On-line optical flow feedback for mobile robot localization/ navigation

Abstract

Open-loop position estimation methods are commonly used in mobile robot applications. Their strength lies in the speed and simplicity with which an estimated position is determined. However, these methods can lead to inaccurate or unreliable estimates. Two position estimation methods are developed in this thesis, one using a single optical sensor and a second using two optical sensors. The first method can accurately estimate position under ideal conditions and when wheel slip perpendicular to the axis of the wheel occurs. A second method can accurately estimate position even when wheel slip parallel to the axis of the wheel occurs. Location of the optical sensors is investigated in order to minimize errors caused by inaccurate sensor readings. Finally, the method is implemented and tested using a potential field based navigation scheme. Estimates of position were found to be as accurate as dead-reckoning in ideal conditions and much more accurate in cases where wheel slip occurs.

Optical Speed Measurement and Applications

“…Sorensen found that the error of the two mice system was smallest when the sensors were as far as possible from the centre of rotation, and when good care were taken of maintaining constant height. He found that when these constraints were met, the system performed significantly better than other dead reckoning systems (Sorensen 2003). In their work Palacin et al found that if measurements from an array of sensors were averaged the error became independent from the distance traveled.…”

“…The difference of the two signals is computed and the frequency of the difference signals corresponds to the true ground speed. Indoor dead reckoning solutions for small mobile robots using optical mice were suggested by several authors (Palacin et al 2006, Bonarini et al 2004, Sorensen 2003 T.W. Ng investigated the usability and accuracy of optical mice for scientific measurements in several articles (Ng 2003, Ng & Ang 2004) with good results.…”

“…This property has been noted by others too. (Palacin et al 2006, Bonarini et al 2004, Sorensen 2003 Another very important question is the connection between the distance of the sensors and the accuracy of the measurement. From the equations (8) it is clear that with greater sensor distance higher accuracy can be achieved.…”

Reciclaje Tecnológico al Servicio de la Ciencia

“…Para medir el desplazamiento de un robot utilizando un ratón óptico, éste se dispone en la cara inferior del robot, mirando hacia el piso, de manera que al desplazarse el robot, el sensor detecte el desplazamiento sobre el suelo. Pero, aunque un ratón da una medida precisa del desplazamiento, no puede medir rotaciones, necesitándose para esto al menos dos ratones (Sorensen et al, 2003). Ng (2003) investigó la capacidad de un ratón óptico para funcionar como sensor de desplazamiento en dos dimensiones y concluyó que el ratón sólo podía obtener mediciones sobre objetos opacos y siempre que la distancia entre el objeto y el ratón fuera menor a 1,25 mm.…”

Outdoor Downward-Facing Optical Flow Odometry with Commodity Sensors

“…Due to their low cost and simplicity, there exists wide interest in the hobbyist robotics community in these sensors. Several examples of their use in limited indoor scenarios exist in the robotics literature (eg [15], [18], and [19]), but they have yet to see use in a field robot application. A method similar to that described here using a webcam and image correlation matching was presented in [12].…”