Wireless robots at the subcentimeter size are often actuated using externally generated magnetic fields. For most applications, these remote magnetic microrobots are located relatively far from the magnetic field generation sources. In this condition, all microrobots receive approximately the same driving magnetic field (which we term a homogeneous field). While some solutions have been presented to allow for the creation of simple onboard tools, the full potential of the homogeneous magnetic field for multi-degrees-of-freedom (DOF) actuation has not been exploited. Here we introduce a design framework to utilize the maximum number of independently controlled DOFs on a microrobot system. We make use of three classes of mechanisms which are commonly used in practice and allow for more complex microrobots with up to eight DOFs. To verify the functionality of our framework, we used it to design an optimized drug delivery robot equipped with a 3-DOF drug-releasing mechanism and a 4-DOF motion mechanism. Experiments are performed to actuate each one of the robot's seven DOFs individually, where the cross-talk error between these seven DOFs averaged 7% with a max error of 18.3%.

Magnetically-driven micrometer to millimeter-scale robotic devices have recently shown great capabilities for remote applications in medical procedures, in microfluidic tools and in microfactories. Significant effort recently has been on the creation of mobile or stationary devices with multiple independently-controllable degrees of freedom (DOF) for multiagent or complex mechanism motions. In most applications of magnetic microrobots, however, the relatively large distance from the field generation source and the microscale devices results in controlling magnetic field signals which are applied homogeneously over all agents. While some progress has been made in this area allowing up to six independent DOF to be individually commanded, there has been no rigorous effort in determining the maximum achievable number of DOF for systems with homogeneous magnetic field input. In this work, we show that this maximum is eight and we introduce the theoretical basis for this conclusion, relying on the number of independent usable components in a magnetic field at a point. In order to verify the claim experimentally, we develop a simple demonstration mechanism with 8 DOF designed specifically to show independent actuation. Using this mechanism with 500 μm magnetic elements, we demonstrate eight independent motions of 0.6 mm with 8.6 % coupling using an eight coil system. These results will enable the creation of richer outputs in future microrobotic devices.

This paper presents a mixed teleoperation/autonomous control approach for navigation and obstacle avoidance in mobile robots. The proposed method builds on an earlier general control framework that systematically combines teleoperation and autonomous control subtasks. This paper considers a scenario in which the user teleoperates a mobile robot while being assisted by an autonomous subtask designed to help avoid collisions with obstacles in the robot task environment. The autonomous subtask control commands are generated by formulating and solving a constrained optimization problem over a rolling horizon window of time into the future. The effectiveness of the proposed model-predictive control obstacle avoidance scheme is demonstrated in teleoperation experiments with a mobile robot using sonar measurements for obstacle localization.