Daniel Nakhaee-Zadeh Gutierrez

Supervisors: Ali Alazmani and Peter Culmer Collaboration: KAIST Biorobotics Lab

School of Mechanical EngineeringFaculty of Engineering

A literature review was performabout the on-going research andavailable products in the market.This created the basis for theinitial design and the inspirationfor future applications. Softactuators have been used before Irehabilitation devices and onunder-water biopsy equipment.

The objective of this project was to create a soft pneumatic finger grasper capable of adapting to the geometry of different objects. The aim with this research is to create a gripper that can replace traditional robotic grippers in

delicate environments like surgery or food processing.

Modelling soft actuators is ahighly complex process since thebehaviour of hyper elasticmaterials has multiple unknowns.The model was tested using finiteelement analysis (FEA) in Abaqus.This helps to identify theperformance and the weaknessesof the model and materials.

The sensor consisted in two maincomponents: a stretchable fabric,use to attach it to the skin surfacesand to give structural rigidity to thesensor; a composite material,produced by multiwall carbonnanotubes (MWCNT) in a polymermatrix, this part can vary is electricalresistivity when deform or stretch.,making it suitable as a sensingmaterial.

The design of soft actuators involvesvarious constraints including:material, morphology, desiredmotion, actuation system. All thesevariables are introduced intopreliminary sketches, as a prove ofconcept. Finally, all the ideas areimplemented in a 3D CAD designusing Solid Works to create

The research has served to study thedesign principles and variablesrelated to the development andfabrication of polymer base softpneumatic actuators, includingmaterial properties and themorphology effects in the motion.This project is still on going andfuture testing is require to create afinal product.

the actuator andcorrespondingmoulds.

Pressurised Air

Air ChamberConstraining Layer

Interaction forces between the Walls

The method used to fabricate thegrasper was an investment or waxcasting manufacturing technique.This method uses a wax core tocreate the shape of the air chamberinside the actuator. Then, thesilicone (Dragon Skin 20) is added tothe mould and cured at roomtemperature. When the polymer iscompletely cured the wax core canbe removed by melting it in an oven.

The fabricated grasper showedgreat performance such as rapidactuation and relaxation andvariable angle of bending.However, this design had a verythick constraining layer, thatlimited the range of movements.An optimized larger version of theactuator was also designed forfuture fabrication and testing.

The goal of this project is to perform a dimensional parameter testing to a soft stretchable sensor in development, to characterise the affects of width and length variation on the its behaviour. The purpose of the sensor is to measure

the multi-axis angle of human joints for both rehabilitation and controlling processes.

For the parameter testing atotal of 12 linear samples with3 different lengths (30, 60 and90 mm) and 4 different widths(5, 10, 15 and 20 mm) werefabricated, using a customdispenser, to ensure highaccuracy. The material wasthen cured and tested forirregularities using a voltmeter.

Figure 1. Currently available soft grasper for industrial use

Figure 2. 3D model of the actuator mould

Figure 3. Meshed part using Abaqus

Figure 4. Working principle of the soft grasper

Figure 5. Fabricated soft grasper in idle (left) and deformed shape (Right)

To obtain a broad range of results forthe application the test was dividedinto two parts. A frequency rangetest was perform at multiplefrequencies (0.25 Hz, 0.5 Hz, 1 Hzand 2 Hz) at a fixed strain of 40% ofthe length of the sample. The secondtest consisted in a constantfrequency test at 0.25 Hz withdifferent elongation percentages(10%, 20%, 30% and 40).

Syringe containing the composite

material

three-direction moving bed

Stretchable fabric

Pressurized air

Linear Stage

Sample

3D printed clamp

Load Cell

Figure 7. Dispenser system used for sensor fabrication

Figure 1. Soft sensor components and applications

For this project there are fourcharacteristics that we are interestedin studying: hysteresis, non -linearity,sensitivity and range and dynamicresponse. This parameters can bemeasured using a customextensometer, which records theforce, the elongation percentage,frequency of oscillation andresistance change in the sample. Allthese data can then be process andthe sensor can be calibratedaccordingly

From the preliminary results and asthe theory predicts, larger sensorswill show lower resistivity, sincestatistically there are more cross-path of carbon nanotubes to allowthe current of electrons. However,these results only take into accountthe static response of the samples.Future work will focused onanalysing the dynamic loadingresults and describe theperformance in real life uses..

Thanks to this research I got theopportunity to travel to Korea andto experience its culture. During mytime in the country I met a lot of……….. inspiring people, who

were also passionateabout engineering.Moreover, I travelled tothe different regions inKorea to learn theirhistory and tradition.

Figure 8. Custom extensometer used for testing the sensors

Figure 9. Members of the KAIST Biorobotics Lab