Mechatronics Term Project May 4, 2009 TEAM 2 : Nicole Abaid Matteo - - PowerPoint PPT Presentation

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Mechatronics Term Project May 4, 2009 TEAM 2 : Nicole Abaid Matteo - - PowerPoint PPT Presentation

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Mechatronics Term Project May 4, 2009 TEAM 2 : Nicole Abaid Matteo Aureli Weiwei Chu Riccardo Romano Outline Goal and motivation Description of components Mechanical system design Electrical system design

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Mechatronics Term Project

TEAM 2:

Nicole Abaid Matteo Aureli Weiwei 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

  • f 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

  • n-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
  • f chamber to eliminate wall effects
  • Automatic

calibration

  • f

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 schematic Input 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

θ θd θ θd

V t th tl V 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