A speed controller is a circuit which is created for the purpose of varying the speed of an electronic motor, or stopping it entirely. Speed controllers are mostly found on electrical linear actuators, and can either be a stand-alone unit, or a part of the linear actuator itself.
There are many reasons why linear actuator speed control is seen as important.
12 volt electric actuators are powerful pieces of machinery and are thus suited for a lot of different tasks. While some tasks are large and have plenty of space for the equipment to work, other tasks require delicacy or may take place in a confined space which will have an effect on the speeds which an actuator can safely be allowed to reach.
Linear actuator speed control is something which can be controlled while at the same time not sacrificing the overall force which a linear actuator can bring to the task at hand. Speed controllers work by adjusting the voltage which makes it 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, but it does not work in the other direction: linear actuators cannot be sped up faster than the top speed they would otherwise manage.
The best method of speed control for an actuator is to institute a velocity control loop which compares the velocity that the actuator can currently attain to the one which is required. Velocity comparison is done by calculating the difference between the position which the linear actuator will hit, and the one it is currently in, and comparing that with the velocity defined by the speed controller. Linear actuators which are controlled by speed controllers will constantly check and recheck their velocity, to prevent any mistakes.
Here you may find a wiring diagram on how to wire linear actuator to the rocker switch and to the speed controller:
It is important to remember that actuators might be negatively affected by the use of a speed controller. While linear actuator speed can only be reduced to a minimum of ten percent 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 is changed, that naturally also affects the movement of the actuator in other ways – 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 mean that the actuator will decelerate much more quickly when it is reaching the target, but too much runs the risk of the equipment overshooting the mark completely.
To stop the loop is a simple thing: what is known as a termination condition can also be called a PID position control. When this is in place, once an actuator has reached its target, the feedback loop collapses, and the equipment stops moving.
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 in the situation, the user can make accurate predictions about the output of the speed controller, and so will be able to make any adjustments which are necessary. A control loop for a speed control is obviously primarily to control the overall velocity of an actuator so that it is better suited for any given task which a user needs it to carry out. Assuming that all the variables will remain the same, feed-forward control will allow users to make an accurate guess as to how the duty cycle of the actuator will translate into velocity according to Sensor Value per second. This duty cycle is something which, when calculated, can be used to more accurately reach target velocity without any danger of either overshooting and missing the target completely, or stopping before it reaches the target, therefore negating the entire point of having the actuator there.
Users of speed controllers should be able to gain an accurate prediction of their actuator by using velocity values while testing their actuator before it is actually put into place. The tests should be carried out with the load which the actuator would be expected to carry, for best 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 out with all the loads before it is installed.