Image forming system and control method therefor, and control unit for image forming apparatus

An image forming system, including an image forming apparatus and a sheet feeding apparatus, comprising:

• a first conveying unit configured to convey to the image forming apparatus a recording material fed by the sheet feeding apparatus;
• a first controller controlling a first conveying speed at which the first conveying unit is to convey the recording material;
• a second conveying unit configured to convey to an image forming unit of the image forming apparatus the recording material conveyed by the first conveying unit;
• a detector detecting a type of the recording material while the recording material is halted by the second conveying unit;
• a second controller controlling, based on detection result by the detector, a conveying speed so that the second conveying unit conveys the recording material to the image forming unit of the image forming apparatus at a second conveying speed, and transmitting the second conveying speed to the first controller,
• wherein, based on printing reservation information for the recording material, the first controller conveys the recording material to a predetermined position located prior to reaching the second conveying unit, and during the time after the recording material reaches the predetermined position, and before the recording material fed by the sheet feeding apparatus reaches the second conveying unit, the first controller maintains the first conveying speed for the recording material, and after the recording material reaches the second conveying unit, the first controller controls the conveying speed to be switched to the second conveying speed, when the second conveying speed transmitted from the second controller is different from the first conveying speed;
• and
• a sheet delivery apparatus including a delivery unit and another controller, the delivery unit configured to deliver the recording material, and the another controller controlling conveying speeds of the recording material,
• wherein the another controller controls the recording material to be conveyed at a third conveying speed determined by the second controller.