Experimental Study on Fast and Energy-Efficient Direct Driven Hydraulic Actuator Unit

Teemu Koitto,Matti Pietola,Heikki Kauranne,Tatiana Minav,Olof Calonius

doi:10.3390/en12081538

Abstract

In this experimental study, a Direct Driven Hydraulics (DDH) system of the closed circuit type was utilized for cyclic vertical actuation in heavy load material handling. The actuator was controlled by a speed-controlled fixed displacement pump. The high energy saving potential of this system has been demonstrated in previous studies by the authors, but the dynamic characteristics of the ramped and P-controlled base system were considered unsatisfactory. Therefore, the system was implemented with an open-loop S-curve control that utilized a pre-calculated RPM (revolutions per minute) profile for the electric motor in order to realize a smooth actuator and load transition as a function of time. The results indicate that S-curve control is exceptionally well suited for producing a controlled lifting–lowering rapid motion with a heavy load, while still keeping the actuator chamber pressures within acceptable limits. In comparison, the motion produced by P-control was characterized by large unwanted pressure peaks together with velocity fluctuations and vibrations at the end of the stroke. Using a combination of S-curve control and hydraulic load compensation, a mass of 1325 kg could be moved 0.26 m in less than 0.5 s. The load compensation reduced the energy consumption by 64%, which would allow downsizing the electric motor and enable cost-efficient DDH implementation.

Highlights

Over the last two decades, the global demand for reducing the energy consumption and pollution emissions of machines has been the driving force for the university researchers and machine manufacturers alike to search for new solutions for the various sub-systems of machines in order to raise their energy efficiency and productivity
This study presents the measurement results of a pump-controlled single-actuator system implemented with a fixed displacement pump and a speed-controlled servomotor; the principle is called Direct Driven Hydraulics (DDH)
The test rig was fitted with an external hydraulic load compensation system, which enabled adjusting the level of compensation, and embodied the possibility of dampening the movement of the load, this was not applied in the tests of this study

Summary

Introduction

Over the last two decades, the global demand for reducing the energy consumption and pollution emissions of machines has been the driving force for the university researchers and machine manufacturers alike to search for new solutions for the various sub-systems of machines in order to raise their energy efficiency and productivity. Doing so will reduce the hydraulic power losses of the hydraulic entirety and provide accurate matching of the supply of pressure and flow rate to the demands of the independent actuators. Another idea is to disconnect the direct connection between the prime mover and the actuators by using hydraulic accumulators and pressure transformers, enabling the prime mover to run at its most energy-efficient operation point, regardless of the status of the actuators. The proposed new solutions enable regenerating hydraulic energy during the lowering of loads or during braking The description of this trend and the associated new fluid power technology can be found in numerous studies. [1] reviewed the approach of direct pump control, [2,3] reviewed solutions that minimize energy loss and utilize regeneration to improve the efficiency of the system, Energies 2019, 12, 1538; doi:10.3390/en12081538 www.mdpi.com/journal/energies

Methods

Results

Discussion

Conclusion