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27
He thought the formation of a mechanism as a consecutive attachment to
a driver link and a rack of kinematic chains, with a zero degree of mobility,
or as it is now common to name, the attachment to the initial mechanism of
Assur's groups (groups of links with a zero degree of mobility).
Initial mechanism is a mechanism consisting of one link for which the
law of motion is given, and connected by kinematic pair with a frame (Fig.
II.26).
For both mechanisms represented in
Fig. II.26
n = 1, P
5
= 1.
The
structural group (Assur's
group
) is the kinematic chain having a
zero motion freedom.
W=0.
For planar mechanisms consisting only from kinematic pairs of 4th and
5th classes the equation can be written as:
W=3n−2p
5
−p
4
=0.
If the mechanism is formed only by pairs of 5th classes (P
4
=0):
W
gr
.=3n−2p
5
=0.
Therefore
nP
2
3
5
= , (I.10)
but n and P
5
can take only integer values, hence the last condition is carried
out only with certain parities of n and P
5
.
n
2 4 6 8
…
P
5
3 6 9 12
…
Questions for discussion.
What purposes are machines intended for?
List main groups of machines from the point of view of their functions.
Give examples of material-working machines.
What does “material-working machine” mean?
What distinctions between transport machines and technological ones
exist?
What does “power machine” mean?
What types of transmissions do you know?
When can we say “It is automatic transfer line”? Explain please.
a) b)
Fig. II.26. Initial mechanisms
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