HP LaserJet 4250 Service Manual - Page 165
Staple level-detection, Stack-mode feed and delivery,
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Staple level-detection The stapler/stacker-driver PCA uses the staple-detection switch to detect the presence and number of staples in the stapler unit. A spring on the staple-detection switch holds the staple-detection flag in the raised position. When this flag is fully raised, the switch is open. A slot is cut into the bottom of the staple cartridge. If the staple cartridge is mostly full of staples, the staples block the staple-detection flag movement so that it cannot move to its raised position. The staple-detection switch is closed, and the stapler/stacker-driver PCA determines that at least 70 staples remain in the cartridge. When fewer than 70 staples remain in the cartridge, the stapledetection flag is no longer blocked, and it moves to the raised position. The staple-detection switch opens, and the stapler/stacker-driver PCA identifies a low-staple condition. A low-staple message appears on the control-panel display. After the stapler/stacker PCA sends the staple command 70 more times, a staple-out message appears on the control-panel display. See Alphabetical printer messages. Figure 5-35 Staple-level detection Stack-mode feed and delivery In this mode, media is stacked in the delivery bin without being stapled. After the leading edge of the media reaches the fuser-delivery sensor (PS108), the dc controller PCA sends a signal to the stacker-driver PCA. The stacker-driver PCA activates the deflector solenoid (SL101) for a specific amount to move the delivery deflector into place, which routes the media to the stacker rather than to the top output bin. The stacker-driver PCA also activates the stacker motor (which rotates at the same speed as the printer main motor) to rotate the feed and delivery rollers. The feed roller moves the media into the stacker. If the dc controller PCA sends a following-page signal (indicating that the job contains another page), the stacker-driver PCA again activates the deflector solenoid (SL101). The delivery rollers move the media to the delivery bin. Stacker and stapler/stacker 151