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Publication numberUS3553421 A
Publication typeGrant
Publication dateJan 5, 1971
Filing dateNov 7, 1968
Priority dateNov 7, 1968
Publication numberUS 3553421 A, US 3553421A, US-A-3553421, US3553421 A, US3553421A
InventorsSchawlow Arthur L
Original AssigneeSchawlow Arthur L
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Method of and apparatus for erasing
US 3553421 A
Abstract  available in
Previous page
Next page
Claims  available in
Description  (OCR text may contain errors)

United States Patent to H0 A.C.

Inventor Arthur L. Schawlow 839 Esplanada Way, Stanford, Calif. 94305 Appl. No. 784,977

Filed Nov. 7, 1968 Patented Jan. 5, 1971 Continuation of application Ser. No. 471,811, July 18, 1965, now abandoned.


U.S.Cl 219/121 Int. Cl 823k 9/00 Field of Search 219/121 [56] References Cited UNITED STATES PATENTS 3,305,666 2/l967 Zaromb 219/383 3,314,073 4/1967 Becker 346/76 Primary Examiner-J. V. Truhe Assistant Examiner Lawrence A. Rouse Attorney-Paul B. Fike ABSTRACT: A method of removing radiation-absorptive material from a base which is relatively nonabsorptive of the radiation. A short pulse at such energy level and in the order of milliseconds or less is generated and directed against the absorptive material. Energy is absorbed by the absorptive material to affect its heating and removal from the base. The base absorbs substantially a minimal amount of radiation and thus remains substantially intact.

PATENTEU JAN 5 I97! ARTHUR L. SCHAWLOW BY M @ML PATENT AGENT METHOD OF AND APPARATUS FOR ERASING The present application constitutes a continuation of applicants prior application Ser. No. 471 ,81 l filed July 14, I965.

The present invention relates generally to erasure techniques and more particularly to a method of and apparatus for erasing printed or typewritten characters from paper or some other base. The invention described herein was made in the performance of work under a NASA contract and is subjected to the provisions of section 305 of the National Aeronautics and Space Act of 1958, Public Law 85-668 (72 Stat. 435; 42 U.S.C. 2457).

Most individuals, and secretaries in particular, are aware of the troublesome nature of making erasures of a typewritten letter or other character from the paper. Conventionally, a rubber eraser is employed by the secretary or other individual to remove the undesired letter with a rubbing, abrasive action. Considerable time is consumed if the erasing effort is to be effective, particularly since movement of the typewriter platen is usually necessary and, if multiple copies are being typed, additional sheets of paper must be inserted between the copies to avoid smudging thereof. The abrasive action leaves a residue including particles of the eraser, the pigment and the paper as well, and these particles frequently drop into the working mechanism of the typewriter to subsequently interfere with its optimal operation. Finally, upon completion of the erasure, an abraded section of paper which is clearly visible remains, thus to spoil the overall appearance of the finally typed page,

Accordingly, it is the general object of the present invention to provide a novel erasing method and apparatus whichfunctions in a neat and rapid fashion so as to overcome all of the mentioned difficulties.

More particularly, it is a feature of the invention to provide a method of erasing which employs radiation as the operating mechanism. I

Yet more specifically, it is a feature of the invention to employ coherent radiation to perform the erasing function so that precise control of the area to be erased can be achieved.

It is a particularly significant feature of the invention to provide an erasing method utilizing a short pulse of radiation which is highly absorbed by the pigment or other material to be erased so as to effect rapid localized heating and subsequent vaporization thereof.

As a correlated feature of the invention, the radiation is chosen so as to be highly reflected by the paper or other base upon which the printed pigment appears to that the entire process is substantially not destructive of the paper.

Quite specifically, it is a feature of the invention to utilize a short pulse of coherent radiation from a laser operating at a predetermined power level to carry out the erasing function.

Accordingly, a correlated feature of the invention is the provision of an erasing apparatus which utilizes a laser conveniently mounted for directing its beam accurately onto the area where the erasure is to occur.

Another feature of the invention relating to the apparatus is the provision for adjustment of the erasing beam so that, for example, typewritten characters of various sizes (e.g. pica or clite type) can be accurately erased.

These as well as other objects and features of the invention will become more apparent from a perusal of the following description of a preferred method for practicing the invention and an exemplary apparatus for carrying out such method in practice.

In its most general terms, the method of the present invention involves first, the generation of radiation at a desired frequency and a chosen power level and then directing such radiation as a beam of controlled size mite area of paper or other base material on which the character to be erased appears. To facilitate understanding, the method and apparatus will both be described in connection with one simple, obvious application, that of erasure of a single typewritten character composed of carbon pigment which has been previously ap plied to a sheet of standard white paper. However, it will become apparent from the following detailed description that many other specific materials can be erased or-removed by substantially the same process and no limitations are therefore to be inferred.

More particularly, the steps of the method involve preferably the generation of a beam of coherent radiation preferably in the light portion of the frequency spectrum which generally includes ultraviolet, visible and infrared waves. Such a beam is readily produced by a laser such as is briefly described hereinafter and in more detail in US. Pat. No. 2,929,922, issued Mar. 22, 1960. The precise frequency ofoperation can vary within limits, but should be controlled so that maximum absorption by the pigment and minimum absorption (or maximum reflection) by or paper occurs. No particular difficulty is experienced when conventional black colored carbon pigment characters appear on white paper since the black carbon approaches in character the so called black body" which has percent absorption in the light spectrum whereas the white paper is highly reflective.

Regardless of the precise frequency chosen, the beam of coherent radiation is highly directional, consisting of waves having substantially planar wave fronts so as to be highly directive and therefore easily controllable. Preferably, the beam is focused by a convex lens or the like so as to be accurately directed onto the area occupied by the character to be erased. Typically, an ordinary character produced by a conventional typewriter occupies an area of 0.1 square centimeter so that a slightly convergent focusing of a typical laser beam can readily be adapted for accurate coverage of such an area.

Although th'earea exposed to the laser beam can be controlled accurately, an additional shielding step can be em ployed to mask off surrounding areas and thus effectively preclude erasure of neighboring typed characters.

When the beam is directed against the exposed area, the highly absorbent carbon pigment is rapidly heated so as almost instantaneously to vaporize whereas the surrounding paper which is highly reflective is heated but slightly and remains substantially undamaged. In addition to the vaporization, it is believed that some burning (oxidation) of the vaporized carbon may take place. Regardless of the precise mechanism, no residue appears and a clean, white, undamaged section of paper remains for retyping of the proper character thereon.

To assure that the paper remains undamaged, it is preferred that the pulse of radiation be extremely short, in the order of milliseconds or less, and that the power level of the radiation be approximately in the range of 5 to I00 kilowatts per square centimeter. While the length of the pulse and the power level can of course vary depending upon the precise characteristics of the paper or other base and the pigment thereon, the ranges specified hereinabove have been determined as extremely satisfactory for removing black carbon pigment from ordinary white stationery to provide effective erasing with no accompanying paper damage. In order to practically carry out the steps of the method as specified hereinabove, an exemplary apparatus can take the form illustrated in the accompanying drawing wherein: a

FIG. 1 is a fragmentary perspective view of an erasing apparatus mounted on'a conventionaltypewriter, and

FIG. 2 is an enlarged fragmentary perspective view of a laser forming part of the apparatus illustrated in FIG. I.

With initial reference to FIG. 1, the laser, indicated generally at 10, is mounted at one end of an arm 12 whose 0pposite extremity is pivoted at one side of a typewriter T for movement about a vertical axis so that the entire laser structure can be moved from an inoperative position adjacent one side of the-typewriter to the illustrated central operative position over the keyboard whereat the laser beam is directed precisely toward a character centered on the typewriter. Thus, when such character has been erased by the radiation impinging thereagainst, the typist is immediately ready to continue by typing the correct character.

While the laser 10 itself is known and its detailed characteristics are described in the aforementioned US. Pat. No. 2,929,922, the illustrated laser, quite briefly can be described as including an outer housing 14 of generally cylindrical configuration, preferably having a reflective interior so that light generated by several flash lamps 16 supported therewithin on suitable spacers 18 is directed substantially toward the axis of the housing whereat a negative temperature medium is supported. While various materials can be utilized, it is known that greater intensities can be obtained with solid materials such as the ruby rod 20 illustrated which is essentially a cylindrical rod of aluminum oxide containing 0.05 percent of chromium oxide. As described in detail in the aforementioned U.S. Pat., No. 2,929,922, the ends of the ruby rod 20 are provided with predominantly reflective coatings 22, 24 which can be thin layers of gold. The coating 24 on the right must be relatively thin so as to have slight transmission capabilities so that a beam generated within the ruby rod 20 when the lamps are flashed emerges from the right of the structure as a highly directive beam indicated at B whose frequency is approximately 6,943 Angstrom units at room temperature. The lamps 16 are energized by discharge of a suitable capacitor bank charged to a DC voltage of approximately 900 volts from a suitable l l() volt AC source, all of this material being preferably housed in a separate box indicated at 26 which may be placed at any convenient location adjacent the typewriter T and connected to the laser structure itself by suitable connecting wires 28. A suitable pushbutton 29 on the laser is depressed to instigate operation.

The highly directive, pencillike beam B of radiation emanating from the laser 10 is preferably directed through a convex lens 30 and the convergent beam emanating from the lens is directed against the typed character C whose erasure is desired. Preferably, after passing through the lens 30, the convergent beam also passes through a generally rectangular aperture in a shield 32 located closely adjacent to the typed character which is to be erased, the material of the shield being highly absorbent to the radiation so as to effectively preclude passage of any misdirected radiation against adjacent printed characters on the paper. Both the shield and the lens are suitably mounted in a tapered extension of the main cylindrical housing 14 of the laser.

In order to accommodate different type sizes, the entire laser housing is preferably mounted slidably in a sleeve 13 carried by the arm 12 for longitudinal or axial adjustment, a simple adjustment screw enabling the typist to make such adjustment quickly and easily when needed.

A typical beam emanating from the described laser 10 can,

,for example, produce a pulse having a length of one-half millisecond and a total power of 2 kilowatts so that a total energy .of one joule is directed against the area occupied by the typed character on the paper, such area as previously mentioned being approximately 0.1 square centimeter. Such a pulse provides effective erasure with no paper damage whatsoever and obviously requires but very little power expenditure.

It will be apparent that the detailed structure described immediately hereinabove and the more detailed steps of the method need not be followed precisely to fall within the scope of the present invention and, accordingly. the foregoing description is to be construed as purely exemplary and not in a limiting sense, and the actual scope of the invention is to be indicated only by reference to the appended claims.

lclaim: I 1. The method of removing radiation-absorptive material from a base which is relatively nonabsorptive of the radiation which comprises the steps of:

generating a short at such energy level and pulse in the order of milliseconds or less of substantially coherent radiation; and

directing such radiation against the absorptive material whereby energy is absorbed therein to effect a heating and removal thereof from the base, the base absorbing substantially a minimal amount of radiation whereby it remains substantially intact.

2. The method of removing radiation-absorptive material according to claim 1 wherein said radiation is directed as a beam against the absorptive material.

3. T e method of removing radiation-absorptive material according to claim 2 which comprises the additional step of focusing the beam so that a predetermined area is exposed to the radiation.

4. The method of removing radiation-absorptive material according to claim 1 which comprises the additional step of shielding the absorptive material so as to limit the area ex posed to radiation.

5. The method of removing radiation-absorptive material according to claim 1 wherein said radiation is generated at a selected frequency and power level and the absorptive material is vaporizable upon exposure to the radiation.

6. The method of removing radiation-absorptive material from a base which is relatively nonabsorptive of the radiation according to claim 1 wherein the relatively nonabsorptive base is composed of paper.

7. The method of moving radiation-absorptive material from a base which is relatively nonabsorptive of the radiation according to claim 1 wherein:

the nonabsorptive base constitutes material capable of receiving meaningful or decorative marks thereon: and the absorptive material takes the form of decorative or meaningful marks, such as a typewritten character.

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US3305666 *Aug 28, 1963Feb 21, 1967Zaromb SolomonMethods and apparatus for treating conductive surfaces
US3314073 *Oct 20, 1964Apr 11, 1967Prec Instr CompanyLaser recorder with vaporizable film
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US3720836 *Mar 12, 1971Mar 13, 1973Sigri Elektrographit GmbhProtection from laser radiation
US3786907 *Sep 22, 1971Jan 22, 1974Muncheryan HLaser eraser for a typewriter
US3832948 *Nov 4, 1970Sep 3, 1974Empire Newspaper SupplyRadiation method for making a surface in relief
US4078164 *Jan 9, 1976Mar 7, 1978Agence Nationale De Valorisation De La Recherche (Anvar)Process for the accomplishment of deep microengraving by a laser beam
US4188139 *May 6, 1977Feb 12, 1980Ing. C. Olivetti & C., S.P.A.Method and apparatus for correctably printing characters with sublimable ink
US4277669 *Jul 6, 1979Jul 7, 1981Hamamatsu T.V. Co, LtdMethod and device for detecting the threshold of generation of a laser beam
US4292092 *Jun 2, 1980Sep 29, 1981Rca CorporationLaser processing technique for fabricating series-connected and tandem junction series-connected solar cells into a solar battery
US4968371 *Jun 13, 1988Nov 6, 1990The Gillette CompanyMethod for removing a marking from a surface
US5282919 *Sep 21, 1990Feb 1, 1994The Gillette CompanyApparatus for removing a marking from a surface
DE2721490A1 *May 10, 1977Dec 1, 1977Olivetti & Co SpaVerfahren und vorrichtung zum loeschbaren drucken von zeichen
U.S. Classification219/121.69, 219/121.85, 400/696, 219/121.68
International ClassificationB43L19/00, B41J29/26, B41J29/28
Cooperative ClassificationB41J29/28, B43L19/0043
European ClassificationB43L19/00E, B41J29/28