Geometric Design and Kinematic Analysis of Roller Gear Cams

Roller gear cam is an intermittent transmission indexing device. It has no backlash error and high positioning accuracy, and suitable for high-speed indexing such as auto tool exchanger for machine tools.

       In this paper, based on the common tangents between the spatial curve of the cam surface and the circle of the roller must be perpendicular to the common normal which connects the two contact points. It is clear that the common normal must be orthogonal to the common tangents at the contact points. To keep the exact contact between the cam and the tool, the tangents of the pitch surface must be also parallel to the common tangents at the contact points between the cam surfaces and the roller follower. Based on the characteristics for the contact between the cam and the roller, we will locate the axial position of the roller by the geometric relation between the cam and the roller to derive the pitch surface and formulate the normal vector of the tool path, then, using the swept surface of the roller path to represent the cam surface.

       With the geometrical relationship between the cam and the roller follower, we can define forces on the cam and the roll to analyze each motion characteristics, such as pressure angle, radius of curvature, acting force, contact stress, horse power(HP), and efficiency.

       With the analyze of cam profile’s motion characteristic, we can clearly understand the effect of the mechanism’s performance form design rules and choice of motion curves.  In this paper, we have discussed the industrial indexing motion transmission and auto tool exchanger for machine tools as two examples,  It is more clear for the designer to understand how will the detailed design rules and different cam shapes with motion curves effect the cam mechanism’s performance.