The vibration method to measure static unbalance of rigid rotors

A vibration method to measure static unbalance of rigid rotors has been developed. The method is based on measuring the period of free oscillations of a system consisting of a pendulum frame and a rotor. After installing and fixing the rotor on the frame, free oscillations of the system are generated, and the period is measured. The position of the rotor is changed, rotating it around its axis by one hundred and twenty degrees, and the oscillation period is measured again. The previous operation is repeated. The rotor unbalance and unbalance angle are calculated using the formulas. The paper derives formulas for calculating the imbalance and its angle based on three values of the period of free oscillations of the frame. There was an ambiguity in determining the unbalance angle due to discontinuities in the function. The conditions under which an unambiguous determination of the angle is ensured are given. For this, it is proposed to divide the circular scale into three identical sectors of one hundred and twenty degrees, depending on the numerical values of the periods. For each sector, a separate angle calculation formula is proposed. Theoretical assessment of metrological accuracy of the method showed that the permissible residual specific imbalance of the rotor corresponds to class G6,3 at a rotation speed of 2000 revolutions per minute. The experimental part of the study is based on multiple measurements with different values of the unbalanced mass and unbalance angle. The calculated values of the imbalance and its angle coincide, taking into account the error of the measuring device. This method does not involve spinning the rotor to high speeds. There is no acceleration or braking of the rotor, which saves time and electrical energy. Instead, the vibrating motion of the rotor is used. Therefore, the risk of injury to a person is much lower. The implementation of the method will improve productivity and safety when balancing rigid rotors. This method opens up the possibility of vibration measurement of the dynamic imbalance of the rotors using three values of the frequency of free oscillations of the frame.