Medium supplying apparatus

1. A medium supplying apparatus comprising:

a separator roller configured to convey media to a downstream side in a conveying direction by being driven to rotate in the conveying direction in which the media are conveyed;

a retard roller that is disposed to face the separator roller and is configured to be driven to rotate in a direction opposite to the conveying direction while applying a predetermined conveying load to the media through a torque control mechanism;

a double feed detecting sensor that is disposed on a downstream side of the separator roller and the retard roller in the conveying direction and is configured to detect a double feed of the media; and

a control unit configured to

convey, by the separator roller, the media to the downstream side in the conveying direction;

detect, by the double feed detecting sensor, a double feed of the media while conveying the media to the downstream side in the conveying direction;

stop, in response to detecting the double feed of the media, rotation drive of the separator roller;

convey, by the retard roller, a part of the media to an upstream side in the conveying direction; and

check, by the double feed detecting sensor, for the double feed of the media repeatedly until the media is determined to become one sheet while the rotation drive of the separator roller is being stopped and the part of the media is being conveyed to the upstream side in the conveying direction,

wherein when the media is determined to become one sheet, the rotation drive of the separator roller is restarted,

wherein the retard roller conveys the part of the media to the upstream side in the conveying direction while awaiting a predetermined time t d before restarting rotation drive of the separator, and

wherein the predetermined time t d satisfies an expression of t d ≥L 0 /V re , wherein L 0 represents a distance from where the separator roller and the retard roller come in contact each other to the double feed detecting sensor, and V re represents a reverse peripheral speed of the retard roller when conveying the media in a conveying direction.

2. The medium supplying apparatus according to claim 1 , further comprising increasing the conveying load applied by the torque control mechanism, in accordance with an increase in a number of times of detecting the double feed of the media detected by using the double feed detecting sensor.

3. The medium supplying apparatus according to claim 1 , wherein, in a case where the rotation drive of the separator roller is restarted, the control unit is configured to convey the media to the downstream side in the conveying direction at a conveying speed lower than a conveying speed at which the media are conveyed before the double feed of the media is detected by the double feed detecting sensor.

4. The medium supplying apparatus according to claim 1 , wherein the torque control mechanism is a DC motor or a brushless DC motor.

5. The medium supplying apparatus according to claim 1 , wherein the rotation drive of the separator roller is restarted after elapse of a predetermined time from when a double feed state of the media is resolved.

6. The medium supplying apparatus according to claim 2 , wherein stopping the rotation drive of the separator roller and conveying the part of the media to the upstream side in the conveying direction according to increasing the conveying load applied by the torque control mechanism.