linear actuator is an actuator that creates movement in a straight line, in contrast to the conventional circular motion of a conventional electric motor. Linear actuators are used in machine tools and industrial machinery, in computer peripherals such as disk drives and printers, in valves and silencers, and in many other places where linear motion is required. Hydraulic or pneumatic cylinders inherently produce linear motion. Many other mechanisms are used to produce linear motion of rotating motors.
Video Linear actuator
Type
Mechanical actuators
Mechanical linear actuators usually operate with the conversion of rotary motion into linear motion. Conversions are usually done through several simple types of mechanisms:
- Screws : head screws, jack screws, ball screws and roller screws all operate on a simple machine principle known as a screw. By rotating the actuator nut, the screw shaft moves in a single line.
- Wheel and axle : Hoist, winch, rack and pinion, chain drive, belt drive, rigid chain, and rigid belt drive operate on wheels and axle principles. The rotating wheel moves cables, shelves, chains or belts to produce linear motions.
- Cam : The camera actuator functions on a principle similar to a wedge, but provides relatively limited travel. As a wheel-like rotating cam, its eccentric shape provides a thrust at the base of the shaft.
Some mechanical linear actuators are only interesting, such as hoists, chain propulsion and belt propulsion. Others just push (like cam actuators). Pneumatic and hydraulic cylinders, or lead screw can be designed to produce styles in both directions.
Mechanical actuators usually change the rotary motion of the control knob or handle the linear displacement through screws and/or gears with which the buttons or grips are attached. Jack jacks or cars are known mechanical actuators. Other actuator families are based on segmented spindles. The rotation of the jack handle is mechanically changed into a linear motion of the jack head. Mechanical actuators are also often used in the fields of lasers and optics to manipulate linear stage positions, rotary stages, mirror stands, goniometers, and other positioning instruments. For accurate and repeatable positioning, index indices can be used on the control buttons. Some actuators include encoders and digital position readings. This is similar to the adjustment buttons used on the micrometer unless the purpose is positioning rather than position measurement.
Hydraulic actuators
The hydraulic actuator or hydraulic cylinder usually involves a hollow cylinder having a piston inserted into it. The unbalanced pressure applied to the piston produces a force that can move an external object. Because the liquid is nearly incompressible, the hydraulic cylinder can produce the right linear piston displacement. The displacement is only along the piston axis. A well known example of a manually operated hydraulic actuator is a hydraulic car jack. Typically, the term "hydraulic actuator" refers to a device controlled by a hydraulic pump.
Pneumatic actuators
Pneumatic actuators, or pneumatic cylinders, are similar to hydraulic actuators unless they use compressed gas to produce a force, not a liquid. They work together with pistons where air is pumped in the chamber and pushed out from the other side of the room. Air actuators are not always used for heavy-duty machines and instances where there is a large amount of weight. One of the reasons pneumatic linear actuators are preferred for other types is the fact that the power source is just an air compressor. Since air is the source of input, pneumatic actuators can be used in many places of mechanical activity. The drawback is, most air compressors are big, big, and hard. They are difficult to move to another area after installation. Linear pneumatic actuators tend to leak and this makes them less efficient than mechanical linear actuators.
piezoelectric actuators
The piezoelectric effect is the property of a particular material in which the application of stress to the material causes it to expand. Very high voltage only relates to small expansions. As a result, piezoelectric actuators can achieve a very fine position resolution, but also have a very short range of motion. In addition, piezoelectric materials exhibit hysteresis which makes it difficult to control their expansions repeatedly.
Electro-mechanical actuators
Electro-mechanical actuators are similar to mechanical actuators except that the control knob or handle is replaced by an electric motor. Motor rotation is converted to linear displacement. There are many modern linear actuator designs and every company that manufactures them is likely to have a proprietary method. The following is a general description of a very simple electro-mechanical linear actuator.
Simplified design
Typically, the electric motor is mechanically connected to rotate the lead screw. The tin screw has a continuous helical thread on its perimeter along the length (similar to a screw thread). Threaded to the main screw is a nut or a ball nut with a corresponding helical thread. The nuts are prevented from spinning with lead screws (usually nut connections with non-rotating parts of the actuator body). Therefore, when the main screw is turned, the nut will be moved along the thread. The direction of movement of the nut depends on the direction of rotation of the lead screw. By connecting the relationship to the nut, the movement can be converted to a usable linear displacement. Actuators are currently built for high speed, high strength, or compromise between the two. When considering actuators for specific applications, the most important specifications are usually travel, speed, power, accuracy, and lifetime. Most varieties are installed on the damper or butterfly valve.
There are many types of motors that can be used in linear actuator systems. This includes a dc brush, brushless dc, stepper, or in some cases, even an induction motor. It all depends on the application requirements and the actuator load is designed to move. For example, linear actuators using induction motors AC integral horsepower driving lead screw can be used to operate large valves at refineries. In this case, high motion accuracy and resolution is not required, but the strength and speed are high. For electromechanical linear actuators used in laboratory instrumentation robotics, optical and laser equipment, or X-Y tables, subtle resolution in micron range and high accuracy may require the use of a fractional linear actuator stepper motor with a fine pitch delivery screw. There are many variations in the electromechanical linear actuator system. It's important to understand the design requirements and application limits to find out which one is the best.
Standard construction vs compact
Linear actuators using standard motors will usually have a motor as a separate cylinder attached to the actuator side, either parallel to the actuator or perpendicular to the actuator. The motor can be attached to the end of the actuator. The driving force is a typical construction with a solid drive shaft directed to the drive nipple or the actuator drive screw.
The compact linear actuator uses a specially designed motor that tries to adjust the motor and actuator into the smallest possible shape.
- The inner diameter of the motor shaft can be enlarged, so the drive shaft can be hollow. The drive screw and nut can occupy the center of the motor, without the need for additional gears between the motor and the drive screw.
- Similarly the motor can be made to have a very small outer diameter, but the polar face is stretched lengthwise so that the motor still has a very high torque when mounted in a small diameter room.
Principles
In most linear actuator designs, the basic principle of operation is from the incline. The lead screw thread acts as a continuous ramp that allows small rotational forces to be used over long distances to achieve large load movements over short distances.
Variations
Many variations on the basic design have been made. Most focus on providing general improvements such as mechanical efficiency, speed, or higher load capacity. There is also a great engineering movement against actuator miniaturization.
Most electro-mechanical designs include lead screw and tin nut. Some use ball screw and nut ball. In both cases the screws can be connected to the motor or manual control buttons either directly or through series of gears. Gears are typically used to allow smaller (and weaker) motors to rotate at higher rpm to be directed downward to provide the torque necessary to rotate the screws under a heavier load than the motor that will be able to drive directly. This effectively sacrifices the actuator speed in favor of increased actuator thrust. In some applications the use of common worms because it allows smaller dimensions are built still allow a great long journey.
A journey-bean linear actuator has motors that remain attached to one end of the lead screw (perhaps indirectly through the gear box), rotating motor screw lead, and controlled tin bearing from spinning so as to trip up and down the lead screw.
Linear actuator winding circumference has a main screw that is passed entirely through the motor. In a linear actuator winding around, the motor "creeps" up and down the main screw that is controlled from the spinning. The only rotating part is inside the motor, and may not be visible from the outside.
Some major screws have many "starters". This means they have multiple threads alternating on the same axis. One way of visualizing this is compared to some of the color lines on candy canes. This allows further adjustment between the screw pitch and the screw/screw threaded contact area, which determines the speed of the extension and load carrying capacity (of the yarn), respectively.
Static load capacity
Linear screw actuators can have static loading capacities, which means that when the motor stops the actuator it basically locks in place and can support an interesting load or push on the actuator. This static load capacity increases mobility and speed.
The actuator braking force varies with the angular pitch of the screw thread and the special design of the thread. The Acme thread has a very high static load capacity, while the ball screw has a very low load capacity and can be almost free-floating.
It is generally not possible to vary the load capacity of a static threaded actuator without additional technology. Threaded screw holder and drive nut design determine specific non-dynamically adjustable load capacity.
In some cases, high viscosity grease can be added to the linear screw actuator to increase the static load. Some manufacturers use this to change the load for special needs.
The static load capacity can be added to a linear screw actuator using an electromagnetic brake system, which applies friction to a spinning drive nut. For example, a spring can be used to apply brake pads to the drive nut, holding it in position when the power is off. When the actuator needs to be moved, the electromagnet fights against the spring and releases the braking force on the drive nut.
Likewise the electromagnetic ratchet mechanism can be used with a linear screw actuator so that the drive system that lifts the load will lock its position when power to the actuator is turned off. To lower the actuator, the electromagnet is used against the strength of the spring and open the ratchet.
Dynamic load capacity
The dynamic load capacity is usually referred to as the number of linear actuator forces that are capable of providing during operation. This style will vary with the type of screw (the amount of friction restriction movement) and the motion motion motors. Dynamic load is a figure that most actuators are classified by, and is a good indication of which applications will be most appropriate.
Speed ​​control
In most cases when using an electro-mechanical actuator, it is preferred to have some type of speed control. Such controls vary the supplied voltage to the motor, which in turn changes the speed at which the lead screw changes. Adjusting the gear ratio is another way to adjust the speed. Some actuators are available with several different setting options.
Duty cycle
Motor duty cycle refers to the amount of time the actuator can run before it needs to cool down. Staying in this manual when operating the actuator is the key to longevity and performance. If the cycle rate is exceeded, then overheating, loss of power, and ultimately burning the motor is risky.
Linear motors
Linear motors are functionally the same as rotary electric motors with rotors and stator circular magnetic field components arranged in a straight line. Where the rotating motor rotates and reuses the same magnetic pole again, the linear magnetic field structure of the motor is repeated physically along the length of the actuator.
Because the motor moves linearly, no lead screw is needed to turn the rotary motion into linear. While high capacity is possible, the limitations of materials and/or motors in most designs are surpassed relatively quickly because of their dependence solely on magnetism and repulsion forces. Most linear motors have low load capacity compared to other types of linear actuators. Linear motors have advantages in the outer or dirty environment because the two parts need not be related to each other, so the electromagnetic driving coil can be watertight and closed to moisture and corrosion, allowing for very long life.
Telescoping linear actuator
Telescoping linear actuators are special linear actuators that are used where there is a space restriction. Their range of motion is many times greater than the length of the non-longest moving member.
The general shape is made of concentric tubes of about the same length that extend and pull back like arms, one inside the other, like a telescopic cylinder.
Another more specialized telescope actuator uses a propulsion member which acts as a rigid linear shaft when extended, but breaks the line by folding, splitting it into pieces and/or unrolling when pulled back. Examples of telescopic linear actuators include:
- Helical band actuators
- Rigid belt actuator
- Rigid chain actuators
- Spindle segmented
Maps Linear actuator
Advantages and disadvantages
See also
- Helical band actuators
- Hoist
- Shelves and pinion
References
External links
- Leo Dorst's linear actuator
Source of the article : Wikipedia
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