Tianmiao Wang

Development of a two-joint robotic fish for real-world exploration

Research on biomimetic robotic fish has been undertaken for more than a decade. Various robotic fish prototypes have been developed around the world. Although considerable research efforts have been devoted to understanding the underlying mechanism of fish swimming and construction of fish-like swimming machines, robotic fish have largely remained laboratory curiosities. This paper presents a robotic fish that is designed for application in real-world scenarios. The robotic fish adopts a rigid torpedo-shaped body for the housing of power, electronics, and payload. A compact parallel four-bar mechanism is designed for propulsion and maneuvering. Based on the kinematic analysis of the tail mechanism, the motion control algorithm of joints is presented. The swimming performance of the robotic fish is investigated experimentally. The swimming speed of the robotic fish can reach 1.36 m/s. The turning radius is 1.75 m. Powered by the onboard battery, the robotic fish can operate for up to 20 h. Moreover, the advantages of the biomimetic propulsion approach are shown by comparing the power efficiency and turning performance of the robotic fish with that of a screw-propelled underwater vehicle. The application of the robotic fish in a real-world probe experiment is also presented.

Novel Method for the Modeling and Control Investigation of Efficient Swimming for Robotic Fish

In this paper, analytical techniques and fuzzy logic method are applied to the dynamic modeling and efficient swimming control of a robotic fish. The bioinspired robotic fish, which follows an exact replica of a live mackerel (Scomber scombrus), is modeled by treating the undulating body and flapping tail independently using analytical methods. Comparing the results of simulations and experiments shows the feasibility of the dynamic model. Using this model, we found that the harmonic control of the Strouhal number and caudal fin angle of attack is a principal mechanism through which the robotic fish can obtain high thrust efficiency while swimming. The fuzzy control method, which is based on the knowledge of the robotic fishs dynamic behavior, has successfully utilized this principal mechanism. By comparing the thrust performance of the robotic fish with different control methods via simulation, we established that the fuzzy controller was able to achieve faster acceleration and smaller steady-state error than what could be achieved from an open-loop and conventional proportional-integral-derivative controller. The thrust efficiency during steady state was superior to that with conventional control methods. We also found that, when using the fuzzy control method, robotic fish can always swim near a “universal” Strouhal number that approximates to the swimming of live fish.

Sambot: A self-assembly modular robot for swarm robot

This paper presents a novel self-assembly modular robot (Sambot) that also shares characteristics with self-reconfigurable and self-assembly and swarm robots. Each Sambot can move autonomously and connect with the others. Multiple Sambot can be self-assembled to form a robotic structure, which can be reconfigured into different configurable robots and can locomote. A novel mechanical design is described to realize function of autonomous motion and docking. Introducing embedded mechatronics integrated technology, whole actuators, sensors, microprocessors, power and communication unit are embedded in the module. The Sambot is compact and flexble, the overall size is 80×80×102mm. The preliminary self-assembly and self-reconfiguration of Sambot is discussed, and several possible configurations consisting of multiple Sambot are designed in simulation environment. At last, the experiment of self-assembly and self-reconfiguration and locomotion of multiple Sambot has been implemented.

Quantitative Thrust Efficiency of a Self-Propulsive Robotic Fish: Experimental Method and Hydrodynamic Investigation

The robotic fish that utilize the body/caudal fin undulatory locomotion has long interested both biologists and engineers. Although a variety of free swimming robotic fish prototypes have already been developed, very few studies addressed the methods for determining quantitative thrust efficiency. In this paper, we propose a novel experimental method that enables the simultaneous measurement of the power, wake flow field, and self-propulsive speed of a robotic fish, which together facilitate a quantitative measurement of its efficiency. Our results show that the optimal thrust efficiency of the robotic swimmer is within the Strouhal number (St) range of 0.3 ≤ St ≤ 0.325 when single-row reverse Karman vortices are produced. Nevertheless, present robotic fish swam at Strouhal numbers outside the optimal region under self-propulsive condition, and produced another type of wake structure: “double-row vortices.” We also show that robotic fish that utilize a low amplitude with a large flapping frequency produce higher self-propulsive speeds, whereas a larger amplitude paired with lower frequency results in higher efficiency. Additionally, a peak efficiency value of 31.6% is recored for the self-propulsive robotic swimmer. The general applicability of this experimental method indicates that broader issues regarding thrust efficiency for biomimetic underwater propulsive robots can be quanlitantively measured.

A wearable wireless fall detection system with accelerators

Falls in elderly is a major health problem and a cost burden to social services. Thus automatic fall detectors are needed to support the independence and security of the elderly. The goal of this research is to develop a real-time portable wireless fall detection system, which is capable of automatically discriminating between falls and Activities of Daily Life (ADL). The fall detection system contains a portable fall-detection terminal and a monitoring centre, both of which communicate with ZigBee protocol. To extract the features of falls, falls data and ADL data obtained from young subjects are analyzed. Based on the characteristics of falls, an effective fall detection algorithm using tri-axis accelerometers is introduced, and the results show that falls can be distinguished from ADL with a sensitivity over 95% and a specificity of 100%, for a total set of 270 movements.

Bionic mechanism and kinematics analysis of hopping robot inspired by locust jumping

A flexible-rigid hopping mechanism which is inspired by the locust jumping was proposed, and its kinematic characteristics were analyzed. A series of experiments were conducted to observe locust morphology and jumping process. According to classic mechanics, the jumping process analysis was conducted to build the relationship of the locust jumping parameters. The take-off phase was divided into four stages in detail. Based on the biological observation and kinematics analysis, a mechanical model was proposed to simulate locust jumping. The forces of the flexible-rigid hopping mechanism at each stage were analyzed. The kinematic analysis using pseudo-rigid-body model was described by D-H method. It is confirmed that the proposed bionic mechanism has the similar performance as the locust hind leg in hopping. Moreover, the jumping angle which decides the jumping process was discussed, and its relation with other parameters was established. A calculation case analysis corroborated the method. The results of this paper show that the proposed bionic mechanism which is inspired by the locust hind limb has an excellent kinematics performance, which can provide a foundation for design and motion planning of the hopping robot.

Fuzzy vorticity control of a biomimetic robotic fish using a flapping lunate tail

Vorticity control mechanisms for flapping foils play a guiding role in both biomimetic thrust research and modeling the forward locomotion of animals with wings, fins, or tails. In this paper, a thrust-producing flapping lunate tail is studied through force and power measurements in a water channel. Proper vorticity control methods for flapping tails are discussed based on the vorticity control parameters: the dimensionless transverse amplitude, Strouhal number, angle of attack, and phase angle. Field tests are conducted on a free-swimming biomimetic robotic fish that uses a flapping tail. The results show that active control of Strouhal number using fuzzy logic control methods can efficiently reduce power consumption of the robotic fish and high swimming speeds can be obtained. A maximum speed of 1.17 length specific speed is obtained experimentally under conditions of optimal vorticity control. The St of the flapping tail is controlled within the range of 0.4∼0.5.

Design and control of the BUAA four-fingered hand

This research presents a multi-fingered hand and computer control system intended for research in dextrous manipulation. The hand mechanism is based on an anthropomorphic configuration with four identical fingers. Each finger has four degrees of freedom actuated by four DC servomotors. The fingers, palm and mechanical interface to a robotic arm are separate components of a modular design allowing the hand to be highly dexterous and flexible. Each finger is a compact module with eight position sensors, and all the four actuators are integrated into the mechanical structure of the finger module. Position control has been implemented using a DSP based computer controller. Experimental results validate that the basic functionality and requirements of the hand system were achieved.

Parameter Synthesis of Coupled Nonlinear Oscillators for CPG-Based Robotic Locomotion

This paper presents a numerical method for parameter synthesis of a central pattern generator (CPG) network to acquire desired locomotor patterns. The CPG network is modeled as a chain of unidirectionally or bidirectionally coupled Hopf oscillators with a novel coupling scheme that eliminates the influence of afferent signals on amplitude of the oscillator. The method converts the related CPG parameters into dynamic systems that evolve as part of the CPG network dynamics. The frequency, amplitude, and phase relations of teaching signals can be encoded by the CPG network with the proposed learning rules. The ability of the method to learn instructed locomotor pattern is proven with simulations. Application of the proposed method to online gait synthesis of a robotic fish is also presented.

A novel method based on a force-feedback technique for the hydrodynamic investigation of kinematic effects on robotic fish

In this paper, techniques of force-feedback control are applied to the hydrodynamic study of a laboratory robotic fish. The experimental apparatus which allows a robotic model to accelerate from rest to a steady speed under self-propelled conditions is clearly described. In the current apparatus, the robotic fish is mounted on a servo guide rail system and the towing speed is not preset but determined by the measured force acting on the body of the fish. Such an apparatus enables the simultaneous measurement of power consumption, thrust efficiency and speed of a robotic model obtained under self-propelled conditions. The thrust efficiency of the robotic fish can be estimated based on a 2-D vortex ring force estimation method. By comparing the thrust performance of carangiform body-shaped robotic swimmer with different typical BCF (body and caudal fin ) swimming modes, i.e. anguilliform, carangiform and thunniform, we show that the robotic swimming fish with the thunniform kinematic movement not only reaches a higher steady swimming speed but is also more efficient than the other two modes However, in the start phase, using the anguilliform kinematic movement, the robotic swimmer accelerates faster among all kinematic movements. Ultimately, we found that the robotic fish always produce a double-row wake structure no matter which swimming mode used.