Globoidal cams for indexing gear boxes

What are Globoidal Cams?

Globoidal cams are found in indexing gear boxes. These high-precision, purely mechanical components are the heart, or you might say the “brain”, of this type of gear unit. They are capable of “storing” the cycle frequency, movement, acceleration ramp and position dwell time. Indexing gear boxes are used not only for filling, portioning and packaging, but can also carry out highly precise assembly work. You would think that nowadays reduction gear units controlled by servomotors would be the first choice. However, this is not the case, as indexing gear boxes have their own advantages. By mechanically coupling multiple of these units together, even of different types, it is possible to implement a very complex process with only one drive motor, all with perfect coordination. They largely do away with the need for expensive electronic control components that are likely to be damaged.

   A Input shaft with continuous rotary movement

B Globoidal cams, simplex or multiplex

C  Engagement cams, mostly ball bearings

D  Output shaft with indexed rotary movement

Obviously the cams must engage in the globoidal cams with no play. Since multiple cams are generally engaged at the same time, even the slightest deviation in the curves will cause the gear to jam.

The globoidal cams are initially milled with an allowance. After the hardening process, they are ready for the grinding process. Traditionally an eccentric grinding device is used for this. If the aim is to achieve good surface quality, then this old process is very slow and also inflexible. Manual reworking is generally required.


Dressing Process

A complete ground globoidal cam with a surface finish of RA 0.07

SCHNEEBERGER follows a different, flexible approach for this. It is based upon the machine data from the milling process. From this information, our grinding software QUINTO calculates both flanks of the cam separately. The two grinding paths can therefore be modified individually, e.g. in order to optimise the beginning of the curve. A dressing unit and a wheel probe are meaningful options when it comes to process optimisation.

Depending on the size of the workpieces and the diameter of the cams, several SCHNEEBERGER machine types can be equipped for this application, normaNGC, geminiNGM and corvusGDS are already in service with manufacturers of indexing gear boxes. Globoidal cams for indexing gearboxes are just one of the many things you can do with a Schneeberger grinding machine such as tool and cutter grinding, blades, etc.

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