Improved Digital Hydraulic Tracking Control of Water Hydraulic Cylinder Drive

Abstract

A position tracking control system is implemented by utilizing parallel-connected on/off valve series. The pulse code modulation method is used to achieve stepwise flow control and four valve series, each having four two-way solenoid valves, are used. A cost function based controller is used to control simultaneously and independently flow paths from supply to cylinder chambers and from chambers to tank. It is shown that controllability can be improved especially at low velocities by allowing three or four valve series to be open simultaneously instead of using classical inflowoutflow control.

Equal Coded Digital Hydraulic Valve System – Improving Tracking Control with Pulse Frequency Modulation

“…The achieved results with low velocity trajectories (50 mm and 15 mm strokes), even with pure PNM control, are better than the results of Linjama & Vilenius [5]. They achieved 1 mm maximum position error with both strokes while the corresponding result of this study was 0.7 mm.…”

“…Test trajectories for the study are selected to be similar than in a study presented in [5]. So fifth order polynomial is used as a position reference with the movement time of 2 seconds.…”

“…An obvious solution is to increase the number of valves but that leads to too small orifices and another solution was preferred. They introduced four edge control and presented improved controllability [5]. The paper also discusses the drawbacks of the solution.…”

“…In order to achieve cavitation free and energy efficient control, simultaneous pressure and velocity control is required and that is difficult at low velocity with limited resolution. Linjama & Vilenius [5] have analysed this topic and noticed the challenge. An obvious solution is to increase the number of valves but that leads to too small orifices and another solution was preferred.…”

Permanent Magnet Synchronous Machine Sizing: Effect on the Energy Efficiency of an Electro-Hydraulic Forklift

“…Other technologies such as pump-controlled actuators or displacementcontrolled actuators have offered new advantages [12]. Digital hydraulics is one of the alternatives of new technologies enabling energy efficiency improvements [13].…”