Know-how for Index drives and rotary index tables
Index drives and rotary index tables generate stepping motions of the output shaft through an evenly formed rotary motion of the drive. How does it function?
The motion sequence in general:
the input shaft →
rotates continuously, advancing one cycle for each revolution. The system runs through the index-angle (Schaltwinkel) and dwell-angle (Rastwinkel) ranges as it does so.
← the output element (shaft, rotary plate)
advances one step whenever the system runs through the index angle (Schaltwinkel) and stops whenever the system runs through the dwell angle(Rastwinkel).
Die Größe des Schrittes wird durch die Stationenzahl bestimmt.
The movement of the output is determined by a law of motion. This is a mathematical function which stipulates the respective position of the output for every position of the drive. In case of the specification of a drive rotary speed, the speed and acceleration of the output is also determined.
The laws of motion of our stepping gear and rotary indexing tables are selected in such a way that an extremely harmonic thrust and jolt-free motion is realized.
The number of stations n establishes how often the output element pauses during a complete revolution, thus determining the size of each step Ψ.
Size of the step Ψ = 360° / Number of stations n
Depending on the construction type of the gear, we supply gears with the following number of stations on a standard basis:
1, 2, 3, 4, 5, 6, 8, 10, 12, 16, 18, 20, 24, 32
Special number of stations can often be made but not always reasonable to realize for technical reasons (e.g.: 29). In such cases, it is always a good idea to consider a step-down unit which is secondary to the index drive.
The impact of the input speed and of the index/dwell angle:
If the gear is driven at constant rotary speed, every revolution of the drive lasts for a specific period which is described as cycle time. The amount of time required to pass through the index angle, is referred to as index time. Analogous to this, the amount of time for passing through thedwell angle is referred to as dwell time.
The rotary speed of the drive is determinant to the attainment of a specific cycle time. A modification of the cycle time affects the index time and dwell time in the same proportion at all times.
To attain a specific index or dwell time at a given rotary speed of drive, the relation of the index to the dwell time must be changed.
The structural set-up:
The drive of the gear forms a cam with a specially formed profile. There are different cam types depending on the construction type of the gear.
The output is formed as a roller star or rotary-table fitted with cam rollers.
The cam rollers are attached to the profile of the cam. If the cam is turned, the rollers follow the profile and generate the motion of the output.
The profile of the cam is formed in such a way that this motion of the output corresponds precisely with the specification of the motion law (see above).
