Autonomous Advertising Mobile Robot for Exhibitions, Developed at BMF

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1 Autonomous Advertising Mobile Robot for Exhibitions, Developed at BMF Kucsera Péter Abstract In this article an autonomous advertising mobile robot that has been realized in practice is going to be described. The whole development is based on industrial components. In the controlling and communication part, Phoenix Contact products were used, whereas the sensing was based on a Sick Laser Scanner. These two companies donated the whole project, and the final aim was to build up a working robot, which should advertise the companies on Hungarian and international exhibitions. The robot was successfully built up in the Process automation lab of the Budapest tech. Kandó Kalman Faculty of Electrical Engineering and was exhibited with great success on Regula 2009, which is the biggest Hungarian automation exhibition. Keywords: mobile robot, navigation, sensors, industrial control, robotics, mobile robotics The aim of the development In 2008 the students of the Process automation lab of the Budapest tech. Kandó Kalman Faculty of Electrical Engineering led by Peter Kucsera took part in the Xplore New Automation Award organized by Phoenix Contact with good results where they built a small experimental mobile robot. This robot could move along a predefined path, and could accomplish docking task with high accuracy. The project was chosen to the finals and it was so successful that Phoenix Contact decided to encourage us to continue the development of the robot and build up an advertising mobile robot of bigger size and more sophisticated mechanics and control. The company together with Sick wanted to have a moving object with a screen for advertising videos running on it, and they also wanted to place some leaflets on the robot for people to take them. It was essential for the robot to be absolutely safe. It is not allowed to run over the visitors, or to move to other companies stands. The accomplished system can be seen in figure 1.

2 2 Figure 1. The accomplished advertising mobile robot system The mobile robot system can be divided into two parts: - The moving mobile robot - The operator workstation placed on the Phoenix Contact stand In the case of a mobile robot system, the following tasks have to be solved. Firstly, information from the environment has to be sensed. Then, this information has to be processed and the proper command has to be sent to the actors. The acting of course changes the environment, so this process has to be done cyclically. The robot has to have some task, given by the operator, sent by a communication channel. Since the robot is moving, only wireless methods can be applied between the operator and the robot. This simple concept can be seen in figure 2. Control system Sensing Acting Real World Enviroment Figure 2. Scheme of mobile robot systems

3 3 Sensing It is really important to have fast distance measurement from the robot to the surrounding obstacles. If we see more, controlling is easier. So a fast 2 or 3 dimensional scanned distance measurement is needed. The typical method to measure distance is based on the time of flight measurement. A wave package is transmitted and after reflecting from the target it gets back to the transmission point and is sensed. Knowing the propagation speed of the wave and the running time, the distance can be calculated. Transmitting sound causes slow and inaccurate measurement, so usually laser light is used. This measuring equipment is called laser scanner. On our platform we used a SICK LMS dimensional laser scanner. This is the smallest scanner on the market whit 20m measuring range and 0.25 O phase resolution in 270 O scanning angle. The product was so new on the market, that we were probably the first who could try it in Hungary. The scanner can handle more predefined safety zones, switched by discrete inputs. This was really practical, since when the robot is turning the path is much different than when it moves straight. Figure 3. The defined safety zone when the robot is turning A web camera was also placed on the mobile part, there was always real time picture information from the robot, which made the operation easier, and the operator screen much more spectacular. Control The controlling system is based on a Phoenix industrial controller (PLC - Programmable Logic Controller). We used medium class PLC, which can handle Ethernet TCP/IP and RS232, serial communication. There are on board integrated I/O-s and industrial Bus couplers, so with connected extension modules new functions can be integrated. Handling the servos only needs two servo drive modules connected next to the PLC. This results in a really flexible system, which can be easily improved. Our whole controlling algorithm only loaded the CPU with 32%,

4 4 so there is still opportunity to improve the program. It is really practical that the Ethernet port is integrated, since it makes it easy to communicate with other devices like the laser scanner, and operator panel. Figure 4. The controller and the servo drives Actors and mechanics The simplest mechanical structure was chosen, which has two independently driven wheels by two brushed DC motors. A third support wheel is used to make the platform stable, and support it. Encoders were used to have feedback from the wheels. The wheel speed is controlled by the drives using PID closed control loop. Applying this structure has a great advantage. From the rotation of the wheels, when they are not slipping, the position can be estimated. This is really useful information in navigation. ϕ x2,y2 r s1 V β L α x1,y1 s2 Figure 5. Calculating the position from the turn of the wheels

5 5 Controlling algorithm The planned algorithm could build up a map from the real environment, and when the map is ready, a root could be defined. The navigation would be based on distance measurement between objects with known position and the robot, in this the position calculation from the wheel movement could help a lot. We had no time to accomplish this algorithm, since on an exhibition there are many dynamic, moving obstacles (the visitors) and it is really hard to make difference between the mapped obstacles and the dynamic ones. We decided to simple down the problem, by let the robot roam, without a predefined root, always looking for free spaces which are enough for it to change its position. When the robot has free area straight ahead, it moves straight, when it is not possible, it starts to rotate the scanning area, and searches the way, closest to the straight, where there is enough space for it to move. Also safety zones are defined in the scanner. If a dynamic object, for example a visitor, steps in the safety zone, the robot stops, and starts searching again for free roots. It was also requirement not to let the robot to move other companies stands. Fortunately, the carpet of the visitor area had different color, so only this had to be detected. Some of the companies stands were on an about 10 cm high podium. To detect them we had to place the scanner as low as possible. Placing the scanner to the lowest point, minimum 5 cm high objects could be detected. Despite these methods, the robot sometimes stuck on some especially difficult locations. For example, if the podium was lower than 5 cm, the robot could not see it, but it was not powerful enough to climb up. It could not detect obstacles which were wider in the upper part, and narrowed down in the lower part. This caused the robot stuck, which meant higher current on the motors, which was detected. A bumper was also placed on the robot. When an error signal came from the bumper or from the motors, the robot stopped, and switched to manual mode, and also on the remote operator panel an alarm was generated. With the help of the IP camera, the operator could actuate, and get the robot out of the problematic situation. Communication On the whole system, standard Ethernet communication was used. Since the PLC, the Laser Scanner, the operator and the webcam were connected, a switch was needed to connect these components together. Standard WLAN communication was used to communicate with the operator. In the system, industrial Ethernet components were used. This equipment is more expensive than the office components, but they are more reliable, it is easier to handle them, and they also have some extra functions. When the communication between the laser scanner and the PLC was tested, it was possible to mirror one communication port of the switch to another. This way, with a network analyzer program we could see the TCP/IP

6 6 packages between the two communicating devices, although the packages were not sent to our computer. The WLAN devices have a fast rooming function, so when a large area has to be covered by more than one Access Point, the client can switch faster between them. Power supply In the case of a mobile robot providing energy for the electric systems is quite an important problem. On our robot we have two DC motors with 120 W maximum power consumption. We also placed an industrial PC on the robot, which has about 80 W power need. Compared to these two loads the other components power consumption is irrelevant. At least one hour continuous working is needed, so a 12 Ah maintenance-free lead gel rechargeable battery can supply the system properly. Operator panel To operate the system, an operator computer is used. On this computer, it is possible to monitor the state of the robot, operate the behavior, switch to manual mode, and give commands manually, and also see the pictures coming from the camera which was placed on the robot. Reading values from the PLC is possible by using a special server program, called OPC server. The OPC server gives us an open source platform, to read the PLC registers. Figure 6. The accomplished operator interface

7 7 Visualizing the read values can be accomplished by an embedded software, but in the industry, there are ready to use software packages, called SCADA software. Since we used a Phoenix Contact controller, it was logical to use the SCADA of the same company which is called Visu+. With Visu+ it was really simple to establish communication with the PLC, reading and writing registers, and also to visualize the picture of the cam. The whole system, with the main components can be seen on figure 7. Figure 6. The accomplished system with the main components The outcome of the project The robot was exhibited with great success on Regula 2009, which is the biggest Hungarian automation exhibition. It gained popularity. Wherever it appeared it attracted attention. After the exhibition numerous companies enquired about the possibilities of borrowing the robot for other exhibitions. The robot was in function for 8 hours for 4 days, and moved at least 10 km. We could not detect any malfunctions. The robot functioned according to our expectations. Since most of the exhibitors had some WLAN device, the communication channel was overloaded, and we lost the connection between the robot and the operator, when the robot went to bigger distances. However, it did not cause any problem, since the platform is autonomous.

8 8 Figure 7. The autonomous advertising mobile robot in function Future Plans The controlling algorithm needs to be further developed. For the next automation exhibition a map based navigation method is planned to be accomplished. Knowing the map of the building, a root is going to be defined, and the robot will move on the predefined root, avoiding obstacles. Conclusion In this article, an autonomous advertising mobile robot is introduced. The robot was developed at Budapest Tech. Kando Kálmán Faculty of Electrical Engineering, in the laboratory of Process Automation. The aim of the project was to develop a working advertizing mobile robot platform for exhibition purposes, sponsored by Phoenix Contact and Sick Sensor Intelligence. Many students worked on the development, and gained useful practical knowledge in the field of automation, industrial communication, and visualization. On the robot, mainly industrial components were used. The main controller is a PLC, the communication based on industrial WLAN, and Ethernet components, and for the operation an industrial

9 9 PC with SCADA software is used. The project was exhibited with great success on Regula 2009, which is the biggest Hungarian automation exhibition. References: Introduction to Autonomous Mobile Robots Siegwart, R, Nourbahsh I R, The MIT Press Massachutsetts institute of Technology Cambridge 2004 Modeling of the Control Strategies of Wheeled Mobile Robots Mester Gy, Proceedings of The Kandó Konference, pp. 1-4, Budapest, ISBN Microcontrollers, Actuators and Sensors in Mobile Robots István Matijevics I4th Serbian-Hungarian Joint Symposium on Intelligent Systems September 29-30, 2006 Subotica, Serbia LMS100 Laser Measurement System application manual LMS100_ProductInformation.pdf, downloaded: User Manual for the WLAN Devices FL WLAN 24 (D)AP and FL WLAN 24 EC um_en_fl_wlan_ap_ec_7190_en_01.pdf, downloaded Letöltve: Uninterruptible Power Supply Unit for Universal Use, db_en_quint_dc_ups_24dc_10_101998_01_gb.pdf, downloaded Letöltve: Installing and Operating the Inline Controllers ILC 330 ETH, ILC 350 ETH, ILC 350 ETH/M and ILC 350 PN um_en_ilc_330_350_6959_en_05.pdf, downloaded: