Mechanisms

Get your notebook please- we are taking a few notes first

What is a Mechanism?A mechanism is the part of a machine which contains two or more pieces arranged so that the motion of one compels the motion of the others.

Generally used to:– Change the direction of movement– Change the type of movement– Change the speed of movement– Change the amount of torque or force

available to do work

Mechanisms - Change Direction

• Meshed gears in a gear train always turn in opposite directions

• The flow of power is reversible only if you can make the input shaft turn by turning the output shaft

Mechanisms - Change Movement

Rotary

LinearReciprocating

Oscillating

Mechanisms - Change Speed

• Gear ratios compare the output (or driven gear) to the input (or drive gear)

• If the output gear is larger than the input gear the speed will decrease

• If the output gear is smaller than the input gear the speed will increase.

Mechanisms – Change Force or Torque

A force is a push or pull in a straight line.

Torque is a push or pull in a circular direction.

Mechanisms – Torque vs Speed

More torque = easier to move = less speed

(like when going up hill)

More speed= harder to move

= less torque

(like when going on straight away or down a hill)

Gear Ratios• Gear ratios compare the output (or driven gear)

to the input (or drive gear)

INPUT_______ = Gear Ratio

OUTPUT

Simple Gear Train1. Input and Output Shafts

parallel3. A - Speed is constant4. B – Speed is increased5. A - Torque is constant6. B – Torque is decreased7. A - Ratio 1:1 8. B - Ratio

36 teeth:60 teeth or 3:59. Flow of Power

reversible10. Gear direction – opposite

A.

B.

Driven

Drive

Driven

Drive

Where Do You Find a Simple Gear Train?

Two meshed gears will rotate in opposite directions.

Watch gears

11. Found in:– Watch– Sewing Machine– Motor

Simple Gear Train with Idler1. Input and Output Shafts

parallel3. Speed is constant4. Torque is constant5. Ratio 1:16. Flow of Power

reversible7. Input and Output Gears

same direction Without Idler Gear different direction

DrivenDriveIdler

Where Do You Find a Simple Gear Train with Idler?

Two meshed gears will rotate in opposite directions.

An Idler Gear allows the drive and driven gears to rotate in the same direction.

8. Found in - Paper Transport Rollers