Inside a Linear Actuator - How a Linear Actuator works
Most Linear Actuators work under the same principal. This particular actuator is powered by a 12VDC brushed motor. It comes with built-in end of travel limit switches to prevent over extension and retraction, a standard feature for our products. Other main components will be the gearbox, lead-screw and acme drive nut which also engages the limit switch once it reaches a certain position. The above picture shows the Linear Actuator in the middle of its stroke travel, meaning it can retract or extend until it reaches the limit switch.
A linear actuator by definition is a motion controlled device that will move objects in a linear direction. Rotational motion is first generated by the electric motor, often in the thousandths of revolutions per minute, and then the ACME leadscrew converts Rotary motion into Linear Motion.
This high speed rotational motion of the motor is then reduced in speed by the gearbox and that also increases the torque that will then be used to turn the lead-screw. Gearboxes often have a reduction ratio such as “100:1” which means for every 100 rotations of the motor, there will be 1 rotation on the final gear of the gearbox which is connected to the lead-screw where the ACME drive nut is attached to move the final Shaft/Rod in a Linear motion.
The combination of the ACME leadscrew and ACME drive nut resulting in the linear motion of the Rod/Shaft is the very same principal as driving a screw into a piece of wood. With Firgelli Actuators we change the length of the leadscrews and Rods/Shafts to get longer or shorter strokes, and we change the gear ratios to give you different options such as force and speed. You can expect because the speed of the DC motor is constant the force and speed always trade-off against each other. This means for a high force Linear Actuator we use a high gear ratio, but this decreases speed and visa versa.
One of the most convenient additions to a linear actuator are built-in end of travel limit switches. Essentially this prevents the actuator from reaching the physical movement limits of the housing which will likely cause the motor to burn out. It also allows for a smoother stopping motion once the end of travel is reached.
The method used in Linear Actuators to stop the Actuators shaft movement at the end of each stroke is by using Micro-Switches to cut the power to the DC motor when the limit is triggered. The Micro-switches have Diodes on them that allow you to reverse the polarity to change direction and the motor can operate in reverse even whilst the limit switch is triggered. Diodes work as a sort of one way street. So Electricity can only go in one direction through a Diode but not in reverse. Once the drive shaft has retracted and is no longer touching the extend limit switch, then electricity goes through the limit switch again allowing movement in both directions.
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