Abstract:
An ejector system for use in an injection molding machine comprises a plurality of rack gears and pinions gears that provide active alignment of plates within the ejector system. As unequal force is experienced in ejecting a molded item, the rack and pinion gears distribute the force to other areas of the ejector system plate, maintaining proper alignment of the plates within the ejector system.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    Injection molding machines are used to produce plastic articles for use in a variety of applications. In general, plastic in liquid form is injected into a cavity which is formed by two mold assemblies. Once the plastic has cooled, the two mold assemblies are separated so as to remove the formed article. Upon separation, the molded article remains in one of the mold assemblies. In order to effect the removal of the formed article from the mold plate, some means of ejecting the article is typically required. A variety of approaches exist for effecting ejection, including the use of ejector or stripper plates, stripping pins and pressurized air.  
           [0002]    Ejector plates are typically associated with one of the mold assemblies and act against the formed article, to force the article from the mold plate. Normally, force is applied to the ejector plate at a single location, which may be located at or near the center of the ejector plate. The ejector plate acts upon ejector pins which in turn force the molded article out of the mold assembly. These systems are called single knockout ejector systems. In certain applications, single knockout ejector systems are very effective. However, in other instances, the plastic article can be of a very complicated design. For example, an article may include deep part walls, deep part ribs, cored holes, and other non-uniform attributes. For these more complicated designs, single knockout ejector systems are less effective. The non-uniform attributes result in unequal forces being generated as the formed article is being ejected from the mold plate. Accordingly, misalignment of the ejector plate within the mold assembly may occur, resulting in cock of the ejector plate. If this situation is not corrected, the ejector plate will eventually bind, forcing the injection molding machine to be shut down and serviced, as well as causing damage to the mold assembly which must be repaired or replaced.  
           [0003]    One approach to solving this problem, has been to incorporate rack and pinion gears into mold assemblies for articles which have non-uniform attributes. While this approach is effective, it is also very expensive. For example, the mold assemblies are constructed uniquely for a given article to be molded. In order to allow for manufacture of replacement parts, the mold assemblies are stored when not in use. Thus, re-use of parts within the mold assemblies for other mold assemblies is not a normal practice. Accordingly, each such mold assembly must incorporate a dedicated set of rack or pinion gears.  
           [0004]    Therefore, it is desirable to provide an ejection mechanism that compensates for the effects of unequal forces as an article is being ejected. It is also desirable that the ejection mechanism be easily adapted for use with a variety of article shapes without the need to add manufacturing steps to the manufacture of mold assemblies. It is further desirable that the ejection mechanism be more cost effective than prior art approaches which use dedicated rack and pinion gears for each mold assembly. Moreover, it is desired that the ejection mechanism use common and relatively inexpensive components.  
         BRIEF SUMMARY OF THE INVENTION  
         [0005]    In accordance with the present invention, a plurality of rack and pinion gears are used within an ejector plate guiding system. According to one embodiment, a system of pinion shafts are mounted to the guiding rails of the ejector plate, each pinion shaft having pinion gears located at each of the pinion shaft ends. The pinion gears are operably engaged with rack gears mounted on the ejector plate. Accordingly, as uneven pressure is applied to any area of the ejector plate, resulting in a change in motion, the change in motion is translated to the rack gears located nearest the location of uneven pressure. The rack gears operate with the pinion gears to translate this motion into the associated pinion shaft, and the motion is thus translated through the pinion shaft to the pinion gears at the opposite end of the shaft and then to the associated rack gears. This translation continues around ejector plate, such that all corners of the ejector plate travel at the same speed. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]    [0006]FIG. 1 is an end view of a portion of an injection molding machine.  
         [0007]    [0007]FIG. 2 is a simplified isometric view of a portion of the injection molding machine of FIG. 1.  
         [0008]    [0008]FIG. 3 is a simplified isometric view of a portion of an ejector mechanism in accordance with the present invention within the injection molding machine of FIG. 1.  
         [0009]    [0009]FIG. 4 is a sectional view of one corner of the ejector knockout plate of FIG. 3.  
         [0010]    [0010]FIG. 5 is a sectional view of an ejector knockout plate of FIG. 3. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0011]    [0011]FIG. 1 is an end view of a portion of an injection molding machine showing typical arrangement and identification of parts within the molding section of an injection molding machine in the open position. The molding machine includes stationary section  100  and movable section  102 . Stationary section  100  includes cover clamping plate  104  and cover block  106 . The stationary mold assembly for the article to be molded is located within cover block  106 . Leader pins  108  and  110  provide for alignment between stationary section  100  and movable section  102 .  
         [0012]    During mold opening and closing, leader pin guide bushings  112  and  114  of ejector block  116  of movable section  102  ride upon leader pins  108  and  110 . Clamping slots  118  and  120  are used in conjunction with a clamp (not shown) to maintain ejector block  116 , which houses the movable mold assembly for the article to be molded, tight against cover block  106  when plastic is being injected into the mold. Sprue bushing  122  is the material entry port into the mold and sprue puller pin  124  ensures that the molded article stays within ejector block  116  when ejector block  116  is moved away from cover block  106 .  
         [0013]    The remaining parts of movable section  102  include support plate  125  and ejector plate  126  which rides within ejector rails  128  and  130  upon guide pins (not shown). Ejector plate  126  is located between ejector retaining plate  132  and ejector clamping plate  134 . Ejection of a molded part is effected by forcing ejector plate  126  toward support plate  125  with a knockout (shown in FIG. 5). Ejector pins (not shown) are mounted upon ejector plate  126  and protrude through the wall of the mold plate housed within ejector block  116 . The ejector pins act upon the molded article to force the article out of the mold plate.  
         [0014]    Referring now to FIG. 2, a simplified isometric view of a portion of a mold assembly and portions of an ejector mechanism are shown. Mold assemblies are specially constructed for each article to be molded. This is because each article presents a unique shape, dictating a mold shape and entry points for ejector pins and vents. Mold assembly  200  includes mold rails  202  and  204  (opposing mold rails are not shown for purpose of clarity). Screws  206 ,  208  and  210 , along with pin  212  are used to attach a mold body (not shown) to mold rail  204  and an opposite mold rail (not shown). The mold body determines the shape of the article to be molded, forming one half of the mold cavity. The mold body includes openings into which ejector pins mounted within ejector pin plate  135  protrude. Ejector pin location is determined by the shape of the article to be molded, and thus are specially located for each article. Ejector pin plate  135  is located on top of ejector plate  136 , both of which are movable within mold rails  202  and  204  (and two mold rails not shown) to eject a molded article.  
         [0015]    In the embodiment of FIG. 2, rack gears  214 ,  216 ,  218 ,  220 ,  224 ,  226 ,  228  and  230  have been attached to ejector pin plate  135  and ejector plate  136 . Rack gears  214 ,  216 ,  218 ,  220 ,  224 ,  226 ,  228  and  230  engage with pinion gears  232 ,  234 ,  236 ,  238 ,  240 ,  242 ,  246  and  248  respectively. Pinion gears  232 ,  234 ,  236 ,  238 ,  240 ,  242 ,  246  and  248  are mounted upon pinion shafts  250  and  252  as well as shafts within mold rails  202  and  204  which are not shown. The pinion shafts are rotatably mounted within the mold rails. Thus, if increased ejection force is experienced within mold assembly  200 , the force is transmitted through ejector pin plate  135  to ejector plate  136  and the rack and pinion gears act to distribute the increased force evenly across ejector plate  136  so as to minimize misalignment of ejector plate  136 . However, because each mold assembly must be uniquely made for each item to be molded, and because the mold assemblies are retained for future use, a unique set of pinion gears and pinions shafts must be specially fitted to each mold assembly used on a machine. Moreover, the positioning of the pinion gears may be constrained by the particular mold assembly. Therefore, rack position on the ejector plate may need to be modified for each mold assembly.  
         [0016]    Referring now to FIG. 3, a simplified isometric view of a portion of an ejector mechanism in accordance with the present invention is shown. The embodiment of FIG. 3 includes portions of two ejector mechanisms including ejector knockout plate  300  and ejector knockout plate  301 . Both ejector mechanisms may be constructed in accordance with the present invention. Ejector knockout plate  300  is located within ejector clamping plate  302  and may act upon ejector plate  136  shown in FIG. 2. However, when the present invention is retro-installed, the ejector rails (discussed below) are extended in order to incorporate the pinion gears and shafts. This extension results in the need for a bolster plate intermediate the ejector knockout plate and the ejector plate, and also reduces the daylight opening of the injection molding machine. Shut height is the overall height of the mold assemblies when the injection machine is closed. Daylight opening is the distance between the mold halves when the injection molding machine is open.  
         [0017]    Ejector knockout plate  300  is maintained in alignment within four ejector rails by ejector guide pins  303 ,  305 ,  307  and  309 . For clarity, FIG. 3 shows only two ejector rails associated with ejector knockout plate  300 , ejector rail  304  and ejector rail  306 . Ejector knockout plate  301  is maintained in alignment within four ejector rails by ejector guide pins  311 ,  313 ,  315  and  317 . However, only ejector rails  308 ,  310  and  312  are shown in FIG. 3. Also shown in FIG. 3 are a plurality of rack and pinion gear assemblies including rack gears  314 ,  316 ,  318 ,  320 ,  322 ,  324 , and  328 , which engage pinion gears  334 ,  336 ,  338 ,  340 ,  343 , and  348  respectively. Another rack gear (not shown) engages pinion gear  346 . Also shown are pinion shafts  350  and  352 . The rack gears are mounted upon ejector knockout plate  300  and the pinion gears and shafts are mounted within the ejector rails as is shown more clearly in FIG. 4.  
         [0018]    [0018]FIG. 4 is a sectional view of one corner of ejector knockout plate of FIG. 3 showing the ejector rails not shown in FIG. 3. Pinion gear  334  is shown connected to pinion shaft  350  which is rotatably connected to rail  400  by bearing  402 . Pinion gear  336  is rotatably fixed within rail  404  and engaged with rack gear  316 . Bolster plate  406  is located above knockout plate  300  which is not clearly shown in FIG. 4.  
         [0019]    Basic ejector operation is described with reference to FIG. 5 which is a sectional view of ejector knockout plate  301  of FIG. 3. In this embodiment ejector knockout plate  301  is configured in the same manner as ejector knockout plate  300 . Pressure is applied to knockout  500  which acts upon ejector knockout plate  301  to force ejector knockout plate  301  in the direction of arrow  502 . As ejector knockout plate  301  moves in the direction of arrow  502 , ejector knockout plate  301  causes pinion gears  504  and  506 , located within rail  310  of FIG. 3, to rotate. Movement of ejector knockout plate  301  causes its associated ejector plate and ejector pin plate to move, thus forcing ejector pins attached to the ejector pin plate to force a molded article from a mold assembly. After the molded article has been ejected, knockout  500  is returned to its original position using means well known in the art.  
         [0020]    Force equalization during ejector operation is described with reference to ejector knockout plate  300  and FIGS. 3 and 4. When an ejection cycle begins, ejector knockout plate  300  is forced by its associated knockout to move in the direction of arrow  370  of FIG. 3. As ejector knockout plate  300  moves, rack gears  314 ,  316 ,  318 ,  320 ,  322 ,  324 , a rack gear not shown and  328 , cause pinion gears  334 ,  336 ,  338 ,  340 ,  343 ,  346  and  348  respectively to rotate. Accordingly, pinion shafts  350 ,  252 , and the pinion shafts within ejector rails  304  and  306  are caused to rotate. Ejector guide pins  303 ,  305 ,  307  and  309  assist in maintaining ejector knockout plate  300  in alignment within ejector rails  304 ,  306 ,  400  and  404  as ejector knockout plate  300  travels. The ejector guide pins provide inactive alignment for the ejector knockout plate, serving only to constrain the movement of ejector knockout plate  300  within the ejector rails along a path in the direction of arrow  370 . This movement continues through ejection of the molded article.  
         [0021]    In the event increased resistance to ejection is experienced in a mold assembly during the above process, that resistive force is translated through the ejector pins, the ejector pin plate, the bolster plate (if used) and the ejector plate to ejector knockout plate  300 . By way of example, if that resistive force is experienced at the corner of ejector knockout plate  300  shown in FIG. 4, the corner shown in FIG. 4 would tend to slow movement of that corner in direction of arrow  370 . This resistive force is translated through rack gears  314  and  316 , tending to slow rotation of pinion gears  334  and  336 . However, the other corners of ejector knockout plate  300  are not immediately affected by this increased resistance, and the pinion gears associated with those corners will instantaneously continue to be rotated at a speed higher than the rotation of pinion gears  334  and  336 . This causes torque to be transferred from pinion gears  338 ,  340 ,  343 ,  346  and  348  through their associated shafts to pinion gears  334  and  336 .  
         [0022]    Transfer of force between adjacent pinion gears is explained in reference to FIG. 3. For example, if a torque has been transmitted to pinion gear  338 , that force is transmitted to rack gear  318 . Rack gear  318  is adjacent to rack gear  320 . Accordingly, force is transferred through ejector knockout plate  300  to rack gear  320  and translated into rotational force by pinion gear  340 . Thus, pinion gears  338  and  340  are operably related through their respective rack gears. This transfer of force also results in a slowing of the rotation of the pinion gears which are not initially affected by the increased resistance. The net effect, is that increased force is transferred to the point of increased resistance while all of the pinion gears are driven to the same rotational speed, thus actively aligning ejector plate  300  within the ejector rails along the path defined by the ejector guide pins.  
         [0023]    While the present invention has been described in detail with reference to certain exemplary embodiments thereof, such are offered by way of non-limiting example of the invention, as other versions are possible. By way of example, but not of limitation, fewer or more rack and pinion assemblies may be incorporated into a particular ejector guide system depending on the design of the ejector plate. Moreover, the present invention is not limited to use in a two station injection machine. Furthermore, in certain applications it may be desired to mount the rack gears upon the guideposts, and secure the pinion gears to the ejector plate. It is anticipated that a variety of other modifications and changes will be apparent to those having ordinary skill in the art and that such modifications and changes are intended to be encompassed within the spirit and scope of the invention as defined by the following claims.