How does a esentric cam mechanism work?

Answer 1

There are many derivations of the eccentric cam, but the basic principle is consistent. The cam itself may be round, elliptical, semi-conical, or irregularly shaped to increase or reduce workload at different points of its rotation. The one constant of an eccentric cam is that the pivot point is NOT located the geometric center of the cam. Sometimes the cam is used in conjunction with a "cam follower". Probably the best known example of this is the cam shaft of an automobile. The "lobes", or high spots on the cam, lift rods (the cam followers) that open the valves of the engine. Another use of an eccentric cam is in a pulley type system. In this system the cam acts like power-torque converter. In other words, it changes the power required to rotate the cam. The math for explaining how this works is fairly complex and is best explained using calculus, so for brevity I will explain with an example. Gently roll a boiled egg end over end on a smooth surface. You will notice that it speeds up and slows down as it goes through the rotations. As the egg rolls to the tip it slows down. As the egg continues to roll past the tip, it speeds up. Then it slows down again and then speeds up. This is how an eccentric pulley works as well. As the "lobe" or thick side of the pulley rotates to the center stress point of the cable, the work required is greater. Once the center of the lobe passes the center of the stress point of the cable the work becomes easier. One of the best known applications of this system is a compound Archery bow. Drawing the bow is hard because the lobe must be pulled between the stress point of the string and the pivot point. Once the bow is drawn, the lobe has passed the stress point of the string. Holding the bow drawn is easy because upon release the string needs to pull the lobe back between the stress point and the pivot point. I hope this helps.