Open Loop and Odometry

Open Loop and Odometry - Open Loop Contol & Odometry...

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Click to edit Master subtitle style 10/15/10 Open Loop Contol & Odometry
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10/15/10 Odo-1 Kinematic model of a robot. . Relates the configuration of a robot in a local coordinate frame, e.g., (x,y) to motor shaft positions, e.g., (Ω1,Ω2). A kinematic model is robot-specific. - A robot with N degrees of freedom needs at least N motors/actuators - The kinematic model describes the static behavior of a robot and does not include the effects of internal and external forces. - Have to take into account the dynamic behavior as well.
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10/15/10 Odo-2 Odometry Determining the position of a robot in an external coordinate system based on counting motor rotations (change in actuator position). The kinematic model is use to determine the instantanous displacement. The integral of the displacement determines current position. Odometry (sometimes referred to as
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10/15/10 Odo-3 Open loop control - using odometry to generate a path in space Method Decompose path into tangent segments Incrementally move along each segment (trajectory generator)
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10/15/10 Odo-4 Odometry of the Tribot Linear Motion: • both wheels rotating • distance = 2 π * wheel radius • accuracy depends on degree of slip R c Rw c Ωw Rotation in place (no displacement): • Ωw defined as wheel rotation • Ωc defined as rotation about cart center point • Rw and Rc are radii of wheel and turning circle respectively (see diagrams at left) R c arc length = radius x angle (radians) Rw x Ωw = Rc x Ωc Ωw = Ωc * (Rc / Rw)
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10/15/10 Odo-5 Open Loop Control - Odometry, cont. 1 • For the Tribot, Rw = 2.8 cm, Rc = 6.61 cm, Rc/Rw = 2.35 • Putting this all together distance = 2 π Rw x Ωw / 360 assuming wheel rotation Ωw in degrees units for distance are the units of Rw Ωw = (360 D)/(2π Rw) = 20.46 D
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Open Loop and Odometry - Open Loop Contol & Odometry...

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