Abstract:
The present invention is a system and method for the automatic control of a debarking system for use in a chip mill, paper mill, or the like. The present invention comprises one or more programmable logic controllers (PLCs) that receive input from ultrasonic sensors that measure the quantity of wood present at various locations within the system. Based on this data, the PLCs reference look-up tables that contain information on start, stop, speed up, and slow down times for various system components based on such criteria as wood variety and season. The control system optimizes the fiber yield from the debarking system while also reducing mechanical wear on components of the system by reducing the time at which components are run at high speed.

Description:
[0001]     This application claims priority based on U.S. provisional patent application No. 60/508,195, filed on Oct. 2, 2003 and entitled “Automatic Fiber Yield System and Method,” which is incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     The present invention relates to control systems for wood fiber processing machinery, and in particular to automatic controls for drum-based debarking machines that incorporate sensors and speed control mechanisms.  
         [0003]     Debarking systems that incorporate rotating drums are known in the art. An example of such a system is taught by U.S. Patent No. RE37,460 to Price et al., which is incorporated herein by reference. Such systems feature a large horizontal drum into which logs are inserted for debarking. The drum is fitted so as to rotate about its horizontal axis. As the drum rotates, the logs inserted within the drum rub against each other, thereby removing bark from the logs as they contact each other. The removal of bark is an essential step in the process of reducing logs to chips, which may ultimately be used in the manufacture of paper and other wood fiber products. Drum debarking may also be performed with respect to logs that are to be used for lumber.  
         [0004]     An elevated, curved hopper is generally positioned at one end of the debarking drum, and the groups of logs to be debarked are fed into the drum using a chain-type conveyor. An auxiliary feed roller may be positioned between the chain conveyor and the drum to aid in the manipulation of longer logs through the rotating drum. A discharge conveyor is positioned on the outlet end of the rotating drum to receive debarked logs. In applications such as the creation of chips for the manufacture of paper, the material may then be feed to a chip mill conveyor for further processing of the raw wood fibers.  
         [0005]     Conventional drum debarkers operate using simple manual controls. Before logs are to be fed into the debarker, the rotating drum and the chain conveyor are placed in the “on” position by the operator using a manual switch. In such systems, the conveyors and debarker drum are constantly in motion during operation. The speed of the conveyors, and the rate of rotation for the drum, is generally not variable. The conveyors and drum are not turned off until all of the logs and debris have moved through the system.  
         [0006]     Simple manual operation of the debarking system has a number of disadvantages. The optimal rate of rotation for the debarking drum is determined, in part, by the number of logs within the drum at any given time. If, for example, the rate of rotation is too great for the number of logs present, then usable wood fiber material will be stripped from the logs after all bark is removed. The wood fiber lost in this manner cannot feasibly be separated from the removed bark, and thus is discarded as waste. Likewise, if the rate of rotation is too slow, then logs will be moved from the debarker without complete debarking having taken place. Since incomplete debarking is unacceptable, current practice is to simply run the debarking drum at a speed that will ensure debarking for any expected number of logs within the debarking drum at any given time. The result is wasted wood fiber material that is removed from the logs when the number of logs in the debarking drum would favor a lower speed.  
         [0007]     The length of time that the logs remain in the debarking drum is also an important variable, which in a manual system is determined by the operator through visual inspection. If the operator leaves the logs in the drum for too long then material is wasted, but if the operator removes the logs too soon then they will have bark remaining and must be run through the debarking system a second time. Logs of varying quality and condition will require variances in the optimal debarking time. Wood variety and the season in which the debarking is performed are especially important factors in determining the optimal debarking time. Since logs of varying quality and condition will require different optimal debarking times, effective manual operation of a debarker requires considerable operator experience. Even with an experienced operator, however, the calculation of an optimal debarking time relies to some extent on guesswork. Training of a new operator requires a considerable amount of time since the new operator must obtain an intuitive feel for the nature of the logs in various conditions and in various seasons in order to operate a debarking system at acceptable efficiency.  
         [0008]     Another disadvantage of the standard manual mode of operation for a debarking system is excessive wear on equipment. The operation of conveyors and debarking drums at full speed with no wood fiber present in the system causes friction and excessive wear of the machine components. These components are designed to operate best when material is present, but in a practical setting it is impossible to maintain an even and steady flow of material at all times during operation. An attempt to remedy this problem by constantly turning conveyors and the rotating drum off and on would also cause excessive wear of the machine components, since start-up and shutdown also causes considerable wear on the machinery. Furthermore, it would be exceedingly difficult for a human operator to constantly monitor the various components of a debarking system simultaneously and switch them on and off in an optimal manner as material moves through the system. Such a task would likely require multiple human operators.  
         [0009]     The related art includes various attempts to develop automated control systems in the wood products industry. For example, U.S. Pat. No. 5,020,579 to Strong teaches an automatic feed control mechanism for a wood chipping machine. An infeed control circuit automatically adjusts infeed material capacity based on a load reading taken on the infeed conveyor. The control system automatically lifts a roller in the machine in order to clear jams, which are indicated by an infeed conveyor load reading that passes a certain pre-set value.  
         [0010]     Another such device is taught by U.S. Pat. No. 6,539,993 to Starr. The system separates single logs, and then reads the diameter and volume of the logs in order to optimize debarking. A ring-style debarker is utilized. An “image” of each log is then taken, which allows an optimization of the log cutting length to be determined. Each log is then cut to length and sorted into bins of similar-length logs.  
         [0011]     U.S. Pat. No. 6,546,979 to Jonkka teaches an automated method for controlling a drum-type debarker. This system utilizes information about both the weight of logs in the debarking drum and the rotational torque of the drum. This information is used to compute information concerning the average log density and top level of the log bunch tumbling within the drum. Alternatively, the drum weight information may be combined with optical sensing of drum filling degree in order to calculate average log density. Based on the information acquired in this manner, the system varies the speed of the drum rotation in an attempt to optimize the debarking operation. The infeed rate and discharge rate may also be varied to achieve the desired parameters. Jonkka teaches that reliance on the filling degree of the drum alone cannot produce satisfactory results in computing a proper debarking time.  
         [0012]     The Jonkaa method offers advantages over manual control systems, but also suffers from important disadvantages. The calculations involved in this control system require precise measurement of the weight of material in the debarking drum as well as torque information related to the rotation of the debarking drum. These measurements require sensitive instruments, such as strain-gauge sensors and shaft transducers, the installation of which would involve substantial re-working of any existing debarking drum equipment already constructed. They would also substantially increase the cost of producing a new debarking drum. These limitations of the related art and others are overcome by the present invention as described below.  
       SUMMARY OF THE INVENTION  
       [0013]     The present invention is directed to an automatic control system for a debarking apparatus that is designed to maximize wood fiber yield. The system may comprise three principal components. The first component is one or more programmable logic controllers (PLCs) or other computational elements. The PLCs control the operation of the conveyors and the debarking drum, in particular controlling the times at which these components may start, stop, speed up, or slow down.  
         [0014]     The PLCs draw on data collected from look-up tables, preferably stored in an electronic or magnetic medium. These look-up tables include information pertaining to the speed and operational timing of conveyors and the debarker drum. No complex calculations in order to compute these numbers are thus required. The present invention accounts for variations in wood quality by the use of multiple sets of look-up tables. The different look-up tables may each reflect a number of factors that influence optimal system operation, such as the variety of wood and the season in which the wood is being milled.  
         [0015]     The third component is one or more sensors that read information concerning the wood present at various points within the system. These sensors are preferably ultrasonic sensors, and may be used to detect the presence and quantity of material in a given location within the system. Preferably there are four locations at which such sensors are present: the drum feed conveyor, the debarking drum, the discharge conveyor, and the chipper feed conveyor. Using information gathered from these sensors, the PLCs access data at particular rows within the various look-up tables, and based on the data found the PLCs control the movements of the system conveyors and debarking drum.  
         [0016]     The invention overcomes the limitations of the related art by achieving a near-optimum fiber yield system for chip mills and paper mills without the complexity of instrumentation required to perform calculations such as average density. Instead, empirical data pertaining to the load of wood being run is stored in look-up tables for simple and immediate access. All necessary information in order to perform the simple PLC calculations called for in the invention is available from the use of ultrasonic sensors, which can measure the quantity of material present at a given location at a given time.  
         [0017]     It is therefore an object of the present invention to provide for an automatic control system and method to optimize fiber yields in debarking systems.  
         [0018]     It is a further object of the present invention to provide for an automatic control system and method that does not rely on complex instrumentation or wood density calculations.  
         [0019]     It is also an object of the present invention to provide for an automatic control mechanism that may be easily retrofitted to existing debarking systems.  
         [0020]     It is also an object of the present invention to provide for an automatic control mechanism for debarking systems that simplifies operation of the debarking system.  
         [0021]     These and other features, objects and advantages of the present invention will become better understood from a consideration of the following detailed description of the preferred embodiments and appended claims in conjunction with the drawings as described following:  
     
    
     DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       [0022]      FIG. 1  is a side elevational view of the major mechanical components for a debarking apparatus according to a preferred embodiment of the present invention.  
         [0023]      FIG. 2  is a diagram illustrating the control system components for a debarking apparatus according to a preferred embodiment of the present invention.  
         [0024]      FIG. 3  is an illustration of example data in a group of look-up tables according to a preferred embodiment of the present invention.  
         [0025]      FIG. 4  is a flow chart illustrating the computational logic for controlling the infeed conveyor of a debarking apparatus according to a preferred embodiment of the present invention.  
         [0026]      FIG. 5  is a flow chart illustrating the computational logic for controlling the debarking drum of a debarking apparatus according to a preferred embodiment of the present invention.  
         [0027]      FIG. 6  is a flow chart illustrating the computational logic for controlling the discharge conveyor of a debarking apparatus according to a preferred embodiment of the present invention.  
         [0028]      FIG. 7  is a flow chart illustrating the computational logic for controlling the chip feed conveyor of a debarking apparatus according to a preferred embodiment of the present invention.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0029]     With reference to  FIGS. 1 and 2 , a debarking apparatus and control system according to a preferred embodiment of the present invention may now be described. The apparatus includes an infeed conveyor (alternatively referred to as a “positive feed” conveyor)  10 , a rotating debarking drum  12 , a discharge conveyor  14 , and a chip feed conveyor  16 . Infeed conveyor  10  is used to direct logs toward debarking drum  12 . In the preferred embodiment, infeed conveyor  10  may be a chain conveyor of conventional type. Infeed conveyor  10  is driven by drive motor  26 . Drive motor  26  (and the other drive motors described herein) may be of a conventional electric or hydraulic type in alternative embodiments. Logs may be fed into infeed conveyor  10  by an overhead crane, a forklift-type loader, or other means (not shown), and are carried by infeed conveyor  10  into debarking drum  12 .  
         [0030]     Debarking drum  12  is shaped as an open-ended cylinder, and is supported by a cradle of rollers  29  in horizontal fashion. Debarking drum  12  is driven by a variable speed motor  28 , which causes it to rotate about its horizontal axis. The rotation of drum  12  causes logs fed into drum  12  from infeed conveyor  10  to rub against one another, and thereby results in the bark being removed from the logs as a result of the friction between the logs. Ideally, the logs are removed from debarking drum  12  just as all bark is removed so that the maximum amount of fiber will be retained in the logs for conversion to paper pulp or other desired wood fiber materials.  
         [0031]     Logs emerging from debarking drum  12  are fed onto discharge conveyor  14 . Like infeed conveyor  10 , discharge conveyor  14  may preferably be a chain conveyor of conventional type, and is driven by motor  30 . Discharge conveyor  14  feeds the debarked logs onto chip feed conveyor  16 , which is driven by drive motor  32 . Chip feed conveyor  16 , which may also be of a conventional chain-conveyor type, may then feed the logs into a chip mill for ultimate use in wood pulp or for other applications. Although chip feed conveyor  16  may be omitted from the invention, it is included in the preferred embodiment since it is traditional for chip mills to use this additional conveyor. Any waste material that may exit debarking drum  12  and thereby travel up discharge conveyor  14  may be dropped in the gap between discharge conveyor  14  and chip feed conveyor  16 . The use of chip feed conveyor  16  thereby improves the quality of the chip material that will eventually be produced from the logs since only a trivial quantity of waste material will find its way to the end of chip feed conveyor  16  in conjunction with the logs.  
         [0032]     Ultrasonic sensors are positioned at key locations along the preferred embodiment of the invention, as depicted in  FIG. 2 . Infeed conveyor sensor  26  is positioned to sense material that is placed on infeed conveyor  10 . Drum sensor  20  is positioned to sense material that is on infeed conveyor  10  just before entering debarking drum  12 . Discharge conveyor sensor  22  is positioned to sense material that is at discharge conveyor  14 , and chip feed conveyor sensor  24  is positioned to sense material that is at chip feed conveyor  16 . In the preferred embodiment, discharge conveyor sensor  22  (as well as the other sensors described herein) are ultrasonic sensors model no. IRU-3135, manufactured by STI Automation of Logan, Utah. Other types of sensors could be used in alternative embodiments, including without limitation other models and brands of ultrasonic sensors as well as various types of optical sensors.  
         [0033]     The major components of the control system of the preferred embodiment may now be described with continued reference to  FIG. 2 . The signals from infeed conveyor sensor  18 , debarking drum sensor  20 , discharge conveyor sensor  22 , and chip feed conveyor sensor  24  are fed as inputs to programmable logic controller (PLC)  34 . PLCs are well-known devices for use in process control applications in industrial plants. They are commercially available in many varieties, options including the number of inputs and outputs, processing speed, and logic complexity. In the preferred embodiment, PLC  34  is one of either Allen Bradley SLC-5 or PLC-5 models, manufactured by Rockwell Automation of Milwaukee, Wis. The PLC programming software used in the preferred embodiment is RSLogix  500 , also available from Rockwell Automation. Many other models of PLCs and various types of programming software could be substituted in alternative embodiments.  
         [0034]     PLC  34  generates output signals that are fed to infeed conveyor motor  26 , debarker drum motor  28 , discharge conveyor motor  30 , and chip feed conveyor motor  32 . These signals are used to stop, start, and vary the speed of these motors, and thereby control the operation of infeed conveyor  10 , debarking drum  12 , discharge conveyor  14 , and chip feed conveyor  16 . Specifically, according to the preferred embodiment infeed conveyor  10  may be turned on and off by control signals sent to infeed conveyor motor  26 ; debarker drum  12  may be set to high-speed rotation, low-speed rotation, or turned off by control signals sent to debarker drum motor  28 ; discharge conveyor  14  may be set to high-speed travel, low-speed travel, or turned off by control signals sent to discharge conveyor motor  30 ; and chip feed conveyor  16  may be set to high-speed travel, low-speed travel, or turned off by control signals sent to chip feed conveyor motor  32 .  
         [0035]     PLC  34  is also in communication with look-up tables  36 . Look-up tables are logical constructs intended to store numbers in designated locations for easy look-up by PLC  34  when needed. Look-up tables  36  may be implemented in any electronic, magnetic, optical, or other computer-readable media. These tables may be read into a random access memory area of PLC  34  in order to be utilized.  FIG. 3  shows the logical arrangement of three exemplary tables  40  according to a preferred embodiment of the invention. (It should be noted that the exemplary values shown in tables  40  do not necessarily represent optimal values for any particular wood variety or season.) The values in the tables  40  are used to control various parameters of the debarking system as will be explained in greater detail below. While three exemplary tables  40  are shown in  FIG. 3 , any number of tables  36  may be implemented in the preferred embodiment of the invention, according to the needs of the system. This will depend upon may factors; for example, the number of wood varieties processed at a particular mill. Personal computer  38  is used to input data to PLC  34 , including the creation and deletion of tables  36 , and the review and editing of the various values in tables  36 .  
         [0036]     Referring now to  FIG. 4 , the computational logic implemented in PLC  34  to control infeed conveyor  10  according to a preferred embodiment of the invention may now be described. At input block  50 , information from infeed conveyor sensor  18  is fed to decision block  52 . This information will be in the form of a bed depth of material on infeed conveyor  10 , preferably measured in inches. At decision block  52 , the amount of material detected at infeed conveyor sensor  18  is compared to the “PFC infeed sensor depth” value at block  53 , which is stored in the appropriate look-up table  36 . If the quantity of material exceeds the value found in look-up table  36 , then processing continues to decision block  54 . At decision block  54 , if infeed conveyor  10  is already on, then processing returns to decision block  52 . If infeed conveyor  10  is currently off, then processing moves to process block  56 . At process block  56 , the infeed conveyor is turned on after a delay as designated in the “PFC infeed delay” value at block  57 . This value is the number of seconds of delay after material is detected that infeed conveyor is to be turned on, and is stored in the appropriate look-up table  36 . After completion of the process at process block  56 , processing returns to decision block  52 .  
         [0037]     If a sufficient quantity of material is not detected at decision block  52 , then processing moves to decision block  61 . At decision block  61 , the logic of PLC  34  inquires whether infeed conveyor  10  is currently stopped. If the answer is yes, then processing returns to decision block  52 . If the answer is no, then processing continues to decision block  58 . At decision block  58 , the delay since the lack of material was first detected is compared to the “PFC delay to stop” value at block  59 . Again, the “PFC delay to stop” value is stored in the appropriate table  36 . If the delay time before stopping has not been reached, then processing is returned to decision block  52 . If the delay time before stopping has been reached, then the conveyor is turned off at process block  60 , and processing returns to decision block  52 .  
         [0038]     Referring now to  FIG. 5 , the computational logic implemented in PLC  34  to control debarking drum  12  according to a preferred embodiment of the invention may now be described. At input block  62 , information from debarking drum sensor  20  is fed to decision block  64 . As was the case for infeed conveyor sensor  18 , this information will be in the form of a bed depth of material, preferably measured in inches, but in this case the measurement will be of material that is just approaching the entrance to debarking drum  12 . At decision block  64 , the amount of material detected that is about to enter debarking drum  12  is compared to the “PFC sensor depth” value at block  65 , which is stored in the appropriate look-up table  36 . If the quantity of material exceeds the value found in look-up table  36 , then processing continues to decision block  68 . At decision block  68 , if debarking drum  12  is already on and running at high speed, then processing returns to decision block  64 . If debarking drum  12  is currently off or running at low speed, then processing moves to process block  70 . At process block  70 , debarking drum  12  is turned to a high speed setting, the rotation per minute (RPM) value of which is designated in the “Drum fast speed” value at block  71 . This value is stored in and is retrieved from the appropriate look-up table  36  by PLC  34 . After completion of the process at process block  70 , processing returns to decision block  64 .  
         [0039]     If a sufficient quantity of material is not detected at decision block  64 , then processing moves to decision block  80 . At decision block  80 , the logic of PLC  34  inquires whether debarking drum  12  is currently stopped. If the answer is yes, then processing returns to decision block  64 . If the answer is no, then processing continues to decision block  66 . At decision block  66 , the logic of PLC  34  inquires whether debarking drum  12  is currently running at its high-speed setting. If so, then processing moves to decision block  72 . Here the logic of PLC  34  compares the delay since the lack of material was first detected with the “Drum delay to slow” value at block  73 , which is stored in the appropriate table  36 . If the delay time before returning to low speed has not been reached, then processing is returned to decision block  64 . If the delay time before returning to low speed has been reached, then debarking drum  12  is turned to its low-speed setting at process block  74 , and processing returns to decision block  64 .  
         [0040]     If at decision block  66  it is determined that debarking drum  12  is not currently running at its high-speed setting, then processing moves to decision block  76 . At decision block  76 , the logic of PLC  34  compares the delay since the lack of material was first detected to the “Drum delay to stop” value at block  77 . Again, the “Drum delay to stop” value is stored in the appropriate table  36 . If the delay time before stopping has not been reached, then processing is returned to decision block  64 . If the delay time before stopping has been reached, then the conveyor is turned off at process block  78 , and processing returns to decision block  64 .  
         [0041]     Referring now to  FIG. 6 , the computational logic implemented in PLC  34  to control discharge conveyor  14  according to a preferred embodiment of the present invention may now be described. Before automatic control begins, the operator generally sets discharge conveyor  14  to run at its low-speed setting using manual controls. Automatic processing them begins at input block  82 , where information from discharge sensor  22  is fed to decision block  84 . As was the case for infeed conveyor sensor  18  and debarker drum sensor  20 , this information will be in the form of a bed depth of material, preferably measured in inches, but in this case the measurement will be of material that is just entering discharge conveyor  14 . At decision block  84 , the amount of material detected that is entering discharge conveyor  14  is compared to the “DDC sensor depth” value at block  85 , which is stored in the appropriate look-up table  36 . If the quantity of material exceeds the value found in look-up table  36 , then processing continues to decision block  86 . At decision block  86 , if discharge conveyor  14  is already on and running at high speed, then processing returns to decision block  84 . If discharge conveyor  14  is currently off or running at low speed, then processing moves to process block  88 . At process block  88 , discharge conveyor  14  is turned to a high-speed setting, the feet per minute value of which is designated in the “DDC fast speed” value at block  89 . This value is stored in and is retrieved from the appropriate look-up table  36  by PLC  34 . After completion of the process at process block  88 , processing returns to decision block  84 .  
         [0042]     If a sufficient quantity of material is not detected at decision block  84 , then processing moves to decision block  90 . At decision block  90 , the logic of PLC  34  inquires whether discharge conveyor  14  is currently stopped. If the answer is yes, then processing returns to decision block  84 . If the answer is no, then processing continues to decision block  92 . At decision block  92 , the logic of PLC  34  inquires whether discharge conveyor  14  is currently running at its high-speed setting. If so, then processing moves to decision block  98 . Here the logic of PLC  34  compares the delay since the lack of material was first detected with the “DDC delay to slow” value at block  99 , which is stored in the appropriate table  36 . If the delay time before returning to low speed has not been reached, then processing is returned to decision block  84 . If the delay time before returning to low speed has been reached, then discharge conveyor  14  is turned to its low-speed setting at process block  100 , and processing returns to decision block  84 .  
         [0043]     If at decision block  92  it is determined that discharge conveyor  14  is not currently running at its high-speed setting, then processing moves to decision block  94 . At decision block  94 , the logic of PLC  34  compares the delay since the lack of material was first detected to the “DDC delay to stop” value at block  95 . Again, the “DDC delay to stop” value is stored in the appropriate table  36 . If the delay time before stopping has not been reached, then processing is returned to decision block  84 . If the delay time before stopping has been reached, then the conveyor is turned off at process block  96 , and processing returns to decision block  84 .  
         [0044]     Referring now to  FIG. 7 , the computational logic implemented in PLC  34  to control chip feed conveyor  16  according to a preferred embodiment of the present invention may now be described. Before automatic control begins, the operator generally sets chip feed conveyor  16  to run at its low-speed setting using manual controls. Automatic processing them begins at input block  102 , where information from chip feed sensor  24  is fed to decision block  104 . As was the case for infeed conveyor sensor  18 , debarker drum sensor  20 , and discharge conveyor sensor  22 , this information will be in the form of a bed depth of material, preferably measured in inches, but in this case the measurement will be of material that is just entering chip feed conveyor  16 . At decision block  104 , the amount of material detected that is entering chip feed conveyor  16  is compared to the “CFC sensor depth” value at block  105 , which is stored in the appropriate look-up table  36 . If the quantity of material exceeds the value found in look-up table  36 , then processing continues to decision block  106 . At decision block  106 , if chip feed conveyor  16  is already on and running at high speed, then processing returns to decision block  104 . If chip feed conveyor  16  is currently off or running at low speed, then processing moves to process block  108 . At process block  108 , chip feed conveyor  16  is turned to a high-speed setting, the feet per minute value of which is designated in the “CFC fast speed” value at block  109 . This value is stored in and is retrieved from the appropriate look-up table  36  by PLC  34 . After completion of the process at process block  108 , processing returns to decision block  104 .  
         [0045]     If a sufficient quantity of material is not detected at decision block  104 , then processing moves to decision block  110 . At decision block  110 , the logic of PLC  34  inquires whether chip feed conveyor  16  is currently stopped. If the answer is yes, then processing returns to decision block  104 . If the answer is no, then processing continues to decision block  102 . At decision block  102 , the logic of PLC  34  inquires whether chip feed conveyor  16  is currently running at its high-speed setting. If so, then processing moves to decision block  118 . Here the logic of PLC  34  compares the delay since the lack of material was first detected with the “CFC delay to slow” value at block  119 , which is stored in the appropriate table  36 . If the delay time before returning to low speed has not been reached, then processing is returned to decision block  104 . If the delay time before returning to low speed has been reached, then chip feed conveyor  16  is turned to its low-speed setting at process block  120 , and processing returns to decision block  104 .  
         [0046]     If at decision block  112  it is determined that chip feed conveyor  16  is not currently running at its high-speed setting, then processing moves to decision block  114 . At decision block  114 , the logic of PLC  34  compares the delay since the lack of material was first detected to the “CFC delay to stop” value at block  115 . Again, the “CFC delay to stop” value is stored in the appropriate table  36 . If the delay time before stopping has not been reached, then processing is returned to decision block  104 . If the delay time before stopping has been reached, then the conveyor is turned off at process block  116 , and processing returns to decision block  104 .  
         [0047]     Each of the delay times, speed settings, and material level settings associated with the operation of each component of the debarking system is stored in an appropriate table  36 . Any number of tables  36  may be used in the preferred embodiment. Each table corresponds to a certain collection of settings that may be based on variables associated with the processing time of the material that is being run by the debarking apparatus. Such variables include, but are not necessarily limited to, the variety of the wood being processed and the season in which the wood is being processed. A different table may be assigned for operation of the debarking apparatus at any given time based upon these factors. The proper table to be used for a particular operating session may be chosen by the operator through computer  38 . The values in each table  36  are determined empirically from actual operation of the debarking apparatus and from the programmer&#39;s experience with such systems. Once a particular table  36  is chosen, the system may be run without change of the chosen table  36  until a change in wood quality (such as wood variety or season) is determined to exist.  
         [0048]     It should be noted that in the preferred embodiment, all of the controls for infeed conveyor motor  26 , debarker drum motor  28 , discharge conveyor motor  30 , and chip feed conveyor  32  may be operated in a manual or override mode as necessary. As is evident from the above description of the control circuitry, the invention allows the debarking of material to be fed to a chip mill or other similar application to generally proceed with little human intervention. The invention saves energy and reduces component wear by slowing down or stopping those components that are not in use at any given time. For example, infeed conveyor  10  will be shut down after a period of time without use; debarker drum  12  will be slowed down after a period of time without use, and will be brought to a stop after an extended period of time without use; discharge conveyor  14  will be slowed down after a period of time without use, and will be brought to a stop after an extended period of time without use; and chip feed conveyor  16  will be slowed down after a period of time without use, and will be brought to a stop after an extended period of time without use.  
         [0049]     It should be noted that while the preferred embodiment has been described, the invention also comprises a number of alternative embodiments. The debarking apparatus components with variable-speed drive systems, which could be any of the components as desired, could be controlled with any number of speed settings rather than the two of the preferred embodiment. Likewise, the speed of these components could be made continuously variable dependent upon a calculation based upon the quantity of material present. The present invention has been described with reference to certain preferred and alternative embodiments that are intended to be exemplary only and not limiting to the full scope of the present invention as set forth in the appended claims.