DE2119715C3 - Electrophotographic device - Google Patents

Description

60

The invention relates to an electrophotographic device for imagewise charging an insulating recording material with a corona charging device which generates an ion flow directed against the recording material arranged on a counter electrode and a photoconductive control device for the core and a photoconductive control device arranged in the ion flow
night of discharge *

lattice and mt ^c ^ ^m ^ Z ₇ lT

Charge and recharge

clear the first control grid sow.> With

tiaiquelle for creating selectable potentials.

both control bars MpnKrhe Off

^^ "SsSÄÄ ^ ntMedt beton legend 1522 5» -) sino £ _{.. During the}

Control grid against the earth potential during the

Generating a charge image ^f ^ £ ^{Auze the} clot material selected to ^d * GraduJ the "°" el · ek ß trical field between the * '* ^α ™ euergitlern in

the exposed areas of ^the / ^u ^ ™ ^ ^s * " _t ^:""" gi «er generated image against the e.neSteuerg.tter and

is directed towards the other control grid in the unexposed areas. Here, the! '''Before utilizes the fact that the photo eitfah.ge., U. ^ Ud, "u S.euergitters after b.ldmaß.gcn Bel.chtung," iikn exposed image areas less Utxrt. charge than in the unexposed B, ldb, ruUu.n aul shows. The potential resulting from the sum of the potential of the surface charge and the potential of the core at the first control grid is different in the exposed areas than in the undefined areas, which is used to generate field gradients of opposite cooling in m di, sm areas . The opposite direction of the field gradients in the exposed and unpopular areas has the consequence that the ions of the ion stream hitting the external control device can only pass through the first control grid in those areas in which the K gradient is against the first control grid and thus is also directed against the cue counter electrode. In the other tseruclien the ions are slowed down and led back to the wide control grid, where their charge is re-iralized.

Since the charge image on the pnotoleittanigen Layer of the first piece through the against the Ion current directed towards the counter electrode does not veranda there is the possibility of following the pictorial Exposing the first control grid a larger one Number of copies of this charge image to be made without the first control grid in between Recharge evenly again and then picture-wise having to expose. As a result of the irreversible dark current, however, occurs both in the exposed as well as in the exposed areas on a charge loss, which leads to the in the a directional field gradient is always smaller and then even reverse their direction. The consequence of this phenomenon is. that the contrast of the BiI-Jc, which can be generated on the recording material - always becomes less. This contrast is based on the fact that in the one image areas the Ions pass through the first control valid can and are prevented from passing through in the other areas. But if now the one field gradient becomes increasingly smaller, then the associated image area more and more blocks the passage of the Ions, in case it was originally the passage of the ions has allowed, or he allows more and more ions to pass if he has previously blocked the ion passage has. Since in the other field gradient

th assigned image areas with regard to the relationship between the size of the dark current and the If the ion enclosure does not change anything, the difference in polarity between the surface of the photo-fogging in the exposed and unexposed conductive layer and the core of the first control area approach each other, which means that a reduction in contrast is irrelevant and therefore does not need to be known means. To be 5.

Although Ks is possible, this reduction in contrast counteract this by applying the potential counter electrode to the core via a capacitor at least one of the two control grids changes in such a way, the first control grid is coupled because this that the originally existing field gradients in with simple means the change of the potential their direction and as far as possible also in their io of the core of the first control grid directly Size can be maintained, which is at least as possible due to the change in the potential of the counter-sound as it is possible through the pictorial trade. This capacitor needs initially exposure of the first control grid generated under- only to be charged so far that between the differ in the surface charge of the photoconductive core of the first control grid and the counter electrode gen layer are present. But since the size of the 15 the desired potential difference is present. Surface charge of the first control grid after the changes the potential of the counter electrode, imagewise exposure is not known and then the potential of the core of the first control charge depletion is not linear, a grid is also automatically to the same extent and in which the experienced operator is not able to change direction without changing

Try the potentials of the control grids in the correct 20 The contrast of an image is in a certain Lm-

To change dimensions. But experiments mean long also of the saturation of the charge of the AuI-

usable copies and are dependent on this drawing material and can in this respect

Reason as well as because of the required period of time can be influenced by the period of time

sore annoying. the recording material of which the ion sirom

The invention is based on the object that a 25 is exposed. When a certain saturation of the electrophotographic device of the aforementioned charging of the recording material achieved Type so that the contrast of the should, it is therefore necessary to reduce the time a charge image of the erUen Steiiergitteis produced during which the recording material dem th copies is automatically kept constant. This ioneiistrom is exposed to the strength of the ion task is solved according to the invention by adjusting a control current. One such is important circuit in which the potential source to apply adjustment especially when through the geder Selectable voltage with the second selected setting of the current stabilizer Sieuergiüer turned away pole over a current con- strength of the! Onenstromes exceeds the normal value Sheath holder is placed on the counter electrode. the. down or not reached. This customization is simpler in itself depending on the charging of the record- 35 possible by taking the integral from voltage mutcrials set in the counter electrode that act on the recording material Potential, the potential of the core of the first control ion current over time, forms the integration grid sets to such a value that the walk with one of the desired saturation correspond-sum compares the potentials of the core and the surface hurrying reference value and if they match photoconductive layer on the after the formation of the integration value with this reference value moderate exposure reached the original value, a further charge of the recording material will. prevents, for example, by switching off the

That can be effected between the counter-electrode and the corona decoating device to be applied to it,

Ordered pole of the potential source lying current, however, it is more advantageous if one. like this at

Constant keeper has the effect that the potential of the counter-45 of a preferred embodiment is the case. the

e ¹ Au ode only remains constant as long as the initial control circuit assigns a control circuit that turns off

lent contrast is present, i.e. the ions through a one at the counter electrode through the bic

the first control grid unimpeded in those Moderate charging caused magnitude of the potential

pass range in which they pass over time integrating integrator and a

should, and in the other areas at passage 50 there is a comparator that has an adjustable setpoint

be prevented. If, on the other hand, the consonance with the integration result compares and with one

traces and thus also ions enter through the specific value of the integration result

Areas of the first control grid, which generates the through control signal, based on it by means of a

occurs block .sholl, or animal ionensirom in the switch of the control circuit between the counter electrode

other areas more and more throttled, then 55 and the grid is interrupted. This can

the potential of the counter-electrode changes accordingly except for the termination of the charging of the

according to the enlargement or reduction of the recording material upon reaching the correct

Recording material acting on the ion-current desired saturation an under- or over-

sneeze. If one changes the potential of the core of the first sation of the load loss on the photoconductive

Control grid to the appropriate extent, then 60 layer of the first control grid can be removed as a result of an unsuitable

the sum of the potentials of the core from the above setting of the current stabilizer prevents

area of the photoconductive layer on which to be.

imagewise exposure reached origin. The following is the invention on the basis of two

keep. However, this means that the regulating system shown in the drawing

keeps the contrast at a constant value as long as 65 explains in detail,

shows the pictorial distribution of the charge on the ΟΙκι- Ls

area of the first control grid is available. Since the (- "fig. 1 is a schematically and in perspective

Regulation takes place automatically, the compiled view plays an initial stage.

Fit:. 2 the circuit of the first embodiment,

Fi μ. 3 shows the circuit of a second exemplary embodiment.

Iiin electrophotographic (ieriit has, as Γ i p. I shows, a counter electrode 1 in the form of a flat plate, which serves as a base for a sheet-like, insulating recording material, which is to be charged imagewise with the aid of the device. In series with the counter electrode 1, a current stabilizer 3 is connected, which can be, for example, an illuminated vacuum photodiode, solid-state current diodes, a vacuum pump or a high-voltage transistor. A corona discharge device 4 of known design is used to generate an ion current and can for this purpose by means of a switch. ^ can be connected to one pole of a potential source, which consists of two series-connected partial sources A and R. The second pole of the potential source is connected to earth potential and to the current stabilizer 3, so that the latter is between the counter electrode and the pole assigned to it Potential source lies, at the same time a About is also grounded.

Between the corona discharge device 4 and of the counter electrode 1 is a photolcitic control device for the image-wise differentiation of the arranged against the counter electrode directed ion stream. This control device has a first Control grid 6 with an electrically conductive core coated with a photoconductive layer and at a distance from this first control grid on the one facing the corona discharge device 4 Side a second Stcucrgitter S on. that is electrically conductive. The core of the first control grille 6 and that second control grid 5, which are arranged parallel to one another and to the counter electrode 1 in a known manner are, consist in the Ausfühningsbeispicl from each other parallel wires, but could also consist of a wire mesh, for example.

The second control grid 5 is electrically conductively connected to the connection between the two Tcilquellen Λ and B of the potential source and is therefore at a potential which is lower than the potential of the corona discharge device. The core of the first controller 6 is via a capacitor? connected to the counter electrode 1.

To produce a charge image on the recording material 2 with the aid of this device First the corona discharge device 4 is switched on by closing the sounder S. It is located the recording material 2 is not yet on the counter electrode 1. The one in the exemplary embodiment Corona discharge device 4 outgoing and at a negative potential If the counterelectrode 1 is directed toward the ion stream, it causes a uniform negative charging of the first control grid 6, as it relates to its photolcilable Layer the negative charges accumulate. The extent of this charge can be determined by the duration the charge time and in particular by the potential of the second control grid 5 are determined because the charging is automatically terminated when the potential difference between the surface charge and the conductive core equal to the potential difference has become between this and the second grille. With the commonly used materials for the photoconductive layer and its usual thickness, it is expedient to use the photoconductive layer Material to a voltage of 300VoIt against ki to charge the core. The charging process is ended by opening the switch .S '.

Now, by charging the capacitor 7, the required pole difference / / between the Core of the first control grid 6 and the counter electrode 1 produced, Ciiile results can be with

> o Achieve a potential difference of 200 volts. This The capacitor 7 maintains voltage.

The radiation pattern. with which the first control grid 6 is exposed imagewise, with the help of the Original generated from which made one or more copies by means of the elctrophotographic device should be. The image-wise exposure increases the surface charge of the first control grating 6 in the exposed areas to about 250 volts compared to the core and in the unexposed areas

a «ranges to about 280 volts from the core reduced.

After the imagewise exposure of the first control grating 6, the recording material 2 is on the counter electrode 1 and the corona detector

* 5 charge device: 4 switched on again. Further potentials of the core of the first control grid 6 and of the second control grid 5 are now chosen so that in those areas of the first control grid 6 in which the corona discharge device conimcndcn Ions are to pass through, a field gradient is present. that of the second control grid 5 against the first control grid 6 is directed. and in those areas in which no ions pass through should, the Fcldgradient from the first control grid 6 to the second control grid 5 is implemented. Should he Ion penetration in the unexposed areas of the first control grid should be possible, so in the positive-positive process are copied, then the above-mentioned steps can be copied with the above given values for the potentials of the surface charge in the exposed and unexposed Areas, for example by a potential of - 1770 volts against earth at the core of the first

Control grid and a potential of 1500 volts relative to earth at the second control grid can be achieved. In the exposed areas of the first control grating the surface of the photoconductive layer then has a potential with respect to earth that equal to the sum of the potential differences between the conductive core and earth and / between the Surface of the photoconductive layer and the core is. For the values mentioned, this is Total ί 1520 VoH. For the negative ions there is therefore a voltage gradient from the first control grid to the second control grid cr5. .vas causes that the clays arriving in the exposed areas of the Stcuergitter 1 braked and to the second Control grid 5 are deflected towards where a charge equalization takes place. In the unexposed areas cr- gives the sum of the voltages of the core with respect to earth and the surface of the photoconductive layer compared to the core the value of -f- 1470 volts with respect to earth at the aforementioned potentials. The gradient of the field between the two Stcuergittcrn 6 and 5 is therefore in the unexposed Regions for the negative ions directed from the second control grid to the first control grid, which is why in these areas the ions are the first

Can pass through tax unhindered .md therefore on the record *,! ,, eruil 2 a .HutUn

The first control element 6 thus modulates in cooperation with the / broad struc- ture validity Ionization directed towards the counter electrode 1 bildäßäßip- whereby on the ^ Mchnun ^ ma cru.1 a positive electrostatic image cnMchl. d.is in can be developed in the usual way.

Since the ionstmm in the production of the Lk un _; If the image on the recording material does not change the charge image existing on the first screen grid 6, further copies can be made of this image. The corona discharge device only needs to be activated after the charging of the An f / c, ch nu V material and the change of the recording material. ,

Usually a new l · · '»^ ¹¹ ""-. ^The current stabilizer is not ordered on every new HiIH aiii iun. soleincie Xj

lay a line image and not a halftone message .st. If, however, the current of the current constant can be set exactly, then a standard is first set and developed. Is, the copy / u heUd nn the setting of the Stromkoiistanthaltus c Ui is changed in going so that the recording mr.tu al χ η a stronger ion flow is applied. A copy that is too dark can be reduced by reducing the ion stream. that reaches the recording material is reduced. / * "* Necessarily the f.instcllungmiler xv us,.

der Bildur.tcrgrund just about v.mi toner rrc.bk bt

The RL / mfliissiiiig of the copies through the Sl ο constanlhallcr is conditioned by the fact that c VM Uiesu r.röBc of the current which drains xon (L, Ulli η trodc and the condenser? Or /.mitsem flows there. But since the K.Midensatm 7 if the table cannot discharge, the Sm m, stanthaitcr determines the current of the counter-electrode and dm also the guanin-

dcn ion stream. ., " _{R / lMll} ,

Soiern from the cr u-th on the first control grid Picture a larger number of copies, according to should be, the loss of charges is evident

the surface of the photoconductive layer d. first control means 6 noticeable as a result of a dark adu. This charge vowel became. ^ 1 ^ \ the capacitor? and the control circuit having the current stabilizer would not be present / lead to a reduction in contrast. NVcnn nam h in the example given above, the potential difference of the surface charge compared to the J

of the first structural grid reduced by 30 volts, for example, as a result of an ^ ^unk ^ ^nt ^, then if the control circuit was not available ^ ard. The potential on the surface of the hot oil ^ ' ¹ ^ "^' ^ _ compared to earth from ■ 1520 volts to - 1490 \ ol did decrease. This would, however, mean that cm degrees between the two control grids cnts eh ν. Ά, R xom the second step 5 to the first stcue, fM6h η g is directed. what ^ bcdcutct. that now also * e bclu.hu.un areas of the ion stream were allowed to pass through unhindered. Since the first charge sense occurs gradually, the contrast would all but decrease. Fine before the con astx r reduction is, however, as long as the picture on the first step still has a sufficient contrast.

s | ^ _{n; iml | ch} ^ ,, _{r allf the} recording

_§ ■, _c | _at " _cn dc ion flow ncncn via the iir-

.au ·, μ m. Slrom constantlial

' ¹ ^' ,, ^ \ ' _ru ,,, _Bcllc , "ncnstrom however there-

/u.^ ^ ^^; _{| uni} , ₍ , _L , _{S Kcnls dcs} first tax

«!, Fen 6 by means of the capacitor 7 to the counter ^, j, _{iljcuhirdl; mi} . |, The core of the control, o ^ ¹¹ ^ X ,. _n , _{scl A} “Low potential, only. _Vcimi , _ulcl , _m ,, _d "Po.enlialdifferenz. / w, -surface of the photoconductive layer ^ control circuit ensures that

and dm K ^. _{/ know} the two

-5 η [; _{(p vk} . _{h auc] l bci L. incm} i. _a di, ngsxcrlust der

' _{] lolol;. iinihjl} , _cl1 Schiel)! Don `t change.

_{[> 1S in} j. i ". ;, dameslellt / while aiisführung bei

, _{icl im} , _crs abandons the execution

■ - ';, """"; _mi , _u . | _s whose it is possible the ^ "i ,,,,. ^ _d er Aiifladinm des Auf / eichni.ngsmatenals. . ^^ j, _bcilf . _IIK influences the contrast, adjusting it to a desired value. This is done by - ^ ScucrunB the period of time during which the

_{/ cichnim} ^ _mi iterially exposed to the stream of ions νιι

■ _]; . _ί , ^. ^ _{wcJM t) ic} economy circuit a _{,, 1ο} , _ιηι! £. _{η Vc} rMarker 9 on. whose outgoing to the V ₀₁₁₁ J _111111,; ,, _{/ w} j _sC hen the capacitor 7 and the ^Λ stromkonsianthalicr 3 is connected. The exit ■ \ -,., Miukers9 is with the entrance of a

^ _rcn network 10 connected. On the off Neuwerkes 10 of the entrance is a Stiiiiri _ar 5 | ntearaiors connected 11 whose output ■ ^ • ■ '^ ^ ^^ ", ^ nosgioCe for a comparator... ^^ ^ ^. ^ _{,: ini} , _{angsgriißc for} the compa- ^ ^ ^ _S o \ hsvr \ . which can be specified with a _contrast setting, nnchum> i 13. '■ _{A (} ^. _Mi , the _{comparator 12} is then other-

. ^^ _ ^ ^ . _Ult Vrdpotential relay 14 connected- " _C connected. whose working contacts 15 in the Vcr- -J _{n Umos} , _{eitlin> 1} mix the counter electrode 1 and _L : _rb indu.igs _P uncl between the current constant, - ^^ _{K (indemalor7 lind dcm} , .., "gang des

_{Vcrs! Arkcrs 9} ,, et.

^ _{Copy process} . _a ] _{so m the} beginning

_uc , "i ade'vorcancs des Auf / cielinungsmaterials is the " ^ ^^ integrator 11. which the am

. ^ ■. _{Amplifier 9 licgcndc} voltage across

_imcericrt . _what a measure of dc on the Auf-J ^tr _hmmesm ^ _{lcrial gclanglc} charge, st equal to zero. ^^ ^, dcVcrscu. the desired value by means of the contrast, euercinrichu.n 13 which is, m Ausfuhrungs _b ^ _ic, is tiomeler _{to cin Polcn,} predetermined, st. 5- P _{Aliscancspr of} the comparator first of ^ ₁₁ ,, _vcrsc h, ed _C n. The relay 14 is therefore ^ energized _χ _ kept closed. The coping and ev entual control process are running there «, ^ _wdsc ^ ^ _{dcm Ausfunrimg} s-

at η ^^^^^^^ _{charge dcs A} ufze, ehnungsma e-

■ Output variable of the integrator 11

"M ^^^ _{f Q} ^ _{Ni hlI} - _{canlal of} the first

_{M raiucrs6} taken into account, which determines the ion _{current to be measured min2srnatt: ria} , _mc . Ha ^ _{Auscanc s} size of the integrator 11 the size of the - ^^ ^ _{n is the} output size of the

Comparator? " 12 to zero, \ v; is a dropout of the relay 14 and thus an opening of the switch 15 result has. As a result of the very curdling capacity which the rear Hlcktrodc I opposite F-rde has rises the potential of the counter-electrode 1, which is now separated from the rest of the circuit, increases very quickly to one high value so that no further charges

10

get more on Has recording material. The amount of charge still reaching the recording material after opening the switch 15 is negligibly small in comparison to the amount of charge already present, so that it practically does not change the charge image on the recording material.

1 sheet of drawings

t-.v

Claims (3)

image-like differentiation of the lone "«. tfomes m » 1. Electrophotographic device for imagewise charging an insulating recording material with a corona discharge device which generates an ion current directed against the recording material arranged on a Gcgenelectrode and a photoconductive control device arranged in the ion current for the imagewise differentiation of the ion current with a first control grid made of an electrically conductive, with a photoconductive layer coated core and a second control grid arranged between this and the corona discharge device and with a device for uniform charging and a device for image-wise exposure of the first control grid and with a potential source for reading selectable poles at the two control lines, characterized by a control circuit the potential source (A, B) "for applying the selectable voltage with the pole facing away from the second sleuer grid (5) via a current constant -, 5 holder (3) is placed on the counter electrode (1) and the. depending on the charge of the recording material (2) i :; the counter electrode (1) set potential, the potential of the core of the first control grid (6) is set to such a value. that the sum of the potentials of the core and the surface of the photoconductive layer is painted on the origins reached after the imagewise exposure. 2. Electrophotographic. 5 device according to claim I, characterized in that the counter electrode (!) is coupled to the core of the first control element (6) via a fine capacitor (7). 3. Electrophotographic apparatus according to claim 1, characterized in that for optional Setting a specific contrast (saturation of the charge of the recording material) a control tower (9 to 15) is assigned to the control circuit? the one from one at the counter electrode (1) caused by the imagewise charge size of the potential over the The time integrator (11) and a comparator (12) are adjustable The setpoint value is compared with the integration result and, if a certain value is reached, the integration result generate a control signal based on dcsscn by means of a switch (15) of the control circuit is interrupted between the counter electrode (I) and the first control grid (6). 55