Most robotic parts used today are rigid, have a limited range of motion and don’t look lifelike. Inspired by nature and biology, a robotic finger designed at FAU looks, feels and works like the real thing.
Most robotic parts used today are rigid, have a limited range of motion and don’t really look lifelike. Inspired by both nature and biology, a scientist from Florida Atlantic University has designed a novel robotic finger that looks and feels like the real thing. In an article recently published in the journal Bioinspiration & Biomimetics, Erik Engeberg, Ph.D., assistant professor in the Department of Ocean and Mechanical Engineering within the College of Engineering and Computer Science at FAU, describes how he has developed and tested this robotic finger using shape memory alloy (SMA), a 3D CAD model of a human finger, a 3D printer, and a unique thermal training technique.
“We have been able to thermomechanically train our robotic finger to mimic the motions of a human finger like flexion and extension,” said Engeberg. “Because of its light weight, dexterity and strength, our robotic design offers tremendous advantages over traditional mechanisms, and could ultimately be adapted for use as a prosthetic device, such as on a prosthetic hand.”
In the study, Engeberg and his team used a resistive heating process called “Joule” heating that involves the passage of electric currents through a conductor that releases heat. Using a 3D CAD model of a human finger, which they downloaded from a website, they were able to create a solid model of the finger. With a 3D printer, they created the inner and outer molds that housed a flexor and extensor actuator and a position sensor. The extensor actuator takes a straight shape when it’s heated, whereas the flexor actuator takes a curved shape when heated. They used SMA plates and a multi-stage casting process to assemble the finger. An electrical chassis was designed to allow electric currents to flow through each SMA actuator. Its U-shaped design directed the electric current to flow the SMAs to an electric power source at the base of the finger.
This new technology used both a heating and then a cooling process to operate the robotic finger. As the actuator cooled, the material relaxed slightly. Results from the study showed a more rapid flexing and extending motion of the finger as well as its ability to recover its trained shape more accurately and more completely, confirming the biomechanical basis of its trained shape.
“Because SMAs require a heating process and cooling process, there are challenges with this technology such as the lengthy amount of time it takes for them to cool and return to their natural shape, even with forced air convection,” said Engeberg. “To overcome this challenge, we explored the idea of using this technology for underwater robotics, because it would naturally provide a rapidly cooling environment.”
Since the initial application of this finger will be used for undersea operations, Engeberg used thermal insulators at the fingertip, which were kept open to facilitate water flow inside the finger. As the finger flexed and extended, water flowed through the inner cavity within each insulator to cool the actuators.
Bottle Pick and Drop Demo UR10 and Shadow Hand
“Because our robotic finger consistently recovered its thermomechanically trained shape better than other similar technologies, our underwater experiments clearly demonstrated that the water cooling component greatly increased the operational speed of the finger,” said Engeberg.
Undersea applications using Engeberg’s new technology could help to address some of the difficulties and challenges humans encounter while working in the ocean depths.
The focus of Engeberg’s BioRobotics Laboratory at FAU is investigating robotics and prosthetics, controller design, bioinspiration and biomemetics.
Source:FAU Image Source: The image is adapted from the FAU press release Video Source: The video is available at the FAU – BioRobotics Lab YouTube page Original Research: Full open access research for “Anthropomorphic finger antagonistically actuated by SMA plates” by Erik D Engeberg, Savas Dilibal, Morteza Vatani, Jae-Won Choi and John Lavery in Bioinspiration & Biomimetics. Published online August 20 2015 doi:10.1088/1748-3190/10/5/056002
Anthropomorphic finger antagonistically actuated by SMA plates
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.
“TRP and Rhodopsin Transport Depends on Dual XPORT ER Chaperones Encoded by an Operon” by Erik D Engeberg, Savas Dilibal, Morteza Vatani, Jae-Won Choi and John Lavery in Bioinspiration & Biomimetics. Published online August 20 2015 doi:10.1088/1748-3190/10/5/056002