JPH01306252A - Ink jet recorder - Google Patents

Abstract

PURPOSE:To obtain substantially constant printing density and thickness even if an ambient temperature varies by relatively accelerating the speed of ink particles injected from the ink injection nozzle of an ink jet head in a low temperature range as compared with that in a high temperature range. CONSTITUTION:When a charging pulse 16 is input to a charge signal terminal 15, a piezoelectric element 13 is abruptly charged through a charging resistor 18, ink in a passage is pressurized to fly ink particles 14. Then, when a discharging pulse 19 is input to a discharge signal terminal 17, the charge of the element 13 is gradually discharged through discharging resistors 18, 20, and returned to its original state. In this case, the speed of ink particles injected from a nozzle is accelerated toward a low temperature range. As a result, ink weight per one dot is so controlled as to approximate a substantial constant to the using ambient temperature. Then, it is always printed with constant density and thickness.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an inkjet recording device, and particularly to a recording device with improved print quality.

[Conventional technology]

Inkjet recording devices perform non-contact printing by ejecting ink droplets onto the recording paper from a moving carriage, so the jetting speed of the ink droplets is kept constant over the entire operating temperature range so that the ink droplet adhesion positions are aligned. I've been controlling it. However, it has been found that the weight of the ink droplets ejected decreases in the low temperature range compared to the high temperature range, resulting in a difference in the density and thickness of the print.

[Problem to be solved by the invention]

The present invention is intended to ensure approximately constant print density and print thickness even when the ambient temperature changes as described above.

[Means to solve the problem]

The present invention is characterized by having a drive control means that makes the speed of ink droplets ejected from the ink ejection nozzles of the inkjet head relatively faster in a low temperature range than in a high temperature range.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings. First, the basic operation of an on-day ink jet head using a piezoelectric element as a pressure means will be explained with reference to FIGS. 1 to 3.

FIG. 1 shows an example of an inkjet head, where 11 is a head body having an ink flow path 12, and 13 is a piezoelectric element. Figure 2 shows an example of the drive circuit, and Figures 3 (a), (b)' (c)
are a charging pulse signal, a discharging pulse signal, and a voltage waveform of the piezoelectric element 13 applied to the drive circuit, respectively.

When a charging pulse 16 enters the charging signal terminal 15, the piezoelectric element 1
3 is rapidly charged via the charging resistor 18, and as shown in FIG.
), the ink in the flow path is pressurized and the ink droplets 14 fly out. Next, when the discharge pulse 19 enters the discharge signal terminal 17, the charge of the piezoelectric element 13 is gradually discharged through the discharge resistor 18° 20. Return to the original state as shown in Figure 1(c).

FIG. 4 is a diagram showing the relationship between the ejection speed of ink droplets (solid line) and the weight of ink droplets per pulse (broken line) with respect to the operating environment temperature of the recording apparatus using one prototype head as an example. The viscosity of the ink changes with the environmental temperature, becoming lower at higher temperatures and higher at lower temperatures. The situation is shown in FIG. 5, taking as an example the ink actually used.

Therefore, in order to make ink droplets fly stably from the inkjet head regardless of the environmental temperature and to ensure high print quality, some means is necessary, such as installing a heater or controlling the drive conditions. The injection speed and particle weight shown by the solid line and broken line in FIG. 4 are the same as the driving voltage HV shown in FIG.
is controlled.

However, as shown by the broken line in Figure 4,
The weight of ink particles decreases in the low temperature range, so the fourth
As shown in Figure 4, the speed of the ink droplets ejected from the nozzle is increased toward the lower temperature range, and as a result, the ink weight per pulse (per dot) is increased as shown in the double-dashed line in Figure 4. The temperature is controlled to be almost constant with respect to the operating environment temperature. Examples of variations in the drive voltage HV at this time are shown by solid lines in FIG.

Generally, the weight of an ink droplet is determined by the product of the ejection speed of the ink droplet ejected from a nozzle, the cross-sectional area of the nozzle, and the ejection time of the ink droplet. Figure 7 shows how ink droplets are ejected.
The injection speed is almost constant in each case at 5℃,
Figures (d), (e), and (f) are examples of the present invention in which the speed is increased in the low temperature range.In other words, it can be seen that in the low temperature range, the ink droplets fly thinly.In the low temperature range, the nozzle breaks. Ink is ejected as if the area becomes smaller,
As a result, the weight of ink particles decreases in the low temperature range.
The reason is presumed to be that as the viscosity increases, the boundary layer on the nozzle wall becomes thicker, and the velocity distribution in the nozzle cross section approaches the velocity distribution as if the nozzle cross section had become smaller. Therefore, as shown in FIG. 7(f), the reduction in the weight of the ink droplets in the low temperature range is compensated for by increasing the jetting speed of the ink droplets.

FIG. 8 shows an embodiment for controlling the drive voltage HV with respect to the environmental temperature. This circuit is a step-up regulator circuit with variable output voltage, and the output voltage H is the error amplifier EA.
The voltages at pins 1 and 2 of I are controlled to be equal. The output voltage HV is variable depending on the resistance value of the thermistor 21 and the resistance value of VH2, and AM is performed using VH2.

The resistance value of the thermistor has a negative characteristic with respect to temperature, and when the head temperature is low, the resistance value of the thermistor increases and E
Since the potential of 2ρin of Al increases and therefore the output voltage HV increases, the characteristics of the thermistor 21 are selected so as to obtain the voltage shown by the solid line in FIG.

〔Effect of the invention〕

As explained above, even though the ink viscosity varies depending on the ambient temperature, it is possible to eject an almost constant weight of ink droplets regardless of the ambient temperature, and therefore it is possible to print with constant density and thickness. It became.

[Brief explanation of the drawing]

1(a) to (C) are diagrams showing an example of an inkjet head, FIG. 2 is a diagram showing an example of a drive circuit, FIG. 3 is a diagram showing an example of a drive signal, and FIG. 4 is a diagram showing an example of a drive signal. Figure 5 is a diagram showing an example of the relationship between ambient temperature and ink drop ejection speed, Figure 5 is a diagram showing the relationship between ambient temperature and ink viscosity, and Figure 6 is a diagram showing an example of the relationship between ambient temperature and drive voltage. , Figure 7 (a
) to Cf) are diagrams showing an embodiment of the state of ink droplet ejection, and FIG. 8 is a diagram showing an embodiment of a drive voltage control circuit. 11... Ink shed head 12... Channel 13... Piezoelectric element 16... One charge pulse signal... Discharge pulse signal 21... Thermistor or above Applicant: Seiko Epson Co., Ltd. Agent Patent attorney Kizobe Suzuki (1 other person) Kano 1 Figure 1/ Figure 2 Figure 3 OIQ 20 30 40 (Oc1 Figure 4 + Vff) (C) (f)

Claims (1)

[Claims] In an inkjet recording device equipped with an inkjet head that jets ink droplets from an ink jetting nozzle, drive control that makes the jetting speed of the ink droplets relatively faster in a low temperature range than in a high temperature range with respect to the operating temperature range of the recording device. An inkjet recording device characterized by having a means.