Abstract:
An apparatus for positioning lumber pieces for end trimming, by means of a succession of gates mounted on traveling chains set at a converging angle with the even end line of uniformly spaced lumber pieces carried transversely on parallel chains towards a multiple saw trimmer. The positioning is accomplished by any one gate pushing against the end of a lumber piece and then retracting when the lumber piece has reached the appropriate position for cutting by stationary trimming saws. The positioning process and the saw selection for each cut are scanner/computer controlled.

Description:
FIELD OF THE INVENTION 
     The present invention pertains to an apparatus for positioning lumber pieces for selective end trimming. 
     BACKGROUND OF THE INVENTION 
     In saw milling, the end trimming operation is the final sawing step before stacking lumber for drying. Its purpose is to cut the pieces into commercial lengths as determined by market demand in North America and overseas, while removing defects which would cause quality downgrading and therefore loss in value. In order to achieve the optimum value recovery, the lumber pieces are first scanned along their whole length to locate defects and to allow a computer to determine the cut to be made at each end of the piece by one of an array of saws disposed at a fixed spacing (ordinarily one or two feet) across the width of a lumber trimmer and therefore along the length of the pieces to be trimmed. Between the scanning and trimming sections, a lumber positioning system is provided along the lumber conveyor wherein each lumber piece is moved along its longitudinal axis so as to place its ends at a planned distance from two saws pre-selected by the computer in accordance with the original length of the pieces and the type of defects determined by the scanning means. 
     A most common method of positioning lumber for end trimming consists at present in placing power driven rolls parallelly to the conveying chains of the lumber conveyor and at a slightly higher elevation, (such as ⅛ of an inch) than that of the chains. Contact of these rolls with the underside of the lumber pieces causes them to move axially, across the chains, until reaching one of several adjustable bumper plates or fences placed side by side, which serve to define a particular cutting position for each piece. The frequency of this individual positioning is up to 2 per second in an average sized sawmill and reaches up to 3 per second in high speed lumber dressing operations for short wood (six to ten feet). In order to complete, within the available time, the necessary axial displacement of up to 2 feet for some pieces, an array of fast rotating 8 foot long rolls is required, plus a number of pneumatically actuated bumper plates disposed side by side along a distance at least equal to the length of the rolls. Sectional lifting skids are also needed between the chains so as to prevent further contact with the rolls for a piece that has reached its planned position within the positioning area. 
     A system such as described represents over two tons of mechanical equipment, with the necessary power input, a considerable supply of compressed air, plus the mechanical maintenance associated with a high speed operation generating heavy impact loads. Besides such inconveniences, this type of system is marginally accurate as the method of positioning the board by propelling it endwise against a stationary bumper produces a “bounce back” effect which varies with the weight of the piece and its acquired speed. 
     One example of this type of machine may be found described in U.S. Pat. No. 5,142,955 issued Sep. 1, 1992 to Hale. 
     OBJECTS AND STATEMENT OF THE INVENTION 
     An object of the present invention is to perform accurate endwise positioning of sawn lumber for the trimming operation; this is achieved by means of an apparatus which is much lighter than the one described above and does not involve high speed travel and abrupt stoppage of the material being positioned. 
     The lumber positioning apparatus of the present invention therefore comprises: 
     a frame; 
     carrying means for lumber positioning gates, mounted on the frame and drivingly associated in synchronism with the conveyor means; 
     a series of successive lumber positioning gates operatively mounted to the gate carrying means; the gates being spaced at intervals corresponding to the uniform spacing of the lumber pieces of the conveyor means; and 
     means responsive to scanner data and computer signals for selectively placing a positioning gate in a vertical position to contact an end of a lumber piece traveling on the conveyor means thereby displacing the lumber piece axially as it moves along the conveyor means; the scanner data responsive means further enabling the gate to be removed from the vertical position and thereby from engagement with the lumber piece whereby the lumber piece is no longer pushed axially as it continues to travel along the longitudinal conveyor direction towards the multiple saw trimmer. 
     In one preferred embodiment, the lumber positioning apparatus of the present invention is composed basically of a pair of parallel chains moving horizontally and joined together by evenly spaced cross bars at one end of which is mounted a pivoting plate, referred to as a “positioning gate”. These chains are installed along one side of a multiple chain transfer which carries lumber pieces transversally and parallel to one another and at an even spacing from one another. The present invention requires that the lumber pieces first be brought to an even end line on one side of the chain transfer, that the spacing of the positioning gates be similar to that of the lumber pieces on the transfer chains, that the speed of the two chain systems be synchronized and that a converging angle be provided between the two chain systems, in their generally common direction of travel. Under these conditions, the position of any gate may be made to coincide at all times with the passage of each piece on the lumber transfer, causing the gate to make contact with and push the corresponding piece axially, as long as such gate is maintained in a vertical position by its actuating mechanism which, in turn, is computer controlled from the scanner data acquired upstream of the system. Whenever, somewhere along the length of the positioning apparatus, a piece has reached its correct position, a signal from the aforesaid computer control system causes the corresponding gate to cease contact by retracting itself to a horizontal position, leaving the piece to continue towards the trimming saws without further longitudinal movement. 
     In view of the low performance level of presently known systems as previously described, it can be said that a main object of this invention is to increase the accuracy of positioning of sawn lumber for the trimming operation, which has a direct effect on realizing the full potential value of each lumber piece. 
     In fact, if it is correctly estimated that the use of a scanner/computer combination to determine the optimum trimming pattern can increase the final product value by some 7% as compared to a visual/manual method, it is no less logical to think that the accuracy in actually locating the pieces with regard to the saws can be responsible for an important part of this gain. 
     Another object of the present invention is the reduction in size and weight of the necessary mechanical means to effect the positioning of the lumber, as well as the required floor space and power input. 
     Yet, a further object is to eliminate the high velocity movement of the individual pieces of lumber, terminating in a destructive impact upon reaching the locating bumper, thus at times causing sudden breakdowns of components with resulting losses of production. 
     Other objects and further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. It should be understood, however, that this detailed description, while indicating preferred embodiments of the invention, is given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art. 
    
    
     IN THE DRAWINGS 
     FIG. 1 is a schematic top plan view of a lumber trimming station using a positioning apparatus in accordance with the present invention; 
     FIG. 2 is an enlarged schematic top plan view showing the positioning apparatus; 
     FIG. 3 is a side elevation of the positioning apparatus; 
     FIG. 4 is a cut-away schematic view of the gates in active and return positions; and 
     FIG. 5 is a cut-away schematic view of the gates in retracted and return positions. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring to FIG. 1, there is shown an overall view of a lumber trimming station, generally denoted  10 , consisting of three lumber conveying sections  12 ,  14  and  16  which serve to convey lumber pieces  18  from a distributor (not shown) at the upstream end thereof to trimming saws  38  and further on to a lumber sorting station (not shown) at the downstream end thereof. 
     Section  12  comprises a series of parallelly disposed chains  20  each having a series of evenly spaced lugs  22  which serve to displace lumber pieces  18  through a scanning station, generally denoted  24 . The scanning station which is well known in the art consists of a bridge type scanner having top and bottom scanning heads (the top supporting beam being shown as  26 ) between which the lumber pieces pass and are scanned along their length to provide information to a computer (not shown) associated with the scanner. 
     Each scanned lumber piece, which is now even ended on line  42 , passes onto positioning section  14  of the trimming station, which is provided with a series of parallel chains  28 , each equipped with a series of evenly spaced lumber contacting lugs  30 . One end of the lumber pieces  18  reaches a positioning apparatus, generally denoted  32 , which will be described in greater detail hereinbelow. Once the lumber pieces have been properly moved axially, as again described hereinbelow, they are conveyed to section  16  of the trimming station which is also provided with a series of chains  34 , each having a series of lumber pushing lugs  36 . Section  16  carries a battery of laterally spaced fixed saws  38  which are vertically moved in and out of sawing position in response to data received from the computer. 
     All chains  20 ,  28  and  36  of the lumber trimming station  10  are mechanically synchronized from a single driving unit (not shown). 
     The positioning apparatus  32  is shown in FIG. 1 as extending axially at a converging angle α with respect to an even end line  42  which is defined by the ends  18   a  of the lumber pieces  18  in the lumber scanning section  24  of the trimming station. 
     Referring to FIGS. 1,  2  and  3 , the positioning apparatus  32  comprises a pair of chains  44  and  46  which are drivingly mounted on sprockets  45  and  47  connected to the head shaft  40 , via a chain  48 , a universal joint  50  and a chain  52  connected to sprocket  53 . The positioner  32  comprises a series of traveling gate mountings  54  that includes a cross piece  56 , connected to both chains  44  and  46 , and a gate  58  pivoting on supporting plate  69  (FIG.  4 ). 
     Each actuating mechanism which controls the position of each gate  58  comprises a pneumatic cylinder  60  supported on a base plate  61  fixed to the positioner frame  70 . One end of the cylinder  60  is connected to a guide plate  62 . The guide plate  62  is pivotally mounted at  64  to a pivot support  65  also supported by base plate  61 . When in the vertical position shown in FIG. 4, guide plate  62  is in contact with a cam roller  66  which is mounted on a lower extension  67  of gate  58 , thus forming a rigid assembly which pivots about an axis  68 . This axis  68  is mounted on an end section  69  of the cross piece  56  that joins the two chains  44  and  46 . Thus, gate  58  as well as its cam roller  66  attached to its extension  67  moves along with chains  44  and  46 . 
     FIG. 5, which is a figure similar to FIG. 4, shows however positioning gate  58  as having pivoted by gravity about axis  68  to an inclined position. This is achieved after cylinder  60  has caused the guide plate  62  to pivot out of its vertical position about axis  64  thereby freeing cam roller  66  of the positioning gate assembly. 
     In operation, the lumber pieces  18  brought to the positioning apparatus  32  have previously been placed individually in front of each row of chain lugs  30 , brought to the even end line  42  on one side of the scanning section and moved towards the trimming section  16  at a speed synchronized at all times with that of the gates  58  carried by chains  44  and  46  of the positioning apparatus  32 . With similar and uniform spacing of the chain lugs  30  and of gates  58 , plus adequate speed synchronization (taking into account the converging angle α), it is therefore assured that each gate  58  of the positioner will be in alignment with a lumber piece on the transfer section  14  of the trimming station. 
     If all gates  58  should remain in their vertical position, such as shown in FIG. 3, it is evident that the only result from the operation of the positioner of the present invention would be to push off all lumber pieces from the original even end line  42  to a new even end line  42 ′(see FIG. 2) whose position would depend on the length of the positioning apparatus  32  and the size of angle α. However, FIG. 4 shows gate  58  in the active or “work” position while FIG. 5 shows the gate  58  in the retracted or “no contact” mode. The difference between FIGS. 4 and 5 indicates that a piece of lumber may be pushed axially or left stationary on the conveying chains, from computer signals derived from scanner data. The return position of these gates  58 , generally vertical as seen in the lower part of the supporting frame, is similar in both FIGS. 4 and 5. 
     In FIG. 3, the assembly of cylinder  60  and guide plate  62  is repeated in side by side mountings for the entire working length of the apparatus. Therefore, gate  58  remains vertical as long as the guide plate  62  opposing it, is vertically maintained by cylinder  60 , and will continue pushing back axially a lumber piece  18  in line with it. When, however, the lumber piece has reached the correct position, guide plate  62  is pushed back in the inclined position shown in FIG. 5 by the cylinder  60  on receipt of a signal transmitted from the computer. The gate assembly, being no longer guided, assumes an inclined position by gravity due to the location of the pivoting axis  68  relatively to the center of gravity of the gate assembly. In this configuration, gate  58  has no further contact with the end  18   a  of the lumber piece which retains a stable position on its way towards the trimming saws  38 . 
     The saws  38  are set at a fixed spacing (generally one or two feet) from one another and are supported by a pivoting frame actuated by a pneumatic cylinder (not shown) which allows each saw to be lowered or raised on a signal from the computer, depending on whether it is to be in cutting position or not for a particular lumber piece. 
     Referring again to FIGS. 1 and 2, the sequence of operations taking place during the entire process can be thus stated: 
     a) Upstream of the trimming station, lumber pieces are being fed one at the time by a distributor unto a lugged chain transfer, and pulled to an even end line on one side of said transfer (not shown). 
     b) Lugged chains  20  move the lumber between top and bottom heads  26  of scanner  24 . 
     c) Each piece  18  is transferred from lugged chains  20  to lugs  30  of chains  28  and moves transversally along the even end line  42 , up to its junction with the travel plane of gates  58 . 
     d) If, according to scanned data for a piece  18 , the first gate  58  to coincide with piece  18  at the point of junction is in the retracted position, then the piece will move on to the trimming section  16 , following along the same even end line. 
     e) If gate  58 , at the same point as in paragraph  4  above, has been programmed to be in a vertical position, it will enter into contact with piece  18  and will push it back axially as it moves along with the chains, because of the angle of convergence between section  14  and positioning apparatus  32 , until the piece reaches the correct position as determined by the computer, at which time gate  58  will retract, leaving the piece stable on the carrying chains of transfer  14 . 
     f) The path then followed by piece  18  until reaching the saws,  38 , will be along a straight line parallel to and located anywhere between lines  42  and  42 ′ (FIGS. 1 and 2) as determined by the computer. 
     g) Further action by the computer will then determine which of the various saws will execute the two end cuts, in view of an optimum solution from the scanned data and the given computer algorithm. 
     The foregoing description pertains to a main embodiment of a pusher type axial positioner for lumber trimming. The design is, of course, subject to a number of variations and component substitution. For instance, the unit as presently illustrated is designed for a maximum off-setting capacity of one foot from the original even end line  42 . This can obviously be increased by lengthening the unit and/or providing a larger converging angle at installation. The chains could be replaced by a single cogged belt of sufficient width and stiffness. Hydraulics could be used instead of pneumatic gate actuators. Also, the entire actuating system could be replaced by a fast acting solenoid actuator directly attached to each of the positioning gates and energized while moving, via commutator tracks mounted in a stationary manner on frame  70 . 
     Similarly, variations in the process heretofore described may be considered in the light of operating experience, in order to bring performance improvements. For example, the application of frictional restraint to suppress axial overtravel of the lumber piece after leaving contact with the gate could be used. It is recognized that such an addition to the process could be desirable, as well as others, whenever operating speeds are pushed to the limit. Such refinements therefore are considered as part of the intent of this invention. 
     It is therefore wished that this invention should not be limited in interpretation except by the terms of the following claims.