Norio Yamashita

Electrostatically Actuated Robotic Fish: Design and Control for High-Mobility Open-Loop Swimming

This paper presents a project that aims at fabricating a biologically inspired robotic fish. The robotic fish is designed to be capable of propelling itself through oscillations of a flexible caudal fin, like a real underwater fish. In this paper, we describe the design features that underlie the operation of the robotic fish. These features include a unique actuator referred to as electrostatic film motor and a light and flexible power transmission system. The electrostatic film motor is made of two pieces of flexible printed circuit film and can be utilized as a new-type artificial muscle. The power transmission system permits reciprocating power to be converted to periodic oscillations and distributed to the caudal fin. Based on several design considerations inspired by biological concepts, we propose several open-loop swimming control strategies for the constructed robotic fish to accomplish fish-like motion (i.e., cruising, turning, and diving). Experiments of Seidengyo I, the first prototype of our electrostatic fish family, are carried out to confirm the validity of the original design and control. We further design Seidengyo II to improve on Seidengyo I and show the results of the experiments.

Design and Control of a Fish-like Robot Using an Electrostatic Motor

This paper presents a project that aims at constructing a biologically inspired fish-like robot. The robot is designed to be capable of propelling itself through oscillations of a flexible caudal fin, like a real underwater fish. In particular, the caudal fin is driven by a mechanism actuated by a unique actuator called electrostatic film motor. In this paper, the dynamics of the electrostatic film motor are briefly introduced so as to well understand its characteristics and behavior. Based on the theoretical analysis and several design considerations inspired by biological concepts, we realize the fish-like robot actuated by an electrostatic film motor and propose swimming control methods for it. Experiments are carried out to confirm the validity of the original design and control. The current robot achieves fish-like maneuvering and approximate velocity of 0.018 m/s in dielectric liquid.

Evaluation of an Electrostatic Film Motor Driven by Two-Four-Phase AC Voltage and Electrostatic Induction

This paper describes a voltage-induction type electrostatic film motor that operates by feeding electric power to the slider by electrostatic induction. In electrostatic film motors, feeding power to slider is important for better output capability and positioning performance. However, the power feeding using electric cables sometimes cause mechanical disturbance to the motor motions. In the new electrostatic motor, the power to the slider is fed by electrostatic induction, thus removing electric cables that can cause mechanical disturbances. The proposed motor has a two-phase electrode in the slider and a four-phase electrode in the stator. In addition, both stator and slider have the induction electrodes so that electric power is transferred to the slider through the induction electrodes. The paper first analyzes the thrust force characteristics of the proposed driving-electrode configuration, and then analyzes the characteristics of voltage induction, both based on capacitance-network analysis. The analyzed result is verified by experiments that showed good agreements with the provided analysis

Capacitive-Type Flexible Linear Encoder With Untethered Slider Using Electrostatic Induction

A novel capacitive linear encoder characterized by its untethered slider is presented. The main components are made of flexible printed circuit films measuring 0.2 mm in thickness that allows the sensor to be set up in thin interspaces or on curved surfaces. The sensor consists of a long receiver film and a short transmitter film, respectively containing four-phase and two-phase electrodes; the transmitter is used as a slider and the receiver as a stator. To realize an untethered slider, the sensor employs a unique approach; electric power is supplied to the transmitter film by electrostatic induction, which removes electric wires from the slider. This untethered slider can facilitate sensitive applications where a mechanical disturbance caused by an electric wire can be a problem. The principle was verified using a prototype encoder, which showed an error of ± 4 ¿ m.

Modeling and system identification of three-layer structure electrostatic film motors for a robotic fish

We have developed an underwater fish-like robot using two-four-phase three-layer structure electrostatic film motors. In the robotic fish, the novel motors actuated the flexible caudal fin to propel itself via an elaborate power transmission system. In this paper, we first theoretically analyze the dynamic properties of the three-layer structure electrostatic film motors by modeling it as a 10-terminal capacitance network, and derive a high-speed open-loop swimming control strategy from the analytical results. Next, a simple theoretical model concerning the power transmission system of the robotic fish is also analyzed to provide a possible explanation for the unique swimming control. Then, we perform experimental verification of the open-loop swimming control for an improved prototype of the robotic fish. Results from experiments performed with the improved robot in an aquarium show good agreement with theoretical predictions. Finally, through these experimental results, we further clarify the relationship between the open-loop motor pattern and motion parameters.

Development of a robotic fish using electrostatic film motors : the Seidengyo II robot

We previously built a fish-like robot named Seidengyo I (based on the Japanese words for electrostatic (seiden) and fish (gyo)), which is a light and flexible robot actuated by a novel electrostatic film motor. This paper describes the design features that underlie the operation of Seidengyo II, which is an evolutional prototype of Seidengyo I. These features include an elaborate three-layer electrostatic film motor, a unique power transmission system and a compact robot controller. The power transmission system permits reciprocating power from the three-layer electrostatic actuator to be converted to periodic oscillations of a caudal fin. The robot controller is capable of easily generating high-frequency and high-voltage driving signals. As a result, we can control the oscillations of the caudal fin of Seidengyo II via synchronous operation to achieve open-loop swimming. We present the experimental results regarding the performance of the constructed controller and verify the validity of the design of the Seidengyo II robot by these experimental results.

Pulse voltage operation of two-to-four-phase voltage-induction-type electrostatic motor

This paper analyzes pulse voltage operations of a two-to-four phase voltage-induction-type electrostatic motor (VITEM) to clarify the appropriate driving sequences. The paper also evaluates transient charge effects that can possibly enhance the thrust force. VITEM has been studied as a novel centimeter-sized electrostatic film motor whose power to the slider is supplied indirectly through its induction electrodes. Since a smooth synchronous driving was aimed in the past stud- ies, high-frequency AC voltages have been used for the driving. This paper demonstrates that straightforward usage of simple pulse sequences cannot realize continuous stepping driving, and proposes several different sets of modified pulse sequences to realize continuous stepping driving using low-switching-rate pulse voltages. In the experiments, the motor showed continuous stepwise driving with a step width of about half of the electrode pitch. In addition, transient characteristics of charges on films were evaluated experimentally under the pulse driving condition, and contribution for thrust force enhancement was clarified.

Wireless Driving of Electrostatic Film Actuator by Pre-Charging Electrodes with DC High Voltages

Electrostatic film actuator is a thin, lightweight and flexible actuator composed of two plastic films with fine-pitched electrodes embedded in them. In this paper, we report a novel driving method for the actuator, in which the electrodes in one film (the slider film) are pre-charged with DC high voltages, and the slider film is driven by AC voltages applied to the electrodes in the other film (the stator film). Typically, the actuator has been driven by applying three-phase AC voltages to the electrodes in both films; in the driving method, the slider film required connections of feeding wires, whose tensions causing disturbance to its motion. The advantage of the pre-charging method is that the slider film is free from the feeding wires; in turn, it requires an additional step before driving: charging of the slider electrodes. To confirm the feasibility of the method, experiments were conducted using a pair of films fabricated by flexible printed circuit technology. Each of the films incorporate 475 strips of electrodes within their overlapping area; the electrodes are 18 mm in length and 40 μm in width, arranged at a constant pitch of 160 μm. DC voltages used for pre-charging the three-phase electrodes in the slider were 500 V, -500V and 0 V, respectively. After the pre-charging, 500 V three-phase voltage applied to the stator drove the slider with maximum thrust force of approximately 120 mN. We also found that the thrust force of the actuator decay with time after pre-charging, which indicate that further investigations are necessary to prolong its duration.

Experimental evaluation of open-loop swimming control for a robotic fish using electrostatic film motors

We have developed an underwater robotic fish using a unique three-layer electrostatic film motor. In the robotic fish, the unique motor actuates a flexible caudal fin to propel the robot via an elaborate power transmission system. In the present study, we describe the major disadvantages of the previous prototype of the robotic fish and improvements of the prototype. In addition, we present experimental evaluations related to the control parameters and locomotion performance of the robotic fish. These control parameters include the frequency and initial phase of AC voltage, and the amplitude and period of frequency sweeping. A simple theoretical model concerning the power transmission system of the robotic fish is also analyzed to provide a possible explanation for the unique swimming control. By appropriately adjusting these control parameters, we achieve cruising, emerging, submerging, and turning of the robotic fish even though only the caudal fin is active. Finally, we show smooth human-operated turn-around motion similar to that seen in real fish. Based on these experimental results, we further clarify the relationships between the open-loop motor pattern and motion parameters.

Prototyping of flexible capacitive encoder with un-tethered slider using electrostatic induction

This paper describes a capacitive linear encoder that is characterized by its un-tethered sensor slider. The main components are made of flexible printed circuit films measuring only 0.2 mm in thickness that allows the sensor to be set up in thin interspaces or on curved surfaces. The sensor consists of a long receiver film and a short transmitter film, respectively containing four-phase and two-phase electrode; the transmitter is used as a slider and the receiver as a stator. To realize an un-tethered slider, the sensor employs a unique approach; electric power is supplied to the transmitter film by electrostatic induction, thus removing electric wires from the slider. This un-tethered slider can facilitate the sensitive applications where mechanical disturbance caused by an electric wire can be a problem. The principle was verified using a prototype encoder, which showed a linearity error of +/- 10 micrometers.