Electro-hydraulic operating system for extensible boom crane

Abstract

An electro-hydraulic operating system for an extensible boom includes one or more hydraulic cylinders for imparting relative motion between the boom sections to retract the boom according to an electronically stored program of sequences of movement and speeds. A source of pressurized hydraulic fluid is fed through appropriate control valves which include solenoid valves in fluid communication with a source of pressurized hydraulic fluid. The solenoid control valves are supplied with control currents proportional to the desired flow rates of fluid to the hydraulic cylinders in order to achieve speed and position control according to the stored program. A metering valve structure is provided for operation in conjunction with the solenoid control valves. The metering valve includes an associated pilot valve which receives variable pressure signals from the solenoid control valves to achieve the metering of fluid to the hydraulic cylinders in proportion to the characteristics of the control current supplied to the solenoid valves. The electrical control signals are such that the hydraulic cylinders may move associated boom sections at gradually increasing speeds during a starting period of any cycle of movement of the section, at a substantially constant speed during an intermediate period of movement and at a gradually decreasing speed during a stopping period preceding the end of the cycle of movement, thereby providing soft start and soft stop of the sections.