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This paper presents dynamic modeling, controller design, and virtual reality (VR)-based human-in-the-loop real-time simulation for a wheel loader control system. In particular, a loader with electrohydraulic actuation is considered. A detailed nonlinear dynamic model is developed for the hydraulic system and the loader linkage. The hydraulic model includes a load sensing pump, valves, and cylinders. The linkage model represents a two degree of freedom loader with lift and tilt functions. A linear quadratic Gaussian based robust controller is designed for automatic bucket leveling to assist the operator by keeping the angle of the bucket leveled while the boom is in motion. The closed-loop control system design is tested with a nonlinear model in a real-time VR simulation. In the VR simulation, the operator interacts with the model using a joystick input. The loader linkage geometry is displayed to the operator in real time using a VR display. The controller performance was assessed in the VR environment. As expected, the controller was found to provide a significant improvement in the accuracy of the bucket leveling, particularly in the case of a novice operator controlling the linkage motion. While prototypes cannot be eliminated, the VR simulation combined with realistic physics and control dynamics provided a useful tool for evaluating hydraulic systems and controls with less reliance on prototype machines.

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Poppet type metering valves have many benefits including low leakage and an economical design. These benefits make the poppet valve an appealing alternative to spool valves in a valve stack. The fact that the metering element is not hydrostatically balanced as in a spool valve leads to control design challenges. In this work, a model of an electro hydraulic metering poppet valve is considered. Due to design compromises, the response of production metering poppet valves tends to be too slow to maintain a desired flow rate when there are fast upstream pressure variations. Redesigning to speed up the response of the valve may lead to stability issues which can be traced to plant uncertainty. Frequency response analysis of the valve model shows that the model varies greatly depending on the operating point chosen for the linearization. The analysis presented will help define the problem of designing hardware and control systems for higher performance but still reliable metering poppet valves.