Inkjet recording device and method for controlling inkjet recording device

Abstract

The present invention is such that: a composite detector connected to a gutter includes a minute charge amount detecting unit for detecting a minute charge amount of ink particles collected in the gutter, and an ink retention detecting unit for detecting retention of the ink particles; and a control part operates the composite detector as the minute charge amount detecting unit or the ink retention detecting unit on the basis of the minute charge amount.

Description

Inkjet recording apparatus and method for controlling the inkjet recording apparatus

[0001] The present invention relates to an inkjet printing apparatus and a method for controlling the inkjet printing apparatus.

[0002] A typical continuous-jet, charge-controlled inkjet recording device vibrates the ink ejected from the nozzle to generate ink particles (ink droplets). Of the generated ink particles, those used for printing are charged and deflected, and then land on the print surface to form characters. Ink particles not used for printing are not charged or deflected, but are collected in a gutter located opposite the nozzle and returned to an ink container by an ink recovery pump for reuse.

[0003] Conventionally, when ink particles are collected from the gutter, the surrounding air is also collected along with the ink particles. The collected ink particles and air are mixed in the ink collection path, and the solvent components in the ink particles volatilize into the air.

[0004] The air containing the evaporated solvent reaches the ink container and is then released from the ink container into the atmosphere. The greater the amount of air that is sucked in and collected along with the ink particles, the greater the amount of solvent that evaporates from the ink particles, and the greater the amount of solvent consumed to replenish the evaporated solvent.

[0005] One example of a technology for reducing solvent consumption to address the above problem is disclosed in Patent Document 1. Patent Document 1 states that "the pressure value generated in the ink recovery path is detected, and the pressure value of the pressure generating means is controlled by the control unit in accordance with the detected pressure value."

[0006] Also, there is Patent Document 2, which states that "the circulation unit is provided with a plurality of detectors, and the control unit detects the ink retention state in the circulation unit based on a plurality of detection signals detected by the plurality of detectors."

[0007] JP 2014-065203 A JP 2017-164964 A

[0008] The technology disclosed in Patent Document 1 estimates the ink recovery state from the pressure on the recovery path and controls the recovery pump. In the recovery path, ink and air are mixed, and installing a pressure gauge on this path will cause air to get into the pressure gauge, making it impossible to accurately measure the pressure and thus to accurately determine the state of the ink. Another problem is that installing a pressure gauge requires additional costs.

[0009] Furthermore, with the technology disclosed in Patent Document 2, in order to detect ink overflow, multiple detection tubes must be installed in multiple recovery paths, and the resistance between the terminals of each tube must be detected to determine whether ink has overflowed. However, installing multiple tubes within the print head increases the size of the print head, making it difficult to arrange them within the print head.

[0010] SUMMARY OF THE INVENTION An object of the present invention is to provide an ink jet recording apparatus that can reduce the cost and space required for an ink accumulation detection mechanism and achieve stable ink recovery.

[0011] An inkjet recording device according to one aspect of the present invention comprises a nozzle that vibrates ink to eject it as ink droplets, a charging electrode that charges the ink droplets, a gutter that captures and collects the ink droplets that are not used for printing, a composite detector connected to the gutter, a recovery pump that generates pressure in an ink recovery path connected to the composite detector, and a control unit that performs predetermined control related to printing, wherein the composite detector comprises a minute charge amount detection unit that detects the minute charge amount of the ink droplets collected in the gutter, and an ink accumulation detection unit that detects the accumulation of the ink droplets, and the control unit operates the composite detector as either the minute charge amount detection unit or the ink accumulation detection unit based on the minute charge amount.

[0012] According to one aspect of the present invention, it is possible to provide an inkjet recording apparatus that can reduce the cost and space of an ink accumulation detection mechanism and achieve stable ink recovery.

[0013] FIG. 1 is a configuration diagram showing the overall configuration of an inkjet recording apparatus. FIG. 2 is a perspective view showing the principle of an inkjet recording apparatus. FIG. 3 is a diagram showing the circulation path configuration of an inkjet recording apparatus. FIG. 4 is a diagram showing the control configuration of an inkjet recording apparatus according to an embodiment of the present invention. FIG. 5 is a diagram showing the circulation path of an inkjet recording apparatus according to an embodiment of the present invention. FIG. 6 is a diagram showing the internal connections of a composite detector of an inkjet recording apparatus according to an embodiment of the present invention. FIG. 7 is a conceptual diagram showing the relationship between detection voltage and pump frequency of an inkjet recording apparatus according to an embodiment of the present invention. FIG. 8 is a diagram showing a control flow for switching detection mechanisms in an inkjet recording apparatus according to an embodiment of the present invention. FIG. 9 is a diagram showing a control flow for determining the frequency of a recovery pump in an inkjet recording apparatus according to an embodiment of the present invention.

[0014] The following describes embodiments of the present invention with reference to the accompanying drawings. Note that the present invention is not limited to the following embodiments, and various modifications and applications within the technical concept of the present invention are also included within its scope.

[0015] The configuration of a continuous jet charge control type ink jet recording apparatus to which the present invention is applied will be briefly described with reference to FIG.

[0016] 1, the print content is determined using an input unit on a display 2 provided on a main body 1 of an inkjet recording device 100. The determined print content is printed on a print target 90 being transported by transport means 5 such as a belt conveyor by continuously ejecting ink droplets from a print head 4. The inkjet recording device main body 1 supplies ink to the print head 4 and controls its operation via a cable 3.

[0017] The operating principle of the inkjet recording apparatus 100 will now be described. As shown in Figure 2, ink in an ink container 15 is sucked and pressurized by a pump 16 to form an ink pillar 7, which is then ejected from a nozzle 8. The nozzle 8 is equipped with an electrostrictive element 9, which applies vibrations to the ink at a predetermined frequency, thereby turning the ink pillar 7 ejected from the nozzle 8 into droplets. The number of ink particles 11 generated in this way is determined by the frequency of the excitation voltage applied to the electrostrictive element 9, and is the same number as that frequency.

[0018] The ink jet head also includes a charging electrode 10 that applies a charge to the ink droplets, a positive deflection electrode 12 that deflects the direction of flight of the charged ink droplets, and a negative deflection electrode 13. The positive deflection electrode 12 and the negative deflection electrode 13 form an electric field for deflecting the charged ink droplets.

[0019] The ink droplets used for printing receive a negative charge when a positive voltage is applied to the charging electrode 10, and as they fly through the electric field formed by the positive deflection electrode 12 and the negative deflection electrode 13, they are deflected toward the positive deflection electrode 12 and land on the object 90 to be printed.

[0020] Furthermore, a gutter pipe 14 (hereinafter referred to as a gutter) is provided to collect ink droplets that are not charged and are not used for printing, and the ink collected by the gutter 14 is supplied again to the nozzle 8 by a pump 16.

[0021] FIG. 3 is an explanatory diagram showing the overall path configuration of the inkjet recording apparatus 100.

[0022] The main body 1 is provided with a main ink container 15 that holds circulating ink, and the main ink container 15 is provided with a liquid level sensor 18 that detects whether the liquid in the main ink container 15 has reached a reference liquid level, which is the appropriate amount to be held inside.

[0023] The main ink container 15 is sucked and pressurized by a circulation pump 20 through a path 101 equipped with an electromagnetic valve 19 for circulating ink from the nozzle 8, and by opening an electromagnetic valve 21, ink that has not been atomized flows into a path 102, and the pressure applied to the ink is detected by a pressure sensor 22 and displayed on the screen.

[0024] This path also includes a path where ink is filtered from the main ink container 15 by a filter 23, passes through a viscosity measuring device 24, which is a drop type viscometer for measuring the viscosity of the ink, and an electromagnetic valve 25 that opens and closes the path, and joins with this path. Here, the viscosity of the ink in the main ink container 15 is measured.

[0025] The solenoid valve 26, which is connected to the main ink container 15 via a path 103, is connected via a path 115 to a pump 27, which is used to suck and pump ink and solvent. The pump 27 is then connected via a path 104 to a filter 28, which removes foreign matter from the ink column.

[0026] The filter 28 is connected to an electromagnetic valve 29 that sets the pressure of the ink pumped from the pump 27 via a path 105 to an appropriate pressure for printing.

[0027] The solenoid valve 29 is connected via a path 106 through the conduit 3 to a solenoid valve 30 which is a switching valve for ink and solvent provided in the print head 4, and to a nozzle 8 which has an ejection port for ejecting ink.

[0028] A charging electrode 10 is arranged in the ink ejection direction from the nozzle 8, and charges the ink droplets 11 ejected from the nozzle 8 with an amount of charge corresponding to the character information to be printed on the droplets. Deflection electrodes 12 and 13 are arranged in the flight direction of the ink droplets 11 charged by the charging electrode 10, and generate an electric field to deflect the charged ink droplets 11.

[0029] A gutter 14 is arranged on the side of the ink droplets 11 in the direction of flight to capture the ink droplets 11 that are not used for printing and therefore are not charged or deflected and fly in a straight line.

[0030] The gutter 14 is connected via a path 107 passing through the conduit 3 to a filter 31 installed in the main body 1 that removes foreign matter mixed in the ink column, and the filter 31 is connected via a path 108 to an electromagnetic valve 17 that opens and closes the path. The electromagnetic valve 17 is connected to a pump 32 that sucks up the ink particles 10 captured by the gutter 14, and the pump 32 collects the ink particles 11 sucked up via path 101 into the main ink container 15.

[0031] The main body 1 is also provided with a solvent container 33 that stores a solvent for eliminating ink contamination occurring in the nozzles 8 and for adjusting the ink concentration, and the solvent container 33 is connected to a pump 34 that sucks and pressure-feeds the solvent via a path 110. The pump 34 is also connected to an electromagnetic valve 35 that opens and closes the path via a path 111, and the electromagnetic valve 35 is connected to the main ink container 15 via a path 112.

[0032] Furthermore, the main body 1 is provided with an auxiliary ink container 34 that holds refill ink, and the auxiliary ink container 34 is connected via a path 113 to an electromagnetic valve 35 that opens and closes the path. The electromagnetic valve 35 is then connected via a path 114 to a path 115.

[0033] In inkjet recording devices, the rotation speed of the recovery pump is constant, so a constant rotation speed is set to ensure sufficient recovery flow even when recovery performance decreases under conditions such as high temperatures or high ink viscosity.

[0034] For this reason, even under normal circumstances, the frequency of the recovery pump must be set high, the number of rotations must be increased to increase the negative pressure in the recovery path, and the recovery flow rate must be increased, resulting in excess air being recovered from the gutter 14. The greater the amount of air that is sucked in and recovered together with the ink particles, the greater the amount of solvent components in the ink particles that volatilize, and the greater the amount of solvent consumed to replenish the evaporated solvent.

[0035] Furthermore, by maintaining the pump at a high rotational speed, the pump will constantly consume extra power.

[0036] FIG. 4 is a diagram showing the control configuration of the inkjet printing apparatus according to the embodiment of the present invention.

[0037] 4, the control configuration of the inkjet recording apparatus in this embodiment comprises an MPU (microprocessing unit) 401 that controls the entire recording apparatus, a RAM (random access memory) 402 that temporarily stores data within the inkjet recording apparatus, a ROM (read only memory) 403 that stores software and data for calculating the write start position, a display device 404 that displays input data and print contents, etc., a panel 405 that inputs character information to be printed, etc., a print control circuit 406 that performs overall control related to printing by the inkjet recording apparatus, a print substrate detection circuit 407, a video RAM 408 that stores video data to be charged to ink particles, a character signal generation circuit 409 that converts the video data stored in 408 into character signals, a solenoid valve control circuit 410 that controls solenoid valves that change the flow of ink and solvent, and a pump control circuit 411 for controlling the rotation speed of the pump.

[0038] The above-mentioned components are connected by a bus line 400, and data and the like are transmitted and received via this bus line 400.

[0039] FIG. 5 is a diagram showing a circulation path of an ink jet recording apparatus according to an embodiment of the present invention.

[0040] In FIG. 5, recovery pump 32 is a recovery pump whose rotation speed can be changed, 14 is a gutter, path 107 is a path through which ink recovered from the gutter flows, 501 is a composite detector (voltage detection circuit) in which a resistor is connected in series with an autophase sensor (hereinafter referred to as the APH sensor) and which is equipped with a power supply for applying voltage across the resistor, and 502 is a signal indicating the voltage value detected from composite detector 501.

[0041] At this time, the gutter 14 and the composite detector 501 are directly connected, and the voltage detection circuit 501 is installed at the closest position to the gutter.

[0042] The composite detector 501 is a composite voltage detector (hereinafter referred to as composite detector) that combines an APH sensor with a sensor for detecting the ink accumulation state near the gutter 14 (hereinafter referred to as ink accumulation sensor), and switching control as needed between using it as an APH sensor or an ink accumulation sensor is performed by the print control circuit 406. The internal configuration of this composite detector will be described later in FIG. 6, and the control method will be described later in FIG. 8.

[0043] Of the ink droplets (ink particles) ejected from the nozzle 8, there are two types of non-printing ink droplets that are not used for printing: ink droplets that are not charged and are collected by the gutter 14 without being charged (hereinafter referred to as uncharged ink droplets), and ink droplets that have a minute charging voltage applied to them, so that even if they are deflected, they fit within the range of the collection port of the gutter 14 (hereinafter referred to as minute charged ink droplets).

[0044] When these minute charged ink droplets are collected by the gutter 14, their charge amount is detected and serves as a signal for detecting the optimum printing phase, and the minute voltage is detected by the APH sensor in 501.

[0045] FIG. 6 is a diagram showing the internal connections of the composite detector of the inkjet printing apparatus according to the embodiment of the present invention.

[0046] 6, reference numeral 61 denotes an APH sensor, one end of which is connected in series to a resistor 62 via a path 600, and the other end is connected to GND via a path 601. When the combined detector 501 is used as an ink retention sensor, a power supply 63 for applying a voltage to the APH sensor 61 is connected to the resistor via a path 602, and is connected to GND via a path 603.

[0047] The APH sensor 61 branches off to an APH detection circuit 64 and a voltage value comparison circuit 65 via paths 604 and 605. It is connected to the APH detection circuit 64 via paths 606 and 607, and to the voltage value comparison circuit 65 via paths 608 and 609. The detection signal (APH signal) of the APH detection circuit 64 is output via path 610, and the detection signal (ink accumulation detection signal) of the voltage comparison circuit 65 is output via path 611 to the MPU 401 that controls the entire printing apparatus.

[0048] When the composite detector 501 is used as the minute charge amount detection unit, it is necessary to detect the minute charge voltage of the minute charged ink droplets described above, so no voltage is applied from the power supply 63 to the composite detector 501 .

[0049] When the combined detector 501 is used as the ink accumulation detector, it is necessary to determine the voltage value from the ink accumulation state in the APH sensor 61, so a voltage is applied from the power supply 63 to the combined detector 501. The control timing and conditions will be described later in the control flow of FIG.

[0050] Here, the APH signal (minute charge amount detection signal) is a signal required to detect the optimum printing phase, and is output from the APH detection circuit 64. The ink accumulation detection signal is output from the voltage value comparison circuit 65. The power supply 63 receives a power ON / OFF control signal from the MPU 401, and controls the ON / OFF switching of the power supply 63.

[0051] When the APH sensor 61 is used to detect minute charge amounts, the power supply 63 is turned off because minute charge voltages cannot be detected when the power supply 63 is turned on. When the APH sensor 61 is used to detect ink accumulation, the power supply 63 is turned on to detect the voltage value by dividing the voltage between the resistor 62 and the APH sensor 61.

[0052] When the composite detector 501 is operated as a minute charge amount detection unit, the minute charge amount detection unit is composed of an APH sensor 61 and an APH detection circuit 64 .

[0053] When the composite detector 501 is operated as an ink accumulation detection unit, the ink accumulation detection unit is composed of an APH sensor 61 , a voltage value comparison circuit 65 , a power supply 63 and a resistor 62 .

[0054] The voltage value comparison circuit 65 compares the voltage value measured by the APH sensor 61 at this time with the voltage value just before ink overflows, which is predetermined in the MPU 401, and outputs an ink accumulation detection signal based on the comparison result.

[0055] FIG. 7 is a diagram showing the relationship between the detected voltage and the pump frequency.

[0056] The pump frequency range in which ink can be collected from the gutter 14 without stagnation and ink does not overflow from the gutter 14 is defined as T １ , the pump frequency region in which ink overflows from the gutter 14 and a sufficient recovery flow rate cannot be maintained to recover the ink is T ２ At this time, the ink has already overflowed from the gutter 14 in the area T ２ and the region T where ink is not overflowing from the gutter 14. １ The pump frequency at the boundary between １ , ink is not overflowing from the gutter 14. １ The pump frequency in the region is H ２ , H ３ (H ２ <H ３ )

[0057] Also, the pump frequency H ２ The detection voltage at this time is V ２ , pump frequency H ３ The detection voltage at this time is V ３ The pump frequency H １ , H ２ , H ３ is determined by an experimental value, and the value is stored in the ROM 403 in advance.

[0058] By controlling the pump frequency to a value just before the ink overflows from the gutter 14, there is no problem with ink recovery and it is possible to reduce the amount of solvent evaporation because excess air is not sucked from the gutter 14. Furthermore, the pump can be operated at a reduced rotational speed, which makes it possible to reduce the power consumed by the pump.

[0059] If the pump frequency is too high, a lot of air will be sucked in at the same time as the ink, which will increase the amount of solvent consumed in the ink container. On the other hand, if the pump frequency is too low, the ink will not be able to be sucked in from the gutter 14, and the ink will overflow. For this reason, a frequency H that satisfies both of these needs is selected. ３ Here, the detection voltage is determined based on the ink accumulation detection signal shown in FIG.

[0060] Next, a process flow for switching and controlling whether the combined detector 501 operates as a minute charge amount detector or an ink accumulation detector is shown in Fig. 8. Fig. 8 shows a process flow for switching and controlling the APH sensor and the ink accumulation sensor. Fig. 9 also shows a process flow for controlling the frequency of the recovery pump based on the detection results obtained from the ink accumulation detector (ink accumulation sensor).

[0061] This processing flow is an example of a control flow performed by the MPU 501 using the detection voltage 502 detected by the composite detector 501 as an input.

[0062] When processing begins in step S800, step S801 first extracts data for characters to be printed that are stored in video RAM 408. As is well known, characters to be printed are made up of multiple dots, some of which are to be printed and some of which are not. Once extraction of the characters to be printed is complete, processing proceeds to step S802.

[0063] In step S802, the dots of the printed characters are analyzed. This analysis determines which dots form printed characters and which do not. Dots to be printed are then charged to form charged ink droplets, and dots not to be printed are uncharged ink droplets or tiny charged ink droplets. Once the analysis of the dots of the printed characters is complete, the process proceeds to step S803.

[0064] In step S803, a process is performed to select whether or not to print ink droplets ejected from nozzle 8. If printing is to be performed (YES determination), the process proceeds to step S807; if not printing is to be performed (NO determination), the process proceeds to step S804.

[0065] Returning to step S803, if printing is not to be performed (NO determination), in step S804, it is determined whether the dots are uncharged. This determination is the process of determining whether the dots are charged ink droplets or uncharged ink droplets, as described above. If the dots are not uncharged ink droplets (NO determination), the dots are treated as charged ink droplets and the process proceeds to step S805.

[0066] On the other hand, if the droplet is an uncharged ink droplet (YES determination), the process proceeds to step S807.

[0067] Returning to step S804, in the case of minute charged ink droplets (determined as NO), in step S805, the charge amount of these minute charged ink droplets is detected by the combined detector 501, and it is necessary to operate the combined detector 501 as the APH sensor 61 for detecting the optimum printing phase. For this reason, no voltage is applied to the combined detector 501 to use it as an ink accumulation detector (ink accumulation sensor). When this process is completed, the process exits to step S806, which is the end of the process.

[0068] In step S807, a voltage is applied to the combined detector 501 so that it can be used as an ink accumulation detection unit (ink accumulation sensor). At this time, the combined detector 501 operates as an ink accumulation detection unit (ink accumulation sensor) and is not used as a minute charge amount detection unit (APH sensor). When the application of voltage to the combined detector 501 is complete, the process proceeds to step S808 (step S900 in FIG. 9).

[0069] When the process starts in step S900, a determination is made in step S901 as to whether the process shown in this flow is the first time or the second time or later. If it is the first time (YES determination), the process proceeds to step S902, and if it is the second time or later (NO determination), the process proceeds to step S905.

[0070] Returning to step S901, in the first processing of this flow (YES judgment), in step S902, as shown in FIG. 7, the pump frequency is set to a high frequency (T １ region) to low frequencies (T ２ The angle is continuously variable toward the target area.

[0071] In step S903, the process returns to step S902, and the voltage value at the continuously variable pump frequency is detected, and in step S903, the detected voltage value is compared. At this time, the threshold value V shown in FIG. ３ If the detected voltage value is lower than the threshold value V ３ If it is higher (YES determination), the process proceeds to step S904.

[0072] In step S904, the threshold value V detected in step S903 is ３ The pump frequency H ３ When the process is completed, the process goes to step S907 to end the process.

[0073] Returning to step S901, the second and subsequent processes (determined as NO) in this flow are steps for determining whether the pump is operating normally without ink overflowing at the pump frequency set in step S904.

[0074] In step S905, the pump frequency H ３ Check the detected voltage at the time, and set the threshold V ２ The threshold V ２ If the detected voltage is higher (YES), the process proceeds to step S904, and the pump frequency is set to H ３ The detection voltage is fixed to the threshold V ２ If it is lower (NO determination), the process proceeds to step S906.

[0075] Returning to step S905, the threshold value V ２ If the detected voltage value is lower (NO determination), the pump frequency is not changed in step S906, and when the process is completed, the process skips to step S907 where the process ends.

[0076] According to the above embodiment, it is possible to provide an ink jet recording apparatus that can reduce the cost of the ink accumulation detection mechanism, save space, and achieve stable ink recovery.

[0077] The present invention is not limited to the above-described embodiments, but includes various modifications. The above-described embodiments have been described in detail to clearly explain the present invention, and the present invention is not necessarily limited to those including all of the described configurations. Furthermore, it is possible to replace part of the configuration of one embodiment with the configuration of another embodiment, and it is also possible to add the configuration of another embodiment to the configuration of one embodiment. It is also possible to add, delete, or replace other configurations with respect to the configuration of each embodiment.

[0078] REFERENCE SIGNS LIST 1 Inkjet recording device main body 2 Operation display unit 3 Conduit 4 Print head 8 Nozzle 9 Electrostrictive element 10 Charging electrode 11 Ink particle 12 Positive deflection electrode 13 Negative deflection electrode 14 Gutter 15 Main ink container 17, 26 Solenoid valve 27, 32 Pump 28, 31 Filter 29 Pressure reducing valve 33 Solvent container 34 Auxiliary ink container 100 Inkjet recording device 501 Composite detector

Claims

1. An inkjet recording device having a nozzle that vibrates ink to eject it as ink droplets, a charging electrode that charges the ink droplets, a gutter that captures and collects the ink droplets not used for printing, a composite detector connected to the gutter, a recovery pump that generates pressure in an ink recovery path connected to the composite detector, and a control unit that performs specified control related to printing, wherein the composite detector has a minute charge detection unit that detects the minute charge of the ink particles collected in the gutter, and an ink retention detection unit that detects the retention of the ink particles, and the control unit operates the composite detector as either the minute charge detection unit or the ink retention detection unit based on the minute charge.

2. An inkjet recording device as described in claim 1, characterized in that the control unit does not apply a voltage to the composite detector when the composite detector is operated as the minute charge detection unit, and applies the voltage to the composite detector when the composite detector is operated as the ink accumulation detection unit.

3. An inkjet recording device as described in claim 2, characterized in that when the control unit operates the composite detector as the minute charge detection unit, it detects the predetermined printing phase by detecting the minute charge of the ink particles.

4. An inkjet recording apparatus according to claim 2, characterized in that the control unit controls the pump frequency of the recovery pump when the composite detector is operated as the ink retention detection unit.

5. An inkjet recording apparatus according to claim 4, characterized in that the control unit controls the pressure in the ink recovery path by controlling the pump frequency of the recovery pump.

6. An inkjet recording device as described in claim 2, wherein the control unit: extracts data of a print character to be printed; analyzes the dots of the print character to determine dots that will form the print character and dots that will not form the print character; the dots to be printed are charged by the charging electrode to be charged ink particles; and the dots that will not be printed are uncharged ink particles or micro-charged ink particles; determines whether the ink particles ejected from the nozzle are the dots to be printed or the dots that will not be printed; if they are determined to be dots that will not be printed, determines whether they are the micro-charged ink particles or the uncharged ink particles; if they are determined to be micro-charged ink particles, does not apply the voltage to the composite detector; if they are determined to be uncharged ink particles, applies the voltage to the composite detector; and if they are determined to be dots to be printed, applies the voltage to the composite detector.

7. An inkjet recording apparatus as described in claim 2, wherein the composite detector has an autophase sensor and a power supply connected to the autophase sensor, the control unit controls switching of the power supply on and off, and when the autophase sensor is used as the minute charge detection unit, the control unit switches the power supply off and does not apply the voltage to the composite detector, and when the autophase sensor is used as the ink retention detection unit, the control unit switches the power supply on and applies the voltage to the composite detector.

8. A control method for an inkjet recording device having a nozzle which vibrates ink to eject it as ink droplets, a charging electrode which charges the ink droplets, a gutter which captures and collects the ink droplets not used for printing, a composite detector connected to the gutter, a recovery pump which generates pressure in an ink recovery path connected to the composite detector, and a control unit which performs specified control related to printing, comprising: a minute charge amount detection step which detects a minute charge amount of the ink particles collected in the gutter by the composite detector; an ink retention detection step which detects retention of the ink particles by the composite detector; and a control step which causes the composite detector to perform either the minute charge amount detection step or the ink retention detection step based on the minute charge amount by the control unit.

9. A control method for an inkjet recording device as described in claim 8, characterized in that the control step: when the composite detector is to perform the minute charge amount detection step, no voltage is applied to the composite detector; and when the composite detector is to perform the ink retention detection step, the voltage is applied to the composite detector.

10. A control method for an inkjet recording device as described in claim 9, characterized in that the control step, when causing the composite detector to perform the minute charge amount detection step, detects a predetermined printing phase by detecting the minute charge amount of the ink particles.

11. A control method for an inkjet recording device as described in claim 9, characterized in that the control step controls the pump frequency of the recovery pump when the composite detector is caused to perform the ink retention detection step.

12. A control method for an inkjet recording device according to claim 11, wherein the control step controls the pressure in the ink recovery path by controlling the pump frequency of the recovery pump.

13. A control method for an inkjet recording device as described in claim 9, wherein the control step comprises: extracting data of a print character to be printed; analyzing dots of the print character to determine dots that will form the print character and dots that will not form the print character; the dots to be printed are charged by the charging electrode to be charged ink particles; and the dots that will not be printed are uncharged ink particles or micro-charged ink particles; determining whether the ink particles ejected from the nozzle are the dots to be printed or the dots that will not be printed; if they are determined to be dots that will not be printed, determining whether they are the micro-charged ink particles or the uncharged ink particles; if they are determined to be micro-charged ink particles, not applying the voltage to the composite detector; if they are determined to be uncharged ink particles, applying the voltage to the composite detector; and if they are determined to be dots to be printed, applying the voltage to the composite detector.