Cams are rotating machine elements that transmit reciprocating (linear) or oscillating movements to other elements known as followers. Cams, depending on their design have either a point of contact or a line interface between them and the followers. This contact is maintained either by gravity, that is the weight of the follower as it rests on the moving cam or by a spring. Generally, cams drive followers, that is the power needed for the mechanism comes from the cams and the follower only responds to the movement of the cams but sometimes the relationship is reversed and the cams are driven by the followers although technically speaking the followers are called followers because they are inherently being driven by something else.
Cams can be classified based on the shape of the cams or the followers or the path that the follower traverses during the operation of the mechanism. Below are some animations of some cam mechanisms to illustrate how they generally work.
Figure 1. Cam and follower configuration I.
Figure 2. Cam and follower configuration II.
Figure 3. Cam and follower configuration III.
The input is from the rotating cam and the output is described by the movement of the reciprocating followers. Note how the different shapes of cams produce different motions in the follower even though all the mechanism configurations have the cam rotating at the same speed.
Springs are mechanisms that have elastic properties which enable them to restrict movements along a certain direction or axis. Consequently, they aid motions in the opposite direction. Springs can also store and release energy in a certain direction or axis. The elastic properties of springs allows them to deform either as a result of compression or extension and return to their original dimensions provided a limit called the elastic limit is not exceeded after which the deformation becomes permanent and failure may occur. Springs can be classified based on a number of criteria such as geometry, how load applied to them or the type of force the spring exerts when it releases stored energy. Below are animations showing how an extension/compression spring and a spiral spring work.
Figure 4. Extension/compression spring under load.
Figure 5. Spiral spring tightening and uncoiling.
Extension springs are designed to resist a tensional load. They stretch when load is applied to them. They are made such that, at their initial state, the coils of the spring are tightly wound together and are in contact without any space between them. Compression springs are basically the exact opposites of extension springs. They resist compressive forces and compress upon being loaded. Some springs however, serve both purposes of compression and extension while they are in use.
Torsion springs are like extension or compression springs but differ in one major element. The applied load is not linear. The load applied is in the form of a twisting motion and therefore the spring is designed to resist rotation or to aid it in a certain direction.
Constant force springs or spiral springs deliver an almost constant force as they unwind from a coiled position. The spring is like a ribbon, made of sheet metal that has been wound around a drum. They are typically designed for purposes where the potential energy stored in the spring is desired to be utilized slowly over a period of time.
We shall see how other mechanisms work in part two of this series.
For more information on mechanisms, check out our mechanism page.
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