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How a Linear Actuator actually works
Inside a Linear Actuator - How a Linear Actuator works.
It Starts with Rotational movement.
We thought you would like to understand exactly how a Linear Actuator works, and that if you understand the basic principals, you would then understand why there is always a Force/Speed trade-off, and how that's important for you when selecting the correct Actuator for your application.
Linear Actuators typically work under the same principal, and that is to convert rotary motion of an AC or DC motor, into Linear motion via a Leadscrew. Most actuators are powered by typically 12V-24 DC motors to create the rotary motion. Through gears and a Leadscrew that rotary motion gets converted to linear motion.
What else is inside an Actuator?
90% of Linear Actuators come with built-in limit switches to automatically stop the Actuator when it gets to the end of its stroke, both in the extended and retracted positions. Other main components include the gearbox, a lead-screw and an acme drive nut that also doubles to engage the limit switch once it reaches its end of stroke position, either extended or retracted. The gears are simply used to reduce the speed from the DC motor that in turn increases the torque force, and when its converted to Linear motion via the leadscrew, it also offers more Linear Force. So as you can expect, the lower the gear ration the lower the force, but higher the speed. Changing these gears is how we offer different speeds and forces for all our Actuators. Below shows the inner workings of an actuator as we are running the motor in both directions.
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. 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 will use a high gear ratio, but this decreases speed and visa versa. Remember the DC motor speed is constant with voltage, running with a higher voltage increases the speed but may reduce life cycle.
All Good Things Come to an End
One of the most important components in a linear actuator are built in end of limit micro switches. These are very important because without these the actuator will simply try to keep moving even when its reached the limit of its travel. The result will be either a mechanical failure internally probably with the DC motor burning out because its still wanting to keep rotating.
You maybe wondering how you are able to reverse an actuator once it triggers the limit switch?. Well as you can see in the diagram below each limit switch also has a DIODE. Diodes work as a sort of one way Check Valle for electricity. They allow flow in one direction but not the other, This means you can still reverse the polarity of the motor and even though it will not go in one direction because its at the end of its travel, the Actuator can still go in the other direction.
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.
To view all our Linear Actuators click here