An SU-8 Microgripper Based on the Cascaded V-Shaped Electrothermal Actuators: Design, Fabrication, Simulation and Experimental Investigations

This chapter presents the design, fabrication, numerical simulations and experimental investigations of a polymeric microgripper designed using the cascaded V-shaped electrothermal actuators. The microgripper has a total length around 1 mm and a total thickness of only 20 μm. The microgripper was simulated using electro-thermo-mechanical finite element method (FEM) in order to check the performance of the gripper. As structural material of the microgripper, the SU-8 biocompatible polymer was used during the fabrication process. A fabrication process was implemented to realize the microgripper using a symmetrically sandwich structure. The metallic micro-heaters were encapsulated in the polymeric actuation structure of the microgrippers to reduce the undesirable out-of-plane displacement of the gripper tips and the mechanical stress, to improve the thermal efficiency, and for obtaining the electrical isolation of the structure. Experimental testing has been performed to determine the openings and the temperatures of the microgripper tips as function of electrical current. A displacement of the tips of more than 50 μm can be obtained at an electrical current of around 26–28 mA. A comparison between the simulation results and the measurements were also presented

Advanced medical micro-robotics for early diagnosis and therapeutic interventions

Recent technological advances in micro-robotics have demonstrated their immense potential for biomedical applications. Emerging micro-robots have versatile sensing systems, flexible locomotion and dexterous manipulation capabilities that can significantly contribute to the healthcare system. Despite the appreciated and tangible benefits of medical micro-robotics, many challenges still remain. Here, we review the major challenges, current trends and significant achievements for developing versatile and intelligent micro-robotics with a focus on applications in early diagnosis and therapeutic interventions. We also consider some recent emerging micro-robotic technologies that employ synthetic biology to support a new generation of living micro-robots. We expect to inspire future development of micro-robots toward clinical translation by identifying the roadblocks that need to be overcome

Characterization Of Commercially Available Conductive Filament And Their Application In Sensors And Actuators

The primary aim of this study is to contribute to the field of additives that would enable the fabrication of electrical sensors and actuators completely via Material Extrusion based Additive Manufacturing (MEAM). The second aim of the study is to provide the necessary characterization to facilitate the development of applications that predicts electrical part performance. The electrical characterization of two conductive poly-lactic acid (PLA) filaments, namely, c-PLA with carbon black and graphene PLA was performed to study the temperature coefficient of the resistance. Resistivity of carbon black filament was compared to a printed single layer and with that of a cube. The raw and printed c-PLA showed a positive temperature coefficient of resistance (α) ranging from ~0.03-0.01 ℃-1 while its counterpart in the study, graphene PLA, did not exhibit significant (α). Parts from graphene PLA with multilayer MEAM exhibited a negative α to a certain temperature before exhibiting positive α. The resistivity of the printed parts was 300 times higher for c-PLA and 1500 times for graphene PLA. However, no microstructural or chemical compositional changes were observed between the raw filaments and the printed parts. Due to the high α of the c-PLA, it was deemed as the better material for constructing electro thermal sensors and actuators using MEAM. First, c-PLA was used to fabricate and package a completely 3D printed flow meter that operates on the principle of Joule heating and hotwire anemometry. When the designed flowmeter was simulated using a finite element package, a flow sensitivity of -2.33 Ω sccm-1 and a relative change in resistivity of 0.036 sccm-1 was expected. For an operating voltage of 12-15 V, the experimental results showed a flow sensitivity within the range of 0.014-0.032 sccm-1 and the relative change in resistivity ranged from 0.039 – 0.065 sccm-1. Thus, a completely 3D printed flowmeter was demonstrated. Second, using the same principle of Joule heating, an actuator inspired from MEMS chevron grippers was designed, simulated, and fabricated. Simulation showed the feasibility of the structure and further predicted a displacement of a few hundred microns with a potential as low as 3 V with a cooling time as little less than 120 seconds. Experimentally, a displacement of 120.04, 97.05, and 88.96 μm were achieved in 15, 10, and 5 seconds with actuation potentials of 12.7, 13.8, and 17.9 V, respectively. As predicted by the simulation results, it took longer for the gripper to cool (close to 180 seconds) when compared to actuation times. During the above studies, we discovered the printing parameters altered the part resistance. Our final study examined how extrusion temperature and printing speed affects the impedance of the MEAM printed parts. Further, anisotropy in the impedance was observed and the influence of the interface to it was examined. From the experimental results, the anisotropy was quantified with a Z/F ratio and was found to be nearly constant, ~2.15±0.23. Impedance scaling with the number of interfaces was measured and showed conclusively that the interlayer bonding was the sole source for the observed Z/F ratio. Scanning electron microscope images shows the absence of air gaps at the interface, and energy dispersion spectroscopy shows the absence of oxidation at the interface. By investigating the role of print parameters and scaling of impedance with interfaces, a framework to model and predict electrical behavior of electro thermal sensors and actuators made via MEAM can be realized

Anthropomorphic Twisted String-Actuated Soft Robotic Gripper with Tendon-Based Stiffening

Realizing high-performance soft robotic grippers is challenging because of the inherent limitations of the soft actuators and artificial muscles that drive them, including low force output, small actuation range, and poor compactness. Despite advances in this area, realizing compact soft grippers with high dexterity and force output is still challenging. This paper explores twisted string actuators (TSAs) to drive a soft robotic gripper. TSAs have been used in numerous robotic applications, but their inclusion in soft robots has been limited. The proposed design of the gripper was inspired by the human hand. Tunable stiffness was implemented in the fingers with antagonistic TSAs. The fingers' bending angles, actuation speed, blocked force output, and stiffness tuning were experimentally characterized. The gripper achieved a score of 6 on the Kapandji test and recreated 31 of the 33 grasps of the Feix GRASP taxonomy. It exhibited a maximum grasping force of 72 N, which was almost 13 times its own weight. A comparison study revealed that the proposed gripper exhibited equivalent or superior performance compared to other similar soft grippers.Comment: 19 pages, 15 figure

Control-based 4D printing: adaptive 4D-printed systems

Building on the recent progress of four-dimensional (4D) printing to produce dynamic structures, this study aimed to bring this technology to the next level by introducing control-based 4D printing to develop adaptive 4D-printed systems with highly versatile multi-disciplinary applications, including medicine, in the form of assisted soft robots, smart textiles as wearable electronics and other industries such as agriculture and microfluidics. This study introduced and analysed adaptive 4D-printed systems with an advanced manufacturing approach for developing stimuli-responsive constructs that organically adapted to environmental dynamic situations and uncertainties as nature does. The adaptive 4D-printed systems incorporated synergic integration of three-dimensional (3D)-printed sensors into 4D-printing and control units, which could be assembled and programmed to transform their shapes based on the assigned tasks and environmental stimuli. This paper demonstrates the adaptivity of these systems via a combination of proprioceptive sensory feedback, modeling and controllers, as well as the challenges and future opportunities they present