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Mechanisms

Mechanisms. Dean Hackett March 2012. Types of motion. Linear Rotary Reciprocating Oscillating. Simple (Basic) Machines. Two ‘families’ Inclined plane lever. Simple Machines. Inclined plane Wedge Screw Lever Wheel and axle Pulley. Work = Force x distance. Classes of Lever.

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Mechanisms

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  1. Mechanisms Dean Hackett March 2012

  2. Types of motion • Linear • Rotary • Reciprocating • Oscillating

  3. Simple (Basic) Machines • Two ‘families’ • Inclined plane • lever

  4. Simple Machines • Inclined plane • Wedge • Screw • Lever • Wheel and axle • Pulley

  5. Work = Force x distance

  6. Classes of Lever • Class 1 • Class 2 • Class 3

  7. Types of Linkage • Parallel • Reverse motion • Bell crank • Treadle • Crank slider

  8. Have a think...

  9. Load xN Effort 10N 4 m 1 m Load yN Effort 10N Fulcrum 1 m 4 m Fulcrum Lever Mechanisms

  10. Mechanical Advantage Load • Mechanical Advantage = Effort Load 40N Effort 10N 4 m 1 m

  11. Velocity Ratio Distance moved by Effort • Velocity Ratio = Distance moved by Load Load 40N Effort 10N 4 m 1 m 200mm 50mm

  12. Efficiency M.A. • x 100% V.R. Efficiency = Load 40N Effort 10N 4 m 1 m 200mm 50mm

  13. Lever Mechanism What load can this person lift?

  14. Rotary Motion A Pulley Mechanism uses rotary motion to transmit rotary motion between two parallel shafts.

  15. Discuss... • How do you attach a pulley to a shaft?

  16. Mechanisms using Rotary Motion

  17. Pulley mechanisms can be used to increase or decrease rotary velocity

  18. Velocity Ratio Distance moved by Effort • Velocity Ratio = Distance moved by Load Velocity Ratio = Distance moved by the driver pulley Distance moved by the driven pulley Diameter of Driven Pulley • Velocity Ratio = Diameter of Driver Pulley

  19. Velocity Ratio Pulley Shaft Rotary Velocities can be calculated using the following formula rotary velocity of driven pulley x diameter of driven pulley = rotary velocity of driver pulley x diameter of driver pulley • rotary velocity of driven = diameter of driver pulley rotary velocity of driver x diameter of driven pulley

  20. What is the rotary velocity of the driven pulley shaft? • rotary velocity of driven = diameter of driver pulley rotary velocity of driver x diameter of driven pulley 30 = revs/min 450 x 90 = 150 revs/min

  21. Pulleys and Belts Vee pulley and section through a vee pulley and belt A section through a grooved pulley and round belt Stepped cone pulleys provide a range of shaft speeds

  22. Flat belts and pulleys A section through a flat pulley and belt Jockey pulley in use Flat belt in use on a threshing machine

  23. Chains and sprockets Bicycle chain and sprockets Graphical symbols

  24. Velocity Ratio = number of teeth on the driven sprocket number of teeth on the driver sprocket 12 • = 36 • = 1 : 3

  25. Example

  26. Pulleys and Lifting Devices The pulley is a form of Class 1 lever

  27. Movable single pulley

  28. Pulleys Distance moved by Effort • Velocity Ratio = Distance moved by Load • Velocity Ratio = the number of rope sections that support the load

  29. Two Pulley System Distance moved by Effort • Velocity Ratio = Distance moved by Load 2x • Velocity Ratio = x Velocity Ratio = 2:1

  30. Four Pulley System Distance moved by Effort • Velocity Ratio = Distance moved by Load 4x • Velocity Ratio = x Velocity Ratio = 4:1

  31. Cams

  32. Cams

  33. Uses Pear shaped cams are used in valve control mechanisms

  34. Cams used in a four cylinder engine http://www.youtube.com/watch?v=OXd1PlGur8M&feature=related

  35. Cam motions

  36. Types of cam follower

  37. Types of cam follower

  38. Springs are used to keep the follower in contact with the cam

  39. Cam Profiles

  40. Displacement graph for a pear shaped cam

  41. Displacement Graphs

  42. Bearings

  43. Thrust Bearings

  44. Bearings

  45. Bearings • Bronze • Nylon • PTFE • Air • White metal • Cast Iron • Sintered

  46. Gears

  47. Gears Gears are not only used to transmit motion. They are also used to transmit force.

  48. Gears Number of teeth on the driven gear • Mechanical Advantage = Number of teeth on the driver gear Number of teeth on the driven gear • Velocity Ratio = Gear Ratio = Number of teeth on the driver gear

  49. Gears

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