U.S. patent application number 11/194823 was filed with the patent office on 2007-02-01 for media registration systems and methods.
This patent application is currently assigned to Xerox Corporation. Invention is credited to Joannes N. M. deJong, Martin Krucinski, Barry P. Mandel, Lloyd A. Williams.
Application Number | 20070023994 11/194823 |
Document ID | / |
Family ID | 37693464 |
Filed Date | 2007-02-01 |
United States Patent
Application |
20070023994 |
Kind Code |
A1 |
Mandel; Barry P. ; et
al. |
February 1, 2007 |
Media registration systems and methods
Abstract
Embodiments herein measure current/voltage levels of a drive
motor when media is in contact with a drive roller so as to
determine the drive force imparted by the drive rollers on the
media. Then, embodiments herein can reference the predetermined
relationship between roller drive force and media/drive roller
velocity ratios to determine a difference between the velocity of
the drive roller and the velocity the media based on the drive
force. Once this velocity difference is determined, embodiments
herein can change the current/voltage levels being applied to the
drive motor if the actual velocity of the media is different than
the intended velocity of the media so as to correct the velocity of
the media. Thus, when referencing the predetermined relationship,
embodiments herein produce a velocity ratio correction factor. This
velocity ratio correction factor can be applied continuously during
any velocity profile of the drive motor, or it can be used to
calculate the accumulated error in sheet position and then to apply
a correction near the end of the velocity profile.
Inventors: |
Mandel; Barry P.; (Fairport,
NY) ; Krucinski; Martin; (Webster, NY) ;
deJong; Joannes N. M.; (Hopewell Junction, NY) ;
Williams; Lloyd A.; (Mahopac, NY) |
Correspondence
Address: |
FREDERICK W. GIBB, III;GIBB INTELLECTUAL PROPERTY LAW FIRM, LLC
2568-A RIVA ROAD
SUITE 304
ANNAPOLIS
MD
21401
US
|
Assignee: |
Xerox Corporation
|
Family ID: |
37693464 |
Appl. No.: |
11/194823 |
Filed: |
August 1, 2005 |
Current U.S.
Class: |
271/226 |
Current CPC
Class: |
B65H 2220/02 20130101;
B65H 2220/01 20130101; B65H 9/002 20130101; B65H 2513/104 20130101;
B65H 2513/104 20130101; B65H 2404/14 20130101; B65H 2515/706
20130101; B65H 2515/706 20130101 |
Class at
Publication: |
271/226 |
International
Class: |
B65H 9/00 20060101
B65H009/00 |
Claims
1. A method comprising: measuring current/voltage levels,
comprising at least one of current and voltage levels, applied to a
drive motor connected to a drive roller in a drive nip assembly
adapted to move media within one of a printing and copying
apparatus; determining a difference between a velocity of said
drive roller and a velocity said media based on said
current/voltage levels; and changing said current/voltage levels
begin applied to said drive motor if an actual velocity of said
media is different than an intended velocity of said media.
2. The method of claim 1, further comprising determining a drive
force on said drive motor based on said current/voltage levels,
wherein said drive force is used in said determining of said
difference between said velocity of said drive roller and said
velocity of said media.
3. The method according to claim 1, further comprising continually
repeating said measuring, said determining, and said changing when
said media is in said drive nip assembly.
4. The method according to claim 1, further comprising: continually
repeating said measuring and said determining when said media is in
said drive nip assembly; and performing said changing as said media
is exiting said drive nip assembly.
5. The method according to claim 1, further comprising: detecting
an initial media skew as said media enters said drive nip assembly;
and using unequal application of at least two drive nip assemblies
to correct for said initial media skew.
6. A method comprising: establishing a predetermined relationship
between current/voltage levels and media/drive roller velocity
ratios, wherein said current/voltage levels comprise at least one
of current and voltage levels, applied to a drive motor connected
to a drive roller in a drive nip assembly adapted to move media
within one of a printing and copying apparatus, and wherein said
media/drive roller velocity ratios comprise velocity relationships
between said drive roller and said media when said media is in
contact with said drive roller; measuring current/voltage levels of
said drive motor when said media is in contact with said drive
roller; referencing said predetermined relationship to determine a
difference between a velocity of said drive roller and a velocity
said media based on said current/voltage levels; and changing said
current/voltage levels begin applied to said drive motor if an
actual velocity of said media is different than an intended
velocity of said media.
7. The method according to claim 6, wherein said predetermined
relationship is associated with said drive nip assembly.
8. The method according to claim 6, wherein said referencing of
said predetermined relationship produces a velocity ratio
correction factor.
9. The method according to claim 8, further comprising applying
said velocity ratio correction factor to all velocity profiles of
said drive motor.
10. The method according to claim 6, further comprising calibrating
said current/voltage levels of said drive motor when none of said
media is present in said drive nip assembly.
11. An apparatus comprising: a drive nip assembly adapted to move
media within one of a printing and copying apparatus; a drive motor
within said drive nip assembly; a drive roller connected to said
drive motor; and a control system connected to said drive motor,
wherein said control system is adapted to: measure current/voltage
levels, comprising at least one of current and voltage levels,
applied to said drive motor; determine a difference between a
velocity of said drive roller and a velocity said media based on
said current/voltage; and change said current/voltage levels begin
applied to said drive motor if an actual velocity of said media is
different than an intended velocity of said media.
12. The apparatus according to claim 11, wherein said control
system is further adapted to reference a predetermined relationship
between said current/voltage levels and media/drive roller velocity
ratios to determine said difference between said velocity of said
drive roller and said velocity of said media.
13. The apparatus according to claim 12, wherein said control
system is further adapted to produce a velocity ratio correction
factor when referencing said predetermined relationship.
14. The apparatus according to claim 13, wherein said control
system is further adapted to applying said velocity ratio
correction factor to all velocity profiles of said drive motor.
15. The apparatus according to claim 11, wherein said control
system is further adapted to calibrate said current/voltage levels
of said drive motor when none of said media is present in said
drive nip assembly.
16. An apparatus comprising: a drive nip assembly adapted to move
media within one of a printing and copying apparatus; a drive motor
within said drive nip assembly; a drive roller connected to said
drive motor; and a control system connected to said drive motor,
wherein a predetermined relationship exists between current/voltage
levels and media/drive roller velocity ratios, wherein said
current/voltage levels comprise at least one of current and voltage
levels, applied to said drive motor, and wherein said media/drive
roller velocity ratios comprise velocity relationships between said
drive roller and said media when said media is in contact with said
drive roller, and wherein said control system is adapted to:
measure current/voltage levels of said drive motor when said media
is in contact with said drive roller; reference said predetermined
relationship to determine a difference between a velocity of said
drive roller and a velocity of said media based on said
current/voltage; and change said current/voltage levels begin
applied to said drive motor if an actual velocity of said media is
different than an intended velocity of said media.
17. The apparatus according to claim 11, wherein said predetermined
relationship is associated with said drive nip assembly.
18. The apparatus according to claim 16, wherein said control
system is further adapted to produce a velocity ratio correction
factor when referencing said predetermined relationship.
19. The apparatus according to claim 18, wherein said control
system is further adapted to applying said velocity ratio
correction factor to all velocity profiles of said drive motor.
20. The apparatus according to claim 16, wherein said control
system is further adapted to calibrate said current/voltage levels
of said drive motor when none of said media is present in said
drive nip assembly.
Description
BACKGROUND
[0001] Embodiments herein generally relate to media
registration/alignment systems and methods within printers and
copiers. Current electronic registration systems use a pair of
narrow drive nips to control the media alignment during
registration, e.g., see U.S. Pat. No. 5,094,442 by Kamprath et al.,
issued Mar. 10, 1992, U.S. Pat. No. 5,697,609, by Williams et al.,
issued Dec. 16, 1997, U.S. Pat. No. 5,697,608, by Castelli et al.,
issued Dec. 16, 1997, U.S. Pat. No. 5,887,996, by Castelli et al.,
issued Mar. 30, 1999, U.S. Pat. No. 5,678,159, by Williams et al.,
issued Oct. 14, 1997, U.S. Patent Application Publication No.
2003/0146567 published Aug. 7, 2003 (Attorney Docket No.
A1351Q-US-CIP); U.S. Pat. No. 4,971,304 by Lofthus, issued Nov. 20,
1990; U.S. Pat. No. 5,169,140 by Wenthe, Jr., issued Dec. 8, 1992;
U.S. Pat. No. 5,219,159 by Malachowski et al, issued Jun. 15, 1993;
U.S. Pat. No. 5,278,624 by Kamprath et al, issued Jan. 11, 1994;
U.S. Pat. No. 5,794,176 by Milillo, issued Aug. 11, 1998; U.S. Pat.
No. 6,137,989 by Quesnel, issued Oct. 24, 2000; U.S. Pat. No.
6,168,153 B1 by Richards et al, issued Jan. 2, 2001; and U.S. Pat.
No. 6,533,268 B2 by Williams et al, issued Mar. 18, 2003, the
complete disclosures of which are incorporated herein by reference.
When heavy media, high accelerations, or high drag forces are
present, the surface of the registration nips becomes strained.
This strain has been demonstrated to cause a media velocity that is
different than the ideal roll surface velocity, and this results in
registration errors. These nip strain errors are worse with narrow
drive nips, such as those often used in registration systems, but
have also been observed to cause process registration errors in
systems which use relatively wide rollers. New feedback control
systems are being developed that enable the control system to
compensate for this nip strain by measuring actual paper movement.
An example of such a system is entitled "Print Media Registration
Using Active Tracking of Idler Rotation, Attorney Docket No.
20031544-US-NP, having U.S. patent Application Ser. No. 10/______,
the complete disclosure of which is incorporated herein by
reference. These systems work well, but add to the cost of the
system, which can be an issue in office class machines or in
systems where multiple registration devices are required. It is
highly desirable to improve registration system performance without
increasing cost.
SUMMARY
[0002] Methods herein supply a program of intended drive motor
current/voltage levels (current and/or voltage levels) to the drive
motor to establish an intended velocity of the drive motor and
corresponding intended velocity of the media moved by the drive
roller(s). For example, methods herein align media within the drive
nip assembly of a printing apparatus by adjusting the intended
current/voltage levels of the drive motor(s). The intended
current/voltage levels are used to adjust the intended velocity of
the drive motor(s) and associated drive roller(s) so as to position
or angle the media within the media path of the printing/copying
apparatus.
[0003] However, because of different effects between the drive
roller and media, the ratio of the velocity of the rollers to the
media may not be as expected from the intended current/voltage
level. In other words, there may be some difference between the
velocity of the roller and the velocity of the media. This velocity
difference or "velocity ratio" is caused by the normal interaction
of the surfaces of the roller and media. The velocity ratio is
different than "slippage" which occurs when the maximum allowable
coefficient of friction between the roller and media is exceeded.
After slippage occurs, it may be difficult or impossible to
establish a relationship between the velocity of the roller and
media; however, before slippage occurs (before the maximum
allowable coefficient of friction is exceeded) the embodiments
herein establish a relationship between drive motor torque (drive
motor current/voltage levels) and the velocity ratio.
[0004] Generally, as more current/voltage is applied to the drive
motor, the drive motor produces more torque, which may increase the
interaction forces between the roller and media, and may in turn
cause the velocity ratio to decrease from an initial value of 1:1
(unity), when no significant drag or inertial forces are present,
to a ratio that is less than or greater than one (e.g., 1:0.95,
1:0.90, 1:0.98, 1:1.02 etc.) when drag or inertial forces cause the
drive force between the rollers and media to increase. Further,
such change in velocity ratio is generally consistent among
different paper types that may be handled by a given drive nip
assembly (or class or type of drive nip assembly). Thus, by only
measuring drive motor current/voltage levels, embodiments herein
can determine the drive force between the drive rollers and media,
which can then be used to determine the velocity ratio at any point
in time and correct the velocity of the roller and the
corresponding velocity of the media accordingly, which avoids
having to provide additional hardware media sensors, etc. to detect
the actual discrepancy between roller velocity and media
velocity.
[0005] More specifically, method embodiments establish a
predetermined relationship between current/voltage levels and
media/drive roller velocity ratios of the specific drive nip
assembly (or type of drive nip assembly). The "current/voltage
levels" comprise current and/or voltage levels applied to the drive
motor and provide an indication of torque being output by the drive
motor. The "media/drive roller velocity ratios" comprise velocity
relationships between the drive roller and the media when the media
is in contact with the drive roller. Because the predetermined
relationship is based on results of testing one (or one type or
class of) drive nip assembly, the predetermined relationship is
considered to be "associated" with a given drive nip assembly.
[0006] The embodiments herein measure current/voltage levels of the
drive motor when the media is in contact with the drive roller so
as to determine the drive force being output by the drive motor.
Then, embodiments herein can reference the predetermined
relationship between current/voltage levels and media/drive roller
velocity ratios to determine a difference between the velocity of
the drive roller and the velocity the media based on the drive
force. Once this velocity difference is determined, embodiments
herein can change the current/voltage levels begin applied to the
drive motor if the actual velocity of the media is different than
the intended velocity of the media so as to correct the velocity of
the media. Thus, when referencing the predetermined relationship,
embodiments herein produce a velocity ratio correction factor. This
velocity ratio correction factor calculation can be done during any
velocity profiles of the drive motor. In addition, the inherent
drag and inertial forces from the motor and drive system can be
calibrated out by measuring the current/voltage levels required to
drive the system through a specified velocity profile when no media
is present in the drive nip assembly.
[0007] Apparatus embodiments herein can include a drive nip
assembly that is adapted to move media within a printing and/or
copying apparatus. A drive motor is included within the drive nip
assembly, and a drive roller is connected to the drive motor.
Further, a control system is connected to the drive motor. The
control system allows the intended current/voltage levels to be
changed if the actual velocity of the drive motor is different than
the intended velocity of the drive motor.
[0008] More specifically, the control system establishes a
predetermined relationship between current/voltage levels and
media/drive roller velocity ratios, as discussed above. After this,
the current/voltage levels of the drive motor can be measured when
the media is in contact with the drive roller to determine a drive
force on the media. The predetermined relationship between
current/voltage levels and media/drive roller velocity ratios is
referenced to determine the difference between the velocity of the
drive roller and the velocity of the media. This allows the control
system to change the current/voltage levels begin applied to the
drive motor if an actual velocity of the media is different than an
intended velocity of the media, so as to provide correction to the
drive nip assembly.
[0009] The control system produces the velocity ratio correction
factor when referencing the predetermined relationship and can
calculate the velocity ratio correction factor for all velocity
profiles of the drive motor. Also, the control system is used to
calibrate the current/voltage levels required to drive the system
when no media is present in the drive nip assembly. The control
system can repeat this calibration periodically to compensate for
changes in friction over the life of the system.
[0010] Before slippage occurs (before the maximum allowable
coefficient of friction is exceeded) the embodiments herein
establish a relationship between drive motor torque (drive motor
current/voltage levels) and the velocity ratio. The current/voltage
levels of the drive motor can be measured when the media is in
contact with the drive roller to determine a drive force on the
media. The predetermined relationship between current/voltage
levels and media/drive roller velocity ratios is referenced to
determine the difference between the velocity of the drive roller
and the velocity of the media. This allows the control system to
change the current/voltage levels being applied to the drive motor
if an actual velocity of the media is different than an intended
velocity of the media, so as to provide correction to the drive nip
assembly. Thus, by only measuring drive motor current/voltage
levels, embodiments herein can determine the drive force that the
rollers are imparting on the media, and then calculate the current
velocity ratio and correct the velocity of the roller and the
corresponding velocity of the media accordingly, which avoids
having to provide additional hardware media sensors, etc. to detect
the actual discrepancy between roller velocity and media
velocity.
[0011] These and other features are described in, or are apparent
from, the following detailed description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] Various exemplary embodiments of the systems and methods are
described in detail below, with reference to the attached drawing
figures, in which:
[0013] FIG. 1 is a graph showing force verses Velocity Ratio curves
according to embodiments herein;
[0014] FIG. 2 is a schematic representation of drive nip assembly;
and
[0015] FIG. 3 is a flow diagram illustrating aspects of embodiments
herein.
DETAILED DESCRIPTION
[0016] Embodiments herein use an "electronic" registration control
scheme that compensates for nip-strain induced errors (that occur
before the maximum allowable coefficient of friction is exceeded)
without requiring additional hardware. The act of accelerating,
translating and deskewing media through baffles generates inertial
and frictional drag forces that result in nip strain, which in turn
causes velocity ratios with a value other than unity between the
media and drive nip.
[0017] The present inventors have discovered that drive torques
applied to the motors in a registration system are proportional to
the drive forces that the nips exert on the media. Thus, the
embodiments herein provide a control system that accurately
predicts the velocity ratio of each nip during any given motion
profile by detecting the current or voltage delivered to the servo
motors (after the nip strain curve for the drive nips of the system
has been previously characterized). Embodiments herein use the
required current or voltage applied to the servo or step motor(s)
to deduce the drive force at the nip(s), and then calculate a
real-time correction to the roll velocity to compensate for
nip-strain. The control system then adjusts the target velocity of
the drive nips so that the media accurately follows the originally
intended velocity profile. Alternatively, instead of compensating
for the nip strain errors in real time, the velocity and media
position errors from the calculated nip strain could be tracked and
a correction made near the end of the registration profile.
[0018] Because of different effects between the drive roller and
media, the ratio of the velocity of the rollers to the media may
not be as expected from the intended current/voltage level. In
other words, there may be some difference between the velocity of
the roller and the velocity of the media. This velocity difference
or "velocity ratio" is caused by the normal interaction of the
surfaces of the roller and media. The velocity ratio is different
than "slippage" which occurs when the maximum allowable coefficient
of friction between the roller and media is exceeded. After
slippage occurs, it may be difficult or impossible to establish a
relationship between the velocity of the roller and media; however,
before slippage occurs (before the maximum allowable coefficient of
friction is exceeded) the embodiments herein establish a
relationship between drive motor torque (drive motor
current/voltage levels) and the velocity ratio.
[0019] FIG. 1 illustrates that different types and thicknesses of
media yield the same or very similar velocity ratio profiles when
subjected to the same drag in the same drive nip assembly or same
type of drive nip assembly. Therefore, FIG. 1 illustrates that the
change in velocity ratio can be known if the load is known. For
each type of drive nip assembly the velocity ratio curves will
match very closely. This type of testing can be done during the
drive nip assembly design phase or during manufacturing. If
desired, the curves can be averaged or processed through other
statistical routines to accommodate specific designer
requirements/tolerances, or to be more generally applied to broader
classes or types of drive nip assemblies. Embodiments herein
observe the load on the motor (which is directly correlated to the
drive force that the roller imparts on the media) to produce a
correction to the velocity ratio, which can be applied in real time
to the drive motor and provide accurate positioning of the media
within the printing apparatus.
[0020] Generally, as more current/voltage is applied to the drive
motor, the drive motor produces more torque, which may increase the
interaction forces between the roller and media, and may in turn
cause the velocity ratio to change from an ideal 1:1 (unity) to a
ratio that is less than or greater than one (e.g., 1:0.95, 1:0.90,
1:0.98, 1:1.02etc.). Further, such change in velocity ratio is
generally consistent among different paper types that may be
handled by a given drive nip assembly (or class or type of drive
nip assembly) and among different velocity profiles that may be
applied to a given drive nip assembly (or type of drive nip
assembly). Thus, by only measuring drive motor current/voltage
levels, embodiments herein can determine the velocity ratio and
correct the velocity of the roller and the corresponding velocity
of all types of media accordingly, which avoids having to provide
additional hardware media sensors, etc. to detect the actual
discrepancy between roller velocity and media velocity.
[0021] Thus, the velocity of media in a drive nip is dependent on
the drag on the media. The ratio of the velocity of the media to
the theoretical velocity of the roller is less than one when the
drag forces act on the media, and can be less than or greater then
one due to the combination of drag forces and inertial forces. This
can cause problems in registration systems, since such systems rely
on a predictable media velocity to achieve process direction
registration, and in many cases, deskew.
[0022] The errors caused by nip strain are largely dependent on the
tangential forces at each nip throughout the registration move.
These forces can vary for each sheet being registered, depending on
a variety of factors: initial registration errors, acceleration
profiles during the registration move, baffle and/or other paper
path component sheet drags. Due to this, the forces cannot be
"calibrated out" via "learning" or a set-up procedure. In many
registration systems media is still in an upstream bend during the
deskew process. Heavy paper and long heavy paper therefore require
higher drive forces, which results in higher nip strain errors.
Large, heavy media that comes in skewed or offset in one direction
will see different nip strain induced errors than media skewed or
offset in the opposite direction. The embodiments herein compensate
for these errors automatically and do not require any knowledge of
the media size or weight being registered.
[0023] As mentioned above, one way to compensate for these errors
is to detect the position of the sheet using an array of additional
sensors or encoders mounted to the drive roll idlers and connected
to a control system. However, this solution requires additional
sensing hardware.
[0024] FIG. 2 shows a two nip registration device in which the two
nips rollers 204 are driven by separately controlled DC servo
motors 200. The skew sensors 212 are used to detect the skew of the
media 206 so that it can be corrected by uneven usage of the
motors/rollers 200/204 before the media 206 reaches the image
transfer point 210. Input sensors 212 are used to detect the
leading edge of the media 206 as well as its speed, position, and
skew.
[0025] As explained above, the drive torques applied to the motors
200 in a two-nip registration system are directly proportional to
the drive forces that the nips 204 exert on the media 206. With
this information, the control system 220 can accurately know the
velocity ratio of each nip 206 during any given motion profile by
detecting the current or voltage delivered to the servo motors 200
after the nip strain curve for the drive nips of the system has
been previously characterized.
[0026] The embodiments herein provide a method of sensing the
current or voltage individually applied to the servo motors, using
that value to calculate a real-time correction to each different
roller velocity to compensate for nip-strain, and then adjusting
the velocity of the drive nips so that the media accurately follows
the originally intended profile. The system comprises the drive nip
assembly shown in FIG. 2 that has one or more drive rollers 204 and
a control system 220 that controls the voltage or current to the
one or more drive motors 200 so that the motors follow a prescribed
velocity profile. The control system 220 also uses the voltage or
current applied to the drive motors 200 to deduce the drive force
exerted by the drive rollers 204 on the media 206, and to provide a
correction factor to the prescribed velocity profile based on the
voltage or current value.
[0027] At least one motor 200, and one drive shaft (gears, etc.)
with at least one drive nip are used in embodiments herein,
although as would be understood by those ordinarily skilled in the
art, two or more motors 200, drive shafts, etc. could be used. The
motor(s) 200 can be DC servo motors, step motors, etc. The drive
rollers 204 can be made from an elastomeric or other similar
material. The position and skew of the lead edge of the media 206
entering the drive system can be detected using input sensors
212.
[0028] The control system 220 establishes a predetermined
relationship between current/voltage levels and media/drive roller
velocity ratios of the specific drive nip assembly (or type of
drive nip assembly). The "current/voltage levels" comprise current
and/or voltage levels applied to the drive motor 200 and provide an
indication of torque being output by the drive motor 200. The
"media/drive roller velocity ratios" comprise velocity
relationships between the drive roller and the media when the media
is in contact with the drive roller. Because the predetermined
relationship is based on results of empirical testing of one (or
one type or class of) drive nip assembly, the predetermined
relationship is considered to be "associated with" or "unique to"
the type of drive nip assembly. The current/ voltage supplied by
the controller to the motor should have sufficient sensitivity
considering the opposing drag/inertial forces. Thus, controller
gain/bandwidth must be sufficiently large to detect these
current/voltage levels.
[0029] The embodiments herein measure current/voltage levels of the
drive motor 200 when the media 206 is in contact with the drive
roller 204 so as to determine the drive force being output by the
drive motor 200. Then, the control system can reference the
predetermined relationship between current/voltage levels and
media/drive roller velocity ratios to determine the difference
between the velocity of the drive roller and the velocity the media
(based on the drive force). Once this velocity difference is
determined, the control system 220 can change the current/voltage
levels begin applied to the drive motor 200 if the actual velocity
of the media is different than the intended velocity of the media
(so as to correct the velocity of the media).
[0030] Thus, when referencing the predetermined relationship,
embodiments herein produce a velocity ratio correction factor. This
velocity ratio correction factor can be applied to all velocity
profiles of the drive motor 200. A velocity profile may, for
example, result in higher forces at the beginning of the movement
(when inertia is higher) and less forces when the media is
partially through the drive nip assembly (when maintaining a
constant velocity of the media). In one example, embodiments herein
will automatically apply a larger voltage or current to the motor
when high drag forces or inertial forces are present. As shown
above, this signal is then used to calculate a correction factor to
the desired velocity profile to compensate for nip strain
errors.
[0031] Different velocity profiles are useful for different aspects
of media movement, as would be understood by those ordinarily
skilled in the art in view of this disclosure. In addition, the
current/voltage levels of the drive motor 200 can be calibrated
when none of the media is present in the drive nip assembly.
Calibration is run on the drive system when no paper is present, so
that the drive torque inherent to the system can be subtracted
out.
[0032] The correction factor is based on the pre-defined
measurement of the variation of media velocity over a range of drag
forces for the drive rollers used in the system. The system drive
force is calibrated by driving the motors when no paper is present,
and using the current or voltage readings measured during this
operation to help deduce the additional drive force exerted on the
media during media transport. The nip velocity error due to nip
strain is corrected on a continuous or frequent basis, and the
accumulated nip strain error can be corrected just before the media
reaches the image transfer station. Alternatively, the errors due
to the deduced nip strain can be tracked (but not corrected on a
continuous basis) and a correction made near the end of the
registration roll velocity profile.
[0033] One exemplary control scheme is shown in flowchart form in
FIG. 3. More specifically, in item 300, the arrival of a new sheet
of media is sensed. The input sensor detects the media's presence
and any skew of the media, again using input sensors 212. Item 302
represents the calculation of the velocity profile which determines
the desired velocity (or position) profile form registration of the
drive rolls. This information is eventually supplied to the
controller in item 306 with supplies a control signal (motor
encoded coded signal) to the current/voltage amplifier (item 312).
The current/voltage is applied to the "plant" (motor, drives, media
drive, rollers, and eventually media) in item 314. A feedback loop
is provided to item 304 from the output of the motors to correct
for any error that may have occurred to the intended signal being
output by item 302.
[0034] Embodiments herein provide an additional feedback loop in
items 308 and 310. More specifically, in item 310 a control signal
being output by the controller in item 306 is measured in terms of
current and/or voltage. This current/voltage is then referenced on
a force calibration look-up table or equation which converts in the
current/voltage into nip the drive forces as shown in item 322.
Then, once the nip drive forces are known, the nip velocity
correction factor (that is based on the nip strain and calibration
curve shown, for example, in FIG. 1, above) is referenced in item
308. Thus, item 308 outputs a correction factor that is based on a
media/drive roller velocity ratio corresponding to the nip drive
forces determined in item 310. This correction factor is supplied
to item 302 so that the velocity profile being output by item 302
can be continually adjusted to account for the dynamically changing
media/drive roller velocity ratio that varies during the
interaction between the media and the nip rollers.
[0035] As shown in FIGS. 2 and 3, the embodiments herein
empirically establish a predetermined relationship between
current/voltage levels and media/drive roller velocity ratios of
the specific drive nip assembly (or type of drive nip assembly) in
item 320 (see discussion with respect to FIG. 1, above). In
addition, for a given motor or motor type, the actual force
associated with a given current or voltage application (draw) can
be obtained empirically to create the force calibration look-up
table shown as item 322. Thus, with the feedback loop input to item
310, embodiments herein measure current/voltage levels of the drive
motor when the media is in contact with the drive roller so as to
determine the drive force being output by the drive motor (item
310). Then, embodiments herein can reference the predetermined
relationship between current/voltage levels and media/drive roller
velocity ratios to determine a difference between the velocity of
the drive roller and the velocity the media based on the drive
force (item 308). Once this velocity difference is determined,
embodiments herein can change the current/voltage levels begin
applied to the drive motor if the actual velocity of the media is
different than the intended velocity of the media so as to correct
the velocity of the media in item 302.
[0036] Thus, when referencing the predetermined relationship,
embodiments herein produce a velocity ratio correction factor that
is supplied from item 308 to item 302. Since the velocity ratio
correction factor is the same or very similar for all media types
(or can be averaged, as discussed above) and is based on the force
applied, the velocity correction factor selected from the look-up
table or equation in item 320 can be universally applied to all
velocity profiles of the drive motor and all media types. In
addition, the current/voltage levels of the drive motor can be
calibrated when none of the media is present in the drive nip
assembly in item 320. The desired velocity profile defined in box
302 of FIG. 3 could function in several ways. It could take the
input from function 308 and correct the velocity of the drive nips
on a continuous basis. Alternatively, it could keep track of the
velocity, and resulting positional, errors in the sheet as a result
of the calculated nip strain, but not make a correction to the nip
velocity profiles until the registration profiles were near
completion. Other variations of these two control options are also
possible, however all make use of the signals sent to the drive
motors to deduce the nip drive forces and from that the nip strain
or velocity ratio for each nip. Also note that although the force
calibration and nip correction factor calculations are shown in
separate boxes in FIG. 3, these functions could be combined and a
single conversion directly from motor current or voltage to nip
velocity correction factor could be performed. Thus, the
embodiments herein provide a control system that accurately
predicts the velocity ratio of each nip during any given motion
profile by detecting the current or voltage delivered to the servo
motors (after the nip strain curve for the drive nips of the system
has been previously characterized). Embodiments herein use the
required current or voltage applied to the servo motor(s) to deduce
the drive force at the nip(s), and then calculate a real-time
correction to the roll velocity to compensate for nip-strain. The
control system then adjusts the target velocity of the drive nips
so that the media accurately follows the originally intended
velocity profile.
[0037] It will be appreciated that the above-disclosed and other
features and functions, or alternatives thereof, may be desirably
combined into many other different systems or applications. Also,
various presently unforeseen or unanticipated alternatives,
modifications, variations or improvements therein may be
subsequently made by those skilled in the art which are also
intended to be encompassed by the following claims.
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