Hydraulic positioning servo system

Claim 1

A HYDRAULICALLY POSITIONED SERVO SYSTEM WHICH INCLUDES A HYDRISTOR AS A POSITION FEEDBACK ELEMENT, SAID HYDRISTOR COMPRISING A CASING WITH A CYLINDRICAL FLUID CHAMBER HAVING A ROTATABLE METERING ELEMENT MOUNTED THEREIN TO MODULATE THE FLUID FLOW THROUGH SAID CHAMBER INTO TWO COMPLEMENTARY FLUID FLOWS RESULTING FROM TWO COMPLEMENTARY HYDRAULIC RESISTANCES, SAID HYDRISTOR PROVIDED WITH TWO FLUID INLET PORTS TO SAID CHAMBER, SAID INLET PORTS BEING FORMED AS ORIFICES THAT ARE CONTROLLED BY SAID METERING ELEMENT, A COMMON OUTLET PORT CONNECTED TO SAID CHAMBER, SAID METERING ELEMENT BEING FITTED AND ROTATABLY POSITIONED WITHIN SAID FLUID CHAMBER AND PROVIDED WITH MOVABLE SURFACES TO PROVIDE TWO COMPLEMENTARY HYDRAULIC RESISTANCES TO ALLOW TWO COMPLEMENTARY FLOWS OVER SAID METERING ELEMENT AND TO SAID COMMON OUTLET, SAID TWO COMPLEMENTARY HYDRAULIC RESISTANCES ARE FORMED BY THE TWO ORIFICES AND THE MOVABLE SURFACES OF THE METERING ELEMENT, SAID SERVO SYSTEM DIVIDED INTO A POWER STAGE AND A FEEDBACK CONTROL STAGE, SAID POWER STAGE COMPRISING A POWER CYLINDER AND PISTON, A MAIN PRESSURE SOURCE AND A FOUR WAY VALVE, SAID FOUR WAY VALVE CONNECTED BY FLUID LINES TO SAID POWER CYLINDER, SAID FEEDBACK CONTROL STAGE COMPRISING SAID HYDRISTOR, AN AUXILIARY PRESSURE SOURCE, A RATIO FLOW DIVIDER TO PROVIDE TWO COMPLEMENTARY RESISTANCES AND TWO COMPLEMENTARY FLOWS, AND A DIFFERENTIAL PRESSURE SENSING DEVICE WHICH IS MECHANICALLY CONNECTED TO SAID FOUR WAY VALVE AND CONNECTED WITH FLUID LINES TO SAID RATIO FLOW DIVIDER AND TO SAID HYDRISTOR, SAID HYDRISTOR HAVING ITS METERING ELEMENT MECHANICALLY CONNECTED TO THE ROTATABLE PISTON OF SAID POWER CYLINDER AS A FEEDBACK ELEMENT, SAID RATIO FLOW DIVIDER COMPRISING A CLOSED CASING WITH A FLUID INLET PORT AT ITS CENTER AND TWO FLUID OUTLET PORTS, ONE AT EACH END OF SAID CASING, A PISTON AND ROD MOUNTED LOOSELY AND CENTRALLY WITHIN SAID CLOSED CASING TO PRODUCE SAID TWO COMPLEMENTARY HYDRAULIC RESISTANCES AND TWO COMPLEMENTARY FLUID FLOWS, SAID ROD PROVIDING THE MEANS FOR A MECHANICALLY PRODUCED INPUT SIGNAL, SAID PISTON ROD EXTENDING THROUGH SAID CASING, SAID DIFFERENTIAL PRESSURE SENSING DEVICE COMPRISING A CLOSED CYLINDRICAL CASING WITH TWO FLUID INLET PORTS AND TWO FLUID OUTLET PORTS, ONE INLET AND ONE OUTLET PORT CONNECTED TO EACH END OF SAID CLOSED CYLINDRICAL CASING TO ALLOW A FLUID FLOW THERETHROUGH, A DIVIDING PISTON WITH ITS PISTON ROD EXTENDING THROUGH SAID CLOSED CYLINDRICAL CASING, AND A RESILIENT ELEMENT POSITIONED ON EACH SIDE OF SAID PISTON TO NORMALLY RETAIN SAID PISTON CENTERED WHEN SAID FLUID PRESSURE ON EACH SIDE OF SAID PISTON IS EQUAL, SAID PISTON OF SAID DIFFERENTIAL PRESSURE SENSING DEVICE CONNECTED TO SAID PISTON OF SAID FOUR WAY VALVE TO CONTROL ITS MOVEMENT AND IN TURN CONTROL THE FLUID FLOW TO SAID POWER CYLINDER, SAID DIFFERENTIAL PRESSURE SENSING DEVICE PROVIDING MEANS TO COMPARE THE RATIO OF THE TWO COMPLEMENTARY RESISTANCES OF THE HYDRISTOR WITH THE RATIO OF THE TWO COMPLEMENTARY RESISTANCES OF THE SIGNAL INPUT VALVE DURING FLUID FLOW, SAID DIFFERENTIAL PRESSURE SENSING DEVICE WHICH INCLUDES SAID RESILIENT ELEMENT ALSO RESPONDING TO PRESSURE CHANGES TO MOVE SAID FOUR WAY VALVE AND CORRECTING AN ERROR SIGNAL WHEN A PRESSURE DIFFERENTIAL EXISTS IN SAID DIFFERENTIAL SENSING DEVICE BY MOVING SAID FOUR WAY VALVE IN THE DIRECTION INDICATED BY THE ERROR SIGNAL AND IN TURN MOVE SAID PISTON OF SAID POWER CYLINDER AND SAID METERING ELEMENT OF SAID HYDRISTOR TO REDUCE SAID ERROR SIGNAL TO ZERO.