Introduction
Control systems are not complete without the installation of actuators. Actuators are the mechanisms which are used by the control system to achieve a process or a function. They are responsible for the motion or control mechanisms which are used by the control system to accomplish their defined operations of functions. Actuators are used to convert the electrical signal from the control system to mechanical movement or motion which then accomplished a desired task or function (Bart et al., 2013).There are different types of actuators used in control systems. The type of actuators used in control systems depend of the source of energy which operates the actuator. Generally, actuators are widely divided into two major categories: electric and pneumatic actuators (Boldea & Nasar, 2012). While electric actuators are operated using electric current, pneumatic actuators employ the use of hydraulic fluid pressure. Electric actuators convert the electrical signal from the control system into motions or movements which performed a present task. On the other hand, pneumatic actuators convert the signal from the control system to hydraulic pressure which is used in moving parts to perform a present function or operation.
Control systems employ the use of both electric and pneumatic actuator to achieve a mechanism through which they act on the environment. Similar to transducers, actuators convert the output signal from a control system into motion. Electric and pneumatic actuators are employed in numerous applications across different fields (Bart et al., 2013). Generally, electric and pneumatic actuators are used in different applications as mechanisms to introduce motions. While electric and pneumatic actuators are used for the same purpose, they exhibit different characteristics, benefits as well as shortcomings (Wickham, Washbourn & Cogan, 2011). These differences allow them to be applied in different applications which suit their characteristics. The major difference is the source of power for their operation. Electric actuator is powered by electric current while pneumatic actuators are powered by pneumatic energy. Pneumatic actuators transform energy produced by compressed air at elevated pressure to either rotary or linear motion. This type of energy is appropriate for the control of the main engine since it has a rapid response in stopping and starting. It allows for the production of significantly large force from relatively small changes in pressure.
Electric Linear Actuators
Electric linear actuators transform the output single from a control system to a mechanical linear movement or motion powered by electric current. It is important to note that electric actuators employ the use of electric energy to generate a linear mechanical energy or motion. The linear motion or movement generated by the electric actuators are used by the control system to accomplish a present or desired task as programmed in the systems controller. Electric linear actuators are used to move a load (components, an assembly or a finished product) in a straight line (Wickham, Washbourn & Cogan, 2011). It accomplishes this task through converting electrical energy into a linear force or motion under the power of electrical current.
Design material and properties
An electric actuator is composed of numerous components but only a few significant parts are critical for its operation. Some of the basic components of an electric linear actuator include a motor, motor start capacitor, a brake, terminal strip, limit switches and conveyer belt. Screw electric motors are composed of acme, a ball and electric motor. The motor is the main component of electric actuator (Boldea & Nasar, 2012). It is used to convert the electric current or output from the control system to torque or mechanical motion. The amount of electrical current supply to the input terminals of the motor determines the amount of speed as well as the amount of torque generated by the motor. The next component of the electric actuator is the brake. It connected and situated on top of the motor and is utilized to control the motor. The motor start capacitor is used to grant the motor with sufficient and necessary force to start operating (Bart et al., 2013).The conveyer belt is used to transform the rotary motion and torque generator by the motor to a linear motion. On the other hand, the terminal strip is utilized to supply electrical power to various electrical components of the system.
Electric linear actuators have the following properties; repeated linear movement, adaptable movement, controlled precision movement and acceleration controlled movement. Electrical linear actuators present the best repeated linear movement used to repeatedly move a load to a consisted position or location (Boldea & Nasar, 2012). This type of actuator is capable of adaptations and changes. Its movement can be synchronized with that of the load thus adaptive movement. Additionally, electric linear actuators are characterized with high accuracy which is far beyond the capabilities of human. They have the ability to perform they work with high precision devoid of human errors.
Operation of electric linear actuators
Electric linear actuators function by converting the output signal from the control system to a linear motion through the use of electric motor. The transformation of the output signal from the control system to mechanical linear motion is powered by electrical current as opposed to hydraulics in pneumatic linear actuators (Bart et al., 2013). The electrical signal received from the output of the control system is converted to mechanical torque by an electric motor. The electrical motor is mechanically connected to either a conveyer belt or a lead screw. This mechanical connection converts the rotary torque produced by the electrical motor to linear motion required by the control system (Wickham, Washbourn & Cogan, 2011). A threaded ball nut with matching threats to the threads of the screw is prohibited from rotating with the screw. The nut is driven along he threats as the screw rotates causing a linear motion. The motion of the actuator is determined by the speed and direction of rotation of the electrical motor.
Applications and technology
Electric linear actuators are used in a myriad of applications across different fields. In most cases, the linear motion generated by the actuator is used in different applications ranging from electric valve control in car engines to transfer of loads in an assembly plant. The applications and uses of electric linear actuators are adopted from their properties of adaptable movement, linear repeated movement, controlled precision movement and acceleration controlled movement (Bart et al., 2013).They are applied in areas that require repeated consistent and continuous motion to coordinate numerous different motions at the same time. Additionally, electric linear actuators are used in areas with require high levels of precision devoid of human errors.
Pneumatic Linear Actuators
Pneumatic linear actuators work in a way similar to electric linear actuators a part from the power source. While electric linear actuators employ the use of electrical current, pneumatic linear actuators employ the use of compressed pressure released through fluids (Cabuz, Ohnstein & Elgersma, 2011). Pneumatic linear actuators are applied in different applications which suit their characteristics instead of the other linear actuators.
Design material and properties
Pneumatic linear actuators are made up of the following components; a piston, a hollow cylinder, external compressor, fluid and a spring. The piston is fitted within the hollow cylinder with fluid on one side of the piston and a spring on the other side of the piston. The fluid is used to generate pressure to cause a linear motion of the piston within the cylinder. The piston is connected to an external rod which transfers the piston motions to mechanical movements. The spring is used to return the piston to its initial position. On the other hand, the external compressor is used to generate pressure which pushes the piston within the cylinder.
As opposed to electric linear actuators, pneumatic actuators employ the use of compressed fluids to generate pressure for the linear movement. It does not require the use of electrical current to function. Additionally, pneumatic linear actuators yield a lot of popularity from their simplicity. They generate relatively high amount of force as compared to other actuators. Most of the pneumatic actuators have a maximum pressure of 150 psi which translates to close to 30 to 7,500 lb of force (Cabuz, Ohnstein & Elgersma, 2011). Also, pneumatic linear actuators present high precision linear motion through accuracy and repeatability. Additionally, pneumatic linear actuators have light weight, require low maintenance and are made from durable materials. The durability of the material components of pneumatic linear actuators make them cost effective as compared to other actuators.
Operation of electric linear actuators
Pneumatic linear actuators operate by converting the pressure supplied from the external compressor to linear motion. The external compressor releases pressure into the hollow cylinder through a compressed fluid via the inlet. The pressure generated by the compressed fluid pushes the piston within the cylinder resulting to a linear motion of the piston. The piston is connected to a rod. The movement of the piston is transferred to the connecting rod which causes mechanical movement outside the cylinder. A spring fitted within the cylinder is used to return the piston to its original position. The process is repeated causing a continuous linear motion.
Applications and technology
While pneumatic linear actuators have a myriad of applications across different fields, they are majorly applied in area with extreme temperatures. As opposed to electric linear actuators, pneumatic linear actuators are capable of operating in areas with extreme temperature range from -40 to 250 Degrees F. In recent years, pneumatic linear actuators have witnessed numerous developments in materials, miniaturization and integration with condition monitoring and electronics. As compared to other actuators, the economical cost of pneumatic linear actuators is extremely low.
The difference between Electric and Pneumatic Linear Actuators
While electric and pneumatic linear actuators are used for the same purpose, they exhibit various differences due to their properties and operation. It is imperative to note that both electric and pneumatic actuators are used to convert the output signal of the control system to a mechanical linear motion. The major difference between the electric linear actuators and pneumatic linear actuators is their source of power. Additionally, the two type of actuators exhibit some differences in the following areas; high force and speed, component cost, operating cost, heating, moisture, torque to weight ratio and stalling (Cabuz, Ohnstein & Elgersma, 2011).
High force and speed: The force and speed offered by the pneumatic linear actuators are relatively higher than the force and speed offered by electric linear actuators. Pneumatic linear actuators offer more speed and force per unit size as compared to the electric linear actuators. As opposed to the electric linear actuators, the speed and force on the pneumatic linear actuators can easily be adjusted to suit the operation or the desired outcome (Rao & Bone, 2012). As a consequence, pneumatic linear actuators offer easy control and regulation of both force and speed as opposed to electric actuators.
Component cost: As opposed to electric linear actuators, the component cost of pneumatic linear actuators is extremely low (Colbrunn, Nelson & Quinn, 2012). Electric linear actuators present high component cost. Additionally, the component used in making pneumatic linear actuators are durable, thus low economic and maintenance cost as opposed to electric linear actuators.
Operating cost: The cost of operating electric linear actuators is considerably lower than the cost used to operate and maintain pneumatic linear actuators. Even though pneumatic linear actuators are made of durable and low cost components, their cost of operation is quite higher than electric linear actuators (Rao & Bone, 2012).
As compared to electric linear actuators, pneumatic linear actuators exhibit low heating since they use compressed fluid to generate the pressure needed for operation unlike the electric linear actuators. Pneumatic linear actuators are designed to resist overheating thus are more suitable in areas and applications with extreme temperatures (Cabuz, Ohnstein & Elgersma, 2011). Conversely, electric linear actuators tend to overheat given that they use electrical current as the source of power. Additionally, it is imperative to keep electric linear actuators away from moisture as opposed to pneumatic linear actuators which are designed to be moisture resistant. Pneumatic linear actuators exhibit high torque to weight ratio as opposed to electric linear actuators.
Advantages and Disadvantages of Electric and Pneumatic Linear Actuators
Electric linear actuators
As opposed to pneumatic linear actuators, electric linear actuators present high precision control and positioning. The high precision in positioning and control helps machines to adapt to flexible routine and process (Rao & Bone, 2012). Additionally, electric linear actuators have low operating cost even though they are made from expensive components. The cost of operating an electric linear actuator is extremely low as compared to the cost of operating pneumatic linear actuator. It is imperative to note that electric linear actuators are most economical when they are used in a moderate scale (Colbrunn, Nelson & Quinn, 2012).
On the other hand, electric linear actuators exhibit high component cost even though they exhibit relatively low operating cost than pneumatic linear actuators. Electric linear actuators present high component cost (Colbrunn, Nelson & Quinn, 2012). Apart from the high component cost, electric linear actuators offer less speed and force per unit size as compared to the pneumatic linear actuators. Also, electric linear actuators tend to overheat given that they use electrical current as the source of power.
Pneumatic linear actuators
The major advantages associated with pneumatic linear actuators include; low component cost, high force and speed, high torque to weight ratio and resistant to moisture. The force and speed offered by the pneumatic linear actuators are relatively higher than the force and speed offered by electric linear actuators. Pneumatic linear actuators offer more speed and force per unit size as compared to the electric linear actuators. Additionally, pneumatic linear actuators exhibit high weight to torque ratio (Rao & Bone, 2012). They are resistant to moisture and are made of durable materials which allow them to operate in areas with extreme temperatures. It is important to note that pneumatic linear actuators exhibit low heating since they use compressed fluid to generate the pressure. While the component cost of pneumatic linear actuators are relatively low compared to electric linear actuators, their cost of operation is relatively high.
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