Method and apparatus for determining optimum ink drop formation-frequency in an ink jet printer

• US 5,940,101 A
• Filed: 07/08/1996
• Issued: 08/17/1999
• Est. Priority Date: 07/08/1996
• Status: Expired due to Fees

• Current Assignee: Silver Seiko Ltd.
• Original Assignee: Silver Seiko Ltd.
• Inventors: Mutoh, Masayuki
• Primary Examiner(s): Le, N.
• Assistant Examiner(s): TRAN, THIEN D
• Application Number:
  US08/676,445
• Time in Patent Office: 1,135 Days
• Field of Search: 347/78, 347/80, 347/81, 347/75, 347/76
• US Class Current: 347/78
• CPC Class Codes: B41J 2/12 testing or correcting charge or deflection

Abstract

The optimum excitation frequency for forming successive ink drops in an ink jet printer is determined by forming a sequence of ink drops at a plurality of different drop-formation frequencies and phases thereof and integrating a detected current representative of the value of the charge on the ink drops as a function of time for each the plural frequencies and phases thereof to create a corresponding plurality of waveforms. The frequency of the optimum waveform, which minimizes the undesired formation of satellite ink drops and undesired drop dispersion, is then selected for use during the next print mode. The optimum waveform is characterized by a single maxima and minima separated in phase by a value no greater than a predetermined maximum value.

Claims

1. A continuous jet type ink jet recording apparatus, comprising:

jet formation means for discharging pressurized ink as a continuous jet from a nozzle and successively disintegrating the continuous jet into ink drops of a uniform size in synchronism with excitation of an oscillator mounted on said nozzle;

charging means for selectively charging the ink drops;

deflection means for applying a deflection electric field perpendicular to a flying axis of the jet to an ink drop charged by said charging means to deflect the ink drop in a direction perpendicular to the jet flying axis;

separation means for intercepting a charged ink drop deflected by said deflection means and allowing a straightforwardly advancing non-charged ink drop to pass thereby;

variable frequency oscillation means for outputting an excitation signal for exciting said oscillator;

switch means for switching the deflection electric field by said deflection means on and off;

probe pulse generation means for generating a probe pulse signal in synchronism with the excitation signal outputted from said variable oscillation means in a condition wherein the deflection electric field is controlled to an off state by said switch means;

phase shifting means for shifting a phase of one of the excitation signal and the probe pulse signal with respect to a phase of the other of the excitation signal and the probe pulse signal;

a conductive drop catcher for catching a charged ink drop charged by the probe pulse signal generated by said probe pulse generation means and having passed by said separation means;

current detection means for detecting the charge of charged ink drops caught by said conductive drop catcher as an electric current value;

analog to digital conversion means for converting the electric current value detected by said current detection means into digital data; and

excitation frequency determination means for delivering an instruction to said variable frequency oscillation means to successively change an excitation frequency of the excitation signal to M stages, M being a positive integer, delivering another instruction to said phase shifting means to successively shift the phase of one of the excitation signal and the probe pulse signal with respect to the phase of the other of the excitation signal and the probe pulse signal by 2π

/N with the excitation frequency at each of the M stages, N being a positive integer, re-arranging the digital data obtained by said analog to digital conversion means from the conversion of the successive phases at each of the M stages and storing the thus re-arranged data as M jet current waveform data sets, extracting, based on the M sets of jet current waveform data thus stored, characteristics of each of the jet current waveforms at the M individual stages as a function of the maximum and minimum jet current values thereof and the phase shift between the maximum and minimum jet current values to determine an optimum excitation frequency having a phase difference between the maximum and the minimum jet current values less than a pre-selected value and delivering a further instruction to said variable frequency oscillation means to output an excitation signal of the so-determined optimum excitation frequency.

2. A continuous jet type ink jet recording apparatus as claimed in claim 1,

wherein said excitation frequency determination means extracts, from each of the M sets of jet current waveform data, a phase corresponding to a lowest value of the jet current, successively moves the phase in a direction in which the excitation signal is delayed with respect to the probe pulse signal to extract a phase with which the jet current exhibits a maximum value, further successively moves, if a difference between the phase with which the maximum value is exhibited and the phase corresponding to the minimum value is smaller than said pre-selected value, the phase in a direction in which the excitation signal is delayed with respect to the probe pulse signal to extract a phase with which the jet current exhibits a minimum value, and stores, if the phase with which the minimum value is exhibited is equal to the phase corresponding to the lowest value, a difference between the maximum value and the minimum value of the jet current as a contrast value at the excitation frequency, then searches the thus stored contrast values for a highest contrast value, and determines the excitation frequency corresponding to the highest contrast value as an optimum excitation frequency.

3. A continuous jet type ink jet recording apparatus as claimed claim 1, wherein said phase shifting means shifts the phase of the excitation signal while the phase of the probe pulse signal is fixed.

4. A continuous jet type ink jet recording apparatus as claimed in claim 1, wherein said phase shifting means shifts the phase of the probe pulse signal while the phase of the excitation signal is fixed.

5. A continuous jet type ink jet recording apparatus as claimed in claim 1, wherein said current detection means includes an integrator.

6. A continuous jet type ink jet recording apparatus, comprising:

n jet formation means each having a respective nozzle for discharging pressurized ink as a continuous jet therefrom and an oscillator mounted on the respective nozzle for successively disintegrating the continuous jet into ink drops of a uniform size in synchronism with excitation of the oscillator, n being an integer equal to or greater than 2;

n charging means each for selectively charging the ink drops;

deflection means for applying a deflection electric field perpendicular to flying axes of the jets to each ink drop charged by said charging means to deflect the ink drop in a direction perpendicular to the jet flying axis;

separation means for intercepting a charged ink drop deflected by said deflection means and allowing a straightforwardly advancing non-charged ink drop to pass thereby;

variable frequency oscillation means for outputting an excitation signal for commonly exciting the oscillator mounted on each respective nozzle;

switch means for switching the deflection electric field by said deflection means on and off;

probe pulse generation means for generating a probe pulse signal in synchronism with the excitation signal outputted from said variable frequency oscillation means in a condition wherein the deflection electric field is controlled to an off state by said switch means;

n phase shifting means each for shifting a phase of one of the excitation signal and the probe pulse signal with respect to a phase of the other of the excitation signal and the probe pulse signal;

a conductive drop catcher for catching a charged ink drop charged by the probe pulse signal generated by said probe pulse generation means and having passed by said separation means;

current detection means for detecting the charge of charged ink drops caught by said conductive drop catcher as an electric current value;

analog to digital conversion means for converting the electric current value detected by said current detection means into digital data; and

excitation frequency determination means for delivering, successively for each of said n jet formation means, an instruction to said variable frequency oscillation means to successively change an excitation frequency of the excitation signal to M stages, M being a positive integer, and then another instruction to the phase shifting means to successively shift the phase of one of the excitation signal and the probe pulse signal with respect to the phase of the other of the excitation signal and the probe pulse signal by 2π

/N with the excitation frequency at each of the M stages, N being a positive integer, rearranging the digital data obtained in regard to each of said jet formation means by said analog to digital conversion means from the conversion of the successive phases at each stage and storing the thus re-arranged data as nxM jet current waveform data sets, extracting, based on the nxM sets of jet current waveform data thus stored, characteristics of each of the jet current waveforms as a function of the maximum and minimum jet current values thereof and the phase shift between the maximum and minimum jet current values to determine an optimum excitation frequency having a phase difference between the maximum and the minimum jet current values less than a preselected value and delivering a further instruction to said variable frequency oscillation means to output an excitation signal of the so-determined optimum excitation frequency.

7. A continuous jet type ink jet recording apparatus as claimed in claim 6, wherein said excitation frequency determination means extracts, from each of the nxM sets of jet current waveform data, a phase corresponding to a lowest value of the jet current, successively moves the phase in a direction in which the excitation signal is delayed with respect to the probe pulse signal to extract a phase with which the jet current exhibits a maximum value, further successively move, if a difference between the phase with which the maximum value is exhibited and the phase corresponding to the minimum value is smaller than a pre-selected value, the phase in a direction in which the excitation signal is delayed with respect to the probe pulse signal to extract a phase with which the jet current exhibits a minimum value, and stores, if the phase with which the minimum value is exhibited is equal to the phase corresponding to the lowest value, a difference between the maximum value and the minimum value of the jet current as a contrast value at the excitation frequency, then searches the thus stored contrast values for the lowest values for the individual jet formation means from among the contrast values whose excitation frequencies are common among said jet formation means, searches the thus obtained minimum values of the jet current for the contrast value, and determines the excitation frequency corresponding to the contrast value as an optimum excitation frequency.

8. A continuous jet type ink jet recording apparatus as claimed in claim 6, wherein said phase shifting means shifts the phase of the excitation signal while the phase of the probe pulse signal is fixed.

9. A continuous jet type ink jet recording apparatus as claimed in claim 6, wherein said phase shifting means shifts the phase of the probe pulse signal while the phase of the excitation signal is fixed.

10. A continuous jet type ink jet recording apparatus as claimed in claim 6, wherein said current detection means includes an integrator.

11. A continuous jet type ink jet recording apparatus, comprising:

n jet formation means each for discharging pressurized ink as a continuous jet from a nozzle and successively disintegrating the continuous jet into ink drops of a uniform size in synchronism with excitation of an oscillator on said nozzle, n being an integer equal to or greater than 2;

n charging means each for selectively charging the ink drops;

deflection means for applying a deflection electric field perpendicular to the flying axes of the jets to each ink drop charged by said charging means to deflect the ink drop in a direction perpendicular to the jet flying axis;

separation means for intercepting a charged ink drop deflected by said deflection means and allowing a straightforwardly advancing non-charged ink drop to pass thereby;

variable frequency oscillation means outputting an excitation signal for commonly exciting the oscillator mounted on each respective nozzle;

switch means for switching the deflection electric field by said deflection means on and off;

probe pulse generation means for generating a probe pulse signal in synchronism with the excitation signal outputted from said variable frequency oscillation means in a condition wherein the deflection electric field is controlled to an off state by said switch means;

n phase shifting means each for shifting a phase of one of the corresponding excitation signal and the probe pulse signal with respect to a phase of the other of the corresponding excitation signal and the probe pulse signal;

n conductive drop catchers each for catching a charged ink drop charged by the probe pulse signal generated by said probe pulse generation means and having passed by said separation means;

n current detecting means each for detecting the charge of charged ink drops caught by the corresponding conductive drop catcher as an electric current value;

n analog to digital conversion means for converting the electric current values detected by said n current detection means into digital data; and

excitation frequency determination means for delivering, simultaneously for said n jet formation means, an instruction to said variable frequency oscillation means to successively change an excitation frequency of the excitation signal to M stages, M being a positive integer, and then another instruction to each of said n phase shifting means to successively shift the phase of one of the excitation signal and the probe pulse signal with respect to the phase of the other of the excitation signal and the probe pulse signal by 2π

/N with the excitation frequency at each of the M stages, N being a positive integer, re-arranging the digital data obtained in regard to each of said jet formation means by said analog to digital conversion means from the conversion of the successive phases at each stage and storing the thus re-arranged data as nxM jet current waveform data sets, extracting, based on the nxM sets of jet current waveform data thus stored, characteristics of the jet current waveforms as a function of the maximum and minimum jet current values thereof and the phase shift between the maximum and minimum jet current values to determine an optimum excitation frequency having a phase difference between the maximum and the minimum values less than a pre-selected value and delivering a further instruction to said variable frequency oscillation means to output an excitation signal of the so determined optimum excitation frequency.

12. A continuous jet type ink jet recording apparatus as claimed in claim 11, wherein said excitation frequency determination means extracts, from each of the nxM sets of jet current waveform data, a phase corresponding to a lowest value of the jet current, successively moves the phase in a direction in which the excitation signal is delayed with respect to the probe pulse signal to extract a phase with which the jet current exhibits a maximum value, further successively moves, if a difference between the phase with which the maximum value is exhibited and the phase corresponding to the minimum value is smaller than a pre-selected value, the phase in a direction in which the excitation signal is delayed with respect to the probe pulse signal to extract a phase with which the jet current exhibits a minimum value, and stores, if the phase with which the minimum value is exhibited is equal to the phase corresponding to the lowest value, a difference between the maximum value and the minimum value of the jet current as a contrast value at the excitation frequency, then searches the thus stored contrast values for the lowest values for the individual jet formation means from among the contrast values whose excitation frequencies are common among said jet formation means, searches the thus obtained minimum contrast values of the jet current for the highest contrast value, and determines the excitation frequency corresponding to the highest contrast value as an optimum excitation frequency.

13. A continuous jet type ink jet recording apparatus as claimed in claim 11, wherein said phase shifting means shifts the phase of the excitation signal while the phase of the probe pulse signal is fixed.

14. A continuous jet type ink jet recording apparatus as claimed in claim 11, wherein said phase shifting means shifts the phase of the probe pulse signal while the phase of the excitation signal is fixed.

15. A continuous jet type ink jet recording apparatus as claimed in claim 11, wherein said current detection means includes an integrator.

16. An optimum excitation frequency setting method, comprising the steps of:

discharging pressurized ink as a continuous jet from a nozzle and successively disintegrating the continuous jet into ink drops of a uniform size in synchronism with excitation of an oscillator mounted on said nozzle;

generating a probe pulse signal in synchronism with an excitation signal for said oscillator;

charging an ink drop with the probe pulse signal thus generated;

detecting the charge of thus charged ink drops as an electric current value;

converting the thus detected electric current value into digital data; and

successively changing an excitation frequency of the excitation signal to M stages, M being a positive integer, successively shifting the phase of one of the excitation signal and the probe pulse signal with respect to the phase of the other of the excitation signal and the probe pulse signal by 2π

/N with the excitation frequency at each of the M stages, N being a positive integer, re-arranging the digital data from the conversion of the successive phases at each stage and storing the thus re-arranged data as nxM jet current waveform data sets, extracting, based on the M sets of jet current waveform data thus stored, characteristics of the jet current waveforms at the individual stages to determine an optimum excitation frequency as a function of the maximum and minimum jet current values and the phase difference between the maximum and minimum jet current values, and outputting an excitation signal of the so-determined optimum excitation frequency.

17. An optimum excitation frequency setting method as claimed in claim 16, wherein the last mentioned step of successively changing an excitation frequency of the excitation signal includes the steps of extracting, from each of the M sets of jet current waveform data, a phase corresponding to a lowest value of the jet current, successively moving the phase in a direction in which the excitation signal is delayed with respect to the probe pulse signal to extract a phase with which the jet current exhibits a maximum value, further successively moving, if a difference between the phase with which the maximum value is exhibited and the phase corresponding to the minimum value is smaller than a pre-selected value, the phase in a direction in which the excitation signal is delayed with respect to the probe pulse signal to extract a phase with which the jet current exhibits a minimum value, and storing, if the phase with which the minimum value is exhibited is equal to the phase corresponding to the lowest value, a difference between the maximum value and the minimum value of the jet current as a contrast value at the excitation frequency, then searching the thus stored contrast values for a highest contrast value, and determining the excitation frequency corresponding to the highest contrast value as an optimum excitation frequency.

18. An optimum excitation frequency setting method, comprising the steps of:

discharging pressurized ink as a continuous jet from each of n nozzles and successively disintegrating the continuous jet into ink drops of a uniform size in synchronism with excitation of an oscillator mounted on each of said nozzles, n being an integer equal to or greater than 2;

generating a probe pulse signal in synchronism with an excitation signal for said oscillator;

charging an ink drop with the probe pulse signal thus generated;

detecting the charge of the charged ink drops as an electric current value;

converting the detected value into digital data; and

successively changing, successively for each of said n nozzles, an excitation frequency of the excitation signal to M stages, M being a positive integer, and successively shifting the phase of one of the excitation signal and the probe pulse signal with respect to the phase of the other of the excitation signal and the probe pulse signal by 2π

/N with the excitation frequency at each of the stages, N being a positive integer, re-arranging the digital data obtained in regard to each of said n nozzles from the conversion of the successive phases at each stage and storing the rearranged data as nxM jet current waveform data sets, extracting, based on the nxM sets of jet current waveform data thus stored, characteristics of the jet current waveforms at the M stages to determine an optimum excitation frequency as a function of the maximum and minimum jet current values and the phase difference between the maximum and minimum jet current values, and outputting an excitation signal of the optimum excitation frequency.

19. An optimum excitation frequency setting method as claimed in claim 18, wherein said successively changing step includes the steps of extracting, from each of the nxM sets of jet current waveform data, a phase corresponding to the lowest value of the jet current, successively moving the phase in a direction in which the excitation signal is delayed with respect to the probe pulse signal to extract a phase with which the jet current exhibits a maximum value, further successively moving the phase in a direction in which the excitation signal is delayed with respect to the probe pulse signal to extract a phase with which the jet current exhibits a minimum value, and storing, if the phase with which the minimum value is exhibited is equal to the phase corresponding to the lowest value, a difference between the maximum value and the minimum value of the jet current as a contrast value at the excitation frequency, then searching the stored contrast values for the lowest values for the individual jet formation means from among the contrast values whose excitation frequencies are common among said jet formation means, searching the obtained minimum values of the jet current for a highest contrast value, and determining the excitation frequency corresponding to the highest contrast value as an optimum excitation frequency.