Have you used any indexers on your automation projects?

I wrote a blog last November on Indexing Rotary Actuators (Rotary Indexing Actuators) and recently I had some engineers contact me about expanding on the use of indexers for automation. Their questions were based around the types available and why use one over another. I hope to answer those questions here for you in this blog.

An indexer is typically a rotary device that rotates to predetermined points on a circle. They are most widely used for rotary indexing automation. Indexers can be built for virtually any indexing angle or number of stops. The most popular are 30 (12 stop), 45 (8 stops), 90 (4 stop) and 180 degree (2 stop), but they can be designed for any angle from 12 to 360 degrees for a fixed cam type indexer and unlimited for a servo type of indexer.

For the fixed cam type of indexer there are ones driven electrically and pneumatically.

The pneumatic driven ones are not only the easiest to specify, but also are the least expensive. If you remember or reviewed the link above to the blog I posted last year on pneumatic indexing actuators, you know that these devices step a fixed increment with a 4-way pneumatic valve. These are great if you only need to turn an indexing table the same direction and you are willing to build your own bearing table to support the stations or nests that you are automating. If not, the company Allen Air builds the complete table including a dial for which you can a fix your tooling. See picture below of one without the top dial plate.

A device like this can be loaded with up to 1000 lbs. (dial plus tooling) and standard index stations from 4 to 24 with an accuracy of +/- .001 inches and a repeatability in the low tenths at each station. They have options for up to 100 stations. For a novice, this is a good indexer to start with.

Some of the reasons that machine builders use this type of indexer are:

  • Low cost
  • Repeatable and accurate positioning
  • Small loads and small parts
  • Simple to operate

The next indexer I would like to discuss is the electrically driven cam indexer of which there are several suppliers. These type of indexers get a little more complicated because they need to be sized for the application as the momentum of the dial plate and the tooling play a large roll into sizing the cams, electric motor and gear box to drive the indexer. With the cam-driven type of indexer you will need to already have designed the dial table and tooling so the unit can be sized. You will also need to have the speed and timing profiles completed so the cams can be designed to handle the load and momentum generated. These type of indexer are more expensive, but they can handle a lot more speed and weight with more accuracy and repeatability. Indexers of this caliber will have an accuracy of 25-50 arc seconds and a repeatability of 5-10 arc seconds with weight capability of up to 100,000 lbs. An option that many of these indexers have is a center thru hole which can be necessary depending on the set up of the automation stations. They come in lots of sizes and configurations to meet the application needs.  You most definitely will need to get a representative from the distributor or manufacturer involved to size this type of indexer. Shown below is a large cam indexer from Destaco’s Camco division.

A device like this can be loaded with up to 1000 lbs. (dial plus tooling) and standard index stations from 4 to 24 with an accuracy of +/- .001 inches and a repeatability in the low tenths at each station. They have options for up to 100 stations. For someone beginning to try indexing this is a good indexer to start with.

Some of the reasons that machine builders use this type of indexer are:

  • Low cost
  • Repeatable and accurate positioning
  • Small loads and small parts
  • Simple to operate

The next indexer I would like to discuss is the electrically driven cam indexer of which there are several suppliers. These type of indexers get a little more complicated because they need to be sized for the application as the momentum of the dial plate and the tooling play a large roll into sizing the cams and electric motor and gear box to drive the indexer. With the cam driven type of indexer you will need to already have designed the dial table and tooling so the unit can be sized. You will also need to have the speed and timing profiles completed so the cams can be designed to handle the load and momentum generated. These type of indexer are more expensive, but they can handle a lot more speed and weight with more accuracy and repeatability. Indexers of this caliber will have an accuracy of 25-50 arc seconds and a repeatability of 5-10 arc seconds with weight capability of up to 100,000 lbs. An option that many of these indexers have is a center thru hole which can be necessary depending on the set up of the automation stations. They come in lots of sizes and configurations to meet the application needs.  You most definitely will need to get a representative from the distributor or manufacturer involved to size this type of indexer. Shown below is a large cam indexer from Destaco’s Camco division.

Some of the reasons that machine builders use this type of indexer are:

  • Controlled acceleration and deceleration
  • Repeatability and accurate positioning
  • High load and high speed to size capability
  • Smooth motion profiles
  • Low maintenance and long life

The last type of indexer I will discuss is a servo drive indexer. These are not as robust as the cam driven indexers, but if you cannot specify the number or location of the station on the dial plate, the servo indexer gives you the ability to stop at any position and accelerate and decelerate with any motion profile that you program. Sometimes this give you more flexibility for the future. If you explore a direct drive type of servo indexer you will find that typically they are for loads up to about 5000 lbs. Accuracy and repeatability are in the same range as the cam style indexers. With these style indexers there is no external motor or gear box. See picture of the Camco DX series below. This indexer features a large center thru hole which is great when you need to pass tooling thru the middle of your indexer.

Popular models of rotary indexers, or stages as they are often referred to, on the market by Parker include the RM Series (shown above), which has large load capacities up to 2220 lbs. with a repeatability of 30 arc seconds, the RT Series with capacity of up to 200 lbs. and a repeatability of 12 arc seconds or the miniature MPR series stage with a capacity of 26.5 lbs. and a repeatability of 11 arc seconds. The other advantage you get with Parker is that they will pair a drive and cables to the indexer, so you get a complete package without the risk of finding a drive that will work with the actuator.

Although I did just explain and show above a direct drive servo indexer you should be aware that there are cam types of servo indexers. These are becoming more popular because of the need to adjust the motion profiles with the servo controller. They look and are sized similar to the cam type of indexers that have an electric motor and a gear box.

To wrap this up I thought I would also make you aware of a few other styles of indexer that are not used frequently and are used for specific high-end heavy-duty automation applications. These other types are the ring style on the left below and horizontal or vertical link conveyors on the right below.

Some of the reasons that machine builders use this type of indexer are:

  • Larger size of parts or larger number of stations
  • Repeatable and accurate positioning
  • High load capability
  • Low Maintenance and long life

I hope that this Indexing 101 blog was valuable to you and you might be more inclined to use an indexer the next time you need simple rotary movements. If you need more info or have questions, please contact me and we can discuss your application.