Patent ID: 8215227

Claim:
A method for controlling a valve system controlling an actuator, wherein the valve system comprises: a first valve series coupled between an inlet port and a first working port, the first valve series comprising a set of valves coupled in parallel for controlling the flow rate gradually; a second valve series coupled between an outlet port and a second working port, the second valve series comprising a set of valves coupled in parallel for controlling the flow rate gradually; a third valve series coupled between the inlet port and the second working port, the third valve series comprising a set of valves coupled in parallel for controlling the flow rate gradually; and a fourth valve series coupled between the outlet port and the first working port and comprising a set of valves coupled in parallel for controlling the flow rate gradually; the method comprising: controlling a first direction of motion of the actuator solely by the first and the second valve series without the help of the third and the fourth valve series; or, controlling a second direction of motion of the actuator solely by the third and the fourth valve series without the help of the first and the second valve series; detecting a fault situation in a valve series responsible for either the first or the second direction of motion; and compensating for an error in the control of the actuator, the error being caused by the fault situation, by also using the third valve series, or the fourth valve series, or both of them, for the control of the first direction of motion; or, compensating for an error in the control of the actuator, the error being caused by the fault situation, by also using the first valve series, or the second valve series, or both of them, for the control of the second direction of motion.