Gerald G. L. Seet

Robust and decoupled cascaded control system of underwater robotic vehicle for stabilization and pipeline tracking

The current paper proposes a robust and decoupled cascaded control system with output feedback control for simultaneous stabilization and pipeline tracking of a remotely operated vehicle (ROV) under hydrodynamic uncertainties. One of the ROV applications on the simultaneous stabilization and tracking was global output feedback with backstepping method on an ODIN ROV. However, the controller design becomes complex, as partial differential equations are required in the backstepping control law and the ROVs is inherently non-linear, highly coupled in motion, unsymmetrical in vehicle design, and vulnerable to hydrodynamic uncertainties. Compared with the backstepping control and other controllers, the computer simulation shows that the proposed method is simpler and performed better in time domain response and other performance measures such as robustness and stability.

Model of gated imaging in turbid media

Range-gated imaging can improve the signal to backscattering noise ratio (SBR) in turbid media. This is achieved by synchronizing a short duration, high intensity pulse with precise camera gating. It is well known that shorter pulse length and shorter camera gate duration can enhance the SBR. However, there is no analytical model of the backscattering noise (as a function of the pulse length and gate timing) that can be used to minimize backscattering noise within the camera-captured signal. We propose a formulation (a modification of Falks lidar equation) that models the backscattering noise as a convolution with a fixed upper limit. This formulation predicts a variation of backscattering noise within the returning signal. In particular, the model predicts higher SBR toward the tail region of the target-reflected irradiance. It confirms the experimental results reported by other authors. Additionally, the model explains experimentally observed SBR improvement for shorter pulses and shorter gating intervals (if adequately positioned within the returning pulse).

Control of an underactuated remotely operated underwater vehicle

Abstract In this paper, a steady state model of a thruster and a general equation of rigid-body motion for an underwater robotic vehicle (URV) is presented. By means of modelling, simulation and experiments, the model parameters have been identified. These are used in the analysis and design of closed-loop stabilizing controllers for two control modes: manual cruise and station keeping. Since the URV under study has fewer actuators than possible degrees of freedom, it is necessary to limit the controllable degrees of freedom. These variables are eventually selected based on the inherent vehicle dynamics. Using the Lyapunov direct method, which has been shown to be appropriate for such non-linear systems, appropriate stabilizing controllers have been designed. The manual cruise mode controller is non-linear and would result in chattering in the thruster outputs, but simulations show that the desired results can be achieved. The station-keeping mode controller has a proportional-integral-derivative (PID) structure and its gain values are designed using a non-linear optimizing approach. Simulation and swimming pool tests for the heave and yaw directions have shown that such a controller is possible.

An improved semi-empirical model for a body and/or caudal fin (BCF) fish robot

To develop useful applications for the underwater robots, the first step is to study its performance, such as thrust force or swimming velocity. In order to avoid numerous parameter studies in evaluating its performance, the prediction model plays an important role. As fishs swimming includes the kinematic of its own body and the hydrodynamic interaction with the surrounding fluid, it is difficult to formulate a precise mathematical model by purely analytical approaches. This paper offers a semi-empirical method to model the performance of a BCF (body and/or caudal fin) biomimetic fish robot. By using a dimensional statistical method, a semi-empirical model for predicting the thrust force generated by a BCF oscillation swimming mode is derived. This model shows good prediction capability. The predicted results are in good agreement with the experiment data. Therefore, the proposed modeling method can be used to solve the engineering problem concerned without a complex theory derivation.

Performance predict model for a body and caudal fin (BCF) biomimetics fish robot

This paper offers a method to model the performance of a BCF (body and/or caudal fin) biomimetic robotic fish. By using a dimensional analysis method, a semi-empirical model for predicting the thrust force generated by a BCF oscillation swimming mode is derived. This model shows good prediction capability, and the predicted results are in good agreement with the experiment data. Therefore, the proposed modeling method can be used to solve the engineering problem concerned without a complex theory derivation.

Quantitative image quality evaluations of enhanced images in turbid water medium

In order to improve underwater visibility, general considerations are planned in two stages. There is hardware upgrading followed by system optimization stage. For the former, we choose to improve the underwater visibility with advanced techniques: range gated imaging system, and the optimization in terms of image processing techniques. Four selected image enhancement technique has been tested, namely Contrast Stretching, CLAHE, Illumination-reflectance Model and Homomorphic Filtering. Quantitative image quality measures are used to evaluate the enhanced imaging techniques. Three image assessment techniques are used to quantify image quality of the imaging system in increased turbidity condition, namely Modified Fidelity (MF), Modified Strehl Ratio (MSR2), and Contrast-to-Noise Ratio (CNR). In the first stage, the quantitative measures have shown at least 40% improvement from non-gated to gated images in increased turbidity. Finally, the enhancement techniques further improve the gated images with limited noise amplification issues.

Hybrid Supervisory Control for Biomechatronic Systems for Non-Invasive Surgery

Several factors affect the safe operation of a bio-mechatronic system such as design limitations of the robots to do complex surgical manoeuvres, malfunction of the system’s components, unpredictability of the working envelope to name a few. One measure that can be taken in order to improve the safe performance is to implement a reliable control system. In our research, an optimal control hierarchy and strategy is considered for implementation for non-invasive surgical applications. A control strategy is proposed for supervisory hybrid control using PID and model-based robust control as the parameterized controllers and its implementation for FUSBOTBS (a custom designed robotic system using Focused Ultrasound Surgery for Breast Surgery) is demonstrated. Mechanical feasibility tests and in-vitro experimental trials supported the results with a positioning accuracy within 0.5mm.

Underwater lidar imaging (UWLI) system in short turbid water tank

We are first to demonstrate the underwater lidar imaging (UWLI) in such a 3 m short water tank with highly turbid water successfully, and show the range-gated phenomenon in water much more clearly based on our newly designed serial targets. The target set comprises a series of three bar test targets (five in total), which are set at intervals of 22.5 cm roughly along the laser illumination direction since the light speed in water is 22.5 cm/ns. We synchronize precisely (approximately 0.5 ns) the UWLI system to range-gate on the targets which we want to capture their images, and to range- gate out the targets which we do not want their images. The attenuation coefficients in water are 1.0/m and 2.3/m (extremely turbid). Compared with non-gated case, the most distinct difference between the gated images and non-gated images in turbid water is that the nearer the target is located, the clearer its image is on the non-gated photos, but for the gated case the situation will be inverted completely when the delay time is adjusted suitably; that is, the image of the farther target could be much clearer than the image of the nearer target even in very turbid water.

Minimally invasive robotic HIFU neurosurgical applications

Due to complex anatomy and functionality of brain, volumetric excision of abnormal tissue targets such as tumors/cancers poses a great risk as it is difficult without causing harm to the overlying normal structures. Minimally invasive and non-invasive robotic approaches are being widely investigated as alternatives to traditional open surgery due to their advantages in accurate planning, registration, navigation and manipulation. In this paper, we present robot-assisted minimally invasive means for volumetric ablation of brain tumors using High Intensity Focused Ultrasound (HIFU) modality through a precise craniotomy. The end-effector is capable of integrating and registering the prevalent single, multiple or phased array applicators coupled to dura-mater using a flexible degassed water chamber. Our customized modular robot named, Neurobot, comprising of various modules that work in active and passive modes and its treatment planning are described. The robot is equipped with alternating end-effectors respectively for drilling and energy delivery and the measured accuracy of this system is within 0.1 mm.