1. Field of the Invention
The present invention relates to a method and device for servicing the ink jet printing heads of ink jet printers, photostats, or fax machines. More particularly, the present invention discloses a servicing method and device where servicing jobs are performed according to the individual status of each nozzle and corresponding driving unit on the ink jet printing head.
2. Description of the Prior Art
Ink jet printing devices typically have an ink jet printing head capable of moving along a print track. The ink jet printing head comprises an ink storage unit for containing ink, a plurality of nozzles, and corresponding driving units for the nozzles. The driving units, such as heaters, can be driven by signals sent from a controller. The driving units, when receiving signals from the controller, can heat ink in the ink storage unit so that the corresponding nozzles on the printing head can jet ink drops to form ink spots on the printing medium to print. Demand of higher printing resolution and speed leads to smaller sizes of nozzles and higher jetting frequency of nozzles (that is, the nozzles have to jet ink more frequently within a unit time). Therefore it becomes even more important to maintain the nozzles in good condition so that each nozzle can function properly.
It is common that an ink jet printing device comprises a servicing device to service the ink jet printing head. The servicing device usually forms a servicing station which has a wiper to wipe the ink jet printing head. After the ink jet printing head moves into the servicing device, the wiper scrapes away remaining ink near nozzles on the ink jet printing head. Different approaches have been proposed for determining an appropriate time to move the ink jet printing head into the servicing device. One example is to service the ink jet printing head when the nozzles on the printing head have jetted ink for a fixed number of times. Another example is to service the ink jet printing head when the printing head has performed printing for a fixed period of time. U.S. Pat. No. 5,583,547 disclosed a more sophisticated determination method. The method includes counting the number of ink drops jetted from each of the nozzles so as to determine an appropriate time to service the ink jet printing head.
However, in U.S. Pat. No. 5,583,547 the servicing device services the entire printing head regardless the different status of each nozzle. Since in a printing job each driving unit and its corresponding nozzle may be driven to jet ink for different number of times, the temperature of each individual driving unit and corresponding nozzle, and the build-up or bubbles accumulated near different driving unit or its corresponding nozzle become various on the same printing head. The differences will cause ink jet printing head instability and therefore degrade printing quality. The prior art disclosed in U.S. Pat. No. 5,583,547 only services the whole ink jet print head without considering the differences between nozzles on the printing head, and thus cannot balance the aforementioned differences between nozzles to obtain satisfactory printing quality.
It is therefore a primary objective of the present invention to provide a servicing method that compensates the different status of each driving unit and corresponding nozzle and thus improves printing quality.
According to the embodiment of the present invention, the ink jet printing device comprises an ink jet printing head capable of moving back and forth along a print track to perform a printing job. The ink jet printing head has a plurality of driving units and corresponding nozzles to jet ink drops. The ink jet printing device further comprises a recording module to record the number of times each driving unit is driven to jet ink by the controller. When a predetermined servicing condition has been satisfied and the ink jet printing head needs servicing, different service jobs are performed for different driving unit and corresponding nozzle on the printing head.
It is an advantage of the present invention that the servicing method considers and compensates the different status of each driving unit and its corresponding nozzle. Therefore the differences between the driving units and corresponding nozzles are minimized, and the printing quality can therefore be improved.
These and other objectives and advantages of the present invention will no doubt become obvious to those of ordinary skill in the art after having read the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings.