Canon NP-70 Service Manual page 32

2-6
NP -70
machine. Their functions and potentials are as follows.:
* Positive Corona:
Radiates a DC voltage of +6.4 kV to charge the drum surface to +1800 ± 100V.
* AC Corona for image formation:
Radiates an AC voltage of 7.0 kV to the drum surface to eliminate the positive
charges on the light portions of the image.
(AC discharge and image exposure are performed simultaneously. This exposure is
called "simultaneous image exposure".)
* Negative Corona:
Radiates a DC voltage of —6:4 kV to charge the drum surface (both, covered and
not covered with toner) to a negative potential.
* Transfer Corona:
Radiates a DC voltage of +6.0 kV to the back of the paper to transfer the image
from the drum to the paper.
* Residual Charge Eliminator for paper charge neutralization:
Radiates an AC voltage of 7.0 kV to neutralize any charges remaining on the paper
to which an image has been transferred.
2.3-6
DEVELOPER ASSEMBLY
The Developer Assembly is located just below the drum. It continuously pumps the fluid
developer upward, so that the rotating drum receives a constant coating of developer. The
proper development of the latent image is ensured by the inclusion of the developing tray;
the tray acts as a development electrode.
The developer contained in the assembly consists of a colloidal suspension of toner and liquid
dispersant, the latter acting as the carrier. The charges assumed by these two elements are as
follows:
* Toner: Charged to a negative (—) polarity.
* Carrier:
Charged to a positive (+) polarity.
2.3-7 DRUM CLEANER ASSEMBLY
This assembly is positioned to the upper right of the drum and functions to wipe off the re-
maining toner on the photosensitive drum after the transfer operation. It enables the conti-
nuous use of the drum. The wiping action is performed by two blades (made of urethane) and
is performed continuously during drum rotation.
2.3-8
CASSETTE AND CASSETTE HOLDER ASSEMBLIES
These two assemblies function together to hold the paper for feeding one by one into the
copier. They are located at the lower left end of the copier body and the Cassette Assembly
is removable from the Holder Assembly to allow the use of cassettes of varying paper size.
Second Printingtilune, 1974 © CANON INC.