This paper presents an 6-axis optical force sensor which can be used in fMRI. Recently, fMRI are widely used for studying human brain function. Simultaneous measurement of brain activity and peripheral information, such as grip force, enables more precise investigations in studies of motor function. However, conventional force sensors cannot be used in fMRI environment, since metal elements generate noise which severely contaminate the signals of fMRI. An optical 2-axis force sensor has been developed using photo sensors and optical fibers by Tada et al., that resolved these problems. The developed force sensor removed all magnetic components from the sensing part. It detected minute displacements by measure amount of light and light traveled through the optical fibers. However, there still remain several problems on this optical force sensor. Firstly, the accuracy is not high compared to the conventional force sensors. Secondly, the robustness is not enough against the contact force to the optical fibers. In this paper, the problems concerning to the acturacy and the sensor output stability has been improved by novel methods of fixing fibers and arithmetic circuit. An optical 6-axis force is developed based on these improvements, and usefulness of our sensor for brain function analysis is confirmed in fMRI experimentations.
