Mehran Mojarrad

Biomimetic robotic propulsion using polymeric artificial muscles

Biomimetic fish-like propulsion using polyelectrolyte ion-exchange membrane metal composites as a propulsion fin for a robotic swimming structure, such as a boat swimming in water medium, was investigated. The membrane was chemically plated with platinum. The resulting membrane was cut in a strip to resemble fish-like caudal fin for propulsion. A small function generator circuit was designed and built to produce approximately /spl plusmn/2.0 V amplitude signal at desired frequency up to 50 Hz. The circuit board was mounted on a buoyant Styrofoam shaped like a boat or a tadpole. The fin was attached to the rear of the boat. By setting the signal frequency to the desired value and thereby setting the frequency of bending oscillation of the membrane, a proportional forward propulsion speed could be obtained. The speed was then measured using a high speed camera. Several theoretical hydrodynamic models were then presented to characterize speed-frequency of the forward motion using available theories on biological fish motion. The results were compared to experimental data which showed close agreement.

Noiseless propulsion for swimming robotic structures using polyelectrolyte ion-exchange membrane

In this paper a NafionTM polyelectrolyte ion-exchange membrane (IEM) was used as a propulsion fin for robotic swimming structures such as a boat or fish-like object swimming in water or aqueous medium. The Nafion membrane was chemically plated with platinum. The resulting membrane was cut in a strip to resemble a fish-like caudal fin for propulsion. A small function generator circuit was designed and built to produce approximately plus or minus 2.0 V amplitude square wave at varying frequency up to 50 Hz. The circuit board was mounted on a buoyant styrofoam shaped like a boat or a tadpole. The fin was attached to the rear of the boat. By setting the signal frequency to the desired value and thereby setting the frequency of bending oscillation of the membrane, a proportional forward propulsion speed could be obtained. The speed was then measured using a high speed camera. Several theoretical hydrodynamic models were then presented to characterize speed-frequency of the forward motion using available theories on biological fish motion. The results were compared to experimental data which showed close agreement. It turned out that the forward speed of the object was directly proportional to the product of frequency and amplitude of the fin oscillation as in biological fishes. This relation was further simplified by keeping the voltage constant and therefore amplitude of the oscillation. The proportionality constant could be measured for a known geometry of the fin-boat assembly and reactivity of the Nafion membrane used. The system as a whole presented an autonomous robotic swimming structure with frequency modulated propulsion to investigate application of polyelectrolyte hydrogel membranes and their effect on hydrodynamic behavior of an undulating swimming object. As in fishes the thrust force of the robot was generated by evolution of vortices on the sides of the undulating fin. For a constant forward speed, this thrust is equal to the drag force due to geometry and skin friction of the swimming robot. It was observed that regardless of the laminar or turbulent flow pattern around the robot the relation between speed and frequency holds. This research was a proof of concept for investigating fish propulsion known best for undulatory swimming motion, using polyelectrolyte ion-exchange-metal composite membrane.

Ion exchange membrane-platinum composites as electrically controllable artificial muscles

Ion exchange membranes (JEM) chemically treated with platinum salt so1uions gives rise to IEM-platinum composites that undergo large deformations in an electric field of a few volts (2-4 volts/mm). They also show remarkable vibrational characteristics of about 80 lIz bandwidth. A simple theoretical treatment as well as some experimental evidence on the dependence of deformation amplitude on the imposed voltages and frequencies are presented.

Linear and platform-type robotic actuators made from ion-exchange membrane-metal composites

In this research, feasibility of using ion-exchange- membrane-metal composite artificial muscles as linear platform type actuators was studied. In order to achieve linear motion from these typically bending type actuators, a series of muscles made from ion-exchange-membrane-metal composites were cut in strips and attached either end-to-end or to one fixed platform and another movable platform in a cylindrical configuration. By especially prepared electrodes embedded within the platforms one can convert the bending response of each strip into linear movement of the mobile platform. By applying a low voltage the movement of free end of the actuator could be calibrated and its response could be measured, accordingly. A theoretical model was developed and was compared to experimental results. Ion-exchange- membrane-model composites are highly active actuators that show very large deformation in the presence of low applied voltage and exhibit low impedance.

Electrically induced large-amplitude vibration and resonance characteristics on ionic polymeric membrane-metal composites artificial muscles

This research identifies key parameters involving the vibrational characteristics of actuators made of ion-exchange- membrane-metal composites. These actuators are made from commercially available ion-exchange membranes chemically treated with platinum to produce composite actuators that are highly deformable in the presence of low amplitude electrical field. They show remarkable bending displacement that follow input signal very closely. When the applied signal frequency is varied, so does the displacement up to a point where large deformations are observed at a critical frequency called resonant frequency where maximum deformation is observed. Beyond which the actuator response is diminished. In this research paper, several samples of the actuators were made and tested with various dimensions to compare the vibrational behavior of the actuators. A data acquisition system was used to measure the parameters involved and record the results in real time basis. This research was in support of active vibration suppression research for flexible structures using ionic polymers as active dampers. It also supported other applications in biomimetics research such as bird flight motion, artificial coral reefs and marine propulsion.

Electrically controllable artificial PAN muscles

Artificial muscles made with polyacrylonitrile (PAN) fibers are traditionally activated in electrolytic solution by changing the pH of the solution by the addition of acids and/or bases. This usually consumes a considerable amount of weak acids or bases. Furthermore, the synthetic muscle (PAN) itself has to be impregnated with an acid or a base and must have an appropriate enclosure or provision for waste collection after actuation. This work introduces a method by which the PAN muscle may be elongated or contracted in an electric field. We believe this is the first time that this has been achieved with PAN fibers as artificial muscles. In this new development the PAN muscle is first put in close contact with one of the two platinum wires (electrodes) immersed in an aqueous solution of sodium chloride. Applying an electric voltage between the two wires changes the local acidity of the solution in the regions close to the platinum wires. This is because of the ionization of sodium chloride molecules and the accumulation of Na+ and Cl- ions at the negative and positive electrode sites, respectively. This ion accumulation, in turn, is accompanied by a sharp increase and decrease of the local acidity in regions close to either of the platinum wires, respectively. An artificial muscle, in close contact with the platinum wire, because of the change in the local acidity will contract or expand depending on the polarity of the electric field. This scheme allows the experimenter to use a fixed flexible container of an electrolytic solution whose local pH can be modulated by an imposed electric field while the produced ions are basically trapped to stay in the neighborhood of a given electrode. This method of artificial muscle activation has several advantages. First, the need to use a large quantity of acidic or alkaline solutions is eliminated. Second, the use of a compact PAN muscular system is facilitated for applications in active musculoskeletal structures. Third, the PAN muscles become electrically controllable and therefore the use of such artificial muscles in robotic structures and applications becomes more feasible. A muscle is designed such that it is exposed to either Na+ or Cl- ions effectively. Muscle contraction or expansion characteristics under the effect of the applied electric field are discussed.

Electrically controllable ionic polymeric gels as adaptive optical lenses

Reversible change in optical properties of ionic polymeric gels, 2-acrylamido-2-methylpropane sulfonic acid (PAMPS) and polyacrylic acid plus sodium acrylate cross-linked with bisacrylamide (PAAM), under the effect of an electric field is reported. The shape of a cylindrical piece of the gel, with flat top and bottom surfaces, changed when affected by an electric field. The top surface became curved and the sense of the curvature (whether concave or convex) depended on the polarity of the applied electric field. The curvature of the surface changed from concave to convex and vice versa by changing the polarity of the electric field. By the use of an optical apparatus, focusing capability of the curved surface was verified and the focal length of the deformed gel was measured. The effect of the intensity of the applied electric field on the surface curvature and thus, on the focal length of the gel are tested. Different mechanisms are discussed; either of them or their combination may explain the surface deformation and curvature. Practical difficulties in the test procedure and the future potential of the electrically adaptive and active optical lenses are also discussed. These adaptive lenses may be considered as smart adaptive lenses for contact lens or other optical applications requiring focal point undulation.

Ion-exchange-metal composite artificial muscle actuator load characterization and modeling

Reported in this work are load characterization of electroactive films made out of polymeric ion-exchange membrane materials treated with a noble metal such as platinum. Load characterization under oscillating voltage input on the resulting composite samples was then performed using a PC-platform data acquisition system, variable signal generator, amplifier and load cells. For fixed signal frequency, various shape signals at low voltage amplitudes were then applied and the corresponding induced forces measured by the load cells and recorded via the data acquisition setup. The applied input signals consisted of sinusoid, square, saw tooth, and triangular form in order to observe the difference in behavior and the resulting output forces of the actuators. A briefdescription ofa proposed theory for this type ofactuator was then discussed. The results showed that these actuators exhibit good force to weight characteristics in the presence oflow applied voltages.