An improved sheet feeder mechanism includes a D-shaped roller (16) that is mounted on a shaft (18) and is positioned transversely to a direction (20) of sheet feed. A D-roller gear (22) is mounted on the shaft (18) and has both a non-recessed geared region and a recessed non-geared region (24) that extends partially about a circumference of the D-roller gear (22). A shaft extension (30) extends from and is attached to the shaft (18), and a spring (34) engages the shaft extension (30) to cause the shaft (18) and the D-roller gear (22) to rotate to a position that enables a gear drive (26, 28) to engage the non-recessed geared region of the D-roller gear (22). A spiral cam assembly (42) is mounted for rotation with the gear drive (26, 28) and includes a spiral cam (52) that is positioned between and resiliently bears upon inner and outer annuli (50, 48) of the cam assembly (44). A control arm (40) engages both the spiral cam (52) and the shaft extension (30) and is responsive to rotation in a first direction of the cam assembly (42) to enable the spring (34) to move the shaft extension (30) and D-roller gear (22) to a position where a non-recessed, geared region aligns with the gear drive (26, 28). The control arm (30) is further responsive to rotation in a second direction of the cam assembly (42), after the first direction rotation, to enable rotation of the D-roller gear (22) by the gear drive (26, 28) so as to cause a sheet feed.
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