Linear Actuators

You may not be familiar with the term linear actuators but odds are very good that you have seen them in action. Linear actuators are devices that generate controlled physical linear movement. There are many ways of achieving this linear displacement, and a few common examples are listed below.

Perhaps some of the most common types are the hydraulic linear actuators. This type consists of a hollow cylinder with a piston inserted into the cylinder. The two sides of the piston (top and bottom for lack of a better definition) are alternately pressurized and then de-pressurized to achieve controlled precise linear displacement of the piston. This, in turn, moves whatever is connected to the piston. The physical movement is only along the axis of the piston and cylinder.

Other types of linear actuators are the electro-mechanical actuators. These types will convert rotary motion into straight line motion. In general, a rotary driver which can be an electric motor or hydraulic motor is mechanically connected to a long shaft that is commonly referred to as the "screw". The rotary motion of the electric motor will turn the screw shaft. The screw shaft has a continuous helical thread machined on its circumference running along the length of the shaft. The screw is inserted into another mechanical body called the ball-nut. The ball-nut also has a matching helical thread machined on its inside diameter. Because the balls are trapped in these matching grooves the ball-nut will convert this rotary motion into linear motion as it turns.

Linear actuators can also be in linear motor form. What this means is that a rotary electric motor is simply laid on its side on a flat surface.

There are many advantages to using linear actuators. One of the most important advantages is that they are self-contained. Also, they only require electrical power and a control interface to use them, making them easy to maintain and easy to operate.

As well, linear actuators can be operated in parallel, using multiple actuators to perform a single task. This gives them an incredible amount of power. The last advantage is that they can be very precise in their movements.

There are also some disadvantages to linear actuators. The most common disadvantage being hydraulic actuators can start leaking and are difficult to control. The electro-mechanical actuators are prone to mechanical wear and tear and will need careful maintenance. And the linear motor types cannot achieve high load capacities.

However, when linear actuators are used in the proper manner and for the proper job, they can be very successful.