Closed-Loop Control of a Helmholtz Coils System for 3-axis Magnetic Field Generation with High Precision

3-axis Helmholtz coils system is capable of generating spatial uniform magnetic field, and has been widely used in biomedical applications for magnetic micro/nanorobot actuation and steering. This paper reports a control scheme for 3-axis Helmholtz coils system to realize precise and fast current tracking. The controller is based on model predict control (MPC) algorithm, and the nominal mathematical model of the coil series connected with the amplifier is obtained by sweeping frequency method, and a 4th-order super-twisting sliding mode observer (STSMO) is proposed for disturbance and state value observation. Moreover, we perform different experiments to validate the feasibility of the proposed scheme. The results show that the electromagnetic coils system can achieve accurate tracking for sine and square current reference. The bandwidth and precision of the system are significantly improved with the proposed control scheme.