1,720,964 research outputs found
Non-Back-Drivable Rotary Mechanism with Intrinsic Compliance for Robotic Thumb Abduction/Adduction
No full textIndependent Long Fingers are not Essential for a Grasping Hand
No full textThe human hand is a complex integrated system with motor and sensory components that provides individuals with high functionality and elegant behaviour. In direct connection with the brain, the hand is capable of performing countless actions ranging from fine digit manipulation to the handling of heavy objects. However the question of which movements mostly contribute to the manipulation skills of the hand, and thus should be included in prosthetic hands, is yet to be answered. Building from our previous work, and assuming that a hand with independent long fingers allowed performance comparable to a hand with coupled fingers, here we explored the actual contribution of independent fingers while performing activities of daily living using custom built orthoses. Our findings show that, when an opposable thumb is present, independent long fingers provide a measureable advantage in performing activities of daily living only when precision grasps are involved. In addition, the results suggest that the remarkable grasping skills of the human hand rely more on the independent abduction/adduction of the fingers than on their independent flexion/extension. These findings are of interest to the designers of artificial hands, including biomimetic prostheses and exoskeletons
Preliminary Design and Development of a two Degrees of Freedom passive compliant prosthetic wrist with switchable stiffness
No full textUnified approach to bi-directional non-back drivable roller clutch design
No full textA non-back drivable mechanism (transmission or clutches) is a device able to transmit torques from its input to the output axis and vice-versa to lock torques applied to its output. These devices are widely used in robotic, mechatronic systems and prosthetics in order to lock joints or to physically engage/disengage transmission axes. An efficient way to implement non-back drivability is to exploit the wedge phenomenon that occurs to rolling elements when they are compressed between circular and cam surfaces. The current literature describing such mechanisms and underlying equations is rather scattered and incomplete. In this paper, a relevant set of equations is presented to optimize their design, which is of particular interest in prosthetics to minimize weight of limbs. The conceptual framework and the general design are described. The relationship between the locking torque and the properties of the components are then derived. Moreover, the sources and effects of tolerance and of operational conditions are introduced. The contact pressures, the input torque required to unlock the clutch, the critical torque and the input backlash are finally analyzed. The final part of the paper is devoted to a step-by-step procedure useful in the design of non-back drivable roller clutches
Exploiting arm posture synergies in activities of daily living to control the wrist rotation in upper limb prostheses: A feasibility study
No full textAlthough significant technological advances have been made in the last forty years, natural and effortless control of upper limb prostheses is still an open issue. Commercially available myoelectric prostheses present limited Degrees of Freedom (DoF) mainly because of the lack of available and reliable independent control signals from the human body. Thus, despite the crucial role that an actuated wrist could play in a transradial prosthesis in terms of avoiding compensatory movements, commercial hand prostheses present only manually adjustable passive wrists or actuated rotators controlled by (unnatural) sequential control strategies. In the present study we investigated the synergies between the humeral orientation with respect to the trunk and the forearm pronation/supination angles during the execution of a wide range of activities of daily living, in healthy subjects. Our results showed consistent postural synergies between the two selected body segments for almost the totality of the activities of daily living under investigation. This is a promising result because these postural synergies could be exploited to automatically control the wrist rotator unit in transradial prostheses improving the fluency and the dexterity of the amputee
Compliant Prosthetic Wrists Entail More Natural Use Than Stiff Wrists during Reaching, Not (Necessarily) during Manipulation
Full text linkDeveloping an artificial arm with functions equivalent to those of the human arm is one of the challenging goals of bioengineering. State-of-the-artprostheses lack several degrees of freedom and force the individuals to compensate for them by means of compensatory movements, which often result in residual limb pain and overuse syndromes. Passive wristsmay reduce such compensatory actions, nonethelessto date their actual efficacy, associated to conventional myoelectric hands is a matter of debate. We hypothesized that a transradial prosthesiswould allow a simpler operation if its wrist behaved compliant during the reaching and grasping phase, and stiff during the holding andmanipulation phase. To assess this, we compared a stiff and a compliant wrist and evaluating the extent of compensatory movements in the trunk and shoulder, with unimpaired subjects wearing orthoses, while performing nine activities of daily living taken from the southampton hand assessment procedure. Our findings show indeed that the optimal compliance for a prosthetic wrist is specific to the phase of the motor task: the compliant wrist outperforms the stiff wrist during the reaching phase, whereas the stiff wrist exhibits more natural movements during the manipulation phase of heavy objects. Hence, this paper invites rehabilitation engineers to develop wrists with switchable compliance
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