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An autonomous mobile robot operating in an unknown indoor environment often needs to map the environment while localizing within the map. Feature-based world models including line and point features are widely used by researchers. This paper presents a novel delayed-classification algorithm to categorize these features using a recently developed high-performance sonar ring within a simultaneous localization and map-building (SLAM) process. The sonar ring sensor accurately measures range and bearing to multiple targets at near real-time repetition rates of 11.5 Hz to 6 m range, and uses 24 simultaneously fired transmitters, 48 receivers and multiple echoes per receiver. The proposed algorithm is based on hypothesis generation and verification using the advanced sonar ring data and an extended Kalman filter (EKF) approach. It is capable of initiating new geometric features and classifying them within a short distance of travel of about 10 cm. For each new sonar reading not matching an existing feature, we initiate a pair of probational line and point features resulting from accurate range and bearing measurements. Later measurements are used to confirm or remove the probational features using EKF validation gates. The odometry error model of the filter allows for variations in effective wheel separation required by pneumatic robot tyres. The implementation of the novel classification and SLAM algorithm is discussed in this paper and experimental results using real sonar data are presented.

Sonar rings are widely used for indoor mobile robota. However, it is difficult to perform on-thedly applications such as map boilding and locnlization using a conventional sonar ring due to low sped, accuracy md interference, Digital Signal Processing @SP) techniques and interference rejection Ideas are applled in this paper to design a new more sophisticated, fast and accnrate sonar ring d e d an advanced sonar ring. The advanced sonar ring consists of 48 ultrasonic transducers 24 acting as transceivers and 24 acting as receivers, seven DSP echo prbcessor boards, twelve four-channel 12-bit 500 lrHz ADCs and low noise variable gain preamplifiers. The sonar ring is able to cover 360 degrees around robot with slmultaoeonsly Bring of all 24 transmitters. Transmission and echo analysis are performed at repetition rates of about 15 Hz, depending ou the environment, for ranges up to sir metres. Aecurate distance and hearing measurements of objects are performed in the DSP system using matebed Mering techniques. The paper presents new transmit coding based on pulse duration to difierentiate neighbouring transmitters in the ring. Experimental date show the eflectiveness of the proposed system. Kcywordr -nllrasonic sensor; SOMI ring; sirndfonroas fibs; mUl@k DSP S e N D I ; PrOerSShg; hlerf0,~~U rejectkm I. b4lRODUCTlONSonar provides robots with a low cost active range sensor. A sonar ring is a set of sonar sensors configured around the robot to provide sensing of the m u n d i n g environment without the mechanical complication and delays associated with scanning sensors. Conventional sonar rings deploy Polaroid ranging modules or equivalent and suffer from poor @uing accuracy and interference problems [l, 21. Furthermore, the performance of robotic tasks such as simultaneously localization and map building, target tracking, obstacle avoidance and navigation are highly dependent on the availability of fast, accurate and on-the-fly sensing. Teruko Yata developed a sonar ring that allows simulbneous firing and thresholding of echo signals to measure reflectors with a bearing accuracy of around 1 degree [3, 41. In contrast, Digital Signal Processor @SP) systems have enabled the ultrasonic echo to be sampled at 12 hit amplitude resolution and 1 microsecond sample time and then processed in near real time to measure range to 0.2 mm and bearing to 0.1 degrees [SI. This approach is fast and accurate but operates in just one direction within the beamwidth of the transducers. Mechanical scanning and many measurements taken in sequence are needed to cover a full 364 degrees. With the decreasing cost and increasing performance of DSPs, it is now possible to petform intensive sonar echo processing around an entire ring of transducers from a single simnlfaneous set of transmissions in near real time. Thus the sequential scanning of the individual sonar sensors has been, condensed into one measurement cycle of the advanced sonar ring. The use of DSP local processing relieves communication problems with a host computer as in [a where a...

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