Motion Of Mechanism Research Articles

Kinematics Analysis of 6-Degrees-of-Freedom Parallel + Serial Type Hybrid Mechanisms Containing Parallel Mechanism With High Coupling Motions

AbstractThe existing displacement of parallel + serial type hybrid mechanisms is mainly solved by the equivalent serial mechanism (SM) method. However, a large number of lower mobility parallel mechanisms (PMs) that have high coupled motions at the end-effector cannot be equivalent to SMs. Thus, the displacement problem especially for the inverse displacement of this type of hybrid mechanisms has not been well solved. On the basis of this situation, this article takes a 6-degrees-of-freedom (DOFs) 3-UPU + 3R hybrid mechanism as an example to give a general method to solve the displacement problem. First, based on the inverse displacement and pose coupling relationship of the 3-UPU PM, its forward displacement is solved by Sylvester’s dialytic elimination method, and then the forward displacement of the 3-UPU + 3R hybrid mechanism is obtained by the superposition method. Second, by skillfully dealing with the relationship between coupling motions of the 3-UPU PM and the motion of hybrid mechanism, three nonlinear equations containing three unknown motion parameters are obtained, and the inverse displacement problem is solved using Sylvester’s dialytic elimination. The research in this article is valuable in the kinematics modeling of hybrid mechanisms.

A geometric and analytic technique for the determination of the instantaneous screw axes in single-DOF spatial mechanisms

In single-degree-of-freedom (single-DOF) mechanisms, the location of the instantaneous screw axes (ISAs) of the relative motions between any two links depends only on the mechanism configuration. In the literature, this property together with the Aronhold-Kennedy (AK) theorem was exploited to devise geometric and analytic techniques that determine ISAs in planar mechanisms, where the ISAs are located by the instant centers (ICs). Despite the fact that an extended Aronhold-Kennedy (EAK) theorem has been demonstrated for spatial mechanisms, too, since 1959, the spatial counterpart of these techniques has not been proposed, yet. Relating ISA locations to the mechanism configuration is important during the mechanism design and provides a deeper comprehension of the mechanism motion by disclosing the role each link plays. Here, a geometric and analytic technique based on the EAK theorem is presented for the ISA determination in single-DOF spatial mechanisms. The proposed method is indeed the extension to spatial mechanisms of those techniques used for the IC determination in planar mechanisms. The effectiveness of the proposed technique is also illustrated through two relevant case studies.

Twist and finite twist analysis of 2UPR-SPR parallel mechanism based upon screw theory

This paper discusses the issue on mobility analysis of parallel mechanism. The analysis is focused on the two-rotational and one-translational 2UPR-SPR parallel mechanism which has interesting motion properties that one rotation of this mechanism has fixed direction, while the other rotation and the translation have variable directions. Twist analysis is conducted to obtain the feasible velocities of the moving platform at any configuration of the mechanism, and finite twist analysis is carried out to obtain the feasible displacements of the moving platform when the mechanism moves away from the initial configuration to any configuration. The obtained parametric velocity space at any configuration and parametric displacement manifold from the initial configuration to any configuration are formulated, which are proved to contain the same motion information and have the same effect in mobility analysis. Through analyzing the 2UPR-SPR mechanism, it is revealed that both twist and finite twist are effective to describe continuous motions of rigid body or mechanism. This enriches the relation between twist and finite twist, and unifies the applications of these two kinds of screws in mobility analysis.

A mechanism motion error sensitivity analysis method based on principal component analysis and artificial neural network

Present sensitivity analysis of motion error usually focuses on the trajectory deviation of the mechanism, which inevitably introduces an intractable time dependent problem. For efficiently and accurately measuring the motion error of the planar mechanism with dimension and clearance uncertainties by global sensitivity analysis (GSA), a novel method is proposed in this work. By applying the principal component analysis (PCA), the motion error is transformed into new vector output and cleverly avoids the time dependent problem. To ensure the accuracy of PCA in the case of small samples, the Bootstrap method is introduced. Based on the PCA results, the artificial neural network (ANN) surrogate model is established between the input variables and the vector output. Then the classical variance-based GSA method is applied to obtain the variable importance ranking for different PCs, and the synthesized GSA indices are introduced. Four representative examples are studied to demonstrate the versatility and effectiveness of the proposed method.

Type synthesis and performance analysis of manipulators with shape adaptability

Manipulators have attracted wide attention in recent years because they are simple and easy to control when grasping objects in space. However, there are not many theoretical researches on manipulator at present. Therefore, based on the principle of simple operation and low cost, a manipulator with high versatility, high flexibility, diverse movement modes, and shape adaptability has laid a solid theoretical foundation and practical significance for the innovative development of robot. In this paper, a 4-RRS& planar four-bar mechanism with bifurcation motion is proposed based on the finite screw theory. The degrees of freedom of the mechanism are analyzed by using the screw theory. Then the closed-loop vector method and instantaneous screw method are used to establish the analytical expression and the velocity Jacobian matrix between the motor actuation angle and the moving platform, respectively. Finally, on the basis of kinematic analysis, the SolidWorks and Matlab software are used to verify the kinematic simulation of the mechanism, so as to ensure the rationality of the mechanism motion and the correctness of the theoretical derivation.

Grassmann line geometry based configuration synthesis of equivalent UU parallel mechanisms with two virtual center-of-motion

This paper investigates a class of equivalent UU parallel mechanisms with two virtual center-of-motions (VCMs) in terms of the geometric characteristics of the equivalent UU model, and proposes a configuration synthesis method based on the Grassmann line geometry and constraint screw multiset. First, the equivalent UU model is proposed concerning the analysis of ankle rehabilitation and the ankle UU model. Three geometric characteristics and four classes of motion and constraint characteristics of the equivalent UU model are given. Second, the motion principle of equivalent UU parallel mechanism is proposed for the characteristics of motion and constraint, which provides a theoretical method for configurable synthesis. Third, a series of constraint limbs satisfying the motion and constraint characteristics of equivalent UU parallel mechanisms are synthesized by using the constraint screw synthesis method in terms of the screw theory and Grassmann line geometry principle. Finally, the concept of multiset is introduced into mechanism synthesis, and a series of equivalent UU parallel mechanisms are synthesized based on the method of constraint screw multiset.

Influence of Part Size Error on the Characteristics of a Feeding Transmission Mechanisms based on a Conjugate Cam-Spatial Linkage

Reasonable size accuracy of the mechanical part may be a key for the design of the complex transmission mechanism; thus, it is very important to evaluate the size errors of each part. Taking the conjugate cam-spatial rank feeding transmission mechanism as an example, the functions, such as the near-dwelling, fast-forwarding, working feeding, slow-forwarding, far-dwelling, fast-returning, quick-feeding-back, and slow-returning, are realized with the appropriate conjugate cam governing equations. The analytical expressions of the conjugate cams and functions of the angular motion and angular velocity between the conjugate cam and crank are derived. Considering the real machining errors of part, a concept of parameter sensitivity is proposed, and the magnitude and direction of the influence of typical parameter errors on the mechanism motion transfer characteristics are evaluated by this concept. This method provides a reliable reference for the precision design of mechanical structure parameters.

Dynamic Modeling and Analysis of Loader Working Mechanism Considering Cooperative Motion with the Vehicle Body

Achieving precise load detection for Intelligent Loaders is an important task, which directly affects the operation energy efficiency and the fatigue life analysis for the loader’s working mechanism. The operation of the mechanism is regarded as a 3-DOF (degree of freedom) planar motion process coordinated with the vehicle body. Affected by complex dynamic coupling in motion, the existing dynamic models of the mechanism have the problem of insufficient accuracy, which is not conducive to the precise calculation of load. Taking the reverse six-linkage loader as the research object, an accurate dynamic model of the mechanism is established considering its cooperative motion with the vehicle body. Firstly, the kinematic description of the mechanism is given by the Rodriguez method. Then, to overcome the coupling effect caused by the cooperative motion, the sufficient inertia forces of the mechanism are established in joint space using the Lagrange method. Furthermore, to overcome the coupling effect caused by the complex structure, the Newton–Euler method is used to establish the force mapping relations between the joint space and the drive space by multi-body modeling. Finally, the dynamic model of the mechanism in drive space is obtained, and the specific mapping relations between the bucket force, the vehicle driving force, and the drive parameters are given. Compared with existing dynamic models in simulation, the analysis shows that the average and maximum absolute errors of the vehicle driving force calculated by the established model do not exceed 20% of the existing model errors, and the corresponding errors of the bucket force do not exceed 10% of the existing model errors, which proves that the motions of vehicle body and front-end mechanism, as well as the force of the tilt hydraulic cylinder, play important roles in improving the model accuracy. The established model is superior to existing models and is more suitable for cooperative motion with the vehicle body.

Design and Simulation of a Novel 6-DOF Hybrid Mechanism Motion Platform for Pose Adjustment of Heavy Equipment

Design and Simulation of a Novel 6-DOF Hybrid Mechanism Motion Platform for Pose Adjustment of Heavy Equipment

An automatic alignment method for discharge arm of mobile crushing station based on binocular vision and fuzzy control

The mobile crushing station is one of the main equipment of the semi-continuous open-pit mining system. The discharge arm and the receiving equipment are manually aligned, which has the problems of long alignment time and low alignment accuracy, which affects the working efficiency of the mining system. According to the development and application of space rendezvous and docking technology at home and abroad, the advantages and disadvantages of different measurement methods are compared and analysed, and the method of applying binocular measurement technology to system positioning in the automatic alignment system of the discharge arm is determined. There are three movements in the mechanical part of the designed discharge arm alignment control system, including the rotary motion of the visual measurement mechanism and the horizontal rotation and telescopic motion of the discharge arm. According to the kinematic analysis and binocular vision measurement theory, the deviation model of the alignment control of the discharge arm is established. A binocular vision measurement and localization method based on the combination of stereo calibration and template matching is proposed, which achieves surprising measurement accuracy. An automatic alignment method of the discharge arm of the mobile crushing station is proposed based on the binocular vision and fuzzy control method. Its validity is verified by simulation and experiment. The strategy of motion decomposition is applied to the alignment system to avoid unnecessary motion of the discharge arm. The research results all show that the alignment method can achieve the angle deviation within ±0.5 degrees, the distance deviation within ±15 mm, and the test alignment time is about 5 minutes, which is better than other alignment control models; the alignment accuracy and the alignment time are improved by more than 50%. The method can control the discharge arm to complete the alignment task quickly and smoothly, which lays a foundation for the further automatic research of the discharge arm.

Development of a Novel Low-profile Robotic Exoskeleton Glove for Patients with Brachial Plexus Injuries.

This paper presents the design and development of a novel, low-profile, exoskeleton robotic glove aimed for people who suffer from brachial plexus injuries to restore their lost grasping functionality. The key idea of this new glove lies in its new finger mechanism that takes advantage of the rigid coupling hybrid mechanism (RCHM) concept. This mechanism concept couples the motions of the adjacent human finger links using rigid coupling mechanisms so that the overall mechanism motion (e.g., bending, extension, etc.) could be achieved using fewer actuators. The finger mechanism utilizes the single degree of freedom case of the RCHM that uses a rack-and-pinion mechanism as the rigid coupling mechanism. This special arrangement enables to design each finger mechanism of the glove as thin as possible while maintaining mechanical robustness simultaneously. Based on this novel finger mechanism, a two-finger low-profile robotic glove was developed. Remote center of motion mechanisms were used for the metacarpophalangeal (MCP) joints. Kinematic analysis and optimization-based kinematic synthesis were conducted to determine the design parameters of the new glove. Passive abduction/adduction joints were considered to improve the grasping flexibility. A proof-of-concept prototype was built and pinch grasping experiments of various objects were conducted. The results validated the mechanism and the mechanical design of the new robotic glove and demonstrated its functionalities and capabilities in grasping objects with various shapes and weights that are used in activities of daily living (ADLs).

Influence of deformation zone length on bending radius of SS304 tubes with small diameters manufactured via free bending-based active motion

In three and six-axis free-bending equipment, the deformation zone length (A) is a fixed mechanical structure parameter modified when the relevant structure is redesigned and manufactured. In this study, a six degree of freedom (6-DOF) parallel mechanism was used as the control mechanism of the bending die, and a new method of changing the deformation zone length (A) was proposed. Firstly, an idealized geometric model of free bending-based active motion was established. Then, the influence of the deformation zone length (A) on the bending moment and the bending radius of the tube was analyzed. In addition, the finite element simulation and a kinematic model of free bending-based active motion controlled by the 6-DOF parallel mechanism were established, and bending processes of the SS304 tube with different deformation zone lengths were investigated. Afterwards, the impact of the deformation zone length (A) on the bending radius, bending moment, wall thickness, and motion of the parallel mechanism were analyzed. Finally, experiments were carried out on the free-bending equipment based on the 6-DOF parallel mechanism. Experiments verified the rules in the theoretical analysis, finite element simulation, and kinematic simulation.

Adaptive nonlinear motion parameters estimation algorithm for digital twin of multi-link mechanism motion trajectory synthesis

Monitoring systems of automated production lines requires high accuracy and processing speed of acquired data. Nowadays digital twin technologies are rapidly developing as part of Industry 4.0. Digital twin is a virtual representation of a physical system that mimics the behaviour of a real object, and is used in real-time control, monitoring and disturbance prediction, without influence on a real object. Digital twin is being used in many fields of application such as: healthcare, manufacturing, education, city development, etc. Nonetheless, despite the rising popularity of digital twin researches, there is no basic approach to digital twin synthesis. Mostly, in state of the art articles, systems with known parameters are considered. In this paper, approach to development of digital twin, based on internal model for multi-link mechanisms with unknown motion parameters, is presented. Described approach intended to ease the task of production line monitoring and extend digital twin technology application field. In this article adaptive controller design, based on internal model, is presented, theoretical explanations of design process are provided, and application of the control algorithm in the task of multi-link mechanism motion trajectory parameters estimation is described. In this work the experimental synthesis of digital twin for Kuka youBot manipulator based on presented approach in real time is described. Adaptive motion parameters estimation was made for two links of the manipulator for the sake of confirmation of presented approach usage in the task of digital twin for systems with unknown parameters. Motion trajectory parameters of the robot links were defined manually with the use of chaotic generators to estimate the accuracy of the adaptive control system. This approach was used in order to calculate the error of reference tracking by comparing the control signal for digital twin with the reference exogenous input for manipulator links. As the results of the experiment, the graphs of the error reference tracking for both links are presented. As the goal of the experiment, the convergence of reference tracking error to the field [–0.005, 0.005] radian was set, and as can be seen from graphs this goal was achieved. There is a small disturbance of the error convergence on the graphs within the desired field which was caused by noised measurements and delays of the chosen modelling environment real-time simulations. In the conclusion of this paper, further work to reduce the influence of mentioned causes is described. The results of this paper can be used in further digital twin technology researches. Presented approach can be implemented in robots remote control tasks, production lines technical condition monitoring and in general motion trajectory parameters estimation tasks for multi-link mechanisms

Assessment of the finger contact surface to promote the spin motion in finger follower mechanisms

This work describes the kinematic properties of finger-follower mechanisms in the spatial domain in relation to the spin motion of the follower. In this framework, the effectiveness of the cylinder-on-sphere coupling as contact condition between finger and follower is assessed in relation to the classical cone-on-sphere coupling, showing the capability of the former to achieve a satisfactory valve spin pivoting radius. An analytical study is performed by taking advantage of a geometrical approach which allows to evaluate 3D layouts, demonstrating that the cylinder-on-sphere coupling requires a higher number of design parameters to fully determine the mechanism. This characteristic increases the complexity of the system, but it adds freedom and flexibility to the design procedure. Several design configurations are evaluated to highlight this aspect thanks to a dedicated parametric study, where the declivity of the contact surface is shown to represent the key parameter controlling the spin pivoting radius. In this context, the possibility to control the cylinder surface declivity on multiple planes may be adopted to improve the stability of the mechanism behavior with respect to the production tolerances.

Optimization design of a bionic horse’s leg system driven by a cam-linkage mechanism

For equine-assisted therapy, a bionic horse configuration is presented. A bionic horse’s single leg system has two degrees of freedom (DOFs), which is driven by a cam-linkage mechanism and can adjust the leg’s endpoint trajectory. Based on analyzing the motion law of the bionic horse and the foot trajectory’s requirements of the leg system, a multi-objective optimization model is established based on the foot trajectory performance index. To determine the objective function, the errors between the ideal foot trajectory and the mechanism motion model’s foot trajectory, and the errors between the actual adjustable values and the target values for the motion range are taken as the optimization objective. In terms of the constraint conditions, the structural constraints, kinematic feasible region conditions, pressure angle requirements, et al., are considered. The ideal mechanism parameters are obtained by the intelligent optimization method. The results are verified by simulation modeling and experimental prototype, and the relevant ideas can provide a reference for the research of similar problems.

Stick–slip in hand guidance of palletizing robot as collaborative robot

Stick–slip is a challenging problem in palletizing robots and constitutes one of the main problems in precision positioning control. This study analyzed the stick–slip of a four-degree-of-freedom ceiling-mounted hand-guiding collaborative robot in a working space. A brief perspective on the focus of the experimental design is presented on the stick–slip friction of a palletizing robot’s hand guidance as a collaborative robot. The palletizing robot typically has a simple mechanical structure but possesses over 16 bearings to constrain the motion of the dual-parallelogram linkage mechanism. First, the hand-guiding force was successfully measured. Second, an image model was built based on the obtained measurement results. Third, the stick–slip results for the working space were analyzed using an image model. Finally, related conclusions and recommendations are provided for precision positioning control. A significant aspect of this study is identifying the hand-guiding force in the working space of a ceiling-mounted collaborative robot. Stick–slip in hand guiding is a critical issue and is therefore important for collaborative robot users. The main contribution of this study is developing a feasible method for helping researchers understand where stick–slip occurs.

Acceleration of hollow carbon nanospheres by gas leakage: An efficient nanomotor

Nanomotors serve as nanoscale engines by converting various energies into mechanical energy. In addition to the huge number of existing nanomotors, we propose a simple nanomotor based on the hollow carbon nanosphere (i.e., fullerene) that is full of gas. We investigate the acceleration of the nanosphere by leakage of gas through a nanopore by molecular dynamics simulations. The nanosphere can be driven to a high speed of 100 m/s under proper simulation conditions, which can be further tuned by temperature, gas density, and pore diameter. We observe rotation of the pore direction during the acceleration process for a nanosphere of different pore diameters. The acceleration process can be well described by the Meshchersky theory. We also simulate the deceleration process of the nanosphere due to the damping force of the gas, which can be analyzed in terms of the kinetic motion of gas molecules. The nanomotor proposed in this work shall be realizable in experiments and may be useful in driving the mechanic motion of fullerenes.

Adaptive Fuzzy Control for a Hybrid Spacecraft System With Spatial Motion and Communication Constraints

This article proposes an adaptive fuzzy control approach with an event-triggered mechanism and spatial motion constraint for a hybrid spacecraft system. The spacecraft system is composed of a rigid body and a slender flexible panel, with coupled dynamics captured by three ordinary differential equations and two partial differential equations. The overall control objective lies in utilizing an event-triggered control input to regulate the angular velocities of the rigid body and stabilize the vibrations of the flexible panel under unknown input disturbances and prescribed spatial motion performance. We collectively address the posture regulation and disturbance rejection purposes by introducing a barrier Lyapunov function and a fuzzy logic system. The event-triggered solution only updates the control signals at some discrete-time instants, and hence the communication burden is reduced significantly. The potential effectiveness and thrifty efficiency of the developed control strategy are theoretically demonstrated and numerically verified.

A repelling-screw-based approach for the construction of generalized Jacobian matrices for nonredundant parallel manipulators

This paper presents a unified and generalized approach for the construction of Jacobian matrices for general, nonredundant parallel manipulators that possess serial and/or mixed-topology limbs. Using linear algebra, a method for the calculation of repelling screws is proposed, based upon which the underlying correlations amongst the screws (twists and wrenches) that correspond to both the permitted, and constrained, motions of general mechanisms are identified and analyzed. The effect of linear combinations on the repelling screw system is revealed, and further used to determine the constraint wrenches/twists of a parallel manipulator and its limbs. By means of utilising repelling screws, the dualities in parallel and serial mechanisms are revisited and extended. Furthermore, a simple and unified method for the identification of unknown twists and wrenches is proposed, based upon which an intuitive and systematic approach for the formulation of generalized Jacobian matrices for nonredundant parallel manipulators is derived. The generalized multilevel hierarchical Jacobian contains complete constraint, singularity, kinematics, and statics information at both limb and platform levels. A number of provided examples demonstrate the effectiveness and application of the proposed approach.

A DNA origami rotary ratchet motor

To impart directionality to the motions of a molecular mechanism, one must overcome the random thermal forces that are ubiquitous on such small scales and in liquid solution at ambient temperature. In equilibrium without energy supply, directional motion cannot be sustained without violating the laws of thermodynamics. Under conditions away from thermodynamic equilibrium, directional motion may be achieved within the framework of Brownian ratchets, which are diffusive mechanisms that have broken inversion symmetry1–5. Ratcheting is thought to underpin the function of many natural biological motors, such as the F1F0-ATPase6–8, and it has been demonstrated experimentally in synthetic microscale systems (for example, to our knowledge, first in ref. 3) and also in artificial molecular motors created by organic chemical synthesis9–12. DNA nanotechnology13 has yielded a variety of nanoscale mechanisms, including pivots, hinges, crank sliders and rotary systems14–17, which can adopt different configurations, for example, triggered by strand-displacement reactions18,19 or by changing environmental parameters such as pH, ionic strength, temperature, external fields and by coupling their motions to those of natural motor proteins20–26. This previous work and considering low-Reynolds-number dynamics and inherent stochasticity27,28 led us to develop a nanoscale rotary motor built from DNA origami that is driven by ratcheting and whose mechanical capabilities approach those of biological motors such as F1F0-ATPase.