TRANSFER MECHANISM
The invention relates to apparatus and methods for transferring flexible adhesive films
using a rotatable and translatable head, with particular relevance in assembling gasket
components and membrane electrode assemblies in manufacturing processes for fuel
cells.
Fuel cells based on proton exchange membrane technology are typically assembled by
laminating together a large number of individual cells. Each cell comprises a membraneelectrode
assembly (MEA) with associated anode and cathode plates on either side of the
MEA. Gaskets are used to ensure a fluid-tight seal around the MEA.
A typical layout of a conventional fuel cell 10 is shown in figure 1 which, for clarity,
illustrates the various layers in exploded form. A solid polymer ion transfer membrane 11
is sandwiched between an anode 12 and a cathode 13. Typically, the anode 1 and the
cathode 13 are both formed from an electrically conductive, porous material such as
porous carbon, to which small particles of platinum and/or other precious metal catalyst
are bonded. The anode 12 and cathode 13 are often bonded directly to the respective
adjacent surfaces of the membrane 11. This combination is commonly referred to
collectively as the membrane-electrode assembly.
Sandwiching the polymer membrane 11 and porous electrode layers 12, 13 is an anode
fluid flow field plate 1 and a cathode fluid flow field plate 15. Intermediate backing layers
12a, 13a, also referred to as diffuser or diffusion layers, may also be employed between
the anode fluid flow field plate 14 and the anode 12 and similarly between the cathode
fluid flow field plate 15 and the cathode 13. The backing layers 12a, 13a are porous to
allow diffusion of gas to and from the anode and cathode surfaces as well as assisting in
the management of water vapour and liquid water in the cell.
The fluid flow field plates 14, 15 are formed from an electrically conductive, non-porous
material by which electrical contact can be made to the respective anode electrode 12 or
cathode electrode 13. At the same time, the fluid flow field plates facilitate the delivery
and/or exhaust of fluid fuel, oxidant and/or reaction product to or from the porous
electrodes 12, 13. This is conventionally effected by forming fluid flow passages in a
surface of the fluid flow field plates, such as grooves or channels 16 in the surface
presented to the porous electrodes 12, 13 .
The anode and cathode fluid flow field plates 14, 15 are electrically insulated from each
other and the flow fields across the plates 14, 15 are kept fluid tight using gaskets that are
positioned around the fluid field areas between the fluid flow plates and the polymer
membrane 11.
To allow useful amounts of power to be generated, individual cells such as that shown in
figure 1 need to be assembled into larger stacks of cells. This can be done by laminating
multiple cells in a planar stack, resulting in alternating anode and cathode plate
connections. Connecting individual cells in series allows for a higher voltage to be
generated by the stack, and connecting cells or groups of cells in parallel allows for a
higher current to be generated. Multiple stacks may be used to generate electrical power,
for example for use in an electrical power unit for a hydrogen-powered vehicle.
Large numbers of cells need to be assembled to form each individual stack.
Manufacturing such stacks therefore requires many separate steps, involving accurate
positioning of the various layers making up each cell. Any misalignment can result in
failure of the entire stack, for example by an electrical short-circuit or through leakage
from fuel or oxidant paths. It is therefore important for the application of fuel cell
technology to mass production that a manufacturing process for assembling the stack is
fast, accurate and reliable.
A particular problem with assembly of such fuel cell stacks relates to the accurate
positioning and alignment of components such as gaskets, which by their nature are
flexible and therefore more difficult to align with respect to other less flexible components
such as the metallic fluid flow field plates. Gaskets may be supplied in the form of die cut
sheets of adhesive gasket material, which require removal from a backing paper before
being positioned in place on a substrate, for example on a fluid flow field plate or an MEA.
Accurately positioning such adhesive materials is difficult to achieve by hand without the
aid of alignment tools, and is highly labour intensive.
A further problem relating to the use of adhesive gasket materials is the possibility of air
inclusions when a gasket is applied to a substrate. The presence of such inclusions could
result in failure of a stack when pressure is applied during final assembly, due to an air
inclusion causing a portion of a gasket to move from its position under pressure and
cause a fluid leak.
It is consequently an object of the invention to address one or more of the above
mentioned problems.
In accordance with the invention there is provided a mechanism for transferring a flexible
sheet material from a first substrate to a second substrate, the mechanism having a head
rotatable and translatable relative to the first and second substrates, the head comprising
a cylindrical curved portion having an outer face across which are provided openings
configured to apply air pressure to sheet material contacting the outer surface such that
the head is adapted to transfer the sheet material from the first substrate to the second
substrate by a combination of rotation and translation of the head.
The invention solves the problems associated with possible inclusion of air when
transferring the sheet material on to the second substrate. This is particularly
advantageous when applying the invention to assembly of fuel cells, where the sheet
material is an adhesive gasket material. The invention also allows for the sheet material
to be lifted away from the first substrate in a controlled manner, thereby minimising or
avoiding distortion.
The mechanism is preferably configured to lift the sheet material from the first substrate
by applying a negative air pressure to the openings while rotating the head during
translation of the head relative to a surface of the sheet material.
The head may be configured to be rotatable and translatable relative to fixed first and
second substrates, although in certain embodiments a portion of the relative translation of
the head may be achieved by translation of the first or second substrate.
The mechanism may also be configured to apply the sheet material to the second
substrate by combined rotation and translation of the head across a surface of the second
substrate.
The mechanism may be configured to apply a positive air pressure to the openings during
or after application of the sheet material to the surface of the second substrate.
The mechanism may be configured to apply mechanical pressure to the second substrate
across the thickness of the sheet material during application of the sheet material to the
surface of the second substrate.
In preferred embodiments, the cylindrical curved portion of the head is rotatable relative to
a central portion of the head, the central portion of the head comprising a first port for
applying negative pressure to the openings with the curved portion in a first rotated
position relative to the central portion and a second port for applying a positive pressure to
the openings with the curved portion in a second rotated position relative to the central
portion.
The first and second ports and the openings in the curved portion may be configured to
sequentially apply air pressure to the openings as the curved portion is rotated relative to
the central portion.
The central portion of the head may comprise a first plenum connected to the first port
extending circumferentially around a first part of the central portion of the head and a
second plenum connected to the second port extending circumferentially around a second
part of the central portion of the head. The first and second plenums are thereby
configured to apply the positive and negative pressures to selected openings on the
curved portion of the head according to the rotational position of the curved portion
relative to the central portion.
According to a second aspect of the invention there is provided a method for transferring a
sheet material from a first substrate to a second substrate using a pick and place
mechanism according to the first aspect of the invention, the method comprising the steps
of:
positioning the curved portion over the sheet material;
rotating and translating the curved portion across the sheet material while applying
a negative air pressure to the openings in the outer face of the curved portion;
translating the sheet material on the head from the first substrate to a second
substrate; and
applying the sheet material to the second substrate by rotating and translating the
curved portion across surface of the second substrate.
10 002349
The method according to the second aspect is preferably applied as part of a method of
manufacturing a fuel cell, where the sheet material comprises an adhesive gasket material
and the second substrate comprises a planar electrode component for a fuel cell
assembly, such as an anode or cathode fluid flow field plate or a membrane electrode
assembly.
Illustrative embodiments of the invention are described in further detail below by way of
example and with reference to the appended drawings in which:
figure 1 is a schematic exploded cross-section of a polymer electrolyte membrane
fuel cell;
figure 2 is a first perspective view of a sequence of operations for transferring a
sheet material from a first substrate to a second substrate;
figure 3 is a second perspective view of the sequence of operations of figure 2;
figure 4 is an elevation view of a pick and place head; and
figures 5a-5c are different cross-sectional views of the pick and place head of
figure 4.
Pick and place mechanisms are commonly used in manufacturing processes, for example
in surface mounting electronic components on to printed circuit boards. Such
mechanisms generally use a pneumatic head that applies a vacuum to pick up a
component and transports the component to a desired position on a circuit board,
positioning the component in place before releasing the vacuum. Such mechanisms
cannot however be used without modification for applying adhesive sheet materials,
because a peeling action is required to remove an adhesive sheet from a backing.
EP0291362 discloses a labeling mechanism for a weigh/price labeling apparatus, in which
self-adhesive labels on a backing strip are fed onto a temporary holder, the label being
held by vacuum on the holder. A label transfer device having a carrier on an eccentric
drive mechanism is used to move the label from the holder to delivery position, where the
label is delivered to an article. The carrier includes a pad having ports for applying a
vacuum or air pressure to hold or discharge the label from the pad. The mechanism is
not, however, suitable for being adapted for use with a pick and place mechanism, and
configured to provide only a limited degree of control over how different labels are
transferred.
Aspects of the invention apply the above different principles in combination to allow
adhesive backed materials to be accurately and repeatably applied from a first substrate
on which the adhesive material is supplied to a second substrate on which the adhesive
material is to be applied. This is achieved by means of a modified pick and place
mechanism that allows for an adhesive sheet material to be peeled away from a first
substrate on to a pick and place head. The head is then translated to transport the sheet
material to a second substrate and the sheet is rolled on to the second substrate, thereby
both accurately applying the sheet material in place and minimising air inclusions between
the sheet and the substrate, while also taking advantage of the flexibility of placement
associated with the use of a pick and place mechanism.
The principle of the invention is illustrated in figures 2 and 3 , which show different
perspective views of the same process according to an aspect of the invention, in which a
rotatable and translatable pick and place head 201 is used to transfer a flexible sheet
material 202 from a first substrate 203 to a second substrate 204. The process is
illustrated in the form of the head 201 being operated through a series of operations
identified as steps A to L in figures 1 and 2 .
The rotatable and translatable head 201 is mounted on to a mechanism (not shown) for
translating the head in vertical and horizontal directions, while the head 201 is itself
configured for rotation. A cylindrical curved portion 205 of the head 201 comprises a
series of openings 206 across an outer face 207, the openings 206 being connected via
internal passageways to a first port 208 for applying a negative air pressure (or vacuum)
and to a second port 209 for applying a positive air pressure. The arrangement of the
ports 208, 209 and the associated internal passageways are illustrated in further detail
below with reference to figures 4 and 5 .
With the head 201 in the position shown in step A, the openings 206 are connected to the
positive air pressure port 209, which acts to force a backing paper 210 that was previously
attached to the outer face of the curved portion 207 away from the head 201 . The head
201 is then translated across to the first substrate 203 to pick up a portion of sheet
material 202 located on the first substrate 203. The sheet material 202 may for example
be a portion of a sheet of die cut adhesive-backed gasket material. At step B, the curved
portion 207 of the head 201 is rotated relative to the central portion 2 11 of the head 201
such that one or more openings towards a leading edge 212 of the outer face 207 are
connected through to the negative air pressure port 208.
In steps B to F, the head 201 is translated relative to the first substrate 203 while the
curved portion 205 of the head synchronously rotates relative to the central portion 2 1 1.
This may be achieved by translating the head 201 while keeping the first substrate 203
fixed, or could alternatively be achieved by translating the first substrate 203 relative to the
head 201 . The effect of this relative translation and rotation is to transfer the adhesive
sheet material 202 from the first substrate 203 to the outer face 207 of the curved portion
205 of the head 201. As the curved portion 205 rotates, further openings along the outer
face are sequentially connected through to the negative pressure port 208, so that the
sheet material 202 is held on to the outer face by vacuum.
As shown in step F, the curved portion 207 has rotated relative to the central portion 2 11
of the head by approximately a quarter of a turn and the sheet material 202 is completely
held to the outer face 207. The head 201 then translates (step G) across to the second
substrate 204 and the sheet material 202 is progressively transferred to the second
substrate 204. As the sheet material is transferred, the curved portion 205 rotates relative
to the central portion 2 11 while the head translates relative to the second substrate 204.
Figures 2 and 3 show an optional protective backing paper 210 being removed as the
sheet material 202 is transferred.
From steps H to L, the openings in the curved portion 205 are progressively transferred
from being connected to the negative pressure port 208 to the positive pressure port 209
until, at step L, the sheet material 202 is completely adhered to the second substrate and
the backing paper 210 is only partially connected to the outer face 207 of the curved
portion 205. During steps H to L, a mechanical pressure is applied across the thickness
of the sheet material while the head 201 is translated and rotated across the second
substrate 204, thereby acting to force out any air between the sheet material and the
second substrate to prevent air inclusions from being formed. As with steps B to F, steps
H to L may include translation of the second substrate in addition to, or instead of,
translation of the head 201 across the second substrate 204.
The process then finishes at step A, where the positive pressure applied through the
openings causes the backing paper 210 to fall away from the head 201 to be disposed of.
The step of applying positive pressure to cause the backing paper 210 to be removed may
be caused by the curved portion 205 being rotated a further amount so that none of the
openings 206 are connected to the negative pressure port 208. After the backing paper
210 is removed, the process then repeats with a subsequent piece of sheet material.
A positive air pressure is optionally applied to the positive pressure port 209 only once the
sheet material 202 has been transferred to the second substrate, to serve the dual
purpose of separating the backing paper 210 from the head 201 as well as performing a
cleaning operation to remove any loose debris from the head prior to a subsequent
transfer operation. In certain embodiments, both the negative and positive air pressures
are continuously applied to the positive and negative air ports 209, 208 during transfer
operations. Control of how the different air pressures are applied can then be dictated
solely by the rotational orientation of the openings 206 on the curved outer portion 205 of
the head 201 relative to the central portion 2 1 of the head 201, as explained in further
detail below. Additional control of the air pressure lines, for example using a controller
and one or more solenoid valves, would therefore not necessarily be required.
The sheet material, for example in the form of an adhesive gasket, is preferably
configured to have a higher degree of tack between the backing paper and the gasket
material compared with that between the gasket material and the first substrate, which
allows the sheet material 202 to be removed from the first substrate by applying a vacuum
as shown in figures 2 and 3 .
Figure 4 illustrates the rotatable and translatable head 201 in side elevation view, showing
the curved portion 205 having openings 206 connected through to the ports 208, 209
(figure 2) via internal passageways 401 within the central portion 2 of the head.
Figures 5a, 5b and 5c show sectional views taken along sections 402, 403, 404 in figure
4 , in which the arrangement of the internal passageways or plenums 401 is further
illustrated. First and second passageways 401a, 40 around an outer circumference of
the central portion 2 of the head 201 are connected to the negative pressure port 208,
and a third passageway 401c is connected to the positive pressure port 209. Arrows in
figure 5a indicate the direction of air flow through openings in the curved portion 205 into
the first passageway 401a towards the negative pressure port 208. Arrows in figure 5c
indicate the direction of air flow from the positive pressure port 209 through the third
passageway 401c towards openings in the curved portion 205. In a general aspect
therefore, the central portion 2 11 of the head 201 comprises a first plenum 401a/401b
connected to a first port 208, the first plenum extending circumferentially around a first
part of the central portion 2 11 of the head 201 . The central portion may additionally
comprise a second plenum 401c connected to a second port 209, the second plenum
401c extending circumferentially around a second part of the central portion 2 1 of the
head 201 , the second part being different from the first part.
Figures 5a-c also show how the curved portion 205 is rotatable relative to the central
portion 2 1, by being connected to a rotatable ring 501 that surrounds the central portion
2 1 . Rotating the ring 501 anti-clockwise from the position in figure 5a relative to the
central portion 2 11 results in successive openings 206 around the curved portion 205 of
the head 201 becoming connected to the negative pressure port 208 via first and second
internal passageways 401a, 401b. Rotating the ring 501 clockwise from the position in
figure 5a, on the other hand, results in successive openings 206 becoming connected to
the positive pressure port 209 via third internal passageway 401c.
The rotatable ring 501 may be connected to a servomotor, which is controlled together
with the translation mechanism to synchronise rotation with translation during transfer of
the sheet material from the first substrate to the second substrate. Alternatively, rotation
of the ring 501 may be actuated by means of the mechanical pressure applied across the
sheet material as the head is translated across the first and second substrates during the
separation and application phases of the process. The mechanism according to the
invention may be used in conjunction with conventional pick and place machinery, which
may be numerically or manually controlled.
Positional registration of the head 201 may be achieved by physically locating one or
more projecting pegs and corresponding holes on the outer surface of the curved portion
of the head and the first and second substrates.
A controlled degree of friction between the rotatable ring and the central portion of the
head may be achieved by means of seals provided to ensure a fluid tight seal for the
internal passageways in the head, or may be achieved through the use of a further
component such as an internal sprung friction pad.
Multiple heads may be employed on extended shafts, which may be configured to
operated in parallel on first and second substrates comprising multiple locations for
transferring sheet material from and to.
Rotational motion of the curved portion of the head may be achieved through friction
alone, or may be controlled by mechanical engagement with the substrates, for example
through the use of a rack and pinion type of arrangement. Servo motor control of the
curved portion of the head may alternatively be used.
In alternative embodiments, the head 201 may be configured to be operable using
negative pressure only, i.e. with no positive pressure supply to force the release of the
backing paper. Instead, the backing paper may be allowed to fall away from the head
after application of the sheet material to the second substrate, or a further component may
be used to mechanically eject the backing paper. In such embodiments, the internal
porting of the head may be configured such that the vacuum applied to the backing paper
210 is fully released after the sheet has been deposited on the second substrate 204
(figure 2). The backing paper may, for example, be released from the head 201 by
actuation of an ejector component configured to protrude from the outer face 207 upon
rotation of the curved portion 205 beyond the position shown in step L of figure 2. The
ejector component may be in the form of a mechanical shoe which protrudes from the
outer face at the appropriate point in the sequence of operations. An advantage of such
alternative embodiments is that a positive pressure line would not be required. Possible
disadvantages of not using a positive pressure line would be that the backing paper might
not be reliably released from the head and incorporating an ejector component would tend
to increase the complexity of the construction of the head.
Other embodiments are also within the scope of the invention, as defined by the
appended claims.
CLAIMS
1. A mechanism for transferring a flexible sheet material from a first substrate to a
second substrate, the mechanism having a head rotatable and translatable relative to the
first and second substrates, the head comprising a cylindrical curved portion having an
outer face across which are provided openings configured to apply air pressure to sheet
material contacting the outer surface such that the head is adapted to transfer the sheet
material from the first substrate to the second substrate by a combination of rotation and
translation of the head.
2. The mechanism of claim 1 wherein the mechanism is configured to lift the sheet
material from the first substrate by applying a negative air pressure to the openings while
rotating the head during translation of the head relative to a surface of the sheet material.
3. The mechanism of claim 1 or claim 2 wherein the mechanism is configured to
apply the sheet material to the second substrate by combined relative rotation and
translation of the head across a surface of the second substrate.
4 . The mechanism of any preceding claim wherein the mechanism is configured to
apply a positive air pressure to the openings during or after application of the sheet
material to the surface of the second substrate.
5 . The mechanism of any preceding claim wherein the mechanism is configured to
apply mechanical pressure to the second substrate across the thickness of the sheet
material during application of the sheet material to the surface of the second substrate.
6. The mechanism of any preceding claim wherein the cylindrical curved portion of
the head is rotatable relative to a central portion of the head, the central portion of the
head comprising a first port for applying negative pressure to the openings with the curved
portion in a first rotated position relative to the central portion and a second port for
applying a positive pressure to the openings with the curved portion in a second rotated
position relative to the central portion.
7. The mechanism of claim 6 wherein the first and second ports and the openings in
the curved portion are configured to sequentially apply air pressure to the openings as the
curved portion is rotated relative to the central portion.
8 . The mechanism of claim 7 wherein the central portion of the head comprises a first
plenum connected to the first port extending circumferentially around a first part of the
central portion of the head and a second plenum connected to the second port extending
circumferentially around a second part of the central portion of the head.
9. A method for transferring a sheet material from a first substrate to a second
substrate using a mechanism according to any one of claims 1 to 8 , the method
comprising the steps of:
positioning the curved portion over the sheet material on the first substrate;
rotating and translating the curved portion across the sheet material while applying
a negative air pressure to the openings in the outer face of the curved portion;
translating the sheet material on the head from the first substrate to the second
substrate; and
applying the sheet material to the second substrate by rotating and translating the
curved portion across surface of the second substrate.
10. A method of manufacturing a fuel cell comprising the method of claim 9 , wherein
the sheet material comprises a gasket material and the second substrate comprises a
planar electrode component for a fuel cell assembly.
11. A method of transferring a sheet material from a first substrate to a second
substrate substantially according to the description herein, with reference to the drawings
of figures 2 , 3 , 4 and 5a to 5c.
12. A mechanism for transferring a sheet material from the first substrate to a second
substrate substantially according to the description herein, with reference to the drawings
of figures 2, 3, 4 and 5a to 5c.