In viscosity measurement, temperature control is very important. In this study, the effects of temperature distribution on vibrational viscometers are investigated. Vibrational viscometers are preferred over other types of viscometers owing to their low cost, easy to use and efficacious continuous viscosity measurement capability. The study was conducted in two parts. In the first part, the challenge of unequal temperature distribution in vibrational viscometers was analyzed. The heat generated by a heater during continuous viscosity measurement disperses every part of a sample fluid and influences the fluid’s viscosity. Therefore, the sample fluid may have inhomogeneous viscosity values because temperature distribution cannot be equal at every point in a fluid. This experiment is repeated several times with different temperature gradients for gaining a better understanding about the effect of unequal temperature distribution on fluid viscosity. Experimental outcomes show that under some conditions, viscosity measurement errors could reach 27.9%. This finding has been verified by mathematical calculations. In the second part of the research, for solving the unequal temperature distribution problem, the use of a magnetic stirrer for mixing up the fluid throughout the viscosity measurement with the aim of achieving homogenous temperature distribution is proposed.

View full abstract

The aim of this research is to establish a quick and robust rotation control method for the air turbine spindle used in ultra-precision machining. In ultra-precision machine tool, such as an aspherical lens generator, air turbine spindles with aerostatic bearing are widely used due to their beneficial properties, such as high precision, high speed, low friction, and low vibration. Nevertheless, when a disturbance force (e.g., cutting force) is given to the spindle, the rotation speed of the spindle tends to decrease. Because methods of controlling the air supply pressure and the flow rate are not sufficiently precise and quick, it has been impossible to control the rotation speed and the output torque of the air turbine spindle. To solve these problems, in this research, we developed a high-precision quick-response pneumatic pressure regulator and applied it to the rotation feedback control of an air turbine spindle. We also set a disturbance force observer in the feedback control system, in order to avoid rotation speed change caused by the disturbance force given to the air turbine spindle. By simulation and experiment, the effectiveness of the proposed method is evaluated.

View full abstract