Abstract:
A method of stacking a veneer sheet carried by a conveyer onto a pile of similar veneer sheets is disclosed. Veneer sheet is separated from the conveyer thereby to allow the sheet to drop from the conveyer toward the pile. The veneer sheet being dropped is restrained by an elongated flexible member which is lowered substantially simultaneously with the above separation and at such a speed that the flexible member is brought into frictional engagement with the veneer sheet at at least one side thereof which extends in substantially perpendicular relation to the length of the elongated flexible member. The flexible member is lowered until it is bent in pressing engagement with the veneer sheet then dropped onto the pile at the above side thereof. An apparatus for performing the method is also disclosed.

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates to a method of stacking a sheet of wood veneer and also to an apparatus for performing the method. 
   According to a conventional veneer sheet stacking method which is performed during a process of manufacturing plywood panels using such veneer sheets, a veneer sheet (or a plurality of veneer sheets laid one on another) is carried by a conveyer having a suitable sheet support to a stacking position, where the support is operated to open thereby to release and allow the veneer sheet (or sheets) to drop onto a pile of similar veneer sheets. Since veneer for such stacking operation is provided in the form of a sheet having a large surface area for its mass or weight, the veneer sheet is easily subjected to the influence of air resistance when it is being dropped, so that it may not fall just straight onto the pile, but placed out of position on the pile, with the result that a disorderly pile of veneer sheets will be formed. During transferring veneer sheets of such a pile to a subsequent station for any further processing, the pile and hence veneer sheets therein are susceptible to damage. 
   An apparatus which addressed such problem is proposed by Examined Japanese Utility Model Application Publication No. S52-22062, which is shown in  FIG. 8 . Reference numeral  73  on the drawing designates an endless conveyer which is operable to transfer a veneer sheet  71  in arrow direction toward the stacking apparatus. The stacking apparatus, which is generally designated by  75 , is located adjacent to the downstream end of the conveyer  73  as seen in the conveying direction of veneer sheet  71 . The stacking apparatus  75  has a plurality of perforated endless belts  77  (only one being shown in  FIG. 8 ) which are operable to hold a veneer sheet by suction or vacuum and movable in arrow direction to carry such veneer sheet to the stacking position that is located immediately above a pile of veneer sheets  89  placed on a support block  81 . Reference numeral  79  depicts a suction device  79  disposed in contact with the upper surface of the bottom horizontal legs of the perforated endless belts  77  for creating vacuum for holding the veneer sheet  71 . 
   The stacking apparatus  75  further has a separating bar  83  which is usually made of steel and movable vertically reciprocally as indicated by double-headed arrow by a linkage  85  which is moved by a rotatable eccentric wheel  87  driven by a motor (not shown). The bar  83  separates veneer sheet  71  from the perforated endless belts  77  thereby to allow the veneer sheet  71  to fall toward the pile  89 . As is apparent from the drawing, the separating bar  87  makes one stroke of reciprocating motion by one complete turn of the eccentric wheel  87 . 
   Between any two adjacent belts  77  is provided a restraining band  91  having one end thereof fixed at a position that is higher than the bottom horizontal legs of the perforated endless belts  77 . As shown in  FIG. 8 , the restraining band  91  droops by its own weight such that a majority part of the band  91  rides on the top veneer sheet in the pile  89  with the distal free end of the band  91  located adjacent to the downstream end of the bottom horizontal legs of the endless belts  77 . Reference numeral  93  designates a sensor for detecting the arrival of a veneer sheet which has been conveyed by the belts  77  to the aforementioned stacking position immediately above the pile of veneer sheets  89 . Though not shown in the drawing, the support block  81  has a suitable means such as hydraulic cylinder for elevating the stacking block  81  in response to a signal generated by a sensor such photocell operable to detect the top position of the pile  89  so that the top of the pile  89  always maintains a predetermined height. 
   In operation of the apparatus, a veneer sheet  71  moved forward by the conveyer  73  is picked up and held by the endless perforated belts  77  under the influence of vacuum developed by the suction device  79  and further conveyed. In the meantime, the veneer sheet  71  is brought into contact with the restraining band  91  and moved further under and in contact with the restraining band  91  until the leading end of the moving veneer sheet  71  is detected by the sensor  93 , which then generates a detection signal. In response to the signal, the motor is activated thereby to operate the separating bar  83  so as to make one complete stoke of up and down movement as indicated by double-headed arrow. Thus, the veneer sheet  71  is separated and dropped off from the belts  77  together with the band  91  then riding on the veneer sheet  71 . Because of the frictional force between the restraining band  91  and the veneer sheet  71  due to the weight of the former riding on the latter, the veneer sheet  71  is dropped substantially vertically straight without swerving or swaying and. Therefore, the veneer sheet  71  is stacked in an orderly manner onto the pile  89 . 
   In the above-described prior art apparatus, the force acting on the veneer sheet  71  in downward direction is provided by the weight of the restraining band  91  (to be more precise, the downward force is actually smaller than the weight of the band  91  because the veneer sheet  71  is then being dropped). If the weight of the restraining band  91  is small, however, the frictional force between veneer sheet  71  and the restraining band  91  is reduced and the veneer sheet  71  cannot be prevented from making irregular movement while it is being dropped. If the weight of the restraining band  91  is increased with an attempt to restrain the movement of the veneer sheet  71 , a force of greater magnitude is applied to the veneer sheet  71  when it is brought into contact with and moved under the restraining band  91  having an increased weight. As a result, the veneer sheet  71  may change its posture or be subjected to a damaging force while it is being moved by the belts  77 . 
   Apart from the prior art apparatus of the aforementioned publication, another apparatus is known in the art in which a veneer sheet carried forward by a conveyer belt such as the belt  77  is separated therefrom by rapidly moving a bar which is similar to the bar  83  but operable to move to force a veneer sheet downward until it is pressed against the top veneer sheet in the pile. The bar is usually made of a rigid material such as steel. When the number of veneer sheets in the pile is still small, the bar may receive a damaging shock of impact when the veneer sheet is pressed by the bar against the top of the pile placed on a stacking block which is also made of a rigid material. 
   SUMMARY OF THE INVENTION 
   The present invention has been made in view of the above drawbacks and, therefore, an object of the present invention is to provide a method of stacking veneer sheets and an apparatus of practicing the method. 
   In order to achieve the object, the present invention provides a method of stacking a veneer sheet carried by a conveyer onto a pile of similar veneer sheets. According to the method, the veneer sheet being carried by the conveyer is separated therefrom at a stacking position in the apparatus that is located immediately above the pile of veneer sheets thereby to allow the separated veneer sheet to fall or drop from the conveyer. The veneer sheet being dropped is restrained by an elongated flexible member which is normally disposed extending above and without interfering with the veneer sheet being carried by the conveyer. That is, the elongated flexible member is operable to be lowered by any suitable means such as air cylinder substantially simultaneously with the separating of the veneer sheet in a taut state and at such a speed that the flexible member is brought into frictional engagement with the veneer sheet at at least one side thereof which extends in substantially perpendicular relation to the length of the elongated flexible member thereby to restrain the veneer sheet being dropped from the conveyer. The elongated flexible member is lowered until it is bent at the aforementioned one side of the veneer sheet which is then dropped onto the pile of veneer sheets, thereby to restrain the veneer sheet. 
   The apparatus of stacking a veneer sheet according to the present invention includes a conveyer for carrying the veneer sheet in a predetermined direction. The conveyer may be in the form of an endless belt having a number of piercing spikes extending outward from the belt and pierceable through a veneer sheet for supporting or holding the veneer sheet. Adjacent to the conveyer is provided means for separating the veneer sheet from the conveyer at a position that is immediately above the pile of veneer sheets thereby to allow the separated veneer sheet to drop from the conveyer; 
   The apparatus further includes an elongated flexible member and means for moving the elongated flexible member between the standby position thereof where the flexible member is disposed extending above and without interfering with the veneer sheet carried by the conveyer and the lowered position thereof where the elongated flexible member is lowered until being bent in pressing engagement with the veneer sheet then dropped onto the pile of veneer sheets at at least one side of the veneer sheet which extends in substantially perpendicular relation to the length of the elongated flexible member. The moving means, which is an air cylinder in the preferred embodiment of the invention, is operable to cause the elongated flexible member to be lowered toward the lowered position in a taut state and at such a speed that the flexible member is brought into frictional engagement with the veneer sheet being dropped. 
   In the apparatus, a sensor is provided for detecting the arrival of the veneer sheet at the above predetermined position and it is operable to generate a detection signal. The detection signal is transmitted to a control which is operable in response to such detection signal to activate the separating means and the air cylinder as the moving means so that the veneer sheet is separated from the conveyer and substantially simultaneously the elongated flexible member is lowered toward the lowered position. 
   In the preferred embodiment of the present invention, the elongated flexible member in the standby position thereof extends substantially in the direction in which the veneer sheet is carried by the conveyer, and the air cylinder is located and operable such that the elongated flexible member in the lowered position thereof is bent in pressing engagement with the veneer sheet at the side thereof which corresponds to the leading end or side of the veneer sheet as seen in the direction in which the veneer sheet is moved by said conveyer. In this embodiment, the elongated flexible member is connected at one end thereof to the extensible rod of the cylinder. 
   In another embodiment of the invention, the elongated flexible member is connected at the opposite ends thereof to the rods of cylinders, so that the flexible member in the lowered position thereof is bent in pressing engagement with the veneer sheet at two sides thereof which correspond to the leading and trailing ends or sides of the veneer sheet as seen in the direction in which the veneer sheet is moved by said conveyer. 
   In the arrangement wherein the elongated flexible member is connected at the opposite ends thereof to any part of the stationary frame of the apparatus, the moving means is a cylinder having an extensible rod with a roller at the distal end thereof and operable to move by way of the roller the elongated flexible member to its lowered position. 
   Features and advantages of the present invention will become more apparent to those skilled in the art from the following description of preferred embodiments of the invention, which description is made with reference to the accompanying drawings, wherein: 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic side view showing a preferred embodiment of veneer sheet stacking apparatus according to the present invention; 
       FIG. 2  is a partially sectional view of the veneer sheet stacking apparatus as seen from line X—X of  FIG. 1 ; 
       FIG. 3  is an illustrative partial side view showing the operation of the apparatus of  FIG. 1 ; 
       FIG. 4  shows a modified embodiment of veneer sheet stacking apparatus of the present invention; 
       FIG. 5  is an illustrative partial view showing the operation of the apparatus of  FIG. 4 ; 
       FIG. 6  shows a further modified embodiment of veneer sheet stacking apparatus of the present invention; 
       FIG. 7  is a schematic illustrative view showing the operation of the apparatus of  FIG. 6 ; and 
       FIG. 8  is a schematic side view showing a conventional veneer stackaing apparatus. 
   

   DETAILED DESCRIPTION OF THE EMBODIMENTS 
   The following will describe a preferred embodiment of veneer sheet stacking apparatus of the present invention with reference to  FIGS. 1 through 3 . 
   Referring to  FIG. 1 , there is provided a conveyer  3  for advancing veneer sheets  1  successively (only one sheet being shown in the drawing) in arrow direction at a spaced interval toward a veneer stacking apparatus which is generally designated by “A”. The veneer sheet  1  is of a rectangular or quadrilateral shape having four sides. 
   Referring to  FIGS. 1 and 2 , the stacking apparatus A has a pair of endless spiked conveyer belts  9  spaced apart in the direction that is perpendicular to the direction in which veneer sheet  1  are moved by the conveyer  3 . Each endless spiked conveyer belt  9  is trained around a positively driven pulley  11  and other three idle pulleys  13  so as to be driven to move constantly in arrow direction indicated at the top leg of the belt  9  at substantially the same speed as the conveyer  3 . The endless belt  9  has a number of pikes or tooth-like projections  7  extending outwardly therefrom and spaced at a predetermined interval for piercing through the veneer sheet  1  as shown most clearly in  FIG. 2  thereby to carry the veneer sheet  1  pierced by the spikes  7  to a stacking position immediately above a pile of veneer sheets  25  formed on a stacking block  5 . 
   The stacking apparatus A further has a pair of parallel bars  15  extending along and adjacent to the bottom legs of the respective endless spiked conveyer belts  9  for separating the pierced veneer sheet  1  from the endless spiked conveyer belts  9 . Each separating bar  15  is connected to rods  17   a  of a pair of air cylinders  17 , as shown in  FIG. 1 . The rods  17   a  of the air cylinders  17  and hence the separating bars  15  connected thereto are normally placed at their raised or standby position, as shown by solid lines in  FIGS. 1 and 2 , where a veneer sheet  1  held by the spikes  7  of the conveyer belts  9  can move below the separating bars  15 . The air cylinders  17  are operable such that their rods  17   a  make one stroke of rapid reciprocating movement between the retracted and extended positions thereof for a length of stroke that is long enough for the veneer sheet  1  held by the spiked conveyer belts  9  to be pressed by the separating bars  15  and released from pierced engagement with the spikes  7  of the belts  9 . The lowered position of the separating bars  15  are indicated by dotted lines in  FIG. 2 . The air cylinders  17  are operatively connected to a control  29  of the stacking apparatus A. 
   An elongated flexible band  19  is disposed extending in the same direction as the veneer sheet  1  is conveyed by the endless spiked belts  9 . To be more specific, the elongated flexible band  19  extends between the paired separating bars  15 , one end of which adjacent to the conveyer  3  is fixed to part  21  of the frame of the apparatus and the other end of which is connected to distal end of a piston rod  23   a  of an air cylinder  23 , for restraining a veneer sheet when it is being dropped off from the endless spiked conveyer belts  9  and also when it is dropped onto the pile  25 , as will be described more in detail in later part hereof. With the rod  23  retracted in the air cylinder  23 , the flexible restraining band  19  is disposed extending substantially horizontally in the direction in parallel to the bottom legs of the endless paired belts  9  and above the veneer sheet  1  being carried by the spiked conveyer belts  9  so that no interference occurs between the flexible restraining band  19  and the veneer sheet  1 , as shown in  FIG. 1 . In the illustrated embodiment, the elongated flexible restraining band  19  has such a length that the band  19  is taut or has an appropriate tension when it is extended as shown in  FIG. 1 . 
   The rod  23   a  is normally placed in its retracted position in the air cylinder  23  as shown in  FIGS. 1 and 2 . When the air cylinder  23  is operated, the rod  23   a  makes one stroke of reciprocating movement between the retracted position and the extended position ( FIG. 3 ) where end portion of the flexible restraining band  19  connected to the rod  23   a  is lowered to a position below the top surface of veneer sheet pile  25  on the stacking block  5  so that the band  19  is then bent at and pressed against the edge of the veneer sheet  1  then dropped onto the pile  25  as shown in  FIG. 3 . It is noted that the air cylinder  23  is operable to cause its rod  23   a  to move downward at a speed faster than a speed at which an object is dropped by its own weight so that the flexible restraining band  19  is brought into frictional or pressing engagement with the veneer sheet one side thereof which extends in substantially perpendicular relation to the length of the restraining band  19  thereby to restrain the veneer sheet that is being dropped off from the conveyer. As shown in  FIG. 1 , the air cylinder  23  is also connected to the control  29 . 
   Reference numeral  27  designates a sensor of reflective type photoelectric tube for detecting the arrival of a veneer sheet moved by the endless spiked conveyer belts  9  at the stacking position immediately above the pile of veneer sheets  25 . The sensor  27  is connected to the control  29  so that a detection signal developed by the sensor  27  is transmitted to the control  29 . 
   The following will describe the operation of the above veneer sheet stacking apparatus A. As described earlier, the separating bars  15  are normally placed in their raised inoperative or standby position by the air cylinders  17  and the rod  23   a  of the air cylinder  23  is in its retracted position so that the flexible restraining band  19  extends substantially horizontally in its standby position, as shown in  FIGS. 1 and 2 . 
   A veneer sheet  1  placed on the conveyer belt  3  is moved forward or rightward as seen in  FIG. 1 . As the veneer sheet  1  has moved to a position on the conveyer belt  3  adjacent to the spiked conveyer belts  9 , it is pierced by the spikes  7  of the belts  9  and carried forward by the spiked conveyer belts  9  in piercing engagement therewith. When sensor  27  detects the arrival of the veneer sheet  1  at the stacking position in the apparatus, the sensor  27  generates a detection signal to the control  29 , which is then operated to transmit a control signal to the air cylinders  17 . Accordingly, the separating bars  15  connected to the rods  17   a  of the air cylinders  17  make a reciprocating movement, so that the bars  15  are pressed against the veneer sheet  1  thereby to release the sheet from pierced engagement with the spiked conveyer belts  9  during the extending movement of the rods  17   a.    
   Substantially simultaneously with the operation of the air cylinders  17  for the separating bars  15 , the control  29  responding to the detection signal from the sensor  27  transmits a signal to activate the air cylinder  23  so that its rod  23   a  is moved reciprocally. During this movement of the rod  23   a , the flexible restraining band  19  having one end thereof connected to the rod  23   a  is lowered to a position, as shown in  FIG. 3 , where the restraining band  19  is bent at and placed in pressing engagement with one side of the veneer sheet  1  which extends in substantially perpendicular relation to the length of the restraining band  19  or, in the case of the illustrated embodiment, the side which correspond to the leading end thereof as seen in the direction in which the sheet is moved by the conveyer belts  9 . 
   Though not shown specifically in the drawing, since the air cylinder  23  is operable to cause its rod  23   a  to move downward at a speed faster than that at which an object is dropped by its own weight, the flexible restraining band  19  is brought into frictional or pressing engagement with the veneer sheet at the above side or end, thus restraining the veneer sheet that is being dropped off from the conveyer. As a result, the veneer sheet  1  after being released from pierced engagement with the spiked conveyer belts  9  falls straight downward in frictional or pressed engagement with the flexible restraining band  19  and stacked onto the pile  25  in an orderly manner, as shown in  FIG. 3 , without making swerving or swaying motion due to the influence of air resistance before being dropped onto the pile  25 . 
   After the rods  17   a  of the air cylinders  17  the rods  23   a  of the cylinders  23  have moved back to their retracted positions, the apparatus A waits for stacking of the next veneer sheet. 
   As apparent to those skilled in the art, since the mass of the band  19  is small, only a small force is necessary to move the band rapidly enough to stack veneer sheets neatly and, therefore, small-sized air cylinders may be used for the cylinders  23 . Additionally, the embodiment can solve the aforementioned problem that a separating bar made of rigid material such as steel receives a damaging shock of impact when the bar is moved into pressing contact with the top of the pile having only a small number of veneer sheet. The magnitude of the frictional force between the flexible restraining band  19  and the veneer sheet  1  can be changed by varying the lowering speed of the restraining band  19 , which can be accomplished merely by controlling the amount of air to be supplied to the air cylinder  23 . 
   Referring to  FIGS. 4 and 5 , the following will describe a modified embodiment of veneer sheet stacking apparatus of the present invention. 
   The modification of  FIGS. 4 and 5  differs from the embodiment of  FIGS. 1 through 3  in that an additional air cylinder  23  is provided in place of the aforementioned part  21  of the frame of the apparatus of  FIG. 1 , so that the flexible restraining band  19  is connected at the opposite ends thereof to the distal ends of the rods  23   a  of the air cylinders  23 . In operation of this stacking apparatus of  FIG. 4 , as the arrival of the veneer sheet  1  moved by the endless spiked conveyer belts  9  at the stacking position in the apparatus is detected by the sensor  27 , the air cylinders  17  are activated to move their rods  17   a  and hence the separating bars  15  downward thereby to separate the veneer sheet  1  from pierced engagement with the spiked conveyer belts  9 . Substantially simultaneously, the air cylinders  23  are also activated to extend their rods  23   a  until the restraining band  19  is bent and presses veneer sheet  1  along the entire dimension thereof as measured along the extension of the flexible restraining band  19 , as well as at the opposite sides or ends of the veneer sheet  1 , as shown in  FIG. 5 . Both air cylinders  23  are operable to extend their rods  23   a  at a rapid speed as in the embodiment of  FIGS. 1 through 3  and, therefor, the flexible restraining band  19  is brought into frictional engagement with the veneer sheet being dropped on the top surface of the veneer sheet  1 , as well as at the opposite sides thereof, thus restraining the veneer sheet that is being dropped off from the conveyer. Thus, the veneer sheet  1  after being released from the separating bars  15  is moved straight downward the pile  25  while maintaining the frictional or pressed frictional engagement with the restraining band  19 . 
   A still another modified embodiment of veneer sheet stacking apparatus of the present invention will be described while having reference to  FIGS. 6 and 7 . 
   In the foregoing embodiment shown, for example, in  FIG. 3  wherein one end of the flexible restraining band  19  is directly connected the distal end of the rod  23   a  of the air cylinder  23 , the cylinder  23  and its rod  23   a  are subjected to a horizontal component of a force which is developed due to the tensile force of the flexible restraining band  19  each time the cylinder  23  is operated to extend its rod  23   a . It is thus necessary for the air cylinder  23  to be mounted firmly enough to resist such force. The modified embodiment shown in  FIGS. 6 and 7  differs from the foregoing embodiments in that the flexible restraining band  19  is not connected to the piston rod  23   a . As shown in  FIG. 6  which show only the relevant part of the apparatus for the sake of description of the modification, the elongated restraining band  19  is connected at the opposite ends thereof to the frame  21  of the apparatus and the air cylinder  23  having a freely rotatable roller  31  at the distal end of the cylinder rod  23   a  is disposed above the restraining band  19  with the roller  23  normally placed in contact with the upper surface of the restraining band  19 . In operation of the apparatus of this modified embodiment, the air cylinder  23  is activated to extend its rod  23   a  and the restraining band  19  is moved downward through he roller  31 , as shown in  FIG. 7 . By using the roller  31  in stead of connecting the restraining band  19  to the rod  23   a , the air cylinder  23  and its piston rod  23   a  will not be subjected to the above-described horizontal component of a force. 
   It is noted that the apparatus of present invention can be further modified or changed in various ways within the spirit of the invention, as exemplified below. 
   In the foregoing embodiments, the flexible restraining band  19  is so arranged that it has an appropriate tension in its inoperative standby position where the rod  23   a  is retracted in its associated air cylinder  23 . However, the restraining band  19  does not necessarily have to be tensioned while it is in inoperative state, but it is tensioned when it is lowered in frictional engagement with a veneer sheet. 
   Though the foregoing embodiments have been described as applied to a method or an apparatus for stacking one veneer sheet at a time, it may be so arranged that two or more veneer sheets which are laid one on another are stacked simultaneously to a pile of veneer sheets. 
   Though the elongated flexible restraining band  19  of the foregoing embodiments is disposed in parallel to the direction in which the veneer sheet is moved by the spiked conveyer belts  9 , one or more restraining bands may be provided in perpendicular relation to the above direction and the air cylinders for moving the band may be arranged, accordingly. Additionally, the flexible restraining band  19  may be substituted by other members such as string, cord or chain which can resist the tension developed during the stacking operation according to the present invention. 
   The flexible restraining band  19  in its standby position need not be horizontal, but it may extend with such a downward slant toward the downstream end of the restraining band  19 , as seen in the moving direction of the veneer sheet  1  carried by the spiked conveyer belts  9 , that no physical interference occurs between the incoming veneer sheet  1  and the restraining band  19 . 
   The endless spiked conveyer belts  9  may be stopped temporarily when the veneer sheet  1  is detected by the sensor  27  at the stacking position and the separating bars  15  may be operated during such temporary stop of the spiked conveyer belts  9 . 
   The spiked conveyer belts  9  for carrying a veneer sheet to the stacking position may be substituted by any suitable conveyer belt having a suction device  79  as shown in  FIG. 8 .