The stability of industrial vehicles, such as forklifts and lifters, is very important from a safety point of view: these vehicles are subjected to variable loading conditions and their design is often optimized to privilege handling in narrow spaces, instead of stability. To study in deep the problem of vehicle capsize prevention, the authors developed a scaled AGV (Automated Guided Vehicle). It is a three wheeled differential drive mobile robot, with front motorized wheels, driven by speed-controlled drivers. The position of the wheels and the loads can be easily modified to simulate different vehicle configurations and operating scenarios. The vehicle is controlled with a Texas Instrument C2000 controller, programmable through Matlab-Simulink Embedded Coder™. In addition, the forces exchanged among the wheels and the ground are monitored using low cost load cells, with miniaturized amplification stages. MEMS three-axial accelerometers and gyros are installed in order to detect inertial loads and to estimate the vehicle pose and, through a proper filtering, the ground slope. The implemented strategy is able to identify the loading conditions of the vehicle by means of a dedicated algorithm: this algorithm evaluates the position of the center of mass from static measurements that are further refined when the vehicle is in motion with an adaptive filtering based on the fusion of both static and dynamic measurements. Once the vehicle is in motion, the controller, to prevent the vehicle capsize, is able to limit its forward speed without changing the geometry of the assigned trajectory. In this work, the results of preliminary testing activities are shown, demonstrating the validity and the effectiveness of the proposed approach
This work describes the design strategy and preliminary testing of an active protection system characterized by low-cost commercial sensors of proven reliability. In the system, each risk level is defined and a particular robot reaction assigned to it. The risk calculation is based on the recursive solution of the manipulator's kinematic problem for the evaluation of the horizontal distance components and the relative speed between operator and machine. Computational effort is minimized, since (1) the protection system procedures can be performed directly in the robot controller with the robot kinematic and dynamic calculations and (2) only the cylinder-shaped volumes around the operator's estimated position have to be defined in order to perform a probabilistic evaluation of the risk levels. Preliminary testing on a simplified setup has validated the system's reliability, its insensitivity to background disturbances, and the ease of use of the sensors.
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