Abstract:
Apparatus request for debarking logs comprising a generally horizontal rotary drum debarker having an inlet end, power drive device for continuously rotating the drum of the debarker generally about a horizontal axis, generally horizontal main conveyor element for conveying groups of tree length logs toward the drum, the main conveyor element having a discharge end below the axis of rotation of the drum, drive apparatus for continuously driving the main conveyor element, and auxiliary feed mechanism below the axis of rotation of the drum and between the discharge end of the main conveyor element and the inlet end of the drum for assisting the movement of groups of logs fed by the main conveyor element into the inlet end of the drum. The questions raised in reexamination request No. 90/003,655, filed Dec. 7, 1994, 90/003,826 filed May 8, 1995, and 90/004,552 filed Feb. 12, 1997 have been considered and the results thereof are reflected in this reissue patent which constitutes the reexamination certificate required by 35 U.S.C. 307 as provided in 37 CFR 1.570(e).

Description:
The present invention relates to a method and apparatus for debarking logs. More particularly, the invention hod and apparatus for debarking tree length logs for efficient high yield further processing to obtain high grade wood chips, or good lumber of substantial lengths, but which can also be used to debark logs of virtually any length. 
     BACKGROUND OF THE INVENTION 
     The most efficient and economical way to debark logs is with the horizontal drum debarker. The drum debarker has a continuously rotating drum which rotates groups of logs so they rub against each other to remove the bark from the logs without any appreciable wear to the drum. To obtain good debarking efficiency, at least several logs must be in the same axial region of the drum, so they can rub against each other to remove the bark. The logs are usually fed into the drum in a continuous stream of groups of logs from an elevated curved hopper at one end of the drum and slide by gravity into the drum. 
     A hopper dimensioned to feed groups of relatively short logs of up to perhaps fifteen feet in length into the drum, does not work well with longer logs. Very long logs such as tree length logs, tend to jam and are bent by the hopper and drum when their lower ends enter the drum and the logs begin to rotate while their upper ends are still above the hopper inlet. Long logs in this position are rotated by the drum and are often damaged by rubbing against the hopper inlet, and the resultant reverse bending sometimes causes such long logs to break. 
     While it may be possible to efficiently debark tree length logs by using a much larger hopper, such a hopper would be very high and difficult to feed logs into, the hopper would be quite expensive, and shorter logs would not feed efficiently through such a larger hopper. 
     Thus, is has been necessary in the past to cut or slash tree length logs to shorter debarking length, before feeding the logs into the hopper. However, the saw used for cutting or slashing logs is costly to install and maintain, and there is some kerf i.e., blade width loss when logs are cut with a saw. 
     Other disadvantages of shorter logs is that there are more ends, which are subject to brooming, shorter logs often tumble in the debarking drum which causes more end damage, and shorter logs are less efficiently chipped, and yield less usable lumber. 
     On the other hand, debarked tree length logs provide a higher yield of usable lumber, and a higher yield of high quality uniform size chips for pulp can also be obtained from debarked tree length logs. 
     The problem has been that there was previously no efficient reliable way to debark tree length logs with a drum barker. 
     In addition to directing relatively short logs into the drum, the hopper for such logs performs a containment function on the logs entering the drum. As the leading ends of the logs enter the continuously rotating drum and engage the inside of the drum, the logs begin to rotate while they are partly in the hopper. Such rotation sometimes causes additional rotation of upstream logs in the hopper by friction, and often causes a somewhat violent whipping motion of the logs entering the drum, which is restricted and contained by the upstream logs in the hopper and the thick walls of the hopper. 
     It has been proposed to feed tree length logs into a debarking drum with a nearly horizontal conveyor. To obtain efficient debarking, the tree length logs must be fed in groups of stacked or side by side logs. The problem with this technique is that the very long logs, perhaps sixty feet in length, begin to rotate and tumble soon after their leading ends enter the drum, while substantial lengths of the logs are still on the conveyor. The rotating and flailing motion of the logs can cause severe damage to the conveyor chain, and the trailing ends of logs leaving the conveyor can catch on and can be grabbed by the downwardly and rearwardly moving return portion of the conveyor. This can cause the trailing end of a log to be pushed down and pulled rearwardly so that the log jams in the chain while its leading end is whipped around by the drum. While the conveyor chain is quite strong and can support and move groups of heavy logs, localized stress in individual links caused by impact, or by grabbing a log at the nose end of the conveyor can damage the chain. 
     A further problem is that logs partly in the drum which are rotating tend to rotate trailing logs on the conveyor by friction. 
     There is therefor, a need for an efficient and reliable technique and apparatus for debarking logs of virtually any length, including tree length logs, in a rotating drum debarker. 
     SUMMARY OF THE INVENTION 
     In accordance with the invention a method and apparatus is provided for continuously debarking tree length logs in a rotary drum debarker, without danger of damage to the conveyor chain, and which is efficient, reliable, and quite economical. 
     This is accomplished by using a somewhat conventional chain conveyor, and providing an auxiliary feed means in the form of a conveyor or low friction feed region between the nose or head end of the chain conveyor and the debarking drum inlet, to avoid damage to the conveyor chain, while continuously feeding stacks or groups of any length logs, into the continuously rotating debarking drum. 
     The purpose of the auxiliary feed means or low friction region is to shield the head end of the main conveyor and to provide a region between the main conveyor and the drum inlet where there is minimal binding or jamming of trailing ends of logs being rotated by the drum. 
     In accordance with one aspect of the invention, the auxiliary feed means is a very rugged auxiliary conveyor located between the head end of the chain conveyor and the inlet of the debarking drum. In a preferred embodiment, this auxiliary conveyor is a feed roller driven independently of the conveyor chain, so that it can be driven at any desired surface speed i.e. the same as or faster or slower than the surface speed of the conveyor chain. 
     In accordance with another aspect of the invention, a short low friction region is provided between the conveyor and the inlet of the drum debarker. This region can be composed of one or more rotatable rollers. 
     In accordance with another aspect of the invention, a forward region of the main conveyor is provided with smooth upright sidewalls of a sufficient height to contain the trailing ends of the logs partly in the debarking drum, so the whipping motion of the logs is minimized. without hampering the forward movement of the logs into the debarking drum. A sidewall height higher than the elevation of the centerline of the debarking drum is usually necessary, but this height can be lower than the height of the top of the drum for construction economy. 
     A distinct advantage of the apparatus is that the conveyor has an open top along its entire length, so that the entire length of the conveyor is available for overhead loading of logs to be debarked. At the forward or head end of the conveyor, adjacent the debarking drum inlet, is a drum end protector plate, having an opening therein of a diameter slightly less than the inner diameter of the drum and which prevents the leading ends of the conveyed logs from impacting against the inlet end of the drum. Structural elements which extend over the head end of the conveyor are provided for securing the protector plate, but these elements are adjacent the inlet of the debarking drum and do not interfere with overhead loading of logs on the conveyor. 
     Accordingly, it is an object of the invention to provide a method and apparatus for continuously debarking tree length logs in a rotating drum debarker, by continuously feeding groups of tree length logs generally axially into the drum with a continuously driven main conveyor, and along a low friction region or auxiliary feed means between the discharge end of the main conveyor and the inlet of the drum. 
     Another object is a method and apparatus according to the above object in which the auxiliary feed means is an auxiliary conveyor. 
     Another object is a method and apparatus in which the auxiliary feed means is a low friction region having at least one rotatable roller. 
     Another object is a method and apparatus in which the auxiliary feed means is a rugged roller driven in rotation. 
     A further object is a method and apparatus in which the auxiliary feed means is a robust roller power driven independently of the main conveyor. 
     A further object is an apparatus according to one or more of the above objects, in which the top of the apparatus is open and unobstructed for loading logs or timber onto the apparatus along substantially its entire length. 
     A further object is an apparatus according to one or more of the above objects, in which the low friction region or auxiliary conveyor occupies only a short longitudinal region between the main conveyor and the inlet of the drum. 
     An additional object is a method and apparatus according to one or more of the above objects in which the sidewalls of the conveyor are smooth and upright to minimize the tendency for rotating logs partly in the drum to roll up or climb up the walls of the conveyor. 
     Other objects and advantages of the invention will become apparent from the drawings and the description which follows which are given as non limiting examples. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic side view in elevation of the system and apparatus of the invention; 
     FIG. 2 is an enlarged view looking along lines  2 — 2  of FIG. 1, and shows the structure of the head or discharge end of the main conveyor; 
     FIG. 3 is an enlarged view looking along lines  3 — 3  of FIG. 1, and shows a first embodiment of low friction means in the form of a driven roller; 
     FIG. 4 is an enlarged view looking along lines  4 — 4  of FIG. 1, from the position of an observer at the inlet of the debarking drum; 
     FIG. 5 is an enlarged partial view in side elevation of the apparatus in the region of the head end of the conveyor, and shows the driven roller and its mounting; 
     FIG. 6 is a side view of a second form of driven roller; and 
     FIG. 7 is a view corresponding to FIG. 5, and showing a second embodiment of low friction means in the form of rotatable rollers. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 shows, according to the invention, a log feeding assembly  10  for continuously feeding groups of logs into a drum debarker  14 . The feeding assembly  10  includes a main conveyor  12 , and a low friction region in the form of an auxiliary conveyor  16 , which is between the discharge end  18  of the main conveyor  12  and the inlet end  22  of the drum debarker  14 . 
     The drum debarker  14  is of conventional construction and includes a drum  24  which rotates about an essentially horizontal axis  25 , being supported in a cradle of rollers or tires  26 , which are driven by a variable speed hydraulic motor  28  to drive the drum in rotation. It is preferred to use a drum  24  which is cylindrical and of uniform inside diameter from its inlet end  22  to its outlet end  32 . 
     Main conveyor  12  has a conveying chain  34  which runs along a bed  36  between a headspool  38  at the discharge end  18  of the conveyor, and a tailspool  40  at the upstream end of the conveyor. Chain  34  has a return portion  42  beneath the conveyor bed, and extends around a drive sprocket  44  and a chain take-up spool  46  mounted on an hydraulic cylinder  48 , so that the spool  46  can be extended and retracted to vary the tension in the return run  42  of the chain. Drive sprocket  44  is chain driven by a speed reducer  52 , which is belt driven by a reversible electric drive motor  54 . This drive arrangement enables the conveyor to be driven in reverse, if required. 
     As shown in FIGS. 1 and 2, a front series  58  of assembly  10  has sloping trough position  60  and high upright sides  62  which extend to the front  64  of the feed assembly  10 . The sloping trough portions extend the entire length of the assembly. The high sides  62  decrease in height at  65 , and merge with lower upright sides  66  that extend along the rearward section  67  of the main conveyor. The sloping trough portions  60  and the sides  62  and  66  are made of steel plate to provide smooth inner surfaces along which the logs can slide. As shown in FIG. 2, the steel plate is supported by structural elements such as I beams  68 , to which the plate is welded. Lengths of circular pipe  69  (FIG. 2) are fixed at the top ends of the sides, along the entire length of the assembly  10  to minimize damage to, and catching of logs along the top of the assembly. 
     In the installation shown, where the debarking drum is on the order of 11 feet in diameter, and 60 feet long, assembly  10  is 60 feet long, with the front section  58  being 20 feet long, and the rearward section  67  whose sides merge upwardly into the front section at  65 , being 40 feet long. The sides  62  extend upwardly to an elevation somewhat higher than the axis  25  of the drum  24 , and in the embodiment shown, are only slightly lower than the top of the debarking drum  24 . The top of the log feeding assembly  10  is open and unobstructed along its length, except at the very front  64 , so that logs can be loaded directly onto the assembly from any position along the length of the assembly. 
     As shown at FIG. 2, the main conveyor has four chains  70 . These chains extend around and are guided by the sides of cylindrical portions  72  of the headspool  38 , when the links  73  engage the slightly smaller diameter cylindrical portions  74  of the headspool. The upper surface  75  of the conveyor bed  36  is smooth and flat, so the chains can slide along the conveyor bed between the guide bars  76 . 
     FIGS. 3 and 5 show one embodiment of auxiliary feed means  16  in the form of a driven cylindrical roller  78  with a smooth exterior surface. Roller  78  is of fabricated construction and includes a cylindrical shell  80  internally reinforced with spaced apart circular disks  82  welded to the inside of the shell, and a shaft  84  keyed to one or more of the disks. Shaft  84  is mounted in bearing blocks  86 , and an hydraulic drive motor  88  is coupled to one end of shaft  84  by a flexible coupling  90 . The hydraulic motor  88  is fixed to and supported by a torque arm  92  which has a flat plate upper portion  93 , secured to a downwardly extending tubular arm  94 , the lower end of which is clamped between clamp plates  95  of a rubber containing shock unit  96  secured to a structural column  97  of the assembly. As shown at FIG. 5, the hydraulic motor  88  has a circular mounting flange  100  which is bolted to the upper portion  93  of the torque arm which has a matching circular array of both holes, and a central opening (not shown) for the drive shaft. 
     The bearing blocks  86  are bolted respectively to support blocks  102 , and spacers or shims  104  are provided between the bearing blocks  86  and the support blocks  102 . By changing the thickness of the spacers  104 , the height of the roller  78  can be adjusted. Adjustment of the height of the roller requires adjustment of the torque arm which is facilitated by the clamp plates  95 , which need only be loosened during the adjustment, and then retightened after the roller  78  is adjusted to the desired height. A roller shield  105  is provided at the discharge end of the assembly. The shield includes a plate  106  spaced slightly from the periphery of the roller  78  and which extends horizontally across the assembly at about the elevation of the effective bottom of the inside of drum  24 . This shield  105  prevents the trailing ends of logs from catching or jamming below the roller  78 . 
     As shown in FIG. 3, the roller  78  is of a length to extend between the sides of the trough portions  60 , so that the top of the roller  78  can be positioned at the elevation of the top of the conveyor chain  34 . As shown at FIG. 5, the roller  78  is positioned closely adjacent to the headspool  38 , and just before the inlet  22  of the drum  24 . 
     FIG. 4 shows a drum end protector plate  110  mounted at the end  64  of the assembly, adjacent to the inlet  22  of the debarking drum  24 . Protector plate  110  extends upwardly from the sloping trough portions and has an arcuate partial circle opening  112  of a diameter slightly less than the effective inside diameter of drum  24 . The portions of plate  110  outwardly of the opening  112  prevent logs from striking the end face of the drum  24  at its inlet  22 , and the edges of the opening  112  contain logs partly in the drum and prevent the logs from rubbing on the inlet edge of the drum. The center of opening  112  is generally aligned with the axis  25  of the drum  24 . For reference, the inside diameter  114  of the drum  24  is shown in phantom lines at FIG.  4 . It can be seen that the lower portion of the drum inlet is protected in part by the trough portions  60  and the roller  78 . To provide support for protector plate  110 , and to strengthen the end assembly  64 , structural elements in the form of beams  116  are secured to the upper edges of plate  110 , and to the upper ends of the side columns of end assembly  64 . 
     Structural elements such as pipes or beams can be used instead of protector plate  110 . Such elements, when used, will shield the end of the drum to prevent logs from striking the drum end. 
     It can be seen from FIGS. 4 and 5 that the top of roller  78  is somewhat above the level of the bottom of the inside of the debarking drum  24 . Where the drum  24  is of a diameter of 11 feet, the roller  78  is mounted so its top surface is about 1½ feet above the bottom of the inside of the drum  24 . The roller  78  is of a diameter slightly greater than the diameter of the headspool  38 , and the top of the roller  78  is substantially in the plane of the top of the conveyor chain  34 . The space required for the roller  78 , is quite short, longitudinally in the direction of feed, and is only about 3 feet when the roller is 2½ feet in diameter. This 3 foot space is substantially less than either the width of the conveyor which is on the order of ten feet wide between its sides  62 , or the diameter of the drum  24  which is about 11 feet. 
     In operation of the apparatus shown at FIGS. 1 to  5 , groups of tree length logs are loaded onto the continuously driven main conveyor  12  with an overhead crane or a forklift loader. The logs move into the drum  24  at an elevation slightly above the bottom of the inside of the drum. Logs partly in the drum begin to rotate and often tilt while their trailing ends are still on the main conveyor  12 , and these trailing ends often flail about and sometimes orbit. The trailing ends of the so moving logs can slide on the smooth inner surfaces of the trough  60  and sides  62  of the main conveyor. When the logs move further into the drum the forward ends of some logs tilt down so that the logs press against the roller  78  while they rotate. The rotating roller  78  provides a low friction moving surface which permits logs pressed against the roller to rotate, so the logs have less tendency to climb across the roller and jam against other logs. This action enables the logs to be advanced by the roller  78 , as well as by the push of upstream logs on the main conveyor. The roller  78  is positioned sufficiently close to headspool  38  that the trailing ends of logs are prevented from catching at the head end of the conveyor and being pulled back, which could damage the chain. 
     It is preferred to rotate roller  78  at a surface speed slightly greater than the surface speed of chain  34  so that the roller provides a positive feeding action. However, the roller can if desired, be rotated at a surface speed the same as or lower than the surface speed of the conveyor chain, and any of these speeds can be obtained by adjusting the speed of the hydraulic motor  88 . 
     The roller  78  shown at FIGS. 3 and 5 has a smooth cylindrical outer surface. The embodiment of roller  118  shown at FIG. 6 has on its outer surface, circumferentially spaced axial ribs  120 . Ribs  120  are straight, extend the length of the roller  118 , and have outer edges  122  which act as low friction surfaces that allow logs engaging the ribs  118  to rotate while the ribs provide a more positive forward drive action to convey the logs into the drum. Where the roller  118  is on the order of 2½ feet in diameter, the ribs can be about ½ inch wide and 1 inch high, and spaced 3 to 5 inches apart around the periphery of the roller. 
     FIG. 7 shows another embodiment of a low friction region  16  usable between the head end  18  of the conveyor and the inlet  22  of the debarking drum  24 . In this embodiment, three rollers  130  are provided. Each roller is mounted in bearings, so the rollers can freely rotate. The rollers are horizontal and coplaner, and the top surface of each roller is coplaner with the top of the conveying chain. These rollers function to protect the head end of the conveyor chain, and provide a low friction region of short length between the main conveyor and the inlet of the drum. These rollers  130  do not provide the positive feeding action of the driven roller  78 , and exhibit higher friction than the driven roller  78 , but are satisfactory in some installations. 
     The stand or mounting block  132  for the rollers  130  is of adjustable height, with shims (not shown) being provided between the bottom of the block and the beam  134 , so the rollers if desired, can be raised to an elevation above the conveyor chain, or can be lowered to an elevation below the conveyor chain. 
     While preferred embodiments have been shown and described changes and variations can be made without departing from the scope of the invention.