Design and Technology - Essay Example

This is a one-event-per- turn cam with a slow build up to the peak and a rapidly decreasing edge. This cam has one deletion only, which Is counter clockwise. CLC Pear A pear shaped cam that is made from a circular disc of material, which is then elongated to create its shape. This cam will provide a steady rise and fall in the in the follower followed by a period where the follower does not move. 0 Eccentric An eccentric cam is a disc with its centre of rotation positioned ‘off centre’.

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This means as the cam rotates the flat follower rises and falls tat constant rate. As it rotates it pushes the flat follower upwards and then allows it to drop downwards. The movement is smooth and at a constant speed. Cranks An arm attached at right angles to a rotating shaft. It Is used to convert a circular motion Into a reciprocating motion. Attached to the end of the crank by a pivot Is a connecting rod. The end of the rod attached to the crank moves in a circular motion, while the other end is usually constrained to move in a linear sliding motion. Gears O Bevel

It is used when the direction of a shaft’s rotation needs to be changed. They are usually mounted on shafts that are 90 degrees apart, but can be designed to work at other angles as well. The teeth on bevel gears can be straight, spiral or hybrid. CLC Spur Spur gears are the most common type of gears. They have straight teeth, and are mounted on parallel shafts. Sometimes, many spur gears are used at once to create very large gear reductions. 0 Worm The worm gear only has one tooth but it is like a screw thread. The worm wheel, colored yellow, is like a normal gear wheel or spur gear.

The worm always drives the worm wheel round, it is never the opposite way round as the system tends to lock and Jam. Pulleys A simple machine consisting essentially of a wheel with a grooved rim in which a pulled rope or chain can run to change the direction of the pull and thereby lift a load. A Fixed fixed pulley changes the direction of the force on a rope or belt that moves along its circumference. Mechanical advantage is gained by combining a fixed pulley with a movable pulley or another fixed pulley of a different diameter. 0 Movable A movable pulley has an axle in a movable block.

A single movable pulley is supported by two parts of the same rope and has a mechanical advantage of two. 0 Combined A combination of fixed and movable pulleys form a block and tackle. A block and tackle can have several pulleys mounted on the fixed and moving axles, further increasing the mechanical advantage. Levers Levers are used to lift heavy weights with the least amount of effort. 1st Class Levers It uses a fulcrum in between, and the applied force and load are at opposite ends. The force must be applied over a long distance, in order to make the heavy load move just a small amount.

By adjusting how far the fulcrum is from the load, you can control the mechanical advantage. The closer it is to the load, the more force is applied. 0 2nd Class Levers The second class lever is one where the fulcrum is at one end, and the applied force at the other. The load that is to be moved is between them. This causes the load to move in the same direction as the force you apply. 0 3rd Class Levers The fulcrum is at one end of the lever, but this time the load is at the other end, and you apply a force in between. This is the application of force between the load and the fulcrum.