JP2008173920A - Liquid ejector - Google Patents

Abstract

An object of the present invention is to provide a liquid ejecting apparatus that can keep the ejection speed constant even if the ink thickens during ejection, and thus can prevent the accuracy of the landing position from being lowered.
A liquid ejecting apparatus includes a driving unit that applies a driving signal to an ink jet head, and ejects a droplet having a diameter smaller than the diameter of an ejection port by the driving unit. Furthermore, the present invention includes an atmosphere measuring unit that measures the atmosphere around the ink jet head, and a storage unit that stores a correction amount corresponding to the rate of change in the ejection speed during printing. The present invention is a liquid ejecting apparatus including a discharge speed adjusting unit that adjusts a discharge speed based on the correction amount stored in the storage unit and the atmosphere measured by the atmosphere measuring unit.
[Selection] Figure 1

Description

The present invention relates to a liquid ejecting apparatus that includes an individual liquid chamber that communicates with an ejection port that ejects liquid, deforms a diaphragm that forms part of the individual liquid chamber by an actuator, and ejects ink droplets, and a control method thereof.

  2. Description of the Related Art Conventionally, inkjet heads that eject ink using piezoelectric elements that are deformed by application of voltage pulses are known. This ink jet head includes an ejection port for ejecting ink and an individual liquid chamber communicating with the ejection port, and a diaphragm is formed on a part of the side surface of the individual liquid chamber.

  The diaphragm is deformed by the deformation of the piezoelectric element, and the individual liquid chambers are expanded and contracted to pressurize and discharge the ink. As a method using the deformation of the piezoelectric element, there are a method using a longitudinal vibration that expands and contracts in the axial direction of the piezoelectric element and a method using a deflection of the piezoelectric element.

As described above, when an inkjet head is driven, a method of applying an auxiliary pulse for expanding the individual liquid chamber again after applying a main pulse has been proposed (for example, see Patent Document 1). In this method, ejection of the liquid column protruding by the main pulse is stopped by the auxiliary pulse, the liquid column is divided, and a droplet having a diameter smaller than the diameter of the discharge port is discharged.
JP 2001-246746 A (page 7, FIG. 9)

  When discharging droplets having a diameter smaller than the diameter of the discharge port, there is a problem in that the discharge speed is gradually reduced if discharged continuously.

  That is, the ink at the center of the meniscus is raised to form a liquid column and ejected as droplets, so that the ink at the outer edge of the meniscus is less likely to be discharged than the ink at the center. Therefore, it is considered that the ink does not change so much and the viscosity is gradually increased and the discharge speed is gradually decreased. Therefore, there is a problem that the landing position accuracy is lowered when the discharge speed is changed.

  In other words, the conventional example has a problem that a droplet having a diameter smaller than the diameter of the discharge port cannot be discharged at a constant speed for a long time.

SUMMARY An advantage of some aspects of the invention is that it provides a liquid ejecting apparatus that can maintain a constant ejection speed even when ink thickens during ejection, and thus can prevent deterioration in accuracy of a landing position.

The present invention relates to an ink individual liquid chamber, an ejection port communicating with the individual liquid chamber, a vibration plate forming a part of the side surface of the individual liquid chamber, and the individual liquid chamber by deforming the vibration plate by applying a voltage pulse. An ink jet head having a piezoelectric actuator for changing the volume of the ink jet head. In addition, the present invention is a liquid ejecting apparatus that includes a driving unit that applies a driving signal to the inkjet head, and ejects a droplet having a diameter smaller than the diameter of the ejection port by the driving unit. Furthermore, the present invention includes an atmosphere measuring unit that measures the atmosphere around the ink jet head, and a storage unit that stores a correction amount corresponding to the rate of change in the ejection speed during printing. The present invention is a liquid ejecting apparatus including a discharge rate adjusting unit that adjusts a discharge rate based on the correction amount stored in the storage unit and the atmosphere measured by the atmosphere measuring unit.

According to the present invention, the diameter of the droplet is made smaller than the diameter of the discharge port, so even if the ink thickens during discharge, the discharge speed can be kept constant, thus preventing the accuracy of the landing position from being lowered. There is an effect that can be done.

  The best mode for carrying out the invention is the following embodiment.

  FIG. 1 is a configuration diagram showing the configuration of an inkjet recording apparatus PR1 that is Embodiment 1 of the present invention.

  The ink jet recording apparatus PR1 is an example of a liquid ejecting apparatus that includes a driving unit that applies a driving signal to the ink jet head, and ejects droplets having a diameter smaller than the diameter of the ejection port by the driving unit. The ink head deforms the diaphragm by applying an ink individual liquid chamber, a discharge port communicating with the individual liquid chamber, a diaphragm forming a part of a side surface of the individual liquid chamber, and a voltage pulse. And a piezoelectric actuator that changes the volume of the individual liquid chamber.

  The ink jet recording apparatus PR1 employs a so-called line system, but other systems may be employed.

  The ink jet recording apparatus PR1 includes a recording head unit 100, guide shafts 101 and 102, feed rollers 103 and 104, and a recovery system unit 105.

  The recording medium P is conveyed to the recordable area of the recording head unit 100 by the feed rollers 103 and 104.

  The recording head unit 100 is guided by guide shafts 101 and 102 so as to be movable. The recording head unit 100 is moved between the recording area and the recovery system unit 105 by a motor (not shown). The recording head unit 100 is equipped with a recording head that discharges ink droplets of a plurality of colors and an ink tank that supplies ink to each recording head. The recording head is arranged over the recording area width. The plurality of colors of ink in the inkjet recording apparatus PR1 are four colors of black (Bk), cyan (C), magenta (M), and yellow (Y).

  A recovery system unit 105 is disposed at the lower right end of the region where the recording head unit 100 is movable, and performs recovery processing of the ejection port portion of the recording head during non-recording operation.

  Next, an example of an ink jet head constituting the recording head will be described.

  FIG. 2 is a plan view of the inkjet head H. FIG.

  FIG. 3 is a cross-sectional view taken along the dashed-dotted line III-III in FIG.

  The ink jet head H includes an orifice plate 1, an ejection port 2, an individual liquid chamber 3, a vibration plate 4, an actuator 5, a base 6, and a communication port 7.

  In the inkjet head H, the orifice plate 1 is provided with an ejection port 2 for ejecting ink. The base 6 is provided with individual liquid chambers 3 corresponding to the respective discharge ports 2, and communicates with the discharge ports 2 through the communication ports 7. A vibration plate 4 that is elastically displaced is provided on a part of the side surface of the individual liquid chamber 3, and an actuator 5 including a piezoelectric element is disposed on the vibration plate 4.

  By applying a drive signal corresponding to the recording information to the actuator 5, the vibration plate 4 is deformed, the volume of the individual liquid chamber 3 is changed, and a recording method in which droplets are discharged from the discharge port 2 is adopted. Yes.

The actuator 5 is provided with electrode wiring (not shown) for supplying power. In Example 1, the discharge port 2 is a round hole with a diameter of 30 μm. The ejected ink has a density of 1.0 × 10 ³ kg / m ³ , a viscosity of 2.0 × 10 ⁻³ Pa · s, and a surface tension of 3.5 × 10 ⁻² N / m.

  Next, a driving waveform for ejecting a droplet having a diameter smaller than the ejection port diameter and ejection of the droplet will be described.

  FIG. 4 is a diagram illustrating the drive signal P1 in the first embodiment.

  The drive signal P1 has signal waveforms F1, F2, F3, and F4.

  FIG. 5 is a diagram illustrating a change in the liquid column 11 at the discharge port 2 in the first embodiment.

  The voltage of the first signal waveform F1 is changed in the direction in which the individual liquid chamber 3 expands, and the substantially flat meniscus 10 is discharged as shown in FIG. 5 (b) as shown in FIG. 5 (a). Pull into outlet 2.

  Then, due to the second signal waveform F2 shown in FIG. 4, the individual liquid chamber 3 contracts, and as shown in FIG. 5C, the meniscus central portion is raised to form the liquid column 11. Due to the third signal waveform F3 shown in FIG. 4, the individual liquid chamber 3 expands, and as shown in FIG. 5 (d), the meniscus outer edge portion 10a is drawn into the discharge port 2 and the thickness of the protruding liquid column 11 is increased. Resize the length and length.

  Finally, the individual liquid chamber 3 contracts by the fourth signal waveform F4 shown in FIG. 4 and returns to the initial potential V1.

  By the above operation, as shown in FIGS. 5E, 5F, and 5G, the protruding liquid column 11 is broken and a droplet 12 having a diameter smaller than the diameter of the discharge port is discharged.

  When ejecting a droplet having a diameter smaller than the diameter of the ejection port, as can be seen from FIG. 5, the ink on the meniscus outer edge portion 10a is not discharged so much and tends to stay. This staying seems to gradually dry the meniscus outer edge portion 10a and increase the viscosity of the ink in the ejection port 2.

  FIG. 6 is a diagram showing experimental results of changes in the discharge speed and changes with time in the discharge amount.

  In FIG. 6, the horizontal axis indicates the discharge time, and the vertical axis indicates the discharge speed and discharge amount normalized by the initial value. Conditions A, B, and C in FIG. 6 are experimental results under different conditions of humidity, and the height of the humidity is condition A <condition B <condition C.

As shown in FIG. 6A, it can be seen that the lower the humidity, the greater the rate of change of the ejection speed. Under conditions A, B, and C, the rate of change in the discharge speed of 5 m / s is as follows:
Condition A: (−0.0094 m / s) / min
Condition B: (−0.0041 m / s) / min
Condition C: (−0.0018 m / s) / min
It is.

  On the other hand, the change rate of the discharge amount is smaller than the change rate of the discharge speed.

  FIG. 7 is a diagram showing a schematic configuration of the ink jet recording apparatus PR1.

  The ink jet recording apparatus PR1 includes an ink jet head H, a driving unit 21, a discharge speed adjusting unit (CPU) 22, an atmosphere measuring unit 23, and a storage unit 24.

  The driving unit 21 applies a driving waveform corresponding to the ejection speed adjusting unit 22 to the inkjet head H. The atmosphere measuring unit 23 measures the humidity around the inkjet head H. Alternatively, the atmosphere measuring unit 23 may measure the humidity and temperature around the inkjet head H. Alternatively, the atmosphere measuring unit 23 may measure the humidity around the inkjet head H and the temperature of the inkjet head H itself.

  The storage unit 24 stores a discharge rate correction amount corresponding to the change rate of the discharge rate at each humidity. This correction amount can be calculated, for example, by measuring the rate of change of the discharge speed according to the change in humidity and converting it to a value according to the adjusting means of the discharge speed adjusting means 22.

  The humidity is divided into several ranges, and a conversion table storing the correction amount of the discharge speed in each humidity range is prepared and stored in the storage unit 24.

  Moreover, you may make it prepare the conversion table according to not only humidity but ambient temperature, the temperature of the inkjet head H, or humidity and temperature. By preparing a conversion table according to temperature as well as humidity, correction can be made more finely.

  Further, the temperature of the inkjet head H may be kept at a specific temperature by a temperature control means such as a heating means or a cooling means.

  By keeping the inkjet head H at a specific temperature, the influence of the temperature on the ink thickening can be reduced and correction can be easily performed.

  The discharge speed adjusting unit 22 adjusts the driving waveform based on the atmosphere measured by the atmosphere measuring unit 23 and the discharge speed correction amount stored in the storage unit 24. Further, there is provided recovery means for performing recovery operation of the inkjet head H when the discharge speed is out of the adjustment range of the discharge speed adjusting means 22.

  Next, the discharge speed adjusting means 24 will be described.

  FIG. 8 is a diagram illustrating the drive signal P1 in the first embodiment.

  FIG. 9 is a diagram showing the dependency of the discharge speed and the discharge amount on the potential difference V2 between the second signal waveform F2 and the third signal waveform F3 obtained by experiments by the inventors of the present invention.

  FIG. 10 is a diagram showing the potential difference dependency of the ejection speed corresponding to the result shown in FIG.

  In the driving waveform in the first embodiment, the potential difference dependency of the discharge amount is smaller than the potential difference dependency of the discharge speed. Therefore, the speed can be adjusted while keeping the discharge amount substantially constant. The dependence of the ejection speed on the potential difference and the dependence of the ejection amount on the potential difference depend on the configuration and dimensions of the inkjet head H, or the ejection amount and speed to be set, and the type of ink to be ejected. be able to.

  Next, an example of calculating the correction value of the conversion table will be described.

  The storage means stores a correction voltage corresponding to the atmosphere. Through experiments, a correction voltage is calculated in advance from the rate of change in speed per unit time and the potential difference dependency.

  In the example shown in FIG. 6, it may be calculated as follows per unit time.

Condition A: -0.0094 (m / s / min) /1.1 (m / s / V)
= 0.0085V / min
Condition B: -0.0041 (m / s / min) /1.1 (m / s / V)
= 0.0037V / min
Condition C: -0.0094 (m / s / min) /1.1 (m / s / V)
= 0.0016V / min
Next, an example of adjustment by the discharge speed adjusting means will be described.

ΔV _n is a correction voltage for the second signal waveform F2 and the third signal waveform F3 for the nth correction. The initial value ΔV ₀ is 0V. In an initial state without thickening, a desired discharge speed and discharge amount can be obtained with a potential difference V2 between the second signal waveform F2 and the third signal waveform F3 set in advance. The correction value of the conversion table stored in the storage unit 24 is α, and the time interval for speed adjustment is T. The (n + 1) th correction potential difference ΔV _{n + 1} can be obtained as follows.

ΔV _{n + 1} = ΔV _n + α · T
By calculating a correction potential difference ΔV _{n + 1} at each speed adjustment time interval and adjusting the potential difference V2 between the second signal waveform F2 and the third signal waveform F3 (set to V22, V23, etc.), thereby increasing the viscosity. A decrease in discharge speed can be corrected.

The correction potential difference ΔV _n may be provided with an upper limit due to drive voltage restrictions. When the potential difference ΔV _{n + 1} exceeds the set value, the recovery system unit recovers the inkjet head H in the liquid ejecting apparatus. After the recovery operation, the correction potential difference ΔV _n may be returned to the initial value ΔV ₀ . In the first embodiment, by performing speed compensation, it is possible to extend the period during which ejection can be performed at a constant speed, and it is possible to prevent the landing position from being lowered.

  FIG. 11 is a diagram illustrating the drive signal P2 in a modification of the first embodiment.

  In the first embodiment, the potential difference (voltage) at both ends of the second signal waveform F2 and the potential difference (voltage) at both ends of the third signal waveform F3 are the same voltage V2. However, as shown in FIG. 11, the potential difference (voltage V2) at both ends of the second signal waveform F2 may be different from the potential difference (voltage) at both ends of the third signal waveform F31.

  The conversion table stored in the storage unit 24 can be calculated by obtaining the potential difference dependency of the discharge speed and the potential difference dependency of the discharge amount by the same method.

  4, 8, and 11, the reference potential is 0, but a potential other than 0 may be used as the reference potential.

  Example 1 is an ink jet recording apparatus, but the recording medium is not limited to paper. In addition to paper, the above-described embodiment can also be applied to a device for printing on cloth, leather, nonwoven fabric, etc., a patterning device or a coating device for attaching a liquid to a substrate, a plate material, a solid material, or the like.

  In the above-described embodiment, the drive waveform adjusting unit 22 keeps the ejection speed constant based on the atmosphere measuring unit 23 around the inkjet head H and the storage unit 24 that stores the correction amount corresponding to the change rate of the ejection speed during printing. Adjust to.

According to the above embodiment, the ejection speed can be kept constant even when the ink is thickened while ejecting a droplet having a diameter smaller than the ejection port diameter. A reduction in position accuracy can be prevented.

1 is a configuration diagram showing a configuration of an inkjet recording apparatus PR1 that is Embodiment 1 of the present invention. FIG. 2 is a plan view of the inkjet head H. FIG. FIG. 3 is a cross-sectional view taken along the alternate long and short dash line III-III in FIG. 2. It is a figure which shows the signal waveforms F1, P2, F3, and F4 in Example 1. FIG. In Example 1, it is a figure which shows the change of the liquid column 11 in the discharge outlet 2. FIG. It is a figure which shows the experimental result of the change of discharge speed, and the time-dependent change of discharge amount. It is a figure which shows the outline of the inkjet recording device PR1. FIG. 6 is a diagram illustrating a drive waveform in Example 1. It is a figure which shows the dependence of the discharge speed with respect to the electric potential difference V2 of the 2nd signal waveform F2 and the 3rd signal waveform F3 which the inventor of this invention experimented, and the discharge amount. It is a figure which shows the electric potential difference dependence of the discharge speed corresponding to the result shown in FIG. FIG. 10 is a diagram illustrating a drive signal P2 in a modification of the first embodiment.

Explanation of symbols

PR1 ... inkjet recording apparatus,
100: Recording head unit,
101, 102 ... guide shaft,
103, 104 ... feed rollers,
105 ... Recovery unit,
1. Orifice plate,
2 ... discharge port,
3 ... Individual liquid chamber,
4 ... Diaphragm,
5 ... Actuator,
6 ... Substrate,
7 ... communication entrance,
P1 ... Drive signal F1, F2, F3, F4 ... Signal waveform,
10 ... Meniscus,
11 ... Liquid column,
21 ... Driving means,
22: Discharge speed adjusting means,
23. Atmosphere measuring means,
24: Storage means.

Claims (8)

An ink individual liquid chamber, an ejection port communicating with the individual liquid chamber, a diaphragm forming a part of a side surface of the individual liquid chamber, and the individual liquid chamber by deforming the diaphragm by applying a voltage pulse. In a liquid ejecting apparatus that includes a driving unit that applies a driving signal to an inkjet head that includes a piezoelectric actuator that changes the volume of the liquid droplets, and that discharges a droplet having a diameter smaller than the diameter of the discharge port by the driving unit. ,
Atmosphere measuring means for measuring the atmosphere around the inkjet head;
Storage means for storing a correction amount corresponding to the rate of change of the ejection speed during printing;
A discharge speed adjusting means for adjusting a discharge speed based on the correction amount stored in the storage means and the atmosphere measured by the atmosphere measuring means;
A liquid ejecting apparatus comprising: In claim 1,
The drive signal is
A first signal waveform that changes a voltage in a direction in which the individual liquid chamber expands;
A second signal waveform for changing the voltage in a direction in which the individual liquid chamber contracts;
A third signal waveform that changes the voltage in a direction in which the individual liquid chamber expands;
A fourth signal waveform for changing the voltage in a direction in which the individual liquid chamber contracts;
Means having
The liquid ejecting apparatus according to claim 1, wherein the discharge speed adjusting means is means for adjusting a potential difference between the second signal waveform and the third signal waveform. In claim 1 or claim 2,
The liquid ejecting apparatus according to claim 1, further comprising a recovery unit that performs a recovery operation of the inkjet head when the discharge speed is out of an adjustment range of the discharge speed adjusting unit. In any one of Claims 1 to 3,
The liquid ejecting apparatus according to claim 1, wherein the atmosphere measuring unit is a unit that measures humidity around the inkjet head. In any one of Claims 1 to 3,
The liquid ejecting apparatus according to claim 1, wherein the atmosphere measuring unit is a unit that measures humidity and temperature around the inkjet head. In any one of Claims 1 to 3,
The liquid ejecting apparatus according to claim 1, wherein the atmosphere measuring unit is a unit that measures humidity around the inkjet head and a temperature of the inkjet head. In any one of Claims 1 thru | or 6,
A liquid ejecting apparatus comprising temperature control means for maintaining the temperature of the ink jet head at a specific temperature. An ink individual liquid chamber, an ejection port communicating with the individual liquid chamber, a diaphragm forming a part of a side surface of the individual liquid chamber, and the individual liquid chamber by deforming the diaphragm by applying a voltage pulse. Of a liquid ejecting apparatus that includes a driving unit that applies a driving signal to an inkjet head that includes a piezoelectric actuator that changes a volume of the liquid droplets, and that discharges a droplet having a diameter smaller than the diameter of the discharge port by the driving unit. In the control method,
An atmosphere measuring step for measuring an atmosphere around the inkjet head;
A storage step of storing a correction amount in accordance with the rate of change in discharge speed during printing in a storage device;
A discharge rate adjusting step of adjusting a discharge rate based on the correction amount stored in the storing step and the atmosphere measured in the atmosphere measuring step;
A control method for a liquid ejecting apparatus comprising:

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