Adaptive Force Tracking Control of a Magnetically Navigated Microrobot in Uncertain Environment

Magnetic navigation microrobotics is a promising technology in micromanipulation and medical applications. A magnetically navigated microrobot (MNM) usually has permanent magnets or ferromagnetic materials attached to it to create interaction force for navigation in the presence of an external magnetic field. During the exploration of the MNM, it is necessary to simultaneously control the position of the MNM and the contact force when the microrobot is constrained by its environment. However, owing to the small size of an MNM and noncontact property of magnetic levitation, installing on-board force sensors is very challenging. This paper presents a dual-axial interaction force determination mechanism that uses magnetic flux measurement, with no need for a conventional on-board force sensor. The interaction force is then used as the feedback force of a position-based impedance controller to actively track the reference force on the MNM in uncertain environment. To reduce the force tracking error caused by environmental uncertainty, an adaptive control algorithm is implemented to generate a reference motion trajectory that attempts to minimize the force error to an acceptable level. The force tracking performance of the robot is experimentally validated. A 2.01 μN root mean square force tracking error is reported. The proposed technique can be applied to biomedical microsurgery, such as for cutting tissue with controlled force.