U.S. patent application number 11/192633 was filed with the patent office on 2007-02-01 for system and method for optically detecting media feeding malfunctions in an image forming apparatus.
Invention is credited to Michael J. Brosnan, John P. Ertel, David C. Feldmeier, Seela Raj D. Rajaiah, Boon Keat Tan.
Application Number | 20070023997 11/192633 |
Document ID | / |
Family ID | 37104407 |
Filed Date | 2007-02-01 |
United States Patent
Application |
20070023997 |
Kind Code |
A1 |
Ertel; John P. ; et
al. |
February 1, 2007 |
System and method for optically detecting media feeding
malfunctions in an image forming apparatus
Abstract
A system and method for optically detecting media feeding
malfunctions in an image forming apparatus captures images of a
surface of a sheet of media as image signals to detect positional
changes of the sheet of media. The detected positional changes are
used to determine that a media feeding malfunction has occurred
when the positional changes satisfy a predefined condition.
Inventors: |
Ertel; John P.; (Half Moon
Bay, CA) ; Feldmeier; David C.; (Redwood City,
CA) ; Rajaiah; Seela Raj D.; (Penang, MY) ;
Tan; Boon Keat; (Penang, MY) ; Brosnan; Michael
J.; (Fremont, CA) |
Correspondence
Address: |
BRINKS HOFER GILSON & LIONE/MARVELL
P.O. BOX 10395
CHICAGO
IL
60610
US
|
Family ID: |
37104407 |
Appl. No.: |
11/192633 |
Filed: |
July 28, 2005 |
Current U.S.
Class: |
271/265.01 |
Current CPC
Class: |
H04N 1/0005 20130101;
B41J 13/0009 20130101; B41J 11/0095 20130101; B41J 13/0018
20130101; H04N 1/0066 20130101; H04N 1/00047 20130101; H04N 1/00039
20130101; H04N 1/00618 20130101; H04N 1/00034 20130101; H04N
1/00694 20130101; H04N 1/00082 20130101; H04N 1/00092 20130101;
H04N 1/00663 20130101; B41J 11/006 20130101; H04N 1/00734 20130101;
H04N 1/00681 20130101 |
Class at
Publication: |
271/265.01 |
International
Class: |
B65H 7/02 20060101
B65H007/02 |
Claims
1. A method for optically detecting media feeding malfunctions in
an image forming apparatus, the method comprising: capturing images
of a surface of a sheet of media being transported along a media
feeding path as image signals; processing the image signals of the
surface of the sheet of media to detect positional changes of the
sheet of media; and determining that a media feeding malfunction
has occurred when the positional changes satisfy a predefined
condition.
2. The method of claim 1 wherein the determining includes
determining that the media feeding malfunction has occurred when
the positional changes do not correlate with an expected amount of
positional changes as a feeding mechanism of the image forming
apparatus is commanded to move the sheet of media.
3. The method of claim 1 wherein the determining includes
determining that the media feeding malfunction has occurred when
the positional changes include a rotational movement.
4. The method of claim 1 wherein the determining includes
determining that the media feeding malfunction has occurred when
the positional changes include a lateral movement, the lateral
movement being in a direction perpendicular to the direction of the
media feeding path and parallel to the surface of the sheet of
media.
5. The method of claim 1 wherein the determining includes
determining that the media feeding malfunction has occurred when
the positional changes include a vertical movement in a direction
normal to the surface of the sheet of media.
6. The method of claim 5 wherein the determining further includes
detecting optical distortion of light reflected from the surface of
the sheet of media to determine whether the positional changes
include the vertical movement.
7. The method of claim 5 wherein the determining further includes
determining a shift of a reflected light beam received to capture
the image signals with respect to a reference point to determine
whether the positional changes include the vertical movement.
8. The method of claim 5 wherein the determining includes
determining the signal strength of said image signals to determine
whether the positional changes include the vertical movement.
9. The method of claim 1 further comprising realigning the sheet of
media using the positional changes derived from the image signals
to correct the media feeding malfunction.
10. A system for optically detecting media feeding malfunctions in
an image forming apparatus comprising: an optical movement tracking
sensor positioned along a media feeding path to capture images of a
surface of a sheet of media, the optical movement tracking sensor
including an array of photosensitive elements that captures the
images of the surface of the sheet of media as image signals; and
at least one processing circuit operatively connected to the
optical movement tracking sensor, the at least one processing
circuit being configured to process the image signals to detect
positional changes of the sheet of media and to determine that a
media feeding malfunction has occurred when the positional changes
satisfy a predefined condition.
11. The system of claim 10 wherein the at least one processing
circuit is configured to determine that the media feeding
malfunction has occurred when the positional changes do not
correlate with an expected amount of positional changes as a
feeding mechanism of the image forming apparatus is commanded to
move the sheet of media.
12. The system of claim 10 wherein the at least one processing
circuit is configured to determine that the media feeding
malfunction has occurred when the positional changes include one of
a rotational movement and a lateral movement, the lateral movement
being in a direction perpendicular to the direction of the media
feeding path and parallel to the surface of the sheet of media.
13. The system of claim 10 wherein the at least one processing
circuit is configured to determine that the media feeding
malfunction has occurred when the positional changes include a
vertical movement in a direction normal to the surface of the sheet
of media.
14. The system of claim 10 wherein the at least one processing
circuit includes a first processing circuit and second processing
circuit, the first processing circuit being integrated in the
optical movement tracking sensor, the first processing circuit
being configured to detect the positional changes of the sheet of
media, the second processing circuit being operatively connected to
the first processing circuit, the second processing circuit being
configured to determine that the media feeding malfunction has
occurred when the positional changes satisfy the predefined
condition.
15. The system of claim 10 further comprising a second optical
movement tracking sensor positioned along the media feeding path to
capture images of a second surface of the sheet of media.
16. The system of claim 10 further comprising a feeding mechanism
to displace the sheet of media along the media feeding path, the
feeding mechanism being configured to skew the sheet of media to
correct the media feeding malfunction.
17. The system of claim 16 wherein the feeding mechanism includes a
roller having a varying diameter, the roller being connected to a
shaft so that the roller can be moved along the length of the shaft
to change the effective diameter of the roller to correct the media
feeding malfunction.
18. An image forming apparatus comprising: a print cartridge to
deposit an image forming material onto sheets of media; a feeding
mechanism to move the sheets of media along a media feeding path;
an optical movement tracking sensor positioned along the media
feeding path to capture images of a surface of a sheet of media,
the optical movement tracking sensor including an array of
photosensitive elements that captures the images of the surface of
the sheet of media as image signals; and at least one processing
circuit operatively connected to the optical movement tracking
sensor, the at least one processing circuit being configured to
process the image signals to detect positional changes of the sheet
of media and to determine that a media feeding malfunction has
occurred when the positional changes satisfy a predefined
condition.
19. The apparatus of claim 17 wherein the at least one processing
circuit is configured to determine that the media feeding
malfunction has occurred when the positional changes do not
correlate with expected positional changes as the feeding mechanism
is commanded to move the sheet of media.
20. The apparatus of claim 17 wherein the at least one processing
circuit is configured to determine that the media feeding
malfunction has occurred when the positional changes include a
vertical movement in a direction normal to the surface of the sheet
of media.
Description
BACKGROUND OF THE INVENTION
[0001] Computer printers, as well as other image forming apparatus
such as copiers, need to transport one or more successive sheets of
paper from a paper tray to a print cartridge, such as an inkjet
cartridge or a laser toner cartridge, during a printing operation.
The transporting of sheets of paper is performed by a feeding
mechanism of the printer, which includes a number of rollers to
drive the sheets of paper along a paper feeding path from the paper
tray to the print cartridge. Due to the mechanical nature of the
paper transporting operation, all printers are susceptible to
occasional paper feeding malfunctions, i.e., paper jams, during a
printing operation.
[0002] When a paper jam occurs, a printer will continue to operate
until the paper jam is detected. Consequently, the printer will
continue to dispense ink or toner and continue to move successive
sheets of paper until the paper jam is detected and the printing
operation is suspended. Thus, it is desirable to detect a paper jam
as soon as possible to minimize the waste of printer consumables,
such as ink, toner and sheets of paper.
[0003] A conventional technique to detect a paper jam in a printer
is to place one or more mechanical sensors along the paper feeding
path of the printer to determine whether or not sheets of paper are
moving correctly along the paper feeding path. As the sheets of
paper are driven through the paper feeding path by the feeding
mechanism, each sheet of paper is expected to reach a particular
mechanical sensor. If the sensor does not detect the sheet of paper
when it should, then the printer can assume that a paper jam has
occurred and execute a predetermined procedure, which may include
activating a paper jam indicator as well as suspending the printing
operation.
[0004] Although this conventional paper jam technique is effective
in detecting paper jams, there is a significant time delay between
the occurrence of a paper jam and the detection of the paper jam.
Thus, the printer will continue with the printing operation during
this time delay, which results in a waste of printer
consumables.
[0005] In view of this concern, there is a need for a system and
method for detecting a paper jam more quickly.
SUMMARY OF THE INVENTION
[0006] A system and method for optically detecting media feeding
malfunctions in an image forming apparatus captures images of a
surface of a sheet of media as image signals to detect positional
changes of the sheet of media. The detected positional changes are
used to determine that a media feeding malfunction has occurred
when the positional changes satisfy a predefined condition. This
optical detecting technique allows for a media feeding malfunction
to be detected quickly so that waste of consumables used by the
image forming apparatus is minimized.
[0007] A method for optically detecting media feeding malfunctions
in an image forming apparatus in accordance with an embodiment of
the invention comprises capturing images of a surface of a sheet of
media being transported along a media feeding path as image
signals, processing the image signals of the surface of the sheet
of media to detect positional changes of the sheet of media, and
determining that a media feeding malfunction has occurred when the
positional changes satisfy a predefined condition.
[0008] A system for optically detecting media feeding malfunctions
in an image forming apparatus in accordance with an embodiment of
the invention comprises an optical movement tracking sensor
positioned along a media feeding path to capture images of a
surface of a sheet of media, the optical movement tracking sensor
including an array of photosensitive elements that captures the
images of the surface of the sheet of media as image signals, and
at least one processing circuit to process the image signals to
detect positional changes of the sheet of media and to determine
that a media feeding malfunction has occurred when the positional
changes satisfy a predefined condition.
[0009] An image forming apparatus in accordance with an embodiment
of the invention comprises a print cartridge to deposit an image
forming material onto sheets of media, a feeding mechanism to move
the sheets of media along a media feeding path, an optical movement
tracking sensor positioned along the media feeding path to capture
images of a surface of a sheet of media, the optical movement
tracking sensor including an array of photosensitive elements that
captures the images of the surface of the sheet of media as image
signals, and at least one processing circuit to process the image
signals to detect positional changes of the sheet of media and to
determine that a media feeding malfunction has occurred when the
positional changes satisfy a predefined condition.
[0010] Other aspects and advantages of the present invention will
become apparent from the following detailed description, taken in
conjunction with the accompanying drawings, illustrated by way of
example of the principles of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 is a diagram of an image forming apparatus in
accordance with an embodiment of the invention.
[0012] FIG. 2 is a diagram of some of the components of the image
forming apparatus of FIG. 1, including a media feeding malfunction
detection system in accordance with an embodiment of the
invention.
[0013] FIG. 3 is a diagram of an optical movement tracking sensor
of the media feeding malfunction detection system in accordance
with an embodiment of the invention.
[0014] FIGS. 4A and 4B illustrate trajectories of a laser beam when
a sheet of media is at different distances from a photosensor array
of an optical movement tracking sensor.
[0015] FIG. 5 is a diagram of a feeding mechanism that uses a
realigning technique in accordance with an embodiment of the
invention.
[0016] FIG. 6 is a process flow diagram of a method for optically
detecting media feeding malfunctions in an image forming apparatus
in accordance with an embodiment of the invention.
DETAILED DESCRIPTION
[0017] With reference to FIG. 1, an image forming apparatus 100 in
accordance with an embodiment of the invention is described. The
image forming apparatus 100 is illustrated and described herein as
a computer printer. However, the image forming apparatus 100 may be
any type of an image forming apparatus, such as a copier, a fax
machine, a ticket printer or a receipt printer. The image forming
apparatus 100 may use inkjet or laser jet technology to print text,
graphics, pictures and/or other images on sheets of media, such as
paper, fabric, plastic or any other medium on which images can be
printed. The image forming apparatus 100 includes a media feeding
malfunction detection system 102, which detects a media feeding
malfunction, e.g., a paper jam, by monitoring positional changes of
a sheet of media as that sheet of media is transported along a
media feeding path within the image forming apparatus 100. As
described in more detail below, the monitoring of positional
changes of a sheet of media is achieved using one or more optical
movement tracking sensors, which use surface features on the sheet
of media to determine relative positional changes, or movement, of
the sheet of media. When the detected positional changes of the
sheet of media satisfy one or more predefined conditions, then a
determination is made that a media feeding malfunction has
occurred. Using this technique in accordance with the invention, an
occurrence of a media feeding malfunction can be detected more
quickly than a conventional detection technique that uses one or
more mechanical sensors. As a result, less consumables used by the
image forming apparatus 100 are wasted when there is a media
feeding malfunction.
[0018] As shown in FIG. 1, the image forming apparatus 100 includes
the media feeding malfunction detection system 102, a media tray
104 and an output platform 106. The media tray 104 is used to store
new sheets of media to be used by the image forming apparatus 100.
The output platform 106 is used to place printed sheets of media.
Thus, during a printing operation, one or more new sheets of media
are transported within the image forming apparatus 100 from the
media tray 104 to the output platform 106 by a feeding mechanism
208 (not shown in FIG. 1) of the image forming apparatus. The
feeding mechanism 208 is illustrated in FIG. 2, which shows some of
the internal components of the image forming apparatus 100. As
shown in FIG. 2, the feeding mechanism 208 of the image forming
apparatus 100 includes rollers 210, 212, 214 and 216 and motors 218
and 220. The rollers 210, 212, 214 and 216 are positioned along a
media feeding path 222, which begins from the media tray 104 and
ends at the output platform 106. The media feeding path 222 passes
by a print cartridge 224 of the image forming apparatus 100. The
print cartridge 224 may be an inkjet cartridge or a toner cartridge
that operates to deposit an image forming material, e.g., ink or
toner, onto sheets of media being transported along the media
feeding path 222. The print cartridge 224 may be designed to be
displaced to scan each sheet of media during a printing
operation.
[0019] The rollers 210, 212, 214 and 216 of the feeding mechanism
208 operate to move sheets of media 225 along the media feeding
path 222 during a printing operation. The motors 218 and 220 are
connected to the rollers 210, 212, 214 and 216 to rotate the
rollers to move the sheets of paper along the media feeding path
222. As an example, the motors 218 and 220 may be connected to the
rollers 210, 212, 214 and 216 via belts and/or gears (not shown) to
rotate the rollers. The motors 218 and 220 may be stepper motors or
DC drive motors. In FIG. 2, the motor 218 is connected to the
rollers 210 and 212, while the motor 220 is connected to the
rollers 214 and 216. Thus, the motor 218 rotates the rollers 210
and 212, while the motor 220 rotates the rollers 214 and 216.
Although only four rollers and two motors are shown in FIG. 2, the
feeding mechanism 208 of the image forming apparatus 100 may
include fewer or more rollers and motors. Furthermore, each motor
of the feeding mechanism 208 may be connected to different number
of rollers to rotate one or more rollers.
[0020] The media feeding malfunction detection system 102 of the
image forming apparatus 100 includes an optical movement tracking
sensor 226 and a central processing circuit 228. The optical
movement tracking sensor 226 is positioned along the media feeding
path 222 to optically monitor the movements of the sheets of media
225 as the sheets of media are being transported along the media
feeding path by the feeding mechanism 208. The optical movement
tracking sensor 226 monitors the movements of a sheet of media by
capturing image information of a surface of the sheet of media,
processing the image information to detect positional changes of
the sheet of media and outputting the detected positional changes
as a digital output signal. The digital output signal is
transmitted to the central processing circuit 228, which processes
the received signal to determine whether the sheet of media is
moving properly along the media feeding path 222 or whether there
is a media feeding malfunction, e.g., a paper jam. The central
processing circuit 228 also controls the motors 218 and 220 of the
feeding mechanism 208 to rotate the rollers 210, 212, 214 and 216
when one or more sheets of media are to be transported along the
media feeding path 222. As used herein, a processing circuit can be
any type of a processing circuit, which uses software, firmware
and/or hardwired logic to perform one or more tasks.
[0021] As shown in FIG. 2, the media feeding malfunction detection
system 102 may include a second optical movement tracking sensor
230, which may be similar in structure and function to the first
optical movement tracking sensor 226. Using the optical movement
tracking sensors 226 and 230, both sides of a sheet of media, i.e.,
the upper and lower surfaces of the sheet of media, can be
monitored. The optical movement tracking sensor 226 is positioned
to monitor the upper surface of a sheet of media, while the optical
movement tracking sensor 230 is positioned to monitor the lower
surface of the sheet of media. Although only two optical movement
tracking sensors are shown in FIG. 2, in other embodiments, the
media feeding malfunction detection system 102 may include
additional optical movement tracking sensors along the media
feeding path 222, especially if the media feeding path is
significantly long. In some embodiments, the media feeding
malfunction detection system 102 may include one or more optical
movement tracking sensors attached to the bottom of the print
cartridge 224.
[0022] The optical movement tracking sensor 226 is now described
with reference to FIG. 3, which illustrates the components of the
sensor. As shown in FIG. 3, the optical movement tracking sensor
226 includes a light source 332, a photosensor array 334, an
analog-to-digital converter (ADC) 336 and a local processing
circuit 338. The light source 332 provides a beam of light 340 that
is used to illuminate a region 342 on a surface of a sheet of media
344 being monitored. The light source 332 may be a light emitting
diode (LED), a laser diode or any other device that can generate a
beam of light. The photosensor array 334 is an array of
photosensitive elements that can image a portion of the surface of
the sheet of media 344 using a reflected beam of light received
from that surface portion of the sheet of media. As used herein, an
image of a media surface may simply mean light reflected from the
media surface, which is received by the photosensor array 334. As
an example, the photosensor array 334 may be a charge coupled
device (CCD) array or a complementary metal oxide semiconductor
(CMOS) array. Each photosensitive element in the photosensor array
334 generates an analog image signal as an accumulated electrical
charge in response to the intensity of received light at that
photosensitive element. The analog image signals generated by the
photosensitive elements of the photosensor array 334 are converted
to digital image signals by the ADC 336 and transmitted to the
local processing circuit 338 for signal processing.
[0023] The image signals of a surface portion of a sheet of media
are captured in frames, where a frame includes a set of
simultaneously captured image signals from the photosensitive
elements in the photosensor array 334. Sheets of media have surface
features, which when illuminated, can be picked up by the
photosensor array 334. The captured frames of image signals include
image information of these features on the surface of the sheet of
media being monitored. The image capture frame rate is
programmable.
[0024] The local processing circuit 338 receives the successive
frames of image signals and processes the frames to determine
positional changes or movement of the sheet of media 344. In
particular, common features in the successive frames are correlated
to determine the relative movement of the sheet of media 344. The
movement of the sheet of media 344 is expressed in terms of changes
in the X and Y direction. As used herein, the X direction is
parallel to the direction of the media feeding path 222, while the
Y direction is perpendicular to the direction of the media feeding
path and parallel to the surface of the sheet of media 344. More
detailed description of exemplary image-based movement tracking
techniques are provided in U.S. Pat. No. 5,644,139, entitled
"Navigation Technique For Detecting Movement Of Navigation Sensors
Relative To An Object", and U.S. Pat. No. 6,222,174, entitled
"Method of Correlating Immediately Acquired And Previously Stored
Feature Information For Motion Sensing", both of which are assigned
to the assignee of the current invention.
[0025] Turning back to FIG. 2, the central processing circuit 228
of the media feeding malfunction detection system 102 uses the
media movement information provided by one or more optical movement
tracking sensors, such as the sensors 226 and 230, to determine
whether a media feeding malfunction has occurred. Usually, a sheet
of media moves straight along the media feeding path 222 (i.e., in
the X direction) with neglible or minimal amount of rotation or
movement perpendicular to the media feeding path (i.e., in the Y
direction). Often when a media feeding malfunction occurs, one part
of the sheet of media stops moving while another part of the sheet
of media continues to move, at least for a short period of time. In
many cases, the fact that different parts of the sheet of media are
moving at different speeds will cause parts of the sheet of media
to rotate, to move in a direction perpendicular to the media
feeding path 222 or to buckle, sometimes causing one or more
z-folds. The central processing circuit 228 determines that a media
feeding malfunction has occurred when one or more of these
indications of a media feeding malfunction are detected.
[0026] The central processing circuit 228 determines that a media
feeding malfunction has occurred when there is no movement of a
sheet of media when that sheet of media should be moving. That is,
when the central processing circuit 228 activates some or all of
the motors 218 and 220 of the feeding mechanism 208 to rotate some
or all of the rollers 210, 212, 214 and 216 and the optical
movement tracking sensors 228 and 230 detect no media motion when
there should be, the central processing circuit 228 determines that
a media feeding malfunction has occurred.
[0027] The central processing circuit 228 can also determine that a
media feeding malfunction has occurred when a sheet of media is
moving too slowly in the X direction. The amount of media movement
in the X direction can be compared to an expected amount of media
motion, which can be correlated to the activation of one of both of
the motors 218 and 220 of the feeding mechanism 208. If the motors
218 and 220 are stepper motors, then the number of steps the motors
are driven will correspond to a certain amount of media motion.
Thus, the number of steps the motors 218 and 220 are driven can be
used to determine the expected amount of media motion. If the
motors 218 and 220 are DC drive motors, then the amount of current
applied to the motors will correspond to a certain amount of media
motion. Thus, in this case, the amount of current applied to the
motors 218 and 220 can be used to determine the expected amount of
media motion. Alternatively, the motors 218 and 220 may include
optical encoders to measure the rotation of the motors when
activated, which can be used to determine the expected amount of
media motion. When the detected amount of motion for a sheet of
media is less than the expected amount of media motion, the central
processing circuit 228 can determine that a media feeding
malfunction has occurred.
[0028] The central processing circuit 228 can also determine that a
media feeding malfunction has occurred when a sheet of media has
significantly rotated or moved in a direction perpendicular to the
media feeding path 222, i.e., in the Y direction. When one or both
of the optical movement tracking sensors 226 and 230 detect a media
rotational movement greater than a predetermined rotational
threshold, the central processing circuit 228 can determine that a
media feeding malfunction has occurred. Similarly, when one or both
of the optical movement tracking sensors 226 and 230 detect a media
later movement in the Y direction greater than a predetermined
movement threshold, the central processing circuit 228 will
determine that a media feeding malfunction has occurred.
[0029] The central processing circuit 228 can also determine that a
media feeding malfunction has occurred when a sheet of media has
significantly moved in the vertical direction, which is normal to
the surface of the sheet of media. Movement in the vertical
direction indicates buckling of a sheet of media during a media
feeding malfunction. One technique to detect a media feeding
malfunction induced buckling is to compare the number of specific
surface features of a sheet of media detected by one or both of the
optical movement tracking sensors 226 and 230 to an expected number
of specific surface features. As a sheet of media moves with
respect to an optical movement tracking sensor, an average number
of specific surface features are expected to be detected by that
sensor. If a light emitting diode is used as the light source of
the optical movement tracking sensor, these specific surface
features becomes blurred when the sheet of media moves away from
the best focus position, i.e., moves toward or away from the
optical movement tracking sensor, which decreases the number of the
specific surface features that are detected by that sensor. If a
laser is used as the light source of the optical movement tracking
sensor, these specific surface features becomes less visible when
the sheet of media moves away from the best focus position since
the reflected laser beam on the photosensor array of the optical
movement tracking sensor will shift such that some of the
photosensitive elements are not well illuminated. This is due to
the fact that the position of the reflected laser beam on the
photosensor array will depend on the distance between the sheet of
media and the photosensor array. As illustrated in FIG. 4A, when a
sheet of media 402 is at an optimal distance (D), the center of the
laser beam 404 from the light source 332 will be at a reference
point 406 on the photosensor array 334, somewhere near the center
of the photosensor array. However, as the sheet of media 402 moves
away from this optimal distance, the center of the laser beam 404
will correspondingly shift on the photosensor array 334. As
illustrated in FIG. 4B, when the sheet of media 402 is at some
distance greater than the optical distance (D+.DELTA.), the center
of the laser beam 402 will have shifted away from the reference
point 406 on the photosensor array 334. The result is that when the
reflected laser beam has significantly shifted from the proper
trajectory, some of the photosensitive elements of the photosensor
array 334 are not well illuminated, which will reduce the number of
specific surface features that are detected by the optical movement
tracking sensor. If the number of these specific surface features
detected by the optical movement tracking sensors 226 and 230
decreases significantly, then it can be assumed that the sheet of
media has moved toward or away from the respective optical movement
tracking sensors. Thus, when the specific surface features detected
by one or both of the optical movement tracking sensor 226 and 230
falls below a certain threshold, the central processing circuit 228
can determine that a media feeding malfunction has occurred.
[0030] If the above detection technique does not work well for
certain types of media, the technique may be improved by first
determining the expected range of detectable surface features for
these types of media based on user media selection or based on
initial reading of detected surface features when one of these
types of media is first loaded.
[0031] There are other methods to determine that the reflected beam
of light on the photosensor array of one or both of the optical
movement tracking sensors 226 and 230 has shifted. A shift of the
beam center can be determined by observing that some photosensor
elements, which are not normally illuminated, are in fact
illuminated or that some photosensor elements, which are normally
illuminated, are in fact not illuminated. Since the lack of
illumination at certain photosensor elements could be caused by
surface features, several frames should be observed to see if the
same photosensor elements are not illuminated, or else look to see
whether an entire strip of photosensor elements along an edge of
the photosensor array is not illuminated (this is unlikely unless
the beam has moved off the center of the photosensor array).
Alternatively, the beam diameter can be reduced so that the entire
beam is contained within the photosensor array, which means that
some of the photosensor elements at the edges or corners of the
array will not be illuminated during normal operation. A shift in
the beam center can then be detected by observing the shape of the
photosensor elements that are illuminated in the photosensor
array.
[0032] Another technique for detecting a media feeding malfunction
induced buckling is to use a signal strength indicator such as the
shutter time reported by an automatic exposure algorithm used for
the optical movement tracking sensors 226 and 230. When media
buckling is sufficiently large, the optical signal strength
received by the photosensor array of the optical movement tracking
sensors will decrease due to a shift in the reflected beam of light
on the photosensor array. Thus, when the signal strength indicator
is less than a predefined threshold, then the central processing
circuit 228 can determine that a media feeding malfunction has
occurred.
[0033] Another technique for detecting a media feeding malfunction
induced buckling is to use a "liftoff detection" method, which is
used to detect when an optical computer mouse has been lifted from
a work surface. Any liftoff detection method may be used to
determine that a sheet of media has moved away from an optical
movement tracking sensor, indicating media buckling. A liftoff
detection method of interest uses a mechanical shouldered plunger
that activates a switch when the plunger moves due to the
separation of the optical mouse and the work surface. Another
liftoff detection method of interest determines that an optical
computer mouse has been lifted from a work surface when the outputs
of the photosensor elements in the optical mouse become uniform.
Details of these liftoff detection methods can be found in U.S.
Pat. No. 6,281,882.
[0034] In an embodiment, when a media feeding malfunction due to
misalignment of a sheet of media has been detected, the feeding
mechanism 108 may be directed to realign the sheet of media to
correct the media feeding malfunction. There are different
techniques to realign a sheet of media when the sheet of media is
misaligned or skewed. One technique is to use a feeding mechanism
with multiple rollers that can be independently controlled with
respect to rotational speed to rotate a sheet of media to realign
the sheet of media. Another technique is to use a feeding mechanism
with multiple rollers in which at least one of the rollers can be
controlled to vary the effective roller diameter to rotate a sheet
of media to realign the sheet of media.
[0035] In FIG. 5, a feeding mechanism 500 that uses the latter
realigning technique in accordance with an embodiment of the
invention is shown. The feeding mechanism 500 includes drive
rollers 502 and 504, pressure rollers 506 and 508, and a motor 510.
The drive rollers 502 and 504 are connected to a shaft 512, which
is connected to the motor 510 that rotates the shaft. The pressure
rollers 506 and 508 are positioned to engage the drive rollers 502
and 504, respectively, so that a sheet of media 514 positioned
between the drive rollers 502 and 504 and the pressure rollers 506
and 508 is displaced when the drive rollers are rotated by the
shaft 512. The drive roller 502 is cylindrical in shape. Thus, the
drive roller 502 has a fixed diameter. However, the other drive
roller 504 is tapered such that the diameter of the roller 504 gets
progressively smaller toward one end, i.e., the end closest to the
motor 510. Thus, the drive roller 504 has a varying diameter. The
drive roller 502 is fixed on the shaft 512. However, the tapered
drive roller 504 can be moved along the length of the shaft 512 so
that the effective diameter of the tapered roller, i.e., the
diameter of the tapered roller at a region engaged with the
pressure roller 508. The tapered roller 504 can be divided into
three regions 516A, 516B and 516C. In the region 516B, the diameter
of the tapered roller 504 is same as the diameter of the drive
roller 502. In the region 516A, the diameter of the tapered roller
504 is smaller than the diameter of the drive roller 502. In the
region 516C, the diameter of the tapered roller 504 is larger than
the diameter of the drive roller 502.
[0036] During normal operation, the tapered roller 504 is axially
positioned on the shaft 512 such that the region 516B is engaged
with the pressure roller 508. Since the diameter of the tapered
roller 504 is same as the diameter of the drive roller 502 at the
region 516B, the sheet of paper 514 will be driven straight along
the X direction by the drive rollers 502 and 504 without any
rotation or skewing. However, when the sheet of media 514 is
misaligned, the tapered roller 504 is moved along the length of the
shaft 512 so that the region 516A or 516C of the tapered roller is
engaged with the pressure roller 508. If the region 516A of the
tapered roller 504 is engaged with the pressure roller 508, the
sheet of media 514 will be rotated in the Y direction since the
diameter of the tapered roller is smaller than the diameter of the
drive roller 502 at the region 516A. If the region 516C of the
tapered roller 502 is engaged with the pressure roller 508, the
sheet of media 514 will be rotated in the negative Y direction
since the diameter of the tapered roller is larger than the
diameter of the drive roller 502 at the region 516C. Using the
feedback from the optical movement tracking sensors 226 and 228,
the axial position of the tapered roller 502 can be adjusted to
maintain a straight media path for a sheet of media being driven by
the feeding mechanism 500 and correct for any skewing of the sheet
of media.
[0037] A method for detecting media feeding malfunctions, e.g.,
paper jams, in an image forming apparatus in accordance with an
embodiment of the invention is described with reference to a
process flow diagram of FIG. 6. At block 602, images of a surface
of a sheet of media being transported along a media feeding path
are captured as image signals. Next, at block 604, the image
signals of the surface of the sheet of media are processed to
detect positional changes of the sheet of media. Next, at block
606, a media feeding malfunction is determined to have occurred
when the positional changes satisfy a predefined condition.
[0038] Although specific embodiments of the invention have been
described and illustrated, the invention is not to be limited to
the specific forms or arrangements of parts so described and
illustrated. The scope of the invention is to be defined by the
claims appended hereto and their equivalents.
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