Abstract:
A web tension control and apparatus uses a lightweight dancer and a control system that detects web tension using the dancer position as well as downstream sensors to maintain a relatively constant web tension. The control system also adjusts the braking force to an unwind roll based on the diameter of the roll, allowing for greater web tension control. A two-phase braking system prevents the unwind roll from spilling excess paper into the production line.

Description:
TECHNICAL FIELD 
     The present invention relates generally to web driven processing systems and more particularly to the control of web tension and braking systems and in particular as those systems relate to the production of envelopes. 
     BACKGROUND OF THE INVENTION 
     Precise web tension control is important in the printing and paper processing industries. Even small variations in web tension prevent effective application of ink and embossing. In high speed web lines, such as those exceeding 500 feet per minute, manual adjustment of web tension is not possible. Such systems therefore require automated tension control systems. 
     In systems which control tension using a dancer, one limitation on effective web tension control is the response time of the dancer. Frequently, the dancer movement lags the actual change in web tension, causing the control system to fall behind in reacting to the change and thereby not properly adjusting the tension maintained in the web. One of the primary causes of such delayed reaction is the weight of the dancer. Another cause is insufficient elasticity in the web. 
     Another problem with achieving precise tension control of a web is the inertia of the web unwind roll which supplies the web to the system. Current systems usually apply braking force to the unwind roll based on web tension, web speed, or supply roll diameter. However, the braking force applied to the supply roll is often poorly matched to the force actually required, since most systems make no provision for possible variations in roll size and weight. The result is that these systems frequently over-apply or under-apply the unwind roll brakes, resulting in large variations in web tension and risking damage to the web as well as the processing equipment. 
     The lagging response of the dancer to changes in web tension also gives rise to rapid web tension variations when shutting down the web processing line, whether the shut down is routine or as a result of an emergency shut down caused by an error which is detected by a sensor. After the shut down signal is sent, the unwind roll in previously available systems continued turning due to its inertia. This situation caused the dancer festoon to overflow rapidly and thereby waste paper and potentially damaging equipment. Current dancer controlled systems do not react to a shutdown quickly enough to prevent this. 
     SUMMARY OF THE INVENTION 
     The invention eliminates the disadvantages of previous web tension control systems by detecting downstream web tension and combining the data with information about the movement of the dancer to take into account the elasticity of the web. The invention also employs a lightweight dancer having a low-friction cylinder and pivoting on low-friction bearings. The control system of the present invention takes the unwind roll inertia into account by activating selected portions of the unwind roll brakes based on the diameter of the roll. Finally, the problems associated with shutdown are solved by monitoring the downstream shutdown controls and generating a short, closed-loop brake pulse to the unwind roll brakes when a shutdown signal is detected. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     While the appended claims set forth the features of the present invention with particularity, the invention may be best understood from the following detailed description taken in conjunction with the following drawings of which: 
     FIG. 1 is a block diagram of an exemplary system incorporating the invention; 
     FIG. 2 is a side view of the unwind section and the cutting and shaping section incorporating the present invention; 
     FIG. 3 is a block diagram and illustration of the web showing the overall function of the control system incorporating the present invention; 
     FIG. 4 is a drawing illustrating the movement of the dancer assembly of the present invention; 
     FIG. 5 is a logic diagram showing the electronic layout of the control system incorporating the present invention; 
     FIG. 6 is a top view of the dancer assembly of the present invention; 
     FIG. 7 is a side view of the dancer assembly in FIG. 6; 
     FIG. 8 is a perspective view of the cleavis of the present invention; 
     FIG. 9 is a side view of the cleavis of the present invention; 
     FIG. 10 is a front view of the cleavis of the present invention; 
     FIG. 11 is side view of the dancer arm support section of the present invention; 
     FIG. 12 is a side view of the dancer arm of the present invention; and 
     FIG. 13 illustrates the placement of the dancer assembly in the unwind unit incorporating the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     An industrial printing and paper processing machine normally performs its tasks on a continuous sheet or “web” of paper. The web of paper is pulled by a power driven “pull” roller through a series of non-driven or “idler” rollers to the various stages of processing, where the paper can be cut into segments, shaped, or stamped. The web is fed into such a machine from a large roll of paper, called an “unwind roll.” An unwind roll normally rotates on an roll stand of some sort. It is usually not driven, relying instead on the pulling capability of pull rollers which are driven at various points in the processing equipment. Many unwind roll systems do have brakes, however, to assist in controlling web tension. 
     One problem with current unwind roll braking systems is that they do not react quickly enough during a machine shutdown to avoid spilling paper into the system, exceeding the capacity of the festoon or dancer. Since these machines often run at speeds of 1000 feet per minute, the amount of wasted paper is considerable. 
     Because the web often moves at different speeds through different sections of the machine, it frequently becomes slack. To prevent a slack web from becoming tangled, bunched, or wrinkled, a web processing system, such as an envelope production system, frequently employs a “festoon” and/or a “dancer.” A festoon is a series of idler rollers designed to hold excess web material in a non-damaging manner. A dancer is typically one or more idler rollers or non-rotating arms that are able to “float” or move freely, usually by being mounted on a pivoting frame of some sort. Such a dancer system controls web tension by increasing or decreasing the distance traveled by the web. 
     Controlling the tension of the web as it travels through a paper processing machine is important for a number of reasons. Variations in web tension can cause smears and imperfections when there is any printing being performed, and can also cause the web paper to be torn or crumpled, resulting in waste. Previous methods of controlling web tension include using the position of a floating dancer arm to gauge the tension and applying or releasing the unwind roll brakes to increase or decrease the tension. While these methods are acceptable for low precision applications where errors of up to plus or minus 0.125 inches are acceptable, they are inadequate for the needs of the current market. 
     An example of an application requiring high precision is in the area of “registered embossing,” in which detailed patterns are stamped onto sections of the web. This kind of procedure can tolerate errors of no more than plus or minus 0.006 inches. This is especially important where printing must be in registration with embossing. Such precision requires the ability to control web tension to within plus or minus 0.5 pounds of a predetermined set point. With such little room for error, the elasticity of the web must be taken into account. 
     A web is said to have low elasticity when it easily stretches, and high elasticity when it does not. When tension changes in a web of low elasticity, there is a slight delay before the dancer arm moves in response. This delay causes the dancer controller to apply too much or too little braking force to the unwind roll, resulting in variations in tension that are unacceptable for applications like registered embossing. The present invention eliminates this problem using an improved control system and dancer. 
     The invention is illustrated as being implemented on an envelope cutting, folding, and gluing system. Persons skilled in the art will appreciate, however, that the invention can also be implemented on any system having a web path, including flexography, gravure and lithography presses as well as rewinders, slitters, and sheeters. 
     FIG. 1 shows a system incorporating the present invention. In a preferred embodiment, this system is a Winkler &amp; Dunnebier Model 399 Envelope Machine. 
     The envelope machine consists of an unwind section  101 , a cutting and shaping section  103 , a dryer section  105 , a repeater and accelerator section  107 , a folding section  109 , and a delivery section  111 . The web is pulled from the unwind section  101  and is cut and shaped in the cutting and shaping section  103 . From this point on, the paper is no longer a continuous web, but is rather a collection of individual sections. These sections of paper then travel through and are processed by the various processing sections  105 - 109  and emerge at the delivery section  111  as completed envelopes. 
     During shutdown of the system, an operator disengages the main drive shaft of the cutting and shaping section  103  to prevent any further advancement of the web into the various sections  105 - 111 . Already cut segments of paper continue through and are processed by the dryer section  105 , the repeater and accelerator section  107 , the folding section  109  and the delivery section  111 . After all web material has been processed, the sections  105 - 111  of the envelope machine are shut down. 
     FIG. 2 is an elevated view of the unwind section  101  and the cutting and shaping section  103 . The unwind section  101  contains an unwind roll  201  from which a web  203  is drawn. The pull roller  205  presses the web  203  against a nip roller  207  to form a nip and pulls the web  205  through the entire path of the unwind section  101 . 
     A dancer  209  is provided to control web tension. The dancer includes a dancer assembly  211  pivotally mounted at a point  213  of the frame of the unwind section  101 . The dancer assembly  211  has a triangular pulley mount  215  at the end of its long section and a cleavis  217  at the end of its short section. During web processing, the web  203  wraps under fixed idler roller  219 , over fixed idler roller  221 , over fixed idler roller  223 , under floating idler roller  225 , over fixed idler roller  227 , under floating idler roller  229 , over fixed idler roller  231 , under floating idler roller  233  and over fixed idler roller  235 . A cylinder  237  is anchored to the frame of the unwind section  101  at its base end and rotatably coupled to the cleavis  217  at its plunger end. The cylinder  237  provides a constant, counterclockwise force on dancer assembly  211 . 
     Upon exiting the idler rollers  219 ,  221 ,  223 ,  225 ,  227 ,  229 ,  231 , and  235 , the web  203  passes over a support roller  239 , under a load cell  241 , and over a support roller  242 . The web  203  then passes through a conventional web aligning system  243 , a conventional web printing unit  245 , and a rotary embossing unit  246 . The rotary embossing unit  246  embosses the envelopes, either to a feature of the envelope such as the envelope&#39;s flap or to an image printed by printing unit  245  while the web is traveling at full speed and registered with the embossing plates and/or printing plates, thereby eliminating the need to individually emboss or print finished envelopes. After leaving the rotary embossing unit  246  and printing unit  245 , the web is pulled into the cutting and shaping section  103  by the drive roller  205 . 
     As seen more clearly in FIG. 3, a control system is employed in the unwind section  103  in the preferred embodiment of the invention. During normal operation, the weight of the dancer assembly  211 , including the pulley mount  215 , and the floating idler rollers  225 ,  229 , and  233  create a counter clockwise torque on the dancer assembly  211  around a point  213 . 
     In operating the envelope machine, an operator sets the desired web tension at a control panel  224  by adjusting a rotating control  226  to cause a pressure regulator  228  to add or release pressure from the air cylinder  237 . Typically in the above identified envelope processing system, this tension is one pound per inch of web width. Upward pressure from the air cylinder  237  adds to the counter clockwise torque on the dancer assembly  211 . Tension in the web  203  creates an upward force on rollers  225 ,  229 , and  233  that, combined with the weight of cleavis  217 , results in a clockwise torque on the dancer assembly  211  around point  213  equal to that of the counter clockwise torque. 
     The dancer assembly  211  remains stationary under these balanced conditions. In the preferred embodiment, the dancer controller  249  is a Warner Electric TCS-210W Dancer Control; the air cylinder  237  is a Bellofram size  24 , stroke F Super Cylinder; and the pressure regulator  228  is a Bellofram Type 41-2 regulator with ¼ inch ports. 
     Any increase or decrease in the tension of the web as a result of machine operations or web  203  breakage changes the force exerted on the floating idler rollers  225 ,  229 , and  233 , causing the dancer assembly  211  to move around pivot point  213  in either a clockwise or counter clockwise direction. A dancer position sensor  247  senses a change in the angular position of the dancer assembly  211  and generates a corresponding signal to the dancer controller  249 . In the preferred embodiment of the invention, the dancer position sensor  247  generates between 0 and 15 volts, where 0 volts represents topmost position of the dancer assembly  211  and 15 volts represents the bottom most position of the dancer assembly  211 . 
     A change in the tension of the web  203  also causes a change in the force applied by the web  203  on a load cell  241 . The load cell  241  senses the change and generates a corresponding signal to the dancer controller  249 . In the preferred embodiment, the signal generated by the load cell  241  is approximately 0.0025 volts per pound of change in web tension, and is positive when the tension of web  203  increases, and negative when the tension decreases. Dancer controller then adds the signal from the load cell  241  to the signal from the dancer position sensor  247  to compensate for the elasticity of the web. In effect, the load cell  241  signal acts as a vernier adjustment to the dancer position sensor  247  signal. 
     The dancer controller  249  then compares this result with the voltage representing an operator-defined neutral position for the dancer assembly  211  and changes the level of the voltage being sent to the unwind roll brake unit  253 . In the preferred embodiment, the dancer position sensor  247  is a Dana/Warner model MCS-605-1 Dancer Position Detector, and the load cell  241  is a pair of transducers (part number MO-04491-40) from Cleveland Machine Controls. 
     The possible positions of the dancer assembly  211  may be seen in FIG.  4 . If the calculated angular position of the dancer assembly  211  is above the neutral position  210 , dancer controller  249  decreases the voltage to brake unit  253 , thereby decreasing the stopping force applied by the unwind roll brakes. This action decreases the total tension of web  203 . If the calculated angular position is below the neutral position  210 , then the opposite effect occurs, and the force applied by the unwind roll brakes increases, slowing the unwind roll  201  and causing an increase in web tension. This control scheme maintains the web tension to within plus or minus 0.5 pound of the operator-set web tension. 
     A control system configured according to the present invention can also be used during shutdown to prevent the unwind roll from spilling excessive amounts of paper into the production line, which can result in wasted paper and damaged equipment. Referring to FIG. 3, when an operator pulls the lever  115  of the gearbox  113  to disengage the main drive shaft of the cutting and shaping section  103 , or when the fault detection circuit  114  automatically shuts the envelope machine down as a result of a malfunction, a shutdown signal is sent to the dancer controller  249 . If the diameter of the unwind roll  201  is small, then the dancer controller  249  does not react to the signal. Although the pull roller  205  stops pulling the web  203  when the main drive shaft is disengaged, the unwind roll  201  continues to rotate due to inertia, and adds paper to the dancer. This extra paper creates slack in the web  203 . As described above, the dancer controller  249  reacts to this decrease in web tension by increasing the braking force of the unwind roll brakes. Eventually, the unwind roll comes to a complete stop. 
     If the unwind roll  201  is large, then the dancer controller  249  reacts to the shutdown by generating a short, high voltage braking signal to the unwind roll braking unit  253 , causing the unwind roll brakes to engage quickly and then disengage. This pre-braking phase eliminates excess inertia from the unwind roll  201 . 
     Following the pre-braking phase, the dancer controller  249  reacts to the decrease in web tension in its normal fashion, as in the case of a small unwind roll. 
     FIG. 5 is a logic diagram showing the control system of a preferred embodiment in detail. An AC power supply  255  provides AC power to the dance controller  249 , a web tension controller  257 , a roll size detector amplifier  259 , a DC power supply  261 , and web tension feedback unit  263 . The DC power supply  261  converts AC power received from the AC power supply  255  into DC power and provides the DC power to a roll size detector  265 . In the preferred embodiment, the AC power supply  255  is a Warner Electric Brake Power Supply model TCS-168, and the DC power supply  261  is a Dana/Warner model 75NG24 24 VDC power supply. 
     During operation of the unwind section  101  and the cutting and shaping section  103  of the envelope machine, any change in the tension of the web  203  causes a change in the angular position of the dancer assembly  211 , and is detected by the dancer position sensor  247 , which sends a corresponding signal directly to the dancer controller  249 . The load cell  241  detects the web tension change directly and sends a signal to the dancer controller  249  via the web tension controller  257  and a web tension feedback unit  263 . The two signals are then summed by the dancer controller  249  to compensate the signal from dancer position sensor  247  for the elasticity of the web  203 . In the preferred embodiment, the web tension controller  257  is a Cleveland-Kidder Tensi-Master, Model TMI, and the web tension feedback unit  263  is a Calex Signal Amplifier, model 178 powered by a Calex Power Supply. The dancer controller  249  then converts the summed signal into compensated dancer position value and compares it with an operator-defined neutral position value. It then increases (if the web tension is too low) or decreases (if the web tension is too high) the voltage supplied to the brake unit  253  via the static switch  267 . In the preferred embodiment, the static switch  267  is a Warner Electric Static Switch, model 819-0360. 
     As shown in FIG. 5, the brake unit  253  is preferably a Warner Electric model 13-13-10, thirteen inch, ten magnet Modular Tension Brake. The brake unit  253  contains ten independent electromagnetic brake coils  273 - 291 . Two coils  273  and  275  always receive voltage. The relays  269 ,  270  and  271  control which of the remaining eight brake coils  277 - 291  receives the voltage supplied by the dancer controller  249 . When the relay  269  or the relay  270  is closed, the coils  289  and  291  receive voltage, while closing the relay  271  causes coils  277 - 287  to energize. 
     The roll size detector  265  senses the outer diameter of the unwind roll  201  and generates a corresponding signal to the roll size detector amplifier  259 . The roll size detector amplifier  259  increases the magnitude of the signal and sends it to the relays  269 ,  270  and  271 . 
     In the preferred embodiment, the relay  269  closes when the unwind roll diameter is between  28  and  36  inches and the relays  270  and  271  close when the diameter is between  36  and  59  inches. Different web systems may require different relay settings, depending on the size and weight of the unwind roll, the speed of the web, and the volume of the dancer assembly. When the unwind roll diameter is less than 28 inches, only the coils  273  and  275  are energized. In the preferred embodiment, the above mentioned components are implemented as follows: the detector  265  is a Dana/Warner model UT30 ultrasonic proximity detector; the amplifier  259  is a Dana/Warner model MCS 680-8 amplifier; the relays  269 ,  270  and  271  are Allen-Bradley 24 VAC/DC model 700 type H relays with gold diffused contacts. 
     When an operator pulls the lever  115  of the gearbox  113  to disengage the main drive shaft of the cutting and shaping section  103 , or when the fault detection circuit  114  automatically shuts the envelope machine down as a result of a malfunction, a first relay  293  closes for a short duration and then reopens. As shown in FIG. 5, the first relay  293  is in series with a second relay  295 . The second relay  295  receives the output of the roll size detector amplifier  259 , and in the preferred embodiment, closes when the unwind roll diameter exceeds 40 inches. In the preferred embodiment, the second relay  295  is an Allen-Bradley 24 VAC/DC model 700, type H relay with gold diffused contacts, while the first relay  293  is an Allen-Bradley 24 VAC/DC model 700, type H one-shot, time delay relay that opens for 0.4 seconds at a time. 
     If a shutdown occurs and the unwind roll diameter is above 40 inches, the second relay  295  closes, and the first relay  293  closes for 0.4 seconds. When these two relays are closed, the dancer controller bypasses the closed loop response of the dancer controller, and for 0.4 seconds, generates “preconditioning” high voltage pulse to the active coils of the brake unit  253 , regardless of any change in web tension. This eliminates the excess inertia of the unwind roll. 
     FIG.  6  and FIG. 7 show a top view and a side view of the dancer assembly  211  of the present invention. The dancer assembly  211  includes arms  501 ,  503 , support pieces  505 ,  507 , and a cross brace  509 . The arm  501  has a cleavis  217  welded to one end. The arms  501 ,  503  are parallel to each other and are preferably about 17.625 inches apart in the preferred embodiment. The arms  501 ,  503  have triangular sections  510  and  512  that support three roller shafts  517 . Each of the roller shafts  517  is about 17.375 inches long, 0.591 inches in diameter, and made of solid steel in the preferred embodiment. The floating idler rollers  225 ,  229 ,  233  are 16 inch long steel tubes 1.5 inches in diameter having 0.222 inch thick steel walls in the preferred embodiment. The floating idler rollers  225 ,  229 ,  233  are preferably rotatably mounted on the three shafts using greased ball bearings (not shown). 
     The cross brace  509  is (not shown) a hollow steel tube 1.325 inches in diameter having 0.125 inch thick walls in the preferred embodiment. The brace  509  is 17.325 inches long in the preferred embodiment and is conventionally mounted to the support sections  507  and  505 . 
     FIG. 8, FIG. 9, and FIG. 10 show the cleavis  217  in greater detail. An upper section  529  is 1 inch thick steel in the preferred embodiment, and has a first section  533  and a second section  535 . The first section  533  is 1.694 inches high and 1.47 inches wide in the preferred embodiment. The second section  535  is 2.694 inches tall and 1.53 inches wide in the preferred embodiment. The lower section  531  is made of 0.5 inch thick steel and is 1.53 inches wide and 1.75 inches long (at its longest point) in the preferred embodiment. The lower section  531  has a hole  536  designed to accommodate the plunger end of the cylinder  237 . 
     Referring to FIG. 12, the arm  501  of the dancer assembly  211  has a triangular section  510  that is 8.862 inches from its base to its tallest point in the preferred embodiment. The triangular section  510  has three holes sized to accommodate a set of roller shafts, as described above. A straight section  511  is 26.687 inches in length and  3  inches in height in the preferred embodiment. The entire arm is made of 0.5 inch thick aluminum in the preferred embodiment. The arm  503  is identical in construction to the arm  501 . 
     Referring to FIG. 11, a support section  505  is made from aluminum and has a height of 3 inches and a length of 9.5 inches in the preferred embodiment. The support section  505  is 0.5 inches thick for a distance of 3 inches starting at end  513 , and 1 inch thick for the remaining 6.5 inches in the preferred embodiment. Holes are drilled appropriately to accommodate bolts for attaching the support section  505  to the arm  501 , and for mounting a cross brace  509 , as shown in FIG.  6 . The support section  505  also has a hole  515  to accommodate a shaft and roller, as described below. The support section  507  identical in construction except that it is oriented to be placed on the opposite side of the dancer assembly  211 . 
     FIG. 13 illustrates the manner of mounting the dancer assembly  211  into the unwind section  101 . A roller shaft  519  is mounted in a fixed position in the dancer assembly  211  at the holes  515  and  516 . In addition, the roller shaft  519  is rotatably mounted in the walls  521  and  523  on greased bearings inside the journal caps  525  and  527 , so that the shaft  519  rotates around its longitudinal axis at the pivot point  213  as the dancer assembly  211  pivots. 
     A first pulley  529  is mounted on the shaft  519 . A belt is wrapped around the first pulley  529  and a second pulley  248  located on the dancer position sensor  247 . As the dancer assembly  211  pivots, the first pulley  529  rotates, causing the second pulley  248  to rotate as well. As described above, this allows the dancer position sensor  247  to detect changes in the angular position of the dancer assembly  211 . 
     Operation of the preferred embodiment of the invention can be illustrated and summarized with an example production run of the envelope machine. An operator engages the drive shaft of the cutting and shaping section  103 . The pull roller  205  engages the web  203  and starts pulling from the unwind roll  201 . The web  203  winds through the fixed idler rollers  219 ,  221 ,  223 ,  227 ,  231 ,  235  and the floating idler rollers  225 ,  229 ,  233  of the dancer assembly  211  as described above. The web  203  then passes through the support rollers  239 ,  242  and under load cell  241 . The web aligning unit  243  keeps the web  203  laterally aligned. 
     The web  203  then enters the printing unit  245  and the rotary embossing unit  246 . The web  203  then travels into nip roller  207  and pull roll  205 . If the web  203  slows down, slack is created at the floating idler rollers  225 ,  229 ,  233 . As a result, the weight of the long end of dancer assembly  211  combined with the force of the air cylinder  237  create a counter clockwise torque on dancer that exceeds the upward force of web  203  on the floating idler rollers. 
     In response, the dancer assembly  211  rotates counter clockwise around the pivot point  213 , and this movement is detected by the dancer position sensor  247 . Furthermore, the slack in the web  203  is also detected by the load cell  241 . The load cell and dancer position sensor information are relayed to the dancer controller  249 , which responds by causing the brake unit  253  to slow the unwind roll  201 . The specific parts of brake unit  253  employed depend on the diameter of the unwind roll  201 , as detected by roll size detector  265 . Slowing unwind roll  201  increases the web tension, causing the dancer assembly  211  to rotate clockwise. As the dancer assembly  211  returns to its neutral position, the dancer controller  249  reduces the unwind roll braking force. 
     When enough envelopes have been produced, the operator disengages the drive shaft of cutting and shaping section  103  by pulling lever  115  of gear box  113 . This action generates a signal to the control system of the present invention. If the unwind roll diameter is large, then dancer controller  249  generates a fixed pulse to the brake unit  253  without regard to the position of the dancer assembly or the load cell tension. The dancer controller  249  then returns to a closed loop mode, using the dancer position and load cell data to control the brake unit  253 . 
     In view of the many possible embodiments to which the principles of this invention may be applied, it should be recognized that the embodiment described herein with respect to the drawing figures is meant to be illustrative only and should not be taken as limiting the scope of invention. For example, those of skill in the art will recognize that the illustrated embodiment can be modified in arrangement and detail without departing from the spirit of the invention. Therefore, the invention as described herein contemplates all such embodiments as may come within the scope of the following claims and equivalents thereof.