Electrophotography – Internal machine environment – Forced air circulation
Reexamination Certificate
2000-11-21
2003-08-19
Grainger, Quana M. (Department: 2852)
Electrophotography
Internal machine environment
Forced air circulation
Reexamination Certificate
active
06608979
ABSTRACT:
RELATED APPLICATION
The present application is a U.S. national stage application of PCT/IL98/00235, filed May 24, 1998.
FIELD OF THE INVENTION
The present invention relates generally to printing systems and more particularly to duplex printing systems for printing variable information on one or both sides of a sheet.
BACKGROUND OF THE INVENTION
Apparatus for duplex copying of documents and for duplex printing by means of laser printers are known in the art. U.S. Pat. No. 4,949,949 to Holmes et al. describes a “Hybrid Sequencing Duplex Automatic Document Handling System” which includes apparatus for handling document sheets both sides of which are to be copied and for making duplex (i.e. to double-sided) copies of such document sheets. The apparatus involve the use of one or more pairs of reversible rollers, lengthy inversion paths, and buffer trays for the handling of the documents and the copy paper prior to and in the course of making duplex copies. U.S. Pat. No. 4,884,794 to Dinatale et al. describes a document handler for duplex photocopying having first and second inverting path segments, which are utilized to re-orient the copy paper prior to duplex copying. U.S. Pat. No. 5,003,355 to Tanzawa describes a sheet transport control apparatus for use in a duplex unit of a laser printer, the apparatus including a transport system and a switchback system, and a series of driving motors and sensors. All these systems described in the prior art share the common feature of being mechanically complex, and they all involve transporting the paper through relatively lengthy and convoluted paths after printing on the first side so as to be able to print on the second side. Other systems for duplex printing are described in U.S. Pat. Nos. 4,806,079; 4,814,822; 4,568,169; 4,639,126; 4,428,667; 4,607,940; 4,375,326 and 5,020,788 and EP publication 0342704.
PCT publication 93/04409 describes a switchback system with a much shorter path than older systems, which allowed for on demand duplex printing without storage of large numbers of sheets.
Systems which utilize the same impression roller and/or the same printing engine for printing both sides of a web are known in the art. However, even in those systems the two sides of the web are printed at different printing positions in the printer and the web is not indexed at an edge.
Also known are systems for reversing sheets between printing stations. One such system is called a “perfecta” type system and comprises a roller that acts to turn over the sheet. Such systems, unlike those used for laser printers, reference the printing sheet from the same edge for printing on both sides.
A prior art perfecta system
10
is shown in
FIGS. 1A and 1B
. This system comprises a first impression roller
12
, which holds a sheet
14
for printing thereon by a print roller (not shown). Sheet
14
is transferred to roller
16
where it is held by a front edge clamp
20
. Roller
16
continues to rotate and the front edge of sheet
14
passes an inverting roller
18
. When the trailing edge reaches inverting roller
18
, a clamp
20
on roller
18
catches the trailing edge of sheet
14
and, as shown in
FIG. 2B
inverts the sheet prior to its being clamped to a second impression roller
22
.
An advantage of perfecta systems is that while the leading edge for printing the first and second sides of the sheet are reversed, the same edge is used as a reference position for printing both sides. Another advantage of perfecta systems, which is related to the first advantage, is that the sheets are always positively held by the system during inversion of the sheet. Positive holding of sheets distinguishes “perfecta” systems from systems which utilize a single printing engine and which generally do not positively hold the sheets during the entire process of transfer and reversal.
However, inverting systems which provide the advantages of perfecta systems are not known in a printer using the same impression roller and printing engine for printing both sides of the sheet.
SUMMARY OF THE INVENTION
One aspect of some preferred embodiments of the present invention provides apparatus and a method for duplex printing of sheets, utilizing the same edge of the sheet for reference for printing both sides thereof, while utilizing the same impression roller and/or the same printing engine.
One aspect of some preferred embodiments of the present invention provides apparatus and a method for duplex printing of sheets utilizing an impression roller for printing both sides of a sheet, while positively holding the sheet during the entire process of reversal and transfer of the sheet. Preferably, this means that the sheet is positively held from the start of the printing process to its end.
In a preferred embodiment of the invention, the same set of one or more printing engines is used in the printing of both sides of all the sheets.
In preferred embodiments of the present invention a perfecta-like system is used. This system includes rollers and/or belts which receive the sheet from one position on the circumference of an impression roller and, after reversing the sheet, delivers the sheet to a second position on the impression roller. Preferably, the path traveled by the sheet between the two positions holds an integral number of sheets. Preferably, the impression roller holds a plurality of sheets and presents them seriatim to one or more print engines. Preferably, the engine or engines are electrographic or other engines providing programmable images such as electrophotographic engines, ink or bubble jet print heads thermal printing heads or any other suitable printing engines.
Other aspects of some preferred embodiments of the invention are concerned with high speed printing engines, especially with high speed electrographic printing engines. In such engines special care must be taken in charging a photoreceptor and, when liquid toner is utilized, in treating and transport of the image. Some aspects of some preferred embodiments of the present invention deal with improvements in such engines especially usefully for high speed printing.
There is thus provided, in accordance with a preferred embodiment of the invention duplex printing apparatus for printing on two sides of a sheet, the apparatus comprising:
an impression roller on which the sheet is held during printing;
a imager which prints an image on a first side of the sheet while it is being held on the impression roller; and
a sheet inverter which removes the sheet from the impression roller, inverts the sheet and returns it to the impression roller for printing on a second side of the sheet by the imager, wherein the sheet is held on said impression roller referenced to a first edge thereof during the printing of the first side thereof and is also held on the impression roller referenced to said first edge during printing of the second side thereof.
Preferably, the sheet inverter positively controls the position of the sheet during the inversion thereof, without releasing the sheet during the inversion.
There is further provided, in accordance with a preferred embodiment of the invention a duplex printing apparatus for printing on two sides of a sheet, the apparatus comprising:
a surface, on which an image to be printed is selectably formed;
an impression roller on which the sheet is held during printing, referenced to a first edge thereof;
a imager which prints an image on a first side of the sheet while it is being held on the impression roller; and
a sheet inverter which removes the sheet from the impression roller, inverts the sheet and returns it to the impression roller for printing on a second side of the sheet by the imager, wherein the sheet inverter positively controls the position of the sheet from the removal of the sheet from the impression roller to the return of the sheet thereto after the inversion thereof, without releasing the sheet.
Preferably, the sheet inverter comprises a perfecta system.
In a preferred embodiment of the invention the sheet inverter comprises:
a paper pick-off system which removes th
Landa Benzion
Rosen Josef
Fenster & Company
Grainger Quana M.
Indigo N.V.
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