Links with Variable Stiffness and Their Applications in Robotics

Caro Diaz, Freddy Santiago

Links with Variable Stiffness and Their Applications in Robotics

Caro Diaz, Freddy Santiago

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Publication Type:: Thesis
Issue Date:: 2024

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Field	Value	Language
dc.contributor.author	Caro Diaz, Freddy Santiago
dc.date.accessioned	2025-06-03T00:30:12Z
dc.date.available	2025-06-03T00:30:12Z
dc.date.issued	2024
dc.identifier.uri	http://hdl.handle.net/10453/187597
dc.description	University of Technology Sydney. Faculty of Engineering and Information Technology.	en_US.UTF-8
dc.description.abstract	Robots that are able to change the stiffness of their members have become a new paradigm in robotics and have captured the attention of a big part of the research community in robotics. This paradigm considers that structural members of a robot should vary their stiffness in order to perform tasks that require different states of flexibility or rigidity. This research focuses on a method to change the stiffness known as Laminar Jamming (LJ). It has a significant potential to achieve high stiffness variation and its manufacturing is based on traditional machining processes. A new mechanism to vary the stiffness of LJ structures has been proposed. It consists of a pneumatic actuator that drives a trapezoidal pin to mechanically interfere with the layers, changing the stiffness of the LJ structure. Then, applications of Laminar Jamming in robot arms were studied. Firstly, a variable stiffness link (VSL) for robot arms was developed based on LJ structures with the trapezoidal pin mechanism. The capacity of this VSL to attenuate impacts in human-robot interactions was investigated. Secondly, the developed VSL was used to build a VSL robot arm with two degrees of freedom whose stiffness in multiple directions and poses was measured and represented through the concept of the Stiffness Envelope that explains how each VSL contributes to the stiffness of the robot arm and how this distribution of stiffness can be used to carry out a specific task. The proposed VSL robot arm was also tested to determine its destiffening time. Experiments and simulations have shown that the LJ structures with trapezoidal pin mechanism reached a maximum stiffness ratio of 3.65, which is 15% higher than the stiffness ratio of an equivalent laminar jamming with flat clamps. The VSL based on the trapezoidal pin mechanism also demonstrated its capacity to reduce the impact force by 12% during a collision against a human being. In addition, the proposed VSL robot arm demonstrated its capacity to reduce its stiffness from a rigid state to a flexible state in approximately 173 ms, showing that the destiffening time of the proposed VSL robot arm could be short enough to be effective in the mitigation of the damage to a human being due to the impact against a cobot. The methodologies applied in this research include bending tests, torsion tests, impact tests, stiffness tests, and Finite element Simulations.	en_US.UTF-8
dc.format	Thesis (PhD)
dc.language.iso	en_US	en_US.UTF-8
dc.relation	https://opus.lib.uts.edu.au/bitstream/10453/187597/1/thesis.pdf
dc.rights	info:eu-repo/semantics/openAccess
dc.rights	The author owns the copyright in this thesis including all reproduction and reuse rights for the work. The work may not be altered without the permission of the copyright owner. Attribution is essential when quoting or paraphrasing from this thesis.
dc.rights	© 2024 Freddy Santiago Caro Diaz
dc.rights	au.edu.uts.lib/cph
dc.title	Links with Variable Stiffness and Their Applications in Robotics	en_US.UTF-8
dc.type	Thesis
utslib.copyright.status	open_access	*

Abstract:

Robots that are able to change the stiffness of their members have become a new paradigm in robotics and have captured the attention of a big part of the research community in robotics. This paradigm considers that structural members of a robot should vary their stiffness in order to perform tasks that require different states of flexibility or rigidity. This research focuses on a method to change the stiffness known as Laminar Jamming (LJ). It has a significant potential to achieve high stiffness variation and its manufacturing is based on traditional machining processes. A new mechanism to vary the stiffness of LJ structures has been proposed. It consists of a pneumatic actuator that drives a trapezoidal pin to mechanically interfere with the layers, changing the stiffness of the LJ structure. Then, applications of Laminar Jamming in robot arms were studied. Firstly, a variable stiffness link (VSL) for robot arms was developed based on LJ structures with the trapezoidal pin mechanism. The capacity of this VSL to attenuate impacts in human-robot interactions was investigated. Secondly, the developed VSL was used to build a VSL robot arm with two degrees of freedom whose stiffness in multiple directions and poses was measured and represented through the concept of the Stiffness Envelope that explains how each VSL contributes to the stiffness of the robot arm and how this distribution of stiffness can be used to carry out a specific task. The proposed VSL robot arm was also tested to determine its destiffening time. Experiments and simulations have shown that the LJ structures with trapezoidal pin mechanism reached a maximum stiffness ratio of 3.65, which is 15% higher than the stiffness ratio of an equivalent laminar jamming with flat clamps. The VSL based on the trapezoidal pin mechanism also demonstrated its capacity to reduce the impact force by 12% during a collision against a human being. In addition, the proposed VSL robot arm demonstrated its capacity to reduce its stiffness from a rigid state to a flexible state in approximately 173 ms, showing that the destiffening time of the proposed VSL robot arm could be short enough to be effective in the mitigation of the damage to a human being due to the impact against a cobot. The methodologies applied in this research include bending tests, torsion tests, impact tests, stiffness tests, and Finite element Simulations.

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http://hdl.handle.net/10453/187597