ch9_012604 - Embedded Systems Design: A Unified...

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1 Embedded Systems Design: A Unified Hardware/Software Introduction Chapter 9: Control Systems
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2 Embedded Systems Design: A Unified Hardware/Software Introduction, (c) 2000 Vahid/Givargis Control System Control physical system’s output By setting physical system’s input Tracking E.g. Cruise control Thermostat control Disk drive control Aircraft altitude control Difficulty due to Disturbance: wind, road, tire, brake; opening/closing door… Human interface: feel good, feel right…
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3 Embedded Systems Design: A Unified Hardware/Software Introduction, (c) 2000 Vahid/Givargis Tracking
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4 Embedded Systems Design: A Unified Hardware/Software Introduction, (c) 2000 Vahid/Givargis Open-Loop Control Systems Plant Physical system to be controlled Car, plane, disk, heater,… Actuator Device to control the plant Throttle, wing flap, disk motor,… Controller Designed product to control the plant
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5 Embedded Systems Design: A Unified Hardware/Software Introduction, (c) 2000 Vahid/Givargis Open-Loop Control Systems Output The aspect of the physical system we are interested in Speed, disk location, temperature Reference The value we want to see at output Desired speed, desired location, desired temperature Disturbance Uncontrollable input to the plant imposed by environment Wind, bumping the disk drive, door opening
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6 Embedded Systems Design: A Unified Hardware/Software Introduction, (c) 2000 Vahid/Givargis Other Characteristics of open loop Feed-forward control Delay in actual change of the output Controller doesn’t know how well thing goes Simple Best use for predictable systems
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7 Embedded Systems Design: A Unified Hardware/Software Introduction, (c) 2000 Vahid/Givargis Close Loop Control Systems Sensor Measure the plant output Error detector Detect Error Feedback control systems Minimize tracking error
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8 Embedded Systems Design: A Unified Hardware/Software Introduction, (c) 2000 Vahid/Givargis Designing Open Loop Control System Develop a model of the plant Develop a controller Analyze the controller Consider Disturbance Determine Performance Example: Open Loop Cruise Control System
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9 Embedded Systems Design: A Unified Hardware/Software Introduction, (c) 2000 Vahid/Givargis Model of the Plant May not be necessary Can be done through experimenting and tuning But, Can make it easier to design May be useful for deriving the controller Example: throttle that goes from 0 to 45 degree On flat surface at 50 mph, open the throttle to 40 degree Wait 1 “time unit” Measure the speed, let’s say 55 mph Then the following equation satisfy the above scenario v t+1 =0.7*v t +0.5*u t 55 = 0.7*50+0.5*40 IF the equation holds for all other scenario Then we have a model of the plant
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10 Embedded Systems Design: A Unified Hardware/Software Introduction,
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ch9_012604 - Embedded Systems Design: A Unified...

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