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"Learning" Algorithm for Registration Device to Reject Average Image Motion Disturbances

IP.com Disclosure Number: IPCOM000033686D
Publication Date: 2004-Dec-23
Document File: 5 page(s) / 145K

Publishing Venue

The IP.com Prior Art Database

Abstract

One of the key enablers for a high speed copier, printer, or multi-function device is to be able to perform proper image to paper registration at high process velocities. By learning the average (i.e. repeatable) drum motion variations during the transfer/fixing roller engage/disengage cycles in a print job, the registration of each individual sheet can be adjusted by the sheet registration mechanism to compensate for the average drum motion variations.

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"Learning" Algorithm for Registration Device to Reject Average Image Motion Disturbances

One of the key enablers for a high speed copier, printer, or multi-function device is to be able to perform proper image to paper registration at high process velocities.  To achieve accurate image to paper registration, two requirements have to be fulfilled:


1) The image has to arrive at the transfer nip at the desired time and the desired velocity
2) The paper has to arrive at the transfer nip at the desired time and the desired velocity


In one configuration, an imaging drum carries the image to the transfer nip, and
the registration mechanism carries the paper to the transfer nip.  The problem is that the drum velocity varies around its nominal value due to the transfer/fixing roller engagement and disengagement, friction variations, run-out errors, etc. This causes the image to arrive at the image transfer nip at a different time than intended, violating requirement 1) above.

By learning the average (i.e. repeatable) drum motion variations during the transfer/fixing roller engage/disengage cycles in a print job, the registration of each individual sheet can be adjusted by the sheet registration mechanism to compensate for the average drum motion variations.   Most of the drum velocity variation is periodic and repeatable due to the periodic nature of the disturbance caused by the transfer/fixing roller engage / disengage cycle.

Drum motion:

Due to a variety of torque disturbances, such as

  1. transfer/fixing roller engage / disengage (major disturbance)
  2. drum once-around friction variations
  3. drum motor and gear once-around friction variations
  4. drum brake friction variations

the drum velocity v(t) varies in a typical example away from the desired nominal velocity vd = 55.00 ips = 1.397 m/s, see the figure below where the dashed line corresponds to the nominal drum velocity, and the solid line is the actual velocity during transfer/fixing engage / disengage cycles.

This implies that the position of an image on the drum, defined as x(t) = ∫ v(t) dt = R θ(t) where R is the drum diameter, and θ(t) is the accumulated drum rotation angle for this image, is different than the desired position which is xd(t) = ∫ vd(t) dt = vd t + C, where C is a constant offset position for each sheet.

The difference between the image position and its desired position at any given time t, i.e. the image position error is e(t) = xd(t) - x(t), and is shown in the figure below. The circles corresponds to the start of a registration move, i.e. t = tr, and the stars correspond to the start of an image transfer, i.e. t = tf. E.g., if t = 23 s, the image position error changes approximately from -0.008 to -0.011 m, i.e. 3 mm from the start to the end of the registration move. This would result in a 3 mm process direction registration error due to drum movement during the registration interval with the current open loop control algorithm.

Registration:

The registration move starts...