Kinematic Chain Mechanism Research Articles

Accurate Detection and Smoothness-Oriented Avoidance Method of Singularity in 5-Axis CNC Machining

As an inherent flaw in the kinematic chain mechanism of 5-axis machine tools, singularity can induce dramatic changes in machine axes motion and unfavorable fluctuations in feedrate. For effective singularity avoidance, it is desirable to first achieve accurate and efficient singularity detection and then eliminate the singularity without impairing tool orientation smoothness. This paper presents a novel approach for accurately detecting and smoothly avoiding the singularity in 5-axis CNC machining. In the detection method, two exclusion criteria are presented to efficiently exclude most non-singular segments of the tool orientation spline, and a curve intersection-based algorithm is thus developed to accurately identify the singular segments. In the singularity avoidance method, a concept of admissible tool orientation annulus (ATOA) is introduced, which serves to confine the range and magnitude of the tool orientation spline’s adjustments, and a local adjustment algorithm is then developed to enable the escape of the tool orientation from the singular region with controllable direction and deviation, while maintaining its continuity and smoothness. The effectiveness of singularity avoidance and the kinematic performance of the tool orientation modified by our method, are comparable to a state-of-the-art singularity avoidance algorithm. Finally, the conducted experiments validate the proposed method.

COLLECTION OF MECHANISMS FOR 10 LINKS KINEMATIC CHAINS OF GROUP G

In this paper a new, easy, reliable, and efficient method to detect isomorphism and a catalogue of fixed link with its corresponding equivalent links in the distinct mechanisms of kinematic chains of Group-G, has been presented. It is helpful to the new researchers and designers to choose the best mechanism to perform the desired task at the conceptual stage of design. The proposed method is presented by comparing the structural invariants ‘sum of the absolute values of the characteristic polynomial coefficients’ [SCPC] and ‘maximum absolute value of the characteristic polynomial coefficient’ [MCPC] of [JJ] matrices. These invariants are used to detect isomorphism in the mechanism kinematic chain having simple joints. The method is explained with the help of examples of planar kinematic chain.

Empirical Study of Constraint-Handling Techniques in the Optimal Synthesis of Mechanisms for Rehabilitation

Currently, rehabilitation systems with closed kinematic chain mechanisms are low-cost alternatives for treatment and health care. In designing these systems, the dimensional synthesis is commonly stated as a constrained optimization problem to achieve repetitive rehabilitation movements, and metaheuristic algorithms for constrained problems are promising methods for searching solutions in the complex search space. The Constraint Handling Techniques (CHTs) in metaheuristic algorithms have different capacities to explore and exploit the search space. However, the study of the relationship in the CHT performance of the mechanism dimensional synthesis for rehabilitation systems has not been addressed, resulting in an important gap in the literature of such problems. In this paper, we present a comparative empirical study to investigate the influence of four CHTs (penalty function, feasibility rules, stochastic-ranking, and ϵ-constraint) on the performance of ten representative algorithms that have been reported in the literature for solving mechanism synthesis for rehabilitation (four-bar linkage, eight-bar linkage, and cam-linkage mechanisms). The study involves analysis of the overall performance, six performance metrics, and evaluation of the obtained mechanism. This identified that feasibility rules usually led to efficient optimization for most analyzed algorithms and presented more consistency of the obtained results in these kinds of problems.

Functional Morphology of the Flight Apparatus of Ephemera vulgata (Ephemeroptera: Ephemeridae) and Implications for the Evolution of Flight in Insects

Abstract The mesothoracic flight apparatus of preserved and freshly killed specimens of Ephemera vulgata is examined in detail by means of functional morphological examinations. The basic drive mechanism of the forewing of Ephemera vulgata constitutes a four-bar kinematic chain, which encompasses the whole mesothorax. Based on this reassessment, the operating principles of the different subsystems of the flight apparatus of the mayfly were newly analysed. As in the Neoptera, the indirect dorsolongitudinal downstroke and dorsoventral upstroke muscles rotate the wing around an axis which runs through the main wing joint of the fulcrum. In contrast to the Neoptera, the wing is driven via the posterior notal wing process and fourth axillary. A strong direct subalar muscle is able to move the subalare (together with the pleural ridge) inwards and to affect the wingstroke via a bistable click mechanism in this unusual way. The axillary sclerites, two frontal first axillaries and one caudal fourth axillary, permit the radioanal plate to rotate forward–backward on the fulcrum. This motion system, which is superimposed on the kinematic chain mechanism, permits alterations of the wingstroke plane. A short muscle of the radioanal plate allows adjusting the passive pronation of the wing during the downstroke and achieving an increase of the aerodynamical angle of attack. The step-by-step derivability of basal flight mechanisms of the main groups of Pterygota indicates a paranotal origin of the wings. The possibility that the Ephemeroptera and Neoptera constitute sister groups is discussed.

Mechanism isomorphism identification based on artificial fish swarm algorithm

The aim of this paper is to propose a practical solution for mechanism kinematic chain isomorphism identification – an artificial fish swarm algorithm. The artificial fish model of mechanism isomorphism identification is established, and behavioral way of the artificial fish is designed. According to isomorphism identification features of topological graph, the process of mechanism isomorphism identification based on artificial fish swarm algorithm is confirmed. The rationality and reliability of artificial fish swarm algorithm on the isomorphic identification of mechanism have been illustrated by a specific example, which provides a new method for intelligent CAD system design of mechanism. It builds a basis for future work in isomorphism identification of mechanism with high efficiency. Isomorphic identification of mechanism will contribute to rational qualitative analysis of mechanism design, perfection of irrationality can be done timely, which is the key factor for mechanical manufacturing. In this paper, we introduce the mechanism kinematic chain firstly, then optimization of artificial fish swarm algorithm is illustrated, and it is shown that how fish swarm algorithm is applied to mechanism kinematic chain. Finally, the feasibility and efficiency of the method are verified by the example of 10 bars, and the complex mechanism can be identified by the example of 14 bars and 18 bars.

An Approach to Modeling Closed-Loop Kinematic Chain Mechanisms, Applied to Simulations of the da Vinci Surgical System

Open-sourced kinematic models of the da Vinci Surgical System have previously been developed using serial chains for forward and inverse kinematics. However, these models do not describe the motion of every link in the closed-loop mechanism of the da Vinci manipulators; knowing the kinematics of all components in motion is essential for the foundation of modeling the system dynamics and implementing representative simulations. This paper proposes a modeling method of the closed-loop kinematics, using the existing da Vinci kinematics and an optical motion capture link length calibration. Resulting link lengths and DH parameters are presented and used as the basis for ROS-based simulation models. The models were simulated in RViz visualization simulation and Gazebo dynamics simulation. Additionally, the closed-loop kinematic chain was verified by comparing the remote center of motion location of simulation with the hardware. Furthermore, the dynamic simulation resulted in satisfactory joint stability and performance. All models and simulations are provided as an open-source package.

Kinematic analysis of a PPPR spatial serial mechanism with geometric errors

The present study focuses on the kinematic analysis of a PPPR spatial serial mechanism with a large number of geometric errors. The study is implemented in three steps: (1) development of a map between the end-effector position error and geometric source errors within the serial mechanism kinematic chains using homogeneous transformation matrix; (2) selection of geometric errors which have significant effects on end-effector positioning accuracy by sensitivity analysis; (3) kinematic analysis of the serial mechanism within which the geometric errors are modelled as interval variables. The computational algorithms are presented for positioning accuracy analysis and workspace analysis in consideration of geometric errors. The analysis results show that the key factors which have significant effects on end-effector position error can be identified efficiently, and the uncertain workspace can also be calculated efficiently.

Synchronization Controller for a 3-RRR Parallel Manipulator

A 3-RRR parallel manipulator has been well-known as a closed-loop kinematic chain mechanism in which the end-effector generally a moving platform is connected to the base by several independent actuators. Performance of the robot is decided by performances of the component actuators which are independently driven by tracking controllers without acknowledging information from each other. The platform performance is degraded if any actuator could not be driven well. Therefore, this paper aims to develop an advanced synchronization (SYNC) controller for position tracking of a 3-RRR parallel robot using three DC motor-driven actuators. The proposed control scheme consists of three sliding mode controllers (SMC) to drive the actuators and a supervisory controller named PID-neural network controller (PIDNNC) to compensate the synchronization errors due to system nonlinearities, uncertainties and external disturbances. A Lyapunov stability condition is added to the PIDNNC training mechanism to ensure the robust tracking performance of the manipulator. Numerical simulations have been performed under different working conditions to demonstrate the effectiveness of the suggested control approach.

An Improved Genetic Algorithm Approach on Mechanism Kinematic Structure Enumeration with Intelligent Manufacturing

During the process of mechanism kinematic structure enumeration, isomorphism identification of graphs is an important and complicated problem. The problem is known to be a NP-complete problem. In this paper, according to the mechanism kinematic chain isomorphism identification criteria, a highly efficient hybrid genetic algorithm model is proposed for isomorphism identification. The model method is coupled with genetic algorithm, optimal choice, and optimal crossover operation. It shows a quick convergence rate of the late operation and can avoid convergence to local optimum. Simulation results show that the hybrid algorithm is more rapid and effective compared with simple genetic algorithm and the improved neural network algorithm.

A new approach for obtaining the dynamic balancing conditions in serial mechanisms

Adaptive balancing means that the mechanical structure of the manipulator is modified in order to achieve the decoupling of dynamic equations. This work deals with a systematic formulation for the adaptive balancing. Basically, two traditional balancing techniques are employed here: the addition of counterweight and counter-rotating disks coupled to the moving links. In addition, the feasibility of the dynamic decoupling for three distinct types of serial manipulators is discussed regarding the achievement of such balancing and the complexity level of the modified mechanical structure. The balancing conditions are developed here for 3-dof spatial and planar open-loop kinematic chain mechanisms, whose topologies are composed of revolute and prismatic joints.

An improved hybrid immune algorithm for mechanism kinematic chain isomorphism identification in intelligent design

In intelligent mechanism design, isomorphism identification of mechanism kinematic chains (IIMKC) is aimed at avoiding repeated mechanism design and is proved to be an NP-complete problem. In this paper, kinematic chains are represented by graphs. An improved hybrid immune algorithm, which integrates the clonal selection immune algorithm with genetic algorithm and the local search algorithm, is proposed to solve IIMKC problem. Moreover, the novel saving and updating operator is proposed to save the best antibodies and maintain a diverse repertoire of antibodies for improving performance of clonal selection. In addition, the pseudo-crossover operator is introduced to enhance the efficiency of genetic algorithm. Simulation results validate the high efficiency and robustness of the hybrid immune algorithm.

Experimental Investigation on Position Analysis of 3 – DOF Parallel Manipulators

Parallel manipulators (PMs) have been the subject of study, of much robotic research during the past three decades. A parallel manipulator (PM) is a closed loop kinematic chain mechanism, that is connected to the base via multiple independent chains. The scope of this research work is to perform the position analyses of the three degrees of freedom PMs (TRIPOD and TRI-GLIDE). The present work has been planned to model the parallel manipulators using the screw joints for very accurate positioning. Experiments were conducted for the position analysis and the angular tilt of the mobile platform along x-axis and y-axis and they were found by actuating the links of the manipulators. In order to confirm the results obtained by the experimental method, ADAMS was used for solving the kinematic problems involved. The Tri-Glide and Tripod manipulators were created in ADAMS based on the fabricated models. The models were simulated for the displacement of the nut and the angle of tilt / rotation of the mobile platform about the x and y axes. The results obtained by the three methods are discussed and analyzed. In a conventional drilling machine, drilling an angular hole requires special fixtures for each specific angle. In the present work, the parallel manipulator mechanisms have been modified to an angular drilling machine, for performing angular drilling operations.

Prime Representation and Isomorphism Identification of Mechanism Kinematic Chains via the Adjacent Matrix

The adjacent relation of mechanism kinematic chain is represented by a primary adjacency matrix by using primes to mark its components.An isomorphism identification matrix results from the primary adjacency matrix and prime products representing secondary adjacent relation,and uses its determinant and solution vector of linear equation system to identify mechanism isomorphism.Dynamically,the identification matrix is modified by new primes on the basis of the classification of solution vector elements.The result generates a solution vector with independent elements,which determines the positions of all nodes in the topological graph of a kinematic chain.Furthermore,a mapping relation,which results in a necessary and sufficient condition for isomorphism,is established between componential codes of two isomorphic mechanisms.As a result,this new identification method utilizes varying primes to virtually destruct the symmetry of the topological graph and change local and secondary adjacency relations among nodes under unchanged topological structure.Then,this method is also available for isomorphism identification of general undirected graphs.Applied examples show that it is very effective and reliable for automatic identification with code mapping of isomorphism mechanisms and polynomial algorithm for computation time.

Parallel Manipulators Applications—A Survey

This paper presents the comparison between serial and parallel manipulators. Day by day, the applications of the parallel manipulator in various field is become apparent and with a rapid rate utilized in precise manufacturing, medical science and in space exploration equipments. A parallel manipulator can be defined as a closed loop kinematic chain mechanism whose end effector is linked to the base by several independent kinematic chains. The classification of various parallel manipulators is presented herewith. The prime focus of the paper is to realize the parallel manipulators applications for industry, space, medical science or commercial usage by orienting manipulator in the space at the high speed with a desired accuracy.

Intelligent Design of Mechanism Kinematic Chains by Advanced Optimal Methods

When using graph theory to conduct intelligent design for kinematic structure enumeration, the isomorphism identification of graphs is an important and complicated problem. In this paper, the methodology of transferring isomorphism identification into optimization issue was introduced. Then the recent development of applying advanced optimal methods for isomorphism identification was reviewed, the advantages and disadvantages of there methods were discussed.

Dynamic Model of a 3-dof Asymmetric Parallel Mechanism

Most research papers about parallel kinematic chain mechanisms investigate symmetric robot manipulators, in which all the limbs connecting the end-effector to the fixed based are composed by the same sequence of links and joints. Contrarily, in some manipulation tasks the velocity and stiffness requirements are anisotropic. In such cases, the asymmetric parallel kinematic chain mechanisms may offer advantages. This works' main objective is to present the inverse dynamic modeling of a 3-dof asymmetric parallel chain mechanism, conceived as a robot manipulator for pick- and-place operations. The type of kinematic structure of the mechanism constrains the motion of the end-effector to only three translations. First, a brief kinematic modeling is carried out. Then, the inverse dynamic modeling is developed by employing the virtual work principle, considering two assumptions: lumped and distributed masses. Based on the model equations, a motion simulation is performed. The same motion is also analyzed by using the ADAMS computing environment to validate the model equations. After the simulation, the results demonstrated a very good agreement between the analyzed variables provided by the dynamic model and those generated by ADAMS. One can also notice that the input torques calculated by the lumped-mass model are quite close to the torques evaluated by the distributed mass model, and might be sufficient for the future development of a motion control law for the mechanism.

A review on graph isomorphism identification of mechanism kinematic chain for intelligent and digital manufacturing

The graph theory is an important method to achieve conceptual design for mechanism. During the process of kinematic structures enumeration using graph theory, isomorphism identification of graphs is an NP-complete problem. So, the graph isomorphism identification is a crucial problem in mechanism creative design. In this paper, some recent literatures are introduced to demonstrate some method to solve this NP-hard problem. These approaches are all proved to be effective in some cases. The purpose of this paper is to provide references and helps for researchers.

Untersuchungen zur Funktionsmorphologie und Evolution des Flugapparates der Schmeißfliege Calliphora erythrocephala (Diptera: Calliphoridae)

The basic drive mechanism of the wingstroke of the blowfly (kinematic chain and click mechanism) and the subordinate mechanisms - for stroke-plane adjustment (via backward-forward folding of the wing) and for pronation-supination adjustment ― influence one another in complicated way. The so-called ,gear-change mechanism' [PFAU 1973], which is interpreted as a device for pronation-amplification at the upper turning-point of the wingstroke, is situated at the ,point of intersection' of several mechanical subunits of the flight apparatus. ― The parascutal click mechanism [BOETTIGER & FURSHPAN 1952] is superimposed by a second bistable mechanism; since this includes the whole kinematic chain of the synthorax it is apostrophized as symmetrical'. ― There are different mechanisms of rotation of the wing about its longitudinal axis: An 'automatic' pronation and supination (which is wingstroke-coupled and correlated with the stroke-amplitude) is caused by the movement of the parascutum; it leads to supination during downstroke and pronation during upstroke, rotating the wing as a whole by changing the steepness of an axis, which runs through the axillary 1-parascutum and axillary I-scutellar lever joints. The superimposed parascutal click mechanism is expected to decelerate and accelerate these wing rotations in each stroke phase. Further pronation-supination mechanisms are superimposed: (1) correlated with the degree of wing-folding or unfolding respectively, the wing is rotated about its longitudinal axis to a greater or lesser extent; (2) several tonic muscles of the axillary 4 and 3 are able to produce and adjust a supinatory twisting of the wing, which is to far extent independent of the stroke. - Hypotheses are presented concerning the evolution of the mechanisms of the flight apparatus, especially the ,gear-change mechanism'.

Maximal Loop Method of Automatic Sketching of Planar Closed Kinematic Chains

Automatic sketching of mechanism kinematic chains affects directly the efficiency and reliability of mechanism design. On the basis of a study of the topologic characteristics of planar closed kinematic chains, the maximal loop method is presented, based on contracted link adjacency matrix, to complete automatic sketching of planar closed kinematic chains. Independent loops of kinematic chains are derived by using the breadth-first spanning tree algorithm, based on which the maximal feasible loop is achieved by means of independent loops add-subtract operation. The maximal feasible loop is step by step modified in accordance with the loop relationships so that all independent loops become its normalized non-crossing inner loops. In the process of automatic sketching of kinematic chains, the joints of kinematic chain are located, from outer lane to inner lane, on the vertices of inscribed regular polygon of the concentric circles on the basis of the outer and inner loops’ relationships. As a result, the sketches of the kinematic chains appear to be normal and beautiful. The development process of this algorithm based on the outer loop and the inner loops relationships is demonstrated with the aid of several mechanism examples. The study and the application of the maximal loop method show that it is simple and comprehensive. And it is applicable for the automatic sketching of planar closed kinematic chains with multiple links and multiple degrees of freedom. It can greatly raise the efficiency in mechanism design.

An improved artificial immune algorithm for mechanism kinematic chain isomorphism identification

An improved clonal selection artificial immune algorithm is presented to identify the isomorphism of the mechanism kinematic chains. The principles of isomorphism identification are based on the graph theory that adjacency matrices of two isomorphic graphs can interconvert. The clonal selection artificial immune algorithm is improved by adding a process named saving and updating operator after the process of refreshing. The high efficiency and robustness of this improved algorithm is proved by comparing it with simple clonal selection algorithm. The simulation results show that the improved algorithm can identify isomorphic kinematic chains successfully and rapidly.