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PanTilt Platform for Cyclops

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PanTilt Platform for Cyclops Powered By Docstoc
					Pan/Tilt Platform for
             Cyclops
           Jeffrey Mascia
                  EE202A
Motivation
   Cyclops camera module provides
    low-cost, low-power, solution
    for imaging in sensor networks
   Hierarchical Paradigm:
       Use many Cyclops to detect events
       Observe in greater detail with few high-power
        high resolution, cameras
   By enabling pan/tilt capability, we can increase our
    coverage area, or reduce number of Cyclops
    needed in network, or focus attention on interesting
    events                                                 2
Goals
   Platform should be:
       Low power
       Low cost
       Made from off-the-shelf components (LEGO’s)
       Controlled by Mica2 mote
       Physically compatible with Cyclops
   High precision is desirable
   Speed is expendable

                                                      3
Current Technology
 Sony SNC-RZ30N

                     CMUcam2




                               4
 System Overview
                                         9V


                                5V Reg

                                GPIO

            ADC                        H-Bridge

                        Mica2

                 GPIO
Sensor Drivers

                                                  5
Control Flow (Implemented in TinyOs)
 Request Handler                                           Event Handler

   Idle
                                                          Sample ADC
                               Command
             NO
                                                                           NO
 Request                         CHECK
  Rx?                                                         New
                                                            Position?
                                Counter ==
   YES                           Request
                   MORE
                                               LESS           YES

 Power On                        EQUAL
                   Turn Left                 Turn Right   Adjust Counter
                                Stop Motor

Goto CHECK                                                Goto CHECK
                                Power Off


                                                                                6
Design Choice: Motor
    Servomechanism
     + Easy control interface
     – High power consumption

    Stepper Motor
     + Quantized movement; no external encoder
     – Physical interface

    Lego DC Motor
     + Physical interface
     + Low power
     – No feedback
                                                 7
LEGO Motor
   Voltage:      9V
   Current:      10 mA
   Speed:        340 rpm
   Use worm gear to lock motor position during
    power down.
   Control motors with H-Bridge



                                                                 8
                 http://www.philohome.com/motors/motorcomp.htm
Design Choice: Position Encoding
   Timing
    + No additional components
    – Inconsistent performance
    – Requires rigorous calibration

   Mechanical Rotary Encoder
    + Can be monitored with uController interrupts
    – High friction; requires too much torque

   Lego Rotation Sensor
    + Easily adaptable physical interface
    – Complex electrical interface
                                                     9
LEGO Rotation Sensor
   Classic quadrature optical encoder
   One-wire interface
   16 steps per revolution (22.5° per steps)




                                                                10
                         http://www.barello.net/ARC/projects/LEGO/
Sensor Driver Circuit
                            3.1 V



                   3.3 k
        ADC                         Sensor




                                   9V
                           4.7 k



      GPIO
             330

                                             11
Power Supply: 9V battery




                                    12
          http://www.duracell.com
System Metrics
   Power Consumption:
       10mA to drive each motor, 40mA to power circuit
   Speed:
       Pan: 39° per second
       Tilt: 31° per second
   Lifetime:
       Assume 90° rotation for each axis (per repositioning)
       Estimated lifetime of greater than 7000 repositions
   Resolution:
       Pan: 416 steps per platform revolution
       Tilt: 356 steps per platform revolution
   Cost: $65.00                                                13
Weaknesses
   Position jitter
       Imprecise gear meshing
       Flex in plastic parts
   Too many wires!
       Control circuit requires many i/o lines
       Next step: fabricate circuit onto breakout board
   No knowledge of absolute position
       Add external interrupt switch

                                                           14
Future Extensions
   Network Coordination
       Maximize visual coverage area
       Multi-angle viewing of single location
   Object Localization
       Use Cyclops image processing libraries to detect object
       Re-position camera to center on object
       Get spherical coordinates
       Using information from multiple nodes, calculate location
   Port code to SOS

                                                                    15
Conclusion
   Demonstrated feasibility of low-cost, low-
    power, pan/tilt platform for remotely aiming
    Cyclops equipped sensor node
   Potential for future improvement and
    exploration

   Special thanks to David Lee, Jonathan
    Friedman, and Mohammad Rahimi for their
    advice

                                                   16

				
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posted:5/9/2013
language:English
pages:16