Avery Berkel CX20 SERIES, Service Manual

Page: 204 / 353

20 — Label and Receipt Printer
20–4 CX20/CX30/CX34 Service Manual
The cassette carries the loaded ticket roll on a fixed drum. The drum has
splines at its upper edge and is sized to allow the paper roll to rotate with a
small amount of friction when pulled by the tractor mechanism. The cassette
has an anvil at the dispensing edge to encourage self–adhesive labels to detach
easily from their backing paper.
The cassette also has a loose–fitted take–up roller. The take–up roller
comprises a plastic moulding which is trapped against the side of the cassette
by a metal keep plate, which is held in position by three countersunk, Posidrive
screws. The outer side of the take–up roller is hollow and is splined internally to
accept a drive from a motor unit. The inner side of the take–up roller comprises
three functional elements:
the core (effectively solid)
two outer tongues (effectively flexible)
a rotary wedge, trapped on a spigot of the core by a clamp washer.
The rotary wedge has two flats on its periphery. When these flats are aligned
with the flat, inner faces of the tongues, they are not in contact and the tongues
are relaxed. When the rounded faces of the rotary wedge are aligned with the
tongues, they are in contact and the tongues are forced outwards by a small
amount, so enlarging the effective diameter of the roller. The backing paper is
wound around the roller in its enlarged size. When the paper roll is exhausted,
the rotary wedge is rotated to align its flats with the tongues and the effective
diameter of the roller is made smaller: this enables the backing paper to be
removed easily from the take–up roller.
The motor which drives the take–up roller is a 24V, 3–pole, can type. It drives
through an integral reduction gearbox mounted on a plate supported from the
printer spine by three stand–off pillars and two stand–off spacers. The output
from the gearbox is transmitted through a rotary shaft on which is mounted a
plastic drive cone having external splines. The drive cone interfaces with the
hollow, splined core of the take–up roller. The output shaft of the gearbox has a
flat machined on to its surface and a threaded hole set axially in the end of the
shaft. The drive cone is attached to the threaded hole of the shaft by a screw
and shakeproof washer in the hollow bore of the cone: the cone can therefore
be changed easily when installed in the unit. The electrical supply to the motor
is connected to a loom interconnection and then to the wiring harness of the
printer, which is connected to PL7 on the main PCB.
The paper tractor mechanism consists of a rubber friction roller, a drive belt
arrangement, and a stepper motor. The friction roller is carried between a hole
in the printer spine and a hole in a bracket at its free end. The bracket is also
attached to the printer spine by two stand–off pillars. The spine end of the roller
is carried in a ball bearing, and the bracket end of the roller is carried in a
phosphor bronze bush. The spine–end of the friction roller carries a splined
drive gear, attached to the shaft of the friction roller by a socket–head, recessed,
grub screw. The extended shaft of the friction roller has a flat machined on to a
surface below the grub screw.
The drive is transmitted to the drive gear of the friction roller by a flexible,
toothed drive belt made of textile–reinforced, rubberized plastic. This is driven
by the stepper motor. The overall gear ratio of the arrangement is approximately
5:1 step–down.