Optimal Control for Hydraulic System with Separate Meter-in and Separate Meter-out

Individual meter-in and meter-out proportional control of hydraulic cylinders allow more flexible strategies how to handle a payload while optimising certain aspects of the motion. An optimal control approach based on the Hamiltonian is used to plan a motion path for a separate meter-in and separate meter-out system. One goal is to avoid oscillations at the end of the motion in the sense of active vibration damping. With the mathematical model presented, it is possible to include the cylinder pressures into the optimisation goals. Not only the the final values for position and speed of the load can be acquired, but also desired values for the pressures at the end of the motion. Maintaining a minimum pressure level is important in order to avoid cavitation and to keep the stiffness of the system. The course of the pressures follows from the design of the motion and will reach the desired values in an open loop control. In order to estimate the computing effort, the algorithm was tested on three platforms. One of those is an ARM-based hardware that represents the computing power of modern embedded systems, to demonstrate that an implementation on such system is possible. Several motion experiments were carried out in simulation to study the behaviour and to discuss application issues.