JP2023059324A - Image forming apparatus - Google Patents

Abstract

To suppress occurrence of faulty spraying in a configuration to apply a same voltage to a plurality of nozzles located at different positions in a sheet conveyance direction.SOLUTION: When a sheet S is not in a first electrode interval (between a first nozzle 71B and a first counter electrode 73), and the sheet S is not in a second electrode interval (between a second nozzle 72B and a second counter electrode 74), a control unit 100 adjusts a potential difference to a first potential difference. When the sheet S is in the first electrode interval, and the sheet S is not in the second electrode interval, the control unit 100 adjusts the potential difference to a second potential difference larger than the first potential difference. When the sheet S is in the first electrode interval, and the sheet S is in the second electrode interval, the control unit 100 adjusts the potential difference to a third potential difference larger than the second potential difference. When the sheet S is not in the first electrode interval, and the sheet S is in the second electrode interval, the control unit 100 adjusts the potential difference to a fourth potential difference larger than the first potential difference and smaller than the third potential difference.SELECTED DRAWING: Figure 2

Description

The present invention relates to an image forming apparatus equipped with a spraying device for spraying a fixer onto a sheet.

2. Description of the Related Art Conventionally, as an image forming apparatus, an image forming apparatus including a spraying device and a control section for controlling the spraying device is known (see Patent Document 1). The spraying device includes a first head and a second head for spraying the fixer, and a counter electrode facing the first head and the second head.

The first head has a first nozzle for spraying fixer fluid and a first nozzle electrode for charging the fixer fluid in the first nozzle. The second head is located downstream of the first head in the sheet conveying direction. The second head has a second nozzle for spraying the fixer and a second nozzle electrode for charging the fixer in the second nozzle.

The controller individually controls voltages applied to the first nozzle electrode and the second nozzle electrode. When the distance between the leading edge of the sheet and the first nozzle reaches a predetermined distance, the controller increases the voltage applied to the first nozzle electrode and causes the first nozzle to start spraying the fixer. When the distance between the leading edge of the sheet and the second nozzle reaches a predetermined distance, the controller increases the voltage applied to the second nozzle electrode and causes the second nozzle to start spraying the fixer.

JP 2017-167245 A

By the way, unlike the configuration in which the voltages applied to the first nozzle electrode and the second nozzle electrode are individually controlled as in the prior art, the same voltage is applied to the first nozzle electrode and the second nozzle electrode by a common power supply. can be considered. However, in this case, the resistance value between each nozzle electrode and the counter electrode changes due to the difference in the amount of the sheet entering between each nozzle electrode and the counter electrode. When the voltage is not controlled, there is a possibility that the atomization failure will occur.

Specifically, for example, in the first situation where the sheet exists only between the first nozzle electrode and the counter electrode, the first situation where the sheet exists between both the first nozzle electrode and the second nozzle electrode and the counter electrode. 2, the resistance value between each nozzle electrode and the counter electrode is smaller. Therefore, for example, if the same voltage as the voltage suitable for the first situation is applied in the second situation, the spray amount may be insufficient in the second situation. Further, for example, if the same voltage as the voltage suitable for the second situation is applied in the first situation, the spray amount may become excessive in the first situation.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to suppress the occurrence of defective spraying in a configuration in which the same voltage is applied to a plurality of nozzles positioned at different positions in the sheet conveying direction.

In order to solve the above problems, an image forming apparatus according to the present invention includes a first nozzle, a first nozzle electrode, a first counter electrode, a second nozzle, a second nozzle electrode, a second counter electrode, A nozzle power supply, a counter power supply, and a control unit are provided.
The first nozzle and the second nozzle are nozzles for ejecting fixing fluid. The second nozzle is located downstream of the first nozzle in the sheet conveying direction.
The first nozzle electrode is an electrode for charging the fixer in the first nozzle.
The second nozzle electrode is an electrode for charging the fixer in the second nozzle.
The first counter electrode faces the tip of the first nozzle.
The second counter electrode faces the tip of the second nozzle.
The nozzle power supply applies a nozzle voltage to the first nozzle electrode and the second nozzle electrode.
The counter power source applies a counter voltage to the first counter electrode and the second counter electrode.
The controller can change at least one of the nozzle voltage and the counter voltage to change a potential difference, which is a difference between the nozzle voltage and the counter voltage.
The controller sets the potential difference as a first potential difference when there is no sheet between the first nozzle and the first counter electrode and when there is no sheet between the second nozzle and the second counter electrode. .
When a sheet is present between the first nozzle and the first counter electrode and no sheet is present between the second nozzle and the second counter electrode, the control unit changes the potential difference to the first potential difference. A second potential difference greater than
When a sheet exists between the first nozzle and the first counter electrode and a sheet exists between the second nozzle and the second counter electrode, the control unit converts the potential difference to the second potential difference. A third potential difference greater than
When there is no sheet between the first nozzle and the first counter electrode and there is a sheet between the second nozzle and the second counter electrode, the control unit converts the potential difference to the first potential difference. and a fourth potential difference smaller than the third potential difference.

According to this configuration, even if the amount of the sheet entering between each nozzle electrode and each counter electrode changes, an appropriate amount of fixer can be discharged onto the sheet from each nozzle, thereby preventing the occurrence of defective spraying. can be suppressed.

Also, the fourth potential difference may be smaller than the second potential difference.

When the sheet is present only between the first nozzle and the first counter electrode, the fixer is not applied to the sheet when the fixer is discharged, whereas the sheet is not applied with the fixer between the second nozzle and the second counter electrode. If there is only a sheet, the fixer is already applied to the sheet when the fixer is ejected. Therefore, when there is a sheet only between the second nozzle and the second counter electrode, the electrical resistance between each nozzle and each counter electrode is higher than when there is a sheet only between the first nozzle and the first counter electrode. Therefore, by making the fourth potential difference smaller than the second potential difference, an appropriate amount of fixer can be discharged onto the sheet from the second nozzle.

The controller changes the nozzle voltage while keeping the counter voltage constant, thereby switching the potential difference to the first potential difference, the second potential difference, the third potential difference, or the fourth potential difference. may

According to this configuration, since the counter voltage can be kept constant, it is possible to suppress the generation of ozone caused by increasing the magnitude of the counter voltage.

Further, the control section may change the values of the second potential difference, the third potential difference and the fourth potential difference according to the type of sheet.

According to this configuration, even if the electrical resistance between each nozzle and each counter electrode changes according to the type of sheet, an appropriate amount of fixer can be discharged from the nozzles.

Further, the control unit may acquire a resistance value of the sheet, and change the values of the second potential difference, the third potential difference, and the fourth potential difference according to the acquired resistance value.

According to this configuration, even if the electrical resistance between each nozzle and each counter electrode changes according to the resistance value of the sheet, an appropriate amount of fixer can be discharged from the nozzles.

Further, the image forming apparatus further includes a temperature/humidity sensor for detecting temperature and humidity, and the controller controls the first potential difference, the second potential difference, and the second potential difference based on the temperature/humidity detected by the temperature/humidity sensor. The values of the three potential differences and the fourth potential difference may be changed.

According to this configuration, even if the electrical resistance between each nozzle and each counter electrode changes due to changes in sheet resistance and air resistance due to temperature and humidity, an appropriate amount of fixer can be discharged from the nozzles. can.

Further, the image forming apparatus further includes a conveying path for conveying a sheet toward the first nozzle, and a sheet detecting section for detecting a sheet passing through the conveying path, wherein the control section controls the sheet The potential difference may be switched to the first potential difference, the second potential difference, the third potential difference, or the fourth potential difference according to the elapsed time after the detection unit detects the sheet.

Further, the image forming apparatus includes a first housing containing a fixing liquid, the first housing having the first nozzle, and a second housing housing the fixing liquid, the second housing having the second nozzle. and a second housing having

Further, the image forming apparatus may further include a guide that guides the sheet and is positioned between the first nozzle and the second nozzle in the conveying direction.

According to the present invention, in a configuration in which the same voltage is applied to a plurality of nozzles positioned at different positions in the sheet conveying direction, it is possible to suppress the occurrence of defective spraying.

1 illustrates a laser printer according to an embodiment; FIG. FIG. 4 is a diagram showing the fixing device in a state where the sheet does not face each nozzle; FIG. 4 is a diagram showing the fixing device in a state where the sheet faces only the first nozzle; FIG. 4 is a diagram showing the fixing device in a state in which sheets face each nozzle; FIG. 10 is a diagram showing the fixing device in a state where the sheet faces only the second nozzle; It is a graph which shows the relationship between a nozzle voltage and time. 4 is a flow chart showing the operation of a control unit; 4 is a graph showing a configuration in which a fourth nozzle voltage value is different from a second nozzle voltage value;

Next, embodiments will be described in detail with appropriate reference to the drawings.
As shown in FIG. 1, a laser printer 1 as an example of an image forming apparatus includes a main housing 2, a feeder section 3, and an image forming section 4. As shown in FIG.

The feeder section 3 has a function of feeding the sheet S to the image forming section 4 . The feeder section 3 includes a supply tray 31 and a supply mechanism 32 . The supply tray 31 is a tray that stores sheets, and is detachable from the lower portion of the main body housing 2 . The supply mechanism 32 supplies the sheet S in the supply tray 31 toward the image forming section 4 .

The image forming section 4 has a function of forming an image on the sheet S. FIG. The image forming section 4 includes an image forming section 5 and a fixing device 7 .

The image forming unit 5 has a function of forming a toner image on the sheet S. As shown in FIG. The image forming section 5 includes a scanner unit SU and a process cartridge 6 .

The scanner unit SU is provided in the upper part of the main body housing 2, and includes a laser emitting section, a polygon mirror, a lens, a reflecting mirror, and the like (not shown). The scanner unit SU emits a laser beam onto the surface of a photosensitive drum 61, which will be described later.

The process cartridge 6 can be attached to and detached from the main housing 2 . The process cartridge 6 includes a photosensitive drum 61 , a charger (not shown), a toner container 62 , a supply roller 63 , a developing roller 64 and a transfer roller 65 .

In this process cartridge 6 , a charger (not shown) charges the surface of the photosensitive drum 61 . The scanner unit SU forms an electrostatic latent image on the surface of the photosensitive drum 61 by exposing the surface of the photosensitive drum 61 with a laser beam.

The supply roller 63 supplies the toner in the toner container 62 to the developing roller 64 . The developing roller 64 supplies toner to the electrostatic latent image on the photosensitive drum 61 to form a toner image on the surface of the photosensitive drum 61 . The toner image on the surface of the photosensitive drum 61 is transferred to the sheet S when the sheet S is conveyed between the photosensitive drum 61 and the transfer roller 65 .

The fixing device 7 is a device that fixes the toner image on the sheet S by spraying a charged fixing liquid toward the toner image on the sheet S by electrostatic spraying. The sheet S ejected from the fixing device 7 is conveyed to the ejection roller R and ejected from the ejection roller R onto the ejection tray 21 .

The laser printer 1 further includes a transport path 22 , a sheet sensor SE<b>1 as an example of a sheet detection unit, a temperature/humidity sensor SE<b>2 , and a control unit 100 .

The transport path 22 is a path for transporting the sheet S from the supply tray 31 toward the fixing device 7 (first nozzle 71B described later). The sheet sensor SE<b>1 is a sensor that detects the sheet S passing through the conveying path 22 . The sheet sensor SE1 includes, for example, a detection arm that swings when pressed by the sheet S, and an optical sensor that detects the swinging of the detection arm.

The temperature/humidity sensor SE2 is a sensor that detects temperature/humidity. The detection results of sheet sensor SE1 and temperature/humidity sensor SE2 are output to control unit 100. FIG.

Next, the configuration of the fixing device 7 will be described in detail.
As shown in FIG. 2 , the fixing device 7 has a first head 71 , a second head 72 , a first counter electrode 73 , a second counter electrode 74 and a fixing housing 75 .

The first head 71 has a first housing 71A, first nozzles 71B, and first nozzle electrodes 71C. The first housing 71A contains a fixer. The first housing 71A has a first nozzle 71B.

The first nozzle 71B is a nozzle for ejecting the fixer inside the first housing 71A. In the drawing, dots indicate the fixer sprayed from the first nozzle 71B and the second nozzle 72B, which will be described later.

A plurality of first nozzles 71B are provided side by side in the width direction of the sheet S. As shown in FIG. It should be noted that multiple rows of nozzle rows each including the plurality of first nozzles 71</b>B arranged in the width direction may be provided in the sheet S conveying direction. In the following description, the width direction of the sheet S is also simply referred to as the "width direction", and the conveying direction of the sheet S is also simply referred to as the "conveying direction".

The first nozzle electrode 71C is an electrode for charging the fixer in the first nozzle 71B. The first nozzle electrode 71C is positioned inside the first housing 71A. The first nozzle electrode 71C may be positioned at a position where the fixer in the first nozzle 71B can be charged, and may be positioned, for example, on the outer surface of the first nozzle 71B.

The second head 72 is located downstream of the first head 71 in the transport direction. The second head 72 has a second housing 72A, a second nozzle 72B, and a second nozzle electrode 72C.

The second housing 72A contains a fixer. The second housing 72A has a second nozzle 72B. A fixer can be supplied from a fixer tank (not shown) to the first housing 71A and the second housing 72A. Further, the same pressure is applied to the fixer in the first housing 71A and the fixing liquid in the second housing 72A by a pressure device (not shown). As for the control of the supply of the fixer and the pressurization of the fixer, the control described in Japanese Patent Application Laid-Open No. 2017-167245 may be performed.

The second nozzle 72B is a nozzle for ejecting the fixer inside the second housing 72A. A plurality of second nozzles 72B are provided side by side in the width direction. In addition, multiple rows of nozzle rows each including the plurality of second nozzles 72B arranged in the width direction may be provided in the transport direction.

The second nozzle electrode 72C is an electrode for charging the fixer in the second nozzle 72B. The second nozzle electrode 72C is located inside the second housing 72A. The second nozzle electrode 72C, like the first nozzle electrode 71C, may be positioned at a position where the fixer in the second housing 72A can be charged.

The first counter electrode 73 faces the tip of the first nozzle 71B with a gap therebetween. In this embodiment, the tip of the first nozzle 71B faces downward, and the first counter electrode 73 vertically faces the tip of the first nozzle 71B. The sheet S can pass between the first nozzle 71B and the first counter electrode 73 .

The second counter electrode 74 faces the tip of the second nozzle 72B with a gap therebetween. In this embodiment, the tip of the second nozzle 72B faces downward, and the second counter electrode 74 vertically faces the tip of the second nozzle 72B. The sheet S can pass between the second nozzle 72B and the second counter electrode 74 .

The fixing housing 75 supports the first head 71 , the second head 72 , the first counter electrode 73 and the second counter electrode 74 . The fixing housing 75 has an upstream guide 76 for guiding the sheet S, an intermediate guide 77 and a downstream guide 78 .

The upstream guide 76, intermediate guide 77 and downstream guide 78 are located between the first nozzle 71B and the first counter electrode 73 in the vertical direction. Specifically, the upstream guide 76, the intermediate guide 77, and the downstream guide 78 each have a guide surface that contacts the sheet S, and each guide surface is positioned at substantially the same position in the vertical direction. Thereby, the distances between the nozzles 71B and 72B and the sheet S are kept constant.

The upstream guide 76 is positioned upstream in the transport direction from the first nozzle 71B. The upstream guide 76 is made of a conductive member such as metal. The upstream guide 76 attracts the sheet S by applying a voltage.

The intermediate guide 77 is an example of a guide, and is positioned between the first nozzle 71B and the second nozzle 72B in the transport direction. The intermediate guide 77 is made of a conductive member such as metal. The intermediate guide 77 attracts the sheet S by applying a voltage.

The downstream guide 78 is located downstream of the second nozzle 72B in the transport direction. The downstream guide 78 is part of the fuser housing 75 .

The laser printer 1 further includes a nozzle power supply P1 and a counter power supply P2. The nozzle power supply P1 is a power supply that applies a nozzle voltage to the first nozzle electrode 71C and the second nozzle electrode 72C. The counter power source P2 is a power source that applies a counter voltage to the first counter electrode 73 and the second counter electrode 74 . The nozzle voltage can be, for example, a positive voltage. The counter voltage can be, for example, a negative voltage.

In a state in which the fixer is sprayed from the nozzles 71B, 72B to the counter electrodes 73, 74, the power sources P1, P2, the nozzle electrodes 71C, 72C, and the counter electrodes 73, 74 constitute one circuit. In this circuit, the first nozzle electrode 71C and the first counter electrode 73 and the second nozzle electrode 72C and the second counter electrode 74 are connected in parallel. Thereby, the potential of the first nozzle electrode 71C and the potential of the second nozzle electrode 72C become the same potential, and the potential of the first counter electrode 73 and the potential of the second counter electrode 74 become the same potential.

A resistance value between each nozzle electrode 71C, 72C and each counter electrode 73, 74 changes according to the position of the sheet S. FIG. In the following description, the space between the first nozzle electrode 71C and the second nozzle electrode 72C and the first counter electrode 73 and the second counter electrode 74 is also simply referred to as "between the electrodes".

The fixing device 7 can take a first state shown in FIG. 2, a second state shown in FIG. 3, a third state shown in FIG. 4, and a fourth state shown in FIG. 5 during print control. A first state is a state in which there is no sheet S between the electrodes. Specifically, the first state is a state in which there is no sheet S between the first nozzle 71B and the first counter electrode 73 and there is no sheet S between the second nozzle 72B and the second counter electrode 74 . In the first state, the resistance value between the electrodes is only the resistance value of air, which is the lowest first resistance value R1.

The second state is a state in which the sheet S faces only the first nozzles 71B. Specifically, the second state is a state in which the sheet S is present between the first nozzle 71B and the first counter electrode 73 and the sheet S is not present between the second nozzle 72B and the second counter electrode 74 . In the second state, the resistance value between the first nozzle 71B and the first counter electrode 73 is the combined value of the air resistance value and the resistance value of the sheet S, and the resistance value between the second nozzle 72B and the second counter electrode 74 is The resistance value is only the air resistance value. Therefore, in the second state, the resistance value between the electrodes becomes a second resistance value R2 that is larger than the first resistance value R1.

A third state is a state in which the sheet S faces both the first nozzle 71B and the second nozzle 72B. Specifically, the third state is a state in which the sheet S is present between the first nozzle 71B and the first counter electrode 73 and the sheet S is present between the second nozzle 72B and the second counter electrode 74 . In the third state, the resistance value between the first nozzle 71B and the first counter electrode 73 is the combined value of the air resistance value and the resistance value of the sheet S, and the resistance value between the second nozzle 72B and the second counter electrode 74 is The resistance value is the combined value of the air resistance value and the sheet S resistance value. Therefore, in the third state, the resistance value between the electrodes becomes a third resistance value R3 that is larger than the second resistance value R2.

A fourth state is a state in which the sheet S faces only the second nozzles 72B. Specifically, the fourth state is a state in which there is no sheet S between the first nozzle 71B and the first counter electrode 73 and there is a sheet S between the second nozzle 72B and the second counter electrode 74 . In the fourth state, the resistance value between the first nozzle 71B and the first counter electrode 73 is the air resistance value, and the resistance value between the second nozzle 72B and the second counter electrode 74 is the air resistance value. A combined value of the resistance values of the sheet S is obtained. In the third state, the resistance value between the electrodes becomes a fourth resistance value R4 that is higher than the first resistance value R1 and lower than the third resistance value R3.

The control unit 100 has a CPU, a ROM, a RAM, etc., and is configured to execute various processes in response to reception of a print command according to a program prepared in advance. The control unit 100 can change the potential difference ΔV, which is the difference between the nozzle voltage and the counter voltage, by changing the nozzle voltage while keeping the counter voltage constant. The potential difference ΔV is the potential difference between the electrodes, and changing the potential difference ΔV changes the spray amount from each of the nozzles 71B and 72B. Specifically, when the potential difference ΔV is increased, the spray amount is increased, and when the potential difference ΔV is decreased, the spray amount is decreased.

As shown in FIG. 6, the controller 100 controls the initial period (time t0-t1) from when the print command is received until the leading edge of the sheet S to be conveyed first is conveyed to a predetermined position on the conveying path 22. , the nozzle voltage Vn applied to each of the nozzle electrodes 71C and 72C is set to the reference nozzle voltage value Vb. The reference nozzle voltage value Vb is a voltage value small enough to prevent the fixer from being sprayed from the nozzle electrodes 71C and 72C. The reference nozzle voltage value Vb is set to a voltage value such that the interface between the fixing fluid and the air at the tips of the nozzles 71B and 72B changes from a recessed state toward the fixing fluid side to a substantially flat state by applying the nozzle voltage Vn. can be set.

The predetermined position may be any position on the transport path 22 as long as it is upstream of the fixing device 7 in the transport direction. For example, the predetermined position can be a position between the photosensitive drum 61 and the fixing device 7 in the transport direction.

Note that, in the present embodiment, in the initial period, even if the state of the fixing device 7 is the first state shown in FIG. Although it is not set to V1, the nozzle voltage Vn may be set to the first nozzle voltage value V1 in the initial period.

After the initial period has elapsed (time t1), if the state of the fixing device 7 is the first state, the control unit 100 sets the nozzle voltage Vn to the first nozzle voltage value V1 that is higher than the reference nozzle voltage value Vb. , the potential difference ΔV is defined as a first potential difference ΔV1. The first nozzle voltage value V1 is a voltage value at which the fixer can be sprayed from each of the nozzles 71B and 72B.

When the state of the fixing device 7 is the second state shown in FIG. 3, the control unit 100 sets the nozzle voltage Vn to the second nozzle voltage value V2, which is higher than the first nozzle voltage value V1, thereby reducing the potential difference ΔV. , a second potential difference ΔV2 larger than the first potential difference ΔV1. The second nozzle voltage value V2 is set to a voltage value that can spray an amount of fixing liquid suitable for fixing when the resistance value between the electrodes is the second resistance value R2.

The timing (time t2) for switching from the first nozzle voltage value V1 to the second nozzle voltage value V2 is before the point when the leading edge of the sheet S reaches the same position as the leading edge of the first nozzle 71B in the conveying direction. can be set. For example, the timing of switching from the first nozzle voltage value V<b>1 to the second nozzle voltage value V<b>2 can be when the leading edge of the sheet S contacts the upstream guide 76 .

When the state of the fixing device 7 is the third state shown in FIG. 4, the control unit 100 sets the nozzle voltage Vn to the third nozzle voltage value V3, which is higher than the second nozzle voltage value V2, thereby reducing the potential difference ΔV. , to a third potential difference ΔV3 larger than the second potential difference ΔV2. The third nozzle voltage value V3 is set to a voltage value that can spray an amount of fixing liquid suitable for fixing when the resistance value between the electrodes is the third resistance value R3.

Note that the timing (time t3) for switching from the second nozzle voltage value V2 to the third nozzle voltage value V3 is before the time when the leading edge of the sheet S reaches the same position as the leading edge of the second nozzle 72B in the conveying direction. can be set. For example, the timing of switching from the second nozzle voltage value V<b>2 to the third nozzle voltage value V<b>3 can be when the leading edge of the sheet S contacts the intermediate guide 77 .

When the state of the fixing device 7 is the fourth state shown in FIG. 5, the controller 100 sets the nozzle voltage Vn to a fourth voltage value lower than the third nozzle voltage value V3 and higher than the first nozzle voltage value V1. By setting the nozzle voltage value to V4, the potential difference ΔV is set to a fourth potential difference ΔV4 that is larger than the first potential difference ΔV1 and smaller than the third potential difference ΔV3. The fourth nozzle voltage value V4 is set to a voltage value that can spray an amount of fixing liquid suitable for fixing when the resistance value between the electrodes is the fourth resistance value R4.

Here, in the second state shown in FIG. 3, the fixer is not applied to the sheet S when the fixer is sprayed, whereas in the fourth state shown in FIG. A fixing liquid is applied to the sheet S. Therefore, the fourth resistance value R4, which is the resistance value in the fourth state, is smaller than the second resistance value R2, which is the resistance value in the second state. However, in this embodiment, considering that the difference between the second resistance value R2 and the fourth resistance value R4 has little effect, the fourth nozzle voltage value V4 is set to the same value as the second nozzle voltage value V2.

Note that the switching timing (time t4) from the third nozzle voltage value V3 to the fourth nozzle voltage value V4 is from the time when the trailing edge of the sheet S reaches the same position as the leading edge of the first nozzle 71B in the conveying direction. can also be set at a later point in time. For example, the timing of switching from the third nozzle voltage value V3 to the fourth nozzle voltage value V4 can be when the trailing edge of the sheet S contacts the intermediate guide 77 .

When the state of the fixing device 7 returns from the fourth state to the first state, the controller 100 changes the nozzle voltage Vn from the fourth nozzle voltage value V4 to the first nozzle voltage value V1 (time t5). The timing (time t5) of switching from the fourth nozzle voltage value V4 to the first nozzle voltage value V1 is from the time point when the trailing edge of the sheet S reaches the same position as the leading edge of the second nozzle 72B in the conveying direction. can also be set at a later point in time. For example, the timing of switching from the fourth nozzle voltage value V4 to the first nozzle voltage value V1 can be when the trailing edge of the sheet S contacts the downstream guide 78 .

After printing is completed, the control unit 100 changes the nozzle voltage Vn from the first nozzle voltage value V1 to the reference nozzle voltage value Vb at a predetermined timing (time t6). After changing the nozzle voltage Vn to the reference nozzle voltage value Vb, the control unit 100 sets the nozzle voltage Vn to 0 at a predetermined timing. The control unit 100 switches the potential difference ΔV according to the elapsed time after the sheet sensor SE1 detects the sheet S. FIG.

In the present embodiment, the nozzle voltage Vn is changed in the order of V1, Vb, and 0 after printing is completed. , the first nozzle voltage value V1 may be changed to zero.

Next, operation of the control unit 100 will be described in detail.
Upon receiving a print command, the control unit 100 executes the spraying process shown in FIG. In the spraying process, the controller 100 first sets the voltage value of each nozzle based on the type of sheet S and the temperature and humidity (S1). Here, the type of the sheet S is specified by the control unit 100, for example, based on information indicating the type of the sheet S included in the print command.

Specifically, in step S1, the control unit 100 sets the second nozzle voltage value V2, the third nozzle voltage value V3, and the fourth nozzle voltage value V4 according to the type of the sheet S. As shown in FIG. When the control unit 100 in step S1 changes the voltage values of the nozzles to values different from those in the previous spraying process, the values of the second potential difference ΔV2, the third potential difference ΔV3, and the fourth potential difference ΔV4 are the previous values. is changed from

Here, since the width and thickness of the sheet S differ depending on the type of the sheet S, the resistance value of the sheet S differs for each type. When at least part of the sheet S exists between the electrodes, the resistance value between the electrodes increases as the resistance value of the sheet S increases. Therefore, the control unit 100 sets each nozzle voltage value according to the type of the sheet S so that the nozzle voltage value increases as the resistance value of the sheet S increases.

Further, in step S1, the control unit 100 controls the first nozzle voltage value V1, the second nozzle voltage value V2, the third nozzle voltage value V3, and the fourth nozzle voltage value based on the temperature and humidity detected by the temperature and humidity sensor SE2. Set the value of V4. When the control unit 100 in step S1 changes the voltage values of the nozzles to values different from those in the previous spraying process, the first potential difference ΔV1, the second potential difference ΔV2, the third potential difference ΔV3, and the fourth potential difference ΔV4 The value is changed from the previous value.

Here, the resistance values of the air and the sheet S increase as the absolute humidity obtained from the temperature and humidity decreases. Therefore, the control unit 100 sets each nozzle voltage value according to the type of the sheet S so that each nozzle voltage value increases as the absolute humidity decreases. As a method of setting each nozzle voltage value, for example, a method of setting based on a table or function showing the relationship between the type of sheet S, the absolute humidity, and the value of each nozzle voltage may be adopted. Also, since the reference nozzle voltage value Vb does not need to be changed even if the resistance value between the electrodes changes, it may be set to a fixed value.

In step S1, after setting the nozzle voltage values, the control unit 100 sets the nozzle voltage Vn to the reference nozzle voltage value Vb, and turns on the nozzle power supply P1 and the opposing power supply P2. As a result, the interface of the fixer in each of the nozzles 71B and 72B becomes substantially flat, and the fixer can be immediately sprayed.

After step S1, the control unit 100 determines whether or not the sheet sensor SE1 has detected the sheet S (S2). The control unit 100 repeats the process of step S2 until the sheet sensor SE1 detects the sheet S (No).

If it is determined that the sheet S has been detected in step S2 (Yes), the control unit 100 determines whether or not the first time has passed since the sheet S was detected, thereby determining whether the leading edge of the sheet S is detected. A determination is made as to whether or not the transport path 22 has reached a predetermined position (S3). The control unit 100 repeats the process of step S3 until the first time elapses (No).

If it is determined that the first time has elapsed in step S3 (Yes), the control unit 100 switches the nozzle voltage Vn to the first nozzle voltage value V1 to set the potential difference ΔV to the first potential difference ΔV1 (S4 ). As a result, spraying of the fixer is started.

After step S4, the control unit 100 determines whether or not a second time longer than the first time has elapsed since the detection of the sheet S, so that the leading edge of the sheet S reaches the vicinity of the first nozzle 71B. It is determined whether or not (S5). The control unit 100 repeats the process of step S5 until the second time elapses (No).

If it is determined in step S5 that the second time has elapsed (Yes), the control unit 100 switches the potential difference ΔV to the second potential difference ΔV2 by switching the nozzle voltage Vn to the second nozzle voltage value V2 (S6 ). As a result, as shown in FIG. 3, when the resistance value between the electrodes becomes the second resistance value R2, the fixing fluid is appropriately sprayed by the second potential difference ΔV2 corresponding to the second resistance value R2. be able to.

After step S6, the control unit 100 determines whether or not a third time longer than the second time has passed since the detection of the sheet S, so that the leading edge of the sheet S reaches the vicinity of the second nozzle 72B. It is determined whether or not (S7). The control unit 100 repeats the process of step S7 until the third time elapses (No).

If it is determined that the third time has elapsed in step S7 (Yes), the control unit 100 switches the nozzle voltage Vn to the third nozzle voltage value V3, thereby switching the potential difference ΔV to the third potential difference ΔV3 (S8 ). As a result, as shown in FIG. 4, when the resistance value between the electrodes reaches the third resistance value R3, the fixing fluid is appropriately sprayed by the third potential difference ΔV3 corresponding to the third resistance value R3. be able to.

After step S8, the control unit 100 determines whether or not a fourth time longer than the third time has passed since the detection of the sheet S, so that the trailing edge of the sheet S is conveyed ahead of the first nozzle 71B. It is determined whether or not the position on the downstream side in the direction has been reached (S9). The control unit 100 repeats the process of step S9 until the fourth time elapses (No).

If it is determined in step S9 that the fourth time has elapsed (Yes), the control unit 100 switches the potential difference ΔV to the fourth potential difference ΔV4 by switching the nozzle voltage Vn to the fourth nozzle voltage value V4 (S10 ). As a result, as shown in FIG. 5, when the resistance value between the electrodes reaches the fourth resistance value R4, the fixing fluid is appropriately sprayed by the fourth potential difference ΔV4 corresponding to the fourth resistance value R4. be able to.

After step S10, the control unit 100 determines whether or not a fifth time longer than the fourth time has elapsed since the detection of the sheet S, so that the trailing edge of the sheet S is conveyed ahead of the second nozzle 72B. It is determined whether or not the position on the downstream side in the direction has been reached (S11). The control unit 100 repeats the process of step S11 until the fifth time elapses (No).

If it is determined in step S11 that the fifth time has passed (Yes), the control unit 100 switches the potential difference ΔV to the first potential difference ΔV1 by switching the nozzle voltage Vn to the first nozzle voltage value V1 (S12 ). As a result, when the sheet S is no longer present between the electrodes, it is possible to prevent a large amount of the fixer from being sprayed unnecessarily.

After step S12, the control unit 100 determines whether or not printing has ended (S13). If it is determined in step S13 that printing has not ended (No), the control section 100 returns to the process of step S2.

If it is determined in step S13 that printing has ended (Yes), the control unit 100 switches the nozzle voltage Vn to the reference nozzle voltage value Vb, and then, at a predetermined timing, turns on the nozzle power supply P1 and the opposing power supply P2. It is turned off (S14), and this processing ends.

Next, the effects of control by the control unit 100 will be described.
As shown in FIG. 1, when the leading edge of the sheet S reaches a predetermined position on the transport path 22, for example, a position between the photosensitive drum 61 and the fixing device 7, the control unit 100 changes the nozzle voltage Vn to the reference nozzle voltage value Vb. to the first nozzle voltage value V1. As a result, as shown in FIG. 2, the minimum necessary amount of fixing liquid is started to be sprayed. At this time, since the sheet S does not exist between the electrodes, the resistance value between the electrodes is the first resistance value R1.

After that, as shown in FIG. 3, when the sheet S faces only the first nozzle 71B, the resistance value between the electrodes becomes a second resistance value R2 larger than the first resistance value R1. sets the nozzle voltage Vn to the second nozzle voltage value V2 corresponding to the second resistance value R2. As a result, it is possible to spray the fixing liquid in an amount suitable for fixing.

After that, as shown in FIG. 4, when the sheet S faces the nozzles 71B and 72B, the resistance value between the electrodes becomes a third resistance value R3 larger than the second resistance value R2. sets the nozzle voltage Vn to the third nozzle voltage value V3 corresponding to the third resistance value R3. As a result, it is possible to spray the fixing liquid in an amount suitable for fixing.

After that, as shown in FIG. 5, when the sheet S faces only the second nozzle 72B, the resistance value between the electrodes becomes a fourth resistance value R4 smaller than the third resistance value R3. sets the nozzle voltage Vn to the fourth nozzle voltage value V4 corresponding to the fourth resistance value R4. As a result, it is possible to spray the fixing liquid in an amount suitable for fixing.

According to the above, the following effects can be obtained in this embodiment.
Even if the amount of the sheet S entering between the electrodes changes, an appropriate amount of fixing liquid can be sprayed onto the sheet S from the nozzles 71B and 72B, so that the occurrence of spraying failure can be suppressed.

Since the counter voltage is kept constant, it is possible to suppress the generation of ozone caused by increasing the magnitude of the counter voltage.

Since the value of the potential difference ΔV is changed according to the type of the sheet S, an appropriate amount of fixer can be sprayed onto the sheet S even if the electrical resistance between the electrodes changes according to the type of the sheet S.

Since the value of the potential difference ΔV is changed based on the temperature and humidity, even if the electrical resistance between the electrodes changes due to the change in the resistance value of the sheet S and the resistance value of the air due to the temperature and humidity, an appropriate amount of fixing fluid can be applied to the sheet S. can be sprayed on

The present invention is not limited to the above-described embodiments, and can be used in various forms as exemplified below. In the following description, members and parameter values that are substantially the same as those in the above embodiment are denoted by the same reference numerals, and descriptions thereof are omitted.

In the above embodiment, the fourth potential difference ΔV4 is the same value as the second potential difference ΔV2, but the present invention is not limited to this. As shown in FIG. 8, the fourth potential difference ΔV4 is smaller than the second potential difference ΔV2 good too. According to this, the fourth potential difference ΔV4 can be set to a value corresponding to the fourth resistance value R4 which is smaller than the second resistance value R2. Can be sprayed.

In the above embodiment, the potential difference ΔV is changed according to the type of sheet S, but the present invention is not limited to this. For example, the control unit 100 may acquire the resistance value of the sheet S and change the values of the second potential difference ΔV2, the third potential difference ΔV3, and the fourth potential difference ΔV4 according to the acquired resistance value.

Note that the resistance value of the sheet S can be calculated, for example, based on a signal from a current sensor that detects the transfer current flowing through the transfer roller 65 . According to this configuration, even if the electrical resistance between the electrodes changes according to the resistance value of the sheet S, it is possible to spray the sheet S with an appropriate amount of fixing liquid.

In the above embodiment, the potential difference ΔV is changed by changing the nozzle voltage Vn, but the present invention is not limited to this, and the potential difference may be changed by changing at least one of the nozzle voltage and the counter voltage. For example, the potential difference may be changed by changing the counter voltage while keeping the nozzle voltage constant, or the potential difference may be changed by changing both the nozzle voltage and the counter voltage.

In the above embodiment, the number of nozzle rows having a plurality of nozzles in the width direction is two, but the present invention is not limited to this, and the number of nozzle rows may be three or more. When the number of nozzle rows is three or more, the nozzles forming the most upstream nozzle row in the transport direction correspond to the first nozzles, and the nozzles forming the most downstream nozzle row in the transport direction correspond to the first nozzles. It corresponds to the second nozzle.

The first counter electrode and the second counter electrode may be configured integrally as one component.

Also, one housing may have the first nozzle and the second nozzle. In this case, the first nozzle electrode and the second nozzle electrode may be configured integrally as one component.

In the above-described embodiment, the intermediate guide 77 as a guide is made of a conductive member such as metal, but the guide may be a part of the fixing housing, for example.

In the above embodiment, the fourth potential difference ΔV4 is switched to the first potential difference ΔV1, but the present invention is not limited to this. For example, when the leading edge of the succeeding sheet S reaches the vicinity of the first nozzle 71B immediately after the trailing edge of the preceding sheet S moves downstream of the second nozzle 72B, the fourth potential difference ΔV4 It may be switched to the second potential difference ΔV2. Further, when the leading edge of the succeeding sheet S reaches the first nozzle 71B before the trailing edge of the leading sheet S reaches the second nozzle 72B during spraying with the fourth potential difference ΔV4, the fourth potential difference The potential difference ΔV4 may be switched to the third potential difference ΔV3. Further, when the interval between the sheets S is extremely small, after the potential difference ΔV is changed in the order of ΔV1, ΔV2, and ΔV3 for the first sheet S among the plurality of sheets S, the potential difference ΔV for the second and subsequent sheets S is changed. may be fixed at ΔV3, and the potential difference ΔV may be switched from ΔV3 to ΔV4 when the last sheet S faces only the second nozzle 72B.

Although the present invention is applied to the laser printer 1 in the above embodiment, the present invention is not limited to this, and may be applied to other image forming apparatuses such as copiers and multi-function machines.

Each element described in the above embodiment and modifications may be implemented in any combination.

1 Laser Printer 71B First Nozzle 71C First Nozzle Electrode 72B Second Nozzle 72C Second Nozzle Electrode 73 First Counter Electrode 74 Second Counter Electrode 100 Control Part P1 Nozzle Power Supply P2 Counter Power Supply S Sheet

Claims (9)

a first nozzle for ejecting a fixer;
a first nozzle electrode for charging the fixer in the first nozzle;
a first counter electrode facing the tip of the first nozzle;
a second nozzle for ejecting a fixer, the second nozzle being located downstream of the first nozzle in the sheet conveying direction;
a second nozzle electrode for charging the fixer in the second nozzle;
a second counter electrode facing the tip of the second nozzle;
a nozzle power supply that applies a nozzle voltage to the first nozzle electrode and the second nozzle electrode;
a counter power supply that applies a counter voltage to the first counter electrode and the second counter electrode;
a control unit capable of changing a potential difference, which is a difference between the nozzle voltage and the counter voltage, by changing at least one of the nozzle voltage and the counter voltage;
The control unit
when there is no sheet between the first nozzle and the first counter electrode and when there is no sheet between the second nozzle and the second counter electrode, the potential difference is defined as a first potential difference;
When there is a sheet between the first nozzle and the first counter electrode and there is no sheet between the second nozzle and the second counter electrode, the potential difference is set to a second potential difference larger than the first potential difference. Let the potential difference be
When a sheet exists between the first nozzle and the first counter electrode and a sheet exists between the second nozzle and the second counter electrode, the potential difference is set to a third potential difference larger than the second potential difference. Let the potential difference be
When there is no sheet between the first nozzle and the first counter electrode and there is a sheet between the second nozzle and the second counter electrode, the potential difference is set to be greater than the first potential difference, and and a fourth potential difference smaller than the third potential difference. 2. The image forming apparatus according to claim 1, wherein said fourth potential difference is smaller than said second potential difference. The controller switches the potential difference to the first potential difference, the second potential difference, the third potential difference, or the fourth potential difference by changing the nozzle voltage while the counter voltage is kept constant. 3. The image forming apparatus according to claim 1 or 2. 4. The control unit according to any one of claims 1 to 3, wherein the controller changes values of the second potential difference, the third potential difference, and the fourth potential difference according to the type of sheet. image forming device. The control unit acquires the resistance value of the sheet, and changes the values of the second potential difference, the third potential difference, and the fourth potential difference according to the acquired resistance value. Item 4. The image forming apparatus according to any one of Item 3. Equipped with a temperature and humidity sensor that detects temperature and humidity,
2. The controller changes values of the first potential difference, the second potential difference, the third potential difference, and the fourth potential difference based on the temperature and humidity detected by the temperature and humidity sensor. 6. The image forming apparatus according to claim 5. a transport path for transporting the sheet toward the first nozzle;
a sheet detection unit that detects a sheet passing through the conveying path,
The control section switches the potential difference to the first potential difference, the second potential difference, the third potential difference, or the fourth potential difference according to the elapsed time after the sheet detection section detects the sheet. 7. The image forming apparatus according to any one of claims 1 to 6. a first housing containing a fixer, the first housing having the first nozzle;
8. The image forming apparatus according to any one of claims 1 to 7, further comprising: a second housing containing a fixer, the second housing having the second nozzle. Device. 9. The apparatus according to any one of claims 1 to 8, further comprising a guide that guides the sheet and is positioned between the first nozzle and the second nozzle in the conveying direction. image forming device.

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