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Chapter 7

Chapter 7. Designing Mechanical Systems. Six Simple Machines. Pulley Wheel and Axle Inclined Plane Wedge Screw Lever. Machines and Tools. Machines and tools are mechanical devices that work by transmitting or converting energy. Machines are made up of a variety of mechanisms.

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Chapter 7

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  1. Chapter 7 Designing Mechanical Systems

  2. Six Simple Machines • Pulley • Wheel and Axle • Inclined Plane • Wedge • Screw • Lever

  3. Machines and Tools • Machines and tools are mechanical devices that work by transmitting or converting energy. • Machines are made up of a variety of mechanisms. • What are some examples of machines.

  4. Mechanisms • Help extend human capability by creating some desired output or motion. • Takes an input motion or force and creates a desired output or force. • Lever • Crank • Wheel • Gear • Cam • Screw

  5. Kinematics • The study of motion without regard to the forces or mass of the things moving. • Kinematic diagrams are scaled drawings symbolizing how mechanisms work. • Page 143 (fig. 7-7)

  6. Motion • Common types of motion: • Linear • Reciprocal • Rotary • Oscillating

  7. Levers and Linkages • Fulcrum • Load • Effort • Classes (p. 146) • First • Second • Third

  8. Mechanical Advantage • The ratio between the load and effort. • Deals only with forces. • Mechanical Advantage > 1 means that the output force will be greater than the input force. (But the input distance will need to be greater than the output distance.)

  9. Velocity Ratio • Deals with the distance gained or lost due to a mechanical advantage. • Velocity Ration >1 means that the input distance (or effort) to move a load will be greater than the output distance of the load.

  10. Linkages • Linkages transmit the motion or force to the desired output location. • Linkages: • change the direction of the force • Change the length of motion of the force • Split the motion and force over multiple paths

  11. Linkages (cont.) • Parallel Linkages • Treadle Linkages • Toggle Linkages

  12. Rotary Mechanisms • Gears, Pulleys, Cams, Ratchets, Wheels, etc. • These transfer of change input rotational motion and force to output motion and force. • Output force can be either rotational or reciprocating.

  13. Gears • Toothed wheels fixed to an axle. • Drive gear – connected to the input axle. • Driven gear – connected to the output axle. • Gear train – when an number of gears are connected together. Number of driven teeth (output) Gear Ratio = Number of driver teeth (input)

  14. Gear Types • Spur • Helical • Worm • Bevel • Rack and Pinion

  15. Belts/Pulleys & Chains/Sprockets • Use belts and chains to convert motion and force. • Uses same measures of Mechanical advantage and Velocity Ratio as gears.

  16. Cams • Eccentric cams – circular disk with the axle placed off center. • Pear shaped devices that convert rotary motion into reciprocating motion. • Cams use followers to conform to their shape and cause motion.

  17. Others • Cranks and sliders • Ratcheting mechanisms • Clutches • Brakes

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