Generally, an ink-jet printer may realize various colors with less noise due to the use of a cartridge and also ensures beautiful quality of printed text, differently from a dot printer, so the ink-jet printer is used more and more.
An ink-jet printer head is a means for discharging fine-droplets-of a printing ink to a desired position on a recording paper to print an image with a predetermined color. For this purpose, an ink droplet is discharged from a nozzle installed to the printer head, and the discharged ink droplet is hit to the recording paper. As intervals of hit droplets are closer, a higher quality of image may be output.
The printing quality using discharged ink droplets may be inspected using on characteristic values such as brightness and resolution of image, and these characteristic values depend on discharge of ink droplet of the ink-jet printer head, namely droplet discharge characteristics (or, jetting characteristics).
The droplet discharge characteristics of the ink-jet printer head act as an important factor to verify reliability of an ink-jet printer, and the droplet discharge characteristics of an ink-jet printer head are generally inspected before the printing process.
As a droplet discharge characteristic inspecting method, there was used a method of hitting an ink discharged from an ink-jet printer head to a paper, and then detecting a hit position of the ink printed on the paper.
However, in this method, a maximum number of ink droplets capable of being printed on an A4-sized paper without overlapping is 300,000, and the number of nozzles provided to an ink-jet printer head is about 100. Thus, in case jetting is conducted several thousand times at each nozzle, the number of droplets may exceed a capacity of one paper, so it may be impossible to determine whether jetting is conducted stably for several hours.
In addition, to solve this problem, there is a method of conducting the printing on a paper roll of several meters, instead of a paper sheet. However, this method has. problems of long-time consumption and much usage of paper, though position errors of hit ink droplets may be distinctly observed for each ink droplet.
As another method, there was proposed an ink droplet checking method that analyzes size and interval of sprayed ink droplets while scanning them according to a nozzle heat of a printer head using a digital camera.
This ink droplet checking method may allow to measure an abnormal jetting error caused by clogged nozzle or contamination, but it is not suitable for measuring a precise deviation required for high precision printing, namely quantitative analysis of droplet discharge characteristics according to velocity and orientation of ink droplets.
As another method, Japanese Laid-open Patent Publication No. 1999-227172 discloses a discharge checking device of an ink-jet printer head, including a printer head driving circuit, a camera, a camera control circuit, a stroboscope, a time delay circuit and a measuring circuit, which photographs an ink droplet discharged from a printer head several times with time intervals to measure a velocity of the ink droplet from a time difference of the ink droplet photograph.
This technique allows measuring an error of discharging timing since a velocity of ink droplet is measured. However, by simply measuring deviation of discharging timing, it is impossible to measure an error of discharging orientation, namely to measure a trajectory of ink droplet discharged from the printer head to a hit point, and also it is impossible to check a composite fine deviation error required for high precision printing.
In particular, simple image observation may allow detecting a serious jetting inferiority, but it has a limit in inspecting stability of ink jetting, required for high precision printing of a substrate that needs precision.