Validation of a modular and wearable system for tracking fingers movements

Supervising manual operations performed by workers in industrial environments is crucial in a smart factory. Indeed, the production of products with superior quality at higher throughput rates and reduced costs with the support of Industry 4.0-enabling technologies is based on the strict control of all resources inside the factory, including workers. This paper shows a protocol for validating a new wearable system for tracking finger movements. The wearable system consists of two measuring modules worn on the thumb and index finger that measure flexion and extension of the proximal interphalangeal (PIP) joint by a stretch sensor and rotation of the proximal phalanx (PP) by an inertial measurement unit. A marker-based opto-electronic system is used to validate the proposed device by capturing specific finger movements. Four movements that simulate typical tasks and gestures, such as grasp and pinch, were specifically performed. The maximum root-mean-square error is 3.7 deg for the roll angle of PP. The resistance changes of the stretch sensors with respect to flexion and extension of the PIP joint is 0.47 Ω/deg. The results are useful for data interpretation when the system is adopted to monitor finger movements and gestures

Flexible Piezoresistive Sensor with the Microarray Structure Based on Self-Assembly of Multi-Walled Carbon Nanotubes

High-performance flexible pressure sensors have great application prospects in numerous fields, including the robot skin, intelligent prosthetic hands and wearable devices. In the present study, a novel type of flexible piezoresistive sensor is presented. The proposed sensor has remarkable superiorities, including high sensitivity, high repeatability, a simple manufacturing procedure and low initial cost. In this sensor, multi-walled carbon nanotubes were assembled onto a polydimethylsiloxane film with a pyramidal microarray structure through a layer-by-layer self-assembly system. It was found that when the applied external pressure deformed the pyramid microarray structure on the surface of the polydimethylsiloxane film, the resistance of the sensor varied linearly as the pressure changed. Tests that were performed on sensor samples with different self-assembled layers showed that the pressure sensitivity of the sensor could reach − 2.65     kPa − 1 , which ensured the high dynamic response ability and the high stability of the sensor. Moreover, it was proven that the sensor could be applied as a strain sensor under the tensile force to reflect the stretching extent or the bending object. Finally, a flexible pressure sensor was installed on five fingers and the back of the middle finger of a glove. The obtained results from grabbing different weights and different shapes of objects showed that the flexible pressure sensor not only reflected the change in the finger tactility during the grasping process, but also reflected the bending degree of fingers, which had a significant practical prospect

Highly Sensitive, Stretchable and Durable Sensors Based on Conductive Polymer Hydrogels

In recent years, wearable sensor devices, which directly attach to human skin for precise and dynamic human motion and physiological signals monitoring, have experienced a rapid development and presented a great use in modern medical systems. Despite the great research progress, the wearable sensors often need synchronized deformation of conductive fillers and flexible substrates to enable the mechanical signals transformation. However, some of the matrices are not flexible and stretchable enough, thus constraining the sensitivity and high precision of devices. Therefore, a stretchable, durable, and highly sensitive material was urgently needed. In this light, conductive hydrogels, offering the advantages of good flexibility, stretchability and biocompatibility, have attracted great interest as body-worn sensors. Additionally, hydrogels enjoy the capacity of tuning their mechanical properties to perfectly match with human skin. Therefore, a large number of stretchable hydrogel-based sensors has been fabricated. However, only a few hydrogel sensors can widely realize commercial application, with insufficient mechanical strength and stretchability as one of the main reasons. In addition, the sensing performance is not satisfactory. Particularly, it is difficult to detect some subtle deformations due to easy interference by external environment, thus leading to poor long-term durability. In this thesis, a novel one-pot technique to synthesize ultrastretchable hydrogel-based strain sensors by integrating carbon nanofibers with a double-network hydrogel matrix was reported. Outstanding mechanical properties of Agar/polyacrylamide(PAAm) double-network (DN) hydrogel, combing with high strain sensitivity given by tunneling effect of carbon nanomaterials, enable it to be a durable human motion sensor. We also prepare a highly anisotropic nanofluidic ionic skin (ANIS) composing of polyvinyl alcohol (PVA) and cellulose nanofibril via thermal stretching method, displaying comparable modulus, higher fracture energy and anti-fatigue property with cartilage and skin. It shows good pressure-independent temperature sensing property. Additionally, anisotropic and ionic conductive PVA/poly(N-isopropylacrylamide) (PNIPAM) DN hydrogel films with both physically and chemically cross-linked networks are created for multifunctional devices via thermal stretching, immersing and etching method. Combining the strong mechanical property of PVA under prestretching and unique thermal sensitivity of PNIPAM, PVA/PNIPAM DN gel can be ideal candidate for multiple sensing upon strain, pressure and temperature