Ch. 13 Mechanical Engineering

  • a branch of engineering that specializes in the ______, ______, ______, ______and ______of technical objects and their moving parts.
  • when designing a technical object we need to consider the ______and

how they will ______.

Linking:

  • when an object has 2 or more parts, the parts (components) are held together by

______

  • links are characterized in four ways:

1. ______vs. ______

2. ______vs. ______

3. ______vs. ______

4. ______vs. ______

Direct vs. Indirect

  • a direct link is when two parts hold together without a linking component

ex. tire and wheel

  • an indirect link is when two parts are held together by a linking component

ex. bolt on an in-line skat)

Rigid vs. Flexible

  • a link is rigid if the linking component or the linked parts cannot be deformed

ex. in line skate

  • a link is flexible if the linking component or surfaces can be deformed

ex. bicycle tire

Removable vs. Non-removable

  • a link is removable if the parts can be separated without damage

ex. in line skate or bicycle tire

  • a link is non-removable if the parts cannot be separated without damage

ex. parts welded together

Complete vs. Partial

  • a link is complete if linked parts cannot move independently of one another

ex. link between tire and wheel

  • a link is partial if the parts can move independently of one another

ex. in line skate

Guiding Components

  • guides control the motion of moving parts along a given trajectory

3 types:

1. ______guide: ensures translational motion

ex. window or drawer

2. ______guide: ensures rotational motion

ex.wheel axle

3. ______guide: ensures translational motion of a part as it

rotates around a given axis

ex. C-clamp

Practice with guides:

examples / type of guide
USB key /
pen /
jam jar lid /
door knob /
dimmer switch /
desk chair /
garbage can /
garage door /
toilet paper roll /

Motion Transmission Systems

  • Transferring the ______of motion from one part of an object to another. (rotational to rotational, translational to translational)

3 parts to a system:

1. ______component  receives the force

2. ______component  receives the motion

3. ______component link between the two

Example: bicycle chain and gears are a motion transmission system

Types of Motion Transmission Systems

1) ______

  • contains at least 2 gears that mesh together
  • direction of parts  alternates from one to another
  • reversibility  yes

Things to consider when building a gear train:

1. Gear teeth (evenly spaced, same size)

2. Gear types (straight vs. bevel)

3. Gear size (bigger or more teeth = slower)

2) ______

  • connects components that are far apart
  • gears don’t touch, they are connected by a chain
  • direction of parts  sprockets inside turn in same direction
  • reversibility  yes

Things to consider when building a chain and sprocket system:

1. Teeth on sprocket must be identical

2. System needs lubrification

3. Smaller sprocket = faster

4. Parts must mesh easily together

3) ______

  • consists of a screw and at least one gear
  • NOT reversible

Things to consider when building a worm and worm gearsystem:

1. Gear teeth must match worm's grooves

2. The driver component MUST be the worm

4) ______

  • similar to gear trains but less efficient (gears can slip)
  • larger gear = slower rotation
  • motion alternates from one to another (clockwise/counter-clockwise)

5) ______

  • pulleys have a groove where belt fits
  • belt must adhere to pulleys
  • smaller pulleys = faster rotation

Speed Change

  • the speed of the driven component depends on the size ratio with the driver

component

  • to calculate the speed we use the following formula:

Speed ratio = diameter (or # of teeth) of driver component

diameter (or # of teeth) of driven component

Ex.

1) If a driver gear has 20 teeth and the driven gear has 10 teeth, what is the speed

ratio?

This means the driven gear is turning twice as fast as the driver gear.

2) If a driver gear with a diameter of 20cm and the driven gear has a diameter of 40cm,

what is the speed ratio?

This means the driven gear is turning twice as slow as the driver gear.

Motion Transformation Systems

  • When motion of one part is transferred to another and the type of motion is changed (ex. rotational to translational)

Types of Motion Transformation Systems

1) ______

  • contains a rack (straight bar with teeth) and a pinion (gear)
  • teeth on rack and pinion must be identical
  • system needs lubrification
  • the greater the # of teeth on the pinion the slower the rotation

2) ______

  • contains a screw and a nut
  • 2 types:

Type 1 screw is the driver, transforms rotational into translational motion

ex. jack to raise a car

Type 2nut is the driver, transforms rotational into translational motion

ex. wrench

3) ______

  • from rotational to translational motion
  • follower must be guided in its motion
  • shape of the cam determines how the follower will move
  • spring keeps the follower in contact with the cam

4) ______

  • translational to rotational motion (ex. to turn the wheels of your car)
  • rod connects the piston to the crank
  • cylinder guides the translational motion of the piston
  • requires lubrification