Abstract:
A control system provides automatic control of winder deceleration and stopping to a preset sheet length, or preset roll diameter. The system utilizes a closed loop control of drive deceleration and automatic compensation for layers slabbed off following a sheetbreak.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a control for a paperwinder, and is more particularly concerned with controlling the winder to stop at a preset web length or a preset roll diameter. 
     2. Description of the Prior Art 
     Papermill customers generally purchase finished paper rolls specified to a guaranteed sheet length on the roll or a roll wound to a guaranteed diameter. Controls are commercially available for stopping a winder at a preset sheet length, but not to a specified roll diameter. Also, conventional stop-to-length controls do not provide closed loop control of winder deceleration and, instead, utilize a two-level stop mode. The winder deceleration starts at an initial set point at a rate fixed by the drive, and continues to some preset slow speed. The winder then runs at this low speed to the second or final stop point. This method can achieve accurate sheet length control; however, it requires a longer stopping time. 
     The ASEA Rolltrimmer is a system of the type set forth above with respect to stop-to-length control. 
     Schommeier U.S. Pat. No. 4,438,889 discloses a computer system for controlling stopping length by switching the drive control between two rates of deceleration; one slightly greater than the desired rate and one slightly less than the desired rate. 
     SUMMARY OF THE INVENTION 
     It is the object of the present invention, therefore, to provide a method and apparatus for controlling a winder to automatically and accurately stop at a specified sheet length or specified roll diameter. 
     An attendant object of the present invention is to provide that the winder deceleration be accurately controlled at a specified rate. 
     Another object of the invention is to provide an accurate stop control in minimum time to either a specified sheet length or roll diameter while providing compensation for damaged layers removed in the event of sheet break during winding. 
     Another object of the invention is to provide a microprocessor-based control system to automate paperwinding to a preset length or a preset diameter, either in English or metric units. 
     The above objects are achieved, according to the present invention, by providing a microprocessor-base control system which accurately controls the winding of paper on a roll and in which a number of essential parameters are known, either as preprogrammed data, measured data or operator inputs. These parameters include the decelerate rate of the drive, the target length or diameter, paper thickness, (caliper), and paper speed. The stopping distance, as a function of paper speed, is computed continuously. Whenever the sum of the stopping distance and cumulative length is greater than the target length, the drive starts to decelerate. It is essential to maintain a constant deceleration rate, so that the stopping distance computation will depend only on the paper speed and not on the inertia of the roll. 
     The drive switches between two deceleration rates. The assumed deceleration will be the arithmetic mean of these two rates. The computer tells the drive to start deceleration and the drive switches to the high deceleration rate. Therefore, the computed stopping distance will be longer than the actual stopping distance. On a subsequent calculation, the computer signals the drive not to decelerate and the drive switches to the low deceleration rate. This process is continuously repeated as the drive slows down. The deceleration rate therefore depend on a so-called &#34;bang-bang&#34; control in which the control loop is active down to zero speed. 
     With most drive systems, a time lag exists from the instant the computer issues a deceleration command to the time the drive starts to slow down. A time advanced factor is required to compensate for the response lag. The need for such compensation is more obvious if the paper is winding at a low speed. 
     In the control-to-diameter mode, the stopping distance along with the caliber of the paper enables computation of the stopping diameter. The relationship between incremental length to incremental diameter is employed to compute a paper &#34;slabbed off&#34; after a sheet break. At the instant of sheet break, the instantaneous diameter is memorized and when winding is resumed (after slab off and splicing) an up-date diameter is computed. The computer will make an automatic adjustment of the cumulative footage based on these data. 
     In the stop-to-length mode, the computer accepts as inputs the signal pulses from a drum tachometer (500 ppr), a roll tachometer (1 ppr) and three status flags, namely, sheetbreak, run and eject from a programmable control, for example, an Allen-Bradley PLC-2 programmable control. The drum tachometer pulses are cummulated in a counter φ (16 bits) of a computer, for example an Intel ISBC 80/24 computer. A software counter (16 bits) is linked to the counter φ to enable storage of 4,300×10 6  counts. 
     The roll tachometer pulses are input to the computer as a first interrupt (when the computer acknowledges this interrupt, it computes the incremental drum pulses from the previous roll tachometer interrupt. Therefore, this routine essentially computes the ratio of the drum tachometer frequency to the roll tachometer frequency. This ratio, along with the program drum diameter, furnishes the information on the wound up roll diameter, updated every wound up layer of paper. 
     The target footage or diameter is entered by way of thumbwheel switches on a benchboard. The drum diameter is also entered by way of binary-coded decimal (BCD) switches located on an auxiliary circuitboard. The caliper of paper is entered through a keyboard connected to a roll structure computer and is subsequently passed on to the stop-to-length computer. The caliper is required for estimating the equivalent number of layers slabbed off after a sheetbreak. These set points are read during initialization only (beginning of a new row). 
     The computer outputs the wound up roll diameter, and accumulative footage to operate light emitting diodes (LED) displays mounted on the benchboard. Other outputs include a deceleration flag, a stop flag to the programmable controller and the drive, and a layer counting flag to the roll structure computer for density computation. 
     The sample rate in a particular embodiment of the invention for closed loop control is half a second. The sample rate clock is a counter (counter 1) of the Intel ISBC 80/24 computer. At countdown, it generates a second interrupt which invokes the routine that pushes the cumulative drum tach count into a last sample count, then reads the current cumulative drum tach count from the counter 5. 
     A sheetbreak signal from the programmable control disables drum tach pulse counting and roll tach pulse interrupt, thus freezing the wound up roll diameter and cumulative footage on the displays. The computer also memorizes the current roll diameter and raises an internal sheetbreak flag. 
     The run signal from the programmable controller enables drum tach and roll tach counting, therefore resuming update of cumulative footage and wound up diameter. 
     An eject signal from the programmable controller initializes the stop-to-length computer. The displayed roll diameter and footage will be reset. The target length or diameter and the caliper are read in for the next roll. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other objects, features and advantages of the invention, its organization, construction and operation will be best understood from the following detailed description, taken in conjunction with the accompanying drawings, on which: 
     FIG. 1 is a front view of a control panel for a cut-to-length/cut-to-diameter control including a display of length and diameter, an encoder input for length and a core chuck sensor; 
     FIG. 2 is a block circuit diagram of a control constructed in accordance with the present invention; 
     FIG. 3 is a flow chart which sets forth the operation of the circuit of FIG. 2; 
     FIG. 4 is a schematic circuit diagram of a modification of an existing drive control for accomplishing &#34;bang-bang&#34; operation; and 
     FIG. 5 is a strip chart recording of drive speed and switching of the deceleration rate. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIGS. 1 and 2, a control channel and a system block diagram are illustrated. The control panel 10 comprises a plurality of control elements or indicators including a sheet length display 14, a rolled diameter display 16, a diameter/length selection switch 18, length set switches 12 and a core chuck sensor (indicator) 20 which may also double as a run switch. 
     In FIG. 2 the control system is illustrated as comprising the panel switches 12 and drum diameter selection switches 30, both set of switches being connected to the diameter/length switch 18. As an alternative, the panel switches 12 may also function as the drum diameter switches 30 on the front panel of FIG. 1 through the actuation of the switch 18. 
     At the left side of FIG. 2, a programmable control 22, for example the aforementioned Allen-Bradley PLC-2 controller is illustrated as providing three signal, namely EJECT,SHT.BRK. and RUN. Also, a drum tachometer 24 and a roll tachometer 26 are illustrated. The programmable control 22 and the tachometers 24 and 26 are connected to and/or through an auxiliary circuitboard 28 which includes an inhibit control 32 having the inputs E and INH. The EJECT signal passes directly through the auxiliary circuitboard 28 to an input RST of a microcomputer 34, for example the aforementioned INTEL ISBC 80/24 computer. The SHT.BRK. signal is connected to the INH input of the inhibit control 32 and to an interrupt input INT4 of the microcomputer 34. The inhibit control 32 provides a signal to the counter or timer φ of the microcomputer 34 and an interrupt signal to the input INT1of the microcomputer 34. 
     The microcomputer 34 provides the aforementioned outputs, in particular the outputs to the roll diameter display 16 and to the length display 14, and an output to the drive control to complete a closed loop back through the programmable control 22 and the tachometers 24 and 26. 
     The system illustrated in FIGS. 1 and 2 and the circuit of FIG. 4 operate in accordance with the flow chart of FIG. 3 and in accordance with the appended computer program and as described above in the summary of the invention. 
     More specifically, after initialization, the main program constantly computes speed from the difference between the current and last drum tachometer counts and the programmed sample rate. The anticipated stopping distance is computed from the speed and the drive deceleration rate. If the sum of the anticipated stopping speed and the cumulative footage is greater than the target length, the deceleration flag is raised. The drive, after receiving this signal from the output 36, will switch to a deceleration rate greater than the programmed rate, this switching being set forth below with respect to FIG. 4. This switching causes the speed to drop below the anticipated value at some subsequent sample. As a consequence, the newly-computed stopping distance will be smaller than anticipated, the deceleration flag will be lowered, and the drive will be switched back to a deceleration rate lower than the programmed value. The rate of speed change will drop and a subsequent computation of the stopping distance will again raise the deceleration flag. Therefore, a bang-bang control of the deceleration is provided down to zero speed. Because of the time lag in the drive, which occurs the first time the deceleration flag is raised, a time advance factor is programmed in to compensate for this one-time system &#34;dead time&#34;. 
     In the control-to-diameter configuration, the anticipated stopping diameter is computed from the stopping distance. To account for the possible layers slabbed off after a sheetbreak, the caliper, the last value of roll diameter before sheetbreak, and the new diameter after run is resumed are used for computing the decremental footage. The formulae for various computations are set forth below on the basis of the equation 
     
         D=V.sup.2 /2a 
    
     where D is equal to the distance, V is the velocity and a is the rate of deceleration. 
     The stopping distance may be computed, on the basis of the Fortran language as 
     
         D=(speed ** 2)/2 * a. 
    
     The stopping diameter may be calculated in accordance with ##EQU1## where V[(N-1)T] is the speed of the roll in ft/sec computed from the last sample; 
     D[(N-1)T] is the roll diameter in inches at the last sample; 
     D(NT) is the stopping distance; 
     c is the caliper of the paper in inches; and 
     a is the rate of deceleration in ft/sec 2 . 
     Based on a 500 ppr drum tachometer rate, the decremental drum tachometer count may be calculated from the relationship 
     
         ΔCT=500(D.sub.L.sup.2 -D.sub.I.sup.2)/96c 
    
     where 
     ΔCT is the decremental drum tach count; 
     D L  is the last diameter before sheetbreak; and 
     D I  is the new diameter after sheetbreak. 
     The resolution of the drum tachometer is 1/500 or 0.2%. Therefore, the resolution limit of layers is ##EQU2## For example for a 30 inch roll and a caliper of 0.002 inch, the resolution error is 15 layers of 118 feet. The error in total footage is 0.2% of the final layer. Thus, for a 60 inch roll, the error is only 4 inches. 
     Referring to FIG. 4, a modification of an existing drive control is illustrated in which the existing drive control comprises a variable resistor 38 connected to a reference voltage V for establishing a reference rate via a resistor 40 and an amplifier 42 having a feedback capacitor 44. This circuit provides a speed reference at an output 52. In order to change the rate of deceleration, it is conventional on drives using analog control circuits to adjust a voltage fed to a speed reference integrator, as in this circuit. The deceleration can then be easily switched between two rates by switching the time constant of the integrator. In the present modification of this circuit, this is easily accomplished by switching another resistor 46 in parallel with the resistor 40 by way of relay contacts 48 and a relay winding 50 controlled by the deceleration control 36 of the microcomputer 34. 
     The present system has been constructed and operated in accordance with the strip charts of FIG. 5 which illustrates the drive speed and switching of deceleration rate for a set sheet length of 4750 feet and a stop length of 4755 feet. This run is typical. One will note the lag time of the drive, from the deceleration command to the actual start of deceleration is about 2.5 seconds. The results of a series of consecutive runs setting various sheet lengths and winder speeds are set forth below. 
     
         ______________________________________WINDERSPEED    SET LENGTH  ACTUAL LENGTH  ERROR(Ft/Min) (Feet)      (Feet)         (Feet)______________________________________2000     5000        4994           -62000     5000        4995           -51500     3000        2990           -101500     3000        2993           -74000     6000        5995           -53000     6000        5994           -64000     6000        5999           -13000     6000        5997           -36000     6000        5995           -55000     6000        6000            04000     4000        4000            03500     4000        3990           -10______________________________________ 
    
     As mentioned, the system operates in accordance with the appended program and in accordance with the flow chart of FIG. 3. 
     Although we have described our invention by reference to particular illustrative embodiments thereof, many changes and modifications of the invention may become apparent to those skilled in the art without departing from the spirit and scope of the invention. We therefore intend to include within the patent warranted hereon all such changes and modifications as may reasonably and properly be included within the scope of my contribution to the art. ##SPC1##