JPH0360068B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Technical Field of the Invention The present invention relates to a detection method for detecting the flying speed of ink droplets in an ink jet recording apparatus.

(b) Background of the Technology Currently, various methods have been proposed for inkjet recording devices, and some methods have already been put into practical use.

For example, in an on-demand type of inkjet recording device, a piezoelectric element provided in an inkjet head that runs at a constant speed is driven in response to information from a host device (for example, a computer). This is a device that performs recording by ejecting ink droplets from the tip of an inkjet.

However, since the ink jet head itself runs at a constant speed and recording is performed by ejecting ink droplets from the ink jet head, differences in the flying speed of ink droplets during ejection can cause disturbances in the recorded image. It appears. Fig. 1 shows this. Fig. 1a is a recorded diagram when ink droplets D adhere at a uniform speed, and Fig. 1b is a recorded diagram when ink droplets D adhere at a uniform speed.
It is clear that the recording quality in FIG. 1b is lower than that in the recording diagrams when the particles were deposited at different speeds. The arrow in the figure indicates the direction of movement of the head.

Such problems are particularly noticeable in the case of multi-nozzle on-demand inkjet recording devices; even if the driving conditions are the same, the ink droplet speed differs depending on the condition of each nozzle, which can cause disturbances in the recorded image. This causes a significant deterioration in recording quality.

Therefore, in order to obtain high-quality recorded images, it is important to equalize the flying speed of ink droplets from each nozzle. It is desirable to have an ink droplet flying speed detection method that can determine the voltage applied to the piezo element and the pulse width suitable for each inkjet recording device, and can also be easily incorporated into the inkjet recording device.

(c) Prior Art and Problems Conventionally, as a means of detecting the flying speed of ink droplets, ink droplets are ejected at fixed time intervals, and a strobe is emitted after a fixed time delay from the ink droplet ejection time. The state of the ink droplets is captured and observed as a still image using an optical device such as a microscope. In this case, the position of the still image of the ink droplets is changed by changing the delay time from the ink droplet ejection time to the strobe light emission. Thereby, the flying speed of the ink droplet can be determined using the following equation.

V=L/T However, V: Flying speed of ink droplets L: Change in position of ink droplets T: Change in delay time However, in this conventional method, the average of many ink droplets in a steady state where they are continuously ejected is However, it is impossible to directly measure the flight speed of individual ink droplets. Further, this method requires expensive equipment such as a delay circuit, a strobe, a microscope, etc., is complicated to operate, and has drawbacks such as a long detection time and a large amount of ink used for detection. Furthermore, in the case of a multi-nozzle inkjet head, positioning and focusing operations are required for each nozzle, which becomes extremely complicated.

A method has also been proposed in which two sensing electrodes are placed between the nozzle tip and the recording medium, the charge applied to the ink droplets is detected, and the flying speed of the ink droplets is detected from the distance between the two electrodes. However, it also has the disadvantage that the configuration is complicated.

(d) Object of the invention In view of the above drawbacks, the object of the invention is to
An object of the present invention is to provide an ink droplet flying speed detection device capable of detecting the flying speed of individual ink droplets. Another object of the present invention is to provide an ink droplet flying speed detection method that can be applied to either a single nozzle or multiple nozzles, has a simple configuration, and does not require complicated operations.

(e) Structure of the Invention The purpose of the invention is to provide a method for detecting the flying speed of ink droplets in an inkjet recording device that records on a recording medium by driving a piezoelectric element in response to an information signal and ejecting ink droplets from the tip of a nozzle. , a nozzle that ejects ink droplets from its tip, an ink droplet adhesion electrode that is provided at a position opposite to the nozzle and on which the ink droplets fly and adhere, and an ink droplet adhesion electrode that is disposed between the ink droplet adhesion electrode and the nozzle. , comprising a charging electrode for charging an ink droplet having a shape that does not obstruct a space in which the ink droplet flies, and a detection means connected to the ink droplet adhesion electrode, and a driving start time of the piezoelectrode element; The time when an ink droplet is ejected from the nozzle tip, the ink droplet adhesion time detected from the electrical change of the ink droplet adhesion electrode due to the adhesion of the charged ink droplet, and the distance between the nozzle tip and the ink droplet adhesion electrode. This is achieved by an ink droplet flying speed detection method that detects the flying speed of ink droplets.

(f) Examples of the invention Hereinafter, examples will be described in detail with reference to the drawings.

FIG. 2 is a schematic diagram of an ink droplet flying speed detection method according to an embodiment of the present invention, in which 1 is a nozzle, 2 is an ink droplet, 3 is a charging electrode, 4 is a charging power source, and 5 is an ink droplet adhesion electrode. . In the case of an on-demand type inkjet, a pulse voltage is applied to a piezo element (not shown) by jetting from a host device and converted into a pressure pulse. This pressure is transmitted to the nozzle tip, and ink droplets 2 are ejected from the nozzle 1. At this time, since a voltage of several 10 to several 100 V is applied to the charging electrode 3 from the charging power source 4, the charging electrode 3 and the nozzle 1 form a kind of capacitor.
The charge of opposite polarity to the voltage applied to the charged electrode 3 is
Induced by the ink before it separates from the nozzle. The ink separates from the nozzle while retaining this charge, becomes a charged ink droplet 2, and flies toward the ink droplet adhesion electrode 5.

Thus, as the charged ink droplet 2 approaches the ink droplet adhesion electrode 5, a charge having a polarity opposite to that of the ink droplet 2 is induced in the adhesion electrode 5, and an induced current flows.

This induced current is detected by the detection circuit shown in FIG. 2 and the flight time is determined, but the induced current is first converted into voltage by a current-voltage conversion circuit consisting of an inverting circuit 6 and a resistor 7, and then by an amplifier 8. is amplified. The amplified signal waveform is shown in FIG. 3a.
This signal is divided into two parts, one of which passes through a low-pass filter 9 and is compared with a reference voltage 11 by a comparator 10. If the signal is greater than the reference voltage, the signal shown in FIG. 3c is obtained. FIG. 3b shows the signal passed through the low-pass filter 9. The other signal passes through a low-pass filter 12 and a differentiation circuit 13 to obtain a waveform signal shown in FIG. 3d. Since this signal crosses the zero level when the ink droplet adheres to the adhering electrode 5, the comparator 14 subsequently detects the zero crossing point of the signal. FIG. 3e shows the signal waveform output from the comparator 14. The output of the comparator 10 (signal output shown in FIG. 3c) and the output of the comparator 14 are connected to the inverter 1.
5 to match the polarities, and the AND gate circuit 16 adds them. Then, the timing at which the ink droplet adheres to the adhesion electrode as shown in FIG. 3f can be obtained.

On the other hand, a piezo drive signal P (a signal for ejecting ink droplets by applying a voltage to a piezo element) is applied to the flip-flop 17, and a counter 18 counts the number of clocks from the clock circuit 19.
In this way, these counting circuits start counting when they receive the piezo drive signal, and then AND
Counting is stopped by the signal shown in FIG. 3f from the gate circuit 16.

At this time, the count value obtained by the counter 18 is sent to the control circuit 20 and multiplied by the clock period to obtain the flight time T of the ink droplet. Furthermore, if the distance between the nozzle 1 and the attached electrode 5 is D, then the average flying speed V of the ink droplets is determined by V=D/T. The control circuit 20 is composed of a microprocessor, memory, etc., and is configured to control the flight speed V calculated in this way.
is output.

FIG. 4 is a schematic diagram of the flying portion when the ink jet head is a multi-nozzle 21. By making the adhesion electrode 25 large enough to cover the multi-nozzle 21 and ejecting ink from each nozzle sequentially, it is possible to detect the flight time of an ink droplet with the same configuration as the single nozzle described above.

FIG. 5 is a diagram showing still another embodiment according to the present invention, and the difference from FIG. 2 is the detection circuit.
The signal processing circuit portion after the comparator 10 and the differentiating circuit 13 is replaced with an AD converter 26 and a control circuit 27. At the same time as a voltage pulse is applied to the piezo element, the AD converter 26 starts operating at a fixed time period, and the input voltage shown in FIG. The flight time and flight speed are calculated by the control circuit 27 based on the captured memory data.

Although the ink droplet flying speed detection method according to the present invention requires two electrodes, a charging electrode and an ink droplet adhesion electrode, it has the advantage of simplifying the circuit configuration because the power supply circuit can be separated from the detection circuit. be.

(g) Effects of the Invention As is clear from the above description, according to the present invention, the flight time of each ink droplet can be automatically detected and the flight speed can be calculated. However, a single nozzle,
It can be used with any multi-nozzle, is inexpensive, has a simple configuration, and is easy to operate. Therefore, it can be used for the development of inkjet recording devices or as a testing device, and the ink drop adhesion electrode according to the present invention can be arranged on the same plane as the recording medium, and other members can be arranged accordingly. This detection method can be incorporated into recording devices and is extremely effective in improving the quality of recording.

[Brief explanation of drawings]

Figures 1a and b are diagrams showing recorded images, Figure 2 is a schematic diagram of a detection method according to an embodiment of the present invention, and Figure 3 is a diagram showing recorded images.
The figure is a diagram showing signal waveforms of each part of the detection circuit shown in Figure 2, Figure 4 is a schematic diagram of the flying part of another embodiment, and Figure 5 is a diagram of a schematic diagram of the detection circuit of yet another embodiment. be. In the figure, 1 is a nozzle, 2 is an ink droplet, 3 is a charging electrode, 4 is a charging power source, 5 is an ink droplet adhesion electrode, 6 is an inverting circuit, 7 is a resistor, 8 is an amplifier, 9 and 12 are low-pass filters, 10 , 14 is a comparator, 1
1 is a reference voltage, 13 is a differential circuit, 15 is an inverter, 16 is an AND gate circuit, 17 is a flip-flop, 18 is a counter, 19 is a clock circuit,
21 is a multi-nozzle, 25 is an ink droplet adhesion electrode,
26 is an AD converter, and 27 is a control circuit.

Claims (1)

[Claims] 1 A method for detecting the flight speed of ink droplets in an inkjet recording device that records on a recording medium by driving a piezoelectric element according to an information signal and ejecting ink droplets from the tip of the nozzle, which is a nozzle that ejects ink droplets from the tip. an ink droplet adhesion electrode provided at a position opposite to the nozzle, on which the ink droplets fly and adhere; and an ink droplet adhesion electrode provided between the ink droplet adhesion electrode and the nozzle to form a space in which the ink droplets fly. It includes a charging electrode for charging an ink droplet having an unobstructed shape, and a detection means connected to the ink droplet adhesion electrode, and detects the drive start time of the piezoelectric element and the ink droplet accompanying the adhesion of the charged ink droplet. An ink droplet flying system characterized in that the flying speed of an ink droplet is detected based on the ink droplet adhesion time detected from electrical changes in the droplet adhesion electrode and the distance between the nozzle tip and the ink droplet adhesion electrode. Speed detection method.