Image forming apparatus

1. An image forming apparatus comprising:

a first developing unit having a photosensitive body;

a second developing unit having a developing roller being moveably installed so that the developing roller selectively contacts the photosensitive body;

a pressing member to selectively press the second developing unit so that the developing roller contacts with the photosensitive body during a developing process but separates from the photosensitive body after the developing process is finished; and

a hinge to hinge the second developing unit on the first developing unit so as to rotate the second developing unit,

wherein a first elastic member is installed on the hinge.

2. The image forming apparatus of claim 1 , further comprising a power transmitting unit comprising an Oldham coupling to transmit power from a drive source to the second developing unit.

3. The image forming apparatus of claim 2 , wherein the power transmitting unit comprises a developing roller gear and a plurality of gears, and the Oldham coupling is coupled to one of the plurality of gears to apply a lighter load than the developing roller gear.

4. The image forming apparatus of claim 2 , wherein the pressing member moves up and down to selectively press the second developing unit.

5. The image forming apparatus of claim 3 , further comprising a first elastic member elastically biasing the second developing unit so that the second developing unit separates from the first developing unit.

6. The image forming apparatus of claim 5 , wherein the first elastic member comprises a spring.

7. The image forming apparatus of claim 6 , wherein the developing roller contacts with the photosensitive body when the pressing member presses the second developing unit but is separated from the photosensitive body via the first elastic member when the pressing member separates from the second developing unit.

8. The image forming apparatus of claim 1 , wherein the pressing member moves up and down to selectively press the second developing unit.

9. An image forming apparatus comprising:

a first developing unit having a photosensitive body;

a second developing unit having a developing roller being moveably installed so that the developing roller selectively contacts the photosensitive body; and

a pressing member to selectively press the second developing unit so that the developing roller contacts with the photosensitive body during a developing process but separates from the photosensitive body after the developing process is finished;

a first elastic member to elastically bias the second developing unit so that the second developing unit separates from the first developing unit; and

a hinge to hinge the second developing unit on the first developing unit so as to rotate the second developing unit,

wherein the first elastic member is installed adjacent to the hinge.

10. The image forming apparatus of claim 9 , further comprising a power transmitting unit comprising an Oldham coupling to transmit power from a drive source to the second developing unit.

11. The image forming apparatus of claim 10 , wherein the power transmitting unit comprises a developing roller gear and a plurality of gears, and the Oldham coupling is coupled to one of the plurality of gears to apply a lighter load than the developing roller gear.

12. The image forming apparatus of claim 10 , wherein the pressing member moves up and down to selectively press the second developing unit.

13. The image forming apparatus of claim 9 , wherein the first elastic member comprises a spring.

14. The image forming apparatus of claim 13 , wherein the developing roller contacts with the photosensitive body when the pressing member presses the second developing unit but is separated from the photosensitive body via the first elastic member when the pressing member separates from the second developing unit.

15. The image forming apparatus of claim 9 , wherein the pressing member moves up and down to selectively press the second developing unit.