The purpose of this study is improvement of a fish robot actuated by four light-weight piezocomposite actuators
(LIPCAs). In the fish robot, we developed a new actuation mechanism working without any gear and thus the actuation
mechanism was simple in fabrication. By using the new actuation mechanism, cross section of the fish robot became 30%
smaller than that of the previous model. Performance tests of the fish robot in water were carried out to measure tail-beat
angle, thrust force, swimming speed and turning radius for tail-beat frequencies from 1Hz to 5Hz. The maximum swimming
speed of the fish robot was 7.7 cm/s at 3.9Hz tail-beat frequency. Turning experiment showed that swimming direction
of the fish robot could be controlled with 0.41 m turning radius by controlling tail-beat angle.
This paper presents an experiment and parametric study of a biomimetic fish robot actuated by the Lightweight Piezocomposite
Actuator (LIPCA). The biomimetic aspects in this work are the oscillating tail beat motion and shape of
caudal fin. Caudal fins that resemble fins of BCF (Body and Caudal Fin) mode fish were made in order to perform
parametric study concerning the effect of caudal fin characteristics on thrust production at an operating frequency range.
The observed caudal fin characteristics are the shape, stiffness, area, and aspect ratio. It is found that a high aspect ratio
caudal fin contributes to high swimming speed. The robotic fish propelled by artificial caudal fins shaped after
thunniform-fish and mackerel caudal fins, which have relatively high aspect ratio, produced swimming speed as high as
2.364 cm/s and 2.519 cm/s, respectively, for a 300 V<sub>p-p</sub> input voltage excited at 0.9 Hz. Thrust performance of the
biomimetic fish robot is examined by calculating Strouhal number, Froude number, Reynolds number, and power
This paper presents a mechanical design, fabrication and test of biomimetic fish robot using the Lightweight Piezocomposite Curved Actuator (LIPCA). We have designed a mechanism for converting actuation of the LIPCA into caudal fin movement. This linkage mechanism consists of rack-pinion system and four-bar linkage. We also have tested four types of caudal fin in order to examine effect of different shape of caudal fin on thrust generation by tail beat.
Subsequently, based on the caudal fin test, four caudal fins which resemble fish caudal fin shapes of ostraciiform, subcarangiform, carangiform and thunniform, respectively, are attached to the posterior part of the robotic fish. The swimming test using 300 V<sub>pp</sub> input with 1 Hz to 1.5 Hz frequency was conducted to investigate effect of changing tail beat frequency and shape of caudal fin on the swimming speed of the robotic fish. The maximum swimming speed was reached when the device was operated at its natural swimming frequency. At the natural swimming frequency 1 Hz,
maximum swimming speeds of 1.632 cm/s, 1.776 cm/s, 1.612 cm/s and 1.51 cm/s were reached for ostraciiform-, subcarangiform-, carangiform- and thunniform-like caudal fins, respectively. Strouhal numbers, which are a measure of thrust efficiency, were calculated in order to examine thrust performance of the present biomimetic fish robot. We also approximated the net forward force of the robotic fish using momentum conservation principle.
Biomimetic actuators that can produce soft-actuation but large force generation capability are of interest. Nafion, an effective ionomeric material from DuPont, has been shown to produce large deformation under low electric fields (<10V/mm). It is now generally accepted that such a response is caused by a direct electro-osmotic effect due to the existence and mobility of cations and subsequent swelling and de-swelling of the material. In this effort, multi-walled carbon nano-tube (MWNT)/Nafion nano-composites were prepared by casting in order to investigate the effect of MWNT loading in the range of 0 to 7 wt% on electromechanical properties of the MWNT/Nafion nano-composites. The measured elastic modulus and actuation force of the MWNT/Nafion nano-composites are drastically different, showing larger elastic modulus and improved electromechanical coupling, from the one without MWNT, implying that the effective MWNT loading is crucial in developing of high-performance biomimetic actuators. In this work, we also attempted to incorporate an equivalent circuit analysis to address the effect of capacitance and resistance of such MWNT/Nafion nanocomposites that would differ from conventional IPMCs.
In designing microelectromechanical systems (MEMS), the robustness of the system critically affects long-lasting system performance. In reality, fabrication errors, material property uncertainty, and environmental uncertainty such as temperature and humidity variations affect the performance of MEMS. These factors are usually referred to as noise factors. This investigation is mainly concerned with the robust design of micro electro-thermal actuators that are to be fabricated by the MEMS fabrication technology. The baseline design is found by topology optimization method which gives an initial optimal shape of an electro-thermal actuator giving the maximum output for a given input. By the mathematical topology optimization method alone, it is difficult or impossible to consider all noise factors in the final design stage. To take into account noise factors, we will employ the robust design methodology and modify the baseline design obtained by the topology optimization. In this work, robust design will be considered with micro electro-thermal actuators. The electro-thermal actuator is an actuating device using the thermal expansion by Joule’s heat, so its performance is affected by the temperature variation of surrounding air, convection, thermal expansion, and applied voltage among others. We consider these noise factors for the final design to improve its robustness against the noise factors. Several micro electro-thermal actuators were fabricated by the MEMS fabrication technology and a series of experiments were conducted to verify the effect of the robust design concept on the final design.
This paper is concerned with the modeling of the rectangular plate bonded with rectangular piezoceramic sensors and actuators, which can have an arbitrary angle with respect to the plate axis. The equations of motion were derived by the Rayleigh-Ritz method. The cantilever plate with piezoceramic sensors and actuators was built to verify the theoretical development. The theoretical frequency response curve based on the equations of motion was then compared to the experimental frequency response curve. The sensor and actuator characteristics were also studied both theoretically and experimentally. The sensor characteristic is defined as the ratio of the tip displacement to the voltage output and the actuator characteristic is defined as the ratio of the applied voltage to the tip displacement. The final objective of the research is to optimize the sensor and actuator locations as well as orientation to maximize the control performance. The control performance will follow.
This paper is concerned with the development of an active vibration isolation device using PZT wafers. The main task of the device is to protect vibration-sensitive instruments from hazardous environments. The device developed in this study consists of S-shaped supporters bonded with PZT wafers, passive damping materials and piezoceramic sensors that can measure the relative motion between the base and the platform. The newly developed device can produce discernible displacement thus providing a way of counteracting external disturbances. Control techniques, which can fully utilize the functions of the device, are also developed. The experimental results show that the proposed device and the control techniques are capable of isolating vibrations thus useful in protecting sensitive instruments from external vibrations.
This research is concerned with the adaptive positive position feedback (PPF) controller design for the vibration suppression of smart structures. The main advantage of the PPF controller is that it can tackle the target mode without disturbing other modes. However, its major drawback is that we should tune the PPF filter frequency to the natural frequency of the target mode. In this study, we developed a new algorithm, which can adaptively trace the optimal PPF filter frequency in real time. To this end, we applied the gradient descent method to the digital PPF controller and derived the adaptive PPF control algorithm in digital form, which can be implemented in real time. The proposed adaptive PPF controller was tested using the simple beam structure. The experimental results show that the adaptive PPF controller is capable of tuning the PPF filter frequency to the optimal one in real time thus achieving vibration suppression in changing environments.
This paper is concerned with the development of the passive-active vibration absorber using piezoelectric actuators. The active vibration absorber system consists of 2 pairs of PZT actuators bonded on aluminum plates making s- shaped device. Hence, the active system is directly connected to the passive system. The rubber attached to the end of the beam is connected to the upper base as a structural member. It allows bending thus maximizing the vertical movement generated by the piezoceramic actuators. This paper also presents the development and the verification of the control techniques for the passive-active vibration absorber. The vibration absorber can be utilized as a passive vibration absorber when the controller is off. It is shown that vibrations can be reduced by 20dB for the first mode, when the SISO PPF controller is operated. The advantage of PPF controller provides us the most effective way of increasing damping for the particular mode of interest. However, the natural mode should be computed in the process of design, to maximize the performance. In reality the target natural frequency is estimated by the frequency response of the vibration-absorbing device and is later applied to the PPF controller as a filter frequency. In this paper, the adaptive PPF controller is considered to cope with the structural change, so that it can modify the filler frequency based on the measurement. It is found that the adaptive PPF controller is effective for the active vibration absorber when the external disturbance is applied with various excitation frequencies. It can be concluded that the proposed passive-active vibration absorber is an effective way of reducing the vibration amplitude of the precise devices in the harsh environments thus enhancing the precision.
This paper is concerned with the real-time automatic tuning of the multi-input multi-output positive position feedback controllers for smart structures by the genetic algorithms. The genetic algorithms have proven its effectiveness in searching optimal design parameters without falling into local minimums thus rendering globally optimal solutions. The previous real-time algorithm that tunes a single control parameter is extended to tune more parameters of the MIMO PPF controller. We employ the MIMO PPF controller since it can enhance the damping value of a target mode without affecting other modes if tuned properly. Hence, the traditional positive position feedback controller can be used in adaptive fashion in real time. The final form of the MIMO PPF controller results in the centralized control, thus it involves many parameters. The bounds of the control parameters are estimated from the theoretical model to guarantee the stability. As in the previous research, the digital MIMO PPF control law is downloaded to the DSP chip and a main program, which runs genetic algorithms in real time, updates the parameters of the controller in real time. The experimental frequency response results show that the MIMO PPF controller tuned by GA gives better performance than the theoretically designed PPF. The time response also shows that the GA tuned MIMO PPF controller can suppress vibrations very well.