JP4610935B2 - Inkjet printer - Google Patents

Description

  The present invention relates to an ink jet printing apparatus that ejects ink using a piezo element (electromechanical conversion element).

  A conventional piezo-type inkjet printing apparatus cannot apply an independent drive waveform to each piezo element constituting the ink nozzle. Therefore, in order to add gradation to the printing result, ink is ejected once at a printing timing by a method called multi-drop, and by the number of ejections to one pixel by ejection at a plurality of printing timings. The gradation expression of printing was obtained by controlling the amount of printing.

For example, according to the technology disclosed in Patent Document 1 as this type of ink jet printing apparatus, as shown in FIG. 1, each one of a large number of piezoelectric elements PZT _{1 to} PZT _m is a common electrode Com, The other electrode is an individual electrode that is individualized for each of the piezo elements PZT _{1 to} PZT _m . A waveform generation circuit b is connected to the common electrode Com through a low impedance output circuit a. On the other hand it is connected to the output terminals _D0 1 ~D0 _m control logic c to each individual terminal of each piezoelectric element _PZT 1 _{~PZT m.}

The waveform generation circuit b adjusts the drive voltage Vp of the drive waveform in addition to the drive timing signal (STB) that determines the timing for generating the drive waveform from the control signal generator d constituted by the microcomputer CPU. A Vp control signal (SVp _{1 to} SVp ₃ ) for selection, a Tr control signal (STr _{1 to} STr ₃ ) for adjusting and selecting the rising time constant Tr of the drive waveform, and the like are input. Three drive waveforms P _{1 to} P ₃ having different drive voltages Vp and different waveform heights are output from the impedance output circuit a to the common electrode Com.

On the other hand, the m-bit shift register c ₂ of the control logic c receives the print data signal and the print data clock signal from the control signal generator d, and prints it in the m-bit latch c ₁ that selects ₁ to m bits. A data latch signal is input. In this case, m is 64, for example.

As a result, an m-bit print data signal is input to the m-bit shift register c ₂ from the control signal generator d, latched with the latch signal, and the waveform generation circuit b is operated with the drive timing signal (STB). when allowed to generate a driving waveform P ₁ and the other terminal of the one of PZT of this time to the specified discharge at m-bit latch c ₁ D0 ₁ ~D0 _m becomes GND level, is this designated PZT drive waveform P ₁ is applied to the ink in an amount corresponding to the drive waveform P ₁ is adapted to be ejected from the nozzle of the PZT.

Similarly, a drive waveform of P ₂ or P ₃ is generated, and a drive waveform of P ₂ or P ₃ is applied to PZT for which ejection is designated by the m-bit latch, and this drive waveform P _{2 is} supplied from the nozzle of this PZT. or the amount of ink corresponding to P ₃ is adapted to be discharged.

  The drive waveform of each nozzle to PZT at this time is as shown in FIG. 2, so that the same waveform is applied although the number of drive waveforms at the time of one-time discharge is different from that at the time of two-time and three-time discharge. It has become.

Japanese Patent Laid-Open No. 10-138475

  As described above, in the above prior art, when printing is performed while performing gradation control, a technique called multidrop is used, and if the amount of ink ejected from a specific nozzle is the same, the same A drive waveform is applied.

  However, the amount of ink ejected when ink is sucked into the ink chamber of the nozzle head and ejected is affected by the volume of the ink chamber and the amount of change with respect to the voltage (drive waveform) applied to the piezo element. .

  The volume of the ink chamber with respect to each nozzle of the nozzle head often varies depending on the manufacturing process thereof, and therefore, even if the same drive waveform is applied to the piezo element, the same ink amount is not necessarily discharged from each nozzle. Is not limited. In particular, when performing gradation printing, the amount of ink ejected from each nozzle is controlled to differ depending on the degree of gradation. At this time, as described above, the amount of ink ejected from the nozzle is controlled. Otherwise, the amount of ink ejected from a specific nozzle may be larger or smaller than the ink ejection amount of the specified gradation and become the same as another adjacent gradation.

  For this reason, the above-described conventional technology cannot provide high-precision gradation printing, and cannot provide high-quality printed matter.

SUMMARY OF THE INVENTION An object of the present invention is to provide an ink jet printing apparatus capable of accurately discharging an amount of ink corresponding to the print gradation of each nozzle regardless of the variation in the volume of the ink chamber by solving the problems of the prior art. In the ink jet printing apparatus in which printing is performed by ejecting ink from a plurality of nozzles using piezoelectric elements, a drive waveform of each piezoelectric element is generated for each piezoelectric element of each nozzle. Connect the waveform generation circuit independently,
A control signal generator for inputting a drive timing signal to each waveform generator is connected to each of the waveform generators. In addition to the drive timing signal from the control signal generator, a print data latch signal and a print signal are printed. A plurality of data including a data clock signal, a multi- bit print data signal including a gradation according to the magnitude of the ink ejection amount, and a gradation for correcting the printing density by the print data signal including a gradation according to the magnitude of the ink ejection amount A bit print data signal is output, and a control logic including a latch to which the print data latch signal is input and a shift register to which the print data clock signal is input is provided for the number of bits of the print data signal. the print data signals of the respective bits inputs separately to the shift register of the control logic, each bit from the control logic A print data latch signal the print data signal to be inputted to each of waveform generating circuits triggered, the print data signal containing gradation by size of the ink discharge amount, is input from the control logic in each waveform generating circuit As a result, each waveform generation circuit generates a drive waveform based on this print data signal, supplies a corresponding amount of ink to each piezo element, performs printing, detects the density of this print, and detects this by the print data signal containing a tone to correct the print density in accordance with the print shade and input from the respective waveform generation circuits each control logic, the print data signal including a tone due to the magnitude of the ink discharge amount The print density is corrected.

In the above-described ink jet printing apparatus, the print data signal including the gradation based on the magnitude of the ink discharge amount output from the control signal generator is 2 bits, and the density of the print based on the print data signal including the gradation based on the magnitude of the ink discharge amount The print data signal including the gradation for correcting the correction is assumed to be 2 bits, and each gradation based on the print data signal obtained by combining each two bits is input from the control logic to each piezo element via the waveform generation circuit. I made it.

According to the present invention, even at one printing timing, the upper part of each printing is independently input via the waveform generation circuit provided independently for each piezo element of each nozzle, and printing is performed according to the magnitude of the ink discharge amount. When the prints printed based on the data signal are shaded, the print data for correcting this is output according to the degree of the shade, whereby the volume of the ink chamber of each nozzle varies, Further, even if there is a change in the voltage (drive waveform) applied to the piezo element, an amount of ink corresponding to the printing gradation can be accurately ejected from each nozzle.

  The best mode for carrying out the present invention will be described with reference to FIG.

In the figure, PZT _{1 to} PZT _m denote piezoelectric elements (electrical elements) connected to the ink chambers of each nozzle in order to drive ink ejection from _{1 to m} nozzles provided in the nozzle head of the inkjet recording head. Mechanical conversion element). In the following description, this may be indicated synonymously with each nozzle. One terminal of each of the piezo elements PZT _{1 to} PZT _m is grounded to GND, and the other terminal is a low impedance output circuit 1 ₁ to 1 _m of the waveform driving circuit A and a waveform generation circuit 2 _1. It is connected to the control signal generator 3 constituted by the microcomputer CPU through ˜2 _m . A drive timing signal (STB) is input from the control signal generation unit 3 to each of the waveform generation circuits 2 ₁ to 2 _m . Note that m represents the number of nozzles, for example, 64.

In the figure, reference numerals 4 ₁ to ₄ 4 denote control logics each composed of an m-bit shift register 4a and an m-bit latch 4b. A print data latch signal is input from the control signal generator 3 to each m-bit latch 4b of each of the control logics 4 ₁ to ₄ 4, and a print data clock signal is input to the m-bit shift register 4a. It is like that.

Further, in the control signal generation unit 3, print information including gradations is transferred to 4-bit print data signals D0 ₁ to _m , D1 ₁ to _m , and D2 ₁ to _m to the waveform generation circuits 2 ₁ to 2 _{m of the} nozzles. , D3 ₁ ~ are converted to _m, each print data signals D0 bit of the first control logic 4 ₁ m-bit shift register 4a, D1 each print data signal bit second control logic 4 ₂ In the m-bit shift register 4a, each D _2- bit print data signal is transferred to the m-bit shift register 4a of the third control logic 43, and each D _3- bit print data signal is transferred to the m bit of the _fourth control logic 44. Each is input to the register 4a.

  Here, in the 4-bit print data signal, the print data signals D0 and D1 are defined as print data including gradation as shown in Table 1.

  Further, the other print data signals D2 and D3 are defined as print data including gradation as shown in Table 2.

The drive waveforms of the piezo elements PZT _{1 to} PZT _m in which the gradations 0 to 3 by the print data signal combining the two bits D0 and D1 shown in Table 1 are input via the waveform generation circuit are as follows: As shown in FIG. 4, the height of the driving waveform of, for example, the first piezo element PZT ₁ to which the gradation 0 is input is “0”, and the second piezo element PZT ₂ to which the gradation 1 is input. fourth piezoelectric element height "small" and the driving waveform, the height of "medium" and the third drive waveform of the piezoelectric element PZT ₃ gradation 2 is input, the tone 3 is input The height of the drive waveform of PZT ₃ is “large”, and an amount of ink corresponding to the height of the drive waveform is ejected from each piezo element.

In the above-described configuration, the print information including gradation is converted into print information of 4 bits (D0, D1, D2, D3) by the control signal generation unit 3, and the control logic 4 ₁ to 4 corresponding to each bit. ₄ is input. The print information _D0- 1 of each control logic _{4 1 ~4 4, D1- 1,} D2- 1, D3- 1 is the first waveform generating circuit _{2 1,} and _{D0- 2,} D1- 2, D2- ₃ , _D3-4 of the print signal is in the second waveform generating circuit _{2 2} are similarly _D0- m _inputs, D1- _m, D2- m, _D3-m is the m-th waveform shaping circuit 2m or less.

The drive waveform of each gradation based on the print data signals D0 and D1 starts each sequence with a print data latch signal input to each of the control logics 4 ₁ to 4 ₄ as a trigger. Each drive source is output during the rise of the drive timing signal (STB).

The drive waveform for each gradation by the print data signals D0 and D1 is individually applied to the waveform generation circuits 2 ₁ to 2 _m of each piezo element, and is thus supplied to each piezo element PZT ₁ to PZT _m (inhalation). The ink is supplied in the indicated amount regardless of the volume difference between the piezo elements PZT _{1 to} PZT _m .

Therefore, there is a variation in the volume of the ink chamber of the nozzle head driven by the piezo element. For example, when the volume is larger than the design value, even if the amount of ink controlled to each of the above gradations 0 to 3 is supplied to this. The amount of ink ejected from the ink nozzles is not ejected by a predetermined amount, so that the print density is lighter than the specified density, and the print when the ink chamber is smaller than the design value is dark. The density of printing at each gradation 0, 1, 2, 3 by each ink nozzle is detected visually or by a density detector, and the density is “normal”, “light”, “lighter”, Four types of “dark” concentrations are detected. At this time, the print density similarly changes even when there is a change in the drive waveform (voltage) applied individually to each of the piezo elements PZT _{1 to} PZT _m .

Then, for example, the gradation of the printing by the first nozzle, for example when light is by its degree, based on Table 2 to the waveform generating circuit 2 ₁ In addition to the printing information of the D0, D1, 0 bits inputting Bruno D2- ₁ and the _D3-1 of 1-bit D3, or 1 bit D2- ₁ and the 1-bit _D3-1 in the waveform generating circuit _{2 1.} As a result, the waveform of gradation 3 shown in FIG. 4 is superimposed on the waveform of “many” or “more” shown in FIG. 5 to increase the ink discharge amount, and printing by the first nozzle is performed. It becomes darker and is corrected from the above-mentioned light state.

Further, overlapping the waveform in the case of "less" the printing is shown in FIG. 5 "dark" was sometimes 0 input the D2- ₁ and 0 bits _D3-1 bit correcting density of the print.

  Note that the driving waveform at this time has a higher peak value than the waveform of gradation 2. Similarly, for example, the peak value in the case of “less” in the gradation 2 is higher than the gradation 1, and is lower than the peak value of the gradation 3 in the case of “more”.

FIG. 6A shows the operation timing of the control signal generator 3, and the drive timing signal (STB) is output at, for example, 10 KHz. In the first half including the data setting unit, as shown in FIG. 6B. In addition, print information D3, D2, D1, and D0 for each piezo element are output as the print data clock signal is transmitted. Then, after each print information is inputted to the shift register 4b of each control logic 4 ₁ to 4 ₄ , a print data latch signal is inputted and latched.

  As described above, in this embodiment, the drive waveform considering the volume of the ink chamber of each nozzle and the amount of shift with respect to the print information applied to the piezo element according to the print gradation of each nozzle is set to each nozzle, that is, piezo. Applied independently to the element.

It is a block diagram which shows the conventional nozzle head drive control part. It is explanatory drawing which shows the drive waveform by the conventional nozzle head drive control part. It is a block diagram which shows the nozzle drive control part which concerns on this invention. It is explanatory drawing which shows the drive waveform by the nozzle drive control part which concerns on this invention. It is explanatory drawing which shows a correction | amendment waveform. (A), (b) is a timing chart which shows the output of each information signal in the nozzle drive control part in this invention.

Explanation of symbols

A: Waveform drive circuit, PZT _{1 to} PZT _m ... Piezo element, 1 ₁ to 1 _m ... Low impedance output circuit, 2 ₁ to 2 _m ... Waveform generation circuit, 3 ... Control signal generator, 4 ₁ to 4 ₄ ... Control Logic, 4a ... m bit shift register, 4b ... m bit latch.

Claims (2)

In an inkjet printing apparatus that performs printing by ejecting ink from a plurality of nozzles using piezoelectric elements,
A waveform generation circuit that generates a drive waveform for each piezo element is connected independently for each piezo element of each nozzle,
A control signal generator for inputting a drive timing signal to each waveform generation circuit is connected to each waveform generation circuit,
In addition to the drive timing signal from the control signal generator, a print data latch signal, a print data clock signal, a multi- bit print data signal including a gradation depending on the magnitude of the ink discharge amount, and the ink discharge amount Output a multi- bit print data signal that includes gradation that corrects the print density of the print data signal that includes gradation depending on the size.
A control logic including a latch for inputting the print data latch signal and a shift register for inputting the print data clock signal is provided for the number of bits of the print data signal.
The print data signal of each bit is individually input to the shift register of each control logic,
The print data signal of each bit from each control logic is input to each waveform generation circuit using the print data latch signal as a trigger,
Each waveform generation circuit generates a drive waveform based on this print data signal by inputting a print data signal including gradations based on the magnitude of the ink discharge amount to each waveform generation circuit from each control logic. A specified amount of ink is supplied to each piezo element to perform printing, the density of this printing is detected, and a print data signal including a gradation that corrects this printing density according to the detected density of printing is output to each control logic. type more each waveform generating circuit, an ink jet printing apparatus being characterized in that so as to correct the density of the printed by the print data signal including a tone due to the magnitude of the ink discharge amount. The print data signal including the gradation based on the magnitude of the ink discharge amount output from the control signal generator is 2 bits, and includes the gradation for correcting the print density by the print data signal including the gradation based on the magnitude of the ink discharge amount. The print data signal is composed of 2 bits, and each gradation of the print data signal obtained by combining two bits is input from the control logic to each piezo element via the waveform generation circuit. The ink jet printing apparatus according to claim 1.

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