Stretching the Media
Overdrive
The overdrive roller stretches the media slightly as it is moved through the plotter. It thus reduces bubbling and media cockle caused by media expansion due to the absorption of water3based ink into the media. Even though the geometry chosen for the plotters minimizes the occurrence of this phenomena, it still could occur on very dense plots.
Operation
(Part illustrations ' page 10325)
The overdrive roller is geared to the media3drive system and has a surface speed 10% greater than that of the drive roller. The lower star wheels on the bail provide a normal force between the media and the overdrive roller. The resulting friction force creates media tension in the area between the upper pinch3wheels and the overdrive roller (the print zone).
The overdrive roller is segmented into small rollers made of polyurethane. A clutch (overdrive gear assembly) is geared to the speed3ratio gear (overdrive gear cluster) and drives the overdrive roller in the forward direction only.
Moving the Carriage
CarriageDrive Mechanics
The Carriage (Y3axis) drive consists of a DC motor driving the carriage by means of a dual, kevlar belt system incorporating three pulleys and two tensioner assemblies.
Operation
(Part illustrations ' pages 10319 and 10321)
1A gear pinion, pressed onto the carriage3motor shaft, drives a small belt tensioned with a self3compensating, spring3loaded idler.
2The small belt drives a double pulley which transfers the motor drive to the main belt.
3The main belt is attached to the carriage via friction3fit belt clamps. It is tensioned using a self3compensating, spring3loaded tensioner wedge and main idler. (Illustration ' page 10315.) The belt moves the carriage along slider rods, which are part of the chassis assembly. The carriage bearing system consists of three bushings.
4Positional feedback is obtained using a 1503line3per3inch linear encoder strip that is spring loaded and passes through the carriage where the small slots are read by an optical encoder. The feedback is used by the carriage3motor servo3control system.
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