Lexmark Optra T522, Service Manual

Page: 156 / 333

Diagnostic Aids
3-25
Infoprint 1120 and 1125
Autocompensator Operation
The autocompensator is a paper pick device that generates its own
normal force. This force generation is inherent in the fundamental
design of the pick arm. If light media is used, it picks very gently. If a
heavy media is used, it picks very aggressively. No customer
adjustments are necessary, therefore no special trays are needed
for card stock or labels. The gearing in the arm is designed so the
input torque from the motor produces a movement about the pivot of
the arm. This movement produces a downward force at the pick
rolls. The friction between the pick roll and the paper produces a
frictional locking condition. If the paper is physically held and not
allowed to feed, then the motor stalls. Slippage between the roll and
the paper is theoretically impossible. When the motor is energized
the pick rolls are driven down into the stack increasing the normal
force and drive force until the bending strength of the paper is
overcome and the paper bends and moves up the dam. Once this
critical threshold is achieved the normal force remains at a level just
high enough to reliably feed the paper. Rather than having a fixed
spring force for feeding all weights of paper like the D-roll, this
device has its own mechanical logic for producing only enough pick
energy to feed a single sheet of paper regardless of its stiffness.
High normal force is one of the most significant contributors to
double feeding paper. The pick arm is counter balanced by an
extension spring located on the pick arm to reduce weight in the rest
state. This spring is factory set to exert no more than ten to fifteen
grams on the stack. This is as light as can be realistically set and
always guarantee there is some force to start the autocompensating
phenomena. This spring is not to be considered an adjustment for
feeding problems unless it is obvious that the pick arm cannot fall all
the way down to the bottom of the tray or has come loose. Poor gear
efficiency can cause the arm to generate higher normal forces. If the
pick assembly is noisy, replacement may be required. The arm must
pivot freely through its full range of motion. On 500 sheet trays there
are wrap springs located on the pivot arbors of the arm. These
springs aid to prevent the arm from bouncing. If the arm appears to
be binding or sticky near the bottom of the tray these springs may be
the problem. Reducing the tension on the counterbalance spring
may be used as a temporary fix to get additional weight at bottom,
until the pick assembly can be replaced. However, the
counterbalance spring is not to be considered an adjustment for
feeding problems.