| 摘要 |
PURPOSE:To prevent the generation of very low frequency air vibration by a method wherein the phase angle of a motor is controlled so that the frequency difference of pressure fluctuations generated by the operations of a plurality of motors will not enter into the frequency range of the very low frequency air vibration. CONSTITUTION:The air vibration detected by a pressure detector (a) is fed to a minimum value decision circuit (c) through a V/F convertor 9 and a filter (b) removing air vibration elements except the one having a very low frequency. The minimum value decision circuit (c) compares sequentially the outputs of the pressure detector (a) when the phase angles of respective motors 1 are changed under a control by a program selection commanding circuit (d), and detects the phase difference of the motors 1, in which the output of the pressure detector (a) shows the minimum value. By detecting such munimum value, the revolutional phase angle preventing the generation of the very low frequency air vibration is traced automatically under controlling the phase and thus the generation of the very low frequency air vibration may be prevented. |
