Abstract: The thickness of a first sheet fed from each tray of the multi-tray sheet feeder is detected by a first sensor and a thickness value is placed in memory for that tray. Each sheet subsequently fed from the same tray is detected by the same sensor and the thickness value sensed is placed in memory and compared with the thickness value in memory for that tray. When a tray is reloaded, the thickness value in memory for the sheets previously loaded in the tray is erased and the first sheet fed from the reloaded tray is sensed and a thickness value for that sheet is placed in memory for the reloaded tray. After the thickness value of a sheet is sensed by the first sensor, the sheets enter into the intermediate tray. The thickness value of a sheet is detected by an outlet sensor as it leaves the intermediate sheet tray and that value is compared to the thickness value in memory which was detected for the same sheet by the first sensor.

Abstract: A sheet metal construction for a fan spider. The spider arms each carry an integral rib running centrally along the arm and each rib is flat on its upper surface to mount a fan blade. The novelty of the invention resides in canting forwardly the spider arms. Such canting reduces certain stresses in the fan, thereby reducing cost of manufacture.

Abstract: A flexible fan blade construction of the type wherein a decamber limiter is carried by each spider arm and bears against one side of its associated fan blade to thereby limit flexing (decamber) thereof. According to this invention, the decamber limiter terminates short of the heel of each fan blade. High stress concentrations due to contact between the heel edge of each fan blade and its associated decamber limiter are avoided by this novel construction.