Planar Mechanisms Research Articles

Design of Obstacle Avoidance Mechanism of Magnetic Levitation Type Inspection Robot for High Voltage Lines

An obstacle avoidance mechanism is designed for the operation mode and the overall structure of high-voltage power lines inspection robot based on magnetic levitation principle. The mechanism is composed of a planar linkage mechanism and a screw nut mechanism with two degrees of freedom. Through the control of two of the original, the robot has a function of opening the shell and obstacle avoidance. The mechanism is simple and occupies less space with flexible movement, compact structure, to meet the requirements of obstacle avoidance to avoid vibration hammer, clamp, straight line towers and other obstacles effectively which solved the contradiction between the small space in the robot and the obstacle avoidance requirements. Two prime bar linkage relationships is obtained according to static analysis of the mechanism. Finally, by means of Kinematics simulation of the obstacle process through Pro/E software, the feasibility of the institution obstacle scheme is verified.

Uncertainty analysis of the hydrodynamic coefficients estimation of a nonlinear manoeuvring model based on planar motion mechanism tests

Uncertainty analysis of the identified hydrodynamic coefficients of a nonlinear manoeuvring model is presented in this paper. The classical parameter estimation method, Least Square, is briefly introduced, and the uncertainty of the hydrodynamic coefficients due to the noise in the measured data is analysed using singular value decomposition. Then, two methods, truncated singular values decomposition and Tikhonov regularization, are introduced to diminish the uncertainty. A nonlinear manoeuvring mathematical model of a marine surface ship is derived using Lagrange's method. The dimensionless hydrodynamic coefficients are obtained using the Least Squares method, truncated singular values decomposition and Tikhonov regularization with Planar Motion Mechanism test data. The validation process is carried out to test the performance and accuracy of the resulting nonlinear manoeuvring models. The result shows that identification of the uncertain parameters using the truncated singular values decomposition and Tikhonov regularization resulted in good estimating the parameters and significantly diminish the uncertainty.

A Simple Two-step Geometric Approach for the Kinematic Calibration of the 3-PRS Parallel Manipulator

SummaryKinematic calibration plays an important role in the improvement of positioning accuracy for parallel manipulators. Based on the specific geometric constraints of limbs, this paper presents a new kinematic parameter identification method for the widely studied 3-PRS parallel manipulator. In the proposed calibration method, the planes where the PRS limbs exactly located are identified firstly as the geometric characteristics of the studied parallel manipulator. Then, the limbs can be considered as planar PR mechanisms whose kinematic parameters can be determined conveniently according to the limb planes identified in the first step. The main merit of the proposed calibration method is that the system error model which relates the manipulator’s kinematic errors to the output ones is not required for kinematic parameter identification. Instead, only two simple geometric problems need to be established for identification, which can be solved readily using gradient-based searching algorithms. Hence, another advantage of the proposed method is that parameter identification of the manipulator’s limbs can be accomplished individually without interactive impact on each other. In order to validate the effectiveness and efficiency of the proposed method, calibration experiments are conducted on an apparatus of the studied 3-PRS parallel manipulator. The results show that using the proposed two-step calibration method, the kinematic parameters can be identified quickly by means of gradient searching algorithm (converge within five iterations for both steps). The positioning accuracy of the studied 3-PRS parallel manipulator has been significantly improved by compensation according to the identified parameters. The mean position and orientation errors at the validation configurations have been reduced to 1.56 × 10−4 m and 1.13 × 10−3 rad, respectively. Further, the proposed two-step kinematic calibration method can be extended to other limited-degree-of-freedom parallel manipulators, if proper geometric constraints can be characterized for their kinematic limbs.

Dynamic Analysis of Planar Mechanisms With Fuzzy Joint Clearance and Random Geometry

The dynamic characteristics of planar mechanisms with fuzzy joint clearance and random geometry are studied in this paper. The dynamics model for the mechanism is constructed by utilizing Baumgarte approach in which the clearance size is a fuzzy number, while the geometry parameters are assumed as random variables. A hybrid contact force model, which consists of the Lankarani–Nikravesh model, improved Winkler elastic foundation model and modified Coulomb friction force model, is applied to construct revolute clearance joint. In order to solve the dynamics model, two methodologies are developed: confidence region method for quantification of random and fuzzy uncertainties (CRMQRFU) and confidence region method with transformation method (CRMTM). In the CRMQRFU, fuzzy numbers are first decomposed into intervals under the given membership level. Then, a general framework is proposed for quantification of random and interval uncertainties in the mechanism. In the CRMTM, a transformation method is applied to transform intervals into deterministic arrays, while probability theory is used to obtain the confidence regions under the given fuzzy values. The confidence region, considering random and fuzzy uncertainties, is obtained by fuzzy set theory. Finally, two examples are used to demonstrate the validity and feasibility of these methods.

Dynamic Response Analysis of Planar Multilink Mechanism considering Wear in Clearances

Clearance wear is one of the factors that affects dynamics for mechanical systems. A numerical methodology suitable for modeling and calculation of wear at multiple revolute clearance pairs in the field of the planar multilink mechanism is proposed. In this paper, the 2‐DOF nine‐bar mechanism considering two revolute clearance joints is regarded as the study object. Normal contact force and friction force models of revolute clearance joints used Lankarani–Nikravesh (L‐N) and LuGre models, respectively. The iterative wear prediction process based upon Archard’s model has been applied to calculate wear characteristics. The wear prediction procedure is integrated with multibody dynamics, wear depths at revolute clearance joints are calculated, and the surface of shaft and bearing is reconstructed twice. The dynamic responses of mechanism considering two nonregular revolute clearances caused by wear are studied in depth. The nonlinear characteristics of the mechanism after wear are studied by the phase diagram and Poincaré map. Influences of different initial constant clearance values and different driving speeds on wear of two revolute joints are also researched. The results show that it is necessary to consider the factor of irregular clearances caused by wear in analysis of dynamics of precision mechanisms. Initial constant clearance values and driving speeds have some influence on wear phenomenon. This research provides a theoretical basis for studying dynamics of the planar multilink mechanism considering wear in multiple clearances.

A Graph-Theory-Based Method for Topological and Dimensional Representation of Planar Mechanisms as a Computational Tool for Engineering Design

In this paper, a graph-theory-based approach for representing planar mechanisms is presented, the Santiago Portilla method (SPM). From the corresponding adjacency matrix, SPM generates an extended matrix containing the complete characterization of a planar mechanism, including all the information about both topology and geometry. This matrix representation can be used for the optimal design of mechanisms, allowing simultaneously the topological and dimensional synthesis by means of computational tools such as the metaheuristic algorithms. A case study corresponding to the design of a fixed-linear-trajectory tracker mechanism is included in order to test the efficiency of the proposed approach. It was carried out by addressing the design as an optimization problem and solving it with the differential evolution algorithm, representing the individuals in its population by the matrix form generated by the SPM. The results of the case study show that the SPM and its matrix representation constitute a useful and flexible tool for the solution of the real engineering problems involving the design of planar mechanisms.

A Flexibly Grasping and Manipulating Mechanism Composed of Many Elastic Cords

The authors have proposed a flexibly grasping and manipulating mechanism composed of two circular rings and many elastic cords between the rings. Aiming to control posture of the grasped object and to give the mechanism a remote center compliance ability, the mechanism is improved so that the relative translation between two rings can be given. A new numerical method to iteratively calculate the posture of a grasped object due to relative angular and translational displacements between the rings is established based on the equilibrium of force and moment applied by elastic cords. A prototype with a planar parallel mechanism with 2 DOF to give a pure relative translational motion between rings is built and experimentally examined. The prototype mounted on a spatial serial robot arm can grasp a cylinder and insert it into a circular hole in inclined surface by utilizing posture control and remote center compliance.

Energy Consumption Minimizing for Electro-HydraulicServo Driving Planar Parallel Mechanism by Optimizing the Structure Based on Genetic Algorithm

Electro-hydraulic servo driving planar parallel mechanism (EHPM) is widely used in simulating large-scale vibration environments. However, the energy consumption of EHPM is large. There is little research on the energy consumption of EHPM. Therefore, this paper presents a structural optimization method, which can effectively reduce the energy consumption of EHPM by changing the arrangement of the planar redundant actuator. First, the mathematical model of the total power of EHPM is established. In order to distinguish the variables that affect energy consumption, the effect of a single structural variable on energy consumption is discussed, respectively, based on the mathematical model of the total power. And then the genetic algorithm is used to optimize the total power objective function with multiple structural variables. The influence of the initial value of the structure variable on the convergence range of total power is also discussed. The simulation results show the effectiveness of changing the actuator arrangement, which can significantly reduce energy consumption. Moreover, the component selecting of the hydraulic cylinder and servo valve can be smaller and the cost of which can be reduced.

Lower leg mechanism for humanoid robots that enables natural transition between resistive/compliant behaviors to gravity and ankle pronation/supination

A novel lower leg mechanism for humanoid robots is designed. The pronation/supination motion of the ankle is added to an existing planar complex knee-ankle mechanism that enables firm support against gravity and natural swinging by gravity. The increase of total moment of inertia is prevented by a linkage mechanism that remotely rotates the ankle, where the motors are assigned at the knee part. A prototype of the machanism was designed on 3D CAD.

Estimation of uncertainty in the position, velocity and acceleration of planar mechanisms

Planar kinematics is a mechanical branch that describes position, velocity and acceleration of mechanisms’ links. In order to model the 2D mechanisms Natural Coordinates have been considered. The kinematic analysis is solved when all links dimensions, and some initial values of position and velocity are known. A new method to determine kinematics’ outputs uncertainties is carry out, using standard UNE EN 22768-1:1993 and the Supplement 1 from the Guide to Expression of Uncertainty in Measurements.

Design of Spatial Inverted Pendulum System

Pendulum-based systems which are highly non-linear and unstable have become one of the most widely studied subject of control theory. The close interest of researchers on inverted pendulum problem arises from its strong representation ability with real engineering applications. This study focuses on the design and production of an experimental setup in which a spatial inverted pendulum can be balanced by means of a planar mechanism in RRRRP configuration. A mechanism with two different motion inputs (rotational and linear) that no studies were performed on before was prototyped. This system is highly unstable and shows non-linear dynamic behavior. The mechanical parts that forms the system were manufactured by a 3D printer and a CNC milling machine. At the end of study, a four-degree of freedom spatial inverted pendulum experimental setup has been established on which the control works can be carried out, by installing the electronic and electro-mechanical equipment.

Primena GWO algoritma za generisanje zatvorene putanje u optimalnoj sintezi ravnih mehanizama

Primena GWO algoritma za generisanje zatvorene putanje u optimalnoj sintezi ravnih mehanizama

Dynamic analysis of a planar multibody system with multiple revolute clearance joints

This paper focuses on the dynamic responses of a planar mechanism with multiple clearance joints. The effect of the impact between the journal and the bearing in the clearance joint is described using an improved impact force model, and a typical four-bar linkage mechanism with multiple clearance joints is presented as an example. Two conditions are considered in this research, one is the single clearance joint with different position, and the other is multiple clearance joints. From a large number of numerical results, some important conclusions are obtained as follows: (1) with the influence of the clearance joint, the dynamic output of system has obvious vibration in comparison to the ideal value. (2) The position of the clearance joint has a clear effect on the response of system; the larger the distance of the clearance joint from the drive motor, the smaller its influence on the output of the system. (3) With the increase in the clearance joint number, the dynamic stability of the multibody system is decreased gradually, and the dynamic characteristic of the system also appears as obvious nonlinear phenomenon. (4) The coupling phenomenon appears when multiple clearance joints in the multibody system are considered, which should be examined seriously during the process of design and numerical analysis.

Single degree of freedom everting ring linkages with nonorientable topology

Linkages are assemblies of rigid bodies connected through joints. They serve as the basis for force- and movement-managing devices ranging from ordinary pliers to high-precision robotic arms. Aside from planar mechanisms, like the well-known four-bar linkage, only a few linkages with a single internal degree of freedom-meaning that they can change shape in only one way and may thus be easily controlled-have been known to date. Here, we present "Möbius kaleidocycles," a previously undiscovered class of single-internal degree of freedom ring linkages containing nontrivial examples of spatially underconstrained mechanisms. A Möbius kaleidocycle is made from seven or more identical links joined by revolute hinges. These links dictate a specific twist angle between neighboring hinges, and the hinge orientations induce a nonorientable topology equivalent to the topology of a [Formula: see text]-twist Möbius band. Apart from having many technological applications, including perhaps the design of organic ring molecules with peculiar electronic properties, Möbius kaleidocycles raise fundamental questions about geometry, topology, and the limitations of mobility for closed loop linkages.

On the Maximization of Joint Velocities and Generalized Reactions in the Workspace and Singularity Analysis of Parallel Mechanisms

SummaryAn approach for calculating the maximum possible absolute values of joint velocities or generalized reactions in a leg of a parallel mechanism has been considered in this paper. The Jacobian analysis and the Screw theory-based methods have been used to acquire the result. These values are calculated for the “worst” directions of the external load or end-effector’s velocity for each leg. The feasibility of using these parameters as the measures of closeness to different types of parallel mechanism singularity is discussed. Further, how this approach is related to the state-of-the-art methods has been illustrated. The key aspect of the discussed approach is that the normalization of vectors or screws is carried out separately for angular and linear components. One possible advantage of such an approach is that it deals only with the kinematic and statics of the mechanism while still providing physically meaningful and practically applicable measures. Case studies of a 3-Degrees Of Freedom translational parallel mechanism and a planar parallel mechanism are presented for illustration and comparison.

Dynamics analysis of planar multi-DOF mechanism with multiple revolute clearances and chaos identification of revolute clearance joints

The clearance joint is one of the important factors which influence system performance and dynamic characteristics. Traditional studies are mainly focused on the planar single degree of freedom (DOF) simple mechanism with one joint clearance, only few researchers investigated mechanisms with more than one DOF considering more than one clearance joint as an object, and few studies systematically analyzed nonlinear characteristics of the clearance joints. This article is devoted to analyzing the effect of multiple clearances and different friction models on the dynamic behavior of a planar multi-DOF mechanism. The 2 DOFs nine bar planar mechanism is selected as the research object. The dynamic model of the planar mechanism with two revolute clearances is built by considering Lagrange equation. The influence of LuGre model and modified Coulomb friction model on the dynamic response of the nine bar mechanism is studied. The effects of the number of clearance joints, clearance values, driving speeds and friction coefficients on the dynamic responses of the mechanism are analyzed. The chaos phenomenon existing in the clearance revolute joints is identified by phase diagram, Poincare map and largest Lyapunov exponent (LLE). Bifurcation diagrams of revolute clearance joints with changing clearance values, driving speeds and friction coefficients are also drawn. A virtual prototype model of 2 DOF nine bar mechanism containing two revolute clearances is built by using ADAMS software to verify the correctness of the numerical results. This research can provide theoretical basis for grasping the dynamic behavior of the planar rigid-body mechanism with clearances and identifying chaos of clearance joints.

Kinematics Modeling and Simulation of GantryShip Welding Manipulator with Hybrid Structure

The existing gantry ship welding robot mechanism is mostly in series, which has the problems of large motion inertia at the end and joint error accumulation.A kind of ship welding robot with hybrid structure is designed. The platform control mechanism and rotary mechanism adopt the form of planar parallel mechanism, which can effectively increase the rigidity and error compensation ability of the actuator.And the adjusting mechanism of welding torch adopts series structure and keeps the flexible output ability.The kinematics model of the welding actuator is established by combining the closed-loop vector method, complex vector method and D-H four-parameter method.The positive solution of the mechanism is given, and the velocity and acceleration are analyzed based on it.Through simulation analysis, we get the workspace and kinematic characteristics curve of some components under given trajectories to verified the feasibility of the proposed mechanism.

Application of the reduced mechanism method to determine the law of motion of a planar mechanism with multiple degrees of freedom

Application of the reduced mechanism method to determine the law of motion of a planar mechanism with multiple degrees of freedom

Experimental Study on Ship-Bank Interaction of Very Large Crude Carrier in Shallow Water

In order to assess the influence of ship-bank interaction on ship manoeuvring motion, planar motion mechanism (PMM) tests on a scale model of the KRISO very large crude carrier (KVLCC2) are conducted in different water depths in circulating water channel (CWC). The asymmetric hydrodynamic derivatives are defined to characterize the bank effect, and they are measured through the straight towing test with varying lateral displacements. The linear and nonlinear hydrodynamic derivatives are determined from the test data of the Fourier integral and mathematical regression model. The rudder and heading angles required at equilibrium conditions in different ship-bank distances are calculated by the manoeuvring model. The directional stability with varying ship-bank distances is studied in terms of eigenvalue analysis. Analysis based on the test results shows that the KVLCC2 model ship appears inherently unstable for keeping course in deep and shallow water conditions. When the ship-bank distance decreases, the increasing ship-bank interaction can dramatically affect some parameters of the criteria for course keeping.

Static behavior of weighing cells

Abstract. Compliant mechanisms in precision weighing technology are highly sensitive mechanical systems with continuously rising demands for performance in terms of resolution and measurement uncertainty. The systematic combination of adjustment measures represents a promising option for the enhancement of weighing cells which is not yet fully exhausted. A novel adjustment concept for electromagnetic force compensated weighing cells designed for 1 kg mass standards is introduced. The effect on the mechanical behavior is analyzed in detail using a planar compliant mechanism with semi-circular flexure hinges. Design equations for a first layout of the mechanical system are derived from a linearized rigid body model. Existing adjustment concepts for the stiffness characteristic and the sensitivity to quasi-static ground tilt are included. They are extended by the novel approach to attach trim weights to the levers of the linear guide. Based on this concept, an optimal design for the weighing cell is determined. The comparison with a finite element model reveals further effects given by the more precise description of the mechanical behavior. By parametric studies of the adjustment parameters in the mechanical models, it is shown that the stiffness and tilt sensitivity can be reduced significantly compared to the non-adjusted weighing cell. The principal correlation of the trim weights and their effect on the mechanical properties is experimentally verified using a commercially available weighing cell.