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A speed controller is a circuit that is created to vary the speed of an electronic motor or to stop it entirely. Speed controllers are mostly found on electrical linear actuators and can either be a stand-alone unit or part of the linear actuator itself. Linear actuator speed control can be regulated without sacrificing the overall force that the linear actuator can bring to the task at hand. Speed controllers’ function by adjusting the voltage that passes through to the actuator itself. With no voltage, the linear actuator cannot function as well as it otherwise might.
Speed controllers allow users to slow down and even stop the linear actuators they are keyed to. Linear actuators cannot, however, be sped up. They will not function above the top speed they can manage. The best method of speed control for an actuator is to institute a velocity control loop that compares the velocity that the actuator can currently attain to that which is required.
Velocity comparison is done by calculating the difference between the position in which the linear actuator will hit and the one it is currently in. This is further compared with the velocity defined by the speed controller.
Linear actuators that are controlled by speed controllers will constantly check and recheck their velocity to prevent any mistakes. Below is a wiring diagram on how to wire a linear actuator to the rocker switch and the speed controller.
A video has also been provided below that includes instructions on how to connect a linear actuator to a DC speed controller. A DC speed controller is very useful to control the speed of an actuator, especially when two or more actuators are used at the same time. The DC speed controller will even out the speed for both electric motors. It is important to remember that actuators might be negatively affected by the use of a speed controller. While a linear actuator’s speed can only be reduced to a minimum of 10% of the overall motor speed, having a speed controller limiting the motor in this manner can reduce the efficacy of the actuator when it comes to working with heavy loads. When the speed of an actuator has changed, the movement of the actuator is naturally affected. The speed of an actuator can be changed for both directions, but that requires specific equipment outside of a speed controller.
Target velocity is, as said above, the difference between the current and target positions taken and multiplied by what is called a control gain. Increasing this will decelerate the actuator much faster when it is reaching the target. Too much of an increase runs the risk of the equipment overshooting the mark completely. To stop the loop, you would simply need to implement the termination condition, also known as the PID position control. Once this is in place and the actuator has reached its target, the feedback loop collapses, and the equipment ceases movement.
When it comes to linear actuators and speed control, there is a concept known as feed-forward control. Feed-forward control works on the assumption that, as the controller, the user can make accurate predictions about the output of the speed controller. They will thus be able to make any necessary adjustments. A control loop for speed control exists primarily to regulate the overall velocity of an actuator so that it is better suited for any given task. Assuming that all the variables remain the same, feed-forward control will allow users to make an accurate assumption as to how the duty cycle of the actuator will translate into velocity based on Sensor Value per second. This duty cycle is something that, when calculated, can be used to accurately reach target velocity while avoiding any errors in assumption. This includes the danger of overshooting and missing the target completely or stopping before it reaches the target, therefore negating the entire point of having the actuator.
The tests done for these user predictions should be carried out with the load which the actuator would be expected to carry, to ensure accurate results. It should be noted that these kinds of calculations will not work if the load which an actuator is expected to carry will change sporadically. For the calculations to work, users should test the actuator with all the loads before it is installed.