Anthropomorphic finger antagonistically actuated by SMA plates

Abstract

Most robotic applications that contain shape memory alloy (SMA) actuators use the SMA in a linear or spring shape. In contrast, a novel robotic finger was designed in this paper using SMA plates that were thermomechanically trained to take the shape of a flexed human finger when Joule heated. This flexor actuator was placed in parallel with an extensor actuator that was designed to straighten when Joule heated. Thus, alternately heating and cooling the flexor and extensor actuators caused the finger to flex and extend. Three different NiTi based SMA plates were evaluated for their ability to apply forces to a rigid and compliant object. The best of these three SMAs was able to apply a maximum fingertip force of 9.01N on average. A 3D CAD model of a human finger was used to create a solid model for the mold of the finger covering skin. Using a 3D printer, inner and outer molds were fabricated to house the actuators and a position sensor, which were assembled using a multi-stage casting process. Next, a nonlinear antagonistic controller was developed using an outer position control loop with two inner MOSFET current control loops. Sine and square wave tracking experiments demonstrated minimal errors within the operational bounds of the finger. The ability of the finger to recover from unexpected disturbances was also shown along with the frequency response up to 7 rad s(-1). The closed loop bandwidth of the system was 6.4 rad s(-1) when operated intermittently and 1.8 rad s(-1) when operated continuously.

Long Shape Memory Alloy Tendon-based Soft Robotic Actuators and Implementation as a Soft Gripper

“…SMA wires with torsional pre-strain have also been used to deform origami-based structures 45,46 . SMA plates have been used in a soft finger with significant force, but requires too much power for practical applications 47 . Twisted and coiled actuators (TCA) made from nylon fishing lines or other polymers can be used to produce large contraction with limited forces 48,49 , dielectric elastomers can produce rapid and small deformations 50 , ionic polymer-metal composites can produce diverse deformations through the movement of cations in a ionic membrane under an applied voltage 51 , and phase changing materials can expand significantly when heated 52 .…”

Fluidic Haptic Interface for Mechano-Tactile Feedback

“…On the other hand, battery-powered partial-hand prostheses embed electro-mechanical actuators (which can be controlled by (surface) Electromyography (EMG) interfaces). For instance, Shape Memory Alloys are integrated into an anthropomorphic finger: heating and cooling the flexor and extensor actuators cause the finger to flex and extend [8]. Other patented prosthetic fingers rely on servo-motors [9].…”

Design of a Soft Composite Finger with Adjustable Joint Stiffness

“…These structures can bend, expand, compress and twist to achieve the desired end effector motion. A pneumatic [7], tendon [8], hydraulic [9], shape memory materials [10], material jamming [11], or electro-active polymers [12] actuation scheme deform the shape and reinforce the structural strength. Due to the nature of inherent softness in both, the body material and actuation scheme, these robots can perform a variety of tasks in unstructured environments and can interact with human beings without causing any harm [13], [14].…”