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Actuators are devices designed to convert energy into motion. For different types of actuators energy comes in different forms: mechanical, electrical and potential energy stored in compressed liquids or gasses.
Most commonly, actuators are used to achieve either linear or rotational motion and when connected to other components a wide range of applications can be covered. Click on this link to see some common applications actuators can be used for.
Based on the energy source, linear actuators are categorized primarily as electromechanical, mechanical, pneumatic and hydraulic.
Both pneumatic and hydraulic actuators utilize the pressure pushing against a piston to produce force and potion. In the case of hydraulic actuators pressure arises in the form of compressed liquid and in the case of pneumatic actuators in the form of gas.
Mechanical actuators convert one type of motion into another. In the case of linear mechanical actuators rotational motion is converted into linear using a gears or screws. Electro-mechanical linear actuators utilize motors to produce rotational motion which is then converted into linear motion using screws, gears or other mechanical elements.
Actuator Parts & Components
Some terms and parts are common to most linear electric actuators. The term stoke for linear actuators refers to the maximum distance of the actuator motion. The length of the actuator body will depend on its stroke, the longer the stroke the longer the actuator body. The actuator can't be shorter than its stoke, and it is usually at least 2 times longer then its stroke.
Mounting brackets are used to make the connection between the linear actuator and the other parts and system components. Pin and clevis type brackets are the most common for actuator mounting. Proper mounting backers are chosen to allow linear motion of the actuator and to minimize any side loading perpendicular to the axis of motion.
The rod is the central part of the linear actuator which extends in and out of the actuator housing. The force is supported or "applied" through the rod in the direction of its motion. Linear actuators are usually not designed to support high loads in other directions.
An electric motor is at the heart of the electric actuator and it is used to drive the mechanism which extends the rod. There are various types of motors that are used in linear actuators, but DC motors are most common.
Linear electric actuators also vary in the way how the motor is integrated in to the actuator body. Some actuators have the motors attached on the side, beside the main body and others have the motor integrated within the body in line with the rod.
Regardless of the type all motors require a power input and a control circuit. Simple control circuits contain only a power supply and a 3 way switch (forward, reverses and off). For a sample wiring diagrams click here.
If the actuator utilizes a DC motor then it will require a DC power supply. Depending on the application the power supply can be chosen to take AC power from a standard 110 V (or 220 V) circuit or it can be powered by batteries. Some higher power actuators utilize AC motors and can be powered directly from the AC circuit without a power supply.
The power and the speed of an electric actuator depend on its motor, as well as the gearing between the motor and the screw. The more powerful motors can move higher loads and move them quicker. However, high power motors are bigger, more expensive and require more electric power. The same motor can be geared down to apply higher load or geared up to achiever higher speed, but unfortunately not both. The mechanical power of a linear actuator Pm is given by the following relationship of its velocity (or speed) v and applied load (or force) F:
Pm = F x v
The above relationship means that at higher speeds the actuator can only move a lighter load than at a lower speed.
Linear electric actuators are usually specified based on their stroke, speed and load capacity, as well as physical dimensions operating environment. Other characteristics such as duty cycle, end play, repeatability, overload protection, integrated brake systems are also taken into consideration during more in-depth design.
Another important actuator parameter, that a user might wish to consider, is its electric power consumption, especially when the actuator will be power using batteries. The electric power draw (Pe) of a linear electric actuator is established based on the actuator operating voltage (V) and its current draw (I):
Pe = V x I
Conventionally the information on the relationship between the force, the speed and the current draw of an electric actuator is provided by the manufacturers as a graph or a table. See below for example.