Sheet feeding or delivering – Feeding – Separator and conveyor
Utility Patent
1998-08-25
2001-01-02
Walsh, Donald P. (Department: 3653)
Sheet feeding or delivering
Feeding
Separator and conveyor
C271S114000, C271S116000, C271S118000
Utility Patent
active
06168147
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a transmission mechanism for a pick-up roller, which is provided between a drive power source (e.g., drive motor) and the pick-up roller. The pick-up roller separates a sheet at a time from the top of a stack of sheets. The transmission mechanism may be used in a paper feed unit for a scanner. The paper feed unit feeds an original document or a recording sheet to a scanning area of the scanner. More broadly, the transmission mechanism of the invention may be used in a copier, a facsimile machine, a copier-facsimile hybrid machine, or a printer.
2. Description of the Related Art
Generally, a sheet feeding unit includes a pick-up roller for separating a sheet at a time from the top of a stack of sheets placed on a paper feed tray, a separate roller for transferring the sheet downstream in a sheet passage from the pick-up roller, and feed rollers for accepting the slightly accelerated sheet in an overfeed manner and conveying it to a discharge tray. Such a sheet feeding unit is disclosed in, for example, U.S. Pat. No. 5,624,109. A drive power is transmitted to the separate roller from a drive motor and then transmitted to the pick-up roller. A transmission mechanism for the pick-up roller includes a gear train to connect the pick-up roller with the separate roller such that these rollers rotate synchronously.
However, when all the sheets are taken up from the paper feed tray, the conventional transmission mechanism operates in an overload condition. Specifically, the pick-up roller rotates pressing a stationary surface such as a bottom of the empty paper feed tray. This may damage the gear train of the transmission mechanism. Further, when the sheet reaches the first feed roller but the tail of the sheet is still in contact with the pick-up roller, the transmission mechanism also operates in an overload condition. Specifically, the pick-up roller is forced to rotate (faster than a speed in a normal condition) by the sheet(s) in the overfeed condition. This may also cause various problems.
SUMMARY OF THE INVENTION
One object of the present invention is to provide a transmission mechanism for a pick-up roller that can overcome the above mentioned drawbacks of the conventional transmission mechanism.
Specifically, the present invention intends to provide a transmission mechanism for a pick-up roller that causes no troubles even if the pick-up roller contacts a fixed surface such as the bottom of the empty paper tray and even if the pick-up roller keeps contacting the sheet in the overfeed condition.
According to one aspect of the present invention, there is provided a transmission mechanism for a pick-up roller, comprising a torque limiter located between a drive power source and the pick-up roller for transmitting a drive power to the pick-up roller from the drive power source to rotate the pick-up roller under a normal condition but interrupting drive power transmission to the pick-up roller from the drive power source under a certain operating condition, and a clutch for preventing drive power transmission from the pick-up roller to the drive power source. The drive power transmission from the pick-up roller to the drive power source occurs, for example, in a sheet overfeeding condition. When the pick-up roller contacts the stationary surface such as the empty paper tray, the torque limiter interrupts transmission of the drive power from the drive power source to the pick-up roller. Therefore, an excessively large load is not exerted on the transmission mechanism. Likewise, when the pick-up roller keeps contacting the sheet in the over-feed condition, the clutch interrupts transmission of the drive power to the drive power source from the pick-up roller. Therefore, the pick-up roller rotates freely (lost motion) so that an excessively large load does not act on the transmission mechanism and a large back tension does not act on the sheet in the over-feed condition.
In order to simplify the structure of the torque limiter, the torque limiter may include a coil spring wound around the pick-up roller. A relatively small unwinding force may be applied to the coil spring when a normal load acts on the pick-up roller, such that the coil spring is still able to transmit the drive power to the pick-up roller. T he relatively small unwinding force does not cause the coil spring to release the pick-up roller so that the drive power is transmitted to the pick-up roller in a normal condition. The pick-up roller rotates upon drive power transmission from the drive power source. When an over load acts o n the pick-up roller, on the other hand, a relatively large unwinding force may be applied to the coil spring so that the coil spring maybe substantially unwound and slip relative to the pick-up roller. For example, when the pick-up roller contacts a stationary surface such as the empty paper tray (overload condition), the coil spring is brought into a loose condition so that there is caused a slip between the coil spring and the pick-up roller. Accordingly, the drive power is not transmitted to the pick-up roller (lost motion of the drive power source). Since the torque limiter is a coil spring, operation of the torque limiter is simple and maintenance is easy.
The transmission mechanism for the pick-up roller according to the present invention is applicable to a document separate and feed device. For instance, the transmission mechanism of the invention may be used in a document feed unit of an image processing apparatus. The image processing apparatus may include both a function of copier and a function of facsimile. It is possible to eliminate troubles caused when there is no sheet in the document feed unit and when a sheet overfeeding condition occurs.
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Nose Yoshitaka
Shige Daisuke
Hogan & Hartson LLP
Jones David A.
Murata Kikai Kabushiki Kaisha
Walsh Donald P.
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