mechatronics term project team 2: nicole abaid matteo aureli weiwei chu riccardo romano may 4, 2009
TRANSCRIPT
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Mechatronics Term Project
TEAM 2:Nicole AbaidMatteo AureliWeiwei Chu
Riccardo Romano
May 4, 2009
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Outline • Goal and motivation
• Description of components
• Mechanical system design
• Electrical system design
• Algorithm and operation instructions
• Mathematical modeling
• Conclusions
Robotic swimmer and school of golden shiner minnows in Dynamical
Systems Laboratory (DSL) at NYU-Poly
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Project goals
• Design a feedback controller to turn the shell of a swimmer at a variety of attack angles in a flow of constant rate
• Use the BS2 as controller
• Include user interface for monitor and control the device
• At least one actuator should be included.
• A sensory feedback loop will be used to control the actuator
• Utilize a digital and analog sensor
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Motivation• Biomimetic, miniature
robotic fish used to study schooling behavior of gregarious fish
• Uses ionic polymer metal composite, an electroactive material, as propulsor
• ABS plastic shell
• Requires optimization of shell shape to house on-board electronics and minimize drag
Robotic swimmers from DSL
Water tunnel in DSL
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Component description
• Actuation– Jameco 12 Volt DC motor
• Sensing– Rotational
potentiometers – Normally-open buttons
• User interface– Liquid crystal display
• Control– Basic Stamp
microcontroller
• Structural– Assorted gears– Aluminum shaft
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Component description
Item Price
Box $2
Screw $2
Transistor $4
Basic Stamp 2
$110
DC motor $25
Item Price
Plexiglass $2
Batteries $8
Switch $4
Button $4
Gears $30
Total Cost: $191
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Mechanical system design
• Low torque, high velocity DC motor requires internal transmission, external gear train to convert to high torque and low velocity
• Thrust bearings to withstand weight force
• Ball bearing to rotational force
• Required to rest on top of water tunnel and position body in center of chamber to eliminate wall effects
• Automatic calibration of maximum range using sensor potentiometer and dial attached to rotating shaft
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Mechanical system design
Lateral view of structure
Mechanical apparatus with motor, gear train, shaft and support
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Mechanical system design
Schematic of gear train and forces
• Maximum efficiency speed: 35 rpm
• Maximum torque: 0.2325Nm
• Transmission ratio is 11 : 3
• Enhances the positioning precision and decrease the angular velocity of shaft
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Mechanical system design
Bird’s eye view of actuation device
Plexiglass casing
Gear train
Dial
Right button Left button
DC motor
Tension screws
Potentiometer
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Electrical system design
Schematic of H-bridge
H-bridge for motor control
• Speed can be controlled via PWM
• High signal enters Q3’s base, Q3 conducts, which allows Q2 to conduct
• Current flows from positive supply terminal through the motor from right to left (forward)
• To reverse the direction, low Q3 and high Q4
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Electrical system design
Input button circuit schematicInput and sensor RC-
potentiometer circuit schematic
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Electrical system design
LCD display
• Display measurement and status information
• Parallax 2×16 serial LCD
• 3-pin connection
• Used with PBasic SEROUT command
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Electrical system design
Device circuitry without sensors connected
BS2 microcontroller
H-bridge
Sensor button circuits
Input button circuits
RC pot circuits
“On” LED
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Electrical system design
User interface
LCD display
Water resistant case
“On” LED
Power switch for BS2 and motor Input pot
Input button 1
Input button 2
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Calibration:
• Automatically moves dial to hit left endpoint button, then right endpoint button
• Uses RCtime command to record potentiometer position at each endpoint
• BS2 calculates middle position for potentiometer, uses PWM to track
• Scale range of dial in RCtime output with ±90o
Algorithm
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Input position and actuation:
• Input reference step or ramp, using button (discrete) or potentiometer (continuous)
• Input in degrees, which BS2 scales to RCtime, in 2 µs units
• Displayed on LCD, scaled to degrees
• Shaft position senses with RCtime command
• Feedback controller uses pulse width modulation
Algorithm
Block diagram of feedback control loop
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Algorithm
θ θd
V
t
th
tl
θθd
θθd
V
t
th
tlV
t
th
tl
Shaft position
PWM signal Pulse width modulation-
• Low time, tl, is constant
• High time, th, is proportional to the error:
th = K (θd - θ)
Mean signal
Mean signal
Mean signal
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Operating instructions• Start the Basic Stamp and motor using external on/off switch
– This switch is the emergency shutdown, resetting and recalibrating system
• Wait as system calibrates automatically• Button 1 pressed at any time after calibration to resets• Select input mode
– Button1: button input– Button2: potentiometer input
• If button input is selected, select position to the left or right of zero position, then degree value
• If potentiometer is selected, choose step or ramp intput– Button1: step input– Button2: ramp input
• If step input is selected, LCD displays reference position which shaft matches.
• If ramp input is selected, potentiometer selects grade of ramp
– Steeper ramp to the left– Shallower ramp to the right
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Modeling
Electrical, mechanical subsystems can be described as the following ODE’s:
• L = inductance of DC motor• R = electrical resistance • i(t) = current• V (t) = voltage applied to DC motor • Vb(t) = back electromotive force • J = moment of inertia of shaft • B = viscous-type dissipative action • ω(t) = angular velocity of motor shaft • τ(t) = torque of motor shaft
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• Input is V (t) • PI controller was implemented and found to lack any
advantage over a strictly proportional control• Proportional feedback control is implemented based on
direct measurement of shaft angular position θ, and reference input θd
• PWM is used to control amplitude of driving voltage V supplied to DC motor.
Modeling
Block diagram of feedback controller
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Conclusions
• Angle of attack of the swimmer is input by the user • A proportional feedback loop guarantees the desired
position• LCD display shows the reference step or ramp input
Future Work-
• Use strain gauge or composite beam to measure forces acting on body
• Consider roll and pitch motions of the body• Implement PID control