This non-provisional application claims priority under 35 U.S.C. §119(a) on Patent Application No. 1021851 filed in The Netherlands on Nov. 6, 2002, which is herein incorporated by reference.
1. Field of the Invention
The present invention relates to an apparatus for guiding a printhead fixed on a carriage. The carriage is provided with plain bearings which are in sliding contact with a set of substantially parallel guide rods. A first plain bearing is in contact with a first guide rod and a second plain bearing is in contact with a second guide rod, the second plain bearing being movably fixed to the carriage by means of a resilient element. The present invention also relates to an inkjet printer provided with such an apparatus.
2. Related Art
An arrangement of this kind is known from U.S. Pat. No. 5,332,321. This arrangement comprises a set of two substantially parallel guide rods on which a carriage is mounted which is adapted to carry various inkjet printheads. The carriage is provided with three plain bearings, one of which is in sliding contact with the back guide rod and two in sliding contact with the front guide rod. Since three bearings are used, the position of the carriage can be accurately determined without the need to use bearings of a considerable length. This arrangement is used to move a number of printheads in a first direction with respect to a receiving material for printing. This first direction is also termed the main scanning direction. Each of the bearings is provided with two bearing surfaces by means of which a bearing slides over the guide rod. In principle, one bearing surface per plain bearing is sufficient for good guidance. However, in order to prevent the carriage from rotating or otherwise shifting in the plane formed by the two guide rods, two bearing surfaces are provided for each plain bearing so that the guide rods are, as it were, enclosed in the plain bearings. In principle, it should be sufficient to equip just one of the bearings with two bearing surfaces, but since the bearings have only a limited length it was decided to provide at least the two bearings on the front guide rod with two bearing surfaces.
The disadvantage of the plain bearings is that they must have a certain length in order to be sufficiently wear-resistant. Because of this length, the alignment of the bearings with respect to the guide rods with which they are in sliding contact is very important. Given poor alignment, the friction between the bearings and the rods is very considerable, and this is accompanied by intensive wear, accompanying noise and the need for a powerful motor to move the carriage over the rods. An alignment of this kind is effected by pre-machining of the bearings, as known from the prior art.
Another problem is that the guide rods are never 100% parallel because the guide rods can never be perfectly aligned with respect to one another and because the guide rods, either initially or through use, are always bent to a certain degree. As a result, at some locations of the set the plain bearings will experience a greater friction than at other locations. In order to prevent this from becoming inadmissibly large, the plain bearing in contact with the back guide rod is movably connected to the carriage so that this bearing can move with respect to the carriage and hence with respect to the other two bearings. Using a spiral spring, this plain bearing is forced to move away from the other two bearings in one direction. As a result of this resilient connection, the third plain bearing can adapt to the non-parallelism in the set of guide rods without any loss of defined position of the carriage with respect to the set. The other plain bearings are not resiliently connected to the carriage because otherwise the carriage could turn round in the plane formed by the two guide rods.
A significant disadvantage of the known arrangement and a printer provided with such an arrangement is that it results, to a varying degree, in a high-frequency noise when the carriage is moved over the set of guide rods. This is very disturbing to a user of the printer in which an arrangement of this kind is provided.