<p class="MsoNormal">The bulldozer is a heavy-duty earthmoving machine used in various ground surface manipulation tasks on worksites. Majority of such machines rely on hydraulic actuators due to their high power to weight ratio. In high performance ground surface grading and traction control of bulldozers, tracking desired surface gradients with the hydraulically actuated manipulator is of high importance. The required motion of the manipulator actuators is based on counteracting the mobile base motion, that would otherwise cause errors in following a desired surface specified in worksite coordinates. This poses challenges that are not present in the motion control of fixed-based hydraulic manipulators. Namely, the actuator motion reference signals cannot be specified beforehand, but must be computed online based on the estimated motion of the machine. Furthermore, the motion control problem must be viewed as that of path following, as the mobile base motion determines the surface elevation and gradient references. In this paper, we present a surface elevation tracking controller for earthmoving work done by heavy-duty bulldozers with hydraulic actuators using IMUs and roof mounted RTK GPS antennas. We show mapping between the desired surface profile and hydraulic actuator position and velocities using the elevation path definition, the mobile manipulator Jacobian and mobile base pose and velocity estimation. With this information available, a hydraulic cylinder length controller is designed in the actuator space. With the proposed method, a relatively simple low-level actuator space motion control scheme can produce sufficient accuracy in varying surface elevation requirements besides leveling work. This makes the controller also suitable for traction control purposes, where the desired elevation is computed online. We showcase the benefits and problems of using a high-bandwidth controller and actuator velocity mapping on a heavy-duty tracked vehicle with high manipulator inertia, hydraulic dynamics, and mobile base vibrations. We implement the proposed solution on a medium size experimental bulldozer with GPS and IMU sensors for localization and joint angle acquisition, and hydraulic fluid pressure sensors for hydraulic cylinder motion control. Experimental results validate the efficacy of the proposed method, also revealing the needs for further development.</p>

Blade Control for Surface Profile Tracking by Heavy-Duty Bulldozers

Paper Proceedings: https://asmedigitalcollection.asme.org/FPST/FPMC2021/volume/85239

2021 ASME/BATH Symposium on Fluid Power and Motion Control (FPMC2021)

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