Ch7: Mechanisms

• Mechanical Advantage:

  (measure of the load in newtons) divided by (the measure of effort in newtons)

  (Load)/(Effort)
• Moment:

  (Force) multiplied by (distance)

  • Used in the law of the lever; where F1 x D1 = F2 x D2
• Lever classes:

  Class 1; Fulcrum in the middle: provides mechanical advantage

  Class 2; Load in the middle: provides mechanical advantage

  Class 3; Effort in the middle: to amplify motion (moves the load a larger distance than the effort moves)
• Velocity ratio of a lever:

  (distance travelled by effort) divided by (distance travelled by load)

  Ex) Effort travels 10cm and the load travels 40cm. The velocity ratio is 10/40 or 1/4 or 0.25
• Bell crank linkage:

  • Often used to change the direction of motion
  • Used with cables attached to the input and output
  • Example; bicycle brakes

  A) Output

  B) Input

  C) Pivot

  D) Pivot

  E) Fixed point

  
• Parallel motion linkage:

  • Ensures that motion occurs in parallel across two sides
  • Consists of a parallelogram shape with the long parallel sides pivoting

  
• Reverse motion linkage:

  • Pushing the top bar to the right causes the bottom bar to go left, and vice versa
  • Works because the middle lever is rotating around the fixed pivot

  A) Fixed pivot

  B) Input

  C) Output

  
• Push-pull linkage:

  • This linkage makes the output direction the same as the input
  • This is because there are two levers on a fixed pivot

  A) Fixed pivot

  B) Input

  C) Output

  
• Scissor linkage:

  • The base (far left of the mechanism) is fixed onto an object (ex; wall) while the pole the mirror is fixed onto, is parallel to the base and extends

  
• Cam and follower:

  • The cam with its non-circular shape causes the follower to bob up and down, in reciprocating motion

  
• Crankshaft:

  • Consists of many cranks on the same axle
  • Connects places of reciprocating motion to a place of rotary motion

  
• Peg and Slot:

  • Converts rotary motion to oscillating motion
  • The peg rotates, making the slot move side to side (oscillation)

  
• Crank and slider:

  • Converts rotary motion into reciprocating motion

  A) slider

  B) crank