We apply three optical coherence tomography (OCT) image analysis techniques to extract morphometric information from OCT images obtained on peripheral nerves of rat. The accuracy of each technique is evaluated against histological measurements accurate to + / − 1 μm. The three OCT techniques are: (1) average depth-resolved profile (ADRP), (2) autoregressive spectral estimation (AR-SE), and (3) correlation of the derivative spectral estimation (CoD-SE). We introduce a scanning window to the ADRP technique, which provides transverse resolution and improves epineurium thickness estimates—with the number of analyzed images showing agreement with histology increasing from 2 / 10 to 5 / 10 (Kruskal–Wallis test, α = 0.05). A method of estimating epineurium thickness, using the AR-SE technique, showed agreement with histology in 6 / 10 analyzed images (Kruskal–Wallis test, α = 0.05). Using a tissue sample in which histology identified two fascicles with an estimated difference in mean fiber diameter of 4 μm, the AR-SE and CoD-SE techniques both correctly identified the fascicle with larger fiber diameter distribution but incorrectly estimated the magnitude of this difference as 0.5 μm. The ability of the OCT signal analysis techniques to extract accurate morphometric details from peripheral nerves is promising but restricted in depth by scattering in adipose and neural tissues.
A robotic surgical device, actuated by Ionic Polymer-metal Composite (IPMC), integrated with a strain gauge to achieve force control is proposed. Test results have proved the capabilities of this device to conduct surgical procedures. The recent growth of patient acceptance and demand for robotic aided surgery has stimulated the progress of research where in many applications the performance has been proven to surpass human surgeons. A new area which uses the inherently force compliant and back-drivable properties of polymers, IPMC in this case, has shown its potential to undertake precise surgical procedures in delicate environments of medical practice. This is because IPMCs have similar actuation characteristics to real biological systems ensuring the safety of the practice. Nevertheless, little has been done in developing IPMCs as a rotary joint actuators used as functional surgical devices. This research demonstrates the design of a single degree of freedom (1DOF) robotic surgical instrument with one joint mechanism actuated by IPMC with an embedded strain gauge as a feedback unit, and controlled by a scheduled gain PI controller. With the simplicity of the system it was proven to be able to cut to the desired controlled force and hence depth.
This paper presents the design, fabrication and experimental characterization of a valveless micropump actuated by an
ionic-polymer-metal-composite (IPMC) soft actuator. The performance of the IPMC varies over time, therefore on-line
iterative feedback tuning (IFT) is used to adaptively tune the PID controller to control the bending deflection of the
IPMC to ensure a constant pumping rate. The pump rate is higher at lower frequencies for a given applied voltage to the
IPMC. A maximum flow rate of 130 μl/min is achieved at 0.1 Hz.
The demand for single cell manipulation to allow scientist to carry out medical researcher is fast increasing. To facilitate
this advanced manipulation systems are required to permit both precise and safe handling of the biological cells. Current
devices can achieve a high level of precision at the micro/nano scale but as a consequence are highly rigid and this
stiffness puts the target cells at risk as there is no compliance or back-drivability. Ionic polymer-metal composites
(IPMCs) are naturally compliant, giving them a 'soft touch', and now with recent advances in their fabrication and
control IPMCs are showing major promise as safe and accurate cell manipulators. This paper presents the development
of an optimally tuned force controller for a 2 degree-of-freedom (2DOF) IPMC actuated micro-manipulator. The control
system has been implemented to demonstrate the ability to control the manipulator's applied force as a step towards
implementing a truly safe system with active compliance control. The controller is adaptively tuned using a model-free
iterative feedback tuning (IFT) approach which is ideal for operation in unknown cellular environments as well as for
controlling the complex time-varying behavior of the IPMC actuators themselves. The IFT algorithm tunes the force
controller by minimizing the design criteria, a least squares error, by 25% in the horizontal direction and 46% in the
vertical direction. Experiments then show that the manipulator can accurately track a reference trajectory up to 4gf or
~40mN in both DOF.
This paper proposes a conclusive scalable model for Ionic Polymer Metal Composites (IPMC) actuators and their
interactions with mechanical systems and external loads. This dynamic, nonlinear model accurately predicts the
displacement and force actuation in air for a large range of input voltages. The model addresses all the requirements of a
useful design tool for IPMC actuators and is intended for robotic and bio-mimetic (artificial muscle) applications which
operate at low frequencies. The response of the IPMC is modeled in three stages, (i) a nonlinear equivalent electrical
circuit to predict the current drawn, (ii) an electro-mechanical coupling term, representing the conversion of ion flux to a
stress generated in the polymer membrane and (iii) a mechanical beam model which includes an electrically induced
torque for the polymer. Mechanical outputs are in the rotational coordinate system, 'tip angle' and 'torque output', to
give more practical results for the design and simulation of mechanisms. Model parameters are obtained using the
dynamic time response and results are presented demonstrating excellent correspondence between the model and
experimental results. This newly developed model is a large step forward, aiding in the progression of IPMCs towards
wide acceptance as replacements to traditional actuators.
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.