Parallel Hip Research Articles

Development and Analysis of a Novel Bio-syncretic Parallel Hip Exoskeleton Based on Torque Requirements

Abstract This paper presents a novel bio-syncretic parallel hip exoskeleton (BsPH-Exo) to address the rehabilitation exercise needs of individuals with lower limb motor dysfunction. BsPH-Exo has six degrees of freedom and can generate all three kinds of rotations that the hip joint can naturally realize. BsPH-Exo effectively solves the problem of misalignment between human and exoskeleton joints, eliminating the need for patients to perform any alignment operations. Considering the varying maximum torque requirements for hip joint rehabilitation in different directions, the limbs of BsPH-Exo are specially arranged to ensure that the maximum torque provided by BsPH-Exo in each direction follows the same law as that of the required torque. As a result, BsPH-Exo exhibits excellent output torque performance, specifically in the flexion/extension direction. Moreover, BsPH-Exo demonstrates weak coupling characteristics in the flexion/extension direction and decoupling characteristics in the adduction/abduction direction, which reduces the difficulty in its control. Compared to currently available parallel hip exoskeletons, BsPH-Exo has several distinct advantages that make it particularly well-suited for rehabilitation applications.

Design and Verification of Parallel Hip Exoskeleton Considering Output Torque Anisotropy

Design and Verification of Parallel Hip Exoskeleton Considering Output Torque Anisotropy

Design and Experimental Verification of a Parallel Hip Exoskeleton System for Full-Gait-Cycle Rehabilitation

Abstract Rehabilitation with exoskeletons after hip joint replacement is a tendency to achieve efficient recovery of people to rebuild their human motor functions. However, the kinematic mismatch between the kinematic and biological hip is a problem in most existing exoskeletons that can cause additional stress in the hip. To avoid secondary damage, the misalignment between the mechanical and biological hip joint of an exoskeleton must be compensated. This paper introduces a novel hip exoskeleton system based on parallel structure. The exoskeleton can inherently address the kinematic mismatch by introducing additional kinematic redundancy, while requiring no additional kinematic components and volumes. To achieve bidirectional full-gait-cycle walking assistance, a remote actuation system is designed for power delivery, and a control scheme is proposed to reject disturbances caused by gait dynamics during walking exercises. Human testing was carried out to evaluate the performance of the system. The results show that the exoskeleton has good human–machine kinematic compatibility and can achieve promising force tracking in the presence of gait dynamics.

Topological Analysis of a Novel Compact Omnidirectional Three-Legged Robot with Parallel Hip Structures Regarding Locomotion Capability and Load Distribution

In this study, a novel design for a compact, lightweight, agile, omnidirectional three-legged robot involving legs with four degrees of freedom, utilizing an spherical parallel mechanism with an additional non-redundant central support joint for the robot hip structure is proposed. The general design and conceptual ideas for the robot are presented, targeting a close match of the well-known SLIP-model. CAD models, 3d-printed prototypes, and proof-of-concept multi-body simulations are shown, investigating the feasibility to employ a geometrically dense spherical parallel manipulator with completely spherically shaped shell-type parts for the highly force-loaded application in the legged robot hip mechanism. Furthermore, in this study, an analytic expression is derived, yielding the calculation of stress forces acting inside the linkage structures, by directly constructing the manipulator hip Jacobian inside the force domain.

Fatigue Life and Reliability Analysis of a Parallel Hip Joint Simulator

SUMMARYAiming at 3SPS+1PS parallel hip joint simulator, the maximum stress of branched chains under the suggested trajectory is obtained by elastodynamic analysis. Based on Corten-Dolan fatigue damage theory and Rain-flow counting method, the dynamic stress of each branched chain is statistically analyzed. The fatigue life prediction shows that branched-chain A2P2C2 is the weakest component for the simulator. Finally, the fatigue reliability is analyzed and the fatigue life and reliability under different structural parameters are discussed. The study shows that the fatigue life of each branched chain can be increased or balanced by increasing structural parameters or exchanging initial motion parameters.

Velocity and Force Transfer Performance Analysis of a Parallel Hip Assistive Mechanism

SUMMARYAgainst the backdrop of accelerated ageing around the globe, an increasing number of individuals suffer from hip motion disability and gait disorders. In this paper, the performance analysis of a novel parallel assistive mechanism with 2 DOF for hip adduction/abduction (AB/AD) and flexion/extension (FL/EX) assistance is completed and evaluated, particularly the velocity and force transfer features. The analysis shows that the assistive mechanism has advantages of fine motion assistive isotropy, high force transfer ratio and large force isotropic radius, which indicates that the parallel assistive mechanism is suitable for hip AB/AD and FL/EX assistance.

Determining the occlusal plane using hamular notch incisive papilla plane evaluator: An in vivo study

Aims:Identification and establishment of the occlusal plane in patients with impaired occlusal plane, presents a major hurdle for the execution of natural esthetics, speech, and function. The aim of this study was to minimize such errors while occlusal rehabilitation, and employ hamular notchincisive papilla (H.I.P) plane as landmark and scribe it on the cast using H. I. P evaluator and utilise for occlusal corrections.Settings and Design:HIP plane being parallel to the occlusal plane could ease the operator when it could be scribed on cast to analyze and restore the compromised occlusal plane.Materials and Methods:Dentulous casts of two hundred participants were mounted on the Hanau Wide–Vue articulator. Reference points were marked on the maxillary right central incisor and maxillary molars on casts for attaining different occlusal planes, the incisive papilla and hamular notch region were also marked for HIP plane. A plane parallel HIP was scribed on cast using HIP Evaluator. The casts were then scanned using a three-dimensional coordinate measuring machine attached to perception V5 laser scanner and measurements were made using Geomagic X design software. The most parallel occlusal plane to HIP plane was evaluated, and the reliability of HIP evaluator was verified.Statistical Analysis Used:ANOVA test, Post hoc-Bonferroni test, and independent sample “t”-test were carried out for the comparison between occlusal planes, among the genders and for the analysis of the angle of deviation of scribed plane on the cast to HIP plane on the right and left sides.Results:Occlusal plane III (Mesio-labial incisal edge of upper right central incisor to Mesio-buccal cusp tips of upper second molars) showed least angle of deviation with 1.316° ± 1.158° to HIP plane among tested subjects. There is no significant difference between the genders. The plane scribed on the cast with H. I. P evaluator showed relative parallelism to H. I. P plane with minimum deviation of 0.010° ± 0.363°.Conclusion:Occlusal plane III is more parallel to H. I. P plane. Scribed plane on the cast using H. I. P evaluator is parallel to H. I. P plane. H. I. P evaluator can be used as an alternative tool to establish the occlusal plane to rehabilitate patient with deficient dentition or disordered occlusal plane.

Natural frequency analysis and experiment for 3SPS+1PS parallel hip joint manipulator based on rigid-flexible coupling theory

For analyzing natural frequency of a 3SPS+1PS parallel hip joint manipulator, a rigid-flexible coupling theory is proposed. 3SPS denotes that the PHJM has three legs and each leg type is SPS. 1PS denotes that the PHJM has one constrained leg and the constrained leg type is PS. The rigid finite element method and flexible finite element method are the base of the rigid-flexible coupling theory. Firstly, the basic element models of the PHJM are established based on the rigid-flexible coupling analysis. Secondly, the elastic dynamic models of the flexible legs are established based on the Lagrange equation and flexible finite method. Finally, the rigid-flexible coupling model of the PHJM is assembled by building the relationship between the rigid and flexible elements. Based on the rigid-flexible model, the natural frequency of the PHJM is analyzed. In addition, the effect parameters of the natural frequency are analyzed. The analysis results of the natural frequency show that the natural frequency is symmetric distribution in the working space, and the minimum value of the 1st order natural frequency is 2.3 Hz. The operating frequency (1 Hz) is much lower than the 1st order natural frequency, so the PHJM will not generate resonance and can operate stably. The analysis results of the parameter show that the PHJM has the minimal sensitivity with the effect parameter E and has the maximal sensitivity with the effect parameter H, so the length of the middle leg has the biggest impact on the natural frequency. Natural frequency analysis results have been checked by the hammer test, which verifies the feasibility of the rigid-flexible coupling theory. At the same time, the regression analysis is carried out based on the hammer test results. Using the rigid-flexible coupling theory to solve the natural frequency of the parallel manipulator, the physical meaning is explicit and the modeling process is clear, so the rigid-flexible coupling theory is a universal method.

Bifurcation and stability analysis for 3SPS+1PS parallel hip joint manipulator based on unified theory

For a parallel hip joint manipulator, the unified kinematics and stiffness model are established based on a novel unified theory, and then the bifurcation and stability are analyzed under the same unified theory framework. In bifurcation analysis, a chaos method is first applied to solve the non-linear bifurcation equations in order to get the full configuration of the parallel hip joint manipulator, which improves the convergence rate and accuracy. Based on the full-configuration solution, the single-parameter and double-parameter simulation for the bifurcation and stability of the parallel hip joint manipulator is performed. The bifurcation simulation results show that the configuration only changes along the corresponding path but cannot change to other paths when the configuration of the parallel hip joint manipulator is at a certain path. The stability simulation results show that when the parallel hip joint manipulator enters into an uncontrolled domain of a bifurcation posture along different paths, the posture component which changes dramatically will lose control first, and the other posture components will move along the changed configuration. In this paper, the kinematics, stiffness, bifurcation and stability of the parallel hip joint manipulator are solved under the same theory framework, which improves the solving efficiency and enriches the mechanical theory for the parallel manipulators.

Configuration and singularity analysis of a parallel hip joint simulator based on the forward kinematics

The singularities of parallel manipulators are usually identified by geometrical methods or by the kinematic principles based on the pose parameters. The methods have limitations in applications that involve singularity avoidance, such as motion planning from input parameters. To identify a singularity from an input parameter point of view, which would make the singularity avoidance strategy more direct and more effective in practical applications, this paper focuses on the relationship between the singularities, the configuration spaces and the input parameters with a 3SPS+1PS parallel hip joint simulator selected to implement this approach. A univariate-form polynomial equation of the forward kinematics is obtained with the aid of the Sylvester dialytic method of elimination, therefore proving that the manipulator has at most eight configurations for a single input. The configurations are then divided into two types of spaces according to their distributions. It is discovered that in practice, we only need concern ourselves with the basic configuration spaces, where the singular loci degenerate into a single surface. Finally, the singular condition is proved to be equivalent to that when the univariate-form input–output equation has a repeated root in the real number field. Therefore, the singular condition equation of the input parameters and the singular loci of the input parameters in the basic configuration spaces are obtained. This study provides new insight into the singularity avoidance of a parallel manipulator, especially for the singularity-free design in the motion planning from input parameters.

Finite Element Method for Kinematic Analysis of Parallel Hip Joint Manipulator

This paper presents a finite element method (FEM) for the kinematic solution of parallel manipulators (PMs), and this approach is applied to analyze the kinematics of a parallel hip joint manipulator (PHJM). The analysis and simulation results indicate that FEM can get accurate results of the kinematics of the PHJM, and the solution process shows that using FEM can solve nonlinear and linear kinematic problems in the same mathematical framework, which provides a theory base for establishing integrated model among different parameter models of the PHJM.

Unified Kinematics Analysis and Low-Velocity Driving Optimization for Parallel Hip Joint Manipulator

Unified modeling for the kinematics analysis of a parallel hip joint manipulator (PHJM) is proposed, and structural parameters of the PHJM are optimized based on the unified model for obtaining low-velocity driving performance. Based on the finite element theory, a unified model for kinematics analysis is established, and the Monte Carlo method is subsequently proposed to solve the workspace for the PHJM. To optimize the workspace, a 6 surface-14 point (6 S-14 P) method is proposed to judge whether the workspace includes the task space. The structural parameters are further optimized to obtain low-velocity driving performance, and the motion performances of the PHJM with the optimal parameter are numerically simulated. The velocity simulation results demonstrate that the maximum relative velocity of the PHJM with the optimal parameter decreases by 23.2%. The unified kinematics analysis and low-velocity driving optimization effectively improve the performance for the PHJM and enrich the optimization theory for parallel manipulators with high velocities and given tasks.

Kinematic calibration analysis of 3SPS + 1PS bionic parallel test platform for hip joint simulator

As the key component of the parallel hip joint simulator, 3SPS+1PS bionic parallel test platform owns four degrees of freedom including three rotations and one translation. When the moving platform stays at a given translation position, the parallel manipulator can represent three-dimensional rotating gait motions of the hip joint for the purpose of evaluating the friction characteristics of biological materials. Because of the manufacturing and assembling errors, the actual structure parameters of the parallel manipulator are not more accurate than the theoretical values and its reduced simulation accuracy will bring the uncertain evaluation. So in order to improve the precisions in the design, manufacture and assembly of the parallel manipulator, it is necessary to calibrate the kinematic parameters. Considering the structural characteristics of the parallel manipulator, its error model and the corresponding compensation method are established based on the complete differential-coefficient theory. According to the constant values of two orientation angles, the orientation residual matrix is constructed by adopting the incomplete measurement method and the forward kinematics functions, so its cost function can be defined. The iterative algorithm based on the least square method is applied to identify the structure parameters and obtain their optimal solutions, and then the actual kinematic calibration process is simulated by numerical method. The simulation results show that the comprehensive orientation error after calibration is greatly decreased, and the effectiveness of the calibration method is validated.

Stiffness analysis of the 3SPS+1PS bionic parallel test platform for a hip joint simulator

SUMMARYA novel parallel hip joint simulator, called 3SPS+1PS bionic parallel test platform, with 4 degrees of freedom including three rotations and one translation is designed to represent three-dimensional motion and compound friction movement of a human hip joint and to be a better simulator for testing the tribology performance of biomaterials for hip joint prosthesis. Stiffness is one of the most important performances of parallel manipulators, as well as for the 3SPS+1PS parallel manipulator with higher speeds. First, the differential kinematic/static model was derived based on the kinematics model. The relationship between the elastic deformation of each active leg and the variation of position/orientation deformation of the moving platform was described based on the virtual work principle. Then, a 6 × 6 global stiffness matrix of the 3SPS+1PS parallel manipulator was derived. The maximum versus minimum eigenvalues of the global stiffness matrix were obtained as its two evaluation indexes. By letting the 3SPS+1PS bionic parallel test platform represent three rotation motions and the dynamic loading of the human hip joint as described by ISO 14242 Part-1, the forces acted on each active leg and their responding elastic deformations were analyzed. The distributions for maximum and minimum stiffness in different workspace were detected. Finally, the results showed that the minimum stiffness in the whole workspace should be larger than the allowable stiffness of the 3SPS+1PS parallel manipulator.

Dynamics analysis of a parallel hip joint simulator with four degree of freedoms (3R1T)

For a hip joint simulator with a 3SPS+1PS spatial parallel manipulator as the core module, a formulation based on the Kane equation was derived for the dynamic characteristics of the simulator from the kinematics analysis of the model. The relationships of the velocities and accelerations between the moving platform and active branched-chains were deduced. The velocity and angular velocity components of the moving platform were served as the generalized velocities. And the dynamic model was established by obtaining the generalized active forces and inertial forces. Then the driving forces and powers of the active branched-chains and the constraint reaction forces of the intermediate branched-chain were simulated in the numerical method. The results showed that the active driving forces of the branched-chains reached their respective maximum when the moving platform rotated into 0.13∘ around X-axis, 2∘ around Y-axis, and 18∘ around Z-axis. And the intermediate branched-chain needed to balance the driving and inertia forces, as well as support the moving platform and load the force of hydraulic cylinder. Therefore, the maximum constraint reaction force of the intermediate branched-chain is along the Z-axis. The research works provided a theoretical basis for the design of the active branched-chains driving system and the structural parameters of the intermediate branched-chain, as well as for the control system.

Kinematic analysis of a 3SPS+1PS parallel hip joint simulator based on Rodrigues parameters

To overcome defects in complex motion simulation and variable dynamic loading of hip joint simulators available in literature, a parallel hip joint simulator with a spatial parallel manipulator as core module is proposed. The simulator has four degrees of freedom (DOFs) including three rotational freedoms which replicate abduction/adduction (AA), flexion/extension (FE) and internal/external rotation (IER) motions in various human motion states and one translational freedom designed for specimen replacement. First, the mobility properties of the simulator were analyzed based on screw theory. Second, its kinematics was analyzed and its active/constrained forces were solved based on Rodrigues parameters. Some analytic formulae were derived for solving the inverse/forward displacements, velocities, accelerations and forces. Third, according to ISO 14242-1:2002(E), a numerical simulation of the inverse kinematics was conducted, the motion configuration scheme of the simulator was determined and the selection of actuators was validated. Then the numerical simulation was validated by an experiment. Finally, higher calculation efficiency of the Rodrigues parameters against the Quaternion was proved. It is shown that the simulator proposed here can replicate motions of a natural hip joint under various motion states via changing control programs but mechanical structure.

DESIGN FEATURES OF A PARALLEL TESTING PLATFORM FOR SIMULATING KINEMATIC CHARACTERISTICS OF HIP JOINT

To simulate the movement of a human during daily activities, such as walking, running, squatting, and kneeling, a novel parallel hip joint simulator whose key movement component is a 3SPS + 1PS parallel manipulator with four degrees of freedom (DOF) was proposed. SPS denotes the spherical-prismatic-spherical leg, and PS denotes the prismatic-spherical leg where only the prismatic joint is actuated and hence underlined. Firstly, the formulae for solving the inverse kinematics of the 3SPS + 1PS parallel manipulator were derived based on the unit quaternion method. Then, the parallel hip joint simulator was designed and finally developed by means of constructing the mechanical module, control module, hydraulic loading module, and data transmission module. In addition, three linear actuators are driven by the scheduled inverse displacement trajectories to enable the moving platform to output rotations about the Z-, Y-, and X-axes for representing flexion/extension, abduction/adduction, and external/internal rotations of the human hip joint. Simultaneously, the hydraulic loading module represents the dynamic loading as described by ISO 14242 Part-1 acting on the hip joint during the kinematic experiment. The kinematic experiment and dynamic loading experiment show that the fitting curves of the experimental results are consistent with the designed movement and loading trajectories. All these illustrate that the developed 3SPS + 1PS parallel hip joint simulator with effective design of all modules can substantially represent the designed movement and loading trajectories. The developed hip joint simulator can provide more reliable tribology test data for artificial prosthesis of hip joint.

Singularity Analysis of a Parallel Hip Joint Simulator Based on Grassmann Line Geometry

A hip joint simulator with a 3SPS+1PS spatial parallel manipulator as the core module is proposed.The spatial parallel manipulator has 4 degrees of freedom,including three rotations and one translation.It consists of a fixed base and a moving platform that is connected by three SPS-type active legs and one PS-type central strut.Singularity has great effects on working performance of parallel manipulator,so the singular characterizes of the hip joint simulator need to be studied.Kinematic model based on Rodrigues parameters is provided and a general formulation of static mechanical conversion matrix is deduced that allows one to determine Plucker vectors associated with six analytical lines for Grassmann analysis.Most singular configurations of the simulator are presented,and the expressions describing corresponding singularities are obtained in closed forms.Numerical simulations show the corresponding motion curves and surfaces of singular configurations with different linear variety ranks from 1 through 5,and the distribution characteristics of singular trajectories are studied respectively.The analysis of the singular configurations provided has great significance for trajectory planning,size optimization and control design of the simulator.

Singularity Analysis of a Parallel Hip Joint Simulator Based on Grassmann Line Geometry

A hip joint simulator with a 3SPS+1PS spatial parallel manipulator as the core module is proposed.The spatial parallel manipulator has 4 degrees of freedom,including three rotations and one translation.It consists of a fixed base and a moving platform that is connected by three SPS-type active legs and one PS-type central strut.Singularity has great effects on working performance of parallel manipulator,so the singular characterizes of the hip joint simulator need to be studied.Kinematic model based on Rodrigues parameters is provided and a general formulation of static mechanical conversion matrix is deduced that allows one to determine Plucker vectors associated with six analytical lines for Grassmann analysis.Most singular configurations of the simulator are presented,and the expressions describing corresponding singularities are obtained in closed forms.Numerical simulations show the corresponding motion curves and surfaces of singular configurations with different linear variety ranks from 1 through 5,and the distribution characteristics of singular trajectories are studied respectively.The analysis of the singular configurations provided has great significance for trajectory planning,size optimization and control design of the simulator.

Kinematic analysis of 3SPS+1PS bionic parallel test platform for hip joint simulator based on unit quaternion

As a novel parallel hip joint simulator, the 3SPS+1PS bionic parallel test platform with 4 degrees of freedom including three rotations and one translation is proposed. SPS denotes the spherical-prismatic-spherical leg and PS denotes the prismatic-spherical leg where only the prismatic joint is actuated and hence underlined. By means of the unit quaternion method, the formulae for solving the inverse/forward displacement, the inverse/forward velocity and the inverse/forward acceleration kinematics are derived. Using the unit quaternion to represent the position and orientation of a moving platform, singularities caused by Euler angles can be avoided. Combining the topological structure characteristics of the 3SPS+1PS bionic parallel test platform and letting the three-dimensional (3-D) motion of a human hip joint as its output movement, the displacement trajectories of three active legs are constructed based on the inverse displacement kinematics. The forward kinematic tests whose data are recorded by a 3-D orientation capture system are carried out on the developed parallel hip joint simulator. Moreover, the results of the forward kinematic tests prove that the 3SPS+1PS bionic parallel test platform can approximately represent human hip joint motion and provide more reliable experimental data for hip joint prostheses in clinical application.