Concept of Feedback. P.S. Gandhi Mechanical Engineering IIT Bombay

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1 Concept of Feedback P.S. Gandhi Mechanical Engineering IIT Bombay

2 Recap Goal of the course: understanding and learning Assignments: optional to start with Contact hour with TAs: Monday AN: time? Meeting with me: call me and come over: office in SMAμL Quizzes: once in two weeks Course will be taught keeping practical implications in perspective Attendance: I would love to see you in class Class participation: understanding of each one of you is equally important for me

3 Remember this always a possibility? Better ask questions and clarify your understanding

4 Why automatic control? Application of automation Industrial: assembly lines Various new gadgets: CD ROM drives, hard drives, robots, cruise control, electronic fuel injection, UAVs, printer, scanner, washing machine, xerox machine, ATM, missile systems, space rockets, the list is endless

5 Important Concepts What is feedback? Open Loop Vs Closed Loop Control What tolls we need to develop such systems? How to process the desired feedback quantity? When goal is given, how to decide what should be the control algorithm? Is it unique? We will answer these questions in this course

6 What is feedback? Monitor the output Compare the output with the reference input Take decision based on the difference In case of sprinkler: soil moisture as a possible feedback

7 Feedback: Example x F Mass Current pos Desired pos Goal: to place mass at a desired position Feedback??? Identify: quantity of interest (output) and quantity you can dictate (input)

8 Feedback: Example Desired pos Goal: to place disc at a desired angle Feedback??? Identify: quantity of interest (output) and quantity you can dictate (input)

9 Feedback: Example Goal: to rotate disc with desired speed Feedback??? Can the angle act as feedback? Identify: quantity of interest (output) and quantity you can dictate (input)

10 Feedback: Example h Goal: to maintain height of liquid constant Feedback??? Identify: quantity of interest (output) and quantity you can dictate (input)

11 Feedback: Example Air conditioning system Goal: to maintain temp constant at 22 o C Feedback??? Identify: quantity of interest (output) and quantity you can dictate (input)

12 Feedback: Example Goal: to maintain focus on object no matter what the distance is Feedback??? Identify: quantity of interest (output) and quantity you can dictate (input)

13 Open Loop Control No relation between input and output Useful for well-defined systems Examples: A sprinkler programmed to run at set times What if it is raining?

14 Example: x So what? If we know Mass F what quantity is fed back and I know the Current pos inputs and outputs Desired pos What s s next? Q: How do I process position so as to reach desired position in small time Without exceeding the desired position

15 Next class Some more concepts Modeling

16 Basic Building Blocks - Example Shower control system Valve/piping system Plant Skin Sensor Brain Controller Limbs Actuator

17 Basic Building Blocks Controller Actuator Mechanical System Sensors Sensors How mechatronics is different from automatic control??

18 2-R R Manipulator Y P f P s y 1 θ 1 l 2 θ 2 P l 1 x 1 X Questions What is meant by command in this case? How much should be the motor torque? What does it depend on? What if we want robot to take P to the final position faster? How much deviation from the straight line will occur? Answers given by study of dynamics and control

19 Spring Mass System c K Load m Potential energy of the system PE= L=KE-PE= mx kx From Lagrange equation x F 2 2 Kinetic energy of the system KE= 1 2 mx kx d ( mx ) + kx = F dt mx + kx = F 2