Mechatronics Notes 7 & 8 PDF

Lecture 7: - Automation uses various control systems - Programming logic controllers have been available since 1960s - PLCs monitor the state of input devices, make decisions based on the input data and custom program, controls the state of the output devices, collect and share data...

Lecture 7: - Automation uses various control systems - Programming logic controllers have been available since 1960s - PLCs monitor the state of input devices, make decisions based on the input data and custom program, controls the state of the output devices, collect and share data to help identify which operations need adjustment - SCADA control system that monitors industrial processes and machines - Objective of automation is to bring added value to a set of raw materials to produce products of higher value - Requires: human intervention - Automation leads to reduced cost of labor and material saving, removal of hazardous work and safety issues, improved product quality and performance, high productivity and quality job creation - PLC is sequential - Example: add milk (Step 1) -> milk addition complete and high-fat cocoe in recipe (transition 1) -> ass high-fat cocao (step2) -> high-fat cocoa addition complete (transition 2) -> add cream (step 3) - There are 5 programming languages for PLCs Instruction list, structure text, function block diagram, ladder diagram, sequential function chart - Hardware is connection through relays, electronic boards, switches: it is more reliable but not flexible for future changes - Software is obtained through programming: it is flexible for future changes but not used for important safety functions - Single protection: position switches or forced open contacts, manually check for periodic safety functions, overzixing of some components like relays and contactors - Single with supervision protection: In addition to some techniques mentioned above, security system must include a self monitoring function, failure detecting circuits made with contactors and relays - Redundant protection: reduction or duplication of critical components/functions, combining the normally open and closed contact interlocks, combining different electrical and non-electrical systems - Redundant with supervision: in addition of a combination of different technologies as described above, a continuous supervision function might be added - Ladder logic: Before PLCs, ladder was used to describe automation technology made by using electromagnetic relays - Electromagnetic relays: Metal plate which is attracted to a coil when the solenoid is energized and pushed by a coil spring when de-energized, an electrical path through the normally closed contacts is created when non-energized a second path through the normally open is created when energized - Learn Ladder and PLC - Modern control objective: control the output, achieve robustness, change response characteristics - Static system: if a system does not change with time, it is called a static system - Dynamic system: If a system changes with time, it is called a dynamic system  - A model is a simplified representation, reality is too complex to copy exactly but a lot of the complexity is irrelevant in problem solving - Black box model is system that produces results without revealing how it arrived at those results, only the input and outputs are known - White box model is a system when the input, output, and internal dynamics of the system is know - Spring-mass-damper system is a dynamic system - RLC circuit is a dynamic system Lecture 8: - Without feedback, a control system is highly sensitive to disturbances - Closed loop control systems decrease sensitivity of variation, reject disturbances, attenuate measurement noise, reduce steady state error, ease the control and adjustment of the transient response of the system - A stable system returns to its original position after a disturbance - Normal system has neutral stability - Linear system satisfies the properties of superposition and homogeneity - The superposition principle states that for all linear systems, the net response caused by two or more stimuli is the sum of the response that would have been caused by each stimulus individually - The homogeneity principle states that the output is always directly proportional to the input. - Linear approximation is as accurate as the assumption of small signals is applicable to the specific problem - Step input, ramp input (integral), parabolic input (integral) - An optimum control system is when the system parameters are adjusted so that the index reaches an extremum commonly a minimum value - Process variable (PV) - system parameter that needs to be controlled (Temp, pressure, flow rate) - Sensor - used to measure the process variable and provide feedback to control system - The set point(SP) - desired or command value for the process variable (such as 100 degrees for temperature in oven) - Error (e) - the difference between the process variable and set point; used by the system to determine the action to take - Rise time - time to go from 10% to 90% if the steady-state or final value - Overshoot - the maximum amount exceed final value - Settling time - time to settle within a certain pertance of a final value - Steady-state error - difference between the process variable and set point - Error = sp-pv - PID controller has proportional, integral and derivative and is the sum of 3 parallel actions to generate a control output - Kp: proportional constant that accounts for present error value - Ki: Integral constant that accounts for historical error values - Kd: Derivative constant that accounts for future errors - PID is accurate, eliminates steady-state error, reduces overshoot and is widely applicable - Proportional controller is easy to implement and understand, quickly responds to large errors and provides consistent correct effort based on real-time errors. The system have residual error and if the proportional gain is too high, it can cause the system to oscillate - Integral action eliminates the effect of disturbances at steady-state - PI controller is simple, eliminates steady-state error. It has a slower response due to integral action, if the integral gain is too, it can cause oscillations - Derivitive is proportional to the rate of change of the error signal - Underdamped systems have oscillations and take a long time to return to equilibrium after an error - Overdamped systems don’t have oscillations and take a longer time to return to equilibrium - Critically damped does not oscillate and returns to equilibrium in the shortest time without overshooting - Proportional decreases rise time - Integral eliminates steady-state error - Derivative removes overshoot and oscillations