Canon NP-70 Service Manual page 68

NP•70
3-27
3.2-3 WHEN COPY PAPER FAILS TO EXIT THE COPIER —CJAM~
The operation of the Jam Detection Circuit, although not essential for copying, is significant
in terms of machine protection. As such, a flowchart is included to show the actions occurr-
ing in the copier when a jam occurs.
Jams are categorized into either "Delay" jams or "Exit" jams, and the response of the Jam
Detection Circuit is different in each case.
1) "DELAY" JAM
A delay jam indicates that the copy paper has, for some reason, been prevented from reaching
the exit area of the copier. As this type of jam usually occurs when the paper is not separat-
ed properly from the drum, the jam detection circuit responds rapidly to prevent damage.
The response to stop copier operations will occur at 410° of drum rotation (4.55 seconds of
operation) from the start of the copying cycle during which the jam occurs.
2) "EXIT" JAM
An exit jam indicates that the copy paper has begun, but has failed to complete, its exit of
the copier. In this type of jam, the paper is usually free of the drum area, but is in conti-
nuous contact with the heater. Because the heater temperature is low (and, thus, the paper
cannot start burning), it is not necessary to cause immediate copier shut-off. Thus, the Jam
Detection Circuit responds to this jam at 1290° of drum rotation (14.33 seconds of operation)
from the start of the copying cycle during which the jam occurs.
The following table (3-4) gives a brief explanation of the actions occumng in each block of
the ~JAM~ flowchart. It is recommended that the ~ JAM ~ flowchart be folded out when
studying Table 3-4.
© CANON INC.
Second Printing-June, 1974