Journal of Materials Processing Technology 167 (2005) 499–507

Recent development in micro-handling systemsfor micro-manufacturing

A.J. Sanchez-Salmerona,∗, R. Lopez-Tarazonb,R. Guzman-Dianab, C. Ricolfe-Vialaa

a Universidad Politecnica de Valencia, Departamento de Ingenier´ıa de Sistemas y Autom´atica,Camino de Vera s/n, 46022, Valencia, Spain

b Robotnik Automation, SLL, C/Berni y Catala 53, 46019, Valencia, Spain

Abstract

A review on existing systems for handling micro-parts was carried out recently by the authors. The work was focused on the analysis ofthe main problems which limit the emergence of automated micro-handling systems. Some of the challenges associated with the handling ofmicro-parts were also examined.

A key problem area limiting the emergence of automated micro-handling technology is lack of flexible and high-precision micro-handlingm d resourceso©

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achinery. Another problem is the lack of standardization due to which equipment makers spend an excessive amount of time ann custom automation solutions.2005 Elsevier B.V. All rights reserved.

eywords:Micro-parts; Micro-handling systems; Automation; Standards

. Introduction

Europe has encouraged research and development inicro-systems technologies over the past decade in the firmelief that these technologies form the basis of a new gen-ration of products, manufacturing techniques and marketpportunities. Nowadays, micro-electromechanical systemsMEMS) are present in very different markets such as auto-otive, medical, aeronautics, military, etc. For example,

ome commercial products presently on MEMS are opticalwitches, dental prosthesis, stents (for coronary and endovas-ular applications), dispensers, pressure sensors, inductors,esonators and thermal ink-jet cartridges.

The extra value MEMS bring to products is widely recog-ised, but still many barriers are to be overcome to introduceEMS in a wide range of products. The main problem is that

∗ Corresponding author. Tel.: +34 963877007x75786;ax: +34 963879579.

E-mail addresses:asanchez@isa.upv.es (A.J. Sanchez-Salmeron),lopez@robotnik.es (R. Lopez-Tarazon), rguzman@robotnik.es

these products consist of several micro-components mfactured by different techniques. These components muexactly assembled in one or more steps to form the deproduct, which requires excellent positioning skills and hflexibility of the micro-handling facilities.

Micro-handling is basically the manipulation of smparts with high accuracy. Some sample parts are illustratFigs. 1–3. Typical part dimensions are in the range of microeters up to a few millimetres and part features may be imicrometer range. The typical location accuracy is inrange of 0.1–10�m.

People usually think in terms of meso-scale, but wtalking about handling methods at the micro-scale, gracannot be considered the main force being applied to theUnwanted surface forces such as van der Waals, electroand surface tension forces appear dominant at such scathose forces are known as adhesive forces[1]. Therefore, thpick-and-place problem is difficult in micro-world becauadhesive forces must be taken into account.

Automated positioning at the meso-scale is eaachieved using conventional closed-loop control and a

R. Guzman-Diana), cviala@isa.upv.es (C. Ricolfe-Viala). ety of output sensors; however, positioning in micro-scale

924-0136/$ – see front matter © 2005 Elsevier B.V. All rights reserved.oi:10.1016/j.jmatprotec.2005.06.027

500 A.J. Sanchez-Salmeron et al. / Journal of Materials Processing Technology 167 (2005) 499–507

Fig. 1. An example of a bulk shape micro-part.

Fig. 2. An example of planar shape micro-part.

becomes a difficult problem. In micro-handling the jointbacklash and the structural vibration due to link flexibilitymust be controlled at the level of microns.

Finally, it is necessary to emphasize that micro-handlingrequires higher manipulation care and cleanliness becausethe micro-parts are very fragile. Sometimes, it is mandatoryto work under clean room conditions.

Due to these problems manual micro-handling is the mostoften used method today. In this case micro-handling tasks arecarried out by operators, who position and align objects man-ually. The application of teleoperating micro-handling, whichtransforms the human operator’s hand motion by means of ajoystick into the finer 3D motion of the system’s manipula-tors systems, is normally tailored to some tasks: an automatedpick-and-place manipulator is only applied on mechanicalparts which can be easily handled using a specific gripper.

A review on existing systems for the handling of micro-parts was carried out recently by the authors. The work isfocused on analysing the main problems which are limitingthe emergence of automated micro-handling systems. Someof the challenges associated with the handling of micro-partsare also examined in this paper.

A key problem area limiting the emergence of automatedmicro-handling technology is the non-availability of flexibleand high-precise micro-handling machinery. Another prob-lem is the lack of standardization which causes equipmentmakers to spend an excessive amount of time and resourceson custom automation solutions.

2. Micro-manipulator systems

Conventional manipulators do not meet the accuracyrequirements needed in the micro-world. A general trend isto reduce the size of the manipulators and to simplify theirdesigns. The scope is to improve the system’s immunity toenvironmental perturbations such as vibrations and thermaldrifts, and to reduce the overall costs (production and runningcosts).

One of the basic challenges in precision handling is theneed for very high accuracy over a large range of motion.This fact involves the design of handling tools and processesa stema blemi tionalm ongt r andt racya

atord andr RSIi enh ed byQa rivest am-p obotf eds s.

torsi r-t loadc figu-r tionsa OFs,a hinesh suallys pre-c 0X,c ms,b

Fig. 3. An example of a tubular shape micro-part.

t multiple scales, and their integration into coherent syrchitectures. One possible approach to solve this pro

s to use a coarse-to-fine strategy. In this case a convenanipulator for coarse motion with low accuracy but l

ravelling distance is used and between the end-effectohe manipulator a fine positioning device with high accund very small travelling distance is mounted.

Another strategy is to use high-precision manipulirectly. Commercial robotic systems with a resolutionepeatability of a few microns are available (e.g.; from Mn Chelmsford, MA, or from Sysmelec in Switzerland). Evigher precision prototype systems have been describuaid and Hollis[2], Zesch[3] and Danuser et al.[4],mong others, who use stepping motors and inertial d

o obtain sub-micrometer motion resolution. Another exle of these precision systems is the parallel RP-1 AH r

rom Mitsubishi Electric, a miniature-format robot designpecifically for high-precision micro-handling application

The state of the art of precision industrial manipulas summarized inTable 1. This table shows the most impoant parameters of workspace, precision, velocity andapacity of some manipulators. The most common conations are SCARA and Cartesian, but other configurare also available. There are important differences in Dccuracy, workspace and load. The most accurate macave a reduced speed. The Cartesian manipulators are ulower than the SCARA-type robots, but have a higherision. The fastest robot of the table, the Yamaha YK-12an perform a pick and place trajectory in less than 300ut with low precision.

A.J. Sanchez-Salmeron et al. / Journal of Materials Processing Technology 167 (2005) 499–507 501

Table 1State of the art of industrial micro-manipulators

MODEL BY TYPE DOFS REP. ACC.(�m)

WS (mm) Load (kg) Speed (mm/s)

E2C EPSON SCARA 4 8 R250 Z100 5 P&P 0.39 sRP-1AH MITSUBISHI SCARA 4 ±5 150× 105× 25 1 400 P&P 0.28 sYK-120X YK-150X YAMAHA SCARA 4 5–10 R110 Z30 0.5 700–2000

P&P< 300TUSBOSCARA SR4-PLUS BOSCH SCARA 4 ±50 R400 Z200 2 1600AUTOPLACE4 00 SYSMELEC CART 4 ±2.5 150× 150× 150, 85× 85× 75 4MP63-25DC FEINMESS CART 3 5 25× 25× 25 2 5MP84 FEINMESS CART 3 3 25× 25× 25, 100× 100× 100 1.5 2501940 KOPF CART 3 1 128× 128× 128MM3A KLEINDIEK RRR (antr) 3 1 100 cm3; z:12;x,y:180◦ 10KLOCKE NANOMANIP RRP (spher) 3 0.001 5× 5× 19 5MRSIEXFO PCS-4100 RPPPR 5 0.4 25× 25× 25 2SEMPREX Univ. Pipette

ManipulatorPPPRPP 6 75× 33× 25, 95◦ 75,200

SOMAPATCH MW3R/L CART 3 0.25 5× 5× 5MRSI Newport PPPR 4 ±10 415× 415 9000

The existing solutions have the common feature of beingexpensive, bulky and inflexible. Due to their dimensions, theyare sensitive to environmental perturbations such as vibra-tions or temperature drifts.

There is a big growing market demand for smaller, cheaperrobotic devices for positioning and assembling. The develop-ment of such robots is now being made possible by new tech-nologies in particular zero-backlash micro-gears and highlydynamic micro-motors with integrated incremental encoders,which are allowing proven robot arm structures to be minia-turised. Furthermore, they allow the use of proven controltechnology and avoid the complexity of alternative actuatortechnologies such as piezo-actuators[5]. Fig. 4shows a cur-rent design of SCARA type micro-manipulator which will bepresented at the Hannover Fair in 2005.

F ctionT

3. Grippers

The force interaction between the part, the gripper and theenvironment must enable the part to be picked and releasedat the final location. One of the basic challenges in micro-handling is the influence of the grip principle on the accuracyof the part gripper relation. Both when gripping and whenreleasing the part, inaccuracies may be introduced. As anexample, when releasing the part, some errors may occur dueto adhesive forces. Many micro-operations demand sensorcontrol in the execution to compensate for several types oferrors such as part dimension variations or inaccuracies inpart gripper relations.

Three main micro-handling principles are to be mainlyreviewed in this paper: friction, pneumatic and magnetic.Finally, a section called “Others” summarizes the remainder.

3.1. Friction

This principle picks a part on the basis of friction betweenthe part and the gripper, usually implemented with a pairof fingers [6]. The main advantage of this kind of grip-per is the ability to centre the part between the grippingjaws and to align it parallel to the jaws. This fact allows amore precise handling of micro-parts by putting them intoa por-t e ofa avail-a art),t thes ram-e parts

of am asiso nt of

ig. 4. Scara robot design of the Institute of Machine Tools and Produechnology, Braunschweig, Germany.

defined location after being gripped. This is an imant attribute in a handling system with a high degreccuracy and speed. The more reference points that areble (that can be applied to the location of the micro-p

he fewer sensors will be needed in order to determineame information. The disadvantage is that gripper paters such as finger dimensions are dependent of theize.

Several types of gripper can be defined on basisechanism with stiff fingers, with elastic hinges, or on bf defonnable piezo-material fingers. Quite a large amou

502 A.J. Sanchez-Salmeron et al. / Journal of Materials Processing Technology 167 (2005) 499–507

research has already been carried out on the development ofmicro-tweezers with integrated actuators and force sensors.Thermally actuated single crystal silicon micro-grippers havebeen fabricated by bulk etching by Chu and Mehregany[7].Keller introduces a micro-gripper design based on thermalexpansion of actuator beams[8,9]. These grippers are knownas “HexSil” micro-grippers due to a hexsil process thatutilizes moulded Polysilicon. Others flexure-based gripperswere also reported in MEMS assembly[10], microsurgery[11] and micro-assembly[12]. Eisinberg et al. controls amicro-gripper based on flexure joints, fabricated by LIGAand instrumented with force sensors[13]. Goldfarbn andCelanovic designed a small-scale flexure-based gripper foran investigation of micro-manipulation in terms of positionand force control[14]. Carrozza et al. developed a micro-gripper for assembling biomedical micro-devices[15],which was also applied to grasping cantilever chips later in[16]. Zhou presents a force controlled micro-gripper designbased on force modelling[17]. Surface forces between asphere and a plane were modelled and studied in detailto assist in the design and fabrication of a micro-gripper.Keoschkerjan and Wurmus present the development of anew micro-gripper which can realise a parallel movementof the gripping arms with the possibility for simultaneouspositioning of the gripped object[18]. Krijnen et al. reportsa protruding electrostatic micro-gripper with force ampli-fi ono ninge IB)m tiono te per[i atedf ardp aserm allyt kem loys( bly[

ongg sicm andpa r forf ea tureg f ano d onfl ande na voedg rna-t s thata stage

[32]. Another similar approach is the Chopstick manipulatorof Sakai et al. [33]. Finally, Hofmann et al.[34] andTanikawa et al.[35] have developed modular micro-grippersor micro-gripper attachments for miniature machiningstations.

3.2. Pneumatic

A significant amount of effort has been expended devel-oping the technology to manipulate micro-scale parts indi-vidually using micro-vacuum tools with robotic systems.

The most relevant components of a vacuum gripper systemare:

(i) Pressure supply or micro-pump: basically these are airpowered or electric powered. Some common pumpsare: regenerative pumps, belt driven pumps, rotary vanepumps or water ring pumps. Some researchers haveinvestigated the use of thermal transpiration micro-pumps like some variations of the Knudsen Compres-sor. Applications of Knudsen Compressors as bothmicro-scale and macro-scale vacuum pumps have beeninvestigated in[36] and[37].

(ii) Pressure regulator: this maintains a constant pressure atits output independently of the input pressure. Regula-tors can hold back 5000 psi of air and let only enough

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cation and parallel jaw motion for in situ manipulatif sub-micrometer thick membranes in combined scanlectron microscopy (SEM)/focussed ion beam (Fachines[19]. Seok presents the design and optimizaf a compliant micro-gripper[20]. Lee et al. presenxperimental results from a study of a compliant grip21]. In [22] a micro-gripper of 2× 3.9× 0.1× mm3 sizes presented consisting of a single device micro-fabricrom a shape memory alloy (SMA thin sheet). Bellouresents another SMA micro-gripper, fabricated by lachining at EPFL in Lausanne, Switzerland, and therm

rained at CAT-RPI[23]. Winzek et al. present tweezer-liicro-grippers based on thin film shape memory al

SMAs) that were developed for high-precision assem24].

Schlick and Zuehlke deal with a design concept for trippers for micro-parts[25,26]. Petrovic presents a clasechanical micro-gripper design as a means to picklace micro-components in an assembly[27]. Kim et al. showpiezoelectric polymer-based sensorised micro-grippe

orce feedback-based handling[28]. Chen and Lin describn approach for the design of a flexure-based miniaripper[29]. Henein et al. design a gripper composed original three-dimensional compliant mechanism baseexible bearings, an inchworm piezoelectric actuator,xchangeable gripping jaws[30]. Voyles and Hulst desigcompact, active, multi-degree-of-freedom, force-ser

ripper[31]. Thompson and Fearing introduced an alteive micro-assembly system based on two 1-DOF probere orthogonal to each other and a 3-DOF translating

air through to bring the rest of the pneumatic systemto the designed operating pressure. Regulators gally have a purge valve to allow purging the air oua pressurized tank. Regulators come in all shapesizes. Some are rated for high pressure but havefeed rate. Other have a high feed rate but only worklow pressures. Some regulators have a gauge totank pressure and another to show regulated pres

(iii) Flow regulator: this allows the control of the vacuupressure at the Venturi or the flow used to blow aparts.

(iv) Micro-valve units: micro-valves can be electronicaswitched to perform the vacuum suction, blow upcleaning operations. They have to restrain the presbuilt up on one side and be able to ‘pop’ compleopen and not restrict the air as it rushes through.

(v) Venturi jet: The Venturi vacuum generator operaunder the Venturi principle.

(vi) Vacuum/pressure sensors: used to detect theence/absence of object to be picked.

vii) Micro-suction pads or pipettes: according to the sizthe parts, different types of grippers are used. Thetypes of suction micro-grippers are:

Micro-suction pads→ (5–0.8 mm)Pipettes or micro-vacuum cups→ (severamicrometers–1 mm)Bernoulli effect vacuum→ (delicate siliconwafers)

A vacuum tool for handling micro-parts is studieddepth in[38].

A.J. Sanchez-Salmeron et al. / Journal of Materials Processing Technology 167 (2005) 499–507 503

3.3. Magnetic

Unlike electromagnets, electronically switch-able perma-nent magnets use electricity for the hold/release switching, aprocess which takes only 0.2 s and can be controlled by pushbutton or via a signal from a PLC or robot computer interface.Once energised, the magnets retain their hold indefinitely andare not affected by failure or interruption of the power sup-ply. Each magnet has two steel outer poles (North and South)and two sets of permanent magnets are sandwiched betweenthem. The magnets of one set are constantly polarised in onemagnetic direction. The magnets of the other set have anelectrical coil wrapped around them and can be polarised ineither direction (i.e. N–S or reversed to give S–N) by passinga short pulse of electricity through this coil. When both setshave a ‘like’ polarity they ‘compliment’ each other and thefull magnetic power is achieved. When both sets have oppo-site polarity they ‘cancel’ each other and the magnet is OFF.In this way, the micro-part can be handled easily.

Finally, Judy and Myung make an extensive study aboutmagnetic materials for MEMS[39], while Yang et al. showsa novel ferromagnetic micromechanical magnetometer[40].

3.4. Others

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(b) Squeeze film levitation (or near field levitationaccording to several authors)[58,63–65]: Thereflector of the standing wave levitation is replacedby the levitated object. Consequently, any weightcan be levitated if the separation distance betweenthe object and the vibrating plate is small enough.

One of the basic challenges in micro-handling is therequirement of flexibility but the grippers are highly depen-dent on the parts properties and the environmental conditions.The part and the environmental features (type of material,geometric and surface properties) play an important role indetermining the applicability of a grip principle.Table 2shows a comparison between some gripping principles whichcan be used in micro-handling.

Commercial available micro-grippers do not offer a con-trol of gripping forces. At the best, a rough estimation ofthe prevailing forces is sometimes possible. The existingintegrated force sensors employ strain gauges, which are lim-ited in their ability to offer the control of gripping force.A small-sized force sensor with plain design, high reso-lution and sensitivity in the nano-Newton range does notexist yet. AFM-based force sensors usually used in scanningprobe microscopy seem to be a promising solution. Only afew results can be found in the literature about the use ofAFM-based force sensors in other fields than scanning probem

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Next the authors present a brief list of other principsed for micro-handling and a reference for more informabout them:

(i) Optical levitation[41–48]: Due to both the beam refletion and refraction, the component undergoes anforce that always pushes it forwards in the directiothe beam and a radial gradient force that traps it incentre of the beam when its refractive index is higthan that of the surrounding medium (water, oil, air. . .).Note that this principle leads to a gripping force thardly reaches 1 nN[49].

(ii) Bernoulli levitation [50] and [51]: Due to the highpressure supply, air flows radially between the gper and the component. The high velocity inducedynamic pressure decrease (Bernoulli effect), leato an upward attracting force on the component.

iii) Air cushion levitation[52]: Pressurized air flows througseveral holes that are drilled all over the gripperleads to an upward levitation force that counterbalathe weight of the component.

iv) Ultrasonic acoustical levitation:(a) Standing waves levitation[53–62]: Small compo

nents can be levitated in the pressure nodes oacoustical standing wave between a vibrating pand a reflector. Moreover, due to the pressure dbution, a radial flow (the velocity of which decreatowards the periphery) induces radial centring byBernoulli effect (reaching up to 30% of the levition force[60]).

icroscopy.

. Manipulator and gripper interfaces

Lack of standardization causes equipment makers to sn excessive amount of time and resources on custom au

ion solutions. Recently some standards have been deor micro-handling systems. One of these standards iIN 32565 norm where a mechanical interface betw

he manipulator and the gripper is defined. This normhe result of the work committee “NAFuO”. It specifiesequirements of an interface between end-effectors andling devices in production equipment for micro-systehere usually tools and grippers are interchanged. Thisefines the principal dimensions, tolerances, and des

ions for manual and automatic end-effectors. One of tefinitions is as follows:

An end-effector interchange interface is composedmachine side (head disk) and an end-effector side (addisk). This norm describes the adapter disk of the interThe implementation of the head disk and the type oflocking device (manual or automatic) is left to the user

All of the commercial available manipulators and gers can be adapted to use this mechanical interface;ossibilities of combining them will be maximized. Thetandards are too new to be used widely by the equipakers, therefore the integration between manipulatorrippers is extremely restricted.

504 A.J. Sanchez-Salmeron et al. / Journal of Materials Processing Technology 167 (2005) 499–507

Tabl

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s 5. Control strategies

The ability to control the grip force is very important inthe case of thin, fragile parts. The handled parts may suffer aplastic or elastic change of shape which can be undesirable.The distribution of the grip force over the surface ofinteraction is important as well, since high peak values of thegrip force may lead to cracks and part breakage. If possible,force sensing at the micro-scale can be used to avoid partand gripper damage during handling. Due to the relativehigh stiffness of some parts (high impedance), the control ofgripping forces requires the gripper to exhibit low grippingimpedance. Otherwise, small perturbations in motion maygenerate large changes in gripping forces. The impedancecontrol method can be applied, but this method needsaccurate modelling and some combination of position andforce control. For this reason, it is desirable that the gripperitself has a passive compliance when contacting with thepart.

The accuracy of the gripping force is affected by themotion resolution of the gripper. To achieve a fine resolu-tion motion for a gripper, not only its mechanism of motiontransmission needs to be backlash-free but also its actuatorsystem including the controller and driver should have a highperformance in terms of resolution and controllability.

There must be no vibrations due to position control atm thes n andt fullyd

t asd r andl erentc oute ler iti c-t ater sireds iquet ovedf e an idalr ng as aper,w inputt

anda con-t ro-h e sizeo

en-d t tot om-p nsivec ilib-

anipulator stop positions. This objective depends ontiffness of the mechanical system, the sensor resolutiohe control algorithm, so these components must be careesigned.

Control of machine vibration becomes very importanesigners attempt to push the state of the art with faste

ighter machines. Many researchers have examined diffontroller configurations in order to control machines withxciting resonances. Even with a sophisticated control

s difficult to rapidly move flexible machines without defleions and vibrations. A more achievable goal is to eliminesidual vibration once the machine has achieved a deet-point. Input shaping is a command generation technhat reduces residual vibration when a machine is mrom one set-point to another. Input shaping works likotch filter that is designed to eliminate decaying sinusoesponses. Input shaping is implemented by convolviequence of impulses, otherwise known as the input shith a desired system command to produce a shaped

hat is then used to command the system.Dynamic models can be used to improve the speed

ccuracy of the handling system under a closed looprol. Modelling and control become more critical in micandling as the accuracy requirements increase and thf parts decreases.

In a micro-domain precise calibration is highly depent on precisely modelled kinematics which is subjec

hermal growth errors. Two common techniques for censating thermal errors include either the use of expeooling systems, or waiting hours for the thermal equ

A.J. Sanchez-Salmeron et al. / Journal of Materials Processing Technology 167 (2005) 499–507 505

rium of the device to stabilize. These types of factors greatlyaffect the cost and reliability of handling systems, thereforereal-time visual feedback can be used effectively in the micro-domain. Many researchers are actively pursuing strategies formanipulating micron-sized objects using vision-based meth-ods[66–69]. However, there are problems with visual controlor image processing in the control of these systems. Someof the main problems are the slow processing speeds, highcost, difficulty in programming and proneness to errors dueto glare, reflection and other unwanted contaminants. It isimportant to emphasize the problems in setting up imageprocessing equipment and the long down times that occurif an error occurs. Even process that may seem straight-forward such as focusing and aligning the camera properlybecome complicated and extremely difficult to carry out atthese micro-scales.

High-precision linear motion systems are becomingsignificantly important to many manufacturing applicationssuch as precision machinery, semiconductor processing,precision metrology, and optical components manufacturing.Increasingly, there is more research conducted in the areaof linear motion control. Robust adaptive compensationfor friction and force ripple is studied in[70], automatedrelay-tuning for PID plus iterative learning controller ispresented in[71], a performance predictable design methodof robust controllers is proposed in[72], and adaptive robustc ps kinga mpli-fi ort ise s anda

f ap beingp

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seds ivea odel.WR ndlep mainf dgeo h thec ore,o m iss

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6. Conclusions

A review of existing systems for the handling of micro-parts was carried out in this paper. A key problem arealimiting the emergence of micro-handling technology is thenon-availability of flexible, high-precision micro-handlingmachinery.

Due to the increasing number of topics related to MEMS,some standards for automated gripping and handling ofmicro-parts have arisen. However, the standardisation ofthese micro-systems is quite new, so there are few standardsdefined at this moment. For example, to deal with differ-ent part sizes an automated interchange tool system can beused (DIN 32565). This norm is the result of the work com-mittee “NAFuO”. It specifies requirements of a mechanicalinterface between an end-effector and a handling device formicro-systems.

The combination of different grip principles in the samegripper is recommended to increase flexibility. Additionally,sensors mounted on smart grippers can help to compensatefor inaccuracies in part gripper relations. Machine vision is awidespread technology for high-precision handling of parts inindustrial environments. In micro-scale, machine vision canbe used to “see” exactly what it is going in the working placeand to “actuate” in consequence. With dedicated algorithms,the features of an object in the image can be extracted for robotl singo

othg osi-t Theh s thet ens-i isionfi y. V-g ergys e them

cro-h

(( ular

(( l and

( cable

A

ov-e 02),E mu-

ontrollers are covered in[73]. Their aims are to develoystems with good performance in terms of motion tracccuracy. In addition, due to the advances in actuators, aers, sensors, and motion controllers, the research effnhanced to build more demanding industrial processepplications.

In order to improve the motion tracking accuracy oositioning stage, several related research areas areursued, including, but not limited to, the following:

(i) Modelling of motion systems.(ii) Identification of model parameters.iii) Derivation and implementation of control algorithmsiv) Dealing with disturbance and parametric uncertain

in control systems

A robust model-reaching control (RMRC) can be uuch that it will follow a motion trajectory closely and drsystem to reach a specified desired performance mith the variable structure control (VSC) approach[74], theMRC scheme is easily implemented and able to haarametric uncertainties and external disturbance. The

eature of the RMRC is that it requires only the knowlef the estimated parameters of the system together witorresponding bounds in the implementation. Furthermnly the bound of the disturbance is needed if the systeubjected to external disturbance.

This control method produces superior tracking abhen compared to the popular PID plus feed-forwardodel-based control schemes[75].

ocalisation and control. For the latter, a real-time procesf images is a crucial issue.

Compliance analysis of micro-handling, including bripper and part is critical for reducing the necessary p

ional accuracy of the system, and therefore the cost.andling system need not require the same precision a

olerance of the locations if a proper use of positioning, sng, modelling, and control tools is made. The use of precxtures can mitigate the need for high positional accuracroove structures, or datum points, or other minimum enurfaces should be used as much as possible to guidicro-parts into desired positions and orientations.The following are key areas of the research in mi

andling systems:

1) “Contactless” and smart micro-grippers.2) Modelling of micro-assembly processes using molec

dynamics simulation (MDS).3) High-resolution micro feeding techniques.4) Plug and produce micro-assembly modules (contro

hardware integration).5) Integration of automated assembly processes appli

to “super-clean rooms”.

cknowledgments

This work was financially supported by the Spanish grnment (CICYT project number DPI2004-08353-C03-uropean Community FEDER funds and European Com

506 A.J. Sanchez-Salmeron et al. / Journal of Materials Processing Technology 167 (2005) 499–507

nity research funds (MASMICRO, Project number 500095-2).

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