Sheet conveyance device capable of detecting shape of sheet, image forming apparatus, sheet shape detecting method

A sheet shape detecting method executed on a sheet conveyance device which includes a first conveyance member, a shape detecting portion, and a speed detecting portion, the first conveyance member being provided on an upstream side of an image forming position included in a conveyance path along which a sheet is conveyed, the first conveyance member being rotationally driven in a driving cycle in which the first conveyance member enters a driven state where the first conveyance member is driven while decelerated in a stepped manner, and then the first conveyance member is decelerated to a stopped state, the shape detecting portion including a light emitting portion and a light receiving portion, the light emitting portion being configured to emit light toward a detection position located between the first conveyance member and the image forming position in the conveyance path, the light extending in a width direction of the sheet perpendicular to the conveyance path, the light receiving portion being configured to receive light that has been emitted from the light emitting portion and reflected on the sheet passing the detection position, and output a detection signal corresponding to an amount of received light, the shape detecting portion detecting a shape of the sheet based on the detection signal, the speed detecting portion being configured to detect a rotation speed of the first conveyance member, the sheet shape detecting method comprising:

• determining whether the first conveyance member is in an accelerated state or in a decelerated state, wherein in the accelerated state, the first conveyance member is accelerated from the stopped state to the driven state, and in the decelerated state, the first conveyance member is decelerated from the driven state to the stopped state;
• and
• when it is determined that the first conveyance member is in the accelerated state, switching an output interval at which the detection signal is output from the light receiving portion, to a first interval that corresponds to the rotation speed detected by the speed detecting portion, and when it is determined that the first conveyance member is in the decelerated state, switching the output interval to a predetermined second interval.