HP 2500c Service Manual - Page 136
Linefeed Accuracy
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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. 6-16 Functional Overview