Image forming apparatus including input element, output element and transmission element for transmitting driving force of motor to roller

An image forming apparatus comprising:

• a motor;
• a roller;
• and
• a power transmission device capable of transmitting a driving force of the motor to the roller,
• the power transmission device comprising:
• a planetary gear mechanism comprising:
• an input element comprising a first helical gear into which the driving force of the motor is inputted;
• an output element comprising a second helical gear for outputting the driving force to the roller;
• and
• a transmission element rotatable to transmit the driving force from the input element to the output element, wherein the transmission element is capable of transmitting the driving force from the input element to the output element when rotation of the transmission element is restricted, whereas the transmission element does not transmit the driving force from the input element to the output element when the rotation of the transmission element is not restricted;
• and
• a restriction member movable between:
• a restricting position where the restriction member restricts the rotation of the transmission element;
• and
• a non-restricting position where the restriction member does not restrict the rotation of the transmission element,
• wherein the input element, the output element, and the transmission element are rotatable coaxially,
• wherein the input element and the output element are positioned adjacent to each other in an axial direction of the planetary gear mechanism, and
• wherein the first helical gear and the second helical gear are provided so that a direction of a first thrust force applied to the first helical gear and a direction of a second thrust force applied to the second helical gear are opposite to each other.