Belt member feeding device and image forming apparatus provided with the same

A belt feeding apparatus comprising:

• a rotatable belt member;
• first and second rotatable rollers configured to stretch said rotatable belt member;
• and
• a steering member configured to stretch said rotatable belt member, said steering member supporting said rotatable belt member at a position adjacent to a downstream side of said first rotatable roller and adjacent to an upstream side of said second rotatable roller with respect to a rotational direction of said rotatable belt member, wherein said steering member includes a rotatable portion rotatable with rotation of said rotatable belt member, frictional portions, provided at both axial ends of the rotatable portion, for slidable contact with said rotatable belt member, a supporting member configured to support the rotatable portion and the frictional portions, and a rotation shaft rotatably supporting the supporting member,
• wherein said steering member moves said rotatable belt member in a rotational axis direction of the rotatable portion by the supporting member rotating by a force produced by sliding between said rotatable belt member and the frictional portions, and
• wherein an elliptical locus having focuses at a rotational center of said first rotatable roller and a rotational center of said second rotatable roller, respectively has a major diameter a and a minor diameter b, and
• said steering member is disposed such that an oblateness c=(a−b)/a and an angle φ formed between a line segment between the rotational center of said first rotatable roller and the rotational center of the rotatable portion and a line segment between the rotational center of said first rotatable roller and the rotational center of said second rotatable roller, satisfy,
• (i) 0<c<0.1, or
• (ii) 0<c<0.25 and 125°<φ<180°.