K. H. Low

Better Endurance and Load Capacity: An Improved Design of Manta Ray Robot (RoMan-II)

An improved design of a biomimetic underwater vehicle (RoMan-II) inspired by manta ray is presented in this paper. The design of the prototype and the swimming motion control are discussed. Instead of using rigid multiple degree-of-freedom linkages as fin rays in the first version, six flexible fin rays are adopted to drive two sided fins which generate thrust through flapping motions. Furthermore, in order to save the energy for a long distance cruising, a bio-inspired gliding motion is incorporated onto the motion control of the improved prototype. With a closed-loop buoyancy control system, the vehicle can perform gliding locomotion in water, which reduces the overall energy consumption. The vehicle can also perform pivot turning and backward locomotion without turning its body. It can achieve an average velocity of one body length per second. The vehicle is able to carry various sensors or communication equipments, as the payload capacity is about 4 kg. Initial testing shows that the operation time of the buoyancy body is estimated to about 6 hours for free swimming and 90 hours for a pure gliding. The flapping frequency, flapping amplitude, and the number of waves performed across the fin’s chord and wave directions can be independently tuned through the proposed control scheme. In general, the present prototype provides a useful platform to study the ray-like swimming motion in a single or combination mode of flapping, undulation and gliding.

On the development of a real time control system by using xPC Target: solution to robotic system control

Constructing a robotic control system usually needs much effort. Furthermore, the real time operating environment is required for a teleoperation/telemanipulation system. Work in this paper aims at developing a real time control system using xPC Target for robotic system control. By utilizing the software package MATLAB, Simulink, Real Time Workshop, xPC Target and a C/C++ compiler, the I/O boards are interfaced between the Simulink block and the robotic system such that the physical system is controlled successfully in the manner of hardware-in-the-loop simulation. The presented developing procedure shows a convenient way to implement a real time robotic control system, which does not require any low level language programming. Three case studies, which are single DC motor control, robotic hand control, and telemanipulation system control, are performed to demonstrate the advantages and easiness of developing robotic control system using xPC Target.

Kinematic modelling and analysis of mobile robots with omni-directional wheels

This paper focuses on the kinematic modelling, mobility analysis and design of an omni-directional wheeled mobile robots (OWMRs). The composite kinematic models of a wheeled mobile robot (WMR)-a WMR is a collection of the platform and the wheel sub-systems-with a platform equipped with three omni-directional wheels is formulated. The analysis on the mobility of a WMR is carried out using the functional matrix. It is shown that a WMR with three omni-directional wheels has a mobility of three. A prototype of a WMR with three omni-directional wheels are designed, built and tested successfully.

Kinematic modeling framework for biomimetic undulatory fin motion based on coupled nonlinear oscillators

The present work is motivated by the need to develop a generic method modeling the biomimetic undulatory motion for fish robots with long fin propulsors. Combined with mechanical design of long fins proposed in current literatures, we explore the application of coupled nonlinear oscillators in the modeling of swimming gaits and propose a kinematic modeling framework. Coupled nonlinear oscillators can also be regarded as models of artificial Central Pattern Generators (CPGs) for swimming gait control of fish robots. The advantages of this method over the normal sinusoidal functions based method are discussed. The synchronization of multiple oscillators is derived, which can be utilized for the coordination of multiple joints of fish robots and the online gait transition. The framework is applied and tested in swimming motion control of an eight-DOF undulatory fin prototype. The effectiveness of the control is shown through experiments.

Parametric Study of an Underwater Finned Propulsor Inspired by Bluespotted Ray

The performance of bluespotted rays was emulated in the design of a bioinspired underwater propulsor in the present work. First, the movement of a live bluespotted ray was captured for the swimming mode and useful information to the biomimetic mechanism design. By virtue of the modular and reconfigurable design concept, an undulatory fin propulsion prototype was developed. With a proper experimental set-up, orthogonal experiments were conducted to investigate the effect of various fin design parameters on the propulsion speed, thrust, and power of the fish robot. The controllable fin parameters include frequency, amplitude, wavelength, fin shape, and undulatory mode. The significance of these parameters was also determined by using the variance analysis. The results demonstrate that the designed propulsor, imitating bluespotted rays with large expanded undulatory fins, is able to propel itself by changing various kinematic parameters.

Locomotion Consideration and Implementation of Robotic Fish with Modular Undulating Fins: Analysis and Experimental Study

This paper presents an environment-friendly robotic system mimicking undulating fins of fish. To mimic the actual flexible fin of a real fish, we model a fin-like mechanism with a series of connecting linkages and attached it to the robotic fish. By virtue of a specially designed strip, each link is able to turn and slide with respect to the adjacent link. The driving linkages are used to form a mechanical fin consisting of several fin segments, which are able to produce undulations, similar to those produced by the actual fins. Owing to the modular design and the flexible structure of the mechanical fin, we were able to construct biomimetic robot fish with various swimming modes by fin undulations. Some qualitative and workspace observations by experiments with the robotic fish are shown and discussed

Adaptive gait planning for multi-legged robots with an adjustment of center-of-gravity

Adaptive gait planning is an important aspect in the development of control systems for multi-legged robots traversing on rough terrain. The problem of adaptive gait generation can be viewed as one of finding a sequence of suitable foothold on rough terrain so that legged systems maintain static stability and motion continuity. Due to the limit of static stability, deadlock situation may occur in the process of searching for a suitable foothold, if terrain contains a large number of forbidden zones. In this paper, an improved method for adaptive gait planning is presented by active compensation of stability margin, through center of gravity (CG) adjustment in the longitudinal axis and/or body translation in the lateral direction. An algorithm for the proposed method is developed and embedded in a computer program. Simulation results show that the method provides legged machines with a much larger terrain adaptivity and better deadlock-avoidance ability.

Reference Trajectory Generation for Force Tracking Impedance Control by Using Neural Network-based Environment Estimation

This paper presents a reference trajectory generation approach for impedance control by using neural networks to estimate the environment dynamics. In this method, the environment dynamics is estimated by a neural network (NN1), which constructs the relationship between the environment deformation and its first and second derivatives, and the interaction force. Another network (NN2) is then used to approximate the statics of the environment, which is the relationship between the interaction force and the deformation. The major advantage of the proposed method is that no exact environment model is required, so that it suites for operations on any unstructured environments. Furthermore, the neural networks have the capability of learning, due to which the precision of the generated reference trajectory will continuously be increased as the robot-environment interaction lasts. The system performance by using the proposed method is evaluated by simulations

A starfish robot based on soft and smart modular structure (SMS) actuated by SMA wires

This paper describes the design, fabrication and locomotion of a starfish robot whose locomotion principle is derived from a starfish. The starfish robot has a number of tentacles or arms extending from its central body in the form of a disk, like the topology of a real starfish. The arm, which is a soft and composite structure (which we call the smart modular structure (SMS)) generating a planar reciprocal motion with a high speed of response upon the actuation provided by the shape memory alloy (SMA) wires, is fabricated from soft and smart materials. Based on the variation in the resistance of the SMA wires during their heating, an adaptive regulation (AR) heating strategy is proposed to (i) avoid overheating of the SMA wires, (ii) provide bending range control and (iii) achieve a high speed of response favorable to successfully propelling the starfish robot. Using a finite-segment method, a thermal dynamic model of the SMS is established to describe its thermal behavior under the AR and a constant heating strategy. A starfish robot with five SMS tentacles was tested with different control parameters to optimize its locomotion speed. As demonstrated in the accompanying video file, the robot successfully propelled in semi-submerged and underwater environments show its locomotion ability in the multi-media, like a real starfish. The propulsion speed of the starfish robot is at least an order of magnitude higher than that of those reported in the literature-thanks to the SMS controlled with the AR strategy.

Numerical and Experimental Research on Modular Oscillating Fin

Fishes are famous for their ability to position themselves accurately even in turbulent flows. This ability is the result of the coordinated movement of fins which extend from the body. We have embarked on a research program designed to develop an agile and high efficient biologically inspired robotic fish based on the performance of hybrid mechanical fins. To accomplish this goal, a mechanical ray-like fin actuated by Shape Memory Alloy (SMA) is developed, which can realize both oscillatory locomotion and undulatory locomotion. We first give a brief introduction on the mechanical structure of our fin and then carry out theoretic analysis on force generation. Detailed information of these theoretical results is later revealed by Computational Fluid Dynamic (CFD), and is final validated by experiments. This robotic fin has potential application as a propulsor for future underwater vehicles in addition to being a valuable scientific instrument.