Design of EM Substrate for Microrobots
Title: Design of Electromagnetic Substrate for Independent Planar Control of Untethered Magnetic Microrobots
Abstract:
Untethered actuated microrobots have become increasingly popular over the last couple of years because of their multitude of applications in medical, biology, and engineering environments. Yet, autonomous motion control of these micro machines is still an important conundrum for operations at the micro-scale. The present work aims to design and manufacture an electromagnetic actuation system to radically improve the independent control of microrobots in a 2D workspace. We focused on increasing the area of the workspace and to enable the generation of more dynamic magnetic and gradient fields. The hexagon design for the electromagnetic substrate allows the six directional mobility for the coil which enables the accurate and precise control of the localized magnetic field strength in a discretized workspace for desired navigation of the microrobots.
Technical Steps:
In determining the design for the electromagnetic setup, it was practical to choose a design that would maximize the amount of directional control over the microrobots in a 2D plane. Having more efficient and precise control of the microrobots is in a way related to the number of magnetic coils used, as each coil introduces a directional magnetic field gradient that drives the microrobots. As a result, an equilateral hexagonal ring structure was chosen such that six axial coils could be supported, each equidistant from the center. The hexagonal substrate shown in figure 1 was modeled on SOLIDWORKS and 3D printed on the Ender 3D printer using Polylactic Acid (PLA).
The dimensions of the electromagnet were determined such that it would fit on the stage of a Zeiss Axiovert 200 Inverted Microscope and an Axioplan 2 upright microscope. The electromagnetic stand is capable of splitting in half so that exchanging microscope slides and changing objectives is convenient. Furthermore, the electromagnet coils are positioned at an angle for two reasons. First, to direct each electromagnetic coil core directly at the center of the microscope slide. If, for example, the coils were positioned horizontally, the diameter of the coil would force the core axis to be too high above the microscope slide potentially resulting in a significant decrease of the magnetic field strength in the region of interest. Secondly, angling the electromagnets downwards provides extra space at the end of the electromagnets and hence increases the area of the workspace and makes a more convenient on the Axioplan 2 stage. The substrate is designed such that the electromagnets are press-fit into properly sized holes on the stand so that they can be exchanged and maintained when needed. The .stl file used for 3D printing of the substrate can be found in Appendix A and can potentially be replicated on any 3D printer.
The electromagnetic coils are wound on a 4-inch-long and 1 cm diameter ferrite rod, with plastic stoppers at two ends separated by 3.5-inches. The plastic stoppers were 4 cm in diameter and 2 mm in thickness. Then the 20-gauge magnetic wire is wrapped around the ferrite rod 51 times for the first pass and then repeated 14 times for a total of 714 turns.
The electrical system was designed using a National Instruments DAQ USB6351 as the microcontroller. The electrical system contains six RFP30N06LE N Channel MOSFETs to power the electromagnets from an external power supply since the DAQ controller itself does not output sufficient current to generate the required magnetic field through the coils. The gate of each mosfet is wired to a digital output on the DAQ USB6351 and controlled using a custom LabVIEW program. The drain of the mosfet is wired to one lead on the electromagnet and the other lead is connected to the positive terminal on the external power supply. The source on the mosfet, negative terminal of the power supply, and ground terminal on the DAQ USB6351 are all connected to the ground. The circuit design is done on a breadboard as shown in figure 2 in the attached project pdf.
Abstract:
Untethered actuated microrobots have become increasingly popular over the last couple of years because of their multitude of applications in medical, biology, and engineering environments. Yet, autonomous motion control of these micro machines is still an important conundrum for operations at the micro-scale. The present work aims to design and manufacture an electromagnetic actuation system to radically improve the independent control of microrobots in a 2D workspace. We focused on increasing the area of the workspace and to enable the generation of more dynamic magnetic and gradient fields. The hexagon design for the electromagnetic substrate allows the six directional mobility for the coil which enables the accurate and precise control of the localized magnetic field strength in a discretized workspace for desired navigation of the microrobots.
Technical Steps:
In determining the design for the electromagnetic setup, it was practical to choose a design that would maximize the amount of directional control over the microrobots in a 2D plane. Having more efficient and precise control of the microrobots is in a way related to the number of magnetic coils used, as each coil introduces a directional magnetic field gradient that drives the microrobots. As a result, an equilateral hexagonal ring structure was chosen such that six axial coils could be supported, each equidistant from the center. The hexagonal substrate shown in figure 1 was modeled on SOLIDWORKS and 3D printed on the Ender 3D printer using Polylactic Acid (PLA).
The dimensions of the electromagnet were determined such that it would fit on the stage of a Zeiss Axiovert 200 Inverted Microscope and an Axioplan 2 upright microscope. The electromagnetic stand is capable of splitting in half so that exchanging microscope slides and changing objectives is convenient. Furthermore, the electromagnet coils are positioned at an angle for two reasons. First, to direct each electromagnetic coil core directly at the center of the microscope slide. If, for example, the coils were positioned horizontally, the diameter of the coil would force the core axis to be too high above the microscope slide potentially resulting in a significant decrease of the magnetic field strength in the region of interest. Secondly, angling the electromagnets downwards provides extra space at the end of the electromagnets and hence increases the area of the workspace and makes a more convenient on the Axioplan 2 stage. The substrate is designed such that the electromagnets are press-fit into properly sized holes on the stand so that they can be exchanged and maintained when needed. The .stl file used for 3D printing of the substrate can be found in Appendix A and can potentially be replicated on any 3D printer.
The electromagnetic coils are wound on a 4-inch-long and 1 cm diameter ferrite rod, with plastic stoppers at two ends separated by 3.5-inches. The plastic stoppers were 4 cm in diameter and 2 mm in thickness. Then the 20-gauge magnetic wire is wrapped around the ferrite rod 51 times for the first pass and then repeated 14 times for a total of 714 turns.
The electrical system was designed using a National Instruments DAQ USB6351 as the microcontroller. The electrical system contains six RFP30N06LE N Channel MOSFETs to power the electromagnets from an external power supply since the DAQ controller itself does not output sufficient current to generate the required magnetic field through the coils. The gate of each mosfet is wired to a digital output on the DAQ USB6351 and controlled using a custom LabVIEW program. The drain of the mosfet is wired to one lead on the electromagnet and the other lead is connected to the positive terminal on the external power supply. The source on the mosfet, negative terminal of the power supply, and ground terminal on the DAQ USB6351 are all connected to the ground. The circuit design is done on a breadboard as shown in figure 2 in the attached project pdf.
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