Closed-loop Control using Electrotactile Feedback Encoded in Frequency and Pulse Width

Jakob L. Dideriksen; Irene Uriarte Mercader; Strahinja Dosen

doi:10.1109/TOH.2020.2985962

Closed-loop Control using Electrotactile Feedback Encoded in Frequency and Pulse Width

Jakob L. Dideriksen^*, Irene Uriarte Mercader, Strahinja Dosen

^*Corresponding author for this work

Research output: Contribution to journal › Journal article › Research › peer-review

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Abstract

Sensory substitution by electrotactile stimulation has been widely investigated for improving the functionality of human-machine interfaces. Few studies, however, have objectively compared different ways in which such systems can be implemented. In this study, we compare encoding of a feedback variable in stimulation pulse width or stimulation frequency during a closed-loop control task. Specifically, participants were asked to track a predefined pseudorandom trajectory using a joystick with electrotactile feedback as the only indication of the tracking error. Each participant performed eight 90 s trials per encoding scheme. Tracking performance using frequency modulation enabled lower tracking error (RMSE: Frequency modulation: 0.27 ± 0.03; Pulse width modulation: 0.31 ± 0.05; p < 0.05) and a higher correlation with the target trajectory (Frequency modulation: 83.4 ± 4.1%; Pulse width modulation: 79.8 ± 5.2%; p < 0.05). There was no significant improvement in performance over the eight trials. Furthermore, frequency-domain analysis revealed that frequency modulation was characterized with a higher gain at lower error frequencies. In summary, the results indicate that encoding of feedback variables in the frequency of pulses enables better control than pulse width modulation in closed-loop dynamic tasks.

Original language	English
Article number	9063550
Journal	IEEE Transactions on Haptics
Volume	13
Issue number	4
Pages (from-to)	818-824
Number of pages	7
ISSN	1939-1412
DOIs	https://doi.org/10.1109/TOH.2020.2985962
Publication status	Published - 1 Oct 2020

Bibliographical note

Funding Information:
Manuscript received September 3, 2019; revised February 24, 2020 and March 23, 2020 and March 31, 2020; accepted March 31, 2020. Date of publication April 10, 2020; date of current version December 21, 2020. This work was supported by Independent Research Fund Denmark, Case-Nos. 8022-00243A (ROBIN) and 8022-00226B. (Corresponding author: Jakob L. Dideriksen.) The authors are with the Department of Health Science and Technology, Aalborg University, 9000 Aalborg, Denmark (e-mail: jldi@hst.aau.dk; iuriar17@student.aau.dk; sdosen@hst.aau.dk). Digital Object Identifier 10.1109/TOH.2020.2985962

Publisher Copyright:
© 2008-2011 IEEE.

Copyright:
Copyright 2020 Elsevier B.V., All rights reserved.

Keywords

closed-loop control sensory feedback
Electrotactile stimulation
sensory substitution.

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10.1109/TOH.2020.2985962

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title = "Closed-loop Control using Electrotactile Feedback Encoded in Frequency and Pulse Width",

abstract = "Sensory substitution by electrotactile stimulation has been widely investigated for improving the functionality of human-machine interfaces. Few studies, however, have objectively compared different ways in which such systems can be implemented. In this study, we compare encoding of a feedback variable in stimulation pulse width or stimulation frequency during a closed-loop control task. Specifically, participants were asked to track a predefined pseudorandom trajectory using a joystick with electrotactile feedback as the only indication of the tracking error. Each participant performed eight 90 s trials per encoding scheme. Tracking performance using frequency modulation enabled lower tracking error (RMSE: Frequency modulation: 0.27 ± 0.03; Pulse width modulation: 0.31 ± 0.05; p < 0.05) and a higher correlation with the target trajectory (Frequency modulation: 83.4 ± 4.1%; Pulse width modulation: 79.8 ± 5.2%; p < 0.05). There was no significant improvement in performance over the eight trials. Furthermore, frequency-domain analysis revealed that frequency modulation was characterized with a higher gain at lower error frequencies. In summary, the results indicate that encoding of feedback variables in the frequency of pulses enables better control than pulse width modulation in closed-loop dynamic tasks. ",

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N2 - Sensory substitution by electrotactile stimulation has been widely investigated for improving the functionality of human-machine interfaces. Few studies, however, have objectively compared different ways in which such systems can be implemented. In this study, we compare encoding of a feedback variable in stimulation pulse width or stimulation frequency during a closed-loop control task. Specifically, participants were asked to track a predefined pseudorandom trajectory using a joystick with electrotactile feedback as the only indication of the tracking error. Each participant performed eight 90 s trials per encoding scheme. Tracking performance using frequency modulation enabled lower tracking error (RMSE: Frequency modulation: 0.27 ± 0.03; Pulse width modulation: 0.31 ± 0.05; p < 0.05) and a higher correlation with the target trajectory (Frequency modulation: 83.4 ± 4.1%; Pulse width modulation: 79.8 ± 5.2%; p < 0.05). There was no significant improvement in performance over the eight trials. Furthermore, frequency-domain analysis revealed that frequency modulation was characterized with a higher gain at lower error frequencies. In summary, the results indicate that encoding of feedback variables in the frequency of pulses enables better control than pulse width modulation in closed-loop dynamic tasks.

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Closed-loop Control using Electrotactile Feedback Encoded in Frequency and Pulse Width

Abstract

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