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Monday, June 22, 2015

Rotary Indexer for Indexing Motion

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3D CAD Rotary indexer
Rotary Indexer
Indexing is the process of intermittent motion where machine starts and stops at precise locations in specified intervals. Indexing motion is required in most machines for many applications since the stopping period (dwell period) of indexing allows other units in the machine do their jobs. If machine runs continuously without indexing, it may be much more difficult and complex for other units to follow the moving object compared with object that stops.
animated gif: indexing motion explained
Indexing Motion
The easiest way to provide the intermittent motion is to start and stop the motor. Probably, a servo motor or a stepping motor can do that with precise intervals and locations. However, when required a high degree of rigidity, a positive motion mechanism to ensure no backlash, the cam-driven indexer is most suitable for the application. The indexer is available from many manufacturers which we can choose from product catalogs according to desired load, indexing interval, indexing profile, number of stops, etc.
displacement-velocity diagram, indexing and dwell
Ideal Displacement and Velocity Diagram of a rotary indexer
The above chart shows 2 cycles of displacement and velocity of the rotary indexer. In each cycle, the rotary indexer rotates (indexing) then stops. The indexing time is the time of indexing and the dwell time is the time when the indexer has no movement (zero velocity). The following picture shows input and output shafts of the indexer.

The input shaft is normally connected to a geared drive (motor) that rotates at a constant speed. The construction inside the indexer (roller gear, cam, conjugate plate cams, etc.) makes the output shaft rotates and stops as shown in the earlier displacement diagram. However, in some applications, it may require longer dwell time for other machine units to do their jobs. For this case, the input shaft (motor) will rotate and stop and wait to extend the dwell time until other machine units have completed their processes then it rotates again. This is also called "cycle-on-demand" application.
input and output shafts of a rotary indexer
Input and output shafts of a rotary indexer
To select the right rotary indexer for your application, there are several parameters to take into account such as number of stops, indexing angle, load (inertia), torque, etc. We will explore more details about those parameters. At the end we will make an excel calculation sheet to calculate values of necessary parameters for selection the right rotary indexer from the manufacturers.

Next: [Indexing Cam Angles Comparison (1/2)]



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