Andrew McDaid

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.

Virtual Normalization of Physical Impairment: A Pilot Study to Evaluate Motor Learning in Presence of Physical Impairment

Motor learning is a critical component of the rehabilitation process; however, it can be difficult to separate the fundamental causes of a learning deficit when physical impairment is a confounding factor. In this paper, a new technique is proposed to augment the residual ability of physically impaired patients with a robotic rehabilitation exoskeleton, such that motor learning can be studied independently of physical impairment. The proposed technique augments the velocity of an on-screen cursor relative to the restricted physical motion. Radial Basis Functions (RBFs) are used to both model velocity and derive a function to scale velocity as a function of workspace position. Two variations of the algorithm are presented for comparison. In a cross-over pilot study, healthy participants were recruited and subjected to a simulated impairment to constrain their motion, imposed by the cable-driven wrist exoskeleton. Participants then completed a sinusoidal tracking task, in which the algorithms were statistically shown to augment the cursor velocity in the constrained state such that it matched position-dependent velocities recorded in the healthy state. A kinematic task was then designed as a motor-learning case study where the algorithms were statistically shown to allow participants to achieve the same performance when their motion was constrained as when unconstrained. The results of the pilot study provide motivation for further research into the use of this technique, thus providing a tool with which motor-learning can be studied in neurologically impaired populations. This could be used to give physiotherapists greater insight into underlying causes of motor learning deficits, consequently facilitating and enhancing subject-specific therapy regimes.

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

Human-inspired robotic exoskeleton (HuREx) for lower limb rehabilitation

A robot exoskeleton which is inspired by the human musculoskeletal system has been developed for lower limb rehabilitation. The device was manufactured using a novel technique employing 3D printing and fiber reinforcement to make one-of-a-kind form fitting human-robot connections. Actuation of the exoskeleton is achieved using PMAs (pneumatic air muscles) and cable actuation to give the system inherent compliance while maintaining a very low mass. The entire system was modeled including a new hybrid model for PMAs. Simulation and experimental results for a force and impedance based trajectory tracking controller demonstrate the feasibility for using the HuREx system for gait and rehabilitation training.

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.

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.

Brain controlled robotic exoskeleton for neurorehabilitation

Robots have been used for decades to enhance productivity, reliability and accuracy for repetitive tasks. More recently robot capabilities have been exploited in medical rehabilitation applications for this same reason. While robots can provide consistent physical therapy there is limited evidence that robot assisted physical therapy has any improved outcomes over human administered therapy. Patient participation is the most important factor for rehabilitating the neural system after injury or stroke and so this research develops a new method for re-connecting the brain to the limbs of a patient. Steady state visual evoked potential (SSVEP) signals are read and decoded to extract the users intent, and then used to control a robot exoskeleton to move the patients limbs for therapy. This artificial reconnection of the brain to the limbs allows therapy in a natural way and provides positive reinforcement for learning and so it is believed it will result in improved outcomes. Two different training protocols are proposed and tested to allow real-time brain control of a lower limb rehabilitation device. Results with healthy patients are extremely good with accuracy to within a knee angle of 1° at 100% reliability after simple training. This gives much promise to future development of brain controlled rehabilitation devices.

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