Information
-
Patent Grant
-
6296703
-
Patent Number
6,296,703
-
Date Filed
Friday, December 4, 199825 years ago
-
Date Issued
Tuesday, October 2, 200123 years ago
-
Inventors
-
Original Assignees
-
Examiners
Agents
-
CPC
-
US Classifications
Field of Search
US
- 254 93 HP
- 254 93 R
- 118 413
- 118 261
- 118 410
- 118 120
- 118 123
- 118 325
- 118 419
- 239 451
- 239 455
-
International Classifications
-
Abstract
A pneumatic actuator for control of the coating thickness or basis weight of a coating apparatus for paper or cardboard webs has a pair of spring metal plates which can be deflected outwardly by a pneumatically extendable cushion between these plates in a frame. One end of the pair of plates is anchored while the other end is attached to a coating pin which works against a compression spring counteracting the outward deflection of the metal plates.
Description
FIELD OF THE INVENTION
My present invention relates to a pneumatic actuator, especially for controlling the transverse profile of a coating device in an apparatus for coating of paper or cardboard webs having elements spaced across the width of the web and which can be adjusted to regulate that transverse profile or coating cross section.
BACKGROUND OF THE INVENTION
For the coating of paper or cardboard webs with viscous coating materials or coating materials which are applied by doctoring or jet coating, especially pigmented materials, sizings and the like, it is important to provide the coating apparatus with the ability to control the cross section of the coating applied, i.e. the transverse profile, both in terms of the basis weight (weight per unit area of the coating) or the thickness thereof. For that purpose a row of adjusting elements may be provided across the width of the web which can control the local basis weight or thickness so that the result of effective positioning of these elements individually is control of the transverse profile. Usually the goal is to eliminate variations in the transverse profile which may result in the production of the coated web and the goal is to insure a uniform coating.
In the coating of paper or cardboard webs, so-called doctor blade apparatuses may be provided in which an excess of the coating material, for example a coloring matter, in a viscous form is applied and the excess is doctored off by an elastic doctoring blade which can also be referred to as a shaving or scraping blade and which removes that excess, leaving a uniform coating. The level of the basis weight of the coating remaining on the web can be adjusted by locally varying the pressing force of the blade against the coating on the web. The blade can thus be backed by a bendable bar upon which the setting elements act.
Such a doctor blade arrangement is described in WO 93/17795 and here the flexible bar is provided with a row of setting elements for adjusting locally varying pressing forces. Each setting element comprises an axially-shiftable rod or pin guided in a holder and positionable by a set screw against the force of a compression spring. The compression spring, the screw and the rod act axially.
In DE-OS 44 32 177, a so-called free jet nozzle applicator is disclosed which utilizes a slit nozzle formed between two lips from which a free jet of the coating material is directed against the web or an applicator roller which applies film of coating material formed on that roller to the web. To adjust a certain transverse profile of the coating of the two lips of the slit nozzle may be yieldable and can be adjusted differently in different zones over its length relative to the other lip. The adjusting elements are adjusting screws spaced apart across the width of the web, prestressed by spring elements. The actuation of the adjusting screws is effected either manually or by means of servomotors or the like.
OBJECTS OF THE INVENTION
It is the principal object of the present invention to provide n improved actuator for a setting element utilizable in a coating apparatus whereby drawbacks of earlier systems are avoided.
Another object of the invention is to provide a system for controlling the transverse profile of a coating, in a coating apparatus, which utilizes structurally simple, reliable and accurately controllable actuators and wherein the actuators have highly reproducible effects with minimum hysteresis.
It is also an object of the invention to provide an improved actuator for use in a coating profile controlled arrangement of the latter type.
SUMMARY OF THE INVENTION
These objects and others which will become apparent hereinafter are attained, in accordance with the invention in a pneumatically-operated actuator which can comprise:
a frame;
a pair of generally parallel, mutually spaced apart sheet-metal spring plates in the frame and secured to the frame at one side of the plates;
a pin longitudinally shiftable in the frame and secured to an opposite side of the pair of plates;
a pneumatic cushion formed between the plates and connectable to a source of compressed air whereby pressurization of the cushion deflects the plates transversely, thereby longitudinally shifting the pin; and
a spring on the frame yieldably counteracting transverse deflection of the plates.
Preferably the pin is guided through a seat for the spring which, advantageously is a coil compression spring braced between these seats and a plate on the pin so that the spring biases the pin axially outwardly with respect to the frame.
To minimize friction between the cushion and the spring plates, a low friction foil may be interposed between the cushion and each plate.
The displacement of the pin can be measured by a displacement-measuring device which directly monitors the axial stroke of the pin or by a measuring device which is a response to deflection of one of the plates
The actuator is preferably used as one of a multiplicity of such actuators in an apparatus for coating a web, especially of paper or cardboard, which has a corresponding number of control elements disposed across the path of the web and positionable to vary the basis weight or profile of the coating applied to the web. The device may include a doctor blade which removes excess material from the coating and which is backed by a bendable member upon which the control elements act, the control elements being spaced apart along this bendable member. The bendable member in turn, acts upon the doctor blade. Alternatively, the control element can act upon a flexible lip of a slit nozzle of the type described.
BRIEF DESCRIPTION OF THE DRAWING
The above and other objects, features, and advantages will become more readily apparent from the following description, reference being made to the accompanying drawing in which:
FIG. 1
is a diagram of a pneumatic actuator according to the invention as seen from the side;
FIG. 2
is a longitudinal section of a concrete embodiment of such an actuator;
FIG. 3
is a longitudinal section through an actuator forming part of an apparatus in which a doctor blade removes excess coating material;
FIG. 4
is a section through the actuator of
FIG. 3
taken in an axial plane perpendicular to the axial plane of the section of
FIG. 3
;
FIG. 5
is a longitudinal section through an actuator provided with a displacement measuring unit for directly measuring the stroke of the pin; and
FIG. 6
is a longitudinal section,through an actuator and a transverse section through a free jet nozzle providing this actuator in a coating apparatus in which the actuator serves for the zonewise deflection of a bendable lip.
SPECIFIC DESCRIPTION
FIG. 1
is a schematic illustration of a pneumatic actuator according to the invention and comprises a rigid frame with two spaced-apart plates, namely, an upper plate
1
and a lower plate
2
which are interconnected at the right hand end as shown in
FIG. 1
by an end plate
3
. Between the two rigid plates
1
and
2
, there is provided a pair of mutually-spaced and generally parallel spring sheet-metal members
4
,
5
which have broad surfaces turned toward one another. The spring plates
4
and
5
are fixed together at one of their longitudinal ends by the end plate
3
. At their other longitudinal end the pair of plates
4
,
5
are affixed to a block
6
which is slidable between the rigid plates
1
,
2
in the longitudinal dimension of the spring plates
4
,
5
.
Between the spring plates
4
,
5
, a bladder
7
forming a pneumatic cushion, is provided, the bladder being connected as shown diagrammatically in
FIG. 1
, to a source
7
a
of compressed air, e.g. via a control valve
7
b
which regulates the degree of pressurization of the bladder
7
.
As the bladder or cushion
7
is pumped up, the spring plates
4
,
5
are deflected outwardly to reduce the effective length of the spring plate pair so that the left hand end of the pair of spring plates and the block
6
are drawn toward the end plate
3
, i.e. to the right in FIG.
1
. At the side of the block
6
turned away the spring plates
4
,
5
, a pin
8
is centrally affixed and thus extends in the longitudinal dimension of the spring plates
4
,
5
. The pin
8
is axially shiftable in an opening
9
a
in a seat
9
which is affixed between the plates
1
,
2
and serves as an abutment for a coil compression spring
10
braced between the seat
9
and a shoulder
11
on the pin
8
.
The compression spring
10
thus acts to counter the transverse deflection of the plates
4
,
5
in the direction of the arrows x and thus is compressed upon a shortening of the effective length of the spring plate pair
4
,
5
. The spring
10
draws the spring plates
4
,
5
planar when the cushion
7
is decompressed.
The spring plates
4
,
5
are so mounted in the frame that their transverse bending suffices for the desirable strokes of the pin
8
. For that purpose, there must be sufficient free space in the frame or the spring plates
4
,
5
must be spaced part by sufficiently large distances from the plates
1
,
2
. When compressed air is admitted to the cushion
7
, the spring plates
4
,
5
are urged apart to foreshorten the effective length of the pair of spring plates, displace the block
6
and the pin
8
to the right and increase the compression of the spring
10
. The transverse forces on the spring plates
4
,
5
are balanced so that there is minimum friction of the pin
8
in the guide
9
. Since the spring
10
counters the transverse deflection of the spring plates
4
,
5
, the adjustment of the pin
8
is accomplished without play and thus the hysteresis is minimal so that the positioning of the pin
8
and any setting element actuated thereby is highly reproducible.
Any axial forces applied from the exterior to the pin
8
are taken up by the spring
10
and absorbed by the seat
9
. There is no compression force applied to the spring plates
4
and
5
in their longitudinal direction. This prevents the spring plates
4
,
5
from buckling inwardly or outwardly. At the same time there is a well-defined relationship between the outward deflection x of the spring plates
4
and
5
and the axial stroke s of the pin
8
. This enables indirect measurement of the stroke by a measurement of the transverse deflection of one of the plates
4
,
5
as has been shown in FIG.
3
. Such an indirect measurement of the stroke s is advantageous when no direct measurement in the region of the pin
8
is possible because there is insufficient space around the pin
8
to provide the measuring device. Comparatively large and inexpensive measuring units can be provided in the region of the spring plate
4
if desired.
To minimize friction between the cushion
7
and the spring plates
4
,
5
, low friction foils
4
a
and
5
a
can be provided between the spring plates
4
,
5
and the cushion
7
. These foils can be cemented on the inner surfaces of the spring plates
4
,
5
if desired. Suitable low friction foils can be composed of polytetrafluoroethylene.
FIGS. 2-6
show concrete embodiments of the actuator and its use in controlling coating via a doctor blade or a nozzle lip in respective zones thereof.
Since it may be desirable to replace the force-generating parts of the actuator upon the discernment of defects, for example the bursting of the compressed air bladder, these force-generating parts can be made separate from the parts carrying the compression spring
10
and its seat
9
and can be attached to these parts by bolting or screw connections.
The frame of the force-generating part can be comprised of the cover plate
1
, the bottom plate
2
, the end plate
3
and two further side plates
25
,
26
which are perpendicular to the plates
1
,
2
and the end plate
3
and laterally close the frame.
The spring plates
4
and
5
are fixed at their rear ends rigidly with the end plate
3
, i.e. are fixedly clamped thereto as has been shown in the drawing and, to this end they are anchored to the pin
12
which has a screw
13
threaded into the end plate
3
.
If the spring plates
4
,
5
are sufficiently bendable, they can be fabricated in a single piece and this single piece can be looped around the pin
12
. At the opposite end, the spring plates
4
,
5
are clamped in the block
6
which can provide the holder affixed to the pin
8
. The block
6
in this embodiment can be movable between plates
1
,
2
. The bladder forming the compressed air cushion
7
is shown here diagrammatically to lie between the deflected plates
4
and
5
.
On the block
6
, between the pin
8
and the clamp
6
a
securing the plates
4
,
5
thereto, a measurement pin
14
is affixed and extends perpendicular to the direction of displacement of the pin
8
through an elongated window
15
in the cover plate
1
. The pin
14
allows the movement of the block
6
and hence of the pin
8
to be followed and can cooperate with a detector for providing a signal representing the stroke of the pin
8
and hence the setting thereof.
The pin
8
can be connected to the block
6
by a plug connector. For this purpose, the block
6
can have at its front end a T groove
16
which receives a bead
17
threaded onto an end of the pin
8
. The pin
8
can extend into a housing
18
which is axially aligned with the shank of the T groove
16
and is connected by a screw-thread arrangement to the side plates of the frame. At the front end of the cover plate
1
, an angled fastening plate
19
is welded and is formed with a central downwardly opening passage
20
through which the pin
8
is guided. The frame with the force-generating parts is connected by screws
21
to the housing
18
, the screws
21
traversing the fastening plate
19
. Upon removal of the fastening screws
21
, the force-generating parts can be removed from the housing
18
. The housing part
18
with the pin
8
and the bead
17
can be slipped out of the T groove
16
upon lifting of the frame. The bottom plate
2
, so that it should not interfere with this movement, ends in the region of the block
6
. Between the bottom plate
2
and the housing
18
there is thus sufficient free plates to enable the end of the pin
8
with the bead
16
to be moved therethrough.
The housing
18
includes a passage
22
through which the pin
8
is guided and which opens via the broad blind bore
23
outwardly. The inner wall of the blind bore
30
forms the seat
9
for a compression spring
10
received in the blind bore
23
around the pin
8
. The outer end of the compression spring
10
presses against a shoulder
24
attached by a screw-thread arrangement to the pin
8
. The outer dimensions of the shoulder
24
are so matched to the blind bore
23
that an axial movement of the pin
8
is not restricted.
The actual embodiment of the device used in practice has the advantage that the housing
18
with the elements contained therein can be fixed on the machine parts of the coating unit permanently. In case of a defect in the force-generating part with the compressed air cushion
7
, this part can be readily removed at low cost and replaced. The housing
18
with the pin
8
can be used for manual displacement without the force-generating part, in which case an adjustment nut can be threaded onto the end of the pin
8
.
FIGS. 3-5
show actuators according to the invention which can be built into a doctor blade device for controlling the thickness or cross section of the coating.
The coating system comprises a metering arrangement for applying the coating material to the web and a scraper blade
27
or the like extending across the width of the web and elastically deformable by a flexible bar
29
. The foot of the blade can be replaceably clamped in the scraper beam
28
. The blade
27
is engaged by the bar
29
, which extends the full width of the web, along the rear side of the bar below its tip. At spaced apart locations, setting elements engage the bar
29
, preferably with the spacing of 50 mm to 150 mm over the entire width. The setting elements generate a pressing force which urges the blade
27
against the coated web so that differences in local thicknesses of the coating can be levelled out.
In direct coating, the blade scrapes excess material from the coating directly on the web whereas for indirect coating the blade scrapes excess coating material from the film on a transfer roller, the transfer roller applying the film to the paper or cardboard web. A metering system of this type is shown, for example, in WO 93/17795.
According to the invention, the setting elements are affixed on the upper side of the beam
28
with their housing parts
18
. In that case, the force-generating part, as has been described previously, can be simply removed. The setting pins which are threaded into the back of the member
29
form both holders for the member
29
and adjustment devices therefor. An axial shift on each setting pin
8
allows the bar
29
to be adjusted differently at each location so that a corresponding series of pressing forces can be applied to the doctor blade
27
and the transverse profile of the coating can be corrected.
In the embodiment of
FIG. 3
, on the cover plate
1
a measuring device
30
is mounted which, through an opening
30
a
in the cover plate
1
, enables measurement of the transverse displacement x of spring plate
4
and thus an indirect measurement of the axial stroke s of the pin
8
. The measuring device
30
can be a contactless proximity sensor.
In
FIG. 5
I have shown an embodiment in which the stroke s of the pin
8
is directly measured. In this case the measuring device
31
is mounted on the cover plate
1
and responds to a displacement of the pin
14
(see
FIG. 2
) in the direction of the arrow s. The measuring device
31
can have a measuring rod
32
forming a sensor which is axially displaceable parallel to the pin
8
and which is biased by a spring
33
against the pin
14
. The movement of the pin
8
is thus transmitted to the measuring device
31
and registered capacitatively or inductively.
FIG. 6
shows the use of the actuators for controlling a free jet nozzle configuration. In this case, the coating device comprises a free jet nozzle formed between the two lips
34
,
35
extending over the working width of the web. From the slit nozzle, the material to be coated onto the paper or cardboard web
37
is guided on a drum and can be projected in a jet
36
onto that web. The nozzle
34
,
35
is connected with a supply passage
38
to which the coating material is fed from the die chamber
39
. The nozzle lip
34
is affixed to an endless side wall
40
of the device via an angled member
41
with respect to which the lip
34
is limitedly bendable, enabling the spacing of the lip
34
from the lip
35
to be varied zonewise across the width of the web.
Adjustment of the spacing of the lips
34
and
35
from one another is effected by means of actuators according to the invention, uniformly spaced across the width of the web, for example at every 100 mm and mounted with their housing portions
18
on the wall
40
. The lip
34
can be extended into a tongue
42
forming a lever arm
43
for each actuator. At the free end of each lever arm
43
, the pin
8
of the respective actuator is screwed. By varying the stroke of the pins
8
, each lever
43
can be tilted up or down about the fulcrum formed by the slender portion
34
a
of the lip to enable the respective zone of the lip to be bent toward or away from the fixed lip
35
varying the cross section of the nozzle slit.
Claims
- 1. A pneumatically operated actuator comprising:a frame; a pair of generally parallel, mutually spaced apart sheet-metal spring plates in said frame and secured to said frame at one side of said plates; a pin longitudinally shiftable in said frame and secured to an opposite side of said pair of plates; a pneumatic cushion formed between said plates and connectable to a source of compressed air whereby pressurization of said cushion deflects said plates transversely, thereby longitudinally shifting said pin; and a spring on said frame yieldably counteracting transverse deflection of said plates.
- 2. The pneumatically operated actuator defined in claim 1 wherein said pin is guided through a seat for said spring, said spring being a compression spring braced between said seat and biasing said pin axially outwardly of said frame.
- 3. An apparatus for coating a web comprising:a plurality of coating control elements disposed across a path of a web to be coated and respectively positionable to vary a basis weight of a coating applied to said web; and a respective pneumatically operated actuator for each of said elements, each of said actuators comprising: a frame, a pair of generally parallel, mutually spaced apart sheet-metal spring plates in said frame and secured to said frame at one side of said plates, a pin longitudinally shiftable in said frame and secured to an opposite side of said pair of plates, a pneumatic cushion formed between said plates and connectable to a source of compressed air whereby pressurization of said cushion deflects said plates transversely, thereby longitudinally shifting said pin, and a spring on said frame yieldably counteracting transverse deflection of said plates.
- 4. The apparatus defined in claim 3 wherein said elements act upon a bendable member extending across at least a portion of the width of said web and acting upon a blade shaving excess coating material from said coating.
- 5. The apparatus defined in claim 3 wherein said elements act upon a bendable nozzle lip of a slit nozzle for dispensing said coating in a free jet onto a surface.
- 6. A pneumatically operated actuator comprising:a frame; a pair of generally parallel, mutually spaced apart sheet-metal spring plates in said frame and secured to said frame at one side of said plates; a pin longitudinally shiftable in said frame and secured to an opposite side of said pair of plates; a pneumatic cushion formed between said plates and connectable to a source of compressed air whereby pressurization of said cushion deflects said plates transversely, thereby longitudinally shifting said pin; a spring on said frame yieldably counteracting transverse deflection of said plates; and a foil between said pneumatic cushion and said plates.
- 7. A pneumatically operated actuator comprising:a frame; a pair of generally parallel, mutually spaced apart sheet-metal spring plates in said frame and secured to said frame at one side of said plates; a pin longitudinally shiftable in said frame and secured to an opposite side of said pair of plates; a pneumatic cushion formed between said plates and connectable to a source of compressed air whereby pressurization of said cushion deflects said plates transversely, thereby longitudinally shifting said pin; a spring on said frame yieldably counteracting transverse deflection of said plates; and a displacement-measuring device for measuring an axial stroke of said pin.
- 8. A pneumatically operated actuator comprising:a frame; a pair of generally parallel, mutually spaced apart sheet-metal spring plates in said frame and secured to said frame at one side of said plates; a pin longitudinally shiftable in said frame and secured to an opposite side of said pair of plates; a pneumatic cushion formed between said plates and connectable to a source of compressed air whereby pressurization of said cushion deflects said plates transversely, thereby longitudinally shifting said pin; a spring on said frame yieldably counteracting transverse deflection of said plates; and a measuring device for measuring deflection of one of said plates perpendicular to a direction of displacement of said pin.
Priority Claims (1)
Number |
Date |
Country |
Kind |
197 53 899 |
Dec 1997 |
DE |
|
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