Before the advent of electricity, pneumatic systems were in full swing.These are the systems which use compressed gas to perform work processes. They exhaust the compressed air to atmosphere after use. Pneumatic Cylinders requires expensive plumbing. They also need position sensing. They are not linear. They have compressible source of power as the cylinders of pneumatic system. They are limited up to high speed applications. They are ultra-sensitive. They are reliable. Their power is up to 25,000 N. They are dependent on designs. They can't work work well under extreme temperatures.
They got replaced after the advent of electricity by Hydraulic Systems as it was the requirement of the time. Hydraulic systems use liquids to perform work processes. They are closed systems so they recirculate the liquids after use. Hydraulic Cylinders also require expensive plumbing. They also need position sensing to prevent the changing of position. They also need electronic/fluid interfaces. They are uncontrollable. They are also ultra sensitive. They are the most powerful. They are also dependent on design and seal wear. They also can't perform well under extreme temperatures. Their cost is less too.
They both depend on force of cylinders and motors to generate force. Hydraulic systems can allow much more pressure than the pneumatic systems. The maximum pressure generated by the compressed air is of little over 100 PSI while liquids can generate up to 10,000 PSI only. That's why Pneumatic Systems got replaced by Hydraulic Systems. Later on, Electromechanical systems substituted them too.
Electro-mechanical Actuators are simply dependent on wiring because all electric operations require it. It has become easier now to connect the components via wiring. This quality of electromechanical systems have made them electrically versatile. The reason behind this versatility lies in the controller. Power output increases the significance of the controller. The power output is supposed to have compatibility with motor and load.
Changes in software do alter the systems performances so one must be careful in using software or computer chips.
If a controller has to drive a dc motor then he is supposed to provide sufficient power to match the requirement of load and motor operating loss.
Wiring shouldn't be sensitized to transitory or steady state electrical interference.
Power lines must not be joined from control signal lines to avoid cross-coupling.
If they do the power source then they can also have an impact on the other equipment connected to the source.
An applied step command should be rid off to avoid the sudden flow of currents.
Limiting current to certain units will limit the motor torque. It will avoid the necessity for mechanical torque limiting.
Voltage limiting is useful too but less than the current limiting.
In electro-mechanical actuators, electric motor is present instead of a handle. The rotary motion of motor is replaced by the linear motion.
On choosing an actuator for a particular application, an emphasis should be laid on the features.
Electrical linear Actuators are repeatable up to ± 0,013 mm.
They have multi-stop capabilities.
They are compatible with standard controls which are programmable.
Their speed is 0 to 2 m/s.
They generate power up to 40,000 N.
Their life is up to millions of spans.
They have standard models rated for -30 c to +70 c.
They don't require energy.
They are inherently energy sufficient.
Their cost is moderately low.
Electro-mechanical linear actuator has an electric motor which rotates a lead screw. This lead screw has a lead nut with helical threads. It is not possible for the nut to rotate with the lead screw so it rotates along the threads. The direction of its movement entirely depends upon the rotation. Electromagnetic motors do reach a state where the magnetization of the material doesn't rise even on increasing the external magnetic field H so they can only bring up to 200 pounds per square inch while in hydraulic systems, situation is entirely different. They bring up to 3000-8000 pounds per square inch only in the aircraft applications.
There are many advantages of Electromechanical Systems. Some are as follows:
They have smaller size of packages
Their cost is low
They carry a light weight.
They have large-scale integration
They consume less power.
They have a greater complexity.
They have high output signals.
Linear actuator systems support many motors but dc brush is the most prevalent among them. All motors are used with respect to the particular application and the loads. A linear actuator which uses standard motors have the motor which works as a separate cylinder. It is affixed to one end of the actuator either its parallel or perpendicular.
Linear actuator works on the basic principle of inclined plane. The threads of a nut work as a plane enabling a rotational force to be used over a large distance . It helps in making the movement of a large load possible over a short distance. Linear screw actuators possess static loading capacity which enhances their mobility and speed.
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