Stacker assembly having variable pressure stacker plate

A stacker assembly for receiving generally flat documents, such as mailing envelopes and flats, in on-edge relation and maintaining the documents in upstanding side-by-side stacked relation as they accumulate in the stacker assembly. A receiving station is supported at one end of a horizontal support plate and guides successive incoming documents into stacked relation transverse to the longitudinal axis of the stacker assembly. A stacker plate is supported to engage the forwardmost document in the stack and is movable longitudinally of the stacker assembly in response to accumulation of documents in the stacker. Means in the form of a negator spring and a wedge plate cooperate with the stacker plate in a manner to apply a variable pressure against the documents so as to accommodate both thin lightweight and heavier documents in the stack while maintaining them in upstanding relation.

BACKGROUND OF THE INVENTION 
The present invention relates generally to stacker assemblies for use in 
document handling systems, and more particularly to a document stacker 
assembly having a novel variable pressure stacker plate. 
Document handling or processing systems are generally known in which a 
plurality of documents, such as mailing envelopes and the like, are 
conveyed in serial upstanding on-edge relation from a feed magazine 
through one or more processing stations, and ultimately to one or more 
stacker stations after sorting. The stacker stations, alternatively termed 
stacker assemblies, receive the sorted documents in serial fashion and 
maintain them in upstanding on-edge stacked relation until removed for 
subsequent handling. See, for example, U.S. Pat. No. 4,955,596 which is 
incorporated herein by reference. 
To maintain documents in upstanding stacked relation as they are fed into a 
stacker station, known stacker stations include vertically oriented 
stacker or pressure plates which engage the leading document in the 
stacker station and move progressively along the length of the stacker in 
response to successive documents fed into the stacker station. It is a 
common practice to apply a biasing force to the stacker or pressure plate 
so as to urge it against the stacked documents and maintain them in 
upstanding relation as the documents are fed into the stack from an 
in-feed conveyor or the like. If the stacker plate pressure is relatively 
light, thin documents, such as mailing envelopes on the order of 0.007 
inch thick, can be readily introduced into the stacker. If the stacker 
plate pressure is too great, the thin mailing envelopes are prevented from 
readily entering the stacker and may jam at the entry into the stacker. If 
the stacker plate pressure is too light, heavier documents, such as 
mailing envelopes or flats up to 0.25 inch thick or greater, introduced 
into the stack at an early stage of stack buildup, may overcome the 
biasing force applied to the stacker plate and "kick" the plate 
rearwardly. This can result in the stacked documents falling to a 
substantially horizontal orientation with resultant malfunction of the 
stacker assembly. The present invention overcomes these problems by 
providing a stacker assembly having a stacker or pressure plate operative 
to support both lightweight and heavier documents fed into the stacker 
assembly. 
SUMMARY OF THE INVENTION 
One of the primary objects of the present invention is to provide a novel 
stacker assembly for use in a document processing system or the like, the 
stacker assembly including a stacker or pressure plate operative to 
maintain both relatively light and heavy documents in upstanding relation 
as they are fed into the stacker assembly while disposed in upstanding 
on-edge relation. 
A more particular object of the present invention is to provide a novel 
stacker assembly for use in a document processing system or the like, 
wherein the stacker assembly includes a stacker or pressure plate adapted 
to engage the leading document of a plurality of documents fed 
sequentially into the stacker assembly while disposed in upstanding 
on-edge relation, the stacker plate being supported for movement to 
accommodate successive documents fed into the stack and being operative to 
apply a variable pressure against the stack so as to maintain both light 
and heavy documents in upstanding relation as they are fed into the 
stacker assembly. 
A feature of the stacker assembly in accordance with the present invention 
lies in applying a first relatively light constant biasing force to the 
stacker or pressure plate throughout its full range of movement in 
response to documents fed into the stacker assembly, and causing the 
stacker plate to apply a second higher pressure against the stack of 
documents during predetermined initial movement of the stacker plate in 
response to documents fed into the stacker assembly. 
Another feature of the stacker assembly in accordance with the present 
invention lies in establishing the higher initial pressure against 
documents fed into the stacker assembly by providing a ramp plate which 
cooperates with the stacker plate to resist initial rearward movement of 
the stacker plate in response to documents fed into the stacker assembly, 
thereby enabling the stacker plate to maintain both heavy and light 
documents in upstanding stacked relation as they are fed into the stacker 
assembly. 
Further objects, features and advantages of the present invention, together 
with the organization and manner of operation thereof, will become 
apparent from the following detailed description when taken in conjunction 
with the accompanying drawings wherein like reference numerals designate 
like elements throughout the several views.

DETAILED DESCRIPTION OF THE DRAWINGS 
Referring now to the drawings, and in particular to FIGS. 1-3, a 
fragmentary portion of a document stacker assembly for use in a document 
handling system is indicated generally at 10. The stacker assembly 10, 
which may alternatively be termed a stacker station, is disposed 
downstream from a document processing or handling system (not shown) for 
processing documents, such as mailing envelopes or "flats". Such document 
handling or processing systems are commercially known which feed documents 
in generally upstanding on-edge relation from an input feeder station in 
singulated fashion to a downstream processing station such as a read 
station having alphanumeric or bar code reader means operative to read 
alphanumeric or bar code data on each successive document and effect 
movement of each document along a conveyor path to a selected one of a 
plurality of sorter stations. See, for example, the aforementioned U.S. 
Pat. No. 4,955,596. Each sorter station may include a stacker assembly or 
station 10 constructed in accordance with the present invention. 
In the illustrated embodiment, the stacker assembly 10 receives upstanding 
on-edge documents from the discharge end of a conveyor path defined in 
part by vertical reaches of endless flat conveyor belts, fragmentary 
portions of which are indicated at 12 and 14 in FIG. 3. The conveyor or 
feeder belts 12 and 14 are trained about suitable drive rollers and idler 
rollers, two of the latter being indicated at 16 and 18 for the respective 
conveyor belts 12 and 14, and are operative to convey documents, such as 
envelopes indicated in phantom at 20a-d in FIG. 3, in serial fashion along 
a predetermined conveyor path. A flat horizontal reach of a further 
conveyor belt (not shown) is preferably supported in generally coplanar 
relation with a support or base plate 22 of the stacker station 10 to 
underlie the lower edges of the conveyor belts 12 and 14 and support the 
bottom edges of documents being conveyed to the stacker assembly 10. 
A diverter arm or plate 26 is supported on the base plate 22 for pivotal 
movement about a vertical pivot axis 26a. In the illustrated embodiment, 
the diverter arm 26 is operable through control means (not shown) to 
divert documents from the conveyor path of conveyor belts 12 and 14 to the 
stacker assembly 10, or to a similar stacker assembly, a portion of which 
is indicated 10' in FIG. 1, forming a generally mirror image with the 
stacker assembly 10. 
Assuming that the diverter arm 26 is pivoted to a position as shown in FIG. 
3, a document, such as indicated at 20c, exiting from the conveyor belts 
12 and 14 in upstanding on-edge relation is diverted by the diverter arm 
to the stacker assembly 10. The momentum of the diverted document causes 
it to engage coplanar guide surfaces 30a, 32a and 34a formed on horizontal 
plates 30, 32 and 34, respectively, which are maintained in vertical 
spaced relation to the base plate 22 by spacer sleeves 36 (FIG. 4). As 
will be described, the plates 30, 32 and 34 define a document receiving 
station operative to receive upstanding documents in successive order from 
the conveyor belts 14 and 16 and orient the documents to positions 
substantially transverse to the longitudinal axis of the stacker assembly 
10. In the illustrated embodiment, the longitudinal axis of the stacker 
assembly 10 is substantially perpendicular to a vertical plane containing 
the conveyor path defined by the conveyor belts 12 and 14. 
The guide surfaces 30a, 32a and 34a lie in a plane which is perpendicular 
to the base plate 22 and forms an included angle of approximately thirty 
degrees with the vertical plane containing the conveyor path defined by 
belts 14 and 16 adjacent their exit ends. The guide surfaces 30a, 32a and 
34a intersect corresponding coplanar edge surfaces 30b, 32b and 34b formed 
on the plates 30, 32 and 34 and which lie in a plane perpendicular to the 
base plate 22 and substantially transverse to the longitudinal axis of the 
stacker assembly. Three coaxial stacker rollers or wheels 40a, 40b and 40c 
are mounted on a vertical drive shaft 42 which extends below the support 
plate 22 and is interconnected to rotary drive means (not shown) operative 
to enable selective rotation of the stacker rollers 40a-c in a clockwise 
direction, as considered in FIGS. 1-3. The rollers 40a-c have high 
friction outer peripheral surfaces which extend slightly outwardly from 
the plane of edge surfaces 30b, 32b and 34b. As will be more fully 
described, when beginning a document sorting operation, the stacker 
rollers 40a-c cooperate with a stacker or pressure plate, indicated 
generally at 44, to define a nip 46 (FIG. 3) which receives the vertical 
leading edge of each successive document directed by the diverter arm 26 
along the guide surfaces 30a, 32a and 34a. The rotating stacker rollers 
feed each successive document to a position lying against the edge 
surfaces 30b, 32b and 34b with its leading edge abutting an upstanding 
side wall or guide plate 48 of the stacker assembly 10. 
It will be understood that after the first document 20a is fed into the nip 
46 defined between the stacker rollers 40a-c and the stacker plate 44, 
successive documents are fed into a nip defined between the stacker 
rollers 40a-c and the prior document fed into the stacker assembly. The 
upstanding side wall or guide plate 48 is normal to the base plate 22 and 
defines a guide or registration surface which extends parallel to the 
longitudinal axis of the stacker assembly 10 and is abutted by the leading 
edge of each document diverted to the stacker assembly 10 from the 
conveyor belts 12 and 14. A rotatably driven feed auger 49 is supported 
parallel to the longitudinal axis of the stacker assembly such that a 
raised spiral or helical feeder ridge 49a extends above the upper surface 
of the base plate 22. The feed auger 49 is positioned so that its helical 
ridge 49a engages the trailing bottom edge portion of each document, such 
as shown at 20b in FIG. 3, as its leading edge enters the nip 46. The feed 
auger moves the trailing portion of each successive document forwardly 
from the plane of the guide surfaces 30a, 32a and 34a so as to assure that 
the leading edge of each successive document will ride along these guide 
surfaces and not be blocked by the trailing edge of the preceding 
document. 
The stacker or pressure plate 44 is generally rectangular and is fixed in 
transverse relation to a tubular sleeve 50 which is slidable along a 
cylindrical horizontal guide rod 52 supported parallel to the longitudinal 
axis of the stacker assembly 10 above the base plate 22, such as in 
generally vertically spaced relation above an upper horizontal edge 48a of 
the guide plate 48. The stacker plate 44 may thus move longitudinally 
along the guide rod 52 while maintained in transverse relation to the 
longitudinal axis of the stacker assembly. 
The stacker assembly 10 as thus far described is of generally known 
construction and is operative to receive documents in upstanding on-edge 
relation from the conveyor path defined by conveyor belts 12 and 14 so 
that the documents are stacked in side-by-side relation between the 
coplanar edge surfaces 30b, 32b and 34b and the stacker plate 44 with the 
leading edges of the documents abutting the guide plate 48. When employed 
to stack relatively lightweight thin documents, such as mailing envelopes 
on the order of 0.007 inch thick, it is a common practice to bias the 
stacker plate against the documents entering the stacker assembly with 
sufficient force to maintain the envelopes in upstanding relation but 
without inhibiting rearward movement of stacker plate in response to entry 
of successive documents into the stacker station. In the illustrated 
embodiment, such biasing is provided by spring means in the form of a 
constant force rotary or reel type spring member 56 which is rotatably 
supported on a bracket 58 to overlie the upper plate 30. The spring member 
56 has an elongated filament, such as a thin flexible wire 60, which is 
connected at one end to the rotary spring member and has its opposite end 
connected at 62 to the sleeve 50. The reel type spring member 56, which 
may be termed a negator spring, is biased in a clockwise rotational 
direction about its rotational axis 56a so as to apply a substantially 
constant longitudinal resistance force to the wire 60 as it is unwound 
from the reel of the spring member. In this manner, the wire 60 applies a 
substantially constant force on the sleeve 50 in a direction to bias the 
sleeve and stacker plate 44 toward the edge surfaces 30b, 32b and 34b. 
Stated alternatively, the constant force spring member 56 establishes a 
substantially constant force resisting movement of the stacker plate 44 
away from the edge surfaces 30b, 32b and 34b on the plates 30, 32 and 34, 
respectively, and the associated stacker rollers 40a-c. 
If the pressure applied by the stacker plate 44 against documents fed into 
the stacker assembly 10 due to the constant force spring member 56 is 
minimized, relatively thin lightweight documents, such as mailing 
envelopes in the order of approximately 0.007 inch thick, can be readily 
fed into the stacker assembly and maintained in upstanding stacked 
relation. If, however, the pressure applied by the stacker plate 44 
against relatively thin lightweight documents fed into the stacker 
assembly is too great, the documents may jam at the nip 46. On the other 
hand, if the pressure applied by the stacker plate 44 is too low, heavier 
documents, such as mailing flats and envelopes up to one-quarter inch 
thick or greater, may overcome the biasing force of the negator spring 56 
and force the stacker plate rearwardly along the guide rod 52 so that the 
documents fall to generally flat positions on the base plate 22 of the 
stacker assembly 10, rather than being maintained in upstanding stacked 
relation. 
To overcome the aforedescribed problem of accommodating both thin 
lightweight and heavier thicker documents in an intermixed stack within 
the stacker assembly, the present invention provides additional biasing 
means cooperative with the stacker plate 44 so as to cause the stacker 
plate to apply a variable pressure against documents received in the 
stacker station between the edge surfaces 30b, 32b and 34b and the 
pressure plate. The additional biasing means cooperates with the negator 
spring wire 60 to cause the stacker or pressure plate 44 to apply an 
increased pressure or reaction force against the documents during initial 
build-up of a stack of documents in the stacker assembly 10 than would be 
applied by the negator spring itself. The increased or additional pressure 
or reaction force acts on the documents during a predetermined distance 
traversed by the stacker plate 44 as it is moved rearwardly along the 
guide rod 52 from a position immediately adjacent the stacker rollers 
40a-c to a predetermined position spaced from the stacker rollers but less 
than the full distance traveled by the stacker plate during normal 
operation. 
The aforedescribed increased pressure or reaction force applied by the 
stacker plate 44 is provided by wedge plate means in the form of a wedge 
plate 64 which, in the illustrated embodiment, is fixed to the upstanding 
guide plate 48 adjacent its top edge 48a. The wedge plate 64 is elongated 
and extends generally from the plane of the edge surfaces 30b, 32b and 34b 
of plates 30, 32, and 34, respectively, longitudinally along the guide 
plate 48 a predetermined distance, such as approximately 2-3 inches. The 
wedge plate 64 has a plurality of ramp surfaces 66 which lie in vertical 
planes and are outwardly inclined relative to the guide plate 48 so as to 
form included angles of incline of preferably about 45 degrees with the 
guide plate which runs parallel to the longitudinal axis of the stacker 
assembly 10. A planar return surface 68 is formed on the wedge plate 
between each adjacent pair of ramp surfaces 66. The return surfaces 68 lie 
in vertical planes which are inclined outwardly from the guide plate 48 at 
generally opposite angles of inclination to the ramp surfaces 66. The 
return surfaces 68 form included angles of preferably approximately 30 
degrees with the guide plate 48, and thus the longitudinal axis of the 
stacker assembly. The ramp surfaces 66 are of equal size to each other, 
and the return surfaces 68 are of equal size to each other. Each ramp 
surface 66 and its associated return surface 68 intersect at a vertical 
line of intersection or apex, such as indicated at 70, such that the lines 
of intersection 76 lie in a common plane parallel to the guide plate 48. 
Preferably, the wedge plate 64 is made of a suitable plastic material so 
that the ramp surfaces 66 and return surfaces 68 establish relatively 
low-friction sliding surfaces. 
The stacker plate 44 carries a wedge plate engaging member 74 which may be 
formed integral with or otherwise suitably secured to the stacker plate. 
In the illustrated embodiment, the wedge plate engaging member 74 is 
releasably and adjustably secured to the stacker plate 44 through a pair 
of screws 76 received through elongated slots in the wedge plate engaging 
member. The wedge plate engaging member 74 has a vertical height 
approximately equal to the height of the wedge plate 64 and has an angled 
outer end surface 74a which lies in a substantially vertical plane when 
the stacker plate 44 is in its normal operating position as shown in FIG. 
1. The angled end surface 74a preferably forms an included angle with the 
plane of the stacker plate substantially equal to the angle of inclination 
of the ramp surfaces 66 with a plane transverse to the longitudinal axis 
of the stacker assembly. Stated alternatively, the angle of inclination of 
the end surface 74a relative to the plane of the stacker plate is selected 
such that such angle, plus the angle of inclination of the ramp surfaces 
66 relative to the longitudinal axis of the stacker assembly, equals 
approximately 90 degrees. As noted, the angle of inclination of the ramp 
surfaces 66 relative to the guide plate 48 is preferably approximately 45 
degrees so that the angle of inclination of the end surface 74a relative 
to the plane of the stacker plate is similarly approximately 45 degrees. 
The ramp plate engaging member 74 is positioned relative to the stacker or 
pressure plate 44 so that with the end surface 74a of member 74 engaging 
the wedge plate 64, a lower or bottom edge 44a of the stacker plate is 
spaced slightly above the base plate 22. The weight of the stacker plate 
44, its pivotal mounting on the guide rod 52, and the distance of the 
wedge plate engaging member 74 from the axis of guide rod 52, are selected 
such that a force is applied by the wedge plate engaging member 74 against 
the various ramp surfaces 66 to create a predetermined reaction force 
acting normal to the stacker plate in a direction resisting movement of 
the stacker plate longitudinally away from the edge surfaces 30b, 32b and 
34b and the stacker rollers 40a-c. It will be appreciated that with each 
ramp surface 66 having an inclined angle of approximately 45 degrees with 
the longitudinal axis of the stacker assembly, and with the tangent of 45 
degrees being unity, the reaction force created by the wedge plate in 
resisting rearward movement of the stacker plate will be approximately 
equal to the force applied to the ramp surface by the ramp plate engaging 
member 74. This force is a function of the weight of the stacker plate and 
the geometrical relation between the stacker plate, the axis of rod 52, 
and the position of stacker plate engaging member 74. It has been found 
that when stacking documents such as mailing envelopes or flats wherein 
the stack will include both relatively thin envelopes of approximately 
0.007 inch thickness and thicker heavier envelopes having up to 
approximately one-quarter inch thickness or greater, and with the negator 
spring wire 60 applying a force of approximately 7 oz. on the stacker 
plate, obtaining a reaction force from the wedge plate 64 of approximately 
8 oz. acting on the stacker plate in a direction resisting movement away 
from the stacker rollers 40a-c will result in requiring an average force 
of approximately 15 oz. to move the stacker plate rearwardly in response 
to initial entry of documents into the stacker assembly; that is, until 
the stacker plate has moved rearwardly past the wedge plate. 
It will be appreciated that as documents enter the stacker assembly and 
overcome the movement-resisting force applied to the stacker plate by the 
wedge plate 64 and the negator spring member 56, the stacker plate 
progresses rearwardly along the various ramp surfaces 66 of the wedge 
plate in a step-like fashion. In this manner, as documents are initially 
fed into the stacker assembly, the stacker plate 44 applies a first force 
of approximately 15 ounces against the documents. The 15 oz. force 
continues during movement of the stacker plate along the wedge plate 64, 
such as a distance of approximately 2-3 inches. After incoming documents 
move the stacker plate 44 a distance greater than the length of the wedge 
plate 64, the force applied to the stacked documents is reduced to the 
spring force applied by the negator spring member 52. Stated 
alternatively, as documents are fed into the stacker assembly, initial 
movement of the stacker plate 44 from its position immediately adjacent 
the stacker rollers 40a-c is resisted by a first resistive force created 
by the negator spring member 56 and the reaction force between the wedge 
plate 64 and stacker plate 44. This force is sufficient to accommodate 
both relatively lightweight thin envelopes and thicker heavier envelopes 
or flats within the stacker assembly without the stacker plate being 
pushed rearwardly by the weight of the heavier envelopes in a manner 
allowing the envelopes to fall to relatively flat positions with 
consequent interruption of proper stacking of the documents. 
As the documents accumulate in the stacker assembly 10 and force the 
stacker plate 44 rearwardly along the guide rod 52 to a position wherein 
the wedge plate engaging member 74 disengages from the wedge plate 64, 
resistance to movement of the stacker plate is reduced to the force 
applied by the negator spring member 56 which is sufficient to accommodate 
additional documents into the stacker assembly while maintaining them in 
upstanding stacked relation. Thus, the wedge plate 64 and negator spring 
member 56 establish a first movement-resisting force to the stacker plate 
during a predetermined length of travel responsive to documents fed into 
the stacker assembly, and establish a second movement-resisting force to 
the stacker plate during movement of the stacker plate along the support 
plate 22 a distance greater than the length of the wedge plate. The angle 
of incline of the return surfaces 68 on the wedge plate 64 is selected so 
that the force applied to the stacker plate by the negator spring wire 60 
is sufficient to return the stacker plate to its initial position adjacent 
the stacker rollers 40a-c when the stacked documents are removed from the 
stacker assembly 10 preparatory to receiving and stacking further 
documents from the conveyor belts 12 and 14. 
To facilitate sliding movement of the lower edge 44a of the stacker plate 
44 along the base plate 22 after the wedge plate engaging member 74a has 
disengaged from the wedge plate 64, at least one elongated strip of low 
friction material is secured to the base plate 22 so as to extend 
longitudinally of the stacker assembly 10. In the illustrated embodiment, 
three strips of low friction material, such as strips 78 having upper 
nylon surfaces, are secured to the upper surface of base plate 22 to 
provide low friction surfaces along which the lower edge of the stacker 
plate slides during movement after release from the wedge plate 64. 
While a preferred embodiment of the present invention has been illustrated 
and described, it will be understood that changes and modifications may be 
made therein without departing from the invention in its broader aspects. 
For example, while the invention has been described as having the wedge 
plate 64 supported in a generally vertical plane to engage the wedge plate 
engaging member 74 when disposed in substantially horizontal relation, the 
wedge plate 64 could be mounted on the base plate 22 with the ramp 
surfaces 66 and return surfaces 68 facing upwardly. In this case the wedge 
plate engaging member 74 would be mounted at a suitable position on the 
stacker plate to cooperate with the wedge plate in the aforedescribed 
manner. 
Various features of the invention are defined in the following claims.