Ultrasonic sensors are very useful for mobile robots because they have the advantage that the systems are simple and are easy to handle. When a mobile robot is navigated using an ultrasonic sensor, the map of the environment should include information about the reflection characteristics of objects. For this purpose, the map using a vector expression is better than a grid map. In this paper, an environment reconstruction method using a vector map is proposed. In this method, the environment is reconstructed from the data obtained by using our novel ultrasonic sensor which can measure the normal direction of walls, and the next sensing point is determined automatically. The experimental results of a map construction using this algorithm are shown. As a result of the experiments, it is found that the measurement of walls is possible using this method and the effectiveness of the planning algorithm for the sensing point is verified.>

With a conventional ultrasonic sensor system for a mobile robot, the distance to an ob- ject can be obtained with a time-of-flight (TOF) method, in which a reflected point is regarded to be located directly on the transducer line-of- sight. However, in an indoor environment, flat walls have specular characteristics. So, the real reflected point is not located on the transducer's lime-of-sight, because an echo from the normal in- cidence only returns to the transducer, since ul- trasonic directivity is not so sharp in air. So, to accurately recognize the position of an object, it is important to detect the direction of the re- flected point. One method to obtain the direction is to calculate it from the time difference between two parallel receivers. In this paper, an ultrasonic sensing method with a wide angle and high res- olution in specular environment is proposed, and accurate environment recognition can be realized.