In the selection of cam indexers, the inertia ratio is an important parameter, which is used to evaluate the relationship between the load inertia and the inertia of the cam indexer output shaft. The calculation method of the inertia ratio is as follows:
1. Calculate the load inertia
Simple shape objects: For some simple shape objects, such as cylinders, spheres, cuboids, etc., the inertia can be calculated based on their geometric dimensions and mass. For example, a cylinder with a mass of m and a radius of r has a moment of inertia J=21mr2 around its central axis.
Complex shape objects: For complex shape objects, you can decompose them into a combination of multiple simple shapes, calculate the inertia of each part separately, and then calculate the total inertia based on the parallel axis theorem and the superposition principle. If the object is composed of multiple parts, you also need to consider the connection method and relative motion relationship between the parts. In practical applications, the inertia of complex objects can also be determined by experimental measurement.
2. Determine the inertia of the cam indexer output shaft
The inertia of the cam indexer output shaft is usually provided by the manufacturer in the product specification. If there is no ready-made data, it can be estimated by theoretical calculation or empirical formula based on the structure and size of the indexer. Generally speaking, the output shaft inertia is related to factors such as the diameter, length, and material density of the shaft.
3. Calculate the inertia ratio
The inertia ratio K is equal to the ratio of the load inertia JL to the cam indexer output shaft inertia J0, that is, K=J0JL.
When selecting, it is generally recommended to control the inertia ratio within a certain range, usually not exceeding 5-10. A large inertia ratio may cause the cam indexer to generate a large impact force during start-up, stop and movement, affecting the segmentation accuracy and service life; a small inertia ratio may mean that the selected indexer is too large, resulting in cost waste.