Tham khảo tài liệu 'mobile robots perception & navigation part 3', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Sonar Sensor Interpretation and Infrared Image Fusion for Mobile Robotics 71 Fig. 1 above shows a schematic of our biaxial sonar scan head. Although a variety of transducers can be used all of the results shown here use narrow-beam AR50-8 transducers from Airmar Milford NH which we ve modified by machining a concavity into the matching layer in order to achieve beam half-widths of less than 8 . The transducers are scanned over perpendicular arcs via stepper motors one of which controls rotation about the horizontal axis while the other controls rotation about the vertical axis. A custom motor controller board is connected to the computer via serial interface. The scanning is paused briefly at each orientation while a series of sonar tonebursts is generated and the echoes are recorded digitized and archived on the computer. Fig. 2 shows the scanner mounted atop a mobile robotic platform which allows out-of-doors scanning around campus. Fig. 2. Mobile robotic platform with computer-controlled scanner holding ultrasound transducer. At the frequency range of interest both the surface features roughness and overall shape of objects affect the back-scattered echo. Although the beam-width is too broad to image in the traditional sense as the beam is swept across a finite object variations in the beam profile give rise to characteristically different responses as the various scattering centers contribute constructively and destructively. Here we consider two classes of cylindrical objects outside trees and smooth circular poles. In this study we scanned 20 trees and 10 poles with up to ten different scans of each object recorded for off-line analysis Gao 2005 Gao Hinders 2005 . All data was acquired at 50kHz via the mobile apparatus shown in Figs. 1 and 2. The beam was swept across each object for a range of elevation angles and the RF echoes corresponding to the horizontal fan were digitized and recorded for off-line analysis. For each angle in the horizontal sweep we .