Abstract: An indexing mechanism for providing intermittent rotation to a device includes a rotatable driven member having a pair of spaced oppositely disposed arcuate slots and a driving member having a pair of angularly spaced driving rollers engageable with the slots for rotatably accelerating and decelerating the driven member. The driven member locking rollers adjacent the slots engageable with the outer periphery of the driving member to prevent rotation of the driven member when it is not being indexed by the driving member. The indexing mechanism further includes a positive lock mechanism actuatable by a cam follower that rides within an endless cam track in the driving member. The positive lock mechanism is actuated by the cam follower to engage the indexed device and prevent rotation of the device when it is not being indexed.