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For electrical driven robots, four major types
of electric drive can be used:
- Stepper Motors: These are used mainly
for simple pick and place mechanisms where cheapness
is more important than power or controllability.
- DC Servos: For the early electric
robots the DC servo drive was used extensively.
It gave good power output with a high degree
of control of both speed and position.
- AC Servos: In recent years the AC
servo has taken over from the DC servo as the
standard drive. These modern motors give higher
power output and are almost silent in operation.
As they have no brushes they are very reliable
and require almost no maintenance in operation.
- Solenoids Actuator: A major advantage
of solenoid actuator is their quick operation.
Also they are much easier to install than pneumatic
or hydraulic actuators. However, solenoid can
only fully open or closed and they don't produce
much force.
Pneumatic robots use compressed air and come
in a wide variety of sizes. A pneumatic robot requires
another source of energy such as electricity, propane
or gasoline to provide the compressed air. Many
of the simple pick and place arms are driven by
pneumatics. This makes them cheap but has the disadvantage
of being difficult to control.
Hydraulic robots use oil under pressure and generally
perform heavy duty jobs. This power type is noisy,
large and heavier than the other power sources.
A hydraulic robot also needs another source of energy
to move the fluids through its components. Hydraulic
drives were used on a large number of the early
robots as it was more rigid and controllable than
pneumatics and it could provide more power than
the electric drives then available. The problems
with hydraulics are that it tends to be fairly slow
in operation and that due to the high pressures
involved leaks can be very messy.
Most robots require a plug into the wall. Hydraulic
robots also need a pump to pressurize the hydraulic
fluid, and pneumatic robots need an air compressor
or compressed air tanks. Furthermore, Pneumatic
and hydraulic robots require maintenance of the
tubes, fittings and hoses that connect the components
and distribute the energy.
For mobile robots, two other important sources
of electric power, solar cells and batteries, are
used. There are lots of types of batteries like
carbon-zinc, lithium-ion, lead-acid, nickel-cadmium,
nickel-hydrogen, silver zinc and alkaline to name
a few. Battery power is measured in amp-hours which
is the current (amp) multiplied by the time in hours
that current is flowing from the battery. For example,
a two amp hour battery can supply 2 amps of current
for one hour. Solar cells make electrical power
from sunlight. If you hook enough solar cells together
in a solar panel you can generate enough power to
run a robot. Solar cells are also used as a power
source to recharge batteries.
There are other forms of power source for special
robot application. For example, power for deep space
probes is traditionally generated by radioisotope
thermoelectric generators or RTGs, which use heat
from the natural decay of plutonium to generate
direct current electricity.
Robots may use all these actuator types.
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