Friction torque reduction by ultrasonic vibration and its application to electromagnetically spinning viscometer

The technology of using ultrasonic vibration to reduce friction was applied in our experiment to improve the accuracy of viscosity measurements. The electromagnetically spinning (EMS) viscometer we developed has a remarkable feature: the sample viscosity can be measured in an entirely noncontact manner. Although the apparatus enables low-viscosity measurements of less than 10 mPa·s, which has been difficult to achieve using conventional rotation viscometers, the accuracy has been limited to 10% because of the harmful effect of mechanical friction. We made a new EMS system equipped with piezoactuators to excite ultrasonic vibration to the sample cell, thereby successfully reducing the mechanical friction to one-third that in the previous system. A theory to describe the mechanical friction between the rotating probe and oscillating substrate was also proposed and examined in comparison with the experimental results.