Aoki_004_Validation of travel simulation model for a crawler excavator and influence of vehicle posture on traveling behavior

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Crawlers are widely used for construction vehicles such as a hydraulic excavator and a bulldozer that require the high trafficability on off-road. Soil conditions at construction and sediment disaster areas are soft ground. When traveling slope, the vehicle skids down due to skidding between the crawlers and soil. In order to follow a target trajectory, the rotational speed of the left and right crawler’s must be adjusted separately according to the amount of skidding. A hydraulic excavator is equipped with an upper swing structure and front work attachments which we call front structures. When the upper structure rotates or the posture of the front structure changes, the center of gravity of the vehicle changes. Then, the amount of skidding for each crawler dynamically changes according to the load distribution. Finally, it needs a skilled operation to suitably adjust the left and right crawlers.
An assist and automated function development are strongly required due to the lack of skilled operators and in-creased awareness of safety and efficiency. To develop those autonomous technologies effectively, a crawler-traveling simulation model on soft ground is needed. The simulation model requires models of ground (crawler-soil interaction) and controller to adjust the crawler speed. It has been reported that the Distinct Element Method (DEM) is used to cal-culate crawler-soil interaction, but DEM takes a long time to calculate. Then, traveling simulations using terramechan-ics, having a relatively short calculation time, have been reported. There are many simulation models of wheels on slopes using terramecanics but relatively few models are for crawler vehicles. Besides, a traveling simulation model in which the center of gravity changes dynamically like a hydraulic excavator has not been reported.
We established a traveling simulation model on a slope by Terramechanics for a crawler vehicle with a changing center of gravity to provide the simulation time much faster than DEM. Our proposed simulation process calculates the static sinkage of the crawler at each time step considering the changing center of gravity. So, the amount of crawler skid is estimated by a more accurate stress distribution by Terramechanics. The ground parameters in our simulation model were identified using the actual test data of the crawler vehicle. And then, the traveling results simulated using the identified were compared with the actual vehicle experiments. As the results, it was verified that our simulation methodology could reproduce the skidding down of a crawler vehicle on slope off-roads. In addition, several case studies were performed to understand the effect of the changing center of gravity to the target trajectory.