U.S. patent number 3,902,713 [Application Number 05/460,584] was granted by the patent office on 1975-09-02 for photoelectric stack height detection device.
This patent grant is currently assigned to Mathias Bauerle GmbH. Invention is credited to Wilhelm Markgraf, Wolf-Rudiger Von Luhmann.
United States Patent |
3,902,713 |
Von Luhmann , et
al. |
September 2, 1975 |
Photoelectric stack height detection device
Abstract
An apparatus for sensing changes in the height of a stack of
sheet material positioned on a lift table for seriatim advancement
of the sheets from the top of the stack to a processing machine,
and for controlling the raising of the lift table to position the
stack from a predetermined lowered level to a feeding level in
response to activation of a photoelectric detection element when
the stack is depleted to the predetermined lowered level. An
illuminating means projects a light beam onto a movable reflective
sensing member resting on top of the stack and the beam is
reflected from the sensing member to the photoelectric element in
any one of a plurality of paths as determined by the height of the
stack. So long as the beam path is directed within a range so as to
be intercepted by the photoelectric element, the photoelectric
element remains inactive and the stack is between the feeding and
the predetermined lowered level. However, as the stack is depleted
to the predetermined lowered level the reflected beam is no longer
within the range to be intercepted by the sensitive element thereby
activating the photoelectric element which, in turn, actuates drive
means for raising the lift table to position the stack at the
feeding level.
Inventors: |
Von Luhmann; Wolf-Rudiger (St.
Georgen, DT), Markgraf; Wilhelm (Tennenbronn,
DT) |
Assignee: |
Mathias Bauerle GmbH (St.
Georgen, DT)
|
Family
ID: |
5885589 |
Appl.
No.: |
05/460,584 |
Filed: |
April 12, 1974 |
Foreign Application Priority Data
|
|
|
|
|
Jun 30, 1973 [DT] |
|
|
2333366 |
|
Current U.S.
Class: |
271/154; 250/230;
250/559.29; 250/559.27 |
Current CPC
Class: |
B65H
1/08 (20130101); B65H 2553/414 (20130101) |
Current International
Class: |
B65H
1/08 (20060101); B65H 001/18 () |
Field of
Search: |
;271/152,153,154,155,156,215,263,262,31,130 ;214/8.5A
;250/561,577,231R |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Schacher; Richard A.
Assistant Examiner: Stoner, Jr.; Bruce H.
Attorney, Agent or Firm: Goldstein; Sol L.
Claims
What is claimed is:
1. A device for sensing changes in the height of a stack of sheet
material lying in a first horizontal plane comprising:
a generally arcuately shaped surface reflective element positioned
in contact with the upper sheet in the stack;
photoelectric detection means including an optical path comprising
an illuminating source and a photosensor positioned relative to one
another defining an illuminating beam projection path and a
sighting path for the photosensor, which paths are generally normal
to one another thereby establishing a reference position for the
stack height where the paths meet for detecting changes in position
of the arcuate element relative to the reference position; and
retainer means for movably supporting said arcuately shaped surface
element relative to said reference position along a guide axis to
complete the optical path.
2. A device as set forth in claim 1 in which the photoelectric
detection means is conditionable to an inactive state in response
to intercepting the beam path and conditionable to an activated
state in response to non-interception of the beam path; and
means responsive to activation of the photoelectric detection means
for lifting the stack to the reference position.
3. A device as set forth in claim 2 in which the means for lifting
the stack comprises a lift table for supporting the stack and drive
means for raising the lift table.
4. A device as set forth in claim 1 in which the reflective element
comprises a spherical member.
5. The device as claimed in claim 1 in which said reference
position lies in a second plane normal to the first plane, said
second plane containing a verticaal reference axis; and mounting
means permitting rotational movement of said retainer so that said
guide axis can be angularly adjusted relative to the vertical
axis.
6. The device as set forth in claim 5 in which the guide axis
coincides with the vertical reference axis.
7. The device as set forth in claim 5 in which the angular position
of the guide axis and the horizontal first plane of the stack form
an angle therebetween in the range of between 90.degree. and
40.degree..
8. An apparatus as set forth in claim 5 in which the arcuate
element comprises a spherical element provided with a reflective
surface.
9. The device as claimed in claim 5 wherein the rotation of said
retainer is about an axis extending normal to said second
plane.
10. The device as claimed in claim 5 wherein said reflective
element is a cylinder having a reflective surface and the axis of
rotation of the cylinder is parallel to said first plane.
11. An apparatus for sensing changes in the height of a stack of
sheet material comprising:
a generally arcuately shaped reflective surface in contact with the
uppermost sheet in the stack for identifying the height of the
stack between a feeding level and a predetermined lower level;
photoelectric detection means including an optical path comprising
an illuminating source and a photosensor positioned relative to one
another defining an illuminating beam projection path and a
sighting path for the photosensor, which paths are generally normal
to one another, thereby establishing a reference position for the
stack height where the paths meet for detecting changes in position
of the light reflective surface relative to the reference position
and conditionable to an activated state when the light reflective
surface is at the predetermined lower level; and
means responsive to the activation of the photoelectric detection
means for lifting the stack to the feeding level.
12. An apparatus as set forth in claim 11 in which the means for
lifting the stack comprises a lift table for supporting the stack
and drive means for raising the lift table.
13. An apparatus as set forth in claim 11 in which the reflective
surface comprises a roller provided with a reflective surface.
14. A device for sensing changes in the height of a stack of sheet
material positioned on a power driven table for feeding individual
sheets lying in a first horizontal plane to a processing machine
comprising:
a generally arcuately shaped reflective surface element in contact
with the uppermost sheet in the stack;
photoelectric detection means including an optical path comprising
an illuminating source and a photosensor positioned relative to one
another defining an illuminating beam projection path and a
sighting path for the photosensor, which paths are generally normal
to one another thereby establishing a reference position for the
stack where the paths meet, for detecting changes in position of
the arcuately shaped surface element relative to the reference
position;
said reference position lying in a second plane normal to said
first plane; and
means for supporting said reflective element permitting
multi-directional movement of the element and the support along a
guide axis relative to said first and second planes.
15. The device as set forth in claim 14 in which the reflective
element comprises a spherical element.
16. The device as set forth in claim 14 in which the reflective
element comprises a roller.
17. The device as set forth in claim 14 in which the guide axis
coincides with the second plane.
18. The device set forth in claim 14 in which the guide axis and
the first plane form an angle of between 90.degree. and
40.degree..
19. The device as claimed in claim 14 wherein said reflective
element is rotationally contained in said support means and adapted
to move along a guide axis generally vertical relative to said
first plane.
20. The device as claimed in claim 19 wherein said support is
rotatably mounted about an axis of rotation that extends in a
direction normal to said second plane.
Description
BACKGROUND OF THE INVENTION
Scanning the height of a stack of sheets by means of a beam of
light directed obliquely onto the plane of the sheets, and
utilizing a photoelectric element for detecting the reflected beam
of light for determining the height of the stack, is known in the
art. Such devices have also been used for determining the presence
of a sheet of paper in a transport line, detecting double sheet
thicknesses and the like. However, these devices are not completely
reliable in operation particularly when utilized in association
with colored or printed paper. Thus, because of the variations
caused by a larger or smaller amount of light absorption by the
colored or printed paper, the scanning capabilities of these light
reflecting devices are limited. Also, folds, creases and/or the
surface quality of the paper may also adversely effect the
operation of such scanning devices.
In high speed sheet feeding devices for feeding various weights of
sheets from the top of the stack and equipped with table raising
mechanisms for maintaining the stack at a proper feeding level, in
order to perform proper feeding operation it is important that the
distance between the top sheet of the stack and the feed element be
held, as uniformly and constantly as possible, at the proper
feeding level. To achieve this, particularly when feeding thin,
light-weight sheets necessitates the use of a lift table which can
be raised in relatively minute increments. However, the degree of
minute incremental movement of the lift table is dependent
primarily on the switching hysteresis of the switching sensitivity
of the scanning device. Known mechanical-electrical and pneumatic
scanning devices do not provide the desired results of minute
incremental movement of the lift table because of their relatively
slow switching sensitivity. Also, known photoelectric scanning
devices in which the light beam is reflected directly onto the
sheet are not completely reliable because of their dependency on
the color and the structural surface quality of the sheet.
SUMMARY OF THE INVENTION
The present invention provides an improved photoelectric scanning
or detection apparatus in which a constant degree of reflection is
obtained with different qualities and colors of paper without
impairing sheet advancement in the feeding of individual sheets
from the stack.
It is an object of the present invention to provide a photoelectric
scanning apparatus comprising a movable element or sensing member
mounted for rotatable and radial movement in contact engagement
with the surface to be scanned. The sensing member is provided with
a highly polished, mirror surface which serves as a reflector.
Optionally, the sensing member may be associated with a mirror
which serves as the reflector. In the preferred embodiment, the
sensing member comprises a spherical element in the form of a steel
ball having a reflective surface. Although a roller having a
reflective surface is functionally equivalent to the steel ball as
will be described hereinafter as an alternate embodiment, the use
of the ball offers simplified construction and thus lower cost.
Another object of the invention is to provide a photoelectric
detection means comprising an illuminating means and a
photoelectric element, each providing an optical axis lying in a
coincident plane, arranged that the optical axes form therebetween
an angle of about 90.degree.. The angle is approximately
symmetrical on either side of a vertical axis of the sensing member
defined by a plane perpendicular to a horizontal plane of a stack
of sheet material on a lift table. Accordingly, only slight
downward movement of the sensing member in response to depletion of
the stack by advancement of the sheets therefrom causes the
reflected light beam from the surface of the sensing member to be
directed in a path which is not within a range to be intercepted by
the optical axis of the photoelectric element thereby conditioning
the photoelectric element to an activated state. Activation of the
photoelectric element actuates the drive means for lifting the
table a controlled amount such that the stack of sheet material is
lifted from the predetermined lowered level to the feeding
level.
A further object of the invention is to provide a reflective
sensing member supported in a retainer means and movable along a
guide axis. The sensing member is mounted within a housing
containing the illuminating means and the sensitive element so that
the radial movement of the sensing member along the guide axis
occurs only in a predetermined axial direction maintaining the
reflection of the illuminating means in a common plane.
A further object of the invention is to provide a photoelectric
detection means in which the response sensitivity thereof may be
increased by positioning the guide axis of the movable sensing
member in the coincident plane of the optical axes of the
illuminating means and the photoelectric element at an angle of
between 90.degree. and about 140.degree. with respect to the
horizontal plane of the lift table.
Another object of the invention is to provide a scanning apparatus
having a rapid response sensitivity by positioning the guide axis
of the sensing member and the optical axis of the illuminating
means such that they form therebetween an angle of about
90.degree.. Adjustment means is provided for diagonally positioning
the guide axis of the sensing member with respect to the
illuminating means and the sensitive element thereby increasing the
angle of deflection of the light beam path while maintaining the
same distance of movement of the sensing member in the direction of
the axis of symmetry of the optical system. This is accomplished by
arranging the sensing member for radial movement along the guide
axis as well as for movement in a sidewise direction.
Another object of the invention is to rotatably support the
retainer means which supports the sensing member on an axis
transverse to the coincident plane of the optical axes of the
illuminating means and the photoelectric element. A manually
operable device is provided for adjusting the retainer means to
selectively settable angular positions between the axis of the
retainer means and the horizontal plane of the lift table, or
between the axis of the retainer means and the coincident optical
axes. In this way the response sensitivity of the scanning
apparatus can be varied and adjusted, for example, to the
particular quality and/or color of the sheets being processed. To
some extent, this arrangement can also be attained by utilizing a
roller as a sensing-reflector by supporting the roller on a lever
and pivotally mounting the lever on an axle which can be adjusted
about the axis of rotation of the roller. Thus, by adjusting the
position of the axle, the axis of pivotal movement of the roller
and the direction of movement of the roller are also positionable
to various selective positions with respect to the incident light
beam, i.e., with respect to the optical axis of the illuminating
means.
Other objects, features and advantages of the invention will appear
hereinafter as the description proceeds.
IN THE DRAWING
FIG. 1 is a perspective view of a lift table for supporting and
lifting a stack of sheet material to a feeding level including a
photoelectric detection means for actuating the raising of the lift
table in response to depletion of the stack to a predetermined
lowered level in accordance with the present invention;
FIG. 2 is a section of one embodiment of the photoelectric
detection means;
FIG. 3 is a section taken substantially along the line designated
A--A in FIG. 2;
FIG. 4 is a section of a preferred embodiment of the photoelectric
detection means;
FIG. 5 is a section taken substantially along the line designated
B--B in FIG. 4;
FIG. 6 is a schematic representation, partly in section,
illustrating the mode of operation of the photoelectric detection
means shown in FIGS. 4 and 5; and
FIG. 7 is another alternate embodiment of a photoelectric detection
means.
DESCRIPTION OF THE PREFERRED EMBODIMENT
With reference to FIG. 1 there is shown a lift table 1 supported
for vertical movement on chains 2. The chains are guided in columns
3, 4 and 5 and are driven in unison by a drive motor 6. Actuation
of the drive motor 6 drives the chains 2 and thus raises the lift
table 1 in minute incremental steps in response to depletion of
sheet material as the sheets are advanced from a stack 7 on the
lift table 1. Although the sheet advancing means may be of any
suitable kind, for purposes of illustration there is shown in FIG.
1 a pneumatic feed device comprising a suction roller 8 for
advancing the top sheet from the stack 7 in the direction of arrow
9.
The photoelectric detection or scanning apparatus of the present
invention is contained within a housing 10 positioned above the top
sheet of the stack 7. The housing 10 is supported on an arm 11
secured to a rail 12 mounted in the columns 3 and 4. The scanning
apparatus senses changes in the height of the stack and, when
activated as will be described hereinafter, actuates the motor 6
for driving the chains 2 which impart incremental lifting movement
to the lift table 1, in the direction of arrow 13, to thereby
position the stack 7 from a predetermined lowered level to a
feeding level defining a reference position therebetween.
In each of the embodiments illustrated in FIGS. 2 - 6, the
photoelectric detection means comprises an illuminating means 14, a
sensitive or photoelectric element 15 and a spherical sensing or
movable element 16 provided with a highly reflective surface. The
illuminating means 14 is contained within a housing 18 and includes
an incandescent lamp 19, a perforated screen 20 and a focusing lens
21. The sensitive element 15 comprises a phototransistor or a
photodiode contained within a housing 22. An optical axis 23 of the
illuminating means 14 forms with an optical axis 24 of the
sensitive element 15 an angle .alpha. of about 90.degree.. The
arrangement of the illuminating means 14 and the sensitive element
15 is such that their optical axes 23 and 24 lie in a coincident
plane and are symmetrical on either side of a vertical guide axis
25 of the sensing member 16.
The housings 18 and 22 are secured respectively to straps 26 and 27
within the housing 10. the arrangement is such that the optical
axes 23 and 24 of the illuminating means 14 and the sensitive
element 15 converge and intersect the vertical guide axis 25 of the
sensing member 16 at a point where the surface of the sensing
member 16 is also intersected by the guide axis 25.
In the arrangement shown in FIGS. 2 and 3, the sensing member 16 is
guided for movement in a sidewise direction along the guide axis 25
and is movable vertically within a bore 28 provided in a bottom
plate 29 of the housing 10. The vertical axis of the bore 28
coincides with the vertical guide axis 25 of the sensing member 16.
Further, the bore 28 is provided at its lower end with an internal
circular band 30 for retaining the sensing member 16 within the
bore 28 while permitting the sensing member 16 to lie freely on the
top of the sheet material of the stack 7.
The preferred embodiment of the photoelectric detection means as
illustrated in FIGS. 4 and 5 differs from that of FIGS. 2 and 3 in
that the sensing member 16 is guided in a retainer means 31 rather
than in the bore 28 of the bottom plate 29. The retainer 31 is also
supported in the housing 10 and is supported for movement about a
horizontal axis 32 extending transverse to the coincident planes of
the optical axes 23 and 24 of the illuminating means 14 and the
sensitive element 15 respectively.
The retainer 31 is supported on rotatable bearings 33 and 34, the
bearing 34 extending outwardly beyond a wall of the housing 10 for
supporting thereon an adjusting knob 36 provided with a pointer 35.
The outerwall of the housing 10 is provided with a scale 37
graduated in degrees for visual observation of a particular angular
setting of the retainer 31 on the angular guide axis 38. The
positioning of the angular guide axis 38 of the retainer 31
supporting the sensing member 16 and the direction of movement of
the sensing member 16 are effected through manual positioning of
the knob 36. In the position of the retainer 31 as shown in FIG. 4,
the angular guide axis 38 forms an angle .gamma. of about
45.degree. with the horizontal plane of the stack 7, i.e., the
angular guide axis 38 defines a plane perpendicular to the optical
axis 23 of the illuminating means 14.
With further reference to FIGS. 4 and 5, in order to maintain a
light-tight condition within the housing 10 there is provided a
plate 40 having a central opening 39 therein to permit the
illuminating means 14 to be projected through the opening 39 onto
the reflective surface of the sensing member 16. The illuminating
beam is reflected from the sensing member 16 upwardly in a path
through the opening 39.
The alternate embodiment illustrated in FIG. 7 utilizes a roller 17
as a reflective sensing element in place of the sensing member 16
described hereinabove. The roller 17 is also provided with a highly
polished surface to reflect the illuminating beam projected by the
illuminating means 14 from the roller 17 in a path to the sensitive
element 15. The roller 17 is rotatably supported on an axle 42
provided in a pivotal lever 41. The lever 41 is supported for
pivotal movement on a wall of the housing 10 such that it can pivot
about a horizontal axis extending transverse to the direction of
sheet advancement from the stack 7. Except for the pivotal movement
of the lever 41, the support for the pivot of the lever 41 may be
mounted in a fixed position on the wall of the housing 10.
It is preferable, however, to arrange the pivot of the lever 41 for
variable adjustment by meanss of a manually operable knob. The
lever 41 may be pivoted about an axis extending parallel with the
axis of rotation of the roller 17 such that the direction of
pivoting motion of the roller 17 may be adjustably set in a manner
substantially analogous to the adjustable setting of the angular
guide axis 38 as described and illustrated with reference to FIGS.
4 and 5.
In this regard, adjustment of the sensitivity of response or the
switching hysteresis may also be obtained by the device shown in
the alternate embodiment of FIG. 7 by altering the position of the
pivot of the lever 41. As the pivot of the lever 41 is moved closer
to the vertical guide axis 25, thereby lowering the roller 17, the
roller 17 is also displaced in a sidewise direction analogous to
the angular positioning of the retainer 31 as described supra. On
the other hand, if the pivot of the lever 41 is arranged at the
height of the horizontal axis of the roller 17, the roller 17 is
movable only in a vertical direction. Such vertical movement of the
roller 17 corresponds to the vertical movement of the sensing
member 16 when, for example, the angular guide axis 38 coincides
with the line of symmetry of the vertical guide axis 25 as
described hereinabove in the alternate embodiment illustrated in
FIG. 2.
The operation of the scanning apparatus of the present invention
will now be described with reference to FIG. 6. As shown therein,
sheets are advanced from the stack 7 from a feeding level indicated
by reference character h1 to a predetermined lowered level
indicated by the reference character h2. For purposes of this
disclosure, the distance between the reference characters h1 and h2
defines a predetermined range of sheets to be advanced from the
stack 7 from the predetermined lowered level h2 to the feeding
level h1, and movement of the sensing member 16 within this range
identifies a reference position.
With the stack 7 positioned at the feeding level h1, the movable
sensing member 16 supported by the retainer 31 assumes the position
shown in full lines in FIG. 6 wherein the vertical guide axis 25 of
the sensing member 16 is perpendicular to the horizontal plane of
the stack 7 and coincides with the line of symmetry of the optical
axes 23 and 24 of the illuminating means 14 and the sensitive
element 15 respectively. The upper periphery of the sensing member
16 intersects this line of symmetry at the point of intersection of
the convergence of the two optical axes 23 and 24. Thus, the
illuminating beam projected from the illuminating source 14
striking the surface or periphery of the sensing member 16 is
reflected and directed in a path to the optical axis 24 of the
sensitive element 15.
The sensitive or photoelectric element 15 detects changes in
position of the movable element 16 relative to the reference
position and is conditionable to an inactive state in response to
intercepting or interrupting the reflected light beam path from the
sensing member 16. As long as the reflected light beam path from
the sensing member 16 is interrupted by the sensitive element 15,
the drive means 6 for the lift table 1 is not actuated and the
stack 7 is not lifted to a raised position. This operation
continues so long as the level of the stack 7 is within the
predetermined range and the sensing member 16 is within the
reference position. However, as the sheet material from the stack 7
is advanced and the stack is depleted to the predetermined lowered
level h2, the sensing member 16 is also lowered such that the light
beam path reflected from the sensing member 16 is no longer
intercepted by the optical axis 24 of the sensitive element. In
this condition, the sensitive element 15 is conditioned to an
activated state and in response thereto actuates the drive means 6
for raising the table 1 and lifting the stack 7 to the feeding
level h1 whereat the lifting action will be arrested as a result of
movement of the sensing member 16 to a raised position wherein the
reflected light beam path from the sensing member 16 is again
intercepted by the sensitive element 15. At such time the sensitive
element 15 is conditioned to an inactive state and in response
thereto deactivates the drive means 6 for lifting the table 1.
Still referring to FIG. 6, as the sheet material is advanced and
the stack 7 is depleted by an amount indicated by the reference
character a, from the feeding level h1 to the predetermined lowered
level h2, the sensing member 16 is lowered along the angular guide
axis 38 from the mid-point position MO to a mid-point position M2
thus moving a distance indicated by the reference character b which
is greater than the distance a. In response to this movement, the
surface of the sensing member 16 is now in a position indicated in
dot-dash lines and the illumination beam projected from the
illuminating means 14 is directed onto the surface of the sensing
member 16 at a point S2 resulting in a reflection angle .beta.2
providing a beam path L2 directed well outside of the range of the
optical axis 24 to be intercepted by the sensitive element 15.
It is to be noted that the dimension a in the embodiment of FIG. 6
is shown greatly enlarged for purposes of clarity and
understanding. In actual practice the dimension a amounts to
between 0.01 and about 0.2 to 0.5 mm., dependent upon the feeding
or setting arrangement and the thickness of the sheet material
being processed.
With the retainer 31 adjusted to a position such that its angular
guide axis 38 is vertical and coincides with the vertical guide
axis 25 of the sensing member 16, depletion of the sheet material
from the stack 7 by the amount a to the level h2 results in
vertical displacement of the sensing member 16 by the amount a from
the mid-point position MO to a mid-point position M1. The position
of the sensing member 16 corresponding to the mid-point position M1
is indicated in dotted lines in FIG. 6. In this position, the
illumination beam projected from the illuminating means 14 to the
surface of the sensing member 16 strikes the sensing member 16 at a
point S1 on the surface of the sensing member 16 and is reflected
therefrom in a path directed at an angle .beta.1. Accordingly, with
a predetermined dimension for the depletion of the sheet material
from the stack 7 as represented by the reference chaaracter a,
although the angle .beta.1 is considerably smaller than the angle
.beta.2 the reflected beam path L1 is still well outside of the
range of the optical axis 24 to be intercepted by the sensitive
element 15. Thus, the sensitive element 15 remains in an inactive
state and the drive means 6 for lifting the table 1 is not
actuated.
From the foregoing, it will be appreciated that the sensitivity of
response can be increased or decreased as desired by selected
positioning of the angle .gamma. of the angular guide axis 38 of
the retainer 31 supporting the sensing member 16. Through the
facilities of the adjustable guide axis 38 the sensitivity of
response and switching hysteresis or the size of the incremental
steps of lifting movement of the lift table 1 may be accurately set
to the particular characteristics of the sheet material to be
advanced from the stack 7.
In all of the embodiments illustrated and described herein, the
reflective movable element in the form of the sphere 16 or the
roller 17 resting on the top of the stack 7, provides slight
frictional resistance to the top sheet in the stack. Because of the
weight of the movable element 16 acting against the top sheet of
the stack, the movable element 16 does not tend to vibrate or
oscillate such as to cause spurious signals or erroneous switching
of the photoelectric element 15 as a result of non-uniform
projection and reflection of the light beam path.
In summary, the present invention provides a simple but reliable
scanning apparatus for detecting and maintaining the height of the
stack of sheet material at a proper feeding level. The sensitive
device is highly responsive to extremely slight movement of the
movable sensing-reflector element as it is lowered in response to
depletion of the stack as the sheets are advanced from the top
thereof. This arrangement provides for feeding sheet material of
various weights, colors, surface qualities and the like, and for
accurately controlling the raising of the lift table in minute
incremental steps corresponding to a predetermined amount of stack
depletion to thereby maintain the top of the stack within a
predetermined range to provide for consistent and uniform
advancement of the sheets from the stack.
* * * * *