Transcript 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. • What are some examples of machines. 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 •Gear •Crank •Cam •Wheel •Screw 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) Motion • Common types of motion: – – – – Linear Reciprocal Rotary Oscillating Levers and Linkages • • • • Fulcrum Load Effort Classes (p. 146) – First – Second – Third 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.) 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. 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 Linkages (cont.) • Parallel Linkages • Treadle Linkages • Toggle Linkages 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. 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. Gear Ratio = Number of driven teeth (output) Number of driver teeth (input) Gear Types • • • • • Spur Helical Worm Bevel Rack and Pinion Belts/Pulleys & Chains/Sprockets • Use belts and chains to convert motion and force. • Uses same measures of Mechanical advantage and Velocity Ratio as gears. 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. Others • • • • Cranks and sliders Ratcheting mechanisms Clutches Brakes