# US 4,394,621 A · Electronic velocity measurement especially for self-clocking write head

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- Number: US 4,394,621 A
- Document ID: US4394621A
- Status: Granted
- Kind: A
- Application number: 06/214,319
- Filed: 1980-12-08
- Granted: 1983-07-19
- Earliest claimed: 1980-12-08
- Assignees: International Business Machines Corporation
- Inventors: James E. Rohen
- Web page: https://patentgrep.com/patent/US4394621A

## CPC

- G06K 7/016: Synchronisation of sensing process
- G06K: GRAPHICAL DATA READING (image or video recognition or understanding G06V); PRESENTATION OF DATA; RECORD CARRIERS; HANDLING RECORD CARRIERS

## Abstract

A time base signal for controlling the recording of binary data is developed by measuring the velocity of a magnetic record. The velocity is measured by providing an inductive read head and a magnetoresistive read head which sense the same flux field on the magnetic record. The difference in the outputs of these read heads is a measure of the record velocity.

## Claims

### Claim 1

Velocity measuring apparatus for producing an electrical measurement of the velocity of an object having at least one magnetically sensible mark thereon, wherein the improvement comprises:
an induced current magnetic field sensing device,
a variable resistance magnetic field sensing device,
means supporting said devices closely adjacent, one to another, for encountering said mark during substantially the same state of relative motion with respect to said object, and
means responsive to a signal output from each of said devices for producing said electrical measurement.

### Claim 2 (depends on 1)

Velocity measuring apparatus, as defined in claim 1, wherein said means responsive to said signal output comprises means for operatively dividing said signals one by the other.