Stack Sheet Feeder
Original Publication Date: 1992-Sep-01
Included in the Prior Art Database: 2005-Mar-24
Eshleman, RA: AUTHOR [+2]
This article describes a mechanism for picking parts from a stack in a container.
Stack Sheet Feeder
describes a mechanism for picking parts from
a stack in a container.
sheets of material from stacks is a common
requirement in manufacturing processes and is typically difficult to
do without the sheets clinging together, resulting in more than one
sheet being picked up at a time. There are three forces to consider
in such a task: vacuum forces, friction forces and electrostatic
forces. If two sheets are pulled apart perpendicular to the mating
surfaces, a vacuum is created between the parts and opposes the
separating force. If two sheets are pulled apart in a direction
parallel to the mating surfaces, friction forces oppose the
separating force. Electrostatic forces may oppose the separating
forces in either case.
successful methods of sheet feeding employ some kind
of feeding mechanism which feeds sheets through a series of opposing
friction wheels such that the top sheet is pulled through some
designated path while sheets stuck to the bottom of the top sheet are
pulled in the opposite direction. A line-embedding system cannot use
such a feeder, however, because embedding is a "clean" process and
the friction wheels would be a potential source of contamination for
the sheets. The mechanism described herein is designed to allow the
top sheet to be picked from a stack and separate any other sheets
clinging to the bottom of it.
of this article is illustrated in the figures.
Figs. 1 and 2 are front and side elevation views, respectively, and
Fig. 3 is a plan view.
sheets 1 are stacked on the top plate 2 and
constrained in the desired orientation by eight locating pins 3. Two
vertical guide shafts 4 are attached to the top plate 2 and move in
two linear ball bushings 5.
sheets 1 are picked from the top of the stack by a
pick and place unit equipped with a vacuum gripper. The top plate 2
is spring loaded to accommodate the depletion of the stack. This
allows for the use of a simple pick and place unit with a fixed pick
elevation. For example, if the stack is full when the gripper moves
to its picking height, the top plate 2 will deflect approximately 1.0
inch. As the stack is depleted, the top plate 2 will deflect less
and less until it is empty, at which point the top plate will deflect
approximately 0.5 inch.
Also attached to the top...