Indexing mechanism

Details Indexing mechanism Indexing mechanism

1999-03-11

2001-01-09

Gutierrez, Diego (Department: 2859)

Machine element or mechanism

Rotary member or shaft indexing, e.g., tool or work turret

With means to axially shift shaft

C074S825000, C033S0010PT

Reexamination Certificate

active

06170358

ABSTRACT:

The present invention relates to an indexing mechanism which enables the relative positioning of two relatively rotatable bodies in one of a plurality of discrete, or angularly indexed positions. Such indexing mechanisms are typically used in metrological apparatus, such as in an articulating probe head for a coordinate measuring machine.
Known indexing mechanisms typically comprise two sets of detent members, which are mutually engageable in a plurality of angularly indexed, repeatable relative positions. One type of such an indexing mechanism is known from U.S. Pat. No. 4,168,576, U.S. Pat. No. 5,185,936 and United Kingdom Patent No. 2,298,488 and includes a circular array of hemispherical detent elements on one of the relatively rotatable bodies, and three elongate cylindrical detent elements on the other of the bodies. At each indexed position, each of the cylindrical bodies engages both mutually convergent surfaces of an adjacent pair of hemispherical elements. The number of indexed positions provided by such a mechanism thus corresponds to the number of sets of convergent surfaces or “pockets” in the circular array, which in turn relates directly to the number of hemispherical elements in the array.
In a further type of indexing mechanism, two identical sets of detent elements are provided, each set of detent elements having a form similar to that of a circular ring of axially projecting gear teeth. Once again, the number of angularly indexed positions provided by the mechanism corresponds to the number of pockets defined by adjacent “gear teeth” in the circular array.
In each of the above mechanisms, the magnitude of the indexing angle, i.e. the angle of which separates adjacent angularly indexed positions, is determined by the physical size of the detent elements. As a consequence, to provide a smaller indexing angle (i.e. a greater number of angularly indexed positions over a given possible relative angular displacement of two bodies), the size of the detent elements must be reduced, with a corresponding increase in the complexity of manufacturing. Furthermore, in motorised indexing mechanisms, a relatively precise, and backlash-free servo mechanism must typically be provided in order to rotate one body relative to another such that the two bodies will engage in the “target” pocket.
The present invention seeks to overcome this problem by providing a pair of serially connected indexing mechanism, in which the indexing angle of the two mechanisms differs by a relatively small amount such that, in combination, the two mechanisms may act as a “vernier” indexing device.


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A. G. Davis Circle Divider and A.A. Gage Ultradex Tables (No date).

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