The present invention is generally related to magnetic read heads and, more particularly, to a versatile reader for sensing both magnetic and optical data from a credit card or other data carrying member.
Credit card alteration, duplication and counterfeiting have become increasingly large problems in recent years. Proposals have been made to provide credit card structures with secure properties or features. One such security feature is disclosed in copending U.S. patent application Ser. No. 581,428, entitled SECURE PROPERTY DOCUMENT AND METHOD OF MANUFACTURE, in the name of Charles K. Beck et al. and assigned to the assignee of the present invention. Briefly, this security feature entails the use of infrared reflectors which are deposited beneath the magnetic media to define optical data elements which are sensed by an IR detector. This optical data may be related in some way to magnetic data recorded on one of the magnetic stripe data tracks, such as disclosed in copending U.S. patent application Ser. No. 581,351, entitled SECURE PROPERTY DOCUMENT AND SYSTEM, filed in the name of Francis C. Foote and assigned to the assignee of the present invention. The application discloses a reading arrangement entailing the use of an optical IR detector and a magnetic read head mounted in a predetermined spacial relationship. The spacing between the optical detector and magnetic read head may be set at the factory to provide proper timing between the magnetic and optical data sets. The timing may also be adjusted electronically through the use of appropriate circuitry. It has been found that temperature changes may alter the spacing between the magnetic read head and optical detector, thereby adversely affecting the relative timing between the magnetic and optical data. This timing may also be adversely affected by thermal expansion or contraction of the credit card due to changes in ambient temperatures.
These various timing problems may be cured to some extent by mounting the magnetic read head immediately beside the optical detector. This, however, is often inappropriate due to the limited width of the magnetic stripe and the fact that the optical data area is located directly beneath the magnetic stripe. It is also important to note that significant timing errors between the optical and magnetic data may be caused due to skewing of the card or data elements relative to the read head.
These problems are resolved through the use of a composite read head of the type disclosed in copending U.S. patent application Ser. No. 581,423, entitled COMPOSITE MAGNETIC/OPTICAL READER AND METHOD. That application was filed in the name of Robert A. Rubenstein and is assigned to the assignee of the present invention. The application discloses a composite reader for sensing magnetic data at the same point in time as the underlying optical data element. This is achieved by directing infrared radiation through the reluctance aperture of the magnetic read head. If a reflector is present in the area directly beneath the aperture, the IR radiation is reflected back through the aperture to appropriate IR detector.
Improved reading and recording accuracy may be achieved by providing a relatively narrow reluctance gap in the range of 1-2 mils. It has been found, however, that in many applications it is difficult to successfully direct a beam of IR radiation through such a narrow gap due to several limitations, such as the refractive index, configuration of the solid material molded into the gap, and the small space available for mounting the required optical components within the magnetic head. These problems may be overcome by directing the radiation through an appropriate prism mounted in a groove formed in the face of the magnetic read head and extending perpendicular to the magnetic reluctance apertures. This arrangement is disclosed in copending patent application Ser. No. 674,562, entitled DATA TRANSDUCER, filed Apr. 7, 1976, in the name of Robert H. Trenkamp and assigned to the assignee of the present invention. The embodiment disclosed therein provides for alignment of the optical and magnetic reading apertures, with the incident radiation focussed through a lens and prism to a plane coincidient with the presented optical reflector.
It has been found that while the transducer disclosed by application Ser. No. 674,562 provides excellent results, the reading accuracy diminishes somewhat after long periods of use. This is caused, at least in part, by wear of the read head contact surfaces through wiping action against the abrasive magnetic stripe medium. As the read head continues to wear, the length of the optical path is shortened and the size of the optical reading aperture is changed to a point which adversely affects the reading accuracy or ability to determine the reflector locations relative to the flux reversals on the magnetic stripe.