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ENABLING TECHNOLOGIESAhmed Shaik with a scaled modelof one design concept, which hasall motors at a fixed location.A novel,six-degree-of-freedomrobot arm design| 56 |The CSIR is combining twomethods of robot design tooffer a solution that couldsubstantially reduce robots’power consumption, whilethey perform the same tasks.The trouble with commonrobotic arms is that their designfixes large motors and gear boxesto their movable axes. This makesthe arms heavy, and the heavierthe object, the more energy isrequired to move it. Engineers atthe CSIR are hard at work solvingthis problem by using a hybridrobot design that they say couldbe more energy efficient, resultingin cost savings over the lifespan ofthe robot.Robotic arm architectureRobotic arms can be programmedto accomplish a wide variety oftasks within their workspace.Some of the uses of robotic armsinclude component assembly;welding; cutting and spraypainting.A central design feature incommonly used robotic arms isthat their motors and gearboxesare located at, or close to, thespecific joint they control.Robots designed in thismanner are called SerialKinematic Machines (SKMs).Though simple and mature,serial architecture has a majordrawback. It significantlyincreases the inertia in roboticarms. Increased inertia alsoaffects accuracy by contributingto dynamic vibration problems.To solve the problem commonto SKMs, parallel architecturewas developed. In most ParallelKinematic Machines (PKMs),all the motors and gear boxeshave a fixed arrangement andposition in space. A numberof arms and links are coupledin parallel from the motorsand gear boxes to the graspingmechanism or tool at the end,forming closed kinematicchains. As such, the motors andgearboxes remain stationaryrelative to the movement of therobotic arm. However, parallelarchitectures are not withoutproblems, the most significantbeing the sizeable machinefootprint in comparison to theuseable workspace.The best of both worldsThe solution lies in using ahybrid design to combine thestrengths of both architectures,says Ahmed Shaik, an engineerat the CSIR’s mechatronics andmicromanufacturing group.A hybrid design allows for anoptimised workspace-to-footprintratioequivalent to that of a serialrobot. It also has a machinemoving-massand agility closer tothat of a parallel robot.“The design that we are workingon is unique, consisting ofpatented mechanisms that enablea full range of six degrees offreedom. The design centres onthe concept of fixing the heavydutymotors in one locationand transferring actuation to aspecific axis located elsewherevia a unique concentric gearingmechanism and other sets ofgears and light-weight connectedlinkages,” explains Shaik.“Actuation transfer from the basegearingsystem can be realisedeither with rigid links, toothedbelts or chains. It would have totransfer torque along multipleconfigurations of the robotarms’ main proximal and distallinks to the respective wristmechanism as efficiently aspossible,” he adds.An energy saver for industryShaik states that their HybridKinematics Machine (HKM)design could have a significantimpact on power consumptionin industry, “This particulardesign reduces the total movingmass of the robotic arm.”“If this HKM were to replacethe popular SKM, having thesame lifespan and performingthe same tasks, it should bemore energy efficient and resultin substantial cost saving forindustry over the long term,”he adds.– Bandile SikwaneEnquiries:Ahmed Shaikashaik@csir.co.za| 57 |
ENABLING TECHNOLOGIESParticle manufacture for industrialapplications – better controlthrough microfluidicsOne of the newest research outflows of the miniaturisation revolution is the useof controllably produced microdroplets. When this technology is perfected, it willrepresent a technological leap in the quest for biological and chemical applications.| 58 |The microfluidic device used to manufacture the particles.Self-immobilised enzymes manufacturedthrough droplet microfuidics.Microfluidics researcher Mesuli Mbanjwa separatesmanufactured microparticles from oil using a centrifuge.“Microfluidicmicrodroplets aremanufactured such that theyare controlled in both theirphysical size and structure,”explains Kevin Land, principaltechnologist and projectleader for microfluidics at theCSIR. “They are produced bymeans of microfluidics which,in simple terms, describesthe study and developmentof systems that manipulate,process and control smallvolumes of fluids.”Simplified further, amicrofluidic device has aminute channel through whichtwo immiscible fluids aresqueezed. One of the fluidsthen breaks up, through aprocess called flow focusing,into tiny (nanolitre or picolitrevolumes) droplets.But why are scientistsinterested in making thesedroplets? Basically, each ofthe droplets has the potentialto be a micro-reactor – thecentral concept is to carry outentire experiments in smalldroplets, allowing for isolationof the reactions – making theexperiment controllable to adegree not previously achievable.Droplets-on-demandThe droplet microfluidics can alsobe used to create monodisperseparticles (particles of similar size)and gels, which are beneficial formany health-related diagnostic,drug encapsulation and industrialproduction applications. Onespecific application is selfimmobilisedenzymes (used asbiocatalysts that can modify orspeed up chemical and biologicalreactions).Says Land: “Free enzymes, usedas biocatalysts, are very difficultto recover and re-use. Selfimmobilisedenzymes, however,can be used and then recovered.This makes them more costeffectiveand environmentallyfriendly.”Land’s team of researchers hasbeen focusing on microfluidicsfor the past two years. Theseself-immobilised enzymes areone of the projects that flowedfrom their work on producingdroplets that can be controlled.The work seeks to improvethe method of making theself-immobilised enzymes byusing droplet microfluidics.“One advantage of usingmicrofluidics to producethese controlled droplets isthat it allows for the preciseintroduction and mixing ofreagents. This means thereaction times are faster andthe droplets that will becomeparticles can be manufacturedmuch more controllably thanwith conventional batchsystems,” he says.A platform to supportparticle manufacturing“We now have an easy-to-useand reliable system and soliddroplet platform that can beused to tailor an applicationaccording to the needs of anyindustrial partner,” states Land.“These include the right peopleas well as facilities such aslaboratories for experimentaland characterisation needsand a clean room. I believethat we are the only facilityin the country that uses thismethod to produce controlleddroplets or particles. The factthat it is adaptable to anyapplication also makes it anattractive option to consider.”He concludes: “I echo thesentiments of Heubner et al,who came to the followingconclusion in a 2008 article:The ability to reproduciblygenerate, process andanalyse isolated droplets ofvarying composition and athigh frequencies defines acolossal leap in technologyfor large-scale biologicalexperimentation.Even though such droplettechnologies are in theirearly years, the power isconvincing.”– Petro LowiesEnquiries:Kevin Landkland@csir.co.za| 59 |
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