Control device for guiding a material web
FIELD AND BACKGROUND OF THE INVENTION 
     The present invention relates in general to control devices for controlling the movement of sheet like material, and in particular, to a new and useful control device for guiding edges or a centerline of a material web which moves over rollers utilizing a circuit which responds to actual position values as well as speed values for the material web to produce a signal for controlling a controlling element to properly align or reposition the material web. 
     While manufacturing and processing web-like or sheet-like materials, it is well known to employ control devices for exactly guiding the edges or the centerline of the material web or sheet. Controllers with hydraulically or electrically actuated correcting elements are used for this purpose, with the correcting elements being embodied by reels and/or control rollers. To obtain a control which is free from hunting, the device for measuring the position of the web must be provided in close proximity to the associated correcting element. This, however, is frequently impossible, for example in instances where the web of material is guided through a kiln that is heated to a high temperature, or through a wet region. In such instances, the position of the web must be determined at a location which is remote from the correcting element, and this as a rule, results in an undesirable hunting movement of the webs. 
     According to U.S. Pat. No. 3,568,904, such a hunting motion may be eliminated by timing the adjustment of the correcting elements, or adjusting them stepwise. 
     A similar situation arises if the correcting element cannot be built in because of the layout of the unit, or if for technological reasons the control must be provided in the preceding zone. In such instances, a second measuring device may be provided at the location where the accuracy in guidance is wanted, and the measuring device which is mounted close downstream of the correcting element is then adjusted stepwise, with the timing depending on the speed in the unit (U.S. Pat. No. 3,568,904). 
     It is disadvantageous in this timed prior art control that the correcting signal is not proportional to the run of the web, so that this run cannot be adjusted to an exact zero deviation. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to an improved control device of the above-mentioned kind which controls the run of the web continuously, without hunting, and adjusts a zero deviation. 
     Accordingly an object of the present invention is to provide a control device for exactly guiding edges or centerlines of material webs which move over rollers and are guided by a correcting element and whose position is ascertained by determining a deviation from a desired value for the web position, the deviation for the desired value being obtained by multiplying an actual value for the position at a predetermined location multiplied by the speed of the material web. 
     The inventive control device has the advantage that an otherwise needed control roller can be omitted, while still maintaining a continuous control. Another advantage is that even in arrangements where the error value is determined at a location remote from the correcting element, a continuous control is ensured. 
     The actual value is measured by means of a measuring device provided at a location remote from the correcting element. In a preferred arrangement, the deviation of the control as variable is transmitted through a proportional controller to the first input of a multiplier and the speed of the web is applied to the other input of the multiplier, and the multiplier is followed by an integrator whose output signal is used for controlling the correcting element. 
     The control action may further be improved by providing a second control circuit which is subordinate to the first one and which is connected between the output of the integrator and the correcting element and comprises a controller for positioning the correcting element, with the position controller being supplied with an actual signal formed of the output of the integrator, which is the desired value, and the actual value of the correcting element or the actual value of the run of the web immediately downstream of the correcting element. 
     A further object of the invention is to provide a control device for controlling the movement of a material web which is simple in design, rugged in construction and economical to manufacture. 
     The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which preferred embodiments of the invention are illustrated. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the Drawings: 
     FIG. 1 is a diagrammatical illustration of one embodiment of the invention; 
     FIG. 2 is a block diagram of the inventive control device; and 
     FIG. 3 diagrammatically shows another embodiment of the invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to the drawings, like parts are designated with the same reference numerals. 
     In FIG. 1, a web of materiall runs in the direction of arrow 2 through a kiln 3. The web is driven through drive rollers 4. A reel provided at the right hand side of the figure and in front of the kiln is not included in the subject matter of this embodiment and therefore not shown. Web 1 runs over a control roller 5 performing the function of a correcting element, to a water tank 6 serving as a water seal at this side, confining the protective gas in the kiln. The web is then strained over a deflection roller 7 to the two drive rollers 4. Drive roller 4 is connected to a tachometer 8 for measuring the speed of the web. Downstream of the drive rollers, a measuring device 9 is provided for determining the position of the web. At this location, the actual value of the position is measured, which is needed for determining the error value. As already mentioned, the correcting element is embodied by control roller 5. In the present example, control roller 5 is mounted on a support 10, for pivoting about an axis 11. The pivoting is effected hydraulically by means of an actuating cylinder 12. The position of the support and thus of the control roller is measured by means of a position pickup 13. 
     FIG. 2 shows a first control circuit starting at 14 and a second control circuit starting at 15 associated therewith. The controlled area or system within which a deviation of the web run is to be eliminated is shown at 16 in FIG. 1 and extends between control roller 5 and the drive rollers 4. Downstream thereof, measuring device 9 is provided for measuring the actual value. This actual value, i.e. the actual position of the web, and the predetermined desired value are delivered to a summing point or unit 17 whose output (the difference value) is applied to the input of a proportional controller 18. The circumstance underlying the invention is that the lateral or deviation speed of the running web within the extension of controlled area 16 equals the product of the advancing speed of the web and the difference value. Therefore, the output signal of proportional controller 18 is applied to the first input of a multiplier 19. The speed of the web is supplied to the control circuit through the second input of the multiplier. For this purpose, the output of tachometer 8 is supplied to the second input of multiplier 19. Multiplier 19 is followed by an integrator 20. The error signal is derived from the output signal of the integrator, by which control roller 5 is adjusted. 
     To form the second control circuit starting at 15, a position pickup 13 is connected between the input of correcting element 5 and a summing point 21. The output of the integrator is also applied to this summing point. The output of integrator 20 is the desired value (set point) for control circuit 15. The position of the control roller, i.e. the correcting element 5, is the actual value. The position of the correcting element is detected or measured by means of position pickup 13. The error signal (difference between actual and desired roller position) is then applied to a position controller 22 whose output signal actuates a servo valve 23 which in turn hydraulically actuates cylinder 12 by which correcting element 5 is hydraulically adjusted. The effect of the two control circuits (at 14, 15) may also be so interpreted that multiplier 19 and integrator 20 form a stabilizing member for the control circuit at 14. Position controller 22 has the characteristic of a proportional controller which is followed by servovalve 21 and actuating cylinder 12 as an integral member. 
     FIG. 3 shows another embodiment of the invention. Web 1 is wound off a reel 25 in the direction of arrow 2, by means of drive rollers 4. Between the reel and the working station 24, the web is run about three deflection rollers 7, 7&#39;, 7&#34;. To control the run of the web, reel 25 is equipped with a frame 26 which is designed as a correcting element acted upon by the piston rod of an actuating cylinder 12. The actual position of the running web is measured first close downstream of reel 25 by means of a measuring device 27, and then upstream of the working station 24 by means of measuring device 9. Devices 9 and 27 may be electric eyes or any other known position sensing arrangement. Drive rollers 4 are again connected to a tachometer 8 for measuring the speed of the web. The position of the reel is adjusted perpendicularly to the run of the web. The control system is generally designated 16. The circuitry is designed in accordance with FIG. 2. To form the second control circuit 15, the output of measuring device 27 which is provided adjacent correcting element 25 is applied to the summing point 21. In FIG. 2. measuring device 27 corresponds to position pickup 13. The output signal of integrator 20 is applied to the summing point. The output signal of integrator 20 is the desired value for control circuit 15. The position of web 1 downstream of correcting element 25 is the actual value. The error signal is applied to position controller 22 whose output signal actuates a following servovalve 21 which in turn hydraulically actuates cylinder 12 by which the correcting element is hydraulically adjusted. 
     While specific embodiments of the invention have been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles.