1. Field of the Invention
The present invention relates to an image recording apparatus for recording images on a recording member, and in particular relates to a conveying device to be provided in the apparatus for conveying a member to be conveyed such as the recording member.
2. Description of the Related Art
An inkjet recording apparatus having an electrostatic-attraction-type conveying device for conveying a member to be conveyed such as a recording member will be described as a conventional image recording apparatus of such a kind, for example, with reference to FIGS. 6 to 7B. FIG. 6 is a schematic sectional view of a conventional image recording apparatus, and FIGS. 7A and 7B are a plan view and an enlarged sectional view of a conveying device for a recording member, respectively.
A recording apparatus 50 shown in FIG. 6 comprises a recording head 51 for recording images and a conveying belt 52, which is an electrostatic-attraction-type conveying member.
The recording head 51 is of a line type in that a number of nozzles are arranged in rows to have substantially the same width as that of the recording member, and can perform rapid image-forming in comparison with a serial type in which a recording head mounted on a carriage is scanned.
However, because of the high speed, ejected ink is unfixed just after recording, so that if anything is brought into contact with a recorded surface, images may be marred. Such a phenomenon may more or less occur even in the serial type image recording apparatus.
Then, in such an apparatus, the rear surface of the recording member is held with the conveying belt 52 having electrostatically-attracting means so as to convey the recording member without coming in contact with anything.
The conveying belt 52 is made by connecting both ends of a band member to be annular, and stretched and looped around a driving roller 58 and a plurality of supporting rollers 59 to 61, so that the recording member such as a paper sheet or plastic sheet is conveyed by rotating the conveying belt 52.
As the electrostatically-attracting means of the conveying belt 52, there is an electrode group (referred to as interdigital electrodes 53 and 54 below), in which strip-shaped electrodes with different polarities are alternately arranged as shown in FIG. 7A, and there are conductive brushes 55 arranged on both sides of the conveying belt 52 as power feeding means, as shown in FIG. 7B.
In such a structure, when one of the interdigital electrodes 53 and 54 is grounded while a predetermined voltage is applied to the other so as to produce a difference in potential, an attracting force due to electrostatic power can be obtained.
However, the conventional technique described above has the following problems.
The conveying belt 52 is driven by the driving roller 58 at a high speed, and foreign particles such as paper dust and oil are stuck to the driving roller 58 during the long time running, so that the frictional force between the driving roller 58 and the conveying belt 52 may be reduced or jamming due to plugged paper or dust may be produced, resulting in the abnormal driving of the conveying belt 52.
If such a case is neglected, the abnormal belt driving may finally result in a serious problem such as head damage or electric leakage, so that first hand stopping has been required.
Then, in order to detect the abnormal belt driving of the conveying belt 52, an encoder 56 attached to the supporting roller 59 is detected with a photosensor 57. Alternatively, although not shown, the driving state of the conveying belt is detected by reading an encoder pattern printed on the conveying belt with a photosensor.
However, as described above, the conventional conveying belt has had additional procedures and cost for attaching an encoder to the conveying belt or printing an encoder pattern thereon in order to detect the driving state of the conveying belt.