Patent Publication Number: US-11020862-B2

Title: Pick-and-place head and method for picking work-pieces

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 15/409,156, filed on Jan. 18, 2017, which application is a continuation of U.S. patent application Ser. No. 14/594,810, filed on Jan. 12, 2015, which application was filed under 35 U.S.C. § 111(a) and § 365(c) as a continuation of International Patent Application No. PCT/US2014/064841, filed on Nov. 10, 2014, which application claims the benefit of U.S. Provisional Patent Application No. 61/909,184, filed on Nov. 26, 2013, which applications are incorporated herein by reference in their entireties. 
    
    
     FIELD 
     The present invention relates to a pick-and-place head for picking work-pieces from one location and placing them at a different location, as well as to a corresponding method. More specifically the present invention relates to a pick-and-place head and corresponding method wherein the picking of work-pieces is by action of a vacuum. 
     BACKGROUND 
     Manufacturing of a product or assembly of some apparatus generally involves the handling of work-pieces, for example components to be assembled. In particular, these work-pieces need to be transported between different locations, like assembly stations, inspection stations, packaging stations, or transport means as they proceed through the manufacturing process. In modern automated or semi-automated manufacturing, such handling of work-pieces is usually done by robots. A large number of components may be handled in parallel. For example, electronic components are often transported in molded matrix carriers, for example JEDEC trays. The electronic components are situated in the pockets, or cells, of the trays. Placing components into the pockets or picking components from the pockets for transferring them to a different location, i.e. for inspection or assembly, is usually done by pick-and-place robots. A pick-and-place robot typically comprises one or several so-called grippers (or pickers) that can pick-up an electronic component from a pocket of a tray and also place an electronic component into a pocket of a tray. The gripper may be mechanically clamping the electronic component or, more commonly, be using vacuum nozzles. 
     In order to increase throughput, pick-and-place robots are often equipped with multiple grippers such that several components can be picked up or placed in parallel. Common configurations are pick-and-place heads that have enough grippers to pick up an entire row of components at the same time or in some cases two entire rows of components at the same time. 
     In a typical manufacturing process most pockets of a tray contain one component that can be picked up by a gripper. There are, however, usually also a few pockets per tray that are empty or pockets that contain an incorrectly placed component, e.g. tilted or rotated. From such pockets no components can be picked up and a vacuum nozzle that is placed above such a pocket will not attain vacuum. Conventional multi-nozzle/gripper pick-and-place robots using vacuum nozzles have therefore independent/individual vacuum/blow-off supply lines along with individual vacuum sensors for each nozzle such that if there is a nozzle at an empty pocket or at an incorrectly placed component, where no vacuum can be attained, other nozzles will not be affected but can pick up components by vacuum, hence, operate correctly. 
     That means that in order to increase the number of grippers or nozzles, the number of vacuum supplies and of vacuum sensors has to be increased as well. Additional hardware on the pick-and-place head increases the mass of the pick-and-place head. For high throughput, however, high accelerations are needed, hence, higher mass is undesirable, and besides also increases costs. And in particular when upgrading existing heads with additional nozzles, many parts of the head need to be modified or changed, especially so that the number of vacuum supplies and of vacuum sensors can be increased as required. 
     While the above has described a typical situation for handling electronic components using vocabulary current in that field, the problem shown in the above example is more general. Wherever large numbers of components or work-pieces, especially components of at least roughly the same geometry, need to be handled during manufacturing, robots, or more generally, pick-and-place devices, may be employed that can pick or place more than one component at once. Using vacuum applied to the work-pieces via nozzles for picking the work-pieces is a widespread concept. For placing a work-piece, or dropping a work-piece from a nozzle, the vacuum for the corresponding nozzle is cancelled, additionally a burst of gas, usually air, may be used to actively blow the work-piece from the nozzle. 
     As has already been indicated above, if a pick-and-place head is to be modified to change the number of nozzles it exhibits so that the number of work-pieces it can handle at once is changed, in typical pick-and-place heads major reconfigurations are required, as each nozzle has its separate vacuum supply, usually with corresponding vacuum sensor. Furthermore, providing separate vacuum supplies and vacuum sensors for each nozzle renders the configuration of the pick-and-place head quite complex. 
     SUMMARY 
     The present invention comprises a pick-and-place head for transporting a plurality of work-pieces from at least one first location to at least one second location, the pick-and-place head having a plurality of nozzles with each nozzle configured to engage one of the plurality of work-pieces, at least one independent vacuum supply configured to attach to one nozzle of the plurality of nozzles, and, at least one shared vacuum supply configured to attach to at least two nozzles of the plurality of nozzles not attached to the at least one independent vacuum supply. 
     The present invention also comprises a pick-and-place head for transporting a plurality of work-pieces from at least one first location to at least one second location, the pick-and-place head having a plurality of nozzles with each nozzle configured to engage one of the plurality of work-pieces, the plurality of nozzles arranged in rows with at least a first and second row, a plurality of independent vacuum supplies with each configured to attach to each nozzle of the plurality of nozzles in the first row, a shared vacuum supply configured to attach to the second row of nozzles, a plurality of vacuum sensors configured to indicate whether or not a sufficient force is being applied to the plurality of work-pieces, wherein the shared vacuum supply and each of the plurality of independent vacuum supplies have one vacuum sensor. 
     The present invention also comprises a pick-and-place device having a pick-and-place head moveable by operation of the pick-and-place device, the pick-and-place head having a plurality of nozzles with each nozzle configured to engage one of a plurality of work-pieces by action of a vacuum, wherein at least one nozzle of the plurality of nozzles has an individual vacuum supply and at least two further nozzles of the plurality of nozzles have a shared vacuum supply. 
     The present invention also comprises a method for picking a plurality of work-pieces with a plurality of nozzles by action of a vacuum, for placing the work-pieces at a different location, the method including the steps of approaching at least one of the plurality of work-pieces with a respective nozzle, and generating a vacuum at each respective nozzle, wherein the generating step is achieved in at least one of the plurality of nozzles by an individual vacuum supply of the at least one of the plurality of nozzles and in at least two further nozzles of the plurality of nozzles by a shared vacuum supply of the at least two further nozzles. 
     The present invention also comprises a method for picking a plurality of work-pieces with a plurality of nozzles by action of a vacuum, for placing the work-pieces at a different location, wherein the plurality of work-pieces and the plurality of nozzles are arranged in respective rows, the nozzles of one first row of nozzles each having an individual vacuum supply, the nozzles of the remaining at least one second row of nozzles having a shared vacuum supply, the method including the steps of: a) positioning, by relative movement between the nozzles and the work-pieces, each row of nozzles above a row of work-pieces; b) attempting to pick up a respective work-piece with each nozzle; c) placing the picked-up work-pieces at a different location; d) verifying if work-pieces failed to be picked up in step b); e1) positioning the first row of nozzles over a verified work-piece that has been verified by step d) as being failed to be picked up; f1) picking up the verified work-piece with a nozzle of the first row of nozzles and placing the verified work-piece at the different location intended for it in step c); g1) repeating steps e1) and f1) until no verified work-pieces which failed to be picked up in step b) remain; e2) testing, if step d) does not indicate work-pieces that failed to be picked up, if at least as many rows of work-pieces remain to be picked up as there are rows of nozzles, and if so, repeat from step a), else consider any remaining rows of work-pieces as if they had failed to be picked up in step b) and proceed from step e1), picking up all the work-pieces in such a row with the nozzles in the first row of nozzles. 
     A general object of the present invention is to provide a pick-and-place head of simpler configuration, which can easily be reconfigured in order to change the number of work-pieces that can be handled at once, and which nonetheless provides for efficient and reliable handling of all the work-pieces to be processed. 
     Another object of the present invention is to provide a method for handling plural work-pieces at once in an efficient and reliable manner. 
     The object with regard to the pick-and-place head is achieved by a pick-and-place head for picking a plurality of work-pieces from at least one first location and for placing the plurality of work-pieces in at least one second location, the pick-and-place head exhibiting a plurality of nozzles, each nozzle of the plurality of nozzles configured to engage one of the plurality of work-pieces by action of a vacuum, wherein at least one nozzle of the plurality of nozzles has an individual vacuum supply and at least two further nozzles of the plurality of nozzles have a shared vacuum supply. 
     The object with regard to the method is achieved by a method for picking a plurality of work-pieces with a plurality of nozzles by action of a vacuum, for placing the work-pieces at a different location, the method including the steps of approaching at least one of the plurality of work-pieces with a respective nozzle and then starting generation of a vacuum at each respective nozzle, wherein generation of a vacuum in at least one of the plurality of nozzles is achieved by an individual vacuum supply of the at least one of the plurality of nozzles and generation of a vacuum in at least two further nozzles of the plurality of nozzles is achieved by a shared vacuum supply of the at least two further nozzles. 
     A pick-and-place head according to the invention exhibits a plurality of nozzles, each of which is configured to engage one of the plurality of work-pieces by action of a vacuum. According to the invention at least one nozzle of the plurality of nozzles has an individual vacuum supply and at least two further nozzles of the plurality of nozzles have a shared vacuum supply. An individual vacuum supply for a nozzle means that the vacuum supply for the nozzle is independent of the vacuum supply for different nozzles, and in particular implies that if a failure to achieve a sufficient degree of vacuum occurs at one or plural other nozzles of the pick-and-place head, this failure does not affect the nozzle with the individual vacuum supply. As at least two further nozzles have a shared vacuum supply, there is, obviously, no need for providing individual vacuum supplies for each of these further nozzles, thus leading to a simpler configuration of the pick-and-place head. A shared vacuum supply by itself, however, has one significant disadvantage. If a sufficient degree of vacuum is not achieved at one of the nozzles sharing a vacuum supply, this will also affect the vacuum at the other nozzles connected to the shared vacuum supply, usually leading to a breakdown of vacuum or failure to achieve a sufficient vacuum at these other nozzles. A failure to achieve vacuum at a single nozzle, affecting then all other nozzles connected to the common vacuum supply, for example occurs if a nozzle is to pick up a work-piece from a position where it is supposed to be, for example a specific pocket of a tray, but the work-piece is not there, i.e. not in the pocket, or is inadequately positioned relative to the nozzle so that it cannot properly seal the nozzle, preventing the build-up of a vacuum. An insufficient degree of vacuum in the shared vacuum supply will thus lead to a failure to pick up work-pieces, usually more work-pieces will not be picked up than just the absent, or inadequately positioned, one. According to the invention therefore the at least one nozzle with individual vacuum supply is provided. While this nozzle in normal operation of the pick-and-place head can be used to pick up work-pieces just as the other nozzles, if a failure of vacuum occurs in the shared vacuum supply, it can be used to pick up all those work-pieces which were not picked up as a result of the insufficient degree of vacuum in the shared vacuum supply. In this way it is ensured that all work-pieces are picked up. Reconfiguration of the pick-and-place head to change the number of nozzles is simpler than in typical heads, as instead of providing separate vacuum supplies, in the pick-and-place head according to the invention it is sufficient to connect nozzles to or disconnect nozzles from the shared vacuum supply. 
     In principle it is conceivable, and sufficient to achieve the object of the invention, that all nozzles but one are connected to a shared vacuum supply, and that only one nozzle has an individual vacuum supply. While this configuration is one configuration within the scope of the invention, many further configurations are possible within the scope of the invention. 
     In one embodiment, the nozzles are arranged in rows. Nozzles with individual vacuum supplies form a number L, where L is equal to or greater than one, of these rows. The remaining nozzles form a number S of rows, where S is equal to or greater than one. The nozzles in each of the S rows share a vacuum supply, but the vacuum supply of each such row is separate from the vacuum supply of all the other rows. 
     In a different embodiment, the nozzles also are arranged in rows. Nozzles with individual vacuum supplies form a number L, where L is equal to or greater than one, of these rows. The remaining nozzles form a number S of rows, where S is equal to or greater than one. All the nozzles in this number S of rows have a shared vacuum supply, i.e. they all are connected to a common vacuum supply. 
     In another embodiment, the nozzles are arranged in rows. At least one nozzle in each row has an individual vacuum supply, and all further nozzles of the respective row have a shared vacuum supply. Nozzles in different rows do not share a vacuum supply. In each of the preceding three embodiments, each row holds the same number of nozzles. As a variant of each of these embodiments, there are at least two rows of nozzles which differ between them as to the number of nozzles they hold. 
     In example embodiments, to each vacuum supply there corresponds a vacuum sensor. The vacuum sensor is configured to indicate whether sufficient vacuum for engaging the work-pieces has been attained or not. Sufficient vacuum has been attained, if the pressure in the interior of a nozzle is sufficiently below the environmental pressure so that the work-piece is pressed against the nozzle by the environmental pressure, countering the weight of the work-piece; otherwise the vacuum is insufficient. In this manner, in case of sufficient vacuum, a nozzle engages a work-piece. For known configuration of a nozzle and known weight and geometry of a work-piece, a threshold for a pressure difference between the pressure in the interior of the nozzle and the environmental pressure may be established. The vacuum in a vacuum supply, or corresponding nozzle, may then be deemed sufficient, if the pressure in the vacuum supply or nozzle, respectively, is further below the environmental pressure than indicated by the threshold. Otherwise the vacuum may be deemed insufficient. If the vacuum sensor indicates that sufficient vacuum has not been achieved, then appropriate measures can be taken. For example, nozzles with individual vacuum supplies can be employed to pick up work-pieces that were not picked up due to the insufficiency of vacuum in the shared vacuum supply. 
     In an example embodiment, the nozzles are located on at least one nozzle carrier mounted on the body of the pick-and-place head. The nozzle carrier is a separate element of the pick-and-place head and exhibits the nozzles of the pick-and-place head. The nozzle carrier can be connected with the rest of the pick-and-place head. In particular supply lines for the vacuum supply in the body of the pick-and-place head can be connected to corresponding lines in the nozzle carrier running to the nozzles and thus establishing lines for the vacuum supply of the nozzles. The pick-and-place head is configured such that the nozzle carrier is exchangeable for a nozzle carrier with a different number of nozzles. In particular, the supply lines for the vacuum supply within the body of the pick-and-place head are configured such that they can cooperate with nozzle carriers having different numbers of nozzles without changing the configuration in the body of the pick-and-place head. In specific embodiments the mounting of the nozzle carrier on the pick-and-place head is via an intermediate element, known as gripper body, which is connected to the pick-and-place head and contains a mount position for a nozzle carrier. Nozzle carrier and intermediate element, or gripper body, form a gripper. The gripper body may be moveable relative to the body of the pick-and-place head. 
     The pick-and-place head is moveable relative to the plurality of work-pieces. In an example embodiment of the above described type where the nozzles are arranged in rows the arrangement of the nozzles furthermore is such that as the pick-and-place head moves relative to the plurality of work-pieces the nozzles with individual vacuum supply follow the nozzles with shared vacuum supply. In this way work-pieces which failed to be picked up by nozzles with shared vacuum supply can be picked up most easily by the nozzles with individual vacuum supply without requiring additional reverse movements of the pick-and-place head. Such an arrangement of nozzles can be realized whether there is shared vacuum supply for each of a number of rows of nozzles or a vacuum supply shared by more than one row of nozzles. 
     As has already been mentioned, the invention can be advantageously employed where the work-pieces handled are electronic components. In particular the work-pieces, or electronic components, in embodiments are picked from at least one tray and placed at a processing station. The processing station may for instance perform assembly, inspection, or packaging of the work-pieces. The pick-and-place head according to the invention may also be used to pick the work-pieces at a processing station and place them into at least one tray. 
     A particular embodiment of the invention is a pick-and-place head for picking a plurality of work-pieces from at least one first location and for placing the plurality of work-pieces in at least one second location. The pick-and-place head exhibits a plurality of nozzles, each nozzle of the plurality of nozzles configured to engage one of the plurality of work-pieces by action of a vacuum. The nozzles are arranged in rows, wherein the nozzles of one first row each have an individual vacuum supply and the nozzles of at least one second row have a shared vacuum supply. A vacuum sensor corresponds to each vacuum supply, each vacuum sensor configured to indicate whether sufficient vacuum for engaging the work-pieces has been attained or not. 
     The method according to the invention, for picking a plurality of work-pieces with a plurality of nozzles by action of a vacuum, in order to place the work-pieces at a different location, includes the steps of approaching at least one of the plurality of work-pieces with a respective nozzle and starting generation of a vacuum at each respective nozzle. It should be noted that moving a pick-and-place head in order to engage a work-piece implies movement of all the nozzles of the pick-and-place head, even if in a specific situation there may be at least one nozzle which will have no work-piece to pick up. 
     According to the invention the generation of a vacuum in at least one of the plurality of nozzles is achieved by an individual vacuum supply of the at least one of the plurality of nozzles and generation of a vacuum in at least two further nozzles of the plurality of nozzles is achieved by a shared vacuum supply of the at least two further nozzles. The meanings of individual vacuum supply and shared vacuum supply have already been discussed above in the context of the pick-and-place head. 
     In an advantageous embodiment of the method, in case one or plural work-pieces fail to be picked up by nozzles with shared vacuum supply, because there is insufficient vacuum in the shared vacuum supply, such work-pieces can be picked up in a subsequent step by nozzles with an individual vacuum supply. In embodiments the generation of a vacuum in each vacuum supply, and therefore in the corresponding nozzles, is monitored by a vacuum sensor provided for each vacuum supply. Each vacuum sensor is configured to trigger an error signal, if a vacuum sufficient to engage work-pieces by the nozzles connected to its respective vacuum supply cannot be achieved. 
     In some embodiments of the method, the work-pieces are to be picked and placed with nozzles arranged in rows. Therein, in particular, each row may contain the same number of nozzles, but embodiments where there are at least two rows of nozzles which differ in the number of nozzles they contain are also considered within the scope of the invention. In either case, there is a number L, equal to or greater than one, of rows of nozzles in which each nozzle has an individual vacuum supply. The remaining nozzles, i.e. those not in the number L of rows just mentioned, are arranged in a number S, equal to or greater than one, of rows and have a shared vacuum supply. The shared vacuum supply may be common to all the nozzles in the number S of rows, or may be common only to the nozzles of each of the number S of rows, but separate from the vacuum supply of any different row. In these embodiments the method includes the steps of attempting to pick up a respective work-piece with each of the nozzles, then placing the picked up work-pieces at a different location, and picking up a work-piece which failed to be picked up by a nozzle having a shared vacuum supply with a nozzle having an individual vacuum supply. The step of attempting to pick up a work-piece with a nozzle involves moving the nozzles such that the work-piece or the work-pieces to be picked up are approached by a respective nozzle, contacting the work-piece(s) with the respective nozzle(s) and starting the generation of a vacuum in the respective nozzle(s) via the respective connected vacuum supplies. The attempt to pick up a work-piece can fail for various reasons: There may be no work-piece for at least one of the nozzles. In such case, the fact of not being able to pick up a non-existent work-piece as such does not constitute a failure, but if the respective nozzle is connected with a vacuum supply shared with other nozzles, then, as there is no work-piece to block the nozzle, there may not be sufficient vacuum generated in the shared vacuum supply for the other nozzles to pick up work-pieces. The same can occur, if there is a work-piece for each nozzle with a shared vacuum supply, but at least one of these work-pieces is misplaced so that it cannot fully block the nozzle, again leading to insufficient vacuum in the shared vacuum supply and thus also at the further nozzles connected with the shared vacuum supply. The nozzles in the rows of nozzles with individual vacuum supply, in addition to picking up work-pieces in a first step, can in a subsequent step or even plural subsequent steps pick up work-pieces that failed to be picked up by nozzles connected to a shared vacuum supply. 
     In a different embodiment, the nozzles are also arranged in rows. In each such row a number L, equal to or greater than one, of nozzles each have an individual vacuum supply and the remaining number S, equal to or greater than one, of nozzles in each row have a vacuum supply common to these S nozzles in each respective row, but separate from the vacuum supply of nozzles in any different row of nozzles. The method here includes the steps of attempting to pick up a respective work-piece with each of the nozzles, then placing the picked-up work-pieces at a different location, and picking up a work-piece which failed to be picked up by a nozzle having a shared vacuum supply, with a nozzle having an individual vacuum supply. The steps of the method correspond to the steps described for the preceding embodiments, the difference here is in the assignment of nozzles to shared vacuum supplies. 
     In a particular embodiment of the method according to the invention for picking a plurality of work-pieces with a plurality of nozzles by action of a vacuum, in order to place the work-pieces at a different location, the work-pieces and the nozzles are arranged in respective rows. The nozzles of one first row of nozzles each have an individual vacuum supply. The nozzles of the remaining at least one second row of nozzles have a shared vacuum supply. In this embodiment, the method is carried out as follows: 
     By relative movement between the nozzles and the work-pieces, each row of nozzles is positioned above a row of work-pieces. Next, an attempt is made to pick up a respective work-piece with each nozzle. The attempt can fail for reasons already discussed above. Work-pieces which have been picked up are then placed at a desired different location. The embodiment of the method also includes a step of verifying if work-pieces failed to be picked up in the attempt just mentioned. This can for example be achieved by vacuum sensors for the vacuum supplies of the nozzles. Insufficient vacuum detected in a shared vacuum supply will then trigger the steps described below with respect to the rows of work-pieces which the rows of nozzles corresponding to the shared vacuum supply with insufficient vacuum attempted to pick up. 
     In order to pick up work-pieces which failed to be picked up before, the first row of nozzles is positioned over a work-piece which failed to be picked up. The work-piece is then picked up with a nozzle of the first row of nozzles and placed at the desired different location. If more than one work-piece failed to be picked up from a specific row of work-pieces, which can easily occur if the shared vacuum supply for the row of nozzles intended to pick up the specific row of work-pieces failed to provide sufficient vacuum, then all such work-pieces can be picked up in one step by the first row of work-pieces. The first row of nozzles proceeds to pick up any work-pieces for which the attempt to pick them up failed, and to place those work-pieces at their respective desired locations. If this is completed or if there were no failed attempts to pick up work-pieces, it is tested whether at least as many rows of work-pieces remain to be picked up as there are rows of nozzles. If so, the rows of nozzles are advanced relative to the rows of work-pieces and the steps just described are repeated. In case of an insufficient number of rows of remaining work-pieces the remaining rows of work-pieces can for example be picked up with the nozzles of the first row of nozzles. 
     These and other objects, advantages and features of the present invention will be better appreciated by those having ordinary skill in the art in view of the following detailed description of the invention in view of the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The nature and mode of operation of the present invention will now be more fully described in the following detailed description of the invention taken with the accompanying drawing figures, in which: 
         FIG. 1  is a schematic representation of a pick-and-place device with a pick-and-place head; 
         FIG. 2  is a schematic representation showing a plurality of nozzles with individual and shared vacuum supplies according to an embodiment of the invention; 
         FIG. 3  is a schematic representation showing an arrangement of nozzles with shared and individual vacuum supplies according to an embodiment of the invention; 
         FIG. 4  is a schematic representation showing an arrangement of nozzles with shared and individual vacuum supplies according to a further embodiment of the invention; 
         FIG. 5  is a schematic representation showing an arrangement of nozzles with shared and individual vacuum supplies according to a further embodiment of the invention; 
         FIG. 6  is a schematic representation showing a nozzle carrier with two nozzles having an individual vacuum supply, the nozzle carrier attached to an element of a pick-and-place head; 
         FIG. 7  is a schematic representation showing a nozzle carrier with one nozzle having an individual vacuum supply and two nozzles having a shared vacuum supply, the nozzle carrier attached to an element of a pick-and-place head; 
         FIG. 8  is a flow diagram of an embodiment of the method to pick and place work-pieces; and, 
         FIG. 9  is an illustration of an embodiment of the method, showing various steps of the picking of work-pieces. 
     
    
    
     DETAILED DESCRIPTION 
     At the outset, it should be appreciated that like drawing numbers on different drawing views identify identical, or functionally similar, structural elements of the invention. While the present invention is described with respect to what is presently considered to be the preferred aspects, it is to be understood that the invention as claimed is not limited to the disclosed aspect. Also, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of the components set forth in the following description or illustrated in the drawings. The invention is applicable to other embodiments or of being practiced or carried out in various ways and is intended to include various modifications and equivalent arrangements within the spirit and scope of the appended claims. 
     Furthermore, it is understood that this invention is not limited to the particular methodology, materials and modifications described and as such may, of course, vary. It is also understood that the terminology used herein is for the purpose of describing particular aspects only, and is not intended to limit the scope of the present invention, which is limited only by the appended claims. 
     Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which this invention belongs. Although any methods, devices or materials similar or equivalent to those described herein can be used in the practice or testing of the invention, the preferred methods, devices, and materials are now described. 
     In the below description, an embodiment is an example or implementation of the invention. The various appearances of “one embodiment”, “an embodiment”, “certain embodiments” or “some embodiments” do not necessarily all refer to the same embodiments. 
       FIG. 1  shows pick-and-place device  1  having pick-and-place head  2 . Pick-and-place head  2  is moveable, as indicated by double arrow A, along rail  3 , in order to pick work-pieces  4  from tray  5  and place them at processing station  6 . Pick-and-place head  2  with picked up work-pieces  4  is shown again in dashed lines in a position over processing station  6 . Pick-and-place head  2  engages work-pieces  4  by nozzles  10 . Nozzles  10  engage work-pieces  4  by action of a vacuum. In pick-and-place head  2  the nozzles are therefore connected to corresponding vacuum supplies (not shown in  FIG. 1 ). In prior art, each nozzle has a separate vacuum supply. According to the invention, at least one nozzle  10  has a separate vacuum supply and at least two further nozzles  10  have a shared vacuum supply. In example embodiments, nozzles  10  can be moved in a direction, indicated by double arrow B, perpendicular to the direction indicated by double arrow A, in order to lift work-pieces out of the tray and also in order to place them onto processing station  6 . In different embodiments, rail  3  may be moveable in the direction indicated by double arrow B. A pick-and-place head according to the invention can also be employed in pick-and-place devices of different configuration, for example, the pick-and-place head may be mounted on a robotic arm. 
       FIG. 2  shows a plurality of nozzles  10 . Some of nozzles  10  have an individual vacuum supply  11 L, while further nozzles  10  have shared vacuum supply  11 S. In particular,  FIG. 2  shows three rows of three nozzles  10  each, wherein one nozzle  10  of each row has individual vacuum supply  11 L, and the remaining two nozzles  10  of each row have shared vacuum supply  11 S. In this embodiment there is no vacuum supply shared between rows of nozzles. 
       FIG. 3  is a schematic representation of nozzles  10 , shown as filled black circles, and the connectivity of the vacuum supplies of nozzles  10 . The vacuum supplies are shown as lines. More precisely, in  FIG. 3  four rows of nozzles  10  are shown, each row containing six nozzles  10 . The nozzles of one of the rows each have individual vacuum supply  11 L, while for the remaining three rows of nozzles  10 , each row has shared vacuum supply  11 S, common to all nozzles  10  of the respective row, but separated from the vacuum supplies of all the other rows of nozzles  10 . 
       FIG. 4  shows a different connectivity of the vacuum supply of nozzles  10 , using the same schematic representation as  FIG. 3 .  FIG. 4  shows four rows of nozzles  10 , each row containing six nozzles  10 . The nozzles of one of the rows each have individual vacuum supply  11 L, while the remaining three rows of nozzles  10  have shared vacuum supply  11 S, common to all nozzles  10  of the three rows. 
       FIG. 5  shows yet another connectivity scheme of the vacuum supply of nozzles  10 , using the same schematic representation as  FIG. 3 .  FIG. 5  shows six rows of nozzles  10 , each row containing four nozzles  10 . One nozzle  10  of each row has individual vacuum supply  11 L, while the remaining three nozzles  10  of each row have shared vacuum supply  11 S. No vacuum supplies are shared between rows. 
     For all embodiments, the vacuum supplies comprise pipes, tubes, channels ultimately connected to a known source of vacuum like one or plural pumps of known type, where the source of vacuum is configured to remove gas, in particular air, from the pipes, tubes, channels and thus also from the interior of nozzles  10  forming an end of the pipes, tubes, channels. If nozzle  10  is blocked by a work-piece, then no gas/air can enter the nozzle to replace the removed gas/air, and a vacuum is generated in the nozzle; in the context of the application generation of a vacuum means generation of a pressure of the gas/air lower than the environmental pressure. A sufficient degree of vacuum is achieved, if the pressure difference between the environmental pressure and the pressure in the nozzle is sufficient to counter the weight of a work-piece to be picked up, so that the work-piece is pressed against the nozzle. 
       FIG. 6  shows an element, often referred to as gripper  20 , which exhibits nozzles  10  and by which nozzles  10  are attached to pick-and-place head  2  as shown in  FIG. 1 . In the embodiment shown, gripper  20  comprises nozzle carrier  21 , also known as pitch adaptor, and gripper body  23 , connected to nozzle carrier  21  by connection means  22 . In pick-and-place head  2  ready for operation, gripper body  23  is mounted to the body of pick- and place head  2 , which includes connecting each of channels  11  to a separate vacuum source. In the embodiment shown, nozzle carrier  21  can be detached from gripper body  23 . When nozzle carrier  21  is attached to gripper body  23 , connecting means  22  not only mechanically secures the connection between gripper body  23  and nozzle carrier  21 , but also establishes a connection for channels  11  from gripper body  23  to nozzle carrier  21 . In the embodiment shown, each channel  11  leads to one nozzle  10 . As each channel  11  is connected to a separate vacuum source, as has been stated, each of the two nozzles  10  shown has an individual vacuum supply, which is established by one of channels  11 , respectively. In the embodiment shown, nozzle carrier  23  may be exchanged for a different one. 
       FIG. 7  also shows gripper  20 . The same gripper body  23  as shown in  FIG. 6  is used, but by connecting means  22  a different nozzle carrier  23  is attached to gripper body  23 . Nozzle carrier  21  of  FIG. 7  exhibits three nozzles  10  instead of two, but, as can be seen from  FIG. 7 , the configuration of gripper body  23  has not changed. Still each of channels  11  is connected to a separate source of vacuum. By the configuration of nozzle carrier  21 , one of channels  11  establishes an individual vacuum supply for one of nozzles  10 , while the other channel  11  establishes a shared vacuum supply for the remaining two nozzles  10 . 
     The gripper body of  FIG. 6  and  FIG. 7  may be configured such and mounted to pick-and-place head  2  in such a manner that it can be moved relative to the pick-and-place head along the direction indicated by double arrow B in  FIG. 1 . This configuration and mounting of gripper body  23  is independent of nozzle carrier  21  used, in particular of the number of nozzles  10  present on nozzle carrier  21 . For placing  FIGS. 6 and 7  into context, one nozzle  10  is shown with work-piece  4  engaged. 
       FIG. 8  is a flow chart of a specific embodiment of the method according to the invention. In this embodiment, a pick-and-place head with three rows of nozzles is used, each row of nozzles having the same number of nozzles. The nozzles of a first one of the rows of nozzles each have an individual vacuum supply, and the nozzles of the remaining two rows have a shared vacuum supply. The description of the method provided by the flow chart applies both if the shared vacuum supply is connected between the two rows and if the vacuum supply is shared between the nozzles of the respective row only. Furthermore, the work-pieces are aligned in rows as well, the distance between subsequent rows of work-pieces corresponding to the distance between the rows of nozzles on the pick-and-place head used, so that three rows of work-pieces can be picked up at once. The pick-and-place head with the nozzles is moveable relative to the work-pieces, such that the row of nozzles with individual vacuum supplies, i.e. the first row of nozzles, follows the rows of nozzles with the shared vacuum supply. 
     In step  100 , by relative movement between the pick-and-place head and the work-pieces, the three rows of nozzles are placed over three rows of work-pieces, one row of nozzles over one row of work-pieces, respectively. Usually, the nozzles are brought in contact with the work-pieces to be picked up. 
     In step  105 , it is attempted to pick up the work-pieces over which nozzles are positioned, simultaneously in a single step, by starting the generation of a vacuum in the respective vacuum supply of each nozzle. 
     In step  110 , the picked up work-pieces are placed at a desired different location, for example a processing station. 
     In step  115  it is checked whether there are any work-pieces which failed to be picked up in step  105 . This checking can be done by any suitable means, for example the rows of work-pieces could be monitored by cameras and image processing could be used. Alternatively, each vacuum supply is provided with a vacuum sensor. Such a vacuum sensor is configured to trigger an error signal if only an insufficient vacuum is attained in its corresponding vacuum supply. The meaning of insufficient vacuum has been explained above. In such a case there will be work-pieces which failed to be picked up in step  105 . If this is the case, branch ‘Y’ in  FIG. 8 , the method proceeds with step  120 . If this is not the case, i.e. if there are no work-pieces which failed to be picked up in step  105 , the method proceeds with step  135 , branch ‘N’ from step  115 . 
     In step  120 , the first row of nozzles is positioned over a work-piece which failed to be picked up, i.e. it is positioned over the location a row of work-pieces, from which at least one work-piece failed to be picked up in step  105 , occupied before step  105 . In step  125 , the at least one work-piece which failed to be picked up in step  105  is picked up with a nozzle from the first row of nozzles. If more than one work-piece from the respective row failed to be picked up in step  105 , then all these work-pieces are picked up simultaneously by the nozzles of the first row of nozzles in one step. The picked up work-pieces are then placed at their corresponding desired different location. 
     In step  130 , it is checked, whether any work-pieces which failed to be picked up in step  105  remain. This can in particular occur, if work-pieces from more than one row of work-pieces failed to be picked up in step  105 . If this is the case, branch ‘Y’ from step  130 , the method returns to step  120 . If this is not the case, branch ‘N’ from step  130 , the method proceeds with step  135 . 
     If step  135  is reached, all work-pieces that were to be picked up in step  105  have been picked up and placed at their respective desired location, either directly by steps  105  and  110 , or via additional steps  120  and  125 . The method then can proceed to pick up any potential further rows of work-pieces. 
     In step  135 , it is tested whether any rows of work-pieces remain. If no, branch ‘T’ from step  135 , the method terminates. It is also tested whether at least as many rows of work-pieces remain to be picked up as there are rows of nozzles, i.e., at least three rows of work-pieces in the specific embodiment described here, and if so, branch ‘Y’ from step  135 , the pick-and-place head is advanced by three rows of work-pieces, to repeat the steps of the method from step  100 . If fewer rows of work-pieces, i.e., fewer than three rows of work-pieces in the specific embodiment described, remain, any remaining rows of work-pieces can be picked up by the nozzles of the first row, as if they had failed to be picked up in step  105 ; therefore, in this case, the method will consider the remaining rows of work-pieces as if they had failed to be picked up and proceed with step  120 , branch ‘N’ from step  135 . 
       FIG. 9  illustrates the method by showing rows of work-pieces at various stages of the method. The stages are indicated, in the order they occur in the method, by letters a, b, c, and d. As in  FIGS. 3, 4, and 5 , filled dots indicate nozzles  10 , lines between nozzles indicate a shared vacuum supply. For ease of reference, the rows of work-pieces are named R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , and R 7 . Crossed squares indicate work-piece  4 , while empty squares indicate a position in a row which could be occupied by a work-piece, but is empty, or a position where a work-piece is misplaced. 
     At the start, stage a, rows R 1 , R 2 , and R 3  are to be picked by nozzles  10 , row R 1  is to be picked by nozzles  10  with individual vacuum supply, while rows R 2  and R 3  are picked by the nozzles with shared vacuum supply. All positions in rows R 1 , R 2 , R 3  are occupied by correctly placed work-pieces, so all work-pieces can be picked up simultaneously, and then placed at their desired location elsewhere, for instance an inspection or assembly station. The positions the work-pieces occupied in the rows here then are empty. Depending on the manufacturing process, it is possible that after a step, like inspection, for which the work-pieces were picked from the rows, they are placed back into the rows, before the next rows of work-pieces are picked. In this case, the positions in rows R 1 , R 2 , R 3  would not be empty, but occupied again. The method moves to stage b. The rows of nozzles  10  are advanced by three rows of work-pieces, so thin at stage b rows R 4 , R 5 , and R 6  are to be picked, more precisely row R 4  by the row of nozzles  10  with individual vacuum supply, rows R 5  and R 6  with the rows of nozzles  10  with shared vacuum supply. 
     All work-pieces in row R 4  can be picked by the nozzles with individual vacuum supply. In row R 5 , however, there is an empty position. In the shared vacuum supply, due to the empty position in row R 5 , no sufficient vacuum can be obtained, as the corresponding nozzle over the empty position is not sealed by a work-piece. In this example, the insufficient vacuum results in all the work-pieces of rows R 5  and R 6  not being picked. The work-pieces picked by the nozzles with individual vacuum supplies, i.e. those work-pieces picked from row R 4 , are placed at their desired location. The method then proceeds to stage c. 
     In stage c, the rows of nozzles with individual vacuum supplies are placed over row R 5 . The nozzles with individual vacuum supplies pick up the three work-pieces in row R 5 . The fact that due to the missing work-piece no sufficient vacuum can be obtained in one of the nozzles operating on row R 5  does not affect the vacuum in the other nozzles, precisely because their vacuum supplies are independent of each other. Depending on how the pick-and-place head is operated, in stage c, as rows R 6  and R 7  are complete, i.e. no work-pieces are missing, these rows could also be picked up at this step, and the work-pieces from rows R 5 , R 6 , and R 7  could be placed at their desired location. The method then would stop, as all work-pieces have been transferred to a different location. Alternatively, and corresponding to the embodiment of the method discussed in the context of  FIG. 8 , the method, at stage c, could proceed to pick up only the work-pieces from row R 5  and place them at their desired location. The method could then proceed to pick up the work-pieces in the remaining rows R 6  and R 7  by the nozzles with individual vacuum supply only. 
     In the latter alternative, the method proceeds to step d, in order to pick the work-pieces from row R 6 , which will be placed at their desired location. After the obvious and not shown operation of moving the nozzles with individual vacuum supplies to row R 7  and repeating the picking and placing with the work-pieces of row R 7 , the method has finished, all work-pieces from rows R 1  to R 7  have been transferred to the desired location. 
     The invention is not limited to those diagrams or to the corresponding descriptions. For example, flow need not move through each illustrated box or state, or in exactly the same order as illustrated and described. 
     Thus, it is seen that the objects of the present invention are efficiently obtained, although modifications and changes to the invention should be readily apparent to those having ordinary skill in the art, which modifications are intended to be within the spirit and scope of the invention as claimed. It also is understood that the foregoing description is illustrative of the present invention and should not be considered as limiting. Therefore, other embodiments of the present invention are possible without departing from the spirit and scope of the present invention as claimed.