JPS6233953B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an ink jet recording apparatus, and more particularly, to an ink droplet charging method in an ink jet recording apparatus capable of performing halftone recording by performing deflection.

Many types of inkjet recording devices have been known in the past. Among these, an ink-on-demand type inkjet recording device using an electroacoustic transducer has advantages such as a simple structure and no need to collect ink because all formed ink droplets are recorded and used. Furthermore, the size of the ink droplet can be changed by an electric signal applied to the electroacoustic transducer, making it possible to record halftones. 2. Description of the Related Art Conventionally, a device for performing halftone recording is known in which recording paper is wound around a drum and the drum is rotated to perform scanning. However, in such an apparatus, it is necessary to wind the recording paper around a drum, so it is desired to improve this point and use a method of scanning by deflecting ink droplets, which makes handling of the recording paper easier. However, the conventionally known electrical deflection method has a problem in that the amount of deflection changes when the size of the ink droplet changes.

SUMMARY OF THE INVENTION An object of the present invention is to provide an ink droplet charging method for an inkjet recording apparatus that is capable of performing halftone recording that allows deflection even when the size of the ink droplet changes, and is effective for multi-nozzle design. It is in.

According to the present invention, ink droplets having a weight corresponding to the concentration are ejected from an on-demand type ink jet head in accordance with a concentration information signal outputted at predetermined time intervals, and the ink droplets are directed in front of the nozzles of the ink jet head. In the ink droplet charging method of an inkjet recording device, the ink droplet is charged by a disposed charging electrode, and the charged ink droplet is deflected by a deflection electrode to which a constant voltage is applied to perform recording. Using an on-demand type ink jet head in which the weight of ink droplets to be used is variable, a drive waveform is selected in advance from among the drive waveforms that ejects ink droplets of a desired weight with a constant flying speed within the range of the weight of the ink droplets to be used. Furthermore, the relationship between the droplet formation time from the time the drive waveform is applied until the ink droplet is cut off from the nozzle is determined for these drive waveforms. A voltage is applied that modulates the amplitude of a waveform having a sawtooth waveform or a staircase waveform that increases at a constant rate and is repeated at the predetermined intervals in proportion to the specified deflection amount, and A drive waveform for ejecting a droplet with a weight corresponding to the density information is selected from among the drive waveforms secured, and the waveform is proportional to the weight of the ink droplet determined by the density signal with respect to the origin of the charging waveform, even for the heaviest ink droplet. The driving waveform is applied to the on-demand type ink jet head with a delay of a time determined by subtracting the droplet formation time of the ink droplet to be ejected at that time from the time determined to be equal to or less than the predetermined time interval. An ink droplet charging method for an inkjet recording device is obtained. Furthermore, according to the present invention, ink droplets having a weight corresponding to the concentration are ejected from an on-demand type ink jet head in accordance with a concentration information signal output at predetermined time intervals, and the ink droplets are directed in front of the nozzles of the ink jet head. In the ink droplet charging method of an inkjet recording device, the ink droplet is charged by a disposed charging electrode, and the charged ink droplet is deflected by a deflection electrode to which a constant voltage is applied to record. Using an on-demand ink jet head whose weight of ink droplets is variable, a drive waveform is selected in advance from among the drive waveforms that ejects ink droplets of a desired weight with a constant flying speed within the range of the weight of the ink droplets to be used. Furthermore, the relation between the droplet formation time from the time when the drive waveform is applied until the ink droplet is cut off from the nozzle is determined for these drive waveforms. A voltage having a sawtooth waveform or a step waveform that increases at a constant rate and is repeated at the predetermined intervals is applied, and the concentration information is selected from among the drive waveforms secured by the concentration information signal. Select a driving waveform for ejecting a heavy droplet, and select a driving waveform to eject a heavy droplet, and the heaviest droplet will have the largest deflection amount in proportion to the product of the ink droplet weight from the concentration signal and the specified deflection amount with respect to the origin of the charging waveform. The driving waveform is applied to the on-demand head after being delayed by a time that is determined by subtracting the droplet formation time of the ink droplet to be ejected at that time from the time set to be equal to or less than the predetermined time interval. An ink droplet charging method for an inkjet recording device is obtained.

The present invention will be described in detail below with reference to the drawings.

FIG. 1 is a schematic diagram for explaining one embodiment of an inkjet recording apparatus according to the present invention. This apparatus includes an ink jet head 1 that can control the size of ink droplets formed by the amplitude of a signal, and a voltage applying means 6 that outputs a periodic waveform, as an example of a sawtooth voltage in this embodiment. a charging electrode 5 that applies a charge to the ink droplet ejected by the nozzle; a deflection amount specifying section 7 that specifies the amount of deflection; and a signal that outputs an electric signal specifying the weight of the ink droplet in synchronization with the sawtooth wave. a source 8, a delay means 9 which receives an electric signal from the signal source 8 and inputs the signal to the ink jet head after delaying the sawtooth wave by a predetermined time depending on the weight of the ink droplet; It consists of a deflection electrode 10 that deflects and a recording medium 12 such as paper. The ink jet head 1 shown here consists of a nozzle 3 filled with conductive ink supplied from an ink supply system (not shown), an ink chamber 4, and a piezo vibrator 2 as an electroacoustic transducer. It is known as an example of on-demand type. When an ink droplet is formed, when a voltage pulse is applied to the piezoelectric vibrator as an electric signal, the piezoelectric vibrator generates stress in response to the voltage, increases the pressure in the ink chamber, and pushes out the ink from the nozzle 3. It is generally known that in such an ink jet head, when the amplitude or pulse width of the driving voltage waveform is changed, the weight and speed of the ejected ink droplets can be changed. In the present invention, combinations of amplitude and pulse width are determined in advance so that various droplet weights are ejected under conditions where the droplet velocity is constant.
From among these, the amplitude and pulse width for ejecting ink droplets of the weight corresponding to the density signal are selected and the head is driven.

Here, the signal input to the piezo vibrator of the ink jet head is, for example, a signal having a constant pulse width and whose amplitude changes in accordance with the weight of the ink droplet. Ink droplets ejected from the nozzle are charged by the voltage applied to the charging electrode 5. After being deflected by a deflection electrode 10 to which a constant voltage is applied from a power source 11, it is driven into a recording medium 12 such as paper. At this time, the amount of deflection can be changed by keeping the deflection electric field constant and changing the amount of charge on the ink droplet.

The charging mechanism according to the present invention will be explained in more detail. First, as an example, consider a case where the amount of deflection is changed in three stages as shown in FIG. 2a. The voltage applying means 6 responds to a deflection amount instruction from the deflection amount specifying section 7 as shown in FIG. Outputs a sawtooth wave modulated in proportion to the This voltage is applied to the charging electrode 5.

In synchronization with this sawtooth wave, the signal source 8 outputs an electrical signal specifying the weight of the ink droplet, as shown in FIG. 2c. This signal is input to the delay circuit 9, and as shown in FIG. 2d, it is delayed for a certain period of time according to the weight of the ink droplet, that is, the amplitude of the electric signal, and then input to the piezoelectric vibrator 2, where an ink droplet is formed. Ru.
This amount of delay is determined by the amount of ink droplet formed when the ink leaves the nozzle (e.g., the voltage of the charging electrode at the time indicated at time t ₁ in FIG. 2d (e.g., V ₁ in FIG. 2b)). When the voltage of the charging electrode is a sawtooth wave as shown in Figure 2b, the delay amount α + pulse width is proportional to the weight of the ink droplet, as shown in Figure 2d. The delay amount α is set so that
All you have to do is control. Here, when the difference β between the falling time of the electric signal applied to the piezo vibrator and the time when the ink is cut off from the nozzle is large, it is necessary to correct the delay amount α by the magnitude of β.

With such a charging mechanism, the ink droplet is charged so that the ratio k between the charge amount q of the ink droplet and the weight m becomes a constant value for the same amount of deflection, and the value of k is proportional to the amount of deflection. Ru. The ink droplet charged in this way is deflected by the deflection electrode 10 to which a constant voltage is applied, but if the value of k is the same, even if the weight of the ink droplet is different, it will be deflected because it will receive the same acceleration. The quantities will be equal.

Further, the amount of deflection is proportional to the value of k.

In the embodiments described above, the signal from signal source 8 can be any analog or digital signal that specifies the weight of the ink drop. In this case, the delay means is one that outputs a pulse having a delay time and amplitude corresponding to the weight of the ink droplets similar to those described above in response to a voltage having a constant waveform output from the voltage application means in response to this signal. must be used.

Next, when changing the size of the ink droplets discontinuously, as shown in Figure 3, the voltage waveform applied to the charging electrode changes the charging of the ink droplets in accordance with the size of each ink droplet. A staircase wave having a voltage value such that the ratio of volume to weight is constant may be applied. In this case, the voltage applied to the charging electrode remains constant for a predetermined period of time, so even if there is some variation in the time when the ink is disconnected from the nozzle during the formation of the ink drop, the amount of charge on the ink drop will change. becomes smaller.

Next, a second embodiment of the control of the ink droplet charging method according to the present invention will be described with reference to FIG.

In this embodiment, the voltage applying means 6 outputs a constant voltage waveform without amplitude modulation, unlike the embodiment shown in FIG. The period of this voltage waveform matches the ink droplet formation period. On the other hand, the signal source 8 outputs an electric signal specifying the weight of the ink droplet to the arithmetic circuit 91 in synchronization with the voltage waveform from the voltage applying means 6. As the electrical signal specifying the weight of the ink droplet, a voltage pulse whose duration or amplitude changes in proportion to the weight of the ink droplet, a binary code proportional to the weight of the ink droplet, etc. can be used.
Further, a deflection amount designation signal from the deflection amount designation means 7 is also input to the arithmetic circuit 91 in synchronization with the voltage waveform from the voltage application means 6. Then, the arithmetic circuit outputs a signal indicating the delay time, which is calculated by subtracting the time required from the time the drive pulse is applied until the droplet is cut off from the nozzle, from the value proportional to the product of the ink droplet weight and the amount of deflection. is input to the delay circuit. The delay circuit 92 delays the charging voltage waveform from the voltage applying means 6 according to a signal from the arithmetic circuit and outputs a piezo drive pulse signal. The ink droplet formed by this pulse signal is cut off from the nozzle with a delay of a time proportional to the product of the ink droplet weight and the deflection amount with respect to the charging waveform of the voltage applying means. Since the charging waveform has a voltage that increases with a constant slope, the voltage value at the time when the ink droplet is cut off from the nozzle is a value proportional to the product of the ink droplet weight and the amount of deflection.

Here, as an example, FIG. 5 shows the relationship between the above-mentioned signals in the case where the weight of the ink droplet is proportional to the amplitude of the piezo element drive pulse.
For simplicity, the deflection amount is designated in three stages as shown in FIG. 5a. There are no particular restrictions on the voltage waveform from the voltage applying means 6, but for the sake of simplicity, it is assumed to be a sawtooth waveform as shown in FIG. 5b. In this example,
Unlike what was previously shown in FIG. 2b, the amplitude of the sawtooth wave is constant. FIG. 5c shows the electrical signal output from the signal source 8 specifying the weight of the ink drop. Here, the weight of the ink droplet is specified by changing the amplitude of voltage pulses having equal time widths. These signals shown in FIGS. 5a, b, and c are all synchronized with the cycle of ink droplet formation. FIG. 5d shows the output signal of the drive circuit 15. Here, the illustration is made on the assumption that ink droplet formation is completed at the falling edge of each drive pulse. These drive pulses correspond to the values of the charging voltages (i.e., V ₁ , V 2 as shown in FIG. 5b) at the time of completion of ink drop formation (i.e., t ₁ , t 2 , t ₃ shown in FIG. _{5d )} . , V ₃ ) are delayed with respect to the charging voltage of FIG. 5b so as to be proportional to the product of the weight of the ink drop and the amount of deflection. However, in this case, it is assumed that the amount of charge on the ink droplet is proportional to the charging voltage. In this case, the delay time α and the time width β for the charging voltage of the drive pulse are determined such that α+β is proportional to the product of the ink droplet weight and the deflection amount. When a driving pulse is applied to the head with a delay of α relative to the charging voltage, the point at which the ink droplet is cut off from the nozzle becomes a value proportional to the product of the weight of the ink droplet and the amount of deflection relative to the origin of the charging voltage. Therefore, in a waveform in which the charging voltage increases at a constant slope from the origin as shown in FIG. When the amount of deflection is zero, the charging voltage is always zero, as shown by A in FIG. 5b, no matter what the weight of the ink droplet. When the amount of deflection is not zero, the range of charging voltage indicated by B or C in FIG. 5b is determined depending on the amount of deflection, corresponding to the maximum and minimum values of the weight of the ink droplet. Therefore, the maximum amplitude of the charging voltage is determined as corresponding to the maximum value of the ink droplet weight and deflection amount.

In the charging control method described above, the charging voltage is not limited to a sawtooth waveform, and any waveform consisting of an arbitrary curved line or polygonal line may be used. Of course, in practice, a waveform that monotonically increases or decreases over time is easier to handle.

In either case, it is important to repeatedly apply a waveform of the same amplitude and shape. Next, the formation of an ink droplet is not necessarily completed at the falling edge of the drive pulse in FIG. 5d. If ink droplet formation is completed earlier or later than the falling edge of this pulse, it is necessary to correct the delay time (for example α in FIG. 5d) to be longer or shorter, respectively. Furthermore, when the width of the drive pulse changes, it is necessary to correct the delay time to shorten or lengthen it for expansion or contraction of the pulse width, respectively.

As explained above, by applying a voltage with a constant periodic waveform to the charging electrode and inputting a drive signal delayed according to the weight of the ink droplet to be formed to the ink jet head, the ink droplet is formed. We have shown a device that can obtain the same amount of deflection even if the weight changes. Also, as is clear from this, the present invention is very advantageous when multiple ink jet heads are used. In other words, when using multiple nozzles, it is possible to make the voltage applied to the charging electrode common to each nozzle. That is, a voltage with a constant waveform is applied to the charging electrode, and an electrical signal delayed depending on the size of the ink droplet is input to each ink jet head. Further, the deflection electrode is common to each nozzle, and the deflection voltage also has the advantage of being constant.

In each of the embodiments of the present invention described above, the formation of ink droplets was explained using an inkjet head as shown in FIG. It is not limited to inkjet heads. For example, it can be applied to the ink jet head described in JP-A-48-9622 and the ink jet head shown in the liquid ejecting device described in JP-A-47-6308.

[Brief explanation of the drawing]

FIG. 1 is a diagram for explaining one embodiment of the inkjet recording apparatus according to the present invention, and FIGS. 2a and 3a are examples of how the amount of deflection by the deflection amount designation section changes over time. Figures 2b and 3b are diagrams showing an example of the voltage waveform applied to the charging electrode, respectively. Figure 2c is the output signal from the signal source, and Figure 2d is the delay. Figure 4 is a diagram showing the signals output from the circuit and input to the piezo vibrator, and Figure 4 is the second diagram related to the control of the ink droplet charging method.
FIG. 5 is a diagram illustrating the relationship between each signal. In the figure, 1 is an inkjet head;
2 is a piezo vibrator, 3 is a nozzle, 4 is an ink chamber,
5 is a charging electrode, 6 is a voltage application means, 7 is a deflection amount specifying section, 8 is a signal source, 9 is a delay means, 10 is a deflection electrode, 11 is a power source, 12 is a recording medium, 13 is an ink droplet, 14 is a synchronization 91 is an arithmetic circuit, 92 is a delay circuit, and 15 is a piezo vibrator drive circuit.

Claims (1)

[Scope of Claims] 1. Ink droplets having a weight corresponding to the concentration are ejected from an on-demand type ink jet head in accordance with a concentration information signal output at predetermined time intervals, and the ink droplets are directed in front of the nozzle of the ink jet head. In the ink droplet charging method of an inkjet recording device, in which charging is performed by a charging electrode placed on the ink droplet, and recording is performed by deflecting the charged ink droplet with a deflection electrode to which a constant voltage is applied, A drive waveform that uses an on-demand type inkjet head in which the weight of the ink droplets to be ejected is variable, and ejects ink droplets of a desired weight each with a constant flight speed within the range of the ink droplet weight to be used from the drive waveform. Select
Furthermore, the relationship between the droplet formation time from the time when the drive waveform is applied until the ink droplet is cut off from the nozzle is determined for these drive waveforms. A voltage is applied that modulates the amplitude of a waveform having a sawtooth waveform or a staircase waveform that increases at the predetermined interval in proportion to the specified amount of deflection, and the voltage that is secured by the concentration signal is applied. A drive waveform for ejecting a droplet having a weight corresponding to the density information is selected from among the drive waveforms, and even the heaviest ink droplet has the predetermined value, relative to the origin of the charging waveform, in proportion to the ink droplet weight determined by the density signal. Inkjet recording characterized in that the drive waveform is applied to the on-demand type inkjet head after being delayed by a time determined by subtracting the droplet formation time of the ink droplet to be ejected at that time from a time determined to be equal to or less than a time interval. Ink drop charging method of the device. 2. In accordance with the concentration information signal output at predetermined time intervals, ink droplets with a weight corresponding to the concentration are ejected from an on-demand type ink jet head, and the ink droplets are ejected by a charging electrode placed in front of the nozzle of the ink jet head. In the ink droplet charging method of an inkjet recording device, which performs recording by charging and deflecting the charged ink droplet using a deflection electrode to which a constant voltage is applied, the weight of the ink droplet ejected according to the shape of the drive waveform. Using an on-demand type ink jet head with variable ink jet head, select in advance from among the drive waveforms a drive waveform that ejects ink droplets of a desired weight each with a constant flying speed within the range of the weight of the ink droplets to be used;
Furthermore, the relationship between the droplet formation time from the time when the drive waveform is applied until the ink droplet is cut off from the nozzle is determined for these drive waveforms. A voltage with a waveform having a sawtooth waveform or a stepwise waveform increasing at a rate and repeated at the predetermined intervals is applied, and a droplet having a weight corresponding to the concentration information is selected from among the drive waveforms secured by the concentration information signal. Select a drive waveform for ejecting the heaviest droplet, and select the driving waveform for ejecting the heaviest droplet at the predetermined value when the largest deflection amount is obtained, relative to the origin of the charging waveform, in proportion to the product of the ink droplet weight from the concentration signal and the specified deflection amount. The inkjet is characterized in that the drive waveform is applied to the on-demand head with a delay of a time determined by subtracting the droplet formation time of the ink droplet to be ejected at that time from a time determined to be less than or equal to the time interval. Ink droplet charging method for recording devices.