Printing system

A printing system including three print engines. One of the print engines is non-operational while the other two print engines are operational. The non-operational print engine is redundant and only actuated in the event that one of the operational print engines develops a malfunction causing it to be non-operational. At that time, the previously non-operational print engine becomes operational. In this way, two print engines are continually in operation with one print engine being non-operational. This printing system significantly improves reliability and minimizes maintenance requirements.

This invention relates to a printing system, and more particularly, 
concerns a plurality of print engines adapted to form duplex prints with 
one print engine being redundant and non-operable while the remaining 
print engines are operative. 
A typical printing systems adapted for use in high speed printing employs 
two print engines arranged in tandem. Each print engine prints on one side 
of the sheet. In this way, duplex prints are formed rapidly and at a high 
productivity. Each print engine may be an electrophotographic print 
engine. These print engines are identical to one another and have a 
photoconductive member that is charged to a substantial uniform potential 
so as to sensitize the surface thereof. The charged portion of the 
photoconductive member is exposed to a light image of a document being 
printed. Exposure of the charged photoconductive member effectively 
dissipates the charge thereon in the irradiated areas to record an 
electrostatic latent image on the photoconductive member corresponding to 
the informational areas desired to be printed. After the electrostatic 
latent image is recorded on the photoconductive member, the latent image 
is developed by bringing a developer material into contact therewith. 
Generally, the electrostatic latent image is developed with dry developer 
material comprising carrier granules having toner particles adhering 
triboelectrically thereto. However, a liquid developer material may be 
used as well. The toner particles are attracted to the latent image, 
forming a visible powder image on the photoconductive surface. After the 
electrostatic latent image is developed with the toner particles, the 
toner powder image is transferred to a sheet. Thereafter, the toner powder 
image is heated to permanently fuse it to the sheet. After the toner 
powder image has been formed on one side of the sheet, the sheet is 
advanced to the next print engine to have information printed on the other 
side thereof. The sheet may be inverted or the print engine may be 
oriented so as to print on the opposed side of the sheet. In any event, 
both print engines are substantially identical to one another and produce 
a sheet having information on opposite sides thereof, i.e., a duplex 
sheet. This is duplex printing. While electrophotographic print engines 
may be utilized, one skilled in the art will appreciate that any other 
type of print engines may also be used. For example, ink jet print 
engines, or lithographic print engines may be used. Furthermore, these 
print engines may be mixed and matched. Thus, the printing system does not 
necessarily require only electrophotographic print engines or only ink jet 
print engines or only lithographic print engines, but rather may have an 
electrophotographic print engine and an ink jet print engine, or any such 
combination. 
In high volume duplex printing of mission critical customer jobs, down time 
associated with one of the print engines being non-operative is an extreme 
disaster. Hereinbefore, the customer frequently had two printing systems. 
One of the printing systems was in operation while the other printing 
system remained as a back-up. Thus, users in this market segment improved 
reliability by purchasing an entire printing system for use as a back-up 
unit. Also, they frequently require on-site service personnel. 
There have been various approaches in the duplicating and printing field 
for printing on a first side and a second side of a sheet. In some 
instances, the print engines are arranged in straight-line tandem. Another 
approach has been to provide a sheet handling mechanism for inverting a 
sheet within one print engine so as to form duplex prints as a output 
therefrom such machines are more compact than the tandem arrangement. 
However, in either case, the reliability of the printing system tends to 
be of concern to the user. The following disclosures appear to be relevant 
to printing system using tandem print engines: 
U.S Pat No. 5,568,246 
Patentee: Keller, et al. 
Issued: Oct. 22, 1996 
U.S Pat. No. 5,598,257 
Patentee: Keller, et al 
Issued: Jan. 28, 1997 
U.S. Pat. No. 5,730,535 
Patentee: Keller, et al 
Issued: Mar. 24, 1998 
The references cited, U.S. Pat. No. 5,568,246; U.S. Pat. No. 5,598,257; and 
U.S. Pat. No. 5,730,535, disclose a printing system including two print 
engines arranged in tandem. Each print engine includes an inverter. The 
print engines are electrophotographic printing machines. As stated in U.S. 
Pat. No. 5,568,246; if one of the print engines fails, the other print 
engine can still be utilized. In this case, the normal single engine 
duplexing operation is used. 
In accordance with one aspect of the features of the present invention, 
there is provided a printing system including a first print engine adapted 
to print information on either side of a sheet. A second print engine is 
adapted to print information on either side of the sheet as well. Finally, 
a third print engine is adapted to print information on either side of the 
sheet. The third print engine is non-operative in response to the first 
print engine and the second print engine being operative to print 
information on opposed sides of the sheet. The third print engine is 
operative, in response to either the first print engine or the second 
print engine being non-operative. The third print engine is adapted to 
print information on the side of the sheet opposed to the side of the 
sheet having information printed thereon by either the first print engine 
or the second print engine. 
Other aspects of the present invention will become apparent as the 
following description proceeds and upon reference to the drawings, which 
is a schematic elevational view showing a printing system having three 
electrophotographic print engines arranged in tandem.

While the present invention will hereinafter be described in connection 
with a preferred embodiment thereof, it will be understood that it is not 
intended to limit the invention to that embodiment. On the contrary, it is 
intended to cover all alternatives, modifications and equivalents as may 
be included within the spirit and scope of the invention as defined by the 
appended claims. 
For a general understanding of the features of the present invention, 
reference is made to the drawing. In the drawing, like reference numerals 
have been used throughout to designate identical elements. 
Referring to the drawing, there is shown a printing system having three 
electrophotographic printing machines arranged in tandem. The printing 
system includes print engine 10, print engine 12, and print engine 14. At 
any one time, only two print engines are operational. The print engines 
are identical to one another. Thus, the sheet having information printed 
thereon passes through two of the three print engines and bypasses the 
third non-operational print engine. In response to one of the operational 
print engines becoming non-operational, the previously non-operational 
print engine becomes operational. In this way, two print engines are 
always operational. The redundant print engine becomes operational when 
one of the operating print engines becomes non-operational due to a 
malfunction. It is thus clear that the printing system of the present 
invention employs two print engines in an operational mode and one print 
engine in a non-operational or back-up mode. This significantly improves 
reliability. Furthermore, each print engine is identical to each other, 
and engine commonality is maintained. This results in significant 
reliability improvements. 
Turning now to the details of print engine 10, a sheet is supplied from 
feed trays 16 or 18 (or optional sheet input 20). The sheet from feed tray 
16 or 18 is advanced in the direction of arrow 22 by transport 24. A gate 
26 directs the sheet either to transport 28 or to bypass transport 30. 
When one print engine 10 is in the operational mode, gate 26 directs a 
sheet onto transport 28. Transport 28 moves the sheet in the direction of 
arrow 32 to transfer station 34. Transport 28 moves the sheet in a times 
relationship with respect to photoconductive belt 36 so that the toner 
image developed thereon advances in registration with the sheet at 
transfer station 34. Transfer station 34 includes corona generators which 
spray ions onto the back side of the sheet to transfer the toner powder 
image from photoconductive belt 36 to the sheet. Thereafter, transport 38 
moves the sheet, in the direction of arrow 40, to fusing station 42. Here, 
the toner powder image adhering to the sheet is permanently fixed or fused 
to the sheet. 
A previously described, photoconductive belt 36 is charged to a substantial 
uniform potential and then exposed to a light image of the document to be 
printed. This records an electrostatic latent image on photoconductive 
belt 36 which is developed with toner particles to form a toner powder 
image thereon. This toner powder image is transferred to the sheet at 
transfer station 34. The electrostatic latent image is formed by using a 
raster output scanner (ROS) which includes a laser imaging system. A laser 
imaging system is modulated by digital information received thereto. 
After passing through fusing station 42, gate 44 deflects the sheet into 
inverter 46. The inverted sheet is then advanced from inverter 46, in the 
direction of arrow 48, to gate 50 which deflects the sheet along output 
path 52 to print engine 12. Print engine 12, operating in the same manner 
as print engine 10, prints the next set of information on the opposed side 
of the sheet forming a duplex print. The duplexed sheet exits print engine 
12 at output path 54 and enters print engine 14. At this time, gate 26 of 
print engine 14 is positioned so as to deflect the sheet along the bypass 
transport 30. The duplexed sheet exits print engine 14 along output path 
56 and moves to a finisher, compiler, or a stacker. 
In the event print engine 10 is non-operational, print engine 12 and print 
engine 14 are operational. In this mode of operation, the sheet is 
deflected along bypass transport 30 of print engine 10 and enters print 
engine 12 to have information printed on one side thereof. Thereafter, the 
sheet, having information printed on one side thereof, outputs print 
engine 12 along path 54 and enters print engine 14. At this time, gate 26 
of print engine 14 deflects the sheet away from bypass transport 30 so as 
to have information printed on the opposed side thereof at transfer 
station 34 of print engine 14. Thereafter, the sheet is advanced to fusing 
station 42 of print engine 14 and, subsequently, to output path 56. 
In the alternative, print engine 12 may be non-operational and print 
engines 10 and 14 operational. In this mode of operation, the sheet has 
information printed on the first side thereof by print engine 10 and then 
enters print engine 12. Gate 26 of print engine 12 deflects the sheet 
along bypass transport 30 of print engine 12 to output path 54 where the 
sheet enters print engine 14. Inasmuch as the sheet has been inverted in 
print engine 10, print engine 14 prints information on the opposed side of 
the sheet resulting in a duplex print being exited along output path 56. 
Thus, it is clear that in this mode as well, information is printed on 
both sides of the sheet by utilizing two of the three print engines. 
Controller 55 is in communication with print engines 10, 12, and 14. The 
controller transmits signals to each one of these print engines to actuate 
various electrical solenoids, sheet deflectors, motors and/or clutches in 
selected steps or sequences as programmed. Sheet path sensors or switches 
are connected to the controller and are coordinated therewith for sensing 
timing and controlling the positions of the sheet in each of the printing 
engines. In this way, the position of the sheet is kept track of and the 
operation of the respective print engine controlled. In operation, 
controller 55 may also determine a malfunction in one of the print engines 
and shut that print engine down automatically. In response to one of the 
print engines being shut down by controller 55, controller 55 actuates the 
non-operational print engine and adjusts the parameters within the other 
print engines to ensure that the sheet moves along the appropriate paths 
in the appropriately timed sequence. Alternatively, controller 55 may 
display on a graphic user interface an alert to an operator that one of 
the print engines is malfunctioning and being shut down. The operator 
would then actuate the other print engine manually. Finally, controller 55 
may merely display a warning to the operator that one of the print engines 
is malfunctioning and the operator may then shut down that print engine 
and actuate the redundant or non-operational print engine. 
The printing system architecture using three print engines also permits 
continuous production while one print engine is being serviced. This 
architecture permits all of the print engines of the same design, 
eliminating unique design requirements for the non-operating print engine. 
In recapitulation, it is clear that the present invention is directed to a 
printing system employing three print engines arranged in tandem with one 
of the print engines being non-operational while the other two print 
engines are operational. In this way, the redundant or non-operational 
print engine may be actuated in response to one of the operational print 
engines developing a malfunction. This significantly increases reliability 
and ensures that high productivity is maintained on a continuous basis. 
It is, therefore, apparent that there has been provided in accordance with 
the present invention, a printing system which fully satisfies the aims 
and advantages hereinbefore set forth. While this invention has been 
described in connection with a specific embodiment thereof, it is evident 
that many alternatives, modifications and variations will be apparent to 
those skilled in the art. For example, although electrophotographic print 
engines have been described, one skilled in the art will appreciate that 
any type of print engine may be utilized, such as an ink jet print engine 
or a lithographic print engine. Accordingly, it is intended to embrace all 
such alternatives, modifications and variations that fall within the 
spirit and broad scope of the appended claims.