Configuration Change and Mobility Analysis of a New Metamorphic Parallel Mechanism Used for Bionic Joint

This paper presents a unique feature of geometric and physical constraint of axes of the reconfigurable-axis (rA) joint and analyses the effectiveness in the constructed limb, resulting in variation of mobility configuration of metamorphic parallel mechanism. This change in mobility is completed by two cases illustrated by a 3(rA)PS metamorphic parallel mechanism having variable mobility from 3 to 6. The underlying principle of the metamorphosis of this rA joint is demonstrated by investigating the dependence of the corresponding screw system comprising of line vectors, leading to evolution of the rA joint from the two types of spherical joints to the three types of variable Hooke joints and the one revolute joint. This new type of metamorphic parallel mechanism has broad application prospects, especially in the field of 3d printing. According to the complexity of the shape of the workpiece, the degree of freedom corresponding to different topologies can be selected, which can reduce the costs and increase the adaptability to different working conditions.

Spherical joint is a type of common kinematic pair in spatial parallel mechanism. The existence of spherical joint clearance has many adverse effects on the mechanism. A method of forecasting the dynamic behaviors of spatial parallel mechanism with spherical clearance joint is proposed. The 4-UPS-UPU spatial parallel mechanism with spherical clearance is taken as the research object, the dynamic response, and nonlinear characteristics of the mechanism are studied. The kinematic model and the contact force model of the spherical clearance are established. The dynamic equation of the spatial parallel mechanism with spherical joint clearance is derived by Newton–Euler method. The above-mentioned dynamic equation is solved by using the ODE113 function that is based on a variable order numerical differential algorithm in matlab. The dynamic responses of moving platform with different clearance values are analyzed. The contact force and the center trajectory of the sphere at the spherical joint are obtained. In addition, the phase trajectory, Poincare map, and bifurcation diagram are analyzed, and the nonlinear characteristics of the spherical clearance joint and the moving platform are obtained. By comparing the results, such as the acceleration of moving platform and the contact force, with virtual prototype simulation, the correctness of the dynamic equation of the spatial parallel mechanism with spherical clearance joint and the analysis results are verified. The researches show that the change of clearance value has a great influence on the motion state of spherical clearance joint, and chaos phenomena appears in the clearance joint with the increase in the clearance value. And the impact phenomenon appears between the spherical joint elements, which makes the mechanism generated vibration.

This paper introduced a new metamorphic parallel mechanism consisting of four reconfigurable rTPS limbs. Based on the reconfigurability of the reconfigurable Hooke (rT) joint, the rTPS limb has two phases while in one phase the limb has no constraint to the platform, in the other it constrains the spherical joint center to lie on a plane. This results in the mechanism to have ability of reconfiguration between different topologies with variable mobility. Geometric constraint equations of the platform rotation matrix and translation vector are set up based on the point-plane constraint, which reveals the bifurcated motion property in the topology with mobility 2 and the geometric condition with mobility change in altering to other mechanism topologies. Following this, a unified kinematics limb modeling is proposed considering the difference between the two phases of the reconfigurable rTPS limb. This is further applied for the mechanism modeling and both the inverse and forward kinematics is analytically solved by combining phases of the four limbs covering all the mechanism topologies.

Multiple bifurcated reconfiguration of double-loop metamorphic mechanisms with prismatic joints

This paper presents two general metamorphic kinematic units which employ only revolute joints. The two kinematic units with reconfigurability are mapped from independent set of line vectors with different geometry. The underlying principle of the metamorphosis of this kind of reconfigurable kinematic units is unraveled by investigating the dependency of corresponding screw system comprised with line vectors. Limb structure that can be used for constructing new parallel mechanisms is proposed. Subphases of the limb are enumerated accompanying to the phase change of the embodied metamorphic units and constraints corresponding to each phase are analyzed based on reciprocity of screws. Two metamorphic parallel mechanisms which can change their configuration from fully 6-DOF phase to 3-DOF translational subphase and 3-DOF spherical subphase are proposed according to geometric conditions that must be met by limbs. The mobility changes of the platform induced by phase change of limbs are addressed.

An investigation on the dynamic modeling and analysis of spatial mechanisms with spherical clearance joints including friction is presented. For this purpose, the ball and the socket, which compose a spherical joint, are modeled as two individual colliding components. The normal contact-impact forces that develop at the spherical clearance joint are determined by using a continuous force model. A continuous analysis approach is used here with a Hertzian-based contact force model, which includes a dissipative term representing the energy dissipation during the contact process. The pseudopenetration that occurs between the potential contact points of the ball and the socket surface, as well as the indentation rate play a crucial role in the evaluation of the normal contact forces. In addition, several different friction force models based on the Coulomb's law are revisited in this work. The friction models utilized here can accommodate the various friction regimens and phenomena that take place at the contact interface between the ball and the socket. Both the normal and tangential contact forces are evaluated and included into the systems' dynamics equation of motion, developed under the framework of multibody systems formulations. A spatial four-bar mechanism, which includes a spherical joint with clearance, is used as an application example to examine and quantify the effects of various friction force models, clearance sizes, and the friction coefficients.

The effect of modeling the knee as a simple spherical or revolute joint during gait, cutting and hopping were evaluated. The results indicate that, even during gait, a revolute joint may be too restrictive in its representation of the knee, with flexion/extension errors as high as 9.4°. By imposing the spherical joint, joint angles showed consistent and strong correlations with the true joint angles for the functional tasks, although internal/external rotation angle were moderately affected (errors up to 4.2°). For both constraint types, the remaining Degrees of Freedom (DOF) were not consistent across subjects and must be considered unreliable, with translation errors of up to 11.0 mm with a spherical joint and 11.9 with a revolute joint.

The joints of traditional foot robots are generally designed as power-driven articulated rotary motion, but this design has some problems such as poor flexibility and adaptability. To optimize joints, this paper selected the African ostrich intertarsal joint which could move at high speed in complex terrain as a biomimetic prototype. Based on the motion acquisition and reverse engineering three-dimensional reconstruction of the intertarsal joint, a rope-driven spherical sub-bionic joint was designed. The angle curves of the bionic joints under different ground conditions were obtained through the hard ground and the motion tests of three different softness sands (medium with different particle sizes). Results showed that the proportion of the vacant period was 35%, 49%, 62% and 63% when the bionic joint moved on the hard ground and three soft grounds (the particle size particles are arranged from large to small),. The range of variation gradually becomes larger, similar to the variation trend of the intertarsal joint during ostrich locomotion. The bionic joint was able to absorb joint impact through the relative slippage of the joint surface and expansion/contraction of the rope, and maintain flexibility when passing through different degrees of softness.

This paper investigates the metamorphic mechanism derived from the hindwing in ladybird beetles, which creates its mathematical models and analyzes kinematics based on screw theory using mathematical software. The hindwing in ladybird beetles is an origami-like structure. Considering the concept of equivalent mechanisms, any origami pattern can be seen as being composed of several spherical multi-bar linkages connecting to each other. Hence, this paper proposes an algebra method to reveal the relations between different joint angles in the spherical multi-bar linkage, using the loop equations and Sylvester’s dialytic elimination method. The results can be used to find the location and the motion trajectory of any desired point in this ladybird wing metamorphic mechanism. The way of analysis of the spherical multi-bar mechanism used in this paper can be widely applied in design and practical applications.

In the space deployable mechanism considering spherical joints with clearance, the kinematic stability and working life of will be seriously affected. To address this problem, this paper proposes a nonlinear stiffness coefficient expression and an improved viscous damping coefficient expression considering the wear reduction properties of coatings, so as to obtain a conformal contact force model based on the analysis and comparison of the existing common normal contact force models. The new contact force model is qualitatively analyzed from three aspects, namely clearance size, recovery coefficient, and material properties, so as to demonstrate the correctness and applicability of the model. In the prefabricated space deployable mechanism (RSSP) with spherical joint clearance, the acceleration variation of the actuator is analyzed and compared by using the new contact force model, and the wear quantity of the spherical joints with clearance and coating is predicted. The dynamic results show that spherical joints with clearance have a significant effect on the acceleration of the actuator, and the long working time will inevitably lead to increased vibration and reduce the motion accuracy and life of the mechanism. By comparing with the calculation results of wear, it is found that the wear of spherical joint clearance with coating decreases significantly in all vector directions, and the wear area of the Euler Angle increases slightly compared with that without coating because of the increase of contact collision frequency. Therefore, the wear calculation method and coating strategy proposed in our work can provide a theoretical basis for improving the kinematic accuracy and working life of space deployable mechanism system considering spherical joints with clearance.

Clearance between the moving joints is unavoidable in real working process. At present, many researches are mainly focused on dynamics of plane revolute joint in plane mechanism, but few on dynamics of spatial spherical joint clearance in spatial parallel mechanism. In this paper, a general method is proposed for establishing dynamic equations of spatial parallel mechanism with spatial spherical clearance by Lagrange multiplier method. The kinematic model and contact force model of the spherical joint clearance were established successively. Lagrange multiplier method was used to deduce the dynamics equation of 4UPS-UPU mechanism with spherical clearance joint systematically. The influence of friction coefficient on dynamics response of 4UPS-UPU mechanism with spherical clearance joint was analyzed. Non-linear characteristics of clearance joint and moving platform were analyzed by Poincare map, phase diagram, and bifurcation diagram. The results show that variation of friction coefficient and clearance value had little effect on stability of the mechanism, but the chaotic phenomenon was found at spherical clearance joint. The research has theoretical guiding significance for improving the dynamic performance and avoiding of chaos of parallel mechanisms including spherical joint clearance.

The parallel manipulators with n<6 spherical joint-prismatic joint-spherical joint (SPS) type active legs and one passive constrained leg have attracted more attention and been used in many practical applications. This kind of parallel manipulator has a larger capability of load bearing and a simple structure of active leg. The paper used 4-SPS/PS four degree-of-freedom (DOF) parallel manipulator for the simulation of ship's heave and swing motion. Mobility property of the 4-SPS/PS parallel manipulator is analyzed by screw theory. The inverse position kinematics model is established and the analytical solution is obtained. It uses extra sensor and Sylvester resultant elimination to derive analytical solutions of forward position kinematics including two real solutions and two imaginary solutions, and uses vector cross product to derive the Jacobian matrix of 4-SPS/PS parallel manipulator. Furthermore, it introduces three performance indicators to analyze the singularity. In order to obtain accurate analysis results of singularity, it calculates the minimum singular value, condition number and manipulability degree of Jacobian matrix for different combination of pose, respectively.

In order to improve the stiffness of the spherical joint of the robot, reduce the difficulty of manufacturing and the complexity of the control system, this paper proposed a method of spherical joint and digital drive of the robot based on the electromagnetic principle. Firstly, introduces the structure and motion principle of the spherical joint of the robot, establishes the mathematical model of the spherical joint and establishes the dynamic model according to the second Lagrange equation. after that, the relationship between the number of ampire-turns of the electromagnet on the spherical joint, the attitude Angle of the rotor and the force of the rotor was obtained by simulating the single degree of freedom of the joint based on Ansys maxwell and Matlab, which provided a basis for the realization of the digital drive of the spherical joint.

Objective. The advent of surgical reconstruction techniques has enabled the recreation of myoelectric controls sites that were previously lost due to amputation. This advancement is particularly beneficial for individuals with higher-level arm amputations, who were previously constrained to using a single degree of freedom (DoF) myoelectric prostheses due to the limited number of available muscles from which control signals could be extracted. In this study, we explore the use of surgically created electro-neuromuscular constructs to intuitively control multiple bionic joints during daily life with a participant who was implanted with a neuromusculoskeletal prosthetic interface. Approach. We sequentially increased the number of controlled joints, starting at a single DoF allowing to open and close the hand, subsequently adding control of the wrist (2 DoF) and elbow (3 DoF). Main results. We found that the surgically created electro-neuromuscular constructs allow for intuitive simultaneous and proportional control of up to three degrees of freedom using direct control. Extended home-use and the additional bionic joints resulted in improved prosthesis functionality and disability outcomes. Significance. Our findings indicate that electro-neuromuscular constructs can aid in restoring lost functionality and thereby support a person who lost their arm in daily-life tasks.

Kinematic modeling and optimization of a new reconfigurable parallel mechanism