Tension controller, medium conveying device incorporating the tension controller, and image forming apparatus incorporating the medium conveying device

A tension controller, comprising:

• a drive device configured to rotate a drive shaft;
• and
• a drive transmission device configured to transmit a rotation driving force of the drive shaft of the drive device to rotate a rotary shaft of a roll of a conveyance target medium,
• the drive transmission device including a tension applying device,
• the tension applying device including a variable speed reducing device and a torque limiter, the variable speed reducing device and the torque limiter being disposed between the drive shaft of the drive device and the rotary shaft of the roll of the conveyance target medium,
• the variable speed reducing device being configured to change a speed reduction ratio between the rotary shaft of the roll of the conveyance target medium and the torque limiter and apply a tension force to the conveyance target medium,
• wherein the variable speed reducing device includes
• conical rollers rotatably supported and coaxially disposed facing each other;
• a semi-sphere-shaped roller disposed in contact with a side face of one of the conical rollers and a side face of an opposed one of the conical rollers;
• and
• a pressing body configured to press the semi-sphere-shaped roller to the side face of the one of the conical rollers and the side face of the opposed one of the conical rollers,
• the semi-sphere-shaped roller is configured to rotate about a shaft, with an axis of the shaft passing a center of the semi-sphere-shaped roller in a direction vertical to axes of the conical rollers, and rotate about another shaft that passes the center of the semi-sphere-shaped roller in a direction vertical to the axis of the shaft, and
• when a first distance from an axial center of said another shaft to a contact point at which the semi-sphere-shaped roller that is rotated about the shaft contacts the one of the conical rollers and a second distance from the axial center of said another shaft to a contact point at which the semi-sphere-shaped roller that is rotated about the shaft contacts the opposed one of the conical rollers are changed, a speed reduction ratio of the conical rollers is varied is varied continuously.