Canon iR C3380 series, Service Manual

Page: 236 / 610

Chapter 7
7-26
7.4 Special Control
7.4.1 Black band sequence
0014-5561
/ / / / iR C3380i / iR C3380 / iR C2880i / iR C2880
If continuous print is carried out while there is no toner being sent on to the ITB cleaning blade, the blade may bend backwards. This sequence feeds non-transferred
toner to the cleaning blade in order to prevent this problem.
1. Timing
- When belt rotation is performed after 1,000 sheets printing.
2. Sequence details
After image formation in the normal sequence, a black band (half-tone pattern) is formed over the total width of the ITB, for a length of 10mm, with density FFh.
Once the black band clears the secondary transfer roller, secondary transfer outer roller cleaning (see Note) is performed.
Further, once the black band is formed, the cumulative counter resets to the default (0).
Negative bias (TR2 signal) is applied to the secondary transfer outer roller to prevent rear soiling of the print paper, and this creates a difference in electro-potential
between the ITB and the roller. As a result, residual negative toner sticking to the secondary transfer outer roller returns to the ITB and is collected in the cleaning
unit by the ITB cleaning blade.
7.4.2 OHP black band sequence
0014-5562
/ / / / iR C3380i / iR C3380 / iR C2880i / iR C2880
OHP sheets are coated with a resistance adjusting agent which will adversely affect transfer efficiency wherever it sticks to the ITB. Also, if a large quantity of this
agent sticks to the ITB, it may cause fusion in the transfer cleaning unit. In order to prevent any image defects or fusion that may arise from the use of OHP sheets,
this sequence feeds non-transferred toner to the cleaning blade.
1. Timing
- During the page interval after 15 OHP sheets have been printed consecutively.
- Upon belt rotation after seven or more sheets have been printed since the previous OHP black band operation.
2. Sequence details
After image formation in the normal sequence, a black band (half-tone pattern) is formed over the total width of the ITB, for a length of 80mm, with density FFh.
Once the black band clears the secondary transfer roller, secondary transfer outer roller cleaning (see Note) is performed.
Further, once the black band is formed, the cumulative counter resets to the default (0).
Negative bias (TR2 signal) is applied to the secondary transfer outer roller to prevent rear soiling of the print paper, and this creates a difference in electro-potential
between the ITB and the roller. As a result, residual negative toner sticking to the secondary transfer outer roller returns to the ITB and is collected in the cleaning
unit by the ITB cleaning blade.
7.4.3 Colour band sequence
0014-5563
/ / / / iR C3380i / iR C3380 / iR C2880i / iR C2880
This sequence forms a band of toner to prevent any deterioration in developing that may occur after continued formation of low duty images.
1. Timing
When the average image duty per sheet falls below the standard value alpha (image ratio 2%).
2. Sequence details
When ATR control is performed, the cumulate image value duty since the previous ATR is extracted and, when the average image duty per sheet falls below the
standard value alpha (image ratio 2%), immediately after ATR patch formation, the toner band width (*1) is calculated and an A4 width colour belt is formed on
the ITB. Then, toner volume equivalent to that used to form the colour band is added to the refill counter by the video counter. This initiates toner refill, thus
preventing any deterioration in developing.
Also, with this function, even if a colour band is not formed, once ATR control is performed, the average image duty standard value alpha and the cumulative
counter both reset to their default values.
*1: The 1dot line (thrust A4 width) x toner band width video count is fixed so that it is equal to the per dot average image duty standard value alpha x average image
duty sheet count - cumulative image duty.
3
Determining the secondary transfer bias The DC controller determines the best secondary transfer bias with reference to the
secondary transfer current feedback and the secondary transfer bias correction value.
Sequence Item Description