Sheet conveying device and image forming apparatus

A sheet conveying device that sequentially conveys a plurality of sheets, comprising:

• a first conveying roller that is driven to rotate by receiving driving force from a first drive unit to convey a sheet;
• a second conveying roller that is provided downstream of the first conveying roller in a sheet conveying direction and is driven to rotate by receiving driving force from a second drive unit to convey the sheet;
• a sheet sensor that is provided between the first conveying roller and the second conveying roller and detects a leading edge and a rear edge of the sheet;
• and
• a speed control unit that controls a conveying speed of the sheet by each of the first conveying roller and the second conveying roller,
• the speed control unit being configured to
• control the first conveying roller and the second conveying roller to be continuously rotated during a sheet conveying operation, and control the rotation of the second conveying roller such that the conveying speed of the sheet by the second conveying roller is always an initial speed,
• where a leading edge of a following second sheet is detected before a first elapsed amount from a first time point at which a rear edge of a first sheet that is fed previously is detected reaches a reference amount corresponding to a predetermined set spacing, change the conveying speed of the sheet by the first conveying roller from the initial speed to a low speed that is slower than the initial speed, and maintain the conveying speed of the sheet by the second conveying roller at the initial speed,
• where the leading edge of the following second sheet has not been detected at a reference time point at which the first elapsed amount from the first time point at which the rear edge of the first sheet that is fed previously is detected reaches the reference amount corresponding to a predetermined sheet spacing, change the conveying speed of the sheet by the first conveying roller from the initial speed to a high speed faster than the initial speed, and maintain the conveying speed of the sheet by the second conveying roller at the initial speed,
• when the conveying speed of the sheet by the first conveying roller is changed from the initial speed to the low speed, calculate sheet spacing at a time point at which the leading edge of the second sheet was detected, based on the initial speed and a time difference between when the rear edge of the first sheet was detected and when the leading edge of the second sheet was detected, calculate, based on the low speed, a time required for the calculated sheet spacing to reach the predetermined set spacing, and determine a time point obtained by adding the required time to the time point at which the leading edge of the second sheet was detected as return timing at which the conveying speed of the sheet by the first conveying roller is returned from the low speed to the initial speed,
• when the conveying speed of the sheet by the first conveying roller is changed from the initial speed to the high speed, calculate an estimated continuation amount Z from the reference time point using the following calculation formula, and determine a time point obtained by adding the estimated continuation amount Z to the reference time point as return timing at which the conveying speed of the sheet by the first conveying roller is returned from the high speed to the initial speed:
• Z
• =
• V
• ⁢
• 2
• ·
• Tb
• /
• (
• V
• ⁢
• 2
• -
• V
• ⁢
• 1
• )
• wherein, V1 represents the initial speed, V2 represents the high speed, and Tb represents a second elapsed amount, and
• return the conveying speed of the sheet by the first conveying roller from the low speed or the high speed to the initial speed at the determined return timing.