Rahim Mutlu

A multistable linear actuation mechanism based on artificial muscles

In this paper, we report on a multistable linear actuation mechanism articulated with electroactive polymer actuators, widely known as artificial muscles. These actuators, which can operate both in wet and dry media under as small as 1.0 V potential difference, are fundamentally cantilever beams made of two electroactive polymer layers (polypyrrole) and a passive polyvinylidene fluoride substrate in between the electroactive layers. The mechanism considered is kinematically analogous to a four-bar mechanism with revolute-prismatic-revolute-prismatic pairs, converting the bending displacement of a polymer actuator into a rectilinear movement of an output point. The topology of the mechanism resembles that of bistable mechanisms operating under the buckling effect. However, the mechanism proposed in this paper can have many stable positions depending on the input voltage. After demonstrating the feasibility of the actuation concept using kinematic and finite element analyses of the mechanism, experiments were conducted on a real mechanism articulated with a multiple number (2, 4, or 8) of electroactive polymer actuators, which had dimensions of 12 × 2 × 0.17 mm 3 . The numerical and experimental results demonstrate that the angular displacement of the artificial muscles is accurately transformed into a rectilinear motion by the proposed mechanism. The higher the input voltage, the larger the rectilinear displacement. This study suggests that this multistable linear actuation mechanism can be used as a programmable switch and/or a pump in microelectromechanical systems (MEMS) by adjusting the input voltage and scaling down the mechanism further.

Artificial muscles with adjustable stiffness

This paper reports on a stiffness enhancement methodology based on using a suitably designed contact surface with which cantilevered-type conducting polymer bending actuators are in contact during operation. The contact surface constrains the bending behaviour of the actuators. Depending on the topology of the contact surface, the resistance of the polymer actuators to deformation, i.e.?stiffness, is varied. As opposed to their predecessors, these polymer actuators operate in air. Finite element analysis and modelling are used to quantify the effect of the contact surface on the effective stiffness of a trilayer cantilevered beam, which represents a one-end-free, the-other-end-fixed polypyrrole (PPy) conducting polymer actuator under a uniformly distributed load. After demonstrating the feasibility of the adjustable stiffness concept, experiments were conducted to determine the stiffness of bending-type conducting polymer actuators in contact with a range (20?40?mm in radius) of circular contact surfaces. The numerical and experimental results presented demonstrate that the stiffness of the actuators can be varied using a suitably profiled contact surface. The larger the radius of the contact surface is, the higher is the stiffness of the polymer actuators. The outcomes of this study suggest that, although the stiffness of the artificial muscles considered in this study is constant for a given geometric size, and electrical and chemical operation conditions, it can be changed in a nonlinear fashion to suit the stiffness requirement of a considered application. The stiffness enhancement methodology can be extended to other ionic-type conducting polymer actuators.

Kinematic modeling for artificial flagellum of a robotic bacterium based on electroactive polymer actuators

Conventional robotic manipulators have been widely studied and proven for their efficiency in macro environment. However, it is unlikely to miniaturize them to mimic a bacterium flagellum type actuator/manipulator. Electroactive polymer (EAP) actuators, also known as artificial muscles, can operate both in wet and dry environments and are very suitable for miniaturising. With this in mind, this paper reports on the kinematics of an artificial flagellum of a bacterium engineered from an EAP actuator. A kinematic model based on backbone curve approach which integrates differential geometry and Denavit-Hartenberg formulation is developed. Simulation results of the artificial flagellum demonstrate the feasibility of such modelling approach for highly flexible EAP actuators. Also, preliminary experiments were conducted. This study recommends that electroactive polymer actuators can be used to build bacteria flagellum type actuators to be used in micro robots for medical purposes such as diagnosis and drug delivery.

A Compliant Translational Mechanism Based on Dielectric Elastomer Actuators

This paper reports on a linear actuation mechanism in the form of a parallel-crank mechanism (i.e., double-crank mechanism) articulated with two dielectric elastomer actuators working in parallel that are fabricated as a minimum energy structure. This structure is established by stretching a dielectric elastomer (DE) film (VHB4910) over a polyethylene terephthalate (PET) frame so that the energy released from the stretched DE film is stored in the frame as bending energy. The mechanism can output a translational motion under a driving voltage applied between two electrodes of the DE film. We have proposed visco-elastic models for the DE film and the frame of the actuator so that the mechanical properties of the actuator can more accurately be incorporated into the mechanism model. The proposed model accurately predicts the experimental frequency response of the mechanism at different voltages. In addition, an inversion-based feedforward controller was successfully implemented in order to further validate the proposed model for sensorless position control of the actuators and the parallel-crank mechanism articulated with these actuators. [DOI: 10.1115/1.4027167]

A Soft Mechatronic Microstage Mechanism Based on Electroactive Polymer Actuators

Smart actuators have a considerable potential to articulate novel mechanisms and mechatronic devices inspired from biological systems. Electroactive polymer actuators (EAPs), as a class of smart and soft actuators, are ideal candidates for bioinspired mechatronic applications due to their compliance and built-in actuation ability originating from the material they are made of. In this paper, we report on a soft mechatronic mechanism, like a positioning stage, fabricated from bending-type EAP actuators as a one-piece fully compliant mechanism inspired from twining structures in nature. We have employed a quasi-static finite-element model combined with a soft robotic kinematic model to estimate the mechanical output of the soft mechatronic mechanism as a function of a single electrical input. Experiments were conducted under a range of electrical step inputs (0.25-1 V) and sine-wave inputs with various frequencies to validate the models. Experimental and simulation results show that this electrically stimulated soft mechatronic mechanism generates a linear displacement as large as 1.8 mm under 1 V out of its fabrication plane like a lamina emergent mechanism, while its bioinspired spiral parts bend and twine. This fully compliant and compact mechanism can find a place in optics as a microstage and/or an optical zoom mechanism.

Effect of flexure hinge type on a 3D printed fully compliant prosthetic finger

Soft robotics, as a new dimension in robotics, is an rapidly growing research area. Fully compliant mechanisms and structures can be built using soft materials. Having a fully compliant system -a monolithic body- will reduce the manufacturing and assembly costs and show a whole-body bending performance similar to its natural counter-parts. Current prosthetics, particularly fingers and hands, require significant manufacturing and assembly operations. Using additive manufacturing (aka 3D printing), low cost and high performance prosthetic devices can be established. In this study, we report on a fully compliant finger which is 3D printed with a modified low-cost 3D printer based on the Fused Deposition Modelling (FDM) technique. Prior to the finger fabrication, the bending behavior of some well-known flexure hinges were modelled and experimentally evaluated to find the most suitable design for a fully compliant prosthetic finger. Experimental and numerical results from the finite element analysis for the hinges and the complaint finger are in good correlation, encouraging us to establish a single piece prosthetic hand in the near future.

An inverted micro-mixer based on a magnetically-actuated cilium made of Fe doped PDMS

In this paper, we report a new micromixer based on a flexible artificial cilium activated by an external magnetic field. The cilium is fabricated from Polydimethylsiloxane doped with Fe microparticles. The fabrication method is based on the standard sacrificial layer technology. The cilium was built on a glass slide, and then was bonded on the top of the micro-mixer chamber in a microfluidic chip. This fabrication process for the miniaturized active mixers is simple and cost effective. An electromagnetic system was used to drive the cilium and induce strong convective flows of the fluid in the chamber. In the presence of an alternating magnetic field, the cilium applied a corresponding alternating force on the surrounding fluids. The performance of the electromagnetically activated cilium was quantified and optimized in order to obtain maximum mixing performance. In addition, the mixing performance of the cilium in a circular micro-chamber was compared with pure diffusion. Up to 80% of a 60 ul liquid in the chamber can be fully mixed after 2 min using a cilium mixer under a magnetic flux density of 22 mT in contrast to the 20 min which were needed to obtain the same mixing percentage under pure diffusion. Furthermore, for a mixing degree of 80%, the mixing speed for the cilia micromixer proposed in this study was 9 times faster than that of the diffusion-based micro-mixers reported in the literature.

Modeling a soft robotic mechanism articulated with dielectric elastomer actuators

In this paper, a translational actuation mechanism in the form of a parallel-crank mechanism (i.e. double-crank 4-bar mechanism) articulated with two dielectric elastomer actuators working in parallel are fabricated. This structure, which is a fully soft mechanism, is established by stretching a dielectric elastomer (DE) film over a PET (polyethylene terephthalate) frame so that the energy released from the stretched DE film is stored in the frame as bending energy. The mechanism generates a translational output under a driving voltage applied between two electrodes of the DE film. The visco-elastic models are proposed for the mechanism so that the mechanical properties of the actuator can more accurately be incorporated into the mechanism model. The proposed model accurately predicts the experimental frequency response of the mechanism at different voltages.

An active-compliant micro-stage based on EAP artificial muscles

Electroactive Polymer actuators (EAPs), also known as EAP artificial muscles, offer a great potential for soft robotics. They are suitable for bio-inspired robotic applications due to their built-in actuation property within the mechanical body. In this paper, we report on a fully compliant micro-stage with built-in actuation. It has been fabricated as one piece inspired from twining structures in nature. We have employed a soft robotic modeling approach and finite element modeling to predict the mechanical output of the stage as a function of the input voltage. Experiments were conducted under a range of electrical inputs (0.25-1.00 V). For a given electrical stimulus, the compliant mechanism results in a linear motion in the middle of the active compliant mechanism, as expected. Experiments and simulation results are in good correlation. The active compliant mechanism can be used as a micro stage as well as an optical zoom mechanism for mobile phone cameras and similar devices.

Mechanical stiffness augmentation of a 3D printed soft prosthetic finger

Soft robotics, as a multi-disciplinary research area, has recently gained a significant momentum due to offering unconventional characteristics relative to rigid robots such as a resilient, highly dexterous, compliant and safer interaction with humans and their physical environments. However, soft robots suffer from not being able to carry their own weight which mainly depends on the modulus of elasticity of the material used to fabricate them. In this paper, we report on a practical and easy-to-implement stiffness augmentation method to enhance stiffness of soft robotic components. We fabricated a soft robotic finger which is fully compliant with flexure hinges using Fused Deposition Modelling (FDM) technique and a stiffness augmenting unit made of thin poly(vinyl chloride)(PVC) sheets. The stiffness of the entire robotic finger was increased mechanically by linearly driving the stiffness augmenting unit. The experimental data presented show that stiffness of the finger was increased by 40 %. Depending on the material properties and thickness used for fabricating the stiffness augmenting unit, a higher rate of stiffness increase can be easily obtained.