Development of non-contact detection method for recorded magnetic information using MI micro magnetic sensors and PRML signal processing

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Conventional public service automatic machines such as the automatic ticket gate, the automated telling machine (ATM) and the automatic vending machine suffer from some troubles of regular replacement of worn magnetic heads (MR head) due to its close contact reading of the recorded magnetic information in the ticket and the bank note, and removing scrumpled bank note at the head position. Therefore, we have tried to introduce a sensitive micro magnetic sensor (MI sensor) for realization of non-contact reading method for recorded magnetic information in these tickets and bank notes for decrease of troubles. The MI sensor has been invented by the chief researcher and commercially produced by the Aichi Steel Co. with the financial support by the JST. In the experiment, we have focused to the automatic ticket gate (the handler made by Omron Co.) and used some amorphous wire CMOS IC type high density fabricated MI sensors made by Aichi Steel Co..Obtained results are as follows :(1) A stable … More non-contact reading was successfully carried out by setting a MI sensor head edge point of an amorphous wire with 20 μm diameter and 2 mm length at around 0.3 mm apart from an Edmonson type magnetic ticket surface recorded by 128 bits digital pattern with 100 μm pitch area and 200 μm pitch area. Angle of the amorphous wire axis for the ticket surface was 45 degree.(2) Waveform of the MI sensor output is geometric (piecewise linear) triangle shape withidentical gradient both in the 100 μm pitch area and 200 μm pitch area. Therefore, the amplitude of the triangle shape ac wave at the 100 μm pitch area is just half of that at the 200 μm pitch area.(3) Rectangular waveform with almost identical amplitude both in the 100 μm pitch area and 200 μm pitch area was obtained by adding a passive RC differential circuit to the output terminal of the MI sensor. That is, the digital output was obtained using the MI sensor without any digital processing circuit.(4) A variation of the amplitude of the MI sensor output pulse train was occurred for non-contact reading of a commuter pass with 240 bit recorded pattern, which was compensated by adding a saturable amplifier to the RC differential circuit.(5) The origin of detected triangle waveform of the MI sensor output was analyzed using a magnetic dipole model for the magnetic ticket considering the size and the angle of the amorphous wire sensor head, in which a rough tendency of triangle shape generation was resulted but not sharp triangle waveform. This is a remaining problem.The PRML method was not necessary due to preparation of sufficiently sensitive MI sensor.The purpose of realization of a non-contact detection method for recorded digital pattern of the magnetic ticket was basically succeeded using a sensitive micro magnetic sensor (amorphous wire CMOS IC MI sensor). The developed non-contact detection method would successfully be applied to the ATM and the automatic vending machines. Less