Model of the excavator arm of CNH Wheeled Excavator for H.I.L.application

Recently CNH developed a new series of wheel excavators equipped with a Electronic Control Unit (ECU) that use a new control software. It was critical to test and validate the design of this new control system before deployment to ensure high customer satisfaction and reducing warranty costs. Test on a Hardware-In-the-Loop (HIL) platform accelerates the verification and validation process. A validated HIL set-up, being a repeatable and reliable test platform with a short turnaround time is ideal for developing standardized processes for ECU testing and calibration. The goal of this paper is to show the development of the wheel excavator model for HIL application. In particular the model of the hydraulic circuit and the mechanical system of the wheel excavator arm are reported. An analytical model of the hydraulic system includes orifice flow equations, fluid compressibility equations for all the oil volumes, as well as the force balance equations for all the cylinders. In order to describe the motion of the excavator arm both kinematic and dynamic models were developed from the fundamental theory for robotic manipulators [1]. The kinematic model is derived following the Denavit-Hartenberg guidelines while the dynamic model is created by writing Newton- Euler equations for each link of the arm. By combining the equations, a dynamical model in terms of the joint variables is obtained. The mathematical model have many nonlinearities because of nonlinear opening characteristics and dead zone of main control valves, geometrical relationship in the kinematic model, frictions, ecc. These aspects make modeling very complex. The model has been built in a modular approach so that model updates due to a modification of the system configurations could be performed starting from available model, by single component specifications, thereby reducing the total effort for the new models. The model must have same specific property due to the HIL application; the first of all is that the model must run in real time. A second general target is that the developed model easily fit into the available simulation models environment for HIL closed-loop simulation, in particular it must turn employing maximum 15% of resources at fixed time step 1ms and with one of the following numerical integrators typologies: ODE1 to ODE4. Simulation results referred to some maneuvers have been compared with acquisition