Abstract:
The disclosure describes a system to provide a steady supply of lumber pieces to a board separating device and insure the correct positioning of each lumber piece, at the proper time, thus allowing the separating device to function at a substantially higher rate than hitherto possible with previously known infeeding arrangements.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a system to be used as a load sensor and regulator, in front of a high piece count transversal type lumber separator such as, for instance, the one described in U.S. Pat. No. 5,518,106 (B. Allard), dated May 21, 1996. The incoming material consists of four-faced or two-faced lumber pieces carried forward laterally in a single layer by parallel chains, towards the separator whose function is to pick out individually each piece of lumber from the incoming stream and to deposit it in turn between rows of lugs affixed on parallel carry-off chains synchronized with the offloading sequence of the separator. 
     BACKGROUND OF THE INVENTION 
     Among the transversal type lumber separators in use today, the apparatus which is the object of the heretofore quoted US patent is considered one of the most efficient performers in the industry, being known to reach piece counts up to 120 per minute, in its original mode of installation. Performance figures, however, have so far been largely influenced by two basic factors particular to the operating conditions, namely: a) the width and length variations of the pieces in the lumber supply, and b) the quality of material flow control in front of the separator. Inadequate regulation of the incoming lumber flow can produce opposite negative effects such as, on the one hand, lack of material at the loading point or, on the other hand, overlapping of pieces due to pressure build up in front of the separating device. It is well known in the industry that a flow of material consisting exclusively of 2″×4″ stock of uniform 8′ length, does not present as many handling problems as does a production in dimensions from, for example, 1″×4″ to 2″×10″, in 8′ to 16′ mixed lengths, and that the capacity of any type of feed system may be greatly affected by the lumber dimension diversity factor. 
     In any event, and whatever might be the limitations of present day feed systems, production advances in sawmilling have made it necessary to raise the piece count for lumber separators from a ceiling of some 120 pieces per minute, under best conditions, to numbers above 180 per minute; in other words, an increase of some 50% in operating potential is required. This need for extra piece handling capacity stems not only from the process of industrial integration which has caused individual mills to grow in size, but also from a forest resource conservation principle which dictates that more lumber should be produced from the small logs available, including the usable portion of tree tops. While this procedure results in larger production volumes, it also causes a disproportionate increase in the number of pieces to be handled through the various manufacturing stages. 
     Beyond the need for ever shorter loading/offloading cycles in lumber feeding devices, a further condition is imposed on these systems as a result of present high conversion rate policies which have now firmly established such processes as curved sawing (producing bowed pieces) and marginal edging (causing imperfect squaring off) as basic rules of production. As a consequence, the overall production volume in a modem sawmill contains an important proportion of rough sawn pieces having shape irregularities to be corrected in the final processes of length trimming and kiln stacking. The industry is therefore faced with an urgent need for performance improvements in feeding systems to all processes, more particularly the final ones, where the total mill production is to be separated into a succession of individual pieces for trimming, sorting and stacking. 
     OBJECTS AND STATEMENT OF THE INVENTION 
     An object of the present invention is to overcome the performance limitations of board and cant separating feeders presently in use, by means of an auxiliary system which provides precise flow regulation of the input material as well as accurate positional control of individual pieces in the loading area of the lumber separator. 
     This auxiliary system is located after a lumber supply transfer which itself follows a preliminary unscrambler providing single layering of the pieces. It comprises a first transfer section somewhat shorter than the minimum length of lumber transported; this is followed by a second section which carries the pieces through to the lumber separating device. These two transfer sections used for load control and piece positioning are individually driven (as well as the supply transfer) and all three are equipped with suitably disposed banks of closely spaced presence sensors. 
     The functions of the above described arrangement can generally be stated as follows: 
     to insure a continuous, regulated flow of lumber from the supply zone to the loading point in front of the separator; 
     to prevent “fanning out” (when several pieces of lumber remain together at one end, while spreading away from one another at the opposite end) and “jackstrawing” (a criss-cross situation existing in a group of lumber pieces) of pieces, which are most likely to occur in random length productions; 
     to maintain close spacing of the pieces but also prevent pressure build-up between them or against the front of the separator; and 
     to provide optimal positioning of the leading piece once it reaches the loading area, and thereafter the proper forward speed with regard to the loading sequence. 
     The present invention relates to a system for sensing lumber pieces and regulating their movement laterally towards a loading station of a lumber separating device which engages individual lumber pieces to deposit the pieces at a controlled rate on a subsequent process feeding apparatus, the system comprising: 
     an individually driven first transfer section following a controlled lumber supply transfer; the first transfer section having first lumber conveying means and a first driving unit possessing instantaneous speed modulation and reversal capability; 
     an individually driven second transfer section downstream of the first transfer section and upstream of the separating device; the second transfer section having second lumber conveying means and a second driving unit possessing instantaneous speed modulation and reversal capability; 
     first lumber detecting means located along the first transfer section for assessing lumber flow conditions along the first section; 
     second lumber detecting means located along the second transfer section for assessing lumber flow conditions along the second section and for monitoring position of the leading piece in front of the loading station; and 
     computer means responsive to the first and second detecting means and associated with the first and second driving units to command acceleration, stoppage or reversal of the first and second conveying means. 
     In one form of the invention, the system also includes third lumber detecting means located in the lumber supply transfer, for controlling the output of lumber to said first transfer section. These third detecting means are linked to the computer means to cause forward/reverse movement or stoppage of the lumber supply transfer individual driving unit hereby designated as the third driving unit. 
     A critical characteristic of the lumber flow control system consists in the performance of the detecting means in providing full information on load conditions, such as gaps between pieces, skewing of individual pieces and exact position of the leading piece throughout the loading sequence. The combination of such “total situation” scanning with an “all cases” computer program, plus instantaneous mechanical response provided by the particular characteristics of the first and second driving units, constitutes the basis of the present invention and also the required condition for reaching its objective of higher lumber separator performance. 
     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. 
    
    
     BRIEF DESCRIPTIONS OF THE DRAWINGS 
     FIG. 1 is a schematic top plan view of the lumber feed system in relation to a separating device; 
     FIG. 2 is a side elevation thereof; 
     FIG. 3 shows a first phase of loading the separator; 
     FIG. 4 shows a second phase of loading the separator; 
     FIG. 5 shows an offloading and reloading phase of the separator; 
     FIG. 6 is a schematic diagram of the scanning and control elements; 
     FIG. 7 a  is a graphical recording of torque in a ten second servo-motor test; and 
     FIG. 7 b  is a graphical recording of speed in a ten second servo-motor test. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENT 
     As illustrated in FIGS. 1 and 2, the infeed control system  10  which is the object of the present invention, consists basically of a fixed frame  38  supporting at least two transfer sections  28  and  30 , section  28  being shorter than section  30 . These sections comprise a multiplicity of parallely disposed carrying chains  40 , having a serrated top portion  41 , plus an array of sensing elements such as, for example, photoelectric cells  34   a  to  34   f , arranged in at least two lines at longitudinal spacings suitable for their purpose. The distance laterally separating the first two lines of sensors  34   a - 34   f  is shorter than the minimal length of a lumber piece processed. A further line of sensors  34   a′  to  34   f′  may be required to the right of sensors  34   a - 34   f  for longer lumber pieces. 
     In a preferred form of the invention, the drive units of the individual sections of the control transfers are electric servo-motors having a maximum torque capacity, in either direction of rotation, of more than twice their rated full load torque and a total reversing time not exceeding one tenth of a second. While it is recognized that some level of speed modulation can be reached by hydraulic means, such a control does not produce the speed of response suitable for total cycle times of less than one third of a second for individual piece loading; in fact, it has also been observed that mere temperature variations of the hydraulic fluid caused unacceptable divergences in modulation timing. 
     The lumber feed system  10 , comprising transfer sections  28  and  30 , provides full control on the flow of material towards unit  14  which is a typical type of separator used in the lumber industry, whose function is to place incoming boards, such as  42   a  and  42   b,  individually between rows of lugs  23  on outfeed chains  24 , after they have been carried away from loading discs  20  by offbearing chains  22 . Since full details of the separator are given in the previously quoted US patent, it will not be described again here, save to mention that it comprises a number of rotating discs  20  carrying loading stations  16 , each equipped with a pivoting hook  18  actuated by a rotator  19 . 
     In front of the controlled feed system  10  is located a lumber supply transfer  12  which is itself preceded by a preliminary unscrambler (not shown) and serves to bring the lumber in a single layer from the production lines. The supply transfer also is individually driven, by a unit  36   c  which has normal “stop-forward-reverse” functions. This transfer also carries, at the head end, one or more groups of sensors, such as the one shown as  34   g  for the purpose of causing chains  32  to move forward whenever no lumber is detected in that area, and to stop these chains whenever there is lumber over both sensor groups  34   g  and  34   f.    
     Once a steady flow of lumber is insured by the above described arrangement, the control function of unit  10  can be fully performed with the purpose of increasing by some 50% the capacity potential of a separator such as shown as  14 , or of any existing sequential lumber separator using some configuration of programmed stop levers and rotating feed wheels. 
     To place the control function of infeed unit  10  in its proper perspective, it must be considered that a high capacity board separator may be required to handle 180 or more pieces per minute, of rough sawn lumber; therefore, the loading-offloading cycle of the unit may be somewhat less than ⅓ second. Generally, the lumber production is of random dimensions, the main part being between 3″ and 10″ in width, and from 8′ to 16′ in length. The pieces have not been length trimmed at this point and, because of natural log taper, most have some dimensional deficiency at one extremity. Some also carry excessive wane (rounded edges) somewhere along their length. Finally, many mills nowadays practice some form of curved sawing which produces longitudinal bowing parallel to the thickness dimension in a number of pieces. Given the stated time frame and natural handicaps, it is easy to understand that any auxiliary equipment which can bring each piece to the board separator exactly on time and in the correct position for loading, may well account for a 50% production increase over the normal performance of similar units using conventional infeed transfer systems. The overall increased capacity is brought about by the system of the present invention by first providing a constant supply and accurate flow regulation of the incoming lumber, secondly by exact positional tracking of the leading piece ( 42   b,  FIG. 2) and, finally, by precisely modulating the speed of advance for this leading piece to close the gap to the loading point exactly on sequence. Such results depend basically on the combined action of the three main characteristics of the system described: 
     a) total, detailed and accurate determination of incoming load conditions; 
     b) adequate computer evaluation of the data and decisional capacity; and 
     c) mechanical capability of instantaneous speed-direction changes in the lumber carrying means. 
     This control process and its effect on the performance of the board separator  14  can be described as follows, with the help of FIG.  2 . The controlled sequence which leads to loading a piece of sawn lumber on the board separator discs  20  begins at the head end of supply transfer  32 . The function of this transfer is to remain as fully loaded as possible with single layered pieces, without exerting lateral pressure on the lumber already on the next transfer section  30 . This is accomplished by “stop-run-reverse” cycling of drive  36   c,  through computer control, according to whether lumber is perceived by sensor banks  34   f  and  34   g  (stop), by only one of the two foregoing banks (run), or by both the foregoing plus bank  34   e  (reverse). 
     Transfer section  30  must maintain a fully loaded condition which at no time should become compressed laterally by lumber on supply transfer  32 , nor apply similar pressures on transfer section  28 . In transfer section  30 , servo-motor  36   b  performs the motion cycling, responding to signals originating from sensor banks,  34   b ,  34   c ,  34   d ,  34   e ,  34   f , and  34   b′ ,  34   c ′,  34   d ′,  34   e ′,  34   f ′ which are installed along parallel longitudinal lines, as shown in FIG.  1 . This arrangement makes it possible to detect “skewing” (non-parallel position) of pieces, by computer count of the individual sensors being energized simultaneously by the passage of a board over two or more opposite banks across the transfer. Upon such a condition being detected, servo-motor  36   b  receives a multiple “stop-reverse-forward” command in a preset timed sequence adequate to bring the misaligned board into parallelism by momentary contact with the incoming lumber load, while causing minimum delay to the overall forward motion. Another function of the transfer section  30  consists in eliminating large voids (such as one board width) in the lumber layer, while maintaining a sufficient gap proportion to constitute a loose but mainly full supply of pieces along its length. Because of the nearly instantaneous response required in all speed and direction changes in this sector, one suitable drive element which can presently meet such conditions is a computer controlled servo-motor. 
     As illustrated, particularly in FIGS. 3,  4  and  5 , the main function of transfer section  28  is to position the lead piece ( 42   b , FIG. 3 or  42   c , FIG. 4) for loading, while the preceding piece ( 42   a , FIG. 3 or  42   b , FIG. 4) reaches a loading station  16  on separator discs  20 . At this point, the closely grouped sensors of bank  34   a ,  34   a′  located in front of loading station  16  are measuring the distance which the front edge of leading piece ( 42   b , FIG. 3 or  42   c , FIG. 5) has to cover for said piece to get into loading position. As will be noticed in comparing FIGS. 3 and 5, the width of pieces  42   a  and  42   b  shown in the loading position is the main factor in the length of travel for the following pieces,  42   b  and  42   c  respectively, to reach this loading position. Assuming that pieces  42   a  and  42   b  have a width of 10″ and 3″, respectively, the distances to be covered by pieces  42   b  and  42   c  in FIGS. 3 and 5 must be at least equal to such assumed width of pieces  42   a  and  42   b . Since the full loading-offloading cycle must be completed in some cases in less than ⅓ second, the actual loading phase can be estimated to last about ⅙ second, which would require average displacement speeds as follows: 
     a) FIG. 3, for piece  42   b:  5′ per second 
     b) FIG. 5, for piece  42   c:  1′ per second 
     Since the above are average speed values over the total distance travelled, accelerating time and the slippage effect must be factored in, leading to required maximum forward speeds up to 10′ per second to be attained during the stated ⅙ second period of loading, and originating at times from a stopped or a reversed run condition. In such high frequency loading unto a lumber separator such as unit  14 , the infeed control system must constantly monitor, through sensor bank  34   a ,  34   a′  the position of the lead pieces ( 42   b,  FIG. 3 and 42 c,  FIG. 5) within a time frame relative to the arrival into loading position of the next station  16   a  moving up along the circumference of rotating discs  20 , and whose position is continuously monitored by encoder  21  driven by rotating shaft  15  on which discs  20  are mounted. From the information transmitted by the sensor bank and encoder, the computer  46  (FIG. 6) calculates instantaneous speed values for servo-motor  36   a  so as to suitably modulate the speed of transfer section  28  carrying pieces  42   b  and  42   c  to the loading station. 
     In the course of the just described positioning process for the successive lead pieces, whenever a no gap situation is signalled by the sensor banks on transfer section  28 , the driving unit  36   a  (FIG. 2) is caused to reverse momentarily in order to relieve the contact pressure of said leading piece against the preceding piece already in loading position and consequently against the circumference of loading discs  20 . 
     FIGS. 7 a  and  7   b  show values for torque  52  and speed  54 , also the frequency of reversals occurring in servo-motor  36   a  driving transfer section  28 , over a ten second test period during which eighteen pieces were positioned and loaded unto a lumber separator, at a corresponding cycling rate of approximately one hundred and ten pieces per minute. Since this test, rates of over one hundred and eighty pieces per minute have been reached both in shop tests and under actual working conditions. According to experimental studies, such results can be attained only by the use of computer controlled driving means having a degree of versatility and response as illustrated in FIGS. 7 a  and  7   b  by graphs of servo-motor performance under actual operating conditions. Because of the very narrow limits in time for regulation of speed and direction, it is doubtful that any alternate drive system, particularly if based on hydraulics, would have the required control characteristics and repetitive performance reliability. 
     The further functions of clamping the loaded piece  42   a  (FIG. 3) by means of pivoting hook  18  and actuator  19 , followed by its release downstream (FIG. 5) to a transfer  22  and a lugged chain section  24 , are performed by a separator generally as described in the previously quoted US patent and therefore are not discussed here. 
     Although the invention has been described above with respect to a specific form, it will be evident to a person skilled in the art that it may be modified and refined in various ways. For example, the serrated top chains could be replaced by belts having a roughened top face. It is therefore wished to have it understood that the present invention should not be limited in scope, except by the terms of the following claims.