Linear Actuators vs Linear Servo Actuators. How do they really differ?

Linear actuators and linear servo actuators are perhaps not as different as many people suppose; they have the same basic function and can fulfill many of the same tasks. However, people can sometimes have difficulty when they need to choose a linear actuator or a linear servo actuator, as the two are very similar in use and in profile.

As this article will show, linear actuators and linear servo actuators are more similar than is perhaps generally known. By going through the differences as well as the similarities in a linear actuator working principle and a linear servo motor people will come to realise the similarities in each piece of equipment and see how both of them can be used in harmony with each other.

Linear Actuator: Working Principle

A linear actuator comes in various forms: the most recent form of actuator is an electric linear actuator, but they come in hydraulic and pneumatic forms as well, both of which are fairly popular for the jobs which they can be used in.

Actuators take the rotational movement of a normal motor and transpose it into linear motion, which can then be used in any particular machinery which requires linear motion over rotational. The actuator normally consists of a linear actuator motor, a cylinder which houses a tube and lead screw, which travels up and down the cylinder, creating the motion.

The movement of a linear actuator can be used in a variety of different industries, from robotics to computing, with linear actuators used in everything from robot arms and fingers to disk drives and valves of all kinds.

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Our 12v Track Linear Actuator

Servo Actuator: how does a Servo Work?

A servo actuator is best understood in two separate terms – the servo motor itself consists of three major parts: the motor (usually a DC motor), a potentiometer (a resistor with two or three terminals which forms a voltage divider through the use of a contact. It can act as a rheostat rather than a potentiometer if there are only two terminals in use), and a single control circuit. The control circuit and motor are attached by a series of gears, and as the motor works, the potentiometer changes resistance to allow the circuit to better control the energy being used and put out by the motor.

A linear servo actuator is, quite simply, a linear servo put into a linear actuator format. So any linear servo actuator would have the same motor, potentiometer and circuits, but would also have a cylinder and lead screw with which to determine the motion.

Differences between Linear Actuator and Servo Motor

Linear actuators are used in a variety of different industries, as has been said, and the invention of the linear electric actuator has only increased the number of areas which it can be used in. Since linear actuators are known for the customisation which can be done to every single aspect of them, this is most likely the biggest difference when it comes to the linear actuator vs servo debate.

Linear actuators can be controlled in a variety of ways, but the speed is something which, once it is set, cannot be changed. Servos allow for the control of linear motion while it is in motion.

Similarly, linear actuators can only be reversed if the polarity of the battery is shifted. This is not the case with servos.

Linear actuators can be fitted with limit switches which automatically stop the cylinder’s movement after a certain amount of time. Servo actuators need to have specific programmes put in place for this to be taken care of.

So Which Should You Choose?

While it does seem like there can be only one choice in the actuator versus servo debate, given the limits which are put on servos, and the customisation ability of linear actuators, the simple answer is that you should choose the best piece of equipment for your project.

Linear actuators are better for precision tasks, it seems, as they can be customised for many different projects and also have limits built into the actuators themselves which keep the motion from going past set limits. Actuators are also useful because they do not draw power when they are standing still – anybody who is wanting to save money or electricity will find that helpful.

Servos, on the other hand, can be programmed to stop whenever their limit has been reached, and people who use them can control the speed of the actuator while it is in motion. These would, therefore, be useful in particular tasks where a steady state of being is not something which is required.

Advantages/Disadvantages of Linear Actuators

  • Mechanical actuators have the advantages of being cheap, self-contained, and non-reliant on a power source, but this comes with the disadvantage of the actuator being entirely manually powered, with no option for automation
  • Electro-mechanical actuators share many of the advantages of mechanical actuators, along with the added benefit that they can be automated. However, this comes with the downside of having a lot of moving parts, which can increase wear and repair time
  • Electric linear (particularly 12 volt electric actuators) actuators have advantages in terms of having a minimum of parts, being capable of high speeds, and extreme precision. This disadvantages of this actuator are that they generally are only capable of low or medium force.

Advantages/Disadvantages of Servo Motors

    Advantages of servo motors include the following:

  • Low cost overall/low cost drive
  • Smooth rotation at low speeds
  • No power is used when the servo isn’t moving
  • The servos can attain high speeds.
    Disadvantages include the following:

  • Lots of maintenance is required
  • Installing them is costly
  • Servos have bad thermal performance
  • It can be difficult to maintain them in hazardous environments

Conclusion

Linear actuators and servo motors are not as different as people seem to think, as this article set out to show. There are similarities between the two, as well as differences, but these differences are so minor that when it comes down to choosing between actuators or servos for a job, the choice can often be as simple as ‘which one works best’.

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