Patent Application
20120249679
This application claims the priority, under 35 U.S.C. §119, of German Patent Application DE 10 2011 015 277.6, filed Mar. 28, 2011; the prior application is herewith incorporated by reference in its entirety.
The present invention relates to an apparatus for printing surfaces, including a plurality of movable print heads each including a plurality of individually actuable nozzles, at least one printing position and at least one parking position for the print heads, in which the print heads are movable into the respective positions. The invention also relates to a system having the apparatus.
So-called inkjet printers having movable inkjet print heads are known from the prior art. Those inkjet printers are used, for example, in the home and office areas, in order to print paper with multiple colors. In that case, a separate print head is available for each printing color. The individual print heads and/or their respective nozzle configurations are identical. When multiple-color prints are produced, the heads are moved at the same time relative to the paper and in the process eject ink droplets at the same time, that is to say all of the heads are active. After the printing, all of the print heads are moved into a common parking position, in which usually cleaning of the heads also takes place, that is to say all of the heads are inactive. Moreover, industrial applications having inkjet heads are also known, in which the heads are accommodated, for example, on large X-Y frames and are used to print large area paper sheets or material webs. In addition, it is also already known to attach inkjet heads to robot arms which can be moved freely in three dimensions, in order for it to be possible in that way to print not only flat but also curved surfaces (as desired), for example body parts of vehicles. During the printing of body parts, however, spray nozzles are usually used, that is to say the parts are loaded with a spray mist. In contrast to inkjet heads, spray nozzles of that type cannot eject individual droplets as a result of individual control pulses. It is therefore disproportionately more difficult to generate (locally multiple-color) image information (in particular, on the basis of pixels) and instead, for example, a body component is usually painted only with one color or with multiple colors (that is to say globally with multiple colors, but locally only with one color). In the following text, examples from the prior art will be described.
German Patent DE 41 20 293 C2 describes a rotatable inkjet head (having individually actuable nozzles, for example according to the piezoelectric principle) on an X-Y frame, with which curves of any desired profile can be printed with a consistent coat thickness. A corresponding number of heads which are, however, identical can also be provided for multiple-color printing (yellow, cyan, magenta, black).
German Patent Application DE 10 2008 053 178 A1, corresponding to U.S. Patent Application Publication No. US 2011/0262622 A1, describes a coating device, for example for body parts of vehicles, with an inkjet head (having individually actuable nozzles, for example according to the piezoelectric principle) being accommodated on a robot arm and therefore making it possible to move it into any desired position and along any desired tracks. The print head can have a part which ejects the coating medium continuously and a part which ejects it in droplets. The print head can also have nozzle openings of different size, for example nozzle rows with large nozzles and nozzle rows with small nozzles. A plurality of identical print heads can also be provided which can be pivoted relative to one another, in order to achieve an improved adaptation to the surface of a curved component (see FIG. 22 of German Patent Application DE 10 2008 053 178 A1, corresponding to U.S. Patent Application Publication No. US 2011/0262622 A1).
European Patent Application EP 970 811 A1, corresponding to U.S. Pat. No. 6,096,132, describes an automatic painting device for vehicles, which automatic painting device has spray pistols for four colors. The four identical spray pistols are accommodated on an X-Y frame in such a way that they can have their respective spacing in the Z-direction from the vehicle surface changed individually.
In the prior art, identical heads, that is to say identical nozzle configurations, are therefore always used if a plurality of heads are used. Moreover, all of the heads are always active at the same time and print, or are inactive and do not print. The adaptation to the surface of a curved component takes place only by guiding the head to the component and guiding it along the component while maintaining the spacing, or by relative positioning of a plurality of heads with respect to one another. The printing of extremely curved surfaces (with small radii of curvature) and, in particular, of surfaces with so-called undercuts (with surface sections which project freely and impede, for example, the free access to other surface sections) can therefore still lead to problems.
A further problem can result from the dimensions of the print head. With an inkjet print head having a length L at a given working spacing A from the surface to be printed and a given tolerance TA of the working spacing, only a surface with a minimum radius of curvature Rmin can be printed due to the geometric conditions (L and A: see
It can be seen from the table that Rmin increases as L increases and decreases as TA increases. Theoretically, that is to say purely from the geometric consideration, Rmin is independent of A. A has therefore been estimated with an appropriate value of 10 mm. In practice, however, Rmin is actually dependent on A after all because it cannot be expected that a print head can achieve the same print resolution at every spacing A from the surface, and therefore Rmin decreases as A increases (at a given print resolution).
It is accordingly an object of the invention to provide an improved apparatus for printing surfaces having a plurality of movable print heads and a system having the apparatus, which overcome the hereinafore-mentioned disadvantages of the heretofore-known apparatuses and systems of this general type and which permit or provide favorable preconditions for the printing of surfaces which are shaped in any desired manner and, in particular, are curved to as pronounced an extent as desired.
With the foregoing and other objects in view there is provided, in accordance with the invention, an apparatus for printing surfaces. The apparatus comprises at least one printing position and at least one parking position, a plurality of movable print heads configured to be moved into the at least one printing position and into the at least one parking position, each of the movable print heads having a plurality of individually actuable nozzles, the movable print heads including at least one first print head and at least one second print head having mutually different nozzle configurations, the at least one first print head being disposed in a printing position and the at least one second print head being disposed in a parking position, in a first mode, and the at least one first print head being disposed in a parking position and the at least one second print head being disposed in a printing position, in a second mode.
The surfaces to be printed are preferably surfaces which are shaped in any desired manner and, in particular, are curved to as pronounced an extent as desired. They can also have undercuts. As a result of the selection of the different nozzle configurations, according to the invention the precondition is provided to print both, for example, flat surface sections and (severely) curved surface sections. In an advantageous way, surfaces with surface sections which are different in terms of their respective topology can also be printed. In each case that nozzle configuration is used locally in this case which is provided for flat, curved or severely curved sections or for sections with undercuts. The apparatus therefore permits a change between heads, that is to say it can be defined which head with which nozzle configuration is to be active and which is to be inactive.
The heads can preferably be moved freely three-dimensionally and can therefore advantageously be guided onto surfaces (surface sections) which are shaped in any desired manner and can be guided along the surfaces (surface sections) on tracks which are shaped in any desired manner. A predefined working spacing from surfaces which are shaped in any desired manner can also be maintained.
The nozzles are preferably inkjet nozzles which produce droplets in a one-dimensional or two-dimensional configuration. The nozzles are preferably not nozzles which generate spray mist or are different from nozzles of that type.
The parking positions can be identical for the different print heads. As an alternative, a separate parking position can also be provided for each print head. Corresponding conditions apply to the printing position/positions.
In accordance with another feature of the apparatus of the invention which is advantageous and therefore preferred for the rapid printing of large, flat surfaces and the slow printing of small, curved surfaces, the nozzle configurations which are different from one another differ in terms of their respective number of nozzles, with the number of nozzles of the nozzle configuration of the first print head being lower than the number of nozzles of the nozzle configuration of the second print head. For example, one print head can have more than ten nozzles and one print head can have less than ten nozzles. In this consideration, the expressions “rapid” and “slow” do not relate to the relative speed between the substrate and the nozzles, but rather to the printed area per unit time—that is to say, for example, using the unit square meters per minute.
In accordance with a further feature of the apparatus of the invention which is advantageous and therefore preferred for the rapid printing of large, flat surfaces and the slow printing of small, curved surfaces, the nozzle configurations which are different from one another differ in terms of their respective spatial configuration of the nozzles. For example, one print head can have a noncurved, linear nozzle configuration and one print head can have a curved (curvilinear), linear nozzle configuration. Furthermore, the nozzle configuration can be hook-shaped and can therefore be used for printing edges or bends.
In accordance with an added feature of the apparatus of the invention which is advantageous and therefore preferred for changing the print heads, at least one first and one second print head are disposed on a common transport apparatus which moves the print heads into the respective positions. Through the use of the transport apparatus, an active print head can be moved into a parking position and an inactive print head can be moved into a printing position, with the activity states changing. The transport apparatus is preferably a rotation apparatus which permits the individual print heads that are accommodated on it to have their respective position (and activity states) changed by rotation. As an alternative, a circulating belt or a (for example, electric) linear drive can be provided.
In accordance with a concomitant feature of the apparatus of the invention which is advantageous and therefore preferred for free, spatial positioning and moving, the common transport apparatus is disposed on a controllable and multiple-member robot arm or an X-Y-Z frame, with X, Y and Z denoting the three spatial directions, in which the transport apparatus can be moved independently of one another through the use of the frame.
In the following text, the invention per se and structurally and/or functionally advantageous developments of the invention will be described in greater detail with reference to the associated drawings and using at least one preferred exemplary embodiment. Elements which correspond to one another are provided in each case with the same designations in the drawings.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in an apparatus for printing surfaces having a plurality of movable print heads and a system having the apparatus, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.
Referring now to the figures of the drawings in detail and first, particularly, to
The apparatus 2 has a plurality of movable print heads 3a to 3c of different geometry which in each case include a plurality of individually actuable nozzles 4a to 4c. In the illustrated exemplary embodiment, three print heads are shown by way of example. Each of the three print heads can be moved into an (active) printing position 5a or an (inactive) parking position 5b or 5c. The printing position 5a is a position in which the print head 3a is disposed within a tolerance TA at a working spacing A from the surface 1. If so-called inkjet heads are used, the working spacing can be limited, for example, by their operating range, that is to say the substantially unimpeded range of the ink droplets. The working spacing can also be limited by a minimum spacing, for example in order to avoid collision. In
As is shown in
A rotation 7′ through 120° counter to the clockwise direction moves the first (active) print head 3a out of the printing position 5a into the parking position 5c and moves the second (inactive) print head 3b out of the parking position 5b into the printing position 5a (the second print head then becomes active and the first print head becomes inactive). In this case, the third print head 3c changes between the two parking positions 5c and 5b. As shown, the rotation apparatus 7 can have a rotatable, central carrier 8 for the number of print heads. The rotation can take place through the use of an electric motor or pneumatically. A rotation which is only back and forth can also be provided instead of a rotation through 360° or more.
The use of the rotation apparatus permits rapid and precise changes to be used between the respective print heads, in particular in conjunction with rapid control/regulation which is provided for the change of the heads and the adapted change of the image data. The respective position of the nozzles 4a-c of the print heads 3a-c is selected in such a way that, during a change of the active print head, no disruptive effects are produced in the printing image during the image transition, that is to say the printed image of the first print head seamlessly follows the printed image of the second print head and vice versa.
Each individual print head 3a-c can have nozzles 4a-c for different colors, paints or inks, in particular for so-called CMYK printing (cyan, magenta, yellow, black). As an alternative, each individual print head 3a-c can also be constructed from a plurality, preferably four, of partial heads each of which print only one color. The color space which can be reached by the image setting can be extended, for example by 6-color printing (CMYK, light cyan and light magenta) and by other color systems. In particular, the color space which can be reached can be extended by the additional use of white colors, paints or inks.
It can also be provided that a hydrostatic compensation mechanism for keeping the ink printing constant in the line system of the inkjet heads (or the respective ink meniscus at the outlet openings of the nozzles) forms a unit together with the print head. That unit is accordingly moved in its entirety during the change from the printing position to the parking position.
In a first mode, the first print head 3a is disposed in a printing position 5a and the second print head 3b is disposed in a parking position 5b. In a second mode, the first print head 3a is disposed in a parking position 5b or 5c and the second print head 3b is disposed in a printing position 5a. As an alternative, it is also possible to move two print heads at the same time into the printing position and to switch over from one to the other print head, in order to generate image transitions without disruptive effects in this way. In this case, a third head remains in a parking position.
In the respective parking position 5b or 5c, the print heads 3a-c can remain fastened to the transport apparatus or can be released from the latter and deposited or stored, for example. The ink supply for the print heads preferably remains connected to the transport apparatus during the depositing or storage of print heads.
The print heads 3a-c which are shown by way of example in the figure in each case include a plurality of individually actuable nozzles 4a-c. The print heads are preferably so-called inkjet heads, preferably operating on the basis of piezoelectrically activatable nozzles. It can also be provided that, in addition to the inkjet heads 3a-c, at least one head which produces a spray mist (that is to say, a head without a plurality of individually actuable nozzles) is provided on the transport apparatus 6, which head is used during large area, single-color painting. Furthermore, it is also possible to use so-called “continuous wave” systems, so-called “valve-jet” printing systems or so-called “bubble-jet” systems in a manner according to the invention.
The print heads 3a-c, which are shown by way of example in
The different print heads 3a-c can be attached to the rotation apparatus 7 at identical spacings from one another. As an alternative to this, the different print heads can also be attached to the rotation apparatus at non-identical spacings from one another, with the result that the entire system of rotation apparatus and print heads is balanced. Likewise as an alternative, a separate balancing weight 13 can be attached to the rotation apparatus.
The belt 14 or an apparatus including the belt and its guide rollers can in turn be disposed on a robot arm 6 or an X-Y-Z frame. As an alternative to the rotation apparatus or the belt apparatus, a linear drive can also be provided for moving the print heads 3a-d.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2011 015 277.6 | Mar 2011 | DE | national |
