Multi Degree-of-Freedom Hydraulic

Human Power Amplifier with Rendering

of Assistive Dynamics

Sangyoon Lee, Perry Y Li

This work is performed within the Center for Compact and Efficient Fluid Power (CCEFP) supported by the

National Science Foundation under grant EEC-05040834. Donation of components from Takako Industries is

gratefully acknowledged.

Human Power Amplifier

• Tool that amplifies human force: in oar form

• Another example: exoskeleton

• Control objective: passive mechanical tool

• Physically connected to the task

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Human Power Amplifier

• Tool that amplifies human force: in oar form

• Another example: exoskeleton

• Control objective: passive mechanical tool

• Physically connected to the task

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Human

Environment

Control Objective

• Controlling the hydraulic actuator force

• Amplify the human force by a factor of

• resulting in the dynamics of target passive mechanical tool:

• ML: apparent inertia of the tool

• Achieved when

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a humanF F

Hydraulic Transformer

• Pressure control by metering

valve causes a significant

throttling losses

• Heat generation

• Transformer eliminates such

losses

• Constant power between input

A’ and load B

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• Hydraulic: high power density, precision, compactness

Flow

Pre

ssu

re

Output

Input

Load connected

to servo valve Load connected to transformer

Can we use transformer for

human power amplifier?

Outline

• Introduction

• System Dynamics

• Control Strategy

• Virtual coordination approach

• Guidance Control

• Experimental Results

• Conclusion

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System Description

• Generalized coordinate

• Hydraulic force from cylinder and motor

• Cylinder for pitch Motor for reach

• Connected to a transformer

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Virtual Coordination Approach

• Direct Force control [1]

• Positive velocity feedback effect

• Not robust

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[1] Li, P. Y., 2004. “Design and control of a hydraulic human power amplifier”. In ASME 2004 International Mechanical

Engineering Congress and Exposition, American Society of Mechanical Engineers, pp. 385–393.

0a dF F F

Virtual Coordination Approach

• Direct Force control [1]

• Positive velocity feedback

• Not robust

• Virtual coordination approach [2]

• Hydraulic actuator = ideal kinematic

actuator in series with nonlinear spring

• Compressibility

• Design controller to mimic the mass-

spring system

• Virtual + Actual

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[1] Li, P. Y., 2004. “Design and control of a hydraulic human power amplifier”. In ASME 2004 International Mechanical

Engineering Congress and Exposition, American Society of Mechanical Engineers, pp. 385–393.

[2] Li, P. Y., 2006. “A new passive controller for a hydraulic human power amplifier”. In ASME 2006 International Mechanical Engineering Congress and

Exposition, American Society of Mechanical Engineers, pp. 1375–1384.

0F

Virtual System

• Virtual inertia acts with

• If coordinated , then resulting

dynamics is

• The target dynamics!

• Guidance

• Passivity:

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Passive Decomposition - Transformation

• Transformation into the velocity spaces [5]

• Transformed dynamics:

• Then, design controller for shape system to

make sure VE 0!

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11 1( )

V

L

L v P

E

v p

M

M

M M M

MM M

Center of the mass

of combined system

Coordination error

[6] Lee, D. J., and Li, P. Y. 2004, “Passive decomposition of multiple mechanical systems under coordination requirements”. IEEE Transactions on

Automatic Control, 58, p. 230.

Locked System

Shape System

PVFC and Obstacle Avoidance

• Using the virtual coordination scheme, we

can add some additional control to the

virtual system such that the physical

system will be naturally guided

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Experimental System

• 2-DOF Human Power Amplifier with a

force handle

• Cylinder driven by transformer

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Computer controlled variable transformer prototype

based on 3.5cc micro-piston pumps

Human Power Amplification

• Wrestling

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Added force input

RMS ~3% with mean desired force

RMS 0.0094 m/s

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PVFC + Obstacle Avoidance

• Obstacle Avoidance + PVFC

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Other developments in Transformer

• Demonstrated controller performance

• Trajectory tracking shown in FPMC 2015

• HPA control shown in DSCC 2015, 2016

• Desire to show efficiency benefit experimentally

• Hardware-In-the-Loop?

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Simulated

Load

Conclusion

• 2-DOF Passive velocity coordination control using a transformer

• PVFC and Obstacle Avoidance to assist the human operator

• Demonstrates transformer need not sacrifice control performance

• Transformer efficiency will be shown

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