Patent Publication Number: US-RE38930-E

Title: Knife holder for a chipper disc

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to an improved knife holder for a chipper disc or film apparatus for producing chips or flakes from a piece of wood. 
     It is common to form chips for producing wood pulp for use in the manufacture of paper products, employing apparatus known as chippers a choppers, and to produce flakes or wafers for use in the manufacture of waferboard or oriented strand board, employing similar apparatus known as waferizers and stranders. All of these apparatus employ a disc rotating in the vertical plane and having one or more knives attached to knife holders disposed so that cutting edges thereof extend beyond the face of the disc. A piece of wood is fed against the face of the disc and the knives, so that cuts are made in the wood, producing the chips or flakes. The knives experience, very large forces and must be held firmly in place. 
     However, the knives must be removable from the knife holder, for reversing a replacing them. It has been a problem to ensure firm attachment of the knives while providing for their easy removal from the knife holders. 
     As a response, Holmberg et al., US. Pat. No. 4,694,995, proposes a knife holder that includes a filler piece fitting into a recess in the chipper disc, and a cassette for holding the knife. The cassette has a top and bottom part that clamps the knife therebetween and a fastener is inserted through the top and bottom parts that extends into the filler piece but not into the chipper disc. The filler piece is separately fastened to the chipper disc. Though it is as explained in the patent, the filler piece is a relatively large and heavy component, while the top part is relatively small and light. It is proposed that the knife may be removed simply by moving the fastener for the cassette and by lifting the small, light top part, while the larger, heavier filler piece remains fixed to the chipper disc. It is also proposed that the fastener for the cassette may be loosened to remove the knife. 
     Whether the fastener for the cassette of Holmberg is removed entirely or merely loosened, the top part of the cassette and the knife become loose and at least the top part must be moved to get at the knife. As the knife is heavy and difficult to handle and it is desirable to be able to use two hands for this purpose, the aforementioned requirement imposed by Holmberg is objectionable. Moreover, to the extent that the fastener for the cassette of Holmberg is smaller and lighter, it is capable of exerting less force on the knife than prior art fasteners for knife holders so that the knife is not held as firmly. 
     Accordingly, them is a need for an improved knife holder for a chipper disc or the like that provides for easier removal of a knife held thereby while providing for more firmly holding the knife during operation of the apparatus. 
     SUMMARY OF THE INVENTION 
     An improved knife holder for a chipper disc or the like according to the present invention solves the aforementioned problems and meets the aforementioned needs by providing a knife holder for holding a knife having a top and bottom side. The knife holder has a first clamping portion and a second clamping portion for clamping the knife therebetween. One of the clamping portions pivots about a pivot point for clamping the knife, and for releasing the knife, so that it may be easily removed from the knife holder. In the relative position of the firsts and second clamping portions in which the knife is clamped and in their relative positions in which a space is opened up around the knife permitting its removal, the first and second clamping portions are rigidly disposed with respect to one another. 
     Preferably, the pivoting clamping portion is employed as a lever with the pivot point functioning as a fulcrum for the lever. An applied force applied to the lever is multiplied at the knife to ensure that the knife is firmly held in place with a minimum amount of the applied force. 
     Therefore, it is a principal object of the present invention to provide a novel and improved knife holder for a chipper disc or the like and method. 
     It is another object of the present invention to provide such a knife holder and method that provides for increased ease of removing the knife from the knife holder. 
     It is yet another object of the present invention to provide such a knife holder and method that provides for removing the knife without removing other parts of the knife holder. 
     It is still another object of the present invention to provide such a knife holder and method that provides for holding the knife with increased firmness and with decreased applied force. 
     The foregoing and other objects, features and advantages of the present invention will be more readily understood upon consideration of the following detailed description of the invention, taken in conjunction with the following drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a pictorial, exploded view of the knife holder of FIG.  1 . 
         FIG. 2  is a cross-sectional view or a knife holder for a chipper disc or the like according to the present invention, in a position showing a knife being clamped. 
         FIG. 3  is a cross-sectional view of the knife holder of  FIG. 1 , in a position showing the knife being released. 
     
    
    
     DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT 
     A knife holder according to the present invention is particularly adapted for attachment to chipper or waferizer discs and drums for cutting wood chips or flakes from pieces of wood, such as whole logs, lumber and waste wood. The application, however, is not essential to the invention. 
     Referring to  FIG. 1 , a preferred, disc embodiment of the invention is shown. The knife holder  10  is adapted to receive an existing removable knife  12  which may have a number of different shapes. For receiving the knife  12 , the knife holder includes a top clamping portion  14  and a bottom clamping portion  16 . Each of the clamping portions is shaped to fit the knife. Particularly, the top clamping portion is shaped to fit a top surface  18  of the knife and the bottom clamping portion is shaped to fit a bottom surface  20  of the knife. 
     The top clamping portion  14  is rigidly attached to a base  50  by bolts  40 . The top clamping portion is seated on a ledge  26  so as to space the top clamping portion above the base. The bottom clamping portion  16  is disposed in the space provided between the top clamping portion and the base. 
     Turning to  FIGS. 2 and 3 , the knife holder  10  is shown in two states of operation, corresponding to two relative positions of the top and bottom clamping portions. In  FIG. 2 , in a clamping position of the clamping portions, the clamping portions clamp the knife. In  FIG. 3 , in an open position of the clamping portions, the knife is exposed for removal or cleaning. To provide for both states of operation, the bottom clamping portion  26  is adapted to pivot about a pivot point  22  on the base  50 , and to clamp the knife against the top clamping portion by this action. It should be understood throughout that the roles of the top and bottom clamping portions may be reversed without departing from the principles of the invention. 
     Pivoting of the bottom clamping portion  16  is driven by a clamping machinists  24 . The clamping mechanism is coupled to the top clamping portion  14  so that the clamping mechanism can translate with respect thereto. The clamping mechanism is connected to the bottom clamping portion with a suitable joint for maintaining the connection during translation of the clamping mechanism. 
     As illustrated in  FIGS. 2 and 3 , the pivot point  22  is preferably part of a rounded surface  23  of the base  50 , and the bottom clamping portion  16  preferably includes a complementary rounded surface  25 . Also as illustrated, preferably, the rounded surface  23  is circular and moves and the rounded surface  25  is circular and concave; however, one of ordinary skill in the art will readily appreciate that other curved surfaces could be employed as well as that the surfaces which are selected to be concave and convex could be reversed. As too be seen by comparing  FIGS. 2 and 3 , the surface  25  is disposed so as to make movable contact with the base  50 , preferably, sliding on the surface  23  in response to movement of the clamping mechanism  24 . 
     Preferably, the clamping mechanism  24  is threadingly received in a hole through the top clamping portion  14 . An end  28  of the clamping mechanism extends beyond the top clamping portion toward the bottom clamping portion  16 . The end  28  has a neck portion  30  that is received in a groove  32  (best seen is  FIG. 1 ) is the bottom clamping portion to form the aforementioned joint. Alternative constructions and configurations of the clamping mechanism and its coupling with the bottom clamping portion will be apparent to those of ordinary skill in the art. 
     Force applied by the clamping mechanism for pivoting the bottom clamping portion is provided through the end  28 . Threading the clamping mechanism so as to move it upwardly or downwardly in the top clamping portion  14  pulls or pushes a driving end  34  of the bottom clamping portion  16  in the same direction. 
     The bottom surface  20  of the knife  12  is received by a driven end  38  of the bottom clamping portion. In turn, the driven end moves in response to movement of the driving end  34 , preferably in the opposite direction as a result of pivoting of the bottom clamping portion  16  about the pivot point  22 . The top clamping portion  14  and the bottom clamping portion  16  clamp the knife therebetween in the clamping position of the clamping portions that provides a minimum spacing equal to the thickness dimension of the knife, as shown in FIG.  2 . In the clamping position of the clamping portions, the clamping mechanism is threaded into the top clamping portion and is disposed toward the base  50  a maximum amount. 
     As the clamping mechanism  24  is threaded out of the top clamping portion  14 , the clamping mechanism pulls the driving end  34  of the bottom clamping portion  16  away from the base. At a maximum amount of travel of the driving end  34 , a maximum space  48  is seated around the knife to permit access thereto for removal or cleaning. 
     Pinch-off surfaces  52  are provided-on the top and bottom clamping portions that are adapted to meet one another when the top and bottom clamping portions tie spaced the maximum relative amount. The meeting of the surfaces  52  serves two functions. First, in conjunction with the connection of the driving end  34  to the clamping mechanism  24 , this immobilizes the bottom clamping portion with respect to the top clamping portion, wedging the second clamping portion between the top clamping portion and the base, i.e., between the pinchoff surfaces and the pivot point  22 . This provides the outstanding advantage of allowing the knife to be removed without the need to hold or handle any of the other parts of the knife holder at the same time. A spring-biased plunger mechanism  51  is preferably also provided to ride the bottom clamping portion  16  during its travel and thereby control movement of the bottom clamping portion between the open and clamping relative positions. 
     A second function of the pinch-off surfaces  32  is that open space  46  that exists behind the knife is cut off from the space  48  for accessing the knife, so that objects within the space  48 , such as portions of the upper and lower clamping portions and the knife, can be cleaned without introducing debris into the open space  46 , which is generally difficult to clean. For example, the space  48  can be blown with compressed air without forcing debris into the open space  46 . The pinch-off surfaces, however, need not provide for both of the aforementioned functions. 
     Preferably, the bottom clamping portion  16  is configured as a lever for multiplying the force that is applied by the clamping mechanism  24  at the knife, to ensure that the knife  12  is firmly held with a minimum of force. In the geometry or  FIG. 1 , leverage is achieved by spacing the end  28  a greater distance from the pivot point  22  than is the knife  12 . 
     It is to be recognized that, while a specific knife holder for a chipper disc has been shown and described as preferred, other configurations could be utilized, in addition to configurations already mentioned, without departing from the principles of the invention. For example, while the pivot point  22  and the top clamping portion  14  are sufficiently rigidly disposed with respect to one another to enable the knife  12  to be firmly clamped firmly between the top and bottom clamping portions, this does not preclude some compliance between the pivot point and top clamping portion. Similarly, though the pinch-off surfaces  52  may provide for maintaining the top and bottom clamping portions in substantially fixed relationship to one another in the open position of the clamping members, the pinch-off surfaces may also be suitably compliant. Moreover, though it is preferable to provide that the driven end counterbalances the driving end about the pivot point  22 , this is not essential for practice of the invention. 
     The terms and expressions which have been employed in the foregoing specification are used therein as terms of description and not of limitation, and there is an intention of the use of such terms and expressions of excluding equivalents of the features shown and described or portions thereof, it being recognized that the scope of the invention is defined and limited only by the claims which follow.