Two-link Chain Research Articles

Simulation Study of Balancing Arm Arrangement for Controlling Base Disturbances in Long Reach Manipulators

The dynamics of the Long Reach Manipulators create disturbances in its supporting base structure. This causes positional and attitude inaccuracies of the end-effector, thwarting the accomplishment of the desired mission task. Hence the base disturbance problem has been a subject of research since long time bringing solutions from varied domains. This paper analyzes the balance link concept for compensating the disturbances. The LRM system is modelled as a two-link serial chain with payload, and the balance arm, as a single link with tip mass that is dynamically varied by controlling the quantity of the hydraulic fluid in the bellows-like reservoir at the tip. The supporting base is modelled as a half car. Simultaneous constraint matrices are set up for the arrangement, and dynamic simulation is performed using SIMULINK. The pitch and bounce motions of the base are studied along with the torque error during compensation. The simulation plots are obtained for two conditions of compensating arm¾with fixed tip mass and with varying tip mass. The results confirm the suitability of the suggested compensating arrangement in controlling base disturbances.

Automated Kinematic Analysis of Closed-Loop Planar Link Mechanisms

The systematic kinematic analysis method for planar link mechanisms based on their unique procedures can clearly show the analysis process. The analysis procedure is expressed by a combination of many kinds of conversion functions proposed as the minimum calculation units for analyzing a part of the mechanism. When it is desired to perform this systematic kinematics analysis for a specific linkage mechanism, expert researchers can accomplish the analysis by searching for the procedure by themselves, however, it is difficult for non-expert users to find the procedure. This paper proposes the automatic procedure extraction algorithm for the systematic kinematic analysis of closed-loop planar link mechanisms. By limiting the types of conversion functions to only geometric calculations that are related to the two-link chain, the analysis procedure can be represented by only one type transformation function, and the procedure extraction algorithm can be described as a algorithm searching computable 2-link chain. The configuration of mechanism is described as the “LJ-matrix”, which shows the relationship of connections between links with pairs. The algorithm consists of four sub-processes, namely, “LJ-matrix generator”, “Solver process”, “Add-link process”, and “Over-constraint resolver”. Inputting the sketch of the mechanism into the proposed algorithm, it automatically extracts unique analysis procedure and generate a kinematic analysis program as a MATLAB code based on it. Several mechanisms are analyzed as examples to show the usefulness of the proposed method.

Physical Scaffolding Accelerates the Evolution of Robot Behavior.

In some evolutionary robotics experiments, evolved robots are transferred from simulation to reality, while sensor/motor data flows back from reality to improve the next transferral. We envision a generalization of this approach: a simulation-to-reality pipeline. In this pipeline, increasingly embodied agents flow up through a sequence of increasingly physically realistic simulators, while data flows back down to improve the next transferral between neighboring simulators; physical reality is the last link in this chain. As a first proof of concept, we introduce a two-link chain: A fast yet low-fidelity ( lo-fi) simulator hosts minimally embodied agents, which gradually evolve controllers and morphologies to colonize a slow yet high-fidelity ( hi-fi) simulator. The agents are thus physically scaffolded. We show here that, given the same computational budget, these physically scaffolded robots reach higher performance in the hi-fi simulator than do robots that only evolve in the hi-fi simulator, but only for a sufficiently difficult task. These results suggest that a simulation-to-reality pipeline may strike a good balance between accelerating evolution in simulation while anchoring the results in reality, free the investigator from having to prespecify the robot's morphology, and pave the way to scalable, automated, robot-generating systems.

Experimental and Simulation Analysis for the Impact of a Two-Link Chain with Granular Matter

The resistance force of the granular matter is modeled as a linear superposition of a static (quadratic depth-dependent) resistance force and a dynamic (quadratic velocity-dependent) frictional force. The impact is defined from the moment the end point of the system comes in contact with the granular matter surface until the vertical linear velocity of the end point is zero. The variables of interest are the final depth at the end of the penetration phase and the stopping time. The results for a two-link kinematic chain with two points of contact were compared to the results obtained by applying the resistance force formulation developed to corresponding CAD simulation models. The results revealed that the final displacement increases with initial velocity, while the stopping time decreases. The sensitivity to the initial velocity was studied and an improvement to the resistance force formulated as a result. A series of expressions are proposed for the resistance force coefficients.

Simultaneous Impact of a Two-Link Chain

The study of the planar collisions of a rigid two-link chain with an external surface is presented. There are two points of contact during the impact process with friction, one for each link. For the normal impact, a nonlinear collision force is employed for the elasto-plastic deformation, and the Coulomb’s law models the frictional effects. The impact of the chain is studied numerically, and the results are compared with experiment data obtained from a high-speed camera. Special attention is given to simultaneous impact, slippage, and rebounds at the contact points.

The use of an incremental repeated acquisition task to assess learning in children

The development of valid animal models of learning is especially important since learning is critical for nearly all aspects of human behavior and identifying appropriate surrogates provides additional opportunity to study various aspects of learning. Examining the factors that affect learning is often complicated by the need to administer the same task repeatedly across experimental conditions. Incremental repeated acquisition (IRA) tasks have been used extensively in animal research because they circumvent this problem by requiring a subject to learn different response chains repeatedly across sessions. The present study examined the association of age, sex of the participant, and IQ on the performance of an incremental repeated acquisition task in 837 children, aged 5-13 years. This task required children to learn to press four response levers in a specific sequence that was randomly chosen. Illumination of colored indicator lights signaled position in the required response chain. Initially, for the first link, only one of the four levers was correct: a response to it resulted in the delivery of a monetary reinforcer (5 cents). After mastery of the first link (i.e. three correct presses), the children were presented with a two-link response chain: a different lever had to be pressed before pressing the previously correct lever. After mastery of the two-link chain, the response chain length was once again increased, and so on until a response chain consisting of six links was completed or until the task timed out. Older children and children with higher IQs mastered longer response chain lengths and were more accurate in performance of this learning task than younger children. In addition, older children and children with higher IQs had higher effective response rates and lower ineffective response rates. No significant effects of the sex of the participant were demonstrated for any of the variables on this task, except overall response rate. The results indicate that this test is sensitive to developmental variables in children, with the degree of sensitivity of certain dependent variables being age-dependent. Characterization of performance of this task by humans facilitates comparisons with animal models employing the same task, thus enhancing its translational utility.

Interrupted super framework of the crystal structure of Cs[Be2(PO4)(PO4H)] cesium diberyllium phosphate hydrophosphate

The crystal structure of cesium diberyllium phosphate hydrophosphate Cs[Be2(PO4)(PO4H)] obtained hydrothermally is analyzed. Unit cell parameters are: a = 4.8860(5) A, b = 10.7330(11) A, c = 13.0061(15) A, α = 92.540(10)°, β = 92.451(9)°, γ = 90.948(9)°, space group P\( \bar 1 \). In the structural motif consisting of PO4 and BeO4 tetrahedra, Be,P two-link chains and ribbons are distinguished, typical of a short a-translation of ≈4.9 A. The presence of ternary and terminal O ligands along with bridging ones determines the term interrupted super framework. The group of two Be tetrahedra with a common edge is detected for beryllium phosphates for the first time.

Stationary Configurations of a Tetrahedral Tethered Satellite Formation

O RBITAL dynamics analysis of a connected multibody system is relevant for several missions, including tethered systems, space robots and manipulators, telescopes, space stations, etc. It is important to determine stationary motions of such structures due to their possible use as nominal motions in energy-saving mode. The study of the behavior of multibody systems in the orbital environment continues to grow since its beginning in the 1960s. Sarychev [1] and Wittenburg [2] investigate the equilibria of two connected rigid bodies in circular orbit with respect to the orbital reference frame. Cheng and Liu [3] consider the in-plane dynamics of a three-body systemwith two equal extreme bodies, examining the equilibrium orientations, bifurcations, and stability with respect to in-plane perturbations. Lavagna and Ercoli Finzi describe planar equilibrium configurations [4] and study their stability [5] for an extended rigid body with two pendulums attached either in a sequence or in a parallel scheme. Quite frequently, the orbital dynamics of multibody systems is studied for models that approximate connected satellites by an open chain of material points linked by weightless straight rods with spherical hinges. Misra and Modi [6] develop the general threedimensional formulation for an n-link chain. For twoand three-link systems, they determine the libration frequencies and study the control laws. In [7,8] this model is used to determine in-plane equilibrium configurations of a two-link chain and to study their stability. Sarychev [9] finds all spatial equilibrium orientations of a two-link chain in a circular orbit and describes their number as a function of problem parameters. Continued interest in such studies was confirmed recently by Correa and Gomez [10], who numerically study the equilibrium configurations of a three-link chain in the plane of the orbit and analyze their stability with respect to in-plane perturbations. An analytical study of chains with arbitrary number of links can be found in [11,12]. The center ofmass of the chain (CMC)moves along a circular orbit. All in-plane equilibrium configurations are described in [11]. All spatial equilibria are listed in [12], in which it is shown that each connecting rod can be oriented with respect to the tangent, normal and binormal to the CMC orbit in one of the following ways: 1) A rod is aligned with the tangent axis. 2) A rod belongs to an NBN group, that is, to a subchain of rods that lies in the plane parallel to normal and binormal so that its center of mass is on the tangent axis. 3) A rod links two NBN groups or an end of an NBN group with the tangent axis. Some of these equilibrium configurations are actually twodimensional, with all the system lying in one of the coordinate planes of the orbital reference frame. Yet, there exist essentially threedimensional configurations, for example, with masses placed at the vertices of a tetrahedron. Tetrahedral satellite formations are of significant interest due to numerous applications and many projects under development, including NASA research programs in formation flying [13–15]. Tetrahedral configuration has been successfully implemented in the Cluster mission to study three-dimensional structure of the Earth’s magnetosphere [16]. Being the simplest spatial configuration, a tetrahedral formation is a natural tool in experiments of this kind, because it enables one to execute simultaneous measurements at points of a large-span three-dimensional basis. In the present article, we apply the general results of [12] to study tetrahedral equilibrium configurations of a tethered satellite system. We identify the spectrum of spatial equilibrium configurations that can be achieved by varying the masses of the bodies and lengths of the rods.We determine the links that can be replacedwith tethers.We study the possibility of controlling such a system and of stabilizing its orientation.

Effect of unsignaled delays between stimuli in a chain schedule on responding and resistance to change

Behavioral momentum theory is an evolving theoretical account of the strength of behavior. One challenge for the theory is determining the role of signal stimuli in determining response strength. This study evaluated the effect of an unsignaled delay between the initial link and terminal link of a two-link chain schedule on resistance to change using a multiple schedule of reinforcement. Pigeons were presented two different signaled delay to reinforcement schedules. Both schedules employed a two-link chain schedule with a variable interval 120-s initial link followed by a 5-s fixed time terminal link schedule. One of the schedules included a 5-s unsignaled delay between the initial link and the terminal link. Resistance to change was assessed with two separate disruption procedures: extinction and adding a variable time 20-s schedule of reinforcement to the inter-component interval. Baseline responding was lower in the schedule with the unsignaled delay but resistance to change for the initial link was unaffected by the unsignaled delay. The results suggest that not all unsignaled delays are equal in their effect on resistance to change.

Effect of signaling reinforcement on resistance to change in a multiple schedule

This study evaluated the effect of a signal on resistance to change using a multiple schedule of reinforcement. Experiment 1 presented pigeons with three schedules: a signaled delay to reinforcement schedule (a two-link chain schedule with a variable-interval 120-s initial link followed by a 5-s fixed-time schedule), an unsignaled delay schedule (a comparable two-link tandem schedule), and an immediate, zero-delay variable-interval 125-s schedule. Two separate disruption procedures assessed resistance to change: extinction and adding a variable-time 20-s schedule of reinforcement to the inter-component interval. Resistance to change tests were conducted twice, once with the signal stimulus (the terminal link of the chain schedule) present and once with it absent. Results from both disruption procedures showed that signal absence reduced resistance to change for the pre-signal stimulus. In probe choice tests subjects strongly preferred the signal stimulus over the unsignaled stimulus and exhibited no reliable preference when given a choice between the signal stimulus and immediate stimulus. Experiment 2 presented two equal signaled schedules where, during resistance to change tests, the signal remained for one schedule and was removed for the second. Resistance to change was consistently lower when the signal was absent.

Kinetic characteristics of the theoretical ecosystems with different extent of openness

In this paper, the influence of the extent of openness of ecosystem that is defined by the dilution rate, which characterizes the extent of flowage of the pond, on the intensity of the biotic circulation in ecosystems with different regulation types, number of trophic links and extent of closing has been investigated. We considered open systems, we took into account the return of the limiting substances, such as nitrogen and phosphorous, into the cycle by degradation of detritus and products of vital functions of consumers. It was shown by the numerical calculations that the increase of the dilution rate in without recycle ecosystems leads to increase of the net primary production up to the maximum value corresponding to the two-link trophic chain (biogenic substance and producer) and then, to gradually decrease. The residual concentration of biogenic limiting substances monotone increases. Net primary production and residual concentration of biogenic limiting substances in systems with recycle with even number of links behaves similarly to that in without recycle ecosystems. In the systems with recycle with the odd number of links that values lies on the stable level. We showed that in wide range of the dilution rate the recycling of the ecosystem can highly increase the net primary production and reduce residual concentration of biogenic limiting substances. The influence of the dilution rate on numbers of links that may exist in the system was analyzed.

Grashof's Condition of Stephenson-type Planar Six-Link Mechanisms

There exist two, four or six solutions of the output angle of the Stephenson six-link mechanism of type III, which is composed of the constituent four-link mechanism and the driving two-link chain, for any value of the input angle. These solutions correspond to link-chain configurations in different domains of motion of the driving link. Domains of motion are corresponded to either parts of the coupler curve of the constituent four-link mechanism which are separated by two limit points or connections of two parts separated by limit and turning points, or the coupler curve or its parts separated by two turning points. So, domains of motion are mapped on four number-lines of the input angle which are discriminated by the sign of the determinant of the equations of the velocity analysis and the sign of the sine of the relative angle of the driving two-link chain. Consequently, all relationships between input and output angles are calculated as a continuous function. In this paper, the identification method of the domains of motion is expanded the grashof's condition, that is, the algorithm for judging whether the driving link can make a continuous rotation in one direction or not.

The Matsumoto-Yor property on trees

Viewing the Matsumoto-Yor property as a bivariate property with respect to the simple tree with two vertices and one edge, we extend it to a p-variate property with respect to any tree with p vertices. The converse of the Matsumoto-Yor property, which characterizes the product of a gamma and a generalized inverse Gaussian distribution, is extended to characterize the product of a gamma and p - 1 generalized inverse Gaussian distributions. A striking feature of this characterization is that we need the independence of the components of random vectors corresponding only to the leaves of the tree. We illustrate our results with two particular trees: the two-link chain and the three-branch 'daisy'.

Crystal structure of urusovite Cu[AlAsO5: A new type of a tetrahedral aluminoarsenate polyanion

The crystal structure of the new mineral urusovite Cu[AlAsO5] has been determined (monoclinic system, sp. gr. P21/c, a = 7.335(1) A, b = 10.255(1) A, c = 5.599(1) A, β = 99.79(1)°, V = 415.0(1) A3, Z = 4). The structure is solved by direct methods and refined to R = 0.048 (wR = 0.103). The structure is built by open-branched {uB, ∞ 2 } [AlAsO5]2− layers parallel to the (100) plane. The layers consist of two-link chains of ∞ 1 [Al2O6] tetrahedra, which are parallel to the z-axis and are connected through the [AsO4]-groups. The sharing-edges [CuO5] tetragonal pyramids link the aluminoarsenate layers to form a three-dimensional framework. The established layer is the second example of an tetrahedral aluminoarsenate polyanion.

Growth, knowledge transfer and European integration

It has been suggested that members in the EC or the EFTA experienced significantly higher growth rates compared to nonmember countries. This suggests that the European integration either captures omitted variables or that it gives rise to increased growth rates through enhanced investment and/or increased knowledge transfer. The present study attempts to resolve this issue. The analysis identifies a two-link chain between European integration (EI) and growth through investment. In addition, on examining whether there are any knowledge spillovers resulting from integration it is found that integrated countries do in fact experience more knowledge spillovers compared to nonintegrated countries. Employing both the neoclassical and endogenous growth approaches, it is found that trade variables are especially important for growth in Total Factor Productivity (TFP). The study is undertaken for a panel sample consisting of 20 OECD countries and covering three time periods between 1976 and 1990. Special emphasis is placed on specification and sensitivity analysis.

Kinematic Analysis of Spatial 7R Link Couplings.

The spatial 7R link mechanism can be used as a shaft coupling which transmits a rotational motion and a troque with constant velocity between two intersecting shafts. Because this shaft coupling is a non-self-supporting type, the kinematic constants of the stationary link as the 7R 7-link mechanism are determind from the relative position between the adjustable input and output axes. The influence coefficients of kinematic constants of the spatial two-link chain to support the input and output axes are analyzed and the error characteristics of the 7R 7-link coupling is investigated theoretically and experimentally.

Nonlinear strain-displacement relations and flexible multibody dynamics

This paper considers dynamics of chains of flexible bodies undergoing large rigid body motions but small elastic deflections. The role of nonlinear strain-displacement relations in the development of the motion equations correct to first order in elastic deflections is investigated. The general form of these equations linearized only in the small elastic deflections is presented, and the relative significance of various nonlinear terms is studied both analytically and through the use of numerical simulations. Numerical simulations are performed for a two-link chain constrained to move in the plane, subject to hinge torques. Each link is modeled as a thin beam. Slew maneuver simulation results are compared for models with and without properly modeled kinematics of deformation. The goal of this case study is to quantify the importance of the terms in the equations of motion that arise from the inclusion of nonlinear strain-displacement relations. It is concluded that unless the consistently linearized equations in elastic deflections and their time rates of change are available and necessary, the inconsistently (prematurely) linearized equations should be replaced in all cases by ruthlessly linearized equations, equations in which all nonlinear terms involving the elastic deflections and their time rates of change are ignored.

Automatic classification of coupler curves of planar six-link mechanisms of the Watt-type. (1st Report. Node and curvature-curve).

A method for determining the nodes, the inflection points, and the maximum-and minimum-curvature points of the coupler curves of Watt six-link mechanisms is proposed for the purpose of their automatic classification. The double points of the coupler curves of mechanisms, in which the fixed and driving links are the binary links or the binary and ternary links, are determined respectively as the points that the two-link chain or the compound three-link chain, in which the end pairing points are the fixed pairing point and the coupler point, can locate their inverse positions. The nodes are distinguished by two relative angles of the component two-link chains from the ordinary intersections. A curve of the curvature of the coupler curve is presented in order to determine the remaining characteristic points and to describe the properties of the coupler curve as a single-valued function.

A displacement analysis of complex six-link mechanisms of the Stephenson-type.

A new method of displacement analysis for complex six-link mechanisms of the Stephenson-type, which are composed of only turning pairs or one sliding and six turning pairs, is developed for the purpose of automatic calculations of kinematic properties. First, the displacements of the links of twenty-three kinds of mechanisms are calculated by the formulas for the geometric analysis of two kinds of five-link structures. Then, the equation of sixth degree is solved by the Strum theorem and the Ferrari method. Second, the composition loops and domains of motion of the driving link are discriminated by domains on four number lines, which are separated on the basis of the limit-positions of motion of the driving link and the special positions of component four- and two-link chains. This discrimination algorithm can also be used as the Grashof condition of complex six-link mechanisms.

A nonlinear canonical correlation analysis of weekly trip chaining behaviour

This research concerns the relationships between the patterns of activities pursued in home-based trip chains and the characteristics of the persons making the chains. The data source is a one-week travel diary reported by persons over 11 years of age in the Netherlands in 1984. All home-based trip chains, including both simple two-link chains and more complex ones, were classified on the basis of the sequence of away-from-home activities. Twenty types were distinguished. The presence or absence of these trip-chain types were then explained in terms of the personal and household characteristics of the travellers using nonlinear canonical correlation analysis. This analysis technique can accomodate multiple dependent variables and nominally-scaled (categorical) variables in both the independent and dependent variables sets. Determined are the category scores for each independent variable that are optimal in explaining patterns in the dependent chain-type variables. Also determined are the optimal combinations of the two variable sets. These results capture the relationships between the sequences of activities in trip chains and the variables age, sex, working status, household income, stage in the family life cycle, household car ownership, and residential location. The most effective variable was found to be life cycle, followed by age and income.