Typically, earthmoving machines do not have wheel suspensions. This lack of components often causes uncomfortable driving, and in some cases reduces machine productivity and safety. Several solutions to this problem have been proposed in the last decades, and particularly successful is the passive solution based on the introduction of accumulators in the hydraulic circuit connecting the machine boom. The extra capacitance effect created by the accumulator causes a magnification of the boom oscillations, in such a way that these oscillations counter-react the machine oscillation caused by the driving on uneven ground. This principle of counter-reacting machine oscillations through the boom motion can be achieved also with electro-hydraulic solutions, properly actuating the flow supply to the boom actuators on the basis of a feedback sensors and a proper control strategy.
This paper proposes an innovative concept for an active system to reduce machine oscillations based on a controller that identifies the frequencies of the oscillation to be damped. Taking a particular wheel loader as reference machine, this paper details the different aspects of the control methodology. The controller is simulated on the basis of a four degrees of freedom vehicle dynamic model of the machine developed within the research used as a plant model, and on realistic dynamic response of the hydraulic system. Simulation results confirm the effectiveness of the proposed control strategy proposed, demonstrating its potential application to earthmoving machines.