小野田 淳次郎

The purpose of this paper is to demonstrate that vibrations of a truss structure can be suppressed nicely by a magneto-rheological (MR) fluid variable damper for semiactive vibration suppression. A variable MR fluid damper was designed and fabricated for this study. The principal characteristics of an MR damper were measured in dynamic tests, and a mathematical model of the damper was proposed. To investigate if the variable damper effectively suppresses the vibration of actual truss structures, semiactive vibration suppression experiments were performed using a cantilevered ten-bay truss beam. The experimental result has shown that the vibration was suppressed nicely by the variable MR damper, and that was compared with that of an electro-rheological (ER) damper investigated in previous research. The MR damper showed a higher performance than that of the ER damper.

A new optimal design methodology is formulated for the placement of piezoelectric actuator and the feedback gains in vibration suppression of flexible structure. For the simultaneously optimal design of the location and sizing of collocated piezoelectric actuator/sensor pairs and the feedback gains, the effect of changes in the mass and the stiffness of the structure by addition of actuator/sensor pairs is considered and combined with control performance index to obtain a composite objective function, and the procedure developed in this paper leads to solutions that are independent of initial conditions of the flexible structure.)Copyright (C) 2001 IFAC.

A liquid-crystal type ER-fluid variable damper was fabricated to semiactively suppress the vibration of space truss structure. The principal characteristics of a liquid-crystal variable damper,cere measured in quasi-static rests, and a simple mathematical Model of the damper was proposed. Semiactive control laws were derived from this model and the LQR theory. Numerical simulations,cere performed to compare the effectiveness of the semiactive vibration suppression using liquid-crystal type and particle-dispersion type ER-fluid variable dampers. The results indicated that the proposed control laws resulted in much better damping performances than is obtained with an optimally tuned passive system. In some cases such as large amplitude vibration, a variable damper using liquid-crystal type ER-fluid showed higher performance than one using particle-dispersion type ER-fluid The results of semiactive vibration suppression experiments with a ten-bay truss beam also demonstrated that the liquid-crystal variable damper effectively suppresses vibration. [S0739-3717(00)00304-4].

The studied damper can be modeled as a variable coulomb-friction damper. The friction in the damper is nut zero, even when no voltage is applied to the electrode of the damper, and is an increasing function of the absolute value of the voltage. Semiactive vibration suppression exploits this variation of friction. To suppress large-amplitude vibrations to small-amplitude ones effectively, we need to vary the friction over a large range. In other words, the ratio of the maximum and minimum values of the frictional force needs to be large. An investigation of decreasing the minimum frictional force by vibrating the electrode of the damper to increase this ratio is reported. The effectiveness of the electrode vibration was demonstrated in static experiments, as well as in semiactive vibration suppression experiments, indicating that electrode vibration reduces the minimum frictional force by 1/3-1/2 without changing the maximum frictional force, thereby greatly reducing the vibration amplitude.

Near optimal design of an open-loop control law for vibration suppression of slewing flexible structures is presented. The control law is derived in modal space. The optimal slewing time is evaluated from the control of the rigid mode of the structure, and for flexible modes, a quadratic control law with free parameters is suggested. Two performance indices which involves system energy and control effort, and control input constraints are derived based on this control law. The vibration suppression of the slewing structures is achieved through the minimization of the performance index subjected to the input constraints. Sequential nonlinear programming is employed in seeking the optimal parameters of the control law. Optimal control of a slewing flexible beam is given to demonstrate the effectiveness of the present proposal. (C) 1998 Elsevier Science Ltd. All rights reserved.

Semiactive vibration suppression with electrorheological (ER)-fluid variable dampers Is proposed and demonstrated to be a robust approach to suppressing the vibration of space structures. The principal characteristics of an ER-fluid variable damper are measured, and a simple mathematical model of the damper is proposed. Based on the mathematical model of the damper, several semiactive on-off control laws are proposed. Their performance is investigated through both numerical simulations and experiments of cantilevered truss beams with ER-fluid variable dampers. Simulation results indicate that most of the proposed laws result in much more effective vibration suppression than is obtained when using an optimally tuned passive system. Under an ill condition, they are also shown to be much more robust than linear quadratic Gaussian active vibration controls whose vibration suppression performance is almost the same. A semiactive vibration suppression experiment with a cantilevered ill-bay truss beam demonstrates that vibrations are suppressed effectively by the ER-fluid variable damper.

This paper presents an open loop near-minimum-time solution for simultaneous slewing and vibration suppression of flexible structures. The problem is formulated as an open-loop, minimum-system energy and/or control effort optimal control problem in modal space. With parametric control law, a two-level problem-solving strategy is presented. In the first stage, a sequence of rigid mode-based time-optimal control problems is solved and the minimum maneuver time is found by gradually reducing the maneuver time until the solution converges. In the second stage, the optimal parameters of the control law are evaluated using nonlinear programming with prescribed performance index as its objective function. The proposed strategy, through time-optimal control of the rigid mode combined with the parametric quadratic control of the elastic modes, determines the control profiles which give both minimum maneuver time and desired value of performance index. As an example, the optimal control of a slewing flexible beam is presented, and high performance slewing maneuver is achieved.

To semi-actively suppress the vibration of space truss structures, a variable damper using electro-rheological (ER) fluid is designed and fabricated. The characteristics of the damper are measured in quasi-static tests, and a simple mathematical model of the damper is proposed. Based on this mathematical model and the LQR control theory, a semi-active control scheme is proposed for vibration suppression. To investigate the performance of the scheme, numerical simulations of the semi-active vibration suppression of a 10-bay truss beam with an ER fluid damper are performed. Simulation results indicate the higher performance of the semi-actively controlled system than the optimally tuned passive system. Vibration tests and semi-active vibration suppression experiments of the 10-bay truss beam with the ER fluid damper are also performed. The characteristics of the damper obtained from the vibration tests are consistent with those from the quasi-static tests. The semi-active vibration suppression experiment results are consistent with the numerical simulation, and demonstrate the effectiveness of the present approach. © 1998 Elsevier Science Ltd. All rights reserved.

The configuration of adaptive structures and the deformation docking used for constructing large space structures is examined, The symmetric adaptive structure, which has symmetric distribution of mass and inertia, is proposed for the deformation docking, In addition, a symmetric motion control is presented, The concept, formulation, and advantages of the symmetric motion control are described, It is shown that there is a reduction of computer requirements, as well as the possibility of obtaining closed-form solutions of workspace, a distribution of singularity points, and a measure of the deformation docking possibility, Numerical and experimental simulations using a four-link structural model are conducted to validate the concepts presented.

A two-dimensionally deployable truss structure is newly proposed for space application, The most significant feature is the small number of mechanisms to be locked when the structure is deployed. its packaging efficiency is shown to be better than that of many known deployable trusses, Several versions of the truss are also proposed. To confirm that the new deployable truss has enough design flexibility, a paraboloidal truss platform is designed fur trial, Furthermore, a numerical investigation shows that the platform is actually deployable and foldable from a practical point of view.

A semiactive vibration suppression approach Is proposed and investigated. It is to control the damping of viscous dampers installed in structures. By using a single-degree-of-freedom (SDOF) example first, vibration damping is shown to be much enhanced by a suitable variation of the damping of the damper according to the phase of vibration. Next, several types of control logic for this approach are proposed, which are applicable to multiple-degree-of-freedom (MDOF) structures with multiple variable dampers. The performance of these types of control logic are investigated by using an SDOF example and an MDOF truss structure example with three variable damping truss members excited by impulsive and random forces. Numerical investigations demonstrate that the vibration suppression capabilities of most of them are much higher than that of the optimally tuned passive system, keeping the robustness of passive systems.

A model reduction method for control system design of large space structures is presented. The control model of the structure is partitioned into several subdomains, and a generalized Craig-Bampton representation is derived. In considering the placement of actuators/sensors that may affect the selection of the candidate modes, the representative degrees of freedom (DOF) of the actuators/sensors are retained as physical DOF in the final coordinate vector. A reduced model for the controller design is obtained based on this representation. As an example, a space truss subject to four actuator forces is analyzed. Comparison with a conventional reduction method based on a complete model of the truss has been made via eigenpairs and dynamic responses. Good agreement is seen to be achieved, and improved accuracy is obtained with the proposed method. The importance of the actuator/sensor related DOF and the effectiveness of the proposed approach in dealing with the very localized DOF are investigated under the extreme condition where only these four actuator/sensor related DOF are considered as the dimension for the model reduction.

This paper proposes using preloaded backlashes to suppress the vibration of truss structures and clarifies the vibration suppression mechanism. With preloaded backlashes, a structure keeps its high stiffness and high static shape accuracy at low external loads and vibration levels. When the response of the structure exceeds a certain level, e.g., allowable level, the joints start slipping, introducing frictional damping and nonlinearity. This nonlinearity transfers energy from lower vibration modes to higher vibration modes. Because higher mode vibrations usually damp sooner, this nonlinear transfer of energy from lower to higher modes results in a quick damping of the entire vibration. Numerical simulations show that energy transfer between the modes drastically enhances the inherent damping capability of the structure. The resulting damping fan be as large as that due to the frictional force at the backlashes, even when the inherent damping ratio of each mode is only 0.2%. The simulation results demonstrate that frictional forces and enhanced inherent damping both suppress vibrations and that they are particularly effective in combination.

This paper proposes using preloaded backlashes to suppress the vibration of truss structures and clarifies the vibration suppression mechanism. With preloaded backlashes, a structure keeps its high stiffness and high static shape accuracy at low external loads and vibration levels. When the response of the structure exceeds a certain level, e.g., allowable level, the joints start slipping, introducing frictional damping and nonlinearity. This nonlinearity transfers energy from lower vibration modes to higher vibration modes. Because higher mode vibrations usually damp sooner, this nonlinear transfer of energy from lower to higher modes results in a quick damping of the entire vibration. Numerical simulations show that energy transfer between the modes drastically enhances the inherent damping capability of the structure. The resulting damping fan be as large as that due to the frictional force at the backlashes, even when the inherent damping ratio of each mode is only 0.2%. The simulation results demonstrate that frictional forces and enhanced inherent damping both suppress vibrations and that they are particularly effective in combination.

As a new method for gravity compensation in two dimensions, it is proposed to decrease the time-average friction by use of in-plane vibration. This dither effect is investigated by using a mass that slides at a constant velocity on a level in-plane vibrating table, Its usefulness is further demonstrated by an experiment. An application of the method to gravity compensation is introduced. A motion test of a link structural model with ball-bearing supports and a level in-plane vibrating table is conducted to evaluate the performance. Experimental results show that the structure slides on the table with a drag-to-weight ratio of about 10(-3) and drag-induced accelerations of about 10(-3)g.

An approach for semiactive vibration suppression of truss structures by means of dry friction is proposed and evaluated. The present approach employs frictional truss members and adaptively controls the frictional forces according to the vibration condition. Because of the passive nature, the resulting system is always stable and requires neither high speed nor accurate control, and thus, the control system can be very simple. Furthermore, the control is suitable for local implementation. Numerical simulations of truss structures with multiple variable-frictional members show that the present approach overcomes the disadvantages of passive-frictional damping. A vibration suppression experiment demonstrates the practicality of this approach.

Satellite on-board components are subject to hard vibration during the launch and retrieval phases. Therefore, it is customary to design these components such that their resonance frequencies are higher than forcing frequencies encounterd in the environment. Howerer, if there are nonlinear elements in the satellite on which the components are installed, nonliear vibration, such as super harmonic vibration, may occur and excite resonance modes of the components. In this study, super harmonic vibration due to clearance of the satellite is investigated by numerical simulation of simple kinetic system and groundtests of the Isothermal Heating Furnace (IHF) subsystem, which will be boarded on SFU.

In order to avoid the potential risk of damage caused by the hammering during the assembling operation of Marman Clamp, an alternative method to unify the tension in the Marman Clamp bands is proposed. The method is to eliminate the effects of friction, which is the cause of the tension nonuniformity, by slightly sliding the clamp block when the band pre-tension is set. In order to confirm the effectiveness of the method, the Marman Clamp of an upper-stage inter-stage joint of Mu-3SII satellite launcher was assembled with and without the application of the present method, and the stain distribution was measured. The comparison of the data clearly indicated the effectiveness of the proposed method.

This paper investigates the vibration suppression by stiffness variation. First, optimal on-off control logic for a single-degree-of-freedom variable-stiffness system is proposed. A control logic for a multiple-degree-of-freedom system with multiple variable-stiffness elements is also proposed. As an example of a variable-stiffness system, a string whose tension is controllable is studied. Numerical simulation demonstrates the effectiveness of the proposed control logic. Next, a dry friction is shown to vary the tension of a string in the same way as this active control when the longitudinal stiffness is high, realizing a passive vibration suppression. The performance of the passive system is studied. To overcome the disadvantages of the passive system, a semiactive control is proposed, that controls the frictional force. Numerical simulations and an experiment demonstrate its effectiveness and robustness, although it is primitive.

An active vibration suppression concept, by varying the stiffness of a new type of variable-stiffness structural member, is proposed and investigated. The characteristics of this type of variable-stiffness system is shown to be different from previously studied types. The active vibration suppression with this type of variable-stiffness member is shown to be always stable. A theoretical investigation on a single-degree-of-freedom system shows potential high efficiency for this type of variable-stiffness system due to its unique hysteretic characteristics. Two different types of control logic are proposed for realistic multi-degree-of-freedom structures with multiple variable-stiffness members. Numerical simulations demonstrate the effectiveness of the proposed strategy. Active vibration suppression experiments of truss structures are performed by using a variable-stiffness member and the proposed control logic, demonstrating the effectiveness of the proposed technique in actual structures.

Three types of newly proposed deployable concepts, Spatial Diagonal-stiffened Truss (SDT), Sliding Hinge Double Fold-11 (SHDF- II), and Deployable Solar Concentrator (DSC), are described. The SDT and tbe SHDF-II are two-dimensional deployable truss structures that can be applied to large antenna structures whereas the DSC is available for large solar concentrator systems. Typical advantages of the SDT and the SHDF-II are their good packaging efficiency and the small number of mechanisms necessary for deployment and/or folding. The SDT has the best packaging efficiency among existing deployable concepts while the SHDF-II has the smallest number of deployable mechanisms (0.25 per module). The DSC is a deployable truss structure with rigid reflector plates. The DSC has the advantage of being able to deploy large-size concentrators automatically. Functional test models of both the SDT and the DSC were fabricated and tested. The test results showed the practicality of the concepts by demonstrating smooth and consistent deployment movement. © 1990 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.