FeedbackControl

FeedbackControl - ME375 Handouts Introduction to Feedback...

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ME375 Handouts 1 School of Mechanical Engineering Purdue University ME375 Feedback Control - 1 Introduction to Feedback Control Control System Design – Why Control? – Open-Loop vs Closed-Loop (Feedback) – Why Use Feedback Control? Closed-Loop Control System Structure – Elements of a Feedback Control System – Closed-Loop Transfer Functions (CLTF) Performance Specifications – Steady State Specifications – Transient (Dynamic) Specifications
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ME375 Handouts 2 School of Mechanical Engineering Purdue University ME375 Feedback Control - 2 Control is the process of causing a system to behave in a prescribed manner. Specifically, control system design is the process of causing a system variable ( output ) to conform to some desired input ( reference ). The objective of the control system is to control the output y by using the input u , such that the output y follows a set of reference inputs r . Control System Design System (Plant) G P ( s ) Input Output U ( s ) Y ( s ) Reference Input R ( s )
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ME375 Handouts 3 School of Mechanical Engineering Purdue University ME375 Feedback Control - 3 Open-Loop Control The control input u ( t ) (or U ( s )) is synthesized based on the a priori knowledge of the system (plant) and the reference input r (t) (or R ( s )). The control system does not measure the output, and there is no comparison of the output to make it conform to the desired output (reference input). Q: Ideally, if we want Y ( s ) to follow R ( s ) ( i.e. want Y ( s ) = R ( s )), how would you design the controller C ( s ) ? Open-Loop vs Closed-Loop G P ( s ) C ( s ) Reference Input (Command) R (s) U ( s ) Control Input System Output Y (s) Plant or System
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ME375 Handouts 4 School of Mechanical Engineering Purdue University ME375 Feedback Control - 4 Open-Loop Control Example Open loop Cruise Control The vehicle speed model can be approximated by a static gain between the throttle angle (input) and the vehicle speed (output). From experiment, on level road, at 55 mph, 1 o of throttle angle causes 10 mph change in speed. When the road grade changes by 1%, 1 o of throttle angle will only change vehicle speed by 5 mph. Design an open-loop cruise controller for this vehicle. R : reference speed, mph U : throttle angle, degree Y : actual speed, mph W : road grade, % Q: What are potential problems with this cruise control ? W - Y U R + Speed Model Cruise Controller
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ME375 Handouts 5 School of Mechanical Engineering Purdue University ME375 Feedback Control - 5 Closed-Loop (Feedback) Control The control input u ( t ) (or U ( s )) is synthesized based on the a priori knowledge of the system (plant), the reference input r (t) (or R ( s )) and the measurement of the actual output y ( t ) (or Y ( s )). For example the temperature control of this classroom: Open-Loop vs Closed-Loop Room Temperature Y (s) Disturbance D (s) Actuator Plant or System Room Heater
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ME375 Handouts 6 School of Mechanical Engineering Purdue University ME375 Feedback Control - 6 Closed-Loop Control Example Closed Loop Cruise Control Same vehicle system as the previous example. The vehicle speed is measured and fed back.
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FeedbackControl - ME375 Handouts Introduction to Feedback...

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