Design of a shuttle used in an innovative pick and place machineconcept

P.A.H. Goede, P.P.H. Verstegen, J.M.M. van Gastel

Abstract— In this paper a novel concept to increase theoutput of a component Pick and Place machine is described. Acomponent shuttle that carries components is used to reducethe distance from pick to place location and hence traveltime is reduced. First design considerations and specificationsare discussed. A prototype was built and test results will bediscussed.

I. INTRODUCTION

Pick and Place machines are used to automatically placeelectronic components on printed circuit boards (PCBs). TheAdvanced Mechatronics group of the Delft University ofTechnology is working on an innovative concept for Pickand Place machines. The AX-501 component mounter (As-sembleon 2002) with a maximum of 20 Pick and Place robotsin parallel is capable of placing up to 160,000 componentsper hour (cph) in total; this means 8,000 cph per Pick andPlace robot with an accuracy of 50 µm (3σ). The layoutof this Pick and Place machine is called a multiple Pickand Place concept [1]; multiple Pick and Place robots areworking simultaneously. The new machine concept must becapable of placing 18,000 small components (6x6x4 mm)per Pick and Place robot per hour with the same accuracyof 50 µm (3σ).

A. Pick and Place cycle

To answer the question why the output of the AX-501component mounter is limited to 8,000 cph per robot thePick and Place cycle must be analyzed. In general a Pick andPlace cycle consists of the processes shown in Fig. 1. Thelength and/or order of the processes can differ in differentmachine concepts.

• Sub. run in The printed circuit board (pcb), substratein general, is inaccurately fed into the Pick and Placemachine.

• BA (board alignment) The position of the pcb ismeasured.

• Sub. Move The pcb is transported to the area wherethe Pick and Place robot can place components ontothe pcb.

The authors acknowledge the support of the Dutch Innovation-drivenResearch Program (IOP-Precision Technology) under Grant No. IPT02313.

P.A.H. Goede, Delft University of Technology, Advanced Mecha-tronics group; Hogeschool Utrecht University of Applied Sciences,MST/ME; The Netherlands; P.P.H. Verstegen Delft University of Tech-nology, Advanced Mechatronics group; Fontys University of applied sci-ences, Mechatronics; The Netherlands PaulGoede@orange.nl;P.Verstegen@Fontys.nl

J.M.M. van Gastel Assembleon; Veldhoven; The NetherlandsSjef.van.Gastel@philips.com

• Pick The Pick and Place robot picks a componentfrom one of the feeders. At this moment the Pick andPlace robot starts with the cycle of processes to placecomponents on the pcb.

• Move The Pick and Place robot moves to the componentalignment position in the machine.

• CA (component alignment) The position of the com-ponent with respect to the nozzle is measured. De-pending on the architecture of the Pick and Placemachine the component alignment can take place whilemoving or at stand still. The travel path depends on thearchitecture of the Pick and Place machine concept. Theconclusion must be that component alignment can addextra time to the Pick and Place cycle.

• Move The Pick and Place robot moves to the placeposition on the pcb.

• Place The Pick and Place robot places the componenton the position of the pcb.

• Move The Pick and Place robot moves to the pickposition to pick a new component.

• Sub. run out All components are placed by this Pickand Place robot so the pcb runs out or moves to thenext placing area of the Pick and Place machine.

With typical parameters of the AX-501 componentmounter such as acceleration, speed and the time neededto pick and place a component, a simulation model is built.This model is based on the layout of the multiple Pick andPlace concept.

As can be seen in the Pick and Place cycle diagram(Fig. 1) the Pick and Place robot often moves from oneposition to another. One of the parameters investigated withthe simulation model is the dependency of the size of the pcbin relation to the output of the machine. The dependency isshown in Fig. 2. This figure clearly shows the contributionof the time used for movements (maximum 500 mm in y)to the total Pick and Place cycle time of the machine.

Fig. 1. The different processes in a typical Pick and Place cycle.

Proceedings of the 2007 IEEEInternational Symposium on Assembly and ManufacturingAnn Arbor, Michigan, USA, July 22-25, 2007

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Fig. 2. Contribution of the different processes to the total Pick and Placecycle time depending on the pcb size. The graph shows the cycle time forplacement of a single component at specified distance. The contribution ofthe process steps Move are significant, especially with larger pcb distances.

B. machine output improvement

Every single process step contributes to the Pick and Placecycle and influences the output of a Pick and Place machine.There are only three solutions to increase the output of asequential machine.

• eliminate process steps• reduce time of process steps• execute processes in parallel

With these three possibilities in mind a new concept isdesigned. The first solution, to eliminate process steps, isexamined but there are no implementations found, all processsteps described are necessary.

Looking at Fig. 2, it is only logical to try to reduce thetime used for the move steps in the Pick and Place cycle.This can be realized in two ways: increasing the accelerationsand/or speeds or decreasing the distance. With help of themodel it can be calculated that an acceleration of 300 m/s2

and a maximum speed of 4.5 m/s will result in an outputof 18,000 cph. A problem with these accelerations is to holdthe components with a vacuum nozzle.

In the z direction the deceleration can go up to 500 m/s2

without losing the component. But the accelerations in xand y direction are limited to 50 m/s2 to avoid relativedisplacement of the component on the vacuum nozzle.

The other solution is to reduce the distance covered in thePick and Place move process step. Instead of picking thecomponents at the beginning of the Pick and Place machine,the components are brought to the Pick and Place head.Using the maximum acceleration of 50 m/s2 for x and yas mentioned above and a distance of 0 mm and 70 mmbetween the pick and place location, theoretically an outputof 13,500 cph per Pick and Place robot can be realized.

By performing different process steps in parallel and byincreasing the acceleration and speed in z it is possible torealize an output of 18,000 cph. The challenge is to designa device that can present components close to the Pick andPlace head.

Fig. 3. Schematic overview of old and new concept. In the new concepttwo shuttles are added to reduce traveling distances. The shuttles are placedbetween the Pick and Place robot and the pcb. Reduction of the travelingdistances results in a higher output.

II. SHUTTLE CONCEPT

Different concepts delivering the components close to thePick and Place head have been investigated. Existing Pickand Place machines reduce the distance by delivering thecomponents at close proximity to the PCB e.g. feeders onboth sides of the machine or tray feeders moving along sidethe PCB. But non of the systems deliver the componentsabove the working area directly at the place position.

One of the promising solutions capable of doing this isa concept where the tape feeder is taken into the workingarea, feeding the Pick and Place robot above the PCB.Keeping the working area clean (peeling off the top layerof the tape produces paper dust) and the disposal of theempty tape are challenging in this concept. The industrialcommittee overruled this concept, not being applicable indifferent assembly machines.

Another promising solution applicable in different assem-bly machines is a device called shuttle. The shuttle is placedbetween the pcb and the Pick and Place robot adding somedistance in the z-direction (Fig. 3). In this concept there isneed for an extra robot to load the shuttle. Designing thesystem in such a way that inaccurate loading of the shuttle(accuracy equivalent to the tape feeder) is possible and byusing gang Pick and Place for the filling robot (longer cycletime possible), costs for the extra robot is kept within limits.

The simulation model is extended with a shuttle. With thesimulation model the influence of several shuttle parameterson the Pick and Place cycle can be tested.

1) height of shuttle: The height of the shuttle will in-fluence the move step. In the first simulation model themovements in z takes partially place while moving in x andor y and partially in the pick or place step. The time of theplace step will not be influenced by adding a shuttle. Lateron in this paper it will be shown that the design of the shuttlehelps to reduce the pick time.

Because the shuttle will be placed between the pcb andthe Pick and Place robot, the height of the shuttle will add

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distance in the z direction. As shown in a previous paper [2]the height of the mirrors to measure components and boardis specified as 2x7=14 mm. The component height is 4 mm.The overall height of the shuttle must be equal or less then10 mm.

Fig. 4. Number of components: The output versus number of componentson shuttle for 10 different pcb-layouts is shown in the graph. For shuttleswith less than 5 components the output highly depends on the positions ofthe components on the pcb.

2) number of components: An investigation to differentPick and Place robot layouts has shown that a cartesianrobot is preferred. In this case the shuttle will have to carrythe components next to each other in a (x,y) grid. To bedetermined is an optimal number of components to be carriedby the shuttle. In Fig. 4 the output versus the number ofcomponents carried by the shuttle is depicted. The output iscalculated for 10 different pcb layouts. For shuttles with amaximum of 5 components the output of the Pick and Placerobot depends on the positions of the components on thepcb. One can conclude from this graph that the curve getsflat around 30 components. So the shuttle should carry atleast 30 components to have maximum advantage of usinga shuttle.

3) accelerations and speeds: The shuttle must be ableto follow the Pick and Place head. This means that in 200ms a distance of 70 mm must be covered. A minimumacceleration of 7 m/s2 is necessary. For the design of theshuttle an acceleration of 10 m/s2 is used.

4) number of shuttles: The shuttle stalks the Pick andPlace robot. To insure continuity of the Pick and Placeprocess not one but at least two shuttles are used. Whilethe shuttle is emptied by the Pick and Place robot the othershuttle is loaded by the filling robot. Exchange of shuttles isdone at the beginning of the pcb.

The next part of this paper will discuss the design consid-erations of the shuttle and the functional model build.

III. DESIGN OF A SHUTTLEFixation of the components is done with vacuum. Vac-

uum is a proven and accepted technology in this field. In

comparison to other fixation methods:• there is no damage to the components

(unlike mechanical, electrostatic and magnetic methods)• it leaves no additives on the components

(unlike adhesives like glue and gel pads)• and has short switching times

(unlike freezing).Disadvantages of vacuum are:• limited force/ air flow due to available area and vacuum

pump• difficult to keep orifices clean• power consumption vacuum/ pressure pumpTo keep the shuttle low cost the design is based on a

passive switching nozzle (Fig. 5). Switching is done bytranslation of the nozzle to the top or bottom position usingexisting pick translations. Furthermore pick from the shuttlemust be reliable and not exceed the collision force of 3 N .

Commonly used strategies to control the collision force aresoft landing (approaching the component with low speed)and ’aerial-pick’. With an aerial-pick the Pick and Placerobot hovers over the component while the component issucked onto the nozzle. The component is airborne. Thesestrategies are time consuming and an aerial-pick can lead toshift of the component. A different approach is to use lowmoving mass(es) and/or low stiffness e.q by decoupling ofmasses by springs. This method is used for designing theshuttle.

A. Shuttle requirementsThe shuttle must be able to:• fixate all existing components in the specified range of

6x6x4 mm• buffer 36 components in total• fit in an envelope of 50x50x10 mm (lxwxh)• follow the Pick and Place robotFurthermore the Pick and Place robot must pick reliable

from the shuttle not exceeding the collision force of 3 N .For a reliable pick the pick repeatability must be:

• rotation < 5 degree• x and y translation < 50 µm

B. Nozzle design shuttleAs mentioned earlier, the design is based on a passive

switching nozzle and switching is done by translation of thenozzle (Fig. 5). In our case switching is done at the loadstation (top position) and by the z translation of the Pickand Place robot (pick; bottom position). This results in anexact and short switch time.

Because the nozzle is low weight (< 1 gram) translatesfreely over 2 mm and the velocity on impact is only 0.25m/s2, the collision force is well below the specification of 3N (friction taken into account) [3]. Due to this low collisionforce it is not necessary to slow down (soft landing) or to useaerial-pick. This means a shorter pick time can be realized.

The shuttle is low cost because of the absence of valvesfor switching each nozzle separately. Furthermore the designis compact and fits in the desired envelope.

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Fig. 5. The nozzle is a dowel pin with a blind cylindrical hole and ahole in the circumference. In the top position the hole is within the vacuumchamber and in the bottom position in contact with the surrounding air.

Advantages:• low collision force• exact and short switch time• low cost due to absence of valves (passive switch)• shorter Pick and Place time (no need for soft landing

or stand still for ’aerial-pick’)• compact (minimum distance added)Disadvantage:• extra distance in height (though small)• vacuum leakage due to tolerancesProblems (to be) solved for the nozzle are:1) fixation of all exiting electronic components (universal

nozzle)2) fixation of the nozzle in top and bottom position3) leakage between nozzle and hole1) Universal nozzle design: A universal nozzle must be

able to fixate all types and sizes of components withinthe specified range of 6x6x4 mm (lxwxh). A simple holeis therefore insufficient. The smallest component (0.5x0.25mm lxw) limits the hole size, the biggest component (6x6x4mm) prescribes the maximum holding force and thus incombination with vacuum the area. Components e.g. withleads can only be fixated with sufficient flow. So the trick isto find a combination of holes, where conflicting parameters,diameter, flow and pressure difference, do not compromisethe overall function.

The solution used in the prototype is given by the knowl-edge that all components are place relatively in the middleof the nozzle. Making use of this, the biggest hole (� 0.3mm) of the array is placed in the middle and thus always’restricted’. The further the holes from the middle the smallerthey get to restrict the flow (loss of pressure; Fig. 6).

The normal force created by vacuum necessary to fixatethe largest component on the nozzle during movement,depends on the acceleration of the shuttle to follow the

Fig. 6. Prototype of shuttle. 6 nozzles are tested. The hole in thecircumference is visible in the nozzle on top of the shuttle. Insert: universalnozzle (top view, total diameter 4 mm). The array of holes depicted isused in the prototype. The biggest hole in the middle is usually covered bya component. The holes further from the center are only covered by ’larger’components. To restrict flow when these holes are not covered the holes getsmaller as they are further from the center.

Pick and Place robot and the mass of the components. Theacceleration of the shuttle was already specified at 10 m/s2.The masses of the components used don’t exceed the 0.5 g.The acceleration force acting on the component and takenin to account the friction coefficient (0.2), the normal forcecreated by vacuum must be at least 25 mN . A realisticpressure difference of 0.4 bar results in a total area Anozzle

of 0.63 mm2.1

2) 3) Top and bottom position nozzle: The dimensionsof the nozzle (dowel pin) and hole are tolerated such thatthe nozzle can translate in the hole. This tolerance leadsto leakage between the nozzle and hole (air gap/smoothtranslation) and loss of the top position (when accelerated).

By designing the nozzle with flanges both problems,leakage and dropping of the nozzle, are solved (see Fig. 5).The flange seals of the air gap (one of them anyway) andthe force on the flange makes sure that the nozzle is fixedin the top position.

IV. EXPERIMENTS

The shuttle is designed to fixate components and switchvacuum when a pick is performed. Reliability of these pro-cesses is essential. Therefore the functions switch off, fixateand pick and place are tested. Prior tests with functionalmodels of the nozzle already showed switching of vacuumworked properly. In this paragraph the focus will be onfixation of the component and reliable pick from the shuttle.

A. Universal nozzle: Suction pressure, flow and leakage

The universal nozzle works with a combination of suctionpressure and flow to create a holding force. The actualsuction pressure and flow created by the nozzle highlydepends on the component type on top of the nozzle. Large

1The prototype has a total area of 0.4 mm2. Making all hole diameters0.2 mm would be adequate.

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components seal off the nozzle completely. Smaller compo-nents only seal off part of the hole array and componentswith leads only restrict flow somewhat but do not seal offany holes. These three possible states make it difficult to giveprocess values for suction pressure and flow. Therefore onlythe maximum/minimum values are investigated.

The measurements are done with 6 nozzles in the shuttle(Fig. 6). Vacuum is generated by a venturi pump (PIAB2010) with a feed pressure of 2.2 bar. The maximum suctionpressure of 0.5 bar is measured when all nozzles are sealed(equivalent with the bottom position). At this state the flowis minimal and equals 0.023 Nl/s. The minimum suctionpressure of 0.16 bar is measured when all nozzles are open(equivalent with the top position). At this state the flowis maximal and equals 0.13 Nl/s. The ratio vacuum flowgenerated through the nozzle and leakage between dowelpin and hole is approximately 10 %. The nozzles in theseexperiments do not have flanges. With flanges the leakageis expected to be half of the measured value and thusperformance will be better.

B. Universal nozzle: Fixation

Fixation of the components on the universal nozzle isnecessary to make sure the components do not shift whenaccelerated. The acceleration of the shuttle is 10 m/s2

(design specification). To test the holding force, the shuttle isfixed onto a robot arm and repeatedly rotated over an angle.During rotation the acceleration is measured and the positionof the components on the universal nozzles are filmed witha high speed camera.

Measurements are done for the 3 different states withthe same venturi pump and feed pressure mentioned earlier.There is no shift detected even at accelerations over 25 m/s2.This result is sufficient to meet the required specification of10 m/s2 .

C. Shuttle: Pick and place reliability

Pick and place reliability is tested using the functionalmodel of the shuttle concept. The test cycle consists of:

• pick from the shuttle• move to component measurement system• measure component• move to previous pick position• reset nozzle• place component (back) on nozzle• repeat 30 timesDue to circumstances it was not possible to measure the

position of the component on top of the universal nozzlebefore pick. Distinguishing the contribution between pick orplace is therefore not possible.

The test cycle is also done without a component and isused as a reference measurement (the nozzle of the Pick andPlace robot measured is stationary). The measured valuesare the repeatability of the component measurement system(vision) and the repeatability of the Pick and Place robot. InFig. 7 the measurements can be seen.

Fig. 7. Pick and place reliability: In the left column the referencemeasurement is shown (y and x translation and rotation of the Pick and Placenozzle). The measured values are the repeatability of the Pick and Placerobot and the component measurement system (vision). In the right columnthe results of the Pick and Place process is depicted (y and x translationand rotation of the component fixed on the nozzle). The difference betweenthese two measurements is the repeatability of the Pick and Place process.Rotational error is within specification. Translations on the other hand areto large.

The Pick and Place was 100 % (no fault pick or place)and the deviations in y (30 µm) and φ (5 degrees) are withinspecification. The deviation in x (70 µm) on the otherhanddoes not satisfy the specification. This is unexpected becausede deviations in x and y are almost the same in the referencemeasurement. There must be external factors that disturb thePick and Place process.

To analyse the pick and place process a high speed camera(1 ms frames) is used. The phenomena depicted in Fig. 8explains the higher deviation. The component is droppedonto the nozzle (see A-F) instead of placed, because contactwith the nozzle is lost during the place action. At the righthand side 4 sequential component measurements after pickare depicted. The variation in the x (horizontal) is greaterthan in y (vertical) explaining the higher variation in y. Thecause is yet unknown.

Better control and understanding of the Pick and Placeprocess is necessary to solve this problem. First test with aleaf spring below the nozzle during the place process givesencouraging results.

V. CONCLUSION AND FUTURE WORK

The Pick and Place concept is build and tests are runningto verify functionality, output and accuracy. The focus inthis paper is on the functionality and accuracy of the deviceshuttle. In the next paragraphs the possibilities, consequencesand future work will be discussed.

A. Conclusion

Analysis of the Pick and Place cycle of Pick and Placemachines show that in general 5 different processes are

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Fig. 8. Place on universal nozzle: The place process is filmed with ahigh speed camera. In the frames A-F the place process is shown and itis clearly to see that the component is dropped instead of placed on thenozzle. At the right hand side 4 sequential component measurements afterpick are depicted. The variation horizontal (x) is greater than the vertical(y) variations explaining the higher variation in x.

present. The process Move depends on the size of the pcband contributes most to the Pick and Place cycle. To reducethe time needed for the movements in the machine a shuttleis added to the Pick and Place robot. If the shuttle moveswithin a range of maximum 70 mm of the Pick and Placehead the output will increase with a factor 1.7 (theoretically).Performing different processes in parallel and increasing theacceleration and speed in the z-direction will result in a Pickand Place robot capable of 18000 cph.

Adding a shuttle to Pick and Place machines requires anextra robot (machine) to load the shuttle. To keep the costsper component cost effective, the loading robot (machine)must be inexpensive taking into account the advantages (e.q.higher output) the shuttle creates.

Loading the shuttle means handling the component twice.This brings extra risk on damage, fault pick and loss ofaccuracy. In practice, fault pick and loss of accuracy ismostly due to peeling off the top layer of the tape and aerial-pick from the tape. In respect to this the pick from the shuttleis more reliable. An extra advantage is the absence of paperdust in the shuttle concept which has constant attention incurrent machines.

The shuttle discussed in this paper solves the problemof component damage. The nozzle’s on the shuttle are lowweight (<1 gram) and translate freely over 2 mm resulting invery low collision forces. The 2 mm translation of the nozzleis used to switch vacuum. Because the pick of the Pick andPlace robot is used for translating the nozzle, switch timesare exact.

By designing the orifices as an array of holes, it is possibleto fixate all desired components by suction pressure or flow,creating a universal nozzle. This feature (universal nozzle)and the fact that the nozzle switches passively makes the

shuttle low cost.Experiments show that switching vacuum on/off and

component fixation work according to specifications. Thecomponents are fixated on the nozzle up to 25 m/s2 withoutcomponent shifting. The specification of 10 m/s2 is easilymet.

The specification for a reliable Pick and Place from theshuttle in x (50 µm) is not yet met, but the componentrotation (< 5 degree) and variation in y (50 µm) arewithin specification. To get x within specification a betterunderstanding and control of the Pick and Place process isneeded. Although x was not within specification all picksand places from the shuttle were successful during the tests.

B. Future Works

The first tests show that the shuttle can be used to transportcomponents to the Pick and Place robot. To improve theperformance the place on the shuttle must be investigatedfurther.

The shuttle is an extra moving part in the Pick and Placemachine. The shuttle moves relatively slow and thus can beused for additional features close to the Pick and Place robote.g. nozzle changing (mass is not a big issue). Because theshuttle moves freely in respect to the Pick and Place headcollision avoidance is necessary. This can limit the outputsomewhat. This problem must be attended in the future.

Possibilities on logistics; the shuttle can present moredifferent components to the Pick and Place head and thusmore freedom in logistics. This will lead to higher utilizationrates for Pick and Place machines. It is also possible toload the shuttle off line. This means that processes are doneparallel and there is no need to change the feeders. Thechangeover of the machine is done fully automatic (software)reducing machine changeover times.

VI. PATENTS

Shuttle concept: Patent application: WO2006011782;

REFERENCES

[1] van Gastel, J., Nikeschina, M., Petit, R., Fundamentals of SMD assem-bly, ISBN 1-902983-14-9 Southampton; RTFB Publishing Limited,2004

[2] Verstegen P.P.H., van Gastel J.M.M., Spronck J.W., Design of a novelsingle camera vision system for both component and board alignmentin pick and place machines, presented at IFAC 2006.

[3] van Vliet, W.P., Development of a fast mechanical probe for coordinatemeasuring machines, ISBN 90-386-0168-9; Technische UniversiteitEindhoven, 1996; p 18-38.

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