A Low-Profile Vacuum Actuator (LPVAc) With Integrated Inductive Displacement Sensing for a Novel Sit-to-Stand Assist Exosuit

• Published in: IEEE access 2021, Vol.9, p.117067-117079
• Main Authors: Kulasekera, Asitha L., Arumathanthri, Rancimal B., Chathuranga, Damith S., Gopura, R. A. R. C., Lalitharatne, Thilina D.
• Format: Article
• Language: English
• Subjects: Actuation; Actuators; Displacement; Exoskeletons; exosuits; High strain rate; inductance measurement; Inductive sensing devices; Low density polyethylenes; Muscles; orthotics; Polyethylene films; Posture; Robot sensing systems; Robots; Sensors; Soft robotics; soft sensors; Spinal cord injuries; vacuum systems; Wearable technology
• ISSN: 2169-3536; 2169-3536
• DOI: 10.1109/ACCESS.2021.3106319

Muscle weakness owing to stroke, spinal cord injuries, or aging can make a person's life sedentary, temporarily as well as permanently. Such persons need to be motivated to break their sedentary postures and attempt independent motion. A key motivator in this aspect is the ability to easily transition from seated to standing posture. If this sit-to-stand transition (STSt) is easy, it will encourage further mobility. A soft wearable device that can assist the STSt, would fill this need perfectly. Such a device should be able to seamlessly assist during STSt and be unobtrusive during sitting. A major limitation that is currently holding back the development of soft exosuits in STSt-assist is the lack of low-profile soft actuators with high strain rate and force-to-weight ratio. Hence, we propose a novel low-profile vacuum actuator (LPVAc) with an integrated inductive displacement sensor that, can be rapidly fabricated, is lightweight (14g), and can provide high strain (65%) and a high force-to-weight ratio (285 times self-weight). The proposed actuator comprises a low-profile spring encased within a low-density polyethylene film with rapid vacuum actuation and passive quick return. The proposed inductive sensor has a sensitivity of 0.0022~\mu H/mm and the hysteresis is below 1.5% with an overall absolute average error percentage of 5.24%. The performance of the proposed integrated sensor in displacement control of the LPVAc is experimentally evaluated. The proposed actuator is integrated into a novel mono-articular STSt-assist exosuit for preliminary testing. Surface electromyography measurements of the gluteus maximus muscles during STSt indicate a mean muscle activity reduction of 45%. This supports the potential use of the proposed actuator in STSt-assist.