HP 220 - Manual (Page 39)

5Ć7 Functional Overview C3187Ć90000
Advancing the Media
MediaĆDrive Mechanics
The media is advanced by the media drive (XĆdrive) system. Components include:
D Mediamotor (XĆaxis motor)
D Worm pinion and helical driveĆroller gear
D Drive roller
(Illustration ' page 10Ć23.)
The main component of the drive system is a fullĆwidth, 6.4Ćcm (2.5Ćinch) diameter roller
with an elastomer skin. This roller directly drives the media and provides the surface that
references the mediato the printĆhead.
The mediaĆmotor position control uses an encoder feedback loop. The encoder wheel is
mounted to the motor shaft, and the optical reader is mounted inside a bell housing attached
to the back of the motor.
MediaĆDrive Accuracy
The main purpose of the media drive system is to accurately move media such that the
alignment of adjacent print swaths is of high enough precision that the plotter specifications
are met and print quality is maintained. The mediaĆdrive accuracy (endĆpoint accuracy, or
XĆaxis accuracy) specifies how accurately a plotter can draw a line of a given length.
(Specifications ' chapter 1.)
The configuration plot draws crossĆhairs 500mm apart that you can use to measure the
plotter's accuracy. (Details ' chapter 7, w Accuracy Calibration.)
Contributors to the Accuracy
All the above components of the media drive system contribute to the mediaĆdrive accuracy.
The following also contribute:
D Radius variations produced by the way the media wraps around the drive roller, and the
way the pinchĆwheels and starĆwheels maintain this radius
D Errors in the media motor's opticalĆencoder feedback system (this system gives feedback
to the motorĆcontrol circuitry)
Dimensional changes in the media will affect lines drawn in both axes either during plotting
or after the plot is drawn. For this reason, media other than polyester film does not support
the mediaĆdrive accuracy specification. Polyester film is the only media that maintains
dimensional stability to within the plotter specification ranges.