Image forming apparatus

An image forming apparatus configured to execute image forming processing of forming an image on a sheet, comprising:

• a photosensitive drum;
• a fixing device including a heater and a roller;
• a main motor configured to generate a driving force;
• a driving mechanism having a connected state in which the driving force is transmittable to both the roller and the photosensitive drum, and a disconnected state in which the driving force is transmittable to the roller but is not transmitted to the photosensitive drum;
• a temperature sensor configured to detect a temperature of the fixing device;
• and
• a controller,
• wherein in a case where the image forming processing is started, the controller sets the driving mechanism into the disconnected state, rotates the main motor at a preheating speed, and executes preheating processing in which the fixing device is heated by the heater,
• wherein in a case where the temperature of the fixing device detected by the temperature sensor is equal to or higher than a given temperature after execution of the preheating processing, the controller executes acceleration processing in which the rotation speed of the main motor is changed to a printing speed that is higher than the preheating speed while maintaining the disconnected state of the driving mechanism, and
• wherein in a case where the rotation speed of the main motor reaches the printing speed after execution of the acceleration processing, the controller changes a state of the driving mechanism from the disconnected state into the connected state, and executes photosensitive drum driving start processing in which driving of both the roller of the fixing device and the photosensitive drum is started.