Variable Geometry Truss Research Articles

Visual Information System for Autonomous Space Docking System Using VGT.

In an autonomous space docking system using a variable geometry truss (VG-T), a docking port is controlled to a direction of a target satellite approaching with various postures and velocities. Consequently, the motion of the target has to be identified, where the target is to be measured at the position apart from the docking system. This paper is concerned with three dimensional measurement of the position and posture of the target as well as the object recognition by using a stereo vision. A hierarchical shape description graph is introduced to perform the stereo matching and model matching efficiently. The normalized fitting function is introduced to reduce an error of the model matching. If values of the fitting function for all of the database model are lower than a threshold value, the object is treated as an obstacle. The efficiency of the proposed system is demonstrated by an experiment.

Optimum Posture Determination of Variable Geometry Truss Structures by Optimality Criteria Method.

This paper describes optimum posture determination of variable geometry truss structures by optimality criteria method. A minimum compliance posture of variable geometry trusses for a given working load vector is realized by adjusting variable elements, where the adjusting control values are determined independently according to optimality criteria transformed from strain energy equation in advance. The validity of optimum posture determination by optimality criteria is confirmed numerically by applying it to the configuration control of a pair of variable geometry trusses containing ten adjustable elements for cooperative work.

Maximizing Kinematic Motion for a 3-DOF VGT Module

This article presents design results for maximizing kinematic motion range in three-degree-of-freedom (DOF) double-octahedral variable-geometry-truss (VGT) modules modeled as extensible gimbals. Design curves are presented to describe motion and results are summarized.

Acquisition of Autonomous Distributed Rule for Posture Control of Variable Geometry Truss by Genetic Programming.

An acquisition technique of autonomous distributed rule for posture control of Variable Geometry Truss (VGT) is suggested by applying the Genetic Programming (GP) method. Each control rule produced by GP consists of hierarchical tree structures. The main tree structure contains condition trees and rule selection trees as function nodes, and control trees as terminal nodes. The acquisition system trains individual rule by the posture control simulation for the randomly given initial postures, and evaluates the rule by the simulation of given test postures. The validity of the acquisition system is confirmed numerically by applying to the stiffness maximization of ten-module VGT.

Optimum Posture Determination of Adaptive Structure by Genetic Algorithm.

In this paper, Genetic Algorithm (GA) to solve the problem which determines the optimum postures of an adaptive truss structure is proposed. It is difficult to obtain a global solution of posture determination problem on adaptive truss containing many adjustable elements using traditional methods. It is said that the global solution can be found with higher probability by GA. The validity of GA is shown numerically through the application to the configuration control of a variable geometry truss containing ten adjustable elements. This paper particularly discusses the problem about the case that the position of the load is constrained.

Kinematics, statics, and dexterity of planar active structure modules

Construction automation could benefit from long-reach, lightweight, dexterous, strong, and stiff manipulators constructed from active structures (variable geometry trusses). Unfortunately, the few systems actually built to date have not delivered these desired characteristics (two such systems are heavy, slow, not dexterous enough, and too flexible) due to lack of unified, integrated, optimized design. This article presents a first step for integrated kinematic, static, dynamic, and control constraints in structural optimization. Workspace area, end-link angle, extension ratio, dexterity, and static loading are all considered in comparisons of basic planar active structure modules which could be used as joints in 3D active structures for construction automation.

Control Experiments of a Docking Mechanism Composed of a Planar Variable Geometry Truss

This paper addresses an experimental docking system using a variable geometry truss (VGT), which is a kind of intelligent adaptive structures. The experimental system is composed of a docking mechanism, a frictionless table system, a computer system, and a vision sensor system. By using the developed experimental system, a PD-control and a computed torque method (CTM) are examined. The dynamics-based control, CTM, shows the superiority over the kinematics-based PD control. This paper proposes a resolved acceleration control (RAG), i.e., a position control, with redundancy considering. The proposed control scheme can avoid a bad condition caused by the redundancy. The CTM and the RAC use the efficient formulation of inverse dynamics that was proposed for real time controls by the present authors. Feasibility and effectiveness of those methods are examined by numerical simulations and experiments.

An Object Oriented Modeling Approach to Intelligent Variable Geometry Trusses

Since an intelligent variable geometry truss (IVGT) is usually equipped with large numbers of redundant actuators for the sake of providing adaptivity, a distributed control is considered a promising approach to dealing with its motion control. In this case, a modeling approach and an integrated model is a key to constructing distributed control systems from both hardware and software. To this end, this paper proposes an object-oriented modeling approach. Through decomposing the control problem domain underlying VGTs into objects, an object model can be obtained to represent various object abstractions and the relationships among these objects. It is shown in this paper that an object model of VGTs is exactly the integrated model for their knowledge organizations as well as the control architectures. Two control schemes resulting from the object models-a hierarchical distributed control and an autonomous distributed control-are discussed in particular. To verify the concepts addressed in this paper, an experimental prototype of IVGTs was manufactured, with a two-level hierarchical distributed control system equipped. With this prototype, an experiment is carried out, simulating a self-construction of space structures with IVGTs in a null gravity space.

Motion control of free-floating variable geometry truss. I - Kinematics

A variable geometry truss is representative of adaptive structures, whose shape can be intentionally altered through shortening or lengthening its adjustable length members, and so has gained some applications in space engineering including space robots, payload isolation, and so on. A new application of variable geometry trusses is proposed, where variable geometry trusses, as components of some larger space structure, might be expected to construct themselves through their adaptivity. Unlike applications such as space manipulators where a variable geometry truss is considered to be fixed on some platform, in this case a variable geometry truss is free floating in three-dimensional space. To this end, the approach on controlling the motion of a free-floating variable geometry truss is discussed from the standpoint of kinematics. Through taking into account the conservation of momentum of the structural system, a family of compact equations is provided to describe the geometry and motion of freefloating variable geometry trusses. Based on the centroid displacement vector d of a variable geometry truss bay, a group of pseudolinear equations for determining the geometry shape of a free-floating variable geometry truss is obtained. With a simple representation for the angular velocity of a variable geometry truss bay, obtained here, the orientation control for the bay's working plane is made possible. Finally, a simulation is performed to demonstrate the validity of the derived equations.

Parallel computing for analysis of variable geometry trusses

A fine-grained parallel algorithm is proposed to perform the integrated geometric/structural analysis of variable geometry trusses (VGTs) with complicated behaviors such as the interaction between the response of an actuator and a member force, and it is implemented to a multiple instruction stream/multiple data stream type parallel computer. One processor is assigned to one truss node, and each node moves synchronously or asynchronously so that its unbalanced nodal force vanishes. The effect of parallel processing is investigated, and the comparison of synchronous and asynchronous algorithms is performed from the viewpoints of processor efficiency, load balance, and interprocessor communications. The parallel integrated structural and geometric analyses of several VGTs are carried out to find the effectiveness of the proposed method.

Large-angle articulated beam truss design methodology considering offset joint modeling

Adaptive space structures (deployable trusses, large space antennas) can use actuated members to vary their geometry. In particular, variable geometry trusses can use the same set of actuators for both deployment and subsequent articulation. Such articulating trusses can be applied in space crane orbital construction applications. Previous structural analyses have used idealized truss models; members connect at a point at each node. Further analysis of practical truss models in articulated geometries will show the difference in structural behavior compared to ideal trusses and the need to include realistic geometric modeling, such as including the hinge offsets to give the correct packaged truss geometry. An analytic example truss verifies the finite element modeling technique used. Stiffness sensitivity trends for a range of articulated geometries reveal two causes of stiffness reduction: decreased truss effective bending inertia because of shortened actuators and batten bending caused by asymmetric geometry and hinge offsets. The analyses lead to a structural design methodology, including an initially curved geometry, to alleviate the stiffness reduction for improved structural performance. The initially curved articulating truss allows the location of maximum stiffness to be designed and provides compact packaging, self-deployment, and geometric articulation. c d[ E F

Motion control of free-floating variable geometry truss. II - Inverse kinematics

The inverse kinematics of a free-floating variable geometry truss are formulated in conjunction with the conservation of momentum, and the Moore-Penrose inverse is employed to give the solution. Based on the generalized Jacobian matrix, a two-order solution of task priority is derived, and its possible applications to obstacle avoidance, shape control, and free-endplane control are also discussed. Moreover, the issues of the dynamic singularities of a free-floating variable geometry truss are addressed, and an approach through actively handling the orientation of the free-endplane of a free-floating variable geometry truss is proposed to reduce the coupling of singularities with its dynamic parameters. With the aim of applications in space engineering, a free-floating variable geometry truss model is manufactured and set up in the laboratory, and a distributed control architecture is constructed to provide it with an effective parallel control. Finally, a docking experiment with this model is carried out.

ロボット研究地図 二次元可変形状トラスの逆動力学計算の効率的定式法

This paper is concerned with an efficient formulation of a planar variable geometry truss (VGT) . Since the VGT has many topological closed-loops, the number of generalized coordinates is less than that of the members. By using a Lagrangian method, an efficient formulation of the inverse dynamics is derived, because the derived equations of motion have a recursive form. Furthermore, the equations have contained the geometric constraints due to the topological closed-loops. The proposed method needs a less number of calculations in comparison with that of the Newton-Euler method. Effectiveness of the proposed method for inverse dynamics is examined by a numerical simulation.

Redundant parallel manipulators

Parallel manipulators are closed-loop mechanisms that feature high nominal load and high positioning ability. Usually, they have the same number of actuators than their degree of freedom, but in some cases, it may be interesting to have more actuators than needed, i.e., to consider redundant parallel manipulators. We will show that redundancy is interesting for solving the forward kinematics, for singularities and obstacle avoidance, for improvement in force control, and for kinematic calibration. Another aspect of redundant parallel manipulators is their use for building variable geometry trusses, i.e., highly redundant spatial structures that may be of interest for spatial applications or for applications where obstacle avoidance is critical. © 1996 John Wiley & Sons, Inc.

Configuration Control of Vaiable-Geometry Truss Structures

The concept of variable-geometry truss structure(VGTS) is introduced as a class of actively controlled adaptive structure. VGTS can purposefully vary its geometric configurations by changing the lengths of some members of the structure. General kinematics and inverse kinematics of a statically determinate VGTS(variable geometry truss structure) are studied. The solution technique is based on the Jacobian matrix obtained via joint equilibrium equations. Pseudoinverse control method is applied to resolve the redundancy of a large VGTS. two types of actuator layout of octahedral type VGTS, VG truss and Stewart platform, are compared. Introducing the concept of performance index, Stewart platform based layout was found to has less consumption energy and manipulation time. A functional VGTS model with 3 octahedral modules is designed and manufactured for the labaratory demonstration. Six vertically located length-variable members are used to create general 6 d.o.f. motions.

知識ベースを用いた可変形状トラスの形態および構造解析

知識ベースを用いた可変形状トラスの形態および構造解析

Posture Determination Technique of Adaptive Truss Structures by Autonomous Distributed Criterion.

An autonomous distributed criterion to determine optimum postures of adaptive truss-type manipulators is suggested. A minimum compliance posture of variable geometry trusses for a given working load vector is realized by adjusting variable elements, where the adjusting values are determined independently according to the strain energy sensitivity of each truss part. The validity of the autonomous criterion is confirmed numerically by applying it to the configuration control of variable geometry truss containing ten adjustable elements.

Dynamics of closed linked variable geometry truss manipulators

This paper presents dynamical characteristics of a variable geometry truss (VGT) manipulator system which consists of a two-dimensional statically determinate truss for space applications. Formulation takes into account geometrical effects of the closed-link constraints, variable length mechanisms, rotational degrees of freedom at the joints and internal control forces; and is developed by Kane's dynamical equations. The conventional formulae of tree-like truss structures are extended to the procedure, which is adapted to statically determine truss structures using a Jacobian matrix derived by geometrical considerations. Inverse kinetics of the variable geometry truss have been formulated considering the minimum norm solution to the equations of motion. A two-dimensional variable geometry truss manipulator is simulated numerically as an example of activities on Space Station. Results show the effects of internal control forces on the attitude of the manipulator system in a space environment, and the characteristics of the inverse kinetics of the manipulator are investigated.

Forward displacement analysis of the decahedral variable geometry truss manipulator

A forward displacement analysis in closed form is performed for the decahedral variable geometry truss manipulator. Based on the simplified geometry model, a system of the constraint equations are formulated. With elimination, this system of equations can be reduced to a 48th degree polynomial equation in one output variable.

Object-oriented approach to modeling and analysis of truss structures

Object-oriented structural and geometric analysis methods for truss structures are proposed. The methods are based on the iterative relaxation of nodal unbalanced forces by moving the nodes. The entities appeared in truss analysis are modeled as classes, and their class hierarchy is established. The knowledge about a truss node, a truss member, a material, and a sectional shape of the member are extracted and constructed as a knowledge base in an object-oriented manner. The object-oriented structural analysis is found to be valid for material and geometric nonlinearities, and the object-oriented geometric analysis where a kinematic problem is converted into a problem for a force equilibrium at the nodes is also found to be effective for determining the geometry of variable geometry trusses. The whole system is written in an object-oriented language, Smalltalk, and several results on structural and geometric analysis are presented. The speed of the computation is discussed along with the size of the structures and the over-relaxation factor. The extension of the knowledge base is also discussed.