Robotic Systems Laboratory
The Australian National University Research School of Information Sciences and Engineering
ADVANCING ACTIVE VISION BY IMPROVED DESIGN AND CONTROL
Orson Sutherland, Harley Truong, Sébastien Rougeaux & Alexander Zelinsky
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• RSL has developed an extensive library of Vision Processing software for :
– Human/Machine interfaces – Human/Robot interaction – Navigation
• The intention is to mount these products into a powerful and robust sensor.
• For this we have chosen Active Vision.
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The Agile Eye
• This presentation will concentrate on:
– the mechanical design – the Hardware – Performance Specifications and Testing – and the Control
of a novel active Vision system named
CeDAR for Cable Drive Active Vision
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• We wanted:
• a high performance • high precision rig • capable of moving a variety of payloads
• For this we required:
• a high precision transmission • and an optimised mechanical structure
Mechanical Design Issues
• Speed & acceleration depend on:
• motor size • load inertia • transmission ratio
• Accuracy depends on:
• encoder resolution • transmission ratio and stiffness • joint stiffness
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• CeDAR is arranged in the more popular Helmholtz configuration. • An important property of the design is that the axes intersect at the optical center of each camera
• Uses a cable drive transmission inspired by the Whole Arm Manipulator (Townsend, MIT) • Same as gear transmission except force is transmitted by tension in cables rather than contact between teeth
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– – – – – – No Backlash No Slippage No lubrication High efficiency No speed limits Torque limited only by strength of cables
• Limited range. • Miniaturisation is limited by the minimum bend radius of the cables.
HOWEVER • In our system, range is only 90°. • Pulleys are integrated into structure.
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• Parallel architecture allows:
– Motors to be fixed at base so they do not contribute to mass in motion
• But means axes are coupled
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The weight/rigidity trade-off was optimised so that maximum angular deflection was 0.01°.
• Fully assembled CeDAR weighs 3.5kg.
• It has a moving mass of 1.7kg including 2x350g digital cameras.
• Maxon DC motors controlled by Motion Engineering, motion card. • Pentium III performs trajectory planning and vision processing
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• The max range, payload and baseline were based on the use of motorisedzoom cameras (350g). • Performance needed to be at least comparable to the human eye:
– 5x90° saccades per second
• We achieved:
• Tilt: 600°.s-1 @ 18000°.s-2 with 0.01° and a saccade rate of 5Hz. • Vergence: 800°.s-1 @ 20000°.s-2 with 0.01° and a saccade rate of 6Hz.
• This means:
• Better performance than the human eye. • Better performance than ESCHeR. • Marginally inferior to the Agile Eye.
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• Extends work by Murray et al. (1992) on Trapezoidal Profile Motion (TPM).
• In theory TPM can achieve optimal saccade and smooth pursuit with one compact algorithm.
Position profiles for saccade and smooth pursuit.
Velocity profiles for saccade and Smooth pursuit.
Two successive real-time saccades
Smooth pursuit of a 0.5Hz sinusoid, sampled at 4Hz.
• Tracking with ZDF and Optic Flows • Face/Feature tracking algorithms
• Hardware Improvements:
• A pan neck
• Future Prototypes:
• Use of plastics and other polymers • Fick configuration
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• CeDAR is a fast, accurate 3DOF stereo head. • CeDAR can carry relatively heavy payloads. • CeDAR’s controller is compact and simple and can implement both optimal saccade and smooth pursuit from the same algorithm.
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