K.H. Low

Biomimetic Motion Planning of an Undulating Robotic Fish Fin

This paper presents a locomotion control implementation of a robotic system mimicking the undulating fins of fish. To mimic the actual flexible fin of a real fish, we created a ribbon fin type actuation device with a series of connecting linkages and attached it to the robotic fish. By virtue of a specially designed strip withaslider, eachlinkisabletoturnandslidewithrespect 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 actual fins. By virtue of the modular and reconfigurable fin mechanisms, two robotic fish with different fin layouts have been designed and constructed: The first prototype is a robotic stingray, swimming by undulations of a pair of lateral fins-the second is a robotic knifefish, swimming by undulations of a long anal fin. The locomotion scheme and mechatronics implementation of the robotic stingray are presented and discussed with a parametric study of the slider’s workspace and joint trajectory. Some experimental observations of the robotic knifefish are alsoshownanddiscussed. Theresults demonstrate that the designed fin mechanisms are able to undulate sections of pectoral and anal fins, with different amplitudes and phases, along the length of the fin in the direction of motion. This may lead to further developments that better mimic the fin locomotion capability of real fish.

A Lagrangian formulation of the dynamic model for flexible manipulator systems

This paper presents a procedure for deriving dynamic equations for manipulators containing both rigid and flexible links. The equations are derived using Hamiltons principle, and are nonlinear integro-differential equations. The formulation is based on expressing the kinetic and potential energies of the manipulator system in terms of generalized coordinates. In the case of flexible links, the mass distribution and flexibility are taken into account. The approach is a natural extension of the well-known Lagrangian method for rigid manipulators. Properties of the dynamic matrices, which lead to a less computation, are shown. Boundary-value problems of continuous systems are briefly described. A two-link manipulator with one rigid link and one flexible link is analyzed to illustrate the procedure.

Development of NTU wearable exoskeleton system for assistive technologies

This paper presents a wearable lower extremity exoskeleton (LEE) developed as a platform for research works on enhancement and assistive the ability of humans walking and load carrying. The whole process of the first prototype design is introduced together with the sub-systems, inner/outer exoskeleton, the attached flexible waist and footpad with sensors. Simulation model and feedback control with the ZMP method were established using Adams and Matlab. The ultimate goal of the current research work is to design and control a power assisted system, which integrates humans intellect as the control system for manipulating the wearable power-aided device. The feasibility and initial performance of the designed system are also discussed.

Development of a lower extremity exoskeleton for human performance enhancement

Exoskeletons for human performance augmentation are controlled and wearable devices or machines that can increase the speed, strength, and endurance of the operator. So far most researchers focus on the upper limb exoskeletons. To help those who need to travel long distances by feet with heavy loads such as infantry soldiers, this paper presents a control principle of a lower extremity exoskeleton. An exoskeleton foot is designed to measure the human and the exoskeletons ZMP. Using the measured human ZMP as the reference together with the human leg position signals, the exoskeletons ZMP is modified by trunk compensation. Test prototypes and initial experiment results are also demonstrated.

Locomotive Control of a Wearable Lower Exoskeleton for Walking Enhancement

This article presents a wearable lower extremity exoskeleton (LEE) designed to augment the ability of a human to walk while carrying payloads. The ultimate goal of the current research is to design and control a wearable power-assisted system that integrates a human’s intellect as the control command. The system in this work consists of an inner exoskeleton and an outer exoskeleton. The inner system measures the movements of the human and controls the outer system, which follows the human movements and supports the payload. A special foot-unit was designed to measure the zero moment points (ZMPs) of the human and the exoskeleton simultaneously. Using the measured human ZMP as the reference, the exoskeleton’s ZMP is controlled by trunk compensation to achieve stable walking. A COTS program, xPC Target, together with toolboxes from MATLAB, were used as a real-time operating system and integrated development environment, and real-time locomotion control of the exoskeleton was successfully implemented in this environment. Finally, some walking experimental results, by virtue of the ZMP control for the inner and outer exoskeletons, show that the stable walking can be achieved.

Development and initial experiment of modular undulating fin for untethered biorobotic AUVs

An environment-friendly propulsion system mimicking undulating fins of cuttlefish or stingray has been built. A nonconventional method was considered to model the flexibility of the fins of cuttlefish or stingray. A two-degree-of-freedom mechanism comprises several linkages was designed and constructed to mimic the actual flexible fin. 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 modularity of the design of the mechanical fin, we were able to construct various biomimetic robots of fish swimming by fin(s) undulations. Two variants are shown in this paper: the first is a biomimetic robot of a South American electric fish swimming by undulations of a long anal fin, and the second is a biomimetic robot of a cuttlefish swimming by undulations of its lateral fins. Some qualitative observations, obtained by experiments, predicted several factors affecting the thrust produced by the mechanical fins. Future work may include development other variants of biomimetic undulating fin robot and further development of the cuttlefish robot for autonomous deployment

Modeling and simulation of printed circuit board drop test

Modeling and simulation of drop tests for printed circuit boards (PCB) was conducted for flip chip on board (FCOB) assemblies. The PCB test vehicle has dimensions of 185 mm by 150 mm with 6 large flip chips (8 mm/spl times/8 mm) and 6 small flip chips (3 mm/spl times/3 mm) mounted with underfill encapsulation. The PCB specimen was clamped at two edges on a test fixture and mounted on the drop test machine platform. A drop height of 1.0 m was used for repeated drop tests. In this study, finite element analysis (FEA) of the drop test for the PCB specimen was modeled using the Pam-Crash software. Dynamic modeling and simulation of the drop test sequence of events was established. The modeling approach employs the experimentally measured displacement history (from the high speed camera) at the clamp edges of the PCB as inputs to the local model analysis to compute the displacement and acceleration. The FEA modeling and simulation results show that the predicted displacements and accelerations at selected locations on the PCB agreed satisfactorily with the measured results.

Gait Planning for Steady Swimming Control of Biomimetic Fish Robots

This paper is dedicated to the implementation of biological fish swimming motion onto biomimetic fish robots. By learning from different species of fish, the mechanism design and the motor control of swimming machines could be shaped in different forms. In general, they can be grouped into two major forms, from an engineering viewpoint: serial open-chain design and parallel mechanism design. The gait planning on both forms is then performed based on the well-established theory of fish swimming. By using the associated kinematics equations, the generic solution of the gait planning for multi-link fish robots in the two respective forms of mechanisms is derived. The solution is taken as the gait control input for the swimming testing of a six-link body and/or caudal fin fish prototype and an eight-link media and/or paired fin fish prototype. The experiments show that smooth steady swimming and forward/backward swimming are achievable by making use of the gait planning and control.

An efficient foot-force distribution algorithm for quadruped walking robots

One of the important issues of walking machine active force control is a successful distribution of the body force to the feet to prevent leg slippage. In this paper, a new force distribution method, the Friction Constraint Method (FriCoM), is introduced. The force distribution during the walking of a typical quadruped crawl gait is analyzed by using the FriCoM. Computation results show that the distributed forces of the feet are continuous during the walking. This reflects the change of the force distribution during actual conditions. The comparison with a pseudo-inverse method shows that the FriCoM is more practical. The FriCom also requires less computation time than that by an incremental optimization method. Some problems, such as the singularity in the application of the FriCoM, are discussed. The FriCoM will be used in the active force control of a quadruped robot that is taken as a platform for the research on the study of terrain adaptation.

Solution schemes for the system equations of flexible robots

In this work, a method for generating the dynamic equations of flexible robots with open-chain linkage mechanisms is developed. A general transformation matrix associated with the elastic deformation is introduced. In determining the elastic response, a method of separation of variables and the Galerkins approach are suggested for the boundary-value problem with time-dependent boundary conditions. Besides the formulation scheme, the present work also studies the difficulty of dealing with the inverse kinematic problem, in which the unknowns involve the rigid-body displacements and the elastic deflections. Finally, the ideas presented here have been implemented in a computer simulation, and the formulation of the boundary-value problem has been employed to obtain the equations of motion of a flexible robot. Simulation results are presented.