Facsimile and static presentation processing – Facsimile – Picture signal generator
Reexamination Certificate
1998-06-19
2001-07-03
Lee, Cheukfan (Department: 2722)
Facsimile and static presentation processing
Facsimile
Picture signal generator
C358S488000, C271S265020
Reexamination Certificate
active
06256119
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a sheet transfer device used for transferring sheet materials such as recording paper sheets and image-carrying paper sheets. In particular, the present invention relates to a sheet transfer device provided with sensors for monitoring the transfer condition of the sheet materials.
2. Description of the Related Art
Sheet transfer devices are widely used in various electrical appliances, such as printers, facsimile machines and the like. Referring to
FIG. 5A
, a conventional sheet transfer device incorporated in a printer for example, may include a paper feed tray
2
′ for holding recording paper sheets
1
′, a feed roller
3
′ disposed adjacent to the paper feed tray
2
′, a platen roller
4
′ arranged in facing relation to a printhead
5
′ of the printer, discharge rollers
6
′ and a discharged paper tray
7
′.
Between the paper feed tray
2
′ and the discharged paper tray
7
′ extends a paper transfer path P along which the recording paper sheet
1
′ is transferred when the above-mentioned rollers
3
′-
6
′ are rotated.
The conventional sheet transfer device is also provided with sensors
8
′-
9
′ for monitoring the transfer procedure of the recording paper sheet
1
′. These sensors are disposed at two locations along the sheet transfer path P: at an upstream position A between the feed roller
3
′ and the platen roller
4
′, and at a downstream position B between the platen roller
4
′ and the discharge rollers
6
′. Typically, these sensors may be mechanical devices which are arranged to generate presence signals or absence signals, depending on whether the sensors
8
′-
9
′ are held in contact with the recording paper sheet
1
′ or not.
The sheet transfer device having the above arrangement operates as follows. Upon actuation of the feed roller
3
′, a recording paper sheet
1
′ is pulled out of the paper feed tray
2
′ and moved along the transfer path P toward the printhead
5
′ of the printer. On its way, when the front end portion of the recording paper sheet
1
′ comes into contact with the upstream sensor
8
′, the upstream sensor generate presence signals, as previously stated. These signals are sent to a CPU (central processing unit) of the printer. Receiving the signals, the CPU begins to control the rotation of the feed roller
3
′ so that the front edge of the recording paper sheet
1
′ is properly brought to a position C between the platen roller
4
′ and the printhead
5
′. (The operation described here is called “the paper feeding step” below.)
When the paper feeding step is finished, the printhead
5
′ starts printing on the recording paper sheet
1
′. While the printing is performed, the recording paper sheet
1
′ is fed stepwise in a known manner. (The operation here is called “the printing step” below.)
When the printing step proceeds smoothly (without having the recording paper sheet
1
′ crumpled, for example), the front edge of the recording paper sheet
1
′ is brought into contact with the downstream sensor
9
′. Then, the downstream sensor
9
′ sends presence signals to the CPU. Upon receiving the signals, the CPU determines that the sheet transfer operation is being properly performed.
Finally, when the printing step comes to an end and the rear end portion of the recording paper sheet
1
′ leaves the upstream sensor
8
′, the upstream sensor sends absence signals to the CPU. At this instant, the CPU changes the transfer mode for the recording paper sheet
1
′ from the currently-performed stepwise motion to a continuous discharging motion, so that the recording paper sheet
1
′ is swiftly sent to the discharged paper tray
7
′.
The conventional sheet transfer device, however, has been found to have the following disadvantage.
As shown in
FIG. 5B
, the front end portion of the recording paper sheet
1
′ is not held between the platen roller
4
′ and the printhead
5
′ during the paper feeding step described above. In this state, the recording paper sheet
1
′ may unduly sag or prematurely leave the upstream sensor
8
′. As a result, the absence signals are sent to the CPU of the printer, whereby the CPU, determining that the rear end portion of the recording paper sheet
1
′ left the upstream sensor
8
′, erroneously changes the transfer mode for the recording paper sheet l′ to the continuous discharging motion.
SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention is to provide a sheet transfer device capable of overcoming the disadvantage described above.
Another object of the present invention is to provide a printer and a facsimile machine which incorporate such a sheet transfer device.
According to a first aspect of the present invention, there is provided a sheet transfer device for transferring a sheet member along a transfer path having an upstream point and a downstream point, the sheet transfer device comprising:
a transfer mechanism for moving the sheet member along the transfer path from the upstream point to the downstream point;
at least one upstream sensor arranged closer to the upstream point than to the downstream point for detecting presence and absence of the sheet member; and
at least one downstream sensor arranged closer to the downstream point than to the upstream point for detecting presence and absence of the sheet member;
wherein the transfer mechanism is arranged to discharge the sheet member only after the downstream sensor detects the presence of the sheet member and the upstream sensor detects the absence of the sheet member.
With such an arrangement, it is possible to prevent the sheet member from being prematurely discharged from a transfer system of the transfer device. Thus, unlike in the conventional sheet transfer device, the sheet member and elements of the transfer system are advantageously protected from damage which would otherwise be caused by improper discharging of the recording paper.
According to a preferred embodiment, the transfer mechanism includes a feed roller arranged between the upstream point and the upstream sensor, an intermediate roller arranged between the upstream sensor and the downstream sensor, and a discharge roller arranged between the downstream sensor and the downstream point.
The upstream sensor and the downstream sensor may be mechanical sensing devices which produce presence signals when the mechanical sensing devices are held in contact with the sheet member, and absence signals when the mechanical sensing devices are held out of contact with the sheet member.
The mechanical sensing device may include a plate member pivotable about an axis upon contact of the sheet member.
The sheet transfer device may further comprise a controller for controlling the transfer mechanism based on the presence signals and absence signals from the upstream sensor and the downstream sensor. Such a controller may be provided by a CPU.
According to a second aspect of the present invention, there is provided a printer for printing on a sheet member transferred along a transfer path having an upstream point and a downstream point, the printer comprising:
a transfer mechanism for moving the sheet member along the transfer path from the upstream point to the downstream point;
at least one upstream sensor arranged closer to the upstream point than to the downstream point for detecting presence and absence of the sheet member;
at least one downstream sensor arranged closer to the downstream point than to the upstream point for detecting presence and absence of the sheet member; and
a printhead arranged between the upstream sensor and the downstream sensor;
wherein the transfer mechanism is arranged to discharge the sheet member only after the downstream sensor detects the presence of the sheet m
Brother Kogyo Kabushiki Kaisha
Lee Cheukfan
Oliff & Berridg,e PLC
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