Advanced Hydraulic Systems for Active Vibration Damping and Forklift Function to Improve Operator Comfort and Machine Productivity of Next Generation of Skid Steer Loaders

Mobile Earth Moving Machinery like Skid-steer loaders have tight turning radius in limited spaces due to a short wheelbase which prevents the use of suspensions in these vehicles. The absence of a suspension system exposes the vehicle to ground vibrations of high magnitude and low frequency. Vibrations reduce operator comfort, productivity and life of components. Along with vibrations, the machine productivity is also hampered by material spillage which is caused by the tilting of the bucket due to the extension of the boom. The first part of the paper focuses on vibration damping. The chassis’ vibrations are reduced by the use of an active suspension element which is the hydraulic boom cylinder which is equivalent to a spring-damper. With this objective, a linear model for the skid steer loader is developed and a state feedback control law is implemented. The paper discusses the development of a Linear Quadratic Regulator (LQR) based compensator to obtain the feedback gains for this linear system with a quadratic cost function. It also discusses the methodology to select the LQR weights to penalize the state error and the input in order to minimize the cost function. The second part of the paper concentrates on the development of a robust path-planning control algorithm which adapts to the position of the boom to maintain a level load to achieve forklift function. The control algorithm comprises of three cascaded loops which act to keep the bucket horizontal. These cascaded loops encompass the feedback of parameters like boom angular position, ground inclination, bucket angular position and bucket pump swash plate position. The paper discusses the measurement setup on a skid steer loader in order to carry out experimental validation of the control algorithms. The experiments performed show about 29 % reduction in vibrations of the skid steer loader at low speed and 25 % reduction in vibrations at high speed. This proves that the controller is effective over wide range of speeds. The experimental results for the forklift function show that the bucket tracks the reference angle very well in order to achieve the forklift function. Thus, this paper discusses control strategies to tackle two major challenges of the skid steer loader related to operator comfort and machine productivity i.e. vibration damping and forklift function.