Actuators provide thrust and
traction of industrial automation. If something moves on the factory floor, it
is most likely that the actuator is involved. Actuators
depend on the type of energy that electromechanical, hydraulic and pneumatic
energy the most common types. Each type has advantages, and understanding the
differences can help maintenance engineers reduce downtime and costs.
Actuator Basics:-
The basic principles for
determining the mechanical requirements of the actuator are similar, regardless
of the type of energy. The designer of the motion application first calculates
the weight of the moving part combined with the frictional force to determine
the force required to move the load. The designer determines the "motion
profile" of the application. This consists of the amount of time the load
will move forward, backward or reverse. The motion profile also includes the
time it takes to accelerate and decelerate from zero speed to the required
speed and vice versa. It can also include acceleration and deceleration times
from one speed to another if it does not start or end at zero speed. The
combined total time of a profile is called a cycle and can be measured in
seconds, minutes or hours.
The designer can generate a
motion profile to calculate the force required to overcome the inertia of the
load as specified in Newton's Law 2 (Force = Mass x Acceleration). The faster
the required acceleration, the more force it will need to overcome inertia. Its
force will be greater than the weight and friction force initially used to
select the actuator. To compensate for this, the best practice is to apply a
service factor or safety factor to the calculated forces. The service factor
protects your equipment and reduces wear. The safety factor protects people
around the equipment.
The weight and friction force
adjusted by the appropriate service and safety factors define the work to be
done. Actuators perform their functions and most industrial applications
provide one of the three main types of actuators for work: pneumatic, hydraulic
or electric. All three types require electrical control for start-stop and
expansion. The three types are generally completely protected from
contamination, protected and similarly mounted, but differ in cost,
installation, energy efficiency, energy density, intelligence and
maintainability.
Electromechanical actuator:-
Electromechanical actuators are
also called electric actuators or cylinders, and if you have a built-in
microprocessor, they are called "intelligent actuators."
To accelerate the cycle, the
electromechanical actuator consists of servo motor, gear and ball screw
drive rod. For intermittent duty cycles (generally 25% of the dynamic load
capacity of the actuator), a DC or AC motor replaces the servo and ball screw
and lead screw options are available. The duty cycle is officially defined by
(On time) / (On time + Off time) x 100 =% Duty cycle, which is limited by the heat
generated inside the engine. Determining the duty cycle for a given load can be
complicated. Under some light loads, the actuator can run for at least several
cycles before the power must be turned off to get closer to the 100% duty cycle
or to cool the engine.
The advantage of
electromechanical actuators is the reduction of operating costs due to their
high efficiency. From a conventional maintenance point of view, this high
efficiency has fewer replacements and does not require air or hydraulic fluid
in the power supply, so there is no leakage. The disadvantage is that with the
expansion of IIoT and the flexibility requirement of existing production lines,
electromechanical actuators begin to integrate into microcontrollers. This adds
a new dimension of work with a new level of maintenance.
Smart maintenance:-
Using the integrated chip, the
electromechanical actuator can be programmed to maintain a constant speed in
load changes. Precisely control acceleration and deceleration. If you wish, you
can monitor and maintain your location without power. Actuators can participate
more easily and profitably in the plant network, promoting the potential
benefits of maintenance functions. This additional level of intelligence
contributes to cleaner and more energy efficient operations. Some older
external devices, such as relays and limit switches, are now being replaced by
internal electronic devices, which eliminates the need for prior effort to
maintain external devices and associated wiring.
These additional benefits of
smart actuators are backed by diagnostic information delivered through the
network bus. For example, on-board electronics can track the number of cycles
executed by the actuator, provide measurements of operating temperature and
current consumption. Analyzing these factors can help you determine if
temperature rise or current consumption is associated with unusual wear or
application demands on your system. In addition, simply closing the process to
protect the application before overheating or current spikes damage the
actuator can help with maintenance.
Hydraulic actuator:-
If power density is your
priority, the hydraulic actuator / cylinder may be your best option. For
example, a 2-inch diameter hydraulic cylinder that operates at 1,000 PSI can push
more than 3,000 pounds. Hydraulic systems require oil tanks, electric motors,
pumps, oil filters, relief valves and directional control valves. The pump size
(GPM) is determined by the required speed and the size of the cylinder, and the
size of the electric motor, the reservoir, the filter, the relief valve and the
directional control valve is determined by the size of the bomb. The higher the
required speed, the higher the cost of the system.
The hydraulic system converts
kilowatts into flow and pressure. There is a loss of pressure in each
component, including conductors, hoses and pipes. With proper design, these
losses can be maintained at a few percentage points. The cylinder is efficient
until it wears around the piston and begins to leak. The pump is also affected
by wear and reflects it through internal leaks.
As the type of hydraulic pump
changes to meet the design criteria, system efficiency may vary. Gear pumps are relatively
cheap and are 85-90% efficient in new cases. The efficiency of the vane and
piston pump is greater than 90%. The most efficient system uses a
pressure-compensated piston pump that automatically runs at idle but maintains
pressure when no flow is needed. The electric pump controlled by a frequency
converter or a pump driven by a servo motor with servo motor will greatly
improve the overall efficiency of the hydraulic system. Proportional valves can
be integrated into the system to control acceleration / deceleration and
achieve intermediate stroke positions. This comparison is for single-axis
actuators, but many hydraulic power units can provide multi-cylinder flow,
which requires a more complex approach.
Vibration and other factors can
cause external leaks in pipe and hose fittings over time. The cylinder rod
itself releases a film of oil in the plant environment every pass. Internal
leaks make maintenance much more difficult. Leaks inside the pumps, pressure
controls, directional valves and cylinders convert pressure and flow into heat
or wasted energy. None of these can slow down the actuator. Maintenance
engineers value the repair of leaks or the replacement of leak actuators.
Pneumatic actuator:-
Pneumatic actuators are mainly
used in simple applications where relatively light load movements between two
positions are required. The movement position of the cylinder is controlled by
the mechanical limits of the actuator or hard stop. Pneumatic actuators tend to
produce noise when the actuator makes contact with the hard stops at each end
of the travel limit, reducing the life of each impact. Most pneumatic
applications do not require position control during movement.
If compressed air is already
available in your plant, pneumatic actuators / cylinders have the lowest
installation and operating costs. If a constant and stable air supply is not
possible, it can provide other benefits of the supply actuator. Pneumatic
actuators are the least efficient in the use of kilowatts, and the maintenance
of air leaks is a constant problem.
