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SENSORES DE ULTRASONIDO

Introducción

Tanto en la actualidad como en el pasado, numerosos robots móviles han utilizado sensores de ultrasonidos para realizar tareas de navegación por el entorno como, por ejemplo, evitar obstáculos, seguir paredes, atravesar puertas, etc. Las razones de su utilización son numerosas y entre ellas cabe destacar su bajo coste, velocidad de procesamiento y una más que aceptable precisión. Sin embargo, la navegación de un robot móvil basada en la información suministrada por un conjunto de sensores de ultrasonidos presenta una serie de inconvenientes debidos, sobre todo, a los numerosos errores que cometen estos sensores en sus medidas.

En efecto, una única medida proporciona poca información acerca del entorno, y mediante la acumulación de la evidencia de una serie de medidas, se incrementa la precisión de la localización de los diversos obstáculos que hay en el entorno. Por tanto, una forma de reducir la incertidumbre intrínseca a los sensores de ultrasonido es la utilización de mapas del entorno donde sucesivamente se vayan plasmando y actualizando las medidas realizadas. Por otro lado, al moverse el robot por el entorno, la incertidumbre en la generación del mapa y su actualización se va acrecentando con el tiempo, debido a que el error en la estimación de la posición del robot respecto a un sistema de referencia general es acumulativo y va creciendo con el tiempo. Por tanto, se debe contar con un procedimiento que permita reducir la incertidumbre de la posición del robot para mantener la coherencia espacial de las diferentes medidas. En definitiva, en la generación y actualización de un mapa basado en la información suministrada por los sensores de ultrasonido embarcados en un robot móvil podemos hablar de dos fuentes de incertidumbre :

  1. .Incertidumbre determinación de la posición de robot, e
  2. .incertidumbre en las propias medidas.
En el presente capítulo haremos en primer lugar una breve descripción de los diferentes errores asociados a los sensores de ultrasonido, pasando a continuación a realizar un estudio más detallado de la incertidumbre asociada a la estimación de la posición del robot. En el apartado siguiente se hará un resumen de las diferentes técnicas utilizadas hasta hoy a la hora de minimizar la incertidumbre de estas dos fuentes. Finalmente, se abordará la descripción del sistema desarrollado incidiendo en el concepto definido en este trabajo como decremento temporal en la certeza de la presencia de obstáculo. Demostraremos cómo con este sencillo principio se puede abordar de una manera fiable las dos fuentes de incertidumbre y se repasarán las diferentes ventajas que se derivan de aplicar este principio a la generación y mantenimiento del mapa de ultrasonidos.

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