step 330 that the actual speed has fallen away from the desired travel speed by an amount greater than the threshold speed (step 330: Y), controller 48 may determine that the load on work tool 14 is too great and responsively adjust a depth of work tool 14 (Step 340). That is, controller 48 may raise work tool 14 out of the ground surface to thereby lower the load on work tool 14. By lowering the load on work tool 14, controller 48 may cause machine 10 to increase in speed back up toward the desired travel speed. It is contemplated that controller 48 may likewise lower work tool 14 further into the ground surface, if desired, to increase loading of work tool 14 when the actual speed becomes too close to (or greater than) the desired travel speed. It should be noted that the lowering of work tool 14 into the ground surface may be limited in some applications by other autonomous algorithms (e.g., by slope control or auto-grading algorithms). Control may return from step 340 to step 300.
When machine 10 is provided with pressure sensor 50, additional functionality may be realized. In particular, as shown in
When controller 48 determines at step 400 that machine 10 is traveling (and traveling in a forward direction) (step 400: Y), controller 48 may begin monitoring the actual speed of traction device 20 and loading of work tool 14 (Step 410). As described above, controller 48 may monitor the actual speed via speed sensor 52 and the loading via pressure sensor 50. Controller 48 may then find a slip speed for machine 10 corresponding to the given loading (Step 420). The slip speed may be a speed found from past experience at which traction devices 20 begin to slip or to slip by an unacceptable amount when work tool 14 is pushing a known load. In some embodiments, the slip speed may be related to loading in an electronic map stored in the memory of controller 48. In these embodiments, controller 48 may find the slip speed by referencing the loading of work tool 14 with the map. In other embodiments, however, controller 48 may be able to find the slip speed for the given loading in other ways (e.g., via an equation).
After completion of step 420, controller 48 may then compare a difference between the actual speed and the slip speed with a threshold speed (Step 430). As long as the difference between the actual and slip speeds remains greater than the threshold speed (step 430: N), control may cycle back to step 400.
However, when controller 48 determines at step 430 that the actual speed is nearing (e.g., slowing down to) the slip speed (i.e., is within the threshold amount of the threshold speed—step 430: Y), controller 48 may adjust the depth of work tool 14 (Step 440). That is, controller 48 may raise work tool 14 out of the ground surface to thereby lower the load on work tool 14. By lowering the load on work tool 14, controller 48 may cause machine 10 to increase in speed away from the slip speed. It is contemplated that controller 48 may likewise lower work tool 14 further into the ground surface, if desired, to increase loading of work tool 14 when the actual speed becomes too far away from the slip speed. As described above, the lowering of work tool 14 into the ground surface may be limited in some applications by other autonomous algorithms (e.g., by slope control or auto-grading algorithms). Control may return from step 440 to step 400.
When machine 10 is provided with both pressure sensor 50 and accelerometer 54, additional functionality may be realized. In particular, as shown in
When controller 48 determines at step 500 that machine 10 is traveling (and traveling in a forward direction) (step 500: Y), controller 48 may begin monitoring the actual speed of machine 10, loading of work tool 14, and an acceleration of machine 10 (Step 510). As described above, controller 48 may monitor the actual speed via speed sensor 52 and the loading via pressure sensor 50. Controller 48 may monitor the acceleration of machine 10 via accelerometer 54. Controller 48 may then calculate an amount of slip currently being experienced by traction devices 20 (Step 520). The slip may be calculated by comparing a change in the actual speed of traction devices 20 with the acceleration sensed by accelerometer 54. A difference in these values may indicate a change in traction device speed that did not translate into an acceleration of machine 10, which can be indicative of the slip condition. After calculating the amount of slip currently being experienced by traction devices 20 under the given loading conditions, controller 48 may update the slip speed map stored in memory (Step 530). This map may then be used by other similar machines that do not have an accelerometer and/or by the same machine 10 in situations where accelerometer 54 is malfunctioning and/or unreliable by following the process of
At any time after completion of step 520 (e.g., subsequent to or simultaneously with step 530), controller 48 may make a comparison of the amount of slip currently being experienced by traction devices 20 with a slip threshold (Step 540). When the amount of slip currently being experienced by traction devices 20 is less than the slip threshold (step 530: N), controller 48 control may return from step 540 to step 500. In some embodiments, however, controller 48 may adjust (i.e., increase) the depth of work tool 14 until the amount of slip is within a desired range of the slip threshold, such that some slip is being experienced by traction devices 20 (i.e., an amount that is less than the slip threshold), before returning to step 500. When the amount of slip currently being experienced by traction devices 20 is more than the slip threshold, controller 48 may decrease the depth of work tool 14 (Step 550), before returning control to step 500.
The disclosed system may provide a way to improve machine productivity and efficiency in a simple and low-cost manner. In particular, because the disclosed system may not need to rely on GPS receivers to determine work tool loading or to detect slip conditions, the system may be inexpensive and require uncomplicated computing algorithms.
It will be apparent to those skilled in the art that various modifications and variations can be made to the control 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 control 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.
