JPS60154075A - Ink jet recording apparatus - Google Patents

Abstract

PURPOSE:To prevent non-emission of liquid droplets by enabling the rapid rising in the characteristics of an ink jet head, by setting frequency for driving the ink jet head at the time of preparatory emitting operation so as to make the same lower than driving frequency at the time of actual recording. CONSTITUTION:When recording start is indicated, a head driving circuit drives a head H at the level of the predetermined digital value of a preset circuit on the basis of the frequency of a lowest frequency signal. This first preparatory emission mode is succeeded for a time T1 and transferred to a second preparatory emission mode at time t3 and the head H is driven at the level of the predetermined digital value on the basis of the frequency of an intermediate frequency signal. Said second mode is transferred to a third preparatory emission mode at time t4 and the head H is driven at the level of the predetermined digital value by a max. head driving frequency signal. When the third preparatory emission mode is finished at time t5, the driving of the head H is prohibited. Thereafter, line memory is driven at time t7 and a recording mode is taken.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to an inkjet recording apparatus for recording characters, symbols, images, etc.

(Description of Prior Art) Conventionally, in inkjet recording apparatuses, an operation of ejecting several droplets before starting recording, a so-called preliminary ejection operation, has been performed in order to prevent clogging of the orifice of an inkjet head.

By the way, even if you do not drive the head for a long time and suddenly perform a preliminary ejection operation, the characteristics of the head remain stable.
Sufficient droplets may not be ejected.

Furthermore, in such a case, even when actual recording begins, no droplets are ejected from the head, and only extremely poor quality images are obtained.

In order to prevent such drawbacks, it is desirable to start recording after confirming that ejection is actually being performed, but it takes a long time to start driving and complicates the apparatus.

(Object of the Invention) In view of the above-mentioned drawbacks, the present invention aims to provide an inkjet recording apparatus that has a simple configuration and is capable of starting up an inkjet head reliably and quickly.

(Description of Embodiment) Hereinafter, one embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a top view of an inkjet printer to which the present invention can be applied.

In the figure, 1 is a platen that winds the recording paper, 2 is a carriage containing an inkjet head H using four piezoelectric elements, 6 is a cap, 4 is a conveyor belt of the carriage 2, and 6 is the cap 6 indicated by an arrow. 7 is a paper feed motor that rotates the platen; 8 is a carriage drive motor that drives the carriage 2 in the direction of arrow B; 10 is a cap position detector that detects that the cap 6 is in the capping position. , 11 is a home position detector that detects that the carriage 2 is at the home position.

To explain the actual recording operation, the cap 3 is separated from the head H, and the carriage 2 is reciprocated in the direction of arrow B by driving the belt 4 by the rotational force of the carriage drive motor 8. Each time the carriage 2 makes one reciprocation, the paper feed motor rotates one step to convey the paper through the platen 1. By repeating the above operations, characters, symbols, or images are formed on the recording paper.

When the recording is completed, the carriage 2 returns to the home position, and then the cap 6 covers the head 2 and the operation of the apparatus ends. By covering the head 2 with the non-recording cap 6 in this manner, it is possible to prevent ink from clogging the orifice portion due to evaporation.

FIG. 2 is a control circuit diagram of this embodiment. In Figure 2, an example of driving one head is shown to simplify the explanation.
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In the figure, 21 is a preset circuit that outputs a predetermined digital value, 22 is a line memory that stores -lines of several-bit digital image data from an image processing circuit (not shown), and 23 is a multiplexer that switches inputs. , 24 is a logic converter that converts a digital value into an analog value, 25 is a head drive circuit that drives the head H, 27 is a clock generator, 28 is a waveform shaping circuit, and 29 is a divider that divides the clock. It has multiple output terminals with different ratios.

'50 is a switch circuit for switching inputs, 61 is a mono-multivibrator that forms a timing pulse of a predetermined width to drive the head, 32 is a control unit that performs overall sequence control, and stores the CPU and the program flow chart shown in FIG. It consists of ROM and RAM jJ-5. 6
6 is a start command switch for instructing the start of recording.

The operation of the control circuit shown in FIG. 2 will be explained below with reference to the program flowchart shown in FIG. 3 and the timing chart shown in FIG.

When the start command switch 66 is operated to instruct the start of recording (time t1), first the home position detector 11
When the carriage is not at the home position, the carriage motor 8 is turned off to return the carriage to the home position.

Then, it is detected whether or not the cap 6 is at the capping position, and if it is not at the capping position fK, the cap is returned to the canopy 2/g position by the capping motor 6.

When it is confirmed that the carriage 2 is at the home position and the cap 5 is at the capping position, time t2
', the multiplexer 23 selects input A. That is, the predetermined digital value of the preset circuit is output to the D/A converter 24. On the other hand, the switch circuit selects input a. The input aK receives a frequency signal obtained by dividing the clock of the clock generator at the highest division ratio, that is, the lowest frequency signal, and outputs it to the mono multivibrator 61.

Therefore, the head drive circuit 25 drives the head H at the frequency of this low frequency signal and at the level of the predetermined digital value of the glisset circuit. This first preliminary ejection mode continues for a time T1, and when the time T1 has elapsed, a time t
5, the mode shifts to the second preliminary ejection mode. In the second preliminary ejection mode, the switch circuit 30 selects the input mode. A frequency signal with an intermediate frequency obtained by dividing the clock by an intermediate division ratio is input to the input terminal, and at this time, multiplexer 2
6 selects the input person.

Therefore, in the second preliminary ejection mode, the dot is driven at the frequency of the intermediate frequency signal and at the level of the predetermined digital value.

Then, at time t4, the switch circuit 60 selects input C,
Transition to the third preliminary ejection mode. The highest head drive frequency signal during the recording operation is input to input C, and at this time the multiplexer 26 selects input A.

Therefore, in the sixth preliminary ejection mode, the head H is driven at a predetermined digital value level and at the highest head drive frequency signal.

That is, the preliminary ejection operation is performed while gradually increasing the frequency.

Then, when the third preliminary ejection mode ends at time t5,
Switch circuit 60 selects input d. Since the input d is grounded, driving of the head is prohibited. Then, the capping motor 6 is driven, and the cap 3 is separated from the head H. Then, the multiplexer selects input B at time t6. In addition, the carriage motor 8 is driven, and the carriage 2
is transferred from the home position controller and preparation for recording operation is completed.

Then, at time t7, the line memory 22 is driven, and the switch circuit 60 selects the input C, and shifts to the recording mode. During the recording mode, the head drive circuit timing pulse and the digital image data from the line memory 22, or the converted value A, are input. Therefore, as shown in FIG. 5, the head H is driven according to the level of the digital image data D. The size of the ejected droplet (dot diameter) is controlled.

When the image data is at zero level, the head is not driven even if a timing pulse is present. Here, the most cylindrical level of the digital image data is a predetermined digital value P of the preset circuit.
Since it is set to match S, a high voltage is applied to the head HK at the time of preliminary ejection, so that the preliminary ejection can be carried out more completely.

When the recording operation is completed, the carriage 2 returns to the home position, the cap 2 comes into contact with the head, and the operation ends.

As explained above, since the head is driven at a low frequency during preliminary ejection, it is possible to quickly improve the characteristics of the head.

Furthermore, since the driving frequency of one head is increased from a low frequency to a high frequency during preliminary ejection, it is possible to more quickly raise the operating characteristics of the head to the maximum driving frequency during recording.

Moreover, since the head is driven at a high voltage level, ink can be ejected even if the ink at the tip of the head is slightly solidified9, and droplet formation due to clogging can be prevented.

In this embodiment, the drive frequency of the head is increased in steps, but it may be configured to increase continuously. Further, the voltage level during preliminary ejection may be set higher than the highest voltage level during recording operation.

In this embodiment, an inkjet head using a piezoelectric element is used as an example, but it can of course be applied to other types of heads, such as an inkjet head that uses a heating element to eject droplets using air bubbles. It is possible.

(Explanation of Effects) As explained in detail above, in the present invention, the frequency for driving the inkjet head during the preliminary ejection operation is set lower than the driving frequency during actual recording, so that the characteristics of the head can be quickly set up. becomes possible.

Therefore, it is possible to prevent the non-ejection of droplets without installing a complicated droplet detector, and it is possible to prevent deterioration of image quality.

[Brief explanation of the drawing]

Figure 1 is a top view of the inkjet printer of this embodiment.
Figure 2 is a control circuit diagram of the printer shown in Figure 1, and Figure 3 is a control circuit diagram of the printer shown in Figure 1.
Figure 4 shows a program flowchart of the control unit in Figure 4.
This figure is a timing diagram of each part of FIG. 2, and FIG. 5 is a diagram showing the relationship between the level of image data and the dot diameter. In the figure, H is an inkjet head, 2 is a carriage, 6 is a cap, 21 is a preset circuit, 22 is a line memory, 26 is a multiplexer, 25 is a head drive circuit as a drive means, 29 is a frequency divider, and 30 is a switch circuit. , 32 is a control unit, 63 is a start command switch, a multiplexer 23, and a branch unit 29. Switch circuit 60. The control section 62 constitutes preliminary ejection control means.

Claims (1)

[Claims] an inkjet head for ejecting minute droplets, a driving means for driving the head, and driving the head at a frequency lower than the maximum head driving frequency of the driving means when recording characters, images, etc., before the recording. An inkjet recording apparatus comprising a preliminary ejection control means for controlling the driving means.