This application is based on and claims the benefit of priority from the prior Japanese Patent Application No. 2005-340139, filed on Nov. 25, 2005; the entire contents of which are incorporated herein by reference.
The present invention relates to a sheet feeder for a printer.
The related-art method for detecting an upper face position of the uppermost sheet involves using a shield plate contacted with the upper face of the uppermost sheet to turn on/off an optical digital sensor placed at a predetermined position, or monitoring a voltage change of an optical analog sensor to keep the upper face position of the uppermost sheet constant based on a detection voltage (e.g., refer to JP-A-7-187422 and JP-A-10-95543). Also, an elastic member is employed as the shield plate in an optical analog sensor (e.g., refer to patent JP-A-2000-188420).
In a sheet feeder for separating the top of sheets by blowing the air, and adsorbing and feeding the sheet on an adsorption transfer belt, it is requisite to keep the upper face position of the uppermost sheet constant at any time to achieve the stable sheet feed.
When the upper face position of the uppermost sheet is detected, a shield plate having a weight of a fixed load or more at the rear end part of the sheet id disposed in contact with the upper face of the sheet so as not to be affected by floating or flutter of the sheet owing to the air for separation, and the upper face position of the sheet keeps constant by moving up a tray based on the presence or absence of detection by an optical sensor placed at a predetermined position. The optical sensor generally employs a digital sensor for sensing the ON/OFF, but it is effective for detecting the upper face position more stably that an analog sensor is used to correct for a variation in the height due to influence of a curl of the sheet. In the optical analog sensor, a change of the light quantity due to a light of the light emitting side, which is shielded by a shield plate, is detected by voltage detected on a light receiving side. The change of the light quantity may not be correctly detected due to a diffraction of the light and may also depend on fluctuation of position of the shield plate.
It is an object of the invention to provide a sheet feed mechanism that is stable and highly reliable by preventing floating or peeling of the elastic shield member.
According to an aspect of the invention, the shield plate detects an upper face position and has a shape like C-character. A surface (C) of the elastic shield member where the elastic member is contact with a light receiving surface of the analog sensor is in the same plane of the surface (D) of the elastic shield member where the elastic shield member is contact with the shield plate. The elastic shield member has a bonding direction to a moving direction of the shield plate.
The related-art sheet feeder is known in which an elastic shield member larger than the shield plate is disposed, and contacted with a sensing face of the analog sensor to detect the accurate upper face position of the sheet. Referring to
In
With the above constitution in
Embodiments of the present invention will be described below with reference to
In
Though in this embodiment, the lower part of the shield plate 6a has the shape like C-character, the shield plate may be provided with a rectangular hole 6b, for example, in which the elastic shield member is passed into this rectangular hole 6b, as shown in
As described above, the elastic shield member 10a is bonded under the contact portion of the shield plate 6a having the shape like C-character on the same plane as in the contact direction. In other words, since the elastic shield member 10a is bonded on the lower part of the shield plate 6a through an interval of the shape like a C-character of the shield plate 6a, while a surface (C) of the elastic shield member 10a where the elastic shield member 10a is contact with a light receiving surface of the analog optical sensor 7 is in the same plane of the surface (D) of the elastic shield member 10a where the elastic shield member 10a is contact with the shield plate 6a. (Refer to C and D of
According to the above embodiment, the stable and reliable sheet feed can be accomplished by providing a highly reliable mechanism that is inexpensive, simply attached, and protected against a deformation of the shield member.
Number | Date | Country | Kind |
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P2005-340139 | Nov 2005 | JP | national |
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Number | Date | Country |
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07-187422 | Jul 1995 | JP |
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Number | Date | Country | |
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20070121025 A1 | May 2007 | US |