BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1A schematically illustrates a conventional document feeder whose sheet pick-up device is in a sheet feeding position;
FIG. 1B schematically illustrates the conventional document feeder whose sheet pick-up device is in a ready position;
FIG. 1C is a schematic perspective view of the sheet pick-up device used in the conventional document feeder;
FIG. 2A is a schematic perspective view of a sheet pick-up device according to a preferred embodiment of the present invention;
FIG. 2B is a schematic exploded view of the sheet pick-up device of FIG. 2A;
FIG. 3A is a schematic cross-sectional view illustrating the spring clutch when the sheet pick-up device is in a sheet feeding position;
FIG. 3B is a schematic cross-sectional view illustrating the spring clutch when the sheet pick-up device is in a ready position; and
FIG. 3C is a schematic cross-sectional view illustrating the spring clutch when the sheet pick-up device touches the upper cover.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to FIGS. 2A and 2B, schematic perspective and exploded views of a sheet pick-up device according to a preferred embodiment of the present invention are respectively illustrated.
As shown in FIGS. 2A and 2B, the sheet pick-up device comprises a driving shaft 41, a sheet pick-up arm 42 and a single spring clutch 43. The sheet pick-up arm 42 is pivotally coupled to the driving shaft 41, and includes a sheet pick-up roller 421 and a sheet separation roller 422. The driving shaft 41 is driven by a motor (not shown) to either descent the sheet pick-up arm 42 to the feeding position or raise the sheet pick-up arm 42 to the ready position.
Please refer to FIG. 2B. The spring clutch 43 includes a collar 431 and a spring 432. The collar 431 is sheathed around the driving shaft 41. An end of the collar 431 has an elongated recess structure 431A. By penetrating a retaining stick 433 though an aperture of the driving shaft 41 and engaging the retaining stick 433 with the elongated recess structure 431A, the collar 431 is fixed on the driving shaft 41 to permit synchronous rotation of the collar 431 and the driving shaft 41.
Please refer to FIG. 2B again. A retractable circular claw member 431B is extended from the other end of the spring clutch 43 facing the spring 432. The retractable circular claw member 431B comprises a plurality of claw pieces 431B1 discretely arranged at a regular interval 431B2. When the collar 431 is sheathed around the driving shaft 41, a gap 45 is formed between each claw piece 431B1 and the driving shaft 41, as is also shown in FIG. 3A. Due to the existence of the interval 431B2 and the gap 45, when an oppressing force generated from the spring 432 is exerted on the claw member 431B, the claw member 431B is deformed toward the surface of the driving shaft 41.
Please refer to FIGS. 2A and 2B again. In the spring clutch 43 of this embodiment, a first end of the spring 432 is sheathed around a sleeve 44 extended from the sheet pick-up arm 42, so that the first end of the spring 432 can be fixed on the sheet pick-up arm 42. A second end of the spring 432 is sheathed around the outer periphery of the claw member 431B. Since the first end of the spring 432 is fixed on the sheet pick-up arm 42, in views of the operating principle of the one-way spring clutch, the spring 432 will be selectively relaxed or compressed according to the rotary directions of the driving shaft 41.
Hereinafter, the operations of the spring clutch 43 will be illustrated in more details with reference to the cross-sectional views of FIGS. 3A, 3B and 3C. As shown in FIG. 3A, when the driving shaft 41 is rotated in the direction R1, the spring 432 is relaxed. Meanwhile, the driving shaft 432 is freely rotated to descend the sheet pick-up arm 42 to the sheet feeding position. Next, as shown in FIG. 3B, when the sheet feeding operation is terminated, the driving shaft 41 is rotated in the direction R2 and the spring 432 is compressed to nip the claw member 431B. Due to a frictional force generated between the spring 432 and the claw member 431B, the sheet pick-up arm 42 is raised to the ready position. Afterward, as shown in FIG. 3C, when the driving shaft 21 is continuously rotated in the direction R2 and the sheet pick-up arm 42 is further raised to touch the upper cover (not shown), the spring 432 is more compressed in response to the counterforce exerted by the upper cover. Meanwhile, the claw pieces 431B1 of the claw member 431B are deformed and thus the contact area between the claw member 431B and the spring 432 is reduced. Due to the reduced contact area between the claw member 431B and the spring 432, the frictional force generated between the spring 432 and the claw member 431B is also decreased. For overcoming the compressive force generated from the compressed spring 432, idle running actions of the collar 431 and the driving shaft 41 are rendered. Under this circumstance, the possibility of striking the upper cover and/or uplifting the upper cover by the sheet pick-up arm 42 is minimized.
While the invention has been described in terms of what is presently considered to be the most practical and preferred embodiments, it is to be understood that the invention needs not be limited to the disclosed embodiment. On the contrary, it is intended to cover various modifications and similar arrangements included within the spirit and scope of the appended claims which are to be accorded with the broadest interpretation so as to encompass all such modifications and similar structures.
Patent Application
20070290430
