Printing – Special article machines – Rotating object
Reexamination Certificate
2000-05-04
2001-05-01
Yan, Ren (Department: 2854)
Printing
Special article machines
Rotating object
C101S124000, C101S127100
Reexamination Certificate
active
06223653
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a screen printing apparatus and, more particularly, to a screen printing apparatus comprising means for rotatably mounting an article to be printed; an approximately planar screen member provided with an open mesh and a printing pattern; ink feeding devices and wiper driving devices for conveying printing inks through the screen member onto the article to be printed; a screen member holder for the approximately planar screen member and drive means for the screen member holder for producing a rolling motion of the screen member in a plane on the article during an essentially slip-free contact of the screen member with the article along a surface line of the article. Particularly the invention relates to an improved drive mechanism for the screen member in this screen printing apparatus.
2. Prior Art
The screen printing process has been used, for the application of printed images on the outside of containers, especially glass bottles. In the case of glass bottles especially screen printing inks are used, for example, which are baked on after their application to the glass surface in a thermal after-treatment and in this way are bonded with the substance of the glass in a practically undetachable manner.
In the predominant number of applications the containers have a rotationally symmetric form. The simplest form possible for a container with a wall is a hollow cylinder. Those containers with a cylindrical outer surface may be printed most easily with the screen printing methods. The container is clamped so that is rotatable about its cylinder axis, which is usually aligned horizontally. The screen member containing the printing pattern moves by contact with the upper outer surface of the container in a tangential direction over the cylinder perpendicular to its rotation axis, whereby by rotation of the container its cylinder surface rolls on the underside of the screen member so that at the same time printing inks are applied on the container through the screen.
In each case the screen member is driven translationally by this rolling motion. The clamped container can be either freely rotating but also may be driven synchronously with the translational motion of the screen member, whereby less slippage and thus a sharper printed image results. One known apparatus for printing a cylindrical object does not require much space, because the screen member is moved only translationally and of course for a distance equal to the cylinder circumference. If the outer wall of the container deviates only slightly from the ideal cylindrical form, for example by a slight conicity or a very slight convexity, the container can still be worked in this way, because the screen of the screen member may generally be pressed by the wiper approximately on the outer surface of the object to be printed. However since the object to be printed in this case no longer has equal peripheral speeds overall and the screen member can only move further with a predetermined speed, the object to be printed has peripheral speeds when its form deviates from a cylindrical form in some regions which are not exactly equal which already effects the sharpness of the printed image for a certain slip.
Conical containers, for example Erlenmeyer flasks, whose conicity is no longer characterized as slight, are frequent application cases. The rolling surface of a conical container with a truncated conical-shaped outer surface on a plane is an annular surface. If on the other hand the container is rotatable about its fixed rotation axis during printing, the container now can no longer roll on the annular surface for printing. Instead the annular surface must roll on the fixed container. This annular surface of part of this annular surface is the screen member. So that the screen member can roll on the article to be printed in a horizontal plane, the article is held in position so that it is rotatable and its rotation axis is inclined about half a cone angle relative to the horizontal, so that the upper surface line of the container, i.e. equivalent to the generatrix, extends horizontally. The screen member must describe a path around a vertical axis, on which the apex of the imaginary extension of the truncated conical-shaped container to be printed lies.
The less the conicity of the container to be printed, the more the rotation axis of the screen member must be spaced from the container to be printed. This means that in the known screen printing apparatus for conical containers, the rotation axis for the screen members must be spaced from the container different distances for containers of different conicity. Built-in lateral supports are thus used for conical containers in the known screen printing apparatus for this reason and are exchangeable in different sizes. These supports have a vertical axis at their end so that the screen member is rotatable about a radius arm in order to be able to perform its annular motion. This requires a considerable storage for exchangeable machine parts and especially requires an at least laterally very large amount of space in the automatic production line. Moreover retooling the production line for containers of different conicity is considerably time consuming.
The above-described method has already been mentioned in German Patent 898 746 from 1953. In this comparatively old prior art patent it already was suggested, especially for printing of bodies with non-cylindrical, e.g. conically-shaped, regions to use a stencil frame in the form of a rotationally symmetric rotating body instead of a planar screen stencil, whose cross-section is the mirror image of a cross-section, which is the exact longitudinal section of the object to be printed along a surface line. This suggestion completely ignores that fact that when contact is made with a non-axially parallel surface line, especially when only one of the bodies rolling on each other is driven, an uncontrollable slipping occurs, which is unacceptable for screen printing with a higher image quality.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a screen printing apparatus of the above-described kind for providing printing of a higher quality on conical objects, which is more compact than current screen printing apparatus of the same type and which may be rapidly adjusted to print containers of different form and requires no additional exchange of parts for the respective print images apart from the screen member during a change from a container of one form to another.
This object, and others which will be made more apparent hereinafter, are attained in a screen printing apparatus for printing an outer surface of a rotationally symmetric truncated cone shaped object, which comprises means for rotatably mounting an article to be printed so that the article is rotatable about a rotation axis thereof; an approximately planar screen member provided with an open mesh and a printing pattern for the article to be printed; means for conveying printing inks through the open mesh of the screen member onto the article to be printed including ink feeding devices and wiper driving devices; a screen member holder for the approximately planar screen member and drive means for the screen member holder for producing a rolling motion of the screen member in a plane on the article during an essentially slip-free contact of the screen member with the article along a surface line of the article.
According to the invention the drive means comprises a number of individual numerically controllable cooperating drive units for moving the screen member holder in two opposite directions in the plane of the rolling motion and a rotary motion of the screen member holder in the plane of the rolling motion, whereby the screen member performs a pivoting motion about a pivot point spaced from the screen member.
By superimposing several individual motions produced by individual drive devices arranged in the immediate vicinity of the screen member, the rotational m
Schott Glas
Striker Michael J.
Yan Ren
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