Patent Application
20070023994
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.
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.
Various exemplary embodiments of the systems and methods are described in detail below, with reference to the attached drawing figures, in which:
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.
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.
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
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
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
As shown in
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
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.
