Programmable valves: a solution to bypass deadband problem of electro-hydraulic systems

The closed-center PDC/servo valves have over-lapped spools to prevent internal leakage so that the system can hold a position even when the power is off. However, the over-lapped spools also introduce deadbands, which are sandwiched by plant dynamics and valve dynamics. The sandwiched deadbands would degrade the achievable control performance and are very difficult to deal with. Instead of trying to solve this sandwiched deadband control problem via complicated advanced controls with limited improvement of achievable performance, this paper bypasses this problem with the use of both valve hardware redesign and advanced controls to overcome this deadband problem completely. Specifically, the hardware is based on the programmable valves, a unique combination of five independently controlled poppet type cartridge valves. This paper compares the programmable valves with traditional PDC/servo valves and demonstrate the ability of completely solving the deadband control problem of the electro-hydraulic systems using the programmable valves. A nonlinear model based adaptive robust controller with deadband compensation is designed for PDC/servo valve and a two-level coordinate controller is designed for programmable valves to maximize the achievable control performance of each. Experimental results show that the best tracking performance is achieved through the programmable valves.