Patent GB-1438805-A (GB)
Title: Method and apparatus for locally magnetizing moving magnetic material
IPC: G01D5/245
Filed: 1973-10-16
Abstract: 1438805 Magnetization NIPPON KOKAN KK 16 Oct 1973 [16 Oct 1972] 48216/73 Heading H1P In apparatus (Fig. 3) for magnetizing moving magnetic laminar material, e.g. steel plate 1 in a press roll line; a U-core 2 and magnetizing coil 3 placed adjacent to the material is pulse energized from D.C. source 5 over an, e.g. transistor switch 4 and is shunted by a transient suppressing series diode and resistor; so as to permanently magnetize an area adjacent the core to an extent dependent on quality, thickness, pulse magnitude, and displacement from the core. To compensate the length of the magnetized area for variations of speed at a constant value, the energizing pulse width is made inversely proportional to the speed of movement. A detector coil and core 11, 12 responsive to the passage of magnetized areas is spaced a critical distance from coil 3 and produces a signal which is amplified and wave shaped in a squarewave generator differentiator, clipper, and inverter 14 to drive a monostable multivibrator 15 giving a train of pulses of fixed length. This is integrated at 16 and clipped at 17 to derive a bias for monostable transistor multivibrator 19, 20 of time constant set by resistor 21 and capacitor 22. The output from 15 is also differentiated by RC circuit 23, 24 to negatively bias transistor 19 over diode 25, and a start pulse generator 27 is connected over switch 26 to capacitor 23. In operation, switch 26 is closed for differentiation at 23, 24 to trigger multivibrator 18 over diode 25, and transistor 20 pulse switch 4 for a prescribed time to magnetize plate 1 over a prescribed length. Motion, of the magnetized area past detector 11 generates a signal dependent on the intersection speed which is converted to a pulse from multivibrator 18 connected to control switch 4. Thus when a magnetized area of the steel plate initiated by a preceding start pulse reaches detector 11, a succeeding start pulse indicates further magnetization, and for constant speed movement of the plate the pulse rate at integrator 16 is constant and the bias on transistor 20 from clipping circuit 17 is also constant. Equidistant magnetized areas separated by a distance corresponding to the inter-coil displacement are formed on the moving plate, and the passing length of plate is indicated by counter 30 as the product of the number of pulses and the displacement between coils 2 and 11. Variations of running speed vary the length of the magmetized areas, and the pulse signal intervals from generator 15 and their integrand from 16 also vary proportionally to the running speed, and the correction voltage from clipping circuit 17 applied to transistor 20 is similarly varied. The voltage developed at capacitor 22 is inversely variable with the running speed, and the output pulses from multivibrator 18 are correspondingly reduced in width so that the pulsations of energization of coil 3 are also inversely proportional to the running speed. Thus the difference in distance between adjacent magnetized areas is restored to the displacement between coils 3 and 11, so that the errors are eliminated and the length of plate passing is accurately measurable. In a modification (Fig. 7) two detection coils 11, 11a are linearly arranged along the travelling plate 1 at a fixed interval corresponding to the length of the magnetized area, and signals therefrom are amplified and wave-shaped at 13, 13a; 14, 14a to drive pulse signal generators 15, 15a whose output pulses are applied respectively to set and reset inputs of flip-flop 33. In operation, switch 26 is initially closed to pulse switch 24 from generator 27 for a prescribed time interval over which the plate is magnetized. When the magnetized area arrives at detector coil 11 a signal is generated so that generator 15 pulses flip-flop 33 to actuate switch 4. On arrival of the magnetized area at detector coil 11a, a signal is generated so that generator 15a pulses flip-flop 33 to reset and disable switch 4. The operation flip-flop period varies inversely with the speed of the travelling plate and the distance between the magnetized areas is corrected with speed variation to that corresponding to the distance between coils 3 and 11; thus enabling the length passing to be accurately determined. A mathematical analysis and the circuit waveforms are given. The speed of the moving plate may also be measured.