An AUV Based Experimental System For The Underwater Technology Education

In this paper, I introduce a series of AUV related basin experiment platforms now we are developing as a set of underwater technology educational tool. Existing AUV platforms are very expensive for general students or schools to purchase as an educational tool so the popularity of AUV technology among the general people is not still so high in Japan. On the other hand, land based robotic contest is very popular in Japan and its educational effect seems good for the wide range of students. I think it is important for us to develop a set of handy and low cost tools oriented to the underwater technology education and AUV related platforms which can use easily in a small basin will be one of the best choices. In this paper I will introduce our concept of the AUV based experimental systems as an underwater technology educational tool. The system is composed of two types of AUV test-beds, precise ultrasound ranging system, LBL coordinate detection system and 2FSK ultrasound communication system. The hardware and software design is introduced in this paper. The AUV test beds are designed considering a convenience of basin experiment using a 7inches-diameter acrylic sphere or 17inches-diameter glass sphere with low-cost embedded system with DOS/V PC 104 based subsystems. We constructed a set of 1 MHz carrier frequency ultrasound ranging system and 100 kHz LBL coordinate detection system. A 2FSK ultrasound communication system for basin experiment was tested. In our case, the basin is 3 m(W)c3m(D)_6m(L). So we designed both AUV testbeds as are enough for the handling and mobility in our basin experiment. The production cost must be suppressed while it has enough equipment for our purpose. The hull is transparent so we can implement optical communication using sets of infrared LED and phototransistor without using any penetrate connectors for the data communication between the inside equipment and outside equipment like an ultrasound module or a land PC. The underwater connector is relatively expensive compared to other equipment so we used it for power supply only and reduced the fabrication cost. On smaller one, the thruster is composed of a 4.5 W coreless motor with planetary gear and a four-blades propeller. We designed and fabricated the magnet coupling for watertight seal of the thruster to reduce the production cost. The smaller type?s total weight in air is about 3 kgf. As the total size is small (0.4 m[L]_0.4 m[B]_0.2 m[H]) we can handle it easily and many robots can swim in our basin. The hull is designed to bear the pressure at least 10 m water depth. We selected Lithium ion battery for power supply and the total capacity is 450 Wh. By power consumption calculation we may use it about 4 hours with one full charge of the batteries. The main PC is PC 104 module (Advantech PCM 3350) of which MPU is NS-Geode 300 MHz and 64 MB RAM. I implemented the RT-Linux based program system in 1 GB compact flash card from which the system boots. It controls the total system through PIC based subsystems. The RS-232 serial communication is used for gaining the ranged distance from the ultrasound controller of which MPU is PIC16F876. This RS-232 signal is also transmitted from the inside MPU to the outside PC by infrared data communication. So we can monitor the information inside the pressure hull without opening it. The program is implemented through Ethernet. The frequency of the sensing and actuation is at most 1 Hz this time, the timing is controlled by the RT-task mentioned later. An electric compass TCM2 is used to detect the heading angle and roll, pitch. I was afraid that the magnet compass is affected by the thruster or inner electric current, but at present, it doesn't matter. Each device like electric compass has its own PIC and all serial communication line is multi-dropped using 12 C through the communication interface PIC. The 6 underwater connector are attached for ultrasound transducers, thrusters, power supply and ethernet. The magnet switch is used for power on and off of 2 DC-DC, which corresponds to 12 V for thruster and 5 V for computers. The system generates maximum 4 PWM signals for the propeller speed control with motor driver ICs. As we mounted a wireless CCD camera inside, we can see the underwater image as far as the robot is near water surface. We have just finished the basic function test in the basin by free swimming. We have not implemented modern controller, we will try path tracking experiment in the next step.