1. Field of the Invention
The present invention relates to a sheet feeding apparatus that includes a sheet stacking portion, which stacks sheets disposed in a sheet feeding apparatus body, and a heated air blowing portion, which blows heated air to the sheets stacked to the sheet stacking portion.
2. Description of the Related Art
In an image forming apparatus, such as a copying machine or a printer, continuously feedable sheets are generally limited to high quality paper or plain paper designated by a copying machine maker. In these sheets, since smoothness of a surface is low and air permeability is high (air can easily pass through the sheets), the air easily flows between the sheets. Accordingly, when each sheet is extracted from the stacked sheets, absorption between the sheets is rarely generated. As a result, overlapping sheet feeding is rarely generated.
Meanwhile, in recent years, with diversification of a recording medium, an image may be formed on thick paper, an OHP sheet, and tracing paper. Further, in order to give a white degree or luster in accordance with a market request for coloring, even in sheets having a smooth surface, such as coat paper and art paper where a surface of a sheet is subjected to coating processing, an image formation request has been increased. In addition, in the OHP sheet, the tracing paper, the art paper, and the coat paper, since smoothness is high and air permeability is low (air rarely passes through them), the air is not easily flown between the sheets. Accordingly, when the sheets are stacked in a high-humidity environment in particular, the sheets can be easily absorbed there between. In a friction separation system that is generally used in a copying machine or a printer according to the related art, separation is not sufficiently made. As a result, overlapping sheet feeding or erroneous feeding is frequently generated.
In regards to the sheets that have the high smoothness and the low air permeability, techniques for suppressing absorption between the sheets and reducing overlapping sheet feeding or erroneous feeding are disclosed in Japanese Patent Application Laid-Open Nos. 6-32473 and 2001-048366.
Specifically, Japanese Patent Application Laid-Open No. 6-32473 discloses a sheet feeding apparatus including an air exhaust portion that blows air heated by a dehumidifying heater provided at the lower side of a housing frame to a top surface or a side surface of a sheet stacked on a stack tray. According to this apparatus, it is possible to resolve a problem of absorption between the sheets by blowing the heated air to the sheets and removing humidity.
Japanese Patent Application Laid-Open No. 2001-048366 discloses a sheet feeding apparatus including an air blowing portion that blows air heated by an air heating portion to sheets stored in a sheet storage portion. According to this apparatus, it is possible to resolve a problem of absorption between the sheets by controlling the air heating portion and blowing air having proper humidity.
Meanwhile, according to the techniques that are related to sheet feeding disclosed in Japanese Patent Application Laid-Open Nos. 6-32473 and 2001-048366, if a sheet bundle is additionally stacked in a state where the sheets are stored in the sheet feeding apparatus, the sheets that are stored in the sheet feeding apparatus are located below the added sheet bundle. The sheets that are located at the bottom portion continuously are stored in the sheet feeding apparatus until there is no sheet that is stored in the sheet feeding apparatus. As such, if a long period of time passes in a state where the sheets are not used, moisture that is contained in the sheets may be continuously evaporated by the heated air blown to the sheets. In addition, if proper moisture is not contained in the sheets, warping is generated in the sheets. As a result, a sheet conveyance defect may be easily generated, or a surface property of the sheet or an electrostatic resistance value varies to cause a defective image to be easily formed. Accordingly, between the sheets that are stored in the sheet feeding apparatus for a long period of time and sheets that are newly stacked, image qualities may be different from each other, even though the same printed material is formed. In order to avoid this problem, a method is considered in which the amount of moisture contained in sheets having various surface properties is measured at the time of feeding the sheets and an image formation condition is changed. However, it is difficult to carry out the method, because the amount of contained moisture should be instantaneously measured at the time of feeding the sheets. Further, a method is also considered in which provided is a measuring apparatus that measures the amount of moisture of the sheets stored in the sheet feeding apparatus. However, if the measuring apparatus is provided, this causes enormous costs.
Accordingly, the present invention provides a sheet feeding apparatus that can properly maintain the amount of moisture contained in a sheet even though a storing period of time of the sheet is increased, prevent a sheet conveyance defect and an image formation defect on the sheet from being generated due to a decrease in the amount of moisture contained in the sheet, and stably output a high-quality printed material.