There are many different ways to implement this motion with the help of an engine. The most popular one is with the help of slider, moving along the guide. The use of such linear actuator varies widely, they can be used in virtually any device – for adjusting the position of the TV, for lifting and lowering ramps for wheelchairs, in industrial equipment, in toys and even in aviation and cosmic technologies.
In the design of linear electric actuators, a helical gear is most often used to create a linear movement. The screw rotates clockwise or counterclockwise, its rotation causes a linear movement.
The motors used in linear actuators are in most cases classic 12V or 24V DC collector motors. But in some cases other types of electric motors and other voltages can be used. In order to change the direction of movement of the linear actuator rod, it is necessary to change the direction of rotation of its motor. In the case of using a DC collector motor, it is enough to change the polarity of the supply.
The existing linear actuators differ in the possible stroke length. With regard to the design of the actuator, this means that the actuators are made with different stem and body lengths. In addition to the stroke length of the actuator, the important characteristics are the speed and force of the rod. To achieve the necessary speed and force between the motor shaft and the screw, a mechanical gearbox is installed. The gear unit with constant engine power changes the ratio of its rotation speed and torque, which ultimately affects the final speed of linear displacement and the force on the actuator rod – the greater the gear ratio, the greater the force and less speed. The screw is also a mechanical transmission, affecting the ratio of speed and force – the smaller the pitch of the screw, the greater the force and the less the speed of rod movement. In any case, without the use of special devices for controlling the speed of the engine, the relationship between the force and the speed of movement is always observed: the higher the rod’s travel speed, the less the force (and vice versa).
To stop the rod in end positions, the actuator is equipped with built-in limit switches (limit switches or microswitches). The limit switches are installed internally on the actuator stem. Triggering of limit switches occurs when the nut reaches the extreme positions inside the actuator – one sensor is set to an extreme extend position, the second – to an extreme retracted position. When the end position is reached, the sensor is activated, the motor power is turned off. Further movement is possible only in the opposite direction – with a change in the polarity of the supply and the reverse of the motor.
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To select the appropriate linear actuator, you need to determine the basic requirements of the system:
- speed of movement (m / s, mm / min, cm / min, mm / s, etc.)
- force of displacement (pushing / pulling back) (N, kgf)
- stroke length (mm, cm, m)
- preferred supply voltage (12V, 24V, 220V)
- longitudinal or transverse position of the engine
This is when the speed controller can help. A speed controller is a device to regulate the speed of your linear actuator or even make it stop. In some cases speed controllers are installed within actuators and in some cases you should buy the one and install it by yourself.
Such controllers are essential in using linear actuators. The point is that some work should be done in a higly delicate way and there is no space for a mistake. This is when speed controllers become handy. Besides, they help you control the speed without any sacrifices in actuator’s power. Another important thing here is that speed controller can influence the speed and stop the device but it surely cannot speed it up.
