With cam gears, you can implement practically any movement required in the scope of process control with a minimum number of gear elements.
The basis for systematic design procedures is offered using standardized laws of movement in the development of new cam gears.
AutoCAD Mechanical creates cams (cam plates and cylindrical cams) based on sections drawn in a movement diagram. AutoCAD creates the movement sections using fifth degree polynomials, the law of movement which offers the widest range of applications. Because calculation of the movement sections is only possible if the border conditions of the adjacent movement sections are known, it is necessary to define these border conditions. Calculation of velocity and acceleration for an existing section of the movement diagram is also possible. The cam curve path can be determined through the calculated cam sections. Also an existing curve path can be scanned and transferred in the movement diagram.
The laws of movement and their fundamentals are derived from a standard like the VDI 2143 standard. The movement sections are defined by the movement (dwell time, constant velocity, reverse and movement). The trick of cam design is to join these movement sections into something smooth and free of impulses:
This explains why velocity and acceleration are necessary, in addition to the curve path. These curves enable you to check whether your curve path is smooth and free of impulses.
There are various laws of movement such as the mathematical formulas for the profile of the movement sections. A guideline like the VDI guideline examines and compares various laws of movement such as parabola, simple sinusoidal wave form, modified sinusoidal wave form, fifth degree polynomial, and others. A table like the table 3 of VDI 2143 page 2, shows the results and recommendations. The fifth degree polynomial is the law of movement that offers the widest range of applications. (It ranked first in 10 of 16 cases and was not inappropriate in any case.) Therefore we used this law of movement.
The calculation of the movement sections is possible only when the conditions of the adjacent movement sections are known. So you must define these conditions.
The velocity f' represents the change in the curve path gradient. f' must not include any step changes. This means we have to accept the border conditions of the adjacent f' curves. This is either possible by nominal default or by specification from drawing using the adjacent f' values. A Æ crossing means that the direction of movement is reversed. If f'="0" and horizontal, the roller on the cam is at standstill. The f' curve represents the driving torque required.
The acceleration f" should not have any step changes either. Its design is subject to the same principles as explained previously. The f" curve represents the inertial forces.
Both curves should be as flat as possible to expose the gears only to moderate stress. You can use border conditions and data points to influence the curve profile.