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  Method and device for stacking flat mail itemsUSPTO Application #: 20070176348Title: Method and device for stacking flat mail items Abstract: In a stacker, a mail item to be stacked is propelled against a stop wall at a stacking point by a stacking roll. A controlled driven underfloor belt and a stack support are displaced from the stack as the stack grows. The mail item to be stacked meets the preceding, already stacked item at an acute angle. Before it is stacked the mass of each item is determined. Stacking forces are measured with a measurement device in a preceding test phase the target values for the stacking pressures and the braking curve of the stacking roll up until the mail items have reached the stop are defined and stored based on statistical analyses in accordance with the mass of the mail items to be stacked. The speed of the respective mail item is reduced according to the braking curve assigned to the determined mass of the mail item. (end of abstract) Agent: Siemens Schweiz Ag I-47, Intellectual Property - Zurich, CH Inventors: Holger Schererz, Armin Zimmermann, Thomas Froehlich USPTO Applicaton #: 20070176348 - Class: 271003200 (USPTO) Related Patent Categories: Sheet Feeding Or Delivering, Feeding And Delivering, Conveyor Releases To Subsequent Conveyor, Including Conveyor Couple The Patent Description & Claims data below is from USPTO Patent Application 20070176348. Brief Patent Description - Full Patent Description - Patent Application Claims
[0001] The invention relates to a method and a device for stacking flat mail items. [0002] In the invention the mail items are transported in turn by a transport means into stackers and are stacked vertically in these. In each stacker a mail item to be stacked is transported to a stop wall by means of a stacking roll. The mail item to be stacked meets the preceding already stacked item at an acute angle. A controlled driven underfloor belt and a stack support coupled in a releasable manner to this or a support which can be driven separately is moved away from the stack as the stack grows. [0003] Each mail item to be stacked is to be guided so that it comes up against the stop wall and its front and lower edge is aligned in a line to the items already stacked. [0004] With a movement away of the part stack in accordance with DE 102 23 349 A1 from the stacking point to make space for the mail item to be stacked, the displacement selected is smaller than the determined thickness of the mail item to be stacked. For this reduction of the displacement in relation to the measured thickness value the starting point used is an average compressibility of the part stack. However if the actual value deviates significantly from the assumed value as a result of non-compressible mail items, there is still a disproportionate rise in the stack pressure since the stacking force is only measured after the mail item hits the stop in the stacking run and a corrective intervention can then be undertaken. In some cases the mail item does not reach the stop wall of the stacker. The spring effect of the mail item stack cannot be taken into account. [0005] If, to avoid this effect, as also in EP 0743269 B1, the part stack is moved away from the stacking point by the full amount determined of the thickness+safety margin (measurement tolerances) the support function of the stacking roll is briefly relinquished. The result, particularly with large-format mail items is that the stack tips, which dramatically influences the quality of the stack. If the mail item has reached the stop wall in the stacker, stacking force measurement in the area of the stacking roll is used to determine the stacking force and in an adjustment process by moving the underfloor belt the stacking force is adjusted in a range which is defined by threshold values for the permitted stacking force range. There is also the fact that after the imprecise positioning of the mail item in the stacker, a force is introduced onto the mail item by the constantly rotating stacking roll in the direction of conveyance which can lead to damage, twisting and warping of the stacked item. [0006] The object of the invention is to create a method and a device for stacking flat mail items in a vertical position in a stacker with which mail items with widely differing dimensions and masses can be stacked in a protective manner aligned on their front and bottom edges. [0007] In accordance with the invention the object is achieved by the features of claims 1 and 6. [0008] In each stacker in which the mail items are stacked in a vertical position, a mail item to be stacked is propelled against a stop wall at a stacking point by a stacking roll that can be displaced away from the stack in opposition to a spring force and that is driven in a controlled manner in a starting-braking mode. A controlled driven underfloor belt and a stack support coupled in a releasable manner to this or a support which can be driven separately is displaced from the stack as the stack grows. The mail item to be stacked in each case meets the preceding, already stacked item at an acute angle. Before it is stacked the mass of each item to be stacked is determined. Stacking forces are measured with a measurement device arranged in the area of the stacking roll on the item transport plane or on the stacking roll itself when the stacking roll has engaged with the mail item to be stacked. In a preceding test phase the target values for the stacking pressures and the braking curve of the stacking roll up until the mail items have reached the stop are defined and stored based on statistical analyses in accordance with the mass of the mail items to be stacked. The speed of the respective mail item is reduced by the stacking roll according to the braking curve that has been assigned to the determined mass of the mail item. [0009] As a result of the displaceable stacking roll the stacking force never exceeds a value which prevents correct stacking regardless of the characteristics of the stack already located in the stacker without the support function being lost. [0010] The mail items are braked independently of their dimensions and masses to reduce the kinetic energy in a defined way such that an optimally aligned stack is produced. The braking of the stacking rolls means that after positioning of the relevant mail item the force introduced onto the mail item in the direction of conveyance is reduced, which avoids damage or twisting of the stacked mail items. [0011] Advantageous embodiments of the invention are set down in the subclaims. [0012] Thus it is advantageous, if the thickness of the mail item to be stacked is determined and for stacking a mail item the underfloor belt and/or the stacking support is moved away from the stacking point by the measured thickness of this mail item plus or minus a correction value for setting the stacking pressure assigned and stored for the mass of the mail item and thereafter, for an actual stacking pressure measured at the stacking roll which deviates from the target stacking pressure for this item is moved to maintain the target stacking pressure. The target stacking pressure depends on the mass and the thickness of the current mail item to be stacked and the spectrum and the characteristics (mass, thickness, compressibility) of the previously stacked mail items. [0013] It is also advantageous for the mass of the mail items to be determined indirectly by the dimensions of the mail item being measured, for the volume to be calculated from these dimensions and multiplied by a defined mass factor per volume. [0014] In the braking process of the stacking roll the braking curve can advantageously be designed so that the speed of the circumference of the stacking roll at the point in time at which the mail item has reached the stop wall is inverse to the mass of the mail item and that the stacking roll is subsequently stopped if the subsequent mail item is far enough away for there to be sufficient time to accelerate the stacking roll again to its rated speed before the mail item has reached it. [0015] If the subsequent mail item is less than a specific distance from the stacker, e.g. if the time for acceleration from 0 to rated speed is not sufficient, it is advantageous to accelerate the speed of the circumference of the stacking roll immediately back to the rated speed of the transport means after the stacking of the relevant mail item. [0016] The invention will be explained below with reference to the drawing in an exemplary embodiment. [0017] The figures show [0018] FIG. 1 a schematic overhead view of a device for stacking, showing a mail item to be stacked, [0019] FIG. 2 a diagram of the speed curve of the stacking roll over time, [0020] FIG. 3 a diagram of the curve of the stacking force plotted against time and against the position of the stacking roll. [0021] As shown in FIG. 1 the stacking roll 1 is arranged so that it can move in the direction of the mail item stack 18 to be created. This is implemented using a motion link 2. A linear arrangement is also possible. [0022] The stacking roll 1 is positioned in its rest position by means of a spring 3 with a defined spring characteristic in the direction of a stop 4. This stop 4 is adjustable which allows calibration of the sensor. Mail items 19 arriving, depending on their thickness, cause a greater or lesser displacement of the stacking roll 1. The size of the displacement creates an increase in the reaction force of the spring 3 and thereby of the stacking pressure. If the characteristic spring curve is designed accordingly there is a guarantee that in this case the stacking pressure only increases to such an extent that all mail items securely reach the stop wall 15. [0023] A further stop 5 prevents an overdeflection of the stacking roll 1 especially when thicker mail items 19 are transported in. [0024] To avoid unwanted oscillations a damping element 6 is fitted to the motion link 2. Continue reading... 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