Kenji Minesugi

Energy-recycling semi-active method for vibration suppression with piezoelectric transducers

*A novel energy-recycling method is studied that enables effective semi-active vibration suppression with piezoelectric transducers embedded or bonded to a structure. In this method, the energy converted from the mechanical energy of a vibrating structure is collected in the capacitor of a piezoelectric transducer as an electric charge, and to suppress vibration, rather than dissipate the energy, the polarity of the charge is changed according to the state of vibration. With this method, no energy is supplied to the total system of the structure and transducers with shunt circuit, which means that the system is stable. A simple electric circuit and a control law for multiple-degree-offreedom systems with multiple piezoelectric transducers are proposed for this method based on energy recycling. Numerical simulation of vibration suppression of a truss structure shows that this method is more effective in suppressing vibration than both a semi-active method without energy-recycling and that based on the use of an optimally tuned passive system. A preliminary experiment with a truss structure also shows that this method can effectively suppress vibration in an actual structure. However, there was some discrepancy in the experimental results compared to the results of the numerical simulation performed assuming ideal linear characteristics of the piezoelectric transducers estimated from a static test. Nomenclature

SIMULTANEOUS OPTIMIZATION OF PIEZOELECTRIC ACTUATOR PLACEMENT AND FEEDBACK FOR VIBRATION SUPPRESSION

Abstract This paper formulated a new optimal design methodology 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 are 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.

Low-Energy-Consumption Hybrid Vibration Suppression Based on an Energy-Recycling Approach

An innovative method of hybrid vibration suppression using piezoelectric materials is proposed. It combines bang‐bang active vibration suppression and energy-recycling semiactive vibration suppression. The piezoelectric materials are electromechanically coupled and convert mechanical energy into electrical energy and vice versa. With this method, a part of the electrical energy needed for suppressing vibration is obtained from the mechanical energy of the vibrating structures and is efficiently recycled. Furthermore, the actively supplied energy is stored in the transducers and is reused many times for vibration suppression. Therefore, the hybrid method has better performance than the case where the bang‐bang active method and the energy-recycling semiactive method are both used, but independently. The hybrid method saves the actively supplied energy and is thus a low-energyconsumption vibration control. Its effectiveness in suppressing vibrations was proven in numerical simulations and experiments using a 10-bay truss structure. Moreover, a novel method to prevent undesired control chattering is proposed to further save energy supplied from the external source.

Hinode Calibration for Precise Image Co-Alignment between SOT and XRT (2006 November-2007 April)

To understand the physical mechanisms for activity and heating in the solar atmosphere, the magnetic coupling from the photosphere to the corona is an important piece of information from the Hinode observations, and therefore precise positional alignment is required among the data acquired by different telescopes. The Hinode spacecraft and its onboard telescopes were developed to allow us to investigate magnetic coupling with co-alignment accuracy better than 1 00 .U sing the Mercury transit observed on 2006 November 8 and co-alignment measurements regularly performed on a weekly basis, we have determined the information necessary for precise image co-alignment, and have confirmed that co-alignment better than 1 00 can be realized between Solar Optical Telescope (SOT) and X-Ray Telescope (XRT) with our baseline co-alignment method. This paper presents results from the calibration for precise co-alignment of CCD images from SOT and XRT.

Semiactive Vibration Suppression with Electrorheological-Fluid Dampers

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 10-bay truss beam demonstrates that vibrations are suppressed effectively by the ER-fluid variable damper.

A self-sensing method for switching vibration suppression with a piezoelectric actuator

This paper discusses a self-sensing vibration suppression method that measures only the value of the piezoelectric voltage. The method separates the electrical status into two cases concerning electrical current and characterizes each of these to establish a self-sensing system using extended system equations and a Kalman filter. Our self-sensing system can avoid estimation blackout during closed-circuit status and lessen harmful influences from residual modes. Experiments revealed that the self-sensing system suppressed vibrations in cooperation with state-switching and synchronized-switching controls. We confirmed that the self-sensing method is robust against model errors in a vibration suppression experiment in which there are model errors caused by an intentional frequency shift.

Comprehensive Assessment of Semi-Active Vibration Suppression Including Energy Analysis

This paper presents an extensive investigation on the LR-switching method (also called the energy-recycling semi-active method). Compared with the energy-dissipative R-switching method, the LR-switching method has been shown to have significantly better vibration suppression performance. However, certain essential issues affecting a system employing the LR-switching method remained to be dealt with. In particular, we had to clarify its vibration suppression mechanism from the viewpoint of mechanical and electrical energy exchange. Second, the robustness of the method against model errors and control time delays had to be verified. The experiments and numerical simulations that we conducted on a 10-bay truss structure demonstrate that the LR-switching method outperforms other suppression methods under sinusoidal and random excitations, which are more common in real systems and more difficult to deal with than transient vibrations. This paper provides fundamental insights on the LR-switching method and gives the method a guarantee for actual applications.

The Solar Optical Telescope onboard the Solar-B

The solar optical telescope onboard the Solar-B is aimed to perform a high precision polarization measurements of the solar spectral lines in visible wavelengths to obtain, for the first time, continuous sets of high spatial resolution (~0.2arcsec) and high accuracy vector-magnetic-field map of the sun for studying the mechanisms driving the fascinating activity phenomena occurring in the solar atmosphere. The optical telescope assembly (OTA) is a diffraction limited, aplanatic Gregorian telescope with an aperture of Φ500mm. With a collimating lens unit and an active folding mirror, the OTA provides a pointing-stabilized parallel beam to the focal plane package (FPP) with a field of view of about 360x200arcsec. In this paper we identify the key technical issues of OTA for achieving the mission goal and describe the basic concepts in its optical, mechanical and thermal designs. The strategy to verify the in-orbit performance of the telescope is also discussed.

Semiactive Isolator With Liquid-Crystal Type ER Fluid for Momentum-Wheel Vibration Isolation

A semiactive isolator filled with liquid-crystal type electro-rheological (ER) fluid was developed to attenuate the disturbances generated by a momentum-wheel and to improve pointing performance. The principal characteristics of an ER isolator were measured in dynamic tests, and a mathematical model of the isolator was proposed. Two control laws for a semiactive approach were proposed. Numerical simulation results indicated that the proposed semiactive control system produced much better isolation performance than a passive system.

Novel Approach to Self-Sensing Actuation for Semi-Active Vibration Suppression

A novel self-sensing method using piezoelectric actuators for semi-active vibration suppression is proposed and investigated. By using extended system equations, this self-sensing method can be implemented with a Kalman filter instead of the conventional bridge circuit technique. The method separates electrical status into two cases concerning electrical current, and characterizes each of these to establish the self-sensing system. This method is applicable to multiple-degree-of-freedom structures with multiple piezoelectric actuators. A numerical vibration suppression simulation demonstrated that the self-sensing method works well on a truss structure and has significant robustness against parameter variations. Experimental results also demonstrated that the self-sensing method suppresses not only single-mode vibration but also multiple-mode vibration.