US1837586A - Magnetic record wiper - Google Patents

Description

DeC- 422,l 1931- c. w.. RHODEHAMEL 1,837,586

MAGNETIC RECORD WIPER Filed Feb. 4, 1929 Patented Dec. 22, 1931 CARL W. RHQDEHAMEL, O HOLLYWOOD, CALIFORNIA MAGNETIC RECORD WIPER.

Application led February 4, 1929. Serial- No. 337,519.

My invention relates to magnetic recorders of electrical impulses, and particularly to a method and apparatus for wiping the record, i. e., for removing from the record, pre- 5 paratory to making a recording thereon, of such non-uniform magnetic Vpolarizations as it may carry. These polarizations may result either from a previous intentional recording or from accidental inuences to which it has l been subjected in the course of manufacture or handling. Whatever the source of such polarizations, they will be referred to herein as recordings.

An object of my invention is to provide a l means of removing previous recordings more completely than has hitherto been possible.

Another object of vmy invention is to pro-` vide a means of preparing a magnetic record for receiving a recording in such a manner 2o that mechanical vibrations of the record will ifiot appreciably aiect the reproduction there- Still another object of my invention is to provide a means of wi ing the record such that even though resi ual polarizations be leftupon the record, they will be of such a nature as to havesubstantially no elect uponv reproduction therefrom. l

My invention possesses other objects and 3o valuable features, some of which will-be set forth in the following description of my invention which isillustrated in the-drawing forming part of the specification. It isto be understood that I do not limit myself to the i showing made by the said description and' drawing, as I may adopt varying forms of my invention within the scope of the claims.'

Ma etic records of electrical impulses are made y passin a steel wire, tape or disc at 40. a constant rate tween the polepieces of an electromagnet or ma a current corresponding to the impulses to be recorded. This polarizes elementary portions of the record, and Aif the impulses are cyclic incharacter, as is ordinarily the case, each cycle occupies a space on the record which is equal tothe speed with which the record is traversed divided by the freuency of the impulses. This s ace may v e called the record wave-lengt of the impulse. Ingen- `ing be removed, and another recording formed on thesame steel.

, polarization.

vention overcomes these diculties. ets, whose coils carry eral the polarizations are transverse to the direction of travel of the record, or of the recording coil if ther record be the stationary member. Reproduction is accomplished b`y moving the record between the polepieces ofa magnet similar to that with which the recording was made. This causes a changing flux thru the windings of the magnet, and if suitable reproducing mechanism s connected to its terminals, the original impulses are duplicated therein. l

This system finds its primary use in the recording of telephonie or soundim ulses, but it is also applicable to the repro uction of telegraphic, televisional or other cyclic or transient impulses.

One ofthe advantages of this method of recording is that the record may be wiped, i. e., the polarizationsicomprising the record- This permi of corrections to a record, and

also greatly reduces thecost when the 'rel cording is neededf-or temporary use only. In the. past the wiping has been accomplished by running the record over the poles of a magnet, thus impressing on. it an unvarying I have found, however, that a record soA wiped will set up undesired and interferent potentials in the reproducing coils as a result of mechanical vibrations, and that subsequent recordings are Vmasked byl noises which are not present if the record is initially in a' wholly unmagnetizedstate. Moreover, it is very difficult to remove completely all former recordings by this method, and ghost recordings conse uently remain to confuse the later repro uctions. My in- Referring-to the drawing: 'l

The ligure is alongitudinal sectional view of'anembodiment of my invention adapted for wiping a ma eticrecord offthe wire. type. Portions `o the electrical circuit are shown schematically. l

'Broadly considered, my-method of wiping the lrecord comprises demaxetizing the v record, the demagnetizing field in referably parallel tothe direction in w ich the 109 55 tense at the end where-the wire enters and record is traversed in recording and reproduction, and having a re'cord wave length' less than that of the highest frequencies that 1n my apparatus by traversing the record with a spatially graduated alternating.

magnetic iield at a rate such that the space traversed on the record by the field during a single cycle is less than the space required for the recording-of a cycle of the highest frequency to be reproduced.

'lhe embodiment of my invention which I have chosen for. detailed description is adapted particularl to wiping a wire record, as this is the orm of magnetic record which in ractice has proved the most generally use ul. y

The wiping device may conveniently be made interchangeable with the recording and reproducing coil box on a wire handling mechanism. comprising essentially a frame 6 which carries a motor 7 coupled by suit-` able gearing 8 to aspin e 9 on which is mounted a receiving reel 10. The wire 11 is fed, from a'delivery reel 12, which is prevented from over-running by a brake 13.

Geared to the spindle'9 is a spooling cam 16, operating a lever 17 which connects by la 4link 18 with a' slide 19 on which the coil box or the wiping device is mounted. By this arrangement, the treated wire is spooled smoothly into placeon the' receivin reel, which'may either be transferred to t e delivery position when filled or by a suitable gear mechanism 4the machine may be reversed and the functions of the two reels interchanged. This mechanism will not be described in detail here, however, since such devices are well known in the art, are not essential to the operation of my device, and would complicate the drawing unnecessarily.

The wipin mechanism which is mountable on the sllde 19 comprises a coil 31 which is wound on a non-magnetic core 32 provided with end flanges 33: The core is conical in form, having a minimum diameter at the end ad'acent the delivery spool, and increasing to su stantially the full diameter of the end flange at the end adjacent the receivinl spool. One ,coil used successfullyconsume about five volt-amperes, giving a total magnetomotive force of about one thousand ampere turns. There is a wide. latitude permissible in the design of the coil, depending on the v lar guide 34 for holding the wire accurately in the. longitudinal axis of the magnetic field 'of` the coil. y

It will be ,appreciated that the field from such a coil is spatially graduated, being indecreasin gradually' to nila short distance beyond w ere the `wire leaves.

Supplying the coill 31 thru the leads 36 is a source 37 of alternating current. This source may be the ordinary city power su ply, but I prefer to use a high frequency oscillator supplying current at a frequency of ten thousand cycles or more per second.

If the usual sixty cycle power supply is used, the driving mechanismis preferably geared down to move the wire at a much slower rate than that used for recording andreproduction, and wiping the wire istherefore a relatively slow process.y Thus, if the no1'- mal recording speed is 5 feet per second, and

. the reproducing mechanism will respond to frequencies up to five thousand cycles per.

second, but not to hi her fre uencies, the shortest record wave ength w ich will be reproduced will be 5/5000 or .001 foot, and

the record wave length of the wiping. frequency is preferably less than this value. If sixty c cle current is used for wipin the record at t e recording speed, the recor wave length would be 5/60 or .083 feet, or 83 times the minimum reproducible wave len h, and in order to reduce it -to the desire value, the record speed must be reduced to less than 1/83rd of the recording s eed. A wiping speed of .O5 feet per secon would therefore be suitablesin this case.

If the high frequency oscillator be used as.y

the source of Wi ing current, the wiping may be accomplishe at the recording speed or even at a greater s ed, as long as the record wave length is hel below the minimum'. In case sound is being recorded, a twentythousand cycle oscillator may be used to wipe the record at the'recording speed,'regardless of apparatus limitations, as the average ear ceases t'o function materiallybelow this fre.

uency. With most present types of reproucing a paratus, however, frequencies of over ten t ousand cycles are rejected, and an etic nates the Aprevious transverse .ppl'arizations forming the recordings. This would obtain even were direct current used' in the coil, and as lon l.as the wire is' moved truly axially of the coil the net eii'ect is to destroytheltransverse polarizations completely. Since, how-l ever, mechanical imperfections or neighboring magnetic structures may distort the wiping field to some extent, the alternating current islused, and, as the 'field is graduated, each portion of the wire is subjected 'to a plurality of alternaticns of ma etomotive force of decreasing amplitude, which finally become vanishingly small. The effect of this is' to reduce the polarizations on the wire correspondingly, and thetransverse components are thus reduced to a second order infinitesimal. The effects are further reduced by the of the record, and each is separately producible. Their combination does not produce merely the sum of the individual effects, but their product, and it is infthis fact that the great advantage of the treatment lies.l A record wiped by my method may be used, for example, to .record the speech of a performer standing many feet from the vmicrophone,

' and when reproduced at the original sound level, the voice is not masked 'by an overwhelming record noise lsuch as has made the magnetic recorder unsuitable for such use inthe past.

I claim:

l. The method of wiping a magnetic record of electrical impulses which comprises traversing each portion of the record 'with a gradually spatially decreasing alternatin magnetic field, said field being distributed over a longer portion of the record than the field used to lproduce recordings thereon.

2. The method of wiping a magnetic record of electrical impulses which comprises traversing the record with a magneticfield transverse to the direction of recording polarizations. i

3. The method of wiping a magnetic record'of electrical impulses which comprises traversing the record with an alternating magnetic eld-transverse to the direction of recording polarizations at a rate such that the space traversed during a single cycle is less than the record wave length of the highest frequency to be reproduced.

4. The method of wiping a magnetic record of electrical impulses which comprises traversing the record with an alternating magnetic field transverse to the direction lof the recording polarizations.

5. The method of wiping a magnetic record of electrical impulses which comprises traversing the record with a spatially decreasing alternating magnetic field transverse to the direction of the recording polarizations.

6. A wiper for magnetic records of electrical impulses comprising means for producing a substantially uniformly spatially graduated alternating magnetic field, and means for moving the record thru said field.

7. A'wiper for magnetic records of elec-4 trical impulses comprising means for producing a substantially uniformly spatially graduated alternating magnetic field,` and means for moving the record thru said field longitudinally thereof.

8. A wiper for magnetic records of electrical impulses comprising a coil having a decreasing number of turns perl unit length along 'the axis thereof, and means for movmg the record thru said coil.

" 9. A Wiper for magnetic records of electrica-l -impulses 'comprising a coil having a decreasing number of turns per .unit length along the axis thereof, means for moving the record thru said coil, and a source of high frequency alternating current connected to said coil.

`10. A wiper for magnetic records uof electric impulses comprising a coil having a conical form, and means for moving the record axially thru said coil.

1l. A Wiper for magnetic records of elec- I tric'impulses comprising a coil having a conical inner form, and means for moving the record axially thru said coil.

In testimony whereof, I have hereunto my hand.

set

CARL w. RHODEHAMEL.

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