Abstract:
The invention relates to a compressed-air-operated vacuum generator or vacuum gripper having at least two vacuum units, wherein each vacuum unit has a suction chamber, an intake opening which opens into the suction chamber, an outflow opening which opens out of the suction chamber, and at least one drive air opening which opens into the outflow opening between the intake opening and the outflow opening, and wherein the vacuum units operate on the basis of at least two different principles (Venturi, Bernoulli, Coanda, vortex, etc.) for generating a negative pressure.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application is the U.S. National Stage of International Application No. PCT/EP2010/067770, filed Nov. 18, 2010, which designated the U.S and has been published as International Publication No. WO 2011/064138 and which claims the priority of German Patent Application, Ser. No. 10 2009 047 083.2, filed Nov. 24, 2009, pursuant to 35 U.S.C. 119(a)-(d). 
     BACKGROUND OF THE INVENTION 
     The invention relates to a compressed-air-operated vacuum generator or vacuum gripper. 
     Multi-stage ejectors with cascaded Venturi nozzles are known, for example, from WO 99/49216 and from the companies Piab, SMC and Vtec. A feature of the multi-stage principle is that the exhaust jet of an upstream stage is the drive air jet of the downstream stage. For example, a combination of the Coanda principle with the Venturi principle may be useful for increasing the suction volume flow. General vacuum generating principles are the Venturi principle with a jet nozzle and a receiver nozzle, the Bernoulli principle, wherein “fast” air with high dynamic pressure produces of a static negative pressure, and the Coanda principle, wherein the air follows a curved surface. 
     It is an object of the invention to provide a vacuum generator or vacuum gripper capable of efficiently generating a negative pressure. 
     SUMMARY OF THE INVENTION 
     This object is attained with a vacuum generator or vacuum gripper having at least two vacuum units, wherein each vacuum unit includes a suction chamber, an intake opening which opens into the suction chamber, at least one outlet opening which exits from the suction chamber, and at least one compressed air or drive air opening which opens into the outlet opening. The at least two vacuum units operate according to at least two different principles for generating a negative pressure. 
     The multi-stage ejector according to present invention includes at least two vacuum generation stages. The exhaust jet of an upstream vacuum generating step hereby forms the drive air jet of a downstream vacuum generation stage, whereby at least two different vacuum generation principles are employed. 
     The following advantages are hereby attained. By combining a principle for high volume flow with a principle for high vacuum, the object to be sucked quickly moves against the intake device due to the high volume flow and is strongly retained due to the high negative pressure. 
     According to the invention, the vacuum unit may here be a vacuum nozzle, an ejector and/or a vacuum generating stage and may, for example, operate according to the Venturi principle, the Bernoulli principle, the Coanda principle or the vortex principle. 
     According to a further embodiment of the invention, at least one exhaust port of a vacuum unit opens into the drive air port of the other vacuum unit. The two vacuum units are connected in series. 
     Advantageously, the vacuum units are combined in parallel and/or in series. One or more vacuum units connected in parallel may here be arranged downstream of the one vacuum unit. 
     Advantageously, the vacuum units may be housed in a common housing to reduce the construction volume. 
     According to a further embodiment of the invention, at least two different suction chambers may be separated from each other or connected to one another by one or more movable flaps. With these flaps, which are preferably designed as a non-return swing valves, the volume flows and the resulting negative pressures can be specifically controlled. 
     The closing or opening of the flaps may be controllable, in particular automatically, depending on the vacuum pressure and/or the volume flow. 
     Advantageously, a blower system opening into the suction chamber may be provided so that the negative pressure can be rapidly relieved and the sucked-in workpiece can be quickly ejected. 
     Preferably, one or more sensors are provided for detecting the flow and/or pressure conditions, in particular in the suction chamber. 
     According to a further embodiment of the invention, the vacuum units operating according to at least two different principles for generating negative pressure operate simultaneously or sequentially. One vacuum unit may hereby be used for generating a high volume flow and the other vacuum unit for generating a high negative pressure. 
     Further advantages, features and details of the invention will become apparent from the description and the accompanying drawings. The features shown in the drawings and described in the description may be important for the invention individually and in any combination. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The drawings show in: 
         FIG. 1  a combination of the Venturi and the Coanda principle with separate vacuum chambers (Venturi nozzle circumferential or several individual nozzles); 
         FIG. 2  a combination of the Venturi and the Coanda principle with a single vacuum chamber, wherein the exhaust air flow of the Venturi nozzles represents the drive air flow of the Coanda nozzle (Venturi nozzle circumferential or several individual nozzles); 
         FIG. 3  a combination of the Venturi and the Bernoulli principle with separate vacuum chambers (Venturi nozzle circumferential or several individual nozzles); 
         FIG. 4  a multi-stage ejector with a combination of a Venturi nozzle with a vortex nozzle in different views. The Venturi nozzles may here also be formed as a Coanda nozzles; 
         FIG. 5  a multi-stage ejector with a combination of a Coanda nozzle with a Venturi nozzle; 
         FIG. 6  a combination of the Coanda and the Bernoulli principle with outwardly guided exhaust air flow; 
         FIG. 7  a combination of the Coanda and the Bernoulli principle with inwardly guided exhaust air flow for sucking in air and for generating a suction force, and 
         FIG. 8  a combination of the vortex and the Coanda principle. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       FIG. 1  shows a combination of two vacuum units  8 , namely a Venturi nozzle  10  and a Coanda nozzle  12  with separate vacuum chambers  14  and  16 , wherein the Venturi nozzle  10  may be formed circumferentially or as several individual nozzles. The reference numeral  18  denotes the compressed air port of the Venturi nozzle  10  and the reference numeral  20  denotes the compressed air supply of the Coanda nozzle  12 . The exhaust air port  22  of the Venturi nozzle  10  opens into the compressed air port  20  of the Coanda nozzle  12 . The reference numeral  24  denotes the compressed air and the reference numeral  26  the suction air. 
       FIG. 2  shows a vacuum gripper  6  with the combination of the Venturi nozzle  10  with the Coanda nozzle  12  according to  FIG. 1  with a single, common vacuum chamber  28 . The compressed air port  18  is here integrated in a housing  30  which also encompasses the suction chamber  28 .  FIG. 2   a ) shows the beginning of the intake process, in which a high volume flow is generated. A flap  34 , in particular a swing check valve  36 , which is moved by the suction flow  26  into the open position, is attached downstream of the intake opening  32  of the Coanda nozzle  12 . When a workpiece  38  is sucked in, the volume flow gradually decreases, closing the flap  34 , as illustrated in  FIG. 2   b ). The Coanda nozzle  12  is now switched off, so that only the Venturi nozzle  10  is operated. The volume flow decreases again as a result, thereby increasing the negative pressure in the vacuum chamber  28 . 
     According to the invention, one vacuum unit  8  is primarily used for generating a high volume flow, while the other one vacuum unit  8  is used for generating a high negative pressure. 
       FIG. 3  shows a combination of other vacuum units  8 , namely, a Venturi nozzle  10  and a Bernoulli nozzle  40  with separate vacuum chambers  14  and  42 , wherein the Venturi nozzle  10  may be formed circumferentially or from several individual nozzles. The exhaust port  22  of the Venturi nozzle  10  opens here also into the compressed air port  20  of the Bernoulli nozzle  40 . 
       FIG. 4  shows a multi-stage ejector  46  with a combination of a Venturi nozzle  10  with a vortex nozzle  48  in various views. The Venturi nozzles  10  may here also be formed as Coanda nozzles  12 . The Venturi nozzle  10  opens into a central main flow channel  50  such that the exhaust air flow  52  is inclined towards the outlet opening  54  ( FIGS. 4   c ) and  4   d )). In addition, the exhaust air flow  52  flows into the central main flow channel  50  at an angle, which lies between the radial direction and the tangential direction ( FIGS. 4   a ) and  4   b )). This produces in the central main flow channel  50  a vortex which is directed towards the outlet opening  54  causing suction air  26  to be sucked in through the lower opening of the central main flow channel  50 . The swing check valve  36  then opens at the beginning of the intake process due to a high volume flow. However, the produced negative pressure, is still low ( FIG. 4   d )). As soon as the flow rate decreases, as illustrated in  FIG. 4   e ), the swing check valve  36  closes and only suction air  26  is sucked in through the Venturi nozzles  10 . This causes an increase of the negative pressure in the vacuum chamber  28 . The reference numeral  60  denotes a sensor, in particular a vacuum sensor. The reference numeral  62  denotes a separately controllable blower system, with which the negative pressure in the vacuum chamber  28  can be rapidly relieved following the suction process. 
       FIG. 5  shows a multi-stage ejector  46  with a combination of a Coanda nozzle  12  and a Venturi nozzle  10  for operating the vacuum gripper  6 , e.g. an area suction gripper. The compressed air  24  flows radially into the Coanda nozzle  12 , and suction air  26  is sucked centrally into the housing  30 . The exhaust port  56  of the Coanda nozzle  12  serves as a compressed air port  18  for the Venturi nozzle  10 . The swing check valve  36  opens at the beginning of the intake process due to a high volume flow. The generated negative pressure is still low ( FIG. 5   a )). As soon as the volume flow decreases, as shown in  FIG. 5   b ), the swing check valve  38  closes and only suction air  26  is sucked in via the Coanda nozzle  12 . The negative pressure in the vacuum chamber  28  is thereby increased. 
       FIG. 6  shows a combination of a Coanda nozzle  12  and a Bernoulli nozzle  40 , similar to  FIG. 3  with separate vacuum chambers  16  and  42 . The exhaust port  56  of the Coanda nozzle  12  serves as a compressed air port  20  for the Bernoulli nozzle  40 . 
       FIG. 7  shows a vacuum gripper  6  with a combination of a Coanda nozzle  12  and a Bernoulli nozzle  40  with an inwardly guided air stream for drawing in suction air  26  and for generating a suction force for the workpiece  38 . Spacers  58  may be provided on the underside of the vacuum gripper  6  for maintaining a permanent flow of suction air  26  even when the workpiece  38  is drawn in. 
       FIG. 8  shows a combination of a Vortex nozzle  48  and a Coanda nozzle  12 . The inflow direction of the compressed air  24  into the Vortex nozzle  48  corresponds to the embodiment of  FIG. 4 , so that a twist which sucks in the suction air  26  is produced in the Vortex nozzle  48 . This twisting exhaust air flow flows substantially radially into the Coanda nozzle  12  and generates a central suction air flow.