Link Position Research Articles

An Improved Harmony Search Algorithm for a Planar Parallel Robot Synthesis

The objective of kinematic synthesis is to determine the mechanism dimensions such as link lengths, positions or joint coordinates, in order to approximate its output parameters such as link positions, trajectory points, and displacement angles. Kinematic synthesis is classified into three categories: function generation, path generation, and motion generation. This paper is dedicated only to path generation. As the number of trajectory points increases, analytical methods are limited to obtain precisely mechanism solutions. In that case, numerical methods are more efficient to solve such problems. Our study proposes an improved heuristic algorithm applied to four-bar mechanism path-generation. The objective of this work is to find optimum dimensions of the mechanism and minimize the error between the generated trajectory and the desired one, taking into consideration constraints such as: Grashof condition, transmission angle, and design variables constraints. Finally, our results are compared with those found by other evolutionary algorithms in the literature.

Computer simulation of three-point linkage parameters for virtual hitch point and optimum depth of operation

A computer program is developed in Visual Basic 6.0 to locate the virtual hitch point of tractor with respect to depth of operation and to optimize the three-point linkage parameters for matching the virtual hitch point with the line of pull. The concept of Cartesian coordinate geometry was used in the program development. The virtual hitch point was calculated by solving the straight line equations of lower and upper link of three-point hitching system at particular depth of operation. For determining the line of pull, draft was calculated from ASAE equation and coordinate of centre of resistance was assumed to the 2/3 of depth of operation in the line of centre of gravity of implement. The optimum depth of operation is the depth for which line of pull passes above and near to VHP which was calculated in the program through the iteration process. The locus of virtual hitch point with respect to depth of operation was observed as parabolic. The distance of virtual hitch point from the rear axle centre increases with increase in depth of operation in all cases. The optimum depth of operation for a test tractor was observed as 269 mm using the developed program. This depth depends substantially on lower link (length and link position) and implements parameters (weight and height of hitch point). Therefore, this program may be very useful in simulating the three-point linkage and implement parameters as per the requirement of depth of operation.

A secure and efficient cluster based location aware routing protocol in MANET

Mobile adhoc network (MANET) is a collection of node under a communication with each other nodes in the network. They are mobile nodes which can change its location according to the requirement. So the location based routing is needed for transmission of packet. For the data packet security, the existing algorithm is enhanced as “A secure location aware routing protocol”. In this nodes are arranged by means of a clustering technique. This protocol will predict the future location of node using particle swarm optimization. The link lifetime, speed, distance and position of node is calculated earlier to find the optimized route. The trust value of node is computed from neighbor node which helps in prediction of future location and also to find malicious node in network to reduce packet loss. To prevent data from malicious node, the packets are encrypted using elliptic curve cryptography. Due to trust value, the routing information can be updated for easily and also improve the network throughput.

Analytical analysis and effect of scrambling on inter-relay interference in a tri-sectored LTE-A network

The incorporation of relay nodes (RNs) in LTE networks for coverage and capacity enhancement generates some inter-relay interference. To mitigate this inter-relay interference in 4G-LTE-A standard, the effect of scrambling technique is discussed in this paper. This makes the proposed technique unique, in the sense that intra-relay distance becomes immaterial, unlike the existing techniques where it is mandatory to maintain a specific distance between the relay nodes of the same sector. A new analytical model for tri-sectorised hexagonal cellular networks is presented in this paper. The expectation values for signal-to-interference noise ratio (SINR) and through-put capacity for all the positions of access link are derived. Simulations are carried out on Matlab software to validate the theoretical analysis. The cumulative distribution function (CDF) curves for both SINR and through-put capacity of each link depict the performance of the proposed model.

Kinematic Synthesis of Mechanism for System with a Technical Vision

A solution to the problem of synthesizing an initial three-dimensional kinematic chain with spherical and rotary kinematic pairs is presented. It is shown that this chain can be used as a structural module for structural-kinematic synthesis of three-dimensional four-link motion generating lever mechanisms by the preset positions of the in-and output links. This paper affects the actual today’s problem of optimal synthesis of spatial link mechanisms. In this regard, the task of developing methods for the synthesis of complex spatial link mechanisms with the desired laws of motion of the input and output elements allowing automatizing the implementation of all design phases with the use of computer is quite relevant. The authors develop machine-oriented method of structural and kinematic synthesis of spatial link mechanisms based on the use of spatial initial kinematic chains (IKC) realizing prescribed motions. A new approach to the design of spatial mechanisms is suggested, according to which the design process is based on the kinematic synthesis of four-link initial kinematic chain (IKC) and associable kinematic chains (AKC).

Robust Tuning Rules for Series Elastic Actuator PID Cascade Controllers

This paper deals with the control of a collaborative robot manipulator with series elastic actuators. In particular, robust tuning rules for cascade control of the joints are presented. Both the motor velocity and link position control loops are considered. The proposed tuning rules allow the online computation of robust control parameters to cope with the different link reflected inertia. Experimental results show the effectiveness of the method in real applications.

The opercular mouth-opening mechanism of largemouth bass functions as a 3D four-bar linkage with three degrees of freedom.

The planar, one degree of freedom (1-DoF) four-bar linkage is an important model for understanding the function, performance and evolution of numerous biomechanical systems. One such system is the opercular mechanism in fishes, which is thought to function like a four-bar linkage to depress the lower jaw. While anatomical and behavioral observations suggest some form of mechanical coupling, previous attempts to model the opercular mechanism as a planar four-bar have consistently produced poor model fits relative to observed kinematics. Using newly developed, open source mechanism fitting software, we fitted multiple three-dimensional (3D) four-bar models with varying DoF to in vivo kinematics in largemouth bass to test whether the opercular mechanism functions instead as a 3D four-bar with one or more DoF. We examined link position error, link rotation error and the ratio of output to input link rotation to identify a best-fit model at two different levels of variation: for each feeding strike and across all strikes from the same individual. A 3D, 3-DoF four-bar linkage was the best-fit model for the opercular mechanism, achieving link rotational errors of less than 5%. We also found that the opercular mechanism moves with multiple degrees of freedom at the level of each strike and across multiple strikes. These results suggest that active motor control may be needed to direct the force input to the mechanism by the axial muscles and achieve a particular mouth-opening trajectory. Our results also expand the versatility of four-bar models in simulating biomechanical systems and extend their utility beyond planar or single-DoF systems.

MATHEMATICAL SIMULATION OF TECHNOLOGICAL EQUIPMENT FOR PROCESSING OF OPTICAL PARTS

The paper describes a functional scheme of a machine-tool for simultaneous abrasive machining of lenses with shallow high-accuracy executive surface. The machine-tools permits flexibly and within long range to control shape-formation process through changing such adjustment parameters as tool and rough workpiece frequency rotation, amplitude value of tool oscillatory motion, their diameters and number of double strokes per minute. While using the given machine-tool for machining process an operating force is directed along normal to the working surface and due to this there is a possibility to accelerate a shape-formation process of optical parts that leads to reduction of local errors on their executive surfaces. The paper considers a structure of the executive machine-tool mechanism which transfers translational motion to the tools and consists of rotational and rectilinear kinematic pairs forming a four-bar linkage and its crank is a guide link. A turning angle of the link is selected as a generalized coordinate of the executive mechanism. A relationship between the generalized coordinates and link positions of the executive machine-tool mechanism has been established in the paper and it permits to obtain analytical dependence between motions of input and output mechanism links with due account of its kinematic transfer function which represents in itself a ratio of angular output link speed to an angular velocity of the input link. An analysis of geometric parameters for backward-rotational motion of the top link in the proposed machine-tool has made it possible to obtain an expression to calculate a rod length of the executive mechanism which ensures symmetrical center position of the above-mentioned link relative to a symmetry axis of the bottom link. As an amplitude value of oscillatory motion for an out-put link in the executive mechanism is regulated in the machine-tool for two-sided lens machining while changing length of its input link (crank) an analytical relationship has been established between these geometric parameters and the rela- tionship provides a possibility purposefully to change a machining intensity in the central or edge zone of a part according to technological blank heredity in the context of allowance which is to be removed and which is distributed along its surface.

Comparing species interaction networks along environmental gradients.

Knowledge of species composition and their interactions, in the form of interaction networks, is required to understand processes shaping their distribution over time and space. As such, comparing ecological networks along environmental gradients represents a promising new research avenue to understand the organization of life. Variation in the position and intensity of links within networks along environmental gradients may be driven by turnover in species composition, by variation in species abundances and by abiotic influences on species interactions. While investigating changes in species composition has a long tradition, so far only a limited number of studies have examined changes in species interactions between networks, often with differing approaches. Here, we review studies investigating variation in network structures along environmental gradients, highlighting how methodological decisions about standardization can influence their conclusions. Due to their complexity, variation among ecological networks is frequently studied using properties that summarize the distribution or topology of interactions such as number of links, connectance, or modularity. These properties can either be compared directly or using a procedure of standardization. While measures of network structure can be directly related to changes along environmental gradients, standardization is frequently used to facilitate interpretation of variation in network properties by controlling for some co-variables, or via null models. Null models allow comparing the deviation of empirical networks from random expectations and are expected to provide a more mechanistic understanding of the factors shaping ecological networks when they are coupled with functional traits. As an illustration, we compare approaches to quantify the role of trait matching in driving the structure of plant-hummingbird mutualistic networks, i.e. a direct comparison, standardized by null models and hypothesis-based metaweb. Overall, our analysis warns against a comparison of studies that rely on distinct forms of standardization, as they are likely to highlight different signals. Fostering a better understanding of the analytical tools available and the signal they detect will help produce deeper insights into how and why ecological networks vary along environmental gradients.

A tunable 3‐D statistical channel model for spatio‐temporal characteristics of wireless communication networks

AbstractA new 3‐dimensional geometric channel model is proposed with multiple degrees of freedom in its scattering volume geometry, which enables accurate modeling of realistic propagation scenarios for emerging machine‐to‐machine wireless networks. Analytical expressions for the joint and marginal statistics in delay and angular domains are derived, and we present the impact of various physical channel parameters such as link distance, antenna height, size and position of the scattering region, as well as shape and orientation of the scattering region on the delay and angular spread of the proposed model. The derived analytical results are validated with simulations and are also shown to provide a good fit to published empirical data sets. Relative to existing models, the proposed model is shown to more accurately adapt to different propagation environments envisioned for emerging communication scenarios such as in indoor picocellular and vehicle‐to‐vehicle communication applications.

A novel 2-DOF planar translational mechanism composed by scissor-like elements

Abstract. The kinematic chain comprised by SLEs (scissor-like elements) has a wide range of motion, which provides a benefit for the mechanism design. A family of SLE-Pa (SLE-parallel) legs which consist of two identical SLE limbs are proposed in this paper. The mobility and kinematics are discussed for three kinds of SLE-Pa legs which are distinguished by the different positions of the middle links in legs. Through assembling these SLE-Pa legs, a novel 2-DOF planar translational mechanism is developed and its work space is studied. For the purpose of adding the recovery function, the elastic elements are installed for this mechanism. The stiffness synthesis of the mechanism is investigated for the various elastic elements and their positions. The approximation of the stiffness coefficient is also derived. Further, this kind of mechanism is applied for the design of the passive docking device. The docking procedure is simulated by Adams, and the prototype of one SLE-Pa leg is presented at the end.

The causative–instrumental syncretism

Causative and applicative morphemes have been central in work on the morphosyntax of argument structure. However, several genetically unrelated languages use a single, syncretic form for both functions, which complicates the traditional view that a causative adds a new subject and an applicative adds a new object. In this paper, I propose an analysis of a morphological syncretism found in the Bantu language Kinyarwanda where the morphological causative and instrumental applicative are both realized by the morpheme –ish. I argue for Kinyarwanda that both causation and the introduction of an instrument are analyzable as two outgrowths of the same semantic notion of introducing a new link into the causal chain described by the verb. The different causative and instrumental readings derive from underspecification of the position of the new link in the causal chain, although its placement is restricted via general constraints on possible event types as well as constraints on verb meaning and argument realization. This analysis provides an explanation for the presence of the causative–instrumental syncretism as well as provides insight into the interface between verb meaning and valency-changing morphology.

Trajectory and Vibration Control of a Single-Link Flexible-Joint Manipulator Using a Distributed Higher-Order Differential Feedback Controller

The trajectory tracking in the flexible-joint manipulator (FJM) system becomes complicated since the flexibility of the joint of the FJM superimposes vibrations and nonminimum phase characteristics. In this paper, a distributed higher-order differential feedback controller (DHODFC) using the link and joint position measurement was developed to reduce joint vibration in step input response and to improve tracking behavior in reference trajectory tracking control. In contrast to the classical higher-order differential (HOD), the dynamics of the joint and link are considered separately in DHODFC. In order to validate the performance of the DHODFC, step input, trajectory tracking, and disturbance rejection experiments are conducted. In order to illustrate the differences between classical HOD and DHODFC, the performance of these controllers is compared based on tracking errors and energy of control signal in the tracking experiments and fundamental dynamic characteristics in the step response experiments. DHODFC produces better tracking errors with almost same control effort in the reference tracking experiments and a faster settling time, less or no overshoot, and higher robustness in the step input experiments. Dynamic behavior of DHODFC is examined in continuous and discontinues inputs. The experimental results showed that the DHODFC is successful in the elimination of the nonminimum phase dynamics, reducing overshoots in the tracking of such discontinuous input trajectories as step and square waveforms and the rapid damping of joint vibrations.

Output feedback assistive control of single-DOF SEA powered exoskeletons

PurposeThis paper aims to overcome some of the practical difficulties in assistive control of exoskeletons by developing a new assistive algorithm, called output feedback assistive control (OFAC) method. This method does not require feedbacks from force, electromyography (EMG) or acceleration signals or even their estimated values.Design/methodology/approachThe presented controller uses feedbacks from position and velocity of the output link of series elastic actuators (SEAs) to increase the apparent integral admittance of the assisted systems. Optimal controller coefficients are obtained by maximizing the assistance ratio subjected to constraints of stability, coupled stability and a newly defined comfort measure.FindingsThe results confirm the effectiveness of using the inherent properties of SEAs for removing the need for extra controversial sensors in assistive control of 1 degree of freedom (1-DOF) SEA powered exoskeletons. The results also clearly indicate the successful performance of the OFAC method in reducing the external forces required for moving the assisted systems.Practical implicationsAs the provided experiments indicate, the proposed method can be easily applied to single DOF compliantly actuated exoskeletons to provide a more reliable assistance with lower costs. This is achieved by removing the need for extra controversial sensors.Originality/valueThis paper proposes a novel assistive controller for SEA-powered exoskeletons with a simple model-free structure and independent of any information about interaction forces and future paths of the system. It also removes the requirement for the extra sensors and transforms the assistive control of the compliantly actuated systems into a simpler problem of position control of the SEA motor.

Kinematics of Actuating Mechanism of Mixer Drives with Unsteady Agitator Motion

Schematic designs of gear-lever actuating mechanisms of mixer drives with intracycle variation of kinematic parameters of agitators are proposed. Analytical correlations of the function of the position, angular speed, and acceleration of the output link of the mechanism, which allow their use for calculating mixer drive, its certification, and reliability of use in hazardous industries and for assessing their influence on mixing intensity and finished product quality are derived.

Developments in quantitative dimensional synthesis (1970-present): four-bar motion generation

Dimensional synthesis is a type of inverse problem in linkage kinematics where the objective is to calculate the linkage dimensions required to achieve prescribed linkage output motion. Motion generation is a particular category of dimensional synthesis where the objective is to calculate the linkage dimensions required to achieve a group of prescribed link positions. In motion generation for a four-bar linkage, positions are prescribed for the coupler link. While early motion generation methods were primarily qualitative, ongoing advancements in computing hardware and software continue to make quantitative motion generation more practical. By providing overviews of works representative of developments in quantitative four-bar motion generation since 1970, this work is essentially an overview that spans over 40 years of developments in quantitative four-bar motion generation.

Developing a fast and tunable micro-mixer using induced vortices around a conductive flexible link

This paper presents a numerical study of a micro-mixer based on the continuous deformation of a conducting flexible link. The induced vortices around the link enhance the mixing process. This micro-mixer consists of one straight microchannel and one conductive flexible link. One end of the link is fixed on the upper wall of the channel and the other end can move freely due to the fluid-solid interactions. Since this link is conductive, vortices form around the link (once the electric field is applied). Applying a time-varying DC electric field causes variation in the applied forces to the link; thus, the link will swipe the channel and acts as a micro-stirrer to enhance mixing results. The presented results show that there is a direct relationship between mixing efficiency and the length of the link, as well as the amplitude of time-varying DC electric field. The effects of Young’s modulus, the average of applied electric field, and link position are also studied. Link with lower Young’s modulus swipes larger area inside the channel and enhances the mixing efficiency. By increasing the length of the conductive link, large vortices will be induced around it and mixing efficiency enhances. Our numerical results show that average mixing efficiency of link with a length of L = 0.625 W = 156.25 μm is about 90%. The proposed micro-mixer is simple to be fabricated and mixes the fluid streams in a short period of time with high efficiency. Such micro-mixers can be used in various microfluidics, biomedical, or chemical applications.

Clearance-induced output position uncertainty of planar linkages with revolute and prismatic joints

The paper presents the first kinematic model to quantify the effects of the joint clearance stack up on the nominal output link position of linkages containing revolute and prismatic joints. It demonstrates the modeling of each joint clearance, how the clearance stacks up is formed, and how the position uncertainty is affected by each joint clearance as well as the combination of all joint clearances. The novelty lies on the simplicity of the kinematic model resulted from the use of Ting's rotatability laws. For the worst case scenario, a chaotic clearance induced output uncertainty analysis at a nominal position of an N-bar linkage is reduced to a simple four-bar linkage analysis. The treatment is valid for all single loop N-bar linkages containing revolute and prismatic joints. The proposed kinematic model is showcased with a slider crank mechanism and an inverted slider crank mechanism.

Tadeusz J. Zieliński, Państwowy Kościół Anglii. Studium prawa wyznaniowego, Wydawnictwo Naukowe ChaT, Warszawa 2016, ss. 457

The reviewed book presents the legal status the Church of England in the last nearly five centuries up to Queen Elizabeth II’s 90th birthday in 2016. The monograph is divided into two parts. The first one includes the evolution of the legal position of the English offi cial church from the Act of supremacy (1534) till the beginning 21st century. The author of the book presents legal acts which were vital for the growth and development of this religious denomination. The second part of the book discusses the current legal regime governing the English offi cial church. It describes the position of the Established Church links with the Monarch, the British Parliament, the government, the judiciary, and local Movernment. It also includes the provisions of law concerning the main areas of the Church of England’s activities.

An algorithm for defining the inner geometry of a snakelike manipulator in case of leading link movements along the incremental trajectory

In the paper, we have formulated the invariant description form for geometry of a spatial, kinematically redundant manipulator with the orthogonal non-coplanar axes of rotation of the joints. We have obtained the explicit equations for determining the angular coordinates from the condition that points of joints belong to the smooth parametrically given curve. Inequality constraints on the relative position of neighboring parts of the manipulator have been formulated. We have proposed an algorithm for solving equations and the method of planning changes for hinge coordinates for the movement of joints points along the spatial curve that is formed by incremental addition of target points for the head link positions of the manipulator. The method has been applied for planning movements of a hyper-redundant manipulator with a fixed root link and a snakelike robot when moving along the path built on the basis of current and forecasted positions of joints in the Cartesian space.