Mechanisms in Everyday Machines - Summary

Mechanisms Overview

  • A mechanism combines machine elements to transmit motion and force, converting input to desired output.
  • Mechanism choice impacts speed, efficiency, and complexity.

Common Mechanisms

  • Levers
  • Gears
  • Chains & Belts
  • Pulleys
  • Linkages

Levers

  • Rigid bar rotating around a fulcrum.
  • Consists of effort, load, and fulcrum/pivot.
  • Purpose: amplify force or velocity ratio.
  • Classes:
    • Class 1: Fulcrum between load and effort.
    • Class 2: Load between fulcrum and effort.
    • Class 3: Effort between fulcrum and load.

Class 1 Lever

  • Fulcrum between load and effort.
  • Can increase force, depending on fulcrum placement.
  • If fulcrum is equidistant from effort and load, F{effort} = F{load}.
  • If fulcrum is closer to load, less effort is needed.

Class 2 Lever

  • Load between effort and fulcrum.
  • Effort arm is longer than load arm, providing mechanical advantage.
  • Increases force, sacrifices speed/range.

Class 3 Lever

  • Effort between load and fulcrum.
  • Effort arm is shorter than load arm.
  • Sacrifices force for speed/range.

Gears

  • Rotating components with teeth to transmit motion and change torque.
  • Benefits: modify speed/torque, transmit force over distance, enable precise control.

Gear Train

  • Two or more gears meshed to transmit motion.
  • Driver: gear receiving rotational force.
  • Follower: gear resulting in the force or motion input.

Idler Gear

  • Placed between driver and follower to allow follower to rotate in same direction as driver, without affecting speed ratio.

Types of Gears

  • Spur Gears: Straight teeth, simple, efficient, but noisy.
  • Helical Gears: Angled teeth, smoother, quieter, but produce axial forces.
  • Rack and Pinion: Convert rotary to linear motion.
  • Bevel Gears: Cone-shaped, change axis of rotation.
  • Worm Gears: Spiral thread, provide high torque and slow movement.

Gear Ratio

  • Determines speed vs torque trade-off.
  • Gear Ratio = \frac{Number of teeth on driven gear}{Number of teeth on driver gear}
  • Driven gear larger than driver gear: speed decreases, torque increases.
  • Driven gear smaller than driver gear: speed increases, torque decreases.

Chains and Belts

Chains

  • Transmit rotary motion from one gear to another, useful for long distances.
  • Advantages: no slippage, high-torque applications, durable
  • Disadvantages: lubrication/maintenance required, can be noisy

Belts

  • Flexible loops running over pulleys, transfer power by friction.
  • Advantages: quieter, lower cost, low maintenance
  • Disadvantages: slippage, cannot handle high torque

Pulleys

  • Wheel with grooved rim guiding a rope, belt, or chain.
  • Help lift/move loads by changing force direction or reducing effort.

Types of Pulleys

  • Fixed: Changes force direction but doesn't reduce effort.
  • Movable: Reduces effort by distributing weight.
  • Compound: Combines fixed and movable, significantly reduces effort.

Linkages

  • Assembly of links and joints transmitting force or motion.
  • Link: Rigid body with at least 2 nodes.
  • Joint: Connection between links allowing motion.

Types of Motion Linkages

  • Reverse Motion: Input motion in one direction, output in the opposite.
  • Parallel Motion: Output motion in same direction as input.
  • Bell Crank: Changes motion direction by 90 degrees.
  • Crank and Slider: Converts rotational to linear motion.
  • Treadle: Converts rotary to oscillating motion.