Craniosynostosis involves premature fusion of the cranial sutures resulting in abnormal skull morphology and elevated intracranial pressure. Surgical intervention is necessary to correct the skull shape and to allow for unrestricted brain growth. This study presents a novel snake robot designed for minimally invasive cranial osteotomies featuring two articulating bending segments. The end-effector comprises a bone-punch for bone-cutting, a dural and scalp retractor, as well as channels for an endoscope and an instrument. The robot's bending mechanism is driven by tendons and utilizes geared linkages to facilitate a smooth curved shape. Pre-tensioned antagonistic tendons allow the robot to modulate its stiffness to adapt to external loads. A follow-the-leader algorithm was implemented to guide the robot along a skull cutting path. Experimental results demonstrated that at maximum bending of$60^{\circ}$for segment 1 and$90^{\circ}$for segment 2 there was a$15.9^{\circ}$and$11.5^\circ$error, respectively. Position errors ranged from 2.5 to 21.5 mm when tracing a curved path. The tool increased stiffness with tendon pre-tensioning from 20–100 N during bent configurations$q_{1}$and$q_{2}$for segments 1 and 2, respectively, at$[q_{1},q_{2}]=[0^{\mathrm{o}},30^{\mathrm{o}}]$and$[30^{\circ},60^{\circ}]$. Tip deflection reduced from 0.42 to 0.03 cm and 0.37 to 0.10 cm during axial loading and from 11.40 to 3.88 cm and 3.62 to 0.48 cm during radial loading for each configuration, respectively. Ex vitro trials demonstrated the robots ability to perform simulated osteotomies on skull models to 68–73% of desired path lengths with a maximum deviation of 8 mm.

Knowledge of the tip contact force in continuum robots, which are often used as medical instruments, is critical for clinical applications. It enhances the interventionalist's decision-making, navigation efficiency, and procedural safety. However, accurately determining the tip contact force in conventionally sized instruments remains challenging. This study introduces a learning-based method for estimating the external contact force at the tip of a continuum robot. By leveraging curvature and bending angle data from a multi-core fiber equipped with fiber Bragg gratings (FBGs) embedded inside the Nitinol tube, the method maps these inputs to the corresponding tip force in 3D. Experiments conducted on an FBG-embedded Nitinol rod validate the feasibility of the proposed method, yielding Mean Squared Error (MSE), Mean Absolute Error (MAE), and Root Mean Squared Error (RMSE) values of 20.9$\left(m N^{2}\right), 2.7(m N)$, and$4.6(m N)$, respectively, which represent a 26 % improvement compared to the learning-based vision methodology.

Endoscopic submucosal dissection (ESD) is a technically difficult, minimally invasive, organ preserving resection technique that yields improved clinical outcomes when compared to current conventional procedures but requires experienced surgeons and specialized skills. Difficulty in applying tension during ESD is recognized as the single greatest barrier to wide adoption of the procedure, and solution of this problem is sure to have wide-reaching and immediate adoption. This work presents a compact wireless retraction device that is magnetically actuated and has a high force output with adaptable traction control. The retraction device is 25 mm long and 4 mm in diameter. The device has two modes of operation: first spooling to collect string slack, then transitions via external permanent magnet to internal string twisting to generate a large retraction force. In slack collection the device can contract 11 cm in length at a speed of 6.88 millimeters per second, then clutch to force mode to reach a peak retraction force of 1.33 N, leveraging the micro-transmission twisted string actuation. The wireless device is designed for endoscopic deployment to any surgical environment or lesion within the gastrointestinal tract.

Magnetic surgical tools benefit greatly from real-time pose estimation, as this is essential for controlling them safely and effectively. Current pose estimation methods for surgical tools either focus on rigid tools, or are developed specifically for the da Vinci surgical system. In this work, we use computer vision from a monocular endoscopic camera to estimate the pose of an articulated magnetic surgical tool. In particular, we present a deep 3D keypoint estimation framework and a particle filter to achieve this. The former method can be used for any articulated surgical tool, while the latter method is specific to magnetic tools. We show that the deep 3D keypoint estimation framework estimates the surgical tool’s joint angles with an average error of 4.0 degrees and a speed of 29 Hz. In addition, we demonstrate the robustness of the magnetic particle filter and the deep pose estimation method for real-time tool pose estimation.

Neurosurgery could benefit from robot-assisted minimally invasive approaches, but existing robot tools are insufficiently small and compact. Magnetic actuation is an attractive approach to medical robotics because it allows small, modular serial mechanisms to be remotely actuated. Despite these advantages, magnetic actuation is relatively weak compared to alternative actuation methods. In this paper, we introduce a novel analytical model for magnetic serial robots, use this model to design two prototypes, and then demonstrate that a 4-mm-diameter prototype without any internal mechanical transmission can produce forces up to 0.181 N: high enough to perform delicate microsurgical tasks. We also demonstrate that the robot can achieve a closed-loop step response rise time of 0.71 seconds with an overshoot of 7.8%: sufficiently fast for surgical motions while maintaining a tip precision of less than 2 mm during a worst-case dynamic motion. These experiments provide strong evidence for the feasibility of directly-driven magnetic tools for neurosurgical applications, and they motivate future investigations in this area.

Dexterity is demanded for an endoscopic tool to handle complicated procedures in neurosurgery, e.g., removing diseased tissue from inside the deep brain along a tortuous path. Current robotic tools are either rigid or lack wristed motion ability at the tip, leading to limited usage in minimally invasive procedures. In this paper, a hybrid steerable robot with a magnetic wristed forceps is proposed to provide enhanced dexterity for endoscopic epilepsy surgery. A set of three precurved Nitinol tubes with concentric deployment, called a concentric tube robot (CTR), serves as a 6 degrees-of-freedom (DoF) robotic positioner. The magnetic wristed forceps is composed of a rotational wrist joint, and forceps at the tip, both of which are actuated remotely by magnetic fields. The magnetic wrist and forceps provide an extra rotational DoF and a gripping DoF on top of the CTR, respectively. The magnetic wrist and gripper are designed to have a hollow channel along their common axis, inside which a soft tube is deployed as a second functional tool for irrigation or suction. An electromagnetic navigation system (eMNS) with 8 coils is used to create the quasi-static magnetic fields. Experimental characterization of the robot kinematics is performed and the results show the mean motion error of CTR is 2.8 mm. The workspace is also analyzed and results indicate that the proposed hybrid robot has a significantly larger reachable area compared to the one of the CTR alone. Mock epilepsy procedures are performed on a brain phantom to validate the feasibility of the hybrid robot for neurosurgery applications.

Tendon-driven continuum robots show promise for use in surgical applications as they can assume complex configurations to navigate along tortuous paths. However, to achieve these complex robot shapes, multiple segments are required as each robot segment can bend only with a single constant curvature. To actuate these additional robot segments, multiple tendons must typically be added on-board the robot, complicating their integration, robot control, and actuation. This work presents a method of achieving two curvatures in a single tendon-driven continuum robot segment through use of a novel magnetic locking mechanism. Thus, the need for additional robot segments and actuating tendons is eliminated. The resulting two curvatures in a single segment are demonstrated in two and three dimensions. Furthermore, the maximum magnetic field required to actuate the locking mechanism for different robot bending angles is experimentally measured to be 6.1 mT. Additionally, the locking mechanism resists unintentional unlocking unless the robot assumes a 0° bending angle and a magnetic field of 18.1 mT is applied, conditions which are not typically reached during routine use of the system. Finally, addressable actuation of two locking mechanisms is achieved, demonstrating the capability of producing multiple curvatures in a single robot segment.

Magnetic torsion springs are capable of producing unique and useful torque-displacement responses that are not possible with elastic springs. Millimeter-scale magnetically-actuated robots, which are gaining increasing interest in biomedical applications, would benefit from the use of magnetic torsion springs. However, existing magnetic torsion springs are difficult to fabricate at that scale and can only produce sinusoid-like responses. Here we show that the magnets embedded in the links of a robot for actuation purposes can also be leveraged to produce torsion spring-like behavior. This Simultaneous Magnetic Actuation and Restoring Torque (SMART) spring design can enable switching or pop-up behaviour in millimeter-scale magnetically-actuated mechanisms. A novel analytical model, validated both numerically and experimentally, is used to design constant-stiffness and nonlinear bistable SMART springs. These springs are integrated into a novel 3.5 mm diameter magnetic robot manipulator.

Wireless robots at the subcentimeter size are often actuated using externally generated magnetic fields. For most applications, these remote magnetic microrobots are located relatively far from the magnetic field generation sources. In this condition, all microrobots receive approximately the same driving magnetic field (which we term a homogeneous field). While some solutions have been presented to allow for the creation of simple onboard tools, the full potential of the homogeneous magnetic field for multi-degrees-of-freedom (DOF) actuation has not been exploited. Here we introduce a design framework to utilize the maximum number of independently controlled DOFs on a microrobot system. We make use of three classes of mechanisms which are commonly used in practice and allow for more complex microrobots with up to eight DOFs. To verify the functionality of our framework, we used it to design an optimized drug delivery robot equipped with a 3-DOF drug-releasing mechanism and a 4-DOF motion mechanism. Experiments are performed to actuate each one of the robot's seven DOFs individually, where the cross-talk error between these seven DOFs averaged 7% with a max error of 18.3%.

Current minimally-invasive surgical tools suffer from lack of scalability and restricted access to some surgical sites using a laparoscopic probe. This paper introduces a proof-of-concept prototype of the first completely wireless surgical scissors capable of dexterous motion and cutting in a remote environment as a mobile microrobotic device. The 15 mm untethered surgical scissors are custom made from sharpened titanium sheets with a magnet on each blade for actuating force and control. A super-elastic nitinol wire acts as a restoring spring and results in a simple design with no pin joint which is difficult to fabricate at small sizes. To actuate and control the scissors, a 3D magnetic coil system is used here for testing and demonstration. An external magnetic flux density of 20 mT can be generated using the coils and is used for cutting as well as orienting, moving and closing the scissors. In this first prototype setup, the scissors can generate up to 75 mN of cutting force, and we demonstrate the cutting of agar. As a proof of concept demonstration of the potential use of the scissors as a completely untethered surgical tool, we robotically maneuver the scissors to a target location in a confined environment where they cut through agar and return to their initial position.

Magnetically-driven micrometer to millimeter-scale robotic devices have recently shown great capabilities for remote applications in medical procedures, in microfluidic tools and in microfactories. Significant effort recently has been on the creation of mobile or stationary devices with multiple independently-controllable degrees of freedom (DOF) for multiagent or complex mechanism motions. In most applications of magnetic microrobots, however, the relatively large distance from the field generation source and the microscale devices results in controlling magnetic field signals which are applied homogeneously over all agents. While some progress has been made in this area allowing up to six independent DOF to be individually commanded, there has been no rigorous effort in determining the maximum achievable number of DOF for systems with homogeneous magnetic field input. In this work, we show that this maximum is eight and we introduce the theoretical basis for this conclusion, relying on the number of independent usable components in a magnetic field at a point. In order to verify the claim experimentally, we develop a simple demonstration mechanism with 8 DOF designed specifically to show independent actuation. Using this mechanism with 500 μm magnetic elements, we demonstrate eight independent motions of 0.6 mm with 8.6 % coupling using an eight coil system. These results will enable the creation of richer outputs in future microrobotic devices.

Untethered mobile microgrippers exhibit flexibility and agility in small and constrained environments as precise and accurate robotic end-effectors, with promising potential applications in cell manipulation and microassembly. Here, we propose the first scheme to independently and simultaneously position two microgrippers on a horizontal plane for parallel targeted cargo delivery using a single global input. The separation and orientation of the two-microgripper pair are modulated by the local magnetic interactions between the two microgrippers, which are governed by a global magnetic field. The microgripper action of grasping or releasing cargoes is fully controlled by the global magnetic field without requiring additional thermal, chemical, or other stimuli. Thus, the proposed strategy only requires a single input, i.e., a global magnetic field, to control two microgrippers and therefore is simple to implement and fast-acting. As a demonstration, two microgrippers are maneuvered by a global magnetic field to pick up two cargoes and deliver them to their respective destinations. The parallel operation of two microgrippers can potentially double the overall throughput and enable the tasks that require team cooperations. The two 3D microgrippers configuration is intuitive in teleoperations, since it imitates the two-hand case of human beings.

Recent work in magnetically actuated microscale robots for biomedical or microfluidic applications has resulted in magnetic actuation systems that can remotely command precise five-degree-of-freedom control of magnetic devices. This paper presents a new type of actuation system, which uses an array of rotating permanent magnets to generate the same level of control over untethered microscale devices with the potential for increased field and gradient strength and minimal heat generation. In contrast with previous permanent-magnet actuation systems, the system proposed here does not require any hazardous translational motion of the control magnets, resulting in a simple, safe, and inexpensive system. The proof-of-concept prototype system presented, with eight permanent magnets, can create fields and field gradients in any direction with variable magnitudes between zero and 30 mT and 0.83 Tm-1, respectively. The effectiveness of the system is shown through characterization and feedback control of a 250-μm micromagnet in a 3-D path-following task with average accuracy of 25 μm. An optimization framework is presented for designing system configurations for targeted applications.

Recent work in magnetically-actuated micro-scale robots for biomedical or microfluidic applications has resulted in electromagnetic actuation systems which can command precise five-degree-of-freedom control of simple magnetic devices at the sub-millimeter scale in remote environments. This paper presents a new type of actuation system which uses an array of large, rotatable, permanent magnets to generate the same level of control over untethered micro-robotic systems with the potential for increased field and gradient strength and minimal heat generation. We show that the system can produce any field or field gradient at the workspace (including a value of zero). In contrast with previous permanent magnet actuation systems, the system proposed here accomplishes this without any hazardous translational motion of the control magnets, resulting in a simple, safe, and inexpensive system. The proof-of-concept prototype system presented, with eight permanent magnets, can create fields and gradients in any direction with strength of 30 mT and 0.83 T·m-1, respectively. The effectiveness of the system is shown through characterization and feedback control of a 250 μm micro-magnet in a path-following task with average accuracy of 39 μm.

We present a method to independently control two millimeter-scale soft-bodied magnetic swimmers, with nominal dimensions of 1.5 × 4.9 × 0.06 mm. A swimmer's speed depends on its relative angle with the actuation magnetic field. The two swimmers under control have different directions of net magnetic moments, and assume distinct orientations in one global magnetic field. With this fixed heading difference between two swimmers, the global actuation field forms different relative angles with the two swimmers. By manipulating these two relative angles, the two swimmers can exhibit different speeds. Theoretically, any speed ratios can be achieved between the two swimmers. In practice, a relatively accurate speed ratio can be obtained when both swimmers have nonzero speeds and one swimmer is no more than twice as fast as the other. Adding the control over the strength of actuation field, two swimmers can obtain independent speeds within a certain range. Two feedback controllers are proposed to control two such swimmers to arrive at independent global points (positioning) and move along paths (path following). Type I Sequential Controller manipulates two swimmers to move to their respective goals in sequence, while Type II Parallel Controller moves both swimmers simultaneously. Experiments are presented in which two swimmers are controlled to pass a series of points to form the letters “UT”.

Mobile microrobots are typically fabricated in a multi-step microfabrication process and then transported into an enclosed workspace for operation. This paper presents a new, 3D printing inspired method for in-situ fabrication of mobile magnetic microrobots with complex topology from a polymer filament on demand directly inside an enclosed operational environment. Through the use of a tip magnet on the filament, the target shape is formed by magnetic guidance from external electromagnetic coils which wirelessly project fields into the workspace as the filament is fed through a hot needle which is inserted into the workspace. A bending model and a shape planner are developed for predicting and controlling the fabrication process. Magnetically-active millimeter-scale robotic devices of different shapes and sizes are fabricated using polylactic acid (PLA) filament with diameter as small as 50 μm. As a demonstration of the in-situ formation of a functional microrobotic device, a force-sensing microrobot with integrated sensing spring is fabricated inside an enclosed space, and then is used to measure the manipulation force during a pushing experiment by optical deformation measurement. We thus show the utility of the fabrication method for creating complex microrobot shapes remotely in enclosed environments for advanced microrobotic applications, with the potential for scaled down applications in healthcare and microfluidics.

This paper presents a new soft-bodied millimeterscale swimmer actuated by rotating uniform magnetic fields. The proposed swimmer moves through internal undulatory deformations, resulting from a magnetization profile programmed into its body. To understand the motion of the swimmer, a mathematical model is developed to describe the general relationship between the deflection of a flexible strip and its magnetization profile. As a special case, the situation of the swimmer on the water surface is analyzed and predictions made by the model are experimentally verified. Experimental results show the controllability of the proposed swimmer under a computer vision-based closed-loop controller. The swimmers have nominal dimensions of 1.5×4.9×0.06 mm and a top speed of 50 mm/s (10 body lengths per second). Waypoint following and multiagent control are demonstrated for swimmers constrained at the air-water interface and underwater swimming is also shown, suggesting the promising potential of this type of swimmer in biomedical and microfluidic applications.

Untethered robots miniaturized to the length scale of millimeter and below attract growing attention for the prospect of transforming many aspects of health care and bioengineering. As the robot size goes down to the order of a single cell, previously inaccessible body sites would become available for high-resolution in situ and in vivo manipulations. This unprecedented direct access would enable an extensive range of minimally invasive medical operations. Here, we provide a comprehensive review of the current advances in biomedical untethered mobile milli/microrobots. We put a special emphasis on the potential impacts of biomedical microrobots in the near future. Finally, we discuss the existing challenges and emerging concepts associated with designing such a miniaturized robot for operation inside a biological environment for biomedical applications.

One major challenge for untethered micro-scale mobile robotics is the manipulation of external objects in the robot's three-dimensional (3D) work environment. Here, we present a method to use the capillary force at a solid-liquid-gas interface to reversibly attach objects to a mobile magnetic microrobot. This is accomplished by the addition of a cavity in the hydrophobic microrobot, in which an air bubble is captured when the microrobot is placed in a water environment. The extension of the air bubble from the cavity is adjusted dynamically by controlling the pressure of the workspace environment. A peak switching ratio between the maximum and minimum gripping forces of 14:1 is shown for controlled attachment/detachment experiments, which allows for reliable pick-and-place operation. This work introduces an analytical capillary adhesion model and demonstrates control of the bubble size for pick-and-place gripping. A proof-of-concept demonstration of 3D manipulation in a fluidic environment shows the potential of capillary gripping for future use in confined environments such as inside microfluidic devices for transportation or assembly of hydrophobic objects.

This paper presents a novel synthesis method for the design of micro-scale robotic flexure mechanisms. A structural optimization method, termed the mechanism-based approach, is used to identify the optimal topology and shape of the flexure mechanisms based on their lump stiffness characteristics. Using several different fitness functions, several optimal flexure designs have been synthesized for use in millimeter-scale mobile grippers (μ-grippers). The stiffness characteristics of the optimal μ-grippers are shown to be better than the thin-beam designs developed using human intuition. Two large-scale prototypes are constructed and experiments are conducted to validate the stiffness analysis. The experimental results are within 20% of the analytical expectations. As a proof of concept, at-scale μ-grippers are constructed based on photolithography and replica molding methods, and demonstrated in simple actuation. The optimal μ-grippers can be applicable for cell manipulations in future works.

A major challenge for untethered micro-scale mobile robotics is the control of many agents in the same workspace for distributed operation. In this work, we present a new method to independently control multiple sub-mm microrobots in three dimensions (3D) using magnetic gradient based direct pulling as the 3D motion generation method. This is accomplished through the use of geometrically or magnetically distinct microrobots which assume different magnetization directions in a rotating magnetic field. Such diversity in design allows for different magnetic forces to be exerted on each, enabling path following with less than 370μm mean path deviation for a set of two microrobots of size 350μm and 1500μm. This addressability method could be used for the 3D control of a team of microrobots inside microfluidic channels or in the human body for localized therapy or diagnostics.

To address some of the challenges in modular micro-robotics, we present a new heat-activated bonding method for assembly. This bonding method quickly forms strong bonds through the use of thermoplastic or solder binding sites integrated into each module face, addressing problems of assembly strength and electrical conductivity. The strength of the bonds for each method are compared for different module styles, bonding conditions and breaking conditions in a destructive test. For 800μm modules, bond strengths of up to 500mN are observed with thermoplastic bonds, which indicates that the assemblies could be potentially used in high-force structural applications of programmable matter, microfluidic channels or healthcare. By magnetically functionalizing the modules using embedded magnetic particles, the modules are moved remotely for assembly using a magnetic coil system. In this way, a set of six modules are remotely assembled one-by-one into an arbitrary shape capable of locomotion to demonstrate the scalability and strength of the system.

We present a new scheme of remote addressable magnetic actuation for sub-mm microrobotics which uses the hysteresis characteristics of multiple magnetic materials to achieve advanced state control of many magnetic actuators sharing the same magnetic control inputs. Using this standard approach, remote magnetic actuation of a single magnet has been achieved for untethered motion control with a single magnetic control input. We propose the simultaneous use of multiple magnetic materials with varying hysteresis characteristics to effectively gain multiple control inputs as different applied magnetic field strengths. As a first experimental implementation of this idea, we present a set of three heterogeneous magnetic modules floating on a liquid surface which can be remotely reconfigured by application of a field of varying magnitude. As a second implementation, we present a team of up to six independently actuated walking microrobots made from a composite material whose net magnetic moment can be selectively turned on or off by application of a large magnetic field pulse. We also demonstrate a team of two addressable microrobots performing a task requiring cooperative teamwork. The presented concept providing multiple magnetic control inputs could be applicable in various areas of milli- or microrobotics to address multiple magnetic elements for motion or actuation control.

In this paper, we propose methods to control multiple untethered magnetic microrobots (called Mag-μBots), with all dimensions under 1 mm, without the need for a specialized surface. We investigate sets of Mag-μBots that are geometrically designed to respond uniquely to the same applied magnetic fields. By controlling the magnetic field waveforms, individual and subgroups of Mag-μBots are able to locomote in a parallel but dissimilar fashion. The control of geometrically dissimilar Mag-μBots and a group of identically fabricated Mag-μBots are investigated, and control strategies are developed for 1-D and 2-D motion. This is accomplished by learning the velocity response of each microrobot to various control signals and using the uniqueness of each microrobot response to achieve independent control. The effect of high-level control parameters are investigated in simulation and in experiments, and the simultaneous independent global positioning of two and three microrobots is demonstrated in 2-D space. As this control method is accomplished without the use of a specialized surface, it has potential applications in areas such as microfluidic systems and biomanipulation.

This study develops autonomous manipulation strategies for a mobile untethered microrobot that operates on a 2-D surface in a fluidic environment. The microrobot, which is a permanent magnet, is under m in all dimensions and is actuated by oscillating external magnetic fields. Two types of manipulations are considered: 1) front pushing, where the microrobot pushes a micro-object by direct contact; and 2) side pushing, which can result in noncontact pushing, where the fluid flow fields that are generated by a translating microrobot are used to displace a micro-object. Physical models are provided to estimate the displacement of the micro-object due to the fluid motion. Model-based controllers to perform contact and noncontact manipulation are proposed, which iteratively correct emerging manipulation behaviors to improve performance. It is found that using a model-based solution as a feed-forward input, which is combined with a learning controller, can significantly improve micro-object pushing performance. Finally, we begin to address the problem to assemble two micro-objects together using the microrobot, which is only successful by using a side-pushing method.

In this work, we develop methods for controlling multiple untethered magnetic micro-robots (called Mag-μBots), with all dimensions under 1 mm, without the need for a specialized surface. We investigate sets of Mag-μBots that are geometrically and magnetically designed to respond uniquely to the same magnetic fields. The responses of geometrically dissimilar Mag-μBots with similar magnetization and a group of identically-fabricated Mag-μBots are investigated. By controlling the magnetic field waveforms, individual and subgroups of Mag-μBots are able to locomote in a parallel but dissimilar fashion. Specifically, the pulsing frequency of the imposed driving magnetic fields is used as a selection method among the Mag-μBots. This method for accomplishing motion discrimination is discussed, modeled, and tested. Independent global positioning of two and three robots is demonstrated in two-dimensional space. While individual Mag-μBot velocities can be as high as 7 mm/s, the effective velocities during multi robot control are found to be up to 2 mm/s. As this control method is accomplished without the use of a specialized surface, it has potential applications in areas such as micro-fluidic systems and bio-manipulation.

A primary challenge in the field of reconfigurable robotics is scaling down the size of individual robotic modules. We present a novel set of permanent magnet modules that are under 1 mm in all dimensions, called Mag-μMods, for use in a reconfigurable micro-system. The modules are actuated by oscillating external magnetic fields of several mT in strength, and are capable of locomoting on a 2-D surface. Multiple modules are controlled using an electrostatic anchoring surface, which selectively prevents specific modules from being driven by the external field, while allowing others to move freely. We model the processes of both assembling and disassembling two modules by analyzing the forces the modules experience, and experimentally verify the accuracy of the models. For disassembly, we employ electrostatic anchoring and externally applied magnetic torques to successfully separate the modules.

This work introduces new strategies for fluid-based manipulation of micro-scale objects using rotating magnetic micro-robots at low Reynolds numbers. By rapidly spinning the micro-robots, rotational fluid flow is induced which acts to move the micro-objects by fluidic drag. Acting in parallel, teams of these micro-robots are shown to work together to rapidly move micro-objects along planned “virtual channel”s to goal positions. As the micro-robots are themselves highly mobile, the manipulation trajectories are controlled to achieve accurate, fast manipulation of multiple micro-objects in 2-D environments. Experiments are performed in a viscous oil (50 cSt) to simulate the physics of micro-robots which are small enough to fit through small micro-fluidic channels or blood capillaries. The micro-robot and micro-object motions are characterized to support the proposed strategies. Spherical micro-robots 380µm in diameter are used to manipulate 200µm diameter particles with controllable speeds of up to 3.5 mm/s.

We propose a method to increase propulsion of a micro-scale swimming robot powered by an artificial flagellum through the use of multiple helices while retaining the simple actuation method of a single rotation axis. Scaled up experiments with similar Reynolds number are carried out to compare the performance of five different propulsion designs with pairs of stiff or flexible flagella. The designs feature stiff helices, straight flexible rods, and flexible helices inspired by bacterial flagella. Results indicate that for a given rotation frequency, thrust is proportional to the number of helices, but that the torque required to drive a flagellum offset from the common rotation axis is increased. Furthermore, shape deformation of flexible helices due to bending forces can positively affect thrust under certain conditions. Therefore, given the ease of fabrication, the use of multiple offset flexible flagella is a potential method to achieve increased thrust force in artificial bacteria flagella.

This paper is an update on the investigation of Distributed Inward Gripping (DIG) as a rapid and robust attachment mechanism for vertical and inverted climbing. DIG is implemented on an 18-DOF hexapod, DIGbot, with onboard power and control system. Passive compliance in the foot, which is inspired by the flexible tarsus of the cockroach, increases the robustness of the adhesion strategy and enables DIGbot to execute large steps and stationary turns while walking vertically on mesh screen. Results of vertical climbing are shown.

A hexapod designed for wall climbing with a body joint and six 3-DOF legs can perform complex maneuvers such as sharp turns, making both interior and exterior transitions between vertical and horizontal surfaces, and traversing obstacles on both surfaces. This paper presents work toward the design and construction of the hexapod DIGbot, named for its utilization of distributed inward gripping (DIG) to generate adhesive forces. The biologically-inspired DIG approach allows robots to climb on surfaces of any orientation with respect gravity, including ceilings, or in zero gravity environments.

Insights from biology have helped reduce the weight and increase the climbing ability of mobile robots. This paper presents Screenbot, see Fig. 1, a new 126 gram biologically-inspired robot that scales wire mesh substrates using spines. Like insects, it walks with an alternating tripod gait and maintains tension in opposing legs to keep the feet attached to the substrate. A single motor drives all six legs. Mechanisms were designed and tested to move the spines into and out of contact with the screen. After the spine engages the substrate, springs along the leg are compressed. The opposing lateral spring forces constitute a distributed inward grip that is similar to forces measured on climbing insects and geckos. The distributed inward gripping (DIG) holds the robot on the screen, allowing it to climb vertically, walk inverted on a screen ceiling and cling passively in these orientations.