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Design of a Control Workstation for Controller Algorithm Testing Aaron Mahaffey Dave Tastsides Dr. Dempsey

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Presentation Preview Project Summary and Objective Hardware Controller Application DC Motor Model Power Amplifier F/V Converter Modeling Summer Circuit Hardware Controller Design Experimental Results

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Presentation Preview Software Controller Application Level Shifting Circuit BSP/Core Functions User Interface Command Signal Sampling Period Summer F/V Converter Digital Controller Digital Controller Results

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Presentation Preview Demonstration Work Final Parts List Future Project Work

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Project Summary Design of a control workstation to test control algorithms for a Pittman DC motor Provide insight to classical and digital control system theory through practical applications First apply control system with all hardware components, then implement as much as possible into software

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Project Summary Quansar Consulting currently develops control workstations for $5,000 Each station requires a PC with an internal A/D and D/A converter Goal is to develop a system at a much lower cost of $400 based on the 8051 development board

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System Block Diagram

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Motor Model Gp(s) = 1949166 _ s 2 + 920s + 114133 Poles at s= -148 and s= -772 rad/sec DC Gain of 17.08

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Power Amplifier Discrete Component Design Internal Controller for Stability Passive Lag Network Internal Feedback Loop Open Loop Crossover Distortion ± 27.5 Volt Output Range

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Power Amplifier

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Power Amplifier Model Closed Loop Gain = 11 Results from Matlab after observing open loop frequency response in PSpice: o Time Constant = 10 us o Pole = 628000 rad/sec G(s) = 11 _ s/628000 + 1

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F/V Converter Modeling Desire Output of 2.5 V for Maximum RPM of 762 o 762 RPM Corresponds to 38.4 kHz o Desired Gain = 2.5/38400 =.0000652 Experimentally Measured Results: o Time Delay = 5 ms o Pole at 388 rad/sec

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F/V Converter Modeling G(s) =.0000652*e -.005s s/388 + 1

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Summer Circuit Produces Error Signal from Difference of Command and Feedback Signals Design using LF412 Operational Amplifier and precision resistors. Experimental Transfer Function V o =.9945V 1 -.9895V 2

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Hardware System Controller Motor Tracking System Motor shaft velocity follows analog command signal All subsystems designed with hardware Drive up to 762 RPM in positive direction Command signal of 0 - 2.5 volts Controller Phase Margin of 60º Steady State Error of zero (integrator)

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Hardware Controller Design PI Controller Proportional Gain Locates necessary crossover frequency to meet 60º phase margin specification Obtained using Frequency Domain Design Integrator Drives Steady State Error to zero

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Hardware Controller Design Design for crossover frequency and adjust gain to get correct PM Final Frequency Design Results from Matlab: o K = 37.6 o PM = 59.6º o wc = 34 rad/sec o Overshoot = 7.06 %

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Experimental Results

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Experimental Overshoot = 33 % Why such a large deviation? D/A phase lag o Sampling Period (T) = 2 ms o Phase lag = -wcT = -3.5 º Motor and F/V time delay o Added time delay = 6.1 ms o Phase lag = -wcT d = -11 º

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Experimental Results Experimental Gain = 40 o Could account for -5º phase lag New phase margin = 40.5º New expected overshoot = 26 % New deviation = 7 %

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Presentation Preview Software Controller Application Level Shifting Circuit BSP/Core Functions User Interface Command Signal Sampling Period Summer F/V Converter Digital PI Controller Digital Controller Results

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Level Shifting Circuit In all applications, a signal is sent from the EMAC D/A Converter D/A Converter Output is 0-5 Volts Desired Signal is ± 2.5 Volts for Bidirectional Drive in Software Application D/A Converter Output must be shifted by -2.5 Volts

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Board Support Package (BSP) Supports all Devices on Board Timer 0 Timer 2 D/A converter A/D converter Keypad LCD

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Core Contains Functions Common in all Applications Summer Conversion routines RPM measurement F/V calculation

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User Interface Communicates with User Ask for sampling period Ask for Proportional Gain Ask if Integration Desired Ask for step magnitude (+ or -) Verify all entries Display current motor RPM

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Command Signal Magnitude and sign provided by user interface routine Value entered is level shifted Value is written to the D/A: 0 – 2.5 Volts -> Negative 2.5 – 5 Volts -> Positive Support for step inputs only

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Sampling Period Entered by user in terms of microseconds Value is converted to a timer reload value Timer 0 is setup with calculated reload value All sample driven functions are called from Timer 0 interrupt service routine

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Summer Subtracts value of F/V converter feedback signal from command signal Software version allows for bidirectional error signal by determining motor direction from encoder signals Called at sampling rate by Timer 0 interrupt service routine

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F/V Converter Timer 2 initialized to auto reload on negative encoder transition and capture on positive transition Capture value in timer 2 registers holds cycles per encoder pulse width RPM and F/V output calculated from measured pulse width Continuously measures pulse width, but calculation occurs once every sampling rate

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Digital P/PI Controller Proportional gain entered by user in 1/255 increments User chooses between P or PI control Integrator mapped in software as: Z _ Z - 1

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Digital Controller Model

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Digital Controller Results For Simulated K = 1 Overshoot = 15.15% tp ≈ 55 ms For Experimental K = 1 Overshoot = 16.4% tp ≈ 60 ms For Simulated/Experimental K = 0.2 No overshoot For Simulated/Experimental K = 5 Unstable

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Digital Controller Results (K=1)

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Digital Controller Results (K=0.2)

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Digital Controller Results (K=5)

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Demonstration Work Model wheel loader demonstrates effectiveness of controller DC generator shaft connected to controlled motor shaft provides voltage to power wheel loader motor Moving bucket arm creates a variable load on the generator

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Demonstration Work Controller maintains constant motor velocity DC generator maintains constant voltage Bucket arm velocity remains constant for moderately varying loads

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Demonstration Work Separate EMAC controls bucket arm movement Two different operation modes Auto - bucket arm moves up and down continuously one second at a time Manual - pressing and holding buttons on keypad moves bucket arm

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Final Parts List Pittman DC Motor 2 x GM9236C534-R2 EMAC x 2 Operational Amplifiers 2 x LF412 Transistors 2 x TIP30 4 x TIP31

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Final Parts List Diodes 2 x 1N5617 D Flip-Flop 7474

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Future Project Work Implement more complex controllers Multiple poles and zeroes Add provisions for ramp or impulse commands Use control workstation to test other devices and types of control Different plants and position control

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Design of a Control Workstation for Controller Algorithm Testing Questions?

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