Document conveying apparatus and document conveying method

1. A document conveying apparatus comprising:

a reading unit, which reads image information on a surface of a sheet-like document; a driving-side discharge unit, which conveys a document in a first direction, first image information on a first surface of the document having been read by said reading unit, in contact with said first surface of said document, and discharges at least a part of said document from said document conveying apparatus;

a driven-side discharge unit, which is arranged so as to face said driving-side discharge unit, and receives transmission of a rotative force from said driving-side discharge unit, when being in contact with said driving-side discharge unit;

a specific-direction conveying unit, which conveys the document conveyed from said driving-side discharge unit in a second direction, which is opposite to said first direction, so that said reading unit reads second image information on a second surface of the document, wherein:

said specific-direction conveying unit includes a pair of conveying rollers, and

said fourth direction and a direction from a position of contact, between said driving roller and said driven roller, toward a position of contact, between said pair of conveying rollers, form an acute angle;

a pressing force applying unit, which applies a force in a third direction to said driven-side discharge unit so that said driven-side discharge unit is in contact with said driving-side discharge unit; wherein:

said driving-side discharge unit includes a driving roller,

said driven-side discharge unit includes a driven roller, and

said movement control unit moves a rotary shaft of said driven roller in said third direction and in said fourth direction;

a movement control unit, which moves said driven-side discharge unit in a fourth direction, which is opposite to said third direction, when said document conveyed by said specific-direction conveying unit is in contact with said driven-side discharge unit; and

a torque limiting unit, which detects a torque exerted on said driving-side discharge unit, and restricts the transmission of said rotative force, when said torque is equal to or larger than a predetermined value.

2. The document conveying apparatus according to claim 1 , wherein

said driving-side discharge unit includes a driving roller,

said driven-side discharge unit includes a driven roller, and

said movement control unit moves a rotary shaft of said driven roller in said third direction and in said fourth direction.

3. The document conveying apparatus according to claim 2 , wherein

said specific-direction conveying unit includes a pair of conveying rollers, and

said fourth direction and a direction from a position of contact, between said driving roller and said driven roller, toward a position of contact, between said pair of conveying rollers, form an acute angle.

4. The document conveying apparatus according to claim 3 , wherein said pair of conveying rollers are in contact with each other at a position higher than a position of contact between said driving roller and said driven roller.

5. The document conveying apparatus according to claim 2 , wherein said movement control unit includes:

a bearing unit, which bears the rotary shaft of said driven roller; and

a rail unit, on which said bearing unit slides in said third direction and in fourth direction.

6. The document conveying apparatus according to claim 2 , wherein a surface of said driven roller includes a material with a friction coefficient which is larger than a friction coefficient of a material on a surface of said driving roller.

7. The document conveying apparatus according to claim 1 , wherein when said driving-side discharge unit conveys said document in the second direction, said specific-direction conveying unit conveys the document faster than a speed, at which said driving-side discharge unit conveys the document.

8. A document conveying method for conveying a sheet-like document in a document conveying apparatus, the method comprising:

reading first image information on a first surface of said document;

conveying said document in a first direction, and discharging at least a part of said document from said document conveying apparatus by means of a driving roller and a driven roller;

detecting a trailing edge of said document conveyed in the first direction;

reversing a conveying direction of said document, and conveying said document in a second direction, which is opposite to said first direction, on a basis of said detecting the trailing edge;

applying a tensile force to said document in a document conveying direction;

moving said driven roller, which applies a pressing force in a third direction to said driving roller, in a fourth direction, which is opposite to the third direction, so that said pressing force is reduced;

reading second image information on a second surface of said document;

detecting torque exerted on said driving roller, when the tensile force is applied to said document in the document conveying direction; and

controlling a rotary shaft of said driving roller, so that said torque is equal to or lower than a predetermined value.

9. The document conveying method according to claim 8 , wherein

the tensile force in said conveying direction is applied to said document by a pair of conveying rollers; and

said fourth direction and a direction from a position of contact, between said driving roller and said driven roller, toward a position of contact, between said pair of conveying rollers, form an acute angle.

10. The document conveying method according to claim 9 , wherein said pair of conveying rollers are in contact with each other at a position higher than a position of contact between said driving roller and said driven roller.

11. The document conveying method according to claim 10 , wherein when conveying said document in the second direction, said document is conveyed by said pair of conveying rollers faster than a speed, at which said driving roller conveys the document.