Evaluation of Friction Torque and Heat Quantity Generated in Spindle (1st Report) : Development of Evaluation System and Evaluation of Air Spindle Characteristics

This paper presents a new method to evaluate the friction torque and the heat quantity generated in a spindle system. The decrease in the rotational speed of spindle during the free run period is precisely measured, and the angular deceleration is calculated. The heat quantity generated during the spindle rotation is evaluated as the product of the moment of inertia of spindle, the angular deceleration and the angular velocity. A device is newly developed to measure the rotational speed of spindle accurately for this purpose, which is basically composed of a photo interrupter attached to the spindle and a crystal oscillator of 2.5MHz clock pulse combined with a counter mounted on a personal computer board. The method was applied to evaluate the heat quantity generated in an air spindle, and it was proved that the heat quantity was accurately evaluated with a repeatability error of less than 1%. The heat quantity is obtained to increase by 4% due to an increase in the coefficient of viscosity of air which is caused by the increase in the air temperature