Braille Block Detection for Autonomous Mobile Robot Navigation

Transcription

1 Braie Bock Detection for Autonomous Mobie Robot Navigation Tomoaki Yoshida Akihisa Ohya Shin ichi Yuta Inteigent Robot Laboratory University of Tsukuba Tsukuba , Japan Abstract A mobie robot can use the was or the piars to ocaize itsef when it navigates in indoor environment. However, in open space or outdoor environment there are few easy detectabe and stabe object that the robot can use. In this paper, we propose a method for the detection of braie bocks, which are originay used for visuay handicapped peope, for autonomous mobie robot navigation. To recognize the braie bock, a CCD camera and a aser fan beam projector are used as sensor to detect bumps on road surface. This paper aso presents the experimenta resuts of braie bock foowing using the sensor system to detect the braie bock position and orientation. This experiment shows effectiveness of the sensor system for the braie bock recognition and impies the possibiity of braie bock based mobie robot navigation unit: mm Figure 1: Two styes of braie bock eft: dot stye bock right: ine stye bock 1 Introduction Locaization is an important function of autonomous mobie robot. In indoor environments, there are many objects which are easiy observed such as was, doors and piars. These objects are aso easiy recognized by human, so environmenta maps for mobie robots can be buit easiy by human. On the other hand, ocaization in outdoor environments is not easy. Some projects use the image processing technoogy for ocaization[2][3][5], but their systems are too compex and too arge to impement into a sma sized mobie robot. There are many paces where braie bocks are paced these days in urban areas in Japan and some other countries. The braie bock is a safety equipment for visuay handicapped peope. Hence they can wak aong the street using information of the braie bocks. In this study, we use the braie bocks to guide the autonomous mobie robot. In this paper, we describe mobie robot navigation using the braie bocks. At first, what the braie bocks are and how the mobie robot uses them for navigation are described. Then the mobie robot system incuding sensors and controers we have deveoped are described. And finay, experimenta resut of the ocaization process using the braie bocks is discussed. 2 The braie bock There are two kinds of braie bocks, dot stye bock and ine stye bock. Fig. 1 shows the shape of bocks having ine stye or dot stye of convex parts which are 5mm high. The standard coor of the bock is yeow, but severa variations are permitted. When a visuay handicapped peope step on the bocks, using the sense of touch through their soes, they can know information about the street such as the they can move and the existence of junctions. Fig.2 shows an exampe of the actua braie bock ar-

2 Line stye bock Dot stye bock Figure 3: Exampe pattern of the braie bock Figure 2: Exampe of braie bocks on pedestrian rangement. Line stye bocks are usuay arranged in ine and figures the position and of the path. At the corner of the path, dot stye bocks are paced. Dot stye bocks are paced aso at the junction of the path and some interesting paces such as bus stops or the entrances of buidings. termina path(60cm) junction path(90cm) path(120cm) termina junction path(90cm) termina 3 Utiization of braie bocks for mobie robots In structured environments, wa foowing and ine tracing are easy and effective method for mobie robot to track the pre-defined ong path. Using sequence of the ine stye bocks as pre-defined path, outdoor environment can be simpified. Basicay the mobie robot foows the sequence of ine stye bock. When a dot stye bock is found, using a map buit in advance by human, the robot can decide the next action. Buiding the map is reativey easy because the path is aready defined as sequence of ine stye bocks and the ength of the path can be measured by counting the number of the bocks. 3.1 Detection of braie bocks Braie bocks have two major specia features which are used to distinguish them from norma road surface. One is its coor, which normay is yeow. This feature is for weak eyesight peope and hep them to find it by its high contrast coor. This feature can be used to detect the bocks with coor camera[6]. However this is recommended feature by the guide ine and not mandatory, so it is not aways yeow Figure 4: Corresponding environmenta map to the bock pattern shown in Fig.3 especiay in sight aware pace. Aso with this feature, it is hard to distinguished the type of braie bock. The other feature is its physica shape. The height of its convex part is 5mm regardess of the type of the braie bock, and the type of the bock can be distinguished ony by the shape of convex part. We use this feature for detecting the braie bocks with the aser fan beam projector and a camera. In this way, it shoud be possibe to detect the existence of bock and recognize the type and position and of the sequence of bocks. 3.2 Map of braie bocks The mobie robot shoud have information about the braie bock arrangement as an environmenta map so that the robot can pan the path using the map. The map shoud contain the foowing information. Length of the sequence of the ine stye bocks The junction or the corner where the dot stye bocks are paced and s of the paths connected to the

3 Camera Camera Height h Camera ange c Laser irradiation ange Target distance Laser source Figure 5: Configuration of the aser source and the camera junction Termina of the sequence of braie bocks Fig.3 shows a exampe pattern of braie bocks, and the corresponding environmenta map shoud contain the information shown in Fig.4. The ength of the path is used to predict that a dot stye bock coud exist at the end of the path. With this prediction, the robot can sow down and carefuy search for the dot stye bock if necessary. 3.3 Navigation with braie bocks By giving the current and target position in the environmenta map, the mobie robot can pan a path on the map and navigates itsef to the target position. Navigation is done by tracing the sequence of ine stye bocks and choosing the proper path at a junction according to the pan. 4 Robot system 4.1 Sensors Using infrared aser fan beam and camera with interference fiter, the difference of height can be detected by trianguation with simpe image processing. To satisfy the requirement of resoution, the aser source and the camera must be carefuy configured. Fig.5 shows the configuration of this sensor system. With a CCD camera which outputs NTSC video signa with a ens whose foca ength is 8.5mm, the camera height shoud be 50cm high and aser irradiation ange must be Figure 6: Mobie robot equipped with the aser source and the camera ess than 10 degrees to gain enough sensitivity to detect bumps of braie bocks that are 5mm high. Fig.6 shows the mobie robot with the sensor system, in the aser irradiation ange is 5 degree and the camera height is 55cm. Fig.7 shows an image taken with the camera. In this figure, aser fan beam can be found around the center of this image and the convex parts of the ine stye bock are figured by the aser fan beam as the shape of it. 4.2 Mobie robot patform The mobie robot which is used for this study is named YAMABICO-fra, one of YAMABICO famiy mobie robots deveoped in our aboratory[1]. Its dimensions are approximatey 40 cm (W) 40 cm (D) 50 cm (H) without camera and 70 cm high incuding it. 4.3 Controers The controer architecture of YAMABICO-fra is shown in Fig.8. Function modues shown in beow haf are the common system of YAMABICO famiy mobie robot. Each function modues have own processor connected with transputer ink or dua port memory and work simutaneousy. A note book PC running Linux is used as image processor and as main controer. The PC and the other function modues are connected with standard seria port to contro ow eve function modues from the PC. Two of three TYPE-II PCMCIA sots are used by a Video capture card and an Ethernet card which is connected to a wireess LAN modue for monitoring the robots status.

4 PCMCIA Video Capture Card PCMCIA Ethernet Card CCD Camera PentiumMMX (Linux2.2.1) Wireess LAN Interface Modue T805 (Liberos) Function Modues Motion Contro Position estimation Utrasonic sensor Map / Pan Figure 7: Image from the camera aimed at the ine stye bock T805(Liberos) MC68000(MOSRA) T805(Liberos) Figure 8: The controer architecture of YAMABICO-fra 5 Recognition of the ine stye bock The purpose of recognition of the ine stye bock is to foow the sequence of ine stye bocks. Hence two parameters must be known. One is the distance between the ine of the bocks and the robot and the other is ange between robot s heading and it of the ine. 5.1 Position of the ine stye bock Because of ine stye bock s shape, the bock can be found by searching for periodicay appearing bumps on the projected aser fan beam in a captured image (see Fig.9). Once the position of the bumps on the captured image determined, the actua position of the bock on the ground can be cacuated using foowing equations. Y htan θ φ h x x c x X f cos θ φ φ arctan y y c y f f : Foca ength of the camera h : Height of the camera position x, y : CCD pixe size θ : Camera ange of depression x c,y c : Position of optica center X,Y : Actua position reative to the camera This function uses the camera position reative to road surface. If the robot becomes unstabe and swing his head Figure 9: The captured image and drawn resut of bump searched on it as vertica ine back and forth, these parameter may change. Assuming the aser irradiation ange is sma enough and reative position of aser source from the camera is fixed, coordinates on the road surface and on the surface of aser fan beam are amost the same. Hence the previous equations can be atered by the foowings (see Fig.10). Y X d cosθ c 1 tanθ c d Y cosφ x x c x cos θ c arctan y y c y f f 2 y y c y f y y c y 2 : Distance between the camera and the crossing point of the optica axis and surface of aser fan beam

5 camera Virtua surface of projection Laser source Y c foor d Figure 10: A mode for coordinate transformation without parameters reative to road surface Figure 12: Experimenta environment Xe W t : actua interva of convex parts on the bock Ye X e,y e : detected interva of bumps w t Figure 11: The ine stye bock on which aser fan beam projected : Distance between the aser source and the crossing point of the optica axis of the camera and surface of aser fan beam θ c : Ange between optica axis of the camera and surface of aser fan beam 5.2 Direction of the ine of bocks Comparing the detected interva of bumps and the actua distance of convex parts on the ine stye bock, the of the ine of bocks can be cacuated as foows (see Fig.5.2). θ arccos X 2 e Y 2 e W t arctan Y e X e θ : reative ange of the ine stye bock points to from the robot 6 Experimenta resuts With the mobie robot YAMABICO-fra, an experiment of ine stye bock foowing and dot stye bock detection has been conducted to confirm the proposed recognition method. In this experiment, the robot does not have the environmenta map and just foows ine stye bocks. Fig.12 shows experimenta environment. The path defined by ine stye bocks incudes a corner without dot stye bock. The experiment has been done just after sunset and aso day time of coudy day. The robot runs at 9cm s and captures camera image every 200ms, and it is frequent enough to get sufficient number of cean images that the aser beam is not crossing the connected points of ine stye bocks. Fig.13 shows the resut of this experiment. The initia position of the robot is at (0,0) and heading to positive of x axis. The robot successfuy foow the ine stye bocks in this experiment. At the corner, it faied tracking ine stye bock in short term because of narrow sensor range. But the robot detects not ony the position of the ine stye bocks but aso their, it coud foow new and start tracking new ine of bocks again.

6 Detected ine stye bock Robot position x [4] S. Yuta, S. Suzuki, Y. Saito, S. Iida, Impementation of an Active Optica Range Sensor Using Laser Sit for In-Door Inteigent Mobie Robot, Internationa Conference of Inteigent Robots and Systems, November [5] S. Tachi, K.Komoriya Guide Dog Robot Internationa Symposium on Robotics Research Vo.2, pp y [6] H. Mori, K. Kobayashi, N. Ohtuki, S. Kotani, Coor Impression Factor: an Image Understanding Method for Outdoor Mobie Robots, Internationa Conference of Inteigent Robots and Systems, pp ,september 1997 unit:mm Figure 13: Detected ine stye bock positions and detected position of the robot 7 Concusion In this paper, we described a detection method of braie bocks for mobie robot navigation and presented sensor system for recognition of braie bocks. Using this sensor system, mobie robot can foow the ine stye bocks and detect the dot stye bocks. The resut of the experiment shows effectiveness of this method in both indoor and outdoor environments. In the future work, we wi impement a dot stye bock detection agorithm which is not described in this paper. Aso we wi construct the navigation system for out door environment using proposed sensor system. References [1] S. Yuta, Autonomous Sef-contained Robot Yamabico and its Controer Architecture, Third Austraia Nationa Conference on Robotics, June 1990 [2] S. Kotani, K. Kaneko, T. Shinoda, H. Mori, Mobie robot Navigation Based on Vision and DGPS Information, Internationa Conference on Robotics and Automation, pp ,may 1998 [3] C.Thorpe, M.H.Hebert, K.Kanade, S.A.Shafer, Vision and Navigation for the Carnegie-Meon Navab, IEEE Transactions on Pattern Anaysis and Machine Inteigence, Vo.10,No.3,pp ,May 1988