Floating Frame of Reference Formulation for a Flexible Manipulator With Hydraulic Actuation: Modelling and Experimental Validation

One of the current and future trends in robotics is to reduce the weight of a robotic manipulator by using lightweight materials, such as ultra-high-strength steel or composites. The reduction in weight results in material and fuel savings, which are highly relevant for heavy-duty, off-highway manipulators found in excavators, truck-mounted cranes, and forestry machines. Due to the highly demanding working conditions of such manipulators, hydraulic actuation is mainly used. Automated and accurate control of these manipulators is very challenging due to the nonlinearities present in the system. Recent studies indicate that nonlinear model-based control (NMBC) methods can provide the most advanced control performance in the case of hydraulic robotic manipulators. An accurate model capturing the dynamics of the physical system is required for effective NMBC design. The present study proposes a hybrid rigid-flexible model for a flexible manipulator combined with a hydraulic actuator, implemented with the help of the floating frame of reference formulation (FFRF). The designed model is validated by comparing simulations with experimental reference data obtained from an OptiTrack motion-capture system and other sensors. The comparative results demonstrate that the model is able to capture the system’s dynamics accurately, which motivates further research on developing NMBC methods using the FFRF.