Towards optimal force distribution for walking excavators

Abstract

Abstract-This paper presents the successful implementation of force control strategies on a 12 ton walking excavator to optimize the ground reaction force distribution for better stability, less terrain damage and to reduce the operation complexity. Using cleverly arrange standard industrial valve components to separately control in-and out-flow of the hydraulic cylinders, we achieve accurate and fast joint torque control purely based on pressure feedback. On the full system level, we realize an automated force distribution to adjust the center of pressure and to level out the cabin of the machine. While the operator has still full control over the excavator, this assistance system guarantees permanent ground contact and ideal force distribution among the all four wheels independent of the level of the terrain. The proposed method significantly improves operability of the walking excavator in rough terrain.

Force Control for Active Chassis Balancing

“…The experiments were chosen to resemble some of the most relevant Driving over a bump with fixed legs (yellow) has a significant influence on the chassis roll and pitch angle. By controlling the two hind flexion cylinders (red, [28]) the chassis pitch can be stabilized. Using a virtual model controller on all four flexion cylinders (blue), the chassis can be leveled completely, without any input from the operator.…”

“…The results in chassis pose control and ground contact force distribution are compared to the simplified setup presented in [28] as well as to manual control by a trained operator. In our setup, an IMU with integrated Kalman filter is used to estimate the chassis orientation (roll and pitch).…”

“…However, when controlling the valve in pressure mode and hence around zero flow, this overlap can be compensated but has to be crossed each time the measured signal crosses its reference. Beside energetic inefficiency, the overlap leads to a deadband, which significantly decreases the controller performance or requires complex setups with a dual valve configuration as proposed in [28].…”

“…Moreover, the load is almost entirely supported by the diagonal axis. When controlling the hind legs as proposed in [28], but keeping the front legs manually operated, the chassis pitch angle can be automatically adjusted while the roll angle remains controlled by the operator (red). The virtual model controller with four automated legs is able to completely compensate for the bumpy terrain and keeps the chassis leveled (blue).…”

“…13(b), yellow). With the method presented in [28], the hind legs automatically follow the commanded front motion such that the machine automatically keeps its pitch orientation (Fig. 13(b), red).…”