Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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A ~Iethod and System for Punchin~ Holes
in a Sheet Material
FIELD OF THE INVENTION
This invention relates to a method and system for punching
holes in a sheet material disposed on a working surface in precise
registration therewith. In particular, the invention relates to such a
5 method and system for use with photo-plotters permitting holes to be
punched through a film material repeatably and precisely with respect to
an artwork formed thereon.
BACKGROUND OF THE INVENTION
In the printed circuit board (PCB) industry, it is known to
use laser plotters for exposing a photographic film so as to produce an
artwork relating to a specific layer of a PCB to be manufactured. The
PCB may comprise several layers each of which must be aligned precisely
with respect to one another. Since each layer relates to a specific
15 artwork, the photographic films which correspond to each of the layers
must themselves be aligned in precise registration.
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Such registration is achieved by punching holes in the
photographic film in precise registration with the holes of other films
relating to other layers of the same PCB. The exposed film bearing the
artwork for each layer is registered on a surface having corresponding
5 registration pins. Since each of the artworks is aligned with the surface
in this manner, they are also aligned with respect to each other, thereby
ensuring that all of the layers of the resulting PCB are in correct
alignment.
Furthermore, since PCBs are mass-manufactured by
10 employing several artworks simultaneously, it is important that the
registration holes produced in the artworks are precisely aligned not only
with respect to the corresponding layers of the PCB, but also with respect
to each other. In other words, not only is precision required but so also
is repeatability.
Several prior art methods and systems exist for punching the
registration holes in the film. Thus, it is known to punch the registration
holes before the film is inserted into the plotter. This, of course, is
analogous to the sprocket holes produced in camera films, permitting such
films to be wound on in the camera. The main drawback with such an
20 approach is that, since the film is punched prior to exposure, the
punching must be performed in a dark room.
Alternatively, the holes may be punched after the film is
exposed. However, this requires the artwork to be aligned with the
punching machine. Since the very purpose of the holes is to permit
25 precise registration of successive artworks during subsequent manufac-
ture, it is clearly unsatisfactory to employ a method which requires that
the exposed film be aligned with the punching machine first in order for
the registration holes to be punched. It is known to achieve such
alignment automatically using electronic vision systems, but the operation
30 is relatively slow and costly.
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In order to overcome this prol~lem, it is known, in flat bed
plotters, to punch the holes in precise registration with the artwork whilst
the film is on the plotter bed. There are several advantages to such an
approach. First, it obviates the need for a dedicated punching machine.
Secondly, the alignment is achieved automatically without the need for
a costly and complicated aligning system and, thirdly, it saves time in the
production process since the punching and the plotting are produced in
a single stage of the manufacturing process whilst the provision of a
separate punching machine clearly imposes an additional stage in the
manufacturing process.
In such flat bed plotters, a conventional punch and die is
provided in respect of each hole to be punched and each punch and die
is pre-aligned in precise registration. The dies are formed within the
surface of the plotter bed towards an edge thereof, and the punch
mechanism is fixedly attached to the end of the plotter bed. In such an
arrangement when the plotter bed moves so too does the punch mecha-
nism so as to maintain the precise registration between the punch and
dies.
Figs. 1 and 2 show a conventional system for punching holes
through a film 1 using a die 2 and punch 3. In this system, the punch 3
is located on one side of the film 1 and the die 2 on the other, and a hole
4 is produced by inserting the punch 3 through the film 1 into the die 2.
Such a system is suitable only if the clearance between the punch 3 and
the die 2 is small enough, i.e. Iess than 10% of the film thickness.
Thus, denoting:
t = the thickness of the film,
Dp = the diameter of the punch, and
Dd = the diameter of the die
it is required that:
Dd -Dp s 0.1t
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When punching the registration holes in accordance with
such a system, the punch, together with its actuator, is attached to the
frame of the plotter and the die is located within the working surface
thereof. The main disadvantage of such an approach is the very high
accuracy required for aligning the punch with the die. Thus, for example,
a film thickness of lOO~m requires that the tolerance of the punch
location in relation to the die be at least 5~m.
Such an arrangement is rendered feasible only because the
punch mechanism is fixed to the plotter bed since, were this not the case,
10 it would not be possible to maintain the precise registration between the
punch and dies which is essential. The punch mechanism is generally
robust and heavy and thus must also be effectively supported by the
plotter's transport mechanism which moves the plotter bed through
mutually orthogonal x and Y axes in order to align a desired co-ordinate
15 on the film with a fixed writing head. As is known, such flat bed plotters
move relatively slowly in the x and Y directions and therefore the extra
mass of the punch mechanism and its consequent load on the plotter's
transport rnechanism can easily be tolerated.
However, this is by no means the case where drum plotters
20 are concerned for two reasons. First, drum plotters rotate at very high
speed and therefore any extra loading on the drum's transport mechanism
is unacceptable. Secondly, fixing a heavy punch mechanism to a
periphery of the drum would unbalance the drum and unacceptably
affect the drum's dynamics.
Regardless of whether a flat bed or drum plotter is used to
plot the artwork, a slight misalignment of the punch with the die not only
causes inaccuracies in the resulting registration holes but, on account of
the force with which the punch is inserted into the die, can damage the
punch itself of even the working surface of the plotter which is made of
30 a softer material than the punch.
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U.S. Patent No. 4,485,713 (Dotta) discloses a punching device
comprising a pair of opposed complementary dies vertically guided by a
pair of guide rods each rotatably connected to a crank pin to continuous-
ly punch band material moving between the dies.
S In use, a band material of paper, for example, is drawn by
a pair of rollers through the gap between the opposing dies and punches
whilst, at the same time, a pair of toothed wheels rotate so that the
punches connected eccentrically thereto perform linear vertical to-and-fro
motion along a pair of guide rods thereby successively engaging and
disengaging with the dies. The dies and punches must be in exact
registration with one another, this being a prerequisite of any punching
machine.
By such means, holes are punched into the band material at
regularly spaced intervals, depending on the traverse speed with which
the band material is drawn through the device.
Furthermore, in the Dotta system, each punch finds the
center of a corresponding die in much the same way that a drill bit
locates a pre-formed hole or center punch. This is achieved by mounting
the punches in a fluid bed so as to provide some lateral play. Thus,
providing that the tip of each punch finds the center of the corresponding
die, the punch can move laterally slightly in order to ensure exact
alignment with the die. It is thus apparent that one of Dotta's objectives
is to ensure precise alignment between the punch and die regardless of
any initial fractional misalignment.
Furthermore, in the Dotta arrangement the respective dies
and punches are mounted on completely planar surfaces and are axially
brought into engagement and disengagement along the pair of parallel
guide rods firmly connected perpendicular to the ends of one of the dies.
It will readily be apparent that the Dotta system is massive
and certainly not adapeable for use with a drum plotter whose drum
rotates at high speed and requires precise balancing.
.
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German Patent No. DT 25 49 937 discloses a punch mounted
on a cylindrical surface and which impacts a flexible substrate which is
larger than the punch.
DT 25 49 937 obviates the need for precise alignment
between the punch and die. However, there is nothing in this reference
to suggest its application to a system for plotting an artwork and for
punching registration holes therethrough in precise registration with the
artwork. There is further no reason to combine the teachings of
DT 25 49 937 with those of the Dotta system, since DT 25 49 937 actually
teaches away from the teachings of Dotta in that in the Dotta system
precise alignment between the punches and dies is required, whilst
DT 25 49 937 obviates the need for such precise alignment.
Even apart from these considerations, neither of these
references is suitable, either singly or in combination, for ensuring that
the punches holes are in precise registration with an artwork previously
or subsequently formed on a film material disposed on a plotter. They
are merely directed to ensuring registration, or alternatively to obviating
the need for such regis~ration, between the punch and die.
U.S. Patent No.3,618,438 (Simson) is directed to cutting webs
of sheet-like material in a web offset printing press simultaneously with
the action of applying ink images to one or both sides of the web of
sheet-like material.
Thus, as shown in Simson, a web of sheet-like material is fed
between two interacting rollers referred to, respectively, as a blanket
cylinder and an impression cylinder. A die having a protruding cutting
edge is secured to the impression cylinder so that on encountering the
sheet material against an opposing surface of the blanket cylinder, a
section is cut out of the sheet material corresponding to the contour of
the die.
Here again, there is no suggestion that the removed section
of the sheet material is in a predetermined and precise registration with
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the sheet material itself still less, of course, with an artwork formed
thereon either prior or subsequent to punching the holes.
It will be borne in mind that in plotters used in the PCB
manufacturing industry, the print head is mounted in precise and known
registration with respect to the working surface. Consequently, if the
punches in particular are mounted within the working surface, their
location must be in known and precise registration relative to the
printing head. This guarantees that the holes thus punched through the
artwork are in precise registration therewith since, obviously, the artwork
is registered relative to a rest position of the print head. This notwith-
standing, no solution has yet been proposed to providing a punch and die
combination integral with the working surface of a plotter which exploits
this fact and which is, at the same time, both light and amenable to
application in drum plotters which have the very rigid dynamic require-
ments as outlined above.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a method and
system for punching holes in sheet material whilst disposed on a working
surface, wherein at least some of the drawbacks associated with hitherto
proposed methods and systems are substantially reduced or eliminated.
According to a broad aspect of the invention, there is
provided in a process for forming an artwork on a sheet material, a
method for punching holes in the sheet material whilst disposed on a
working surface in precise registration with the artwork, the method
comprising the steps of:
(a) providing for each hole to be punched a corresponding socket in
said working surface,
(b) securing the sheet material on the working surface so as complete-
ly to overlap all of the sockets,
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(c) forming the artwork on the sheet material in precise registration
with a predetermined origin of the working surface,
(d) associating with each of the sockets a punch and block combina-
tion disposed on opposite surfaces of the sheet material, said block
being formed of a softer material than the punch and having an
operating surface larger than a cutting surface of the punch,
(e) for each of said punch and block combinations, aligning the punch
with the block so that the operating surface of the blocl; complete-
ly overlaps the cutting surface of the punch, and
10 (f) effecting relative axial displacement of the punch towards the
block aligned therewith so as to punch a hole through the sheet
material in precise registration with the artwork.
There exist two different approaches for carrying out such
a method. In both approaches, sockets are formed in the working surface
of the plotter, each corresponding to a hole required to be punched and
having an operating surface larger than the cutting surface of the punch.
In one system, the sockets are filled with material, such as
plastics, which is relatively soft compared to the cutting surface of the
punch. The punch is then brought into exact alignment with the working
surface, such that the operating surface of the socket completely overlaps
the cutting surface of the punch. The punch is then displaced towards
the socket so as to punch a hole through the film, whilst any damage to
the punch is completely avoided since the sharp corners associated with
the dies in hitherto proposed methods are dispensed with. In such a
system, a single punch can be provided which is successively aligned with
each of the pre-formed sockets so as to punch the registration holes as
required. However, although the need for high accuracy is eliminated,
there still exists a repeatability problem. This problem can be overcome
by employing a plurality of punches, each in respect of a corresponding
hole and pre-aligned with the respective socket along at least one axis in
the plane of the working surface of the plotter.
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In an alternative system, a plurality of punches is again
employed, but this time each being fixedly mounted within a correspond-
ing socket in the working surface of the plotter and having a cutting
surface protruding slightly above the working surface. In order to punch
5the holes, a block formed of a material such as aluminum, being
relatively soft compared to the cutting surface of the punch and having
an operating surface larger than the cutting surface of the punch, is
approximately aligned with each punch in turn above the surface of the
sheet material mounted on the working surface so as to completely
10overlap the cutting surface of the punch. The block is then displaced
towards the punch under pressure, whereby a clean hole is punched
through the sheet rnaterial in precise and guaranteed registration with the
working surface of the plotter.
15BRIEF Dl~:SCRIPTION OF THE D~AWINGS
The invention will now be described, by way of non-limiting
example only, with regard to a method and system for forming an
artwork and registration holes in situ on a drum plotter and with reference
to the accompanying drawings, in which:
20Fig. 1 shows, in perspective, a conventional system employing a
punch and die;
Fig. 2 is a sectional view of the arrangement shown in Fig. 1,
pointing out some of the requirements and drawbacks with hitherto
proposed systems;
25Fig. 3 is a pictorial representation showing a first embodiment
according to the invention;
Fig. 4 is a pictorial representation showing in perspective a
practical arrangement relating to the first embodiment shown in Fig. 3;
Fig. 5 is a pictorial representation of a second embodiment
30according to the inveniion; and
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Fig. 6 is a pictorial representation of a third embodiment according
to the invention.
DETAILED DESCRIPTION OF PREFERKED E~BOI)IMENTS
Referring to Fig. 3, there is shown in part-sectional view a
first embodiment of a drum plotter according to the invention comprising
a cylindrical drum 10, an upper surface of which constitutes a working
surface 11 for accommodating thereon a flexible photographic film
material 12. An artwork 13 is formed on the film rnaterial in precise
registration with an origin (not shown) of the working surface 11. It will
be appreciated that since the film material 12 is secured to the working
surface 11 prior to forming the artwork 13 thereon, no special alignment
of the film material 12 with the working surface 11 is required.
~ormed within the drum 10 and flush with the working
surface 11 thereof is a plurality of sockets of which two are shown,
designated 14 and 15, each corresponding to a hole required to be punched
through the photographic film 12. Disposed within the sockets 14 and 15
are blocks 17 and 18 formed of a plastics material.
Mounted adjacent an uppermost surface 20 of the sheet
material 12 is a punch 21 having a cutting surface 22 which is smaller
than an uppermost surface of the sockets 14 and 15 adjacent to the
working surface 11 of the drum 10 (and constituting an operating surface
of the sockets). The punch 21 is operably coupled to an alignment means
(not shown) for displacing the punch 21 relative to the working surface
11 of the drum 10 to a predetermined position wherein the punch 21 is
substantially aligned with one of the sockets 14 or 15.
The operation of the system is as follows. The artwork 13
is plotted in conventional manner. Thereafter, without removing the film
12 from the working surface 11 of the plotter, the punch 21 is substantial-
Iy aligned with one of the sockets 14 or 15 such that the operating surface
of the respective socket completely overlaps the cutting surface 22 of the
punch 21.
A displacing means (not shown) coupled to the punch 21
then operates so as to displace the punch 21 axially under impact towards
S the corresponding socket 14 or 15, thereby penetrating the film 12 and
forming a hole therein. In such an arrangement, when the punch 21 is
displaced under impact towards the socket 14 or 15, the plastics material
17 or 18 within the socket distorts under the impact, allowing a clean hole
to be punched through the film 12.
The arrangement shown pictorially in Fig.3 employs a single
punch 21 which must be aligned successively with each socket in turn
until all the registration holes have been formed in the film.
There will now be described with reference to Fig. 4 of the
drawings an alternative arrangement for producing three registration
holes through a film 25 mounted on a working surface 26 of a drum 27
and employing three punches 28, 29 and 30. The punches 28, 29 and 30
are pre-aligned parallel to a longitudinal axis 32 of the drum 27 with
corresponding sockets 34, 35 and 36 formed in the working surface 26 of
the drum 27. Disposed within each of the sockets 34, 35 and 36 is a
corresponding block 38,39 and 40, each formed of a plastics material and
having an operating surface larger than the corresponding cutting
surfaces of the respective punches 28, 29 and 30.
In use, the drum 27 is rotated about the axis 32 until the
sockets 34, 35 and 36 are aligned with the respective punches 28, 29 and
30, their operating surfaces completely overlapping the cutting surfaces
of the respective punches. Thereafter, the punches are displaced under
impact towards the sockets so as to deform the blocks within the sockets,
thereby producing a clean hole through the film 25.
In Fig. 4 the sockets 34, 35 and 36 are shown as being
substantially aligned in a direction parallel to the longitudinal axis 32 of
the drum 27. However, it will be understood that this need not necessari-
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ly be the case and, in general, it is merely desirable that each of the
punches 28, 29 and 30 be pre-aligned with the corresponding sockets 34,
35 and 36, either in a direction parallel to the longitudinal axis 32 of the
drum 27 or, alternatively, along an axis perpendicular thereto.
For drum plotters, it is preferable that the punches 28, 29
and 30 be substantially aligned, as shown, so as to be operable by a single
displacing mechanism coupled thereto. However, when flat-bed plotters
are employed, optimal registration with guaranteed repeatability can
most satisfactorily be achieved by aligning each of the punches with
corresponding sockets along two mutually perpendicular directions. Such
an approach is theore~ically possible with drum plotters also, but would
require separate displacing mechanisms, operating in different planes, in
respect of each of the punches.
In all cases, the artwork may be plotted either before or
after the holes are punched, the only condition being that the film
remains secured to the drum during both operations.
Referring now to Fig. 5 of the drawings, there is shown in
part-sectional view a second embodiment according to the invention for
punching holes through a film 45 mounted on a working surface 46 of a
rotating drum 47. Formed within the drum 47 is a plurality of sockets of
which two are shown, designated 49 and 50. For the sake of clarity, it is
assumed that the two sockets 49 and 50 are not aligned and that the
socket marked 50 is not within the section-plane denoted by cross-
hatching. Mounted in each of the sockets 49 and 50 is a respective punch
51 and 52, each having a respective cutting surface 53 and 54 protruding
above the working surface 46 of the drum 47. Thus, the film 45 bulges
slightly at the areas marked 55 and 56 where it overlaps the respective
punches 51 and 52. However, it should be noted that the bulges 55 and
56 are only very slight, since the amount of protrusion itself is small and,
in any case, is insignificant seeing that no artwork is printed on the
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photographic film 45 in the vicinity of the registration holes to be
punched by the respective punches 51 and 52.
Mounted adjacent an uppermost surface 58 of the film 45 is
a block 60 formed of aluminum and having an operating surface 61
5 greater than the cutting surfaces 53 and 54 of the corresponding punches
51 and 52. The block 60 is operatively coupled to a displacing means
designated generally as 62 via a ball and socket joint 63.
In operation, the drum 47 is rotated until the block 60 is
approximately aligned with each of the sockets 49 and 50, in turn, the
10 operating surface of the block 60 completely overlapping the respective
cutting surfaces 53 and 54 of the punches 51 and 52. The displacing
means 62is then operated so as to apply a uniform pressure to the block
60 towards the corresponding punch 51 or 52, whereby the punch 51 or 52
penetrates the film 45 so as to form a hole therethrough.
If, alternatively, the block 60is formed of plastics, then an
impact must be applied to the displacing means 62 so that the plastics
material of the block 60 will deform as explained above with reference
to Figs. 3 and 4 of the drawings.
It will be appreciated that in the arrangement shown in Fig.
20 5, only approximate alignment of the block 60 with each of the punches
51 and 52 is required, the only requirement being that the operating
surface 61 of the block 60 completely overlaps the cutting surfaces 53 and
54 of the corresponding punches 51 and 52. This requirement is met in
practice using comparatively simple registration means permitting
registration holes to be produced at high accuracy and repeatability with
low cost.
Such an embodiment guarantees that the holes are punched
in precise registration with the artwork since, regardless of whether the
artwork is plotted before or after the holes are punched, both operations
30 are performed without removing the film material from the working
surface of the drum. Moreover, since the punches themselves are
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disposed within the working surface of the plotter, an extremely high
degree of both registration and repeatability can very easily be ensured.
It will be understood that whilst, in the preferred embodi-
ment, the alignment between the block 60 and each punch 50 and 51 is
effected by rotating the drum 47, it is equally possible for the drum 47
to remain stationary and for the alignment to be effected by displacing
the block 60 with respect thereto.
Fig. 6 shows in part-sectional elevation a third embodiment
similar to the second embodiment described above with reference to Fig
5 of the drawings The second and third embodiments are identical in all
respects except with respect to the displacing means 62 and to this extent
identical reference numerals are employed in the two figures.
Thus, the displacing means 62 shown in Fig. 6 includes a
roller 65 permanently in contact with the working surface 46 of the drum
47. In operation, the drum 47 rotates whereby the roller 65 passes over
the respective cutting surfaces 53 and 54 of the punches 51 and 52. The
rotation of the drum 47 itself causes a uniform pressure to be applied by
the corresponding punch 51 or 52 towards the roller 65 through the
photographic film 45, whenever the protruding cutting surfaces 53 and 54
pass under the roller 65. In this manner the punch 51 or 52 penetrates the
film 45 so as to form a hole therethrough.
In such an arrangement the displacing means 62 remains
stationary, the cutting operation being effected directly by rotation of the
drum 47, no displacement of the displacing means 62 being required. The
time taken to punch the holes is therefore faster than in the second
embodiment wherein, after alignment of the block with the punches 51
and 52, the disp]acing means 62 must be actuated.
