Chytra Pawashe

Modeling and Experimental Characterization of an Untethered Magnetic Micro-Robot

Here we present the control, performance and modeling of an untethered electromagnetically actuated magnetic micro-robot. The microrobot, which is composed of neodymium—iron—boron with dimensions 250 μm 1 130 μm 1 10 μm , is actuated by a system of six macro-scale electromagnets. Periodically varying magnetic fields are used to impose magnetic torques, which induce stick—slip motion in the micro-robot. These magnetic forces and torques are incorporated into a comprehensive dynamic model, which captures the behavior of the micro-robot. By pivoting the micro-robot about an edge, non-planar obstacles with characteristic sizes comparable to the robot length can be surmounted. Actuation is demonstrated on several substrates with different surface properties, in a fluid environment, and in a vacuum. Observed micro-robot translation speeds can exceed 10 mm s-1 .

Two-Dimensional Contact and Noncontact Micromanipulation in Liquid Using an Untethered Mobile Magnetic Microrobot

This paper presents the manipulation of microspheres under water by use of an untethered electromagnetically actuated magnetic microrobot (Mag-muBot), with dimensions 250 times 130 times 100 mum³. Manipulation is achieved by two means: contact and noncontact pushing modes. In contact manipulation, the Mag-muBot is used to physically push the microspheres. In noncontact manipulation, the fluid flow generated by the translation of the Mag-muBot is used to push the microspheres. Modeling of the system is performed, taking into account micrometer-scale surface forces and fluid drag effects to determine the motion of a sphere within a robot-generated fluid flow. Fluid drag models for free-stream flow and formulations for near-wall flow are both analyzed and compared with the experiments, in which pushing of two sphere sizes, i.e., 50 and 230 mum diameters, is characterized in a controlled, robot-generated flow. Dynamic simulations are provided using the developed physical models to capture this behavior. We find that the near-wall physical models are, in general, in agreement with the experiment, and free-stream models overestimate microsphere motion.

Multiple magnetic microrobot control using electrostatic anchoring

Addressing power and control to individual untethered microrobots is a challenge for small-scale robotics. We present a 250×130×100 μm3 magnetic robot wirelessly driven by pulsed external magnetic fields. An induced stick-slip motion results in translation speeds over 8 mm/s. Control of multiple robots is achieved by an array of addressable electrostatic anchoring pads on the surface, which selectively fixes microrobots, preventing translation. We demonstrate control of two microrobots in both uncoupled individual motion and coupled symmetric motion. An estimated anchoring force of 23.0 μN is necessary to effectively fix each microrobot.

Control of Multiple Heterogeneous Magnetic Microrobots in Two Dimensions on Nonspecialized Surfaces

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.

Two-Dimensional Autonomous Microparticle Manipulation Strategies for Magnetic Microrobots in Fluidic Environments

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.

Assembly and disassembly of magnetic mobile micro-robots towards deterministic 2-D reconfigurable micro-systems

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 by using an electrostatic anchoring surface, which can selectively prevent specific modules from being driven by the external field while allowing others to move freely. We address the challenges of both assembling and disassembling two modules. Assembly is performed by bringing two modules sufficiently close that their magnetic attraction causes them to combine. Disassembly is performed by electrostatically anchoring one module to the surface, and applying magnetic torques from external sources to separate the unanchored module.

An untethered magnetically actuated micro-robot capable of motion on arbitrary surfaces

This work presents an untethered magnetic micro- robot with dimensions of 250 mum x 130 mum x 100 mum. The robot is composed entirely of neodymium-iron-boron fabricated using laser micro-machining. It is actuated by a system of five macro-scale electromagnets. By using electromagnets to control the robot, the surface on which the robot operates need not be specialized, smooth, patterned, nor conductive. Two control methods, both based on periodic excitation of the robot, are attempted and compared. Controllable motion at speeds in excess of 2.8 mm/s, approximately 11 body lengths per second, is demonstrated. Teleoperated motion in two dimensions is shown, and the assembly of micro-particles is demonstrated underwater. Potential future applications include micro-scale manipulation, fabrication, and assembly of micro-systems.

Control methodologies for a heterogeneous group of untethered magnetic micro-robots

In this work, we develop methods for controlling multiple untethered magnetic micro-robots (Mag-µBots) without the need for a specialized substrate. We investigate Mag-µBots that are geometrically and magnetically designed to respond uniquely to the same input magnetic fields. Designs include: (1) geometrically similar Mag-µBots with different values of magnetization; (2) geometrically dissimilar Mag-µBots with similar magnetization; and (3) geometrically dissimilar Mag-µBots with dissimilar magnetization. The responses of both magnetically hard and soft Mag-µBots are investigated. By controlling the input magnetic fields, individual and sub-groups of Mag-µBots are able to locomote in a parallel fashion. Specifically, the magnitude and frequency of the imposed driving magnetic fields are used as selection methods among the Mag-µBots. Various methods for accomplishing motion discrimination are discussed, modeled, and tested. It is found that while fully decoupled control is not possible with this method, parallel actuation of sub-groups of Mag-µBots is possible and controllable.

Atomic force microscope based two-dimensional assembly of micro/nanoparticles

This research aims at achieving two-dimensional micro/nanomanipulation and assembly of micro/nanoscale particles using atomic force microscope (AFM). Unlike prior works, the presented manipulation models include friction models based on both the normal forces as well as the adhesion forces. Pull-off forces are modeled using the Johnson-Kendall-Roberts (JKR) contact mechanics model. This model is used to determine whether critical conditions for particle motion are achieved. Pushing manipulation experiments are performed on polystyrene microparticles. A top-view high resolution optical microscope, used for probe and particle position and motion detection, facilitated real-time visual feedback. A piezoelectric XYZ positioning stage with few nanometers precision enabled the two-dimensional precise assembly of the polystyrene microparticles. Using the real-time visual feedback, the behavior of particles manipulated by an AFM probe, is investigated. The results from the experiments matched those from the simulation, successfully verifying the developed models. The modeling, simulation and the experiments have enhanced the understanding of the interaction forces at the micro/nanoscale during micro/nanoassembly and particle manipulation

Two-dimensional vision-based autonomous microparticle manipulation using a nanoprobe

Autonomous micromanipulation has been an emerging interest in constructing and assembling micro-objects. Manual assembly and manipulation of small-scale objects through teleoperation is possible; however, autonomy is necessary for large-volume manipulation and manufacturing. In this study, we discuss a two-dimensional autonomous manipulation system, which is based on an optical microscope and a nanoprobe. We demonstrate the manipulation of polystyrene and silica microspheres, which are detected through image processing using the generalized Hough transform. Using an atomic force microscope nanoprobe as an end-effector, microspheres are autonomously pushed to a user-defined configuration. Furthermore, we demonstrate motion planning in micromanipulation by using the Wavefront expansion algorithm, which is necessary in manipulating microspheres without colliding into obstacles. In experiments, we successfully demonstrate the automatic arrangement of 4.5 μm polystyrene and 5 μm silica microspheres into user-defined patterns with an average precision of around 0.5 μm, which is limited by the microscope imaging resolution. This autonomous microparticle arrangement system could be applied to fabricate mold templates for micro/nanoprinting and prototyping micro/nanodevices.