Patent ID: 7311012

Claim:
An elongation measuring device for measuring an elongation in a belt-like member included in a driving device having a rotating drive member supported for rotation about an axis, a rotative driving means for driving the rotating drive member for rotation, and the belt-like member wound round the rotating drive member and holding a movable object to be moved to a desired position, said elongation measuring device comprising: an angular position measuring means for measuring an angular position of the rotating drive member; a movable object detecting means for detecting the movable object positioned at a reference position on a path along which the movable object moves; and an arithmetic means for comparing an angular position of the rotating drive member at a present stage when the movable object is positioned at the reference position and an angular position of the rotative driving means at a past stage when the movable object was positioned at the same reference position a predetermined time before the present stage; wherein the rotating drive member is provided with a plurality of driving protrusions circumferentially arranged at intervals, the belt-like member is provided with a plurality of driven protrusions arranged at longitudinal intervals, the belt-like member is wound round the rotating drive member with the driving protrusions of the rotating drive member engaged with the driven protrusions of the belt-like member, respectively, and a plurality of reference positions are set at intervals on the path of the movable object.