Chains
24 July 2024
07:31
Car WIper
The car wiper looks too complicated.
A link has joints.
A joint connects two links allowing some
mobility.
If every link is connected to at least two other
joints, it is a closed chain.
Else open chain.
The simplest closed chain has three links which
forms a structure.
The chain with four links, or four joints is the
next.
4bar in UK and USA, 4R in Europe.
We can also have 3RP, which is also a 4bar.
The closed chain has an assembly issue.
Mechanism Page 1
IC Engine
Mechanism
24 July 2024
08:55
A mechanism is a chain with one link fixed to the
ground. Now it becomes useful.
OAOB is also a (ground) link, even though it may not
be "link-like". Very often, link 2 is the driven link.
Link 3 "couples" link 2 to the driven link 4
The chain can be put to different uses by fixing
alternate links.
Can OAA rotate completely? If it does, it is called a
crank.
Else it goes back and forth and is called a rocker.
Grashoff : If
, then only the smallest
link rotates completely about all the other links.
The location of the smallest link with respect to the
ground determines the behaviour of Grashoff
mechanism
Mechanism Page 2
Motion limits
24 July 2024
14:25
A Grashoff rocker does not cross the line of centres.
The largest link of a non-Grashoff mechanism is an
inward rocker.
A Grashoff chain cannot transit between elbow up and
elbow down solutions without disassembly.
The motion limits are reached when links are stretched
out or if they overlap.
and at
The triangles are formed by lengths
the other extreme,
, for the right and left
limits of
Mechanism Page 3
3RP or Slider Crank
24 July 2024
22:19
The slider crank has
as
link parameters and s as the
variable, like for the case of 4R
Does link 2 do a full rotation?
Where has gone?
If
in a 4R is infinitely long, the
arc at B becomes a straight line.
The longest link is infinitely long.
In fact, there are two infinitely long
links. Their difference is e which is
finite.
Link 2 will do a full rotation if it is
the smallest link and satisfies the
Grashoff condition for 3RP.
Mechanism Page 4
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