CIM Bulletin, Vol. 98, No. 1085, 2005
S. Frimpong and Y. Hu
Hydraulic shovels are widely used for primary production in surface mining operations. The efficiency and costs of mining operations greatly depend on the efficient use of these capital-intensive machines. The shovel-truck mining method is flexible and efficient, however, it can be rendered inefficient from field and operator constraints. Physical and mechanical properties of the formation have a severe impact on a shovel’s efficiency. Variability in material diggability, unstructured mining environments, and limited space and operator inefficiency affect the performance of these shovel excavators. The resulting fatigue failure in equipment components cause unplanned downtime, reduced effeciency, and high production costs. An intelligent shovel excavation (ISE) system (see figure) is being proposed to solve these problems. The ISE system will use force-torque sensors, vision, and display systems to capture and display the resistance due to excavation on an on-board screen in the operator’s cabin. Using the displayed information, an operator can assess local formation variations and make real-time decisions on primary or secondary blasting, in-pit blending, and material stockpiling.
Previous studies have treated shovel excavators in a form similar to the equations of motion of robotic manipulators. Machine kinematics and dynamics are used to develop geometrical relations among the front-end components of the shovel. The cylinder hydraulic forces and joint interactive forces of the shovel are determined given the formation of resistive forces. The associated non-linear differential equations of this approach are difficult to solve, given the joint frictions and hydraulic fluid properties. Scaled or full-scale shovel excavators have also been used to directly measure the resistive forces due to excavation and the hydraulic forces in the cylinders using sensors inside the shovel components and/or the formation. The scaled models have the advantage of simulating realistic real-time excavation, however, they are expensive and time-consuming.
This paper advances an important foundation for ISE technology in the area of hydraulic shovel kinematics and dynamics using the modified Newton-Euler method and virtual prototype simulation. Kinematics modelling is used to examine the angular and linear displacements, velocities, and accelerations in the geometrical space of the shovel excavator. Dynamic models are used to determine the hydraulic shovel’s excavation forces and torques, which are essential for understanding and improving machine performance. A virtual simulator is developed to simulate the hydraulic shovel’s performance in the ADAMS environment. The simulator is validated with data on shovel geometry and the physical and mechanical properties of a formation in a typical surface mining environment. Through detailed experimentation, the simulator is used to examine the shovel kinematics, dynamics, and the effects of digging trajectories and cycle times on a shovel’s power consumption.
The results of the shovel kinematics and dynamic simulation show the variations of the optimized joint angles and the hydraulic forces in the boom, stick, and bucket cylinders within a cycle for this formation environment. For efficient excavation, the motion of the front-end assembly must mimic the optimized joint angles. The forces within the boom and bucket cylinders increase rapidly and peak halfway in the cycle and decrease with similar geometric profiles. The results also show that a shorter digging time increases the shovel’s operating power requirements, and the required peak power increases by 100% when the digging time is reduced by 50%. For given formation characteristics and trajectory profile, a digging time which is faster than the optimum increases the formation resistance and hence the power requirements. The simulation results also show that a shallow trajectory facilitates the digging process, with 50% reduction in peak power requirements compared to a deep one. For given formation characteristics and trajectory profile, the simulator can be used to generate optimized joint angular motions, cylinder forces, digging times, and trajectory profiles for efficient excavation process. This simulator provides a powerful tool for performance monitoring, excavation process designs, and structural optimization of hydraulic excavators.