Abstract:
The present invention pertains to a device for applying fluid material on a substrate. The device includes a valve body, a pole piece, and an electromagnetic drive unit that generates a magnetic field that moves the valve body relative to a pole piece between a closed position that interrupts the flow of material and an open position that releases the flow of material. The effect of the magnetic field provided by the drive unit is strengthened by the presence of a flux element. The flux element incorporates a portion, such as a slit, that eliminates circumferential electrical current paths, which allows the flux element to demagnetize more quickly when the drive unit is de-energized to remove the electromagnetic field. The rapid demagnetization decreases the cycle time for moving the valve body from the open position to the closed position.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application is a continuation-in-part of application Ser. No. 09/855,964, filed May 15, 2001, the disclosure of which is hereby fully incorporated by reference herein. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The present invention pertains to a device for applying fluid material on a substrate and, in particular, to an application valve for such a device.  
         BACKGROUND OF THE INVENTION  
         [0003]    In many industrial applications, fluid applying devices are used for intermittent delivery and application of liquids onto various objects (substrates), for example, in order to apply adhesives, coloring materials or the like onto automobile parts, packages, furniture or paper, on whole areas, in beads or in dots. The so-called application head with the valve assembly and nozzle assembly is part of a complex application system which includes a container for the fluid material, a transport pump, and a control unit for controlling and/or regulating the individual components. The substrate can be moved relative to the application head with the help of a transport system, or the application head may be attached to a robot arm, or the like, and can move relative to the substrate.  
           [0004]    Intermittent application means that the flow or stream of the fluid material in the supply canal, and thus the emission of the material from the outlet opening of the nozzle assembly, is alternately released or interrupted by intermittent activation of the valve assembly. In this way, an interrupted pattern of material is created on the substrate; that is, for example, dots separated by intervals or interrupted longitudinal beads, or spaced rectangular sections of material when the material is applied on areas.  
           [0005]    Particularly in applications where objects are to be moved past the application head at high speed and to have fluid material applied, intermittent interruption of the flow of material is necessary. At high relative speeds between the substrate and the application head and/or to create application patterns with small intervals between individual coated areas or short lengths B in the direction of relative motion B of coated area, the valve assembly must be activated at high switching frequency, or in other words, the valve body, which interrupts the flow of material in the supply canal, must be moved back and forth at high speed and high frequency.  
           [0006]    Conventional application heads rely on a coil spring to pre-tension the valve body in the closed position. The fluid material, for example, adhesive, is supplied in an upper area of the main body and then flows through a canal which runs essentially axially in the main body, toward the outlet opening of the outlet canal, and at the same time flowing around the coil spring which is located in the outlet canal. A disadvantage of the known apparatus is that the flow path for the material through the main body is relatively long, which leads to relatively large pressure losses.  
           [0007]    An additional known problem is that the adhesive fluid material in the portion of the flow path through and about the coil spring and armature introduces drag that increases as the pressure or viscosity of the adhesive fluid material increases. The drag dramatically slows the movement of the armature for interrupting the flow of adhesive fluid material in the supply canal. As the adhesive fluid material flows through and about the entire length of the coil spring and armature, adhesive fluid materials of relatively high viscosity, in particular, are difficult to apply in accurate amounts due to the high drag experienced by the coil spring and the armature.  
         SUMMARY OF THE INVENTION  
         [0008]    The present invention provides an apparatus in which a valve assembly can be switched rapidly and with high frequency so that the flow of material can be interrupted or released with high frequency. The apparatus promotes reliable, intermittent application of materials with high viscosities, especially liquid adhesives.  
           [0009]    According to the invention, the apparatus includes a supply canal for supplying material from a source of material, a main body with an outlet canal which communicates with the supply canal and ends in an outlet opening for delivering the material, and with a valve assembly located in the main body for optional interruption of the flow of material in the outlet canal. The valve assembly has a valve seat and a valve body which can move relative to the valve seat, as well as a tensioning device which biases or pre-tensions the valve body in either a closed or open position. A drive unit moves the valve body between a closed position which interrupts the flow of material and an open position which releases the flow of material. The supply canal is located in a lower part of the main body and is connected to the outlet canal. The tensioning device for pre-tensioning the valve body is located in the lower part of the main body.  
           [0010]    The apparatus of the invention reduces the effect of pressure variations in the fluid material, especially in the supply canal, on the application of the material and on the activation of the application valve. The total flow path, and thus the pressure loss within the applicator, is significantly smaller than in known devices. Furthermore, impairment of the tensioning device by the fluid material, especially sticking of the tensioning device, which is preferably in the form of a coil spring, can be prevented. Moreover, with the apparatus in accordance with the invention, highly viscous fluids can be applied reliably and high switching frequency of the valve assembly can be realized.  
           [0011]    In one embodiment, in which the tensioning device is a coil spring, the valve assembly includes a needle valve with an elongated, needle-like valve body and an essentially ring-shaped projection on the valve body against which the coil spring rests. In the ring-shaped projection are flow canals through which the fluid material can flow, producing a simple design with low resistance to flow.  
           [0012]    In accordance with an alternative embodiment, the outlet canal extends in the axial direction with reference to a longitudinal axis of the main body and the supply canal extends essentially in the radial direction in reference to the longitudinal axis of the main body. The supply canal intersects in the outlet canal in the area of the coil spring. This allows a compact construction to be achieved overall and allows sufficient space for connecting hoses or the like for supplying the fluid material.  
           [0013]    In an alternative embodiment of the invention the outlet canal is disposed at least partially inside of a sleeve inserted into the main body. A sleeve of this sort is easily manufactured and can be designed in such a way that its fluid mechanics are optimal. Furthermore, the main body can consist of a different material. This optimizes the apparatus and lowers the overall production costs.  
           [0014]    In another embodiment of the invention, the drive unit for moving the valve body has an electromagnetic coil arrangement configured to produce a magnetic field which operates on the valve body to move it to the closed or open position. A coil arrangement of this sort can be activated rapidly at high frequencies, so that a high switching frequency can be achieved for the valve assembly. The coil arrangement is easily controlled and eliminates the need for a source of pressurized air, such as is necessary for pneumatically operated valves. The application of force needed to move the valve body can be amplified by locating at least one magnetically active element, preferably in the form of a pole element or flux ring, adjacent to or close to the coil.  
           [0015]    According to one aspect of this embodiment, an adjusting element is movable relative to the main body and can be secured in various positions, forming a stop for the movable valve body, so that the stroke of the movable valve body is adjustable. Preferably, the adjusting element has male threading and can be screwed into the main body or into a threaded sleeve which is set into the main body.  
           [0016]    The adjusting element may be in the form of a pole piece that is permeable by the magnetic field induced by the coil assembly so that a relatively strong force is generated which acts in the axial direction on the valve body to move the valve body back and forth. In one operating state, the valve body preferably rests directly against the magnetically active adjusting element. The adjusting element may be pre-tensioned relative to the main body by a coil spring.  
           [0017]    In accordance with an additional aspect of the invention, an advantage of manufacturing technique results from having the main body made of synthetic material. The other components of the applicator can be embedded, for example, in a cast main body. If the applicator is subject to high mechanical loads, the main body can be enclosed in a housing made of a hardened material, such as a sheet metal.  
           [0018]    A separate connecting adapter, with a section of the supply canal, can be attached to the main body and receive a hose connector. This facilitates easy connections and attachments.  
           [0019]    In another embodiment of the invention, an electrically-operated dispensing module includes a main body having an outlet canal capable of receiving viscous liquid and an outlet opening for discharging the fluid material flowing through the outlet canal onto the substrate, a pole piece positioned within the main body, and a valve assembly positioned within the outlet canal. The valve assembly has a valve seat and a valve body movable relative to the valve seat between a closed position interrupting the flow of fluid material in the outlet canal by engaging the valve body with the valve seat and an open position releasing the flow of fluid material in the outlet canal to the outlet opening by disengaging the valve body from the valve seat.  
           [0020]    The dispensing module further includes an electromagnetic drive unit capable of generating a magnetic field for moving the valve body relative to the pole piece between the closed and open positions and a flux element positioned proximate to the electromagnetic drive. The flux element includes a portion capable of interrupting circumferential electrical current paths therein. As a result, any magnetic field induced by eddy currents in the flux element readily dissipates after the electromagnetic drive is denergized, which permits the dispensing module to be rapidly moved from the open position to the closed position. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0021]    Various additional features, objects and advantages will be readily recognized upon further review of the exemplary embodiments. The invention is described below on the basis of the exemplary embodiment with reference to the attached drawings:  
         [0022]    [0022]FIG. 1 is a cross-sectional view of an apparatus in accordance with the invention;  
         [0023]    [0023]FIG. 2 is a partially cut away perspective view of an apparatus in accordance with the invention;  
         [0024]    [0024]FIG. 3 shows a top view of the apparatus of FIG. 2; and  
         [0025]    [0025]FIG. 4 shows a partially exploded view of the apparatus of FIG. 1.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0026]    The device  1  illustrated on the basis of the sample implementation in accordance with FIGS.  1 - 4  is used to deliver and apply adhesive or other fluid materials on any desired substrate. The applicator head  1  is part of an application system which includes a source of material in the form of a container, a transport pump, lines or hoses through which the material can be transported to the applicator head  1 , and control devices (not shown) for controlling and regulating individual components of the application system.  
         [0027]    For purposes of this description, words of direction such as “upward,” “vertical,” “horizontal,” “right,” “left,” “upper,” “lower,” “above,” “below” “beneath” and the like are applied in conjunction with the drawings for purposes of clarity in the present description only. As is well known, liquid dispensing modules may be oriented in substantially any orientation, so these directional words should not be used to imply any particular absolute directions for an apparatus consistent with the invention.  
         [0028]    As can be seen from FIGS. 1 and 2, the applicator head  1  has a main body  2  of cast synthetic material, which can be a hardened casting material such as polyurethane. The main body  2  is surrounded by a protective housing  4 , which can be manufactured for example by injection molding and can consist of polyamide. Located in the main body  2  are a valve assembly  6 , an outlet canal  8  which ends in an outlet opening  10 , and a drive unit  12  for the valve assembly  6 . A supply canal  14 , which is connected to the source of material, communicates with the outlet canal  8 .  
         [0029]    A block-shaped connecting adapter  18  is screwed onto the side of the main body  2  by a spacer plate  16 . The adapter  18  has a drilled hole or canal  20  and a second drilled hole or canal  22  at a right angle to canal  20 . A hose connection adapter  24  is screwed into a threaded hole  26 , which communicates with the canal  20 , so that fluid material can flow through the hose, the connection adapter  24 , the threaded hole  26 , canals  20  and  22 , and the supply canal  14 , into the outlet canal  8 , when the valve assembly  6  is in its open position.  
         [0030]    The supply canal  14  is formed inside a sleeve  28  that is positioned radially relative to a longitudinal axis  29 . The sleeve  28  is inserted through a hole drilled in the spacer plate  16  and the main body  2  and is screwed by its male threads into female threads in a sleeve  50 . In the sleeve  28 , a central flow canal forms the supply canal  14 . The connection adapter  18  is attached to the main body  2  by means of threaded connections. An assembly clamp  30  is provided for attaching the applicator head  1  to a frame, robot arm or the like, and is screwed onto the connection adapter  18 .  
         [0031]    The valve assembly  6  comprises a valve seat  32  and a valve body  34  which can move relative to the valve seat  32 , and a tensioning device in the form of a coil spring  36  for pre-tensioning the valve body  34  in the closed position (as shown) or in an open position (not shown). The valve seat  32  has a contact surface  38  and is part of a nozzle assembly  40 . The nozzle assembly  40  also includes a nozzle  42  that has the outlet opening  10 , a sleeve  44  that partially limits the outlet canal  8 , and a nut  46 . The sleeve  50  has a mounting adapter  48 . The nut  46  has female threads and is screwed onto the mounting adapter  48  on the sleeve  50 . Sleeve  50  is inserted into the main body  2  and protrudes from the main body  2 . The outlet canal  8  is formed in part by the hole drilled in the sleeve  50 .  
         [0032]    The valve body  34  has the form of an elongated needle and is mounted on the main body  2 , more precisely on an upper bearing section  52  of the sleeve  50 , so that it can be moved axially back and forth translationally in the direction of the longitudinal axis  29 . The valve body  34  can be moved from an open position, in which a ball-shaped lower part  54  of the valve body  34  is out of contact with the valve seat  32 , so that a free flow section results, to a closed position in which the ball-shaped section  54  is in contact with the valve seat  32 . The coil spring  36  is positioned inside the sleeve  50  and in the outlet canal  8 . One end of the coil spring  36  is in contact with a projection formed on the sleeve  50 . The other end of coil spring  36  contacts a ring-shaped projection  56  formed on the valve body  34  and pre-tensions the valve body  34  in the direction of the closed position. The projection  56  includes flow canals (not shown) so that material can flow through in the direction of the outlet opening  10  of the outlet canal  8 .  
         [0033]    The outlet canal  8  is formed in a lower area of the main body  2  and runs essentially in the axial direction with respect to the longitudinal axis  29 . The supply canal  14  runs radially to the longitudinal axis  29 .  
         [0034]    In a lower section of the main body  2 , that is, on the side of the outlet opening  10 , the supply canal  14  is connected to the outlet canal  8 . The flow path from where the supply canal  14  joins the outlet canal  8  (see reference symbol  58  in FIG. 1) to the outlet opening  10  is relatively short, so that only small losses of pressure occur. The tensioning device in the form of the coil spring  36  is also located in a lower section of the main body  2 .  
         [0035]    The drive unit  12  for moving the valve body  34  is an electromagnetic coil arrangement with a ring-shaped coil  60 , which creates a magnetic field for exerting a force on the elongated, needle-like valve body  34  in the direction of the axis  29 . Positioned concentric to the coil  60  is a sleeve-shaped magnetizable upper flux element or ring  68 . Beneath the coil  60  is an additional adjoining magnetizable lower flux element or ring  64 .  
         [0036]    A pole piece  66  is positioned partially inside the ring-shaped coil  60  and is likewise magnetically operative. The arrangement of the pole piece  66 , the flux ring  68  and the flux ring  64  causes a strong magnetic field to be formed, so that a strong axial force can be applied to the valve body  34  in order to move the closing body intermittently at high frequency from the open to the closed position and vice versa in conjunction with the coil spring  36 .  
         [0037]    Flux ring  64  includes a longitudinal slit  80  that extends along the entire axial dimension of flux ring  64  and extends radially relative to axis  29  through the thickness of flux ring  64 . Similarly, extending along the entire axial dimension of flux ring  68  is a longitudinal slit  82 , which also extends radially through the thickness of flux ring  68 . The major dimension of each of the slits  80 ,  82  is aligned generally in the direction of the longitudinal axis  29 , although the invention is not so limited. In particular, slits  80 ,  82  merely have to be aligned axially in a manner effective for disrupting circumferential current paths in flux rings  64 ,  68 .  
         [0038]    Slits  80 ,  82  are not occupied by the electrically-conductive material forming each of the corresponding flux rings  64 ,  68 , which effectively interrupts potential closed-loop current paths in the flux rings  64 ,  68 . As a result, electrical currents cannot circulate circumferentially about the flux rings  64 ,  68 . Slits  80 ,  82  may be filled with the cast synthetic material of main body  2 , which is an electrical insulator, or may constitute air-filled gaps encased within the cast synthetic material. The slits  80 ,  82  ensure that a magnetic field which has been generated by eddy currents in the flux rings  80 ,  82  decays rapidly, so that high switching frequencies of the drive unit  12  and, thus, rapid movements of the valve body  34  at high frequency are possible. Specifically, the magnetic field in flux rings  64 ,  68  dissipates more quickly, after the coil  60  is de-energized, due to the absence of circumferentially-extending electrical currents.  
         [0039]    Inside an upper bearing section  63  of the valve body  34  is a central drilled hole  65  and a transverse hole  67  connecting to it. Fluid material can flow through at that point and possibly circulate when the valve body  34  is not in contact with the contact surface  70  of the pole piece  66 .  
         [0040]    The pole piece  66  is designed as an adjusting element which can be moved relative to the main body  2  and secured in various positions forming a stop for the movable valve body  34 , so that the stroke of the movable valve body  34  is variable. To that end, the pole piece or adjusting element  66  has male threads which engage female threads in a sleeve  68 , so that when the pole piece  66  is rotated around the longitudinal axis  28 , the pole piece  66  moves axially. This changes the position of the lower contact surface  70  of the pole piece  66  relative to the main body  2 , so that the position of the pole piece  66 , which functions as a stop for the valve body  34 , is varied.  
         [0041]    A pre-tensioning force is exerted on the pole piece  66  by means of a coil spring  72 . The coil spring  72  is in contact with an extended grip section  74  that is knurled on its circumferential surface. The pole piece  66  can easily be turned manually by the grip section  74  for adjusting the axial position of the pole piece  66 . The invention contemplates that access to the grip section  74  of pole piece  66  may be restricted after the axial position of pole piece  66  is adjusted to provide a desired stroke. The limited accessibility reduces the occurrence of inadvertent or unintentional axial movement of pole piece  66 .  
         [0042]    As can be seen from FIG. 3, markings  78  are provided on the surface of the housing  4  in the area of a projection  76 . Markings  78 , together with a marking (not shown) on the grip section  74  of the pole piece  66 , indicate the axial position of the pole piece  66  and, thus, of the contact surface  70 .  
         [0043]    While the present invention has been illustrated by a description of a preferred embodiment and while this embodiment has been described in some detail, it is not the intention of the Applicants to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. The various features of the invention may be used alone or in numerous combinations depending on the needs and preferences of the user. This has been a description of the present invention, along with the preferred methods of practicing the present invention as currently known. However, the invention itself should only be defined by the appended claims, wherein we claim: