Appeal No. 2002-1788 Page 7
Application No. 09/217,667
the registration controller can generate the velocity profiles for registration at
datum 3 (D3). The registration accuracy is evaluated at datum 3 (D3) with
leading edge sensors 124, 126 (process direction) and edge sensors 132 and
134.
The accuracy of the registration depends on the accuracies of sensors
124, 126, 130, 132, 134 which measure the position of the paper upon entering
of the nips. Candidate sensors to measure the lateral edge position use a light
source and a detector. The shadow of the edge is imaged onto the detector and
the amount of light measured by a photodiode is a function of the lateral edge
position. The non-linearity, offset, temperature drift etc. affect the accuracy of the
final registration at datum 3 (D3). This invention describes a method for
substantially reducing these effects through in-situ real-time calibration.
When the paper arrives at datum 2 (D2) sensors 130 and 132 measure
the lateral position of the paper edge. These values determine the lateral
displacements required to have the paper registered when it arrives at datum 3
(D3). A request for these displacements is made to the steering algorithm which
determines the appropriate nip velocity profiles. Sensor inaccuracies caused by
nonlinearity, offset, gain errors, temperature drift, etc. cause inaccurate values to
be reported to the steering algorithm. Ultimately this results in registration errors.
This invention describes a method for overcoming this difficulty. The method
involves an in-situ determination of a correction that is added to the measured
sensor values before they are reported to the steering algorithm.
The details of the method for calibrating sensor 132 are described below.
Calibration of sensor 134 proceeds in a similar manner.
Before describing the invention it is useful to introduce some definitions
and notation.
X2 is the actual lateral position of the paper at sensor 132 when the paper
is at datum 2.
Xs2 is the lateral position of the paper as measured by sensor 132 when
the paper is at datum 2
Xs3 is the lateral position of the paper measured by sensor 134 when the
paper is at datum 3 The paper will be considered registered when Xs3 =0.
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