Planar Mechanisms Research Articles

Study on Wear Characteristics of Revolute Clearance Joints in Mechanical Systems.

The existence of clearance causes contact-impact forces in joints, which lead to surface wear and incessant material loss of the joint surface during the motion of mechanisms. In this work, the wear characteristics of dry revolute clearance joints in planar mechanisms are studied using a computational methodology. The normal contact force model and the tangential friction force model are established to describe the contact-impact in clearance joints. Then, the dynamic wear model based on the Archard’s wear model is established to predict the wear characteristics of clearance joints in mechanisms. The dynamic wear depths of clearance joints are obtained in two steps. The first step is the dynamics analysis of mechanisms to obtain the contact and sliding characteristics between the bearing and journal in the clearance joint. The second step is the dynamic wear depth analysis of clearance joints based on dynamic Archard’s wear model. Finally, a planar slider-crank mechanism with two revolute clearance joints between the connecting rod and its adjacent links is used as the implement example. Different case studies are performed to investigate the wear characteristics of clearance joints in mechanical systems.

Effective workspaces of parallel robots

AbstractAn approach for calculating the effective workspaces of parallel mechanisms has been considered in this paper. The effective workspace is a set of reachable by the end-effector points, where an important parameter (or parameters) from the point of view of operation is not higher than critical. In this article, the speed and torque in the drive and the stiffness of the mechanism are considered as such parameters. An approach to determining the appropriate effective workspace is presented for each parameter. The optimization process, which is based on presented methods, allows one to choose basic technical solutions of the designed robot: the links (lengths and cross-sections), the drives, and types of hinges, which guarantee its operability at the specified operational characteristics. Case studies of a delta robot with four degrees of freedom and a planar five-bar mechanism are presented for testing these approaches. The presented methods are of great practical importance because it uses movement parameters or operational characteristics that are decisive for this mechanism and have clear physical meaning.

A geometric and analytic technique for studying multi-DOF planar mechanisms’ dynamics

Most approaches of analytical mechanics (e.g., D'Alembert principle) build dynamic models of mechanisms that are difficult to relate with clear geometric interpretations. This feature is a drawback that confines their use to the implementation of algorithms in multi-body-dynamics software, whose results must be interpreted by using the designer intuition when the mechanism must be modified to match particular design requirements. Here, starting from D'Alembert principle, the dynamic model of any multi-degrees-of-freedom (multi-DOF) planar mechanism (PM) is obtained by suitably combining the dynamic models of all the single-DOF PMs generated by locking all the actuated joints, but one. The dynamic models of the so-generated single-DOF PMs are written by using an approach, presented in a previous paper, which admits a geometric interpretation through diagrams, named “active-load diagrams”, and fully discloses the role of instant centers (ICs) in the dynamic behavior of single-DOF PMs. Accordingly, the resulting dynamic model of the generating multi-DOF PM admits a geometric interpretation that reveals the role of ICs in multi-DOF PMs’ dynamic behavior. Such geometric interpretation is so effective that, formally, the model could be written starting from it without any analytic consideration the same way as the equilibrium equations can be written from free-body diagrams in the Newton-Euler formulation. The presented model is general and, as far as this author is aware, is novel. The proposed model and the associated algorithms for solving dynamic problems are also illustrated through a case study. The obtained results are of interest in mechanism analysis and design.

Dynamic Analysis of a Planar Suspension Mechanism Based on Kinestatic Relations

The dynamic characteristics of a vehicle are significantly influenced by the suspension mechanism. In this paper, the nonlinear kinestatic relations of a planar suspension mechanism are taken into account in the dynamic analysis of a vehicle. A planar suspension mechanism can be considered a 1-DOF parallel mechanism. The Jacobian is used for the kinestatic analysis of the suspension. The motions of the suspension can be represented by instantaneous screw. Based on these kinematic and static relations, the dynamic performances of a quarter-vehicle model with a planar suspension mechanism are described in terms of Lagrangian equations. Finally, as illustrated in the examples, two different kinds of road disturbances are inputted into the wheel. The dynamic responses of a quarter-vehicle model are simulated and compared with the simulation software Adams/View for the validity of the theoretical method.

Multi-stability of a planar three-limb flexible mechanism

In general, the classical multi-stable mechanisms are made of single-loop bi-stable mechanism elements, but this paper proposes a novel structure of a planar three-limb flexible mechanism whose multi-stability is dependent on the structure parameters. The structure of this flexible mechanism is ingeniously designed to have a large selection range of the original limb length, resulting in the variation of the multi-stability distribution and the possible switching paths. To analyze the variation of this flexible mechanism, the paper introduces a method avoiding computational singularity to determine the stability by contour map and a method to draw the multi-stability topology to seek for the possible switching paths. Using these methods, the paper presents the variation of the multi-stability topology of an axisymmetric and two mirror-symmetric planar three-limb flexible mechanisms as the original length of the limbs increases. The results shows the mulita-stability of this flexible mechanism can be determined by the original length of the limbs and limb arrangement. The whole statements provide a theoretical basis for designing and applying such type of flexible multi-stable mechanism.

Extending the Force Balancing Method of Adjusting Kinematic Parameter to Spatial Mechanisms

Robotic mechanisms is one that the mechanism includes no less than one variable speed actuator. As for force balancing, which refers to mechanisms with a complete cancelation of the inertia-induced force on the ground (shaking force). A few strategies are accessible for reducing shaking force, including the counterweight (CW), add-of-spring (AOS), add-of-linkage (AOL), and adjusting kinematic parameter (AKP). AKP is only applicable to planar robotic mechanisms when it was developed. The primary goal of the present paper is to extend AKP approach to a spatial mechanism. Considering the complex kinematic characteristics of spatial mechanism, a simple spherical parallel robot (SPR) is used as the research tool. The equations for force balancing of the spherical robotic mechanism using AKP were derived. Simulation verification was performed by a reliable software called SPACAR available in the Matlab environment. The results demonstrated the effectiveness of the AKP method in eliminating the unbalanced force to spatial mechanisms. The main contribution is the provision of a new force balancing method to spatial mechanisms, which will enrich the field of balancing of spatial robotic mechanisms.

Calculated Torque Control of a Planar Parallel Robot 2-RR

<div><p class="4">This paper introduces the design, structure and control method of a five-bar planar mechanism with five revolute joints and two degrees of freedom. The control is realized by calculating the torque in the joint space to obtain the required trajectory. The direct and inverse kinematics of position and velocity are proposed, and the inverse kinematics of acceleration is taken as the parameter required by the control law. The method selected for this parallel robot is advantageous because it allows to obtain the dynamic equations similar to the traditional series robot modeling, which is helpful to the realization of nonlinear control technology. The effectiveness of the method and the functionality of the controller are verified by experiments, and a circular trajectory is generated by the actuator. Although the simulation results are consistent with the experimental results, it is suggested that the future work is to change the control strategy to compensate for the influence of the unmodeled system.</p></div>

Innovative design and optimization of the modular high deployment ratio two-dimensional planar antenna mechanism

With the improvement of space-to-earth observation range and observation accuracy, the demand for large deployable antenna mechanism is becoming increasingly urgent. This paper proposes a new configuration that can realize two-dimensional planar deployment and designs a new large-scale two-dimensional deployable planar antenna mechanism. First, four folding schemes are proposed, and the folding scheme with the best comprehensive performance is determined through optimization. The antenna mechanism is designed in detail. The kinematic model of the basic configuration is established to analyze its kinematic characteristics. The antenna can be deployed smoothly by planning the deployment speed. The finite element model of the antenna is then established. The structural parameters of the antenna are optimized, the rigidity of each joint hinge is reasonably configured, and the comprehensive mechanical properties of the antenna are improved. Finally, the principle prototype of the two-dimensional deployable antenna is developed by 3D printing technology. The rationality and feasibility of the folding principle of the antenna are verified by experiments.

A new synthesis method for planar Rubik’s cube mechanism

Planar mechanism is a kind of important mechanism, which plays a key role in daily life and industrial life. This paper presents a new synthesis method for planar Rubik’s cube mechanism (PRCM). Firstly, the composition and motion mechanism of the PRCM are introduced combined with a symmetrical four-axis PRCM. The reconfigurable motion process of two kinds of PRCMs is described and analyzed, and the conditions of realizing reconfigurable motion of PRCMs are obtained. Next, a new synthesis method of PRCM is put forward, and the detailed process and flow chart of PRCM synthesis are given. Then, the factors affecting the topological structure of the PRCM are determined from the synthesis process. Finally, the cases of each type of PRCM are synthesized by setting specific parameters. The PRCM synthesis method is of great significance to perfect and enrich the plane reconfigurable mechanism synthesis theory.

A novel approach for optimal synthesis of path generator four-bar planar mechanism using improved harmony search algorithm

ABSTRACT Since last few decades, a lot of work has been done on the evolutionary techniques to solve the optimisation problems. With the time passes, these techniques were modified, and also new algorithms were introduced to improve the performance. These techniques had been used by many researchers in synthesis of mechanisms to get the optimum results with minimum design errors. Improved harmony search (IHS) algorithm is developed from harmony search technique by improvising the harmony in HS algorithm. This technique is inspired by searching the best state of harmony in musical process in which a jazz musician make practice after practice to find the same. In this paper, IHS algorithm is utilized to synthesize four-bar path generation mechanism. A mathematical model was derived using vector loop closure equation, wherein the error function, representing positional error between actual and desired points, was considered for forming objective function. The penalty function was used to prevent violation of structural constraints corresponding to Grashof’s criteria and input crank angle sequence. Three different cases were studied with ten, fifteen and eighteen precision points with and without prescribed timings. The results obtained from the study, compared with other evolutionary techniques from literature, and found significant competition.

Passive chaos suppression for the planar slider-crank mechanism with a clearance joint by attached vibro-impact oscillator

Chaotic dynamic behavior in clearance joints is the prominent nonlinear factor for multibody systems. This study presents a passive chaos suppression method to stabilize the planar slider-crank mechanism with a clearance joint. The strategy resorts to a vibro-impact oscillator attached to the slider. Primarily, the impact principle is employed to characterize the dynamics in clearance joints. The mathematical model of the integral system is conducted subsequently. The chaotic system behavior is evaluated by bifurcation analysis varying clearance size and crank speed. When the controller is activated, parametric optimizations of the stiffness, clearance coefficient, and particle mass are conducted to achieve optimum chaos elimination. Phase portraits, the largest Lyapunov exponent, and time-frequency distribution are evaluated. Numerical results illuminate that an adjusted oscillator can suppress the chaotic high-frequency composition of system response and help to maintain continuous contact between the joint elements. The results suggest applying the identical clearance size in the revolute joint and vibro-impact oscillator for fast optimization. Moreover, the method is still technology valid when considering different contact principles. Ultimately, a test platform is established to achieve some experimental validations.

The Nab2 RNA-binding protein patterns dendritic and axonal projections through a planar cell polarity-sensitive mechanism.

RNA-binding proteins support neurodevelopment by modulating numerous steps in post-transcriptional regulation, including splicing, export, translation, and turnover of mRNAs that can traffic into axons and dendrites. One such RNA-binding protein is ZC3H14, which is lost in an inherited intellectual disability. The Drosophila melanogaster ZC3H14 ortholog, Nab2, localizes to neuronal nuclei and cytoplasmic ribonucleoprotein granules and is required for olfactory memory and proper axon projection into brain mushroom bodies. Nab2 can act as a translational repressor in conjunction with the Fragile-X mental retardation protein homolog Fmr1 and shares target RNAs with the Fmr1-interacting RNA-binding protein Ataxin-2. However, neuronal signaling pathways regulated by Nab2 and their potential roles outside of mushroom body axons remain undefined. Here, we present an analysis of a brain proteomic dataset that indicates that multiple planar cell polarity proteins are affected by Nab2 loss, and couple this with genetic data that demonstrate that Nab2 has a previously unappreciated role in restricting the growth and branching of dendrites that elaborate from larval body-wall sensory neurons. Further analysis confirms that Nab2 loss sensitizes sensory dendrites to the genetic dose of planar cell polarity components and that Nab2-planar cell polarity genetic interactions are also observed during Nab2-dependent control of axon projection in the central nervous system mushroom bodies. Collectively, these data identify the conserved Nab2 RNA-binding protein as a likely component of post-transcriptional mechanisms that limit dendrite growth and branching in Drosophila sensory neurons and genetically link this role to the planar cell polarity pathway. Given that mammalian ZC3H14 localizes to dendritic spines and controls spine density in hippocampal neurons, these Nab2-planar cell polarity genetic data may highlight a conserved path through which Nab2/ZC3H14 loss affects morphogenesis of both axons and dendrites in diverse species.

Series of the Largest Dish-Shaped Dysprosium Nanoclusters Formed by In Situ Reactions.

A three-dimensional supermolecule structure is easily formed due to the diverse coordination modes of high-oxidation-state lanthanide metal ions. However, the design and construction of zero-dimensional (0 D) dish-shaped high-nuclearity lanthanide clusters are difficult. Herein, for the first time, we synthesized a series of the largest dish-shaped high-nuclearity lanthanide nanoclusters (1-4) by in situ tandem reactions under solvothermal one-pot conditions. The formation of 1 and 2 involved an in situ reaction of aldehydes and amines, while the condensation reactions between aldehydes occurred in 3 and 4. Based on the structural characteristics of the dish-shaped lanthanide clusters, we proposed two possible assembly mechanisms involving Dy1 → Dy7 → Dy13 → Dy19 (planar epitaxial growth mechanism) and Dy1 → Dy12 → Dy18 → Dy19 (planar internal growth mechanism).

Innovative design method for planar mechanism configuration based on component similarity discrimination

Abstract. Obtaining new models of mechanical equipment to conduct mechanical innovative design through kinematic chain configuration synthesis is an effective method. However, in practice, due to the existence of similar components, existing innovative design methods easily produce redundant design schemes, which require extensive isomorphic discrimination operations, and the design process is complex. In view of existing problems, this study analyzes a method for discriminating between similar components of mechanisms from the perspective of graph theory and then applies it to the specialization of topological graphs to solve the problem of redundant design schemes. Finally, using the innovation of a drilling rig drilling arm mechanism as an example, 52 feasible schemes without redundancy are obtained. This paper provides a reference for the innovation of the configuration of planar mechanisms without design redundancy.

Configuration spaces of hinged mechanisms, and their projections

Abstract Our subject is the geometry of planar hinged mechanisms. The article contains a formalization of basic concepts of the theory of hinged-lever constructions, as well as some information from real algebraic geometry needed for their study. We consider mechanisms with variable number of degrees of freedom and mechanisms that have more than one degree of freedom but each hinge of which moves with one degree of freedom. For the last type we find the dimension of the configuration space. We give a number of examples of mechanisms with unusual geometric properties and formulate open questions. Bibliography: 17 titles.

Design and Motion Simulation Analysis of a Novel 2D Bionic Flutter Aircraft

In order to improve the symmetry of the flutter mechanism in the bionic flutter aircraft, and then improve the overall motion stability of the flutter aircraft. In this paper, an innovative flutter wing configuration is designed based on a planar crank-slider mechanism and a sparrow model. The geometric relationship of the flutter mechanism is established, the motion of the flutter aircraft is modeled, and the dimensions of the model are optimized. The geometric relationship of the flutter structure was simulated and analyzed by CATIA. The results show that the upper limit angle of the designed flutter structure is βmax=25.82° and the lower limit angle is βmin=6.34°. The CATIA simulation data are consistent with the theoretical values of the established structural geometry model. Meeting the needs of small and medium-sized flutter aircraft.The design provides a theoretical basis for the design and development of the bionic flutter vehicle and the fabrication of a solid prototype.

Kinematic motion analysis of the members of a double jaw crusher

Computational technology makes it possible to accelerate and simplify the processes of kinematic and dynamic analysis. The paper deals with the problem of kinematic analysis of a planar six-joint mechanism of a jaw double-spring crusher. Computational techniques and software support have been used in the kinematic analysis. The obtained results are compared with the results of the graphical solution. The graphical solution has been carried out by using CAD software. MSC.Adams/View program was used to create a model and simulate the jaw crusher motion. In both cases there was agreement of the obtained results.

Research on accurate modeling of hydrodynamic interaction forces on AUVs operating in tandem

The hydrodynamic interaction force between autonomous underwater vehicles (AUVs) operating in tandem can adversely affect the hydrodynamic prediction of individual AUVs and the formation control of the tandem fleet. Accurate modeling of hydrodynamic interaction forces is crucial to the model-based controller design of AUVs. In this paper, we innovatively propose a modeling method that can describe the hydrodynamic interaction relationship accurately and continuously (when the spacing between adjacent AUVs changes). First, an accurate hydrodynamic model for individual AUVs in tandem fleets is established by modifying the typical model through the consideration of memory effects. Second, a model of hydrodynamic interaction forces is derived by subtracting hydrodynamic forces acting on a single AUV operating independently from those acting on an AUV operating in tandem. To enable this model to continuously describe the hydrodynamic interaction relationship when the spacing changes, this model is further derived by taking the spacing as an independent variable based on the parameter conversion method. Finally, planar motion mechanism (PMM) tests are carried out using the computational fluid dynamics (CFD) method to verify the accuracy and continuity of the proposed modeling method. The results show that compared with the typical model, the average error of hydrodynamic forces predicted by the proposed model is reduced by 5.36%, which verifies the feasibility and effectiveness of the proposed modeling method.

A design approach for gravity compensators using planar four-bar mechanisms and a linear spring

This paper presents a design approach for gravity compensators using planar four-bar mechanisms and a linear spring. This work enables the development of a class of gravity compensators encompassing 42 different types, which are characterized by high performance and kinematic simplicity. The gravity compensators are constructed by combining planar four-bar mechanisms with a rotating mass and attaching a linear spring to each mechanism, then permuting the springs. The parameters of the gravity compensators are derived from an optimization procedure that minimizes the actuator torque within a specified balancing zone. The performances of the gravity compensators were demonstrated via both numerical examples and experiments. The results showed their design feasibilities and high performances in which a torque reduction rate of 87.8% was practically achieved. Lastly, an application of the proposed gravity compensators to serial robots is described. It was found that the actuator torque of a serial robot over a prescribed workspace could theoretically be reduced by 98.2%. A prototype of a serial robot was also built to validate the applicability of the gravity compensators.

Dynamic Analyses of Whitworth Quick Return Mechanism

Herein, we present a dynamic analysis on a Whitworth quick return mechanism, which was proposed as a class project to engage Mechanical Engineering students in the Machine Dynamics course. The objectives of the project are to teach (1) kinematic analysis on planar linkage mechanism using complex numbers and (2) kinetic analyses using distributed and lumped mass models. The analytical models were implemented using an engineering math software – Mathcad, and the results were validated by a multibody dynamics simulation software – Inventor. Loop closure equations were first built and solved to find link positions, and then velocities and accelerations were confirmed with numerical differentiation in Mathcad. Based on the solved kinematic quantities, a kinetic analysis was carried out using distributed and lumped mass models as well as in Inventor. The reactions and torques at the input link of the distributed mass model were found identical to those derived from Inventor. It was found the maximum reactions at pin joints were 11% to 100% different between the distributed mass model and the simplified lumped mass model. However, the shaking forces found in both models were nearly identical, and the peak values of the shaking moments were comparable. It is confirmed the lumped mass model can serve as a quick method to find the magnitude of the shaking forces and moments without solving simultaneous equation systems.