Vibration Isolation Control Research Articles

Analysis of a high T/sub c/ superconducting levitation system with vibration isolation control

This paper presents a method for controlling vibrations of a levitated high Tc superconducting body subjected to base disturbances. To have the control forces, an actuator consisting of a permanent magnet with an electromagnet was presented. The analytical solution for calculating levitation forces due to the permanent magnet and the control currents in the electromagnet was obtained. The levitation forces obtained coincide with the previously published results. The equation of motion of the levitated body subjected to base disturbances under the control was presented. Nonlinear vibrations of the body were first discussed; then the method of vibration isolation control using the direct disturbance cancellation combining the velocity feedback control was investigated. Numerical calculations were carried out for the levitation forces, with respect to the levitated body subjected to harmonic or pulse base excitations. It was clarified that the present method Is valid for controlling nonlinear systems like the magnetically levitated superconducting body.

Active Damper Using Electrorheological Suspension and Its Application to Vibration Isolation Control.

The concepts and the damping characteristics of an active damper using electrorheological (ER) fluids containing numerous dielectric particles have been proposed, and applications to vibration isolation control have been investigated numerically, based on the analytical model of the ER damper involving the approximate function of pressure drops across an ER valve obtained experimentally. The ER damper was found to be analogous to the hybrid damper having a viscous damper with constant damping and an electrically variable friction damper. Therefore, the ER damper under constant input voltage behaves like a coulomb friction damper, and the active damper can be constructed, by electrically varying the friction like forces proportional to the piston speed, to be a linear viscous damper with electrically variable damping coefficient. Three methodologies of vibration isolation control using the ER active damper were applied to a single-degree-of-freedom excited vibration system consisting of a mass, a spring, and the ER damper. Among these control methodologies, the nonlinear feedback control of the square root of the absolute velocity of the mass was found to be most effective to reduce the vibration transmissibility of the system, and to enable control of transmissibility approaching that which can be achieved with a full active vibration isolation system using an actuator.

An Intelligent Control System for Multiple Degree-of-Freedom Vibration Isolation

Multiple degree-of freedom (DOF) vibration isolation and suppression capabilities are essential for precision control of a wide range of space-borne structures as well as earth-based systems. This paper presents the system design and implementation, control algorithms, parallel computing architecture, and real-time experiments of a six DOF Hexapod Active Vibration Isolation (HAVI) system developed at Intelligent Automation, Inc. The system design of the HAVI is based on the hexapod (Stewart Platform) concept. A novel geometric arrangement of a hexapod, called the "Cubic Configuration" is used. Magnetostrictive material Terfenol-D actuators are employed. A two-layer control system architecture incorporating local force feedback control and a robust adaptive filter control for active vibration isolation are employed. A high performance parallel computation engine MDSP-100 with multiple DSP processors and maximum 566 MFLOPs throughput is also developed for the HAVI applications and was used to implement proposed control algorithms. The unique architecture and functionality of the MDSP-100 facilitate the data acquisition and control law computation operations in a parallel computing fashion. Mechanical hardware for the HAVI system has been fabricated and tested. The six channel simultaneous active vibration control experiments were performed to demonstrate HAVI system's 6 DOF vibration isolation and suppression capabilities. A wide band (below 250 Hz) active vibration attenuation for all six channels was obtained in the real-time experiments.

Active control of vibration of a magnetic levitation platform

A study on active control of vibration isolation of a magnetic levitation platform used for the calibration of precision inertia instruments is presented in this paper. Nonlinear and linearized dynamic models of the system in state‐space were deduced by using the theory of an electromagnetic field. The stability of both the open‐ and closed‐loop system was investigated in the cases of different configuration of the current coils. A LQG optimal control strategy was employed in the control syntheses of the magnetic levitation system, since the system input perturbance is a stochastic excition acting on the fixed base from the ground. The transfer functions from the exciting current or the control current or the base displacement to the vibratory displacement of the levitation platform were verified experimentally. Open‐ and closed‐loop vibration responses were calculated. The results show that compared to the base displacement, the vibration of the magnetic levitation platform can be attenuated more than 20...

Direct disturbance cancellation with an optimal regulator for a vibration isolation system with friction

A method is presented for direct disturbance cancellation with an optimal regulator for a vibration isolation system with friction. As an example, a DC servomotor is considered as an actuator. The analytical expressions for the control method are first derived. Results of experimental tests are also presented, and it is shown that the present method has advantages as compared to the usual active vibration isolation control methods. For the usual vibration isolation control systems, the maximum transmissibility is greater than or equal to unity, while when the present method is used the transmissibility becomes less than 20 percent of the external disturbance for a practical system with friction. When there is no friction, the transmissibility will, of course, become smaller.

Analysis of a High Tc Superconducting Nonlinear Levitation System with Actuators Changing Magnetic Flux Densities and its Vibration Isolation Control.

This paper discusses an actuator consisting of a permanent magnet with an electromagnet and a high Tc superconducting disc. An analytical solution for calculating levitation forces for the system was obtained. The obtained levitation force coincided with the previously published result. The equation of motion of the levitated body subjected to base disturbances under control was presented. Numerical calculations were carried out for some typical cases. Nonlinear vibrations of the system were first discussed, then the method of vibration isolation control using the direct disturbance cancellation combining the velocity feedback control was discussed. It was clarified that the present control method is valid for controlling the nonlinear system like the magnetically levitated superconducting body.

LQG Control and H.INF. Control of Vibration Isolation for Multi-Degress-of-Freedom Systems.

This paper deals with a problem of vibration isolation control for multi-degees-of-freedom systems by applying the optimal control theory using a Kalman filter and H∞ control theory. A four-degees-of-freedom system for an experimental model is reduced into a two-degees-of-freedom system in order to control vibrations of the fundamental and second modes. As a result of numerical calculations and experiments, it is shown that the spillover problem occurring from the model reduction dose not affect the vibration isolation performance for multi-degees-of-freedom systems and it is important to determine how to reduce the vibrations of low modes of which vibration levels are high. Furthermore, it is demonstrated that the control characteristics depend on the adopted objective functions and the vibrations of the low modes are effectively reduced by introducing a frequency-shaped function in H∞ control theory.

Actuators for a Noncontact Magnetic Levitation Table and Its Application to Vibration Isolation Control.

This paper proposes a drag-force-type magnetic levitation actuator consisting of pairs of permanent magnets and electromagnets. For general magnetic levitation actuators, there is a nonlinear relationship between magnetic force and control current, so that a linear control theory is not applicable. In the actuator proposed, the relationship between the force and the current is linear. This implies that the position and velocity feedback controls can be applied without consideration of interferences. A control method using a combination of techniques of disturbance cancellation and optimal regulation was presented taking into consideration the interference between perpendicular and vertical motions. To verify the applicability of present actuator and control method, experimental tests were carried out.

Dynamic System Synthesis With a Bond Graph Approach: Part II—Conceptual Design of an Inertial Velocity Indicator

This work develops the conceptual design of an inertial velocity sensor drawing upon the impedance synthesis method in Part I of this paper. Specifications are frequency based impedances and resulting designs are configurations of dynamic energy storing and dissipation elements. The design procedure can be extended to a class of systems design problems where frequency response performance is of primary importance. A key to this work is that the method designs systems from scratch; initial configurations are unknown. As a theme example to demonstrate the utility of the method for conceptual design, constrained and unconstrained inertial velocity sensors are configured based on input-output performance requirements. Such sensors find application in many motion control problems including mechanism and manipulator control, and vibration isolation control. The design methodology generates a number of different sensors that can measure absolute velocity for some or all ranges of frequency.

Stabilization of Synchronized Active Vibration Isolation by Active Damping Control.

This paper presents a stabilization method of synchronized active control for machinery vibration isolation. The stability of the synchronized vibration control can be lost when occuring changes in the vibration characteristics of the system. The stabilization is accomplished by active damping control using the actuators for isolation, which smoothes the curves of the transfer functions between the control signals and the residual vibrations. Three damping control methods are proposed : (1) Feedback of the velocity at the actuator upper part ; (2) Feedback of the velocity at the actuator lower part ; (3) Feedback of the integrated force through the isolator. For the typical modal models of vibration systems, the stabilization performances of these feedbacks are examined numerically, evaluating eigen values of the state transition matrix of the synchronized isolation control. The effectiveness of these methods is demonstrated experimentally, using a machinery model supported by 4 piezoelectric actuators. It is also found that the isolation effects are increased by the active damping control.

Cancellation Control for Active Machinery Vibration Isolation by Estimating Exciting Force.

This paper proposes a cancellation control method for active machinery vibration isolation supported by multi-isolators. In this method, the cancellation signals are produced by simple independent analog circuits for each actuator, which use exciting forces that are estimated by measuring the accelerations of the actuators and the forces transmitted through the isolators. By analyzing the control equations, it can be observed that the control system is stable and causes high isolation effects for both lower order modes, where the machine vibrates as a rigid body, and higher order modes, where the natural vibrations of the machine dominate. The effectiveness of this method in wide frequency ranges is demonstrated experimentally by using a machinery model supported by four piezoelectric actuators.

Synchronized Modal Control for Active Vibration Isolation.

This paper deals with control methods and the stability of synchronized active control for machinery vibration isolation. It shows that the instability of the coupled control of the multi actuator system is caused by changes in the sensitivity of sensors, gains of actuators and the natural frequencies of the system. To adapt the system to these changes, the modal control method for the rigid body mode of the machine is proposed, through which the transfer functions between the control signals and the residual vibrations can be obtained by one excitation of actuators. The instability of the coupled control and the effectiveness of the modal control are demonstrated experimentally, using a machinery model supported by 4 piezoelectric actuators. Furthermore, applicable frequency ranges of the modal control, coupled control and independnt control of each actuator are clarified by calculating the convergence properties of the experimental model.

Control issues of microgravity vibration isolation

Active vibration isolation systems contemplated for microgravity space experiments may be designed to reach given performance requirements in a variety of ways. An analogy to passive isolation systems proves to be illustrative but lacks the flexibility as a design tool of a control systems approach and may lead to poor designs. For example, it is shown that a focus on equivalent stiffness in isolation system design leads to a controller that sacrifices robustness for performance. Control theory as applied to vibration isolation is reviewed and passive analogies are discussed. The loop shaping trade-off is introduced and used to design a single degree of freedom feedback controller. An algebraic control design methodology is contrasted to loop shaping and critiqued. Multi-axis vibration isolation and the problems of decoupled single loop control are introduced through a two degree of freedom example problem. It is shown that center of mass uncertainty may result in instability when decoupled single loop control is used. This results from the ill conditioned nature of the feedback control design. The use of the Linear Quadratic Regulator synthesis procedure for vibration isolation controller design is discussed.