[0001] This invention relates to a method of and apparatus for printing on metal sheets.
Such apparatus is commonly known as a sheet-fed metal decorating press.
[0002] Known apparatus for printing on metal sheets comprises impression and blanket cylinders
in rolling contact with each other, between which the sheets are passed successively,
and a plate cylinder in rolling contact with the blanket cylinder. All three cylinders
are geared together so that adjacent cylinders contra-rotate at the same constant
peripheral speed. The plate cylinder carries a printing plate which is pre-inked in
known manner and which transfers ink to the blanket cylinder which transfers it in
turn to each metal sheet. The blanket cylinder carries a rubber blanket which is,
say, 2 mm. thick. In order accurately to register, that is to say locate in position,
each sheet relative to the impression cylinder, said cylinder carries two axially-spaced
cyclically-moveable stops, which are known as front lays, for the front edge of the
sheet. These stops comprise the free ends of respective levers which are pivoted on
the impression cylinder inside its periphery. The levers are actuated by stationary
cam means which cause them to extend and retract during the appropriate part of each
revolution of the impression cylinder. The action of the cam means is such that during
the operative part of their retraction the stops travel substantially tangentially
towards the impression cylinder. However, due to the location of the lever pivots,
the path of the stops relative to the impression cylinder is such that when the sheet
makes contact with the stops at the start of the operative part of their retraction,
the speed of travel of the stops is appreciably less than the peri pheral speed of
the impression and blanket cylinders. Each sheet is fed towards the nip of said cylinders
on a flat table known as an infeed by chain-driven spring-loaded pusher means at substantially
the same speed as said peripheral speed until it contacts a location face on the
stops, when it is abruptly decelerated to the speed of the stops at that point in
their cycle and then allowed to accelerate progressively back to said peripheral
speed as the stops return to their retracted position. The table is normally horizontal
but need not be. With this arrangement, comparatively high forces must be exerted
by the pusher means in order to accelerate the sheet and avoid its being left behind
by the stops, just before it is clamped to the impression cylinder and then enters
the nip, by a distance which may be of the order of 0.15 mm.
[0003] The object of the present invention is to avoid the disadvantages caused by the
need to accelerate the sheet subsequent to its deceleration.
[0004] According to one aspect of the invention, a method of printing on metal sheets by
successively pushing them on a table towards the nip of impression and blanket cylinders
which contra-rotate at the same constant peripheral speed; causing the front edge
of each sheet to make contact, prior to entering the nip, with cyclically-moveable
stop means carried by the impression cylinder; and finally passing each sheet between
said cylinders whilst maintaining it in contact with the stop means; is characterised
in that each sheet is pushed, prior to contacting a location face on the stop means,
at a speed faster than the constant peripheral speed of said cylinders, and thereafter
until it enters the nip is restrained by the stop means to travel at a speed substantially
the same as said constant peripheral speed.
[0005] According to another aspect of the invention, apparatus for printing on metal sheets
comprising impression and blanket cylinders which contra-rotate at the same constant
peripheral speed, means for successively pushing the sheets on a table towards the
nip of said cylinders, and cyclically-moveable stop means for the front edge of each
sheet which stop means are carried by the impression cylinder, is characterised in
that the stop means are constrained to extend and retract relative to the impression
cylinder during the appropriate part of each revolution thereof in a substantially
involute path the base circle of which is the periphery of the impression cylinder.
[0006] Preferably, the stop means comprise the free ends of two cam-actuated levers pivoted
on the impression cylinder outside its periphery, so that the stop means are constrained
to move relative to said cylinder in an arcuate path approximating to an involute
curve.
[0007] A preferred embodiment of the invention will now be described, by way of example
only, with reference to the accompanying drawings of which:-
Fig. 1 is a diagrammatic end view of a sheet-fed metal decorating press;
Fig. 2 is a detailed end view of stop means for the front edge of each sheet and of
an arrangement for moving the stop means cyclically;
Fig. 3 is a view of the stop means in the direction of the arrow 3 in Fig. 2;
Fig. 4 shows the positions of the stop means at one degree intervals during the operative
part of their retraction;
Fig. 5 is a graph showing the speed of each sheet relative to the angular position
of an impression cylinder of the press;
Fig. 6 is a view corresponding to part of Fig. 1 of such a press as arranged hitherto;
and
Fig. 7 is a graph corresponding to Fig. 5 for such a press as arranged hitherto.
[0008] Referring now to Fig. 1 (and Fig.6) of the drawings, a sheet-fed metal decorating
press comprises a blanket cylinder 101 in rolling contact with an impression cylinder
102 and a plate cylinder 103. The cylinders 101, 102 and 103 are geared together so
that adjacent cylinders contra-rotate at the same constant peripheral speed. Sheets
are successively fed towards the nip of the blanket cylinder 101 and the impression
cylinder 102 on a horizontal flat table 104 known as an infeed by chain-driven spring-loaded
pusher means (not shown). The plate cylinder 103 has secured on its periphery a curved
printing plate 105 which is pre-inked in known manner and which transfers ink to the
blanket cylinder 101 which transfers it in turn to each metal sheet. The blanket cylinder
101 has secured on its periphery a rubber blanket 106. In order accurately to register,
that is to say locate in position, each sheet relative to the impression cylinder
102, said cylinder carries two axially-spaced cyclically-moveable stop means indicated
generally at 107, which are known as front lays, for the front edge of the sheet.
Devices (not shown) for gripping the front edge of the sheet but lacking stops are
also provided in known manner. As thus far described, the press is conventional.
[0009] Referring now to Figs. 2 and 3 of the drawings, each stop means 107 is disposed at
the free end of a lever 108 which is pivoted about a common axis 109 on the impression
cylinder 102 outside its periphery. The stop means 107 has an inclined face 110, a
location face 111, and a gripper blade 112 one end of which projects beyond the location
face 111. The stop means is mounted on the lever 108 by means of an adjustment device
113 so that the distance between its location face 111 and the axis 109 can be varied.
The two levers 108 are cyclically moveable in unison by an arrangement including a
shaft 114 journalled in the impression cylinder 102 parallel to its axis and inside
its periphery, and having secured at one of its ends an arm 115 carrying a cam follower
in the form of a roller 116. Said roller engages with a stationary cam (not shown)
in known manner. Each lever 108 is pivotally connected by a link 117 to another link
118 which is pivotally connected to one of two arms 119 secured to the shaft 114.
The link 118 and the arm 119 are urged together by spring means (not shown) against
an adjustable stop 120 so that they tend to move as one. Conventional cut-outs 121
are provided in the impression cylinder 102 to accommodate the levers 108 and stop
means 107 when in the retracted position shown in Fig. 2. Pusher means (not shown)
of conventional construction comprise three mechanisms operating in series to advance
each sheet along the table 104 - first of all belt means; then a first chain drive
moving faster than the belt means and having dogs which positively engage the rear
edge of the sheet; and lastly a second chain drive having spring-loaded pushers which
resiliently engage the rear edge of the sheet to allow it to decelerate when it contacts
the location face 111, and when it has been clamped as hereinafter described are then
lowered, returned towards the table 104, and raised to engage the next sheet. The
sur face of the table 104 is disposed parallel to, and lower by say 8 mm. than, the
tangent 122 to the impression cylinder 102. As shown in Fig. 1 the point 123, hereinafter
referred to as top dead centre, where said tangent touches the impression cylinder
102 is disposed in advance, by say eight degrees, of the nip, that is to say the point
124 where the blanket cylinder 101 touches the impression cylinder 102.
[0010] In operation, the profile of the stationary cam is such that it acts as hitherto
to cause extension and retraction of the stop means 107 through a suitable radial
distance during the appropriate part of each revolution of the impression cylinder
102, said stop means travelling substantially along the tangent 122 towards top dead
centre during the operative part of their retraction. However, the location of the
axis 109 outside the periphery of the impression cylinder 102 constrains the stop
means 107 to move relative to said cylinder in an arcuate path closely approximating
to the ideal path which is an involute curve the base circle of which is the periphery
of said cylinder. Thus, due to the novel location of the axis 109, the speed of travel
of the stop means 107 along the tangent 122 during the operative part of their retraction
is substantially the same as the constant peripheral speed of the cylinders. The
second chain drive of the pusher means, although conventionally constructed, is caused
in novel manner to feed each sheet towards the nip of the blanket cylinder 101 and
the impression cylinder 102 at a speed faster by, say, 13 per cent than the constant
peripheral speed of the cylinders.
[0011] Referring now to Fig. 4, the sheet is approximately at position 45, that is to say
at approximately 45 degrees before top dead centre, when the stop means 107 moves
through the plane containing the surface of the table 104. The sheet contacts the
inclined face 110 of the stop means 107 approximately at position 32 and rides up
the face 110 until it contacts the location face 111 at approximately 15 degrees before
top dead centre, when it is abruptly decelerated to the speed of the stop means 107,
that is to say to substantially the constant peripheral speed of the cylinders, and
then continues to advance at that speed until it has been subsequently gripped and
then rolled through the nip. As shown in Fig. 5, there is still an initial shock as
the sheet contacts the location face 111 but thereafter there are no further changes
in the speed of the sheet, in contrast to the situation hitherto which is shown in
Fig. 7. At a point 125 (see Fig. 1) approximately four degrees before top dead centre,
the sheet is clamped by the retraction of the stop means 107 between the periphery
of the impression cylinder 102 and the projecting end of the gripper blade 112. This
causes the link 118 and the arm 119 to pivot slightly apart at the adjustable stop
120, against the action of the spring means urging them together, by an amount which
is dependent on the thickness of the sheet and may be of the order of 0.2 mm. The
sheet is additionally clamped at point 125 by the action of four gripper devices without
stops which are also provided on the impression cylinder 102 but not shown as they
are conventional.
[0012] One advantage of not needing to accelerate the sheet is that high pusher forces are
no longer required. This enables thinner or softer sheets to be fed to the press,
for example steel sheets only 0.12 mm. thick, or aluminium sheets. Another advan
tage resulting from the lower pusher force is that sideways location of the sheets,
which is particularly difficult when the sheets are not square or rectangular, is
rendered easier. A further advantage resulting from each sheet travelling at its
correct speed and position for a significant length of time prior to entering the
nip is that accurate registration of the sheets is achieved, enabling higher printing
speeds to be employed.
[0013] It should be understood that the ambit of the invention includes stop means moveable
relative to the impression cylinder in a true involute path as well as in an arcuate
or other path approximating closely to an involute curve.
1. A method of printing on metal sheets by successively pushing them on a table (104)
towards the nip of impression and blanket cylinders (102, 101) which contra-rotate
at the same constant peripheral speed; causing the front edge of each sheet to make
contact, prior to entering the nip, with cyclically-moveable stop means (107) carried
by the impression cylinder (102); and finally passing each sheet between said cylinders
whilst maintaining it in contact with the stop means;
characterised in that each sheet is pushed, prior to contacting a location face (111)
on the stop means (107), at a speed faster than the constant peripheral speed of said
cylinders (102, 101), and thereafter until it enters the nip is restrained by the
stop means to travel at a speed substantially the same as said constant peripheral
speed.
2. Apparatus for printing on metal sheets comprising impression and blanket cylinders
(102, 101) which contra-rotate at the same constant peripheral speed, means for successively
pushing the sheets on a table (104) towards the nip of said cylinders, and cyclically-moveable
stop means (107) for the front edge of each sheet which stop means are carried by
the impression cylinder (102), characterised in that the stop means (107) are constrained
to extend and retract relative to the impression cylinder (102) during the appropriate
part of each revolution thereof in a substantially involute path the base circle of
which is the periphery of the impression cylinder.
3. Apparatus according to claim 2, wherein the stop means (107) comprise the free
ends of two camactuated levers (108) pivoted on the impression cylinder (101) outside
its periphery, so that the stop means are constrained to move relative to said cylinder
in an arcuate path approximating to an involute curve.
4. Apparatus according to claim 3, wherein each lever (108) is connected by a linkage
to one arm (119) secured on a shaft (114) journalled in the impression cylinder (102)
parallel to its axis and inside its periphery, another arm (115) secured on the shaft
carrying a follower (116) for a stationary actuating cam and the linkage being extendable
against the action of resilient means.
5. Apparatus according to claim 4, wherein the linkage comprises a link (117) pivotally
connected to the lever (108) and to another link (118) pivotally connected to said
one arm (119), said other link (118) and said one arm (119) being urged together by
spring means against an adjustable stop (120).