| 摘要 |
PURPOSE:To prevent unaligned piling while to save energy by exciting forcefully only at the moment of attraction on the basis of a signal for detecting approach to a magnet roller through variation of voltage or current while exciting thereafter with sustaining current. CONSTITUTION:The flux phi of magnet roll will increase from the time (t1) when the leading edge of steel plate will approach to a magnet roll thus to increase the terminal voltage of coil 30 Vr=VR+KXdphi/dt through counter electromotive force. The variation of Vr is differentially detected through detection circuit 5 to function a relay RY thus to function an off-delay timer T. A limiting resistor R is shortcircuited by said delay time signal to perform the maximum excitation thus to attract the leading edge of steel plate reliably at the time (t2). At the time point (t3), the coil terminal voltage Vr will be same with source voltage Vs to produce zero differentiation value while at the time point (t4), contact Ta will open to reduce the excitation current Ic to such level as to hold the self-weight of steel plate, thus to save energy. |
