With any rotating or indexing application whether it be mechanical or servo driven the drive torque required is a function of two quantities – angular acceleration, α, and moment of inertia, I. For many indexing applications it is desirable to minimize index time so that throughput can be maximized. Keeping index time as short as practical requires that angular acceleration be as large as possible. Since Torque = Iα, large accelerations require large torques and large torques require large drives which are more costly and can occupy considerably more space. If torque is to be conserved while maintaining a short index time, the designer has but one choice. – Minimize the load’s moment of inertia (I from the equation above).
Figure 1 illustrates the difference in inertia between steel and aluminum dial plates of equal size.
To optimize your indexer or rotary application for cost and performance consider the following:
- Use lightweight materials such as aluminum, delrin or other engineered plastics on all rotating components whenever possible.
Remember, a steel dial of equal size to an aluminum dial requires 3 times the drive capacity.
- Keep dial diameters as small as practical.
- Mount fixtures on the dial as close to the center as possible.
- When dials become large or thick, consider fabrications, to conserve weight and inertia.
- Take in to account the allowable deflection your application requires and adjust the dial thickness accordingly.
- Consider lightening holes (cut-outs) when feasible.
- Make index times as long as practical for your process.Remember, doubling the index time reduces the drive requirements by a factor of four