Common Myths of Servo vs. Mechanical Indexers

Servo Indexers are more expensive than mechanical indexers.

Actually up until recently Servo Indexers (SI) were more expensive than mechanical indexers. However with advances in servo technology, cost has declined to the point where SI can actually be lower in cost than mechanical indexers. This is especially true in larger size units. In many large diameter applications mechanical indexers are removed from consideration because project cost won’t tolerate the expense. This is an ideal situation to consider SI. In general, as diameter increases the cost savings of using SI increases. With smaller size indexers the cost advantage is less dramatic and at first glance SI may appear to be more expensive. But when you consider the whole package, SI are a very cost effective solution. With SI there is no need for a home switch or an at-station sensor and no need for a mechanical overload device. These features come standard with SI. Some SI come fully assembled, wired and tested and therefore there are no assembly and wiring costs. And finally, what cost do you add for the home-adjust feature of an SI or the ability to add stations.

Programming servo indexers is complicated and typically requires some programming experience.

SI can be pendant controlled to such a degree that no programming is required. All changes are made in plain English with a few simple key strokes of the the hand held pendant.

Servo indexers are more difficult to integrate into new and existing applications.

Properly designed SI require a simple “Go” signal to start an index and return a simple “Done” signal when the index is complete. These signals are typically communicated with the end users controller (PC or PLC). Although palm buttons or foot switches are also common.

Wiring and start-up of servo indexers can be tricky and time consuming.

Most SI come already wired and startup is as simple as connecting power and entering a series of keystrokes on the hand held pendant.

Servo indexers don’t perform as well as mechanical indexers.

Properly designed and applied SI have higher accuracy and repeatability than mechanical indexers. And because they incorporate position feedback they can compensate for wear over time. This result can be significant in applications where positional accuracy must be maintained throughout the life of the project.

If I know how many stations I need there is no reason to choose a servo indexer.

Even when the number of stations in a process is fixed there are advantages to using SI.

  • SI have an integral home switch – no need to purchase or install
  • SI have an integral at station switch – no need to purchase or install
  • SI come wired, assembled and tested
  • SI have electronic torque control. A mechanical overload device may be unnecessary
  • The home position can be adjusted very precisely – electronically, simplifying start up and debug
  • Communication between the SI and PLC is simple
  • Accuracy and repeatability is better