Kinematics Of Platform Research Articles

Reduction of Kinematic Short Baseline Multipath Effects Based on Multipath Hemispherical Map.

Multipath hemispherical map (MHM) is a kind of multipath mitigation approach that takes advantage of the spatial repeatability of the multipath effect under an unchanged environment. This approach is not only suitable for static environments, but also for some kinematic platforms, such as a moving ship and airplane, where the dominant multipath effects come from the platform itself and the multipath effects from the surrounding environment are considered minor or negligible. Previous studies have verified the feasibility of the MHM approach in static environments. In this study, we expanded the MHM approach to a kinematic shipborne environment. Both static and kinematic tests were carried out to demonstrate the feasibility of the MHM approach. The results indicate that, after MHM multipath mitigation, the root mean square (RMS) of baseline length deviations are reduced by 10.47% and 10.57%, and the RMS of residual values are reduced by 39.89% and 21.91% for the static and kinematic tests, respectively. Power spectrum analysis has shown that the MHM approach is more effective in mitigating multipath in low-frequency bands; the high-frequency multipath effects still exist, and are indistinguishable from observation noise. Taking the observation noise into account, the residual reductions increase to 41.68% and 24.51% in static and kinematic tests, respectively. To further improve the performance of MHM for kinematic platforms, we also analyzed the influence of spatial coverage and resolution on residual reduction.

GNSS Precise Kinematic Positioning for Multiple Kinematic Stations Based on A Priori Distance Constraints.

When applying the Global Navigation Satellite System (GNSS) for precise kinematic positioning in airborne and shipborne gravimetry, multiple GNSS receiving equipment is often fixed mounted on the kinematic platform carrying the gravimetry instrumentation. Thus, the distances among these GNSS antennas are known and invariant. This information can be used to improve the accuracy and reliability of the state estimates. For this purpose, the known distances between the antennas are applied as a priori constraints within the state parameters adjustment. These constraints are introduced in such a way that their accuracy is taken into account. To test this approach, GNSS data of a Baltic Sea shipborne gravimetric campaign have been used. The results of our study show that an application of distance constraints improves the accuracy of the GNSS kinematic positioning, for example, by about 4 mm for the radial component.

A Tool for Beamforming and Real-Time Link Budget Analysis in Aeronautical Communications Using Kinematics

Aeronautical Communication (AC) systems are likely to be a part of future tiered communication network structures. Therefore maintaining a robust AC link with a minimum power burden on the host platform has a critical importance. In this paper, we analyze the AC systems from a link budget analysis point of view and define the requirements for the parameters of link budget with an emphasize on antenna gains. First, we study the link budget analysis in an AC system. Then, we present a mathematical framework to provide an end-to-end link budget analysis utilizing the platform kinematics. Finally, we present the numerical results for typical AC scenarios and discuss that these results can be used for calculating the real-time link budget and electronic beamforming to provide a robust link.

PRECISE INDOOR LOCALIZATION FOR MOBILE LASER SCANNER

Abstract. Accurate 3D data is of high importance for indoor modeling for various applications in construction, engineering and cultural heritage documentation. For the lack of GNSS signals hampers use of kinematic platforms indoors, TLS is currently the most accurate and precise method for collecting such a data. Due to its static single view point data collection, excessive time and data redundancy are needed for integrity and coverage of data. However, localization methods with affordable scanners are used for solving mobile platform pose problem. The aim of this study was to investigate what level of trajectory accuracies can be achieved with high quality sensors and freely available state of the art planar SLAM algorithms, and how well this trajectory translates to a point cloud collected with a secondary scanner. In this study high precision laser scanners were used with a novel way to combine the strengths of two SLAM algorithms into functional method for precise localization. We collected five datasets using Slammer platform with two laser scanners, and processed them with altogether 20 different parameter sets. The results were validated against TLS reference. The results show increasing scan frequency improves the trajectory, reaching 20 mm RMSE levels for the best performing parameter sets. Further analysis of the 3D point cloud showed good agreement with TLS reference with 17 mm positional RMSE. With precision scanners the obtained point cloud allows for high level of detail data for indoor modeling with accuracies close to TLS at best with vastly improved data collection efficiency.

GNSS navigation and positioning for the GEOHALO experiment in Italy

GEOHALO is a joint experiment of several German institutes for atmospheric research and earth observation where exploring airborne gravimetry over Italy using the High Altitude and LOng Range (HALO) aircraft data is one of the major goals. The kinematic positioning of the aircraft, on which all remote sensing instruments are located, by Global Navigation Satellite System (GNSS) is affected by the characteristics of long-distance, long-time duration, and high-platform dynamics which are a key factor for the success of the GEOHALO project. We outline the strategy and method of GNSS data processing which takes into account multiple GNSS systems (GPS and GLONASS), multiple static reference stations including stations from the International GNSS Service (IGS) and the EUropean REFerence network (EUREF), multiple GNSS-receiving equipments mounted on the kinematic platform, geometric relations between multiple antennas, and assumptions of similar characteristic of atmospheric effects within a small area above the aircraft. From this precondition, various data processing methods for kinematic positioning have been developed, applied and compared. It is shown that the proposed method based on multiple reference stations and multiple kinematic stations with a common atmospheric delay parameter can effectively improve the reliability and accuracy of GNSS kinematic positioning.

Navigation and Control of Mecanum Wheeled Chair for Handicaps

This paper proposes a novel navigational system for handicap wheeled chair with mecanum wheels. The wheels provide a flexible mobility represented with its 3DOF (Three Degrees Of Freedom) ability of mobility. The chair provides assistance for the user according to his/her medical situation. The user can control the chair using joy stick or vocal command signals. The main contribution of this work is defined by the platform kinematics, dynamics modeling and its navigational control system. The mobile platform is kinematically and dynamically modeled and tested on the simulation level to illustrate its performance. The chair is able navigate in a smart environment, for example, in handicap house with a known map. The navigation system implemented on the chair will provide position, collision avoidance and local navigation behaviors. The environment is configured as nodes and the chair should follow series of nodes to reach the desired room. Firstly, a node generator will propose a sequence of nodes, which must be reached respectively. The node generator is created using neural networks algorithms. Secondly, the position control will drive from one node to another assuming reference trajectory of a straight line between each two nodes. Thirdly, the fusion between the position control and the collision avoidance will enable each behavior according to the situation. The navigational control system is implemented on a hardware prototype and the experimental results are illustrated to show the acceptable performance of the whole system. Copyright © 2014 Praise Worthy Prize S.r.l. - All rights reserved.

Stepping Response During Constrained and Unconstrained Standing in Moving Environments

The purpose of this study was to determine the differences in human stepping response reaction between constrained and unconstrained standing while being exposed to simulated wave-induced platform motions. Twenty subjects (10 male and 10 female), with limited experience recreating or working in motion-rich environments, performed a constrained and an unconstrained standing task on a six-degrees-of-freedom motion bed while being exposed to two different simulated platform motion conditions. Stepping occurrence was greater during unconstrained standing than constrained standing during all three motion conditions. However, no significant differences in platform kinematics were found between stepping cases. These results suggest that stepping occurs more frequently than originally hypothesized. As such, stepping should not be considered as a last resource when all fixed-support options have been exhausted. This should be taken into consideration to ensure ecological validity when developing models to predict stepping occurrence.

Adaptive Backstepping Controller Design for Leveling Control of an Underwater Platform Based on Joint Space

This paper focuses on high precision leveling control of an underwater heavy load platform, which is viewed as an underwater parallel robot on the basis of its work pattern. The kinematic of platform with deformation is analyzed and the dynamics model of joint space is established. An adaptive backstepping controller according to Lyapunov's function is proposed for leveling control of platform based on joint space. Furthermore, the “lowest point fixed angle error” leveling scheme called “chase” is chosen for leveling control of platform. The digital simulation and practical experiment of single joint space actuator are carried out, and the results show high precision servo control of joint space. On the basis of this, the platform leveling control simulation relies on the hardware-in-loop system. The results indicate that the proposed controller can effectively restrain the influence from system parameter uncertainties and external disturbance to realize high precision leveling control of the underwater platform.

Contribution of slip cue to curvature perception through active and dynamic touch.

Haptic perception of curvature depends largely on the kind of touch. An active and dynamic touch is considered to be the most natural way of exploring. In this study, we have designed and evaluated a kinematic platform for curvature perception through active and dynamic touch. This platform can independently orient, elevate, and translate a flat plate; by exploring forward and backward along the flat plate with a finger, users can achieve curvature feeling of extruded objects. The mechanism of platform and the way of touch have maximally respected the cues for curvature perception, especially the slip cue. Psychophysical evaluation demonstrated that the discrimination threshold of curvature for virtual shapes is close to that for real shapes, and the virtual shape is felt equally curved as the real one. The curvature perception of mono-convex surfaces was then expanded to perception of more complex surfaces: large textures, which have a sinusoidal profile. The evaluation has accessed the correspondence between the virtual and real large textures.

A Practical Fuzzy Adaptive Control Strategy for Multi-DOF Parallel Robot

Multiple Degrees of Freedom (DOF) parallel robots possess the advantages of being compact structure, great stiffness, stability and high accuracy, so such platforms have been widely used in application areas as diverse as the spacecraft motion simulators, radio telescopes, and medical rehabilitation devices. In this paper, after giving a brief review on the control strategies for parallel robot, a 6-DOF robot system for medical purposes based on simulation as well as real environment is established. In order to improve the position tracking accuracy for such objects with time-varying and nonlinear parameters, a practical fuzzy adaptive controller is designed based on the kinematics of parallel platform, where fuzzy inference units are utilized to modify the PID parameters in real-time by using the position feedback from the robot actuators. Finally, both virtual and actual experiment results demonstrate that the proposed algorithm is able to effectively reduce the position tracking errors compared with the traditional PID controller, and the reliability and feasibility of such parallel robotic system can also be guaranteed.

Effect of Age and Activity Level on Lower Extremity Gait Dynamics

Elderly adults should perform exercises that maintain or improve balance to reduce risk of injury from falls. Bone fractures secondary to falls in the elderly, particularly sedentary females, continue to pose a major health and economic problem. A greater understanding of the processes that contribute to the propensity for falling may be obtained by considering changes in gait biodynamics with age and activity level. Therefore, the purpose of this study was to quantify the relationships between age/activity level and selected biodynamic parameters of the lower extremity during normal gait. Seventeen healthy women, 9 young and 8 elderly, were divided into groups of 9 active and 8 sedentary subjects. Three-dimensional (3D) video motion and force platform kinematic and kinetic data were collected from the hip, knee, and ankle of the right lower extremity as the subjects walked at self-selected speeds. Data were analyzed as functions of age and activity level by using a 2-way analysis of variance. As expected, our results show that the elderly group had significantly greater (p < 0.05) functional and mobility limitations in their lower extremity joints than did the younger group. Significant, age-related lower-limb gait alterations were manifested primarily at the ankle, whereas activity-related alterations were manifested most prominently at the hip. The knee showed the fewest changes accompanying age or activity level. Thus, age and activity level affect gait, which may have a role in the subsequent development of a predisposition to gait-related imbalances and resultant falling and increased hip fracture risk. Strength and conditioning professionals may consider these factors related to age and activity level when individualizing exercise regimens for their older, or sedentary, clients. Prophylactic physical activities involving specific, controlled 3D body movements may help prevent abnormal lower-limb joint kinematics (and their hypothetically coupled, intrinsic postural control strategies), thereby reducing fall and fracture propensity.

A Comparison of Platform Motion Waveforms During Constrained and Unconstrained Standing in Moving Environments

OCCUPATIONAL APPLICATIONS Using a principal component waveform analysis technique to examine the platform kinematics during motion-induced interruptions and motion-induced corrections found that these events significantly differ in perturbation magnitude at the time of stepping initiation. These results suggest that differences between the motion-induced interruptions and motion-induced corrections are more than just theoretical, and therefore, when examining these events in offshore environments, they cannot be considered one and the same. Since these change-in-support reactions may be an alternative instead of a last resource response, they may also not be a clear indicator of ship operability. Therefore, when evaluating the risks associated with performing tasks in moving environments, the resultant effects of the change-in-support reactions, such as motion-induced interruptions or motion-induced corrections and their potential effect on injury mechanisms, must also considered. TECHNICAL ABSTRACT Background: Postural response research suggests that change-in-support reactions involving the movement of feet may occur long before the physics-based stability limits have been reached. As such, the current definition of a motion-induced interruption used to describe change-in-support reactions in offshore environments may not be valid, and the alternative motion-induced correction definition may be more appropriate. However, differences between motion-induced interruptions and motion-induced corrections are currently unknown. Purpose: The purpose of this study was to determine the differences in platform motion waveforms between motion-induced interruption and motion-induced correction occurrences when standing on a 6 degree of freedom motion platform. Methods: Twenty participants (ten male, ten female) with little or no experience working in marine environments performed a constrained and unconstrained stationary standing task while being exposed to a continuous multi-directional wave-like perturbation. The constrained standing task was representative of motion-induced interruptions, while the unconstrained standing task was representative of motion-induced corrections. Principal component analysis was incorporated, permitting the preservation of temporal characteristics unique to each motion curve in the analysis. Students’ t-tests were performed on the derived significant principal component scores to determine if these components were statistically significantly different between constrained and unconstrained standing. Results: Analysis of pitch and roll axes suggest that most of the variability of platform motions between motion-induced interruptions and motion-induced corrections can be described by two principal components. The first component, accounting for 80%–90% of all variability, was a magnitude modifier and suggests that there are quantifiable differences in the platform motions that cause motion-induced interruptions and motion-induced corrections. Conclusions: The results of this research suggest that it is likely that the motions to induce these events are distinctly different; therefore, motion-induced interruptions and motion-induced corrections should be considered as different events when examining the human response to wave-induced ship motions and ship operability.

A model of the basal ganglia in voluntary movement and postural reactions

A basal ganglia central pattern generator (CPG) is developed and its role in voluntary movements on the ground and postural reactions on a disturbed platform are studied and analysed by simulation. Biped dynamics and platform kinematics are utilised. The effects of agonist–antagonist muscular co-activation and joint stiffness are formulated. The implementation of the necessary counter-manoeuvres for maintaining balance and postural stability is studied. A control strategy, applicable to large systems, is formulated. The biped manoeuvres and transitions terminate in pre-specified intervals of time. Gravity is included and compensated for. Certain voluntary and postural adjustment strategies are the same but are initiated differently. Further experimental/computational research may identify the central nervous system and sensory paths that lead to the CPG. All actuator forces linearly evolve in time from their original values to their terminal values. There are no central continuous feedback loops present. Monitoring and sensing, however, are ongoing. The counter-manoeuvres are based on learned human-like voluntary movements that are triggered by the disturbance. The required central inputs to the musculoskeletal system are designed in the CPG. A functional structure for the CPG is proposed. The effect of certain disorders and malfunctions of the CPG are studied by simulation.

Dynamics Analysis of 6-DOF Platform under the Condition of Unbalanced Force

During the use of 6－DOF(six degrees of freedom) platform the gravity center of force tends to deviate from the center of the upper platform, resulting in six rods are forced unbalanced. This paper firstly introduces the characteristics of the 6－DOF platform, then establishes simulation model of platform through the PRO/E software, and analyses the kinematics of platform by use of the ADAMS (Automatic Dynamics Analysis of Mechanical System) software, finally proceeds with dynamics analysis of six rods in unbalanced condition.Those will get the influence degree of rods under the unbalanced force,and provide some proposal for the rational use of the platform.

Kinematics Analysis and Simulation of Stabilizing Platform in Non-inertial System

Based on the analysis theory of multi-rigid-body system, the basic research and simulation analysis of stabilizing platform kinematics in non-inertial system are discussed. A compensation algorithm of the stabilizing platform for helicopter landing safely is presented firstly, and then the motion relationship of rigid bodies in ship-based stabilizing system is analyzed to establish the adjoint transformation between the moving platform motion in non-inertial system and the generalized motion of ship and helicopter. The relative values between undercarriage and moving platform are calculated which can be used as a feedback to realize real-time measurement and control of the stabilizing platform. Secondly, the Lee brackets Jacobin matrixes of the stabilizing platform based on the Lie group and Lie algebra are defined, and the adjoint mapping between moving branch inputs and generalized motion values is derived. In order to represent this adjoint mapping, the influence coefficient matrix of the stabilizing platform in non-inertial system is obtained. Finally, the virtual prototyping simulation system of the stabilizing platform is built to verify the correctness of the presented kinematics analysis method for stabilizing platforms in non-inertial system.

Analyses of Error and Precision of 6-DOF Platform

A particular subset of 6-DOF parallel mechanisms is known as Stewart platforms (or hexapod). Stewart platform characteristic analyzed in this paper is the effect of small errors within its elements (strut lengths, joint placement) which can be caused by manufacturing tolerances or setting up errors or other even unknown sources to end effector. The biggest kinematics problem is parallel robotics which is the forward kinematics. On the basis of forward kinematic of 6-DOF platform, the algorithm model was built by Newton iteration, several computer programs were written in the MATLAB and Visual C++ programming language. The model is effective and real-time approved by forwards kinematics, inverse kinematics iteration and practical experiment. Analyzing the resource of error, get some related spectra map, top plat position and posture error corresponding every error resource respectively. By researching and comparing the error spectra map, some general results is concluded.

Design and Evaluation of a new mechatronic platform for assessment and prevention of fall risks

BackgroundStudying the responses in human behaviour to external perturbations during daily motor tasks is of key importance for understanding mechanisms of balance control and for investigating the functional response of targeted subjects. Experimental platforms as far developed entail a low number of perturbations and, only in few cases, have been designed to measure variables used at run time to trigger events during a certain motor task.MethodsThis work introduces a new mechatronic device, named SENLY, that provides balance perturbations while subjects carry out daily motor tasks (e.g., walking, upright stance). SENLY mainly consists of two independently-controlled treadmills that destabilize balance by suddenly perturbing belts movements in the horizontal plane. It is also provided with force sensors, which can be used at run time to estimate the ground reaction forces and identify events along the gait cycle in order to trigger the platform perturbation. The paper also describes the customized procedures adopted to calibrate the platform and the first testing trials aimed at evaluating its performance.ResultsSENLY allows to measure both vertical ground reaction forces and their related location more precisely and more accurately than other platforms of the same size. Moreover, the platform kinematic and kinetic performance meets all required specifications, with a negligible influence of the instrumental noise.ConclusionA new perturbing platform able to reproduce different slipping paradigms while measuring GRFs at run time in order to enable the asynchronous triggering during the gait cycle was designed and developed. Calibration procedures and pilot tests show that SENLY allows to suitably estimate dynamical features of the load and to standardize experimental sessions, improving the efficacy of functional analysis.

Chronic imaging of cortical sensory map dynamics using a genetically encoded calcium indicator

In vivo optical imaging can reveal the dynamics of large-scale cortical activity, but methods for chronic recording are limited. Here we present a technique for long-term investigation of cortical map dynamics using wide-field ratiometric fluorescence imaging of the genetically encoded calcium indicator (GECI) Yellow Cameleon 3.60. We find that wide-field GECI signals report sensory-evoked activity in anaesthetized mouse somatosensory cortex with high sensitivity and spatiotemporal precision, and furthermore, can be measured repeatedly in separate imaging sessions over multiple weeks. This method opens new possibilities for the longitudinal study of stability and plasticity of cortical sensory representations.

Motion Drive Algorithm for Flight Simulator Based on the Stewart Platform Kinematics

To improve the fidelity of the motion cueing in the flight simulator, an improved adaptive motion drive algorithm was presented. In this algorithm, the motion limits of single degree of freedom, which calculate according to the Stewart platform kinematics, was introduced in to reduce the possibility of actuators exceeding theirs motion limits. So the algorithm parameters can be tuned more “open up” to improve the fidelity of motion cueing. The improved motion drive algorithm was verified in the airplane takeoff and landing. The results show that the algorithm can improve the fidelity when the platform has more available motion space; and can avoid exceeding motion limits when the platform has small motion space.

Free-leg Hexapod: A novel approach of using parallel kinematic platforms for developing miniature machine tools for special purpose operations

The paper reports on the development, calibration and exploitation of a novel configuration of parallel kinematic platform, Free-leg Hexapod (FreeHex), on which the base (fixed) platform has been removed; thus, each leg can be individually positioned on workpiece surfaces of non-flat geometries. To enable the utilisation of FreeHex as a miniature machine tool, calibration methods (to reference the platform against the workpiece), work volume calculations, and collision assessment procedures have been developed. The concept of this novel miniature machine tool was demonstrated by generating standard test pieces as well as freeform surfaces followed by accuracy assessments.