The invention disclosed herein pertains to an accumulator for accumulating a substantial length of a running web such that if the infeed to the accumulator is stopped or slowed for a short interval, the web in storage is paid out continuously to a web utilizing machine so the machine has a constant supply and need not be stopped or slowed during any part of the interval.
One common use of a web accumulator is where a web is fed from a primary supply reel and it is necessary to splice the leading end of the web from a standby supply reel to the trailing end of a web from the primary supply reel in a manner which will not cause interruption of the web supply to a web consuming or utilizing device. In some known accumulators there is a row of spaced apart rollers on one swingable arm cooperating with another row of rollers which may be stationary or swingable on another arm. When the one arm with a row of spaced apart rollers on it is swung away from stationary rollers or the row of rollers on the other arm and the web is looped around the two sets of rollers, a substantial length of web can be accumulated. During normal running of the web, the arms will be urged to their maximum separation from each other for accumulating and storing the maximum length of web. If the supply of web to the accumulator is stopped for a short interval, the tension due to drawing web from the outfeed end of the accumulator causes the sets of rollers to move toward each other while the length of web in storage is paid out. After the end of the interval during which web infeed to the accumulator is stopped, the two relatively movable sets of rollers separate again to accumulate and store another length of web.
There is another general type of accumulator which has a set of rollers mounted on a movable carriage which can run linearly toward or away from a set of corresponding stationary rollers. The web is looped back and forth between the rollers on the movable and stationary components so that web is accumulated as the movable carriage moves away from the stationary assembly.
In application of web accumulators where web tension is of concern, designers must face the problems associated with friction and inertia. The consequence of these two factors may be appreciated when it is realized that the web may be running at a very high rate of speed when suddenly, for some reason, such as when making a splice, the infeeding web is stopped or decelerated. This change in web motion will result in a reaction by the components of the accumulator. Most notable of these reactions is the motion imparted to the movable assembly of the accumulator, whether swinging arm or linear carriage. Minimizing the inertia and friction associated with this reaction will minimize tension transients, and is a prime advantage of the invention described herein.
Also notable is the change in speed of the individual rollers. While roller inertia can actually be of benefit during a sudden deceleration, it must also be overcome when the infeeding web is returned to the original running speed. The roller nearest the infeed may have come to a complete stop, while each succeeding roller has slowed to some speed slightly higher than the roller preceding it. As the web at the infeed is accelerated it can only be drawn into the accumulator as fast as the rollers can resume their original speeds. Since the force to accelerate these rollers is provided only by the tension in the web, it can be seen that minimizing the number of rollers and their inertias can allow a given system to operate successfully at lower web tensions. In prior art machines, friction and inertia are significant factors which limit their usefulness at low tensions. Thus, there is an important need for a web accumulator which provides the benefits of low friction and minimized inertia, allowing it to handle the most delicate of webs at high speeds without breakage or loss of control.