THIS section is still being built!

Omnimagnets

The basis of this system is the idea of an omnimagnet. It is an electromagnet with orthogonal coils, one for each direction, and a spherical ferromagnetic core in the center. By controlling the current to each of the coils, we are able to generate a magnetic field in any direction. We can change the currents however we want to change the magnetic field, including making rotating magnetic fields. I've attached the paper that goes much more in detail on these.

Prior Papers

Omnimagnet: An Omnidirectional Electromagnet for Controlled Dipole-Field Generation

"An Omnimagnet is an omnidirectional electromagnet comprising a spherical ferromagnetic core inside of three orthogonal nested solenoids. It generates a magnetic dipole field with both a variable dipole-moment magnitude and orientation with no moving parts. The magnetic and physical properties (e.g., dipole moment, weight, resistance, and inductance) of any Omnimagnet are derived. These general relationships are used to design an optimal Omnimagnet subject to the constraints that it has the same dipole-moment per applied current in any direction, each solenoid has no quadrupole contribution to the magnetic field, and the spherical core size maximizes the strength of the resulting dipole field. This optimal design is analyzed using FEA tools and is verified to be dipole-like in nature. Finally, the optimal design is constructed and its utility is demonstrated by driving a helical capsule-endoscope mockup through a transparent lumen."

First Demonstration of a Modular and Reconfigurable Magnetic-Manipulation System

"Abstract - This is the first demonstration of a modular and reconfigurable magnetic-manipulation system with integral ferromagnetic material. This system—which includes multiple Omnimagnets, each comprising three orthogonal solenoids and a spherical ferromagnetic core—is capable of dexterous manipulation of a magnetic tool. The magnetization coupling of an arbitrary arrangement of spherical ferromagnetic cores is solved, enabling an analytical solution for the magnetic forces and torques. Thus, the system does not require extensive field maps or in situ field characterization. If the positions and orientations of the Omnimagnets are sensed, the Omnimagnets can be actively rearranged during manipulation while maintaining control of the tool. This could enable new capabilities in medical procedures because the manipulation system can be modified to accommodate the imaging systems and enable physician access without loss of control. The capabilities of this system are demonstrated through five-degree-of-freedom manipulation (position and heading) of a permanent-magnetic tool with several arbitrary Omnimagnet configurations."

Background

Standard magnetic manipulation systems utilizing multiple electromagnets with ferromagnetic cores cannot be mathematically solved for due to the coupling effects of the coils. This means that once the system has been set up it requires an extensive field map or in situ calibration. If it ever moves or changes it must be completely recalibrated.

Prior work has shown that by designing the omnimagnets in a specific way and actively sensing their position and orientation, we are able to actively rearrange the magnets while maintaining control of the tool.

The Goal

The goal of this project is to build a robust reconfigurable modular magnetic manipulation system that is able to retain dextrous control of a tool in the workspace while the magnets themselves are being actively recalibrated.

The Main System

In the lab we have built a system that can control up to 6 omnimagnets at a time. Each coil of each omnimagnet is controlled by an amplifier. With three coils per omnimagnet that means we have 18 amplifiers down below the table. Our system has 5 omnimagnets mounted on passive sensing arms. A 6th magnet can be placed bellow the workspace to be used to offset gravity. These arms can be moved manually however you'd like to position the magnets as desired and use potentiometers to report live omnimagnet orientation.

A stereo camera mounted above the system can be used for live tracking of the tool in the workspace.

Passive Arm Sensing

Each is equipped with four potentiometers to describe omnimagnet position and orientation. Each omnimagnet also has three thermocouples (one for each coil) to sense potential coil overheating. The below diagrams show how the arms are wired.

Sensing Overview

Individual Arm Wiring Diagram

Software

The main system runs off of C++ running of a Linux desktop. This code tracks the position and orientation of the tool and omnimagnets using camera tracking and sensing respectively. It also tracks the temperatures of each electromagnet coil. Using this information, the main code calculates the optimal current for each coil for a desired wrench.

Passive arm sensing as well as coil temperature sensing is all done by an auxiliary Arduino that communicates with the desktop via serial communication.

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