Feedback Control System !!!
Let’s start with a scenario, in a cricket match bats man hits a long shot and after it, fielder is running for a catch. He is continuously monitoring that ball and adjusts his speed and body position so that he could catch that ball.
So what was that? It is a perfect example of feedback control. Fielder is getting information by continuous monitoring of ball and by the use of that information he is controlling his body speed and position.
In robotics and other control system feedback control plays an important role. To understand the feedback control we should start from feedback.
What is feedback in control System?
Feedback is basically a signal. It is result of an action which happened on physical word. Feedback may be Analog or Digital signal, well it is depend on instrument which detect action and generate an electrical signal.
What is feedback loop in control system?
In a control system, method for getting feedback from an action to controller is called feedback loop. The purpose of feedback loop is to provide information from field to control centre. Further these feedback loops can be classified in two categories. One is open feedback loop and other is Close feedback loop.
A feedback loop is a powerful design aspect for a control system. In Robotics feedback control system is widely used. All robot actuators operate on basis of feedback control system. Now to understand the open and close feedback loop, first we have to understand open and close loop control system.
What is Open Loop control System?
Here control system doesn’t consider feedback signal in processing of control command. These feedback are only used by operator and control command works on predefined logic.
What is Close Loop Control System?
Here the system output command is based on its feedback signal. Feedback signal mixed with system desired output variable and generate an error. And in the basis of control algorithm error signal generated output command. A proportional–integral–derivative controller (PID controller) is widely used in industry for a continuous close loop control system. So getting feedback, processing it and generating a command to control action is called feedback loop. This type of control system is also called close loop control system.
How to implement feedback control system in robotics?
First we have to choose sensor for our robot. There is a lot of verity available for sensor. I will recommend active sensors because they don’t required a separate power source and can be easily compatible with a micro-controller board. Remember operating voltage level of sensor should be equivalent to the voltage of microprocessor input and output terminal. Generally it will be 5 volt. If there is difference of operating voltage your sensor will not work.
For different purpose there are different sensors. For example detection of position you can use limit switches, RF type proxy sensors and magnetic sensors. Light dependent resister is also a good choice for detection of obstacle but it causes a lot of disturbance due surrounding lights.
Well after assembling your sensor come to the programming part. Here you will write an algorithm and program you bot behavior for a particular sensor signal. For more details of programming a bot please check my blog “6 Must Know Languages for coding a Robotic Project.”
Before coding a program you should understand about your robot actuator. Generally for actuator purpose DC electric motor is used and for some precision control stepper motor is used. If you are using DC motor, don’t forget to use DC motor driving circuit because due to high current it may cause of failure of your micro-controller board. After installation of your sensors and actuators, configure sensor signal on the micro-controller board Input terminal and connect actuator (motor) on micro-controller board output terminal. In you program write a code for actuator and trigger or call this code when sensor signal goes true.
You can also use many programming technique and complex code for you bot. If you will go for autonomous bot you can’t work with close loop control system. Concept of Close loop control system is very basic fundamental of robotic.
Here I would like to recommend a free book “A Beginner’s Guide to Robotic”. It is basically a PIC Robotics guide. It is a McGrawHill 2004 publication. No doubt it is based on PIC controllers, which are not in fashion but here in this book you can understand basic function and design guide line. After going through this book you can easily understand that “How intelligence can be develop by using some feedback control”.