1. Field of the Invention
The present invention relates to an image forming apparatus, including a printer, a facsimile machine or a multi-function machine, and more particularly, to a pickup error-sensing apparatus of an image forming apparatus, and method therefor, capable of sensing a pickup error, generated as a result of inadequate movement of a pick-up roller, using a paper sensor installed at a paper tray or cassette
2. Description of the Related Art
Generally, an image forming apparatus, including a printer, a facsimile machine or a multi-function machine includes an automatic document or paper feeder (hereinafter referred to as an automatic paper feeder ), arranged at an upper part thereof, to automatically feed a sheet of document or paper thereinto.
As shown in FIG. 1, a general automatic paper feeder 10 has a paper tray or cassette 11, for stacking or loading sheets of paper therein, having a knock-up plate 13 elastically supported by a elastic spring (not shown) so as to be movable upward and downward. A paper sensor unit 17 senses the sheets of paper, and a pickup unit (not shown) picks up and conveys a sheet of paper from the paper cassette 11.
The paper sensor unit 17 comprises a photo sensor 25, having a light emitting part and a light receiving part, positioned on a fixing bracket 29 of a frame. A sensing actuator 19 protrudes through a paper sensing hole 15 of the knock-up plate 13 so that it is lifted up by the sheets of paper P to operate the photo sensor 25 when the sheets of paper P are placed on the knock-up plate 13, as shown in FIG. 2.
The sensing actuator 19 includes an actuating member 20 protruding through the paper sensing hole 15 of the knock-up plate 13 due to its own weight so as to be lifted up by the sheets of paper P. A sensing trigger 21, movable between the light emitting part and the light receiving part of the photo sensor 25, operates the photo sensor 25. A supporting rod 22 is rotatably supported at the frame and integrally formed with the actuating member 20 and the sensing trigger 21.
The pickup unit is provided with a cylindrical pickup roller (not shown) having a shaft connected with a gear train (not shown) that transmits a driving force of a driving motor (not shown).
The operation of the conventional automatic paper feeder 10 constructed as above is as follows.
After sheets of a document or paper P are placed, or loaded, on the knock-up plate 13, the paper cassette 11 is mounted in the image forming apparatus. As shown in FIG. 2, the sheets of paper P lift up the actuating member 20 of the sensing actuator 19, so that the sensing trigger 21, integrally connected to the actuating member 20 through the supporting rod 22, separates from the photo sensor 25, and moves upward.
As a result, the light receiving part of the photo sensor 25 receives light from the light emitting unit, and sends a “high” signal to a control unit (not shown), and thereby the control unit senses that the sheets of paper P are stacked in the paper cassette 11.
When a command for scanning or printing is input to the image forming apparatus, the control unit supplies electric power to the driving motor to drive the pickup roller, and thereby the pickup roller is rotated.
Accordingly, as the sheets of paper P are separated, one-by-one, by a paper separating unit such as a friction pad (not shown), a sheet of paper P is picked up at the paper cassette 11 by the pickup roller, and conveyed into the image forming apparatus.
In the conventional automatic paper feeder 10, since the photo sensor 25 of the paper sensing part 17 senses only whether the sheets of paper P are loaded in the paper cassette 11, the printing operation may still be carried out when, due to inadequate movement of the pickup roller, one of the sheets of paper P is not picked up, thereby resulting in contamination of the image forming apparatus. Accordingly, in order to sense the pickup error and prevent the contamination of the image forming apparatus, the conventional automatic paper feeder 10 would need to additionally install a separate paper sensor on a paper feeding path in the image forming apparatus.
However, the additional installation of a separate paper sensor, complicates the structure of the image forming apparatus and increases fabrication cost.