Demagnetization of thin film magnetic recording transducers utilizing a decreasing AC current

• US 4,970,621 A
• Filed: 09/09/1988
• Issued: 11/13/1990
• Est. Priority Date: 09/09/1988
• Status: Expired due to Fees

• Current Assignee: Hewlett-Packard Company (HP Inc.)
• Original Assignee: Hewlett-Packard Company (HP Inc.)
• Inventors: Simmons, Ralph F., Gailbreath, Samuel H.
• Primary Examiner(s): Pellinen, A. D.
• Assistant Examiner(s): Osborn, David
• Application Number:
  US07/267,144
• Time in Patent Office: 795 Days
• Field of Search: 361/149, 361/150, 361/151, 361/154, 361/155, 361/267, 307/104, 307/264, 360/46, 360/66, 360/67, 360/110, 360/111, 360/112, 360/113
• US Class Current: 361/149
• CPC Class Codes: G11B 15/125 conditioned by the operating function of the apparatus
• CPC Class Codes: G11B 19/04 Arrangements for preventing, inhibiting, or warning against double recording on the same blank or against other recording or reproducing malfunctions
• CPC Class Codes: G11B 5/465 Arrangements for demagnetisation of heads

Abstract

Noise in the readback signal of a magnetic recording device resulting from spurious pulses in the readback signal produced by transitions of the magnetic remanent state of the yoke in the read/write transducer is eliminated by controlling the occurrence of the spurious pulses. Immediately following the completion of the write process, a decreasing amplitude alternating current is applied to the read/write coil of the transducer to drive the yoke remanent state to a stable or zero remanent state prior to the commencement of the read process.

Claims

1. In a magnetic recording and reading apparatus including a magnetic transducer having a magnetic yoke element forming a magnetic circuit and at least one read element and at least one write element, a method for controlling the random occurrence of spurious pulses induced in the read element of a magnetic transducer when the magnetic field in said transducer elements decays from a metastable, non-zero remanent state to a stable remanent state resulting in a net change of magnetic flux through the transducer read element, said method comprising the step of applying an alternating current having a first value through said transducer write coil while decreasing said alternating current to a second value less than said first value.

2. The method of claim 1 including the step of monotonically decreasing said alternating current from said first value substantially equal to a value of write current applied to said write element during a data write process to said second value.

3. The method of claim 1 including the step of applying said alternating current to said write element at the completion of a data write process, said alternating current applied for a predetermined period of time prior to the commencement of a data read process.

4. The method of claim 2 wherein said second value is substantially zero.

5. The method of claim 1 wherein said read element and said write element comprise a single time-shared read/write coil.

6. The method of claim 1 including the steps of:

generating a data write signal, said data write signal including a plurality of demagnetization pulses at the trailing end thereof;

generating a write current signal; and

modulating said data write signal with said write current signal to provide said decreasing alternating current.

7. In a magnetic data recording and reading device including at least one magnetic transducer having a magnetic yoke element forming a magnetic circuit and a read element and a write element, both said read and write elements influenced by said magnetic circuit, apparatus for generating an alternating current demagnetizing signal comprising:

a controllable current source responsive to a write current control signal for providing a write current signal having predetermined characteristics; and

circuit means coupled to said current source and to said write element, said circuit means responsive to said write current signal to modulate a data write signal and provide a modulated write current to said write element, said modulated write current including a data signal portion followed by a decreasing alternating current portion, said decreasing alternating current signal causing said magnetic transducer to have a stable magnetic remanent state prior to the commencement of a data read process.

8. The apparatus as in claim 7 wherein said read element and said write element comprise a single time-shared read/write coil.