Abstract:
An actuator for advancing a rod which enables release of the rod from an actuating mechanism by rotating the rod to allow the rod to be retreated. The actuator may also provide a mechanism for disabling the driving mechanism as the rod is fully advanced to prevent damage by excessive forces being applied to the rod. The actuating mechanism can be fully enclosed in a stock of a dispenser gun or applicator, facilitating cleaning of the dispenser gun. The disclosed dispenser gun is particularly suitable for dentistry applications.

Description:
RELATED APPLICATION 
     The present application claims priority to EP Application No. 10196813.9 filed Dec. 23, 2010, which is incorporated herein in its entirety by reference. 
     TECHNICAL FIELD 
     The present invention relates to an actuator for advancing a rod and, in particular, a dispenser or applicator using such an actuator to apply a dispensing pressure to a viscous material. More particularly, the present invention relates to such a dispenser or applicator for dentistry applications. 
     BACKGROUND ART 
     Viscous material, such as mastic caulking material, is commonly supplied in a cartridge having a discharge nozzle. The cartridge can be mounted in a dispensing appliance, often called a dispensing gun or applicator. An example of such a dispensing gun is described in British patent GB1555455. The gun has a plunger or a push rod slideably mounted in a cartridge. The cartridge is mounted in a keep before the plunger. The plunger is advanced by means of a catch plate linked to a trigger lever engaging the rod. When a dispensing force is applied to the trigger lever, the plunger forces a piston, inside one end of the cartridge, forward to urge the material from the nozzle at the other end. The trigger and catch plate are reset at the end of a dispensing stroke and the dispensing force can be reapplied. 
     Between trigger strokes the plunger is held against the piston by means of a locking plate. In order to retreat the plunger, for example to remove the cartridge, a force is applied to the locking plate to disengage the locking plate from the rod and allow retreat of the rod. The locking plate can be arranged to either substantially prevent any retreat of the rod during dispensing or to allow a small amount of retreat of the rod to release pressure applied to the cartridge, as disclosed, for example, in European patent EP0448375. In order to be able to retreat the plunger, the locking plate must be accessible so that a releasing force can be applied to it, either directly or by an intermediate mechanical linkage where the locking plate is within a housing together with the remaining actuating mechanism, for example as disclosed in U.S. Pat. No. 5,370,282. 
     The inventors have realized that, for a number of reasons, it may be undesirable to require access to the locking plate or a corresponding release lever or button in order to release the locking plate to allow retreat of the rod. For example, if the locking plate or lever is arranged such that it can be actuated by the thumb of a user&#39;s hand holding the gun to leave the other hand free to retreat the rod, this will compromise the design freedom in designing the gun, in particular for dispensing guns of overall small size. Similarly, the need for an external locking plate or lever tends to make the dispensing gun more difficult to clean, even if the remaining actuating mechanism is enclosed in a housing. These considerations are particularly relevant for dentistry applications, where the nature of the work and the small quantities of material to be dispensed means that the dispenser is likely to be of a small form factor and where the ease of maintaining the dispensing gun cleanliness is paramount. However, it will be understood that these considerations are not limited to dentistry applications. 
     SUMMARY OF THE INVENTION 
     In an embodiment of the invention, there is provided an actuator for advancing a rod, the actuator comprising a catch member for engaging the rod, a trigger member for moving the catch member to advance the rod in one direction and a locking member for engaging the rod to prevent the rod retreating in the other direction. The actuator further comprises a release arrangement for transforming a torque applied to the rod into a releasing force disengaging the locking member to enable retreat of the rod in the other direction. 
     The release arrangement enables the release of the locking member by rotation of the rod, thereby dispensing with the need for a locking plate (or corresponding lever) which is separately actuatable by user. Rotation of the rod thus urges the locking member away from a configuration in which it is engaged with (bites on) the rod, preventing the rod&#39;s retreat, to disengage the locking member from the rod. The user can release and retreat the rod with a single hand gesture, thereby addressing the problems discussed above and increasing ease of use of the actuator generally. 
     In some embodiments, the release arrangement comprises a cam member and a cam follower. The cam member slidingly accepts the rod and defines a cam at one end. The cam engages the cam follower to transfer rotation of the rod to translation of the cam follower, thereby applying the releasing force to the locking member. In embodiments where the catch member is biased to engage the rod when the trigger member is not actuated, the release arrangement is arranged to transform the torque applied to the rod to a releasing force disengaging the catch member, as well as the locking member, to enable retreat of the rod. In some embodiments, the locking member and/or catch member are biased into an engaged attitude with respect to the rod and the releasing force causes rotation of the locking and/or catch member away from the engaged attitude. 
     In some embodiments, the locking member is forward of the catch member in the one direction. This enables a space efficient arrangement of the actuator in a confined housing, making use of the space forward of the catch member to accommodate the locking member. 
     In some embodiments, the actuator provides end of stroke release, releasing the catch member when the rod reaches a predetermined (usually fully advanced) position to prevent further pressure being applied to the rod and the corresponding risk of damaging the actuator and/or dispenser or dispensing cartridge to which the actuator is applied. In these embodiments, the actuator comprises a holding member for holding the catch member in a disengaged relationship with respect to the rod when the rod is advanced to the predetermined position. At this point, further actuation of the trigger member does not advance the rod any further. In some embodiments, the rod comprises a protrusion, for example a pin extending on one or both sides of the rod, for engaging the holding member and thus to advance the holding member with the rod as the rod advances to a predetermined position. In some embodiments, the cam member defines a channel in which this protrusion is slideably accepted to cause the cam member to rotate with the rod. In some embodiments, the holding member is a sleeve disposed between the rod and the cam member, resulting in a compact arrangement in which the rod is supported by the sleeve and cam member to provide a journal close to the actuating mechanism and, in particular, the catch member. 
     Irrespective of the presence of a holding member, in some embodiments the rod includes a protrusion, for example as described above, and the cam member defines a channel slideably accepting this protrusion to cause the cam member to rotate with the rod. 
     In an embodiment of the invention, there is provided a dispenser for dispensing a viscous material, the dispenser comprising an actuator as described above for applying a dispensing pressure to the viscous material. 
     In some embodiments, the dispenser fully encloses the catch member, locking member and release arrangement. The dispenser is, in some embodiments, arranged for use in dentistry. 
     In some embodiments of the invention, there is provided a dispenser for dispensing a viscous material, the dispenser comprising an actuator for advancing a rod to apply a dispensing pressure to the viscous material. The dispenser comprises a window through which the advance of the rod can be observed. In some embodiments, the window comprises graduations indicating the amount of advance of the rod as a result of a complete actuation of the trigger member. In some embodiments, the feature is a shoulder between portions of the rod having different diameters. 
     In some embodiments of the invention, there is provided an actuator for advancing a rod, the actuator comprising means for advancing the rod in response to actuation of a trigger lever and means for preventing retreat of the rod. The actuator further comprises means for releasing the rod in response to rotation of the rod in order to enable retreat of the rod. 
     An embodiment of the invention is now described by way of example only and with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a dispenser in accordance with an embodiment of the invention; 
         FIG. 2  is a top elevation view of the dispenser; 
         FIG. 3  is a side elevation view of the dispenser; 
         FIG. 4  is a view exposing an actuating mechanism inside the dispenser; 
         FIG. 5  depicts a partial cross-section along the line A-A of  FIG. 2 ; 
         FIG. 6  depicts a partial cross-sectional view along the line B-B in  FIG. 3 ; 
         FIG. 7  is an exploded view of components of an actuating mechanism for advancing a rod of the dispenser; and 
         FIG. 8  is another exploded view of components of the actuating mechanism, including the rod. 
     
    
    
     DETAILED DESCRIPTION 
     With reference to  FIGS. 1 ,  2  and  3 , a dispenser or applicator comprises an actuator  2  and a cartridge holder  4 . The actuator  2  comprises a stock  6  and a trigger lever  8  movable relative to the stock  6 . A rod  10  is disposed slideably within the stock  6  and a mechanism inside the stock  6 , described in detail below, is arranged such that actuation of the trigger lever  8  causes the rod  10  to advance with respect to the stock  6  and the cartridge holder  4  into a cartridge (not shown) held in a slot  12  of the cartridge holder  4 . A positioning member  14  is biased by a disc spring (non shown) to protrude into the slot  12 , thereby applying a resilient positioning force to a rear end of the cartridge held in the slot  12 . The cartridge holder  4  comprises a window  16  through which the advance of the rod  10  can be observed. At a rear end, the rod  10  carries a knob  18  for enabling a user of the dispenser to rotate the rod  10  in order to release the mechanism inside the stock  6  such that the rod  10  can be retreated, for example to change a cartridge once the rod  10  has been advanced into it. 
     With reference to  FIGS. 4 to 8 , a driving mechanism of the actuator  2  comprises the trigger lever  8  being pivotably secured to the stock  6  by pivot  20 . A lower portion  22  of the trigger lever  8  is configured for actuation by a user&#39;s fingers pulling the trigger lever  8  towards the stock  6  and an upper portion  24  opposed to the lower portion  22  across the pivot  20  comprises a trigger pin  26  for engaging a catch plate  28 . The trigger lever  8  is biased into a rest orientation with the lower portion  22  disposed away from the stock  6  by a torsion spring  29 . The catch plate  28  has an aperture  30  accepting the rod  10  and is biased against the trigger pin  26  and into engagement with the rod  10  by a first helical spring  32  disposed forward of the catch plate  28  towards the cartridge holder  4  and resting against a forked cross member  34  providing a seat for the first helical spring  32 . The forked cross-member  34  accepts the rod  10  between its prongs extending across the interior space inside the stock and locating between support struts  36  at their free ends. A locking plate  38  has an aperture  40  accepting the rod  10  and is disposed forward of the catch plate  28  and the forked cross member  34 . A second helical spring  42  rests against a rear end of the cartridge holder  4  providing a seat for the second helical spring  42 . The second helical spring  42  biases the locking plate  38  against a cross bar  44  rearwards of the locking plate  38  and thereby into engagement with the rod  10 . 
     The arrangement of the catch plate  28  and locking plate  38  means that they bite on the rod when the rod is pulled rearwards relative to the catch and locking plates  28 ,  38  but allow the rod to be pushed forward. Consequently, the catch plate  28  bites on the rod  10  when the trigger lever  8  is pulled towards the stock  6 , advancing the rod, and slides across the rod as the trigger lever  8  returns to its rest position away from the stock  6 , while the rod  10  is held in position by the locking plate  38  biting on it. Thus, repeated actuation of the trigger lever  6  towards the stock  6  advances the rod  10  in a forward direction towards the slot  12  with each stroke of the trigger lever  8 . 
     A cam member  46  comprises a sleeve  48  accepting the rod  10  and defines channels  50  accepting protruding portions of a pin  52  disposed in a hole through the rod  10 . An interior forward wall of the channels  50  limits the advance of the pin  52  in the channels  50  and hence advance at the rod  10 . Similarly, a stop  54  extending from an interior wall of the stock  6  limits the retreat of the rod  10  in the other direction. At one end facing the cartridge holder  4  the cam member  46  defines a flange  56  abutting an interior wall  58  of the stock  6 . The interior wall  58  defines an aperture  60  rotatably accepting a front end  62  of the cam member  46 . A leaf spring  64  extends from the cam member  46  in a direction perpendicular to the direction of the pin  52  between the channels  50 , the cam member  46  and the leaf spring  64  being molded in one piece. The leaf spring  64  is held in an aperture  66  of a strut wall  68  of the stock  6  and defines a rest orientation for the cam member  46  in which the pin  52  and channels  50  extend substantially perpendicularly on either side of a mid plane of the stock  6 . Cams  70  extend forward from the end  62  on either side of the rod  10 , aligned with the direction of the leaf spring  64 . 
     A cam follower  72  is disposed generally around the rod  10  forward of the cam member  46  and comprises a first portion  74  disposed between the cam member  46  and the catch plate  28  linked to a second portion  76  by a linking portion  78 . The second portion is disposed between the forked cross member  34  and the locking plate  38 . The linking portions  78  extend between the first and second portions  74 ,  76  on either side of the rod  10  and the catch plate  28  and first helical spring  32  around it and between the prongs of the forked cross member  34 . Further, the linking portion  78  extends forward of the second portion  76  on either side of the locking plate  38 . In this way, the cam follower  72  is held in rotational alignment with the catch plate  28  and locking plate  38 , and hence, the stock  6 , preventing rotation of the cam follower  72  relative to the stock while allowing reciprocating movement of the cam follower  72  along the rod  10 . A cam engaging surface  80  of the first portion  74  face the cams  70  and is shaped to have troughs aligned with the cams  70  in the rest orientation of the cam member  46  and lobes to the sides of the troughs aligned perpendicularly to a direction defined by the cams  70  in the rest orientation. In this orientation, the cam member  46  and cam follower  72  are disposed relative to each other such that the cams  70  are disposed inside the troughs and between the lobes of the cam engaging surface  80 . 
     The cam member  46  is constrained for only rotational movement relative to the stock  6  by virtue of being disposed in the aperture  60  with movement along the direction of the rod being prevented by the flange  56  engaging the wall  58  and a rear end  82  of the cam member  46  engaging the stop  54 . Excessive rotation of the rod  10  and cam member  46  is prevented by a nub (not shown) protruding from an interior surface of the stock  6  locating inside a recessed portion  84  of the flange  56 , thus limiting the rotational range to the angular extent of the recessed portion  84  of the flange  56 . 
     As described above, both the catch plate  28  and locking plate  38  prevent retreat of the rod  10 . By virtue of the cam member  46  and cam follower  72 , a user can disengage the catch plate  28  and locking plate  38  by rotating the rod  10  by means of the knob  18 . The rotation of the rod  10  is transferred to the cam member  46  by the pin  52 . As the cam member  46  rotates, the cams  70  engage the lobes between the troughs of the cam engaging surface  80 , urging the cam follower  72  away from the cam member  46 , the interaction between the cams  70  and cam engaging surface  80  thus causes the cam follower  72  to move longitudinally forward along the rod  10  to engage the catch plate  28  and locking plate  38  with, respectively, the first portion  74  and second portion  76 , causing the catch plate  28  and locking plate  38  to rotate away from their respective engaged attitudes with respect to the rod  10  in which they bite on the rod  10  until the catch plate  28  and locking plate  38  are held between the respective helical spring and portion of the cam follower  72  in a disengaged attitude relative to the rod  10  so that the rod can slide freely allowing the rod  10  to be retreated. 
     A bushing  86  is disposed around the rod  10  and the cam is slidingly accepted by member  46  and the first portion  74  of the cam follower  72 . A lip  88  prevents the bushing  86  from sliding the rearwards past the first portion  74 . The length of the bushing is selected such that the pin  52  engages a rear aspect of the bushing  86  as the rod  10  approaches the end of its forward travel and takes the bushing  86  with it on the last stroke of the trigger lever  6 , holding the catch plate  28  in a disengaged attitude relative to the rod  10  between the first helical spring  32  and the lip  88  at or close to the position of the trigger pin  26  when the trigger lever  6  is fully depressed. As a result further actuation of the trigger lever  6  applies no further advancing force to the rod  10 , the trigger pin  26  not making contact with the catch plate  28  over all or nearly all of the stroke of the trigger lever  6 . The interaction between the pin  52  and the bushing  86  thus acts as a end of stroke release mechanism, ensuring that no, or no significant, advancing forces are applied to the rod  10 , thus preventing potential damage to the mechanism at the end of the stroke. 
     The cartridge carrier  4  comprises an outer portion  90  and an insert  92 , acting as a bushing for the rod  10 . The rod  10  comprises a first portion  94  which is of a larger diameter than a second portion  96 , defining a shoulder  98  between the two portions. The first portion  94  is engaged by the catch plate  28  and the locking plate  38  and the second portion  96  acts as a plunger advanceable into a cartridge held in the slot  12 . The first portion  94  is journaled by the insert  92  adjacent to the locking plate  38  and by the bushing  86  adjacent to the catch plate  28 . The window  16  described above extends through the outer portion  90  and insert  92  so that the rod  10  is visible. The window  16  has graduations  100  corresponding to the position of the shoulder  98  at the end of each stroke between the rod&#39;s  10  fully advanced and fully retreated positions. By virtue of the window  16  and graduations  100 , a user can immediately see how many strokes of the trigger lever remain before the material in the cartridge is fully dispensed, at least for cartridges in which the range of movement of the cartridge&#39;s piston corresponds to the range of movement of the rod  10 . In any event, the graduations  100  provide a measure of the amount of material remaining which can be dispensed with the dispenser. 
     Most components of the above described dispenser are molded from suitable plastic materials, for example glass filled Nylon, polycarbonate (PC), polyethersulfate (PES), ABS. In the embodiment depicted in the drawings there are nine separately molded components, the knob  18 , the cartridge holder  16  outer portion  90  and insert  92 , the positioning member  14  the cam follower  72 , the cam member  46 , the trigger lever  8  and two halves of the stock  6 . The cartridge holder  4  is held relative to the slot by flanges engaging corresponding slots in the stock and the two halves of the stock are ultrasonically welded together although other securing methods, such as adhesive bonding, can equally be applied. The remaining components are made of suitable metal materials, for example stainless steel. In one particular embodiment specifically adapted for the use in dentistry, plastic materials that can be sterilized in an autoclave are employed, such as PES or PC and stainless steel is used for all non-plastic parts. 
     It will be understood that the above description of an embodiment of the invention has been made by way of example to illustrate aspects of the invention and that many alterations, modifications and juxtapositions of the features described above are possible and intended to be covered by the scope of the appendent claims. 
     For example, the catch plate may not be engaged with the rod  10  in the rest configuration of the trigger lever  6 , with no dispensing force applied to the trigger lever  6 , but rather rest in a disengaged attitude from the rod  10  against an abutment or other feature of the stock  6 , so that the cam follower  72  only needs to release the locking plate  38  in order to enable retreat of the rod  10 . It is generally possible to reverse the order of the catch plate  28  and locking plate  38  and in embodiments where the catch plate  28  is not engaged with the rod  10  in the trigger lever&#39;s  8  rest configuration, this enables the cam follower  72  to be simplified so that only a single portion carrying the cam engaging surface  80  and arranged to disengage the locking plate  38  is necessary. Likewise, the bushing  86  may be omitted from some embodiments, with a corresponding reduction in the aperture of the cam member  46  and/or cam follower  72  being possible to ensure secure journaling of the rod  10 . 
     While a particular cam arrangement for transforming rotating of the rod into a releasing force for releasing the locking plate  32  and/or catch plate  28  has been discussed above, it will be appreciated that many other arrangements are possible in alternative embodiments of the invention. For example, the cam member may have only a single cam, omitting one of the cams of the specific embodiment described above. In yet other embodiments, a cam or cams are directly attached to an arm or arms extending away from the rod in a suitable orientation to directly interact with the catch and/or locking plate to nudge them into a disengaged position in response to rotation of the rod. Similarly, a cam or cams directly nudging the locking and/or catch plate can be mounted on a gear or cog wheel directly or indirectly driven by rotation of the rod. Numerous other arrangements are equally possible. 
     Finally, it will be understood that the skilled person would select suitable materials and/or form factors, as well as open or closed stock designs and cartridge holders with or without a window for observing the advance of the rod, as a function of the particular application, without departing from the invention.