Sheet conveying device and image forming apparatus

1 . A sheet conveying device, comprising:

a conveying roller pair that conveys a sheet toward an image transfer position at which a toner image formed by an image forming unit is transferred to the sheet;

a resist roller pair that is provided between the image transfer position and the conveying roller pair;

a sheet sensor that is provided between the resist roller pair and the conveying roller pair and detects a leading edge of the sheet;

a resist control unit that controls rotational driving of the resist roller pair such that the sheet is conveyed by the conveying roller pair while the resist roller pair is stopped to deflect the sheet whose leading edge has reached the resist roller pair and then the sheet is fed out at predetermined feed timing in accordance with transfer start timing at which transfer of the toner image to the sheet starts at the image transfer position; and

a conveying speed control unit that controls, on a basis of an elapsed time from predetermined writing timing at which light scanning on a photoreceptor drum included in the image forming unit starts to the leading edge detection timing at which the sheet sensor detects the leading edge of the sheet, a rotational speed of the conveying roller pair such that a feeding amount of the sheet after the leading edge detection timing is a predetermined reference conveying amount, wherein

the conveying speed control unit:

controls rotation of the conveying roller pair such that the sheet is conveyed at a predetermined initial speed Vd until the leading edge detection timing,

controls, where the leading edge detection timing is predetermined reference timing, rotation of the conveying roller pair such that a conveying speed of the sheet gradually decreases from the initial speed Vd to a low set speed Vr lower than the initial speed Vd at predetermined reference deceleration start timing,

determines, where the leading edge detection timing is earlier than the reference timing, first deceleration start timing earlier than the reference deceleration start timing by a time corresponding to the elapsed time, and controls rotation of the conveying roller pair such that the conveying speed of the sheet gradually decreases from the initial speed Vd to the low set speed Vr at the first deceleration start timing, and

determines, where the leading edge detection timing is later than the reference timing, second deceleration start timing later than the reference deceleration start timing by a time corresponding to the elapsed time, and controls rotation of the conveying roller pair such that the conveying speed of the sheet gradually decreases from the initial speed Vd to the low set speed Vr at the second deceleration start timing,

the resist control unit controls rotation of the resist roller pair such that the sheet is conveyed at a transfer conveying speed Vp faster than the initial speed Vd after the feed timing, and

the conveying speed control unit controls rotation of the conveying roller pair such that the sheet is conveyed at the transfer conveying speed Vp after the feed timing.

2 . An image forming apparatus, comprising:

a conveying roller pair that conveys a sheet toward an image transfer position at which a toner image formed by an image forming unit is transferred to the sheet;

a resist roller pair that is provided between the image transfer position and the conveying roller pair;

a sheet sensor that is provided between the resist roller pair and the conveying roller pair and detects a leading edge of the sheet;

a resist control unit that controls rotational driving of the resist roller pair such that the sheet is conveyed by the conveying roller pair while the resist roller pair is stopped to deflect the sheet whose leading edge has reached the resist roller pair and then the sheet is fed out at predetermined feed timing in accordance with transfer start timing at which transfer of the toner image to the sheet starts at the image transfer position; and

a conveying speed control unit that controls, on a basis of an elapsed time from predetermined writing timing at which light scanning on a photoreceptor drum included in the image forming unit starts to the leading edge detection timing at which the sheet sensor detects the leading edge of the sheet, a rotational speed of the conveying roller pair such that a feeding amount of the sheet after the leading edge detection timing is a predetermined reference conveying amount, wherein

the conveying speed control unit:

controls rotation of the conveying roller pair such that the sheet is conveyed at a predetermined initial speed Vd until the leading edge detection timing,

controls, where the leading edge detection timing is predetermined reference timing, rotation of the conveying roller pair such that a conveying speed of the sheet gradually decreases from the initial speed Vd to a low set speed Vr lower than the initial speed Vd at predetermined reference deceleration start timing,

determines, where the leading edge detection timing is earlier than the reference timing, first deceleration start timing earlier than the reference deceleration start timing by a time corresponding to the elapsed time, and controls rotation of the conveying roller pair such that the conveying speed of the sheet gradually decreases from the initial speed Vd to the low set speed Vr at the first deceleration start timing, and

determines, where the leading edge detection timing is later than the reference timing, second deceleration start timing later than the reference deceleration start timing by a time corresponding to the elapsed time, and controls rotation of the conveying roller pair such that the conveying speed of the sheet gradually decreases from the initial speed Vd to the low set speed Vr at the second deceleration start timing;

the resist control unit controls rotation of the resist roller pair such that the sheet is conveyed at a transfer conveying speed Vp faster than the initial speed Vd after the feed timing;

the conveying speed control unit controls rotation of the conveying roller pair such that the sheet is conveyed at the transfer conveying speed Vp after the feed timing; and

the toner image being transferred to the sheet is conveyed by the sheet conveying device to the image transfer position.