Jam detection system

An apparatus for predicting a location of a sheet being transported along a path of movement after the occurrence of a sheet jam. A sheet jam detecting device is disposed along the path of movement of the sheet. The sheet jam detecting device detects the sheet jam along the path of movement and generates a sheet jam signal. A sensor is operatively associated with the transport to detect the continued movement of the transport after the jam detecting device detects the sheet jam. The sensor generates a transport signal. A processor is in communication with the jam detecting device and the sensor for receiving the sheet jam signal and the transport signal. The detector predicts the location of the sheet as a function of these signals. An apparatus of this type may be used in a printing machine for detecting the location of sheets after the occurrence of a sheet jam.

The present invention relates to a printing machine, and more particularly, 
concerns detecting jammed sheets along a path of movement in the printing 
machine 
Generally, an electrophotographic printing machine includes a 
photoconductive member which is charged to a substantially uniform 
potential to sensitize the surface thereof. The charged portion of the 
photoconductive surface is exposed to a light image of an original 
document being reproduced. This records an electrostatic latent image on 
the photoconductive member corresponding to the informational areas 
contained within the original document. After the electrostatic latent 
image is recorded on the photoconductive member, a developer mix is 
brought into contact therewith. This forms a powder image on the 
photoconductive member which is subsequently transferred to a copy sheet. 
Finally, the copy sheet is heated to permanently affix the powder image 
thereto in image configuration. One skilled in the art will appreciate 
that in lieu of a dry developer material, a liquid developer material may 
be used. 
In today's high speed electrophotographic printing machines, copy sheets 
are handled and advanced throughout the various processing stations of the 
printing machine. Not only must each copy sheet be handled without marring 
or destroying the sheet, but also, misfeeds and multiple feeds must be 
detected and prevented. The foregoing not only applies to copy sheets, but 
also to original documents being handled by document handling systems. 
As the copy sheet is being conveyed through the various processing stations 
in the printing machine, there is a possibility that the sheet may become 
jammed in the printing machine. Various types of devices has been 
developed for detecting sheet jams. For example, the leading and trailing 
edges of the sheet may be detected, and, in the event the trailing edge is 
not detected, a sheet jam declared. It is not only important to detect the 
occurrence of a sheet jam, but it is also important to determine the 
location of the sheet jam. In high speed printing machines, many sheets 
may be moving along the sheet path in addition to the jammed sheet. Only 
in this way will the machine operator be capable of easily removing all of 
the sheets and returning the printing machine to operational status. The 
printing machine has a tendency to coast after a sheet jam has occurred. 
This results in many of the sheets stopping further downstream than where 
the sensors indicated. Thus, it is highly desirable to be capable of 
predicting where the sheets will actually stop after the jam is detected. 
The following disclosures may be relevant to various aspects of the present 
invention: 
U.S. Pat. No. 4,054,380 Patentee: Donohue, et al. Issued: Oct. 18, 1977 
U.S. Pat. No. 4,084,900 Patentee: Yamaoka, et al. Issued: Apr. 18, 1978 
U.S. Pat. No. 4,163,897 Patentee: Hubbard, et al. Issued: Aug. 7, 1979 
U.S. Pat. No. 4,213,190 Patentee: Finlay, et al. Issued: Jul. 15, 1980 
The relevant portions of the foregoing disclosures may be briefly 
summarized as follows: 
U.S. Pat. No. 4,054,380 discloses a jam detection system which interrogates 
switches in the paper path. If the paper is not on a paper path switch at 
the right time or is on a paper path switch at the wrong time when the 
logic cycles are sampled, the appropriate type of jam will be declared and 
the machine will be stopped. 
U.S. Pat. No. 4,084,900 describes a jam detecting circuit for detecting a 
copy paper jam in the printing machine. A circuit measures a time interval 
between a starting circuit and a second paper detecting circuit. If the 
time interval measured exceeds a predetermined period of time defined in 
an alarm circuit, an alarm either visual or auditory, is actuated 
providing an indication to the machine operator that a paper jam has 
occurred at some place in the copying machine. In addition, the alarm 
circuit may cause the copying machine to stop subsequent copying 
operations. 
U.S. Pat. No. 4,163,897 discloses a jam detection circuit which transmits a 
jam detected signal. The detection of the jam stops the production of the 
copies in the printing machine. The operator then opens the door to the 
printing machine and removes partially completed copies residing therein. 
Such removal may require the operator to move portions of the copy path 
transport. Upon completion of the physical recovery of the sheets, the 
operator actuates a misfeed reset switch signifying to the printing 
machine that the operator has completed the physical portion of the jam 
recovery. A switch then sends a signal over a line to reinitiate operation 
of the printing machine in the recovery mode. 
U.S. Pat. No. 4,213,190 describes detecting a sheet jam and clearing the 
copy sheets form the paper path while the photoconductor drum is coasting 
or has just coasted to a stop. 
In accordance with one aspect of the present invention, there is provided a 
printing machine of the type having a moving photoconductive member and 
processing stations disposed about the path of movement thereof. A jam 
detecting device is disposed along the path of movement of the sheet. The 
jam detecting device detects a sheet jam along the path of movement and 
generates a sheet jam signal. A sensor is operatively associated with the 
photoconductive member to detect the continued movement of the 
photoconductive member after the jam detecting device detects the sheet 
jam. The sensor generates a photoconductor signal. A processor, in 
communication with the jam detecting device and the sensor, receives the 
sheet jam signal and the photoconductor signal, and, in response thereto, 
predicts the location of sheets along the path of movement. 
Pursuant to another aspect of the present invention, there is provided an 
apparatus for predicting the location of sheets being advanced along a 
path of movement by a transport after an occurrence of a sheet jam. The 
apparatus includes a jam detecting device, disposed along the path of 
movement of the sheets, for detecting a sheet jam along the path of 
movement thereof, and generating a sheet jam signal. A sensor is 
operatively associated with the transport and detects the continued 
movement of the transport after the jam detecting device detects the sheet 
jam and generates a transport signal. A processor, in communication with 
the jam detecting device and the sensor, receives the sheet jam signal and 
the transport signal. The processor predicts the location of the sheets 
along the path of movement. 
Pursuant to still another aspect of the present invention, there is 
provided another method of predicting the location of sheets moving along 
a path in a printing machine after the occurrence of a sheet jam. The 
printing machine has processing stations disposed about a photoconductive 
member to form indicia on the sheet. The method includes detecting a sheet 
jam along the path of movement thereof and generating a sheet jam signal. 
The continued movement of the photoconductive member after the detecting 
step is sensed and a photoconductor signal generated. The sheet jam signal 
and the photoconductor signal are processed to predict the location of the 
sheets along the path of movement.

While the present invention will hereinafter be described in connection 
with a preferred embodiment and method of use thereof, it will be 
understood that it is not intended to limit the invention to that 
embodiment or method of use. On the contrary, it is intended to cover all 
alternatives, modifications, and equivalents that 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 drawings. In the drawings, like reference 
numerals have been used throughout to identify like elements. Turning 
initially to FIG. 2, FIG. 2 schematically depicts the various components 
of the illustrative electrophotographic printing machine incorporating the 
sheet jam detection system of the present invention therein. It will 
become apparent from the following discussion that this sheet jam 
detection system is equally well suited for use in a wide variety of 
printing machines and is not necessarily limited in its application to the 
particular embodiment and method of use discussed herein. Furthermore, the 
sheet jam detection system may be used in a non-printing machine 
environment. It may be used in any transport system in which it is 
desirable to predict the location of sheets after the occurrence of a 
sheet jam. 
Inasmuch as the art of electrophotographic printing is well-known, the 
various processing stations in the FIG. 2 printing machine will be 
hereinafter shown schematically and their operation described briefly with 
reference thereto. 
As shown in FIG. 2, the illustrative electrophotographic printing machine 
employs a belt 10 having a photoconductive surface comprising an anti-curl 
layer, a supporting substrate layer, and an electrophotographic imaging 
single layer or multiple layers. The imaging layers may contain 
heterogeneous, inorganic, or organic composition. Preferably, finely 
divided particles of the photoconductive inorganic compound are dispersed 
in an electrically insulating organic resin binder. Generally, these 
inorganic photoconductive materials are deposited as a relatively 
homogeneous layer. The anti-curling layer may be made of any suitable film 
such as a flexible thermoplastic resin. The substrate layer may be made 
from any suitable conductive material, such as Mylar.RTM.. Another 
well-known conductive material that can be used in the substrate layer is 
aluminum. Belt 10 moves in the direction of arrow 12 to advance successive 
portions of the photoconductive surface sequentially through the 
processing stations disposed about the path of movement thereof. 
Belt 10 is entrained about stripping roller 14, tensioning roller 16, and 
drive roller 18. Stripping roller 14 is mounted rotatably so as to rotate 
with belt 10. Tensioning roller 16 is resiliently urged against belt 10 to 
maintain belt 10 under the desired tension. Drive roll 18 is rotated by a 
motor coupled thereto by suitable means, such as a belt drive 22. A 
controller 24 controls motor 20 in a manner known to one skilled in the 
art to rotate roller 18. As roller 18 rotates, it advances belt 10 in the 
direction of arrow 12. An encoder wheel 19 (shown at FIG. 1), is mounted 
on the shaft of roller 18 and rotates in unison therewith to indicate the 
location of various portions of belt 10. 
Initially, a portion of the photoconductive surface of belt 10 passes 
through charging station A. At charging station A, a corona generating 
device, indicated generally by the reference numeral 26, charges the 
photoconductive surface to a relatively high, substantially uniform 
potential. 
Next, the charged portion of the photoconductive surface is advanced to 
imaging station B. Imaging station B includes a document handling unit, 
indicated generally by the reference numeral 28. Document handling unit 28 
sequentially feeds successive original documents from a stack of original 
documents placed by the operator face up in the normal forward collated 
order on the document handling and supporting tray. The uppermost sheet of 
the stack of documents is placed closely adjacent to a sheet feeder, 
indicated generally by the reference numeral 30. Sheet feeder 30 advances 
the topmost sheet from the stack of document to transport belt 32. 
Transport belt 32 advances the original document to platen 34. At platen 
34, the original document is positioned face down. Lamps 36 illuminate the 
original document on transparent platen 34. Light rays reflected from the 
original document are transmitted through lens 38. Lens 38 forms a light 
image from the original document which is projected onto the charged 
portion of the photoconductive surface of belt 10 to selectively dissipate 
the charge thereon. This records an electrostatic latent image on the 
photoconductive surface which corresponds to the informational areas 
contained in the original document. After illumination, the original 
document returns to the bottom of the stack of documents supported on tray 
40. 
After imaging, belt 10 advances the electrostatic latent image recorded on 
the photoconductive surface to development station C. At development 
station C, a magnetic brush developer unit, indicated generally by the 
reference numeral 42, advances developer material into contact with the 
electrostatic latent image recorded on the photoconductive surface of belt 
10. Preferably, magnetic brush development unit 42 includes two magnetic 
brush development rollers 44 and 46. These rollers each advance developer 
material into contact with the latent image. Each developer roller forms a 
brush comprising carrier granules and toner particles. The latent image 
attracts the toner particles from the toner granules, forming a toner 
powder image on the photoconductive surface of belt 10. As successive 
latent images are developed, particles are depleted from developer unit 
42. A toner powder dispenser 48 furnishes additional toner particles to 
developer housing 50 for subsequent development by the developer unit. 
Toner particle dispenser 48 stores a supply of toner particles which are 
subsequently dispensed into the developer housing 50 to maintain the 
concentration of toner particles therein substantially uniform. After the 
latent image is developed with toner particles to form a toner powder 
image on the photoconductive surface of belt 10, belt 10 advances the 
toner powder image to transfer station D. 
At transfer station D, a copy sheet is moved into contact with the toner 
powder image recorded on the photoconductive surface of belt 10. Copy 
sheets are fed from either tray 52 or 54. Each of these trays has a stack 
of sheets thereon. Sheet feeder 30 is also used herein to advance the 
topmost sheet of the stack. Conveyer 56 receives the sheet advanced from 
the respective feed tray by sheet feeder 30 and advances it to feed 
rollers 58. Feed rolls 58 advance the sheet to transfer station D. Sheet 
jam detection devices 59 are located adjacent conveyer 56 and between feed 
rolls 58, as well as being positioned adjacent all other sheet paths. The 
details of sheet jam detection device 59 will be described hereinafter 
with reference to FIG. 1. Prior to transfer, lamp 60 illuminates the toner 
powder image adhering to the photoconductive surface of belt 10 to reduce 
the attraction therebetween. Thereafter, a corona generating device 62 
sprays ions onto the backside of the copy sheet. The copy sheet is charged 
to the proper magnitude and polarity so that the copy sheet is tacked to 
the photoconductive surface of belt 10 and the toner powder image 
attracted thereto. After transfer, a corona generating device 64 charges 
the copy sheet to the opposite polarity to detack the sheet from belt 10. 
Conveyer 66 advances the copy sheet to fusing station E. 
Fusing station E includes a fusing assembly indicated generally by the 
reference numeral 68, which permanently affixes the transferred toner 
powder image to the copy sheet. Preferably, fuser assembly 68 includes 
heater fuser roller 70 and back-up roller 72 with the powder image on the 
copy sheet contacting the fuser rolls 70. Back-up roller 72 is cammed 
against the fuser roller 70 to provide the necessary pressure to 
permanently affix the toner powder image to the copy sheet. After fusing, 
conveyer 74 advances the copy sheet to gate 76. Gate 76 functions as an 
inverter selector. Depending upon the position of gate 76, the copy sheet 
will either be deflected into a sheet inverter, indicated generally by the 
reference numeral 78 or bypass the inverter 78 and be fed directly into a 
second decision gate 80. The copies which bypass inverter 78 are inverted 
so that the image side which has been transferred and fused is face up at 
this point. However, if the inverter path is selected, the opposite is 
true and the last printed side is face down. Decision gate 80 then either 
deflects the sheet directly into an output tray 88 or deflects the sheet 
into the transport path which carries them on without inversion to a third 
decision gate, 82. Decision gate 82 either passes the sheet directly on 
without inversion into the output path of the printing machine or deflects 
the sheet into a duplex inverting roller transport 84. Inverting roller 84 
inverts and stacks the sheets to be duplexed in duplex tray 86. Duplex 
tray 86 provides buffer storage for those copies which have been printed 
on one side and on which an image will be printed subsequently on the 
opposed side. For those sheets being duplexed, the process is repeated, 
with the fused image being affixed to the opposed side. 
Invariably, after the copy sheet is separated from the photoconductive 
surface of belt 10 and transfer station D, some residual particles remain 
adhering thereto. These residual particles are removed from the 
photoconductive surface at cleaning station F which includes a rotatably 
mounted fibrous brush 90 in contact with the photoconductive surface. The 
particles are cleaned from the photoconductive surface by the rotation of 
the brush in contact therewith. Subsequent to cleaning, a discharge lamp 
(not shown) floods the photoconductive surface with light to dissipate any 
residual or electrostatic charge remaining thereon prior to the charging 
thereof for the next cycle. 
Controller 24 is preferably a programmable microprocessor which controls 
all of the machine steps and functions heretofore described. Controller 24 
includes a processor 25 and a display 27, both of which are shown in FIG. 
1. Exemplary control systems for use in electrophotographic printing 
machines are described in U.S. Pat. No. 4,062,061, issued Dec. 6, 1977 to 
Batchelor, et al.; U.S. Pat. No. 4,132,155 issued Oct. 31, 1978 to Upert; 
U.S. Pat. No. 4,125,325, issued Nov. 14, 1978 to Batchelor, et al.; and 
U.S. Pat. No. 4,144,550 issued Mar. 13, 1979 to Donohue, et al., the 
relevant portions of the foregoing patents being incorporated into the 
present application. 
It is believed that the foregoing description is sufficient for purposes of 
the present application to illustrate the general operation of an 
electrophotographic printing machine incorporating the sheet jam detection 
apparatus of the present invention therein. 
Referring now to FIG. 1, encoder wheel 19 is mounted on shaft 21 which in 
turn also has roller 18 mounted therein. A light source 92, such as a 
light emitting diode, is disposed on one side of encoder wheel 19. 
Photosensor 94 is located on the other side of encoder wheel 19. Encoder 
wheel 19 has a multiplicity of equally spaced slots 96 in the marginal 
region thereof. As slots 96 pass between light source 92 and photosensor 
94, photosensor 94 transmits a signal to processor 25. A sheet is advanced 
by forwarding rollers 58 in the direction of arrow 98 between plates 100. 
A light source 102, for example a light emitting diode, is disposed 
adjacent one of the plates opposed from an opening therein, and 
photosensor 104 is positioned adjacent the other plate opposed from an 
opening therein. The openings in plate 100 are colinear with one another 
and light rays emitted form light source 102 are received by photosensor 
104. When the sheet moving in the direction of arrow 98, is interposed 
between light source 102 and photosensor 104, no light rays are received 
by photosensor 104. Processor 25 receives the signals from photosensor 
104. Processor 25 detects when the lead edge of the sheet is sensed or 
interposed between light source 102 and photosensor 104, and when the 
trail edge of the sheet exits from between light source 102 and 
photosensor 104. Processor 25 periodically interrogates photosensor 104. 
If the time interval between receiving the signal indicating that the 
leading edge has been interposed between photosensor 104 and light source 
102 and that the trailing edge of the sheet has exited therebetween 
exceeds a predetermined time interval, processor 25 indicates that a sheet 
jam has occurred along a path of movement of the sheet and generates a 
sheet jam signal. In response to the sheet jam signal, the printing 
machine is shut down. However, due to the high speed of the printing 
machine, other sheets in the sheet path of the printing machine will 
continue to advance and have to be removed therefrom as well as the jammed 
sheet. The effect of this inertia is measured by determining when the 
photoconductive belt 10 stops moving. Thus, processor 25 interrogates 
photosensor 94 and determines when encoder wheel 19 is no longer rotating. 
At this time, processor 25 develops a photoconductor signal. Processor 25 
includes information as to the size of the sheet, and basis or weight of 
the sheets being advanced in the printing machine. This information may be 
inputted by the machine operator. In addition, processor 25 measures the 
time interval between receiving the sheet jam signal and the 
photoconductor signal. Processor 25 then predicts the location of the 
sheets in the sheet path of the printing machine as a function of the 
measured time interval between the sheet jam signal and the photoconductor 
signal, and the basis or weight of the copy sheets being advanced in the 
printing machine. In addition, the size or length of the sheet is also 
used as a parameter to assist in predicting sheet location. 
In recapitulation, it is clear that the sheet jam detection device of the 
present invention determines the initial location of the jammed sheet and 
determines the continued movement of any sheets along the sheet path of 
the printing machine. This is accomplished by measuring the time interval 
between detecting the sheet jam and detecting when the photoconductive 
belt stops moving. Alternatively, encoder 19 may be mounted on the drive 
system advancing the sheet. In this instance, the signal will be 
indicative of the continued drive mechanism's movement after the jammed 
sheet is detected. In this way, it is clear that the sheet jam detection 
system of the present invention may be used in any sheet transport system. 
The sheet parameters, such as weight and size, are also used to assist in 
predicting the location of the sheets along the sheet path after the 
occurrence of a sheet jam. 
It is, therefore, evident that there has been provided in accordance with 
the present invention, a sheet jam detection system which fully satisfies 
the aims and advantages hereinbefore set forth. While this invention has 
been described in conjunction with a specific embodiment and method of use 
thereof, it is evident that many alternatives, modifications, and 
variations will be apparent to those skilled in the art. Accordingly, it 
is intended to embrace all such alternatives, modifications and variations 
which may fall within the spirit and scope of the appended claims.