Actuation and Addressability for the Manipulation of Objects by Magnetic Microrobotic Capillary Grippers

Abstract

Untethered mobile microrobots, robotic systems where the untethered mobile component has a characteristic length under 1 mm and is dominated by microscale forces, are being pursued as valuable research tools for accessing small spaces towards applications in medicine, microfluidics, and micromanufacturing. Remote actuation by magnetic fields has become a popular method of actuating microrobots as magnetic fields are able to apply large forces and torques at long distances and safely through various materials, including human tissue. Previous workhas focused on actuating single and multiple magnetic microrobots in two-dimensional (2D) air and fluidic environments as well as in three-dimensional (3D) fluidic environments, using both swimming and gradient pulling methods. Previous work has shown the serial 2D manipulation of planar and spherical microscale objects.Few solutions to the manipulation of arbitrarily shaped components in 3D have been proposed, and current proposed methods have either limited the geometry or weight of the object. This thesis introduces a capillary gripping magnetic microrobot for the manipulation ofarbitrarily shaped objects with dimensions between 50 \x16m and 1 mm using external pressure as the attachment control method. Initial work showed imprecise transport of silicon cargo in a 3D liquid environment, and this thesis shows the position control of objects of various geometriesand surface energies. A precision 3D demonstration is provided as well as discussions on how to maximize the attachment forces while minimizing the required detachment force. Traditional magnetic microrobots actuated by gradient pulling have been able to actuate with five-degrees-of-freedom (DOF). Microrobots are able to translate in 3D and rotate about two rotation axes that align the microrobot’s magnetization axis with the magnetic field. However,there is no mechanism to rotate the microrobot about the magnetization axis. This constraint can hinder the placement of components or the alignment of complex parts. This thesis introduces a method to induce a rigid-body torque using auxiliary magnetic components and internal magnetization profiles. Initial work gives a proof of concept using multiple discrete magnets, but the fabrication technique is not scalable and the rotation about the magnetization axis is limited to an immediately observed axis. Magnetic shape anisotropy is utilized to generate single body submillimeter magnetic microrobots capable of 6-DOF actuation. Through knowledge of the magnetization profile, a method of controlling all 6-DOF simultaneously is presented, and a method to rotate the microrobot without knowledge of the 6th DOF orientation is discussed anddemonstrated. Many magnetic untethered mobile pick and place gripping tools are actuated by magnetic gradientpulling. When the size scale of the manipulator is between 1 and 100 microns, swimming becomes the preferable actuation methodology. However, addressability of swimming microrobots remains an unsolved challenge. This thesis examines and validates a recently proposed theory to couple multiple magnetic helices in the propulsion direction but decoupled in their ability to rotate, which generates the propulsion. Through this method, the speed-frequency response profiles can be precisely designed for new motion primitives, and is towards selectively drivenmagnetic microswimmers. This thesis provides a foundation for submillimeter untethered mobile pick-and-place manipulators with the ability to manipulate heterogeneous parts in all 6-DOF. Future work will extend these principles into automated microfactories, where complex autonomous gripping tasks will be controlled by intelligent computational systems. Capillary gripping microrobots may evenoperate in the human body to assemble implants or affix delayed-release drug capsules. A preliminary discussion of capillary gripping under medical imaging techniques is given as a first step towards revolutionary medical procedures. Microrobotic assembly of heterogeneous 3D complex structures on size scales ranging from a few microns to a few millimeters is thus poised to become a technology of interest in the coming decades.