Pneumatic Feedback for Wearable Lower Limb Exoskeletons Further Explored
For optimal control of wearable lower limb exoskeletons the sensory information flow should also be (partly) restored, especially when the users are Spinal Cord Injury subjects. Several methods, like electrotactile or electromechanical vibrotactile stimul
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Department of Biomechanical Engineering, MIRA Institute of Biomedical Technology and Technical Medicine, University of Twente, Enschede, The Netherlands [email protected] 2 Department of Biomechatronics and Human-Machine Control, Institute of Mechanical, Maritime and Materials Engineering, Delft University of Technology, Delft, The Netherlands
Abstract. For optimal control of wearable lower limb exoskeletons the sensory information flow should also be (partly) restored, especially when the users are Spinal Cord Injury subjects. Several methods, like electrotactile or electromechanical vibrotactile stimulation, to provide artificial sensory feedback have been studied thoroughly and showed promising results. Pneumatic tactile stimulation might be an alternative to these methods, because the stimulation amplitudes can be larger and in cases of force feedback, the modality of stimulation and sensing can be matched. In this study we have developed a setup that can provide pneumatic feedback with four feedback levels via three stimulation modalities: (1) amplitude modulation, (2) position modulation and (3) frequency modulation. The differences in subject stimulus perception between these three stimulation modalities were evaluated through a magnitude estimation task performed with 10 healthy subjects. Percentages correctly identified feedback levels were significantly higher for frequency modulation than the other two stimulation modalities. Also through questionnaires the subjects indicated that feedback through frequency modulation was the most intuitive and the only method where addition of an extra feedback level was indicated as possible. The results of this study show that pneumatic feedback is feasible, can provide high percentages of feedback level discrimination that are at least comparable to vibrotactile stimulation and therefore encourages further research to optimize the pneumatic setup. Keywords: Pneumatic modulation
feedback
Wearable
exoskeleton
Stimulus
1 Introduction In recent years, a large number of developments has been presented in the field of wearable lower limb exoskeletons. Despite the progress made, the exoskeletons still cannot provide a natural walking pattern and patients depend on crutches for balance. It is hypothesized that the lack of providing sensory information from the exoskeleton to the user could be one of the reasons for this latter shortcoming of the current © Springer International Publishing Switzerland 2016 F. Bello et al. (Eds.): EuroHaptics 2016, Part I, LNCS 9774, pp. 90–98, 2016. DOI: 10.1007/978-3-319-42321-0_9
Pneumatic Feedback for Wearable Lower Limb Exoskeletons
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exoskeletons. Furthermore, for Spinal Cord Injury users, also sensory information coming from below the level of the lesion is missing. Sensory information that is used for human balancing normally comes from three sources: (1) the visual system, (2) the vestibular system and (3) the proprioceptive and exteroceptive system of the lower limbs. The latter source is disturbed in the case o
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