Design of a variable stiffness index finger exoskeleton

Robotica ◽

10.1017/s0263574721000965 ◽

2021 ◽

pp. 1-17

Author(s):

Abhishek Attal ◽

Ashish Dutta

Keyword(s):

Index Finger ◽

Variable Stiffness ◽

Stiffness Index ◽

Linear Actuator ◽

Fingertip Force ◽

Variable Compliance

Abstract This paper presents the design and experimentation of a variable stiffness index finger exoskeleton consisting of four-bar mechanisms actuated by a linear actuator. The lengths of the four-bar mechanism were optimized so that it can follow a recorded index fingertip trajectory. The mechanism has a fixed compliance at the coupler of the four-bar link and a variable compliance at the linear actuator that moves the four-bar. The skeletal shape of the coupler of the finger link has been optimized using FEM. The exoskeleton can apply a constant fingertip force irrespective of the position of the fingers.

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A Reconfigurable Variable-Stiffness Parallel Beam for Compliant Robotic Mechanisms Towards Safe Human Interaction

10.1115/detc2021-70226 ◽

2021 ◽

Author(s):

Jiaming Fu ◽

Dongming Gan

Keyword(s):

Variable Stiffness ◽

Human Robot Interaction ◽

Human Interaction ◽

Design Parameters ◽

Parallel Beam ◽

Element Analysis ◽

Cross Sectional ◽

Hollow Beam ◽

Robotic Joints ◽

Variable Compliance

Abstract To co-work with humans, robotic mechanisms need to have variable stiffness with high rigidity for performance and low compliance for safe interactions. This paper introduces a reconfigurable variable-stiffness parallel beam (VSPB) which can be used in both robotic joints and links for variable compliance. The VSPB is a compliant cantilever mechanism with hollow parallel beams in the middle and solid connections at both ends. Stiffness adjusting can be realized by changing the cross-sectional area property of the hollow beam segment discretely through a bistable mechanism block or continuously by the block sliding. Detailed stiffness models of the two VSPB stiffness modes with the block on and off are derived using the approach of serially connected beam modeling and superposition combination. The developed model not only works for thin-walled flexure beams but also general thick beam models. The stiffness change relationship with various design parameters is investigated using the developed model and validated by finite element analysis (FEA) results. The correlation between parameters and errors between FEA and theoretical values is observed and analyzed to optimize the model. These methods and results provide a new concept and theoretical basis for developing new variable stiffness robotic mechanisms towards safe human-robot interaction applications.

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Fingertip force analysis of the index finger and thumb in turning the knob

The Proceedings of the Bioengineering Conference Annual Meeting of BED/JSME ◽

10.1299/jsmebio.2018.30.1c01 ◽

2018 ◽

Vol 2018.30 (0) ◽

pp. 1C01

Author(s):

Hiroto NISHIMURA ◽

Toru TSUMUGIWA ◽

Ryuichi YOKOGAWA

Keyword(s):

Index Finger ◽

Force Analysis ◽

Fingertip Force

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Synergistically configured shape memory alloy for variable stiffness translational actuation

Journal of Intelligent Material Systems and Structures ◽

10.1177/1045389x19828487 ◽

2019 ◽

Vol 30 (6) ◽

pp. 844-854 ◽

Cited By ~ 1

Author(s):

D Nalini ◽

K Dhanalakshmi

Keyword(s):

Shape Memory Alloy ◽

Shape Memory ◽

Variable Stiffness ◽

Large Displacement ◽

Linear Actuator ◽

Shape Memory Alloy Wire ◽

Alloy Wire ◽

Active Compliance ◽

Wide Range ◽

Stiffness Profile

The structural composition of two elastic elements, shape memory alloy wire (active actuating element) and spring (the passive bias), offers variable stiffness actuation. Based on this principle, a variable stiffness linear actuator is conceptually designed and developed. It is electromechanical by nature, that is, it is electrically activated and creates translational/linear motion. The variable stiffness linear actuator engages shape memory alloy wire(s) along with a passive compression spring to work synergistically. The biasing element offers recovery force to the shape memory alloy wire as well as compliance to the whole structure. The synergistic configuration exhibits an aiding force, thereby allowing an actuation with large displacement and a wide range of stiffness. The actuator mechanism is implemented through parallel action and further proposes two different modes of operation: pull mode (i.e. the disc moving along a fixed shaft) and push mode (i.e. linear reciprocating motion of the pushrod). The shape memory alloy configured actuator mechanism is analysed theoretically; the working model of the variable stiffness linear actuator is developed and investigated experimentally. The results apprise that the variable stiffness linear actuator is capable of offering large displacement and in reproducing the stiffness profile for active compliance control applications.

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Configurable Compliance for Series Elastic Actuators

Volume 6B: 37th Mechanisms and Robotics Conference ◽

10.1115/detc2013-13614 ◽

2013 ◽

Cited By ~ 3

Author(s):

Viktor Orekhov ◽

Derek Lahr ◽

Bryce Lee ◽

Dennis Hong

Keyword(s):

Force Control ◽

Joint Stiffness ◽

Variable Stiffness ◽

Effective Length ◽

In Series ◽

Primary Advantage ◽

Variable Compliance ◽

Natural Dynamics ◽

Series Elastic Actuators ◽

Series Elastic

Variable compliance has been a growing topic of interest in legged robotics due to recent studies showing that animals adjust their leg and joint stiffness to adjust their natural dynamics and to accommodate changes in their environment. However, existing designs add significant weight, size, and complexity. Series Elastic Actuators, on the other hand, are designed with a set stiffness usually tuned for actuator performance. We propose a new concept for implementing a physical spring in series with a linear SEA using a cantilevered spring. A movable pivot is used to adjust the stiffness by changing the effective length of the cantilever. While the proposed design does not allow for variable compliance, it does retain many of the benefits of passive spring elements such as absorbing impacts, storing energy, and enabling force control. The primary advantage of the design is the ability to adjust the stiffness of each joint individually without the increased weight and complexity of variable stiffness designs. This paper introduces the motivation for configurable compliance, describes the proposed design concept, explains the design methods, and presents experimental data from a completed prototype.

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Fingertip Force Analysis of Index Finger and Thumb in Rotating the Knob

The Proceedings of the Bioengineering Conference Annual Meeting of BED/JSME ◽

10.1299/jsmebio.2018.30.1c02 ◽

2018 ◽

Vol 2018.30 (0) ◽

pp. 1C02

Author(s):

Sakura FUJITA ◽

Toru TSUMUGIWA ◽

Ryuichi YOKOGAWA

Keyword(s):

Index Finger ◽

Force Analysis ◽

Fingertip Force

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IMPACT OF FINGERTIP ACTIONS ON TOTAL POWER OF SURFACE ELECTROMYOGRAPHY FROM EXTRINSIC HAND MUSCLES

Journal of Mechanics in Medicine and Biology ◽

10.1142/s0219519411004800 ◽

2012 ◽

Vol 12 (03) ◽

pp. 1250056

Author(s):

D. D. YANG ◽

W. S. HOU ◽

X. Y. WU ◽

J. ZHENG ◽

X. L. ZHENG ◽

...

Keyword(s):

Surface Electromyography ◽

Index Finger ◽

Statistical Significance ◽

Middle Finger ◽

Total Power ◽

Force Level ◽

Hand Muscles ◽

Fingertip Force ◽

Hand Muscle ◽

The Relationship

Quantizing the relationship between finger force and multitendoned extrinsic hand muscles could be useful for understanding the control strategies that underlie the coordination of finger movements and forces. The objective of this study is to explore the relationship of fingertip force production and total power of surface electromyography (sEMG) recorded on extrinsic hand muscles under isometric voluntary contraction. Thirteen healthy volunteers were recruited to participate in this study. In the designed force-tracking tasks, all volunteers were required to produce a certain force with either index finger or middle finger to match the target force for 5 s. Meanwhile, the sEMG signals were acquired from two extrinsic hand muscles: extensor digitorum (ED) and flexor digitorum superficialis (FDS). For each trial, sEMG of the effective force segment was extracted; then, the power spectrum was estimated based on autoregressive (AR) model and from which the corresponding total power of sEMG was computed. The experimental results reveal that the total power of sEMG linearly increases with force level regardless of the task finger and extrinsic hand muscle. It is also found that the total power obtained from index finger is significantly less than that of middle finger for FDS at the same force level (p < 0.05), while this kind of statistical significance cannot be found for ED. However, with respect to the measurement of total power, the type of extrinsic hand muscle has not exhibited significantly different contribution to the task finger under a certain fingertip force level. The findings of this study indicate that the total power of the extrinsic hand muscle's sEMG can be used to characterize finger's activities.

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