3D Printed Hydraulic Actuation

Design and Evaluation of a 3D Printed Hydraulic Actuation System

Master thesis (2021)

Authors

J.J. Tiel Groenestege Mechanical Engineering

Contributors

G. Smit Medical Instruments & Bio-Inspired Technology - Mechanical, Maritime and Materials Engineering (supervisor 1)
Faculty
Mechanical Engineering
Copyright: © 2021 Jurjen Tiel Groenestege
Additive Manufacturing 3D Printing Hydraulic Actuation Prosthesis Upper limb
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Published Date

14-01-2021

Language

English

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Faculty

Mechanical Engineering

Abstract

Objective: The objective of this study was to develop and evaluate a 3D printed hydraulic actuation system, applied in a multi-articulate upper limp prosthesis. The prosthesis was designed to produce sufficient pinch force to be competitive with comparable devices (30 N), and weigh less than a human hand (<0.43 kg). The actuator should function at a high operating pressure (>1.4 MPa) and be compact, such that it fits within the mechanism of the hand.
Method: The prosthesis was designed according to a modified V-model design methodology. A prototype was made that embodies the index finger, thumb, and part of the palm. The structural parts were printed using FDM. The actuators were printed in a single step using SLA, requiring only cleaning and curing. To evaluate the performance of the actuators, a set of measurements was carried out, measuring geometrical accuracy, static pressure, and friction in the cylinder. The prototype was tested on pinch force, closing time and weight.
Results: Cylinders that are printed at an angle of 90 degrees with respect to the build plate, have a higher roundness that cylinders that are printed at 45 degrees. The actuators were tested at pressures of up to 4.5 MPa, showing no signs of plastic deformation, and have a theoretical maximum pressure of up to 5.9 MPa. While lifting a mass of 6.49 kg, a cylinder friction force of 25.7 N was measured, which is higher than expected. The prototype could reliably deliver a pinch force of 30 N, with a maximum measured value of 41 N. When operating at high pressures, leakage through the piston O-ring seal was not prevented.
Conclusion: This study presents the first hydraulic actuation system that is fabricated entirely with 3D printing. A prototype was built to demonstrate that the prosthetic hand that is designed, is able to produce a pinch force of >40 N, showing that it can compete with similar devices. Its mass (0.35 kg without pump and battery) is less than that of a human hand. Controlling friction and leakage remains a serious concern due to the geometrical accuracy of 3D printing. Future possibilities are increased customization and reduced fabrication cost of hydraulically actuated mechanical systems.