In our previous work we introduced the inverted MiniMag, a magnetic manipulation system capable of 5 degree-of-freedom (5-DOF) wireless control of micro- and nano structures. In this work, we implement a depth tracking algorithm to provide feedback on the z-position of manipulated particles in the absence of a side camera. We demonstrate 3D closed-loop servoing of magnetic microbeads along predefined trajectories. We successfully position magnetic microbeads functionalized with antibodies in close proximity to macrophages with sub-cellular resolution and record the phagocytosis of the beads. We also show that the system can be used for 3D targeted microtissue manipulation inside microfabricated devices.

This paper presents a manipulation system capable of five degree of freedom (5-DOF) control of a magnetic nanoagent (3-DOF position, 2-DOF orientation) implemented on an inverted microscope. Magnetic fields up to 50 mT and gradients up to 5 T/m at frequencies up to 6 kHz can be achieved. The independent generation of field and gradient vectors enables holonomic 5-DOF wireless magnetic manipulation at the nanoscale. Multiple types of motion were investigated for nickel nanowires of different lengths and analyzed using resistive force theory.

Dexterous manipulation of intraocular microrobotic devices has the potential to significantly augment ophthalmic surgeons' capabilities. Microrobots can be employed for targeted drug delivery and for procedures such as retinal-vein cannulation that require a high degree of dexterity. For precise externally generated magnetic control of microdevices, their position in the magnetic field is needed. Since the interior of the human eye is externally observable, computer-vision techniques can be used for localization. In this paper, the complex optics of the human eye are taken into account, and an algorithm that localizes microrobotic devices based on their 3-D structure is proposed. The sensitivity of the algorithm with respect to uncertainties in optical parameters is evaluated. A human-like model eye is designed and fabricated for experiments, precision analysis is performed, and the algorithm is used for visual servoing.

The automated or semiautomated control of microrobots for targeted drug delivery, retinal surgeries, and other ophthalmic procedures has the potential to significantly augment the capabilities of human surgeons. For accurate magnetic control, the position of the microrobots is required. In this paper, we extract the intraocular projection mapping and use it in the established CAD-model-based pose-estimation framework. Our algorithm requires no focus information. This is the first work that treats a complicated refractive imaging system, such as the eye, in a model-based localization framework. We design a model-eye chamber with human-like optical elements in which we control a microrobot and estimate its position using monocular vision.

Central to the challenge of building sub-mm robots, or microrobots, is the development of effective power storage and locomotion mechanisms. In 2007 we introduced the Wireless Resonant Magnetic Micro-actuator (WRMMA) and its application in a successful microrobotic platform, the MagMite. The term MagMite is derived from Magnetic Mite-a tribute to the underlying magnetic propulsion principle and the microscale dimensions of the robot. The device harvests magnetic energy from the environment and effectively transforms it into impact-driven mechanical force while being fully controllable. It can be powered and controlled with oscillating fields in the kHz range and strengths as low as 2 mT, which is only roughly 50 times the average earth magnetic field. These microrobotic agents with dimensions less than 300 μm × 300 μm × 70 μm are capable of moving forward, backward and turning in place while reaching speeds in excess of 12.5 mm/s or 42 times the robot's body length per second. The robots produce enough force to push micro-objects of similar sizes and can be visually servoed through a maze in a fully automated fashion. The devices exhibit an overall degree of flexibility, controllability and performance unmatched by other microrobots reported in the literature. The robustness of the MagMites leads to high experimental repeatability, which in turn enabled them to successfully compete in the RoboCup 2007 and 2009 Nanogram competitions. In this video contribution we offer an integrated explanation of the non-intuitive MagMite actuation principle. This is achieved with the help of computer animation in direct comparison with real experimental footage. Furthermore, new recordings of the microrobots operating under dry and wet conditions while performing automated microhandling tasks are presented.

We demonstrate five-degree-of-freedom (5-DOF) wireless magnetic control of a fully untethered microrobot with a magnetic steering system we call OctoMag. Although only occupying a single hemisphere, this system is capable of isotropically applying forces on the order of 1-40 μN with unrestricted control of the 2 orienting DOF. These capabilities are enabled through the use of soft-magnetic-cores which provide an increase of approximately 20× that of air cores in magnetic-field strength, but comes at the cost of more complicated interactions between coils. We propose a modeling mechanism that assumes the field contributions of the individual currents superimpose linearly when using cores with large linear regions and negligible hysteresis. When designing the system, the locations and quantity of electromagnets were optimized with regards to the force generation in the worst-case direction predicted by the model. The resultant system is capable of both open and closed-loop operation over a workspace of 4 cm3. OctoMag was primarily designed for the control of intraocular microrobots for delicate retinal procedures, but also has potential uses in other medical applications or micromanipulation under an optical microscope.

We demonstrate five-degree-of-freedom (5-DOF) wireless magnetic control of a fully untethered microrobot (3-DOF position, 2-DOF pointing orientation). The microrobot can move through a large workspace, and is completely unrestrained in the rotation degrees of freedom. We accomplish this level of wireless control with an electromagnetic system that we call OctoMag. OctoMag's unique abilities are due to its utilization of complex nonuniform magnetic fields, which capitalizes on a linear representation of the coupled field contributions of multiple soft-magnetic-core electromagnets acting in concert. OctoMag was primarily designed for the control of intraocular microrobots for delicate retinal procedures, but it also has potential uses in other medical applications or micromanipulation under an optical microscope.

The artificial bacterial flagellum (ABF), a helical swimming microrobot, has the potential to be used for biomedical applications such as cellular and intracellular manipulation. The velocity and the propulsive force of the ABF can be controlled by the input frequency of the rotating magnetic field. In this paper the swimming behavior of the ABF near a solid surface is reported. Three regions have been observed for the frequency-dependent swimming behavior of the ABF, i.e. the step-out, the linear and the drift-dominated region. At low frequencies it has been found that the desired screw-type motion is replaced by a wobbling swimming movement with a frequency-dependent precession angle. Moreover, the experimental results show that the wobbling motion of the ABF enhances the undesired sidewise drift due to wall effects. Additionally, the cause of the precession motion has been investigated by a hydrodynamic model. Our results imply that the linear range of the input magnetic frequency and the output ABF velocity is not only limited by the applicable torque at high frequencies but also by the wobbling of helical swimming at low frequencies.

We demonstrate five-degree-of-freedom (5-DOF) wireless magnetic control of a fully untethered microrobot (3-DOF position and 2-DOF pointing orientation). The microrobot can move through a large workspace and is completely unrestrained in the rotation DOF. We accomplish this level of wireless control with an electromagnetic system that we call OctoMag. OctoMag's unique abilities are due to its utilization of complex nonuniform magnetic fields, which capitalizes on a linear representation of the coupled field contributions of multiple soft-magnetic-core electromagnets acting in concert. OctoMag was primarily designed to control intraocular microrobots for delicate retinal procedures, but it also has potential uses in other medical applications or micromanipulation under an optical microscope.

Wireless resonant magnetic micro-actuators have been previously described as highly effective propulsion mechanisms for untethered mobile microrobots. The discussion thus far has been primarily relegated to a characterization of stationary devices and the de facto observation of their mobility. Before applications of microrobots can be more fully explored, devices are required that can operate reliably and repeatably in a host of operating environments. In this paper, we analyze the in situ performance of resonant magnetic actuators for microrobotic locomotion to better understand their durability, substrate requirements, and driving characteristics.

Artificial bacterial flagella (ABF) are swimming microrobots that mimic the swimming motion of bacteria. The helical swimmer consists of an InGaAs/GaAs/Cr helical nanobelt tail fabricated by a self-scrolling technique with dimensions similar to a natural flagellum, and a thin soft-magnetic metal ¿head¿ consisting of a Cr/Ni/Au multi-layer. The swimming locomotion of ABF is precisely controlled in 3-D by external rotating magnetic fields. Microsphere manipulation is performed by ABF, and experimental results show that both the position and the orientation of microspheres can be precisely controlled. The propelling force of ABF is in the pico-Newton range. We also describe a swarm-like behavior in which three ABF swim in a pack, indicating the potential to handle several micro objects in parallel. Self-propelled devices such as these are candidates for wireless 6-DOF micro and nanomanipulation tools for handling cellular and sub-cellular objects.

Primary challenges in the building of untethered sub-millimeter sized robots include power supply, propulsion methods, and control. We present a novel type of microrobot termed Magmite that utilizes a new class of wireless magnetic actuator which accomplishes all three tasks. The device harvests magnetic energy from the environment and effectively transforms it into mechanical propulsion while being fully controllable. This microrobotic agent with dimensions less than 300 mum times 300 mum times 70 mum is capable of maneuvering with 3 degrees of freedom. A specially prepared substrate allows for adjustable speeds exceeding 12.5 mm/s or 42 times the robot's body length per second (see accompanying video). It is powered by oscillating fields in the kHz range and strengths as low as 2 mT - roughly 50 times the average Earth magnetic field.

Few rotational actuators currently exist with the ability to transmit motion at different speeds, torques, and directions at the nanometer scale. We present work regarding the application of helical nanobelts as linear-to-rotary and rotary-to-linear motion converters. We discuss their ability to rectify device rotation to linear motion for untethered microrobotic applications as well as their application as rotary sample stages for nanoscale imaging.

When designing a mobile robotic team, an engineer is faced with many design choices. This paper discusses the design of a team consisting of two different models of robots with significantly different sensing and control capabilities intended to accomplish a similar task. Two new robotic platforms, the COTS Scout and the MegaScout are described along with their respective design considerations.

When a distributed robotic system is assigned to perform reconnaissance or surveillance, restrictions inherent to the design of an individual robot limit the system's performance in certain environments. Finding an ideal portable robotic platform capable of deploying and returning information in spatially restrictive areas is not a simple task. The Scout robot, developed at the University of Minnesota, is a viable robotic platform for these types of missions. The small form factor of the Scout allows for deployment, placement, and concealment of a team of robots equipped with a variety of sensory packages. However, the design of the Scout requires a compromise in power, sensor types, locomotion, and size; together these factors prevent an individual Scout from operating ideally in some environments. Several attempts to address these deficiencies have been implemented and are discussed. Among the prototype solutions are actuating wheels, allowing the Scout to increase ground clearance in varying terrains, a grappling hook enabling the Scout to obtain a position of elevated observation, and infrared emitters to facilitate low light operation.

Small scale distributed robotic systems are ideal for tasks that larger, more expensive robots may not be able to undertake such as surveillance or inspection in enclosed areas. Small scale robots also have the advantage of being easily portable to an area of interest. However, the advantages related to the small size and portability cause an increase in the complexity of development. In addition, the more pronounced effects of interacting with the environment in terms of mobility and communications lead to robotic systems of limited functionality. In order to address such deficiencies, several novel developments and improvements have been made to the Scout robot, which will be discussed. These improvements include the development of a communication relay system facilitating longer distance operation, an improved actuating wheel system increasing the Scout's mobility and a grappling hook system to elevate the Scout. By enhancing the Scout robotic team in this way, the functional use of the team is expanded, allowing more practical use.