Integration of 3D Printed Flexible Pressure Sensors into Physical Interfaces for Wearable Robots

Abstract

Sensing pressure at the physical interface between the robot and the human has important implications for wearable robots. On the one hand, monitoring pressure distribution can give valuable benefits on the aspects of comfortability and safety of such devices. Additionally, on the other hand, they can be used as a rich sensory input to high level interaction controllers. However, a problem is that the commercial availability of this technology is mostly limited to either low-cost solutions with poor performance or expensive options, limiting the possibilities for iterative designs. As an alternative, in this manuscript we present a three-dimensional (3D) printed flexible capacitive pressure sensor that allows seamless integration for wearable robotic applications. The sensors are manufactured using additive manufacturing techniques, which provides benefits in terms of versatility of design and implementation. In this study, a characterization of the 3D printed sensors in a test-bench is presented after which the sensors are integrated in an upper arm interface. A human-in-the-loop calibration of the sensors is then shown, allowing to estimate the external force and pressure distribution that is acting on the upper arm of seven human subjects while performing a dynamic task. The validation of the method is achieved by means of a collaborative robot for precise force interaction measurements. The results indicate that the proposed sensors are a potential solution for further implementation in human–robot interfaces.

Improved Motion Classification With an Integrated Multimodal Exoskeleton Interface

“…More specifically, it is known that the variability of EMG signals can be significant across time due to artefacts and crosstalk (Bi et al, 2019 ). On the other hand, we found that pressure measurements are generally more stable signals across a particular pattern, which is in line with previous research on the topic (Connan et al, 2016 ; Langlois et al, 2021 ). This leads us to expect the pressure sensing would improve a more general motion classification across a large sample size as well.…”

“…At the beginning of every trial the sensors are calibrated relative to the force sensing of the cobot. The design of the pressure sensors and the calibration process are described in detail in Langlois et al ( 2021 ).…”

“…A sensor that has yet to be combined with EMG are pressure sensors located at the physical interface of exoskeletons. The integration of pressure sensors in physical interfaces has been investigated in the robotics community (De Rossi et al, 2011 ; Tamez-Duque et al, 2015 ; Wilcox et al, 2016 ; Langlois et al, 2021 ) and have shown their relevance for the unimodal detection of the user motion intention (Lenzi et al, 2011 ). Additionally, pressure sensors can ensure a more safe and comfortable operation of such devices (He et al, 2017 ).…”

Usability, User Acceptance, and Health Outcomes of Arm-Support Exoskeleton Use in Automotive Assembly

“…To understand comfort, several studies have quantified interaction forces/pressures at the user-exoskeleton interface, or assessed contact pressures with different physical interface designs or materials. [43][44][45][46][47] Levesque et al, 43 in particular, offered several interface design recommendations, including a cuff that can accommodate large inter-and intra-subject variability in limb shape and dimensions, as well as changes due to muscle contraction, and that can tilt to maintain broad contact regardless of body segment movements. Kozinc et al 45 reported that pressure tolerance is highly variable between individuals, and lower for women.…”

An Occupational Shoulder Exoskeleton Reduces Muscle Activity and Fatigue During Overhead Work

“…It was shown that effort expectancy affects exoskeleton acceptance [34], suggesting that the worker's preferred tool is likely to be the tool that is easy to use, optimizing the worker's well-being and overall performance without compromising its natural kinematics or comfort [35], [36], while it also reduces the physical workload. This is a delicate balance, as higher torques result in higher forces applied on the body, and higher pressures at the level of the human-robot interfaces, which were associated with discomfort [37], [38].…”