Patent Publication Number: US-2010128559-A1

Title: Tabletop device for mixing and discharging multi-component compounds

Description:
The invention relates to a tabletop device for the mixing and dispensing of multicomponent compounds, in particular of dental impression compounds or dental mold compounds, in accordance with the preamble of claim  1 . 
     Such a tabletop device is known from EP 492 413 A1, wherein the plungers serving for the pressing out of the containers with the individual components are movable selectively either by an electric motor or manually via a handwheel. The latter in particular serves for the positioning of the plungers into a desired location, for example after the insertion of an only partly filled container and before the actual pressing-out procedure. The advantage of the manual positioning procedure is in the time gain associated therewith in comparison with a slow plunger movement which is powered via the electric motor and which is designed for the pressing-out procedure. To change over the tabletop device from the motor-powered operating mode to the manual operating mode and vice versa, a magnetic coupling is provided which can be activated synchronously with the electric motor. The known tabletop device suffers from the disadvantage that the use of a magnetic coupling brings along a comparatively high construction effort and has relatively large room requirements in addition to the high costs associated with it. 
     A tabletop device is known from EP 1 531 001 A1 in which the electric motor acts via a lever onto a plurality of clamping elements which act on the plungers and move them via a disk cam. This construction makes high demands on precision on its manufacture, associated with high expense, due to the required interaction of a plurality of mechanical clamping elements in a very small space. 
     It is the underlying object of the invention to provide a tabletop device of the initially named kind which has a compact structure while avoiding the aforesaid disadvantages and taking account of the required dispensing accuracy as well as taking a small cost and a simple manufacturing capability into account. 
     This object is satisfied in accordance with the invention by a tabletop device defined by claim  1 . The wrap spring represents a simple and effective coupling element to reduce the space requirements and to ensure a reliable function thereof by way of construction. To satisfy the special demands of coupling in and out with respect to an alternately manual and motor-powered operation of the tabletop device, it is proposed to use the wrap spring such as is defined by claim  2 . 
    
    
     
       The invention will be explained in more detail in the following with reference to a preferred embodiment and to the drawings with reference to which further properties and advantages of the invention result. There are shown: 
         FIG. 1  a tabletop device in accordance with the invention for the dispensing of multicomponent compounds in a perspective outer view; 
         FIG. 1A  a section of the tabletop device in accordance with the invention in accordance with the plane IA in  FIG. 1 ; 
         FIG. 2  the inner structure of the tabletop device shown in  FIG. 1  in a corresponding perspective view; 
         FIG. 2A  a detailed view of the switchable coupling of the inner structure of the tabletop device shown in  FIG. 2 , with the force flow acting on the pressing down of the housing cover being symbolized by arrows; 
         FIG. 3  the inner structure of the tabletop device in a perspective side view rotated through 90° with respect to  FIG. 1  and  FIG. 2 , with the replaceable cartridge having been removed; 
         FIG. 4  a switchable wrap spring coupling in accordance with the invention of the drive of the dispensing plunger in the tabletop device shown in  FIG. 1-FIG .  3  in a perspective view for the switching between a motor drive and a freewheel; 
         FIG. 6  the wrap spring coupling shown in  FIG. 4 , with the switching sleeve extending along the outer periphery having been removed; and 
         FIG. 6  the wrap spring coupling shown in  FIG. 4  in a sectional view along the axis of rotation. 
     
    
    
     A tabletop device  1  shown in  FIG. 1  includes a housing  2  whose lower side is bounded by a planar base  2   a , whereas the upper boundary surface  2   b  is inclined toward the front side and extends beyond the base  2   a  in the direction of the rear side of the tabletop device  1 . 
     A manual operation member in the form of at least one handwheel  3   a  or  3   b  respectively is provided at both side surfaces  2   c  and  2   d  respectively, said handwheel being operatively connected to the mechanism in the housing interior and serving for the manual forward feed or back stroke of the dispensing plungers. For the simplified operation of the handwheels  3   a ,  3   b , they are made with gripping aids. 
     The front surface  2   e  of the housing  2  has an opening through which the end of the cartridge  6  projects at whose end the dynamic mixer  4  for the mixing of the components is fastened by means of a retainer nut  4   a.    
     A substantially rectangular cover  5  which can be flipped open, on the one hand, and thus provides access to the cartridge space is formed in the front section of the upper boundary surface  2   b . On the other hand, the cover  5  satisfies the function in the folded closed state of a push button which is operatively connected to the mechanism in the interior space of the housing, in particular to the control of the motor drive. It is prevented for safety reasons with this concept that the dispensing procedure can be carried out with an open cover. Independently of the type of drive used and of a coupling optionally connected thereto, the realization of the cover  5  as a push button which can be flipped open thus has the advantage that sources of damage and danger are reduced. 
     The mechanical structure in the interior of the housing  2  of the tabletop device  1  is shown in  FIGS. 2 and 3 . The manually replaceable cartridge  6  includes two substantially cylindrical storage containers  6   a  and  6   b , with the storage container  6   a  having a larger diameter and thus a larger volume in comparison with the storage container  6   b . A plunger plate  7   a ,  7   a  is arranged at the respective rear ends of the storage containers  6   a ,  6   b . A respective cylindrical dispensing plunger  8   a ,  8   b  is arranged adjacent to the respective rear ends of the plunger plates  7   a ,  7   b . The dispensing plungers  8   a ,  8   b  in turn have a rigid connection to a carriage  9  at their respective opposite ends with respect to the plunger plates  7   a ,  7   b.    
     The carriage  9  is made in the shape of a half-frame and is movable in the axial direction of extent of the dispensing plungers  8   a ,  8   b  or of the storage containers  6   a ,  6   b . As is shown in  FIG. 1A , the carriage  9  is guideably journaled for this purpose within laterally arranged guide grooves  9   a ,  9   b  in the direction of displacement of the dispensing plungers  8   a ,  8   b . The guide grooves  9   a ,  9   b  are made as sheet metal rails which have a U shape in their cross-sections and which are each fastened in projections of the left hand or right hand lateral housing inner walls  2   c ,  2   d . A straight-line, simultaneous movement of the dispensing plungers  8   a ,  8   b  is ensured by the guidance of the carriage  9  in the guide grooves  9   a ,  9   b  at both sides and a canting of the dispensing plungers  8   a ,  8   b  and of the plunger plates  7   a ,  7   b  fastened thereto at the end sides is effectively avoided in the inner space of the cartridge during the dispensing procedure. 
     It is clear to the person of ordinary skill in the art that the named advantages of the carriage  9  also come into effect in a conventional apparatus for the mixing and dispensing of multicomponent compounds, independently of the manner and of the construction of the coupling used and independently of the use of a motor-powered drive or of only a manual drive for the movement of the slide  9 . 
     Again with reference to the mechanical structure shown in  FIGS. 2 and 3 , for the movement of the carriage  9 , it is pivotally connected beneath its left hand and right hand boundaries respectively to two oppositely disposed ends of a guide chain  10   a  and  10   b  respectively. The direction of traction of the guide chain  10   a  and  10   b  respectively is defined in the axial direction of extent of the dispensing plungers  8   a ,  8   b  or of the storage containers  6   a ,  6   b  by two deflection chain gears  11   a ,  12   a  and  11   b ,  12   b  respectively arranged at the left and the right respectively. The drive of the guide chain  10   a  and  10   b  respectively takes place by a drive chain gear  13   a  and  13   b  respectively which is arranged on the left hand side and right hand side respectively of a main shaft  14  extending in the transverse direction of the tabletop device  1 . 
     On the one hand, a manual drive of the main shaft  14  and thus of the carriage  9  is provided. For this purpose, a respective external gear  15   a  and  15   b  is fastened to the left hand outer end and to the right hand outer end respectively and is operatively connected via a respective idler gear  16   a  and  16   b  and a respective handwheel gear  17   a  and  17   b  to the respective handwheels  3   a  and  3   b  arranged at the side of the housing  2 . 
     In addition, a motor drive of the main shaft  14  is provided. A switch between the manual and the motor drive is realized by a wrap spring coupling  30  arranged centrally on the main shaft  14 . The drive side  31  of the wrap spring coupling  30  is operatively connected to the output of the transmission  19  via a transmission gear  18  by its gear-type formation  31   a.    
     A slip clutch or friction clutch  20  is provided at the transmission input and is connected via a toothed belt  21  to a transmission shaft  22  which is located beneath the position of the cartridge  6  or of the dispensing plungers  8   a ,  8   b  substantially in the direction of extent thereof. The transmission shaft  22  is connected directly to the drive motor  24  via a further toothed belt  23  arranged at the front end of said transmission shaft. The speed of the drive motor  24  of, for example, 2700 revolutions per minute is in this respect stepped down to approximately 400 revolutions per minute of the transmission shaft  22 . The friction clutch  20  serves as a security against overload, in particular for the case that the dynamic mixer was not replaced after hardening of a multicomponent compound from a preceding mixing procedure. 
     In addition, a transmission of the torque of the transmission shaft  22  takes place to a mixer shaft  25  which is arranged above and parallel thereto and which opens into the dynamic mixer  4  to drive it. The coupling between the transmission shaft  22  and the mixer shaft  25  is realized by a respective shaft gear  22   a  and  25   a  arranged at its rear end which mutually engage into one another. A rotation of the mixer shaft  25  results from this with an equivalent speed of approximately 400 revolutions per minute. 
     Beside the drive side  31  of the wrap spring coupling  30 , the latter has a switching element in the form of a switching sleeve  32  which has a toothed arranged  32   b  at the right hand end in which the gear  26   a  of a freewheel  26  dependent on the direction of rotation engages. The freewheel  26  dependent on the direction of rotation is fastened at the respective left hand and right hand sides to the lever  27   a  and  27   b  respectively which is respectively pivotally connected to an upwardly directed ram  28   a  and  28   b  respectively. The rams  28   a  and  28   b  respectively are upwardly loaded, while in contact with the cover  5  of the housing  2 , by a respective spring  28   a  and  29   b . A switch  24   a  is located beneath the right hand lever  27   b  in its direction of pivoting and the drive motor  24  is activated on its actuation. 
     The tabletop device  1  described above includes diverse individual elements with a wrap spring, in particular the friction clutch  20  for the limiting of the torque and the freewheel  26  dependent on the direction of rotation whose operations can be considered known. In contrast, the use of the wrap spring coupling  30  is based in accordance with the invention on an innovative principle and will be explained in more detail in the following with reference to  FIGS. 4-6 . 
     The output side of the wrap spring coupling  30  is formed by the main shaft  14  which is formed substantially cylindrically, whose diameter at the two marginal regions  14   a ,  14   b  is identical and whose central region has a section  14   c  with a diameter larger in comparison therewith and a section  14   d  with an even larger diameter along a step. A drive chain gear  13   a  and  13   b  respectively is arranged at the respective left hand and right hand marginal regions  14   a  and  14   b  and drives the carriage  9  via the chains  10   a  and  10   b  respectively. 
     The drive side of the wrap spring coupling  30  in the form of a drive hub  31  is rotatably journaled by a slide bearing  33  arranged therebetween on the section  14   c  of the central region of the main shaft  14 . The drive hub  31  substantially has the shape of a hollow cylinder with a constant inner diameter and different sections with outer diameters respectively decreasing in steps from left to right. The toothed arrangement  31  is arranged at the left hand outer section with the largest outer diameter and engages into the drive gear  18  to take up the torque of the motor drive. The right hand outer section has the smallest outer diameter which substantially coincides with that of the adjacent central section  14   d  of the main shaft  14 . 
     A wrap spring  34  is pushed onto these mutually adjacent outer surfaces with a substantially constant diameter. The inner diameter of the wrap spring  34  in the relaxed state before the pushing on is in this respect smaller than that which is produced after the pushing on and on the wrapping around of the mutually adjacent outer surfaces. A force-transmitting connection or friction connection is formed by the spring tension between the wrap spring  34  and the two outer surfaces and accordingly a rigid connection between the drive hub  31  and the main shaft  14 . 
     A switching sleeve  32  is rotatably attached to the sections covered by the wrap spring  34 . The switching sleeve  32  has the form of a hollow cylinder whose right hand outer region has a peripheral toothed arrangement  32   b  which in turn cooperates with the freewheel gear  26   a  of the freewheel  26 . Furthermore, a drive slit  32   a  is provided at the right hand margin in which an end hook  34   a  attached to the right hand end of the wrap spring engages. 
     The end hook  34   a  is moved along contrary to the sense of the winding direction of the wrap spring  34  by rotation of the switching sleeve  32  in the direction of rotation D of the transmission drive which is symbolized by an arrow in  FIG. 4 . With a preferred angle of rotation of approximately 3-15°, the friction connection of the wrap spring  34  releases from the central section  14   a  of the main shaft  14 . A freewheeling of the main shaft  14  with respect to the transmission drive is thereby ensured and it enables a manual drive via the handwheel gears  17   a ,  17   b  of the handwheels  3   a ,  3   b.    
     A possible procedure on the operation of the tabletop device  1  in accordance with the invention will be explained in detail in the following: 
     If the carriage  9  is located at its rearmost position, a cartridge  6  can be inserted into the tabletop device after opening the cover  5 . In this respect, the wrap spring coupling is located at its position rotated by approximately 3°-15° in the direction of rotation D so that the main shaft  14  is decoupled from the drive shaft  31 . By actuating the handwheel  3   a ,  3   b , the cartridge can be moved quickly in the forward direction (and back) until the plunger plates  7   a ,  7   b  of the dispensing plungers  8   a ,  8   b  contact the dispensing piston of the cartridge  6 . 
     After the cover  5  has been closed, its end at the dispensing side can be used as a push button. The force flow acting on the pressing of the cover is shown by the arrows in  FIG. 2A . By actuation thereof, the rams  28   a ,  28   b  are pressed downward (arrow I), against the action of force by the springs  29   a ,  29   b  (arrow II). This in turns results in a pivot movement of the levers  27   a ,  27   b  toward the bottom, with in particular the switch  24   a  for the activation of the drive motor  24  being actuated by the right hand lever  27   b . At the same time, the freewheel gear  26   a  of the freewheel  26  carries out a corresponding rotational movement (arrow III). The latter simultaneously produces a movement of the switching sleeve  32  (arrow IV) coupled thereto by approximately 3°-15° opposite to the direction or rotation D so that the wrap spring  34  is guided back into its tightly wound original position and enters into a friction connection with the main shaft  14 . It is thus coupled into the drive side  31 . 
     The transmission spindle  22  is driven via the toothed belt  23  by the drive motor  24  at a speed of e.g. approximately 400 revolutions per minute. It, on the one hand, drives the mixer spindle  25  of the mixer  4  via the gears  22   a ,  25   a.    
     The drive gear  18  whose torque is transmitted via the wrap spring coupling  30  to the main shaft  14  is located at the drive output. The torque of the main shaft  14  is transmitted by the guide chains  10   a ,  10   b  via a linear traction movement into the carriage  9  so that the dispensing plungers  8   a ,  8   b  are loaded to bring the individual components into the dynamic mixer  4  which are mixed there and subsequently dispensed. 
     After the dispensing of the desired quantity of the multicomponent compound, the cover is released, whereby the rams  28   a ,  28   b  and the levers  27   a ,  27   b  are guided back upwardly into their starting position via the springs  29   a ,  29   b . The switching sleeve  32  on the wrap spring coupling  30  is thereby guided back into its position rotated by 3°-15° in the direction of rotation D and the transmission drive is decoupled from the main shaft  14 . At the same time, a deactivation of the drive motor  24  takes place by unloading the switch  24   a  via the lever  27   b.    
     As a result of the fast decoupling of the drive  24 , an immediate unloading of the carriage  9  or of the dispensing plungers  8   a ,  8   b  takes place which enables the immediate relaxation of the cartridge  6  via the cartridge pistons and thus largely prevents the continued flowing of the mixed components from the dynamic mixer  4 . 
     After the replacement of the mixer  4 , the device is ready for the next dispensing. 
     Since an automatic decoupling of the drive  24  takes place after every dispensing procedure, a manual moving back of the carriage  9  into the starting position is possible at any time by means of the handwheels  3   a ,  3   b . This allows the removal of the partly or fully emptied cartridge  6  after the opening of the cover  5 .