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Automatic Pouring Robot
Akilah Harris-WilliamsAdam Olmstead
Philip Pratt-SzeligaWill Roantree
OverviewObjective and MotivationMechanical SystemModeling, Simulation and Verification
TiltPan
Pouring Trajectory GenerationControl Design
TiltPan
Webcam Image ProcessingUncertainty Analysis
Objective and Motivation
To develop an Automatic Pouring RobotIndustrial Applications
Casting RobotHazardous Materials Robot
Purpose
Smoothly pour water from a bottle into a cup without spillingConsists of a bottle, a pan/tilt mechanism, a computer controller, a cup and a webcamThe bottle will be mounted on the mechanismComputer controller will rotate the bottle towards the cupWebcam will view the height of water in the cup.
Mechanical System
Tilt ModelingMass Properties change with tilt angle and water volume. System dynamics are variable.Visual Basic program extracts Center of Mass, Inertial Tensor and Mass from Solidworks API at varying angles and volumes.
Tilt Friction/Gravity Model
Upper Level SystemTilt DynamicsEquation of Motion
Tilt Friction/Gravity ResultsExperimental system response versus Simulated system response to force of gravity.
Tilt Friction/Gravity Cancellation
Pan Modeling
Vaaa 321 )sgn( =++ θθθ
Used full parameter identification methodChirp inputa1=1.9080a2=6.0656a3=8.44290.08 radSteady-State Error
Basic Trajectory
Basic Trajectories
Polynomial Trajectories
Basic Return Trajectories
Return Trajectories
Tilt Control
Needs to follow a smooth trajectorySpecifications:
Mo ≤ 0%, tr ≤ 0.75 s, ess ≤ 1%Used PID controller
System behaved similarly to modelLinear model assumes constant volumeDue to modeling error, needed an easily tweaked controller
Tilt Controller – SimulatedSimulatedMo = 2.87%tr=0.327 sess=0.81%ActualMo = -0.13%tr=0.104 sess=0.138%
Tilt Controller - Actual
Simulation was run assuming a constant volumeValues will change due to:
Constantly changing amount of liquidAny modeling error
Values tweaked from simulation to dampen overshoot
Tilt Controller on Actual Trajectory
Pan ControlUsed for Disturbance Rejection
Needs to have a quick rise time and low steady-state error
SpecificationsMo ≤ 5%, tr ≤ 0.4 s, ess ≤ 2%
Lead-Lag Controller
)9.0)(486.19()266.1)(493.6(30)(
++++
=ss
sssD
Pan Controller - Design
Pan Controller - SimulationSimulated:Mo = 0.367 %tr=0.336 sess=0.037 %Actual:Mo = 5.23 %tr= 0.133 sess= 0.936 %
Tweaked Pan Controller
Actual:Mo=1.55 %tr=0.134sess=0.016 %ts=0.356s (2%)ts=1.548s (1%)
Sensor Subsystem - Webcam
Objective: Pour a specified amount of liquid into a cupNeed to know when to stop pouring to get the desired amountOur solution: Webcam
Image Processing AlgorithmWant to find the volume of liquid in the cup
Find highest pixel row occupied by the colored liquid (determined by green and blue thresholds)Correlate these pixels to actual volumes via experimentation
Webcam Timing
Average frame rate with processing is 13 fps.When the volume in the cup approaches a certain percentage of the desired volume, MATLAB triggers xPC target to stop pouring.Percentage at which the trigger is sent is a function of:
Return trajectoryCommunication delay between MATLAB and xPCTargetFlow rate before stopping
Webcam Data of Sample Pour
Stop Triggered
Uncertainty Analysis
Modeling errorTilt: Friction IdentificationPan: Steady-State Error
Webcam errorNoisy dataSlow feedback
Other sources of errorOccasional encoder spikes
Modeling Error – Tilt Friction ID
Velocities never converge to a steady-state value, due to water sloshing in the bottleDifferent values in each direction
Average was taken
Modeling Error - PanIdentified parameters work fairly well with data used to generate them.
ess of only 0.08 rad = 4.6°Does not work as well for all inputs
AssessmentMechanical System
Sturdy apparatus key to entire project
Model of Dynamic Tilt ParametersWorks well after initial calibration of mass
Webcam Image ProcessingGood response but prone to inaccuracies
Disturbance RejectionFunctions well, but with large settling time for large disturbances
Pouring ControlOccasionally spills due to stationary cup
Overall Success!
Conclusion
Areas of ImprovementThird degree of motion Faster and more precise cup volume feedbackImplement fuzzy logic controller based on constant webcam dataImprove models and parameter identification