Patent Application
20070137822
The present invention relates generally to paper processing, and more particularly to cutting sheets of paper.
It is well known for the input portion of an inserter system to include a mechanism for cutting a continuous sheet of paper (i.e. a paper web) into individual sheets of paper. See, for example, US Patent Application No. 2004/0221700 of Williams et al. which was filed Nov. 11, 2004 and which is incorporated herein by reference. As inserter technology has advanced over the years, inserters have been designed to operate at faster rates, but this has caused problems in connection with cutting a continuous sheet of documents into individual pages.
A guillotine cutter is used in conventional systems, to cut the paper web while it the paper stationary. A transport mechanism advances the paper web and stops it at prescribed positions. When the web is stopped, the guillotine cutter blade descends and cuts the web transversely. After the web is cut, and the guillotine cutter is raised, the web must be quickly accelerated and decelerated again to get the web in position for the next guillotine cut.
Mechanisms for feeding the web must be robust enough to handle extreme accelerations and decelerations, and must also be accurate enough that sheets are consistently cut at the desired positions. In typical prior art arrangement, the transport mechanism is comprised of servo motors that are electronically controlled to stop and start in the required positions.
While the servo motor solution has been found to be acceptable under a wide range of conditions, such a solution places limits on the speed of paper cutting, the accuracy of paper cutting, and on the lifetime of paper cutting equipment. New paper cutting technology is needed for inserter systems, in order to achieve similar or greater accuracy, in order to reduce wear that eventually destroys expensive servo motor mechanisms, and in order to simplify control of the system.
Typically, a continuous web cutter is used to cut a continuous web of material into cut sheets, and provide the cut sheets to a sheet accumulator, where the accumulated sheets are moved to an insertion station in a mass mailing inserting system. In a typical web cutter, a continuous web of material with sprocket holes on both sides of the web is fed from a fanfold stack into the web cutter. The web cutter has a tractor with pins or a pair of moving belts with sprockets to move the web forward toward a guillotine cutting module for cutting the web cross-wise into separate sheets. Perforations are provided on each side of the web so that the sprocket hole sections of the web can be removed from the sheets prior to moving the cut sheets to other components of the mailing inserting system. In particular, some continuous web cutters are used to feed two webs of material linked by a center perforation. In the cutter, a splitter is used to split the linked webs into two separate web portions before the linked webs are simultaneously cut by the cutting module into two cut sheets.
In a feed cycle, the paper is advanced past the blade of the guillotine cutting module by a distance equal to the length of the cut sheet, and is then stopped. In a cut cycle, the blade lowers to shear off the sheet of paper, and then withdraws from the paper. As soon as the blade withdraws from the paper path, the next feed cycle begins. The feed and cut cycles are carried out in such an alternate fashion over the entire operation.
In some web cutters, it is desirable to achieve a cutting rate of 25,000 cuts per hour or more, for example. This means that the web cutter has a feed/cut cycle of 144 ms. Typically the length of the cut sheet is 11 inches (27.94 cm). If the time to complete a cut cycle is about 34 ms, then the total time in a feed cycle is 110 ms (i.e. 144 minus 34). This means that the web must be accelerated from a stop position to a predetermined velocity and then decelerated in order to stop again within 110 ms. The acceleration and deceleration action of the tractor causes the paper web immediately upstream of the tractor to whip up and down uncontrollably. If the whipping motion is severe, the web may break. As the cutting rate increases, the problem becomes more acute.
Lorenzo (U.S. Pat. No. 5,768,959) discloses a web cutter wherein two separate modules are used to take in a web from upstream: a slitter module for slitting the web into two web portions so as to allow a cutter module to separately cut the web portions into sheets. Like Williams, Lorenzo used clutch/brake motors and servos to accelerate the paper material, then decelerate it to a stop at the present increment. However, clutch and brake systems are prone to slippage, and both clutch/brake and servos are subject to inertial factors, timing issues and also hysteresis factors, all of which contribute to positional inaccuracies.
The present invention provides a mechanical substitute for the usual servo-driven start-and-stop motion of the paper web. Instead of using servo motors to control the starting and stopping, that is instead controlled mechanically, during cutting operations. A fixed or variable indexing mechanism is positioned between the motor and the rollers that roll the paper web. This indexing mechanism is tolerant of motor positional inaccuracies in both start and stop timing, as well as location inaccuracies, while additionally maintaining a controlled index increment that is inherently precise.
The paper web is moved from an upstream source by a transport mechanism, and is cut into individual sheets of paper by a blade. The transport mechanism operates in a start-and-stop motion cycle to move the web intermittently. During the stop periods, the blade cuts the web. The transport mechanism includes a driving member, and also includes a driven member that performs a start-and-stop motion in response to simultaneous non-stop motion of the driving member. The driven member is arranged to cause the web to move to the blade, and each cutting occurs when the driven member is in a substantially stopped position. The interface between the driving member and the driven member is mechanical only.
This can be accomplished by using a fixed or variable profile Geneva drive mechanism coupled with a closed loop motor control system, motor and sensors. The acceleration and deceleration profile can be varied by employing a transmission. The motor is coupled either directly with the primary stage engagement mechanism or through a flywheel and clutch system. The engagement between primary power input stage and the secondary indexing stage is accomplished through mechanical, electromechanical, electromagnetic, magnetic, pneumatic or hydraulic coupling. The fixed or variable profile Geneva drive mechanism, coupled with a closed loop motor control system, motor and sensors for indexing continuous bulk paper in accurate controlled increments, allows increased speed, accuracy, and longevity of the paper cutting device.
The angular velocity of a Geneva driving member determines the duration between cuttings. A transmission situated between the Geneva driven member and the paper web determines how fast paper is fed. Thus, the transmission can be used to alter the size of the individual sheets of paper that are produced by the cutter.
The use of a secondary stage fixed or variable indexing mechanism allows for motor positional inaccuracies in both start and stop timing, as well as location, while maintaining a controlled index increment that is inherently precise. The secondary stage isolates motor inaccuracies from the final motion profile.
The motor is coupled either directly with the primary stage engagement mechanism, or through a flywheel and clutch system. The engagement between the primary power input stage and the secondary indexing stage is accomplished through mechanical, electromechanical, electromagnetic, magnetic, pneumatic or hydraulic coupling. The acceleration/deceleration profile is either fixed in process or variable. This type of arrangement provides greater tolerance for motor positional errors and/or drift. Increased isolation of inertial factors prevents them from affecting desired the motion profile, be they inherent mechanical inertia factors or factors related to inertia of the material being conveyed/indexed. This invention also presents the possibility of reduction in the motor power requirement, increased throughput, and reduction in mechanism complexity. A gear mechanism eliminates complexity from the software and electronics, and provides a robust system without sacrificing accuracy of positioning.
The accompanying drawings illustrate presently preferred embodiments of the invention, and together with the general description given above and the detailed description given below, serve to explain the principles of the invention. As shown throughout the drawings, like reference numerals designate like or corresponding parts.
The present invention is a material conveyance indexing system whereby predefined increments of motion can be derived. It consists of two basic stages: the primary motivator and the secondary indexing mechanism. The primary motivator consists of a closed loop sensor/encoder controlled component, which provides the power to drive the secondary indexing mechanism. A typical implementation is an engagement system driven by a servomotor and/or a flywheel coupled to a clutch/brake system. The primary motivator incorporates a method by which it engages the secondary indexing mechanism.
The engaged motion profile could be either fixed or adjustable, allowing for a secondary modifier to the acceleration/deceleration profile independent of the angular velocity of the primary motivator. In its simplest embodiment, this invention consists of a slotted wheel that is intermittently engaged by a driving pin through an arc of motion. Each 360 degree rotation of the primary motivator causes the secondary mechanisms to index by a fixed 90 degree arc. This ratio could be changed depending on the number of engagement points provided in the primary.
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Various different embodiments of the present invention are possible, as will be understood be a person skilled in the art. Examples of a few such embodiments will now be briefly described. A linear or other non-circular geometry can be used for the primary mover and/or the secondary mechanisms, instead of using an angular primary mover. Also, a magnetic or electromagnetic engagement can be used between the primary motivator and the secondary mechanisms, instead of using a mechanical engagement. When an angular primary mover is used, the angular increments can be other than 90 degrees. The contact point between the primary mover and the secondary mechanisms can be articulated and/or retractable. The primary mover can be operated directly by a servo motor, or instead can be operated indirectly, via a flywheel. The device can have a static engagement profile, or the engagement profile can be adjustable by using a transmission or the like. The transmission can be a controlled variable transmission mechanism, or a preset manual transmission for linkage between the secondary and the final motion system. Also, a 90 degree pinch-type power takeoff mechanism can be utilize between the secondary and final-motion systems. Multiple primaries can be driven by a single secondary, or multiple secondaries can be driven by a single primary.
It is to be understood that the present figures, and the accompanying narrative discussions of embodiments, do not purport to be completely rigorous treatments of the methods and systems under consideration. A person skilled in the art will understand that the steps of the present application represent general cause-and-effect relationships that do not exclude intermediate interactions of various types, and will further understand that the various structures described in this application can be implemented by a variety of different combinations of hardware and/or software, and in various configurations which need not be further elaborated herein.
