Differential Soft Sensor-Based Measurement of Interactive Force and Assistive Torque for a Robotic Hip Exoskeleton

Abstract

With the emerging of wearable robots, the safety and effectiveness of human-robot physical interaction have attracted extensive attention. Recent studies suggest that online measurement of the interaction force between the robot and the human body is essential to the aspects above in wearable exoskeletons. However, a large proportion of existing wearable exoskeletons monitor and sense the delivered force and torque through an indirect-measure method, in which the torque is estimated by the motor current. Direct force/torque measuring through low-cost and compact wearable sensors remains an open problem. This paper presents a compact soft sensor system for wearable gait assistance exoskeletons. The contact force is converted into a voltage signal by measuring the air pressure within a soft pneumatic chamber. The developed soft force sensor system was implemented on a robotic hip exoskeleton, and the real-time interaction force between the human thigh and the exoskeleton was measured through two differential soft chambers. The delivered torque of the hip exoskeleton was calculated based on a characterization model. Experimental results suggested that the sensor system achieved direct force measurement with an error of 10.3 ± 6.58%, and torque monitoring for a hip exoskeleton which provided an understanding for the importance of direct force/torque measurement for assistive performance. Compared with traditional rigid force sensors, the proposed system has several merits, as it is compact, low-cost, and has good adaptability to the human body due to the soft structure.

Characterization and Evaluation of Human–Exoskeleton Interaction Dynamics: A Review

“…Other than questionnaires, visual analog scales (VAS) were also used to extract perceived discomfort [ 18 ]. Among the sensor solutions presented in the recordings, 14 (28%) proposed customized sensor solutions for their pHEI measurements [ 9 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 ]. Most of the developed solutions were FSR-based [ 19 , 25 , 30 , 33 , 35 ] or air-based pressure sensors [ 18 , 23 , 28 , 29 , 31 ].…”

“…Among the sensor solutions presented in the recordings, 14 (28%) proposed customized sensor solutions for their pHEI measurements [ 9 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 ]. Most of the developed solutions were FSR-based [ 19 , 25 , 30 , 33 , 35 ] or air-based pressure sensors [ 18 , 23 , 28 , 29 , 31 ]. Optical solutions were divided into optical-fiber sensors [ 26 , 27 , 36 ] and optoelectronic laser-based sensors [ 9 , 20 , 21 ].…”

Development of a Novel Anesthesia Airway Management Robot

“…As the early phase of the robot development, the proposed anesthetic airway management robot was verified to be valid. In future studies, the comfort and safety of the robot will be further optimized, and the scope of its clinical application will be further investigated [20][21][22].…”

Sensors and Actuation Technologies in Exoskeletons: A Review

“…When high band signals are important, i.e., in real time force control, piezoelectric sensors are usually preferred. Pressure sensors can also be used inside soft-sensors, as in the work by Wang et al [ 109 ], where a wearable, low-cost and compact soft sensor system for direct force measurement in a hip exoskeleton is presented. The sensor is based on a soft pneumatic chamber, in which the dynamic interaction forces are converted into the air pressure changes and measured though a differential air pressure sensor.…”

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