Abstract:
The invention concerns a vacuum gripper for suctioning workpieces with an vacuum port, an elastic vacuum element and a vacuum element holder, wherein the vacuum element has a sealing lip on its side facing the workpiece, which delimits the vacuum chamber, and the vacuum chamber is flow-connected to the vacuum port, wherein the vacuum gripper has means that display the suction state.

Description:
[0001]     The application claims Paris Convention priority of DE 10 2006 005 872.0 filed Feb. 6, 2006 the complete disclosure of which is hereby incorporated by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     The invention concerns a vacuum gripper for suctioning workpieces, comprising a vacuum port, an elastic vacuum element and a vacuum element holder, wherein the vacuum element has a sealing lip on its side facing the workpiece, which seals a vacuum chamber, and the vacuum chamber is flow-connected to the vacuum port, wherein the vacuum gripper has means for determining or displaying the state of wear disposed on an element subject to wear during use of the vacuum gripper causing the removal of material and disposed in the region of the sealing lip.  
         [0003]     Vacuum grippers are used for suctioning objects or workpieces to thereby either fix and/or handle them. When the vacuum grippers are located on manipulators, the suctioned object can be transported. It is thereby important that the object is correctly suctioned and the underpressure in the vacuum chamber is sufficiently high to ensure that the object is reliably held. Vacuum sensors are used to determine the underpressure. They are provided in the vacuum line to the vacuum gripper and pass on the detected value to a machine control which switches off the underpressure source when the desired underpressure has been reached, or blocks off the vacuum line. When the underpressure is not obtained, the vacuum gripper may be faulty or worn, and must be replaced.  
         [0004]     DE 1 963 250 A1 discloses a vacuum suction plate for lifting and transporting objects, which seats on the object with a plurality of sealing lips. DE 42 29 208 A1 discloses a device for lifting and transporting loads, the device having a mechanism which issues an alarm when the vacuum below the vacuum plate slowly decreases due to an unacceptably high leakage rate. Further embodiments of vacuum grippers are disclosed in DE 198 17 216 C2 and DE 198 17 323 A1.  
         [0005]     It is therefore the underlying purpose of the present invention to design a vacuum gripper of the above-mentioned type which is inexpensive and clearly indicates whether or not it is still fully operative.  
       SUMMARY OF THE INVENTION  
       [0006]     This object is achieved in accordance with the invention by a vacuum gripper having the elements of the independent claim.  
         [0007]     The inventive vacuum gripper permits detection of a faulty vacuum gripper or, in particular, vacuum element, before determining that an underpressure can no longer be obtained, since e.g. the sealing lip fails to tightly seal the vacuum chamber or the suction element has become porous.  
         [0008]     The wear limit is detected at an earlier time, since the vacuum gripper has means that indicate its state of wear. For this reason, measures can be taken at an early stage before the vacuum gripper fails, to prevent any malfunction during suctioning of the workpiece, e.g. in consequence of insufficient underpressure. It is particularly advantageous to display the state of wear of the vacuum grippers that are subjected to wear, in particular, to maintain safety in production plants.  
         [0009]     The means comprise an element that is worn or abraded during use of the vacuum gripper. The state of wear can be detected or displayed on or via this element that is subjected to wear. This element that is subjected to wear is thereby e.g. subjected to abrasion, wherein the element is advantageously disposed in the area of the sealing lip, i.e. in the area that engages or abuts the workpiece to be suctioned.  
         [0010]     In an embodiment, the vacuum element has, at least in sections, an element whose color changes with time or with the number of alternating stress or through application of an underpressure. This color change displays the state, in particular, the state of wear of the vacuum gripper. It may show e.g. the age of the vacuum gripper, whether the vacuum gripper has been frequently or rarely used, or whether or not the desired underpressure is applied to the vacuum gripper to achieve the desired suctioning force.  
         [0011]     In a further embodiment, an RFID element is integrated in the vacuum gripper and, in particular, in the vacuum element, which is flow-connected to the vacuum chamber. This permits storing and/or generation of retrievable data that determines e.g. the production date of the vacuum gripper or the obtained underpressure.  
         [0012]     Further advantages, features and details of the invention can be extracted from the dependent claims and the following description which shows in detail particularly preferred embodiments with reference to the drawing. The features shown in the drawing and mentioned in the description and the claims may thereby be essential to the invention, either individually or collectively in arbitrary combination. 
     
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0013]      FIG. 1  shows a cross-section through a vacuum gripper;  
         [0014]      FIG. 2  shows a schematic representation of a vacuum gripper with an electrically conducting insert;  
         [0015]      FIG. 3  shows a schematic representation of a vacuum gripper with a colored coating;  
         [0016]      FIG. 4  shows a schematic representation of a vacuum gripper comprising a material whose color changes,  
         [0017]      FIG. 5  shows a schematic representation of a vacuum gripper with wearing elements with different heights;  
         [0018]      FIG. 6  shows a schematic representation of a vacuum gripper whose color changes at a certain underpressure;  
         [0019]      FIG. 7  shows a schematic representation of a vacuum gripper with an electrically conducting insert that fails after a certain number of load changes;  
         [0020]      FIG. 8  shows a schematic representation of a vacuum gripper with a channel and a floater disposed in the channel;  
         [0021]      FIG. 9  shows a schematic representation of a vacuum gripper with a channel and a display element disposed on the channel;  
         [0022]      FIG. 10  shows a schematic representation of a vacuum gripper with an abrasive electrically conducting elastomeric layer;  
         [0023]      FIG. 11  shows a schematic representation of a vacuum gripper with level markings on the sealing lip edge;  
         [0024]      FIG. 12  shows a schematic representation of a vacuum gripper with an integrated proximity switch or a light barrier;  
         [0025]      FIG. 13  shows a schematic representation of a vacuum gripper with an integrated RFID element; and  
         [0026]      FIG. 14  shows a schematic representation of a vacuum gripper with integrated vacuum sensor. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0027]      FIG. 1  shows a cross-section through a vacuum gripper that is designated in total with  10 . Reference number  12  designates a vacuum element holder. It has a vacuum port  14  with e.g. an inner thread  16 . The outer side of the vacuum element holder  12  has two peripheral beads  18  to which an elastic vacuum element  20  is securely fixed. This vacuum element  20  is approximately bell-shaped and has a circumferential lower edge which is formed as a sealing lip  22 . The vacuum element  20  also has a central opening  24  which communicates with the vacuum port  14 . The opening  24  terminates in a vacuum chamber  26  which is surrounded by the sealing lip  22  which is disposed onto the surface  30  of a workpiece  32 .  
         [0028]     The right-hand sides of  FIGS. 2 through 12  each show the worn state of the vacuum gripper  10 .  
         [0029]     In  FIG. 2 , wherein a conducting object  28 , e.g. a metal gauze or a metallic thread, is cast into the vacuum element  20 . This object  28  terminates in the area of the sealing lip  22  which is disposed onto the workpiece  32 . When the sealing lip  22  is worn, the free end of the object  28  is exposed and contacts the surface  30  of the workpiece  32  providing electric contact with the workpiece  32  which activates a signal generator  34 , e.g. a lamp  36 . In this fashion, the wear limit of the vacuum gripper  10  can be displayed when the free end of the object  28  defines this limit. Other displays such as e.g. loudspeakers  64  ( FIG. 12 ) are feasible.  
         [0030]     In  FIG. 3 , the suction element  20  has a colored coating  38  which is gradually worn in the area of the sealing lip  22  which is designed as a wearing element  40  and is supported on the surface  30  of the workpiece  32 . When the coating  38  has been completely removed from the supported location, the material  42  below the coating  38  is visible, which has a different color, thereby indicating the wear limit.  
         [0031]      FIG. 4  shows an embodiment, in which the vacuum element  20  is produced from a plastic material, whose color changes over time. In this fashion, the age of the vacuum gripper  10  can be displayed irrespective of its use. The vacuum gripper  10  or the vacuum element  20  can also be provided with a sticker  44  whose color changes with time. The color change may e.g. be caused by the influence of oxygen or UV light.  
         [0032]     In the embodiment of  FIG. 5 , the sealing lip  22  or the wearing element  40  is provided with a groove  46  whose depth determines the degree of wear. When the groove  46  is no longer visible, the vacuum element  20  has reached its wear limit.  
         [0033]     In  FIG. 6 , the material of the vacuum element  20  consists of a colored plastic material which changes its color at a certain underpressure. When the vacuum gripper  10  does not reach this underpressure, the color does not change which, in turn, determines that the wear limit has been reached. Reference numeral  48  designates the underpressure in the vacuum gripper  10 .  
         [0034]     In the embodiment of  FIG. 7 , an electrically conducting element, in particular, a thread is cast into the elastic vacuum element  20  which breaks after a certain number of load changes. Breaking of the thread  50  indicates that the wear limit has been reached, which may be visually displayed by the lamp  36 , whose current supply is interrupted.  
         [0035]      FIG. 8  shows an embodiment, in which the vacuum element  20  is provided with a channel which is closed on its inner side, i.e. in the direction of the vacuum chamber  26 . This channel  52  is opened towards the vacuum chamber  26  due to use of the wearing element  40  on the lower side of the vacuum element  20 , such that the underpressure that prevails in the vacuum chamber suctions a floater  54 . This is visible from the outside in that the floater  54  disappears completely or partially in the vacuum element  20 .  
         [0036]     In the embodiment of  FIG. 9 , the vacuum element  20  also has a channel  52  which is initially closed to the inside, and is opened towards the vacuum chamber  26  when the wear limit has been reached. The outer side of the channel  52  terminates in a bubble  56  to which the underpressure that prevails in the vacuum chamber  26  is applied when the wear limit has been reached, such that the bubble  56  collapses. This can also be seen from the outside.  
         [0037]     In the embodiment of  FIG. 10 , the wearing element  40  consists of an electrically conducting elastomeric layer and forms e.g. the sealing lip  22  or part thereof. Two cables  58 , to which a lamp  36  is connected, terminate in this wearing element  40 . When the wearing element  40  has been worn to such an extent that there is no longer an electric connection between the two cables  58 , the current supply to the lamp  36  is interrupted which can also be visually detected.  
         [0038]      FIG. 11  shows an embodiment, wherein the vacuum element  20  has level markings  60  on its outer side in the area of the edge of the sealing lip  22 . The level markings  60  are also worn through wear of the sealing lip  22 . The level markings  60  may thereby be divided into areas, in particular, three areas, such as full function (green), warning (yellow), exchange (red).  
         [0039]      FIG. 12  shows an embodiment, wherein a proximity switch  62  or a light barrier are vulcanized into the vacuum element  20 . The proximity switch  62  is exposed by wearing off the wearing element  40  and e.g. a warning is triggered via a loudspeaker  64 .  
         [0040]      FIG. 13  shows an embodiment, wherein an RFID element  66  is embedded in the vacuum body  20  which stores data about the state and product, such as e.g. the production date, and can be read e.g. using a reader  68 . In this fashion, the age of the vacuum gripper  10  can be determined from the outside.  
         [0041]     In the embodiment of  FIG. 14 , a vacuum sensor  70  is integrated in the suction element  20 , which is connected to the vacuum chamber  26  and connected to an evaluation unit  72 . The evaluation unit  72  detects any failure to reach the required underpressure in the vacuum chamber  26 , and defines it as the wear limit.  
         [0042]     The inventive vacuum gripper  10  determines the wear limit in a simple fashion, and the vacuum gripper  10  can be replaced before the wear limit is reached.