Kean C. Aw

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.

Bio-applications of ionic polymer metal composite transducers

Traditional robotic actuators have advanced performance which in some aspects can surpass thatof humans, however they are lacking when it comes to developing devices which are capable ofoperating together with humans. Bio-inspired transducers, for example ionic polymer metalcomposites (IPMC), which have similar properties to human tissue and muscle, demonstratemuch future promise as candidates for replacing traditional robotic actuators in medical roboticsapplications. This paper outlines four biomedical robotics applications, an IPMC stepper motor,an assistive glove exoskeleton/prosthetic hand, a surgical robotic tool and a micromanipulationsystem. These applications have been developed using mechanical design/modelling techniqueswith IPMC ‘artificial muscle’ as the actuation system. The systems are designed by firstsimulating the performance using an IPMC model and dynamic models of the mechanicalsystem; the appropriate advanced adaptive control schemes are then implemented to ensure thatthe IPMCs operate in the correct manner, robustly over time. This paper serves as an overview ofthe applications and concludes with some discussion on the future challenges of developing real-world IPMC applications.Keywords: ionic polymer metal composite (IPMC), medical robotics, bio-inspired(Some figures may appear in colour only in the online journal)1. IntroductionConventional mechanical actuators, for example electro-magnetic drives and hydraulic/pneumatic machines, have allbeen extensively investigated. Although these devices andtheir control systems are well understood and have advancedperformance which in some aspects can surpass that ofhumans, they are lacking when it comes to developingdevices which are capable of operating together with humansto augment their capabilities. The main limiting factors forthese devices are size, weight, power requirements, stiffnessand scalability, most of which cannot be resolved throughincremental research. New approaches to device developmentmust therefore be taken.Bio-inspired transducers which have similar properties tohuman tissue and muscle, in particular mechanical com-pliance, high power-to-weight and power-to-volume ratios,and precise and embedded control capabilities aredemonstrating much promise as candidates for replacing tra-ditional robotic actuators [1–5]. Ionic polymer-metalliccomposites (IPMC), a type of electroactive polymer (EAP)whose actuation mechanisms can mimic biological muscle,have been utilized in this research due to their desirablecharacteristics when compared with traditional and othersmart material actuators including flexibility, biocompat-ibility, small mass and low voltage. IPMCs act as actuatorsunder the influence of an electric field and conversely producean electric potential when mechanically deformed. Typically,IPMCs are fabricated in strips and are operated in a cantileverconfiguration where a voltage is either applied or measured atthe base through a set of clamped electrodes. A beam typeactuation greater than 90° can be achieved with small appliedvoltages, typically less than 5V. There has been a lot ofresearch on the fundamental aspects of IPMC actuation[6–11], as well as some examples of medical applicationssuch as an organ compression device for cardiac problems

A compliant surgical robotic instrument with integrated IPMC sensing and actuation

Robotic assisted surgery is becoming widely adopted by surgeons for a number of reasons, which include improved instrumentation control and dexterity as well as faster patient recovery times and cosmetic advantages. Robotic assisted surgery is currently one of the fastest growing applications in robotics. Although the traditional robotic actuators which are currently used have advanced performance which can, in some aspects, surpass that of humans, they simply do not have the capabilities and diversity required to meet the demand for new applications in robotic surgery. Novel transducers which have advanced capabilities and which allow safe operation in delicate environments are needed. Ionic polymer–metal composites (IPMCs) have extensive desirable characteristics when compared with traditional actuators and as their transduction mechanisms can mimic biological muscle they have much potential for future advanced biomedical and surgical robotics. In this research, a complete two degree-of-freedom (2DOF) surgical robotic instrument has been developed, which with the attachment of surgical tools (scalpel, etc.) has the ability to undertake surgical procedures. The system integrates an IPMC sensor and actuator at each joint. A gain scheduled (GS) controller, which is tuned with an iterative feedback tuning (IFT) algorithm, has been developed to ensure an accurate and adaptive response. The main advantages of this device over traditional devices are the improved safety through a natural compliance of the joints as well as the mechanical simplicity which ensures ease of miniaturisation for minimally invasive surgery (MIS). The components of the system have been tested and shown to have the capabilities required to operate the device for certain surgical procedures, specifically a device work envelope of 1600 mm2, compliance of 0.0668 m/N while still maintaining enough force to cut tissue, IPMC sensor accuracy between 3–22% and a control system which has shown to guarantee zero steady state error.

Indoor WiFi energy harvester with multiple antenna for low-power wireless applications

This research proposed a WiFi energy harvester for low-power wireless applications. The proposed system harvests energy using three antennas to cover three ISM (Industrial, Scientific, and Medical) channels with central frequencies at 2.412 GHz, 2.439 GHz, and 2.462 GHz. For each channel, a co-planar waveguide antenna is designed to harvest energy from indoor WiFi transmitters. FR4 substrate with relative permittivity of 4.3 and loss tangent of 0.025 is used to form the antennas. The output from each harvester antenna is then connected to a seven-stage multiplier circuit. The multiplier circuit is to rectify and boost the harvested energy to a higher voltage level and then stored temporarily in a super capacitor. A dc-dc boost-charger circuit with battery management is used to increase the output voltage level to 2 V. An experiment with the proposed system has been conducted using transmitted energy from available WiFi transmitters. The power density at the harvesting antenna front is between -80 dBm and -50 dBm. The proposed harvester system takes about 6 to 7 hours to charge up the first stage super capacitor up to the minimal threshold voltage (0.45V). This minimal threshold will start the boost-charger circuit charging the secondary storage device. This research demonstrates that the proposed system can supply energy for low-power wireless sensors that operate with an input power less than 1 mW.

Validation of a hybrid electromagnetic–piezoelectric vibration energy harvester

This paper presents a low frequency vibration energy harvester with contact based frequency up-conversion and hybrid electromagnetic–piezoelectric transduction. An electromagnetic generator is proposed as a power source for low power wearable electronic devices, while a second piezoelectric generator is investigated as a potential power source for a power conditioning circuit for the electromagnetic transducer output. Simulations and experiments are conducted in order to verify the behaviour of the device under harmonic as well as wide-band excitations across two key design parameters—the length of the piezoelectric beam and the excitation frequency. Experimental results demonstrated that the device achieved a power output between 25.5 and 34 μW at an root mean squared (rms) voltage level between 16 and 18.5 mV for the electromagnetic transducer in the excitation frequency range of 3–7 Hz, while the output power of the piezoelectric transducer ranged from 5 to 10.5 μW with a minimum peak-to-peak output voltage of 6 V. A multivariate model validation was performed between experimental and simulation results under wide-band excitation in terms of the rms voltage outputs of the electromagnetic and piezoelectric transducers, as well as the peak-to-peak voltage output of the piezoelectric transducer, and it is found that the experimental data fit the model predictions with a minimum probability of 63.4% across the parameter space.

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

Soft Pneumatic Bending Actuator with Integrated Carbon Nanotube Displacement Sensor

The excellent compliance and large range of motion of soft actuators controlled by fluid pressure has lead to strong interest in applying devices of this type for biomimetic and human-robot interaction applications. However, in contrast to soft actuators fabricated from stretchable silicone materials, conventional technologies for position sensing are typically rigid or bulky and are not ideal for integration into soft robotic devices. Therefore, in order to facilitate the use of soft pneumatic actuators in applications where position sensing or closed loop control is required, a soft pneumatic bending actuator with an integrated carbon nanotube position sensor has been developed. The integrated carbon nanotube position sensor presented in this work is flexible and well suited to measuring the large displacements frequently encountered in soft robotics. The sensor is produced by a simple soft lithography process during the fabrication of the soft pneumatic actuator, with a greater than 30% resistance change between the relaxed state and the maximum displacement position. It is anticipated that integrated resistive position sensors using a similar design will be useful in a wide range of soft robotic systems.