This paper focuses on design, fabrication and characterization of a biomimetic, compact, low-cost and lightweight 3D printed humanoid hand (TCP Hand) that is actuated by twisted and coiled polymeric (TCP) artificial muscles. The TCP muscles were recently introduced and provided unprecedented strain, mechanical work, and lifecycle (Haines et al 2014 Science 343 868-72). The five-fingered humanoid hand is under-actuated and has 16 degrees of freedom (DOF) in total (15 for fingers and 1 at the palm). In the under-actuated hand designs, a single actuator provides coupled motions at the phalanges of each finger. Two different designs are presented along with the essential elements consisting of actuators, springs, tendons and guide systems. Experiments were conducted to investigate the performance of the TCP muscles in response to the power input (power magnitude, type of wave form such as pulsed or square wave, and pulse duration) and the resulting actuation stroke and force generation. A kinematic model of the flexor tendons was developed to simulate the flexion motion and compare with experimental results. For fast finger movements, short high-power pulses were employed. Finally, we demonstrated the grasping of various objects using the humanoid TCP hand showing an array of functions similar to a natural hand.
Several works have been reported in powered hand orthosis in the last ten years for assistive or rehabilitative purposes. However, most of these approaches uses conventional actuators such as servo motors to power orthosis. In this work, we demonstrate the recently reported twisted and coiled polymeric (TCP) muscles to drive a compact, light, inexpensive and wearable upper extremity device, iGrab. A 3D printed orthotic hand module was designed, developed and tested for the performance. The device has six 2-ply muscles of diameter 1.35 mm with a length of 380 mm. We used a single 2-ply muscle for each finger and two 2-ply muscles for the thumb. Pulsed actuation of the muscles at 1.8 A current for 25 s with 7% duty cycle under natural cooling showed full flexion of the fingers within 2 s. Modeling and simulation were performed on the device using standard Euler–Lagrangian equations. Our artificial muscles powered hand orthosis demonstrated the capability of pinching and picking objects of different shapes, weights, and sizes.
Twisted and Coiled Polymer (TCP) muscles are soft actuators made by inserting twist in a precursor fiber while attaching a dead weight at the end, followed by heat treatment. TCP muscles are thermally driven actuators with high power to weight ratio, large strain and low cost. These muscles have a wide variety of applications in engineering, specifically for robotics since these actuators have large linear deformation in response to applied power (Joule’s Effect). The performance of these muscles depend on numerous fabrication parameters such as speed of the coiling, dead weight used, precursor fiber type, number of filament in precursor fiber, number of plies and training cycles. An in-depth study of the fabrication parameters is required to understand the performance of the muscles. We have designed experimental setup to study the performance of the muscles on different input parameters such as load, current, voltage and output results such as displacement, force and temperature. We present the study of single, double and tripled plied muscles that are fabricated by plying together a twisted and coiled filament. Further, the power consumption of the muscles under various conditions is discussed. This study would help to establish a procedure to fabricate these materials with consistent properties.
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