SE1450359A1 - Method of gripping a top bundle of flexible substrates by means of grippers on a two-armed robot - Google Patents

Abstract

ABSTRACT The invention concerns a method of gripping a top stack (15) offlexible sub-strates (12) arranged in a substrate pile (13) by means of a pair of grippers (6,7) arranged on a two-arm robot (1). The method comprises the steps of scan-ning a topography of said substrate pile (13) by means of a sensor (16, 17)arranged on one of said grippers (6, 7) in order to gather outline data and topcontour data of said substrate pile (13); of inserting a first lower finger (10, 11)of a first gripper (6, 7) below said bottom substrate (12) at a pile location de-termined by means of said topography; of inserting a second lower finger (10,11) of a second gripper (6, 7) alongside the inserted first finger (10, 11); ofmoving at least one of the inserted lower fingers (10, 11) along said substratepile (13), on a path determined by means of said topography, to a final grip-ping position; and of eventually having both grippers (6, 7) grip the top stack(15) thus determined. Elected for publication: fig. 1

Description

AWAPATENT AB Kontor/HandläggareVäxjö/Svante Franzen/SF Yaskawa Nordic ABVår referens SE-21065956 Ansökningsnr 1 METHOD OF GRIPPING A TOP STACK OF FLEXIBLE SUBSTRATES BYMEANS OF GRIPPERS OF A TWO-ARM ROBOT Technical Field The present invention relates to a method of gripping a top stack offlexible substrates arranged in a substrate pile by means of a pair of grippers,said grippers being arranged on one arm each of a two-arm robot and eachhaving a lower finger and a corresponding upper finger, wherein said lowerfingers are arranged to be inserted into said substrate pile below a bottomsubstrate of said top stack and said corresponding upper fingers are arrangedto abut on a top substrate of said substrate pile in order for all fingers to jointlygrip said top stack. ln this context, flexible substrates is meant to comprise all sorts offlex-ible substrates which can be provided in piles, that is for instance papersheets, whether printed or not, plastic substrates, sheets of metal foil, or evensheets of pastry or pasta.

Prior ArtA method according to the preamble is known from the published doc- ument WO 2012/069056 A1. According to the known method a gripping ac-tion is performed in order to aerate a gripped stack of flexible substrates,which is an important task for instance in a printing factory, because insuffi-ciently aerated substrates tend to stick together and cause misalignment ofindividual or a plurality of substrates in a following production stage andhence lead to production disturbances.

Obiect of the invention Although a robot thanks to its endurance is very useful in this case inpoint, it has been found that a gripping action by means of grippers of a two-arm robot from time to time can cause damage to single or multiple flexiblesubstrates. Damages noticed are wrinkling or even tearing of substrates in contact with the grippers or scratches caused by the grippers on prints on thesubstrates.

Further, a stack being incorrectly gripped by said pair ofgrippers, canlead to quality problems downstream an aeration step as well, such as a cut-ting step. ln such a step the correct number or proper alignment of substratesin a stack to be cut is vital for quality, which an incorrectly assembled orgripped stack is prone to impede. ln the light of the above an object of the invention is to create a methodeliminating or at least mitigating the above quality related problems.

Brief Summary of the lnvention According to the invention in a method according to the preamble thisis achieved by means of the steps of scanning the topography of said sub-strate pile by means of a sensor arranged on one of said grippers in order togather outline data and top contour data of said substrate pile; of inserting ofa first one of said lower fingers below said bottom substrate at a pile locationdetermined by means of said topography; inserting of a second one of saidlower fingers alongside the inserted first one; of moving of at least one of theinserted lower fingers along said substrate pile, on a path determined bymeans of said topography, to a final gripping position; and of eventually hav-ing both grippers grip the top stack thus determined.

By scanning the topography according to the method of the invention,knowledge of both the outline and the top contour of a top stack to be grippedis acquired and later on used to handle the grippers of the two-arm robot in anoptimal way, wherein the coordination between the scanning action and thelater gripping action is simplified by involving one of the grippers in both.

Preferably, the method according to the invention comprises the addi-tional step of having a first sensor on a first one of said grippers scan the to-pography of a first part of said substrate pile, while a second sensor on asecond one of said grippers simultaneously is scanning the topography of asecond part of said substrate pile. By this the time for scanning can be re-duced considerably compared to scanning by means ofjust one sensor and gnppen When scanning by means of two sensors and grippers, it is preferredto let said grippers work in parallel and to have said first sensor scan the to-pography of a first half of said substrate pile and to have said second sensorscan the topography of a second half of said substrate pile. ln that way thetime for the scanning operation can be reduced to half the time compared toscanning by means ofjust one gripper and sensor. ln order to facilitate the whole process, according to an embodiment ofthe invention there is the additional step of having said pair of grippers emitpatterns of visible light in order to assist an operator to place a substrate pilecorrectly in front of said two-arm robot. By this moves of the robot can beshortened and hence time be save.

Preferably, according to a preferred embodiment of the invention saidsensors are used to emit patterns of visible light in order to assist an operatorto place a substrate pile correctly in front of said two-arm robot, which reduc-es costs and facilitates assembly. ln its simplest but still useful form, the visible light is emitted verticallydownwards, wherein each of said patterns comprises a single dot of visiblelight. To project such a simple pattern an ordinary light emitting diode doesfine.

Brief Description of the Drawinqs ln the drawings a preferred embodiment of the method according to theinvention is illustrated schematically, wherein: Fig. 1 is a perspective view showing a two-arm robot behind a first pileof flexible substrates; Fig. 2 is a perspective view showing a two-arm robot behind a secondpile of flexible substrates; Fig. 3 is a perspective view showing a two-arm robot behind a third pileof flexible substrates; and Fig. 4 is a perspective view showing the two-arm robot from behindwhen gripping a stack offlexible substrates.

Detailed Description of a Preferred Embodiment Below the method according to the preferred embodiment of the inven-tion will be described in detail with reference being had to the accompanyingdrawings. ln these similar reference numbers are used to denote correspond-ing items. ln figs. 1-4 a robot 1 is shown schematically. lt comprises a base 2,which can be mounted on a stand (not shown) and bears a top 3 in a rotata-ble way. The top 3 has two arms 4, 5 hinged thereto, said arms being multiplypivoted and holding grippers 6, 7 at their distal ends.

Each gripper 6, 7 comprises an upper finger 8, 9 and a lower finger 10,11, respectively, the upper 8, 9 and lower 10, 11 fingers being movable to-wards or away from each other in order to grip or release items.

With its pair ofgrippers 6, 7 the two-arm robot 1 is according to a me-thod of the present invention used to handle items in the form of flexible sub-strates 12, which are supplied in a pile 13 on a support 14, such as a pallet.The flexible substrates 12 can be of many different kinds, such as paper,plastic or metal sheets, and may be blank, coated or bear a print. lf a plurality offlexible substrates 12 are laid out in a pile 13, their flex-ibility can cause a top 13' of the pile 13 to deviate considerably from an all flatshape, especially if each substrate 12 bears a print not covering the entiresubstrate 12, or if the support 14 does not support the pile 13 evenly. Theresult of this is illustrated in figs. 1-3 by means of a first, a second and a thirdpile 13, respectively, all three deviating from a strictly parallelepipedic shape.Thus, for instance the first pile 13 of fig. 1 has a convex top 13', the secondpile 13 of fig. 2 a concave top 13' and the third pile 13 of fig. 3 an undulatedtop 13”.

Now, if a two-arm robot 1 is to grip just a stack 15 of flexible substrates12 from the top 13' of a pile 13, in order to size the stack 15 correctly the ro-bot 1 has to have knowledge of the exact position of its grippers 6, 7 in rela-tion to the pile 13 as such and to the top 13' of the pile 13 in particular. To thisthe lower fingers 10, 11 of the grippers 6, 7 are provided with sensors (c.f.arrows 16, 17 indicating their placement in figs. 1-3), which by emitting lightvertically downwards (c.f. light beams 18, 19 in figs. 1-3) and by measuring light reflected from a surface hit by the light can help provide the robot 1 withthe position information needed.

To this the grippers 6, 7 are while measuring moved above the pile 13in order scan a topography of the pile 13 by gathering outline data and topcontour data of the pile 13. This is done most effectively by moving the grip-pers 6, 7 in parallel and by having their sensors 16, 17 scan the topography ofa first half of the pile 13 and of a second half of the pile 13, respectively.

Once the scanning is done, the topography information is used to placethe grippers 6, 7 in front of and close to a side 13" of the pile 13. Then a firstlower finger, such as the lower finger 10 of the gripper 6, is inserted below abottom substrate 12 of a future stack 15 at a pile height determined by meansof said topography and the desired stack size or thickness, while the corres-ponding upper finger, such as the upper finger 8 of the gripper 6, is placedabove a top substrate 12 of the pile 13.

When said first lower finger 10 is inserted, the second lower finger, thatis in this case the lower finger 11 of the gripper 7, is inserted along the finger10 into a void created by that finger 10, such that said second lower finger 11is placed immediately under the same bottom substrate as said first lowerfinger 10 and the corresponding upper finger, such as the upper finger 9 ofthe gripper 7, is placed above the top substrate 12 of the pile 13.

The next step according to the method of the invention is again to usethe topography information to move at least one of the inserted lower fingers10, 11 along the side 13" of the pile 13, such that spaced apart positions ac-cording to fig. 4 are achieved for the grippers 6, 7. While moving a lower fin-ger 10, 11 the gripper 6, 7 involved does not necessarily have to follow astraight horizontal line, but can deviate upwards or downwards in correspon-dence with the pile topography. Thus, the risk of damaging the flexible sub-strates 12 during the gripper moving action, e.g. by wrinkling or even tearingthem or by scratching prints on them, can be avoided or at least mitigated.And further, the risk of incorrectly gripping or sizing a stack 15 of substrates12 is minimized too.

I one embodiment of the method according to the invention the lightemitted by the sensors of the grippers 6, 7 can be light visible by humans.

Thus, a clearly visible pattern, such as simple dots 20, 21, can be projecteddownwards in order to assist an operator to place a substrate pile 13 correctlyin front of said two-arm robot 1.

Claims (6)

1. A method of gripping a top stack (15) offlexible substrates (12) arranged ina substrate pile (13) by means of a pair ofgrippers (6, 7), said grippers (6, 7)being arranged on one arm (4, 5) each of a two-arm robot (1) and each hav-ing a lower finger (10, 11) and a corresponding upper finger (8, 9), whereinsaid lower fingers (10, 11) are arranged to be inserted into said substrate pile(13) below a bottom substrate (12) of said top stack (15) and said corres-ponding upper fingers (8, 9) are arranged to abut on a top substrate (12) ofsaid substrate pile (13) in order for all fingers (8-1 1) to jointly grip said topstack(15), characterized bythesteps of scanning the topography of said substrate pile (13) by means of a sensor(16, 17) arranged on one of said grippers (6, 7) in order to gather outline dataand top contour data of said substrate pile (13), of inserting of a first one of said lower fingers (10, 11) below said bottom sub-strate (12) at a pile location determined by means of said topography,inserting of a second one of said lower fingers (10, 11) alongside the insertedfirst one, of moving of at least one of the inserted lower fingers (10, 11) along said sub-strate pile (13), on a path determined by means of said topography, to a finalgripping position, and of eventually having both grippers (6, 7) grip the top stack (15) thus deter-mined.

2. The method according to claim 1, comprising the additional step of havinga first sensor (16) on a first one of said grippers (6) scan the topography of afirst part of said substrate pile (13), while a second sensor (17) on a secondone of said grippers (7) simultaneously is scanning the topography of asecond part of said substrate pile (13).

3. The method according to claim 2, comprising the additional steps of havingsaid grippers (6, 7) work in parallel and of having said first sensor (16) scan the topography of a first half of said substrate pile (13) and of said secondsensor (17) scan the topography of a second half of said substrate pile (13).

4. The method according to any one of claims 1-3, comprising the additionalstep of having said pair ofgrippers (6, 7) emit patterns of visible light (18, 19)in order to assist an operator to place a substrate pile (13) correctly in front ofsaid two-arm robot (1).

5. The method according to claim 2 or 3, comprising the additional step ofhaving said sensors (16, 17) emit patterns of visible light (18, 19) in order toassist an operator to place a substrate pile (13) correctly in front of said two-arm robot (1).

6. The method according to claim 4 or 5, wherein visible light (18, 19) is emit-ted vertically downwards and wherein each of said patterns comprises a sin-gle dot (20, 21) of visible light.