JPH0342185B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to an ink jet printer that prints images such as characters, symbols, figures, etc. by ejecting minute ink droplets.

(B) Prior Art As an ink droplet ejecting device that controls the main part of an inkjet printer, there is an on-demand type ink droplet ejecting device that ejects only the ink droplets necessary for printing an image. FIG. 1 shows the above-mentioned on-demand type ink drop ejecting device disclosed in Japanese Patent Application Laid-Open No. 57-8163. This curved vibration is intensively transmitted to a small-area diaphragm 4 through a transmission medium filled in a horn-shaped pressure displacement chamber 3, and an ink chamber 5 in front of this diaphragm 4 is caused to vibrate in a curved manner. The ink located at the ink is ejected as ink droplets from an orifice 6 having a minute diameter.

In this way, on-demand type ink droplet ejecting device 1
In order to eject ink droplets by the vibration of a vibrating body such as the piezoelectric vibrator 2, it exhibits a frequency characteristic in which the threshold voltage varies at a specific frequency as shown in FIG. Particularly at high frequencies, the residual vibrations from the previous ink drop ejection may not completely disappear by the time of the next ink drop ejection, and at some frequencies the residual vibrations may be synchronized with the period of the next ink drop ejection, or vice versa. The threshold voltage fluctuates significantly when the period shifts by 1/2.

For example, the above-mentioned on-demand type ink droplet ejecting device 1
When driven by an alternating wave such as an alternating pulse wave or a sine wave (in the following explanation, an alternating pulse wave will be explained as an example), the on-demand ink droplet ejecting device 1 will emit ink only when necessary. In order to eject the droplets, the drive signal HP is a reference signal.
Even if the alternating pulse width t of CP is changed, the period T ₁ ,
T ₂ , T ₃ ... Tn alone includes multiple frequency components f ₁ , f ² , f ₃ , ... fn as shown in FIG. There is.

On the other hand, it is widely known that the on-demand type ink droplet ejecting device 1 changes the particle size of the ink droplets ejected in response to the level of the electrical signal supplied. Attempts have also been made to control the particle size of the ink droplets by electrical signal levels to print images with shading (halftones).

(C) Problems to be Solved by the Invention However, as described above, in the on-demand type ink droplet ejecting device 1, the threshold voltage generally varies depending on the driving frequency, and the driving signal HP has a plurality of frequency components _f1. , f ₂ , f ₃ ...fn are driven under different threshold voltages, and ink droplets with non-uniform particle sizes are ejected even though the same level of drive signal is applied. There is. In particular, when trying to simulate an image with shading by the number of ink droplets ejected per unit area, that is, the density of ink droplets, if ink droplets of uniform particle size are not obtained, image quality may deteriorate. Become.

(d) Means for solving the problems The present invention has been made in view of the above points,
The on-demand ink drop ejecting device has a drive signal that is formed by dividing only the cycle of a reference signal with an alternating waveform by 1/n (n is a natural number), and the threshold voltage varies according to the drive frequency. The inkjet printer is characterized in that the frequency of the reference signal is set so that the threshold voltages corresponding to each of the plurality of frequency components included in the drive signal are approximately equal.

(E) Embodiment FIG. 4 specifically shows the relationship between the threshold voltage and the driving frequency of the on-demand ink droplet ejecting device 1 having the structure shown in FIG. 1.
On-demand type ink droplet ejecting device 1 having such a structure
In this example, a so-called unimorph type piezoelectric vibrator 2 with a diameter D10 mmφ, which is formed by pasting a metal plate on a piezoelectric ceramic plate based on lead zirconate titanate, is attached to the long diameter end of a horn-shaped pressure displacement chamber 3 so that the vibration diameter D becomes 8 mmφ. A diaphragm 4 made of stainless steel with a thickness of δ30μm is fixed to the minor diameter end of the pressure displacement chamber 3 with an opening diameter of d2mmφ so that it can vibrate freely, and an orifice 6 with a diameter of 50μm is bored in the center with a small gap of 400μm in between. A sagging orifice plate 7 is attached to form an ink chamber 5 having a thickness of Δ400 μm, and finally, filling holes (not shown) are opened in the ink chamber 5 and the pressure displacement chamber 3 and filled with ink.

Therefore, in the on-demand ink droplet ejecting device 1 having the specifications as described above, by setting the frequency of the reference signal CP to 20KHz, the frequency components f ₁ , f ₂ , f ₃ , ...fn of the drive signal HP can be adjusted. is 20KHz, 10KHz,
20/3KHz, . . . 20/nKHz, and as is clear from FIG. 4, the threshold values at each of the above frequencies are approximately equal to about 110V.

As a result, even if drive signals HP of the same level and different frequencies are applied, the ink droplet ejecting device 1 will eject ink droplets of the same diameter according to the level.

(F) Effect As is clear from the above description, the present invention sets the frequency of the reference signal that is the basis of the drive signal so that the threshold voltages corresponding to each of the plurality of frequency components included in the drive signal are approximately equal. Therefore, if the drive signal is at the same level, it is possible to eject ink droplets with the same diameter even if the frequency is different. Therefore, it is very easy to make the ink droplet diameter almost uniform, and in particular, it is possible to eject ink droplets with the same diameter even if the frequency is different. This is useful when printing images with shading through density control.

[Brief explanation of drawings]

Figure 1 is a cross-sectional view of an ink droplet ejecting device that controls the main parts of an inkjet printer, Figure 2 is a threshold voltage characteristic diagram versus driving frequency of the on-demand ink droplet ejecting device, and Figure 3 is a reference signal and drive signal. FIG. 4 is a waveform diagram showing the relationship between the ink droplet jetting device and the threshold voltage characteristic diagram with respect to the driving frequency of the ink droplet jetting device which controls the main part of the inkjet printer of the present invention. Vibrator, 4
indicates a diaphragm, and 6 indicates an orifice.

Claims (1)

[Claims] 1 The period of the reference signal of the alternating waveform is 1/n (n
is a natural number), the inkjet printer drives an on-demand ink droplet ejecting device in which the threshold voltage varies depending on the drive frequency, using a drive signal formed by dividing the frequency of An inkjet printer characterized in that the frequency of the reference signal is set so that the threshold voltages corresponding to each of the plurality of frequency components are substantially equal.