The presented work addresses the tip-over endangerment of hydraulic excavators. Investigating methods of protection from tip-over showed that current excavators rely on the OPS in most cases. This mandatory system, supplying the driver with an acoustic warning upon approach of an overload situation, is limited to quasi-static motion only. More advanced systems, called rated capacity indicators, increase accuracy and ease of use, but are also limited to quasi-static movements. A major drawback of both these systems is that they are not capable of monitoring stability during excavation work. In order to improve the given state of the art, the objective was set to find a method to actively prevent tip-over situations independent to the driver. The chosen approach was to predict tip-over situations by continuously monitoring the system. Thereby, otherwise imminent tip-overs should be prevented using an automated emergency stop of the entire machine. Feasible approaches of stability assessment were found in the field of robotics for the general case of mobile manipulators. A comparison of existing approaches revealed NDESM as candidate for the given use-case. This method was tested in simulation for the general case in a wide range of critical usage scenarios. Therein, the state of the art did not reveal methods of comprehensive examination of tip-over prediction behavior for mobile manipulators. The issue was approached using empirical tests, investigating multiple usage scenarios in different circumstances for a broad range of parameters. NDESM in its original formulation was found insufficient as it only detected 81.52% of all occurred tip-over occasions. Modifications were made by excluding stabilizing components of inertial loadings and by considering coast down effects of articulated parts of the manipulator. Using these modifications achieved successful prediction of tip-overs in all tested use-cases. The modified version of NDESM was named NTOPv3, which was then implemented on a mobile hydraulic excavator. NTOPv3 was tested with successful results using the simulation model of the target excavator, and was again tested physically in field tests. Successful prevention of tip-over situations was achieved, proposing NTOPv3 as a feasible method for tip-over prevention in hydraulic excavators.
|Bennett, Mehmet Nureddin
Active Tip-Over Prevention for Mobile Excavators
Hydraulic Excavators are subjected to tip-over situations with potential hazardous outcome. The given work analyses the state of the art of tip-over protection methods, including the current mandatory overload protection system. Using methods derived from the area of robotics, an algorithm for use as an assistance system was developed to predict and actively prevent dangerous tip-over situations. The developed method was evaluated in multi-body simulation models and in physical field tests.