Modeling and Motion Control of a Magnetically Navigated Microrobotic System

Abstract

-This paper presents a technology for remotely navigating a magnetized microrobot in three-degree-of-freedom (3-DOF) using magnetic energy. The magnetic energy source is a magnetic drive unit that consists of six iron-core electromagnets, a soft-iron yoke, and a soft-iron pole-piece. The dynamic models of the magnetically navigated microrobot were derived from the magnetic field model in the workspace. An experimental method was applied to define the magnetic field model. Based on the derived dynamic models, a feed-forward plus standard PID controller was used to control the motion of the microrobot with 3-DOF. Experiment was conducted to validate the performance of the proposed controller. The experimental results showed 20µm motion accuracy in 3-DOF in a motion range of 10 × 10 × 30mm 3 .Keywords: Magnetic navigation, Microrobot, Magnetic field, PID plus feedforward controller IntroductionMicromanipulation involves performing tasks using macro scale end-effectors that have micro motion accuracy, and using micro scale end-effectors directly. For the first case, the end-effector of a micromanipulator has a mechanical arm connecting it to its base. This type of micromanipulator includes lead-screw driving stages and piezoelectric actuators [1,2,3]. However, the mechanical connection produces frictions, vibration, and backlash that degrade the performance of micromanipulation. For the second case, an end-effector is remotely manipulated without any mechanical connection to the base of a micromanipulator. This type of micromanipulator is capable of working in hazard and out-of-reach environments. Magnetic levitation micromanipulators, having remotely manipulated micro end-effector and micrometer motion accuracy, are most frequently studied and have promising potential in biomedical applications [4,5,6,7,8].Active magnetic navigation of a microrobot requires a controlled magnetic field source. Generally, electromagnets are used for multi-dimensional manipulation of a microrobot [9,10,11,12]. The magnetic field generated by electromagnets is controlled by a current. The multi-degree of motion freedom of a robot is achieved by setting up special configurations of multi-electromagnets. Since the strength of the magnetic field decays rapidly as the distance from electromagnet increases, an iron-core is commonly used to significantly enhance the magnetic field strength outside the electromagnet. This enhanced magnetic field can then expand the workspace of the microrobot.Modeling the magnetic field in the microrobots workspace is crucial to developing a magnetic navigation system. For systems that have air-core coils and permanent magnets produced magnetic field, analytical methods such as Bio-Savart Law and Amperes Law are applied to find a closed-form magnetic field model. However, for systems that have iron-core electromagnets produced magnetic field, the iron results in high nonlinearity in the whole system. Therefore, it is difficult to find a closed-form for modeling the magnetic field in the workspace. Al...