Patent Description:
In many types of printers, a print head carriage is moved relative to a medium such as a sheet or a roll of paper or foil of plastic or the like. Such printers are also sometimes designated as "scanning printing systems". The "scanning printing systems" comprise a carriage configured to, in printing operation, move in reciprocation in a main scanning direction over the medium. The print head carriage carries a print head, which marks the medium with a marking agent such as ink or a conductive paste in order to create text, patterns, colors, images, electrical circuits and/or the like on the medium.

The print head carriage typically moves bidirectionally along a linear path and is typically mounted between two so-called runner blocks, which in turn are moveably arranged on a respective one of two guidance rails installed in parallel in the printer. The mounting of such a guidance rail in a carriage printing system is usually designed to be equidistant, for example with a mounting pitch of <NUM> millimeters.

<CIT> discloses a guiding structure for a print head carriage in which equidistant mounting sites are provided for an array of mounting bodies for mounting the guiding structure to the rest of the printer.

<CIT> describes an assembly for moving a carriage of a printer. Regarding a vibration problem that may arise when the carriage moves, it is suggested to include a flexible support element and a tensioner assembly for tensioning the flexible support element. By controlling the tension of the flexible support element, it is endeavored to dampen vibrations of the assembly caused by the movement of the carriage.

<CIT> discloses a printer with a guiding structure according to the preamble of claim <NUM>.

It has been found by the inventors that the typical equidistant arrangement of the mounting sites of the guidance rail may lead to an undesired increase in vibration in and of the guidance rail due to the movement of the print head carriage. In particular, when the print head carriage is moving with a constant speed along the guidance rail for an extended period of time, this induces vibrations in the guidance rail. Since the guidance rail is fixated at each of the mounting sites which are equidistant in the prior art, this creates a regular pattern of fixed points. Between these fixed points at the mounting sites, the guidance rail is comparatively freer to shift. Consequently, such a guidance rail installed in a printer is susceptible to particular vibration frequencies induced by the print head carriage, in particular to frequencies that are integer multiplies of the base distance between the mounting sites. Vibrations in the guidance rail, in turn, negatively affect the longevity and the precision of the print head carriage.

It is therefore an objective of the present invention to provide a printer with a guidance rail, which are less susceptible to these types of vibrations.

Accordingly, the invention provides a printer according to claim <NUM>.

In other words, the mounting sites of the guidance rail are non-equidistant overall as there is at least one distance between one pair of adjacent mounting sites which is different from at least one other distance between one other pair of adjacent mounting sites (wherein the one pair and the other pair may have at most one mounting site in common).

Advantageously, by arranging the mounting sites non-equidistant, the strict regularity of the arrangement of mounting sites is removed and the susceptibility of the guidance rail to vibrations is reduced. It is preferred that there is a plurality of first distances between adjacent mounting sites which are different from a plurality of second distances between adjacent mounting sites. In general, the less regular the arrangement of mounting sites on the guidance rail is, the less susceptible the guidance rail is to vibrations.

The mounting site being arranged essentially in a row may be understood to mean that they are arranged in a strict row as much as usual tolerances allow or that they are arranged in a row with perpendicular deviations of each mounting site from an ideal, strict row between (including) zero and a maximum deviation value, MDV. The MDV may as low as zero and as large as, for example, the size of the mounting site in the direction perpendicular to the ideal, strict row. This direction may also be simply designated as the "perpendicular direction", i.e., perpendicular to the longitudinal direction along which the guidance rail itself extends. Thus, the maximum distance between any two mounting sites in the perpendicular direction may be two times MDV, in case that one of the mounting site is maximally deviated in the positive perpendicular direction and another one of the mounting sites is maximally deviated in the negative perpendicular direction.

In some advantageous embodiments, refinements, or variants of embodiments, equidistant center positions for the mounting sites are defined, each mounting site is arranged within a predefined tolerance interval around a respective one of the center positions, and the relative position of each mounting site to the respective center position is different for at least two of the mounting sites. In each tolerance interval, there is only a single center position and only a single mounting site.

The equidistant center positions have the effect that the guidance rail is, on average, fastened to the printer at regular (equidistant) intervals such that at no point of the guidance rail there is an excess of play. On the other hand, since the mounting sites are not arranged exactly at the center positions but at (at least partially, i.e., at least for some mounting sites) different relative positions thereto, the strict regularity of the mounting sites is advantageously broken, and the guidance rail is less susceptible to vibrations.

Taking this idea further, more preferably each mounting site is randomly arranged within the predefined tolerance interval around its respective center position. This strongly reduces the chances that the guidance rail has any resonance frequency that can be excited by the movement of the carriage. The term "randomly" shall here be understood to include both true randomness as well as pseudo-randomness in the mathematical sense.

In some advantageous embodiments, refinements, or variants of embodiments, each distance between any two adjacent mounting sites is different. This is another way to strongly reduce the chances that the guidance rail has any resonance frequency that can be excited by the movement of the print head carriage.

In some advantageous embodiments, refinements, or variants of embodiments, at least two different distance values are defined for adjacent mounting sites, and wherein the at least two different distance values alternate regularly along the row of mounting sites. It should be noted that whenever herein distances between mounting sites are discussed, this pertains to distances between adjacent mounting sites unless explicitly specified otherwise. Two different distances values A, B mean that the distances between pairs of adjacent mounting sites along the longitudinal direction vary as A-B-A-B-A. For three different distances values A, B, and C, the order may be A-B-C-A-B-C-A. The largest resonance frequency would be the largest common divisor of A, B, C,. and so on which will in general be the smaller, the more different distance values, A, B, C, D,. and so on are present.

Advantageously, the ratio of adjacently applied distance values (i.e. the ratio of A:B, of B:C,. and so on) is between <NUM>:<NUM> and <NUM>:<NUM>, preferably between <NUM>:<NUM> and <NUM>:<NUM>, more preferably between <NUM>:<NUM> and <NUM>:<NUM>. These values empirically provide a good balance between the advantages of fixing the guidance rail at equidistant mounting sites for reasons of stability and the advantages of reducing its susceptibility to vibrations.

In some advantageous embodiments, refinements, or variants of embodiments, the mounting sites are configured as holes or bores through which mounting elements for mounting the guidance rail to the printer can be inserted. The mounting elements may in particular be mounting means such as screws, bolts, and/or the like. The extent of the hole or bore in the perpendicular direction, as a percentage of the extent of the guidance rail itself along the perpendicular direction, is preferably larger than <NUM>%, more preferably larger than <NUM>%.

The invention further provides a printer comprising at least one guidance rail according to an embodiment of the present invention, the at least one guidance rail being mounted to the printer by mounting elements attached at the mounting sites of the guidance rail. Preferably, at least (or exactly) two guidance rails are provided and mounted to the printer, more preferably in parallel for providing additional stability to the moving print head carriage.

It is further preferred that the first, second, third,. and so on mounting sites of the first guidance rail are positioned at different positions along the longitudinal direction than the respective first, second, third,. and so on mounting sites of the second guidance rail. This will further reduce the susceptibility of the assembly of the guidance rails and the print head carriage to vibrations. In other words, starting from a mounting site of a first guidance rail and moving towards another guidance rail along the perpendicular direction, it is preferred if no other mounting site is encountered at the same position with respect to the longitudinal direction.

The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying schematic drawings which are given by way of illustration only, and thus are not limitative of the present invention, and wherein:.

The present invention will now be described with reference to the accompanying drawings, wherein the same reference numerals have been used to identify the same or similar elements throughout the several views, and in some instances throughout the several embodiments.

<FIG> schematically illustrates a part of a printer <NUM> according to an embodiment of the present invention. Parts of the printer <NUM> which are well known but not essential for the description of the present invention are omitted for the sake of clarity. For example, no housing, medium transport system, print head and so on are shown although they will typically be present in the printer <NUM>.

What is shown in <FIG> is that the printer comprises, among other parts, two guidance rails <NUM> arranged in parallel to one another, each extending along a (the same) longitudinal direction L but at a perpendicular distance from one another. Along each guidance rail <NUM>, mounting sites <NUM> are provided which will be described in more detail in the following. A print head carriage <NUM> is moveably mounted between the guidance rails <NUM> such as to be moveable by an actuator (not shown) bidirectionally in the longitudinal direction L. In the shown depiction, the print head carriage <NUM> would carry a print head configured to eject the marking agent (e.g. ink) in the downward direction. The distances between the mounting sites <NUM> are not shown to scale in <FIG>.

<FIG> shows further details of the assembly shown in <FIG>, with the print head carriage <NUM> now left out. In this embodiment, the mounting sites <NUM> are provided as holes or bores in the guidance rail <NUM>. The holes or bores may be punched out of a blank metal strip to produce a metal guidance rail <NUM>, or they may be bored out of a blank metal strip. The guidance rail <NUM> could also be made from plastic in which case the mounting sites <NUM> may be cut into a blank plastic strip to produce a plastic guidance rail <NUM>, or the guidance rail <NUM> may be produced by injections molding as already comprising the holes, or the guidance rail <NUM> may be produced by additive manufacturing (e.g. "3D printing") from a material comprising (or consisting of) metal, plastic and/or ceramics as already comprising the holes.

<FIG> also shows that the guidance rail <NUM> may be mounted to a framework <NUM> of the printer <NUM> (or any other part of the printer <NUM>) using mounting elements <NUM>. These mounting elements <NUM> may be any type of mounting means, for example, screws or bolts. A runner block <NUM> is moveably mounted to the guidance rail <NUM> such as to be able to move along the longitudinal direction L. The print head carriage <NUM> may be mounted on at least one runner block <NUM> on each guidance rail <NUM>.

<FIG> schematically illustrates a guidance rail <NUM> according to the prior art (e.g. according to <CIT>), wherein mounting sites <NUM> are arranged at equidistant intervals. A schematic graph <NUM> indicates in an exaggerated manner how much play the different portions of the guidance rail <NUM> have due to the positioning of the mounting sites <NUM>: the play is minimal at each mounting site <NUM>, increases up towards a maximum precisely halfway between that mounting site <NUM> and the next, and then decreases again to the minimum. The regularity of this graph <NUM> indicates the susceptibility of the guidance rail <NUM> of the prior art to vibrations, as the graph <NUM> can also be interpreted to show the fundamental vibration mode between adjacent mounting sites <NUM>.

<FIG> schematically illustrates a guidance rail <NUM> according to an embodiment of the present invention. Along the guidance rail <NUM>, equidistant center positions <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>,. (in short: <NUM>-i) are defined for the mounting sites <NUM>-<NUM>, <NUM>-<NUM>,. (in short: <NUM>-i). The center positions <NUM>-i are marked by diamond symbols and the mounting sites <NUM>-I by circles. Each center position <NUM>-i is at the center of a periodically repeating cell <NUM>. Both the center positions <NUM>-i and the cell <NUM> are not necessarily marked on the guidance rail in any way but are defined and described in order to understand the embodiment better.

Each mounting site <NUM>-i is arranged within a predefined tolerance interval around a (or: its) respective one of the center positions <NUM>-i. The tolerance interval in this respect is preferably only considered along the longitudinal direction L. The tolerance interval is preferably arranged symmetrically around its respective center position <NUM>-i, or, in other words, each center position <NUM>-i is arranged at the center (in the longitudinal direction L) of its respective tolerance interval.

The relative position of each mounting site <NUM>-i to the (or: its) respective center position <NUM>-i is different for at least two of the mounting sites <NUM>-i. As an example, <FIG> shows a distance d12 between a first mounting site <NUM>-<NUM> and a second mounting site <NUM>-<NUM> being smaller than a distance d23 between the second mounting site <NUM>-<NUM> and a third mounting site <NUM>-<NUM>.

The tolerance interval may extend up to half the distance between the center position <NUM>-i and the respective next center position <NUM>-j, with j=i+<NUM> or j=<NUM>-i. Preferably, the total width of the tolerance interval is smaller than the (constant and equal throughout the guidance rail <NUM>) distance between two adjacent center positions <NUM>-i, <NUM>-(i+<NUM>), more preferably smaller than <NUM>% of that distance, most preferably smaller than <NUM>% of that distance. Again, this provides a suitable balance between the advantages of different distances d12, d23,. between the mounting sites <NUM>-<NUM>, <NUM>-<NUM>,. (in order to reduce vibration) and the advantages of equidistant distances (in order to provide stability of the mounting of the guidance rail <NUM> to the printer <NUM>). Preferably, each mounting site <NUM>-i (and only one) is randomly arranged within the predefined tolerance interval around its respective center position <NUM>-i.

In <FIG> a graph <NUM> has been included as well which, as in <FIG>, indicates (in an exaggerated manner) the play that the guidance rail <NUM> has in the perpendicular direction P and, consequently, also the fundamental mode of vibration. Because of the different distances d12, d23,. it is evident that also these fundamental modes of graph <NUM> in <FIG> are (preferably) all different and that therefore no vibrational mode of the guidance rail <NUM> as a whole can be induced.

<FIG> schematically illustrates a guidance rail <NUM> according to another embodiment of the present invention.

In the guidance rail <NUM> of <FIG>, two different distance values (e.g. designated as A and B) are defined for adjacent mounting sites <NUM>-i, and the two different distance values A and B alternate regularly along the row of mounting sites <NUM>-i. This means that d12=A, d23=B, d34=A,. The ratio of adjacently applied distance values (here: the ratio of A:B) is between <NUM>:<NUM> and <NUM>:<NUM>, preferably between <NUM>:<NUM> and <NUM>:<NUM>, more preferably between <NUM>:<NUM> and <NUM>:<NUM>. Although the guidance rail <NUM> of the embodiment of <FIG> (or any other embodiment with a larger number of regularly alternating distance values A, B, C,. ) will in general be more susceptible to vibrations than the still less regular embodiment of <FIG>, it has the advantage that its manufacture may be easier, as also in the manufacturing, the present regularities can be exploited to reduce the manufacturing effort.

While detailed embodiments of the present invention are disclosed herein, it is to be understood that the disclosed embodiments are merely exemplary of the invention, which can be embodied in various forms. In particular, features presented and described in separate dependent claims may be applied in combination and any advantageous combination of such claims are herewith disclosed.

It will be evident that the described embodiments may be varied in many ways. All such modifications as would be evident to one skilled in the art starting from what is explicitly described are intended to be included.

Claim 1:
A printer (<NUM>) comprising a print head carriage (<NUM>) and further comprising two guidance rails (<NUM>; <NUM>) arranged in parallel, wherein at least one runner block (<NUM>) is movably mounted on each guidance rail (<NUM>; <NUM>), and the print head carriage (<NUM>) is mounted on the at least two runner blocks (<NUM>), the two guidance rails (<NUM>; <NUM>) being mounted to the printer (<NUM>) by mounting elements (<NUM>) attached at mounting sites (<NUM>-i) of the guidance rail (<NUM>; <NUM>), the mounting sites (<NUM>-i) being arranged essentially in a row and configured for applying mounting elements (<NUM>) for mounting the guidance rail (<NUM>; <NUM>) to the printer (<NUM>), characterized in that at least two distances (d12, d23, d34) between any adjacent mounting sites (<NUM>-i, <NUM>-(i+<NUM>)) are non-equal.