1. Introduction to
    control engineering

1.1 Open and closed loop control

In control engineering, we differentiate between open and closed loop control.

Open loop control

Open loop control is a process in a system in which an output variable is rigidly influenced by an input variable. This is based on the principles of the system.

The key characteristic is the open sequence of action. The output variable is not measured and is therefore unknown. Faults that cause unwanted changes in the output variable are not detected and therefore cannot be compensated for.

Control without feedback

closed loop control

Closed loop control is a process in a system in which an output variable to be controlled is continuously detected and compared with the input variable.

The result of this comparison is fed back to the system via a controller and influences its behaviour in the desired way. The aim is for the output variable to match the input variable.

This enables the influences of faults to be compensated for.

The key characteristic is the sequence of action in a closed control loop.

Control with feedback (control loop)

Open and closed loop control:
This video clearly explains what constitutes a system in control engineering and where the differences between Open and closed loop control lie.

Practical examples from industry

Open loop control:
3D-
Printer

  • simple

  • stepper motors

  • limited accuracy

  • faults are neglected

Closed loop control:
CNC
lathe

  • complex

  • position controlled

  • highly accurate

  • faults are corrected