Microrobot Research Articles

Mechanical Imaging of Soft Tissues With Miniature Climbing Robots.

Systematically mapping the mechanical properties of skin and tissue is useful for biomechanics research and disease diagnostics. For example, later stage breast cancer and lymphoma manifest themselves as hard nodes under the skin. Currently, mechanical measurements are done manually, with a sense of touch or a handheld tool. Manual measurements do not provide quantitative information and vary depending on the skill of the practitioner. Research shows that tactile sensors could be more sensitive than a hand. We propose a method that uses our previously developed skin-crawling robots to noninvasively test the mechanical properties of soft tissue. Robots are more systematic and repeatable than humans. Using the data collected with a cutomoter or indenter integrated into the miniature robot, we trained a convolutional neural network to classify the size and depth of the lumps. The classification works with 98.8% accuracy for cutometer and 99.6% for indenter for lump size with a diameter of 0 to 10 mm embedded in depth of 1 to 5 mm in a simulated tissue. We conducted a limited evaluation on a forearm, where the robot imaged dry skin with a cutometer. We hope to improve the ability to test tissues noninvasively, and ultimately provide better sensitivity and systematic data collection.

Tiny robots make big advances

This special issue showcases developments in microactuation, microparticle control, and micro/nanorobots for biomedicine.

Autonomous Navigation of Magnetic Microrobots in a Large Workspace Using Mobile-Coil System

Untethered magnetic miniature robots have attracted much attention in recent years, due to their minimally invasive features in biomedicine and highly flexible traits in micromanipulation. Autonomous control is one of the essential issues for magnetic microrobots, however, which remains challenging, especially for complex and large-workspace environments. To this end, this article proposes a novel navigation framework, using a home-designed eye-in-hand mobile-coil system. A three-step motion planner is designed to know entire surroundings and generate optimal paths, which contains environment reconstruction, position registration, and modified A* path searching. Moreover, a double-loop motion controller is designed to make the microrobot accurately follow the computed path and intelligently avoid collisions: The inner loop performs mechanism following; the outer loop decides appropriate magnetic fields for actuation, which includes a disturbance observer (DOB), a fuzzy logic modifier (FLM), and a model predictive controller (MPC). Experiments demonstrate the effectiveness of the proposed strategy: Feasible trajectories in a maze-like environment of diameter 230 mm can be planned, and autonomous navigation of microrobot is realized with both global accessibility and local adaptability.

Design of a Miniature Bi-Directional Non-Back Drivable Mechanism with High Retaining Torque

Ensure the safe operation of a mechanical system that involves motion is essential; some traditional ways to achieve this goal are mechanical devices such as breaks or clutches. This paper presents the design, manufacturing, and test of a bi-directional non-back-drivable mechanism for its application in miniature mechanical systems, like prostheses, robotics, or micro-machine tools. The bi-directional non-back-drivable mechanism operates as a locking device, limiting the torque transmission from the output into the input axle. Application of Design for X methods served to identified and prevent the main drawbacks of the mechanisms used for locking tasks, namely wear and backlash, to make the novel mechanism less sensitive to such factors, keeping high transmission performance in a tight space and with minimum parts. The presented set of design equations and selection graphs are for ABS plastic. A unified approach for the design of the bi-directional non-back-drivable mechanism is presented. The final section of the paper is devoted to the manufacturing and test of a sample of the mechanism.

End-Effector Contact and Force Detection for Miniature Autonomous Robots Performing Lunar and Expeditionary Surgery.

The U.S. Space Force was stood up on December 20, 2019 as an independent branch under the Air Force consisting of about 16,000 active duty and civilian personnel focused singularly on space. In addition to the Space Force, the plans by NASA and private industry for exploration-class long-duration missions to the moon, near-earth asteroids, and Mars makes semi-independent medical capability in space a priority. Current practice for space-based medicine is limited and relies on a "life-raft" scenario for emergencies. Discussions by working groups on military space-based medicine include placing a Role III equivalent facility in a lunar surface station. Surgical capability is a key requirement for that facility. To prepare for the eventuality of surgery in space, it is necessary to develop low-mass, low power, mini-surgical robots, which could serve as a celestial replacement for existing terrestrial robots. The current study focused on developing semi-autonomous capability in surgical robotics, specifically related to task automation. Two categories for end-effector tissue interaction were developed: Visual feedback from the robot to detect tissue contact, and motor current waveform measurements to detect contact force. Using a pixel-to-pixel deep neural network to train, we were able to achieve an accuracy of nearly 90% for contact/no-contact detection. Large torques were predicted well by a trained long short-term memory recursive network, but the technique did not predict small torques well. Surgical capability on long-duration missions will require human/machine teaming with semi-autonomous surgical robots. Our existing small, lightweight, low-power miniature robots perform multiple essential tasks in one design including hemostasis, fluid management, suturing for traumatic wounds, and are fully insertable for internal surgical procedures. To prepare for the inevitable eventuality of an emergency surgery in space, it is essential that automated surgical robot capabilities be developed.

Liquid Crystal Elastomer-Based Magnetic Composite Films for Reconfigurable Shape-Morphing Soft Miniature Machines.

Stimuli-responsive and active materials promise radical advances for many applications. In particular, soft magnetic materials offer precise, fast, and wireless actuation together with versatile functionality, while liquid crystal elastomers (LCEs) are capable of large reversible and programmable shapemorphing with high work densities in response to various environmental stimuli, e.g., temperature, light, and chemical solutions. Integrating the orthogonal stimuli-responsiveness of these two kinds of active materials could potentially enable new functionalities and future applications. Here, magnetic microparticles (MMPs) are embedded into an LCE film to take the respective advantages of both materials without compromising their independent stimuli-responsiveness. This composite material enables reconfigurable magnetic soft miniature machines that can self-adapt to a changing environment. In particular, a miniature soft robot that can autonomously alter its locomotion mode when it moves from air to hot liquid, a vine-like filament that can sense and twine around a support, and a light-switchable magnetic spring are demonstrated. The integration of LCEs and MMPs into monolithic structures introduces a new dimension in the design of soft machines and thus greatly enhances their use in applications in complex environments, especially for miniature soft robots, which are self-adaptable to environmental changes while being remotely controllable.

Tiny robots and sensors need tiny batteries - here's how to do it.

Improve materials and architectures to shrink microscopic devices. Improve materials and architectures to shrink microscopic devices.

Implicit coordination for 3D underwater collective behaviors in a fish-inspired robot swarm.

Many fish species gather by the thousands and swim in harmony with seemingly no effort. Large schools display a range of impressive collective behaviors, from simple shoaling to collective migration and from basic predator evasion to dynamic maneuvers such as bait balls and flash expansion. A wealth of experimental and theoretical work has shown that these complex three-dimensional (3D) behaviors can arise from visual observations of nearby neighbors, without explicit communication. By contrast, most underwater robot collectives rely on centralized, above-water, explicit communication and, as a result, exhibit limited coordination complexity. Here, we demonstrate 3D collective behaviors with a swarm of fish-inspired miniature underwater robots that use only implicit communication mediated through the production and sensing of blue light. We show that complex and dynamic 3D collective behaviors-synchrony, dispersion/aggregation, dynamic circle formation, and search-capture-can be achieved by sensing minimal, noisy impressions of neighbors, without any centralized intervention. Our results provide insights into the power of implicit coordination and are of interest for future underwater robots that display collective capabilities on par with fish schools for applications such as environmental monitoring and search in coral reefs and coastal environments.

Omnidirectional Free-Degree Wireless Power Transfer System Based on Magnetic Dipole Coils for Multiple Receivers

Wireless power transfer (WPT) technology offers a potential solution for the energy-supply problem. In this paper, we propose a novel magnetic coupling mechanism for omnidirectional and multiple-pickup energy transfer based on the magnetic dipole coils. Firstly, a cubic transmitter structure capable of generating three-dimension (3D) homogeneous magnetic field is fabricated to weaken directional sensitivity of receiving coil. Furthermore, the direction of current flowing through each dipole coil is also studied in detail. Numerical and simulated analysis is implemented to verify the omnidirectionality of the transmitter. Secondly, the equivalent circuit model for WPT systems with ferrite is analyzed. In addition, optimal loads, power distribution and transfer efficiency for multiple receivers are discussed and used to achieve the proper system design. Finally, experimental prototype is set up to validate the transmission performance of the proposed WPT system. The results have showed that genuine 3D high degree of freedom (DoF) can be achieved. Meantime, above 60% efficiency at least 30 W of total output power can be obtained for WPT systems with eight pick-ups. We believe the proposed system will give a new guideline for future low power electronic applications, such as monitoring sensors, miniature robots and household devices.

A Multiple Pheromone Communication System for Swarm Intelligence

Pheromones are chemical substances essential for communication among social insects. In the application of swarm intelligence to real micro mobile robots, the deployment of a single virtual pheromone has emerged recently as a powerful real-time method for indirect communication. However, these studies usually exploit only one kind of pheromones in their task, neglecting the crucial fact that in the world of real insects, multiple pheromones play important roles in shaping stigmergic behaviors such as foraging or nest building. To explore the multiple pheromones mechanism which enable robots to solve complex collective tasks efficiently, we introduce an artificial multiple pheromone system (ColCOS $\Phi $ ) to support swarm intelligence research by enabling multiple robots to deploy and react to multiple pheromones simultaneously. The proposed system ColCOS $\Phi $ uses optical signals to emulate different evaporating chemical substances i.e. pheromones. These emulated pheromones are represented by trails displayed on a wide LCD display screen positioned horizontally, on which multiple miniature robots can move freely. The color sensors beneath the robots can detect and identify lingering “pheromones” on the screen. Meanwhile, the release of any pheromone from each robot is enabled by monitoring its positional information over time with an overhead camera. No other communication methods apart from virtual pheromones are employed in this system. Two case studies have been carried out which have verified the feasibility and effectiveness of the proposed system in achieving complex swarm tasks as empowered by multiple pheromones. This novel platform is a timely and powerful tool for research into swarm intelligence.

Locomotion of Miniature Soft Robots.

Miniature soft robots are mobile devices, which are made of smart materials that can be actuated by external stimuli to realize their desired functionalities. Here, the key advancements and challenges of the locomotion producible by miniature soft robots in micro- to centimeter length scales are highlighted. It is highly desirable to endow these small machines with dexterous locomotive gaits as it enables them to easily access highly confined and enclosed spaces via a noninvasive manner. If miniature soft robots are able to capitalize this unique ability, they will have the potential to transform a vast range of applications, including but not limited to, minimally invasive medical treatments, lab-on-chip applications, and search-and-rescue missions. The gaits of miniature soft robots are categorized into terrestrial, aquatic, and aerial locomotion. Except for the centimeter-scale robots that can perform aerial locomotion, the discussions in this report are centered around soft robots that are in the micro- to millimeter length scales. Under each category of locomotion, prospective methods and strategies that can improve their gait performances are also discussed. This report provides critical analyses and discussions that can inspire future strategies to make miniature soft robots significantly more agile.

Magnetic Soft Robot With the Triangular Head–Tail Morphology Inspired By Lateral Undulation

In this article, extend the uses of a deformable structure of magnetic elastomer to develop a bio-inspired locomotion system for millimeter-scaled robots. As proposed in other researches, this material allows a possibility of the motor-less mechanism powered by magnetic field. The actuating mechanism of the robot mainly relies on the body deformation due to magnetic alignment. On the other hand, herein, the magnetic soft robot with the triangular head-tail morphology and sine-based magnetization utilizes a high degree of freedom provided by magnetic compliance for mobility in a form of lateral undulation. Under the oscillating magnetic field, dynamic torque primarily acts to the head, the tail passively waves, and the whole body propagates a series of lateral body-waves for self-propulsion in fluid, instead of pushing out surrounding fluid to make a swimming gait. We achieve the independent control of the laterally undulating robot in force-free swimming, and demonstrate its tunable body deformation to swim in various diameters of the fluid-filled tubes. A by-product of the undulation can transfer a force rate to swim through the fabric-media. By the increase of the actuating frequency, the undulating robot propels faster to retain a stable swimming in the flow. The versatilities of the robot with the proposed mechanism can be applied to serve the diverse purposes as a reliable and effective locomotion system with a minimal control. Particularly in biomedical applications, miniature soft robots with a potential mechanism for self-propulsion can contribute the great results to pursue minimally invasive treatments.

Millimeter-Scale Soft Continuum Robots for Large-Angle and High-Precision Manipulation by Hybrid Actuation.

Developing small‐scale soft continuum robots with large‐angle steering capacity and high‐precision manipulation offers broad opportunities in various biomedical settings. However, existing continuum robots reach the bottleneck in actuation on account of the contradiction among small size, compliance actuation, large tender range, high precision, and small dynamic error. Herein, a 3D‐printed millimeter‐scale soft continuum robot with an ultrathin hollow skeleton wall (300 μm) and a large inner‐to‐outer ratio (0.8) is reported. After coating a thin ferromagnetic elastomer layer (≈100–150 μm), the proposed soft continuum robot equipped with hybrid actuation (tendon‐ and magnetic‐driven mode) achieves large‐angle (up to 100°) steering and high‐precision (low to 2 μm for static positioning) micromanipulation simultaneously. Specifically, the robot implements an ultralow dynamic tracking error of ≈10 μm, which is ≈30‐fold improved than the state of art. Combined with a microneedle/knife or nasopharyngeal swab, the robot reveals the potential for versatile biomedical applications, such as drug injection on the target tissue, diseased tissue ablation, and COVID‐19 nasopharyngeal sampling. The proposed millimeter‐scale soft continuum robot presents remarkable advances in large‐range and high‐precise actuation, which provides a new method for miniature continuum robot design and finds broad applications in biomedical engineering.

Design of a Low-Cost Miniature Robot to Assist the COVID-19 Nasopharyngeal Swab Sampling.

Nasopharyngeal (NP) swab sampling is an effective approach for the diagnosis of coronavirus disease 2019 (COVID-19). Medical staffs carrying out the task of collecting NP specimens are in close contact with the suspected patient, thereby posing a high risk of cross-infection. We propose a low-cost miniature robot that can be easily assembled and remotely controlled. The system includes an active end-effector, a passive positioning arm, and a detachable swab gripper with integrated force sensing capability. The cost of the materials for building this robot is 55 USD and the total weight of the functional part is 0.23kg. The design of the force sensing swab gripper was justified using Finite Element (FE) modeling and the performances of the robot were validated with a simulation phantom and three pig noses. FE analysis indicated a 0.5mm magnitude displacement of the gripper's sensing beam, which meets the ideal detecting range of the optoelectronic sensor. Studies on both the phantom and the pig nose demonstrated the successful operation of the robot during the collection task. The average forces were found to be 0.35N and 0.68N, respectively. It is concluded that the proposed robot is promising and could be further developed to be used in vivo.

Reconfigurable multifunctional ferrofluid droplet robots

Magnetically actuated miniature soft robots are capable of programmable deformations for multimodal locomotion and manipulation functions, potentially enabling direct access to currently unreachable or difficult-to-access regions inside the human body for minimally invasive medical operations. However, magnetic miniature soft robots are so far mostly based on elastomers, where their limited deformability prevents them from navigating inside clustered and very constrained environments, such as squeezing through narrow crevices much smaller than the robot size. Moreover, their functionalities are currently restricted by their predesigned shapes, which is challenging to be reconfigured in situ in enclosed spaces. Here, we report a method to actuate and control ferrofluid droplets as shape-programmable magnetic miniature soft robots, which can navigate in two dimensions through narrow channels much smaller than their sizes thanks to their liquid properties. By controlling the external magnetic fields spatiotemporally, these droplet robots can also be reconfigured to exhibit multiple functionalities, including on-demand splitting and merging for delivering liquid cargos and morphing into different shapes for efficient and versatile manipulation of delicate objects. In addition, a single-droplet robot can be controlled to split into multiple subdroplets and complete cooperative tasks, such as working as a programmable fluidic-mixing device for addressable and sequential mixing of different liquids. Due to their extreme deformability, in situ reconfigurability and cooperative behavior, the proposed ferrofluid droplet robots could open up a wide range of unprecedented functionalities for lab/organ-on-a-chip, fluidics, bioengineering, and medical device applications.

A Shapeshifting Ferrofluidic Robot.

To create a miniature shapeshifting robot capable of controlled movement, subdivision, regeneration, passage through small channels, engulfment of particles, object manipulation, and flow manipulation, a droplet of magnetically responsive ferrofluid is used. The ferrofluidic robot can achieve the aforementioned functions when both its position and shape are controlled using a custom electromagnetic field generation system. It is demonstrated that the proposed robot can perform these functions with submillimeter and subdegree error. A robot having these capabilities can remotely perform medical and microassembly tasks requiring fine dexterity that are currently difficult or impossible.

3-D Visual Servoing of Magnetic Miniature Swimmers Using Parallel Mobile Coils

Untethered magnetic microrobots can be remotely controlled by dynamic magnetic fields. The ability to pass through complex and narrow regions makes them have great potential in biomedical applications. To date, various magnetic actuation systems and control methods have been developed to drive these tiny agents. However, steering their 3D locomotion at the human scale using electromagnetic systems is still challenging. In this regard, this article explores a closed-loop control strategy that guides swimming of magnetic microrobots at low Reynolds numbers in a large workspace. An eye-in-hand stereo-vision mobile-coil system is adopted to provide required dynamic magnetic fields and vision information. Both corkscrew-type and flexible-oar-type swimmers are analyzed, and a unified kinematic model is established. Based on the system and model, a triple-loop visual servoing scheme is proposed to fulfill simultaneous mechanism tracking and swimmer steering. Two different scaled-up untethered microrobots are employed in the path following experiment. Our prototype magnetic actuation system reaches a cylindrical workspace of diameter over 200 mm, and the mean error of path tracking is within 2 mm. These results provide a preliminary study for dexterous magnetic actuation of miniature robots for medical treatment.

Miniaturization re-establishes symmetry in the wing folding patterns of featherwing beetles

Most microinsects have feather-like bristled wings, a state known as ptiloptery, but featherwing beetles (family Ptiliidae) are unique among winged microinsects in their ability to fold such wings. An asymmetrical wing folding pattern, found also in the phylogenetically related rove beetles (Staphylinidae), was ancestral for Ptiliidae. Using scanning electron, confocal laser scanning, and optical microscopy, high-speed video recording, and 3D reconstruction, we analyze in detail the symmetrical wing folding pattern and the mechanism of the folding and unfolding of the wings in Acrotrichis sericans (Coleoptera: Ptiliidae) and show how some of the smaller featherwing beetles have reverted to strict symmetry in their wing folding. The wings are folded in three phases by bending along four lines (with the help of wing folding patches on the abdominal tergites) and locked under the closed elytra; they unfold passively in two phases, apparently with the help of the elasticity provided by resilin unevenly distributed in the wing and of convexities forming in the cross-sections of the unfolding wing, making it stiffer. The minimum duration of folding is 3.5 s; unfolding is much more rapid (minimum duration lowest recorded in beetles, 0.038 s). The folding ratio of A. sericans is 3.31 (without setae), which is greater than in any beetle in which it has been measured. The symmetrical wing folding pattern found in A. sericans and in all of the smallest ptiliids, in which ptiloptery is especially pronounced, is the only known example of symmetry re-established during miniaturization. This direction of evolution is remarkable because miniaturization is known to result in various asymmetries, while in this case miniaturization was accompanied by reversal to symmetry, probably associated with the evolution of ptiloptery. Our results on the pattern and mechanisms of wing folding and unfolding can be used in robotics for developing miniature biomimetic robots: the mechanisms of wing folding and unfolding in Ptiliidae present a challenge to engineers who currently work at designing ever smaller flying robots and may eventually produce miniature robots with foldable wings.

Design of A GIS Pipeline Robot for 220KV Substation

As an important development direction of substation equipment, a large number of GIS equipment are installed in the power system. Once the GIS equipment has internal faults, it is very inconvenient to find and deal with. This article designs a miniature maintenance robot for GIS equipment, which can be put into the busbar be through the GIS equipment maintenance hand hole cover; the robot has the ability to walk in the GIS equipment busbar tube; the robot carries a small camera device, which can check internal problems and return images; The robot is equipped with a manipulator, with vacuuming and grasping functions, which can complete simple cleaning and bolt tightening operations.

Robots fuel up

Microrobots Batteries are a convenient source of energy for untethered miniature robots. However, the low specific energy of small-scale batteries sets limits on how long such a robot can operate. Yang et al. report an insect-scale robot called RoBeetle that is powered by the controlled catalytic combustion of methanol, a fuel with more than 10 times the specific energy of a small-scale battery. RoBeetle, with size and mass comparable to a small insect, can carry payloads of up to 2.6 times its body weight, crawl on rough surfaces, and ascend inclines of 15 degrees. Sci. Robot. 5 , eaba0015 (2020).