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Wheelchair Kinematics & Position Estimation: Steering Methods & Drive Systems, Slides of Computer Science
An overview of wheelchair kinematics, focusing on position estimation techniques such as ackerman steering, synchro drive, and omni-directional drives. Topics include the instantaneous centre of curvature (icc), basic position estimation equations, ackerman steering geometry, and the advantages and disadvantages of different drive systems. Additionally, the document discusses beacon-based localization methods, including trilateration and triangulation.
Typology: Slides
2012/2013
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- Lecture
Wheelchair kinematics
Recapping
Rolling wheels
Instantaneous Centre of Curvature (ICC)
motion must be consistent
Nonholonomic constraint Docsity.com
Ackerman Steering
- The inside front wheel is rotated slightly
sharper than the outside wheel (reduces
tire slippage).
- Ackerman steering provides a fairly
accurate dead-reckoning solution while
supporting traction and ground clearance.
- Generally the method of choice for outdoor
autonomous vehicles.
Ackerman Steering (cont.1)
Θo Θi
Ackerman equation:
l
d cotΘ (^) i −cotΘ o = where:
Θi = relative steering angle of inner wheel; Θo = relative steering angle of outer wheel; l = longitudinal wheel separation; d = lateral wheel separation. Docsity.com
Synchro Drive
- Three or more wheels are mechanically coupled. All wheels have one and the same orientation and rotate in the same direction at the same speed.
- Improved dead reckoning.
- Synchro drives use belt, chain or gear drives.
- Problems in steering accuracy with wear/tear
Synchro Drive
Dead reckoning for synchro-drive:
Tricycle Problems
- When going uphill the center of gravity of the
wheelchair tends to move away from driven
wheel. Causing loss of traction.
- As Ackerman-steered design causes surface
damage.
Omni-Directional Drives
- Minimum is a 3 wheel configuration.
- Each individual motor are driven
independently, using velocity control.
Beacon-based Localization
- Trilateration
- Determine wheelchair position from distance measurements to 3 or more known beacons.
- Triangulation
- Determine wheelchair position for angular measurements to 3 or more known beacons.
Triangulation
- Solution to constraint equations relating the pose of an observer to the positions of a set of landmarks.
- Usually, the problem is considered in the 2D case.
Active triangulation
Photo detector
- one- or two-dimensional array detector such as a CCD camera or photosensitive line.
Calibration – signals are measured on two preliminary known distances between the sensors and the object.