Virtual Chain Research Articles

Control of Redundant Kinematic Degrees of Freedom in a Closed-Loop Brain-Machine Interface.

Brain-machine interface (BMI) systems use signals acquired from the brain to directly control the movement of an actuator, such as a computer cursor or a robotic arm, with the goal of restoring motor function lost due to injury or disease of the nervous system. In BMIs with kinematically redundant actuators, the combination of the task goals and the system under neural control can allow for many equally optimal task solutions. The extent to which kinematically redundant degrees of freedom (DOFs) in a BMI system may be under direct neural control is unknown. To address this question, a Kalman filter was used to decode single- and multi-unit cortical neural activity of two macaque monkeys into the joint velocities of a virtual four-link kinematic chain. Subjects completed movements of the chain's endpoint to instructed target locations within a two-dimensional plane. This system was kinematically redundant for an endpoint movement task, as four DOFs were used to manipulate the 2-D endpoint position. Both subjects successfully performed the task and improved with practice by producing faster endpoint velocity control signals. Kinematic redundancy allowed null movements whereby the individual links of the chain could move in a way that cancels out and does not result in endpoint movement. As the subjects became more proficient at controlling the chain, the amount of null movement also increased. Task performance suffered when the links of the kinematic chain were hidden and only the endpoint was visible. Furthermore, all four DOFs of the joint-velocity control space exhibited task-relevant modulation. The relative usage of each DOF depended on the configuration of the chain, and trials in which the less-prominent DOFs were utilized also had better task performance. Overall, these results indicate that the subjects incorporated the redundant components of the control space into their control strategy. Future BMI systems with kinematic redundancy, such as exoskeletal systems or anthropomorphic robotic arms, may benefit from allowing neural control over redundant configuration dimensions as well as the end-effector.

Dynamic Analysis and Simulation of 4R 3-DOF Wrists

In this paper, a systematic algorithm for the dynamic analysis of 4R 3-DOF wrists is presented. Based on the theory of graph, kinematics is completed. Links are divided into primary links and secondary links. The generalized inertia force of the system results from the motions of primary links and secondary links. The concept of virtual 3R 3-DOF open-loop chain and additional link are introduced to describe the primary links. The generalized inertia forces of 3R 3-DOF open-loop chain, additional link and secondary links are derived by Lagrangian formulation, respectively, based on their location in the wrist. Then the dynamic equation of 4R 3-DOF wrists is got by making a combining. A simulation is performed to illustrate the efficiency of the algorithm.

The vulnerability and resilience of a city's water footprint: The case of Flagstaff, Arizona, USA

AbstractResearch has yet to operationalize water footprint information for urban water policy and planning to reduce vulnerability and increase resilience to water scarcity. Using a county‐level database of the U.S. hydro‐economy, NWED, we spatially mapped and analyzed the Water Footprint of Flagstaff, Arizona, a small city. Virtual water inflow and outflow networks were developed using the flow of commodities into and out of the city. The power law distribution of virtual water trade volume between Flagstaff and its county trading partners broke at a spatial distance of roughly 2000 km. Most large trading partners are within this geographical distance, and this distance is an objective definition for Flagstaff's zone of indirect hydro‐economic influence—that is, its water resource hinterland. Metrics were developed to measure Flagstaff's reliance on virtual water resources, versus direct use of local physical water resources. Flagstaff's reliance on external water supplies via virtual water trade increases both its hydro‐economic resilience and vulnerability to water scarcity. These methods empower city managers to operationalize the city's Water Footprint information to reduce vulnerability, increase resilience, and optimally balance the allocation of local physical water supplies with the outsourcing of some water uses via the virtual water supply chain.

Whole Body Control of a Dual-Arm Mobile Robot Using a Virtual Kinematic Chain

Dual-arm manipulators have more advanced manipulation abilities compared to single-arm manipulators and manipulators mounted on a mobile base have additional mobility and a larger workspace. Combining these advantages, mobile dual-arm robots are expected to perform a variety of tasks in the future. Kinematically, the configuration of two arms that branches from the mobile base results in a serial-to-parallel kinematic structure. In order to respond to external disturbances, this serial-to-parallel kinematic structure makes inverse kinematic computations non-trivial, as the motion of the base has to take the needs of both arms into account. Instead of using the dual-arm kinematics directly, we propose to use a virtual kinematic chain (VKC) to specify the common motion of the two arms. We formulate a constraint-based programming solution which consists of two parts. In the first part, we use an extended serial kinematic chain including the mobile base and the VKC to formulate constraints that realize the desired orientation and translation expressed in the world frame. In the second part, we use the resolved VKC motion to constrain the common motion of the two arms. In order to explore the redundancy of the two arms in an optimization framework, we also provide a VKC-oriented manipulability measure as well as its closed-form gradient. We verify the proposed approach with simulations and experiments that are performed on a PR2 robot, which has two 7 degrees of freedom (DoF) arms and a 3 DoF mobile base.

Virtualization of food supply chains with the internet of things

Internet technologies allow supply chains to use virtualizations dynamically in operational management processes. This will improve support for food companies in dealing with perishable products, unpredictable supply variations and stringent food safety and sustainability requirements. Virtualization enables supply chain actors to monitor, control, plan and optimize business processes remotely and in real-time through the Internet, based on virtual objects instead of observation on-site. This paper analyses the concept of virtual food supply chains from an Internet of Things perspective and proposes an architecture to implement enabling information systems. As a proof of concept, the architecture is applied to a case study of a fish supply chain. These developments are expected to establish a basis for virtual supply chain optimization, simulation and decision support based on on-line operational data. In the Internet of Things food supply chains can become self-adaptive systems in which smart objects operate, decide and learn autonomously.

Determination of the Workspace of a Three-Degrees-of-Freedom Parallel Manipulator Using a Three-Dimensional Computer-Aided-Design Software Package and the Concept of Virtual Chains1

The determination of workspace is an essential step in the development of parallel manipulators. By extending the virtual-chain (VC) approach to the type synthesis of parallel manipulators, this technical brief proposes a VC approach to the workspace analysis of parallel manipulators. This method is first outlined before being illustrated by the production of a three-dimensional (3D) computer-aided-design (CAD) model of a 3-RPS parallel manipulator and evaluating it for the workspace of the manipulator. Here, R, P and S denote revolute, prismatic and spherical joints respectively. The VC represents the motion capability of moving platform of a manipulator and is shown to be very useful in the production of a graphical representation of the workspace. Using this approach, the link interferences and certain transmission indices can be easily taken into consideration in determining the workspace of a parallel manipulator.

Recent Developments in LS-DYNA to close the Virtual Process Chain for Forming, Press Hardening and Welding

Forming, press hardening and welding are a well-established production processes in manufacturing industry, but predicting the finished geometry and the final material properties of the processed parts is still a major issue. In particular, deformations caused by welding are often neglected in the virtual process chain, although they have to be compensated for in order to fulfill the requirements on shape tolerance. This presentation will give an overview on novel features of LS-DYNA implemented particularly for welding simulations.To begin with, new keywords will be presented that allow applying the heat generated by the weld torch. LS-DYNA offers a very convenient way to define the well-known Goldak heat source, but it is also possible to define arbitrarily shaped torch geometries.In order to obtain a predictive model for welding simulations, specific material models have been devised in LS-DYNA. The properties of filler material in weld seams are accounted for by a ghost material approach. Material is initialized as ghost material and is activated, i.e. it is given base material properties, when the temperature reaches the melting point. This approach has been implemented for a relatively simple thermo-elasto-plastic material formulation *MAT_CWM as well as for the more complex material law *MAT_UHS_STEEL. The latter has initially been implemented for press hardening simulations and is able to predict the microstructure of steel alloys including phase transformations and the resulting mechanical properties.In this contribution, details of the material formulations and novel features are presented. Examples will demonstrate how these features can be applied to multistage processes including several forming and welding stages.

VIP

Energy-efficient user-interactive and display-oriented applications on handhelds rely heavily on multiple accelerators (termed IP cores) to meet their periodic frame processing needs. Further, these platforms are starting to host multiple applications concurrently on the multiple CPU cores. Unfortunately, today's hardware exposes an interface that forces the host software (Android drivers) to treat each IP core as an isolated device. Consequently, the host CPU has to get involved in the (i) processing of each frame, (ii) scheduling them to ensure timely progress through the IP cores to meet their QoS needs, and (iii) explicitly having to move data from one IP core to the next, with main memory serving as the common staging area. We show in this paper through measurements on a Nexus 7 platform that the frequent invocation of the CPU for processing these frames and the involvement of main memory as a data flow conduit, are serious limitations. Instead, we propose a novel IP virtualization framework (VIP), involving three key ideas that allow several IPs to be chained together and made to appear to the software as a single device. First, chaining of IPs avoids data transfer through the memory system, enhancing the throughput of flows through the IPs. Second, by using a burst-mode, the CPU can initiate the processing of several frames through the virtual IP chain, without getting involved (and interrupted) for each frame, thereby allowing better energy saving and utilization opportunities. Removing the CPU from this loop, requires alternate orchestration of frame flows to ensure QoS guarantees for each frame of each application. Our third enhancement in VIP creates several virtual paths, one for each flow, through these IP chains with the hardware scheduling the frames to enforce QoS guarantees despite any contention for resources along the way. Our experimental evaluations demonstrate the effectiveness of VIP on energy consumption and QoS for multiple applications.

Development and validation of a CAE chain for unidirectional fibre reinforced composite components

Current development of composite components made by Resin Transfer Moulding (RTM) requires numerous manual iteration steps to find the optimal design in conjunction with optimal process control. Still, such components are often highly oversized since the real material behaviour is influenced by the processing history and cannot be sufficiently predicted by simulations. The draping process is the predominating process for the fibre alignments, resulting in varying fibre orientations and local draping effects. These material characteristics influence the moulding process as well as the mechanical performance and need to be considered for sizing and virtual validation of RTM structures. Therefore, a continuous virtual process chain (CAE chain) is developed in this work, where geometry and material data are transferred between the finite element models by using a neutral exchange format and mapping algorithms. The CAE chain is applied and validated by a complexly curved RTM part. To demonstrate the benefit of the CAE chain, a reference model is used, where the fibre orientations are simply projected to the component’s surface. For experimental validation, the simulation results are compared to pressure and temperature measurements in the case of moulding simulation, and to tension and bending tests in the case of structural simulation.

Development of a new 4-DOF endoscopic parallel manipulator based on screw theory for laparoscopic surgery

Development of rigid manipulators for Minimally Invasive Surgery (MIS) becomes essential to replace wire driven manipulators which are problematic due to possible cutting of the wire during the surgery. In this paper, a 4-DOF dexterous endoscopic parallel manipulator for MIS is designed and implemented. The manipulator is developed based on the concept of virtual chain and screw theory. The manipulator consists of four links; two links are 2-PUU (each leg consists of one active prismatic joint and two passive hook joints); the other two links are 2-PUS (each leg consists of one active prismatic join, one passive hook joint and one passive spherical joint). The inverse and forward kinematics solutions are derived analytically and numerically, respectively. The singularity analysis is investigated using screws algebra. The manipulator workspace is obtained using MATLAB software. The known problem of limited bending angles found in previous existing surgical manipulators was solved as the proposed manipulator can reach ±90° in any direction. The proposed surgical manipulator is designed, manufactured and tested successfully. The system model utilizing PID and PI controllers has been built using MATLAB software. Co-simulation using ADAMS/MATLAB software is implemented to validate the achieved bending angles and the proposed tracking control. The results show that the performance of the tracking control is satisfactory since the tracking error is about 2.5%.

Learning to explore the structure of kinematic objects in a virtual environment.

The current study tested the quantity and quality of human exploration learning in a virtual environment. Given the everyday experience of humans with physical object exploration, we document substantial practice gains in the time, force, and number of actions needed to classify the structure of virtual chains, marking the joints as revolute, prismatic, or rigid. In line with current work on skill acquisition, participants could generalize the new and efficient psychomotor patterns of object exploration to novel objects. On the one hand, practice gains in exploration performance could be captured by a negative exponential practice function. On the other hand, they could be linked to strategies and strategy change. After quantifying how much was learned in object exploration and identifying the time course of practice-related gains in exploration efficiency (speed), we identified what was learned. First, we identified strategy components that were associated with efficient (fast) exploration performance: sequential processing, simultaneous use of both hands, low use of pulling rather than pushing, and low use of force. Only the latter was beneficial irrespective of the characteristics of the other strategy components. Second, we therefore characterized efficient exploration behavior by strategies that simultaneously take into account the abovementioned strategy components. We observed that participants maintained a high level of flexibility, sampling from a pool of exploration strategies trading the level of psycho-motoric challenges with exploration speed. We discuss the findings pursuing the aim of advancing intelligent object exploration by combining analytic (object exploration in humans) and synthetic work (object exploration in robots) in the same virtual environment.

Improving Techniques in Statically Equivalent Serial Chain Modeling for Center of Mass Estimation

Any articulated system of rigid bodies defines a statically equivalent serial chain (SESC). The SESC is a virtual chain that terminates at the center of mass (CoM) of the original system of bodies. An SESC may be generated experimentally without knowing the mass, CoM, or length of each link in the system given that its joint angles and overall CoM may be measured. This paper presents three developments toward recognizing the SESC as a practical modeling technique. Two of the three developments improve utilizing the technique in practical applications where the arrangement of the joints impacts the derivation of the SESC. The final development provides insight into the number of poses needed to create a usable SESC in the presence of data collection errors. First, modifications to a matrix necessary in computing the SESC are proposed, followed by the experimental validation of SESC modeling. Second, the problem of generating an SESC experimentally when the system of bodies includes a mass fixed in the ground frame are presented and a remedy is proposed for humanoid-like systems. Third, an investigation of the error of the experimental SESC versus the number of data readings collected in the presence of errors in joint readings and CoM data is conducted. By conducting the method on three different systems with various levels of data error, a general form of the function for estimating the error of the experimental SESC is proposed.

VRM: A Unified Framework for Closed-Form Solutions of a Special Class of Serial Manipulators

This paper proposes the virtual reconfiguration method (VRM) to construct the unified framework for closed-form solutions of a special class of serial manipulators. Central to the research is the inverse kinematics problem (KP) of 6- and 7-DOF serial manipulators, which contain either the Pieper's geometry or the Duffy's geometry. Given the desired end-effector pose of the manipulator, a virtual single chain (SLC) is developed by connecting the base and the end-effector with a hypothetical link. The equivalent single open chain (SOC) with different configurations can be obtained by cutting open the virtual SLC at one link between adjacent joints. Kinematic equivalence between the original manipulator and the new SOC is proven. Closed-form solutions of the original manipulator can be determined by solving the KP of the equivalent SOC. The VRM is further developed on the basis of the relationship between the manipulator and its equivalent SOC. In this paper, the KPs of 6-DOF manipulators with the spherical ...

Crash simulation of wound composite tubes based on multi-level modelling

Fibre reinforced plastics are widely used for energy absorbing parts. Due to their superior strength to density ratio they provide a high performance and are ideal for lightweight design for crashworthiness. For this, it is essential that the mechanical behaviour of fibre reinforced composites be predicted correctly by simulation. However, due to the complex inner structure, this is still a challenging task, in particular in case of highly nonlinear crash loading. In order to provide an alternative in this paper a virtual manufacturing simulation chain is proposed to gather detailed geometrical information about the roving structure of a filament wound tube on meso-scale. In addition effective material properties, based on calibrated models of the individual constituents, for the filament–matrix interaction are derived by micro-scale calculations. Both, combined with a USER MATERIAL model for the roving structure finally provide a complete finite element model which is used for the crash simulation of the filament wound tube. By comparing the numerical results to experimental data, the potential of the approach is shown and occurring differences are discussed as well as possible subsequent investigations are proposed.

Simulation Analysis of the Three-Dimensional Ball Motion

For the problems of the human geometric modeling by using software, such as more complex, poor fidelity and controllability, the optimized mathematical model for human simulation movement is designed at first. A three-dimensional human motion system coordinate is established to construct the simplified virtual human geometric model. Using the knowledge of computer graphics, and Denavic-Hartenberg method, construct a space joint coordinate system of virtual hierarchal human movement chain. 3DS MAX is used in realistic geometric modeling to achieve the three-dimensional motion simulation analysis in basketball motion. The results show that the model is realistic, the optimized geometric model in software is easy to control, and the overall effect is good. It greatly enhances the realism and action effects of the three-dimensional motion simulation, and achieves a good virtual basketball motion.

A BP-GA Approach to Solve the Inverse Kinematics of Virtual Human's Upper Limb Kinematic Chain

The human’s Upper Limb Kinematic Chain (ULKC) is the most frequently used and most complicated kinematic chain. It is difficult to compute its Inverse Kinematic (IK) solution quickly and accurately by using neural network or Genetic Algorithm (GA) due to ULKC’s high degree of freedom. Combining BP neural network and GA, we proposed a method to solve its IK problem. Firstly, the joint-units of ULKC and its mathematical model were constructed based on D-H method. Then the BP neural network produced a local optimal solution, which could be served as an individual of GA’s initial population. We could determine the searching domain by its optimal solution. Finally, the high accuracy solution was obtained by using the adaptive GA. The experimental results showed that the proposed approach could obtain the high accuracy solution efficiently with the BP neural network high-speed and GA high-accuracy.

A Virtual Chain Performance Model for Small Companies

Several business companies implement electronic processes to do business online and to exchange with their clients. These electronic businesses affect the ways that small firms exchange goods and services with suppliers and clients. Digital markets are multiplying every day and small companies need to implement a supply chain model to do cost-effective business with their partners. Using models from the literature, this study will highlight that a virtual value chain performance model integrated to open business systems is needed to provide effective services to business partners. In this paper, the author of this research will demonstrate that a virtual value chain performance model is needed to achieve operational effectiveness and efficiency for small businesses.

An approach to solving the inverse kinematics problem of virtual human's lower limbs kinematic chain

The lower limbs kinematic chain (LLKC) is the important part of human body. It contains two joints with four degrees of freedom (DOF). As it is difficult to compute LLKC’s inverse kinematic solution quickly and accurately by using neural network or genetic algorithm (GA) due to its high degree of freedom, we proposed a BP-GA approach by combining BP neural network and GA to resolve it. Firstly, the mathematical model of LLKC was built based on D-H method. Then BP neural network output a local optimal solution, which could be served as an individual of GA initial population. And the searching domain of GA could be determined by local optimal solution. Finally, the high-accuracy solution was searched by using the adaptive GA. The actions of walking, squatting and seated position were simulated and results showed that the precise solution could be calculated efficiently by using the proposed approach with the BP neural network high-speed and GA high-accuracy.

Application of Virtual Kinematic Chains in Cooperating Robot Systems

Removed due to plagiarism. The original was published by Springer: Kinematics Programming for Cooperating Robotic Systems, Authors: Cristiane Tonetto, Carlos. Rocha, Henrique Simas, and Altamir Dias, link: http://link.springer.com/chapter/10.1007%2F978-3-642-28255-3_21

Virtual Chain Approach for Mobility Analysis of Multiloop Deployable Mechanisms

In this paper, we present a virtual chain approach for the mobility analysis of multiloop deployable mechanisms. First, the relative motion of the links of single-loop units in multiloop mechanisms are analyzed using the equivalent motion of certain types of open-loop virtual kinematic chains; these kinematic chains comprise some types of joints connected in series by flexible links. This reveals that the links in these virtual chains are not rigid when the mechanism is moving. The parameters of these virtual kinematic chains (such as the link length, the twist angle of two adjacent revolute joint axes, and so on) are variable. By using this approach that involves equivalent kinematic chains, the multiloop mechanisms can be considered equivalent to single-loop mechanisms with flexible links; the closure equations of such multiloop mechanisms can also be derived. The analytical procedures are explained using examples of multiloop mechanisms in which Myard mechanisms as used as the basic single-loop units. A prototype is also fabricated to demonstrate the feasibility of the proposed multiloop mechanism. The proposed method yields a more intuitive and straightforward insight into the mobility of complicated multiloop mechanisms.