Roland Moser

MRI/fMRI-compatible robotic system with force feedback for interaction with human motion

This paper presents a robotic system that is compatible with anatomical magnetic resonance imaging (MRI) as well as with the more sensitive functional MRI (fMRI), and can safely and smoothly interact with human motion during the imaging. The system takes advantage of the electromagnetic shield that encloses the MR room by placing the interfering or sensitive components outside the shield, in the control room. This eliminates the need for extensive compatibility testing before each use. The concept is based on a conventional actuator placed outside the scanner room and a hydrostatic connection to transmit force and motion to an MR-compatible slave placed next to or inside the MR scanner. A force sensor, based on reflected light intensity measurement over optical fibers, measures interaction forces with the human subject. A robotic interface for wrist motion demonstrates the MR compatibility of this concept and the possibility to interact with various dynamic environments during functional imaging. This technology provides a basis for applications such as assistive devices for interventional MRI and haptic interfaces for neuroscience investigations.

Optimization of Repulsive Passive Magnetic Bearings

Passive magnetic bearings are an attractive alternative to conventional ball bearings in applications where wear and tear must be minimal and cost or construction restrictions ban the use of active magnetic bearings. They also find applications as miniaturized high-speed bearings where no other low-friction solutions are available. We show that, for a given cylindrical construction volume, an optimized repulsive bearing design with respect to a maximal radial stiffness can be found. This optimal configuration is independent of the aspect ratio of the bearing, but is determined by the width of the air gap between rotor and stator. Our method can determine the optimal configuration for any bearing geometry. We develop a design for a miniaturized high-speed bearing as an example.

A Versatile MRI/fMRI Compatible Spherical 2-DOF Haptic Interface

Haptic devices compatible with functional magnetic resonance imaging (fMRI) could become an invaluable tool for the study of human brain functionality and motor learning. This paper presents a spherical two-degree-of-freedom (DOF) device made entirely from polymers and suitable for use within an MR environment. The design includes a 2-DOF force sensor for measurement and control of interaction forces. It can be actuated by wire transmission from a remote or well-shielded place. This paper presents the realized prototype and discusses its application as haptic joystick, and its extension for 2-DOF planar displacement for use as x-y-manipulandum as well as tactile stimulator for the fingertips

Characterization of Surface Cracks Through The Local Magnetic Field Induced by Eddy Currents

It is important to reliably characterize cracks in metallic mechanical parts in order to assess the serenity of damage due to fatigue. The most important parameter for this is the crack depth. This is notoriously difficult with standard Eddy current techniques. We show here that this can be achieved by measuring the local magnetic field induced by Eddy currents flowing around the crack. This is done by using a high-density array of micro-Hall sensors integrated in a single CMOS chip with a spatial resolution of 10 mu m. We present the dependence of the signal on varying crack depths, liftoff and yaw angle. Finally, we study the response of the sensor to cracks in a DC magnetic field, i.e. the flux leakage due to the presence of a crack. This is especially relevant to cases where cracks appear predominantly close to edges with complex geometries for which it is difficult to induce clean Eddy currents.