Low-Cost Force Sensors Embedded in Physical Human–Machine Interfaces: Concept, Exemplary Realization on Upper-Body Exoskeleton, and Validation

Abstract

In modern times, the collaboration between humans and machines increasingly rises, combining their respective benefits. The direct physical support causes interaction forces in human–machine interfaces, whereas their form determines both the effectiveness and comfort of the collaboration. However, their correct detection requires various sensor characteristics and remains challenging. Thus, this paper presents a developed low-cost sensor pad working with a silicone capsule and a piezoresistive pressure sensor. Its measurement accuracy is validated in both an isolated testing environment and a laboratory study with four test subjects (gender-balanced), and an application integrated in interfaces of an active upper-body exoskeleton. In the material-testing machine, it becomes apparent that the sensor pad generally features the capability of reliably determining normal forces on its surface until a certain threshold. This is also proven in the real application, where the measurement data of three sensor pads spatially embedded in the exoskeletal interface are compared to the data of an installed multi-axis load cell and a high-resolution flexible pressure map. Here, the consideration of three sensor pads potentially enables detection of exoskeletal support on the upper arm as well as “poor” fit conditions such as uneven pressure distributions that recommend immediate system adjustments for ergonomic improvements.

A Compliant Actuator-Sensor Unit using a Shape Memory Alloy and Capacitive Force Sensing for Active Exoskeleton Interfaces

“…Capturing exoskeleton-human interaction forces is crucial for secure, comfortable deployment [17] and enhanced user experience. Current methodologies explore various sensor technologies, from 3D force sensors and inertial measurement units (IMUs) for monitoring lower limb and classifying human motions [18] to soft barometric sensors [19]- [21]. However, these sensors may be limited by rigidity, bulkiness, or error-proneness due to ambient pressure changes and spatial user motion [22].…”

Estimación de carga sobre un actuador SMA para rehabilitación

“…En otro estudio presentado por (Wang et al, 2022), se desarrolló un sensor vestible de fuerza basado en la medida de presión del aire en una cámara neumática. Un enfoque similar se presenta en el trabajo de (Hoffmann et al, 2022), donde se introduce un sensor de fuerza de bajo costo basado en una cápsula de silicona y un sensor de presión piezoresistivo. Además, (Zhang et al, 2021) utilizaron un sensor blando neumático para desarrollar una nueva estrategia de control de asistencia en el paso.…”

Design and Manufacturing Considerations of a Constant-Force Mechanism for Low Force Regimes

“…Constant-force mechanisms (CFMs) have resurfaced as a research topic in recent years owing to them constituting a cheap and simple force-control solution for but not limited to overload protection and robotic end-effectors (Wang and Xu 2018). While low-cost alternatives do exist, they generally add complexity (Kim, et al 2021) or require special operation regimes (Hoffmann, et al 2022).…”