Design of joint locks for underactuated fingers

Abstract

Modern multifunctional hand prostheses have many degrees of freedom, but strong limitations on weight and size. The actuators commonly used in these systems are relatively large and heavy, so their number should be kept as low as possible. This is often accomplished by underactuation, which causes a natural motion of the fingers when grasping an object but reduces the ability to execute a variety of grasps. To remedy this, a series of locking mechanisms can be implemented to fix the position of one or more joints. This paper focuses on the development of such a joint locking system that could be used in anthropomorphic prosthetic fingers. Two lock concepts are implemented in a single-joint test setup and evaluated. A gear-based concept is tested, though its actuation requirements prove too high for viable implementation in a prosthesis. A mechanism based on friction amplification is shown to exhibit self-locking properties, which allows for a minimal lock actuation force while withstanding joint torques of over 2 Nm. The friction amplification mechanism is found suitable for prosthesis use, and will be developed further for implementation in a future prosthesis prototype.

How to achieve precise operation of a robotic manipulator on a macro to micro/nano scale

“…The mechanical part with a dexterous structure of a robotic manipulator is like the human skeleton; it lays the very foundation for precise operation. This part, like the skeleton to human, constitutes the basic structure of the manipulator and has been studied by numerous researchers (Peerdeman et al , 2012; Jung et al , 2007; Li et al , 2013; Carrozza et al , 2003; Massa et al , 2002). In the macro field, the structure of a robotic hand has been extensively studied to guide the design of manipulators.…”

Development of an underactuated hand prosthesis with compliant control

“…Based on initial test results, a new set of friction pawls has been designed for implementation in a phalanx-sized enclosure. The contact surface of these pawls follows a logarithmic spiral around its rotation axis [16], as shown in Figure 4.5. The effect of this surface is shown in Figure 4.5 as well: the effects of changes in the distance between drum and pawl (due to play and tolerances in the components, for example) on the contact angle are minimized.…”

“…• "Design of Joint Locks for Underactuated Fingers" [16], published in: Proceedings of the IEEE International Conference on Biomedical Robotics and Biomechatronics (BioRob), 2012.…”

“…In Peerdeman et al [16] two joint locking concepts were evaluated; a gear-based system and a friction-based system. The gear-based system has an inherent indexing resolution and was found to require a higher actuation force.…”

“…There has been some research on mechanisms that passively disengage joints [55,56], as well as active electrostatic joint locking on robotic grippers [78]. In Peerdeman et al [16], the use of miniature mechanical joint locks is explored for use in hand prostheses. The limitations imposed by an anthropomorphic hand prosthesis lead to a lock actuation system integrated into the phalanges of the fingers, as well as a lock design which eliminates the need for continuous actuation.…”