Cam mechanisms are one of the most popular devices for generating intermittent motion and are widely used in many areas. The advantages of the cam mechanisms are its simplicity and its great versatility in synthesizing motion patterns. In the cam manufacturing, design of the cam mechanism and machining of the designed cam profile are very difficult and need a lot of times.
This work is composed of three sections that are design of the cam mechanism, machining of the precision cams and a CAD/CAM software for cam manufacturing.
In the design section, a study on the application of a cubic spline to the basic curve of cam motion is presented. Using the cubic spline, a piecewise function is produced that is continuous in displacement, velocity, and acceleration. The purpose of this study is to derive a cam curve with the optimum dynamic characteristics among all possible curves. The optimum cam curve is obtained by changing the weights of the objective function to fit the given condition. For the proposed objective function, the result shows improvements in all dynamic characteristics of the velocity, acceleration, and jerk compared with the modified sine curve.
In the machining section, this work is concerned with the algorithm of generating a new circular arc interpolation. A new circular interpolation method called a triarc, in which a segment span is composed of three circular arcs, is suggested. Triarc curve fitting has the advantage of generating arc splines easily. In the triarc method, the first arc is generated from the starting knot point to the position where the maximum error is equal to a given allowable tolerance, and the other arcs are generated from this position to the terminal knot point of each span. This paper explains a circular interpolation using a new biarc curve fitting, which is a special case of the triarc method. In the new biarc fitting, an additional condition which guarantees a smooth curve fit is that the second arc radius r2 is the same as the first arc radius r1. Therefore, this technique makes two arcs from a segment span for the triarc curve fitting. In generating the machining data for various cam curves in CNC machining using the biarc method and the new biarc method, the latter accomplished fast NC-code generation, short NC-code block formation and machined the same cam profile efficiently.
In the CAD/CAM software section, composite curve is automatically generated without discontinuities in velocity and acceleration by classification for the elementary curves. In the design and machining of the precision cams, it needs about 1 month with an expert but this software can it only 1 day without an expert.