METHOD FOR CONTROLLING MAGNETICALLY LEVITATING DEVICE DURING LIFT-OFF

摘要

PURPOSE:To avoid shock on a levitating body by estimating a gap at the time of lift-off, the load of the levitating body due to the electric current of a coil and further a gap corresponding to zero-power, and generating a gap command value based on these. CONSTITUTION:Displacement of a levitating body is controlled by a deviation between a command from a gap command generator 36 and an actual gap, through a current value to an coefficient element 45 which gives the suction force of an electromagnet and an integral element 44 for zero-power control is connected to it under a condition that a pre-determined gap is formed and current is controlled to become zero so that the load is supported by the suction force of a permanent magnet. In case the levitating body is lifted-off under a condition that the power supply is cut, the value of load is calculated by a load estimating device 50 based on the value of a gap and the value of current and further the value of a gap corresponding to zero-power is estimated by an estimating device 60 and the gap command value from the command generator 36 changes its value so that a switching to the zero-power control is carried out smoothly. Thus, shock and vibration to the levitating body such as a device for conveying wafers, etc., can be avoided.