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Constantinos Mavroidis1

Associate Professor,ASME Mem

e-mail: mavro@jove.rutgers.edu

Kathryn J. DeLaurentisGraduate Student,

ASME Student Meme-mail: kjdela@jove.rutgers.edu

Jey WonUndergraduate Research Assistant,

ASME Student Mem

Munshi AlamGraduate Student,

ASME Student Mem

Robotics and Mechatronics Laboratory,Department of Mechanical and

Aerospace Engineering,Rutgers University,

The State University of New Jersey,98 Brett Rd.,

Piscataway, NJ 08854-8058

Fabrication of Non-AssemblyMechanisms and RoboticSystems Using Rapid PrototypingIn this paper, the application of Rapid Prototyping in fabricating non-assembly robsystems and mechanisms is presented. Using two Rapid Prototyping techniques,olithography and Selective Laser Sintering, prototypes of mechanical mobile jointsfabricated. The designs of these component joints were then used to fabricate the alated structure of experimental prototypes for two robotic systems: (1) a three-leparallel manipulator, (2) a four degree-of-freedom finger of a five-fingered robotic haThese complex multi-articulated, multi-link, multi-loop systems have been fabricatone step, without requiring assembly while maintaining their desired mobility. The febility and usefulness of Rapid Prototyping as a method for the fabrication of theseassembly type mechanisms and robotic systems is the focus of this work.@DOI: 10.1115/1.1415034#

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1 IntroductionIt is always desirable to evaluate a proposed robot design p

to full prototyping to ensure the swiftest and most cost effectdesign changes. Even though powerful three-dimensional Cputer Aided Design and Dynamic Analysis software packasuch as Pro/ENGINEER, IDEAS, ADAMS and Working Mod3-D are now being used, they cannot provide important vishaptic and realistic workspace information for the proposedsign. In addition, there is a great need for developing methodgies and techniques that will allow fast design, fabrication atesting of robotic and other multi-articulated mechanical systeA framework for the feasibility and usefulness of applying RapPrototyping in fabricating mechanisms and robotic systems issented here.

Rapid Prototyping~RP!, also known as Layered Manufacturinor Solid Freeform Fabrication, is a technique for fabricatingthree-dimensional solid model in a layer-by-layer manner throthe fusion of material under computer control. Rapid prototypof parts and tools is a rapidly developing technology@1,2# thatprovides many advantages:~a! time and money savings,~b! quickproduct testing,~c! expeditious design improvements,~d! fast er-ror elimination from design,~e! increased product sales, and~f!rapid manufacturing. Its main advantage is early verificationproduct designs. Additionally, Rapid Prototyping is quickly bcoming a valuable key for efficient and concurrent engineeriThrough different techniques, engineers and designers areable to bring a new product from concept modeling to part tesin a matter of weeks or months. In some instances, actualproduction may even be possible in very short time. Rapid Protyping has indeed simplified the task of describing a concepdesign teams, illustrating details to engineering groups, specifparts to purchasing departments, and selling the produccustomers.

The advantages of using Rapid Prototyping techniques

1Corresponding author.Contributed by the Mechanisms and Robotics Committee for publication in

JOURNAL OF MECHANICAL DESIGN. Manuscript received Aug. 2000. AssociaEditor: J. S. Rastegar.

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mechanism and robot design and fabrication are numerous. WRapid Prototyping techniques, physical prototypes of the mecnism or robot that is being designed can be obtained in a vshort time, thus making quick design evaluation possible. Bying these physical prototypes, several properties of the menisms can be evaluated immediately such as:~a! workspace evalu-ation, ~b! identification of singular configurations includinuncertain configurations where the mechanism has internal moity, ~c! determination of link interference, and~d! visualization ofjoint limits. Evaluating these fundamental properties of the RaPrototyped mechanism can considerably reduce the time andprove the quality of the design process. Furthermore, Rapid Ptotyping allows the fabrication of complex three-dimensionstructures, which could not be produced with conventional fabcation processes. Such possibilities make the incorporationattachment of sensors, actuators and transmission elements wthe structure and joints of the mechanism easier. Finally, RaPrototyping allows one-step fabrication of multi-articulatemulti-link systems as a whole, without requiring assembly ofstructural members and joints after fabrication. This one steprication technique can drastically change the way that mechanand robots are currently built. This is very important as it callow rapid fabrication of fully functional and mobile systems.this paper, these mechanisms and robotic systems whose marticulated structure is built in one step are callednon-assemblymechanisms.

Robotic systems have been used as a part of a Rapid Protoing process@3,4#. However, the application of Rapid Prototypinin robot and mechanism design and fabrication has beenlimited. Professor Gosselin and his group at Laval Universusing a Fused Deposition Modeling Rapid Prototyping machifabricated several mechanisms such as a six-legged six degrefreedom parallel manipulator@5,6#. These rapidly manufacturedmechanisms required assembly after Rapid Prototyping ofmechanism parts. Professor Cutkosky and his group at StanUniversity using a different Rapid Prototyping process calShape Deposition Manufacturing developed planar, non-assemmechanisms and robotic systems with embedded sensors antuators @7,8#. These components were inserted in the mu

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articulated structure during its fabrication as opposed to theirtegration in post-fabrication assembly phases. This groupproposed methods for performing the systematic design, eanalysis and optimal pose selection for these mechanisms@9–12#.Additionally, researchers at the Georgia Institute of technoloproposed methods to develop complex devices with embedcomponents using the Stereolithography technique@13,14#.

During the last two years our group at Rutgers University hstudied the fabrication of non-assembly mechanism using twoferent Rapid Prototyping processes: Stereolithography~SL! andSelective Laser Sintering~SLS!. Preliminary results of our workwere presented in@15–17#. In this paper our design consideations, results, and prototypes in building complex, spatial, nassembly mechanisms are presented in detail. To the autknowledge, this is the first successful fabrication of multi-joimulti degree-of-freedom, spatial robotic systems and mechanwithout requiring any assembly using the SL and SLS procesThe demonstration of non-assembly, mechanism fabrication,cluding discussions on manufacturing accuracies, joint clearaand the required design modifications that take into accountspecial characteristics of Rapid Prototyping techniques is themary scope of the paper. Our future goals, which are outsidescopes of this paper, will include the detailed study of how tothese novel mechanism fabrication techniques for mechanismsign evaluation and the development of theoretical and mematical tools needed in the design optimization and automa

Using the Stereolithography machine model SLA 190, fromSystems, CA a set of joints that include revolute, prismatic, uversal and spherical joints, were fabricated. In addition, a thlegged, six degree-of-freedom Rapid Prototype of a parallelnipulator was built in one step, without requiring assembly. Ealeg of this three-legged parallel manipulator is composed ofprismatic joint and two spherical joints, which connect to the ttriangular platforms. Further prototype joints, similar to those faricated with the Stereolithography process, were Rapidly Protyped using the Selective Laser Sintering Sinterstation 2000DTM Corporation of Austin, TX. Finally, a four-degree-offreedom finger of a robotic hand with four fingers, a thumb anpalm are constructed as non-assembly type mechanisms. Ation of the joints of the rapidly prototyped systems is outsidescope of this paper and will be studied in our future work.

2 Rapid PrototypingRapid Prototyping or Layered Manufacturing is a fabricati

technique where three-dimensional solid models are construlayer upon layer by the fusion of material under computer contThis process generally consists of a substance, such as flwaxes, powders or laminates, which serves as the basis for mconstruction as well as sophisticated computer-automated eqment to control the processing techniques such as depositiontering, lasing, etc.@18,19# Also referred to as Solid Freeform Fabrication, Rapid Prototyping complements existing conventiomanufacturing methods of material removing and forming. Itwidely used for the rapid fabrication of physical prototypesfunctional parts, patterns for molds, medical prototypes suchimplants, bones and consumer products@20#. Its main advantageis early verification of product designs. Through quick design aerror elimination, Rapidly Prototyped parts show great cost sings over traditionally prototypes parts in the total product lcycle @21#.

Currently, there are over 30 different types of Rapid Prototing processes in existence. Some of these techniques are comcially available while others are still in development in resealaboratories@21#. Over the years, major improvements in the ovall quality of prototyped parts have been achieved throughhancements in accuracy, material choice and durability,throughput, surface texture, and alternative RP processes. Timprovements have led to an evolution of the functionality ofprototypes@19,20#. Evolution of the techniques and application

Journal of Mechanical Design

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of Rapid Prototyping is a continually developing and expandfield. Current research is leading to a more functional rapiprototyped part with an increasing number of applications apart feature enhancements. The two Rapid Prototypes techniqStereolithography~SL! and the Selective Laser Sintering~SLS!,used here are described in more detail in the pages that follo

2.1 Stereolithography. Stereolithography~SL! is a three-dimensional building process, which produces a solid plamodel. In this process, an ultraviolet~UV! laser traces two-dimensional cross-sections on the surface of a photosensitiveuid plastic~resin!. The laser partially cures the resin through loenergy absorption of laser light thus producing a solid. The ficross-sectional slice is built on a depth-controlled platform, whis fully submerged under the first thin layer of resin. This and easuccessive thin layer of liquid resin has a depth equal to that ofvertical slice thickness of the part. After each slice is traced onsurface of resin, the platform lowers by a depth equal to that ofslice thickness. Successive 2-D slices are cured directly ontoprevious layer as the part is built from bottom to top.

Support structures are needed to maintain the structural inrity of the part and supports overhangs, as well as provide a sing point for the overhangs and for successive layers on whicbe built. These supports are constructed from a fine lattice stture of cured resin. After the part is fully built, the support strutures are removed and the part is cleaned in a bath of solvent,air-dried. The prepared parts are then flooded with high-intenUV light in a Post-Cure Apparatus~PCA! to fully cure the resin.The Department of Mechanical and Aerospace EngineeringRutgers University is equipped with a SLA 190 machine. Avaable basis materials for this machine include photo-polymer reepoxies with various physical properties.

2.2 Selective Laser Sintering. Selective Laser Sintering~SLS! is a three-dimensional building process based on the sining of a metallic or non-metallic powder by a laser. The SLprocess involves the heating of the powder using a CO2 localizedlaser beam. This localized heating raises the temperature opowder such that solidification by fusion occurs without meltinThe model is built on a platform that is situated within a horizotal platen. The platform, which is initially flush with the platen,lowered a depth equal to that of the slice thickness. A powdethen rolled, scraped or slot-fed onto the platform and thenlaser draws the two-dimensional cross-section. This lowerpowdering and lasing process is repeated until the partcomplete.

Unlike the SL process, no support structures are necessarSLS since the part rests on and within the non-sintered powPost-curing is not necessary except in the case of ceramic pAvailable materials include polycarbonates, nylons, polyamidelastomers, sand casting materials and steels. The fabricatiothe SLS prototype parts used in the present investigation was dthrough a professional Rapid Prototyping service provider for Smanufacturing.

3 Joint Fabrication

3.1 SL Fabricated Joints. The first step in building roboticsystems with a Rapid Prototyping machine is to be able to scessfully fabricate joints. Different types of mechanical joinsuch as revolute, spherical, primatic and universal joints werericated with the SLA machine~Fig. 1!. These joints were pro-duced without requiring assembly.

Through a trial and error process, different features suchclearance, part size and support structure generation weremized to produce working mechanical joints. Of these featudetermination of clearances was very important in successfulfabrication. The optimum clearances for the SLA 190~Cibatool®SL 5170 resin!, between two near surfaces, were determined to0.3 mm for flat surfaces and 0.5 mm for circular surfaces. Al

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the size of these parts is in the order of a few centimeters. Twas done to determine the limits of the available apparatus asas to conserve processing time and material.

The tests to determine these clearances were performed onthe SLA 190 ~SL 5170 resin!, at a layer thickness setting o0.1524 mm~0.0069!. The trials were systematic in that the initiaclearances for both the flat and circular surfaces began atmillimeter and decreased by 0.1 mm each successive buildthe joint was no longer mobile. The clearances were thencreased by 0.05 mm until the joint mobility was clear and fremoving. Finally, the optimal joint clearances were found whthere was enough space between the surfaces of the joint to afree movement yet not too great that supports were built betwthe surfaces to prevent movement. The above tolerances have

Fig. 2 Revolute joint built with SL „all dimensions are in mm …

Fig. 1 Stereolithography joint fabrications

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sistently given the same results for identical parts as well avariety of different parts made over the past two years.

In Fig. 2 the CAD drawings and pictures of the revolute joinare shown. The revolute joint consists of two rings, each witsmall stem attached. The two rings are connected, throughcenters of the ring holes, by a pin that acts as the axis revolut

Spherical joints with varying sizes for the ball and socket webuilt. Two slightly different designs of spherical joints were faricated. In the first design, shown in Fig. 3, the bottom of tsocket is cut slightly to create an opening for the support structo go through and hold the ball in place, so that the ball wouldfuse to the socket during fabrication. This spherical joint was oented as shown in the line drawing such that the ball and sopart was built first before building the link arm. The second tyof design for a spherical joint is shown in Fig. 4. In this desigsince the ball and socket was built last~the build orientation isshown in the line drawing of Fig. 4!, the ball did not need anysupport as it was supported by the vertical link itself. The appromate time of fabrication for this joint was 5.75 hours.

Initially, the prismatic joint or sliding joint was characterized bthat of a piston-cylinder type assembly. Poor sliding of the joresulted from a volume of trapped resin in the chamber that conot be effectively or easily removed prior to final ultra-violet cuing. Also evident in the joint assembly was the presence of undired additional degrees of freedom. The joint was then redesigwith these two factors as limiting constraints. The final designthe joint is a one degree-of-freedom sliding joint that doeshave any closed cavities. Also, the rectangular shape entavoided the SLA machine software’s linear approximationcurved lines resulting in closer clearance of parts. This joint w

Fig. 3 Type I of spherical joint built with SL „all dimensions arein mm …

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fabricated in the upright position along its length and is shownFig. 5. The completion of this build cycle took approximatelyhours.

The universal joint design is a classical cross-type assemwhich consists of two different constitutive components; the tyokes and the connecting cross hub. One of the two initial univsal joint designs is shown in Fig. 6. The outer diameter of the liof the universal joint shown in Fig. 6 is 20.32 mm~0.89!, the innerdiameter is 15.24 mm~0.69! and the total length is 36.73 mm~1.459!. Using the revolute joint as a design reference, the univ

Fig. 4 Type II of spherical joints built with SL „all dimensionsare in mm …

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sal joint was also fabricated using the 0.5 mm circular surfaclearance. This joint was fabricated in the upright position aloits length and a picture of the prototype is also shown in Fig.The completion of this build cycle took approximately 8.4 hou

When building joints at an oblique configuration, instead overtical one~upright configuration!, a special effect appears callethe ‘‘step effect’’ or ‘‘staircase effect.’’ This effect can reduce thquality of fabrication of the joint. This is the result of approximaing a continuous curved surface in the vertical direction withdiscrete set of horizontal thin layers. Obviously, the thinnerlayer or building the part in an orientation closer to a verticconfiguration reduces this effect.

3.2 SLS Fabricated Joints. Joints of a robotic finger werebuilt using Selective Laser Sintering. The basis material chowas a polyamide. Clearances similar to that established for jofabricated using the Stereolithography SLA 190 process were u

Fig. 6 Universal joint built with SL

Fig. 5 Prismatic joint built with SL „all dimensions are in mm …

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as trial values. These values are conservative as the Sinterst2000 has a greater level of accuracy,60.0059–0.00759 versus60.00759, and a smaller layer thickness, 0.0059 versus 0.0069,over that of the SLA 190.

Two different types of joints were fabricated with the SLS mchine: revolute joint and a spherical joint. Both joints are partsa rapid prototyped robotic hand that is presented in SectionBecause of their use in a robotic hand the joints needed to saspecific design criteria.

The revolute joint, shown in Fig. 7, connects the ends of tlinks of the finger. The range of motion for this joint is restricteto approximately 100° of revolution. This limitation on the ranof motion was accomplished through the rounding of just one sof the yoke section of the fixed link side. As can be seen infigure, the other side was not rounded to act as a stop.~Often,

Fig. 7 Revolute joint

Fig. 8 Views of „a… modified socket and „b… modified ball

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revolute joints provide a full 180° range of motion.! Thus, thisrounding allows the links to clear each other in revolution onthrough the desired range of motion.

The spherical joint, which serves as the ‘‘knuckle’’ at the fingepalm interface~see Fig. 13!, is to have approximately 90° of revolution and about615° of side-to-side freedom in the fully extended configuration and 0° of side-to-side freedom in the fucontracted configuration. This is an approximation on the rangmotion present in an average human finger. The limitationspherical range of motion was achieved by slotting the socsection in a shape as seen in Fig. 8~a!. Another restriction was thaof minimizing the range of twist about the extended-finger axThis was accomplished by removing material from diametrihemispheres of the inner ball and adding material to the insection of the socket resulting in a modified spherical joint~Fig.8~b!!. The combination of the modified ball and the slotted soc~Fig. 9! will not fully restrict but will serve to limit the range oftwist to approximately610°; a value acceptable in preliminarprototypes.

As seen in Fig. 10, using the SLS process to build noassembly type joints proved successful. Both parts exhibited gmobility through the desired ranges of motion. Also, the preseof the ‘‘staircase effect’’ was reduced due to the Sinterstation pcess’ thin layer thickness. The fabrication of these two joints isfirst verification step in the robotic hand construction.~Note, thatsince the fabrication of these parts was through a professiRapid Prototyping service provider for SLS manufacturing tbuild duration was not documented.!

The improvement in rounded surface quality has important csequences in the design of these joints. First, the decreasedeffect’’ means that the clearances between moving surfaces careduced to a lower value. Another important effect is the dimished importance of part orientation during the fabrication procin rounded as well as in flat and sloped components. SelecLaser Sintered parts do not require any computer or manugenerated support structures. This is an important process adtage. Parts do not have to be designed with the consideratiosupport structure placement in part orientation during the bucycle and in addition, the task of support removal is eliminate

Fig. 9 Modified spherical ‘‘Knuckle’’ joint

Fig. 10 SLS fabricated joints

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Fig. 11 A leg of the parallel manipulator

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4 Fabrication of Complex Mechanisms

4.1 Parallel Manipulators. A three-legged 6-DOF parallemanipulator was chosen as the first mechanism to be fabricwith the Stereolithography SLA 190. First, one leg of the paramanipulator was built to demonstrate the feasibility. The leg ofparallel manipulator consists of two spherical joints, one at eend, and a prismatic joint at the middle of the leg. The designthe joints presented in Section 3.1 were used. The fabricatedare shown in Fig. 11.

The final platform was built with three identical legs. The toand bottom platforms are two triangular ternary links~links con-nected to three joints! having the same dimensions of 2.54c32.54cm32.54cm~19319319! on three sides of the triangle anthe thickness was 2 mm~0.078749!. To save fabrication time, thetriangular platforms were not completely filled. Since the fabriction of each joint was tested separately, the fabrication of thewas favorably completed. In Fig. 12, pictures of the fabricarapid prototype of the parallel manipulator are shown in two dferent configurations. This prototype was built overnight durin12-hour period.

4.2 Robotic Hand. Another complex system that has bedesigned and is currently being fabricated is that of a robotic hwith five fingers and a palm; all constructed as one non-assemtype mechanism~Fig. 13!. This robotic hand is designed with thfuture purpose of using a Rapidly Prototyped robotic hand apossible replacement for mechanically driven prosthetic hanThe fingers are composed of three cylindrical links connectedtwo revolute joints~Fig. 14!. Each of the fingers is to be attacheto the palm section by modified spherical joints~see Figs. 8~a! and8~b!!.

Actuation of the robotic hand is to be achieved through a cobination of cables and Shape Memory Alloy artificial muscwires. Shape Memory Alloy~SMA! wires are characterized by

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reduction in length when resistive heat is generated throughlength of the wire by the flow of electricity. The SMA wires to bused in this design have a wire diameter of approximately 1microns~0.0069!. The cables will be connected close to the pivpoints of the revolute joints and will run through the incorporat‘‘pathways’’ ~Fig. 15! within the length of the fingers. The cablewill be crimped to SMA muscle wires proximal to the palm. Itnecessary to run the cables through the hand rather than the Sthemselves as the activation temperature of the SMA is 70–9and the melting temperature of the SL material is 85°C.~Themelting temperature is not a consideration with the SLS mateas its melting temperature is 185°C.! The use of SMA wires willbe the first attempt at actuating a Rapidly Prototyped systemRutgers University.

Figure 15 shows a cutaway view of the channels withinfinger for routing of the cables used for actuation. These pa

Fig. 12 Three legged parallel manipulator

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ways, 2.54 mm~0.19! in diameter, were designed to guide thcables through the finger links so as to decrease stress oncables while maintaining the required tension. One chanthrough the middle link appears in a diagonal pattern, as sfrom this side view, for the above-mentioned purpose. In additithe cables intended for flexion and extension of the distal ltravel over top of the revolute joint between the middle and promal ~last! links so that the movement of these two revolute joinis uncoupled. The channels through the proximal link fanaround the ball and socket~which could be seen from a dorsal otop view!. Two cable pathways, one for flexion and one for etension of the modified spherical joint, run through the socketthe palmar and dorsal~back of hand! sides to allow for 90° rota-tion during actuation. Currently, abduction and adduction~side toside! movement at the finger spherical joint is passive.

Another important design consideration in this robotic ha

Fig. 13 CAD rendering of robotic hand

Fig. 14 CAD view of a robotic finger

Fig. 15 Cable channels in SLS finger

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prototype is to have the same range of motion and similaritysize to that of an average human hand. The former guiding defeature necessitated the use of modified joint designs to partrestrict some of the degrees of freedom. The design featuresfabrication of these joints was presented in Section 3.2.

Presently, a single robotic finger has been fabricated usingSLS process as shown in Figs. 16~a! and~b!. The SLS procedurehere was similar to that of the revolute and spherical jointsscribed in Section 3.2. The SLS process produced a quality, fassembled finger with good joint mobility, clearances, and ranof motion. The SLS glass filled nylon material used for this asembly provided for less joint friction than the previously polymide fabricated single joints. The clearances are such that thesome additional movement in the joints than desired, so it wobe possible to reduce these tolerances in the future. As inprevious SLS constructions, the joints fully reach the designrange of motion. Additionally, all the pathways and cable assebly holes were clear of material. The Selective Laser Sinterprocess successfully fabricated this multi-joint, multi-degree-freedom robotic finger. Figure 16~b! shows the SLS fabricatedfinger with the tendons~cables! attached in a post-fabricationphase.

5 DiscussionThe joints and systems fabricated using the Stereolithogra

machine model SLA 190 as well as the SLS Sinterstation 2produced quality plastic parts. Joints fabricated using boththese prototyping methods exhibited good overall movement cacteristics and near-surface clearing. The two RP processchines used and the main experimental features noted aresented in Fig. 17. Note that the table shown in Fig. 17 is notall-encompassing description of the machines and their comp

Fig. 16 Robotic finger built with SLS and actuated with SMAwires

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capabilities. The major results of the experimentation as itbeen described in Sections 3 and 4 are summarized in Fig. 1

The joints fabricated using the Stereolithography SLA 190cluded spherical, revolute and prismatic type joints. These jowere designed with clearances of 0.3 mm and 0.5 mm for flatcircular near surfaces, respectively. An essential design consation in the SL process is the support structure requirementaddition to an initial base support structure necessary priorinitial part fabrication, additional supports provide structural sbility and a starting point for overhangs and new layers to initialayering. The SL joints showed good smoothness and evenneflat vertical and horizontal surfaces. For rounded or oblique stions, the parts showed acceptable surface agreement with Cmodels.

The joints fabricated using Selective Laser Sintering includspherical and revolute type joints. These were determined to ba higher quality in overall part prototyping. This can partially battributed to the Sinterstation 2000’s greater level of accuracyplanar detail and resolution in layer thickness over the SLA 1These advantages directly lead to a number of machadvantages.

Due to a reduced staircase effect, the sliding-friction in tjoints was reduced in the SLS fabricated parts over the SL facated parts. Also, the SLS process produced joints with smaclearances and smoother rounded surfaces. These improvemare the result of a more accurate Rapid Prototyping machine inSinterstation 2000 over the SLA 190. In contrast, the SL produparts showed much greater smoothness and regularity over thparts. Another important advantage is that the Selective Lasertered parts do not require any computer or manually generasupport structures. Parts do not have to be designed withthought of support structure placement in part orientation durthe build cycle as well as manually performing the task of suppremoval.

Both Rapid Prototyping processes constructed joints withdesired ranges of motion and size, however the SLS procshowed more apparent advantages over the SL process in aber of regards. It is important to note that the majority qualadvantages of the SLS parts over the SL parts cannot be so

Fig. 17 Brief comparison of two RP processes

Fig. 18 Summary of experimental results

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attributed to the Rapid Prototyping processes alone. To makmore competitive comparison between the two RP processehigher-end model of the Stereolithography machine ought be uin SL part fabrication. This would provide a better basis for coparison on areas such as step effect, overall surface qualityminimum clearances.

From the comparison conducted using the two somewhatequally matched RP machines, there are a number of differebetween the RP processes themselves, which will be presengardless of the machine model variation. For example, theprocess is based on the photo-polymerization of a liquid rewhereas the SLS process is based on the sintering of powdThese differences will produce parts with varying mechaniproperties due to build material choices. Post-processing conerations play an increasingly important role in complicatmechanisms and robotic systems. As previously mentioned,SLS process does not require the generation of support structThis provides an advantage in part design freedom and protoorientation during the fabrication process.

Though primarily a comparison between two different RP pcesses has been made, it is worth mentioning that RP techniin general have provided benefit. The time saved for buildprototypes using one of these methods is significant when cpared with traditional building techniques. For example, a Rutgaluminum finger prototype similar in design to the RP fingshown in Figs. 16~a! and 16~b! took approximately two weeks tobuild versus hours to build these prototypes. Also, Fig. 16 shotwo different design types that were easily fabricated for compson. The cable channels shown in Fig. 15, and implementedthe second design~Fig. 16~b!! were an improvement over thprevious design with respect to the desired cable movementvided. This type of design feature was easily achieved withuse of the RP process. Additionally, complex systems were mafactured using the techniques mentioned in this paper thatdifficult or impossible to do with traditional forms of manufactuing. An example of this is the modified spherical joint~Figs. 8 and9!. This spherical joint design is unique; and it is unlikely ththese modifications could be easily made by traditional mewhile still maintaining the quality of mobility presented here.

As Rapid Prototyping technologies continue to improvmechanisms and robotic systems built using this methodologycompete with and eventually surpass those of traditional fabrtion techniques. Ideally, the clearances necessary to effecticompete with assembled components and mechanisms neeimprove by an order of magnitude. Avenues to approach this nmay be currently possible through the use of system technologwhich are currently under development. For example, MicroTof Duisburg, Germany has developed a microstereolithograprocess that can produce parts with layers as thin as 1mm~0.000049! @21#. This is a 150-fold reduction over the SLA 1900.0069 minimum slice thickness.

Rapid Prototyping has been shown to be a viable meanssimple and quick fabrication of prototypes for the articulatstructures of robotic systems. Several joints and robotic systhave been fabricated using this framework. The successful facation of the robotic hand gives further confidence in this RaPrototyping framework. In the future, actuation of rapidly fabcated prototypes will be investigated through the use of ShMemory Alloy artificial muscles or other types of smart materiaAdditionally, the entire compilation of the robotic design, fabriction and actuation of the hand will be the topic of a future pap~also, see@17#! for further information!.

AcknowledgmentsThis work is supported by a CAREER grant~DMI-9984051!

from the National Science Foundation. The Center for Computional design of Rutgers University, The Center for Advancedformation Processing~CAIP!, and the NASA Space Grant Con

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sortium provided additional support. Kathryn DeLaurentissupported by a National Science Foundation Graduate ReseFellowship.

References@1# Ashley, S., 1995, ‘‘Rapid Prototyping is Coming of Age,’’ Mech. Eng.~Am.

Soc. Mech. Eng.!, 117, No. 7, pp. 63–68.@2# Ashley, S., 1998, ‘‘RP Industry’s Growing Pains,’’ Mech. Eng.~Am. Soc.

Mech. Eng.!, 120, No. 7, pp. 64–67.@3# Tse, W. C., and Chen, Y. H., 1997, ‘‘A Robotic System for Rapid Prototypin

Proceedings of the 1997 IEEE International Conference on Robotics andtomation,Albuquerque, NM, pp. 1815–1820.

@4# Vergeest, J., and Tangelder, W., 1996, ‘‘Robot Machines Rapid PrototypInd. Robot,23, No. 5, pp. 17–20.

@5# Laliberte, T., Gosselin, C., and Coˆte, G., 1999, ‘‘Rapid Prototyping of Mecha-nisms,’’ Proceedings of the 10th World Congress on the Theory of Machand Mechanisms,Oulu, Finland, Vol. 3, pp. 959–964.

@6# Laliberte, T., Gosselin, C., and Coˆte, G., 2000, ‘‘Rapid Prototyping of Lower-Pair, Geared-Pair and Cam Mechanisms,’’Proceedings of the 200 ASMEMechanisms and Robotics Conference,Baltimore MD, September 10–132000, Paper DETC2000/MECH-14202.

@7# Cham, J. G., Pruitt, B. L., Cutkosky, M. R., Binnard, M., Weiss, L., aNeplotnik, G., 1999, ‘‘Layered Manufacturing with Embedded ComponenProcess Planning Issues,’’Proceedings of the 1999 ASME DETC/DFM Coference,Las Vegas, NV, Sept 12–15, 1999, Paper DETC99/DFM-8910.

@8# Bailey, S. A., Cham, J. G., Cutkosky, M. R., and Full, R. J., 2000, ‘‘Biommetic Robotic Mechanisms via Shape Deposition Manufacturing,’’RoboticsResearch: The Ninth International Symposium,John Hollerbach and DanKoditschek~Eds!, Springer-Verlag, London.

@9# Rejagopalan, S., and Cutkosky, M. R., 1998, ‘‘Tolerance RepresentationMechanism Assemblies in Layered Manufacturing,’’Proceedings of the 1998ASME DETC/DFM Conference,Atlanta, GA, Sept 13–16, 1998, PapeDETC98/DFM-5726.

@10# Rajagopalan, S., and Cutkosky, M. R., 1999, ‘‘Optimal Pose Selection

524 Õ Vol. 123, DECEMBER 2001

isarch

,’’Au-

, ’’

es

dts:-

i-

for

r

for

In-Situ Fabrication of Planar Mechanisms,’’Proceedings of the 1999 ASMEDETC/DFM Conference,Las Vegas, NV, Sept 12–15, 1999, Paper DETC9DFM-8958.

@11# Goel, P., Rajagopalan, S., and Cutkosky, M. R., 2000, ‘‘Error Analysis forIn-Situ Fabrication of Mechanisms,’’Proceedings of the 2000 ASME DETCDFM Conference,Baltimore, MD, Sept 13–16, 2000, Paper DETC2000/DFM14019.

@12# Binnard, M., 1999,Design by Composition for Rapid Prototyping,KluwerAcademic Press.

@13# Kataria, A., and Rosen, D., 2000, ‘‘Building Around Inserts: Methods fFabricating Complex Devices in Stereolithography,’’Proceedings of the 2000ASME Mechanisms and Robotics Conference,Baltimore MD, September 10–13, 2000. Paper DETC2000/MECH-14206.

@14# Geving, B., and Ebert-Uphoff, I., 2000, ‘‘Enhancement of Stereo-LithograpTechnology to Support Building Around Inserts,’’Procedings of the 2000ASME Mechanism and Robotics Conference,Baltimore MD, September 10–13, 2000. Paper DETC2000/MECH-14207.

@15# Alam, M., Mavroidis, C., Langrana, N., and Bidaud, P., 1999, ‘‘MechanisDesign Using Rapid Prototyping,’’Proceedings of the 10th World Congress othe Theory of Machines and Mechanisms,Oulu, Finland,3, pp. 930–938.

@16# Won, J., DeLaurentis, K., and Mavroidis, C., ‘‘Rapid Prototyping of RoboSystems,’’Proceedings of the 2000 IEEE International Conference on Robics and Automation,April 24–28 2000, San Francisco, CA, pp. 3077–3082

@17# Won, J., DeLaurentis, K., and Mavroidis, C., ‘‘Fabrication of a Robotic HaUsing Rapid Prototyping,’’Proceedings of the 2000 ASME Mechanisms aRobotics Conference,Baltimore, MD, September 10–13, 2000. PapDETC2000/MECH-14203.

@18# Dolenc, A., ‘‘An Overview of Rapid Prototyping Technologies in Manufactuing,’’ http//www.cs.hut.fi/;ado/rp/rp.html, Helsinki Univ. of Technology,1994.

@19# Crawford, R., and Beaman, J., 1999, ‘‘Solid Freeform Fabrication: A NManufacturing Paradigm,’’IEEE Spect.,February 1999, pp. 34–43.

@20# Bylinsky, G., 1998, ‘‘Industry’s Amazing Instant Prototypes,’’ Fortune,137,No. 1.

@21# Wohlers, T.,Rapid Prototyping and Tooling State of the Industry: 1999 Worwide Progress Report,Wohlers Associates, 1999.

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