Abstract:
An ink jet system printer of the charge amplitude controlling type includes a beam gutter for collecting ink droplets not contributing to the actual printing operation. An ink returning system is provided for returning the collected ink liquid to an ink liquid reservoir. An optical detection system is provided in the course of the ink returning system for detecting whether the ink liquid is properly collected by the beam gutter. When the ink liquid is not observed by the optical detection system for a period longer than a preselected period, a determination system develops a control signal for terminating the formation of the ink droplets.

Description:
BACKGROUND AND SUMMARY OF THE INVENTION 
     The present invention relates to an ink jet system printer of the charge amplitude controlling type and, more particularly, to a check system for detecting an abnormal ink issuance direction in an ink jet system printer. 
     Generally, an ink jet system printer of the charge amplitude controlling type includes a carriage travelling in a lateral direction. An ink droplet issuance unit is mounted on the carriage. A deflection system is employed to deflect travelling ink droplets in a vertical direction, thereby printing a desired symbol in a dot matrix fashion. The deflection amount must be accurately controlled to ensure a clean printing. It will be clear that the direction of the ink droplets emitted from the ink droplet issuance unit must be accurately controlled to ensure the accurate deflection operation. 
     Accordingly, an object of the present invention is to provide a check system for detecting the direction of the ink droplets emitted from an ink droplet issuance unit in an ink jet system printer of the charge amplitude controlling type. 
     Another object of the present invention is to provide a detection system for detecting the direction of the ink droplets which do not contribute to the actual printing operation in an ink jet system printer of the charge amplitude controlling type. 
     Other objects and further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. It should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 
     To achieve the above objects, pursuant to an embodiment of the present invention, a detection system is provided in the course of a recirculation path connected to a beam gutter for detecting whether ink liquid is properly collected by the beam gutter. If the ink liquid is not collected by the beam gutter for more than a preselected period of time, the detection system develops a control signal for indicating the abnormal issuance direction of the ink liquid emitted from the ink droplet issuance unit. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will be better understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, and wherein: 
     FIG. 1 is a schematic sectional view of an ink jet system printer of the charge amplitude controlling type of the prior art; 
     FIG. 2 is a waveform chart showing a charging signal applied to a charging tunnel included in the ink jet system printer of FIG. 1; 
     FIG. 3 is a schematic section view of an embodiment of an ink jet system printer of the charge amplitude controlling type of the present invention; 
     FIG. 4 is an enlarged sectional view of an ink liquid detection system included in the ink jet system printer of FIG. 3; 
     FIG. 5 is a schematic block diagram of a detection system of the present invention included in the ink jet system printer of FIG. 3; 
     FIGS. 6 and 7 are charts showing signals occurring within the detection system of FIG. 5; and 
     FIG. 8 is a flow chart for explaining an automatic control of the ink issuance direction is another embodiment of the ink jet system printer of the charge amplitude controlling type of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     An ink jet system printer of the charge amplitude controlling type generally includes an ink liquid reservoir 10 for containing ink liquid therein, an ink droplet issuance unit 12, an ink liquid supply conduit 14 and a supply pump 16 for supplying the ink liquid of a predetermined pressure to the ink droplet issuance unit 12 via the ink liquid supply conduit 14. 
     The ink droplet issuance unit 12 includes a nozzle for emitting ink droplets and an electromechanical transducer attached to the nozzle for vibrating the nozzle at a given frequency of an excitation signal which is developed from an oscillator 18. Thus, the nozzle emits the ink droplets at the given frequency. A charging tunnel 20 is disposed in front of the ink droplet issuance unit 12 for charging the ink droplets in accordance with the print information signal. The thus charged ink droplets are deflected while they pass through a high voltage constant electric field established by a pair of deflection electrodes 22 and 24. The deflected ink droplets are directed to a record receiving paper 26 supported by a platen 28. The deflection is conducted in the vertical direction. The above-mentioned ink droplet issuance unit 12, the charging tunnel 20 and the pair of deflection electrodes 22 and 24 are mounted on a carriage which is driven to reciprocate in the lateral direction, whereby desired symbols are printed on the record receiving paper 26 in the dot matrix fashion. 
     Ink droplets not contributing to the actual printing operation are neither charged nor deflected. The ink droplets not contributing to the actual printing operation are directed to a beam gutter 30. The ink liquid collected by the beam gutter 30 is returned to the ink liquid reservoir 10 via an ink liquid returning conduit 32 and a returning pump 34. 
     In a typical system, the nozzle included in the ink droplet issuance unit 12 has an orifice about 30 μφ through 50 μφ. The initial velocity of the ink droplets emitted from the ink droplet issuance unit 12 is about 18 m/sec. A preferred excitation signal frequency is about 50 KHz through 100 KHz. Therefore, the ink droplets are provided at the given excitation frequency, 50 KHz through 100 KHz. 
     FIG. 2 shows an example of the charging signal applied to the charging tunnel 20. The charging signal of FIG. 2 is for printing two columns of solid lines in 5×7 matrix format with interpolation droplets which are provided between each adjacent two ink droplets contributing to the actual printing operation. More specifically, the ink droplets charged to the zero level (0), normally not charged, are directed to the beam gutter 30 for recirculation purposes. The ink droplets charged to the first dot level (1) are directed to the seventh dot position in one column in the 5×7 dot matrix format. The ink droplets charged to the seventh dot level (7) are directed to the uppermost first dot position in one column in the 5×7 dot matrix format. 
     It will be clear from the foregoing description that the tip end of the beam gutter 30 should be located between the ink droplet position of the zero level (0) and the seventh dot position corresponding to the first dot level (1). If the direction of the emission of the ink droplets is deviated upward due to the unstability of the droplet formation condition, there is a possibility that the ink droplets charged to the zero level (0) will pass over the beam gutter 30 and reach the record receiving paper 26. This precludes the accurate printing and the stable operation of the ink jet system printer. Contrarily, when the direction of the ink droplet emission is deviated downward, there is a possibility that the ink droplets charged to the first dot level (1) will be caught by the beam gutter 30. This also precludes the accurate printing. The former condition is more serious in the ink jet system printer of the charge amplitude controlling type because the ink droplets not caught by the beam gutter 30 will damage the printer system. 
     The present invention is to detect the condition where the ink droplets charged to the zero level (0) pass over the beam gutter 30. FIG. 3 shows an embodiment of an ink jet system printer of the charge amplitude controlling type of the present invention. Like elements corresponding to those of FIG. 1 are indicated by like numerals. 
     A temporary ink container 36 is disposed in the ink liquid returning conduit 32 near the beam gutter 30. The temporary ink container 36 is made of a transparent material. A light emitting element 38 and a light responsive element 40 are disposed in a fashion to sandwich the temporary ink container 36. FIG. 4 shows, in detail, the relationships between the temporary ink container 36 and the light emitting element 38 and the light responsive element 40. 
     The light responsive element 40 is connected to a detection system shown in FIG. 5. The detection system includes a retriggerable one-shot multivibrator 42 of which an input terminal is connected to the output terminal of the light responsive element 40. The retriggerable one-shot multivibrator 42 develops a detection output indicating an abnormal emission direction of the ink liquid. 
     The suction rate of the returning pump 34 is selected higher than the developing rate of the supply pump 16. As already discussed above, the interpolation droplets are disposed between the adjacent two ink droplets contributing to the actual printing operation. Accordingly, in the normal operation mode, the ink liquid and the air appear alternatively in the temporary ink container 36 as shown in FIG. 4. More specifically, in the normal operation mode, the light beam emitted from the light emitting element 38 is repeatedly shielded by the ink liquid appearing in the temporary container 36 with a time interval of which period is determined by the droplet formation frequency, the volume of the temporary container 36 and the suction rate of the returning pump 34. When the light beam emitted from the light emitting element 38 is shielded by the ink liquid, the output level of the light responsive element 40 is reduced. 
     FIG. 6 shows an example of the output level of the light responsive element 40. The output level of the light responsive element 40 becomes low at every time when the ink liquid appears in the temporary ink container 36. The low level output signal of the light responsive element 40 functions to trigger the retriggerable one-shot multivibrator 42, whereby the retriggerable one-shot multivibrator 42 develops an output signal of the logic low. 
     When the ink droplets charged to the zero level (0) are not caught by the beam gutter 30, the output level of the light responsive element 40 is maintained at the high level as shown in the right part of FIG. 6. Thus, the retriggerable one-shot multivibrator 42 is not triggered for a period more than a preselected period T, as shown in FIG. 7. The output signal of the retriggerable one-shot multivibrator 42 bears the logic high as shown in the right part of FIG. 7 to indicate the abnormal direction of the ink liquid emitted from the ink droplet issuance unit 12. In response to the detection output derived from the detection system, the control system functions to terminate the operation of the supply pump 16 for terminating the ink droplet formation. 
     FIG. 8 shows an operation flow for automatically adjusting the direction of the ink droplets emitted from the ink droplet issuance unit 12. 
     For automatically adjusting the direction of the emitting ink droplets, the ink droplets of the zero level (0) are emitted from the ink droplet issuance unit 12. First, the maximum bias voltage is applied to the charge control circuit so that the ink droplets of the zero level (0) pass over the beam gutter 30. Then, the bias voltage applied to the charging tunnel 20 is gradually reduced till the detection system of FIG. 5 develops an output signal showing the normal operation condition. 
     It is preferable for ensuring the rapid response that the temporary ink container 36 is positioned near the beam gutter 30. 
     The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications are intended to be included within the scope of the following claims.