This article will take an in-depth look at electric actuators.
The article will bring more detail on topics such as:
In this chapter, we will explore the fundamentals of electric actuators, such as their production techniques, integral parts, functional principles, and effectiveness.
Electric actuators are mechanisms that move a load or perform actions requiring force, like clamping, by utilizing an electric motor to generate the needed force.
The electric motor induces rotary motion in the spindle or rotor. Inside the actuator, a helical screw links to the motor spindle via the drive shaft, spinning within a ball screw nut.
The creation of electric linear actuators begins with the electric motor, which includes two primary sections: the stator, a fixed permanent magnet, and the rotor, situated at the stator's center, revolving within the magnetic field generated by the stator.
Every part is precisely crafted on an automated assembly line inside the electric actuator plant. The process is continuously monitored, from coiling the rotor's copper to fitting the shaft screw. Quality assurance rigorously checks each production batch. Efficiency is increased by producing different motor parts concurrently, facilitating the efficient assembly of each linear actuator.
Mechanical arms and conveyor systems transport raw materials and finished components to subsequent production stages. Following assembly, trained workers finalize assembly under detailed guidance documented by engineers. Quality assurance specialists conduct thorough inspections at each production step.
Fully assembled actuators are sent to Quality Control for a first article inspection, confirming dimensions and meeting all standards. The initial unit is stress-tested to ensure compliance with IP ratings, operational temperature ranges, and duty cycle specifications.
Upon passing Quality Control, the batch is cleared for the distribution center shipment. Products are re-evaluated by a product engineer upon reaching the warehouse to confirm adherence to specifications and absence of transport damage.
After verification, products enter stock ready for sale. Post-purchase, logistics conducts final testing before secure packing and preparing units for shipment.
This section delves into the various components making up an electric actuator.
This U-shaped metal piece features holes at each end to accommodate a pin, bolt, or other fasteners. It allows actuators to attach to applications with front and rear clevis fittings for secure mounting.
Known also as the cover tube, this extruded aluminum tube shields the linear actuator's external parts and houses all inner components.
Also referred to as the extension, translation, piston, or drive tube, this part, typically made from aluminum or stainless steel, holds the spindle during retraction. It's connected to the threaded drive nut, which travels the rotating spindle to extend or retract the tube.
Known as the rotating screw, lead screw, or lifting screw, the spindle is a straight rod rotating within a machine, controlling the inner tube's extension and retraction. Crafted from durable steel, it can be threaded in various ways for differing speed and load specifications.
This feature, at the spindle's end, prevents the inner tube from overextending.
Attached to the outer tube's end, the wiper seal stops contaminants like dust and liquids from invading the spindle area. It ensures a proper seal between the inner and outer tubes, influencing the actuator's IP rating.
Sliding along the spindle and attached to the inner tube, the drive nut facilitates retraction and extension. Can be made from plastic or metal, and sometimes keyed to avert inner tube rotation.
These switches control the inner tube's position when fully extended or retracted by halting the motor’s current. They prevent overextension or overretraction and can send signals.
Constructed from plastic or steel, these gears interact with other gears to modify speed relationships between the driving mechanism and driven parts. The gear linked to a power source like a motor is the drive gear.
This enclosure protects the gear motor and internal components from damage, typically made from high-quality plastic.
The actuator derives its power from the direct current motor. DC motors are available in various types, with brushed motors being the most common. Each motor comprises these parts:
The stator is the motor’s stationary exterior, comprising housing, caps, and two permanent magnets, creating a magnetic field around the rotor.
Also called the armature, the rotor is the inner rotating motor part, including the shaft, steel laminates, copper windings, and commutator.
Mounted on the motor shaft, these plates connect with the electromagnet coil. The commutator reverses polarity, maintaining rotation and preventing torque loss.
Carbon brushes transfer current using sliding friction from the stator to the rotor.
This connects the gear motor to the DC motor’s stator base.
These sensors relay the actuator’s stroke position to the control box MCU, crucial for applications needing precise operations like synchronization and position memory. Available output sensors include:
This sensor provides a signal based on surrounding magnetic fields. When magnetic density surpasses a threshold, the sensor produces Hall voltage as output. Position feedback from a Hall sensor enhances accuracy and trustworthiness in linear actuators.
Featuring a wiper and end connections, this sensor adjusts the electrical signal output. The linear actuator’s lead screw rotates, altering resistance between the wiper and connections, each corresponding to a specific actuator position.
A magnetic device working as a switch activated by a magnetic field. With ferrous metal reeds in sealed glass, contacts usually remain open but close under magnetism, completing the circuit and halting actuator power.
In creating rotary motion, the electric motor induces spindle or rotor rotation. Coupled to a helical screw via the drive shaft, the motor spindle spins within a ball screw nut.
The ball screw nut moves longitudinally on the helical screw as the spindle turns, coupling with a hollow piston rod to convert motor rotation into straight linear motion. This action depends on motor rotation direction, either clockwise or counterclockwise.
The actuator's movement is managed via an electric drive, adjusting rotation speed and linear velocity. A feedback system allows precision, like moving to designated positions, pausing movement, or returning to a start point.
Torque output corresponds to motor power, determining the actuator's effective force capability.
```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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