Thermo-mechanical actuators such as twisted and coiled polymer (TCP) actuators and shape memory alloys are flexible actuators similar to biological muscles. These new materials opened up unprecedented opportunities for soft robotics applications. However, these actuators have been long criticized for their slow response and low efficiency. Although some researchers have improved on these challenges through active cooling and high pulse actuation, the results are far from the expectation of the scientific community. To address of these issues and auxiliary issues caused by these limitations are addressed in this article with a proposed solution through a 3D-printed scalable mechanical transmission system.
Sensors detect a change in a physical parameter around them and convert it to a measurable signal that can be construed and analyzed for further applications such as automation, wearable devices, human-machine interfaces, and medical devices, among countless other applications. For example, sensors in the biomedical field help to detect the physiological course of a body. Conventionally sensors are produced using photolithography and screen printing. These conventional methods are limited by the complexity and flexibility in manufacturing the sensors. But, additive manufacturing presents a flexible option to produce the sensors and integrate them into structures as a single unit. This paper shows an extrusion-based 3D printing method to print sensors using conductive filaments. A comb-shaped capacitive sensor was 3D printed using commercially available conductive filament on a 3D printed PLA substrate. Printing two different materials with different properties always remains a challenge in FDM, so this paper also explains the stepwise process for printing a conductive composite material along with a thermoplastic. Further experimental characterization of the filament and sensor was also performed. This paper compares the electrical properties of the feedstock and 3D printed parts to understand the impact of extrusion on the material. A custom-made experimental setup was designed to characterize the sensor. One of the challenges is the low melting point of 3D printed parts, limiting their use to low-power applications. However, most biomedical sensing applications are low power, so these sensors remain suitable for such applications. Hence, in the end, the authors have explored the viability of the integration of these 3D printed sensors with medical implants to manufacture smart biomedical devices.
Partial or total upper extremity impairment affects the quality of life of a vast number of people due to stroke,
neuromuscular disease, or trauma. Many researchers have presented hand orthosis to address the needs of rehabilitation
or assistance on upper extremity function. Most of the devices available commercially and in literature are powered by
conventional actuators such as DC motors, servomotors or pneumatic actuators. Some prototypes are developed based on
shape memory alloy (SMA) and dielectric elastomers (DE). This study presents a customizable, 3D printed, a
lightweight exoskeleton (iGrab) based on recently reported Twisted and Coiled Polymer (TCP) muscles, which are
lightweight, provide high power to weight ratio and large stroke. We used silver coated nylon 6, 6 threads to make the
TCP muscles, which can be easily actuated electrothermally. We reviewed briefly hand orthosis created with various
actuation technologies and present our design of tendon-driven exoskeleton with the muscles confined in the forearm
area. A single muscle is used to facilitate the motion of all three joints namely DIP (Distal interphalangeal), PIP
(Proximal Interphalangeal) and MCP (Metacarpophalangeal) using passive tendons though circular rings. The grasping
capabilities, along with TCP muscle properties utilized in the design such as life cycle, actuation under load and power
inputs are discussed.
This paper presents a biomimetic, lightweight, 3D printed and customizable robotic hand with locking mechanism consisting of Twisted and Coiled Polymer (TCP) muscles based on nylon precursor fibers as artificial muscles. Previously, we have presented a small-sized biomimetic hand using nylon based artificial muscles and fishing line muscles as actuators. The current study focuses on an adult-sized prosthetic hand with improved design and a position/force locking system. Energy efficiency is always a matter of concern to make compact, lightweight, durable and cost effective devices. In natural human hand, if we keep holding objects for long time, we get tired because of continuous use of energy for keeping the fingers in certain positions. Similarly, in prosthetic hands we also need to provide energy continuously to artificial muscles to hold the object for a certain period of time, which is certainly not energy efficient. In this work we, describe the design of the robotic hand and locking mechanism along with the experimental results on the performance of the locking mechanism.
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