h three flow control proportional valves has been proposed for the control of elevator velocity and non-synchronous error between the cylinders ofa twin cylinder hydraulic elevator. A pseudo-derivative feedback control scheme has shown tobe an appropriate technique to achieve a desired velocity pattern. Furthermore, this system guarantees low non-synchronous error by applying a constrained step PD controller. The test results show that the non-synchronous error can be kept within ±2 mm. A certain discrepancy between the desired pattern and the actual velocity pattern isdue mainly to the hysteresis of the electro-hydraulic proportional valves. A new solenoid actuated non-return valve has been designed, fabricated and tested, and proves tobea good hydraulic device for preventing cab sinking.
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