Indexing cam angles comparison (1/2)

In post [Rotary Indexer For Indexing Motion], we explained the meaning of indexing with the example of displacement and velocity diagram to give an idea how the indexing mechanism works. We also showed the location of input and output shafts of the rotary indexer. In this post, we're going to see how both shafts work and the meaning of indexing angle.

Geared motor and Turret plate connected to the rotary indexer

Basic equipment setup of indexing system is as shown in the picture. The input shaft of the rotary indexer is connected to the geared motor or other drive components e.g. pulley, gear, etc. In this example, we use a "hollow shaft" geared motor which allows indexer's input shaft to insert directly into the hollow gear shaft without using any shaft couplings. But they must be carefully align in order to avoid misalignment between shafts.

At the output side of the rotary indexer, the output shaft or flange can be mounted to a turret plate. There will be tools mounted on the turret plate at the same P.C.D. (pitch circle diameter). The tool at each station is usually work-piece holder. When the turret plate indexes, it will transfer the work-piece from one station to another station in order to complete all required processes at different stations.

Indexing motion from the rotary indexer doesn't require stopping of the motor since it has internal construction with cam and rollers that generate indexing motion at the output shaft while the input shaft runs continuously. As a machine designer, to select the right indexer for the application, the first thing to do is to select number of stations. Usually we will provide additional spared positions for future improvement i.e. if required number of stations is 6, we may select 8 stations instead.

Number of stations is usually "number of stops (S)" on the indexer. In the following picture, the indexer has number of stops = 4. In each turn of the input shaft (or geared motor's shaft), the output shaft (turret plate) moves 1/4 turn. Therefore, the displacement of the turret plate (h_m) in degree can be calculated using:

h_m = 360/S

where:
h_m = displacement of the turret plate (deg.)
S = number of stops

Number of stops (S), indexing angle (b_m) and displacement (h_m)

Hence, the displacement of the turret (h_m) is 360/4 = 90 deg. The displacement is also an important factor of the acceleration which we we explore more in later posts.

The indexing angle (b_m) is the total angle at the input shaft to rotate the output shaft (turret) to another station. If the rotary indexer has S=4 and b_m = 120 deg., it means that when the input shaft turns 120 deg., the turret will completely turn from one station to another with the displacement of 90 deg.

See how different indexing angles move in the next post.