Kinematic analysis of a deployable truss structure with flat-form storability

A technique is introduced for the kinematic synthesis of deployable cable-stiffened truss structures. This technique, which is an extension of a prior procedure [l-21 for generating deployable truss structures, can be applied to generate all concepts of cable-stiffened truss structures as well as all their deployable derivatives. Examples illustrating the implementation of this new technique, along with a discussion of the results achieved. are included in this article. The primary function of a deployable structure is to maintain a stable configuration in its deployed state. This is reflected in current design practices of trading off decreased deployment or retraction performance for increased structural performance. As a result, various designs of deployable truss structures (with, and without cables) have been introduced that are over-constrained during deployment/retraction, i.e. deployment/retraction of these structures can only be achieved through the deformation of individual links or by exploiting symmetric features of the structure. The number of different conceptual designs of deployable structures that are based on a given structural configuration is unlimited, if deployable structures are permitted to be overconstrained during deploymenthetraction. For this reason, researchers in the area of deployable structures have given little attention to the systematic design of deployable truss structures and have instead devoted much of their attention to the introduction and discussion of novel concepts of deployable truss structures [3-171. If, on the other hand, it is assumed that the primary function of a deployable structure is to serve as a mechanism with a minimum number (i.e. at least one) of degrees-of-freedom, then the number of different conceptual designs that are based on a given structural configuration is finite. Hence, it is then possible to generate all possible designs for a given structural configuration. The assumption that a deployable structure is not constrained during deployment/retraction has enabled the development of a technique for the generation of all conceptual designs of deployable truss structures that can be used as building blocks (modules) of much larger structures [I-21. It should be noted that this technique, referred to as kinematic synthesis of * Sr. Mechanical Engineer, Member AIAA deployable structures, does not assume that the structural configuration is known but instead uses the characteristics of a given class of structures (i.e. truss modules) to generate all possible configurations of structures in this class. The limitation of this technique to truss modules has been avoided in the Explosion-Implosion technique [19], developed by the same authors, for the generation of allconceptual designs of deployable truss structures of which the locations of the nodes are known. Both techniques have been shown to result in the generation of an enormous, yet finite, number of novel conceptual designs as well as those that have been reported in the literature. Furthermore, by limiting the degrees-of-freedom available at individual joints, conceptual designs can be generated of deployable structures that are overconstrained during deployment/retraction. Although the kinematic synthesis technique and the explosionimplosion technique result in the generation of an enormous number of conceptual designs of deployable truss structures, they are not applicable to truss structures with cables. Yet, cable-stiffened truss structures have important advantages such as the reduction in mass and/or reduction in joints that can be achieved by replacing links in truss structures with cables. The objective of this article is to modify the technique introduced in [I-21 such that the new technique is also applicable to cablestiffened truss structures. This new approach can then be applied to generate novel concepts of deployablecable-stiffened truss structures as well as those that have been reported in the literature.

The inter-connectivity and type selection of joints in a mechanism can be represented by a graph. In this article a technique is presented for the generation of such a graph for a (spatial) deployable truss structure. First a fundamental graph is constructed which reveals all possible joint connections in a deployable structure. This graph, which can be derived from the geometry of a deployable structure, is then reduced to the graph of the kinematic structure (revealing the joint inter-connectivity) by applying a set of rules. The process of joint specification is completed by assigning joint types to edges in the graph such that the required mobility of the deployable structure it represents is ensured. Procedures are provided that incorperate the techniques introduced in this article and which can be used to generate all possible joint assignments for a given deployable structure.

Scissor-like element has a number of applications in deployable structures such as planar deployable structure (PDS) and ring deployable structure(RDS). However, the mobility analysis of the multi-loop deployable structures is made more difficulty by the traditional mobility formula, because the deployable structure is a very complex structure with multi-loop. Therefore, On the basis of screw theory, the calculation method of mobility of deployable structures of SLE is thoroughly discussed. In order to investigate the mobility, decomposing and composing structures(DCS) are developed, and the basic units are able to be obtained. On the basis of the deployable structures’ geometrical characteristics, there exists a closed-loop quadrilateral structure and some non-closed-loop quadrilateral structures in PDS. Also, a six legs parallel structure is present in RDS. The basic units’ mobility can be solved by both the methods of screw theory and topology constraint graphs. Then, composing the related basic units, the formula of planar deployable structures’ mobility can be built and solves the mobility of ring deployable structure. The analysis method solves the mobility analysis of the multi-loop deployable structures which is difficulty by the traditional method, and plays an important role in further research about the mobility of other complex deployable structures.

Kinematic of symmetric deployable scissor-hinge structures with integral mechanism mode

Deployable bundle modulus structures with reciprocal linkages for emergency buildings

Vibration isolation and precision pointing control will be essential to the success of future space science missions such as Next Generation Space Telescope (NGST). This research investigated the use of actively controlled piezoelectric stack actuators to reduce the transmission of mechanical disturbances to the optics and to coarsely point the telescope. Initial actuator requirements were based on approximate expected motions on the spacecraft side (due to unbalanced reaction wheel assemblies), the structural dynamic properties of the flexible, deployable truss structure that supports the active optics, and the allowable motions on the telescope side. Piezoelectric actuator design was based on flextensional motion amplification, with sizing details determined using results from finite element analysis. A compressive pre-load was maintained on the fragile piezoceramic stacks via a mechanical interference (center block) fit into the actuator frame. Device performance characteristics, including blocked force, passive stiffness, free displacement, motion amplification factor, natural vibration frequencies, and electromechanical coupling coefficient were determined numerically and experimentally, with good agreement. An initial controlled isolation test of the entire system reduced the transmissibility by more than 80% over the frequency range from 4-20 Hz. Finally, an active isolation system with dual sensor feedback was implemented and shown to successfully reduce telescope motion by a factor of 10 (from 4-40 Hz) and to provide lower-frequency pointing capability. Introduction As space systems continue to grow in complexity and require greater precision, piezoelectric materials will be investigated for an increasing number of actuator applications, including precision pointing and vibration isolation and control. There are several approaches to vibration isolation, which have been successful in the past. Vibration isolation can be achieved through passive or active techniques or a combination of the two. The chosen method of isolation depends primarily on the application and requirements of the system. Precision pointing, on the other hand, is achieved solely by active control systems, which combine the necessary structural and mechanical components with a control design. Pointing systems are primarily limited by the quality of the mechanical system as well as the drive system, which is actuating movement. The structure (holding the pay load) to be controlled can be a rigid body, quasi-static flexible body, or a dynamic flexible body. With the classical arrangements of sensors and actuators in these control systems, only the rigid body configuration is commonly controlled. NGST (Next Generation Space Telescope) is the successor to the Hubble Space Telescope (HST) mission. NGST is a deployable 8-meter diameter truss structure holding the telescope and instruments such as cameras and spectrometers that are required by the scientific goals of the mission. In order to meet the scientific goals or projects such as the Origins of Galaxies studies [Mather, et al] along with independent science projects dealing with current scientific interests, positioning the optics and minimizing vibratory loads are very important. Positioning control for the HST was done as a rigid structure pointed as a unit to a precision of a small fraction of an arcsecond, but NGST is a dynamic flexible structure with sub-micron positioning performance. For NGST, the isolation system is to be used to reduce the ultrafine pointing requirements on the fine pointing system (fast steering mirror and adjusters distributed across the mirror) by as much as 1 2 orders of magnitude. This isolation system is aimed to reduce the estimated 30-nm peak disturbances at the mast to 6-nm or less in a range of 4 4 0 Hz, with most concern on the 15 20 Hz region. By substantially reducing these axial disturbances, the dynamic, wavefront error correction requirements will also be reduced, and the fine pointing system will have less of a burden. In order to achieve these requirements, piezoelectric stack actuators are ideal because they can provide sufficiently high output forces with large bandwidths. Individually, piezoelectric stack displacements are extremely small, on the order of approximately 2000 jiie; therefore, multiple stacks can be used in series to produce the desired output. In addition to this, mechanical amplification devices can be used to increase actuation displacement by reducing the actuation force. Compliant mechanisms, flexurehinged mechanisms and flextensional mechanisms Copyright © 2001 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved. (c)2001 American Institute of Aeronautics & Astronautics or Published with Permission of Author(s) and/or Author(s)' Sponsoring Organization. are commonly used for motion amplification, depending on the application. The flextensional actuator used in this research is shown in Figure I and consists of four stacks of piezoceramics connected in parallel to a flextensional mechanism that amplifies and converts the output

This paper aims at investigating precisely the dynamic performance of deployable structure constituted by scissor unit mechanisms with clearance joint. Based on the motion law in real joints, the contact model is established using an improved Gonthier nonlinear continuous contact force model, and the friction effect is considered using LuGre model. Moreover, the resulting contact force is suitable to be included into the generalized force of the equations of motion of a multibody system and contributes to replace motion constraints. In the sequel of this process, the effect of joint clearance is successfully introduced into the dynamical model of scissor deployable structure and the dynamic characteristics of deployable structure with joint clearance are obtained using a direct default correction method, which can directly modify the coordinates and speed of the system to avoid the numerical results divergence. Also, the new hybrid contact force model of revolute joint clearance is verified through comparing with the original model. The numerical simulation results show that the improved contact model proposed here has the great merit that predicts the dynamic behavior of scissor deployable structure with joint clearance.

In this paper, the dynamic behaviors of a elastic rod connected by a joint with clearance of deployable truss structures are investigated. A one-dimensional cantilever with joint support is examined in the deployable truss structure. These formulations consist of the nonlinear joint dynamic stiffness model and damping models are formulated and the dynamic characteristics of free-vibrating structures are estimated. The natural frequency transitions are investigated by considering the contact and noncontact conditions of the clearances, then the formulation of dynamic stiffness model is obtained. The friction models are mathematically formulated and simplified to make them easy to calculate. The impact damping models are formulated using the linear envelope of the time response and it can be negligible when the speed is small. The dynamic characteristics can be estimated by integrating these models and formulations using the energy loss factors. Experimental evaluations show the dynamic characteristics and demonstrate the validity of the formulations.

An experimental investigation on the Half Scissor-Like Elements (H-SLEs) mechanism deployable structure under compression axial load is presented. Two prefab cylindrical shape H-SLEs mechanism deployable steel structures namely M1 (Bolted base column) and model M2 (Unbolted base column) were tested on their performance in term of strength and stability performance. The model prototype consists coldformed and hot roll steel with bolted connection and tested at deployed vertical configuration. Compression axial load was applied at the middle top of loading platform, transferred equally to the six H-SLEs deployable mechanism through supporting beams. The experimental results obtained indicated that three types of failure modes, i.e. excessive bearing capacity failure at lipped C-section flange around bolt hole perimeter, instability due to horizontal displacement at mid-height of H-SLEs deployable mechanism (Bolted joint area) and member buckling. Among these failures, horizontal displacement nominated the overall structure stability while section thickness impacts member bucking and bearing capacity. The experimental ultimate load was 1.63% greater than BS EN 1993 design load resistance for M1 condition while 30% less for M2 condition. The applied load difference between these two model prototypes was 31.15%. Thus, M1 ultimate loads capacity was satisfactory since less than 15% acceptable level while M2 not satisfactory. Beside, horizontal displacement was identify highly impacted scissor mechanism deployable structure instability and suitable member thickness may avoid section premature failure.

Deployment analysis of large space antenna using flexible multibody dynamics simulation

In this paper, an evolutionary optimization method is presented for weight minimum problem of a 3-dimensional truss structure in terms of nodal coordinates and element cross-sectional areas. The structure is subject to stress, local buckling and displacement constraints. Two types of design variables with different natures are optimized separately: (1) a fully stressed design (FSD) and scaling techniques are applied to sizing variables and (2) the evolutionary node shift method is applied to shape variables. Alternating procedure is utilized to couple the two types of variables and to combine the results. The optimum solution is achieved gradually from the initial configuration design. Two typical truss structures are examined to illustrate the validity of the method.

Design and analysis of scissor-like hoop truss deployable antenna mechanism with arbitrary curvature support ribs

The deployable structure is critical to the overall success of the space mission. This paper introduces a large-scale spatial deployable structure (SDS), which is developed to deploy and support the payload panels in a precise configuration once on the track. And segmental researching in the design, kinematics and dynamics analysis of SDS's prototyping system are presented. Geometric construction method and Bar-groups method are adopted to analysis the dimensions and coordinates of the SDS, which finally construct an well-determined mathematical model to raise the productivity and efficiency during optimization and analysis work. Be reasoned with the large-scale of the truss structures, flexible multibody dynamic simulations are developed, which present much more authentic stress transfer and kinematics behaviors. According to the deployment experiments of SDS's prototyping system, the correctness and validity of the flexible multibody simulation work are well proved.

Furlable structures are a class of deployable structures that utilize distributed material strain as a means for compact packaging. Elastic Memory Composite (EMC) materials are ideally suited for furlable structures because they offer high strength, stiffness, and strain capacity for efficient packaging and deployed structural performance. EMC components are packaged in their soft-resin state, which enables higher packaging strains than traditional hard-resin composites. For example, packaging strains on the order of 2-5% are commonly achieved in carbon-fiber-reinforced EMC materials whereas non-EMC, carbon-fiber composites are limited to less than 1% strain. The present paper summarizes two recent advancements in the state-of-the-art of EMC materials: 1) improvments to the design of EMC longerons, key structural elements in furlable truss booms, and 2) advancements in analytical models for EMC material behavior through the use of a Multicontinuum Theory. Preliminary results are presented that illustrate the significant potential for these advancements to further improve the performance and capability of furlable EMC space structures.

In this study, a passive truss-link mechanism applicable to large-scale deployable structures was designed to achieve successful deployment in space. First, we simplified the selected truss-link mechanisms to the two-dimensional geometry and calculated the degrees of freedom (DOF) to determine whether a kinematic over-constraint occurs. The dimensions of the truss-link structure were determined through a deployment kinematic analysis. Second, a deployment simulation with the truss-link was conducted using multibody dynamics (MBD) software. Finally, a deployment test was performed considering gravity compensation, and the results were compared with those of MBD simulation. The results of the deployment simulations were confirmed to be slightly faster than those of the deployment test due to friction effects existing in the joints and gravity compensation devices. To address this issue, inverse identification of the equivalent frictional torque (EFT) at the revolute joints in the deployment test was conducted through response surface methods (RSM) combined with the central composite design technique. As a result, we confirmed that the deployment angle history of the deployment simulation was similar to that of the deployment test.