Apparatus for producing simplex of duplex copies

Apparatus operable in duplex and simplex modes for making copies having images on one or both sides thereof. In the duplex mode, first and second transferable images are formed on a movable image transfer member by an image forming device, a copy sheet is supplied from a copy sheet supply into transfer relationship with the transfer member and the first image is transferred to a first side of a copy sheet at a first image transfer station. A vacuum drum located adjacent to the transfer member is rotated in a first direction to separate the copy sheet from the transfer member. After the copy sheet has been separated, the drum is rotated in a second opposite direction to invert the copy sheet while the first image is unfixed and to register the second side with the second transferable image on the transfer member at a second image transfer station. In the simplex mode, a first image is formed on the transfer member by the image forming device, a copy sheet is supplied from the supply into contact with the vacuum drum and the drum is rotated in the second direction to assist in registering the first side of the copy sheet with the first image on the transfer member at the second transfer station. Preferably an image fixing device is provided to fix the duplex or simplex images to the copy sheet. A control may also be provided to coordinate the operation of the apparatus in the simplex or duplex modes.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to apparatus for producing simplex or duplex copies. 
More particularly, this invention relates to apparatus for transferring 
unfixed transferable images to either one or both sides of a copy sheet 
before fixing of either image to the copy sheet. 
2. Description of the Prior Art 
Several techniques are known in the prior art for forming duplex images on 
a final copy medium such as a web or sheet. One such technique requires 
the use of two photoconductors upon which first and second transferable 
images are formed respectively. The copy medium is generally passed 
between the photoconductors and the first and second images are 
transferred to opposite sides of the copy medium. Another technique 
similar to the above but involving the use of only one photoconductor, 
utilizes an intermediate image storage member such as a drum, to receive 
the first image formed on the photoconductor before transfer to a final 
copy medium. These techniques suffer the disadvantages of increased cost, 
machine complexity and size and decreased reliability necessitated by the 
use either of two photoconductive and optical systems or of additional 
components before transfer to a final copy medium. Additionally there is 
the probability of degradation in image quality when an intermediate 
storage member is used. Furthermore, in some instances the developed 
images are tackified by use of solvent vapors which are potentially 
flammable and which require the use of a consumable fluid which must be 
replaced periodically. 
A further duplexing technique utilized in certain commercial 
electrophotographic machines includes a single photoconductor wherein 
first fixed images developed sequentially on the first sides of a 
plurality of copy sheets by an electrophotographic process are collected 
in an intermediate tray. The copy sheets are then sequentially transported 
back through the electrophotographic process to develop second fixed 
images on the second sides of the copy sheets, thus producing duplex 
copies. The latter "two-pass" process has several disadvantages. Because 
the first sides of all the copy sheets are developed before development of 
the second sides of the copy sheets, a duplex copy is not available for 
inspection until all of the first sides of the copy sheets and one set of 
the second sides thereof have been developed. In addition, the relatively 
long paper paths required in passing a copy sheet through the entire 
electrophotographic process twice greatly increases the possibility of 
paper jams and other potential copy handling complications. Moreover, 
environmental conditions of image formation and the physical parameters of 
the copy sheet may change resulting in images of varying quality on 
opposite sides of a single sheet and misregistration between images on 
opposite sides of a copy sheet may also result. 
Still aother duplex copying technique which may be considered especially 
relevant to the present invention involves fixing images to both sides of 
a copy sheet during a single pass through the disclosed 
electrophotographic processes. U.S. Pat. Nos. 3,506,347; 3,672,765; 
3,869,202; and 3,947,270 disclose various embodiments of this technique. 
In the first patent just listed a first tackified image is formed on a 
transfer drum, the image is transferred to the first side of a copy sheet, 
and the sheet is inverted while the first tackified image dries and 
becomes fixed on the copy sheet. Thereafter, a second tackified copy image 
is formed on the transfer drum and the copy sheet is fed back into contact 
with the drum to transfer the second image to the second side of the copy 
sheet which is then transported to an output tray. In the latter three 
patents electrophotographic apparatus is disclosed for making copies 
wherein two images of an original are formed sequentially on a 
photoconductor, the images are developed and the first developed image is 
transferred to the first side of a copy sheet. The copy sheet is passed 
through a fuser to fuse or fix the first transferred image, is turned over 
and the opposite side of the copy sheet is brought into contact with the 
second developed image on the photoconductor. The second image is then 
transferred to the second side of the copy sheet, the copy sheet separated 
from the photoconductor and the second image fused by means of a second 
fuser. The disclosed techniques have several disadvantages. Since the 
first image is fixed before transfer of the second image, either two 
fusers must be used with attendant increase in cost, power and 
environmental heat or solvent fixing is used resulting in safety hazards 
and the inconvenience of handling consumable liquids. 
SUMMARY OF THE INVENTION 
The present invention alleviates the above and other disadvantages of prior 
duplex copiers. According to one feature of the invention a single copying 
process is provided resulting in decreased cost, size and complexity and 
increased reliability with no image degradation since no intermediate 
storage member is used. According to another feature of the invention 
unfixed images are formed on either one or both sides of a copy sheet 
before fixing of the images thus eliminating the need for a second fuser 
with attendant decrease in power usage, environmental heat and cost or for 
solvent fixing thus eliminating safety hazards and the inconvenience of 
replenishing liquids. Another feature of the invention reduces the length 
of the copy path from that required for "two-pass" duplexing thus reducing 
side to side copy quality variability and misregistration and the 
incidence of paper jams and increasing the production of a finished duplex 
copy. 
In general, according to the present invention there is provided apparatus 
for producing simplex and duplex copies including a movable image transfer 
member; image forming means for forming transferable images on said 
transfer member; first and second image transfer stations located in image 
transfer relationship with said image transfer member; and vacuum drum 
means located adjacent to the image transfer member between the transfer 
stations. Preferably a supply for supplying copy sheets is also provided. 
According to an aspect of the invention, when the apparatus is operated in 
the duplex mode, the image forming means forms first and second 
transferable images on the image transfer member and a copy sheet is 
supplied by the copy sheet supply into transfer relationship with the 
image transfer member at the first image transfer station in registration 
with said first image. The vacuum drum means is rotated in a first 
direction to separate by vacuum attraction the copy sheet from said 
transfer member after transfer of said first image to the first side of 
the copy sheet. The drum means is then rotated in a second opposite 
direction after said copy sheet has been separated from said transfer 
member to invert said copy sheet while said first image is unfixed so as 
to register the second side of said copy sheet with the second image on 
said transfer member at said second transfer station. 
According to another aspect of the invention, when the apparatus is 
operated in the simplex mode, the image forming means forms a first 
transferable image on said image transfer member, said vacuum drum means 
is rotated in the second direction and said supply means supplies a copy 
sheet into contact with said vacuum drum means which assists in 
registering the first side of said copy sheet with the first image on said 
transfer member at said second transfer station. 
According to another aspect of the invention, fixing means which preferably 
includes a pair of heated fuser rollers, is provided to fix the unfixed 
duplex or simplex images to the copy sheet. 
A copy sheet diverter may also be provided between the vacuum drum means 
and the transfer member to remove the copy sheet from the drum and to 
guide it into transfer relation with the transfer member at the second 
transfer station in either the simplex or duplex mode. 
The invention and its features and advantages will be set forth and become 
more apparent in the detailed description of the preferred embodiment 
presented below.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to the drawings, there is disclosed apparatus for producing 
duplex or simplex copies incorporating a preferred embodiment of the 
present invention. In FIG. 1 apparatus 1 is shown as an 
electrophotographic copier which may include, among other elements, an 
image transfer member 2, an image forming means 3, a copy sheet 
duplexing/simplexing section 4, copy sheet input and output sections 5 and 
6, respectively, and a logic and control unit 7. Image forming means 3 
forms transferable images on image transfer member 2, copy sheet input 
section 5 supplies copy sheets, copy sheet duplexing/simplexing section 4 
transfers simplex or duplex images from transfer member 2 to a copy sheet, 
copy sheet output section 6 fixes the images to the copy sheet to produce 
a final copy and delivers the final copy to an output hopper or to a copy 
handling accessory and logic and control unit (LCU) 7 coordinates the 
operation of the various elements of apparatus 1 to produce final copies. 
The term "sheet" as used in this application is used in reference to a 
single expanse of thin essentially flat material such as paper or 
transparencies having two opposed sides. "Simplex" refers to a sheet 
having only one side having an image; "duplex" refers to a sheet having 
images on both sides. A "copy sheet" is a sheet which receives simplex or 
duplex images. A "final copy" is a copy sheet having simplex or duplex 
images which are fixed to the copy sheet. 
Image Transfer Member and Image Forming Means 
Image transfer member 2 may be any member upon which transferable images 
may be formed and from which the images may be transferred to a copy 
sheet. In the preferred form of apparatus shown in FIG. 1, member 2 may 
incorporate a transparent support 8 and a photoconductor 9 backed by a 
conductive layer (not shown) grounded by grounding brushes 100 and may be 
trained about transport rollers 10, 11, 12, 13, 14 and 15. Roller 10 is 
coupled to a drive motor 16 controlled by LCU 7 to move member 2 in a 
clockwise direction indicated by arrow 17 past various electrophotographic 
work stations to be described laer in greater detail. 
Image forming means 3 includes a charging station 18 at which the 
photoconductor 9 of member 2 receives a uniform electrostatic charge from 
a suitable device such as a corona charger; an exposing station 19 at 
which the image of an original to be copied is projected onto 
electrostatically charged photoconductor 9 of member 2 thereby dissipating 
the electrostatic charge at the exposed areas of member 2 to form a latent 
electrostatic image corresponding to the original image; and a developing 
station 20 at which developing power including toner particles having an 
electrostatic charge opposite to that of the latent electrostatic image is 
brushed over member 2 to develop the latent electrostatic image into a 
toner image corresponding to the original image. 
Charging station 18 is shown as including a corona charger which may for 
example be a three-wire grid-controlled type which establishes a uniform 
negative surface potential on member 2. Other types of known charging 
devies may also be used such as open wire corona chargers or the like. 
Exposing station 19 is shown as including a transparent exposure platen 21 
upon which originals to be copies are positioned, an illumination source 
22 including flash lamps 23 and 24, and projection optics such as mirrors 
26 and 28 and lens 27 which may be movably mounted to permit reduced or 
enlarged image reproduction. A recirculating feeder 25 may be positioned 
on the top of platen 21 and may for example take the form of that 
disclosed in U.S. Pat. No. Re. 27,976 wherein a plurality of original 
documents having images only on first sides thereof are repeatedly fed in 
succession from a supply stack to the exposure platen 21 of copier 1. The 
feeder may also take the form of that disclosed in Research Disclosure 
Bulletin, Vol. 156, April, 1977, Item 15671 wherein original documents 
having images on both sides thereof are repeatedly fed in order to the 
exposure platen with alternate sides of each sheet being presented to 
platen 21. 
In either case, feeder 25 places a selected side C of a sheet of an 
original document S with side C facing platen 21. When energized, flash 
lamps 23 and 24 illuminate side C of document S to produce a light image 
of the original image which is projected onto member 2 by mirrors 26, 28 
and lens 27 to produce a latent electrostatic image corresponding to the 
original image. 
Development station 20 may include a magnetic brush developer which brushes 
developer including toner particles having an electrostatic charge 
opposite to that of the latent electrostatic image over member 2. The 
toner particles adhere to the latent electrostatic image to form a 
transferable visible toner image which corresponds to the original image. 
A post development erase station 29 including an infrared illumination 
source may be provided to reduce photoconductor fatigue i.e. electrical 
stress on the photoconductor which decreses its ability to accept or hold 
electrostatic charge. 
Copy Sheet Input, Duplexing/Simplexing and Output Sections 
Copy sheet input section 5 includes supplies 30 and 31 of copy sheets S' of 
any suitable material such as paper, transparencies or the like. Copy 
sheets S' are supplied from the top of either supply 30 or supply 31 by 
means of oscillating vacuum rollers 32, 33, respectively. When apparatus 1 
is operating in the duplex mode, copy sheets S' are supplied from supply 
31 along path 80 to registration mechanism 34 which registers the first 
side of copy sheet S' with the first toned image on member 2 at the first 
transfer station 35 and synchronizes the movement of copy sheets S' with 
member 2. When apparatus 1 is operating in the simplex mode copy sheets S' 
are supplied from supply 31 along path 81 by transport belts 82 to nip 
rollers 83 and thence over guide 84 to vacuum drum means 37 or from supply 
30 to nip rollers 83 and thence to vacuum drum means 37. 
When apparatus 1 is operating in the duplex mode, image forming means 3 
forms first and second transferable toner images on member 2. Copy sheet 
duplexing/simplexing section 4 is provided to effect transfer of the toner 
images to copy sheets and includes first and second image transfer 
stations 35 and 36 and vacuum drum meas 37 located adjacent to member 2 
between transfer stations 35 and 36. 
First transfer station 35 may include a first transfer corona charger 38 
which has a negative DC potential applied to its corona wire and a first 
detack charger 39 which has an AC potential applied to its corona wire. 
Registration mechanism 34 registers a copy sheet S' with the first toner 
image formed on member 2 at first transfer station 35 where first transfer 
charger 38 impresses a negative charge on sheet S' to cause the positively 
charged first toner image to be transferred from member 2 to a first side 
C' of sheet S'. Detack charger 39 neutralizes the negative charge on copy 
sheet S' so that it can be easily separated from member 2. 
Vacuum drum means 37 is rotatable in first and second opposite directions 
by means of motor 40. In the duplex mode, drum means 37 is rotated in a 
first direction to separate by vacuum attraction a copy sheet S' from 
member 2 after the first toner image has been transferred to a first side 
C' of copy sheet S' at transfer station 35 and to move the sheet along 
sheet turn around path 41. Drum means 37 is then rotated in a second 
direction after copy sheet S' has been separated from member 2, to invert 
sheet S' while the first toner image on side C' is unfixed and to assist 
in registering the second or opposite side C" of copy sheet S' with the 
second toner image on member 2 at second transfer station 36. At station 
36, the second image is transferred to side C" of sheet S'. Copy sheet 
diverter 42 removes the copy sheet from drum means 37 and guides it into 
transfer relation with the second image on member 2 at second transfer 
station 36. 
Second transfer station 36 is similar to first transfer station 35 and 
includes second transfer charger 43 and second detack charger 44. Second 
transfer charger 43 impresses a negative charge on a sheet S' to transfer 
a second toner image from member 2 to side C" of sheet S' and second 
detack charger 44 neutralizes any charge remaining on sheet S' so that it 
may be easily separated from member 2. 
After transfer of both toner images to sheet S' it is separated from member 
2 and directed to output station 6 which includes a fixing means 45 for 
fixing the unfixed toner images to copy sheet S'. As shown, fixing means 
45 may be a roller fuser including heated rollers 46 and 47 for heating 
and fusing the toner particles to sheet S' to form a final copy. Sheet S' 
may then be transported to an output tray 48 or to a copy handling 
accessory 49 such as the finisher disclosed in Research Disclosure 
Bulletin, Vol. 167, March, 1978, Item 16731, which effects straight or 
offset stacking and stapling of copy sheets or sets of copy sheets. 
Copier 1 may be operated in a simplex mode wherein only first images are 
formed on member 2 and transferred to first sides of copy sheets S'. In 
such case, as described above, a copy sheet is supplied from either of 
supplies 30 or 31 to vacuum drum means 37 by nip rollers 83. Vacuum drum 
means 37 is rotated in the second (clockwise) direction to direct the 
first side of a copy sheet S' into registration with the first image on 
member 2 at second transfer station 36 where the first image is 
transferred to the copy sheet. Either rollers 83 or drum means 37 may be 
used to register copy sheet S' with the simplex image on web 2. Thereafter 
the image is fixed by fixing means 45 to produce a final copy which is 
transported to tray 48 or accessory 49. 
A cleaning station 50 is provided to effect mechanical and electrical 
cleaning of photoconductor 9 of web 2. Station 50 includes a cleaning 
assist erase lamp 51 which exposes the photoconductor to radiation to 
reduce more of the charge remaining from the transfer and detack steps; a 
cleaning assist charger 52 which impresses an AC charge on photoconductive 
surface 9 of web 2 to neutralize the charges on untransferred toner 
particles; and a brush 53 which removes any residual toner from surface 9 
and deposits it in a suitable collection container (not shown). 
Vacuum Drum 
Referring now to FIGS. 2, 3A-3D and 4 there is shown in greater detail 
vacuum drum means 37 and the operation of duplexing/simplexing station 4 
when operating in the duplex and simplex modes. As shown, drum means 37 
includes a cylindrical outer shell 54 and a cylindrical inner shell 55. 
Shell 54 has a plurality of holes 56 extending around the circumference 
and substantially the width thereof and is rotatable in first and second 
opposite directions by reversible motor 40. Shell 55 is stationary and is 
provided with a baffle 57 and an opening 58 which is adapted to 
communicate with holes 56 of shell 54 and with a source of vacuum 80 by 
means of conduit 81. Drum means 37 is located substantially adjacent 
member 2 in the region of roller 13 between transfer stations 35 and 36. 
Sheet diverter 42 is mounted for movement between a first position as shown 
in solid lines in FIG. 2 where it is in contact with shell 54 of drum 
means 37 and a second position as shown in dotted lines where it is out of 
contact with shell 54. Diverter 42 may be moved between such first and 
second positions by any suitable means such as rotary solenoid 59. 
Referring to FIGS. 3A-3D there is shown in more detail the operation of 
drum means 37 in the duplex mode. In FIG. 3A, shell 54 is shown being 
rotated in a first (counterclockwise) direction to separate copy sheet S' 
from transfer relation with member 2 after a first toner image has been 
transferred from member 2 at first transfer station 35 to a first side C' 
of sheet S'. Diverter 42 has been moved to its second position out of 
contact with shell 54 so that copy sheet S' can be wrapped around shell 54 
without interference from diverter 42. In FIG. 3B, copy sheet S' is shown 
completely wrapped around shell 54, the counterclockwise rotation of which 
has been halted and diverter 42 has been moved to its first position in 
contact with shell 54. Since the unfixed first toner image transferred to 
side C' of copy sheet S' is facing outwardly there is no disturbance of 
such image and thus no need for the fixing of the first image to sheet S'. 
As shown in FIG. 3C, shell 54 is rotated in a second (clockwise) direction 
to register the second unimaged side C" of copy sheet S' with the second 
toner image on web 2 at second transfer station 36. Diverter 42 is shown 
in substantial contact with shell 54 to effect a guide path for sheet S' 
from drum means 37 to member 2. 
FIG. 3D shows sheet S' after it has cleared shell 54 and diverter 42 as it 
passes under transfer station 36 for transfer of the second toner image to 
side C" of copy sheet S'. Subsequently, diverter 42 would be moved to the 
position shown in FIG. 3A, the direction of shell 54 would be reversed and 
the sequence of FIGS. 3A-3D would be repeated with respect to the next 
copy sheet S'. 
Referring now to FIG. 4, there is shown duplexing/simplexing station 4 as 
it is operated in the simplex mode. Copy sheets S' are supplied by rollers 
83 over guide 84 to vacuum drum means 37. Shell 54 is rotated in the 
second (clockwise) direction to direct a sheet S' over diverter 42 into 
transfer relationship with member 2 at second transfer station 36 in 
registration with the simplex image which is transferred to the first side 
of sheet S'. After image transfer, sheet S' is directed to output station 
6. 
Logic and Control Unit 
As shown in FIG. 1, and more particularly in FIG. 5, operation of copier 1 
and its related accessories such as feeder 25 and copy handling accessory 
49 is monitored and controlled by a digital microprocessor incorporated in 
logic and control unit (LCU) 7. LCU 7 may include a central processing 
unit (CPU) and memory module 65 and an input/output module 66. Module 65 
includes a central processing unit (CPU) which processes data in digital 
format, a program memory such as a read only memory (ROM) which stores 
basic logic and control subroutines and a random access memory (RAM) which 
is used for temporary memory and for maintaining a short term account of 
the flow of original documents and of copies being processed. Module 66 
provides all of the control signals and data bus connections to 
communicate with the CPU, ROM and RAM of module 65. 
A control and display panel 67 is provided on copier 1 and includes 
operator selectable switches and controls for such functions as number of 
copies desired, choice of simplex or duplex copying etc. and also includes 
displays to indicate information such as number of copies selected, number 
of copies produced, jam conditions in the copier or its accessories, etc. 
Input signals to LCU 7 are derived from various switches, sensors and the 
like which monitor copier operation, track the passage of copy sheets, 
etc., and from a timing generator generator 60. As disclosed in U.S. Pat. 
No. 3,914,047, member 2 may include a series of perforations along an edge 
thereof which are sensed by a sensor such as a piezoelectric or optic 
sensor 60. The perforations provide a means of generating timing signals 
which are related to the movement of web 2 and which are used to 
synchronize the various mechanisms of copier 1 and its accessories with 
the location of the images formed on web 2. 
Output signals from LCU 7 control the various work stations of the copier 
including turning drive motor 16 on and off, initiating flash lamps 23 and 
24 and controlling the direction of motor 40 to effect operation of drum 
assembly 37 during duplex and simplex operation. 
The inventiion has been described in detail with particular reference to 
preferred embodiments thereof but it will be understood that variations 
and modifications can be effected within the spirit and scope of the 
invention.