Invest in ring drive indexers for superior results

The advent of new indexer geometries allows special-purpose machine builders to design rotary assembly machines with a radically new approach. While based on the time-proven design of preloaded right-angle cam and cam follower systems, new generation ring drive indexers offer wide open through holes to accommodate auxiliary equipment inside the indexer.

The photograph effectively illustrates the advantages of ring drive indexers. In this application, up to six independent pad printing heads are mounted in the center of the machine, keeping the outer periphery free for operator access and maintenance. Earlier versions of this machine placed printing heads on the outside of the indexer, taking up more floor space and limiting accessibility to the tooling and printed products.

Another benefit of the ring drive indexer concept is the ability to offer a large number of stations. The ring drive can be specified for up to 60 stations, providing opportunities to assemble complex parts on one machine, eliminating part transfer to downstream rotary dials. Ring drive indexers are a viable alternative to more expensive precision link conveyors, providing a large number of work stations while eliminating the complexity and cost of precision machined links and idle work stations. In the case of a 40- or 60-station ring drive, the inherent accuracy of the geometry is also an important benefit. Since the cam driving the tooled ring is approximately the same radius as the work station, accuracies can be in the realm of +/- .001” vs. three to five times that value on a precision link conveyor. This is a great benefit in the pad printing application, allowing for accurate registration of colors and superior print quality.

For more information about ring drives, visit http://www.camcoindex.com/ring_drive.htm.

Needle bearing cam followers vs. solid cam followers

Why is the IMC Needle Bearing Cam Follower better than a solid cam follower?

Backlash

One of the contributors to the inaccuracy of an indexer is backlash in the cam followers, specifically follower location and follower looseness, size tolerance and concentricity. Preloading the cam followers against the cam improves indexer accuracy by removing cam follower backlash.

A solid cam follower cannot be preloaded to remove backlash in the output. If it were possible to make the perfect solid cam follower and locate it perfectly, it would still have backlash. There must be a small gap (.0003 - .0005 of an inch) to allow oil to flow between the stud and the outer race. The IMC Needle Bearing Cam Follower has spaces between the needles or rollers, which allows the passage of oil without excessive backlash.

Under load, the solid cam follower has more internal friction compared to needle bearing followers due to the very large angle of wrap between the inner and outer race. This friction produces heat and reduces the mechanical efficiency, limiting the maximum operating speed.