Sheet conveying device and image forming apparatus

An image forming apparatus comprising:

• a sheet conveying device applied to at least one of an intermediate transfer unit and a fixing unit, wherein
• the sheet conveying device conveys a sheet to a nip portion formed by pressing a first roller over which an endless belt is supported and a second roller arranged opposite to the first roller against each other with the endless belt therebetween, and
• the sheet conveying device includes
• a first driving unit that drives the endless belt,
• a fluctuation information acquiring unit that acquires fluctuation information of the endless belt,
• a fluctuation detecting unit that detects a fluctuation of the endless belt generated when the sheet is brought into contact with a predetermined position of the endless belt at an upstream side in a conveying direction from the nip portion, based on the fluctuation information acquired by the fluctuation information acquiring unit,
• an entry timing estimating unit that estimates entry timing of the sheet into the nip portion based on a detection of the fluctuation by the fluctuation detecting unit,
• a correction control unit that corrects a speed fluctuation of the endless belt generated when the sheet enters the nip portion by performing a feedforward control of the first driving unit based on the entry timing estimated by the entry timing estimating unit, and
• a third roller over which the endless belt is set, and that is movably supported to a main body of the device and biased by a biasing unit in a direction that gives a tension to the endless belt, wherein
• the fluctuation information acquiring unit includes
• an upstream side fluctuation information acquiring unit that acquires the fluctuation information of the endless belt from the predetermined position to the third roller in an upstream direction of the conveying direction, and
• a downstream side fluctuation information acquiring unit that acquires the fluctuation information of the endless belt from the predetermined position to the third roller in a downstream direction of the conveying direction, and
• the fluctuation detecting unit produces difference data of the fluctuation information acquired by the upstream side fluctuation information acquiring unit and the downstream side fluctuation information acquiring unit, and detects the fluctuation of the endless belt generated when the sheet is brought into contact with the endless belt from the difference data.