TM 5-6675-324-14
The development stage converts the electrostatic latent image on the drum surface
into a visible image by means of developer powder. The developing system consists
of a fixed, six-pole, cylindrical magnet, a concentric stainless-steel sleeve rotat-
ing around it, a skimming blade, and a scraper. A single-component developer pow-
der that combines toner and carrier in each solid particle is used. The toner is
made of tiny particles of magnetic material embedded in a resin. The toner is an
insulator, and each particle acquires a negative charge by friction with the rotat-
ing stainless-steel cylinder. Because each toner particle has magnetic properties,
the cylindrical magnet inside the sleeve can attract a thick layer of powder to the
sleeve as it revolves through the reservoir. A concentrated magnetic field forms
between the magnetic poles and the edge of the skimming blade. Some particles will
be attracted to the edge of the blade and form a curtain that follows the concen-
trated magnetic field. This curtain acts as a skimmer which maintains a uniform
layer on the sleeve. When the drum, with its latent image of positive charges,
approaches the layer of toner on the revolving stainless-steel sleeve, the negative-
ly charged particles are attracted to the drum, where they adhere to the positive
charges on the surface. Thus, the electrostatic latent image on the drum becomes
visible so that it can be transferred to a sheet of paper. Toner remaining on the
stainless-steel developing sleeve after the image transfer is scraped off by the
scraper and returned to the toner supply area of the developing assembly, where it
circulates through the window in the scraper.
An ac bias voltage of 1 kV (peak to peak) at 0.4 kHz is applied to the developing
. The voltage rises to +653 V, but falls to only -347 V (1.88:1 ratio). The
reason is to assure distribution of toner proportional to the electrostatic latent
image. Operation is based on the fact that unlike charges attract and like charges
repel each other. The drum has a distribution of positive charges of about 600 V in
image (dark) areas and negative charges in nonimage areas. Each toner particle has
a negative charge. The developing sleeve bias varies continually from positive to
negative to positive, so there is a continual variation in the electric field.
Toner particles will adhere to positive charges on the drum, but a gap of 100
microns separates the drum from the layer of toner on the sleeve. When the sleeve
is negative, toner particles are projected onto the drum and adhere to both light
and dark areas. When the sleeve is positive, some of the particles on the dark
areas and most of the particles on the light areas return to the sleeve. Because
the sleeve voltage varies, dark areas are developed with toner particles and light
areas remain clear of toner particles; thus, the light area remains free of fogging.
The same bias is applied to the skimming blade so that there is no interference
between blade and sleeve.
3-37