**2.1 Mechanical system**

For the convenience of maintenance and also under the security consideration, we separate the battery system from other electronics systems, see Fig. 2. Main frame is made of AL-6061, fixing parts for camera and range sonar are made of POM. To increase the hydrodynamic mobility in the underwater horizontal plane, the open frame of vehicle is wrapped in a two-piece of FRP (Fibre-Reinforced Plastic) shell (Li et al., 2010).

Throughout its underwater missions, P-SURO is always keeping zero pitch angle using two vertical thrusters. With this kind of stability in its pitch dynamics, the vehicle's horizontal 3DOF motion is steered by two horizontal thrusters. From control point of view, this is a typical underactuated system. And how to design path tracking or following scheme for this kind of underactuated system has become one of most intense research area in the nonlinear control community (Jiang, 2002; Do et al., 2004; Li et al., 2008b).

Fig. 2. Mechanical arrangement of P-SURO AUV.

22 Autonomous Underwater Vehicles

As aforementioned, P-SURO AUV is a test-bed for developing underwater technologies. And most of its experimental tests will be carried out in an engineering basin in the PIRO with dimension of 12(L)×8(W)×6(D)m. Under these considerations, the vehicle is designed to be compact size with easiness of various algorithm tests (Li et al., 2010). The general

For the convenience of maintenance and also under the security consideration, we separate the battery system from other electronics systems, see Fig. 2. Main frame is made of AL-6061, fixing parts for camera and range sonar are made of POM. To increase the hydrodynamic mobility in the underwater horizontal plane, the open frame of vehicle is

Throughout its underwater missions, P-SURO is always keeping zero pitch angle using two vertical thrusters. With this kind of stability in its pitch dynamics, the vehicle's horizontal 3DOF motion is steered by two horizontal thrusters. From control point of view, this is a typical underactuated system. And how to design path tracking or following scheme for this kind of underactuated system has become one of most intense research area in the nonlinear

wrapped in a two-piece of FRP (Fibre-Reinforced Plastic) shell (Li et al., 2010).

control community (Jiang, 2002; Do et al., 2004; Li et al., 2008b).

Fig. 1. P-SURO AUV and its open frame.

specification of the vehicle is as Table. 1.

**Depth rating** 100m **Weight** 53kg

**Payload** ≤4kg

**2.1 Mechanical system** 

Table 1. General specification of P-SURO AUV.

**Item Specifications** 

**Dimension** 1.05(L)×0.5(W)×0.3(H)m

**Max. speed** FW: 2.5knot; BW, UP/DW: 1.5knot **Battery system** 400W·hr, Lithium Ion, Endurance: 2.5hrs

**2. P-SURO AUV overview** 


Table 2. Sensor & thrust system of P-SURO AUV.

Development of a Hovering-Type Intelligent Autonomous Underwater Vehicle, P-SURO 25

Software frame for each core module consists of thread-based multi tasking structure. For each module, there are various sensors connected through serial and analogue channels. And these serial sensors, according to their accessing mechanism, can be classified into two types: active sensor (frequently output measurement) and passive sensor (trigger mode). For these passive sensors as well as analogue sensors, we read the measurements through *Timer( )* routine. And for each of active sensors, we design a corresponding thread. In most of time, this thread is in *Blocking* mode until there is measurement output. And this kind of real-time sensor interface also can be used to trigger other algorithm threads. For example, in the navigation module, there is a thread designed for interfacing with AHRS sensor (100kHz of output rate). After accessing each of attitudes, gyro, and accelerometer output measurement, the thread will trigger *Navigation( )* thread. Moreover, some of these threads

As with the most of other AUVs so far, the P-SURO AUV has the similar overall software frame, which can be divided into two parts: surface remote control system and the vehicle software system. For surface system, the main functions of it are to monitor the vehicle and deliver the user command. According to the user command (mission command in this case), the vehicle will plan a series of tasks to accomplish the mission. For P-SURO AUV, its most experimental field is in a small cuboid. In this kind of environment, it is well known that underwater acoustic channel is vulnerable. For this reason, the vehicle is required to possess relatively high level of autonomy, such as autonomous navigation, obstacle avoidance, path

From the control architecture point of view, the software architecture of P-SURO AUV can be classified into hybrid architecture (Simon et al., 1993; Healey et al., 1996; Quek & Wahab, 2000), which is a certain combinaiton of hierarchical architecture (Wang et al., 1993; Peuch et al., 1994; Li et al., 2005) and behavioral architecture (Brooks, 1986; Zheng, 1992; Bennett, 2000). As aforementioned, because of the limitation of underwater acoustic communication in the engineering basin in PIRO, it is strongly recommended for the vehicle to selfaccomplish its mission without any of user interface in the water. For this consideration, the control architecture of P-SURO AUV is featured as a behavioral architecture based hybrid

are cautiously set with different priority values.

Fig. 4. Hybrid control architecture for P-SURO AUV.

planning and so on.

system (see Fig. 4).
