Adaptive tuning of a 2DOF controller for robust cell manipulation using IPMC actuators

Identification of an ionic polymer metal composite actuator employing Preisach type fuzzy NARX model and Particle Swarm Optimization

A new method to fabricate ionic polymer metal composite (IPMC) actuators with a 3-dimensional preshaped form by a simple thermal treatment process is demonstrated. The effects of the thermal treatment process on the properties of the actuator are analyzed and the characteristics of the actuator, such as stiffness, displacement and resonance, generating force, and repeated motions, are compared with those of unheated IPMC actuators. The experimental results show that thermal-treated IPMC actuators have improved generating force as well as preshaping of the 3-dimensional form.

The ionic polymer metal composite (IPMC) actuator is one of the most promising smart actuators that possesses unique advantages and is suitable for underwater applications. However, there are challenges to employ it directly in such applications for precise tracking. The IPMC suffers from high nonlinearity due to the existence of inherent creep and hysteresis phenomena. Furthermore, the IPMC actuator is always subject to uncertainty and external disturbance due to the working environment. Therefore, to cope with the aforementioned restrictions and to make the IPMC applicable for real-life applications, designing a high-accuracy tracking control technique is an urgent demand. In this article, a new integral nonlinear hyperplane-based sliding mode controller is dedicated for an underwater IPMC actuator. The proposed controller employs an adaptive tuning law in the discontinuous part to overcome any prerequisite for knowing the upper bound of the model uncertainty and external disturbance. Extensive experiments have been carried out to verify practical effectiveness of the proposed controller in comparison with conventional nonsingular terminal sliding mode in terms of fast convergence, accurate tracking, and the robust performance.

Underwater microrobots are in urgent demand for applications such as pollution detection and video mapping in limited space. Compact structure, multi-functionality, flexibility, and position precision are normally considered incompatible characteristics for underwater microrobots. To accomplish our objectives, we developed several novel bio-inspired biomimetic locomotions with ionic polymer metal composite (IPMC) actuators. IPMC actuator could implement a fast response and high bending deformation, which could be used as artificial muscles to propel robots backwards and forwards with a compact structure. To implement the position precision of IPMC actuator, we proposed an electromechanical model and analyzed the deformation and actuating force of the IPMC equivalent cantilever beam, which were used for the biomimetic locomotion. Then a conventional PID controller for IPMC actuators was designed from the identified model. Based on the IPMC equivalent cantilever beam model, we developed several kinds of underwater microrobots with the compact structure, multi-functionality, flexibility, and position precision.

Mechanics and electrochemistry of ionic polymer metal composites

For the first time, the ionic polymer metal composite (IPMC) actuator is integrated with a radio frequency identification (RFID) tag antenna for achieving frequency reconfiguration in the ultrahigh-frequency (UHF) band. Here, the IPMC movable flap serves as an actuator that can effectively tune the tag resonant frequency. By applying a two-layer-crenelated structure and employing a surface patterned electrode for restraining back relaxation, the deflection of the IPMC actuator can be significantly improved. The IPMC actuator can move in two directions, enabling two-degree frequency tuning. Numerical and experimental data confirm that the tip displacement of the IPMC actuator can be enhanced up to 266% with the use of the two-layer-crenelated structure. The IPMC actuator allows the resonant frequency of the tag antenna to be tuned back by as much as 35 MHz, after deviating due to placing on an unintended object. UHF RFID application is also performed using a portable commercial RFID reader. Good frequency reconfiguration and broad tuning range, along with far read distances, have been achieved with our tunable UHF RFID tag antenna.

Compact structure, multifunction, and flexibility are normally considered as incompatible characteristics for legged microrobots. Most robots focused on complex structure of multi-joint legs to attain the multifunction and flexibility, while others had poor flexibility for miniaturization. In the field of underwater monitoring for applications such as pollution detection and video mapping in limited space, underwater microrobots are urgently demanded. To realize these purposes, we have developed several types of microrobots with both compact structure and flexible locomotion. However, they just realized walking, rotating, swimming, or floating motions. Without biomimetic fingers, they could not do some simple operations, such as grasping and carrying any objects to desired place. So, in this paper, we designed a novel type of biomimetic locomotion employing ionic polymer metal composite (IPMC) actuator as one-DOF leg. Then we proposed a new type of underwater microrobot using ten ionic polymer metal composite (IPMC) actuators as legs or fingers, which could realize walking, rotating, floating, and grasping motions. Also, we developed a prototype of this underwater microrobot and carried out some experiments to evaluate its walking and floating speeds. In addition, we used six IPMC actuators as fingers to grasp some small objects and float up. To realize the closed-loop control for the microrobot, we used three proximity sensors to detect and avoid the obstacle while walking.

In the present paper, equivalent beam and equivalent bimorph beam models for IPMC(ionic Polymer-Metal Composite) actuators are described. Physical properties of an IPMC, such as Young's modulus and electro-mechanical coupling coefficient. are determined from the rule of mixture, bimorph beam equations, and measured force-displacement data of a cantilevered IPMC actuator. By using a beam equation with estimated physical properties, actuation displacements of a cantilevered IPMC actuator was calculated and a good agreement between the computed tip displacements and the measured data was observed. Finite element analysis(FEA) combined with the estimated physical properties was used to reproduce the force-displacement relationship of an IPMC actuator. Results from the FEA agreed well with the measure data. The proposed models might be used for modeling of IPMC actuators with complicated shapes and boundary conditions.

An ionic polymer-metal composite (IPMC) actuator is one of polymer-based soft actuators. It is produced by chemically plating gold or platinum on both surface of a perfluorosulfonic acid membrane which is known as an ion-exchange membrane. It is able to be activated by a simple driving circuit and generate a large deformation under a low applied voltage (0.5-3 V). However, individual difference and characteristics changes from environmental conditions should be considered for realizing a stable or precise control. To solve these problems, we applied a stochastic ON/OFF controller to an integrated IPMC actuator with parallel connections. The controller consists of a central controller and distributed controllers. The central controller broadcasts a control signal such as an error signal to distributed controllers uniformly. The distributed controllers switch the ON/OFF states based on the broadcasted signal stochastically. The central controller dose not measure the states of each IPMC actuator, and the control signals is calculated by using the output signal of the integrated actuator and reference signal. The validity of the applied method was investigated through numerical simulations and experiments.

In this work, flapping wings actuated by IPMCs are designed and simulated to mimick birds wing. In order for the wing to generate lift and thrust during flapping motion, the wing must be able to flap and twist at the same time. For design of such wings, shape of the IPMC actuator need to be designed such that the actuator can create bending and twisting motions during wing strokes. To determine the shape of the IPMC actuator, an equivalent bimorph beam model has been proposed based on the measured force-displacement data of an IPMC. The equivalent model and thermal analogy are used for numerical simulation of IPMC actuated wings to determine suitable shape of the IPMC actuator. In this way, we could select a best performing wing that can create the largest twist motion during flapping of the wing.

This paper reports a microreservior-based drug delivery device that is activated by ionic polymer metal composite (IPMC) actuator. The actuator is fabricated with Nafion 117 membrane and plated with silver layer electrodes. To fit with biocompatible properties, the device body, including the drug reservoir, was constructed using polydimethylsiloxane (PDMS) material. Experimental measurement of the fabricated IPMC actuator shows a maximum deflection displacement of 0.076 ~ 0.077 mm at two consecutive actuation cycles. To study the concentration of the drug released from the developed device, fluorescent dye was loaded in the reservoir and the released intensity was measured using well plate reader. An increase of the fluorescent intensity shows that IPMC actuator successfully unseals the microreservoir and achieves the targeted application.

Ionic Polymer Metal Composite (IPMC) is a new smart material that can be used as both sensors and actuators in numerous industrial and medical applications. However, IPMC actuators have many disadvantages, such as hysteresis nonlinearity, which make it difficult to model accurately. In this paper, we presented a precise dynamic nonlinear model with temporal operation for IPMC actuators based on a recurrent fuzzy neural network (RFNN) with interpretability, universal approximation ability and learning ability, a nonlinear auto-regressive with exogenous input (NARX) structure with potential to predict future outputs, Adaptive Weighted Particle Swarm Optimization (AWPSO) algorithm with local and global optimization capability and recurrent least squares (RLS).Firstly, a suitable mathematical model with temporal relations using RFNN-NARX structure was constructed. Then, AWPSO and RLS were employed to identify unknown parameters by using the collected experimental data. Finally, verification results were provided to show the capability of the presented method to effectively and accurately predict the actual displacement of IPMC actuators.

In this paper, model-based precision force and position control of an ionic polymer metal composite (IPMC) is presented. A 23.8 mm × 3.4 mm × 0.16 mm IPMC strip was used as an actuator in a cantilever configuration. Open-loop force and position responses of an IPMC are not repeatable, and hence closed-loop precision control is of critical importance to ensure proper functioning, repeat-ability and reliability. After feedback controllers were designed and implemented with empirically obtained fourth-order plant transfer functions, the overshoot decreased from 460 to 2.8 per cent and the settling time was reduced from 37.5 to 3.22 s in force control. In position control the overshoot decreased from 333 to 20.3 per cent and the settling time was reduced from 21.5 to 2.56 s. Microscale precision force and position control capabilities of the IPMC actuator were also demonstrated experimentally. An 8 μN force resolution was achieved with a force noise of 0.5μN r.m.s., and the position resolution was 6 μm with a position noise of 2.5 μm r.m.s. The maximum force and tip displacement achieved with the IPMC actuator under closed-loop control were 2 mN and 5 mm respectively. The IPMC actuator could follow various commanded force and position trajectories such as sinusoidal and trapezoidal position profiles, and a velocity profile with a 3 mm/s maximum velocity. A novel hybrid force and position control strategy demonstrated its utility in practical micromanipulalion applications where the actuator force must be limited to prevent damaging micro-objects. High-precision control of the IPMC at low force level proved its potential for micromanufacturing and micromanipulation applications such as robotic and biomedical microgrippers.

This paper presents dynamic modeling of an innovative contractible ionic polymer-metal composites (IPMC) actuator with a helical configuration. The helical shaped IPMC actuator is fabricated through the thermal treatment of an IPMC strip, which is helically coiled on a glass rod. This type of a soft actuator can be used to realize not only bending motion but also torsional and longitudinal motion. For the first time, an explicit analytical expression is developed for the computation of mode shapes and dynamic responses of a helical IPMC actuator based on the intrinsic equations of the naturally curved and twisted beam. The numerical transfer-matrix method is used to solve the systems of 12 linear ordinary differential equations with boundary conditions. In particular, the effect of the structural parameters on the performance of the helical IPMC actuator is evaluated, using experimental results and an analytical model. The validation of the proposed model is achieved through comparison with computational results using a commercial finite-element (FE) program as well as experimental results. The present experimental and theoretical results show that diameter, among the structural parameters, plays an important role in the actuation performance of a helical IPMC actuator. The proposed modeling is general and can also be used in solving other cylindrical or noncylindrical helical IPMC actuators with different cross-sectional shapes as well as various end conditions.

Minimally Invasive Surgery (MIS) is receiving much attention for a number of reasons, including less trauma, faster recovery and enhanced precision. The traditional robotic actuators do not have the capabilities required to fulfill the demand for new applications in MIS. Ionic Polymer-Metal Composite (IPMC), one of the most promising smart materials, has extensive desirable characteristics such as low actuation voltage, large bending deformation and high functionality. Compared with traditional actuators, IPMCs can mimic biological muscle and are highly promising for actuation in robotic surgery. In this paper, a new approach which involves molding and integrating IPMC actuators into a soft silicone tube to create an active actuating tube capable of multi-degree-of-freedom motion is presented. First, according to the structure and performance requirements of the actuating tube, the biaxial bending IPMC actuators fabricated by using solution casting method have been implemented. The silicone was cured at a suitable temperature to form a flexible tube using molds fabricated by 3D Printing technology. Then an assembly based fabrication process was used to mold or integrate biaxial bending IPMC actuators into the soft silicone material to create an active control tube. The IPMC-embedded tube can generate multi-degree-of-freedom motions by controlling each IPMC actuator. Furthermore, the basic performance of the actuators was analyzed, including the displacement and the response speed. Experimental results indicate that IPMC-embedded tubes are promising for applications in MIS.