Abstract:
An apparatus for adjusting die clearance for an extruder producing a sheet in a die having an adjusting device for adjusting the die clearance between an upper die and a lower die, a measuring device for measuring thicknesses of the sheet at a plurality of positions in the direction of width on the sheet, a setting device for setting desirable thicknesses at the positions, an adjusting data producing device for producing data with respect to die displacement to be adjusted from the measured data and the desirable thicknesses, and control device for controlling the adjusting device in order that the die clearance coincides with the desirable thickness. Rough adjustment can be effected by tightening or loosening the bolts while fine adjustment is achieved by heating the bolts with an electrical heater disposed thereabout.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to a method and apparatus for adjusting die clearance for an extruder producing a sheet, film or coating on a magnetic record of a thermoplastic resin, cellulose, rubber and the like, paper, cellophane hopper or printing ink and the like. 
     In a die device for molding a sheet or film of this kind (hereinafter referred to as the &#34;sheet&#34;), as shown in FIGS. 1 and 2, the size of die clearance 11 is adjusted by pushing or pulling a plurality of bolts 12 disposed in the direction of width in order to change the pushing force acting upon a backface 15 of an upper die element 13 and to thereby adjust the degree of bending at a neck portion 14 of upper die element 13. 
     However, upper die element 13 is a continuous body and when a specified bolt is manipulated, the die clearance changes not only at the position where that specified bolt acts but also at the other portions. This phenomenon is referred to as the &#34;mutual interference effect&#34;. Ideally, the effects should be additive according to the &#34;principle of superposition&#34;. Unfortunately, they are not. Thus, as shown in FIG. 3, the lip deviation when only the eighth bolt of twenty-two adjusting bolts is manipulated (curve a) or when only the fifteenth (curve b) is manipulated cannot be added to determine the deviation when both eighth and fifteenth (curve c) are manipulated. Thus, at the position of the 8th bolt curve a is 30, curve b is 10 and curve c is 35, not 40. 
     The adjustment of die clearance has been mostly carried out empirically through manual work of an operator. Therefore, some difference for adjusting occurs from operator to operator, resulting in low accuracy of die clearance, time-consuming adjustment and danger in adjustment. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention is directed to a method and apparatus for automatically adjusting the die clearance which eliminates the problems mentioned above. More specifically, the present invention is directed to a method and apparatus for adjusting the die clearance, which measures the thickness of the sheet in the direction of width during molding, detects whether or not the measured sheet thickness attains a predetermined thickness and, when not, automatically operates the adjusting bolts for adjusting the die clearance while considering the abovementioned &#34;mutual interference effect&#34; so as to adjust the die clearance to the predetermined sheet thickness. Rough adjustment can be effected by tightening or loosening the bolts while fine adjustment is achieved by heating the bolts with an electrical heater disposed thereabout. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 illustrates a perspective view showing a conventional die of the prior art; 
     FIG. 2 illustrates a side view as viewed from an arrow Z in FIG. 1; 
     FIG. 3 illustrates a diagram showing the relation between adjusting bolts and lip displacement; 
     FIG. 4 illustrates a block diagram showing an embodiment of the present invention; 
     FIG. 5 illustrates a perspective view showing a die device and automatic rotating device of the embodiment of FIG. 4; 
     FIG. 6 illustrates a side view as viewed from an arrow Y in FIG. 5; 
     FIG. 7 illustrates a diagram showing how the deformation of the die as a whole is effected by adjusting one bolt; 
     FIG. 8 illustrates another embodiment for adjusting die clearance; 
     FIG. 9 illustrates a detailed block diagram of a calculation unit; and 
     FIG. 10 illustrates a flow chart for explaining the operation of the calculation unit. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     An embodiment of the present invention will be explained with reference to FIGS. 4, 5 and 6. In FIG. 4, a die device 21 is mounted on an extruder (not shown) and has a lip portion 11A which is formed between an upper die element 13A and a lower die element 13B as shown in FIGS. 5 and 6. 
     The degree of opening at the lip portion, which forms the aforementioned die clearance, may be adjusted by adjusting bolts 12A each of which is rotated by a tool 101 rotatably mounted on an automatic rotating device 100. Device 100 is arranged so as to be movable along the direction in which adjusting bolts 12A extend and to stop at each adjusting bolt 12A. For this purpose, automatic rotating device 100 is slidably mounted on a guide rail 103. 
     A wire 110 between pulleys 111 and 112 extends through holes 118 and 119 of a plate 117 which supports member 102. Member 102 has a mechanism for transmitting rotation of motor 116 and effecting movement in the vertical direction. The wire is also attached to supporting plate 117 by a screw 120. 
     Therefore, automatic rotating device 100 may be moved in the direction along which adjusting bolts 12A extend by rotating pulley 111 connected to a shaft 115 of a motor 113. A rotary encoder 114 produces a signal representing the position of automatically rotating device 100. 
     Through lead wires 121 and 122 connected to supporting plate 117 from a power control unit 32 shown in FIG. 4 are applied control signals and electric power, respectively. The control signals control the rotation, which is measured by a resolver 116A, of a servo motor 116 which rotates tool 101. The control signals still further control the position of tool 101 in the vertical direction. Tool 101 descends to a vertical position at which tool 101 fits into the hollow of the head portion of bolt 12A. Rotating device 100 is stopped at each adjusting bolt. Each numeral 11A, 12A, 13A, 14A and 15A designate elements corresponding to the elements of numerals 11, 12, 13, 14 and 15 shown in FIGS. 1 and 2. 
     Referring to FIG. 4, a sheet 22 extruded out from lip portion 11A travels around a cooling roller 23 and a conventional treating processer 24 to a winder 33 where it is taken up by the winder. The thickness of sheet 22, after it is treated by processer 24, which may stretch sheet 22, is continuously measured by a measuring device 25 for example, using B-rays. The sheet thicknesses measured by device 25 are compared by comparator 27 with the desirable values set by a manually operable thickness setter 26 for setting the sheet thicknesses at a plurality of predetermined positions in the direction of width of die device 21. Thus, comparator 27 determines the die clearance to be varied in accordance with the difference values between setting thickness and measured thickness at each position mentioned above. The die clearances to be varied as derived from comparator 27 are fed to a calculation unit 29 to which also data from a memory device 28 are fed. 
     The data stored in memory device 28 represent a group of coefficients relating displacement quantities and loads on each adjusting bolt 12A at each position mentioned above. Calculation unit 29 therefore calculates displacement quantities for each adjusting bolt 12A. 
     A display device 30 such as a cathode ray tube displays the displacement quantities calculated by calculation unit 29. Print-out is also possible if the output of calculation unit is fed to a printer 31. A power control unit 32 supplies signals to servo motor 116 to cause rotation until the measured displacements of bolts 12A reach those calculated by calculation unit 29. 
     Having the above-described construction, the apparatus of the present invention operates in the following manner. It will now be assumed that in FIG. 7, when a bolt load P 1  is applied only to the first bolt 12a of eight adjusting bolts, the deformation of the die exhibits a displacement quantity δ 1 , δ 2 , . . . δ 8  at each of the predetermined positions. Thus, 
     
         δ.sub.I =f.sub.I,1 P.sub.1                           (1) 
    
     where f I ,1 is a coefficient of the die clearance at the first position with respect to the load onto first bolt 12a. 
     Generally, the displacement quantity δ I  is given by: 
     
         δ.sub.I =f.sub.I,J P.sub.J (J=1, 2, 3, . . . n)      (2) 
    
     The constant f I ,J represents a matrix of coefficients inherent to each die device and can be obtained theoretically or experimentally. The matrix of coefficients are stored in advance in memory 28. 
     The desirable sheet thickness E I  at each of the plural predetermined positions is set into setter 26. Comparator 27 compares this set value with the measured value (EM I ) given from measuring device 25 and calculates the displacement quantity δB I  of the die clearance to be varied by each adjusting bolt from the difference between the set value and the measured value, as e I  (I=1, 2, . . . n). If the displacement quantity of each load onto the bolt required for obtaining each e I  is expressed as ΔP J  (J=1, 2, . . . n), the relationship between ΔP J  and e I  is given as follows by using the coefficient f I ,J stored in memory device 28. ##EQU1## Namely, 
     
         e.sub.1 =f.sub.1,1 ΔP.sub.1 +f.sub.1,2 ΔP.sub.2 +f.sub.1,3 ΔP.sub.3 + . . . +f.sub.1,n ΔP.sub.n 
    
     
         e.sub.2 =f.sub.2,1 ΔP.sub.1 +f.sub.2,2 ΔP.sub.2 +f.sub.2,3 ΔP.sub.3 + . . . +f.sub.2,n ΔP.sub.n 
    
     
         e.sub.3 =f.sub.3,1 ΔP.sub.1 +f.sub.3,2 ΔP.sub.2 +f.sub.3,3 ΔP.sub.3 + . . . +f.sub.3,n ΔP.sub.n 
    
     In other words, multiple simultaneous linear equations are solved for ΔP J  by GAUSE-SEIDEL method or asymptotic method, for example. The displacement quantity for each bolt, δBI, is given by the following Equation (4) in consideration of the bolt&#39;s deformation by compressing. ##EQU2## where k is a spring constant of the bolt. 
     The bolt displacement quantity δ BI  is determined in the abovementioned manner and it is applied from the calculation unit 29 to display 30 using the CRT or to printer 31. It is also applied to power control unit 32 to achieve the predetermined die clearance. In this manner, the drawbacks first herein described can be eliminated. 
     In addition in FIG. 4, it may also be possible that measuring device 25 is located just after cooling roller 23 as shown with broken lines. 
     Furthermore, FIG. 8 shows another way to provide fine displacement in the direction of die clearance to upper lip 15A by heating adjusting bolt 12A. In FIG. 8, holder 51 mounting bolt 12A provides an elongated heating unit 52 parallel with bolt 12A, so that bolt 12A can be heated through holder 51 by heating unit 52. Electric current is applied through a wire 53, which is connected to power control unit 32 as shown in FIG. 4. Holder 51 is also provided with an inlet 54 and an out flow passage 54A for cooling fluid, for example, air at low temperature. This permits quick response to the desired thermal displacement of bolt 12A. Holder 51 is also provided with a thermo-couple 55 for measuring the temperature of the portion adjacent bolt 12A. In this embodiment, calculation unit 29 calculates a desirable temperature θ I  for each bolt, which corresponds to the displacement quantity δBI mentioned above. 
     FIG. 9 illustrates a block diagram for explaining the details of calculation unit 29 and power control unit 32 shown in FIG. 4. More specifically, FIG. 9 illustrates a combination for rotating and heating bolt 12A shown in FIG. 5 and FIG. 8, respectively. 
     In FIG. 9, calculation unit 29 has a calculation portion 201 which calculates the displacement quantity δBI at each position of bolt 12, a setting portion 202 on which is set a value &#34;m&#34; corresponding to the value of minimum resolution of servomotor 116 shown in FIG. 5, and a dividing portion 203 which divides the displacement quantity δBI into the rough value &#34;δBI (R)&#34; and the fine value &#34;δBI (F)&#34;, as shown in the FIGURE, where R stands for rough and F for fine. The integer N is selected according to the following expressions. 
     
         δBI (R)=N·m 
    
     
         δBI (F)=δBI-δBI (R)&lt;m 
    
     Calculation unit 29 also includes rotating angle conversion portion 204A and temperature conversion portion 204B. Portion 204A converts the value &#34;N·m&#34; to a rotation angle for servo motor 116 and portion 204B converts the value &#34;δBI (F)&#34; to a temperature value corresponding thereto. Power control unit 32 has rotating control portion 205A and temperature control portion 205B, to which are applied feedback signals from resolver 116A and thermo couple 55, respectively. 
     FIG. 10 illustrates the flow chart showing the process of execution in calculation unit 29. In FIG. 10, step 1 of the process shows the measuring of sheet thickness EM I  at the each measuring position. Step 2 shows the calculating of displacement quantity δBI. At step 3, it is checked whether the value &#34;δBI&#34; is larger than or equal to &#34;m&#34; or not. 
     When &#34;δBI&#34; is larger than or equal to &#34;m&#34; at step 3, the value N·m is calculated at step 4 where &#34;N&#34; is an integer and the following expression results: 
     
         δBI-m&lt;N·m≦δBI 
    
     When &#34;δBI&#34; is smaller than &#34;m&#34; at step 3, the value of &#34;N&#34; is set as zero at step 5. 
     At step 6, the calculated value &#34;N·m&#34; is converted to the rotating angle of servo motor 116. 
     At step 7, the remaining value &#34;δBI (F)&#34; (which equals to &#34;δBI-N·m&#34;) determined, and at step 8, the value &#34;δBI (F)&#34; is converted to the value of the temperature of bolt 12A for producing thermal displacement of the bolt. By using the combination of rotating and heating the bolt as shown in FIG. 9 and FIG. 10, it is possible to minimize the electric power supply requirements for heating the bolt. Furthermore, it is possible to constitute a quick response system for reducing the difference e I  between the desirable value E I  and measured value EM I  at each position. 
     It is to be understood that the invention is not limited in its application to the details of construction and arrangement of parts illustrated in the accompanying drawings since the invention is capable of other embodiments and of being practiced or carried our in various ways.