<s>
A	O
rotary	B-Algorithm
actuator	I-Algorithm
is	O
an	O
actuator	B-Algorithm
that	O
produces	O
a	O
rotary	O
motion	O
or	O
torque	B-General_Concept
.	O
</s>
<s>
The	O
simplest	O
actuator	B-Algorithm
is	O
purely	O
mechanical	O
,	O
where	O
linear	O
motion	O
in	O
one	O
direction	O
gives	O
rise	O
to	O
rotation	O
.	O
</s>
<s>
The	O
most	O
common	O
actuators	B-Algorithm
are	O
electrically	O
powered	O
;	O
others	O
may	O
be	O
powered	O
pneumatically	O
or	O
hydraulically	O
,	O
or	O
use	O
energy	O
stored	O
in	O
springs	B-Algorithm
.	O
</s>
<s>
The	O
motion	O
produced	O
by	O
an	O
actuator	B-Algorithm
may	O
be	O
either	O
continuous	O
rotation	O
,	O
as	O
for	O
an	O
electric	O
motor	O
,	O
or	O
movement	O
to	O
a	O
fixed	O
angular	O
position	O
as	O
for	O
servomotors	B-Algorithm
and	O
stepper	B-Algorithm
motors	I-Algorithm
.	O
</s>
<s>
A	O
further	O
form	O
,	O
the	O
torque	B-General_Concept
motor	O
,	O
does	O
not	O
necessarily	O
produce	O
any	O
rotation	O
but	O
merely	O
generates	O
a	O
precise	O
torque	B-General_Concept
which	O
then	O
either	O
causes	O
rotation	O
or	O
is	O
balanced	O
by	O
some	O
opposing	O
torque	B-General_Concept
.	O
</s>
<s>
Stepper	B-Algorithm
motors	I-Algorithm
are	O
a	O
form	O
of	O
electric	O
motor	O
that	O
has	O
the	O
ability	O
to	O
move	O
in	O
discrete	O
steps	O
of	O
a	O
fixed	O
size	O
.	O
</s>
<s>
If	O
the	O
stepper	O
is	O
combined	O
with	O
either	O
a	O
position	B-Algorithm
encoder	I-Algorithm
or	O
at	O
least	O
a	O
single	O
datum	O
sensor	O
at	O
the	O
zero	O
position	O
,	O
it	O
is	O
possible	O
to	O
move	O
the	O
motor	O
to	O
any	O
angular	O
position	O
and	O
so	O
to	O
act	O
as	O
a	O
rotary	B-Algorithm
actuator	I-Algorithm
.	O
</s>
<s>
A	O
servomotor	B-Algorithm
is	O
a	O
packaged	O
of	O
several	O
components	O
:	O
a	O
motor	O
(	O
usually	O
electric	O
,	O
although	O
fluid	O
power	O
motors	O
may	O
also	O
be	O
used	O
)	O
,	O
a	O
gear	O
train	O
to	O
reduce	O
the	O
many	O
rotations	O
of	O
the	O
motor	O
to	O
a	O
higher	O
torque	B-General_Concept
rotation	O
,	O
a	O
position	B-Algorithm
encoder	I-Algorithm
that	O
identifies	O
the	O
position	O
of	O
the	O
output	O
shaft	O
and	O
an	O
inbuilt	O
control	O
system	O
.	O
</s>
<s>
The	O
input	O
control	O
signal	O
to	O
the	O
servo	B-Algorithm
indicates	O
the	O
desired	O
output	O
position	O
.	O
</s>
<s>
A	O
simple	O
low-cost	O
servo	B-Algorithm
of	O
this	O
type	O
is	O
widely	O
used	O
for	O
radio-controlled	O
models	O
.	O
</s>
<s>
A	O
recent	O
,	O
and	O
novel	O
,	O
form	O
of	O
ultra-lightweight	O
actuator	B-Algorithm
uses	O
memory	O
wire	O
.	O
</s>
<s>
As	O
a	O
current	O
is	O
applied	O
,	O
the	O
wire	O
is	O
heated	O
above	O
its	O
transition	O
temperature	O
and	O
so	O
changes	O
shape	O
,	O
applying	O
a	O
torque	B-General_Concept
to	O
the	O
output	O
shaft	O
.	O
</s>
<s>
Both	O
hydraulic	O
and	O
pneumatic	O
power	O
may	O
be	O
used	O
to	O
drive	O
an	O
actuator	B-Algorithm
,	O
usually	O
the	O
larger	O
and	O
more	O
powerful	O
types	O
.	O
</s>
<s>
As	O
their	O
internal	O
construction	O
is	O
generally	O
similar	O
(	O
in	O
principle	O
,	O
if	O
not	O
in	O
size	O
)	O
they	O
are	O
often	O
considered	O
together	O
as	O
fluid	O
power	O
actuators	B-Algorithm
.	O
</s>
<s>
Fluid	O
power	O
actuators	B-Algorithm
are	O
of	O
two	O
common	O
forms	O
:	O
those	O
where	O
a	O
linear	O
piston	O
and	O
cylinder	O
mechanism	O
is	O
geared	O
to	O
produce	O
rotation	O
(	O
illustrated	O
)	O
,	O
and	O
those	O
where	O
a	O
rotating	O
asymmetrical	O
vane	O
swings	O
through	O
a	O
cylinder	O
of	O
two	O
different	O
radii	O
.	O
</s>
<s>
The	O
differential	O
pressure	O
between	O
the	O
two	O
sides	O
of	O
the	O
vane	O
gives	O
rise	O
to	O
an	O
unbalanced	O
force	O
and	O
thus	O
a	O
torque	B-General_Concept
on	O
the	O
output	O
shaft	O
.	O
</s>
<s>
Vane	O
actuators	B-Algorithm
require	O
a	O
number	O
of	O
sliding	O
seals	O
and	O
the	O
joints	O
between	O
these	O
seals	O
have	O
tended	O
to	O
cause	O
more	O
problems	O
with	O
leakage	O
than	O
for	O
the	O
piston	O
and	O
cylinder	O
type	O
.	O
</s>
<s>
Where	O
a	O
supply	O
of	O
vacuum	B-General_Concept
is	O
available	O
,	O
but	O
not	O
pneumatic	O
power	O
,	O
rotary	B-Algorithm
actuators	I-Algorithm
have	O
even	O
been	O
made	O
to	O
work	O
from	O
vacuum	B-General_Concept
power	O
.	O
</s>
<s>
These	O
used	O
the	O
manifold	O
vacuum	B-General_Concept
of	O
a	O
petrol	O
engine	O
to	O
work	O
a	O
quarter-turn	O
oscillating	O
vane	O
actuator	B-Algorithm
.	O
</s>
<s>
Such	O
windscreen	O
wipers	O
worked	O
adequately	O
when	O
the	O
engine	O
was	O
running	O
under	O
light	O
load	O
,	O
but	O
they	O
were	O
notorious	O
that	O
when	O
working	O
hard	O
at	O
top	O
speed	O
or	O
climbing	O
a	O
hill	O
,	O
the	O
manifold	O
vacuum	B-General_Concept
was	O
reduced	O
and	O
the	O
wipers	O
slowed	O
to	O
a	O
crawl	O
.	O
</s>
<s>
Rotary	B-Algorithm
actuators	I-Algorithm
are	O
used	O
in	O
a	O
vast	O
range	O
of	O
applications	O
.	O
</s>
<s>
These	O
require	O
actuators	B-Algorithm
of	O
all	O
sizes	O
,	O
power	O
and	O
operating	O
speed	O
.	O
</s>
<s>
These	O
can	O
range	O
from	O
zero	O
power	O
actuators	B-Algorithm
that	O
are	O
only	O
used	O
as	O
display	O
devices	O
,	O
such	O
as	O
air	B-Algorithm
core	I-Algorithm
gauges	I-Algorithm
.	O
</s>
<s>
Others	O
include	O
valve	O
actuators	B-Algorithm
that	O
operate	O
pipeline	O
and	O
process	O
valves	O
in	O
the	O
petrochemical	O
industry	O
,	O
through	O
to	O
actuators	B-Algorithm
for	O
large	O
civil	O
engineering	O
projects	O
such	O
as	O
sluice	O
gates	O
and	O
dams	O
.	O
</s>
