This article will take an in-depth look at electric actuators.
The article will bring more detail on topics such as:
This chapter will cover the basics of electric actuators, including their manufacturing processes, components, operational mechanisms, and efficiency.
Electric actuators are devices capable of creating motion of a load, or an action that requires a force like clamping, making use of an electric motor to create the force that is necessary.
When the spindle or rotor rotates, rotary motion is generated by the electric motor. Within an electric actuator, a helical screw is connected to the motor spindle through the drive shaft, which then turns within a ball screw nut.
The production of an electric linear actuator starts with the electric motor. Each motor comprises two main components: the stator, a stationary permanent magnet, and the rotor, which is positioned at the center of the stator and rotates due to the magnetic field generated by the stator.
Each component is meticulously manufactured on an automated assembly line within the electric linear actuator factory. Every phase of the process is monitored, from winding the copper coils on the rotor to inserting the shaft screw into the motor. Quality assurance experts rigorously inspect each batch. To enhance efficiency, different parts of the motors are produced simultaneously to streamline the assembly of each linear actuator.
Raw materials and finished components are moved to the next production stage using mechanical arms and conveyor belts. Once the electric linear actuators are assembled, the final stage involves more hands-on work. Trained assembly workers, guided by a manufacturing document prepared by engineers, complete the final assembly. Quality assurance experts oversee each step, thoroughly inspecting the components before proceeding to the next phase.
After the actuators are fully assembled, they are sent to the Quality Control team for a first article inspection. This inspection verifies dimensional accuracy and ensures all parameters are met. The first article unit undergoes stress testing to confirm compliance with IP ratings, operating temperature limits, and duty cycle requirements.
Once the Quality Control team is satisfied with the results, the entire batch is approved for shipment to the distribution center. Upon arrival at the distribution center, the products are received into the warehouse. The units are then re-inspected by a product engineer to ensure they meet all specifications and were not damaged during transportation.
After inspection, the products are added to stock and made available for purchase. Following a purchase, the logistics team performs another round of testing before carefully packing the units and preparing them for shipment.
This section will cover the different components of an electric actuator.
This component is a U-shaped metal piece with holes at each end for inserting a pin, bolt, or other fastening devices. It allows the actuator to be mounted to the application using clevis attachments at the front and rear.
Also known as the cover tube, this is an extruded aluminum tube that safeguards the external parts of the linear actuator and encloses all the internal components.
Also known as the extension tube, translation tube, piston, or drive tube, the inner tube is typically made from aluminum or stainless steel. It houses the spindle when retracted and is connected to the drive nut, which is threaded and moves along the rotating spindle to extend or retract the tube.
Referred to as the rotating screw, lead screw, or lifting screw, the spindle is a long, straight rod that rotates within a tool or machine. This part of the linear actuator controls the extension and retraction of the inner tube, generating linear motion. Made of steel for strength and durability, the spindle can be threaded in various ways to accommodate different speed and load requirements.
Located at the end of the spindle, the safety stop prevents the overextension of the inner tube.
Attached to the end of the outer tube, the wiper seal prevents contaminants like dust and liquids from entering the spindle area. It ensures a proper seal between the inner and outer tubes, affecting the actuator's IP rating.
The drive nut moves along the spindle and is attached to the inner tube, enabling its retraction and extension. It can be made from plastic or metal and is sometimes keyed to prevent the inner tube from rotating.
Limit switches manage the position of the inner tube when fully extended or retracted by cutting the electrical current to the motor. They prevent the actuator from overextending or over-retracting and can also serve as signal-sending devices.
These are made from plastic or steel and mate with other gears to alter the relationship between a driving mechanism’s speed and the driven part’s speed. The gear that is connected to a power source like the motor is known as the drive gear.
This housing encloses the gear motor and all internal components, protecting them from external damage. The motor housing is usually constructed from high-quality plastic.
The direct current motor is where all of the electric actuator’s power comes from. DC motors are found in different types. There are the most commonly used motors called brushed motors. The motors consist of the following components:
The stator is the stationary outer part of the motor, comprising the motor housing, caps, and two permanent magnets. It creates a stationary magnetic field that surrounds the rotor.
Also known as the armature, this is the rotating inner part of the motor. It includes the motor shaft, silicon steel laminates, copper windings, and commutator.
These are a pair of plates mounted on the motor shaft that provide connections for the electromagnet coil. The commutator reverses the motor's polarity, maintaining continuous rotary motion and preventing torque loss.
These utilize sliding friction to transfer electrical current from the stator to the rotor of the motor.
This part connects the gear motor to the base of the stator on the DC motor.
These components communicate the actuator’s stroke position to the control box MCU. Position feedback is essential for linear actuators in applications requiring advanced functions such as synchronization and memory positioning. Various output sensors are available, including:
This sensor outputs a signal based on the magnetic field density around it. When the magnetic flux density exceeds a preset threshold, the sensor generates a Hall voltage, which serves as the output voltage. A linear actuator with position feedback, such as that provided by a Hall sensor, ensures high accuracy and reliability.
This sensor features a wiper and two end connections that adjust the electrical signal output. As the linear actuator's lead screw turns, the resistance between the wiper and the end connections varies. Each resistance value corresponds to a specific position within the actuator's stroke.
This sensor is a magnetic positional device that functions as an electrical switch activated by a magnetic field. It consists of a pair of ferrous metal reeds enclosed in a sealed glass envelope. The contacts typically remain open but close in the presence of a magnetic field, thereby completing the circuit and cutting off power to the actuator.
The electric motor creates a rotary motion during the rotation of the spindle or rotor. The motor spindle rotates in a ball screw nut. This motor spindle is coupled directly to a helical screw via the shaft of the drive.
The ball screw nut moves forward or backward along the helical screw as the spindle rotates. Attached to this nut is a hollow piston rod, which converts the rotational motion of the motor into linear motion within the actuator, whether moving clockwise or counterclockwise.
An electric drive regulates the motor, allowing for adjustments in the rotation speed and, consequently, the linear speed of the actuator. A feedback mechanism provides positional data, enabling the actuator to be programmed to move to specific positions, halt, resume movement, or return to its resting position.
The torque generated is directly related to the motor's power, which also influences the force that can be effectively utilized by the actuator.
Different types of electric actuators include:
This smart linear actuator offers precise linear output displacement. It features high-quality, stable materials and design, ensuring durability and safety. This actuator is versatile and can be used in a variety of applications, including control of valve types such as ball valves and butterfly valves.
These actuators support integrated standard signals, converting them into angular displacements. This allows for mechanical control of the valve and facilitates automatic adjustment tasks.
In automatic adjustments, the system ensures mechanical, physical, and bi-directional control without interference. It comprises two components: the actuator and the servo amplifier. These can be controlled physically or remotely with high speed.
This electric actuator comes in two power supply models: AC single-phase and AC three-phase. It is designed to achieve precise linear reciprocating motion based on a control signal from the regulator.
This electric actuator series is used for controlling regulating valves. It adjusts the valve's position based on the signal and physical function of the actuator. It is widely utilized in industries such as metallurgy, power generation, papermaking, environmental protection, petrochemical, and light industries.
This full electronic actuator receives 4mA – 20mA or 1V – 5V DC input signals from an operator, PC, or regulator and operates with a single-phase AC power supply of 220V. It features an integrated servo system, eliminating the need for an additional servo amplifier. The actuator's controller uses complex, mixed integrated circuits that are resin-hardened and tested for aging behavior.
This actuator is designed to be highly resistant to moisture and vibration. When mounting with a base and crank, the position of the crank's zero end can be adjusted randomly within a range of 0 to 360 degrees Celsius. Additionally, the electric actuator features temperature, overload, and torque safety switches. It boasts high reliability, precise control, and various adjustable mechanisms for angular travel, making it suitable for regulating angular travel in electric valves.
These electric actuators offer various benefits, including controlled and predictable acceleration and speed. They achieve multiple positions with high accuracy and repeatability, and forces can be nearly automatic. With no need for compressed air, energy costs and infrastructure requirements are reduced. These actuators are designed for ease of processing and installation.
The settings for function parameters are predetermined, and there is a simplified mode for quick operation. SMC electric actuators come in various forms including sliders, AC servo sliders, rod and guided rod types, AC servo rods, slide tables, rotary actuators, grippers, miniature actuators, and both controllers and drivers.
This section will analyze and differentiate electric actuators from their alternatives.
When comparing electric actuators with pneumatic actuators, it becomes clear that:
The primary distinction between these actuators lies in their power sources. Pneumatic actuators require an air supply ranging from 60 to 125 PSI and are operated via a solenoid valve controlled by AC or DC voltage. In contrast, electric actuators are used when an air supply is not available.
Double-acting pneumatic actuators are generally up to 70% more compact than electric actuators.
Pneumatic actuators typically take between half a second to a full second to operate a valve, depending on the model. Electric actuators usually require around six seconds or more to achieve the same action.
Pneumatic actuators suit a wide variety of ambient temperatures, and their rated temperature range is -20 degrees Fahrenheit and 350 degrees Fahrenheit. Electric actuators are susceptible to overheating in applications that involve high temperatures and are often rated between 40 degrees Fahrenheit and 150 degrees Fahrenheit. However, the temperature restrictions vary according to the product and the guidelines of the company for rating their products.
High-quality pneumatic actuators with a rack and pinion design can endure up to 1,000,000 cycles when operated within their specified conditions. Electric actuators typically have a cycle life of around 250,000 cycles, though this can vary depending on their application.
A spring-return or failsafe feature ensures that a valve actuator moves to a safe position in case of power or signal failure. Pneumatic actuators commonly offer a variety of spring-return options. Electric actuators, however, may not easily incorporate this feature.
Electric ball valves generally have a higher price point compared to pneumatic ball valves. Despite this, pneumatic ball valves often offer a longer lifespan when used according to their specifications, potentially providing better overall value for certain applications.
When comparing electric actuators with hydraulic actuators, consider the following:
In hydraulic systems, force is determined by the equation pressure x area. For instance, a 3-inch cylinder can generate 15,000 lbf (66,723.3 kN) at 2200 psi. However, hydraulic cylinders are frequently oversized, which can obscure the true force requirements of an application. Hydraulic actuators depend on pressure buildup to generate force.
Electric actuators use the current flowing through a servo motor to create torque that drives the power screw and produces force. Many electric linear actuators feature roller screws for efficient force transmission. The force generated by electric actuators is available instantly.
Hydraulic actuators perform well in simple position applications but may require costly servo hydraulic systems for complex motion profiles. Electric actuators with servo motors offer precise control over position, acceleration, deceleration, velocity, and output force. They allow for real-time adjustments, providing superior accuracy and repeatability compared to hydraulic systems.
Achieving high force can be challenging for both hydraulic and electric actuators. Hydraulic cylinders require ample pressurized oil to reach high speeds and forces, which may necessitate an accumulation system to maintain the necessary pressurized volume within the system.
Electric actuators rely on motor RPM, torque, and screw characteristics to produce high force. Speed is limited as RPM decreases with increasing torque in larger servos. However, electric actuators benefit from their ability to control the entire motion profile, allowing for potentially higher peak velocities through shorter, more precise movements.
While hydraulic cylinders have a compact footprint at the point of operation, they require a substantial amount of floor space for the hydraulic power unit, which manages oil pressure and flow. Additional components like gauges, heat exchangers, accumulators, and cables also take up space. In contrast, electric actuators offer a compact overall footprint, integrating the actuator, drive, motor, cables, and cabinet into a smaller space. An electric servo system occupies only a fraction of the space needed for a hydraulic cylinder and its associated power unit.
Hydraulic systems exhibit significant temperature sensitivity. In cold conditions, the oil thickens and moves more slowly, leading to sluggish and inconsistent performance. High temperatures can degrade the oil or damage seals, necessitating the use of additional equipment such as tank heaters to manage cold temperatures and heat exchangers to address overheating. These additions increase system costs.
In contrast, electric actuation systems are less affected by temperature variations. They can be designed to operate effectively within specific temperature ranges required for their tasks. For improved performance in cold environments, electric actuators can be equipped with specialized extreme-temperature grease, reducing sensitivity to temperature changes.
Hydraulic cylinders are durable and can provide long-term service if maintained properly. However, maintenance involves time, costs for new seals, oils, filters, and machine downtime. Electric linear actuators, when correctly sized for the application, require no maintenance, thereby eliminating downtime. Choosing the right electric rod involves calculating the actuator's life accurately to ensure longevity and reliability.
Basic hydraulic systems lack data collection and reporting capabilities. Only advanced and costly servo-hydraulic systems can monitor and track metrics like position, force, and velocity. Electric actuators come with built-in sensing capabilities as part of their servo systems. They can monitor motor current to track force and repeatability, and motor feedback provides data on position and velocity, which is reported through a PLC and drive system.
Hydraulic systems typically convert electrical energy to motion with 40 to 50% efficiency. Electric linear actuators generally achieve higher efficiency, operating in the range of 75 to 80%.
Hydraulic systems are prone to leaks, which can create environmental contaminants, safety hazards, and high clean-up costs. Electric actuators are much cleaner, with only the potential for grease on the roller screw being a contaminant. Special greases can be used to further minimize environmental impact.
This section explores the various applications and advantages of electric actuators.
Electric actuators find use in a variety of applications, including:
Electric actuators offer several advantages, including:
Electric actuators are more straightforward to integrate compared to hydraulic or pneumatic systems. They often come with programmable controllers and microprocessors that facilitate the operation of modern industrial equipment.
Electric actuators provide exceptional precision in motion control. They allow for precise adjustments in torque, speed, and force at various stages throughout the motion process.
Unlike their hydraulic and pneumatic counterparts, electric actuators are not prone to contamination or leaks. This makes them cleaner and more secure, offering a more convenient solution for many applications.
In the long term, electric actuators are often more cost-effective compared to other types. They require minimal maintenance, are simple to operate and install, and are built to endure various environmental conditions. Their durability and reliability further contribute to their overall value.
Additional advantages of electric actuators are detailed below:
Some of the disadvantages of electric actuators include:
Despite their drawbacks, the advantages of electric actuators far exceed their disadvantages.
Electric actuators are essential for applications requiring force. Unlike pneumatic linear actuators, which produce force through pressure on a piston, electric actuators rely on the motor's torque capabilities to generate force. When selecting an actuator, it's crucial to consider factors such as the load to be moved, surface friction, and the load's angle of elevation or decline.
For pneumatic actuators, the distance the load needs to travel determines the actuator’s stroke length. Electric actuators have similar requirements but with some nuances. To avoid overextension, the maximum stroke should be the usable stroke but should not exceed four times the pitch of the helical screws. Electric actuators offer multiple positioning options, so the total movement should match the required stroke. Various screw pitches are available based on the bore size, allowing for versatile component combinations to suit different application needs.
Choosing between electric and pneumatic actuators depends on the availability of compressed air. If compressed air is not available and hydraulic options are not an option, electric actuators become the preferred choice. They are especially advantageous for applications requiring multiple positions, and they offer benefits such as low noise, high precision, rigidity, controllability, and reduced operating costs.
Electric actuators provide exceptional control and precision in positioning. They enhance machine adaptability to flexible processes and are cost-effective due to their energy efficiency, often resulting in significant savings.
Electric actuators are particularly advantageous in applications requiring precise multiple positions. Unlike pneumatic cylinders, which need various accessories to achieve similar functionalities, electric actuators maintain high accuracy and efficiency over time. Additionally, they excel in responsiveness, starting and stopping almost instantaneously compared to hydraulic or pneumatic systems.
Electric actuators operate without delays or lag. In contrast, pneumatic cylinders require continuous compressor operation to maintain pressure. Electric actuators only operate when needed, which can lead to substantial savings on electricity costs for your business.
Electric linear actuators are devices that convert electrical energy into motion. There are different types of electrical actuators offering different capabilities. Electric actuators are more advantageous than their counterparts since they can be easily assembled, are more precise and cost less, only to mention a few benefits. They can also be safely used in a wide variety of applications.
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