Method and apparatus for optimizing planer mill output
FIELD OF THE INVENTION 
     The present invention relates to woodworking production, and in particular relates to a method and apparatus for optimizing the output of a planer mill. 
     BACKGROUND OF THE INVENTION 
     A planer mill is a woodworking operation of the type used in large volume lumber manufacturing. A planer mill typically includes a number of individual machines grouped together in a production line setting. One of the key machines in a planer mill is a planer unit, or &#34;planer-matcher&#34;, a device which planes wood to predetermined dimensions; i.e. smoothes or levels flat or uniformly contoured surfaces of wood using relatively wide edged blades. The planer-matcher often works in combination with other machines positioned in the production line, such as circular saws, band saws, or log gang saws and related machines, and to which the planer-matcher is connected by chain or belt conveyors. 
     Typically, a planer-matcher can operate at a faster speed than some of the other units in a woodworking or lumber mill. As a result, the planer can operate no faster than the speed of the slowest unit in the production line Stated differently, some other portion of the mill usually represents the rate determining step. If the planer were to operate at a speed faster than the speed of the slower conveyor unit for example, the planer would produce an overabundance of planed wood, resulting in a jam-up. Under such circumstances, which tend to occur in manually operated plants, an operator then must stop the production line and remove the jam. This can be costly in terms of production. For example, if such a line stops for ten minutes, and the planer operates at a feed rate of about 100 pieces of wood per minute, such a jam-up and the related down time would account for a productivity drop of 1,000 pieces of planed wood that otherwise could have been manufactured during that time period. 
     In general, planers are usually operator controlled. The operator observes the general rate at which wood pieces or boards are being fed into and out of the planer and then uses a potentiometer or similar control to either speed up or slow down the planer-matcher to obtain a desired rate. This technique offers a number of disadvantages, however, particularly the lack of precise control over the speed of the planer-matcher. As stated above, if wood is being treated by the planer-matcher at rates of up to 100 pieces per minute, an operator may experience difficulty in estimating and hand-controlling the speed of the planer-matcher in an attempt to maintain a speed that both prevents downstream jam-up of planed wood, while at the same time speedily working all of the wood being fed into it without causing input delays. 
     Therefore, the need exists for a more precise control of a planer-matcher in a manner which moderates the differences in speed that can occur during overall mill operations, while avoiding the inherent difficulties in trying to do so manually. 
     OBJECTION AND SUMMARY OF THE INVENTION 
     It is the object of the present invention to provide a method of optimizing the method of output production of a woodworking tool such as a planer-matcher. The invention meets this object with a method of optimizing the output production of a particular tool in a production line of the type in which in which individual boards are sequentially handled by different tools that typically operate at different speeds. The invention comprises selecting a target rate of board treatment by the woodworking tool, measuring the difference between the actual rate of board treatment by the woodworking tool and the selected target rate, calculating the tool speed required to reduce the difference between the target rate and the actual rate to zero, and then periodically adjusting the tool speed of the woodworking tool based on the calculated speed required to reduce the difference to zero. 
     In another embodiment the invention comprises the apparatus for optimizing the output production of a woodworking tool such as a planer-matcher in a production line of the type just described. 
    
    
     The foregoing and other objects, advantages and features of the invention, and the manner in which the same are accomplished, will become more readily apparent upon consideration of the following detailed description of the invention taken in conjunction with the accompanying drawings, which illustrate preferred and exemplary embodiments and wherein: 
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram of the planer-matcher production control system of the present invention. 
    
    
     DETAILED DESCRIPTION 
     The present invention is a method of optimizing the output production of a woodworking tool in a production line of the type in which individual boards are sequentially handled by different tools that typically operate at different speeds. The invention comprises selecting a target rate of board treatment by the woodworking tool, measuring the difference between the actual rate of board treatment by the woodworking tool and the selected target rate, calculating the tool speed required to reduce the difference between the target rate and the actual rate to zero, and periodically adjusting the tool speed of the woodworking tool based on the calculated speed required to reduce the difference to zero. 
     As stated above, in a typical woodworking mill, a planer, also referred to in this art as a &#34;planer-unit&#34; or a &#34;planer-matcher&#34; (particularly when it concurrently planes more than one surface), is often the fastest tool in the entire production line. Therefore, in preferred embodiments, an optimal use the invention is in conjunction with a planer-matcher. 
     Similarly, in preferred embodiments, the step of selecting a target rate of board treatment by the woodworking tool comprises selecting a target rate based upon a known constant dimension of each board, the maximum rate of production desired, and the maximum speed of the woodworking tool being used. In this regard, in typical planing situations, the invention further comprises the step of feeding boards to the planer with the boards in a longitudinal or lengthwise orientation and along a lengthwise path of travel parallel to their longitudinal orientation. Thus, in the preferred embodiment the step of selecting a target rate based on a known constant dimension of each board comprises selecting the target rate based upon a known constant length of each board. Such a step merges nicely with the typical operation of a woodworking mill in which a conveyor typically feeds boards such as the classic &#34;2×4&#34; to a planer-matcher. 
     In the preferred embodiment, the step of measuring the difference between the actual rate of board treatment by the woodworking tool and the selected target rate comprises counting the number of boards that pass a predetermined point adjacent the woodworking tool during a measured time period, and in the most preferred embodiments comprises counting the number of boards that have been treated by the planer-matcher during a measured time period. This is particularly useful when the woodworking tool is the preferred planer-matcher. First, the boards being fed to a planer-matcher are typically butted together making it more difficult to count individual pieces. The boards exit the planer separately, however, making it easier to count individual boards when they leave the planer-matcher rather than when they enter it. More fundamentally, because the invention is a control system for the particular tool, and preferably a planer-matcher, the necessary count is that of boards treated by that tool, rather than the number of boards that may be being directed or fed towards it. Thus, the most accurate count for purposes of the calculations described herein is a count of what exits the tool rather than what enters it. 
     In a preferred embodiment, the step of counting the boards comprises counting the boards using a video camera of a type known to those familiar with such arts which basically can conduct a line scan operation that need only count the leading edge of each board that passes in order to accurately produce such a count. It will be understood, however, that other counting devices or detectors can be just as useful in the use of the invention. 
     In preferred embodiments, the step of calculating the tool speed required to reduce the difference between the target rate and the actual rate to zero comprises calculating the number of boards to be treated by the woodworking tool during a given time period. In the more preferred embodiments, the step of calculating the tool speed required to reduce the difference between the target rate and the actual rate to zero comprises defining a measuring time interval and an adjusting time interval, and then counting the boards processed during the measuring time interval that includes the most recently processed boards. Thereafter, the tool speed is adjusted during the next adjusting time interval. 
     In the more preferred embodiments, the adjusting time interval is smaller (i.e. a shorter time period) than the measuring time interval. This results in a smoother operation than if the measuring and adjusting time intervals were identical to one another. For example, in one preferred embodiment, the measuring time interval is a period of eight minutes, and the adjusting time interval is one minute. 
     Further to this preferred embodiment, the measuring time interval is selected to be the integer sum of several adjusting time intervals as just described with the preferred eight-minute and one-minute intervals. In this embodiment, the step of calculating the required tool speed comprises sequentially updating the measured time interval by dropping the oldest adjusting time interval from the calculation while including the most recent adjusting time interval. Expressed with respect to the above example, the method comprises the step of calculating the average number of boards treated per minute, but calculated on the basis of the most recent eight-minute interval. Thus, on an every minute basis, the oldest minute is dropped from the eight-minute interval, the newest minute added, and the eight minute average recalculated. 
     In contrast to earlier systems that counted board speed or distanced travelled, in the invention the step of selecting a target rate of board treatment comprises selecting the number of boards to be treated during any given time interval, typically a one-minute time interval as just described. Furthermore, it will be understood that the step of periodically adjusting the speed of the woodworking tool can comprise either periodically increasing the speed or periodically decreasing the speed. 
     In another embodiment, the invention comprises the apparatus for optimizing the output production of a woodworking tool such as a planer-matcher in a production line of the type just described. In this embodiment, and as illustrated in FIG. 1, the invention comprises a counter illustrated as the video limit switch 10 for counting boards that pass the video unit during production; a planer-matcher (planer drive system) 11 or other woodworking tool operatively associated with the video unit and having a variable tool speed; a central processing unit illustrated as the host computer 12 for comparing the rate at which boards pass the video unit to a preselected target rate and for calculating the tool speed required to reduce the difference between the target rate and the actual rate to zero; and a tool speed control system 13 operatively associated with the central processing unit 12 for moderating the speed of the planer il in response to the calculations of the central processing unit 12. Typically, the central processing unit 12 will comprise a microprocessor and the tool speed control system 13 will include means for moderating the rate at which boards are planed by the planer-matcher. 
     In the preferred embodiments, a most useful form of carrying out the calculations is that of a P-I-D proportional-integral-derivative) algorithm. An appropriate program can be used by the central processing unit 12 and FIG. 1 schematically illustrates this relationship. An appropriate computer program written in Basic language and suitable for use on typical microprocessors is included in this specification at the end of the description, but before the claims. Additionally, a more general description of P-I-D techniques, although applied somewhat differently, is set forth in U.S. Pat. No. 5,043,682 to Takahasi et al., the contents of which are incorporated entirely herein by reference. 
     FIG. 1 further illustrates that an operator can set a desired target rate, or feed other useful data to the computer, but is no longer required to attempt to manually control the planer&#39;s speed. ##SPC1## 
     In the drawings and specification, there have been disclosed typical disclosed embodiments of the invention, and, although specific terms have been employed, they have been used in a generic and descriptive sense only and not for purposes of limitation, the scope of the invention being set forth in the following claims.