TechTalks from event: Technical session talks from ICRA 2012

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Micro and Nano Robots II

  • Motion Control of Tetrahymena Pyriformis Cells with Artificial Magnetotaxis: Model Predictive Control (MPC) Approach Authors: Ou, Yan; Kim, Dal Hyung; Kim, Paul; Kim, MinJun; Julius, Agung
    The use of live microbial cells as microscale robots is an attractive premise, primarily because they are easy to produce and to fuel. In this paper, we study the motion control of magnetotactic Tetrahymena pyriformis cells. Magnetotactic T. pyriformis is produced by introducing artificial magnetic dipole into the cells. Subsequently, they can be steered by using an external magnetic field. We observe that the external magnetic field can only be used to affect the swimming direction of the cells, while the swimming velocity depends largely on the cells’ own propulsion. Feedback information for control is obtained from a computer vision system that tracks the cell. The contribution of this paper is twofold. First, we construct a discrete-time model for the cell dynamics that is based on first principle. Subsequently, we identify the model parameters using the Least Squares approach. Second, we formulate a model predictive approach for feedback control of magnetotactic T. pyriformis. Both the model fitness and the performance of the feedback controller are verified using experimental data.
  • Robust H-Infinity Control for Electromagnetic Steering of Microrobots Authors: Marino, Hamal; Bergeles, Christos; Nelson, Bradley J.
    Electromagnetic systems for in vivo microrobot steering have the potential to enable new types of localized and minimally invasive interventions. Accurate control of microrobots in natural fluids requires precise, high-bandwidth localization and accurate knowledge of the steering system’s parameters. However, current in vivo imaging methodologies, such as fluoroscopy, must be used at low update rates to minimize radiation exposure. Low frame rates introduce localization uncertainties. Additionally, the parameters of the electromagnetic steering system are estimated with inaccuracies. These uncertainties can be addressed with robust H-infinity control, which is investigated in this paper. The controller is based on a linear uncertain dynamical model of the steering system and microrobot. Simulations show that the proposed control scheme accounts for modeling uncertainties, and that the controller can be used for servoing in low viscosity fluids using low frame rates. Experiments in a prototype electromagnetic steering system support the simulations.
  • Magnetic Dragging of Vascular Obstructions by Means of Electrostatic and Antibody Binding Authors: Khorami Llewellyn, Maral; Dario, Paolo; Menciassi, Arianna; Sinibaldi, Edoardo
    Exploitation of miniature robots and microrobots for endovascular therapeutics is a promising approach; besides chemical strategies (typically systemic), topical mechanical approaches exist for obstruction removal, which however produce harmful debris for blood circulation. Magnetic particles (MPs) are also studied for blood clot targeting. We investigated magnetic dragging of clots/debris by means of both electrostatic and antibody binding. We successfully produced magnetotactic blood clots in vitro and experimentally showed that they can be effectively dragged within a fluidic channel. We also exploited a magnetic force model in order to quantitatively analyze the experimental results, up to obtaining an estimate of the relative efficiency between electrostatic and antibody binding. Our study takes a first step towards more realistic in vivo investigations, in view of integration into microrobotic approaches to vascular obstructions removal.
  • Coordination of Droplets on Light-Actuated Digital Microfluidic Systems Authors: Ma, Zhiqiang; Akella, Srinivas
    In this paper we explore the problem of coordinating multiple droplets in light-actuated digital microfluidic systems intended for use as lab-on-a-chip systems. In a light actuated digital microfluidic system, droplets of chemicals are actuated on a photosensitive chip by moving projected light patterns. Our goal is to perform automated manipulation of multiple droplets in parallel on a microfluidic platform. To achieve collision-free droplet coordination while optimizing completion times, we apply multiple robot coordination techniques. We present a mixed integer linear programming formulation for coordinating droplets given their paths. This approach permits arbitrary droplet formations, and coordination of both individual droplets and batches of droplets. We then present a linear time stepwise approach for batch coordination of droplet matrix layouts.
  • Mobility and Kinematic Analysis of a Novel Dexterous Micro Gripper Authors: Xiao, Shunli; Li, Yangmin
    The paper presents the design and analysis of a dexterous micro-gripper with two fingers and each finger has 2-DOF translational movement function. The two fingers can move independently in hundreds of microns' range, and can cooperate with each other to realize complex operation for micro objects. The mobility characteristics and the inverse parallel kinematic model of a single finger are analyzed by resorting to screw theory and compliance and stiffness matrix method, which are validated by finite-element analysis (FEA). Both FEA and the theoretical model have well validated the movement of the fingers moving in translational way, the designed micro gripper can realize a lot of complex functions. Properly selecting the amplification ratio and the stroke of the PZT, we can mount the gripper onto a positioning stage to realize a larger motion range, which will make it be widely used in micro parts assembly and bio-operation systems.