CA1051504A

CA1051504A - Electrographic recording stylus

Info

Publication number: CA1051504A
Application number: CA222,098A
Authority: CA
Inventors: George G. Lunde
Original assignee: Minnesota Mining and Manufacturing Co
Current assignee: 3M Co
Priority date: 1974-04-08
Filing date: 1975-03-14
Publication date: 1979-03-27
Also published as: JPS5738899B2; US3879737A; IT1035210B; DE2515120C2; FR2266908A1; AU7988575A; DE2515120A1; FR2266908B1; GB1493101A; JPS50138835A

Abstract

ELECTROGRAPHIC RECORDING STYLUS
ABSTRACT
An improved electrographic recording stylus for electrographic recording systems includes a magnetic flux concentrating portion and a separate and distinct electrode portion connected to electronic circuitry furnishing voltage potential record pulses to the stylus for electronically charging toner that is in contact therewith.

Description

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EL~CTROGRAPHIC RECORDING STYLUS

The present invention relate~ in general to electrographic apparatus ror the recording of toner images on a recording medlum, and more specifically to a recordlng stylus that i5 employed in such apparatus.

A prior art recording system to which the present invention is related includes a cylindrical -developer roll with permanent magnet sectors and an array of magnetically permeable recordlng styli disposed on the developer roll~ The magnetic fields of the magnet sectors are concentrated in the recording styli~ thus, providing a relatively strong magnetic flux density at the outer ends of the styliO The styli are selectively pulsed with voltage potentials by dr~ve electronics to produce dot depositions of magnetic toner powder on a recording medium, which powder is presented to the recording medium by the developer roll~ There is a magnetic attractive .
force at the recording end of each stylus that is signi~icantly higher than the surrounding magnetic field;
consequently a dense concentration of powder at the outer :
end of each stylus results~ The net effect on the I quality of the recorded deposition is an increase of dot ~:l density and dot definition (resolution) wi~h relatively :!
. low recording voltagesO :

All of the prior art' styli constructions include the magnet~c portion of the stylus as an lntegral, , -:.

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electr~cally continuous portlon Or the electrode portlon,l.e., the magnetic portion provlde~ both the magnetlc control o~ the toner and the eleckrical control o~ the toner.

The present invention provldes an improved stylus constructlon that separates the magnetic stylus into two functionally separate constitutents that are inseparable as far as the recordin~ process is concerned~ The magnetic portion of the stylus does not contribute to the electrical current flow to the recording toner~ and the electrlcal portion of the stylus does not contribute to the magnetic control of the tonerO Thls approach gives startling simplicity to the construction of the styli array, and high quality in the recording process results.

The present invention resides in improved recording styli for electrographic recording systems havlng ~ recording electrode contacting one side of a ; recording medium, a developing means with a rotating inner magnet assembly, and an array of the recording styli spaced from said recording medium to de~ine a recording region therebetween. The improved styli each include a first portion in which the magnet assembly of the developing means induces a magnetic flux density and a second portion that is connected to electronic circuitry furnishing voltage potential record pulses to the styli ~or electronlcally charging toner powder bridglng the recording region to produce depositions o~ toner on the . mediumO

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According to -tlle present i.nvention there iS pro~ided in an elect.rographic recording system that lncludes a recordlng electrode electrically connected to one side of a recordi.ng medium, a toner developing means having an inner rotating magnet assembly and an outer shell, a plurality of recording styli fixed on the outer shell of said developing means and spaced from the opposite side of said recording medium to define a recording region therebetween that is bridged by toner powder transported on said developing means, and electronic circuitry for providing voltage potential record pulses to said styli, each recording stylus characterized by the features of: a magnetic portion having one end positioned radially outward from said ou-ter shell and formed of a magnetic material such that magnetic flux provided by the magnetic field ., of said inner magnet assembly is concentrated at the outer end of said :~ stylus to cause a concentration -thereat of said toner powder; and a non-.~ magnetic electrode portion positioned near said end of said magnetic portion and connected to said electronic circuitry in order that voltage potential record pulses may be applied to said electrode portion to electronically charge the toner powder bridging the recording region and produce deposition ~; ~
of said toner on said recording medium in accordance with applied record . 20 pulses.

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A plurallty of the improved styll may be fGrmed in a dense printin~ array by uslng a magnetically permeable crossbar positioned a~ially of the surface of the recording member to serve as the first portion of the styll, and overlying the crossbar are a plurality of spaced apart electrically conductive leads that serve as second portions of the styli. In a first preferred embodiment, the cross-bar is electrically nonconductive, and each electrically conductive lead together with the crossbar forms an lndividual stylus. To facilitate fabricatlon of the styli, flexible printed circuitry may be employed to pro-vide a plurality of conductive leads that are densely arranged in contact with the crossbar, and yet can be fanned out to standard connector spacing to readily ; 15 connect to the electronic circuitry that furnishes the voltage record pulses. The flexible printed circuitry is bonded on the developer roll in a smooth arrangement to provide relatively no obstruction to the flow of toner as it tumbles around the circumference of the tube.

In a second preferred embodlment, the conductive leads are insulated from the crossbar to prevent elec- -trical contact between the two portions of the styli.
Thus, the crossbar may be formed from a wide variety of magnetic materials including those that are electrically ~onductive, such as iron, without the danger of electrical shorting between ad~acent styli.

In both of the above described embodiments, the conductive leads are formed from a nonmagnetic material ' :

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wlth relatively little shunting e~fect on the magnetic field lnduced in the crossbar o;f the styli. The crossbar serves as a path of hlgh permeability for the magnetic ~lux llnes of ~orce emanating from the developing means magnet assemblyO As a result, a high magnetic gradient exists at the outer edge of the styli crossbar to provide a strong attractive force for toner presented at the recording region. The magnetic toner i8 attracted to the styli and is concentrated in the form of toner chains ; 10 that bridge between the recordin~ medium and the styli causing dense quantities of toner to be deposited on the recording medium when a record pulse is applied to the styli.

Two embodiments of the present inventlon are 15 described below with re~erence to the drawings, wherein: -igD 1 iS a diagrammatic side view of an electro-graphic recording system incorporating the pre~ent lnvention and including a toner powder reservoir, a developer roll, ;~
a recording member, and a pulse control circuit;

Flg. 2 is a fragmentary perspective view o~ the developer roll of Fig. 1 illustratlng an enlarged view of a first embodiment of a prlnting array disposed thereon;

Fig. 3 is an enlarged view of ~lexible circuitry that ~orms a portion of the printing array of Figo 2;

- 25 Figo 4 is an enlarged, fragmentary vlew of a second embodiment of the printlng array that mounts on the developer roll of Fig o l; '''-;' ~ ,': ':
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Fi.g. 5 ~s an enlarged, fragmentary view o~ a modified embvdiment of the prlntlng arra~ Or Fig. 4;

Fig. 6 is an enlarged, fragmentary view of another modified embodiment of the printing array of Fig. 4; and Fig. 7 ls an enlarged, ~ragmentary ~iew of yet another modified embodiment of the printing array of Fig. 4.

Referring now to Fig. 1 of the dra~ings, a schematic view is shown of a prior art eleckrographic recording system for which the present invention is part~cularly adapted to be used. This prior art system includes a toner powder reservoir 1, a cylindrical dev-eloper r~ll 2, a rotatable recording member 3, and a -pulse electronic c1rsuit 4.

The developer roll 2 preferably has an inner magnet rotor 5 and an outer cylindrical shell 6 that is "
~: electrically nonconductive and is nonmagnetic. The term "nonmagnetic" with reference to a material is used herein to mean that the material acts nearly the same as air or a vacuum in the presence c~ a magnetic field. A magnetic . , circuit ~field passing between North and South magnetic poles) is not affected by the introduction of the material, and the material itself is not magnetized due to the magnetic fleldO The term "magnetic material" ls herein used to mean a material that easily passes magnetic flux (has a high permeability to the magnetic field~ and there~
~ore has a high susceptibility to being magnetized by a ~ .
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ma~netic field. The magnet ro~or S includes a cylindrical, magnet ~upport core 7 and a plurality of magnet sectors ~
arranged about the cylindrical ~urface of the ~upport core 7I the sectors 8 defining an ouker surface of alternate North and South magnetic poles. The developer roll 2 is mounted on an axle 9 with the support core 7 preferably rotated in a clockwise direction, whereas the outer shell 6 is spaced from the magnet rotor 5 and is preferably fixed in position.

Arranged on a line that runs axially of the exterior surface of the shell 6 are a plurality of individual, spaced apart recording styli 10 (only one of which is shown in Fig~ 1~. The styli 10 are normally utilized to form a printing matrix and the number of styli 15 included in the matrix is dependent upon the printing ~-appllcation ~or which the matrix is to be used. In the case of a standard computer output line width Or 136, 5 x 7 dot matrix characters, nearly 1000 styli are employed. ~ :

The recording member 3 mounts an a~Ie 11 that is ~ 20 parallel to the developer roll axle 9, and is rotatably ; driven clockwise. The recordlng member 3 is preferably formed of an electronically conductive~ cylindrical electrode 12 and an endless recording medium 13 that over- `, lies the cylindrical surface of the electrode 12. The electrode 12 is positioned in a spaced, opposed relation-ship with the styli 10 to de~ine a recording region 14 ~ -,`~ therebetween. The electrode 12 also serves as a support ~. :
means for the recording medium 13~ which is preferably ~ ~
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formed from an anodized alumlnum.

The toner powder re~ervoir 1 is filled with a magnetically attractable) electronically conductlng toner powder 15. The reservoir 1 includes a doctor blade 16 for metering the toner 15 in an even layer onto the outer shell 6 of the developer roll Z0 The toner 15 i8 held on the perlphery o~ the outer shell 6 by the magnetic fields of the magnet sectors 8 and becomes arranged in the form o~ toner partlcle chains 17. The toner chains 17 are transported by the developer roll 2 to the recording region 140 While in the recording region 14 certain of the . ~ , toner chains 17 bridge between the recording medium 13 and the styli 10, and portions of the toner chains 17 in `~ sontact with the recording~medlum 13 are deposited thereon.

Deposition of portions of the toner chains 17 ~ :~
occur when recording ~oltage pulses of su~ficient magni~
~- tude are applied to various ones of the styli 10 by the `- electronic recording pulse circuit 4. The record pulses ~ produce a voltage potential be~ween the cylindrical elec-: ~ 20 trode 12 and the styli 10, which re ults in a force ;~ :
pattern of intelllgence that exerts a force on the portions -o~ the toner chains 17 contaQting the medium 13. Such force opposes and overcomes the magnetic attraction of the magnet sectors 8 for portions of the toner chains 17 ~ .
: 25 associated with the styli 10 to whlch the record pulses ~ ~;
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The constructlon of the styli 10 1~ uniquel~

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Referring now to Fig. 2, a Pirst preferred embodiment of the styli 10 of the present invention is shown forming a printing array 20 mounted on the developer roll 2, The printing array 20 includes a magnetically so~t ~:
crossbar 21 having one lengthwlse edge seated in a slot cut in the periphery of the developer roll outer shell 6, ~-and an opposite edge that protrudes radially outward from the periphery of the shell 6. The bar 21 is formed of a ; ma~net~c material that is substantially electrically non-conductive. Each lengthwise side o~ the bar 21 is shielded by an encapsulating materlal in the form of two wedge :
. shaped ramps 22, The bar 21 extends axlally of the ~ :
exterior surface of the outer shell 6 and a plurality of .
spaced apart nonmagnetic electrodes 23 are fixed on the ~;
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: 20 ramps 22 to extend acro~s and overlle the outer edge of : the bar 21. A relatively electrically nonconductive mat- :
erial ~orms the bar 21 so that the electrodes 23 are ~ : :
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electrically isolated from one another. Each electrode ;-~
23 together with the bar 21 defines one of the prlnting 25 styli lOo For purposes of clarity the electrodes 23 are::
shown considerably enlarged in ~he drawings, and normally ~ ;~
; over 100 electrodes per inch would be employed in the array 20~ The particular dlmensions of the styli 10 are ~ ~

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not crltical and may vary dependlng upon the recording application. However, it ha,s been ~ound that ror magnetically optlmum conditlons, the distance between the outer and lnner lengthwlse edges of the bar 21 should be ten tlmes greater than the distance between the ramps 22.

Sheets o~ ~lexible printed circuitry 24, as indicated by Fig. 3, are pre~erably used to provide the .~ plurality o~ electrodes 23 ~or the styli 10. The clr-cuitry 24 is well known in the electronic art and ls formed of a plurality of electrically conductive leads that are bound together by an electrically insulative material. One end of each sheet of the circuitry 24 is :. bonded to the bar 21 and the ramps 22 and the leads on the : 15 sheet provide electrodes 23 that are closely aligned togetherD The opposite end o~ the electrodes 23 of the sheets of circultry 24 are fanned out to furnish a . relatively wlde separation therebetween for making a suitable connection with the record pulse circuitry 4. By use o~ the flexible circuitry 24 the possibility of a short occurring between the electrodes 23 is signi~icantly dim-: inished in comparison to that presented by former styli constructions. .-The above described styli construction thus provides a two portion stylus including an electrically conducting portion and a magnetic portionO High quality .
recording of toner ~mages is provided by the styli 10 because the bar 21 provides a path o~ high magnetic ~ _ g :'. , la)5J~s~

permeab:llity ror the magrletic flux o~ each Or the magnet sectors 8, Accord:lngly, when a rnaKnet sector 8 is allgned wlth t~e bar 21 a narrow area Or high denslty magnetlc flux along the length of the bar 21 extends out from the outer edge of the bar 21 in a perpendicular relationship wlth the recording medium 13 and back to the magnet rotor 5. The quality of the images provided by the styli 10 is in part dependent upon the radial length and positionlng of the bar 21 for two reasons. Flrst, the closer the inner edge of the bar 21 is brought to the magnet rotor 5, the greater the magnetic flux density in the bar 21 due to a narrowing of the low permeability air gap between the bar 21 and rotor 5. Secondly, if the protrusion of the outer edge .~ of the bar 21 is increased, the differential between the . : .
flux extending from the outer edge of the bar 21 and the surroundlng flux field emanating from the magnet rotor 5 ~ -also increasesO The bar 21 furnishes a narrow planar ~-surface in the re~cording region 14 having a strong mag-netlzation for attracting and aligning the toner chains 17 ~ .
- 20 in the region 14. When the toner chains 17 approach the .~ :~
printing array 20, they are attracted to and concentrated ~ -at the outer end of the bar 21, whereas the areas on -~
either side of the bar 21 are substantially void of toner.
The electrodes 23 may be conductive along their entire length but the printing area of a given styli 10 ls .. ~ determined by the intersectlon of the electrode 23 for the : ..
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: given styli 10 and the magnetic lines of force extending ~ from the bar 21 ad~acent to the given styli 10. ~ :
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It i~ not essential to t,he present invention that the electrodes 23 are ln electrlcal contact with the bar 21 since the bar 21 functions only as a means o~ supplying a strong magnetlc ~ield to the electrodes 23. 'rhls is evidenced by a second embodiment of the present lnvention represented by printing styll 28~ as shown in Fig. 4, forming a printing array 29. The array 2g is similar to ; the array 20 in that .it includes a bar 30 formed of a magnetic material positioned on the shell 6 in the same manner as the bar 21, and is bordered on both lengthwise sldes by wedge shaped ramps 31. However, the array 29 differs ~rom the array 20 in that overlying and bonded to the exterior of the ramps 31 and the outer edge o~ the bar 30 is a flexible printed circuit that includes both an 15 electrically insulating support layer 32 and a copper layer . -etched to furnish an appropriate pattern of electrodes 34 that extend across the outer edge of the bar 30. Con-sequently, the bar 30 is electrically lnsulated ~rom the electrodes 34 by the layer 32) and as a result the bar 30 20 may be ~ormed from a material that is electrically con- ..
ducti~e, such as ironO Cover sheets 35 Or lnsulative material~ as shown in Fig. 5, may be bonded to the ramp surfaces of the elec~rodes 34 to provide a smoother surface for the toner chains to flow over~ but such sheets are merely a matter o~ preference.

; The above described embodiments are not exhaust1ve in describing the present invention for a number of ~ -.
variations of the above.embodiments would readily be

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perceived to ~all with1n the inventive spirit of the present lnvention~ For example, referring now to Fig. 6, in which a modifled form of the second embodimenk i5 illustrated, it may be seen that lt is not essential to s 5 the present invention that the electrodes 34 bridge across the outer edge of the bar 30. Instead the bridging portlon of the electrodes 34 and the end portlon of the cover : sheet 35, if Dresent, may be removed to leave only end portions 36 of the electrodes 34 exposed. Also, as shown 10 ln Fig~ 7, the portion of the insulating layer 32 covering the outer end of the bar 30 may be ground away to expose the outer ~nd of the bar 30 An advantage of this latter -~
configuratlon is that the bar 30 can be electrically grounded when desired to aid in erasing previously 15 recorded material on the recording medium 13u Other variations of the present invention may : :
:: include shaping of the hars 21, 30 to change the shape : ; -. of the magnetic field near the exposed ends of the - :
electrodes 23, 340 The bars 21, 30 can also have slots cut 20 to form teeth whlch are each located directly under the ~ exposed ends of the electrodes 2~, 340 Moreover, the top : of the bars 21, 30 can be cut at an angle to form a ; ~ ~
~ sharp edge which is located in a llne under the exposed - ~ .
: ends of the electrodes 23, 340 Either of these modifi~a- :
, 25 tions tends to increase the strength o~ the magnetic ; field at the exposed portion o~ the electrodes 23, 34, but also make construction of the styli arrays 20, 29 -:
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Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. In an electrographic recording system that includes a recording electrode electrically connected to one side of a recording medium, a toner developing means having an inner rotating magnet assembly and an outer shell, a plurality of recording styli fixed on the outer shell of said developing means and spaced from the opposite side of said recording medium to define a recording region therebetween that is bridged by toner powder transported on said developing means, and electronic circuitry for providing voltage potential record pulses to said styli, each recording stylus characterized by the features of:
a magnetic portion having one end positioned radially outward from said outer shell and formed of a magnetic material such that magnetic flux provided by the magnetic field of said inner magnet assembly is con-centrated at the outer end of said stylus to cause a concentration thereat of said toner powder; and a nonmagnetic electrode portion positioned near said end of said magnetic portion and connected to said electronic circuitry in order that voltage potential record pulses may be applied to said electrode portion to electronically charge the toner powder bridging the recording region and produce deposition of said toner on said recording medium in accordance with applied record pulses.

2. In a recording system as recited in claim 1 wherein the magnetic portion of each of said recording styli is formed from an electrically nonconductive material and said electrode portion of each of said styli overlies and is in physical contact with said magnetic portion.

3. In a recording system as recited in claim 1 wherein the magnetic portion of each of said styli is electrically insulated from said electrode portion.

4. In a recording system as recited in claim 3 wherein said magnetic portion is electrically conductive.

5. In a recording system as recited in claim 1 wherein an electrically insulating layer overlies the end of said magnetic portion and said electrode portion overlies said insulative layer.