Overview

7.1. Overview#

A control system is the decision-making part of a mechatronic device. It continuously reads values from sensors and then commands actuators to perform tasks. In a modern system with a microcontroller, the control system is almost always implemented in software, usually as an infinite loop that constantly checks sensor data and decides what action to take next.

There are two broad categories of control:

  • Open-Loop Control - Actions are carried out without checking the result. The system does not know if it achieved the goal.

  • Closed-Loop Control - Actions are adjusted based on sensor feedback. The system constantly compares what it wants to happen with what is actually happening.

A toaster is a simple example of open-loop control: once started, it runs the heating element for a fixed time regardless of how brown the bread becomes. An oven, by contrast, is a closed-loop system: it measures the internal temperature and switches the heater on and off to keep the temperature close to the setpoint.

../../_images/open_closed_loop.png

7.1.1. Open vs Closed Loop#

In this module we will begin with open-loop systems, looking at their strengths and weaknesses. These systems are simple, low-cost, and useful when the environment is predictable. But they are also limited, because they cannot adjust when conditions change.

We then introduce closed-loop systems, where sensors provide feedback to the controller. Feedback allows the system to correct errors, resist disturbances, and achieve much more precise behaviour. Control Methods

Within closed-loop systems, there are several different control strategies. We will explore them in increasing complexity:

  • Bang-Bang Control (also called On/Off Control) - The simplest form of feedback. The controller switches the actuator fully on or off depending on whether the measurement is above or below the target. Examples include thermostats, fridges, and automatic doors.

  • PID Control - A more advanced strategy widely used in robotics, drones, cars, and industry. PID stands for Proportional–Integral–Derivative. Each part contributes in a different way to reduce error and keep the system stable. We will study P-only, PD, and full PID control to see how each improves performance.