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.
Multiple design iterations often require repeated stress analyses to be performed as the design is modified slightly. A method is presented that combines the meshless stress analysis method with a reanalysis technique to avoid repeating the time-consuming steps of remeshing and solving for small design changes. An iterative reanalysis method based on the preconditioned conjugate gradient method is introduced and compared to the linear Taylor series, simple iteration, and combined approximations reanalysis methods. The asymptotic running time is presented for each reanalysis method, and accuracy is compared for two example problems: a cantilever beam and a hole-in-plate. Results show the Taylor series to have the fastest run time, followed in order by simple iteration, preconditioned conjugate gradient, and combined approximations. For the two example problems, accuracy of the simple iteration method is poor for design changes greater than 5%. Taylor series accuracy depends greatly on the choice of the design variable, the example problem, and the method for computing the sensitivity. The combined approximations and preconditioned conjugate gradient methods both demonstrate less than 10% error up to a 100% change in height for the cantilever beam and 30% change in radius for the hole-in-plate example. Multiple design iterations often require repeated stress analyses to be performed as the design is modified slightly. A method is presented that combines the meshless stress analysis method with a reanalysis technique to avoid repeating the time-consuming steps of remeshing and solving for small design changes. An iterative reanalysis method based on the preconditioned conjugate gradient method is introduced and compared to the linear Taylor series, simple iteration, and combined approximations reanalysis methods. The asymptotic running time is presented for each reanalysis method, and accuracy is compared for two example problems: a cantilever beam and a hole-in-plate. Results show the Taylor series to have the fastest run time, followed in order by simple iteration, preconditioned conjugate gradient, and combined approximations. For the two example problems, accuracy of the simple iteration method is poor for design changes greater than 5%. Taylor series accuracy depends greatly on the choice of the design variable, the example problem, and the method for computing the sensitivity. The combined approximations and preconditioned conjugate gradient methods both demonstrate less than 10% error up to a 100% change in height for the cantilever beam and 30% change in radius for the hole-in-plate example. Disciplines Mechanical Engineering Comments Nomenclature
This paper presents dynamic modelling, control design, simulation results, and real time Virtual Reality (VR)-based human-in-the-loop testing for a wheel loader control system. In particular, a loader with electro-hydraulic 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. An LQG-based (Linear Quadratic Gaussian) robust controller is designed for automatic bucket levelling to assist the operator during the boom motion. The controller design is tested with a nonlinear model in a real-time VR simulation. In this 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.
Interactive design gives engineers the ability to modify the shape of a part and immediately see the changes in the part's stress state. Virtual reality techniques are utilized to make the process more intuitive and collaborative. The results of a meshless stress analysis are superimposed on the original design. As the engineer modifies the design using subdivision volume free-form deformation, the stress state for the modified design is computed using a Taylor series approximation. When the designer requests a more accurate analysis, a stress re-analysis technique based on the pre-conditioned conjugate gradient method is used with parallel processing to quickly compute an accurate approximation of the stresses for the new design. ABSTRACTInteractive design gives engineers the ability to modify the shape of a part and immediately see the changes in the part's stress state. Virtual reality techniques are utilized to make the process more intuitive and collaborative. The results of a meshless stress analysis are superimposed on the original design. As the engineer modifies the design using subdivision volume free-form deformation, the stress state for the modified design is computed using a Taylor series approximation. When the designer requests a more accurate analysis, a stress reanalysis technique based on the pre-conditioned conjugate gradient method is used with parallel processing to quickly compute an accurate approximation of the stresses for the new design. INTRODUCTIONFinite element analysis has enabled designers to approximate product performance and predict product failure early in the design process before physical prototypes are built and tested. However, as products become more complex, longer computation times are needed to calculate these performance parameters. In addition, when a designer wishes to change the shape of a part in order to investigate multiple product design options, the entire finite element analysis must be recalculated. The intent of this research is to provide the designer with a design environment where part shapes can be modified and stresses can be examined interactively. We call this interactive design.
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