Open-loop controller

[2] It does not use feedback to determine if its output has achieved the desired goal of the input command or process setpoint.

"[4] An open-loop controller is often used in simple processes because of its simplicity and low cost, especially in systems where feedback is not critical.

The drawback of open-loop control of steppers is that if the machine load is too high, or the motor attempts to move too quickly, then steps may be skipped.

For this reason, more complex robots and machine tools instead use servomotors rather than stepper motors, which incorporate encoders and closed-loop controllers.

However, open-loop control is very useful and economic for well-defined systems where the relationship between input and the resultant state can be reliably modeled by a mathematical formula.

For example, determining the voltage to be fed to an electric motor that drives a constant load, in order to achieve a desired speed would be a good application.

In order for the conveyor to run at a constant speed, the voltage of the motor must be adjusted depending on the load.

Thus there are many open-loop controls, such as switching valves, lights, motors or heaters on and off, where the result is known to be approximately sufficient without the need for feedback.

This means that whenever the load is being accelerated or decelerated, a proportional amount of force is commanded from the actuator regardless of the feedback value.