1. Field of the Invention
The present invention relates to a fixing device to be used in an image forming apparatus, such as a copying machine, a facsimile, a printer, and other similar devices, and more particularly, to a belt-type fixing device that can prevent a fixing belt of the fixing device from rubbing against the toner image.
2. Discussion of Background
Generally, an image forming apparatus, such as a copying machine, facsimile, printer, and a printing machine, includes a fixing device that fixes a toner image on a sheet-like recording medium. The sheet-like recording medium may be a normal recording medium, such as plain paper, which is generally used for copying. Instead, the sheet-like recording medium may be a special recording medium, such as overhead transparency film sheets, pieces of cardboard, envelopes, and other similar special recording medium on which images can be recorded, having a greater thermal capacity than the thermal capacity of the normal recording medium.
Two types of fixing devices are commonly known. A first type of fixing device is referred to as a heating roller type. A second type of fixing device is referred to as a belt type.
A heating roller type fixing device is typically comprised of a heating roller, which has a heating source inside thereof and which is rotatably driven, and a pressure roller, which is in pressure-contact with the heating roller and which is driven by the heating roller. In the heating roller type fixing device, a sheet-like recording medium is conveyed by the heating roller and pressure roller to a nip formed between the heating roller and the pressure roller. A toner image is fixed in the nip by heat and pressure.
A belt type fixing device is typically comprised of an endless fixing belt, which conveys the sheet-like recording medium, a heating roller and a fixing roller on which the fixing belt is spanned, and a pressure roller provided at a position opposed to the fixing roller via the fixing belt.
In the heating roller type fixing device, rubbing of the toner image does not occur unless the toner image, formed on a sheet-like recording medium, touches either the surface of the heating roller or the pressure roller before the sheet-like recording medium is conveyed into the nip formed between the heating roller and the pressure roller.
In the belt type fixing device, rubbing of the toner image is more likely to occur because the fixing belt is extended to an upstream side of a fixing region, in which the pressure roller abuts against the fixing belt, in a conveying direction of the sheet-like recording medium so that the toner image is disturbed.
The reasons why the toner image touches the fixing belt are, as follows: (1) a precise setting of a spanning direction of the fixing belt at the upstream side of the fixing region in the conveying direction of the sheet-like recording medium is not easily performed; and (2) the spanning direction of the fixing belt and the conveying direction of the sheet-like recording medium have not been considered in relation to the problem of the toner rubbing.
The present invention has been made in view of the above-mentioned and other problems and addresses the above-discussed and other problems.
The present invention advantageously provides a novel fixing device wherein a rubbing of a toner image by a fixing belt is prevented by precisely setting a spanning direction of the fixing belt and by setting an angle formed between the spanning direction of the fixing belt and an approaching direction of a sheet-like recording medium.
According to an example of the present invention, a fixing device includes: a fixing belt, in an endless form, to convey a sheet-like recording medium on which a toner image is fixed; a heating roller and a fixing roller for supporting the fixing belt; a pressure roller provided at a position opposed to the fixing roller so as to pass the fixing belt between the pressure roller and the fixing roller; a first fixing region where the pressure roller opposes only the fixing belt; a second fixing region arranged at downstream side of the first fixing region in a moving direction of the fixing belt where the pressure roller opposes both the fixing belt and the fixing roller; and an abutting member, which abuts against the fixing belt, provided at a position between an upstream side of the fixing roller and a downstream side of the heating roller in the moving direction of the fixing belt so as to expand the first fixing region.
According to another example of the present invention, the fixing device includes: a fixing belt, in an endless form, to convey a sheet-like recording medium on which a toner image is fixed; a heating roller and a fixing roller for supporting the fixing belt; a pressure roller provided at a position opposed to the fixing roller so as to pass the fixing belt between the pressure roller and the fixing roller; a first supporting member to support the pressure roller with respect to a main body of the fixing device; and a second supporting member to support the fixing belt, the heating roller, and the fixing roller with respect to the first supporting member.