JP2005106950A - Wet type image forming apparatus and liquid developer concentration detecting method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a high quality image of satisfactory color reproducibility by correctly detecting the concentration of liquid developer with supersonic waves, without being affected by a water current caused by the circulation of the liquid developer. <P>SOLUTION: Supersonic waves having many periods are burst-transmitted into the liquid developer 17. The concentration of the liquid developer 17 is detected for a long time. The average of the received supersonic waves obtained by a CR integration circuit 115 that performs the integration of all the periods of the received supersonic waves propagated in the liquid developer 17 is used as concentration data in order to reduce the adverse effect of the nonstable detection of the concentration, which is caused by a water current. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a wet image forming apparatus that forms a developed image with a liquid developer whose density is kept constant, and a liquid developer density detection method.

  In a wet image forming apparatus that obtains a visible image using a liquid developer in which toner particles are dispersed in a carrier liquid, the toner concentration in the developer is always kept constant in order to obtain high image quality. There is a need. Therefore, the toner concentration in the liquid developer in the developing container is detected, and a concentrated toner having a high toner concentration is supplied to the developing container according to the density detection result, or only the carrier liquid having no toner particles is supplied to the developing container. Devices for feeding are known.

As a method for detecting the toner concentration in the liquid developer, the output is likely to fluctuate due to the adhesion of toner particles, the color of the toner particles, or the scattering by the agglomerated toner. Therefore, a conventional method has been proposed in which ultrasonic waves are transmitted to the liquid developer and the toner concentration is detected from the attenuation of the received ultrasonic waves propagated in the liquid developer (for example, Patent Document 1, Patent Document 2).
JP 2001-142306 A (3rd and 4th pages, FIGS. 2 and 3) However, in the case of detecting the concentration of the liquid developer using ultrasonic waves as in (Patent Document 1) or (Patent Document 2), the inside of the developer container is disclosed in JP-A-2003-15426. However, since the liquid developer is used while being circulated, it is necessary to consider that there is a considerable water flow. Actually, regardless of the liquid developer concentration being constant, due to the difference in the water flow in the developer container, the attenuation rate of the received ultrasonic waves varies by several percent to several tens percent in each period of the ultrasonic waves. There is also a case. Due to the instability of the received ultrasonic waves due to such a water flow, accurate concentration control of the liquid developer concentration in the developing container cannot be obtained, and image quality may be deteriorated.

  Therefore, the present invention solves the above-mentioned problems, removes the instability of received ultrasonic waves regardless of the water flow generated in the developing container, and accurately detects the toner concentration in the liquid developer to perform density control. Accordingly, an object of the present invention is to provide a wet image forming apparatus capable of obtaining high image quality with good color reproducibility. Another object of the present invention is to provide a liquid developer concentration detection method for accurately detecting the toner concentration in the liquid developer.

  The present invention accommodates, as means for solving the above-mentioned problems, an image carrier for holding an electrostatic latent image, and a liquid developer containing carrier liquid and toner particles for developing the electrostatic latent image. A toner tank, a developing device that supplies the liquid developer to the electrostatic latent image to form a developed image, and multi-period ultrasonic waves are transmitted in bursts into the liquid developer stored in the toner tank. A transmitting piezoelectric element, a receiving piezoelectric element that receives multi-period received ultrasonic waves that are propagated in the liquid developer in bursts, and a multi-period receiving ultrasonic wave for each burst. A density detector for detecting density data of the liquid developer from a calculation result of the calculation circuit having a calculation circuit for calculating a total period; and a liquid developer stored in the toner tank according to the density data. Adjust toner density It is intended to provide a supply device for supplying a replenishing solution to be.

  According to another aspect of the present invention, as means for solving the above-described problems, a transmission step of transmitting multi-period ultrasonic waves in a liquid developer in a burst form, and a multi-cycle formed by propagating the ultrasonic waves into the liquid developer. The receiving step of receiving the received ultrasonic waves in a burst form and the calculating step of calculating the whole period of the multi-cycle received ultrasonic wave for each burst to obtain density data are performed.

  According to the present invention, even if the received ultrasonic wave is influenced by the water flow by calculating the total wave number of the received ultrasonic wave formed by propagating multi-cycle burst ultrasonic waves into the liquid developer, Sound waves can be transmitted and received for a certain period of time, the reception results can be averaged, and the influence of water flow can be reduced. Therefore, the instability of the received ultrasonic waves is reduced, the toner concentration in the liquid developer can be detected more accurately, and more accurate concentration control can be obtained based on the detection result, resulting in high image quality with good color reproducibility. It is done.

  In the present invention, in order to reduce the instability of the received ultrasonic wave due to the water flow in the developer container at the time of density detection, the ultrasonic wave is propagated in the liquid developer for a long time using a burst wave of multiple wave numbers, Long-term detection of received ultrasound attenuation. Further, the total wave number of the detected received ultrasonic waves is integrated or added, and the received ultrasonic waves are averaged to perform accurate toner concentration detection.

  Hereinafter, the present invention will be described in detail with reference to Example 1 shown in FIGS. FIG. 1 shows an image forming unit 10 of an electrophotographic apparatus which is a wet image forming apparatus. For example, an image bearing member in which an organic or amorphous silicon photosensitive layer is provided on a conductive rigid substrate such as aluminum, and a protective layer made of fluorine resin silicone resin or the like is further formed thereon. Around a certain photosensitive drum 12, a charging device 13 including a well-known scorotron charger and the like, and exposures 14 modulated according to image information are sequentially irradiated along the rotation of the photosensitive drum 12 in the direction of arrow r. A laser exposure device 16 for forming an electrostatic latent image is arranged.

  Further, around the photosensitive drum 12, a developing device 18 for storing the liquid developer 17 in the developing container 18a is disposed. The developing device 18 includes a developing roller 21 and a developing roller cleaner 18b for supplying the liquid developer 17 to the surface of the photosensitive drum 12. The developing roller 21 rotates in the direction of arrow s, and a developing bias is applied by the developing bias device 21a. In the liquid developer 17, for example, positively charged toner particles and negative ions are present in a carrier liquid made of insulating isopar due to the action of the charge control agent. The discharge side of the developing container 18a is connected to the toner tank 71 by a pipe 71a, and the supply side of the developing container 18a is connected to the toner tank 71 by a pipe 74 having a pump 74a to circulate the liquid developer.

  In the downstream of the developing device 18 around the photosensitive drum 12, in order to prevent fogging of a white background portion of the toner image that is a developed image, the excess liquid developer is squeezed from the photosensitive drum 12 to thin the liquid developer. A squeeze device 23 having a squeeze roller 22 is provided. The squeeze roller 22 rotates in a direction of arrow t opposite to the direction of rotation of the photosensitive drum 12 in the direction of arrow r at a speed that is about three times the peripheral speed of the photosensitive drum 12.

  To the squeeze roller 22, squeeze bias having the same polarity as the toner particles is applied by the squeeze bias device 22a, and the toner particles adhering to the electrostatic latent image on the surface of the photosensitive drum 12 are moved to the photosensitive drum 12 side by electrophoresis. Pressed. A cleaning blade 24 is provided around the squeeze roller 22. The squeeze device 23 is connected to the toner tank 71 via a pipe 78 in order to reuse the recovered excess liquid developer.

  Downstream of the squeeze device 23, a drying device 26 is provided that blows high-speed air onto the photosensitive drum 12 to dry excess carrier liquid on the photosensitive drum 12. Further, a transfer device 30 is provided downstream of the drying device 26 around the photosensitive drum 12 so as to be able to contact and separate from the photosensitive drum 12. The transfer device 30 includes a backup roller 27 and an intermediate transfer roller 28 that is pressed against the photosensitive drum 12 by the backup roller 27. The developed image formed on the photosensitive drum 12 is primarily transferred to the intermediate transfer roller 28 using the adhesive force and pressure of toner particles, and then secondarily transferred to the paper P.

  The backup roller 27 rotating in the arrow v direction is cleaned by the backup roller cleaner 27a, and the intermediate transfer roller 28 rotating in the arrow u direction is cleaned by the intermediate transfer roller 28a. In the downstream of the transfer device 30 around the photosensitive drum 12, the photosensitive drum 31 contacts the photosensitive drum 12 and removes the toner image remaining on the photosensitive drum 12 after the transfer is completed, and the surface of the photosensitive drum 12 remains. An erasing lamp 32 is provided to remove charges.

  Next, the circulation system 60 shown in FIG. 2 for circulating and supplying the liquid developer 17 having a predetermined concentration suitable for development from the toner tank 71 to the developing container 18a will be described in detail. A toner tank 71 that circulates and supplies a liquid developer 17 having a predetermined concentration suitable for development to the developing container 18 a is a supply device that supplies a toner 72 a that is a replenisher having a higher toner concentration than the liquid developer 17. The tank 72 is connected by a pipe 76 having a valve 76a. Further, the toner tank 71 is connected to an isoper tank 73 which is a supply device for supplying isopar 73a which is a replenisher by a pipe 77 having a valve 77a.

  A density detector 70 is installed in the toner tank 71. The density detector 70, the valve 76a, and the valve 77a are controlled by the control circuit 75. The control circuit 75 stabilizes the concentration of the liquid developer 17 in the toner tank 71 by controlling the opening / closing of the valve 76a or the valve 77a in accordance with the density detection result by the density detection device 70. The concentration of the liquid developer 17 used in a normal developing operation is about 1 wt% to 5 wt% in solid content with respect to Isopar, and the toner 72 a has a solid content of about 10 wt% to 50 wt% with respect to Isopar. .

  As shown in FIG. 3, the transmitting piezoelectric element 100 and the receiving piezoelectric element 101 of the density detector 70 are installed in the toner tank 71 with a distance L (m) therebetween. The transmitting piezoelectric element 100 is connected to the transmitting unit 105 of the ultrasonic transmitting / receiving circuit 104 of the concentration detecting device 70, and the receiving piezoelectric element 101 is connected to the receiving unit 106 of the ultrasonic transmitting / receiving circuit 104 of the concentration detecting device 70. Is done. As illustrated in the block diagram of FIG. 4, the transmission unit 105 includes a logic circuit 110, a capacitor 111, and an amplifier circuit 112.

  The logic circuit 110 produces a logic signal as shown in FIG. 5 for determining the burst width R and burst period T of the burst signal supplied to the transmitting piezoelectric element 100 from the resonance frequency clock signal of the transmitting piezoelectric element 100. To do. Only the AC component of the logic signal is supplied to the amplifier circuit 112 via the capacitor 111, and is amplified to a predetermined voltage by the amplifier circuit 112. The drive voltage 108 of 32 cycles, burst width R, burst cycle T shown in FIG. And supplied to the transmitting piezoelectric element 100. As a result, a burst ultrasonic wave 103 having a frequency of 2.4 MHz is transmitted from the transmitting piezoelectric element 100. The transmitted ultrasonic wave 103 propagates through the liquid developer 17 and reaches the transmitting piezoelectric element 101 after D hours.

  In order to average the received ultrasonic waves that vary due to the water flow in the toner tank 71 and perform more accurate density detection, it is better to drive the transmitting piezoelectric element 100 for a certain length of time. Accordingly, it is preferable that the period of the burst-like ultrasonic wave is large, and a burst signal having a period of several hundreds to several thousands may be used.

However, the width R of the burst signal is D, the time from the transmission of the ultrasonic wave by the transmission piezoelectric element 100 to the reception of the reception ultrasonic wave by the reception piezoelectric element 101, and the distance between the transmission piezoelectric element 100 and the reception piezoelectric element 101. When L (m) and the ultrasonic velocity are v (m / s),
R <D = L / v
It is constrained to become. This is because the ultrasonic wave transmitted from the transmitting piezoelectric element 100 and the received ultrasonic wave received by the receiving piezoelectric element 101 are driven by the same ultrasonic transmission / reception circuit 104, the time of the transmitted wave and the received ultrasonic wave overlap. This is to prevent the mutual signals from being induced and influenced. This restriction is not necessary if the transmission circuit and the reception circuit are completely separated.

Furthermore, the burst period T of the burst signal is
T> R + 2D = R + 2 × L / v
It is necessary to satisfy the relationship. This is because, in general, multiple reflection occurs between the piezoelectric elements arranged opposite to each other, so that the influence of multiple reflection is prevented. The ultrasonic wave reflected by the receiving piezoelectric element 101 returns to the transmitting piezoelectric element 100 again. The returning ultrasonic wave is considerably attenuated. However, if the driving voltage 108 is supplied to the transmitting piezoelectric element 100 in the presence of the returning ultrasonic wave, the phase of the reflected wave and the driving voltage 108 may be matched or shifted. As a result, driving by the driving voltage 108 becomes very unstable. Therefore, the next burst signal is output in a state where the influence of the reflected wave from the receiving piezoelectric element 101 is eliminated.

  Note that the reflected wave from the receiving piezoelectric element 101 becomes smaller each time multiple reflections occur, and the influence of the second reflected wave is negligible, so that the burst period T does not overlap with the first reflected wave. Is set to When the influence of the reflected wave was actually investigated using ultrasonic waves having a frequency of 1 MHz to 5 MHz and the distance L between the piezoelectric elements being 2 cm to 6 cm, the burst period T was set so as to avoid the first reflected wave. No effect on the driving of the transmitting piezoelectric element 100 was observed.

  Next, as shown in the block diagram of FIG. 7, the receiving unit 106 amplifies the reception ultrasonic wave, an amplification circuit 113, a half-wave rectification circuit 114 that extracts a positive waveform, and an arithmetic operation that integrates and averages all periods of the positive waveform. A CR integration circuit 115 as a circuit and a data hold circuit 116 for holding the integration result are provided. The receiving unit 106 further includes an amplifier circuit 117 that amplifies the half-wave rectified plus waveform, and a logic circuit 118 that generates a timing for holding the integration result and inputs the timing to the data hold circuit 116. The reception result integrated and averaged by the receiving unit 106 is input to the control circuit 75.

  Next, the operation will be described. The photosensitive drum 12 is uniformly charged by the charging device 13 by the rotation of the photosensitive drum 12 in the direction of the arrow r at the start of the image forming process, and then modulated by the exposure device 17 based on the image information. Are selectively irradiated to form an electrostatic latent image, and a liquid developer 17 is supplied by the developing device 18 to form a toner image. Next, after the excess liquid developer 17 is removed by the squeeze roller 22 and the fog is removed, the photosensitive drum 12 passes through the drying device 26 and is dried and removed by high-speed air. The transfer device 30 is reached. The excess liquid developer 17 removed by the squeeze roller 22 is collected in the toner tank 71 for reuse.

  In the transfer device 30, the toner image on the photosensitive drum 12 is primarily transferred to the intermediate transfer roller 28 by heating and pressurizing, and is further transferred to the sheet P conveyed between the backup roller 17 and the intermediate transfer roller 28 in the direction of the arrow w. Transfer and complete a fixed toner image on paper P. Thereafter, the residual toner is removed from the photosensitive drum 12 by the photosensitive cleaner 31, and the residual charge is removed by the erasing lamp 32, and the next image forming process is awaited.

  In the circulation system 60 during image formation in this way, the toner concentration of the liquid developer 17 in the toner tank 71 is detected by the following process, and the toner 72a or isopar 73a is replenished according to the detection result. Thus, the toner concentration of the liquid developer 17 is maintained at a predetermined concentration. In the circulation system 60, when the image forming process is started, the pump 74a is driven to start the circulation of the liquid developer 17 between the developing container 18a and the toner tank 71. As a result, the toner particles that have sunk in the toner tank 71 are agitated. At the same time, the toner density detection of the liquid developer 17 is started by the density detector 70.

  An ultrasonic wave 103 is transmitted from the transmitting piezoelectric element 100 by the driving voltage 108 shown in FIG. The received ultrasonic wave that is attenuated by propagating the ultrasonic wave 103 in the liquid developer 17 reaches the receiving piezoelectric element 101 with a delay of D time from the transmission. A reception voltage 109 shown in FIG. 6B is supplied from the reception piezoelectric element 101 to the reception unit 106 by reception ultrasonic waves. In the receiving unit 106, the reception voltage 109 is amplified by the amplifier circuit 113 as shown in FIG. 8A, and then a plus waveform shown in FIG.

  Next, the plus waveform is integrated by the CR integration circuit 115. Since the integrated value (Vout) at the peak of the output signal shown in FIG. 8C is a signal correlated with the value obtained by integrating all the positive waveforms, that is, the average of all the positive waveforms. ) Holds the integrated value (Vout) at the peak of the output signal by the data hold circuit 116 to create density data 107 and inputs it to the control circuit 75 as the detection result of the density detector 70.

  On the other hand, the plus waveform input from the half-wave rectifier circuit 114 to the amplifier circuit 117 is input to the logic circuit 118 to generate a hold signal for holding the integrated value at the peak. The logic circuit 118 binarizes the plus waveform to create the logic signal shown in FIG. 8D synchronized with the reception voltage 109, and further in FIG. 8E synchronized with the peak of the output signal from the CR integration circuit 115. A hold signal is generated and input to the data hold circuit 116. As a result, the received voltage 109 is averaged from the data hold circuit 116, and the signal shown in FIG. 8 (f) held for each burst is output as the density data 107. This density data 107 is output from the receiving unit 106 to the control circuit 75. Entered.

  The density data 107 is output from the data hold circuit 116 every time a burst is completed, and the value is changed for each burst as shown in FIG. The receiving unit 106 does not output the density data 107 that changes for each burst shown in FIG. 8 (f) as a detection result as it is, but also performs an averaging process on the output values of all bursts by an external circuit or the like, and then performs control. It may be input to the circuit 75 or the like.

  The control circuit 75 controls the opening / closing of the valve 76a or the valve 77a to adjust the density of the liquid developer 17 by inputting the averaged density data 107 from the density detector 70. However, at the beginning of the image forming process, the liquid developer 17 in the toner tank 71 is not sufficiently agitated by circulation, and the density data 107 from the density detector 70 varies greatly, for example, as indicated by C in FIG. . Accordingly, the control circuit 75 does not perform density adjustment while the fluctuation of the density data 107 is indicated by C, and after the range indicated by C has elapsed, the fluctuation of the density data 107 from the density detector 70 is determined in advance. The control of density adjustment is started after waiting for the density data 107 to become smaller than the range and become almost constant. The specified range is arbitrary according to the characteristics of the density detection device 70 and is set in the control circuit 75 in advance.

  When the density adjustment control is started, the control circuit 75 determines that the toner concentration of the liquid developer 17 is in the range of 2.5 wt% to 3.5 wt% with respect to the isopar from the density data 107 from the density detector 70. If the toner particles are 2.5 wt% or less with respect to Isopar, the valve 76a is opened and the toner 72a is supplied to the toner tank 71. If the density detector 70 detects that the toner density reaches 3.0 wt% while circulating the liquid developer 17, the control circuit 75 closes the valve 76a.

  If the toner concentration of the liquid developer 17 is 3.5 wt% or more with respect to Isopar by the concentration detector 70, the controller 75 opens the valve 77 a and supplies the isopar 73 a to the toner tank 71. . When the liquid developer 17 is circulated and the density detector 70 detects that the toner density has reached 3.0 wt%, the control circuit 75 closes the valve 77a. As described above, the control circuit 75 controls the opening / closing of the valve 76a or the valve 77a in accordance with the averaged density data 107, thereby holding the toner density of the liquid developer 17 within a density range suitable for development.

  If comprised in this way, the ultrasonic wave 103 by the burst drive voltage 108 for 32 periods is used for density | concentration detection for the whole period of the received ultrasonic wave which propagates in the liquid developer 17, and the received voltage by a received ultrasonic wave 109 total cycles are integrated, and an average value of 32 cycles is input to the control circuit 75 as density data. Thus, even if a water flow is generated by the circulation of the liquid developer 17 in the toner tank 71, the toner density can be detected for a long time by multi-cycle burst ultrasonic waves, and the density data 107 can be averaged. Therefore, the influence of instability of density detection due to water flow is reduced, and more accurate density control results can be achieved from more accurate density detection results, resulting in high image quality with excellent color reproducibility. It is done.

  At the start of the image forming process, the control circuit 75 performs density control after the toner particles are sufficiently agitated in the liquid developer 17 in the toner tank 71 and the density data is stabilized. As a result, density control due to erroneous detection of density can be prevented, and high image quality with excellent color reproducibility by accurate and stable density control can be obtained.

  10 and 11 show a second embodiment of the present invention. The present embodiment is different from the first embodiment in the signal processing of the received ultrasonic wave at the receiving unit. The same parts as those in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted. In this embodiment, the reception voltage 109 by the reception ultrasonic wave received by the reception piezoelectric element 101 is signal-processed by the reception unit 120 shown in FIG. The reception unit 120 adds an amplification circuit 113 that amplifies the received ultrasonic wave, a half-wave rectification circuit 114 that extracts a positive waveform, an AD conversion circuit 119 that performs AD conversion on the entire period of the positive waveform, and an AD conversion result, and adds up the total period. And an adder circuit 120 that is an arithmetic circuit for calculating. Further, the reception unit 120 includes an amplifying circuit 117 that amplifies the half-wave rectified plus waveform, an AD conversion timing of the AD conversion circuit 119, and a logic circuit 118 that generates a timing signal that takes the addition timing of the addition circuit 120. The sum obtained by adding all the periods of the burst signal in the receiving unit 120 is input to the control circuit 75.

  Then, when the reception voltage 109 is generated by the reception piezoelectric element 101 by reception of the reception ultrasonic wave, the reception unit 120 amplifies the reception voltage 109 by the amplification circuit 113, and then the half-wave rectification circuit 114 performs FIG. Take out the plus waveform shown in The plus waveform is input to the AD conversion circuit 119 and the amplification circuit 117, respectively. The plus signal amplified by the amplifier circuit 117 is binarized by the logic circuit 118 to be a logic signal shown in FIG. 11B synchronized with the reception voltage 109, and the AD conversion circuit 119 and the addition for the AD conversion timing and the addition timing. This is supplied to the circuit 120.

  The AD conversion circuit 119 and the addition circuit 120 perform AD conversion for the entire period of the plus signal while taking the timing with the logic signal shown in FIG. 11B, and further add the AD conversion values for the entire period, resulting in the addition result. The sum total of all cycles is input to the control circuit 75 as density data 121. The control device 75 waits for the fluctuation of the density data 121 to decrease, and from the density data 121 that is the sum of all the periods of the burst-like received ultrasonic waves input from the density detection device 70, the toner density of the liquid developer 17. The valve 76a or the valve 77a is controlled to open and close as necessary.

  With this configuration, the entire period of the reception voltage 109 is added after AD conversion, and the total of 32 periods is input to the control circuit 75 as density data. As a result, even if a water flow is generated by circulation of the liquid developer 17 in the toner tank 71, the toner concentration is detected for a long time by a multi-cycle burst-like ultrasonic wave, and the instability of concentration detection due to the water flow is detected. The influence can be reduced, and more accurate density control of the liquid developer can be realized from more accurate density detection results, and high image quality with excellent color reproducibility can be obtained.

  Similarly to the first embodiment, when the density data is stabilized at the start of the image forming process, the density control is performed by the control circuit 75. Therefore, density control due to erroneous detection can be prevented, and accurate and stable density control is performed. High image quality with excellent color reproducibility can be obtained.

  FIG. 12 shows a third embodiment of the present invention. In the present embodiment, the transmitting piezoelectric element and the receiving piezoelectric element are switched and used in the first embodiment. The same parts as those in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted. In this embodiment, the ultrasonic transmission / reception circuit 104 includes a switch unit 130 including a first switch 132 that switches between the a terminal 132a and the b terminal 132b, and a second switch 133 that switches between the c terminal 133c and the d terminal 133d. The switch unit 130 switches the drive voltage 108 from the transmission unit 105 to the transmission piezoelectric element 100 or the reception piezoelectric element 101 and supplies the drive voltage 108, and the reception voltage 109 from the transmission piezoelectric element 100 or the reception piezoelectric element 101 is switched. Input to the receiving unit 106. The ultrasonic transmission / reception circuit 104 includes a control unit 131 that controls the transmission unit 105, the reception unit 106, and the switch unit 130.

  First, the control unit 131 controls the image forming process. The first switch 132 connects the transmitting piezoelectric element 100 to the a terminal 132a, and the second switch 133 connects the receiving piezoelectric element 101 to the d terminal 133d. To do. As a result, the transmitting piezoelectric element 100 is connected to the transmitting unit 105, supplied with the driving voltage 108, and transmits the ultrasonic wave 103. The receiving piezoelectric element 101 is connected to the receiving unit 106, and inputs a reception voltage 109 based on received ultrasonic waves to the receiving unit 106.

  The reception unit 106 performs signal processing on the reception voltage 109, averages the reception voltage 109, and inputs the signal shown in FIG. 8F held for each burst as density data 107 to the control circuit 75. In this state, the image forming process is performed while adjusting the density of the liquid developer 17.

  After the image forming process is finished, at the start of the next image forming process, the control unit 131 controls the switch unit 130 to switch the transmitting piezoelectric element 100 to the b terminal 132b and to switch the receiving piezoelectric element 101 to the c terminal 133c. To do. Thereby, the transmitting piezoelectric element 100 is connected to the receiving unit 106, and the receiving piezoelectric element 101 is connected to the transmitting unit 105. That is, the receiving piezoelectric element 101 transmits the ultrasonic wave 103 a, and the transmitting piezoelectric element 100 inputs the reception voltage 109 by the receiving ultrasonic wave to the receiving unit 106.

  Thereafter, every time the image forming process is started, the switch unit 130 repeatedly switches the first switch 132 and the second switch 133 to switch between the transmitting piezoelectric element 100 and the receiving piezoelectric element 101 for use. As a result, heat generation due to ultrasonic transmission and mechanical distortion are not generated only on the transmitting piezoelectric element 100 side, and deterioration of the transmitting piezoelectric element 100 is reduced. In particular, in burst-like ultrasonic transmission with large heat generation and mechanical distortion, deterioration of the transmitting piezoelectric element 100 can be more effectively reduced.

  Note that the switching timing in the switch unit 130 can be switched for each burst of ultrasonic waves, or switched for every several bursts. However, regardless of which piezoelectric element 100 or 101 receives the density data 107 output from the receiving unit 106, both piezoelectric elements 100 and 101 have the same output characteristics in order to obtain an accurate detection result. desirable. Therefore, it is desirable that the transmitting piezoelectric element 100 and the receiving piezoelectric element 101 are used by switching as frequently and evenly as possible so as to maintain substantially the same characteristics.

  According to this configuration, similarly to the first embodiment, the toner density can be detected for a long time using multi-period burst-like ultrasonic waves, and the influence of the instability of density detection caused by the water flow can be reduced. From the detection result, more accurate density control of the liquid developer can be realized, and high image quality with excellent color reproducibility can be obtained. Further, the transmitting piezoelectric element 100 and the receiving piezoelectric element 101 are switched by the switch unit 130 to alternately transmit and receive ultrasonic waves. Therefore, deterioration of the piezoelectric element caused by repeated heat generation and mechanical distortion due to ultrasonic transmission can be distributed almost equally between the transmitting piezoelectric element 100 and the receiving piezoelectric element 101. As a result, the lifetimes of the transmitting piezoelectric element 100 and the receiving piezoelectric element 101 can be averaged, and as a result, the lifetime of the density detecting device that performs toner density detection using multi-cycle burst-like ultrasonic waves can be increased.

  The present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the present invention. For example, the structure of the image forming apparatus is arbitrary, and a liquid developer that requires density adjustment is used. Any color image forming apparatus may be used. The arithmetic circuit may be constituted by an integration circuit or a CR circuit having an appropriate time constant as long as the density data can be detected by calculating the entire period of the received ultrasonic wave. Further, the signal for calculating the received ultrasonic wave may be a negative waveform shown in FIG. 13 (b) obtained by half-wave rectifying the received voltage shown in FIG. 13 (a) as in another modification shown in FIG. There is no limitation to a plus waveform obtained by folding a minus waveform as shown in FIG.

  Further, the concentration detection position of the liquid developer by the concentration detection device may be provided in the developing container of the development device or the like as long as the concentration detection of the liquid developer used for development is possible. Is arbitrarily detected during the image forming process, or is detected at a predetermined interval. The timing from the start of the image forming process to the start of density control using density data may be set in advance, for example, after the ready time of the image forming apparatus has elapsed, without being linked to fluctuations in the detection result. . Furthermore, the frequency of the ultrasonic wave is not limited as long as it is multi-period and bursty.

1 is a schematic configuration diagram illustrating an image forming unit of an electrophotographic apparatus according to a first exemplary embodiment of the present invention. It is a schematic explanatory drawing which shows the circulation system of Example 1 of this invention. It is a schematic explanatory drawing which shows the density | concentration detection apparatus of Example 1 of this invention. It is a block diagram which shows the transmission part of Example 1 of this invention. It is a schematic explanatory drawing which shows the logic signal which determines the burst signal supplied to the piezoelectric element for transmission of Example 1 of this invention. The signal used for the density | concentration detection of Example 1 of this invention is shown, (a) is the drive voltage signal, (b) is a schematic side view which shows the received voltage signal. It is a block diagram which shows the receiving part of Example 1 of this invention. FIG. 4A shows signal processing of a received voltage according to the first embodiment of the present invention. FIG. 5A shows a signal after amplification by the amplifier circuit 113, FIG. 5B shows a positive waveform signal after rectification, and FIG. (D) is a logic signal for generating the hold signal, (e) is the hold signal, and (f) is an explanatory diagram showing the density data. It is a graph which shows the fluctuation | variation of the detection result by the density | concentration detection apparatus of Example 1 of this invention. It is a block diagram which shows the receiving part of Example 2 of this invention. The signal processing of the received voltage of Example 2 of the present invention is shown (a) is a positive waveform signal after the rectification, (b) is an explanatory diagram showing the logic signal for the timing of the AD conversion and addition processing. It is a schematic explanatory drawing which shows the density | concentration detection apparatus of Example 3 of this invention. The rectification signal of the received voltage of the other modification of this invention is shown, (a) is the received voltage signal, (b) is the minus waveform signal after the rectification, (c) is the minus waveform after the rectification. It is explanatory drawing of a signal.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Image forming part 12 ... Photosensitive drum 13 ... Charging device 14 ... Exposure 16 ... Laser exposure device 17 ... Liquid developer 18 ... Developing device 18a ... Developing container 18b ... Developing roller cleaner 21 ... Developing roller 22 ... Squeeze roller 23 ... Squeeze device 26 ... Drying device 27 ... Backup roller 28 ... Intermediate transfer roller 30 ... Transfer device 31 ... Photoconductor cleaner 32 ... Erase lamp 60 ... Circulating system 70 ... Density detector 71 ... Toner tank 72 ... Concrete toner tank 72a ... Conch Toner 73 ... Isopar tank 73a ... Isopar 75 ... Control circuit 76a, 77a ... Valve 100 ... Transmission piezoelectric element 101 ... Reception piezoelectric element 104 ... Ultrasonic transmission / reception circuit 105 ... Transmission unit 106 ... Reception unit 108 ... Drive voltage 109 ... Reception voltage 110 ... logic circuit 111 ... Capacitor 112 ... amplifier circuit 113 ... amplifier circuit 114 ... half-wave rectifier circuit 115 ... CR integration circuit 116 ... data hold circuit 118 ... logic circuit

Claims (5)

An image carrier for holding an electrostatic latent image;
A toner tank containing a liquid developer containing carrier liquid and toner particles for developing the electrostatic latent image;
A developing device for supplying the liquid developer to the electrostatic latent image to form a developed image;
Transmitting piezoelectric elements that transmit multi-period ultrasonic waves in bursts into the liquid developer housed in the toner tank, and multi-period received ultrasonic waves that propagate the ultrasonic waves into the liquid developer. A receiving piezoelectric element for receiving a burst and a calculation circuit for calculating the entire period of the multi-cycle reception ultrasonic wave for each burst, and detecting the concentration data of the liquid developer from the calculation result of the calculation circuit A concentration detector;
A wet image forming apparatus comprising: a supply device that supplies a replenisher that adjusts a toner concentration of the liquid developer stored in the toner tank according to the density data.   The wet image forming apparatus according to claim 1, wherein the arithmetic circuit is an integrating circuit that calculates an average value of the received ultrasonic waves.   The wet image forming apparatus according to claim 1, wherein the arithmetic circuit is an adding circuit that calculates a sum of the received ultrasonic waves. The concentration detector is
When the ultrasonic burst period is T, the ultrasonic burst width is R, and the time from transmission of the ultrasonic wave to reception of the received ultrasonic wave is D,
T> R + 2D
The wet image forming apparatus according to claim 1, wherein the relationship is satisfied. A transmission step of transmitting multi-period ultrasonic waves in a liquid developer in bursts;
A receiving step of receiving, in burst form, multi-period received ultrasonic waves formed by propagating the ultrasonic waves into the liquid developer;
A liquid developer concentration detection method, comprising: a calculation step of calculating density data by calculating the entire period of the multi-cycle received ultrasonic wave for each burst.

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