DE4036975C2 - Electrophotographic or electrostatic printing or copying machine - Google Patents

Description

The invention relates to an electrophotographic or electrostatic printing or copier according to claim 1.

From JP 60-191958 a printing device is known in the transport rollers for Apply application to transport paper sheets through the printing device. In this known printing device discharge brushes are used, which are arranged on a sheet outlet, said discharge brushes primarily touching a common rotary shaft on which the transport rollers are arranged at an axial distance from each other. Touch the discharge brushes but also a paper sheet, which by the mentioned transport rollers is transported. However, in each case with this known construction transported leaf is also touched at surface areas by the discharge brushes, which have not been brought into contact with the transport rollers so that especially if the known printing device with high paper transport speeds operated, a negative charge on the respective Paper sheet can form strip-shaped.

From JP 59-113472 a sheet removal mechanism is known which consists of a single take-off roll and a friction pad is. Downstream of  The sheet withdrawal area can be arranged a discharge brush, the very can be designed differently and can also be arranged differently. In one embodiment of this known construction, the width correspond to the previous take-off roll in about the width of a discharge brush. However, in this known sheet withdrawal mechanism and Sheet transport mechanism no higher sheet transport speed realized.

The object underlying the invention is an electrophotographic or to provide electrostatic printing or copying apparatus, which can be operated at high sheet transport speeds without thereby unevenly distributed charges on the transported paper sheets can arise and thus the security of the paper transport is increased.

This object is achieved by the in the characterizing part of Claim 1 listed features solved.

The present invention is based on the finding that the problem of charging of paper sheets with increasing sheet transport speeds increases. Extensive research has shown that the phenomenon of Charging the transported paper sheets very pronounced from the speed depends on which the contact between two touching Objects (eg a sheet transport roll on one side and a paper sheet on the other side) is solved. In other words, the charge becomes a sheet of paper the more pronounced and uneven the faster the separation between the paper sheet and the relevant transport roller takes place.

Particularly advantageous embodiments and refinements of the invention result from the dependent claims.

In the following the invention will be described with reference to exemplary embodiments explained in detail on the drawing. It shows  

Fig. 1 is a side view showing an entire structure of an electrophotographic copying machine in which a paper conveying apparatus having features of the invention is applicable;

Fig. 2 is a partial side view of an end portion of a transport path defined in the copier of Fig. 1;

Fig. 3 is a perspective view of a Lagebezie hung between transport rollers and unloading brushes, which are shown in Figure 2;

Fig. 4 in section enlarges a front view of a part of a brush holding unit;

Fig. 5 is a sectional side view of the Bürstenhalteein unit of Fig. 4;

Fig. 6 is a sectional view of an experimental arrangement for determining whether a paper sheet has been loaded or not;

Fig. 7 is a side view of an experimental arrangement for measuring the amount of charge applied to a paper sheet and

Fig. 8 is a side view of an arrangement to experimentally tell a relationship between the position of the discharge brush and the amount of charge applied to a paper sheet.

In Fig. 1, an electrophotographic copying apparatus is Darge provides, which ge belongs to the family of recording devices and in which the invention can be applied. The copier has a housing 1 , a glass plate 3 , an automatic document feeding unit (ADF) 4 , which is disposed above the glass plate 3 to convey a document 2 to the glass plate 3 . Optical devices 9 are arranged under the glass plate 2 to focus a light image constituting the original 2 on a photoconductive member 10 which is implemented as a movable endless belt. The optical units 9 have a lamp 5 for illuminating the original 2 , mirrors 6 and 7 and a lens arrangement 8 . A loader 11 , a developing unit 12 , a transfer unit 13 and a cleaning unit 14 are arranged around the belt 10 around. A copy tray 15 , an additional tray 17 and a number of Papierzuführabschnitte 19 are arranged in the housing 1 and in this order from the upper side in the direction of the bottom of the housing 1 . The addi tional tray 17 is disposed opposite the upper end of a Förderban 16 .

The paper feed sections 19 each have a feed roller 18 . A transport path 21 connects the Papierzuführab sections 19 with a paper outlet 20 which is formed by a side wall of the housing 1 . A fixing unit 22 is arranged on the transport path 21 . A Zuführab cut 23 for large-sized paper is associated with the copier and has the same function as the Papierzuführabschnit te 19th A finishing unit 24 is also associated with the pierier and has, for example, a stapler 26 . Paper sheets or copies, which are successively discharged from the housing 1 through the outlet 20 are stapled by means of the stapler 26 and then discharged onto a tray 25 .

As shown in Fig. 2, a selector unit in the form of a pivotable jaw 28 on the transport path 21 (seen in the transport direction) is arranged after the fixing unit 22 to selectively guide sheets of paper over a transport path 27 in the direction of the additional tray 17 . Another selection unit or a pivotable claw 30 is net angeord near the end of the paper transport path 21 . The selecting unit 30 selectively directs sheets of paper in the direction of the copy tray 15 via an arcuate trans port 29 or in the direction of the paper outlet 20th A number of transport roller assemblies with respective transport rollers 31 are successively arranged on the transport paths 21 , 27 and 29 after the fixing unit 22 . More specifically, as shown in Fig. 3, the transport rollers 31 of each arrangement are positioned at respective intervals from each other across the width of a paper sheet 32 .

As shown in Fig. 2, Entladebürsten arrangements, each having Entladebürsten segments 34 , in the transport direction behind the transport roller assembly 31 , which is adjacent to the outlet to the additional tray 17 , behind the selector 30 and behind the transport rollers -Anordnung 31 , which is the outlet to the copy tray 15 adjacent, arranged and fixed so that the brush segments 34, the paper sheet 32 touch. The discharge brushes 34 are each made of stainless steel, carbon, conductive synthetic resin or the like conductive material. As shown in Figs. 4 and 5, the Entladebürsten segments 34 are each Anord tion firmly held on an approximately U-shaped holding part 35 , which is made of metal and grounded. As shown in Fig. 3, the Entladebürsten segments 34 are arranged substantially over the same length as the axial length of the associated transport rollers 31 , so that the brush segments 34 come into contact only with those parts 32 a of the paper sheet 32 , with which also the rollers 31 come into contact. The holding part 35 is electrically connected to the base plate or a ähnli Chen component of the copier.

During operation, the charger 11 charges the photoconductive belt 10 . Via the optical units 9 , a template 2 placed on the glass plate 3 is illuminated and the image reflected from the front 2 is focused onto the charged surface of the tape 10 . Consequently, a latent electrostatic image of the original 2 is formed on the belt 10 . The developing unit 12 develops the latent image so as to form a toner image. The Übertragungssein unit 13 transmits the toner image from the tape 10 to the paper sheet 32 , which has been supplied from one of the Papierzuführabschnitte 19 via the transport path 21 . By means of the fixing unit 22 , the toner image is then fixed on the paper sheet 32 . The paper sheet 32 with the fixed toner image is then transported along the web 21 depending on the Stel settings of the dials 28 and 30 either to the addi tional tray 17 , the copy tray 15 or the Endverarbei processing unit 24 .

In general, the paper sheet 32 is electrostatically charged during transport, as stated above. A number of attempts have been made by the Applicant to determine and determine the cause of the application of a charge on the paper sheet 32 , as described below.

As shown in Fig. 6, a copier was used without the discharge brush 34 for a first try and see near the end of the transport path 21 with an aluminum plate 38 ver to see whether the plate 38 draws the paper sheet 32, ie, whether the Paper sheet 32 has been loaded. The test was carried out under the following different conditions and conditions:

A: A fresh paper sheet 32 has been transported which has not been subjected to image transfer or fixation;

B: A paper sheet 32 , which has been subjected to image transfer and fixation, was transported;

C: A paper sheet 32 was transported within 10 minutes after fixation.

D: Each side of the fresh paper sheet 32 which has not undergone image transfer or fixation was dried by a dryer for 2 minutes, and then the dried paper sheet 32 was further transported.

E: Slits 39 ( Fig. 3) were formed in parallel on opposite ends of the individual transport rollers 2 on a paper sheet 32 , and the paper sheet 32 subjected to image transfer and fixation was trans ported.

The result of the first attempt is in the following Table 1:

requirement Result A not dressed B dressed C not dressed D dressed e Only parts that came in contact with rollers were put on

As shown in Table 1, the transport rollers 31 frictionally load a part of the paper sheet 32 which has undergone fixing, and the paper sheet 32 dried by a dryer.

As shown in Fig. 7, in a second experiment, all the aluminum plates 40 and 41 were arranged at the outlet 20 of the conveying path 21 so as to face each other and pass through the paper sheet 32 therebetween. Another aluminum plate 42 was net angeord under the aluminum plate 41 and grounded. An electrometer 43 and a recording device 44 were connected to the aluminum plate 41 . A charging brush assembly 34 was disposed on the transport path 21 (in the transporting direction) after a transport roller assembly 31 adjacent to the outlet 20 and connected to the holding member 35 and a switch 45 connected to ground. A paper sheet 32 having undergone image transfer and fixing was conveyed out through the outlet 20 , and the loading potential of the paper sheet 32 was measured by means of the electrometer 43 . The result is shown in Table 2 below. In Table 2, A is a state in which the switch 45 was opened so that the brushes 34 were floating, and B was a state in which the switch 45 was closed, thereby grounding the brushes 34 .

State charge A | 180V B 60V

As shown in Table 2, the brushes 34 discharge the paper 32 more strongly when grounded than when they are not grounded.

As shown in Fig. 8, in a third experiment, the aluminum plate 41 which has been connected to the electrometer 43 and a recorder 44 and the aluminum plate 42 which is grounded, were arranged after the outlet 20 and at a predetermined distance from each other. Grounded discharge brush assemblies have been placed at particular locations P1 to P5 (viewed in the direction of transport) after individual transport rollers 31 . The amount of charge applied to the paper sheet 32 was measured by means of the electric meter 43 . Here, a smaller amount of charge means a larger discharge effect. The experiment was carried out, wherein the number and the combination of unloading brush arrangements that is changed at positions P1 to P6. The Entladebürsten arrangements were each arranged so that they touch the entire surface of the paper sheet 32 . The result of this experiment is shown in Table 3 below.

Number and position of a brush arrangement charge 0 60-150V 1, positions P1~P5 60-150V 1, position P6 -20 V 2, arbitrarily combined positions 40~140V 3, arbitrarily combined positions 20-120V 4, arbitrarily combined positions -30 ~ -20 V 5, arbitrarily combined positions -60 ~ -30 V 6, positions P1~P6 -20 V

As shown in Table 3, although the charge amount decreases, that is, the discharge efficiency increases with the increase in the number of discharge brush assemblies, an excessively large number of discharge brush assemblies load the paper sheet 32 negatively. The paper sheet 32 was reloaded by the transport roller assemblies even when unloaded (seen in the direction of transport) at the positions in front of the roller assemblies, ie the result was slightly better than in the case where the discharge brushes were not were used. Consequently, the unloading brush assembly (as viewed in the direction of transport) must be located adjacent the end of the transport path at a location subsequent to the transfer roller assembly.

Regarding the brush assembly, which is arranged in the position P6, the negative charge applied to the paper sheet 32 is largely attributable to the fact that the brushes which contact the whole surface of the paper sheet negatively load the parts of the paper sheet 32 which have not been loaded by the transport rollers 31 . This is precluded if the unloading brushes are grouped so that they come into contact only with those parts of the paper Pierblattes 32 , with which the transport rollers 31 have come into contact, as shown in Fig. 3.

In the illustrated embodiment, the brush segments 34 behind the transport rollers to orders 31 at the end of those Trans arranged that end at the copy tray 15 , the additional tray 17 or the outlet 20 . The brush segment 34 is arranged parallel to and over the same length as the roller assembly 31 . Thus, although the paper sheet 32 which has undergone image transfer and has been dried by fixing is charged by the rollers 31 , the charge is removed by the brushes 34 . Since the paper sheet 32 , which has been dried by the fixing unit 22 and is therefore susceptible to loading, is discharged at the end of the conveying path 21 , it is prevented from being loaded again after unloading. Such a discharge effect is further promoted because the brush segments 34 are grounded through the associated te holding member 35 . The parts of the paper sheet 32 which do not come into contact with the rollers 31 are not charged so much that jamming occurs, as found in the first attempt. It is also verhin changed that these parts of the paper sheet 32 are negatively charged because they do not come into contact with brushes at all.

According to the invention, rotatable transport rollers are on one Transport path arranged and stand with a part of a Pa pierblattes in the width direction of the paper sheet in Kon clock, while conductive discharge brush segments, which in the we sentlichen over the same width as the transport rollers he stretch, also at the transport path at least in places (Seen in the direction of transport) after the rollers are, which are fixed at the extreme end of the web. The brush segments come only with those parts of a paper  leaf in contact, which has been loaded by the rollers are, whereby the charge applied by the rollers zer zer is scattered. Further, since the brush segments are the parts of the paper sheet Do not touch those which are not in contact with the rollers come, prevents the paper sheet from being negatively charged becomes. As a result of the invention, paper jams are consequently less frequent and it ensures a decent stacking of paper sheets guaranteed.

Claims (4)

An electrophotographic or electrostatic printing or copying machine having paper transporting means disposed along a paper transporting path and in the paper transporting direction behind said provided conductive discharge brushes which are in touching contact with a surface of the conveyed paper sheet and electrostatically discharging the sheet

• - The paper-transport devices each consist of several individual side by side and at a distance from each other on a common, transverse to the paper conveying direction axis arranged transport rollers predetermined width,
• - The arranged parallel to the axis of the transport rollers discharge brushes of several individual juxtaposed and spaced apart discharge brush segments of predetermined width, each such discharge brush segment is assigned to a preceding transport roller and the width and position of the respective segment of the width and the position the associated preceding transport roller on the axis of the paper-conveying device corresponds, so that the brush segments are in contact only with the paper surfaces in which the preceding transport rollers have touched the paper, and wherein
• - The brush segments are electrically connected to each other and grounded.

2. Printing or copying apparatus according to claim 1, characterized in that the transport rollers ( 31 ) are arranged with the associated discharge brushes on the transport path ( 21 ) in the paper transport direction behind a fixing unit of the device. 3. Apparatus according to claim 1 or 2, characterized in that the transport rollers ( 31 ) are arranged with the associated discharge brushes on the transport path to a paper output ( 20 ) of the device. 4. Apparatus according to claim 1, characterized in that the Entladebürsten segments are held by a rail-shaped holding part ( 35 ), which is grounded.