Ionic polymers are a recently discovered class of active materials that exhibit bidirectional electromechanical coupling. They are `soft' transducers that perform best when the mechanical deformation involves bending of the transducer. Ionic polymers are low voltage actuators -- they only require inputs on the order of 1V and cannot tolerate voltages above approximately 10V. The mechanisms responsible for the electromechanical coupling are not yet fully understood, and reports of the capabilities and limitations of ionic polymer transducers vary widely. In addition, suitable engineering models have not been developed. This document presents a dynamic model for ionic polymer transducers that is based on a pair of symmetric, linearly coupled equations with frequency dependent coefficients. The model is presented in the form of an equivalent circuit, employing an ideal transformer with a frequency dependent turns ratio to represent the electromechanical coupling. The circuit elements have clear physical interpretations, and expressions relating them to transducer dimensions and material properties are derived herein. The material parameters required for the model: modulus, density, electrical properties, and electromechanical coupling term are determined experimentally. The model is then validated by comparing simulated and experimental responses, and the agreement is good. Further validation is presented in the form of extensive experiments that confirm the predicted changes in transducer performance as transducer dimensions are varied. In addition, reciprocity between mechanical and electrical domains is demonstrated. This reciprocity is predicted by the model, and is a direct result of the symmetry in the equations on which the model is based. The capabilities of ionic polymer sensors and actuators, when used in the cantilevered bender configuration, are discussed and compared to piezoceramic and piezo polymer cantilevered benders. The energy density of all three actuators are within an order of magnitude of one another, with peak values of approximately 10J/m^3 and 4mJ/kg for ionic polymer actuators actuated with a 1.2V signal. Ionic polymer sensors compare favorably to piezoelectric sensors. Their charge sensitivity is approximately 320E-6C/m for a 0.2 x 5 x 17mm cantilevered bender, two orders of magnitude greater than a piezo polymer sensor with identical dimensions. This work is concluded with a demonstration of feedback control of a device powered by ionic polymer actuators. An ionic polymer sensor was used to provide the displacement feedback signal. This experiment is the first demonstration of feedback control using an ionic polymer sensor. Compensator design was performed using the model developed in the first chapter of this document, and experiments confirmed that implementation of the control scheme improved, in a narrow frequency range, the system's ability to track sinusoidal inputs. / Ph. D.

Ionomeric polymer metal composites can be used as transducers characterized by high strain and low force. They are created by bonding a thin conductive electrode to the surfaces of an ionomeric polymer. Much of the work in the past has focused on using a voltage across the thickness of the polymer to produce mechanical motion. That work has often demonstrated that the mechanism of transduction within the polymer was associated with the accumulation of charge in the polymer. This thesis will discuss the use of current as a means to better control the accumulation of charge. Better control of the charge will provide more reliable control of the mechanical motion of the polymer. The data presented in this thesis demonstrates that the response of an ionomeric polymer to a current input is repeatable. The repeatability is a desirable result; however, using current to actuate the polymers also produces back relaxation in the response. Examination of the back relaxation reveals a low frequency non-linearity. The nonlinearity is quantified by the fact that the gain associated with the back relaxation does not increase linearly with an increase in input current. There is also a change in the response at certain voltage thresholds. For example, when the voltage across the polymer exceeds 3 V, the rate of back relaxation increases. The repeatability of the response will aid in implementing reliable control of the polymer, but the non-linearities in the back relaxation will provide a considerable challenge in developing a model to be used in control. / Master of Science

This thesis describes the open-loop behavior of an ionic polymer metal composite (IPMC) strip as a novel actuator, the empirical force and position models, the control system and the improved dynamic characteristics with the feedback control implemented. Ionic polymer metal composite is a novel polymer in the class of electroactive polymers. IPMC consists of a base polymer coated with electrodes made up of highly conducting pure metals such as gold. The actuation behavior of IPMC can be attributed to the bending of an IPMC strip upon application of voltage across its thickness. The main reasons for the bending are ion migration on the application of voltage and swelling and contraction caused by water content. An experimental setup to study the open-loop force and tip displacement of an IPMC strip in a cantilever configuration was developed, and real time controllers were implemented. In open loop, the force response of the IPMC strip of dimensions 25 mm x 3.9 mm x 0.16 mm to a 1.2-V step input is studied. The open-loop rise time was 0.08 s and the percent overshoot was 131.62 %, while the settling time was about 10 s. Based on this open-loop step response using a least-square curve-fitting methodology, a fourth-order empirical transfer function from the voltage input to the force output was derived. The tip displacement response of an IPMC strip of dimensions 23 mm x 3.96 mm x 0.16 mm to a 1.2-V step input was also studied. The step response exhibited a 205.34 % overshoot with a rise time of 0.08 s, and the settling time was 27 s. A fourth-order empirical transfer function from the step input to the tip displacement as output was also derived. Based on the derived transfer functions lead-lag feedback controllers were designed for precision control of both force and displacement. The control objectives were to decrease the settling time and the percent overshoot, and achieve reference input tracking. After implementing the controllers, the percent overshoot decreased to 30% while the settling time was reduced to 1.5 s in case of force control. With position control, the settling time was reduced to 1 s while the percent overshoot decreased to 20%. Precision micro-scale force and position-control capabilities of the IPMC were also demonstrated. A 4 ?N force resolution was achieved, with a force noise of 0.904-?N rms. The position resolution was 20 ?m with a position noise of 7.6-?m rms.

This thesis describes the open-loop behavior of an ionic polymer metal composite (IPMC) strip as a novel actuator, the empirical force and position models, the control system and the improved dynamic characteristics with the feedback control implemented. Ionic polymer metal composite is a novel polymer in the class of electroactive polymers. IPMC consists of a base polymer coated with electrodes made up of highly conducting pure metals such as gold. The actuation behavior of IPMC can be attributed to the bending of an IPMC strip upon application of voltage across its thickness. The main reasons for the bending are ion migration on the application of voltage and swelling and contraction caused by water content. An experimental setup to study the open-loop force and tip displacement of an IPMC strip in a cantilever configuration was developed, and real time controllers were implemented. In open loop, the force response of the IPMC strip of dimensions 25 mm x 3.9 mm x 0.16 mm to a 1.2-V step input is studied. The open-loop rise time was 0.08 s and the percent overshoot was 131.62 %, while the settling time was about 10 s. Based on this open-loop step response using a least-square curve-fitting methodology, a fourth-order empirical transfer function from the voltage input to the force output was derived. The tip displacement response of an IPMC strip of dimensions 23 mm x 3.96 mm x 0.16 mm to a 1.2-V step input was also studied. The step response exhibited a 205.34 % overshoot with a rise time of 0.08 s, and the settling time was 27 s. A fourth-order empirical transfer function from the step input to the tip displacement as output was also derived. Based on the derived transfer functions lead-lag feedback controllers were designed for precision control of both force and displacement. The control objectives were to decrease the settling time and the percent overshoot, and achieve reference input tracking. After implementing the controllers, the percent overshoot decreased to 30% while the settling time was reduced to 1.5 s in case of force control. With position control, the settling time was reduced to 1 s while the percent overshoot decreased to 20%. Precision micro-scale force and position-control capabilities of the IPMC were also demonstrated. A 4 ?N force resolution was achieved, with a force noise of 0.904-?N rms. The position resolution was 20 ?m with a position noise of 7.6-?m rms.

Ionic polymer metal composite (IPMC) is used in various bio-inspired systems, such as fish and tadpole-like robots swimming in water. The deflection of this smart material results from several internal and external factors, such as water distribution and surface conductivity. IPMC strips with a variety of water concentration on the surfaces and surface conductivity show various deflection patterns. Even without any external excitation, the strips can bend due to non-uniform water distribution. On the other hand, in order to understand the effects of surface conductivity in an aquatic environment, an IPMC strip with two wires connected to two distinct spots was used to demonstrate the power loss due to the surface resistance. Three types of input signals, sawtooth, sinusoidal, and square waves, were used to compare the difference between the input and output signals measured at the two spots. Thick (1-mm) IPMC strips were fabricated and employed in this research to sustain and drive the robot with sufficient forces. Furthermore, in order to predict and control the deflection, researchers developed the appropriate mathematical models. The special working principle, related to internal mobile cations with water molecules, however, makes the system complicated to be modeled and simulated. An IPMC strip can be modeled as a cantilever beam with loading distribution on the surface. Nevertheless, the loading distribution is non-uniform due to the non-perfect surface metallic plating, and four different kinds of imaginary loading distribution are employed in this model. On the other hand, a reverse-predicted method is used to find out the transfer function of the IPMC system according to the measured deflection and the corresponding input voltage. Several system-identification structures, such as autoregressive moving average with exogenous (ARX/ARMAX), output-error (OE), Box-Jenkins (BJ), and prediction-error minimization (PEM) models, are used to model the system with their specific mathematic principles. Finally, a novel linear time-variant (LTV) concept and method is introduced and applied to simulate an IPMC system. This kind of model is different from the previous linear time-invariant (LTI) models because the IPMC internal environment may be unsteady, such as free cations with water molecules. This phenomenon causes the variation of each internal part. In addition, the relationship between the thickness of IPMC strips and the deflection can be obtained by this concept. Finally, based on the experimental results above, an aquatic walking robot (102 mm × 80 mm × 43 mm, 39 g) with six 2-degree-of-freedom (2-DOF) legs has been designed and implemented. It walked in water at the speed of 0.5 mm/s. The average power consumption is 8 W per leg. Each leg has a thigh and a shank to generate 2-DOF motions. Each set of three legs walked together as a tripod to maintain the stability in operation.

No description available.

Ionomeric polymer transducers (IPTs) are an exciting new class of smart materials that can serve a dual purpose in engineering or biomedical applications as sensors or actuators. Most commonly they are used for mechanical actuation, as they have the ability to generate large bending strains and moderate stress under low applied voltages. Although the actuation capabilities of IPTs have been extensively studied, the sensing capabilities of these transducers have yet to be fully explored. The work presented herein aims to investigate the fundamental sensing characteristics of these transducers and apply the acquired knowledge toward the development of an electronic stethoscope for digital auscultation. The sensors were characterized both geometrically and electrically to determine their effectiveness in resolving a signal from sub 1 Hz to 2 kHz. Impedance spectroscopy was used to interrogate the sensing mechanism. Following the characterization of the transducer, a bio–acoustic sensor was designed and fabricated. The bio–acoustic sensor was placed over the carotid artery to resolve the arterial pressure waveform in situ and on the thorax to measure the S1 and S2 sounds generated by the heart. The temporal response and spectral content was compared with previously known data and a commercially available electronic stethoscope to prove the acquisition of cardiovascular sounds. / Master of Science

The ability to convert electrical energy into mechanical motion is of significant interest in many energy conversion technologies. For more than a decade Ionic polymer-metal composite (IPMC) as an electroactive smart polymer material has been extensively studied and has shown great potential as soft robotic actuators, artificial muscles and dynamic sensors in the micro-to-macro size range. IPMC consists of an ion exchange polymer membrane sandwiched between two noble metal electrodes on either side of the membrane. Under applied potential, the IPMC actuator results in bending deformation because of ion migration and redistribution across its surface due to the imposed voltage. Nafion are highly porous polymer materials which have been extensively studied as the ion exchange membrane in IPMC. Nafion has also been mixed with carbon nanotubes, graphene, and metallic nanoparticles to improve actuation and bending characteristics of electro-mechanical actuators. For the first time, liquid phase exfoliated Transition Metal Dichalcogenides (TMDs)-Nafion nanocomposite based electro-mechanical actuators has been studied and demonstrate the improvement in the electromechanical actuation performance. In this thesis, we create a 2D model of the TMD-Nafion based electromechanical actuator in COMSOL Multi-physics software. The behavior of the model is examined at different electric potentials, frequencies, and actuation lengths. The simulation results were compared with the experimental data for validation of the model. The data showed improvement in the actuation for TMD-Nafion actuator when compared with pure Nafion actuator. The improvement in the actuation was due to the increase in diffusivity of the TMD-Nafion actuator in comparison with pure Nafion actuator. This increase in the diffusivity as seen in the model is because of the new proton conducting pathways being established with the addition of TMDs. The model also shows an increase in the stress and strain values with the incorporation of TMDs. With the same length of the actuator we were able to obtain more stress and strain with the addition of TMDs. This helps in improving the performance of the actuator as it would be able to handle more stress cycles which also increases the life of the actuator.

This thesis describes the use of an ultrasonic goal-seeking algorithm while using ionic polymer metal composite (IPMC), an electroactive polymer, as the actuator to drive a vessel towards a goal. The signal transmitting and receiving circuits as well as the goal seeking algorithm are described in detail. Two test vessels were created; one was a larger vessel that contained all necessary components for autonomy. The second was a smaller vessel that contained only the sensors and IPMC strips, and all power and signals were transmitted via an umbilical cord. To increase the propulsive efforts of the second, smaller vessel, fins were added to the IPMC strips, increasing the surface area over 700%, determined to yield a 22-fold force increase. After extensive testing, it was found that the three IPMC strips, used as oscillating fins, could not generate enough propulsion to move either vessel, with or without fins. With the addition of fins, the oscillating frequency was reduced from 0.86-Hz to 0.25-Hz. However, the goal-seeking algorithm was successful in guiding the vessel towards the target, an ultrasonic transmitter. When moved manually according to the instructions given by the algorithm, the vessel successfully reached the goal. Using assumptions based on prior experiments regarding the speed of an IPMC propelled vessel, the trial in which the goal was to the left of the axis required 18.2% more time to arrive at the goal than the trial in which the goal was to the right. This significant difference is due to the goal-seeking algorithm’s means to acquire the strongest signal. After the research had concluded and the propulsors failed to yield desired results, many factors were considered to rationalize the observations. The operating frequency was reduced, and it was found that, by the impulse-momentum theorem, that the propulsive force was reduced proportionally. The literature surveyed addressed undulatory motion, which produces constant propulsive force, not oscillatory, which yields intermittent propulsive force. These reasons among others were produced to rationalize the results and prove the cause of negative results was inherent to the actuators themselves. All rational options have been considered to yield positive results.

Smart materials have been widely used for control actuation. A robotic hand can be equipped with artificial tendons and sensors for the operation of its various joints mimicking human-hand motions. The motors in the robotic hand could be replaced with novel electroactive-polymer (EAP) actuators. In the three-finger gripper proposed in this paper, each finger can be actuated individually so that dexterous handling is possible, allowing precise manipulation. In this dissertation, a microscale position-control system using a novel EAP is presented. A third-order model was developed based on the system identification of the EAP actuator with an AutoRegresive Moving Average with eXogenous input (ARMAX) method using a chirp signal input from 0.01 Hz to 1 Hz limited to 7 ± V. With the developed plant model, a digital PID (proportional-integral-derivative) controller was designed with an integrator anti-windup scheme. Test results on macro (0.8-mm) and micro (50-μm) step responses of the EAP actuator are provided in this dissertation and its position tracking capability is demonstrated. The overshoot decreased from 79.7% to 37.1%, and the control effort decreased by 16.3%. The settling time decreased from 1.79 s to 1.61 s. The controller with the anti-windup scheme effectively reduced the degradation in the system performance due to actuator saturation. EAP microgrippers based on the control scheme presented in this paper will have significant applications including picking-and-placing micro-sized objects or as medical instruments. To develop model-based control laws, we introduced an approximated linear model that represents the electromechanical behavior of the gripper fingers. Several chirp voltage signal inputs were applied to excite the IPMC (ionic polymer metal composite) fingers in the interesting frequency range of [0.01 Hz, 5 Hz] for 40 s at a sampling frequency of 250 Hz. The approximated linear Box-Jenkins (BJ) model was well matched with the model obtained using a stochastic power-spectral method. With feedback control, the large overshoot, rise time, and settling time associated with the inherent material properties were reduced. The motions of the IPMC fingers in the microgripper were coordinated to pick, move, and release a macro- or micro-part. The precise manipulation of this three-finger gripper was successfully demonstrated with experimental closed-loop responses.