Sheet feeding or delivering – Delivering – To receiver for pack of sheets
Reexamination Certificate
1998-10-23
2001-05-29
Walsh, Donald P. (Department: 3653)
Sheet feeding or delivering
Delivering
To receiver for pack of sheets
C271S215000, C271S217000, C271S214000
Reexamination Certificate
active
06237910
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a sheet processing apparatus provided with a sheet sensor, and more specifically, to a sheet processing apparatus provided with, for example, sheet stack means on which discharged sheets are sequentially stacked and to an image forming apparatus provided with the sheet processing apparatus.
2. Related Background Art
A sheet processing apparatus arranged such that the upper surface of sheets stacked on a stack tray is set to a prescribed height at all times is known.
The sheet processing apparatus comprises a discharged sheet tray on which discharged sheets are sequentially stacked, lifting/lowering device for lifting and lowering the discharged sheet tray, an upper surface sensor for sensing the upper surface of the uppermost sheet of the sheets stacked on the discharged sheet tray and a control for controlling the lifting/lowering device based on a result sensed by the upper surface sensor. A light transparent type sensor, for example, is used as the upper surface sensor. The sensor is composed of a light emitting unit and a light receiving unit disposed on the right side and the left side of the sheet discharge tray, respectively, and the optical axis of them travels a predetermined height above the discharged sheet tray in a right and left direction.
Each time a sheet is stacked on the stack tray, the height of the uppermost sheet is increased. When the uppermost sheet reaches the optical axis, the emitted light is blocked by the sheet, that is, the sensor senses the uppermost sheet. The control lowers the stack tray by controlling the lifting/lowering device based on the result sensed by the sensor. A lowering amount of the stack tray at the time is set to an amount necessary to restore the optical axis shaded by the uppermost sheet. The repetition of the above operation effected each time a sheet is discharged onto the stack tray and stacked thereon permits the uppermost sheet of the sheets on the stack tray to be maintained to the prescribed height at all times.
With this operation, since the height from a discharge port from which a sheet is discharged to the uppermost sheet, that is, a falling height of a sheet when it is discharged can be maintained to the prescribed height, sheets can be discharged and stacked well.
However, according to the above prior art, when sheets discharged onto the stack tray are partially drawn out in a batch, the position of the uppermost sheet on the stack tray is lowered and the falling height of a sheet is increased when it is discharged. Thus, there is a possibility that sheets are discharged and stacked badly.
SUMMARY OF THE INVENTION
An object of the present invention is to solve the aforesaid problem, that is, to provide a sheet processing apparatus for preventing sheets from being discharged and stacked badly when sheets on sheet stack means (the stack tray in the above description) are partly drawn out in a batch and an image forming apparatus provided with such a sheet processing apparatus.
In accordance with these objects, there is provided a sheet processing apparatus comprising a sheet stacking tray supported for upward and downward movement, lifting/lowering means for lifting upward and lowering downward the sheet stacking tray, first sensor means for sensing a position of an upper most surface of a batch of sheets on the stacking tray and for moving the stacking tray a prescribed amount by control of the lifting/lowering means and second sensor means for sensing that the batch of sheets on the sheet ray is partially drawn out and for moving the sheet stacking tray by control of the lifting/lowering means to thereby return the sheet stacking tray to a position proper to discharge sheets.
More specifically, the first and second sensors are each a light transparent type sensor having a light emitting unit and a light receiving unit, the light emitting unit and the light receiving unit of the first sensor forming an optical axis which is approximately parallel with a plane on which the batch of sheets is stacked and the light emitting unit and the light receiving unit of the second sensor forming an optical axis which intersects the plane on which the batch of sheets is stacked.
The following operations will be mainly achieved based on the above arrangement.
When the sheets stacked on the sheet stack means are partly drawn out and the position of the upper surface of the uppermost sheet is lowered, the second sensor senses it and the sheet stack means is lifted until the optical axis of the first sensor is blocked by the sheets stacked on the sheet stack means and thereafter lowered until the optical axis of the first sensor is transmitted. With this operation, since the uppermost sheet of the sheets stacked on the sheet stack means can be disposed in the vicinity of the light axis of the first sensor, the dropping height of the sheets when they are discharged can be set properly, whereby sheets can be preperly discharged onto and stacked on the upper surface of the uppermost sheet.
As described above, according to the present invention, when the sheets on the sheet stack means are partly drawn out, defective discharge and defective stacking of sheets can be effectively prevented.
REFERENCES:
patent: 4189133 (1980-02-01), Arrasmith et al.
patent: 4390175 (1983-06-01), Takahashi et al.
patent: 4647034 (1987-03-01), Sawa
patent: 5621501 (1997-04-01), Matsuo et al.
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Miller Jonathan R
Walsh Donald P.
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