1. Field of the Invention
The present invention relates to an inkjet recording apparatus including a recording head configured to discharge an ink to record an image on a recording medium.
2. Description of the Related Art
The recording apparatus, such as printers, copying machines, and facsimile machines, or output devices for computers, word processors, and work stations have the capability of recording an image (including letters and symbols) on a sheet based on image information.
Furthermore, the recording apparatus can record an image on a plastic film (e.g., OHP sheet) or other recording medium. An exemplary recording unit for a recording apparatus is an inkjet type, a wire-dot type, a heat-sensitive type, a heat-transfer type, or a laser beam type.
A serial type recording apparatus includes a carriage performing a main scanning operation in a direction perpendicular to a carrying direction (sub scanning direction) of a recording medium. When a user sets a recording medium on a predetermined recording position, the recording apparatus starts recording an image using a recording head mounted on the carriage shifting (scanning) in the main scanning direction.
When a recording operation for one row (corresponding to one recording/scanning operation) is completed, the recording apparatus feeds (carries) the recording medium forward by a predetermined amount and starts the next image recording operation. The recording apparatus repeats the above-described recording operation and the carrying operation to record an image in a desired range on the recording medium.
An inkjet-type recording apparatus (printer) includes a recording head capable of discharging small ink droplets from small nozzles to form an image on a recording medium. The recording head includes a heater capable of causing film boiling of a stored ink in a nozzle and generating a pressure for discharging an ink droplet from a discharge port.
The inkjet-type recording apparatus can stably obtain an intended image because there is no intervening member such as an intermediate transfer member for an electro-photographic system. On the other hand, an inkjet system is not free from clogging of a nozzle due to dusts or thickened ink, or open circuit of a heater, or an ink droplet closing a nozzle port. Thus, the inkjet system may cause ink discharge defectiveness.
The ink discharge defectiveness includes a non-discharge state where no ink droplet can be discharged from a nozzle, an insufficient-discharge state where a discharged ink droplet has an insufficient amount, and a deviated-discharge state where an impact position of a discharged ink droplet is deviated.
If an ink droplet is discharged from a recording head having ink discharge defectiveness, the impact position of an ink droplet may offset from a target position on a recording medium. A recorded image may include a white streak or a black streak extending along the scanning direction of a recording head.
As discussed in U.S. Pat. No. 6,224,183, the non-discharge state of ink can be detected by discharging an ink droplet between a light-emitting element and a light-receiving element so that an output signal level of the light-receiving element decreases when the ink droplet passes across the light emitted from the light-emitting element.
A recording apparatus having the aforementioned detection arrangement can promptly perform cleaning processing when any non-discharge state is detected. Thus the recording apparatus can avoid clogging of a nozzle and, as a result, can improve the reliability.
As discussed in U.S. Pat. No. 6,659,580, a recording apparatus having a multipass printing function can complementarily print a high-quality image by using a different nozzle to form (i.e., record) a dot if a nozzle designated to form the dot is in a defective state. Thus, the recording apparatus can suppress reduction in image quality even in a situation where a nozzle cannot recover from a non-discharge state regardless of cleaning processing or other recovery operation.
Furthermore, if an image is complementarily recordable in a situation where a non-discharge nozzle is present, a recording apparatus can reduce the operation frequency and the time for the cleaning processing. The ink consumed for the cleaning processing can be decreased.
However, the aforementioned conventional recording apparatus has the following problems with respect to ink discharge defectiveness.
In an attempt to suppress reduction in the image quality caused by the ink discharge defectiveness, the interval for performing discharge defectiveness detection processing can be set to a relatively short value.
Paper dusts or the like tend to adhere on a discharge port surface. Discharge defectiveness, which may be caused by an open circuit of a heater, occurs at a relatively higher rate in a recording apparatus having been used for a relatively long time. In general, accumulation of paper dusts or the like adhering on a discharge port surface of a recording apparatus increases when the operation time of a recording apparatus becomes longer. Surface abrasion of heaters increases when the total number of ink discharges becomes larger.
Water components contained in ink solvent may evaporate from a discharge port of a nozzle. The water evaporation increases the viscosity of ink in the nozzle and causes clogging. If the discharge operation of ink droplets develops bubbles in an ink passage, the bubbles may disturb the discharge operation and cause discharge defectiveness.
The discharge defectiveness due to an increase in the ink viscosity or generation of bubbles tends to occur at a constant probability throughout the life of a recording apparatus (i.e., without depending on the life of a recording apparatus).
In a conventional recording apparatus, detection of discharge defectiveness is performed at relatively short intervals, so as to detect the discharge defectiveness depending on the operation time of a recording apparatus as well as the discharge defectiveness not depending on the operation time of the recording apparatus.
In other words, the conventional recording apparatus performs a discharge defectiveness detecting operation based on a situation where the discharge defectiveness occurs at a higher probability. Furthermore, generation of the discharge defectiveness greatly varies depending on the composition of ink.
If a recording apparatus forms an image using plural inks, the recording apparatus performs a discharge defectiveness detecting operation at an interval corresponding to an ink having a highest discharge defectiveness generation rate.
Recently some recording heads have become longer in size and include a plurality of nozzles densely arrayed. This structure causes the time for a single discharge defectiveness detecting operation tends to increase correspondingly.
Therefore, if the discharge defectiveness detecting operation is performed at short internals (i.e., with a large margin of safety), the reliability of a recording apparatus can be improved. On the other hand, the recording time increases, and the throughput of the recording apparatus decreases.
Furthermore, the discharge amount of ink consumed in a single discharge defectiveness detecting operation increases if a recording head has a longer size and includes a plurality of nozzles densely arrayed.