Historically indexers were controlled through the use of motor contactors and 2-speed motors. The 2-speed motors were utilized because indexers needed to be recovered from an “out of position” condition at a lower speed due to the steeper angle that is cut into the cam and sheering threshold of the cam followers. As the Variable Frequency Drive (VFD) became a more cost effective solution to achieve the same recovery result, the use of the motor contactors faded from existence as a method of controlling indexers. This made it possible to used Inverter Duty single speed AC motors controlled by the VFD. This also lead to a more versatile style of indexer which utilizes a constant lead cut cam and is controlled by a “closed loop” positioning system. This system differs from the “fixed position” indexers in that the “fixed position” indexer has the motion profile cut directly into the cam. The newer “closed loop” positioning system utilizes the VFD to control the motion profile. While this is a more flexible system it is more fraught with opportunities to incorrectly control the indexer and therefore damage the cam followers and cam.
Motion Index Drives