Based on dean-flow-coupled elasto-inertial effects, 3D particle focusing in a straight channel with asymmetrical expansion–contraction cavity arrays (ECCA channel) is achieved. First, the mechanism of particle focusing in both Newtonian and non-Newtonian fluids was introduced. Then particle focusing was demonstrated experimentally in this channel with Newtonian and non-Newtonian fluids using three different sized particles (3.2μm, 4.8 μm, 13 μm), respectively. The influences of flow rates on focusing performance in ECCA channel were studied. Results show that in ECCA channel particles are focused on the cavity side in Newtonian fluid due to the synthesis effects of inertial and dean-drag force, whereas on the opposite cavity side in non-Newtonian fluid due to the addition of viscoelastic force. Compared with the focusing performance in Newtonian fluid, the particles are more easily and better focused in non- Newtonian fluid. A further advantage is three-dimensional (3D) particle focusing in non-Newtonian fluid is realized according to the lateral side view of the channel while only two-dimensional (2D) particle focusing can be achieved in Newtonian fluid. Conclusively, this Dean-flow-coupled elasto-inertial microfluidic device could offer a continuous, sheathless, and high throughput (>10000 s-1) 3D focusing performance, which may be valuable in various applications from high speed flow cytometry to cell counting, sorting, and analysis.
Within the areas of cell biology, biomedicine and minimal invasive surgery, there is a need for soft, flexible and dextrous biocompatible manipulators for handling biological objects, such as single cells and tissues. Present day technologies are based on simple suction using micropipettes for grasping objects. The micropipettes lack the possibility of accurate force control, nor are they soft and compliant and may thus cause damage to the cells or tissue. Other micromanipulators use conventional electric motors however the further miniaturization of electrical motors and their associated gear boxes and/or push/pull wires has reached its limits. Therefore there is an urgent need for new technologies for micromanipulation of soft biological matter.
We are developing soft, flexible micromanipulators such as micro- tweezers for the handling and manipulation of biological species including cells and surgical tools for minimal invasive surgery. Our aim is to produce tools with minimal dimensions of 100 μm to 1 mm in size, which is 1-2 orders of magnitude smaller than existing technology. We present newly developed patterning and microfabrication methods for polymer microactuators as well as the latest results to integrate these microactuators into easy to use manipulation tools. The outcomes of this study contribute to the realisation of low-foot print devices articulated with electroactive polymer actuators for which the physical interface with the power source has been a significant challenge limiting their application. Here, we present a new bottom-up microfabrication process. We show for the first time that such a bottom-up fabricated actuator performs a movement in air. This is a significant step towards widening the application areas of the soft microactuators.
Performance of the conducting polymer actuators (CPAs) are affected by material uncertainties, operating conditions and
time of operation. The same size CPAs may have different actuation capabilities, which can also degrade over the course
of operation. For accurate and repeatable position tracking, the uncertainties and variations in the actuator dynamics have
to be carefully addressed to achieve a desirable control performance.
This paper presents a systematic approach for the identification of parametric uncertainties and designing robust H∞ control to achieve a guaranteed performance when the CPA is used for position tracking. We identify the uncertainties in
actuator dynamics by performing series of experiments using two geometrically equivalent CPAs. A set of system
models is obtained to determine the average actuation capability. The variations in the actuator dynamics are modeled as
a parametric uncertainty. H∞ controllers are designed and the robustness of the controllers is validated by experiments on two different but same sized CPAs. The performance of the H∞ controller is also compared with a proportional-integralderivative (PID) controller. We demonstrate that the robust H∞control strategy performs repeated acceptable performances on both samples.
The object of this paper is to characterise the stiffness of microfabricated cantilevers consisting of two electroactive
polymer (polypyrrole (PPy)) layers, and two gold layers with a negligible thickness and a layer of porous polyvinylidene
fluoride (PVDF), which serves as a backing layer and electrolyte storage tank. This composite cantilever structure is
used as polymer actuators or famously known as artificial muscles when tailored appropriately. The polymer
microactuators considered in this study, which were fabricated using a laser ablation technique, could operate both in
aqueous and non-aqueous media. The stiffness characterization of the microactuators is critical to assess their suitability
to numerous applications including the micromanipulation of living cells, bio-analytical nanosystems, datastorage, labon-
chip, microvalve, microswitch, microshutter, cantilever light modulators, micro-optical instrumentation, artificial
muscles for micro and macro robotic sytems and similar. The stiffness measurement method followed in this study is a
static deflection measurement method, using an atomic force microscope (AFM). The stiffness constants of the
microactuators while they were in passive (no electrochemical activation) and active (electrochemically activated) states
were measured separately, and their statistical comparison was provided. The possible error sources for the stiffness
measurement method are elaborated.
Conducting polymer trilayers are attractive for use in functional devices, given low actuation voltages, operation in air
and potentially useful stresses and strains; however, their dynamic behavior must be understood from an engineering
perspective before they can be effectively incorporated into a design. As a step towards the identification of the actuator
dynamics, frequency response analysis has been performed to identify the magnitude and phase shift of displacement in
response to a sinusoidal voltage input. The low damping of the trilayer operating in air and the use of a laser
displacement sensor has allowed the frequency response to be continuously identified up to 100Hz, demonstrating a
resonant peak at 80Hz for a 10mm long actuator. Two linear transfer function models have been fitted to the frequency
response of the trilayer displacement (i) a 3rd order model to represent the dynamics below 20Hz and (ii) a higher
complexity 6th order model to also include the resonant peak. In response to a random input signal, the 3rd order model
coarsely follows the experimental identified displacement, while the 6th order model is able to fully simulate the real
trilayer movement. Step responses have also been obtained for the 3rd and 6th order transfer functions, with both models
capable of following the first 4 seconds of experimental displacement. The application of empirical transfer function
models will facilitate accurate simulation and analysis of trilayer displacement, and will lead to the design of accurate
positional control systems.
In this paper the behavior of conjugated polymers as mechanical sensors is experimentally characterized and modeled. A
trilayer conjugated polymer sensor is considered, where two polypyrrole (PPy) layers sandwich an amorphous polyvinylidene
fluoride (PVDF) layer, with the latter serving as an electrolyte tank. A theory for the sensing mechanism is proposed
by postulating that, through its influence on the pore structure, mechanical deformation correlates directly to the concentration
of ions at the PPy/PVDF interface. This provides a key boundary condition for the partial differential equation (PDE)
governing the ion diffusion and migration dynamics. By ignoring the migration term in the PDE, an analytical model is
obtained in the form of a transfer function that relates the open-circuit sensing voltage to the mechanical input. The model
is validated in experiments using dynamic mechanical stimuli up to 50 Hz.
Trilayer polypyrrole benders are capable of generating voltages and currents when applied with an external force or
displacement, demonstrating potential as mechanical sensors. Previous work has identified the effects of dopant and
electrolyte on the sensor output, and a 'deformation induced ion flux' model was proposed. The current work aims to
identify the change in sensor response with input amplitude and bender geometry as a function of frequency. The
current and charge output from the trilayer benders were found to increase proportionally with input displacement and
bender strain for multiple input frequencies, indicating linearity. Sensitivities of the current and charge output have also
been calculated in response to strain, and are found to increase as the volume of the conducting polymer is increased.
Some guidelines for sensor geometry are then suggested, using the identified sensitivities as a guide.
Small, highly-mobile "swimming" robots are desired for underwater monitoring operations, including pollution
detection, video mapping and other tasks. Actuator materials of all types are of interest for any application where space
is limited. This constraint certainly applies to the small-scale swimming robot, where multiple small actuators are
needed for forward/backward propulsion, steering and diving/surfacing. A number of previous studies have
demonstrated propulsion of floating objects using IPMC type polymer actuators [1-3] or piezoceramic actuators [4, 5].
Here, we show how propulsion is also possible using a multi-layer polypyrrole bimorph actuator. The actuator is based
on our previously published work showing very fast resonance actuation in polypyrrole bending-type actuators .
The bending actuator is a tri-layer structure, in which the gold-PVDF (porous poly(vinylidene fluoride) membrane)
substrate was coated on both sides with polypyrrole layers to form an electrochemical cell. Polypyrrole films on gold
coated PVDF were grown galvanostatically at a current density of 0.10 mA/cm2 for 12 hours from propylene carbonate
(PC) solution containing 0.1 M Li+TFSI-, 0.1 M pyrrole and 1% (w/w) water. The polypyrrole deposited PVDF was
thoroughly rinsed with acetone and stored in 0.1 M Li+TFSI- / PC solution. The edges of the bulk film were trimmed
off and the bending actuators were prepared as rectangular strips typically 2mm wide and 25 mm long.
These actuators gave fast operation in air (to 90 Hz), and were utilised as active flexural joints on the tail fin of a fishshaped
floating "boat". The actuators were attached to a simple truncated shaped fin and the deflection angle was
analysed in both air and liquid for excitation with +/- 1V square wave at a range of frequencies. The mechanical
resonance of the fin was seen to be 4.5 Hz in air and 0.45 Hz in PC, which gave deflection angles of approximately 60°
and 55° respectively.
The boat contained a battery, receiver unit and electronic circuit attached to the actuator fin assembly. Thus, the boat
could be operated by remote control, and by varying the frequency and duty cycle applied to the actuator, the speed and
direction of the boat could be controlled. The boat had a turning circle as small as 15 cm in radius and a maximum
speed of 2m/min when operating with a tail frequency of approximately 0.7 Hz. The efficiency of the flapping tail fin
was analysed and it was seen that operation at this frequency corresponded with a Strouhal number in the optimal range.
The reduction-oxidation (redox) level of a conjugated polymer has significant impact on its electro-chemo-mechanical
properties, such as conductivity, impedance, and Young's modulus. A redox level-dependent impedance model is developed
in this paper by including the dynamics of ion diffusion, ion migration, and redox reactions. The model, in the form
of a transfer function, is derived through perturbation analysis around a given redox level. Experimental measurements
conducted under different redox conditions correlate well with the model prediction and thus validate the proposed model.
This work, for the first time, incorporates the effect of redox level into the dynamics of conjugated polymers, and facilitates
the future use of nonlinear control methods for the effective control of these materials.
Conjugated polymers have promising applications as actuators in biomimetic robotics and bio/micromanipulation.
For these applications, it is highly desirable to have predictive models available for feasibility study and design
optimization. In this paper a geometrically-scalable model is presented for trilayer conjugated polymer actuators
based on the diffusive-elastic-metal model. The proposed model characterizes actuation behaviors in terms of
intrinsic material parameters and actuator dimensions. Experiments are conducted on polypyrrole actuators of
different dimensions to validate the developed scaling laws for the quasi-static force and displacement output,
the electrical admittance, and the dynamic displacement response.
The ability of conducting polymer actuators to convert electrical energy into mechanical energy is influenced by many
factors ranging from the actuators physical dimensions to the chemical structure of the conducting polymer. In order to
utilise these actuators to their full potential, it is necessary to explore and quantify the effect of such factors on the
overall actuator performance. The aim of this study is to investigate the effect of various geometrical characteristics such
as the actuator width and thickness on the performance of tri-layer polypyrrole (PPy) actuators operating in air, as
opposed to their predecessors operating in an appropriate electrolyte. For a constant actuator length, the influence of the
actuator width is examined for a uniform thickness geometry. Following this study, the influence of a varied thickness
geometry is examined for the optimised actuator width. The performance of the actuators is quantified by examination of
the force output, tip displacement, efficiency as a function of electrical power and mechanical power, and time constant
for each actuator geometry. It was found that a width of 4mm gave the greatest overall performance without curling
along the actuator length (which occurred with widths above 4mm). This curling phenomenon increased the rigidity of
the actuator, significantly lowering the displacement for low loads. Furthermore, it was discovered that by focussing a
higher thickness of PPy material in certain regions of the actuators length, greater performances in various domains
could be achieved. The experimental results obtained set the foundation for us to synthesize PPy actuators with an
optimised geometry, allowing their performance to reach full potential for many cutting applications.
Conjugated polymers are promising actuation materials for bio and micromanipulation systems, biomimetic
robots, and biomedical devices. Sophisticated electrochemomechanical dynamics in these materials, however,
poses significant challenges in ensuring their consistent, robust performance in applications. In this paper an
effective adaptive control strategy is proposed for conjugated polymer actuators. A self-tuning regulator is
designed based on a simple actuator model, which is obtained through reduction of an infinite-dimensional
physical model and captures the essential actuation dynamics. The control scheme is made robust against
unmodeled dynamics and measurement noises with parameter projection, which forces the parameter estimates to
stay within physically-meaningful regions. The robust adaptive control method is applied to a trilayer polypyrrole
actuator that demonstrates significant time-varying actuation behavior in air due to the solvent evaporation.
Experimental results show that, during four-hour continuous operation, the proposed scheme delivers consistent
tracking performance with the normalized tracking error decreasing from 11% to 7%, while the error increases
from 7% to 28% and to 50% under a PID controller and a fixed model-following controller, respectively. In the
mean time the control effort under the robust adaptive control scheme is much less than that under PID, which
is important for prolonging the lifetime of the actuator.
Piezoelectric (PZT) actuators are commonly employed to drive flexure-jointed mechanisms with a nanometer resolution. There are three issues related to piezoelectric actuators; hysteresis, creep and vibration. Although the first two problems have been studied widely, a little attention has been given to the vibration analysis of piezoelectric actuators and elastic (compliant) mechanisms they drive. When a piezoelectric actuator is coupled with an elastic system (e.g. a flexure-jointed mechanism), the effect of the resulting vibration on the accuracy of the piezo-actuated flexure-jointed mechanism is significant, and therefore, the vibration problem deserves a systematic investigation. In this paper, we report on vibration analysis of such systems, and the influence of the actuator and mechanism dynamics on the system accuracy through a
numerical analysis. A flexure jointed Scott-Russell mechanism is considered as the mechanism driven by a piezoelectric actuator. This mechanism can be used not only to change the direction of a translation motion by 90° but also to be a mechanical displacement amplifier. Numerical results are provided to quantify the interaction between the actuator dynamics and the mechanism dynamics from vibration and positioning accuracy points of view. Further, the influence of the type of input signals on the positioning accuracy of the piezo-electric actuated flexure-jointed micromanipulation systems is elaborated with extensive numerical results.