Method and apparatus for process control, tension control, and testing of magnetic media

• US 5,408,505 A
• Filed: 10/29/1993
• Issued: 04/18/1995
• Est. Priority Date: 04/09/1993
• Status: Expired due to Fees

• Current Assignee: Washington University In St Louis
• Original Assignee: Washington University In St Louis
• Inventors: Indeck, Ronald S., Muller, Marcel W.
• Primary Examiner(s): Cain, David C.
• Application Number:
  US08/145,943
• Time in Patent Office: 536 Days
• Field of Search: 380/4, 380/23, 380/25, 360/73.05, 360/71
• US Class Current: 713/176
• CPC Class Codes: G06F 21/101 by binding digital rights to specific entities
• CPC Class Codes: G06F 21/79 in semiconductor storage media, e.g. directly-addressable memories
• CPC Class Codes: G06F 2211/007 Encryption, En-/decode, En-/decipher, En-/decypher, Scramble, (De-)compress
• CPC Class Codes: G06K 1/125 by magnetic means
• CPC Class Codes: G06K 19/12 the marking being sensed by magnetic means
• CPC Class Codes: G06K 7/015 Aligning or centering of the sensing device with respect to the record carrier
• CPC Class Codes: G07F 7/08 by coded identity card or credit card or other personal identification means without personal verification means G07F7/02
• CPC Class Codes: G07F 7/086 by passive credit-cards adapted therefor, e.g. constructive particularities to avoid counterfeiting, e.g. by inclusion of a physical or chemical security-layer for security documents G07D7/00; for the reading of record-carriers in general G06K7/00; for the design of coded credit-cards G06K19/10
• CPC Class Codes: G11B 15/43 Control or regulation of mechanical tension of record carrier, e.g. tape tension
• CPC Class Codes: G11B 15/62 Maintaining desired spacing between record carrier and head
• CPC Class Codes: G11B 20/00086 Circuits for prevention of unauthorised reproduction or copying, e.g. piracy indicating unauthorised use of record carriers in general G11B23/28; scrambling for television signal recording H04N5/913; network architectures or network protocols for network security H04L63/00; cryptographic mechanisms or cryptographic arrangements for secret or secure communication H04L9/00
• CPC Class Codes: G11B 20/00094 involving measures which result in a restriction to authorised record carriers
• CPC Class Codes: G11B 20/00123 the record carrier being identified by recognising some of its unique characteristics, e.g. a unique defect pattern serving as a physical signature of the record carrier
• CPC Class Codes: G11B 21/106 on disks
• CPC Class Codes: G11B 23/284 on the record carrier
• CPC Class Codes: G11B 5/59611 Detection or processing of peak/envelop signals
• CPC Class Codes: G11B 5/59633 Servo formatting G11B5/59627, G11B5/59677, G11B5/59683, G11B5/59688 take precedence

Abstract

A method and apparatus is disclosed for using the remanent noise of a magnetic medium as a fingerprint for benchmark testing of the magnetic medium as it is both manufactured and used. A cross-correlation is made between the fingerprint at various times as the magnetic medium is manipulated and is indicative of the integrity thereof. This cross-correlation media may be used to control manufacturing and recording processes, including tape tensioning and channel equalization. This cross-correlation between fingerprints can be used to control the tension applied to a thin film magnetic medium during record and/or playback.

Claims

1. In a device having a head for at least reading data magnetically encoded on a magnetic medium, said device having means for controlling the tension of said magnetic medium as it passes by said head, the improvement comprising means for cross-correlating a magnetic fingerprint of said magnetic medium and controlling said tension control means in response thereto.

2. The device of claim 1 wherein said cross-correlating means includes means for intermittently cross-correlating said magnetic fingerprint as said magnetic medium moves past said head.

3. The device of claim 2 wherein said magnetic medium has its magnetic fingerprint for intermittent portions thereof magnetically encoded thereon, and wherein said cross-correlating means includes means for reading a magnetic fingerprint at said intermittent portions and comparing said read magnetic fingerprint with said magnetic encoded magnetic fingerprint.

4. The device of claim 3 wherein said comparison means includes means for implementing a normalized cross-correlation coefficient r where ##EQU2## for determining the degree of similarity between said magnetic fingerprints.

5. A method for controlling the tension of a magnetic medium as magnetically encoded data is at least read therefrom by a head, the method comprising the steps of:

cross-correlating a magnetic fingerprint of said magnetic medium, and

controlling the tension of said magnetic medium in response thereto.

6. The method of claim 5 wherein the step of cross-correlating includes the step of:

intermittently cross-correlating a magnetic fingerprint of said magnetic medium as said magnetic medium moves past said head.

7. The method of claim 6 wherein said magnetic medium has its magnetic fingerprint for intermittent portions thereof magnetically encoded thereon, and wherein the step of intermittently cross-correlating includes the steps of:

reading a magnetic fingerprint at intermittent portions of said magnetic medium, and

comparing said read magnetic fingerprint with said magnetically encoded fingerprint.

8. The method of claim 7 wherein the step of comparing includes the step of implementing a normalized cross-correlation coefficient r, where ##EQU3## for determining the degree of similarity between said magnetic fingerprint.

9. A method for detecting a variation in a magnetic medium as said magnetic medium is manipulated, said method comprising the steps of:

determining a magnetic fingerprint of a portion of said magnetic medium,

determining again, after passage of time, a magnetic fingerprint of the same portion of said magnetic medium, and

cross-correlating said two magnetic fingerprints to ascertain any differences therebetween, said differences being indicative of a variation over time in said magnetic medium.

10. The method of claim 9 wherein said magnetic medium is a hard disk in a hard disk drive, said hard disk drive including a head for at least reading magnetically encoded data from said hard disk, and wherein the method further comprises the step of storing on said hard disk said magnetic fingerprint and wherein the determining again step includes the step of reading said stored magnetic fingerprint with said head, said differences therebetween being also indicative of a variation in head function.

11. The method of claim 10 further comprising the step of adjusting electronically any data at least read from said hard disk in response to said cross-correlating.

12. The method of claim 10 wherein the step of cross-correlating includes the step of implementing a normalized cross-correlation coefficient r, where ##EQU4## for determining the degree of similarity between said magnetic fingerprint.

13. The method of claim 9 further comprising a step before said step of determining again, said step before comprising processing said magnetic medium.

14. The method of claim 9 wherein the step of cross-correlating includes the step of determining whether there is a fixed relationship between said magnetic fingerprint.