1. Field of the Invention
The present invention relates to magnetic card recording/ reproducing apparatus and method for recording/reproducing magnetic information into/from a magnetic card.
2. Description of the Related Art
Recently, magnetic cards such as credit cards, bank cards, etc. have generally propagated as if these cards are indispensable for daily life. On the other hand, electric equipment from which magnetic flux necessarily leaks, personal ornaments for health in which magnetic field is positively generated, etc. have been put in the market, and these elements have frequently induced various troubles such as destruction of data stored in magnetic cards, instability of data (making the memory state unstable), etc.
In order to avoid these troubles, a magnetic card which is protected from being effected by magnetic field around it by increasing the coercive force thereof starts to appear. For example, the coercive force of magnetic cards specified in JIS1 type or credit cards is set to 300 oersted, and the coercive force of bank cards in Japan is set to 650 oersted. In the case of magnetic cards which are mainly put in the European and American markets, the coercive force of these magnetic cards is set to 1750 oersted or 2750 oersted, and further a magnetic card whose coercive force is enhanced to 4000 oersted to enhance the protection function starts to appear. Further, in Japan, magnetic cards whose coercive force is enhanced to the same level as the European and American magnetic cards are used as high-way cards, telephone cards, etc.
Most of the above-described magnetic cards are designed substantially in the same outer dimension, and thus if a magnetic recording/reproducing apparatus is commonly used for magnetic cards having various different coercive forces, this is extremely favorable. However, any magnetic card recording/reproducing apparatus supporting magnetic cards which are different in coercive force has not been put in the market from the viewpoint of the cost, the complication of structure, etc. The reason for this will be described with reference to FIG. 1.
FIG. 1 is a diagram showing the recording status of magnetic information in a magnetic card. In FIG. 1, a core 1 constituting a substantially ring-shaped magnetic head is formed of magnetic material, and it is designed to have a gap 12 of about 20 to 40 .mu.m (in order to make easier the understanding of the present invention, the gap is illustrated as being larger than the actual gap in the drawings) at the tip portion thereof and wound by a coil 2 at the base portion thereof. The coil 2 is connected to a current generator 4 for generating and supplying exciting current at a recording time of magnetic information through a matching unit 3 which performs impedance matching as well as amplification of the exciting current. A magnetic stripe 6 coated with magnetic material is adhesively attached to a magnetic card 5, and it is fed in the direction indicated by an arrow a at a constant speed, for example.
When exciting current flows in the coil 2, magnetic flux 13 corresponding to magnetomotive force occurs. In this case, magnetic flux directing in the direction indicated by a solid-line arrow or magnetic flux directing in the direction indicated by a broken-line arrow occurs in accordance with the direction of the current. The magnetic flux 13 forms magnetic field which expands in the neighborhood of the gap of the core 1. By intermittently supplying positive or negative pulse current to the coil 2 in accordance with the feeding of the magnetic card 5, magnetized areas 9, 10, 11 are formed in the magnetic stripe 6 in accordance with the polarity of the magnetic field.
When the magnetized areas are formed, that is, the magnetic information is recorded, the peak value of the pulse current supplied to the coil 2 is determined in accordance with the coercive force of the magnetic stripe 6. Accordingly, when a magnetic card 5 having small coercive force is inserted into a magnetic card recording/reproducing apparatus which is designed to support magnetic cards having large coercive force and then pulse current having a large peak value is supplied to the coil 2, magnetic field 8' which expands in the feeding direction of the magnetic card affects the magnetized area 9 or 10 in which the magnetic information has been already recorded. For example, when the polarity of the exciting current is inverted, the magnetization state is deteriorated or lost. On the other hand, when a magnetic card 5 having large coercive force is inserted into a magnetic card recording/reproducing apparatus which is designed to support magnetic cards having small coercive force, the intensity of the magnetic field which is generated by the pulse current is insufficient, and thus it is impossible to record the magnetic information.
Therefore, in order to attain a magnetic card recording/reproducing apparatus which can support various magnetic cards that are different in coercive force, a recording/reproducing system having plural recording magnetic cards which are respectively designed to support respective magnetic cards having different coercive forces must be provided, and thus it is difficult to implement the magnetic card recording/reproducing apparatus.