Power-Assistive Finger Exoskeleton With a Palmar Opening at the Fingerpad

Abstract

This paper presents a powered finger exoskeleton with an open fingerpad, named the Open Fingerpad eXoskeleton (OFX). The palmar opening at the fingerpad allows for direct contact between the user's fingerpad and objects in order to make use of the wearer's own tactile sensation for dexterous manipulation. Lateral side walls at the end of the OFX's index finger module are equipped with custom load cells for estimating the wearer's pinch grip force. A pneumatic cylinder generates assistance force, which is determined according to the estimated pinch grip force. The OFX transmits the assistance force directly to the objects without exerting pressure on the wearer's finger. The advantage of the OFX over an exoskeleton with a closed fingerpad was validated experimentally. During static and dynamic manipulation of a test object, the OFX exhibited a lower safety margin than the closed exoskeleton, indicating a higher ability to adjust the grip force within an appropriate range. Furthermore, the benefit of force assistance in reducing the muscular burden was observed in terms of muscle fatigue during a static pinch grip. The median frequency (MDF) of the surface electromyography (sEMG) signal from the first dorsal interosseous (FDI) muscle displayed a lower reduction rate for the assisted condition, indicating a lower accumulation rate of muscle fatigue.

A Finger Grip Force Sensor with an Open-Pad Structure for Glove-Type Assistive Devices

“…For large flexion angles, the RMSE was high, and the error increased as the angle increased. Moreover, the estimation accuracies obtained below 5 N in this study showed better performance compared with our previous study using load cells (0.653 N, RMSE for the index finger) [45] and other study (1.179 N, mean error for the index finger) [41]. For the middle finger (Figure 7b), the errors were low for all flexion angles and periods.…”

“…The capacitive sensor on the ulnar side is placed in a more dorsal position than For each finger, the proposed sensor is placed on the dorsal side of the distal segment, where two capacitive sensors are attached to the lateral surfaces of the finger. Although the sensor is placed on the dorsal side, we found that the installation of the fingertip sensors on the human finger did Sensors 2020, 20, 4 3 of 15 not affect a person's ability to catch objects from our previous research [45]. There are openings on the palmar surfaces of the fingers of the glove so that the fingers can make contact with the object being manipulated, as shown in Figure 1c.…”

“…The user can detect the sense of touch through the exposed skin, specifically the information received from varying pressure or vibration against the skin from the mechanoreceptors, which can measure high-frequency stimuli up to 300 Hz. If there is the obstacle between the human skin and the object, it is reduced that the frequency range of vibration stimulus human can feel [45]. We selected the size of the hole to be as large as possible so that the fingertip force sensors are completely covered by the glove to protect the developed sensor from the external environment, such as from water and foreign substances.…”

“…We previously proposed a grip force sensing method based on the lateral expansion force that is produced by exerting a grip force for an assistive hand exoskeleton [45]. This exoskeleton has one active DoF for the index finger, and the entire exoskeleton was built with rigid materials.…”

Peripheral device to quantify grip and pinch capacity of children

“…Many authors have developed peripheral devices and exoskeletons, but these should be positioned on the upper limb to operate properly (Dovat et al, 2008;Hasegawa et al, 2012;Heo and Kim, 2014). The peripheral device proposed in this paper does not use any sensor positioned for the upper limb of the volunteer, which gave more freedom of movement.…”