Abstract:
In some aspects, a magnetic workpiece handling device includes a housing, a housing bottom having an end face, a magnetic piston, and a fluid connection for delivering a working fluid into the housing for moving the piston between an operating position and a rest position. The working fluid is delivered at least first and second working pressures, the first working pressure transferring the piston into the operating position near the housing bottom and the second working pressure transferring the piston into the rest position away from the housing bottom. The handling device includes a detection device to detect the presence of a workpiece and to determine a pressure of the working fluid. The piston has a vertically movable holding magnet that faces the housing bottom for holding the workpiece. The holding magnet controls a valve arrangement of the detection device.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority under 35 U.S.C. §119(a) to European Application No. 10 015 772.6, filed on Dec. 17, 2010, the entire contents of which are hereby incorporated by reference in their entirety. 
       TECHNICAL FIELD 
       [0002]    The invention relates to magnetic workpiece handling devices. 
       BACKGROUND 
       [0003]    EP 2 085 349 A1 discloses an example workpiece magnetic grab that includes a housing having a housing bottom that has an end face facing a workpiece to be grabbed. A magnetic piston that can be moved up and down is arranged in the housing. Disposed on the housing is a connection for a drive fluid for moving the magnetic piston so that the magnetic piston can be subjected to a first working pressure and transferred into an operating setting (i.e., an operating position). In the operating setting, the magnetic piston is positioned on or close to the housing bottom. Using a second working pressure, the magnetic piston can be transferred back into a rest setting (i.e., a rest position) into a movement chamber, in which the magnetic piston is positioned away from the housing bottom. 
         [0004]    It can be advantageous for such magnetic grabs to automatically detect whether or not a workpiece has been picked up and whether the workpiece has been lost (e.g., dropped) during transport. Monitoring takes place via a detection device that is inserted separately into the magnetic piston and has a controllable valve having a separate permanent magnet which is guided so that it can be moved up and down in the magnetic piston, while the holding magnet is anchored in the magnetic piston. 
       SUMMARY 
       [0005]    The combination of a holding magnet and a detection device in a magnetic piston allows for the simplification in the design and construction of a magnetic grab. Therefore, in some aspects, a magnetic workpiece handling device or magnetic grab includes a holding magnet arranged in the magnetic piston such that it can be moved up and down in the magnetic piston. The holding magnet functions as both a holding magnet and a detection magnet which opens and closes a valve arrangement in the detection device. As a result, when a workpiece is magnetized and grabbed by the magnetic grab, it is possible for the holding magnet to be in an active operating position and for a working pressure of a working fluid of the detection device to be maintained. In this operating position, the holding magnet simultaneously closes the valve arrangement of the detection device and acts as a detection magnet to control the detection device. As a result, the detection device detects whether a workpiece is present and gripped by the magnetic grab. If a workpiece is not grabbed by the magnetic grab, the holding magnet remains in an inactive operating position. As a result, the valve arrangement of the detection device remains open so that the working pressure drops and the detection device detects that there is no workpiece or a workpiece has not been gripped by the magnetic grab. 
         [0006]    The magnetic piston, which can be moved up and down in the magnetic grab, typically has a recess that is open towards the housing bottom and in which the holding magnet is guided and can move up and down. As a result, the holding magnet is guided in a secured manner in the magnetic piston and can be moved independently of the magnetic piston to control the valve arrangement of the detection device depending on whether or not a workpiece is present. 
         [0007]    Typically, the holding magnet is accommodated in a sliding guide in the magnetic piston so that the holding magnet can be transferred smoothly into at least one operating position. This sliding guide is typically configured as a cup-shaped lifting piston that is guided such that it can be moved up and down in the recess of the magnetic piston. Alternatively, a sliding guide can also be formed between the holding magnet and the recess of the magnetic piston. 
         [0008]    In certain embodiments, in order to arrange the holding magnet in an inactive operating position (i.e., a starting position) with respect to the magnetic piston, an elastically resilient element (e.g., a spring element) is arranged to retain the holding magnet inside the recess. As a result, the holding magnet rests in the inactive operating position in which the valve arrangement is slightly open without the assistance of a vacuum force or a magnetic force. 
         [0009]    In some embodiments, the magnetic grab includes a locking element to secure the elastically resilient element against the holding magnet, the sliding guide, or a contact surface of the recess. The locking element is secured to an end-side wall portion of the recess. This allows the elastically resilient element to be mounted and arranged in a simple manner. Similarly, the elastically resilient element can easily be replaced in the event of fatigue. 
         [0010]    The restoring force of the elastically resilient element is typically greater than the weight force of the holding magnet and a valve-closing member of the valve arrangement or greater than the weight force of the holding magnet in the sliding guide and the valve-closing member of the valve arrangement. The restoring force of the elastically resilient element is also typically less than a magnetic force generated by the holding magnet when a workpiece is present. As a result, the inactive operating position of the holding magnet with respect to the magnetic piston can be set easily with a transfer of the holding magnet into an operating position being ensured at the same time. The magnetic force of the holding magnet, which typically extends, in terms of area, over at least half of the diameter of the magnetic piston, is much greater than the restoring force of the at least one elastically resilient element. Spring elements (e.g., spring washers, plate springs or other pressure elements) can be used as elastically resilient elements. 
         [0011]    In some embodiments, a through-bore is provided as a valve opening in the floor of the recess of the magnetic piston. The through-bore is used for opening and closing a valve-closing member that typically acts based on the position and movement of the holding magnet. A valve seat of the valve opening is arranged in a conical manner and includes a sealing element, in which a valve-closing member having a cooperative fitting shape acts so that in the event of a lifting movement of the holding magnet from the inactive operating position into the active operating position, the valve-closing member is transferred into a closing position and the conical surfaces of the valve-closing member and the valve opening adjoin one another. As a result, the necessary closing force for controlling and sealing off the valve opening can be applied simultaneously via the holding magnet. 
         [0012]    Furthermore, in the inactive operating position of the holding magnet in the recess of the magnetic piston, the valve-closing member is disposed in an opening position. Typically, the valve-closing member is secured in place via a setting mechanism, the height of which can be changed with respect to the holding magnet. Typically, a threaded screw is used so that the closing movement of the valve-closing member can be adapted easily in a corresponding manner to the maximum lift of the holding magnet in the recess. 
         [0013]    The detection device, in some embodiments, has a passage that extends from the valve opening in the floor of the recess of the magnetic piston into at least one duct portion between the holding magnet or the sliding guide and the floor of the recess. The passage extends outward radially to a relief bore that extends through an outer wall of the recess. As a result, when a workpiece is not present, a vacuum that has built up in the magnetic grab to produce a lowering movement of the magnetic piston from the rest setting into the operating setting can be decreased. As long as the workpiece is not resting against the end face of the magnetic grab or is not in the immediate vicinity thereof, the holding magnet is typically not transferred from the rest setting into the operating setting, that is to say that the valve arrangement of the detection device is not closed. On account of this passage, which remains open when a workpiece is not present, the vacuum can be decreased via a through-bore in the magnetic grab, which is connected to the ambient air environment. A control unit of the detection device detects that a component is not present. 
         [0014]    In some embodiments, an annular duct between the at least one duct portion and the at least one relief bore is formed in the floor of the recess. Thus, a small number of duct portions are sufficient to guide the air flowing in via the valve arrangement to the relief bore or to a plurality of relief bores via the annular duct. As a result, less manufacturing processing is typically required. In addition, assembly can be simplified since a particular installation direction has to be taken into account. 
         [0015]    Furthermore, the at least one duct portion is typically formed as a trough-shaped cavity in the floor of the recess or in an outer side of the sliding guide or the holding magnet. Such a duct portion can be formed in the holding magnet when the magnetic grab does not include a sliding guide, which typically has a cup-shape and surrounds the holding magnet apart from the end side facing towards the housing bottom. 
         [0016]    In some embodiments, for the transfer of the magnetic piston into the operating setting, a negative pressure (e.g., a vacuum) is applied as the working pressure so that the detection device maintains the applied working pressure during grabbing and handling of the workpiece. As a result, the magnetic grab can detect and monitor the presence of workpieces more easily using the working pressure. Certain conventional magnetic grabs can be modified to include similar detection and monitoring systems that use the working pressure to detect and monitor workpieces. 
         [0017]    In some embodiments, for the transfer of the magnetic piston into the operating setting, a negative pressure (e.g., a vacuum) is applied as the working pressure, and the working pressure decreases while the workpiece is not present, being released, or deposited onto a working area. This is based on the fact that, on account of the resiliently elastic element, the holding magnet is returned into its inactive operating position and simultaneously the valve arrangement is opened. As a result, ambient air can flow in via a through-bore that leads into the movement chamber of the magnetic piston and can pass through the passage to the detection device. 
         [0018]    Furthermore, the detection device typically has a sensor that detects at least one working pressure for transferring the magnetic piston into the operating setting. This configuration of the sensor makes it possible, when multiple magnetic grabs are provided for handling a workpiece, for each individual magnetic grab to be monitored by a sensor assigned thereto, with the sensors being disposed in a valve bank remote from the magnetic grab. 
         [0019]    Some of the magnetic grabs described herein can be designed to have fewer components and to have a simpler construction for more efficient manufacturing and production than certain other magnetic grabs. 
         [0020]    Additionally, the magnetic grabs described herein having detection devices integrated into the magnetic piston can be manufactured to be smaller in diameter than certain conventional magnetic grabs. 
         [0021]    Aspects of the invention and also further advantageous embodiments and developments thereof are explained and described in more detail in the following text on the basis of the examples illustrated in the drawings. The features which can be gathered from the description and the drawings can be applied according to the invention individually per se or multiply in any desired combination. 
     
    
     
       DESCRIPTION OF DRAWINGS 
         [0022]      FIG. 1  is a schematic side view of a magnetic grab. 
           [0023]      FIG. 2  is a schematic cross-sectional view of the magnetic grab of  FIG. 1  along the line I-I in  FIG. 1 , with a magnetic piston in a rest setting. 
           [0024]      FIG. 3  is a schematic cross-sectional view of the magnetic grab of  FIG. 1  along the line I-I in  FIG. 1 , with a magnetic piston in an operating setting. 
           [0025]      FIG. 4   a  is an enlarged schematic view of the magnetic piston of the magnetic grab of  FIG. 3  in an inactive operating position. 
           [0026]      FIG. 4   b  is an enlarged schematic view of the magnetic piston of the magnetic grab of  FIG. 3  in an active operating position. 
           [0027]      FIG. 5  is a schematic side view of the magnetic piston of  FIG. 3 . 
           [0028]      FIG. 6  is a schematic top view of the magnetic piston of  FIG. 3 . 
       
    
    
     DETAILED DESCRIPTION 
       [0029]      FIG. 1  shows a schematic side view of a magnetic workpiece holding device or magnetic grab  11 , which has a neck  12  and, at an upper end, a fastening device  14  for fastening the magnetic grab  11 , for example, to a robot arm or to a handling device. At an opposite, lower end, a housing bottom  17  is fastened (e.g., screwed) to a cup-shaped housing  16 . The housing bottom  17  has an end face  18  that can be rested against a workpiece  19  (partially illustrated) to be grabbed or handled by the magnetic grab  11 . The workpiece  19  is typically a ferromagnetic (e.g., steel) plate. 
         [0030]      FIG. 2  is a sectional view of the magnetic grab  11  along the line I-I in  FIG. 1 . In the housing  16 , a magnetic piston  21  is guided to move up and down in a movement chamber  24 . The magnetic piston  21  in  FIG. 2  is shown in a rest setting or rest position  37 , that is to say that the magnetic piston  21  is held in an upper position. 
         [0031]    The magnetic piston  21  includes a guide ring  22  having a seal  23  that separates a movement chamber  24  above the magnetic piston  21  from a piston chamber  26  between the magnetic piston and the housing bottom  17 . The size of the two chambers  24 ,  26  is determined by the position of the magnetic piston  21  in the housing  16 . The movement chamber  24  is open to the ambient air environment via a through-bore  27 . The through-bore  27  can include a screen  28  (e.g., a filter) in order to protect the movement chamber from contamination. The piston chamber  26  is connected to a connection (e.g., a pneumatic connection)  31  to which a pressure line  32  is connected. The pressure line  32  is connected to a pneumatic valve bank having multiple control valves  30 . Via the valve bank  33 , multiple pressure lines  32  are actuated by control valves  30 , with each pressure line  32  typically being assigned one sensor  35 , which monitors the working pressure in the pressure line  32 . The signals detected by the sensor  35  are sent to a control unit (e.g., a microprocessor) for evaluation and also for controlling the magnetic grab  11 . 
         [0032]    In order to move the magnetic piston  21  from the rest setting  37  (shown in  FIG. 2 ) into an operating setting or operating position  36  (shown in  FIG. 3 ), a working pressure (e.g., a negative pressure or a vacuum) is applied to the piston chamber  26  via the connection  31 . The magnetic piston  21  is sealed from the movement chamber  24  via the seal  23  so that the piston chamber  26 , which is connected to the pressure line  32 , forms a virtually closed fluid chamber. Although the valve arrangement  59  of the detection device  41 , which is coupled to the holding magnet  34 , remains open, this opening or gap, which has a small cross section, does not significantly impair the lifting movement of the magnetic piston. 
         [0033]    On account of the applied working pressure, the magnetic piston  21  is transferred into a lower position. On account of the magnetization of the workpiece  19 , a magnetic holding force acts between the holding magnet  34  and the ferromagnetic workpiece  19 . As a result, the holding magnet  34  is transferred from an inactive working position  43  (shown in  FIG. 4   a ) into an active working position (shown in  FIG. 4   b ) that results in the valve arrangement  59  closing. The workpiece  19  is held against the housing bottom  17  only by this magnetic holding force. In the operating setting, a further working pressure (e.g., ambient pressure) is applied to the top of the magnetic piston  21  in the movement chamber. In order to deposit or otherwise release the workpiece  19 , the vacuum applied to the piston chamber  26  is decreased or pressure pulses are introduced into the piston chamber  26 . As a result, the holding magnet  34  is pushed back into the inactive operating position  43  (shown in  FIG. 4   a ) and the valve arrangement  59  is opened, and the magnetic piston  21  is pushed into a raised position with respect to the housing bottom  17  (i.e., into the rest setting  37  shown in  FIG. 2 ). The movement of the magnetic piston  21  thus takes place in the piston chamber  26 , that is to say that no large volume flows of compressed air or vacuum have to be made available. 
         [0034]    The holding magnet  34  of the magnetic piston  21  serves to actuate the detection device  41  while simultaneously holding the workpiece  19  by magnetization. The functioning and interaction of the holding magnet  34  and the detection device  41  will now be explained with reference to  FIGS. 4   a  and  4   b , in which the magnetic piston  21  is illustrated in an enlarged manner. The magnetic piston  21  includes a recess  45  that is open towards the housing bottom  17 . The holding magnet  34  is arranged in the recess  45  such that it can move up and down, that is to say that, within the recess  45 , the holding magnet  34  can move along a stroke length from the inactive operating position  43  (shown in  FIG. 4   a ) to the active position  42  (shown in  FIG. 4   b ). 
         [0035]    The holding magnet  34  is positioned in a sliding guide  47  that is formed in a cup-shaped manner and acts as a reciprocating piston. Alternatively, the holding magnet  34  can also be arranged directly in the recess  45  (e.g., without a sliding guide  47 ). This sliding guide  47  has a peripheral wall  48  that slides against an outer wall  49  of the recess  45  and is guided thereby in the axial direction. To arrange the holding magnet  34  in the inactive operating position  43 , a resiliently elastic element  51  is arranged on top of a locking element  52  attached to the outer wall  49  and provides an upward force against the sliding guide  47 , the peripheral wall  48 , or the holding magnet  34 . The locking element  52  is releaseably connected to the guide ring  22  (e.g., as an annular screw element). The resiliently elastic element  51  can include a compression spring or a plate spring. Similarly, resilient rubber elements can be used. In the recess  45 , the sliding guide  47  has a collar  54  that engages at least partially in an annular duct  56  formed in the recess  45 . The position of the holding magnet  34  in the recess  45  in the inactive operating position  43  can typically be determined by the height of the collar  54 . 
         [0036]    The detection device  41  includes the valve arrangement  59  having a valve-closing member  61 , which has a holding portion  63  that passes through a valve opening  65  to engage in a bore  67  arranged along the longitudinal central axis of the sliding guide  47  and the holding magnet  34 . Typically, the holding portion  63  is threaded, so that the valve-closing member  61  can be set at a desired distance from the holding magnet  34 . Additionally, the closing position of the valve arrangement  59  can be adapted to the maximum desired stroke length of the holding magnet  34  from the active operating position  42  to the inactive operating position  43 . The valve-closing member  61  typically has a conical top that acts on a conical valve seat. A seal  69  can also be provided in the valve seat. 
         [0037]    A passage  71  is formed between the movement chamber  24  and the piston chamber  26 , the passage  71  is open when the detection device  41  is inactive, that is to say when the holding magnet  34  is arranged in the inactive operating position and the valve-closing member  61  is lifted with respect to the valve opening  65 . This passage  71  includes the valve opening  65  and also at least one adjoining duct portion  73 , which extends radially outwards and merges into at least one relief bore  74 , which opens into an annular chamber  76  (shown in  FIGS. 2 and 3 ) that is connected to the pneumatic connection  31  and adjoins the piston chamber  26 . 
         [0038]      FIG. 5  is a schematic side view from outside of the magnetic piston  21  with its outer wall  49  having at least one relief bore  74 . 
         [0039]      FIG. 6  is a schematic top view of the magnetic piston  21 , in which, by way of example, a duct portion  73  leading to the relief bore  74  is illustrated by dashed lines. The duct portion  73  can be incorporated into the floor of the recess  45  as a groove or trough to create a fluid connection between the valve opening  65  and the relief bore  74 . The collar  54  on the sliding guide  47  is interrupted at individual points so that passages are formed to the annular duct  56 , which is in turn connected to at least one relief bore  74 . 
         [0040]    In order to arrange the holding magnet  34  in the inactive operating position  43 , a restoring force of the resiliently elastic element  51  is greater than the combined weight force of the holding magnet  34 , the sliding guide  47 , and the valve-closing member  61 . If no sliding guide  47  is provided, the restoring force of the resiliently elastic element  51  is greater than the weight force of the holding magnet  34  and the valve-closing member  61 . 
         [0041]    The detection device  41  detects and monitors a workpiece  19  held by the magnetic grab  11  in the following manner. The magnetic grab  11  is positioned with respect to the workpiece  19  to be handled. At the same time, a low pressure (e.g., a vacuum) is applied in the piston chamber  26  so that the magnetic piston  21  is transferred from the rest setting  37  (shown in  FIG. 2 ) to the operating setting  36  (shown in  FIG. 4   a ). If a workpiece  19  is present below the magnetic grab  11  for magnetization, the sliding guide  47  and holding magnet  34  are transferred within the magnetic piston  21 , on account of the acting magnet force, from the inactive operating position  43  (shown in  FIG. 4   a ) into the active operating position  42  (shown in  FIG. 4   b ). Once the sliding guide  47  and holding magnet  34  reach the active operating position  42 , the valve arrangement  59  closes so that the passage  71  for pressure equalization is closed off and the vacuum is thus maintained. As a result, the control unit determines that the workpiece  19  has been grabbed and is present. 
         [0042]    If the workpiece  19  is not grabbed, the sliding guide  47  and holding magnet  34  are not transferred from the inactive operating position  43  to the active operating position  42  and the valve arrangement  59  is not closed. In case the workpiece  19  is lost after it has been grabbed, the holding magnet  34  moves along a return stroke from the active operating position  42  to the inactive position  43  on account of the restoring force of the resiliently elastic element  51 . When the sliding guide  47  and the holding magnet  34  are in the inactive position, the passage  71  is open so that air can flow in from the movement chamber  24  and thus pressure equalization can occur. On account of the pressure difference, the control unit detects that the workpiece  19  is no longer present or has not been grabbed. 
         [0043]    On account of the lifting movement of the holding magnet  34  in the magnetic piston  21  and the resulting actuation of the valve arrangement  59  of the detection device  41 , the magnetic grab  11  can be designed more simply in order to detect and hold ferromagnetic workpieces. 
         [0044]    A number of embodiments have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. Accordingly, other embodiments are within the scope of the following claims.