The effect of joint locks in underactuated hand prostheses

Master thesis (2011)

Authors

Contributors

D.H. Plettenburg (mentor)
Department
BioMechanical Engineering (Mechanical, Maritime and Materials Engineering) (TU Delft)
Copyright: © 2011 Pape, R.
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Published Date

24-01-2011

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Faculty

Mechanical, Maritime and Materials Engineering

Department

BioMechanical Engineering

Abstract

The concept of underactuation is increasingly applied to hand prostheses because it minimizes the number of actuators while the fingers are adaptive to the grasped objects. However, current underactuated grasp mechanisms suffer from an intrinsic stability problem which disables them to obtain a pinch grasp, hence they fail to grasp small objects. In an attempt to solve this problem joint locks are applied to an underactuated pulley-tendon driven hand. Joint locks might also have an effect on the power grasp strength. Therefore the effect of joint locks on the pinch grasp performance and power grasp strength of underactuated hand prostheses is investigated. This effect is quantified by two grasp performance metrics: the ability to pinch and the ability to hold. To find the optimal joint lock configurations for pinch grasp performance and power grasp strength, the effect of different joint lock configurations on both performance metrics is calculated using a static grasp model. The results of this model are validated by measurements on a prototype. Both the model and the measurements showed that joint locks do not have a significant effect on the pinch grasp performance when only the range of object sizes for which a pinch grasp equilibrium exists is considered. However, the measurements showed that a pinch grasp is more easily established with joint locks. Additionally, both the model and the measurements showed a significant increase in the power grasp strength.