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Research Papers

Analysis of Small-Scale Hydraulic Actuation Systems

[+] Author and Article Information
Jicheng Xia

e-mail: xiaxx028@umn.edu

William K. Durfee

e-mail: wkdurfee@umn.edu
Department of Mechanical Engineering,
University of Minnesota,
111 Church Street SE,
Minneapolis, MN 55455

1Corresponding author.

Contributed by the Mechanisms and Robotics Committee of ASME for publication in the Journal of Mechanical Design. Manuscript received January 11, 2012; final manuscript received May 5, 2013; published online July 2, 2013. Assoc. Editor: Alexander Slocum.

J. Mech. Des 135(9), 091001 (Jul 02, 2013) (11 pages) Paper No: MD-12-1020; doi: 10.1115/1.4024730 History: Received January 11, 2012; Revised May 05, 2013

We investigated small-scale hydraulic power actuation systems using a system level analysis, where small-scale refers to systems generating 10 to 100 W output power, to determine whether the high power density advantage of hydraulics holds at small sizes. Hydraulic actuator system power density was analyzed with simple physics models and compared to an equivalent electromechanical system comprised of off-the-shelf components. Calculation results revealed that high operating pressures are needed for small-scale hydraulics to be lighter than the equivalent electromechanical system. The analysis was limited to the actuator and conduit as those are the components that must be located on the mechanism. A complete comparison should add the weight and efficiency of the power supply.

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References

Figures

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Fig. 2

Ideal hydraulic cylinder used for analysis

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Fig. 1

Architecture for powered actuation system. Top row is generic, middle row is electromechanical, bottom row is hydraulic.

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Fig. 3

Wall loading scenario used to calculate wall thickness

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Fig. 5

Experimentally determined cylinder force efficiency as a function of pressure for two rod speeds. The lines are the predicted efficiency curves from the O-ring model for the extremes of the coefficient of friction.

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Fig. 6

Experimentally determined cylinder force efficiency as a function of cylinder bore and two rod speeds. Overlaid are the equivalent results from the O-ring model.

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Fig. 7

Comparison between the actual weight and the weight predicted from the theoretical analysis for 187 commercial cylinders. The solid line indicates an exact match between actual and predicted. The inset expands the data for light weight cylinders.

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Fig. 9

Method for calculating the weight of a hydraulic system

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Fig. 4

Cylinder efficiency as a function of bore size. The plot was generated assuming 500 psi operating pressure and 0.1 m/s rod speed.

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Fig. 8

Hydraulic conduit efficiency at several pressures and levels of output power, showing that the efficiency of the conduit is high unless the pressure is low. Conduit length: 1 m, conduit inner diameter: 5 mm.

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Fig. 10

Motor weight vs. output power

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Fig. 11

Motor efficiency vs. output power

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Fig. 12

Ball screw weight vs. rated dynamic load at.01 m (top) and.04 m (bottom) stroke

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Fig. 16

Hydraulic and electromechanical system weight at several stroke lengths. Output power: 10 W, velocity: 0.01 m/s, transmission line length: 0.1 m.

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Fig. 17

Hydraulic and electromechanical system weight at several stroke lengths. Output power: 100 W, velocity: 0.01 m/s, transmission line length: 0.1 m.

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Fig. 18

Hydraulic and electromechanical system weight at several transmission line lengths. Output power: 10 W, stroke: 0.05 m, velocity: 0.01 m/s.

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Fig. 19

Hydraulic and electromechanical system weight at several transmission line lengths. Output power: 100 W, stroke: 0.05 m, velocity: 0.01 m/s.

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Fig. 22

Ankle torque (solid) and velocity (dashed) for one step when walking at normal speed. The vertical dotted-dashed line marks the peak power point. Data from Ref. 21.

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Fig. 13

Method for calculating the weight of an electromechanical system

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Fig. 14

Hydraulic and electromechanical system weight at several output velocities. Output power: 10 W, stroke: 0.05 m, transmission line length: 0.1 m. The 100 psi, 100 mm/s data point is missing because there is no low pressure, high speed hydraulic system that can match the efficiency of the equivalent electromechanical system.

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Fig. 15

Hydraulic and electromechanical system weight at several output velocities. Output power: 100 W, stroke: 0.05 m, transmission line length: 0.1 m.

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Fig. 20

Hydraulic and electromechanical system weight at several output powers. Stroke: 0.05 m, velocity: 0.01 m/s, transmission line length: 0.1 m.

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Fig. 21

Operating pressure required for the hydraulic system to be the same weight as the equivalent electromechanical system at several output powers. Stroke: 0.05 m, velocity: 0.01 m/s, transmission line length: 0.1 m.

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Fig. 23

Conceptual design for a hydraulic AFO.

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