HP 2500C Series - Manual (Page 136)

Functional Overview 6-16
Paper Paths and Components
Linefeed Accuracy
A closed loop drive system was used to ensure good positional accuracy of the
transmission system. This involved the use of a rotary encoder disc mounted on the drive
roller shaft in conjunction with a three gears gear-train design. The mounting of the
encoder disc directly on the drive shaft helps to eliminate gear and motor errors and at the
same time offer direct feedback on the position of the drive roller shaft. However, errors
due to encoder disc eccentricity, drive roller run-out and media-roller interface will still
be present.
The encoder disc is a rotary disc made from Kodak LPF7 film. A total of 1440 counts
were printed on the disc at an optical diameter of 58.2125 mm. The count to count
spacing is 200 LPI. This spacing translate into a linear movement of 1/300 inch on the
circumference of the
∅
38.808 mm drive roller.