What you need to know when sizing a Linear Actuator
This article will help you size an appropriate linear actuator for your application and will cover some key criteria that can used to identify the actuator that is right for you. If you feel you need to learn more about linear actuators first, check out our Actuator 101 blog or our How Linear Actuators Work post.
Sizing an Actuator can be put into 3 main sections. 1. Force required, 2. Stroke needed and 3. Speed required. Typically one of these will be the most important to you like the stroke because to open or close something the stroke is something that cannot be traded-off. Strokes are the distance the actuators move through. Force, is typically next and represents how much force is required to push or pull the device you want to move. lastly Speed, this is the feature most people need and so it can be traded-off against force. Remember, the higher the force the lower the speed, and visa versa.
Lets go through each feature one by one:
Force
The force you require from your linear actuator is related to how much weight you are pulling, pushing, lifting or holding. There are two types of force specifications that linear actuator manufacturers will give: Dynamic and Static and the units we are are pounds (lbs) you may also see Newtons (N) used too.
Dynamic Force (or load) is the maximum force the actuator can apply to move an object. You will use this specification to determine whether or not an actuator will be able to move your desired load. Some linear actuators will have a different dynamic load specification for pushing and pulling, which means that the actuator cannot push or pull the same maximum force.
Static force (or load) is the maximum weight the actuator can hold when it’s not moving. Static load limit is important to consider in applications like a Sit-Stand Desk, where the actuator may be expected to hold a large weight when not moving.
The force you require in any application depends on more than just the amount of weight you are moving, but also the number of actuators in use and the physical geometry of your design. To determine the exact force requirements, you can apply two basics physics formulas: summation of forces and summation of torques. If you are only moving an object along one axis, you simply need to ensure the total force from all your actuators is greater than the weight you are moving, like the block diagram to the right. But if you are using actuator to open a lid, for example, this becomes more complex because forces involved will be applied at different angles. If you are good at trigonometry and you know your physics, you can use the summation of forces and torques to determine your exact force requirement. But if not, you can use our handy Linear Actuator Calculator, which is designed just for these difficult situations.
NOTE: Once you have determined your desired force requirement, it is best practice to select an actuator that has a greater static and dynamic force specification that you require as these specifications should be the absolute limits of your operational capacity.
Stroke Length
The distance you need to move an object with a linear actuator is your stroke length requirement. You may need to use some trigonometry to identify the exact distance you need from your desired linear actuator in applications like opening a lid. Depending on the type of actuator you are using, the stoke length might mean something slightly different (i.e. like in track actuators, the stroke length is the length of the track). But for the most part, once you know the distance you want your linear actuator to move, you should choose an actuator with a stroke length at or above that value. Stroke length will impact some of features of the linear actuator including the total length.
Speed
In some applications, speed will be a key requirement in your design, while in other situations, it may be less important than stroke length or force. Like stroke length, if you have a desired speed that you want your actuator to move, then you should select a linear actuator with speed specification at or around your desired speed. Although, the actual speed at which your actuator will move at will be affected by size of the load it is moving. This affect is not always significant, but some linear actuators manufacturers will provide Speed vs Load performance graphs, like below, that allows you to get an estimate of the actuator’s speed for a given load.
Generally speaking, for electronic linear actuators, the higher force actuators will move slower than low force actuators. If you need a high-force and high-speed actuators, you may need to consider other types of actuators.
Top speed is not always important, sometimes you want control. If you require speed control, you will need to interface your actuator with a motor driver and Arduino microcontroller. You’ll want to want to make sure that your actuator can easily be able to interface with your motor driver and potential provide feedback if closed-loop control is desired.
Power Requirements
There are two aspects of the power requirements for any electronic linear actuator, voltage input and max current draw. Input voltage or rated voltage is the voltage the actuator is designed for and should be the maximum voltage supplied to the actuator. Input voltage can be either AC or DC and are typically standard values, like 12V DC or 120V AC. Max current draw is the maximum amount of current the actuator will safely draw and unlike voltage, the actual current draw of your actuator should by lower than this value. The actual current draw of your actuator will be a related to the size of the load on the actuator, a larger the load will result in higher current draw.
If your actuator is the main electro-mechanical feature of your project, you can simply use its power requirements to identify the power supplies and other electrical components for your project. But in more complex system, like a robotic platform, you may be constrained to a particular voltage or maximum current draw. Power requirements will also be important in battery powered applications as the higher your current draw, the faster your battery will die. If possible, you could use a higher voltage actuator (i.e. going from 12V to 24V) as higher voltage actuators will draw less current for the same level of force and speed.
Application Specific Considerations
While this blog has covered some key specifications to size your linear actuator, there will always be application specific needs you’ll need to consider when selecting the right linear actuator. Like the environment in which your actuator will be in working, which may impact durability and would include specifications like operating temperature, enclosure protection class (IP), and material of the actuator. Physical size and mounting options available for an actuator may or may not work within project. Other important requirement considerations include: duty cycle requirement, noise level requirement, or a feedback requirement.
Now that you have the needs tools to size the right actuator for your needs,, you can check our selection of linear actuators at Firglli Automation.
[1] https://techathlon.com/ip68-ip67-code-rating-smartphones/
