Medium feeding apparatus and image forming apparatus

1. A medium feeding apparatus comprising:

an apparatus main body; and

a medium cassette removably inserted into the apparatus main body, the medium cassette being configured to store a medium in a medium placing region;

wherein the medium cassette includes:

a medium positioning unit that determines a position of the medium; and

a locking unit that locks a movement of the medium positioning unit when the medium cassette is inserted into the apparatus main body and before the medium cassette reaches a predetermined position in the apparatus main body;

wherein the apparatus main body includes a contacting section that faces a bottom surface of the medium cassette in the medium placing region when the medium cassette reaches the predetermined position in the apparatus main body;

wherein the locking unit locks the medium positioning unit by contacting the contacting section; and

wherein the medium cassette has a hole through which the locking unit protrudes downward from the medium cassette.

2. The medium feeding apparatus according to claim 1 , wherein the contacting section includes a slope portion that is inclined with respect to a bottom portion of the medium cassette.

3. The medium feeding apparatus according to claim 1 , wherein:

the medium positioning unit includes a medium guide movably provided on the medium cassette; and

the locking unit locks a movement of the medium guide.

4. The medium feeding apparatus according to claim 1 ,

wherein the medium cassette includes a medium tray for storing the medium, and the medium guide is movably provided on the medium tray;

wherein the locking unit includes a third engaging portion movably provided on the medium guide so as to be contactable with the contacting section of the apparatus main body, and

wherein the third engaging portion is swung by contact with the contacting section of the apparatus main body, and engages a fourth engaging portion formed on the medium tray to lock the movement of the medium guide, to thereby lock the movement of the medium guide.

5. The medium feeding apparatus according to claim 4 , wherein the third engaging portion protrudes downward from the medium tray through an opening formed on the medium tray, and

wherein the fourth engaging portion is formed on a part of the medium tray facing the third engaging portion protruding through the opening.

6. The medium feeding apparatus according to claim 4 , wherein the third engaging portion and the fourth engaging portion have convex-and-concave portions that engage each other.

7. The medium feeding apparatus according to claim 4 , wherein the third engaging portion and the fourth engaging portion have friction contact portions that contact each other.

8. The medium feeding apparatus according to claim 4 , wherein the third engaging portion has a swingable body swingably provided on the medium guide, and a surface of the swingable body engages the fourth engaging portion.

9. The medium feeding apparatus according to claim 8 , wherein the swingable body comprises an engagement portion that engages the fourth engaging portion, and a biasing portion that biases the engagement portion toward the fourth engaging portion.

10. The medium feeding apparatus according to claim 4 , further comprising a guide member for guiding the third engaging portion.

11. An image forming apparatus comprising:

the medium feeding apparatus according to claim 1 ; and

an image forming portion that forms an image on the medium fed by the medium feeding apparatus.

12. The medium feeding apparatus according to claim 1 , wherein the medium cassette has a guide portion provided along the hole, the guide portion protruding downward from the medium cassette.

13. A medium feeding apparatus comprising:

an apparatus main body; and

a medium cassette removably inserted into the apparatus main body, the medium cassette being configured to store a medium;

wherein the medium cassette includes:

a medium positioning unit that determines a position of the medium; and

a locking unit that locks a movement of the medium positioning unit when the medium cassette is inserted into the apparatus main body and before the medium cassette reaches a predetermined position in the apparatus main body;

wherein the apparatus main body includes a contacting section provided so that the contacting section faces the medium cassette when the medium cassette reaches the predetermined position in the apparatus main body;

wherein the locking unit locks the medium positioning unit by contacting the contacting section;

wherein the medium positioning unit includes a medium guide movably provided on the medium cassette;

wherein the locking unit locks a movement of the medium guide;

wherein the medium guide includes a rack portion;

wherein the medium cassette includes a rotatable pinion gear that engages the rack portion of the medium guide; and

wherein the locking unit includes a first engaging portion that engages the pinion gear to thereby lock the movement of the medium guide.

14. The medium feeding apparatus according to claim 13 , wherein:

the pinion gear is movable in an axial direction of the pinion gear, and is contactable with the contacting section of the apparatus main body; and

the pinion gear moves toward the first engaging portion by contact with the contacting section.

15. The medium feeding apparatus according to claim 14 , wherein:

the medium cassette includes a biasing member that biases the pinion gear in a direction away from the first engaging portion; and

the pinion gear has a second engaging portion that engages the first engaging portion when the pinion gear moves toward the first engaging portion resisting a biasing force of the biasing member.

16. The medium feeding apparatus according to claim 15 , wherein the first engaging portion and the second engaging portion have convex-and-concave portions that engage each other.

17. The medium feeding apparatus according to claim 16 , wherein an arrangement pitch of each of the convex-and-concave portions of the first engaging portion and the second engaging portion is smaller than a pitch of the pinion gear.

18. The medium feeding apparatus according to claim 17 , wherein the second engaging portion is provided on an end of the pinion gear in an axial direction thereof.

19. The medium feeding apparatus according to claim 15 , wherein the first engaging portion and the second engaging portion have friction contact portions that contact each other.

20. The medium feeding apparatus according to claim 13 , wherein the medium cassette has a hole through which the locking unit protrudes downward from the medium cassette.

21. The medium feeding apparatus according to claim 20 , wherein the medium cassette has a guide portion provided along the hole, the guide portion protruding downward from the medium cassette.