Canon imageCLASS MF8450c, Service Manual

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Chapter 8
8-8
Print speed when the throughput down control is executed
When the throughput down control is ON, print speed is switched step by step depending on the paper type or the temperature on the edge of the fixing sleeve etc.
Following shows the print speed list in case of the minimum throughput.
T-8-3
8.2.5 Throughput-down Control
0020-9281
imageCLASS MF8450c
The machine prevents an abnormal temperature increase at the edge of the fixing sleeve by increasing an interval between sheets while keeping the paper feeding
speed as needed.
Control of the fixing assembly is performed to keep the temperature of the fixing heater higher than the target temperature while the paper is transported so that the
target fixing temperature is maintained (print temperature control).
When the paper is displaced to one side, the paper does not pass a certain area at the edge of the fixing sleeve. In this area, no heat is transported to the paper, causing
temperature increase every time the paper passes the area.
Even when the temperature of the fixing heater is set lower than the target temperature between sheets (control of temperature between sheets), the effect of tem-
perature increase is reinforced when continuous printing is performed, and therefore an abnormal temperature increase occurs at the edge of the fixing sleeve.
To prevent an abnormal temperature increase, the machine increases an interval between sheets when the paper is fed displaced to one side, and promotes a tem-
perature decrease between sheets.
The machine uses the paper displacement sensor (SR714) located at the right side of the registration shutter in order to detect the paper displacement.
The sensor detects whether the paper width is smaller than the specified paper width or whether the paper is displaced to the left side of the feed path.
Whether the paper width is smaller than the specified paper width or whether the paper is displaced to the right side of the feed path can be detected by the fixing
sub thermistor (TH2) because an abnormal temperature increase occurs at the left edge of the fixing sleeve.
F-8-8
Different throughput-down controls are executed depending on the result of detection performed by the paper displacement sensor and fixing sub thermistor.
Paper Print speed (ppm)
Type Size 1st level 2nd level 3rd level Last level
Plain paper/Plain paper H/Recycled paper/Color paper B5R/A5R/EXECR 20.2 4.6 3.5 2.86
Heavy paper 1/Heavy paper 2/Rough paper B5R/A5R/EXECR 16.1 4.4 3.4 2.76
Transparency - 3.6 2.4 - 1.8
Postcard/Return postal card - 10.1 3.8 3 2.5
The paper is displaced to the right.
The paper is not displaced.
The paper is displaced to the left.
The paper width is smaller.
Registration shutter
Paper
TH2 Fixing sleeve
SR714