Paper transport device and image forming apparatus

1. A paper transport device comprising:

a transport section that transports paper to a reversal position in a first direction on a first transport path, and reverses a transport direction to a second direction that is a direction opposite to the first direction at the reversal position, to transport the paper onto a second transport path that branches from the first transport path; and

a detecting section that detects that the paper is transported in the first direction, and has arrived at the reversal position,

wherein the detecting section includes

a first member that is arranged closer to the reversal position side than a branch point on the first transport path branched to the second transport path, and changes posture thereof among a first posture free of the contact with paper, a second posture where the first member comes into contact with the paper transported in the first direction and has rotated in the first direction from the first posture, and a third posture where the first member comes into contact with the paper transported in the second direction and has rotated in the second direction from the first posture, after the paper has passed in the first direction,

a second member that changes posture thereof between a fourth posture and a fifth posture by rotation,

a detector that (i) detects whether the second member is in the fourth posture or in the fifth posture, and (ii) keeps detecting the second member even if the first member rotates toward the third posture from the first posture, and

a joint member that couples the first member and the second member together, allows the second member to be in the fourth posture when the first member is in the first posture, rotates the second member to the fifth posture when a movement in which the first member rotates toward the second posture from the first posture is transmitted to the second member and the first member has rotated to the second posture, and does not transmit a movement in which the first member rotates toward the third posture from the first posture, to the second member, and keeps the second member in the fourth posture.

2. The paper transport device according to claim 1 ,

wherein the first member has a detecting claw that changes to the first to third postures, and a rotating shaft that supports the detecting claw at one end thereof and extends in a paper width direction,

the joint member is arranged between an other end of the rotating shaft and the second member, and

an urging member is further provided at the one end of the rotating shaft to urge the detecting claw from the second posture toward the first posture.

3. The paper transport device according to claim 2 , further comprising:

a rotation inhibiting portion that comes into contact with the second member in the fourth posture to inhibit a rotation in a direction opposite to a rotation that is directed toward the fifth posture from the fourth posture.

4. The paper transport device according to claim 3 ,

wherein the second member has a center of gravity at a position farther from a rotating shaft of the second member than a middle point of a line segment that connects the rotating shaft of the second member and a tip farthest from the rotating shaft of the second member in a radial direction.

5. The paper transport device according to claim 1 , further comprising:

a rotation inhibiting portion that comes into contact with the second member in the fourth posture to inhibit a rotation in a direction opposite to a rotation that is directed toward the fifth posture from the fourth posture.

6. The paper transport device according to claim 5 ,

wherein the second member has a center of gravity at a position farther from a rotating shaft of the second member than a middle point of a line segment that connects the rotating shaft of the second member and a tip farthest from the rotating shaft of the second member in a radial direction.

7. The paper transport device of claim 1 ,

wherein the first member has a detecting claw that changes to the first to third postures, and a rotating shaft that supports the detecting claw at one end thereof and extends in a paper width direction, and

wherein the joint member is arranged between an other end of the rotating shaft and the second member.

8. An image forming apparatus comprising:

an image forming section that forms an image on one side of transported paper;

a transport section that transports paper to a reversal position on the downstream side of the image forming section, in a first direction passing through the image forming section on a first transport path that goes via the image forming section, reverses a transport direction to a second direction from the first direction at the reversal position, to transport the paper on a second transport path branching from the first transport path and bypassing the image forming section, and reverses the front and back of the paper to join the paper to the first transport path again on the upstream side of the image forming section to direct the paper to the image forming section; and

a detecting section that detects that the paper is transported in the first direction, and has arrived at the reversal position,

the detecting section including:

a first member that is arranged closer to the reversal position side than a branch point on the first transport path branched to the second transport path, and changes posture thereof among a first posture free of the contact with paper, a second posture where the first member comes into contact with the paper transported in the first direction and has rotated in the first direction from the first posture, and a third posture where the first member comes into contact with the paper transported in the second direction and has rotated in the second direction from the first posture, after the paper has passed in the first direction;

a second member that changes posture thereof between a fourth posture and a fifth posture by rotation;

a detector that (i) detects whether the second member is in the fourth posture or in the fifth posture, and (ii) keeps detecting the second member even if the first member rotates toward the third posture from the first posture; and

a joint member that couples the first member and the second member together, allows the second member to be in the fourth posture when the first member is in the first posture, rotates the second member to the fifth posture when a movement in which the first member rotates toward the second posture from the first posture is transmitted to the second member and the first member has rotated to the second posture, and does not transmit a movement in which the first member rotates toward the third posture from the first posture, to the second member, and keeps the second member in the fourth posture.

9. The image forming apparatus according to claim 8 ,

wherein the first member has a detecting claw that changes to the first to third postures, and a rotating shaft that supports the detecting claw at one end thereof and extends in a paper width direction,

the joint member is arranged between an other end of the rotating shaft and the second member, and

an urging member is further provided at the one end of the rotating shaft to urge the detecting claw from the second posture toward the first posture.

10. The image forming apparatus according to claim 9 , further comprising:

a rotation inhibiting portion that comes into contact with the second member in the fourth posture to inhibit a rotation in a direction opposite to a rotation that is directed toward the fifth posture from the fourth posture.

11. The image forming apparatus according to claim 10 ,

wherein the second member has a center of gravity at a position farther from a rotating shaft of the second member than a middle point of a line segment that connects the rotating shaft of the second member and a tip farthest from the rotating shaft of the second member in a radial direction.

12. The image forming apparatus according to claim 8 , further comprising:

a rotation inhibiting portion that comes into contact with the second member in the fourth posture to inhibit a rotation in a direction opposite to a rotation that is directed toward the fifth posture from the fourth posture.

13. The image forming apparatus according to claim 12 ,

wherein the second member has a center of gravity at a position farther from a rotating shaft of the second member than a middle point of a line segment that connects the rotating shaft of the second member and a tip farthest from the rotating shaft of the second member in a radial direction.

14. The image forming apparatus according to claim 8 ,

wherein the first member has a detecting claw that changes to the first to third postures, and a rotating shaft that supports the detecting claw at one end thereof and extends in a paper width direction, and

wherein the joint member is arranged between an other end of the rotating shaft and the second member.