Globoidal cam indexing theory

The relative movement between the input cam and the output turret of the cam indexer is also called spatial movement, and this type of transmission is also a kind of cam mechanism. There are two ways of movement of the indexer output turret. According to the required mechanical movement, it is divided into intermittent rotation and reciprocating swing. This kind of cam mechanism can make the output turret have a larger stroke, or can realize a special movement law under the action of the input cam. At this stage, it is widely used in the automation machinery of various industries.

The profile of the indexer input cam is composed of complex spatial curved surfaces. It is a relatively complicated task to calculate the spatial coordinates of the profile according to the motion law of the output turret. In addition, from a manufacturing point of view, it is usually not necessary to perform processing according to the coordinates of the space surface. Therefore, in the conventional spatial cam design, approximate methods are often used. For example, the cylindrical surface of the cylindrical cam is expanded into a rectangular plane. The conical surface of the conical cam is expanded into a fan-shaped plane, etc., and then the contour curve coordinates of the expanded contour are calculated according to the contour curve design method of the planar cam.

For the arc cam mechanism with indexing transmission between two vertical staggered shafts, in the case of intermittent motion, the input cam of the indexer is a circular arc slewing body with a ridge-like contour. Needle roller bearings evenly distributed along the peripheral direction. When the cam rotates, the contour of the indexing section pushes the roller needle, and then drives the indexing index of the turntable; when the cam turns to the range of the angle of repose, the two rollers on the turntable span the torus of the cam On the ridge, the turntable stops rotating to realize the self-locking function of the indexer.

It can be seen from the motion state of the indexer that the positioning curve is located in the center of the cam, which is suitable for high-speed, light-loaded, and fewer rollers; when the positioning curve is located at the two ends of the cam, it is suitable for more rollers. Medium, low speed and medium and heavy load occasions. The cambered indexing cam of the indexer is similar to the cambered worm with variable helix angle, and its turntable is equivalent to a turbine with roller teeth. Therefore, the cambered cam of the indexer is divided into single-lead, multi-lead, left-handed and right-handed. The relationship between the cam and the direction of rotation of the turret is similar to that of a worm gear.