Enrico Haemmerle

Control of IPMC Actuators for Microfluidics With Adaptive “Online” Iterative Feedback Tuning

Ionic polymer metal composites (IPMCs) are actuators that lend themselves well to microfluidic applications due to their lightweight, flexibility, ability to tailor their geometry, as well as the capability to be miniaturized and implanted into microelectro-mechanical systems devices. The major issue with implementing IPMCs into such devices is the ability to control their actuation and, hence, their reliability over a long period of time. This paper presents a novel iterative feedback tuning (IFT) algorithm that tunes the system online using experimental data during normal system operation. The controller adaptively tunes the highly nonlinear and time varying IPMC for a newly proposed micropump. This demonstrates the ability of the system to have a reliable performance over a long period of time without the need of any offline tuning or system identification. The system was run for 20 controller updates. This corresponds to 10 and 20 min of operation for the 0.1 and 0.05 Hz reference inputs, respectively. 100 and 300 μm amplitudes were tested to demonstrate the ability of the system to adaptively tune to different input signals. Experimental results show the newly proposed IFT algorithm has successfully tuned the controller to achieve up to 92% better performance when compared with a conventional model-based tuned controller.

A conclusive scalable model for the complete actuation response for IPMC transducers

This paper proposes a conclusive scalable model for the complete actuation response for ionic polymer metal composites (IPMC). This single model is proven to be able to accurately predict the free displacement/velocity and force actuation at varying displacements, with up to 3 V inputs. An accurate dynamic relationship between the force and displacement has been established which can be used to predict the complete actuation response of the IPMC transducer. The model is accurate at large displacements and can also predict the response when interacting with external mechanical systems and loads. This model equips engineers with a useful design tool which enables simple mechanical design, simulation and optimization when integrating IPMC actuators into an application. The response of the IPMC is modelled in three stages: (i) a nonlinear equivalent electrical circuit to predict the current drawn, (ii) an electromechanical coupling term and (iii) a segmented mechanical beam model which includes an electrically induced torque for the polymer. Model parameters are obtained using the dynamic time response and results are presented demonstrating the correspondence between the model and experimental results over a large operating range. This newly developed model is a large step forward, aiding in the progression of IPMCs towards wide acceptance as replacements to traditional actuators.

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

Rapid advancement in medicine and bioscience is causing demand for faster, more accurate and dexterous as well as safer and more reliable micro-manipulators capable of handling biological cells. Current micro-manipulation techniques commonly damage cell walls and membranes due to their stiffness and rigidity. Ionic polymer-metal composite (IPMC) actuators have inherent compliance and with their ability to operate well in fluid and cellular environments they present a unique solution for safe cell manipulation. The reason for the downfall of IPMCs is that their complex behaviour makes them hard to control precisely in unknown environments and in the presence of sizeable external disturbances. This paper presents a novel scheme for adaptively tuning IPMC actuators for precise and robust micro-manipulation of biological cells. A two-degree-of-freedom (2DOF) controller is developed to allow optimal performance for both disturbance rejection (DR) and set point (SP) tracking. These criteria are optimized using a proposed IFT algorithm which adaptively updates the controller parameters, with no model or prior knowledge of the operating conditions, to achieve a compliant manipulation system which can precisely track targets in the presence of large external disturbances, as will be encountered in real biological environments. Experiments are presented showing the performance optimization of an IPMC actuator in the presence of external mechanical disturbances as well as the optimization of the SP tracking. The IFT algorithm successfully tunes the DR and SP to an 85% and 69% improvement, respectively. Results are also presented for a one-degree-of-freedom (1DOF) controller tuned first for DR and then for SP, for a comparison with the 2DOF controller. Validation has been undertaken to verify that the 2DOF controller does indeed outperform both 1DOF controllers over a variety of operating conditions.

Development of an ionic polymer–metal composite stepper motor using a novel actuator model

A novel ionic polymer–metal composite (IPMC) actuated stepper motor was developed in order to demonstrate an innovative design process for complete IPMC systems. The motor was developed by utilizing a novel model for IPMC actuators integrated with the complete mechanical model of the motor. The dynamic, nonlinear IPMC model can accurately predict the displacement and force actuation in air for a large range of input voltages as well as accounting for interactions with mechanical systems and external loads. By integrating this geometrically scalable IPMC model with a mechanical model of the motor mechanism an appropriate size IPMC strip has been chosen to achieve the required motor specifications. The entire integrated system has been simulated and its performance verified. The system has been built and the experimental results validated to show that the motor works as simulated and can indeed achieve continuous 360° rotation, similar to conventional motors. This has proven that the model is an indispensable design tool for integrated IPMC actuators into real systems. This newly developed system has demonstrated the complete design process for smart material actuator systems, representing a large step forward and aiding in the progression of IPMCs towards wide acceptance as replacements for traditional actuators.

Design, Analysis, and Control of a Novel Safe Cell Micromanipulation System With IPMC Actuators

This paper presents the design, analysis, and control of a novel micromanipulation sys-tem to facilitate the safe handling/probing of biological cells. The robotic manipulatorhas a modular design, where each module provides two degrees-of-freedom (2DOF) andthe overall system can be made up of a number of modules depending on the desired levelof dexterity. The module design has been optimized in simulation using an integratedionic polymer-metal composite (IPMC) model and mechanical mechanism model toensure the best system performance from the available IPMC material. The optimal sys-tem consists of two modules with each DOF actuated by a 27.5 mm long by 10 mm wideactuator. A 1DOF control structure has been developed, which is adaptively tuned usinga model-free iterative feedback tuning (IFT) algorithm to adjust the controller parame-ters to optimize the system tracking performance. Experimental results are presentedwhich show the tuning of the system improves the performance by 24% and 64% for thehorizontal and vertical motion, respectively. Experimental characterization has also beenundertaken to show the system can accurately achieve outputs of up to 7 deg and resultsfor position tracking in both axes are also presented. [DOI: 10.1115/1.4024226]Keywords: ionic polymer-metal composites (IPMC), micromanipulation, iterativefeedback tuning (IFT), design, control, actuator

Development of a 2DOF micromanipulation system with IPMC actuators

This paper presents the design and control of a novel 2 degree-of-freedom (2DOF) micromanipulator to facilitate the safe handling and manipulation of biological materials. The manipulator is driven by two IPMC actuators for each DOF and the system controller is adaptively tuned online using a model-free iterative feedback tuning (IFT) algorithm to adjust the controller parameters to optimize the system performance. A 2DOF controller structure was implemented for each axis of motion so both the disturbance rejection (DR) and set point (SP) response can be optimized, making the system ideal for operating in unknown environments. Simulations are presented which utilize an IPMC model and mechanical manipulator model to show the system performance has been improved by 37% for the DR and by 24% and 28% for SP in the horizontal and vertical direction respectively. Experimental results are also presented to validate the design and show the system can achieve outputs of up to 7° in both axes.

Experimental performance and feasibility of a miniature single-degree-of-freedom rotary joint with integrated IPMC actuator

Ionic Polymer Metal Composite (IPMC) materials are bending actuators that can achieve large tip displacements at voltages less than 10V, but with low force output. Their advantages over traditional actuators include very low mass and size; flexibility; direct conversion of electricity to mechanical energy; biocompatibility; and the potential to build integrated sensing/actuation devices, using their inherent sensing properties. It therefore makes sense to pursue them as a replacement to traditional actuators where the lack of force is less significant, such as micro-robotics; bio-mimetics; medical robotics; and non-contact applications such as positioning of sensors. However, little research has been carried out on using them to drive mechanisms such as the rotary joints. This research explores the potential for applying IPMC to driving a single degree-of-freedom rotary mechanism, for a small-force robotic manipulator or positioning system. Practical issues such as adequate force output and friction are identified and tackled in the development of the mechanical apparatus, to study the feasibility of the actuator once attached to the mechanism. Rigid extensions are then applied to the tip of the IPMC, as well as doubling- and tripling the actuators in a stack to increase force output. Finally, feasibility of the entire concept is considered by comparing the maximum achievable forces and combining the actuator with the mechanism. It is concluded that while the actuator is capable of moving the mechanism, it is non-repeatable and does not achieve a level that allows feedback control to be applied.

Development of a 1x2 Piezoelectric Optical Fiber Switch

This paper presents the design, fabrication and performance of a 1×2 piezoelectric optical switch. The optical switch is developed based on the concept that the input fiber is directly moved by the deflection of a piezoelectric tube actuator. The piezoelectric tube actuator used in this switch is manufactured through an electrophoretic deposition process. The tube is inexpensive to produce and compact in size with high mechanical performance. It has a maximum deflection of 30μm which is capable to actuate the input fiber for switching. The multimode fiber optical switch has been successfully assembled. To reduce the misalignment loss between the fibers, the output fibers are precisely aligned in silicon vgrooves. Different components are bonded with low shrinkage adhesive in order to minimize their position inaccuracy. The performance characteristics of the optical switch have been measured, with an insertion loss of 1dB, crosstalk of -45dB and switching speed from 5 to 10ms. The switch also shows good reliability and requires small driving power. The development of multimode optical switch prototypes proves that the idea of piezoelectric switching is feasible. Further developments include the improvement of switching performance, reduction of the prototype size and the fabrication of multiple output prototypes.

CHARACTERIZATION OF BST PRODUCED BY HIGH TEMPERATURE HYDROTHERMAL SYNTHESIS

Barium strontium titanate (BST) was produced in a teflon lined pressure vessel using a high temperature hydrothermal technique and controlling the processing parameters of Ba+Sr concentration, Ba and Sr ratio, temperature, reaction period and TiO2 concentration. It was found that this technique produces BST powders of less than 200 nm particle size with high degree of crystallinity. However, most BST powders tend to be strontium rich. Thus, excess barium in the initial solution was essential in order to produce a high barium content in the final product, which was important to obtain good electrical properties. A high TiO2 concentration was also crucial in producing BST with a high Ba content, though this parameter was responsible for a multiphase structure. The period of hydrothermal reaction was important for stoichiometric reaction.

P-TYPE ALUMINIUM-NITROGEN CO-DOPED ZnO FILMS PREPARED BY THERMAL OXIDATION OF SPUTTERED Zn3N2:Al PRECURSORS

P-type (Al, N) co-doped ZnO films have been prepared by thermal oxidation of sputtered Zn3N2:Al precursor films. The Zn3N2:Al precursors are deposited by RF magnetron sputter and then annealed in oxygen atmosphere at different temperatures. The doped ZnO films are characterized by XRD, XPS and Hall effect measurement. The results indicate that the ZnO films only show p-type conductivity with an annealing in a temperature window: ZnO films show the best p-type characteristics with a hole concentration of 4.2 × 1017cm-3, mobility of 0.52 cm/V.s and resistivity of 28Ωcm after an annealing at 550°C. Using these p-type ZnO films, ZnOp-n junctions are prepared which show good diode characteristics. The chemical states of N and Al dopants in the ZnO host material are investigated by XPS method after annealing at different temperatures; and the doping mechanisms are discussed based on the XPS results.