Belt tensioner apparatus

A non-resilient belt tensioning mechanism monitors and maintains tension in a photoreceptor belt. The belt tensioning mechanism causes one of at least a pair of rollers, around which a photoreceptor belt is entrained, to exert pressure against the photoreceptor belt to apply and maintain substantially constant tension in the belt.

BACKGROUND OF THE INVENTION 
Cross-reference is hereby made to copending and commonly assigned U.S. 
patent application Ser. No. 09/363,782 filed Jul. 29, 1999 and entitled 
Closed Loop Photoreceptor Belt Tensioner by Daniel W. Costanza et al. 
The present invention relates generally to an electrostatographic printing 
machine, and more particularly, concerns improving color registration of 
images on a flexible photoreceptor within such a machine. 
Flexible electrostatographic imaging members are well known in the art. 
Typical electrostatographic imaging members include, for example, 
photoreceptors for electrophotographic imaging systems and 
electroreceptors such as ionographic imaging members for electrographic 
imaging systems. These imaging members generally comprise at least a 
supporting substrate layer and at least one imaging layer comprising 
thermoplastic polymer matrix material. The "imaging layer" as employed 
herein is defined as the dielectric imaging layer of an electroreceptor or 
the photoconductive imaging layer of a photoreceptor. In a photoreceptor, 
the photoconductive imaging layer may comprise only a single 
photoconductive layer or a plurality of layers such as a combination of a 
charge-generating layer and a charge transport layer. 
Although the discussions hereinafter focus only on flexible 
electrophotographic imaging members, nonetheless the problems encountered 
therewith are equally applicable to electrographic imaging members. 
Generally, in the art of electrophotography, the process of 
electrophotographic copying is initiated by exposing a light image of an 
original document onto a substantially uniformly charged photoreceptive 
member. Exposing the charged photoreceptive member to a light image 
discharges a photoconductive surface thereon in areas corresponding to 
non-image areas in the original document while maintaining the charge in 
image areas, thereby creating an electrostatic latent image of the 
original document on the photoreceptive member. This latent image is 
subsequently developed into a visible image by depositing charged 
developing material onto the photoreceptive member surface such that the 
developing material is attracted to the charged image areas on the 
photoconductive surface. Thereafter, the developing material is 
transferred from the photoreceptive member to a receiving copy sheet or to 
some other image support substrate, to create an image, which may be 
permanently affixed to the image support substrate, thereby providing an 
electrophotographic reproduction of the original document. In a final step 
in the process, the photoconductive surface of the photoreceptive member 
is cleaned with a cleaning device, such as elastomeric cleaning blade, to 
remove any residual developing material, which may be remaining on the 
surface thereof in preparation for successive imaging cycles. 
The electrostatographic copying process described hereinabove, for 
electrophotographic imaging, is well known and is commonly used for light 
lens copying of an original document. Analogous processes also exist in 
other electrostatographic printing applications such as, for example, 
digital laser printing where a latent image is formed on the 
photoconductive surface via a modulated laser beam, or ionographic 
printing and reproduction where charge is deposited on a charge retentive 
surface in response to electronically generated or stored images. One of 
the drawbacks to the above-described process utilizing a flexible imaging 
member belt is that the belt, a photoreceptor belt in particular, 
stretches during repeated use. This is due to the machine belt module 
design employing a number of backer bars and small diameter belt support 
rollers to support the photoreceptor belt for movement during 
electrophotographic image processing cycles and keeping the belt under 
tension at all times. The constant tension on the photoreceptor belt, the 
positioning of the backing bars, and the positioning of the small diameter 
rollers causes substantial belt fatigue through bending stress/strain 
build-up in the charge transport layer, promoting the onset development of 
premature charge transport layer stretching and cracking as a result of 
repetitions of the photoreceptor belt flexing over the small diameter belt 
support rollers and backer bars during machine cyclic photoreceptor belt 
function. 
Stretching of the photoreceptor is considered to be a major mechanical 
failure since misregistration of color images during image-on-image 
printing manifests itself into copy print out defects. 
Therefore there is a need for a photoreceptor belt tensioning system that 
achieves superior color registration while reducing belt tension during 
belt steering actuations. 
PRIOR ART 
The following disclosure may be relevant to certain aspects of the present 
invention: 
U.S. Pat. No. 5,708,924 
Patentee: Daniel K. Shogren et al. 
Issued: Jan. 13, 1998 
U.S. Pat. No. 5,708,924 is directed to a customer replaceable unit that 
includes a corner and support structure for supporting a photoreceptor 
belt while it is packaged, shipped and inserted over drive and idler rolls 
in a machine. It prevents a machine operator from having to handle the 
belt itself and provides protection from extrinsic damage. A machine is 
described that includes backer bars for tensioning the photoreceptor belt 
during use. 
SUMMARY OF THE INVENTION 
Accordingly, pursuant to the features of the present invention, a 
non-resilient tensioning mechanism is disclosed that sets and controls 
tension roll systems in photoreceptor belt modules, such as in 
electrophotographic printing machines. The tensioning mechanism acts on 
one of at least a pair of rollers around which a photorector belt is 
entrained to maintain substantially uniform tension as belt length varies.

All references cited in this specification, and their references, are 
incorporated by reference herein where appropriate for teaching additional 
or alternative details, features, and/or technical background. 
While the present invention will be described hereinafter in connection 
with a preferred embodiment thereof, it should 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 in 
the appended claims. 
DETAILED DESCRIPTION OF THE INVENTION 
For a general understanding of the features of the present invention, 
reference is made to the drawings. In the drawings, like reference 
numerals have been used through out to identify identical elements. 
FIG. 1 schematically illustrates an electrophotographic printing machine 
which generally employs a photoconductive belt 10 mounted on a belt 
support module 90. Preferably, the photoconductive belt 10 is made from a 
photoconductive material coated on a ground layer which, in turn, is 
coated on an anti-curl backing layer. Belt 10 moves in the direction of 
arrow 13 to advance successive portions sequentially through the various 
processing stations disposed about the path of movement thereof. Belt 10 
is entrained about stripping roll 14, drive roll 16, tensioning roll 21, 
and idler roll 20. The details of the tensioning mechanism for tensioning 
roll 21 will be described hereinafter with reference to FIG. 2 and 3. As 
roll 16 rotates, it advances belt 10 in the direction of arrow 13. 
Initially, a portion of the photoconductive belt surface passes through 
charging station A. At charging station A, a corona generating device 
indicated generally by the reference numeral 22 charges the 
photoconductive belt 10 to a relatively high, substantially uniform 
potential. 
At an exposure station B, a controller or electronic subsystem (ESS), 
indicated generally be reference numeral 29, receives the image signals 
from RIS 28 representing the desired output image and processes these 
signals to convert them to a continuous tone or greyscale rendition of the 
image which is transmitted to a modulated output generator, for example 
the raster output scanner (ROS), indicated generally by reference numeral 
30. Preferably, ESS 29 is a self-contained, dedicated microcomputer. The 
image signals transmitted to ESS 29 may originate from RIS 28 as described 
above or from a computer, thereby enabling the electrophotographic 
printing machine to serve as a remotely located printer for one or more 
computers. Alternatively, the printer may serve as a dedicated printer for 
a high-speed computer. The signals from ESS 29, corresponding to the 
continuous tone image desired to be reproduced by the printing machine, 
are transmitted to ROS 30. ROS 30 includes a laser with rotating polygon 
mirror blocks. Preferably a nine-facet polygon is used. The ROS 30 
illuminates the charged portion on the surface of photoconductive belt 10 
at a resolution of about 300 or more pixels per inch. The ROS will expose 
the photoconductive belt 10 to record an electrostatic latent image 
thereon corresponding to the continuous tone image received from ESS 29. 
As an alternative, ROS 30 may employ a linear array of light emitting 
diodes (LEDs) arranged to illuminate the charged portion of 
photoconductive belt 10 on a raster-by-raster basis. 
After the electrostatic latent image has been recorded on photoconductive 
surface 12, belt 10 advances the latent image to a development station C, 
which includes four developer units containing c m y k toner, in the form 
of liquid or dry particles, is electrostatically attracted to the latent 
image using commonly known techniques. The latent image attracts toner 
particles from the carrier granules forming a toner powder image thereon. 
With continued reference to FIG. 1, after the electrostatic latent image is 
developed, the toner powder image present on belt 10 advances to transfer 
station D. A print sheet 48 is advanced to the transfer station D, by a 
sheet feeding apparatus 50. Preferably, sheet feeding apparatus 50 
includes a feed roll 52 contacting the uppermost sheet of stack 54. Feed 
roll 52 rotates to advance the uppermost sheet from stack 54 to vertical 
transport 56. Vertical transport 56 directs the advancing sheet 48 of 
support material into registration transport 125 past image transfer 
station D to receive an image from photoreceptor belt 10 in a timed 
sequence so that the toner powder image formed thereon contacts the 
advancing sheet 48 at transfer station D. Transfer station D includes a 
corona-generating device 58, which sprays ions onto the backside of sheet 
48. This attracts the toner powder image from photoconductive surface 12 
to sheet 48. After transfer, sheet 48 continues to move in the direction 
of arrow 60 by way of belt transport 62, which advances sheet 48 to fusing 
station F. 
Fusing station F includes a fuser assembly indicated generally by the 
reference numeral 70 which permanently affixes the transferred toner 
powder image to the copy sheet. Preferably, fuser assembly 70 includes a 
heated fuser roller 72 and a pressure roller 74 with the powder image on 
the copy sheet contacting fuser roller 72. The pressure roller is crammed 
against the fuser roller to provide the necessary pressure to fix the 
toner powder image to the copy sheet. The fuser roll is internally heated 
by a quartz lamp (not shown). Release agent, stored in a reservoir (not 
shown), is pumped to a metering roll (not shown). A trim blade (not shown) 
trims off the excess release agent. The release agent transfers to a donor 
roll (not shown) and then to the fuser roll 72. 
The sheet then passes through fuser 70 where the image is permanently fixed 
or fused to the sheet. After passing through fuser 70, a gate either 
allows the sheet to move directly via output 17 to a finisher or stacker, 
or deflects the sheet into the duplex path 100, specifically, first into 
single sheet inverter 82 here. That is, if the second sheet is either a 
simplex sheet, or a completed duplexed sheet having both side one and side 
two images formed thereon, the sheet will be conveyed via gate 88 directly 
to output 17. However, if the sheet is being duplexed and is then only 
printed with a side one image, the gate 88 will be positioned to deflect 
that sheet into the inverter 82 and into the duplex loop path 100, where 
that sheet will be inverted and then fed to acceleration nip 102 and belt 
transports 110, for recirculation back through transfer station D and 
fuser 70 for receiving and permanently fixing the side two image to the 
backside of that duplex sheet, before it exits via exit path 17. 
After the print sheet is separated from photoconductive surface 12 of belt 
10, the residual toner/developer and paper fiber particles adhering to 
photoconductive surface 12 are removed therefrom at cleaning station E. 
Cleaning station E includes a rotatably mounted fibrous brush in contact 
with photoconductive surface 12 to disturb and remove paper fibers and a 
cleaning blade to remove the nontransfered toner particles. The blade may 
be configured in either a wiper or doctor position depending on the 
application. Subsequent to cleaning, a discharge lamp (not shown) floods 
photoconductive surface 12 with light to dissipate any residual 
electrostatic charge remaining thereon prior to the charging thereof for 
the next successive imaging cycle. 
Controller 29 regulates the various machine functions. The controller is 
preferably a programmable microprocessor, which controls all of the 
machine functions hereinbefore described. The controller provides a 
comparison count of the copy sheets, the number of documents being 
recirculated, the number of copy sheets selected by the operator, time 
delays, jam corrections, etc. The control of all of the exemplary systems 
heretofore described may be accomplished by conventional control switch 
inputs from the printing machine consoles selected by the operator. 
Conventional sheet path sensors or switches may be utilized to keep track 
of the position of the document and the copy sheets. 
Referring now to the subject matter of the tensioning mechanism for tension 
roll 21, FIG. 2 depicts the cam 38 in a tensioning position as it is 
slightly rotated by the weight 31, which controls the movement of cam 38 
to precisely tension photoreceptor belt 10 into a tensioned image 
receiving position. The cam 38 was designed in conjunction with constant 
weight 31 to provide the proper force to be applied to the photoreceptor 
belt 10 to maintain a constant belt tension. At very low belt wrap angles, 
the required tension between tension roll 21 and the belt 10 is quite 
small At these angles a small amount of friction in the tensioning 
mechanism will significantly affect the tension applied to belt 10. 
Cam 38 is fixedly connected to cam gear 32. Cam gear 32, idler gear 33 and 
tension gear 34 are rotatively supported on unit plate 35. The idler gear 
33 engages the tension gear 34 and is engaged by the cam gear 32. The 
appropriate gear ratio increases the mechanical advantage of the weight 
required to apply the proper tension and reduces cam position sensitivity 
during tension control. 
Referring now to FIG. 3, tension gear 34 is fixed to the shaft of pivot 
roll 36. Two pivot arms 37 are connected to pivot roll 36 and tension roll 
21. When tension gear 34 rotates, the pivot arms 37 cause the tension roll 
21 to apply tension to belt 10. 
In operation a predetermined amount of tension is placed on photoreceptor 
belt 10 through downward movement of the weight 31, which causes 
counterclockwise rotation of cam 38 and cam gear 32. Cam gear 32 rotates 
the tension gear 34 counterclockwise via the idler gear 33. With rotation 
of tension gear 34, the pivot roll 36 rotates, causing pivot arms 37 to 
apply tension to the belt 10 via the tension roll 21. 
To detension belt 10 for removal, cam 38 may be rotated in a clockwise 
direction, which lifts weight 31 and reverses the tensioning action of the 
pivot arms 37 and tension roll 21. 
As can be appreciated, the length of the belt varies as a function of 
manufacturing tolerances and stretch during operation. The tensioning 
mechanism of the present invention not only sets the initial tension for 
operation of the belt, as described above, but also maintains the belt 
under substantially constant belt tension as the belt stretches. This is 
accomplished through the continued action of the constant weight acting to 
slightly rotate the cam and gear mechanism, thereby rotating the pivot arm 
which moves the tension roll against the belt to maintain belt tension as 
tension decreases through belt stretch. As the cam rotates, the cable acts 
on a different cam radius, thereby maintaining a constant tension as the 
photoreceptor belt length changes. 
It should now be apparent that a non-resilient belt tensioner apparatus has 
been disclosed that sets and maintains tension on a photoreceptor belt to 
improve drive capacity if friction is reduced between the photoreceptor 
belt and a drive roll during operation. 
While the invention has been described with reference to the structure 
herein disclosed, it is not confined to the details as set forth and is 
intended to cover any modification and changes that may come within the 
scope of the following claims.