Backward Kinematics Research Articles

A novel motion planning algorithm for a three DoF foldable parallel compensation platform based on prediction and B-spline

Foldable parallel mechanisms are suitable to compensate for the motion of vessels due to their compact structure, multidimensional motion, and large carrying capacity. However, the vessel sways violently under harsh sea conditions, challenging the rational utilization of the mechanism workspace. This work proposes a novel motion planning algorithm based on motion prediction and the B-spline for a three-degrees-of-freedom foldable parallel compensation platform. First, for harsh sea conditions, the motion law of a guardian vessel is studied, and the encoder-decoder model is used to predict the roll, pitch, and heave motions of the vessel. Second, we propose a multidimensional motion compensation strategy under the limits of the mechanism dimensions. Then, a backward kinematics model is developed. Its workspace under the structural and actuator limitations is proposed. Finally, based on the theory of the nonuniform rational B-spline curve and target motion prediction, a dynamic motion planning algorithm is proposed, and experiments are conducted. The motion planning algorithm can provide smooth motion commands under the mechanism workspace, velocity, acceleration constraints. It can be realized using asynchronous calculation, which meets real-time motion control requirements.

Low energy protons as probes of hadronization dynamics

Energetic quarks liberated from hadrons in nuclear deep-inelastic scattering propagate through the nuclear medium, interacting with it via several processes. These include quark energy loss and nuclear interactions of forming hadrons. One manifestation of these interactions is the enhanced emission of low-energy charged particles, referred to as grey tracks. We use the theoretical components of the BeAGLE event generator to interpret grey track signatures of parton transport and hadron formation by comparing its predictions to E665 data. We extend the base version of BeAGLE by adding four different options for describing parton energy loss. The E665 data we used consists of multiplicity ratios for fixed-target scattering of 490 GeV muons on Xe normalized to deuterium as a function of the number of grey tracks. We compare multiplicity ratios for E665 grey tracks to the predictions of BeAGLE, varying the options and parameters to determine which physics phenomena can be identified by these data. We find that grey tracks are unaffected by modifications of the forward production. Thus their production must be dominated by interactions with hadrons in the backward region. This offers the advantage that selecting certain particles in the forward region is unlikely to bias a centrality selection. We see a strong correlation between the number of grey tracks and the in-medium path length. Our energy loss model does not reproduce the suppression observed in the projectile region. We see an underprediction of the proton production rate in backward kinematics, suggesting that a stronger source of interaction with the nuclear medium is needed for accurate modeling. These results lay an important foundation for future spectator tagging studies at both Jefferson Lab and at the Electron-Ion Collider, where neutron and proton grey track studies will be feasible down to very small momenta.

Design and Analysis of a Series-Parallel Compliant Manipulator

Because of friction and assembly clearance, the accuracy of traditional rigid parallel mechanism cannot be maintained for a long time. Compliant mechanism has the advantages of light weight, high precision and low wear. Combining the characteristics of the two mechanisms, this paper designs a series-parallel compliant manipulator structure, and studies its forward and backward kinematics. Finally, it uses MATLAB software to study its workspace. Motion analysis was carried out.

Extraction of Beam-Spin Asymmetries from the Hard Exclusive π^{+} Channel off Protons in a Wide Range of Kinematics.

We have measured beam-spin asymmetries to extract the sinϕ moment A_{LU}^{sinϕ} from the hard exclusive e[over →]p→e^{'}nπ^{+} reaction above the resonance region, for the first time with nearly full coverage from forward to backward angles in the center of mass. The A_{LU}^{sinϕ} moment has been measured up to 6.6 GeV^{2} in -t, covering the kinematic regimes of generalized parton distributions (GPD) and baryon-to-meson transition distribution amplitudes (TDA) at the same time. The experimental results in very forward kinematics demonstrate the sensitivity to chiral-odd and chiral-even GPDs. In very backward kinematics where the TDA framework is applicable, we found A_{LU}^{sinϕ} to be negative, while a sign change was observed near 90° in the center of mass. The unique results presented in this Letter will provide critical constraints to establish reaction mechanisms that can help to further develop the GPD and TDA frameworks.

Analysis of typical working conditions and experimental research of friction stir welding robot for aerospace applications

In an attempt to address the limitations of single function and the poor process flexibility of existing friction stir welding equipment, a new friction stir welding robot has been developed to address practical problems in three-dimensional surface welding. Based on an analysis of the components of the robotic system, a kinematics model was established, and the forward and backward kinematics solutions were derived for the robot. An iterative nearest point algorithm, iterative closest point based on point cloud matching, was used to plan the welding trajectory for the most complex petal welding conditions, and an experimental study was conducted. The results show that the kinematic and dynamic test results were consistent with the acquired simulation curves for specific sizes of the rocket cap flaps under appropriate welding conditions. The normal error of the weld was less than 85 µm, the average tensile strength was 359 MPa, and the elongation was 7.20%, 78.0%, and 72.0% of 2A14-T6 aluminum alloy. The friction stir welding robot exhibited robust performance, and the proposed trajectory planning method is practical and effective. The appearance, geometric dimension, and mechanical properties of the weld achieved the expected criteria, and high-precision welding of large complex thin-walled surfaces is possible.

Modeling human gait cycle using FE method and results of backward kinematics

Biomechanical models of the human body are important tools in understanding the functioning of human movement and its coordination. Creating movable models of the human musculoskeletal system is pa...

Specific features of mobile machine reverse movement

The study deals with questions related to mobile machine manoeuvring when reversing. When the mobile machine is moving backward kinematics of processing various manoeuvres coincides with kinematics of forward movement. This fact gives the possibility to use analytical dependences obtained when the mobile machine is moving forward to describe reverse movement. To estimate the effectiveness of training mobile machine driving when moving backward both laboratory research using a hardware and software complex and full-scale tests using an automobile were conducted. The process of simulation the driver’s impact on the mobile machine steering system when moving backward is effectively implemented using a hardware and software complex. Maximal discrepancies in the results of theoretical and experimental studies do not exceed 10…15 per cent. The obtained results of experiments with an automobile were close to the results of experiments with hardware and software complex, the divergence was relatively small: from 3 to 9 per cent. This fact confirms the possibility of using the given complex to impart elementary skills of driving a mobile machine when moving backward. To simplify driving a mobile machine when moving backward the method of driving a mobile machine when moving backward was suggested.

Comment on the frozen QCD coupling

The frozen QCD coupling is a parameter often used as an effective fixed coupling. It is supposed to mimic both the running coupling effects and the lack of knowledge of α s in the infrared region. Usually the value of the frozen coupling is fixed from the analysis of the experimental data. We present a novel way to define such coupling(s) independently of the experiments. We argue that there are different frozen couplings which are used in double-logarithmic (DL) and single-logarithmic (SL) approximations. We introduce four kinds of frozen couplings: the coupling used in DLA with a time-like argument (i.e. the coupling present in the non-singlet scattering amplitudes and DIS structure functions), which we find to be 0.24 approximately; the DLA coupling with a space-like argument (e + e --annihilation, in DY processes and in any scattering amplitude in the hard or backward kinematics) which is a factor two larger, namely 0.48. We also show that the frozen coupling in the SL evolution equations like BFKL can be defined with much less accuracy compared to DLA, and our estimate for this coupling is 0.1. Our estimates for the singlet and non-singlet intercepts are also in a good agreement with the results available in the literature.

HEXAPOD - SIX-LEGGED WALKING ROBOT CONTROLLED WITH TODA-RAYLEIGH LATTICE

Abstract Movement of six-legged robot is considered. The robot is built to conduct research on the control of different modes of walking with a particular focus on switching from one mode to another. The robot parameters are identified from real-time control experiments. A number of identical servo motors are responsible for the mobility of the hexapod. Therefore, in addition to the construction of hexapod and its control system and the ability to generate different gaits, it is important to create a simulation model of the hexapod including servo motors. The full state observer for the servo motor is an integral part of this model. Forward and backward kinematics of the robot legs is implemented. The six node Toda-Rayleigh lattice model is created and numerically simulated. The lattice is applied as the robot controller. Three different modes of robot gait are achieved. The algorithm used for the gait mode change is equipped with parameters that are experimentally chosen.

A Statistical Approach to the Forward Kinematics Nonlinearity Analysis of Gough‐Stewart Mechanism

Both the forward and backward kinematics of the Gough‐Stewart mechanism exhibit nonlinear behavior. It is critically important to take account of this nonlinearity in some applications such as path control in parallel kinematics machine tools. The nonlinearity of inverse kinematics is straightforward and has been first studied in this paper. However the nonlinearity of forward kinematics is more challenging to be considered as there is no analytic solution to the forward kinematic solution of the mechanism. A statistical approach including the Bates and Watts measures of nonlinearity has been employed to investigate the nonlinearity of the forward kinematics. The concept of standard sphere has been used to check the significance of the nonlinearity of the mechanism. It is demonstrated that the length of the region, defined as the linear approximation of the lifted line, has a significant impact on the nonlinearity of the mechanism.

Detailed analysis of two-boson exchange in parity-violatinge-pscattering

We present a comprehensive study of two-boson exchange (TBE) corrections in parity-violating electron-proton elastic scattering. Within a hadronic framework, we compute contributions from box (and crossed box) diagrams in which the intermediate states are described by nucleons and Delta baryons. The Delta contribution is found to be much smaller than the nucleon one at backward angles (small epsilon), but becomes dominant in the forward scattering limit (epsilon -> 1), where the nucleon contribution vanishes. The dependence of the corrections on the input hadronic form factors is small for Q^2 < 1 GeV^2, but becomes significant at larger Q^2. We compute the nucleon and Delta TBE corrections relevant for recent and planned parity-violating experiments, with the total corrections ranging from -1% for forward angles to 1-2% at backward kinematics.

Electron scattering from high-momentum neutrons in deuterium

We report results from an experiment measuring the semi-inclusive reaction $d(e,e'p_s)$ where the proton $p_s$ is moving at a large angle relative to the momentum transfer. If we assume that the proton was a spectator to the reaction taking place on the neutron in deuterium, the initial state of that neutron can be inferred. This method, known as spectator tagging, can be used to study electron scattering from high-momentum (off-shell) neutrons in deuterium. The data were taken with a 5.765 GeV electron beam on a deuterium target in Jefferson Laboratory's Hall B, using the CLAS detector. A reduced cross section was extracted for different values of final-state missing mass $W^{*}$, backward proton momentum $\vec{p}_{s}$ and momentum transfer $Q^{2}$. The data are compared to a simple PWIA spectator model. A strong enhancement in the data observed at transverse kinematics is not reproduced by the PWIA model. This enhancement can likely be associated with the contribution of final state interactions (FSI) that were not incorporated into the model. A ``bound neutron structure function'' $F_{2n}^{eff}$ was extracted as a function of $W^{*}$ and the scaling variable $x^{*}$ at extreme backward kinematics, where effects of FSI appear to be smaller. For $p_{s}>400$ MeV/c, where the neutron is far off-shell, the model overestimates the value of $F_{2n}^{eff}$ in the region of $x^{*}$ between 0.25 and 0.6. A modification of the bound neutron structure function is one of possible effects that can cause the observed deviation.

Probing the origin of the EMC effect via tagged structure functions of the deuteron

We demonstrate that measurement of tagged structure functions of the deuteron in (e, e′N) semi-inclusive reactions can discriminate between different hypotheses on the origin of the nuclear EMC effect. By choosing extreme backward kinematics for the spectator nucleon to minimize effects from the deuteron wave function and final state interactions, one can isolate the modifications in the structure of the bound nucleon within the impulse approximation. The same reaction can be used to extract the large-x neutron to proton structure function ratio.

Collective excitations in 12C(e, e'p0) and 12C(e, e'n0) reactions at low momentum transfer

Abstract Predictions of coincidence 12 C(e, e′ x ) reactions at low momentum transfer are presented in a continuum self-consistent RPA theory with Skyrme forces. SK3 and SKM interactions are used. We investigate the role of different form factors and multipolarities in 12 C(e, e′p 0 ) and 12 C(e, e′n 0 ) angular distributions at forward and backward electron kinematics. The incident electron energy is E i = 126 MeV and ω = 22.5 MeV is the nuclear excitation energy. The sensitivity of 12 C(e, e′p 0 ) angular correlations in forward direction to monopole excitations is especially emphasized.