Member for intermittent feed motion

Claim 1

An intermittent drive mechanism comprising: a shaft rotatable about an axis, a spiral groove formed in the outer periphral surface of the shaft leading in one axial direction, and a tip end portion of a movable member riding in the spiral groove, the spiral groove having a plurality of groove portions which are discrete and separate from each other and positioned circumferentially staggered in stepwise axial increments along the spiral groove, each groove portion having a bottom wall oriented at a minimal lead angle to the axis of the shaft and inclined side walls opposing each other on each side of the bottom wall such that the tip end portion of the movable member can ride along the bottom wall of the groove guided by the inclined side walls, said bottom wall being flat, linear, and having a predetermined length in the direction transverse to said shaft axis that despite small angular movements of the shaft said tip end riding thereon can move along the length of the groove without any significant axial movement, the spiral groove including feed portions which interconnect adjacent groove portions, said feed portions being formed as substantially discontinuous transition lines wherein said tip end portion must move into one or the other of two adjacent groove portions upon encountering a feed portion, whereby the tip end portion is intermittently driven in stepwise axial increments along the one axial direction as it rides along successive groove portions of the spiral groove in conjunction with rotation of the shaft, the movable member is controlled to move in discrete stepwise axial increments by rotation of the shaft, and the movable member is held stably at incremental axial positions despite small angular movements of the shaft.