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=
−
⋅
−
⋅
=
W .
Having removed a roller 2 (or having fixed it
motionlessly to the pusher 3) the movement of a
driven link - follower 3 will not change.
n′ = 2; P
5
= 2 (R
1,4
, T
3,4
); P
4
= 1 (RT
2,1
)
113232 =
−
⋅
−
⋅
=
W .
Similar passive links are applied to reduce
the loading of mechanism links, help the
mechanism of an uncertain position, or (as in
the last example) to decrease the friction force (by replacement of sliding
friction to rolling friction), which results in improvement of mechanism
performance.
4. Classification of mechanisms
There are exceedingly a lot of types of mechanisms which are used in
the modern technology. The study of their various properties with reference
to each separate mechanism is practically impossible and inexpediently by
virtue of variety of existing kinds of mechanisms, that is why, not only
existing kinds of mechanisms are used in engineering but they are constantly
being improved and created. Therefore, for systematic study of mechanisms
it is convenient to adhere to some certain classification and to study general
properties intrinsically to the given class of mechanisms.
Some general properties of mechanisms inherent to separate classes are
usually put as a basis of one or another classification of mechanisms .The
following classification types are mostly applied:
1. By constructive design:
a). lever mechanisms;
b). connecting rod-crank mechanisms;
c). crank-and-slider mechanisms;
d). rocker mechanisms;
e). gears units;
f). cam mechanisms;
g). frictional mechanisms etc.
2. By functional purpose (pumps, conveyors, internal combustion
engines etc.).
3. By structural attributes.
The Russian scientist professor Leonid Vladimirovich Assur offered the
last classification in 1914 − 1917.
1
2
3
4
Fig. II.25.
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