US20070023994A1

US20070023994A1 - Media registration systems and methods

Info

Publication number: US20070023994A1
Application number: US11/194,823
Authority: US
Inventors: Barry Mandel; Martin Krucinski; Joannes deJong; Lloyd Williams
Original assignee: Xerox Corp
Current assignee: Xerox Corp
Priority date: 2005-08-01
Filing date: 2005-08-01
Publication date: 2007-02-01
Also published as: CA2553357A1; JP2007039247A; BRPI0603029A; CN1908824A; CN1908824B; CA2553357C

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.

Description

BACKGROUND

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

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.
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.
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.
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.
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.
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.
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.
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.
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.
These and other features are described in, or are apparent from, the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

Various exemplary embodiments of the systems and methods are described in detail below, with reference to the attached drawing figures, in which:
FIG. 1 is a graph showing force verses Velocity Ratio curves according to embodiments herein;
FIG. 2 is a schematic representation of drive nip assembly; and
FIG. 3 is a flow diagram illustrating aspects of embodiments herein.

DETAILED DESCRIPTION

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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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).
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.
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.
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.
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.
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.
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.
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.
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.

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

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 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

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.