AN ISOBUS-NETWORKED ELECTRONIC SELF-LEVELING CONTROLLER FOR THE FRONT-END LOADER OF AN AGRICULTURAL TRACTOR

摘要

There has been a growing trend toward electronic control of hydraulic systems in agricultural machinery to improve operator comfort. Rapid advances in information and communications technology and the expansion of agricultural attachments have led to the introduction of control systems following the ISOBUS standard. Feedback control of a front-end loader (FEL) using electro-hydraulic proportional valves and sensors allows automatic activation of the boom and bucket cylinders and repetitive operational sequences of FEL functions. The mechanical self-leveling systems commonly used to prevent rollback have a limited range of operation and provide overcompensation beyond that range, therefore requiring considerable driver attention when operating the FEL. This article describes the development and evaluation of an ISOBUS-networked electronic self-leveling system that uses three electronic control units (ECUs), i.e., loader, joystick, and virtual terminal ECUs, to automatically adjust the orientation of the loader bucket with respect to the ground based on real-time measurements of bucket angle and angular velocity. Key improvements to the system, compared to a previous study that developed a proportional and integral (PI)-based self-leveling controller include the addition of a velocity feedback element and a dead-time effect computation to the control loop. An embedded electronic controller was implemented on agricultural tractors to test its ability to maintain the desired bucket angle regardless of varying ground slopes or the lifting or lowering motion of the boom. In laboratory testing with a FEL simulator, the use of the velocity feedback loop enabled the bucket angles to reach reference angles of +20 degrees, showing reductions in rise times from 0.75 to 0.51 s and from 0.84 to 0.39 s on ascending and descending slopes, respectively, compared to the PI-based self-leveling algorithm. At a traveling velocity of 2.5 km/h, there was little change in bucket angle, with an almost constant level of &1 degrees. However, at a velocity of 7.5 km/h, inflection points on the paved road caused relatively large deviations from the reference angle ranging from 3 degrees to 5 degrees, thus requiring the use of a look-ahead method to predict sudden changes in slope using a LIDAR sensor that can characterize the ground surface. In an outdoor bench test using a joystick to raise and lower the boom of a FEL, the self-leveling algorithm allowed the bucket angle to be maintained at the desired level, with RMSEs of 2.1 +/- 0.65 degrees and 3.4 +/- 0.81 degrees in the raising and lowering modes, respectively; thus, it could be implemented in an electronic self-leveling system for a FEL, which could then be employed in an ISOBUS-networked tractor offering the potential to eliminate the possibility of load rollback.