Mechanical systems – what
you need to know
• Analyse and design simple mechanical systems of
the type used for pop-up cards and interactive
pages in educational and story books
• Levers and linkages – select appropriate levers,
linkages and rotating discs to design mechanisms
that bring about required changes of movement.
Select components for joining and acting as pivots,
paper fasteners, eyelets, plastic rivets
•Pop up systems – based on V-fold mechanisms,
multiple layers (parallelogram) mechanisms
• http://www.technologystudent.com/cams/c
amdex.htm
• http://www.robives.com/mechs
• http://www.bbc.co.uk/schools/gcsebitesize/
design/systemscontrol/mechanismsrev1.s
html
V-fold mechanism
V-fold mechanism
Multiple layers
mechanism
Multiple layers mechanism
Rotary mechanism
Other simple pop up - mouth
Parallel slide
mechanism
Types of motion
• Types of motion
• There are four basic types of motion in mechanical
systems:
• Rotary motion is turning round in a circle, such as a
wheel turning.
• Linear motion is moving in a straight line, such as on
a paper trimmer.
• Reciprocating motion is moving backwards and
forwards in a straight line, as in cutting with a saw.
• Oscillating motion is swinging from side to side, like
a pendulum in a clock.
• Many mechanisms take one type of input motion, and
output it as a different type of motion.
Cams
Cams are used to convert rotary motion into
reciprocating motion. The motion created
can be simple and regular or complex and
irregular. As the cam turns, driven by the
circular motion, the cam follower traces the
surface of the cam transmitting its motion to
the required mechanism.
Cams can be shaped in any number of ways
and this is determined by the way the
follower is to move. The shape of the cam
is called the PROFILE. Examples of
various cam profiles can be seen below.
• Cam follower design is important in the way the profile of the cam is
followed. A fine pointed follower will more accurately trace the
outline of the cam. This more accurate movement is at the expense
of the strength of the cam follower.
• As the cam turns it has a tendency to push the cam follower to one
side. To overcome this a separate cam follower and push rod can be
used as in this mechanism. Here the cam follower drags over the
cam surface, accurately tracing the surface of the cam. Any
movement of the cam follower is transferred directly to the push rod
Levers
• A lever is a length of rigid material, such
as card, with a pivot somewhere along it.
The lever rotates about the pivot.
• By putting the pivot in different positions
you can increase or decrease the amount
of movement that takes place at the end of
the lever.
Linkages
• Linkages are made by joining two or
more levers together with pivots. There
are 2 types of pivot that are used. A
fixed pivot attaches the linkage to the
background while a movable pivot joins
two parts of the linkage together.
Reverse-motion linkage
A reverse-motion linkage changes the
direction of motion. In the diagram
below, note how the linkage looks a
little like a "Z". See how the central
rod moves around a central fixed
pivot. By pulling (or pushing) the
linkage in one direction, it creates an
exact opposite motion in the other
direction. If the fixed pivot was not
central, it would create a larger or
smaller motion in the opposite
direction.
• Parallel-motion linkage
• A parallel-motion linkage creates an identical
parallel motion. In the diagram below, note how the
linkage looks a little like an "n". This time, it is the
two side rods that move around two central fixed
pivots, while the top of the "n" moves freely. By
pulling (or pushing) the linkage in one direction, it
creates an identical parallel motion at the other end
of the linkage.
• Bell-crank linkage
• A bell-crank linkage changes the direction of movement
through 90°. A bell-crank linkage tends to look a little like an
"L" or, as shown in the diagram below, a mirror image of an
"L". By pulling (or pushing) the linkage in one direction, it
creates a similar motion at the other end of the linkage. For
example, a bell-crank linkage could be used to turn a vertical
movement into horizontal movement, as in a bicycle braking
system.
Pivots
• When making mechanisms from card or
thin plastic you can use paper fasteners,
eyelets and click rivets as pivots.
• The position of the pivot is very important
in all linkage mechanisms. It can affect
how much the mechanism moves and
which direction it moves in.