Apparatus for separating a letter stack

#The present invention relates to an apparatus for the separate discharge of letters and similar flat items from a stack of such items, the apparatus being of the type including a movable support supporting the stack of items, a rotating withdrawal mechanism in engagement with the foremost item in the stack, means defining a supporting wall manually movable into an initial position for supporting the trailing end of the stack, a motor connected to drive the supporting wall toward the withdrawal mechanism under control of a switch actuated in dependence upon the force being exerted by the stack on the withdrawal mechanism.

#The movable support in such apparatus is usually a movably mounted endless base belt which is likewise driven in dependence on the actuation on the abovementioned switch in the direction toward the separating belt, generally at the same speed as the supporting wall. Such a device is disclosed, for example, in U.S. Pat. No. 3,981,493 and is shown in FIGS. 1 and 5 thereof.

#Controlling the drive for the supporting wall in dependence on the force exerted by the stack on the withdrawal mechanism has the purpose of keeping this force essentially constant. This is necessary because the withdrawal mechanism operates reliably, i.e., with a minimum of removal errors, in particular a minimum of double removals, only within a certain range of contact force.

#FIG. 1 is a simplified top plan view, the basic components of a first preferred embodiment of separating apparatus according to the invention.

#FIG. 2 is a view similar to that of FIG. 1 of a second preferred embodiment of apparatus according to the invention.

#FIG. 1 illustrates apparatus including a base plate 1 on which a shaft 2 is mounted to be freely rotatable. A roller 3 is fastened to shaft 2. The shaft 2 itself serves to pivotally hold a rocker 4 which carries the shaft 5 of a withdrawing roller 6 as illustrated in detail, for example, in the above-cited U.S. Pat. No. 3,981,493. A withdrawal belt 7 whose outer surface has a high coefficient of friction is trained around the roller 3 and the withdrawal roller 6.

#The shaft 2 is driven in the direction of the arrow associated therewith by means of a conventional electromagnetic clutch and a motor (both now shown). A conventional stripper disposed opposite the roller 3 is also not shown. A stack 20 of items is mounted on a base belt 23 and items separated from the stack are brought into a continuing conveying path of which two conveyor belts 10 and 11, which are guided around two rollers 8 and 9, are shown.

#An arm 12 is fastened to rocker 4 and a compression spring 13 is held between base plate 1 and arm 12. A microswitch 14 is also mounted on base plate 1 and is arranged to be actuated by arm 12, its function being described further below. Since, due to its pivotal mounting and the action of spring 13, the angular position of rocker 4 depends on the pressing force exerted by the stack 20 against the withdrawal belt 7, the switch 14 is actuated in a respective direction whenever this pressure force exceeds or falls below a certain given value.