Abstract:
An apparatus for feeding sheets of material, such as paper, sequentially from the bottom of a stack of sheets comprises a suction chamber, a perforated belt movable over the suction chamber, a sheet restraining gate above the downstream end of the suction chamber, and a roller to produce an upward corrugation in the bottom sheet only of the stack. The gap between the bottom of the gate and the belt is profiled to match the corrugation in the bottom sheet to enable the bottom sheet only to pass through. The profile preferably includes a shallow triangular recess in the bottom edge of the gate.

Description:
FIELD OF THE INVENTION 
     This invention relates to methods of and apparatus for feeding sheets of material sequentially from a stack, and is more particularly concerned with the separation and feeding of sheets from the bottom of a stack. 
     BACKGROUND OF THE INVENTION 
     Various forms of bottom feeder for stacks of sheet material, such as sheets of paper, are known. These include inter alia U.S. Pat. No. 5,797,597, U.S. Pat. No. 4,336,929, GB2137178A, GB2109352A, EP0459667, EP0446889 and EP0030410. In a number of these prior art machines, the stack of sheets is held in place by a restraining means and one has to adjust the height of the restraining means to define the size of a gap underneath it for the passage of a sheet in dependence upon the thickness of the sheets to be fed. That makes these machines very difficult to set up, as well as requiring readjustment of the restraining means each time that there is a change in the sheets which are to be fed. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a method of and apparatus for feeding sheets of material sequentially from the bottom of a stack in which the means of adjustment necessary in order to be able to feed sheets of different thickness through the mechanism is extremely simple. 
     It is a further object of the present invention to provide a bottom feeder which is substantially less costly than top feeders but which is reliable in operation and able to feed sheets of different thickness. 
     It is yet a further object of the present invention to provide a bottom feeder which will feed very thin paper right up to very thick card with only very simple adjustment being necessary. 
     In accordance with one aspect of the present invention there is provided an apparatus for feeding sheets of material successively from the bottom of a stack of sheets, comprising means defining a suction chamber, one or more perforated belts moveable over the suction chamber, means defining the position of a stack of sheets above the suction chamber so that the stack is in contact with the belt or belts, restraining means for the sheets of the stack positioned towards the downstream end of the suction chamber and arranged to define a gap between the bottom of the restraining means and the belt or belts, and means to produce an upward corrugation in the bottom sheet only of the stack in advance of the restraining means, wherein the profile of the gap is such as to permit the passage of the corrugated bottom sheet. 
     In accordance with another aspect of the invention there is provided a method of feeding sheets successively from the bottom of a stack of sheets, which comprises generating suction within a suction chamber, moving a perforated belt or belts around the suction chamber thereby to generate a suction force at the surface of the belt or belts, positioning a stack of sheets above the suction chamber in contact with the upper surface of the belt or belts, restraining the forward movement of the sheets towards the downstream end of the suction chamber by restraining means which defines a profiled gap between itself and the surface of the belt or belts, arranging for corrugation means to produce an upward corrugation in the bottom sheet only of the stack in advance of the restraining means, and generating an intermittent suction effect within the suction chamber, thereby to effect feeding of the corrugated bottom sheet of the stack through said profiled gap. 
     Preferably, the restraining means comprises a gate positioned towards and above the downstream end of the suction chamber which has the capacity for adjustment relative to the belt or belts but which does not need to be adjusted in accordance with the thickness of the sheets to be fed. The only adjustment which needs to be made to accommodate the feeding of sheets of different thickness is an adjustment of the corrugation means in terms of the amount of distortion it produces in the bottom sheet. 
     The corrugation means is preferably a roller within a single belt and which is capable of adjustment in a direction perpendicular to the direction of movement of the belt, in order to vary the profile of the belt. 
     Preferably, the restraining means is provided with a recess in a substantially linear bottom edge thereof, in alignment with the corrugation means. This recess is preferably in the form of a notch whose shape mimics the shape of the bottom sheet distorted by the belt. The combination of such a recess and the aligned corrugator means that just by varying the height of the corrugator and thus the amount of distortion of the belt, sheets of a wide range of thicknesses can be fed from the stack without misfeeds or double-feeds. This avoids the need both for repeated setting of the restraining gate and also for careful re-setting of the gap between the restraining gate and the underlying belt. 
     Preferably, to assist in the separation of the bottom sheet of the stack, and so that only the bottom sheet is held down against the belt, air is blown continuously at the sides of the stack, towards the bottom sheet. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In order that the invention may be more fully understood, embodiments of apparatus in accordance with the invention, and their method of operation, will now be described by way of example and with reference to the accompanying drawings. In the drawings: 
     FIG. 1 is a schematic side view of a first embodiment of feed mechanism in accordance with the invention; 
     FIG. 2 is a view of the restraining plate or gate in FIG. 1; 
     FIG. 3 is a schematic plan view of the feed mechanism shown in FIG. 1; and 
     FIG. 4 is a schematic representation of an alternative embodiment, shown in plan view. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the drawings, there is shown a feed mechanism, indicated generally at  10 , for the separation and onward feeding of the bottom sheet of a stack  11  of sheets of material. The feed mechanism comprises a suction chamber  14  which is defined by a housing  16  which has a drivable roller at each end, one roller  18  at the upstream end of the housing and the other roller  20  at the downstream end of the housing. The rollers  18  and  20  are rotationally driven by respective drive shafts  22  and  24 . A pipe  19  connects the housing to a source of suction  21 . Around the housing  16  and the rollers  18  and  20  and in contact therewith so as to be driven by the rollers is a belt  26  which is provided with rows of parallel equispaced perforations  27  as shown in FIG.  3 . The direction of movement of the belt  26  is indicated in FIG. 1 by arrows  25 . The housing  16  is provided with a plurality of parallel elongate slots  28  therethrough which are in alignment with the respective rows of perforations  27  in the belt, so that the creation of a suction effect within the suction chamber  14  will produce suction at the surface of the belt at the rows of perforations  27 . As shown, there are five rows of perforations on each side of the centreline of the belt, but only the outer four rows on each side overlie the suction slots  28 . 
     The suction chamber housing  16  incorporates a recess  29  in which is mounted a corrugating roller  30 , within the confines of the belt  26 . The roller  30  is carried on a pin  30   a  which is connected to a rotatable shaft  30   b . Manually or otherwise, the shaft  30   b  can be rotated, thereby to cause the pin and the roller  30  to rise or fall and the amount of protrusion of the roller  30  above the housing to increase or decrease. This movement is indicated by arrow  30   c  (FIG.  1 ), the movement being in a direction substantially perpendicular to the direction of movement  25  of the belt  26  as it passes above the roller. An endless tie or cable  31 , shown in FIG. 1 but omitted from FIG. 3, links the drive rollers  18  and  20  and the corrugating roller  30 , each being grooved as shown, to effect rotation of all three rollers. The purpose of roller  30  is to act as a corrugator, producing a distortion in the centre of the belt towards the downstream end of the upper run of the belt. The amount of protrusion of the roller  30  above the surface of the housing will cause varying amounts of distortion or corrugation of the belt and hence a greater or lesser effect on the central zone of the bottom sheet of the stack  11 . The roller  30  is positioned in relation to the upstream/downstream length of the belt approximately one third from the leading edge and two thirds from the trailing edge, as indicated by the dimensions a and b in FIG.  3 . 
     Above and towards the downstream end of the upper run of the belt  26 , there is provided a substantially vertical restraining plate  32  which extends the full width of the feed mechanism and which defines a gap  33  between the bottom edge of the plate  32  and the underlying belt  26 . The restraining plate  32 , which acts as a gate, is capable of adjustment movement in a vertical direction to vary the size of the gap  33 . As shown in FIG. 2, the restraining plate  32  is generally rectangular with a recess  34  in its otherwise substantially linear bottom edge  35 , at the centre, in alignment with the corrugating roller  30 . This recess  34  has the general shape of a shallow triangle and substantially mimics the shape of the bottom sheet of the stack  11  when it is distorted by the corrugated belt, so that it will pass therethrough and under the gate. It has been found that the combination of the corrugating roller  30  and the recess  34  enables the feeding of individual sheets through the gap. 
     Beyond the gap there is provided a pair of nip rollers  36 ,  38  which are arranged to grip the sheets as they are fed through the gap  33  and to deliver them onwards for further processing, as indicated by arrow  39 . 
     Means are provided to direct jets of air from each side of the feed mechanism towards the bottom sheet of the stack  11  of sheets to assist in its separation from the bottom of the stack. These air jets are indicated schematically at  40  in FIG.  3 . 
     In operation, a stack  11  of sheets is laid on the feed mechanism with the front edges of the sheets in contact with the restraining plate  32 . The position of the plate  32  is adjusted to set an appropriate gap  33  and the position of the roller  30  is then adjusted in relation to the housing in order to produce an amount of protrusion of the belt  26  which is appropriate for the particular type, e.g. thickness, density, material, of sheets which are to be fed by the mechanism. Then, air is blown towards the sides of the bottom sheet of the stack through jets  40  and the belt  26  is driven intermittently from drive shafts  22 ,  24  with the synchronised intermittent generation of suction within the chamber  14 . The bottom sheet of the stack  11  is attracted towards and is held down against the belt  26  by the suction, is separated from the remainder of the stack, is corrugated at its centre by the distortion in the belt, and is fed onwards through the gap  33  while the sheets above it are restrained by the plate  32 . Only the bottom sheet adapts to the profile of the belt; the other sheets are blocked. 
     If sheets of a different thickness or a different density or a different material then are to be fed by the mechanism, the only adjustment which is necessary is an adjustment of the height of the roller  30  to vary the amount of distortion of the belt  26 , i.e. its profile, so as to be appropriate for the replacement sheets. 
     Although the feed mechanism has been described with a single belt  26  and with a roller  30  acting against the inside of the belt, which is the preferred arrangement, an alternative arrangement would be to provide two or more separated, parallel belts, arranged symmetrically in relation to the roller  30 , and with the roller acting not against a belt but directly against the bottom sheet of the stack,i.e. between two belts. This is shown schematically in FIG.  4 . Two perforated belts  16   a ,  16   b  replace the single belt  16 , with the corrugating roller  30  set therebetween. The belts are driven by drive shafts  22   a ,  22   b ,  24   a ,  24   b . The setting of the corrugating roller  30  is adjustable by means of control rod  30   b.    
     Also, other forms of corrugator than a simple roller could be used. 
     The foregoing description of the invention has been given for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form described. Many modifications and variations are possible in the light of the teaching above. It is intended that the scope of the invention be defined by the claims appended hereto.