Abstract:
The assembly head ( 15 ) comprises a permanent retaining circuit for all pipettes ( 1 ) with a vacuum flow. In a placing or picking station the relevant pipette is additionally connected to a stationary regulator valve, the working pressure of which may be superimposed on the permanent vacuum to regulate between over- and under-pressure. The process reliability of the assembly head may thus be significantly improved.

Description:
[0001]    This application is the national phase under 35 U.S.C. § 371 of PCT International Application No. PCT/DE02/01920 which has an International filing date of May 24, 2002, which designated the United States of America and which claims priority on German Patent Application number DE 101 27 735.0 filed Jun. 7, 2001, the entire contents of which are hereby incorporated herein by reference. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The invention generally relates to an insertion head. Preferably, it relates to one with a stator moving in a linear guide and a stepwise rotatable rotor which has a plurality of pipettes for picking up electrical components. The pipettes may be connected to a pneumatic line, with one of the pipettes being moved to a placing or picking position and with the pipette located in this position being pressurized by a compressed air pulse via a regulator valve and connected by a circular slide to a stationary line.  
         BACKGROUND OF THE INVENTION  
         [0003]    It is known from DP 0 879 550 B1 that the regulator valve may be designed as a mechanically actuated changeover valve through which the pipette can be connected either to a vacuum or to compressed air as required. In this case it is normal to store threshold values of the vacuum for the different pipette types in order to be able to detect the presence or absence of a component. Pipettes for very small components have correspondingly small suction openings, with the pressure difference between the open and closed suction channel being very small. Even slight changes in the ambient pressure or the suction cross-section due to dirt lead to detection errors, resulting in faulty operation of the insertion device.  
         SUMMARY OF THE INVENTION  
         [0004]    An object of an embodiment of the invention may be to increase the operating reliability of the insertion device.  
           [0005]    This object is achieved by an embodiment of the invention. As a result of the overlay control it is now no longer necessary to switch off the vacuum, so that the individual wear-susceptible valves can be dispensed with. All that is needed for this is to make sure that the channels leading to the valve are sealed outside the placing position by the slide valve and are connected to the regulator valve only in the placing position. By way of the line geometry in the area of the branch and by control of the pressure pulse it can be ensured that this does not affect the pressure conditions in the other pipettes.  
           [0006]    The regulator valve isolated from the other pipettes by the slide valve can generate a vacuum of sufficient force so that maximum suction pressure is securely achieved when picking the component, regardless of whether the vacuum in the other pipettes fluctuates between a higher and lower level with full or low component loading.  
           [0007]    The selector valve may represent a simple component that can be used particularly for handling uncritical components.  
           [0008]    The regulator valve may enable the pressures in the control line to be set precisely to the most effective values in each case.  
           [0009]    By way of the regulator valve, the control circuit within the regulator valve may be formed with a suitable short control cycle. The sensor and regulator valve form an integrated unit with defined line relationships and suitable accuracy in the event of the omission of an additional sensor.  
           [0010]    The jet pump may be a simple, compact component that can be quickly and accurately regulated, with it being possible to adjust the actuating element acting as a backpressure restrictor particularly rapidly and accurately to the set control position by means of the controlled drive, e.g. with the aid of a path measuring device.  
           [0011]    By way of a further development, the vacuum permanently present at each of the pipettes may be generated easily without the vacuum being switched off and is modified or overcompensated in a very short changeover time in order to be able to generate a compressed air pulse within a very narrow time frame at the moment of placement. However, it is also possible to connect the suction lines of the individual pipettes to a powerful central vacuum line. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    The present invention will become more fully understood from the detailed description of preferred embodiments given hereinbelow and the accompanying drawings, which are given by way of illustration only and thus are not limitative of the present invention, and wherein:  
         [0013]    [0013]FIG. 1 shows a schematic of a known insertion head,  
         [0014]    [0014]FIG. 2 is a similar but enlarged view of an insertion head according to an embodiment of the invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0015]    [0015]FIG. 1 shows a revolver-type insertion head with radially projecting pipettes  1  for picking components  2 . The pipettes are mounted on a rotor  3  and each is connected to a pneumatic line  4  that terminates in a changeover valve  5 . Suction lines  6  lead from this to a rotary slide valve-type distributor  7 .  
         [0016]    The rotor  3  can rotate in steps in the direction shown by the rotation arrow such that one of the pipettes  1  in each case is brought to a placing position in which the component  2  can be mounted on a printed circuit board or removed from a component store. The distributor  7  is located at the interface between the rotor  3  and a stator  8  and is arranged such that the particular suction line  6  in the placing position is temporarily connected to a stationary control line  9 . The remaining suction lines  6  are connected to a permanent vacuum source of the stator  8 . A pressure sensor  11 , by which the pressure in the suction lines  6  can be monitored, is connected to the control line  9 .  
         [0017]    The control line  9  terminates in a selector valve  12  through which it can be switched to another vacuum source  10 . The changeover valves  5  are actuated by a stationary mechanical drive  13  and remain in the selected setting during further rotation. Before the placement of the components  2 , the changeover valves are at through flow, so that the pipettes  1  are connected to permanent vacuums. The selector valve  12  is also connected to a vacuum during the setting phase, so that the associated pipette  1  is supplied with a vacuum.  
         [0018]    The changeover valve  5  located in the placing position is also temporarily connected to the compressed air source  14 . After placing the component  2  on the printed circuit board, the mechanical drive  13  switches the changeover valve  5  to the compressed air source  14 , from which a short compressed air pulse is output that reliably separates the component  13  from the pipette tip. The changeover valve  5  thus remains in this selected position, in which the pipette vents and the vacuum is switched off.  
         [0019]    When the components  2  are picked, the drive  13  switches the changeover valve  5  to a different position, in which the pneumatic line  4  is connected with the control line  9  connected to the vacuum. This causes the component  2  to be picked. Because the changeover valve remains in this position when rotated further in the retaining circuit of the vacuum supply, the pipette also continues to remain under vacuum.  
         [0020]    After the component  2  has been picked by the pipette  1  located in the mounting position, the vacuum in the control line  9  increases beyond a preset threshold value. This process is detected by the pressure sensor  11  and interpreted as correct. If on the other hand the vacuum threshold is not exceeded, an evaluation device detects the component as not correctly picked. Because the suction openings of the pipettes  1  are matched to different size components, the result, particularly with smaller components, is slight pressure differences which can be overlaid by the effect of environmental influences, so that a reliable evaluation is not possible. If a component cannot be picked or is subsequently lost, this leak can reduce the vacuum power of the vacuum source  10 .  
         [0021]    [0021]FIG. 2 shows a modified insertion head  15  according to an embodiment of the invention that is also fitted with pipettes  1  radially projecting from a rotor  16 . The pipettes  1  are each connected to a pneumatic line  17  that branches into a suction line  18  and a control line  19 . All the suction lines  18  are each connected to a jet pump  32  secured to the rotor and rotating with it, said pump being permanently and directly connected via a connecting line to a central pressure line  20  of the rotor  16  and generating a permanent vacuum in the suction line.  
         [0022]    The control lines  19  each terminate in an opening  21  of the rotor  16  that is closed by a circular slide valve  22  of a stator  23 . At the bottom placing positing of the pipettes  1 , this has a slide valve opening  24  complementary to opening  21  that is connected by a stationary control line  25  to an internal jet pump  26  designed as a Venturi nozzle of a control valve  27  of the stator  23 . The regulator valve  27  has a sensor  28  connected to the stationary line  25  for monitoring the working pressure in the control line  25  or  19 .  
         [0023]    The outlet opening of the jet pump  26  can be changed by a mechanically driven actuating element  29  in such a way that the pressure in the stationary control line  25  can be changed in fine stages. The sensor  28  and the mechanical drive are connected by electrical lines  30  to an electronic controller  31  in which the pressure values assigned to the different pipette types and/or component types are stored.  
         [0024]    When the component  2  is placed on a circuit board, the working pressure in the control line  19  can be increased so much that it overlays the vacuum of the suction line  18  in the pneumatic line  17 , so that a compressed air pulse controlled with regard to power and duration can be output to the component in order to separate this reliably from the pipette  1  and place it on the printed circuit board. When a component  2  is picked from a feed device, the suction pressure in the pneumatic line  17  can be monitored by way of the sensor  28 .  
         [0025]    The branch geometry between the suction line  18  and the control line  19  can be designed so as to be largely neutralizing, with the result that the vacuum in the suction line  18  barely influences the conditions in the control line  19  and the short pressure pulse of the control line  19  is only slightly coupled into the suction line  18 .  
         [0026]    Exemplary embodiments being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the present invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.