A Comparison Study of a Novel Self-Contained Electro-Hydraulic Cylinder versus a Conventional Valve-Controlled Actuator—Part 1: Motion Control

Abstract

This research paper presents the first part of a comparative analysis of a novel self-contained electro-hydraulic cylinder with passive load-holding capability against a state of the art, valve-controlled actuation system that is typically used in load-carrying applications. The study is carried out on a single-boom crane with focus on the control design and motion performance analysis. First, a model-based design approach is carried out to derive the control parameters for both actuation systems using experimentally validated models. The linear analysis shows that the new drive system has higher gain margin, allowing a considerably more aggressive closed-loop position controller. Several benefits were experimentally confirmed, such as faster rise time, 75% shorter settling time, 61% less overshoot, 66% better position tracking, and reduction of pressure oscillations. The proposed control algorithm is also proven to be robust against load variation providing essentially the same position accuracy. In conclusion, the novel self-contained system is experimentally proven to be a valid alternative to conventional hydraulics for applications where passive load-holding is required.

A Novel Solution for the Elimination of Mode Switching in Pump-Controlled Single-Rod Cylinders

“…By connecting a hydraulic pump directly to the actuator, its velocity may be controlled by varying either the speed of the prime mover, the displacement of the pump, or a combination of both [1]. This eliminates the need for throttling of the hydraulic fluid, allowing energy efficiencies superior to that of conventional valve-controlled systems [2,3]. This also facilities the construction of compact electrohydraulic drives, combining the advantages of electrical actuation (e.g., energy efficiency, plug-and-play functionality and no external piping) with those of the hydraulic actuation (e.g., long service life, high force availability and good overload protection) [2][3][4].…”

A Comparison Study of a Novel Self-Contained Electro-Hydraulic Cylinder versus a Conventional Valve-Controlled Actuator—Part 2: Energy Efficiency

“…The cylinder's piston extends and retracts between the start position x C,0 = 50 mm and the desired position x C,re f = 450 mm, at a desired maximum velocity v C,max = 120 mm/s. The SCC is operated in closed-loop, including position feedback control, velocity feedforward, pressure feedback, and passive load-holding, according to the control strategy and the control algorithm presented in the first part of this comparison study [28]. In passive load-holding mode, the load-holding valves are closed by deactivating the electro-valve and switching off the signal enabling power to the prime mover when motion is not desired.…”

“…As described in the first part of this study [28], the SCC can be operated with two different load-holding strategies, namely passive load-holding (PLH) and active load-holding (ALH). The electric power and energy consumption when utilizing these two strategies are compared in Figure 9.…”

“…A SCC concept able to operate in four quadrants, including passive load holding, and suitable for power levels above 5 kW was proposed in [10] and implemented on a singleboom crane in [12]. A further analysis of this solution is presented in the first part of this research [28], including the control design and the motion performance comparison against the valvecontrolled cylinder (VCC) discussed in [29]. Concerning the paper structure, Section 2 presents the two considered actuation systems while Section 3 the theoretical background.…”

Guidelines to Select Between Self-Contained Electro-Hydraulic and Electro-Mechanical Cylinders

“…An EHC concept comprising passive load-holding devices, sealed tank, capable of recovering energy, four quadrants operations, and suitable for power levels above 5 kW was proposed in [14], and implemented on a load carrying application in [15]. Hagen et al present further investigations on this concept with a focus on motion performance [20] and energy efficiency [21] showing that EHCs significantly improves conventional hydraulics.…”