Mechanical motion

Mechanical Motion AHL Topic 10 Mechanical Design from http://www.bisnet.or.id/vle/mod/resource/index.php?id=155

Mechanisms are devices that have been designed to make jobs easier. They all have certain things in common: They involve some kind of motion . They involve some kind of force . They must have some kind of input to make them work. They produce some kind of output. If we connect mechanisms together we can build mechanical systems called machines. Machines help to make our lives easier and more comfortable.

Linear motion ,[object Object],[object Object]

Rotary Motion ,[object Object]

Intermittent Motion ,[object Object],Intermittent motion is usually the end result of a mechanism rather than the starting point for conversion.

Oscillating Motion ,[object Object]

Reciprocating Motion ,[object Object],Jigsaws and scroll saws which are often used in school workshops have blades that cut by reciprocating motion.

Irregular Motion ,[object Object],[object Object]

Linkages ,[object Object],[object Object]

Mechanical Motion in Context ,[object Object],[object Object],[object Object],[object Object],Discuss the following products, what motions do they use?

Torque ,[object Object],[object Object],A simple example is to look at what happens when a nut is tightened by a spanner. A force F (newtons) is applied by hand at a distance r (metres) from the centre of the nut. F x r = Torque (Nm) 100 x 0.2 = 20Nm (newton metres) If the same force is applied to a longer spanner at distance r from the centre of rotation, the torque is greater.

Ratchet and Pawl ,[object Object],Ratchets consist of a gearwheel or linear rack with teeth, and a pivoting spring-loaded finger called a pawl that engages the teeth.

Cam followers As the cam turns, driven by the circular motion, the cam follower traces the surface of the cam transmitting its motion to the required mechanism. Cam follower design is important in the way the profile of the cam is followed. A fine pointed follower will more accurately trace the outline of the cam. This more accurate movement is at the expense of the strength of the cam follower.

[object Object],REMEMBER : A rack and pinion is a pair of gears which convert rotational motion into linear motion. A bell crank is a type of crank that changes motion around a 90 degree angle. Toggle clamp

Toggle clamps ,[object Object],[object Object],A toggle clamp usually consists of two links on a common pivot. The free end of one link is attached to a fixed pivot. The free end of the second lever is constrained to move in a straight line. When a force is applied to the common pivot, the lower end of the toggle clamp is pushed downwards against the item being clamped. The clamp locks in position once the common pivot is pushed slightly 'over centre', usually against a stop. Only by applying a force from the side can the clamp be unlocked. The toggle principle is used on push chairs to hold them open in use.

Parallel Motion ,[object Object],[object Object]

Treadle linkage ,[object Object]

Bell Crank ,[object Object],The photo on the right shows a bell crank linkage connecting the foot brake pedal in a car to the front and back drum brakes.

[object Object],[object Object]

Mechanical motion

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Mechanical motion