Function of Cams, Belts and Drives

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  • Topic: Roller chain, Belt, Timing belt
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  • Published : May 21, 2012
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The cam can is a component that creates a movement and a drive from circular to reciprocating or sometimes oscillating motion. An example is the camshaft of a car, which takes the rotary motion of the engine and converts it into the reciprocating motion it requires to function the intake and exhaust valves of the cylinders. Cams can also be seen as information storing and transmitting components, this can be viewed within the cam drums that operate movements of a screw machine's various tools and chucks.

Probably the most commonly used cam is the plate cam also known as a disc radial or edge cam, these are cut out of a strip of flat metal or plate. In this application the follower’s motion is in a plane horizontal to the axis of rotation of the camshaft. It should be recognised that this cam, where the follower is in contact with the edge of the cam disc, is only capable of producing motion to its follower in one direction only, this is when the cam the is driving the follower in a rising motion. During the falling motion of the cam operation the follower should always be in direct contact with the cam by the size and weight of the follower and the mechanism or more commonly by a spring. Which of these methods you would use would depend on the application they were required for.

The Cylindrical Cam (also known as a barrel cam) has a profile that rotates and moves its follower in a back and forth motion vertically. When the follower hits maximum height the cylinder cam then rotates in the reverse direction and the follower will come back down. These cams are considered unusual normally consisting of a cylinder which has a groove cut out of one side this is for the follower to locate into and allows it to move up and down. This type of cam can be found in certain clocks and also sewing machines use them a lot for the guidance of the motion of the needle and thread. Cylindrical cams are perfect for machines that are required to perform repetitive movements. The cam is constructed of a rotating cylinder with a groove in the curvature of its surface. The follower that locates into the groove is usually required to be tapered.

A roller follower is a follower that eliminates the problem of wear which in some instances can be very fast when there is a sliding motion in this application this is replaced by a roller action. Nevertheless some sliding will still occur this is down mainly to the speed of the cams operation. The follower center position point of contact changes depending on whether it is in a rise or fall motion, this has to taken into consideration when constructing the cam profile.

On a flat foot follower only one side thrust is present this can be advantageous due to the friction between the follower and the cam. As opposed the knife edge follower the problem of wear is not as great which means maintenance is reduced, the reason for this is that the point of contact of contact between the cam and follower moves across the follower depending on the profile of the cam. Another way to further reduce friction would be to allow the follower to axially rotate with the axis of the follower to be placed to one side of the cam. This would mean contact with the cam would cause the follower to rotate. All cam profiles using this type of follower have to be convex this is for the prevention of the corners of the follower from digging into the cam.

A mechanical linkage is an assembly of components linked to one another to utilise movement and forces relevant to it. The connections between links should provide smooth movement pure rotation or sliding for example they can also be called joints. If a linkage combines a network of rigid links and ideal joints it is known as a kinematic chain. It is possible for linkages to be made up of other components such as open and closed chains or a combination of both each link of the chain would be connected to the next by a joint. The movement of an ideal joint is governed...
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