JPH0360069B2 - - Google Patents

Description

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

(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 on-demand multi-nozzle inkjet recording devices; even if the driving conditions are the same, the ink droplet speed differs depending on the state of each nozzle, and this causes a difference in the quality of the recorded image. This results in disturbance and 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 flight speed detection device that can be easily incorporated into an 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. From this, 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. Even when ink is ejected from the same nozzle, the flying speed of each ink droplet varies. 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 is extremely 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. Still another object of the present invention is to provide an ink droplet flight speed detection device 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 an ink droplet flying speed detection device for 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. , an ink drop adhesion electrode provided at a position opposite to the nozzle and to which the flying ink droplets adhere; a charging power supply unit that applies a constant voltage between the ink drop adhesion electrode and the nozzle; connected to the droplet deposition electrode,
a detection means for detecting the adhesion of an ink droplet; a driving start time of the piezoelectric element; an ink adhesion time detected from an electrical change in a flat ink droplet adhesion electrode accompanying the adhesion of a charged ink droplet; This is achieved by an ink droplet flight speed measuring device equipped with a measuring means for measuring the flight speed of the ink droplet based on the distance from the droplet adhesion electrode.

(f) Embodiment of the invention Hereinafter, an embodiment will be described in detail with reference to the drawings.

FIG. 2 is a schematic diagram of an ink droplet flight speed detection device according to an embodiment of the present invention, in which 1 is a nozzle, 2 is an ink droplet, 3 is an ink droplet adhesion electrode, 4 is a charging power source,
5 is resistance. In the case of an on-demand type inkjet, a pulse voltage is applied to a piezo element (not shown) based on information 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 from the charging power source 4 to the adhered electrode 3 via the resistor 5, the adhered electrode 3 and the nozzle 1 form a kind of capacitor; A charge of opposite polarity to the applied voltage is induced in 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 an ink droplet adhesion electrode 3.

Thus, as the charged ink droplet 2 approaches the ink droplet adhesion electrode 3, a charge having a polarity opposite to that of the ink droplet 2 is induced in the adhesion electrode 3, and this induced current flows through the capacitor 6. capacitor 6
is a DC-cut capacitor that prevents the charging voltage from the charging power source 4 from being applied to the detection circuit.

The induced current flowing through the capacitor 6 in this way is detected by the detection circuit shown in FIG.
Flight time is required. The induced current is first converted into a voltage by a current-voltage conversion circuit consisting of an inverting circuit 7 and a resistor 8, and then amplified by an amplifier 9. The amplified signal waveform is shown in FIG. 3a. This signal is 2
one is passed through a low-pass filter 10 and compared with a reference voltage 12 by a comparator 11;
If the signal is greater than the reference voltage, the signal will be as shown in FIG. 3c. Figure 3b shows the low pass filter 10.
It shows the signal passing through. The other signal passes through a low-pass filter 13 and a differentiating circuit 14.
The waveform signal shown in Figure d is obtained. Since this signal crosses the zero level when the ink droplet adheres to the adhering electrode 3, the comparator 15 subsequently detects the zero crossing point of the signal. FIG. 3e shows the signal waveform output from the comparator 15. Output of the comparator 11 (signal output shown in FIG. 3c)
and the output of the comparator 15 are matched in polarity by the inverter 16, and the AND gate circuit 17
Add by. 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 18, and a counter 19 counts the number of clocks from the clock circuit 20.
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 17.

At this time, the count value obtained by the counter 19 is sent to the control circuit 21, and multiplied by the clock cycle to obtain the flight time T of the ink droplet. Furthermore, if the distance between the nozzle 1 and the attached electrode 3 is D, then the average flying speed V of the ink droplets is determined by V=D/T. The control circuit 21 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 31. By making the adhering electrode 33 sufficiently large to cover the multi-nozzle 31 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 11 and the differentiating circuit 14 is replaced with an AD converter 36 and a control circuit 37. At the same time as a voltage pulse is applied to the piezo element, the AD converter 36 starts operating at a fixed time period, and the input voltage, which is similar to the voltage signal shown in FIG. The control circuit 37 calculates the flight time and flight speed based on the captured memory data.

(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 can also be incorporated into recording devices, making it an extremely effective detection device for 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 device according to an embodiment of the present invention, and Figure 3 is a diagram showing recorded images.
The figure shows the 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 detection device of still another embodiment. be. In the figure, 1 is a nozzle, 2 is an ink droplet, 3 is an ink droplet adhesion electrode, 4 is a charging power source, 5 is a resistor, 6 is a capacitor, 7 is an inverting circuit, 8 is a resistor, 9 is an amplifier,
10 and 13 are low-pass filters, 11 and 15 are comparators, 12 is a reference voltage, 14 is a differential circuit,
16 is an inverter, 17 is an AND gate circuit, 1
8 is a flip-flop, 19 is a counter, 20 is a clock circuit, 21 is a control circuit, 31 is a multi-nozzle, 33 is an ink droplet adhesion electrode, 36 is an AD converter, and 37 is a control circuit.

Claims (1)

[Scope of Claims] 1. An ink droplet flying speed detection device for 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, comprising: a sheet of ink droplet adhering electrode to which flying ink droplets are attached, which is provided at a position opposite to the ink drop adhering electrode; a charging power supply section for applying a constant voltage between the ink drop adhering electrode and the nozzle; and the ink droplet adhering electrode. a detection means connected to the nozzle for detecting the adhesion of ink droplets; a driving start time of the piezoelectric element; an ink droplet adhesion time detected from an electrical change in a flat plate ink droplet adhesion electrode accompanying the adhesion of charged ink droplets; An ink droplet flight speed detection device comprising: a measuring means for measuring the flight speed of an ink droplet based on the distance between the tip and an ink droplet adhesion electrode.