ABSTRACT
Rapid development in wearable electronics and systems continues to impose challenges on portable energy storage sustained over time, and thus human energy harvesting is a potentially attractive means of sustainable, long-term energy. We introduce a novel 'controlled slip' energy harvesting approach for capturing energy during human locomotion. While slip is normally considered undesirable, controlled slip holds potential to enable a significant amount of energy harvesting during each step of human gait. Custom-designed 'controlled slip' energy harvesting shoes were fabricated by mounting a sliding plate and a generator with a one-way bearing to the sole of standard walking shoes, which induces controlled forward slip during early stance while energy is harvested. Fourteen healthy subjects performed treadmill walking trials with the 'controlled slip' energy harvesting shoes which generated average electrical power of 1.15-1.44 W at walking speeds of 2.9-4.3 km/h. Interestingly, without prompting, subjects chose to walk with the 'controlled slip' energy harvesting shoes in either one of two distinct ways: landing with the heel first (heel strikers) or landing with the toe first (toe strikers). While heel strikers and toe strikers exhibited similar electrical power output and hip flexion angle at initial foot contact, heel strikers had higher peak ankle power and lower knee flexion angle at initial foot contact than toe strikers. 'Controlled slip' energy harvesting could potentially generate electrical power for a broad spectrum of wearable devices.
Subject(s)
Bioelectric Energy Sources , Walking/physiology , Wearable Electronic Devices , Adult , Algorithms , Biomechanical Phenomena , Equipment Design , Gait/physiology , Healthy Volunteers , Heel , Humans , Male , Shoes , Toes , Young AdultABSTRACT
Soft and integrated design can enable wearable haptic devices to augment natural human taction. This paper proposes a novel, soft, haptic finger-worn wearable device based on compliant and adhesive silicone skin and lightweight twisted and coiled polymer (TCP) actuators using ultra high molecular weight polyethylene (UHMWPE) fibers to provide lateral skin stretch sensations. Recently, silicone elastomers have been used in wearable sensors and in haptic applications for their high compliance or adhesion. TCP actuators have also demonstrated high power to weight ratios, large stroke length, simple mechanism, and inherent softness. Lateral skin stretch is sensitive to small motions and has been used for intuitive proprioceptive feedback applications. We combined these characteristics to design and manufacture a wearable, functional haptic prototype. Prototype performance was evaluated using an optical tracking system, a force gauge test bench, and compared to vibrotactile haptic feedback in a experiment with 14 healthy participants. Results showed that participant mean reaction times were comparable to those of a vibrotactile feedback system, though task completion times were longer. This paper is the first to employ TCP actuators for haptic stimulation and could serve as a foundation for future applications involving soft wearable haptics in gaming, health, and virtual reality.
Subject(s)
Feedback, Sensory/physiology , Touch Perception/physiology , Touch/physiology , Adult , Equipment Design , Female , Fingers/physiology , Humans , Male , Physical Stimulation , Polymers , Reaction Time/physiology , Silicones , Skin , User-Computer Interface , Vibration , Wearable Electronic Devices , Young AdultABSTRACT
Technological developments in the last decade have enabled the integration of sensors and actuators into wearable devices for gait interventions to slow the progression of knee osteoarthritis. Wearable haptic gait retraining is one area which has seen promising results for informing modifications of gait parameters for reducing knee adduction moments (KAM) during walking. Two gait parameters which can be easily adjusted to influence KAM include foot progression angle (FPA) and step width (SW). The purpose of this study was to: (1) determine whether a custom haptic ankle bracelet using binary vibrotactile and tactile apparent movement feedback could retrain ten healthy subjects to walk with a modified FPA and SW within a short training session with 80% accuracy; and (2) whether there was a difference between the number of steps required to complete the retraining task based on the two feedback schemes being tested. Retraining multiple gait parameters using a single device was a novel aspect of this work and we found that nine out of ten subjects were able to retrain their gait using the ankle bracelet in both feedback schemes to within 2° and 39mm of target FPA and SW respectively. We also found no difference in the number steps required for completion between the two schemes (p>0.05). Future research will investigate the device performance with patients with knee osteoarthritis and the effective change in KAM by modifying a combination of FPA and SW.
Subject(s)
Ankle Joint/physiology , Biofeedback, Psychology/physiology , Gait/physiology , Wearable Electronic Devices , Adult , Female , Humans , Male , Young AdultABSTRACT
Tactile feedback in recent decades has allowed humans to receive information through technology beyond traditional visual and auditory senses. Lateral skin stretch has the potential to be a mode of tactile feedback, reliably enabling the perception of directional cues through the use of a single actuator. Experiments were conducted to explore sensitivity to skin stretch on nine locations on the human lower leg. Thirty-two stimuli were presented to subjects, exploring effects of displacement (from 0.2-2.0 mm) and speed (from 0.5-4.0 mm/s) on the perception of left and right directions. Higher accuracy came from stimuli having higher displacements and speeds. Three of the locations: soleus, calcaneal tendon (upper), and fibularis longus (lower) all had a mean accuracy of at least 85 percent and are suitable locations for a skin stretch tactile feedback device.
