Force Control for Active Chassis Balancing

Abstract

Abstract-This paper presents the realization of the worldwide first automated walking excavator chassis. To this end, the authors build a new generation of high-performance hydraulic valves with integrated pressure feedback to achieve fast and accurate cylinder force tracking. This allows to automatically adapt the legs to uneven terrain and to optimally shape the ground reaction forces in order to change orientation and height of the cabin. Due to the contact redundancy, automated balancing is implemented as a contact force optimization problem including constraints on contact forces and joint torques. The corresponding prioritized optimization problem can be simplified by using a quasi-static approximation of the system dynamics and a complexity reduction due to the kinematic structure of the legs. Our approach considers the unknown configuration and load of the cabin, arm, and bucket as system disturbances, whereby gravitational effects are approximated as well as possible. It is tested in a Gazebo simulation and validated in different experiments using a prototype walking excavator machine. The proposed method revolutionizes operator control of these versatile but complex multi-purpose vehicles: instead of manual and coordinatively very demanding cylinder position adjustment, the operator can command simple high-level commands like cabin pose. Furthermore, it significantly reduces peak forces in the cylinders and at the contact points, which causes less damage to the mechanics and the ground.

Autonomous Free-Form Trenching Using a Walking Excavator

“…the quadrupedal robot HyQ [6], highly rely on the superior performance of servo valves. Also our previous advances on active control of the excavators chassis [7] leveraged servo valves, motivating the use of these also on the arm automation shown in this work. The creation of more complicated shapes than flat bottom trenches also requires geometric feedback from the manipulated terrain, as inferring the terrain only from the bucket edge motion is not sufficient.…”

“…1 provides an overview of the major changes. To achieve active balancing and adaptation to uneven ground [7], all 14 hydraulic cylinders in the chassis were exchanged with cylinders that include integrated control modules that allow for precise control of leg positions and ground interaction forces.…”

“…The excavator controls the distance to the excavation point by driving forward and backwards. The active chassis [7] adapts to the ground while driving and guarantees a stable stance for excavation.…”

Long-Stroke Hydraulic Robot Motion Control With Incremental Nonlinear Dynamic Inversion

“…Combining (1) and 5through the relation F = A p P L , the overall dynamic model of a hydraulic robot is given. Note that good lubrication is assumed for the hydraulic actuator and that frictions are considered as small continuous disturbances.…”

“…They still have higher power-to-weight ratios and inherently higher stiffness and rigidity compared with electrical motors. For applications where high precision control performance is required, such as legged robots control [1], [2], manipulator impedance control [3], [4] and flight simulator motion control [5], high performance controller development is receiving increasing attention in the academia.…”