sec 2 mechanism notes for students 2009 sem2

8/14/2019 Sec 2 Mechanism Notes for Students 2009 Sem2

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TECK WHYE SECONDARYSCHOOL

Secondary 2 Exp / NA / NT

Design & Technology 2009

Mechanism Module

Name : _________________________

Index No. : ____________

Class : ____________

Year of study : ____________

Teacher : __________________________


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Sec 2 Design & Technology Mechanism Module

Introduction to Mechanism

Mechanisms are devices that have been designed to make jobs easier. They

all have certain things in common:

they involve some kind of motion

they involve some kind of force

they must have some kind of input to make them work

they produce some kind of output

If we connect mechanisms together we can build mechanical systems calledmachines. Machines help to make our lives easier and more comfortable

Forces cause, or tend to cause, a change in the position or state of a body.

If a body remains at rest, the forces acting on it are in equilibrium. Force is a

vector quantity and is measured in Newtons (N).

Motions in Mechanism

There are basically 4 kinds of motions:

rotary motion

oscillating motion

linear motion

reciprocating motion

So, what are they actually?

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Rotary Motion

Motion in a circular is called rotary motion. The number of complete

revolutions made per minute (rpm), is called rotary velocity/speed. It is pivoted

in the centre.

Oscillating Motion

Oscillating motion is motion backwards and forwards in a circular arc. E.g.

playground swings and clock pendulums.

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Linear Motion

Linear motion is motion in a straight line.

An example of linear motion is the cutting arm of a paper guillotine

Reciprocating Motion

Reciprocating motion is linear motion backwards and forwards in a

straight line.

Sewing machines make use of this type of motion.

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Mechanism Simple and Complex Gear Drive

A simple gear system uses two gears, which may be of different sizes.

If one of these gears is attached to a motor or a crank then it is called

the driver gear. The gear that is turned by the driver gear is called the

driven gear.

Idler gear is a gear meshed between the driver and driven gear. It

allows the turning of both driver and driven to be in the same direction.

Complex gear system uses more than 1 set of gears.

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INCLUDEPICTURE "http://ww

Idler Gear

Simple Gear System

Complex Gear System
http://www.dtonline.org/apps/infopage/app?1&6&1&33&1&0http://www.dtonline.org/apps/infopage/app?1&6&1&33&1&0


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Mechanism Spur Gear

A type of gear that has straight, flat-topped teeth set parallel to the

shaft. Spur gears are the most common type of gears used.

Spur gears are meshed at parallel axles.

The driver and driven gears rotated in the opposite direction

Speed of the gear can be varied by varying the sizes of the gear

diameter

Mechanism Bevel Gear

Bevel gears are gears with cone-shaped teeth cut at an angle.

Bevel gears have axes with two shafts intersect at 90 degrees and can

also be designed to work at other angles

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Mechanism Worm wheel / Worm Gear

It is a gear drive consisting of a long, cylindrical device with a spiraling

groove (worm gear) that intersects with the teeth of a wheel-like gear

(worm wheel).

A worm gear drive is used to transmit motion between nonintersecting

perpendicular shafts

The worm gear is always the driver gear.

It is used when large gear reductions are needed

Mechanism Rack & Pinion

The rack and pinion mechanism consists of a straight rod (the rack)

which has a number of gear teeth with a small gear wheel (the pinion).

The pinion is fixed on a shaft. When the pinion turns it makes the rack

move in a straight line. Pulling or pushing the rack makes the pinion

turn.

Revised by Tan KH7

Worm gear

Worm wheel

PinionRack


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Mechanism Belt & Pulley

One method of transmitting force and rotary motion from one shaft to

another is by using Belts and Pulleys.

It utilizes a V-belt to connect the pulley together

Speed of the pulley can be varies by varying the size of the pulley

diameter

Mechanism Crank

A crank is an arm that has one end connected to a shaft.

Cranks can be used alone as handles

Usually linked to other mechanical component

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INCLUDEPICTURE "http://w

Belt

Pulley


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Mechanism LeadScrew

Leadscrew also known as a power screw or translation screw

It is designed to translate rotary motion into linear motion

It comes with a matching nut of the same diameter

It has precise and accurate linear motion

It is self-locking

Mechanism Linkages

Linkages are used in mechanical control systems to allow forces and

motion to be transmitted to where they are needed

They consist of a series of levers which can change the direction of a

movement, or make things move in a particular way

We are going to look into 3 types of linkages:

1. Reverse Motion

2. Parallel Motion

3. Crank & Slider

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http://en.wikipedia.org/wiki/Linear_motionhttp://en.wikipedia.org/wiki/Linear_motion


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Reverse Motion Linkage

Reverse Motion Linkages are used to change the direction of motion. A single

lever with a pivot at its centre reverses an input motion without affecting the

input force. The input force and length of transmitted movement can be

increased or decreased by altering the position of the pivot.

Linkage connecting accelerator pedal to carburettor

Parallel Motion Linkage

Parallel linkages are used to make two or more parts of a mechanism move

together and stay parallel to each other as the linkage moves

Tree sawing machine

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Crank and Slider

A crank and slider mechanism consists of a rotating crank connected to a

slider by a connecting rod.

Water Pump

Exercise 1 Fun with Mechanisms

In this exercises, you are to investigate each mechanism set. You are required

to answer all the questions. You can answer the questions in any order.

Reminder:

You are to take care of the equipment. Do not remove any parts from

the kit.

Reverse Motion Linkage

1. Describe how the system works in terms of:

a. Input and Output motions

b. Conversion of motions

c. Directions of the motions

Example: As the input linkage is pushed in, the Output linkage moves in the

opposite direction of the Input linkage. This is also the same if the input

linkage is pulled out. Input motion is reciprocating while Output motion is

reciprocating

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Inputlinkage

Outputlinkage


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Parallel Linkage



b. Conversion of the motions

c. Direction of the motions

Crank & Slider





Spur Gears

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Input linkageOutput linkage

Input CrankOutput linkage /slider

Input Gear

Output Gear


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Rack & Pinion





Worm wheel & Worm Gear

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Input Pinion

Output Rack

Input Worm gear

Output Worm wheel


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b. Conversion of the motionsc. Directions of the motions

Belt & Pulley





Exercise 2 Combination of Mechanism

In this exercises, you are to investigate each combined mechanism set. Youare required to answer all the questions. You can answer the questions in any

order. Reminder:

You are to take care of the equipment. Do not remove any parts from

the kit.

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Crank

Pulley

Worm gear/worm wheel

Let this bethe Input

Input pulley

Output pulley

Let this bethe Output


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1. Identify the mechanism/s that is applied:`


a. Conversion of the motions

b. Directions of the motions

c. Speed of the motions

As the input crank is turned in a clockwise direction (rotary), the worm gear

will turned (rotary) in the same direction. The worm gear (rotary) in contact will

turn the worm wheel (rotary). This is the same if the crank is turned in the

opposite direction. The worm wheel (rotary) will turn the Output pulley (rotary).

The speed of the Output pulley is slower than the speed of the turning crank

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Let this bethe Input



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1. Identify the mechanism/s that is applied:




c. Speed of the component

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Let this bethe input /crank

Let this betheOutput/Shaft


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Revised by Tan KH17

Let this bethe input Let this be

the Output


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Let this be theinput



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Exercise 3 Mechanism Application

Your task is to investigate each Mechanism Application in a workshop

environment. Reminder: You are to take care of the equipment in the workshop during your

investigation.

You are to observe all Safety rules at all times

From your observation:

1. Identify the mechanism that is applied:

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F-Clamp

Handle

Stationarypart

Movablepart


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Leadscrew

2. Describe how this tool works



As the handle is turned (rotary) in the clockwise direction, the movable part

will move towards the stationary part. The movable part is moving in a linear

motion. As the handles is turned in the anticlockwise direction, the movable

part moves apart from the stationary part.

3. Identify the following part.

a. Which is the Input? Handle

b. Which is the Output? Stationary part



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Machine Vice

Handle

Fixed jaw

Movable jaw


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a. Which is the Input? __________________________

b. Which is the Output? _________________________





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Bench Drilling Machine

Table top


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Bench DrillingMachine

Chuck / ChuckKey


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2. Describe how this tool worksa. Conversion of the motions



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Bench DrillingMachine

Motor

Drill bitshaft


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Bench Vice

Crank

Movable jaw


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Sawingmachine

Movable Saw


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b. Which is the Output __________________________


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Bandsaw

Wheel2

Wheel1

Motorizedwheel

Toolpost


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b. Which is the Output __________________________

Lathe turning machineHandwheel

sec 2 mechanism notes for students 2009 sem2

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