Design and Control of a Magnetic Hammer Millirobot for Tissue Penetration



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Millirobots propelled by magnetic fields show promise for minimally invasive surgery or drug delivery. MRI scanners can generate magnetic gradients to apply propulsive forces on ferromagnetic objects. However, MRI gradient forces are insufficient for tissue penetration. This project presents a millirobot design and control methods to produce pulsed forces. A ferromagnetic sphere inside a hollow robot body can move back and forth between a spring and an impact rod. Repeated impacts convert the kinetic energy of the sphere into large pulsed forces that can penetrate tissue. An estimator helps achieve the maximum possible average impact velocity with minimal sensing, for a given set of material and geometric parameters, and input magnetic gradient force. Prototypes were 3D printed and tested on a custom magnetic test bed. Analytical, numerical and experimental results are presented.



Medical robotics, Robotics, Minimally invasive surgery, Force control