Variable Geometry Truss Research Articles

A hyper-redundant manipulator

Hyper-redundant manipulators have a very large number of actuatable degrees of freedom. The benefits of hyper-redundant robots include the ability to avoid obstacles, increased robustness with respect to mechanical failure, and the ability to perform new forms of robot locomotion and grasping. The authors examine hyper-redundant manipulator design criteria and the physical implementation of one particular design: a variable geometry truss. >

Concepts of Deployable Space Structures

This paper presents several concepts of deployable space structures with emphasis on their relation to the basic principles of mechanics on which the concepts depend. The following subjects are treated: the coilable longeron extendible mast and the theory of “Elastica” by Euler and Kirchhoff; the two-dimensionally deployable array and the theory of elastic surfaces (“Plate Elastica”) by Miura and Tanizawa; the variable geometry truss and the theory of truss by Mobius; the tension truss antenna and the theory of truss.

Application of New Homotopy Continuation Techniques to Variable Geometry Trusses

A VGT, or Variable Geometry Truss, can be thought of as a statically determinate truss that has been modified to contain some number of variable length members. These extensible members allow the truss to vary its configuration in a controlled manner. Some of the typical applications envisioned for VGTs are as booms to position equipment in space, as supports for space antennae, and as berthing devices. Recently, they have also been proposed as parallel-actuated, long chain, high dexterity manipulators. This paper will demonstrate the use of homotopy continuation in solving the kinematics of relatively complex variable geometry trusses (VGTs) including the octahedron and the decahedron. The procedural aspects are described in detail with the help of examples.

The Inverse Kinematic Solution of the Tetrahedron Based Variable-Geometry Truss Manipulator

The Tetrahedron Based Variable Geometry Truss Manipulator is comprised of a series of tetrahedrons stacked upon one another in a spiraling manner. When one link of each “cell” is made variable in length, the system can be effectively used as a remote manipulator. The manipulator is kinematically equivalent to a serial link manipulator consisting only of revolute joints where the angle between successive axes is 120°. In this paper, a closed-form analytic solution for the six-celled (6R series) variable geometry truss manipulator is obtained. It is shown that a sixteenth order polynomial in one of the joint angles is found which leads to at most sixteen solutions.

Closed-Form Inverse Kinematic Analysis of Variable-Geometry Truss Manipulators

A variety of applications for variable-geometry truss manipulators (VGTMs) have been demonstrated or proposed in the literature. Most of these applications require solution to the inverse kinematic problem, yet only a few isolated examples of closed-form solution methods have been presented to date. This paper provides an overview to the general problem of inverse kinematic analysis of variable-geometry truss manipulators and presents new closed-form solution techniques for problems of practical importance.

Adaptive Structures Research at ISAS, 1984-1990

This article reviews the research and development on adaptive structures and intelligent structural systems done by the structures and structural dynamic group at the Institute of Space and Astronautical Science (ISAS) from 1984 to 1990. Our activity is closely linked to the practical needs for actively controlled structures on board scientific satellites and interplanetary vehicles which ISAS launches annually. The subjects described here are: the proposal of novel structural concepts such as the variable geometry truss, the adaptive structure and the tension truss antenna; the proposal of vibration control schemes for flexible structures and the shape control scheme for precision antenna reflectors; and the study on construction of large space structures by assembling adaptive structures.

Control of Intelligent Adaptive Structures. 2nd Report. Hardware Experiments of Optimal Trajectory Control.

This paper is concerned with an experimental study on optimal trajectory control of a variable geometry truss, which is one of the intelligent truss structures composed of a truss-type mechanism. The intelligent structure considered here is assumed to have many sensors and actuators. Thus, the intelligent structure utilized as a manipulator arm has high redundancy. In the first report, two efficient methods were proposed for manipulation trajectory control under the relaxed conditions of optimality, and the validity of the proposed methods is demonstrated through numerical simulations. In this study, the proposed methods are applied to a hardware experiment. The experimental results confirm the validity of the proposed control methods. Also, it is shown that an optical sensor feedback is effective for the precise control of the position and orientation of the end tip of the trus along the trajectory, even when these controllers have some modeling errors.

Shape Synthesis and Optimization Using Intrinsic Geometry

The present paper outlines a method of shape synthesis using intrinsic geometry to be used for two-dimensional shape optimization problems. It is observed that the shape of a curve can be defined in terms of intrinsic parameters such as the curvature as a function of the arc lenght. The method of shape synthesis, proposed here, consists of selecting a shape model, defining a set of shape design variables and then evaluating Cartesian coordinates of a curve. A shape model is conceived as a set of continuous piecewise linear segments of the curvature; each segment defined as a function of the arc length. The shape design variables are the values of curvature and/or arc lengths at some of the end-points of the linear segments. The proposed method of shape synthesis and optimization is general in nature. It has been shown how the proposed method can be used to find the optimal shape of a planar Variable Geometry Truss (VGT) manipulator for a prespecified position and orientation of the end-effector.

A Comparison of Actuators for Vibration Control of the Planar Vibrations of a Flexible Cantilevered Beam

The methods and results of an analytical study comparing the effectiveness of four actuators in damping the vibrations of a planar clamped-free beam are presented. The actuators studied are two inertia-type actuators, the proof mass and reaction wheel, and two variable geometry trusses, the planar truss and the planar truss proof mass (a combination variable geometry truss/inertia-type actuator). Actuator parameters and loca tions used in the models were chosen based on the results of a parametric study. A full- state, LQR optimal feedback control law was used for control in each system. Numerical simulations of each beam/actuator system were performed in response to initial condition inputs. These simulations provided information such as time response of the closed-loop system and damping provided to the beam. This information can be used to determine the "best" actuator for a given purpose.

Forward and Inverse Kinematic Solution of the Variable Geometry Truss Robot Based on an N-Celled Tetrahedron-Tetrahedron Truss

The Tetrahedron-Tetrahedron truss (or TT truss for short) has exceptional stability, stiffness, and load-carrying capabilities. Because of this fact, the TT truss is well suited for use as a variable geometry truss manipulator (VGTM) by appropriately choosing certain links whose variable lengths can be controlled. Since the TT truss is composed of n-cells, its applications include the retrieval of equipment, bridges over and around obstacles, and applications which utilize collapsible programmable structures capable of relatively large displacements. In this paper an actuation scheme and the general solution to the forward and inverse kinematics problems for an n-celled TT truss are presented. Numerical examples are also presented.

Variable geometry truss and its application to deployable truss and space crane arm

The purpose of this paper is to describe the variable-geometry-truss concept and to discuss its applications to deployable linear and curvilinear trusses and a manipulator arm. The variable geometry truss consists of the repetition of an octahedral truss module longitudinally. The geometrical transformation of an octahedron is the basis of the present concept. The principal mechanical feature of the truss is that the lateral members of the truss are variable length beams, while the diagonal members are fixed length beams. Through such mechanisms, the truss can be transformed to varieties of configurations. Both simultaneous and sequential modes for transformation, that is, deployment are shown. An application of the concept to a manipulator arm having multiple degrees of freedom is discussed. The resulting VGT-manipulator can be programmed to retreat and deploy and take a position in any desired configuration. The basic kinematic geometry of the VGT manipulator is established.