Printing medium supplying apparatus and image forming apparatus having the same

An image forming apparatus comprising:

• a main body having a developing apparatus;
• a supply cassette configured to be detachable from the main body and in which printing media are stacked;
• a knock-up plate configured to elevate the printing media in the supply cassette;
• an opening/closing unit configured to move the supply cassette back and forth to open and close the supply cassette;
• and
• a driving unit configured to operate the knock-up plate and the opening/closing unit,
• wherein the driving unit comprises:
• a driving source configured to generate power;
• a first power control apparatus configured to control the power transmitted from the driving source to the knock-up plate;
• and
• a second power control apparatus configured to control the power transmitted from the driving source to the opening/closing unit,
• wherein the first power control apparatus and the second power control apparatus are independently operated,
• wherein the supply cassette is provided to be movable between a first position of insertion into the main body and a second position of separation from the main body,
• wherein the first power control apparatus includes:
• a first coupling gear;
• and
• a second coupling gear provided at the supply cassette and selectively coupled to the first coupling gear when the supply cassette is at the first position, and
• wherein the first power control apparatus transmits power to the knock-up plate by having the first coupling gear engaged with the second coupling gear when the supply cassette is at the first position.

A printing medium supplying apparatus provided to be separable from a main body to supply printing media, the printing medium supplying apparatus comprising:

• a supply cassette provided to be movable between a first position of insertion into the main body and a second position of separation from the main body to stack the printing media;
• a driving unit having a driving source configured to generate power and an opening/closing power control apparatus configured to selectively transmit power from the driving source;
• an opening/closing unit configured to selectively receive power from the opening/closing power control apparatus and configured to move the supply cassette between the first position and the second position;
• and
• a knock-up plate configured to elevate the printing medium stacked on the supply cassette,
• wherein the driving unit further comprises an elevation power control apparatus configured to receive power from the driving source to elevate the knock-up plate,
• wherein the opening/closing power control apparatus and elevation power control apparatus are independently operated, and
• wherein the opening/closing unit comprises:
• a guide unit which extends from a side surface of the supply cassette in a first axis direction parallel to a forward and rearward direction to be rotated;
• and
• a guide rail formed on an outer surface of the guide unit in a spiral shape and configured to guide movement of the supply cassette by rotation of the guide unit.