Electro-hydraulic proportional control of twin-cylinder hydraulic elevators

The large size of the cab of an electro-hydraulic elevator necessitates the arrangement of two cylinders located symmetrically on both sides of the ca b. This paper reports the design of an electro-hydraulic system which consi sts of three flow-control proportional valves. Speed regulation of the cab and synchronization control of the two cylinders are also presented. a pseu do-derivative feedback (PDF) controller is applied to obtain a velocity pat tern of the cab that proves to be close to the given one. The non-synchrono us error of the two cylinders is kept within +/- 2 mm with a constrained st ep proportional-derivative (PD) controller. A solenoid-actuated non-return valve, i.e, a hydraulic lock, is also developed to prevent cab sinking and allow easy inverse-fluid flow. (C) 2001 Published by Elsevier Science Ltd.