Abstract—This work demonstrates a novel approach to steering a magnetic swimming robot in two dimensions with a single pair of Maxwell coils. By leveraging the curvature of the magnetic field gradient, we achieve motion along two axes. This method allows us to control medical magnetic robots using only existing MRI technology, without requiring additional hard- ware or posing any additional risk to the patient. We implement a switching time optimization algorithm which generates a schedule of control inputs that direct the swimming robot to a goal location in the workspace. By alternating the direction of the magnetic field gradient produced by the single pair of coils per this schedule, we are able to move the swimmer to desired points in two dimensions. Finally, we demonstrate the feasibility of our approach with an experimental implementation on the millimeter scale and discuss future opportunities to expand this work to the microscale, as well as other control problems and real-world applications.
more »
« less
Steering Magnetic Robots in Two Axes with One Pair of Maxwell Coils
Abstract—This work demonstrates a novel approach to steering a magnetic swimming robot in two dimensions with a single pair of Maxwell coils. By leveraging the curvature of the magnetic field gradient, we achieve motion along two axes. This method allows us to control medical magnetic robots using only existing MRI technology, without requiring additional hard- ware or posing any additional risk to the patient. We implement a switching time optimization algorithm which generates a schedule of control inputs that direct the swimming robot to a goal location in the workspace. By alternating the direction of the magnetic field gradient produced by the single pair of coils per this schedule, we are able to move the swimmer to desired points in two dimensions. Finally, we demonstrate the feasibility of our approach with an experimental implementation on the millimeter scale and discuss future opportunities to expand this work to the microscale, as well as other control problems and real-world applications.
more »
« less
- Award ID(s):
- 1739308
- NSF-PAR ID:
- 10191221
- Date Published:
- Journal Name:
- IROS
- ISSN:
- 0166-5464
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
null (Ed.)Combining functional magnetic resonance imaging (fMRI) with models of neuromotor adaptation is useful for identifying the function of different neuromotor control centers in the brain. Current models of neuromotor adaptation to force perturbations have been studied primarily in whole-arm reaching tasks that are ill-suited for MRI. We have previously developed the MR-SoftWrist, an fMRI-compatible wrist robot, to study motor control during wrist adaptation. Because the wrist joint has intrinsic dynamics dominated by stiffness, it is unclear if these models will apply to the wrist. Here, we characterize adaptation of the wrist to lateral forces to determine if established adaptation models are valid for wrist pointing. We recruited thirteen subjects to perform our task using the MR-SoftWrist. Our task included a clockwise (CW) - counterclockwise (CCW) - error clamp schedule and an alternating CW-CCW force field schedule. To determine applicability of previous models, we fit three candidate models - a single-state, two-state, and context dependent multi-state model - to behavioral data. Our results indicate that features of sensorimotor adaptation reported in the literature are present in the wrist, including spontaneous recovery, and anterograde and retrograde interference between the learning of two oppositely directed force fields. A two-state model best fit our behavioral data. Under this model, adaptation was dominated by a fast learning state with minor engagement of a slow learning state. Finally, all adaptation models tested showed a consistent over-estimation of performance error, suggesting that the control of the wrist relies not only on internal models but likely other mechanisms, like impedance control, to reject perturbations.more » « less
-
We propose a new method to compute magnetic surfaces that are parametrized in Boozer coordinates for vacuum magnetic fields. We also propose a measure for quasisymmetry on the computed surfaces and use it to design coils that generate a magnetic field that is quasisymmetric on those surfaces. The rotational transform of the field and complexity measures for the coils are also controlled in the design problem. Using an adjoint approach, we are able to obtain analytic derivatives for this optimization problem, yielding an efficient gradient-based algorithm. Starting from an initial coil set that presents nested magnetic surfaces for a large fraction of the volume, our method converges rapidly to coil systems generating fields with excellent quasisymmetry and low particle losses. In particular for low complexity coils, we are able to significantly improve the performance compared with coils obtained from the standard two-stage approach, e.g. reduce losses of fusion-produced alpha particles born at half-radius from $17.7\,\%$ to $6.6\,\%$ . We also demonstrate 16-coil configurations with alpha loss ${<}1\,\%$ and neoclassical transport magnitude $\epsilon _{\text {eff}}^{3/2}$ less than approximately $5\times 10^{-9}$ .more » « less
-
Magnetically-actuated swimming microrobots are an emerging tool for navigating and manipulating materials in confined spaces. Recent work has demonstrated that it is possible to build such systems at the micro and nanoscales using polymer microspheres, magnetic particles and DNA nanotechnology. However, while these materials enable an unprecedented ability to build at small scales, such systems often demonstrate significant polydispersity resulting from both the material variations and the assembly process itself. This variability makes it difficult to predict, let alone optimize, the direction or magnitude of microswimmer velocity from design parameters such as link shape or aspect ratio. To isolate questions of a swimmer's design from variations in its physical dimensions, we present a novel experimental platform using two-photon polymerization to build a two-link, buoyant milliswimmer with a fully customizable shape and integrated flexible linker (the swimmer is underactuated, enabling asymmetric cyclic motion and net translation). Our approach enables us to control both swimming direction and repeatability of swimmer performance. These studies provide ground truth data revealing that neither the first order nor second order models currently capture the key features of milliswimmer performance. We therefore use our experimental platform to develop design guidelines for tuning the swimming speeds, and we identify the following three approaches for increasing speed: (1) tuning the actuation frequency for a fixed aspect ratio, (2) adjusting the aspect ratio given a desired range of operating frequencies, and (3) using the weaker value of linker stiffness from among the values that we tested, while still maintaining a robust connection between the links. We also find experimentally that spherical two-link swimmers with dissimilar link diameters achieve net velocities comparable to swimmers with cylindrical links, but that two-link spherical swimmers of equal diameter do not.more » « less
-
In this work we present the design of a swimming robot that is inspired by the body shape modulation of small microorganisms. Amoebas are small single celled organisms that locomote through deformation and shape change of their body. To achieve similar shape modulation for swimming propulsion in a robot we developed a novel flexible appendage using tape springs. A tape spring is an elongated strip of metal with a curved cross-section that can act as a stiff structure when loaded against the curvature, while it can easily buckle when loaded with the curvature. We develop a tape spring appendage that is capable of freely deforming its perimeter through two actuation inputs. In the first portion of this paper we develop the kinematics of the appendage mechanisms and compare with experiment. Next we present the design of a surface locomoting robot that uses two appendages for propulsion. From the appendage kinematics we derive the local connection vector field for locomotion kinematics and study the optimal gait for forward swimming. Lastly, we demonstrate robot swimming performance in open water conditions. The novel appendage design in this robot is advantageous because it enables omnidirectional movement, the appendages will not tangle in debris, and they are robust to collisions and contact with structures.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Conference Paper:
- The DOI is not currently available.
