GB1165704A - Elektromagnetic Control Apparatus - Google Patents

Abstract

1,165,704. Electric railways. NATIONAL RESEARCH DEVELOPMENT CORP. 8 Sept., 1966 [27 Aug., 1965], No. 36929/65. Heading B7L. [Also in Divisions B8, F2, G1, G3 and H2] An electromagnetic levitation system supports a ferro-magnetic element 12 by means of an electromagnet 11 whose energizing coil 13 is supplied with A.C. through a capacitor 14 such that a resonant condition is provided whereby movement of the element, towards and away from the electromagnet, causes the current to decrease and increase respectively to provide a stable position for the element, together with damping means which exert a force, dependent on the rate of change of separation distance, on the element. The damping force is provided by a sheet of copper partially surrounding the element, the sheet being slotted so that the eddy currents follow long horizontal paths but short vertical ones to give heavy damping of vertical movement. Alternatively the system shown in Fig. 7 can be used where movement of element 12 alters the output of photo-cell 28 and this output is differentiated and applied to amplifier 26 to provide a current in coil 25 which may buck or boost the magnetic field produced by coil 13. The current in coil 13 may be varied to alter the separation between element 12 and electromagnet core 10. In a further embodiment, the photo-cell signal may be used to alter the frequency of the A.C. supplied to the coil and thereby alter the effective stable position, Figs. 4 and 8 (not shown). Alternatively the value of the capacitance in the supply circuit may be varied. In a modification, Fig. 5 (not shown), the element may form a stationary structure, and the electromagnet, together with the necessary circuit elements, form a moving structure which can be propelled by a linear motor or air jets. The element may have copper damping sheets or be connected in the circuit shown in Fig. 7. The element may have a vane attached for measuring the flow of gases, Fig. 6 (not shown) with a mirror provided on the element which reflects light on to a photo-cell to provide a pulse for each revolution. The device may also be used as a lifting jack by sequentially using a different size of capacitor in the supply circuit. In both these cases the element is rotatable and the device forms a friction-free bearing.