JPH09106176A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device capable of keeping a developing gap at high accuracy for a long period by reducing the number of times of the pressure switching operation of developing units. SOLUTION: In the image forming device which is capable of selecting plural image forming modes (positive and negative modes), provided with a photoreceptor (image carrier) 1 carrying a toner image and positive and negative developing units 5 and 6 and presses the corresponding developing unit 5 (6) against the photoreceptor 1 and separates the other developing unit 6 (5) from the photoreceptor 1, in each image forming mode, the pressed states of the developing units 5 and 6 contributed to the formation of an image are kept after an image forming operation is completed as well and when the image forming mode is changed, the pressed states of the developing units 5 and 6 are switched, the developing unit 6 (5) corresponding to the changed image forming mode is pressed against the photoreceptor 1 and the other developing unit 5 (6) is separated from the photoreceptor 1. Thus, only when the image forming mode is changed, the developing units 5 and 6 are switched so that the number of the pressure switching operation times of the developing units 5 and 6 is reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a microreader printer capable of selecting a plurality of image forming modes and having an image carrier for carrying a toner image and a plurality of developing devices corresponding to each image forming mode. The present invention relates to an image forming apparatus such as a twin color copying machine and a full color copying machine.

[0002]

2. Description of the Related Art FIG. 7 shows a negative / positive microreader printer as a conventional image forming apparatus adopting an electrophotographic method.

That is, FIG. 7 is a cross-sectional view of a main part of a microreader printer. In the microreader printer, the rotation direction of the photoconductor 1 (around the photoconductor 1 such as an OPC photosensitive drum having a negative charging property) is shown. A primary charging device 3, a positive developing device 5, a negative developing device 6, a post charging device 7, a transfer charging device 8, a separation charging device 9 and a cleaner 10 are arranged in this order along the direction (in the direction of the arrow in the figure), and after the visible image transfer. A fixing device (not shown) is arranged on the downstream side (left side in FIG. 7) of the transfer material (not shown) in the conveying direction.

As shown in FIG. 8, each of the developing devices 5 and 6 has a developing sleeve 11 for coating a thin layer of toner, and developing rollers 12 connected to both axial ends of the developing sleeve 11. It is configured to include.

Thus, an electrostatic latent image is formed by projecting the image exposure pattern 4 which has passed through the film original on the photoconductor 1 which is uniformly charged by the primary charger 3. Then, chromatic fine powder (toner) having electrostatic charges is attached to the electrostatic latent image, and the electrostatic latent image is developed as a visible image.

Here, as a method of developing the electrostatic latent image on the photosensitive member 1, there are a negative mode for obtaining a positive print from a negative film original and a positive mode for obtaining a positive print from a positive film original. In the negative mode, a portion on the surface of the photoconductor 1 is strongly exposed corresponding to an image portion of a negative film original, and a negative image is formed by using a negative developing device 6 to form a positive image. is there. Further, in the positive mode, a portion on the surface of the photoconductor 1 corresponding to a bright background portion of a positive film original is strongly exposed, and a positive image is formed by developing with a positive toner positively charged using the positive developing device 5. It is a thing.

By the way, the post charger 7 charges a visible image on the photosensitive member 1 by superposing an alternating current (AC) bias with a direct current (DC) bias having the same polarity as that of the toner, and the toner is transferred to paper or the like in the transfer step. The transfer material is easily transferred.

Then, the transfer material is brought into close contact with the visible image on the photoconductor 1, and the transfer charger 8 such as a corona charger applies a charge having a polarity opposite to that of the toner from the back side of the transfer material, whereby the photoconductor 1 The visible image above is electrostatically transferred to a transfer material.

After that, the transfer material is subjected to an alternating current (AC) charge by a separation charging device 9 composed of a corona charging device to be discharged, and is peeled off from the photoconductor 1. Next, the transfer material is conveyed to a fixing device (not shown), where the visible image is fixed by heat or the like in the fixing device, and then discharged to the outside of the apparatus main body.

Here, the developing process will be described in detail.

In the developing method using the non-contact method, the distance between the developing sleeve and the photosensitive member (developing gap) is, for example,
In this case, the developing roller 12 having a diameter larger than that of the developing sleeve 11 is attached to both ends of the developing sleeve 11 in the axial direction as shown in FIG.
By pressing the developing roller 12 against the photoconductor 1 as shown in FIG. 5, the developing gap δ is formed by the difference in diameter between the developing sleeve 11 and the developing roller 12.

In order to properly use the two print modes of the negative mode and the positive mode, an unused developing device is exposed to light in order to avoid toner consumption from the unused developing device and mixing of different kinds of toner during printing. It is necessary to separate it from the body surface.

Therefore, in the standby state of the printer,
As shown in FIG. 7, the negative developing device 6 which is frequently used is pressed against the photoconductor 1 and the positive developing device 5 is released from the pressure so that the photoconductor 1 is separated from the photoconductor 1.

Therefore, as shown in the flow chart of FIG. 10, when the print is started in the negative mode, the image formation is immediately started (STEP of FIG. 10).
1-3).

On the other hand, to print in the positive mode,
First, the pressures of the developing devices 5 and 6 are switched, the positive developing device 5 is pressed against the photoconductor 1, and the negative developing device 6 is separated from the photoconductor 1 (STEP 4 in FIG. 10). Then, in this state, the image forming process is started (STEP 5 in FIG. 10), and after the completion of all the processes, the pressures of the developing devices 5 and 6 are switched again, the positive developing device 5 is separated from the photoconductor 1, and the negative developing device is released. 6 is pressed onto the photoconductor 1 (STEP 6 in FIG. 10).

[0016]

However, in the conventional image forming apparatus, when the negative mode is continuously used, the negative developing device 6 is constantly pressed against the photoconductor 1, but when the positive mode is continuously used. Changes the pressurization of the developing devices 5 and 6 each time the printing operation is performed (pressurizes the positive developing device 5 to release the pressurization of the negative developing device 6 and then presses the positive developing device 5).
The operation of releasing the pressure of (1) to pressurize the negative developing device 6) is performed.

By the way, in the non-contact developing system, a high accuracy is required for a developing gap of several 100 μm.

However, when the positive mode is continuously used,
As described above, the pressure switching operation of the developing devices 5 and 6 is frequently repeated, so that the possibility that foreign matter may be mixed in the contact portion between the surface of the photoconductor 1 and the developing roller 12 increases, and the developing roller 12 Therefore, the accuracy of the developing gap is likely to be impaired in the long term.

The present invention has been made in view of the above problems, and an object of the present invention is to form an image in which the number of pressure switching operations of the developing device can be reduced to maintain the developing gap with high accuracy for a long period of time. To provide a device.

[0020]

In order to achieve the above object, the present invention comprises an image carrier capable of selecting a plurality of image forming modes and carrying a toner image, and at least one non-contact developing device. An image forming apparatus that has a plurality of developing devices including the image forming apparatus and presses the corresponding developing device to the image bearing member in each image forming mode and separates the other developing devices from the image bearing member. The pressure state of is maintained even after the image forming operation is completed, and when the image forming mode is changed, the pressure state of the developing device is switched, and the developing device corresponding to the changed image forming mode is used as the image carrier. It is characterized in that pressure is applied and another developing device is separated from the developing device.

Therefore, according to the present invention, since the developing device is kept pressed after the image forming process and the developing device is switched only when the image forming mode is changed, the developing device is added. The number of pressure switching operations is reduced, and the development gap can be maintained with high accuracy for a long period of time. Further, since the number of pressure switching operations of the developing device is reduced, mechanical fatigue of the developing device and the pressure switching mechanism is suppressed, and the durability of the device is improved.
Reduction of operating noise is achieved.

[0022]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

<First Embodiment> FIGS. 1 and 2 are schematic configuration diagrams of an image forming apparatus according to a first embodiment of the present invention, FIG. 3 is a flow chart showing the operation of the image forming apparatus, and FIG. 4 is a developing device. FIG. 5 is a perspective view of the pressure switching mechanism, and FIG. 5 is a front view of the operation panel.

The image forming apparatus according to the present embodiment has a positive mode in which an electrostatic latent image on the photoconductor 1 which is an image carrier is formed on a document using a positive developing device 5, and a negative developing mode. A micro-reader printer capable of selecting a negative mode for forming a negative image on a document by using the device 6.
The printer is constructed as shown in FIG.

That is, in the printer according to the present embodiment, the primary charger 3 for uniformly charging the surface of the photosensitive member 1 and the photosensitive member 1 around the photosensitive member 1 such as an OPC photosensitive drum having a negative charging property. A non-contact type positive developing device 5 that develops an electrostatic latent image into a positive image, a non-contact type negative developing device 6 that develops into a negative image, and a post-charger 7 that charges a toner image to improve transfer efficiency. A transfer charger 8 for transferring the toner image on the photoconductor 1 to the transfer material, a separation charger 9 for peeling the transfer material from the photoconductor 1, and a cleaner 10 for removing the toner remaining on the photoconductor 1 are provided as the photoconductor. 1 are arranged in order along the rotation direction of 1 (the direction of the arrow in the drawing), and the downstream side (the left side in FIG. 1) in the transport direction of the transfer material (not shown) after the toner image transfer
Is provided with a fixing device (not shown). FIG.
And in FIG. 2, 2 is pre-exposure and 4 is image exposure.

By the way, a pressure switching mechanism 30 is provided near the positive developing device 5 and the negative developing device 6.
The pressure switching mechanism 30 includes a positive developing device pressing arm 15 and a negative developing device pressing arm 16 which are rotatably fixed to a pressing arm shaft 17, and sensors such as sensors for knowing the positions of the pressing arms 15 and 16. Detecting means 22 and pressure cam drive shaft 14
The pressure cam 13 is fixed to the pressure cam 13, the CPU 20 that controls the drive of the pressure cam drive shaft 14, and the operation unit 21. The pressure arms 15 and 16 are driven to rotate by the pressure cam drive shaft 14. The pressure cam 13 is pressed.
As shown in FIG. 5, the operation unit 21 has a copy key 19
And mode selection keys (negative mode selection key 18N and positive mode selection key 18P).

Next, the operation of the printer according to this embodiment will be described with reference to the flowchart shown in FIG.

When the copy key 19 is pressed in the operation unit 21 shown in FIG. 5 (STEP 1 in FIG. 3), the CPU 20 selects either the negative mode or the positive mode, that is,
Negative mode selection key 18N or positive mode selection key 18
It is determined which of P is pressed (STEP 2 in FIG. 3).

When the negative mode is selected, the detecting means 22 determines which of the positive developing device 5 and the negative developing device 6 is in the pressurized state (STEP 3 in FIG. 3), and the developing devices 5 and 6 are pressurized. Decide whether to switch.

That is, when the copy mode 19 is pressed after selecting the negative mode selection key 18N on the operation unit 21, the detection means 22 detects that the negative developing device 6 is being pressed as shown in FIG. The signal is CPU
When it is transmitted to 20, the pressure switching operation is not performed, and the negative image forming process is immediately started using the negative developing device 6 (STEP 4 in FIG. 3).

Further, as shown in FIG. 2, when the positive developing device 5 is pressurized in the main body of the apparatus, that is detected by the detection means 22 and the signal is transmitted to the CPU 20 to switch the pressure. The operation is performed (STEP in FIG. 3)
5). That is, the CPU 20 switches the position of the pressure cam 13 by rotationally driving the pressure cam drive shaft 14 of the pressure switching mechanism 30 by a drive source (not shown). Then, the pressure applied to the positive developing device 5 by the positive developing device pressing arm 15 is released,
As shown in FIG. 1, the negative developing device pressing arm 16 presses the negative developing device 6 against the photoconductor 1, and then the negative image forming step is executed (STEP 4 in FIG. 3).

After the image forming process is completed, the pressure switching operation is not performed (STEP 6 in FIG. 3), and the positional relationship between the developing devices 5 and 6 is not changed.

On the other hand, in the operation unit 21, when the positive mode is selected by the positive mode selection key 18P, the detecting means 22 determines which of the positive developing device 5 and the negative developing device 6 is in the pressurized state ( In STEP 7) of FIG. 3, it is determined whether to switch the pressure of the developing devices 5 and 6.

That is, when the copy mode key 19 is pressed after the positive mode selection key 18P is selected on the operation section 21, it is detected by the detection means 22 that the positive developing device 5 is pressed as shown in FIG. The signal is CPU
When it is transmitted to 20, the pressure switching operation is not performed, and the positive image forming step is immediately started using the positive developing device 5 (STEP 8 in FIG. 3).

Further, as shown in FIG. 1, when the negative developing device 6 is pressurized in the main body of the apparatus, that is detected by the detection means 22 and the signal is transmitted to the CPU 20 to switch the pressure. The operation is performed (STEP in FIG. 3)
9). That is, the CPU 20 switches the position of the pressure cam 13 by rotationally driving the pressure cam drive shaft 14 of the pressure switching mechanism 30 by a drive source (not shown). Then, the pressure applied to the negative developing device 6 by the negative developing device pressing arm 16 is released,
As shown in FIG. 2, the positive developing device pressing arm 15 presses the positive developing device 5 against the photoconductor 1, and then the positive image forming step is executed (STEP 8 in FIG. 3).

After the image forming process is completed, the pressure switching operation is not performed (STEP 6 in FIG. 3), and the positional relationship between the developing devices 5 and 6 is not changed.

As described above, in the present embodiment,
After the completion of the image forming process, the developing devices 5 and 6 are kept in the pressed state, and only when the image forming mode is changed.
Since the switching operation of No. 6 is performed, the number of pressurization switching operations of the developing devices 5, 6 is reduced, and the developing gap can be maintained with high accuracy for a long period of time.

Further, since the number of pressurizing switching operations of the developing devices 5 and 6 is reduced, mechanical fatigue of the developing devices 5 and 6 and the pressurizing switching mechanism 30 is suppressed, and the durability of the apparatus is improved and the operating noise is reduced. In addition to the above, the first copy speed when copying continuously in the same print mode is increased.

<Second Embodiment> Next, a second embodiment of the present invention will be described with reference to FIG. 6. FIG. 6 is a flowchart showing the operation of the image forming apparatus according to this embodiment.

In the first embodiment, the pressurization state of the developing devices 5 and 6 is detected by using the detection means 22 such as a sensor. In this embodiment, the executed print mode is stored in the memory of the main body at the end of the printing operation. A memorizing method is adopted.
The image forming apparatus according to this embodiment also has the same configuration as that of the first embodiment.

That is, the copy key 19 in the operation unit 21
When is pressed (STEP 1 in FIG. 4), the CPU 20 operates the operation unit 2
The print mode currently selected in 1 and the print mode stored in the memory are compared (STEP in Fig. 4
2) If both modes match, the pressure switching operation is not performed and the image forming process is directly performed (STEP of FIG. 4).
3).

On the other hand, when the print mode currently selected by the operation unit 21 is different from the print mode stored in the memory, the pressure switching operation of the developing units 5 and 6 is performed (STEP 4 in FIG. 4), Then, the process proceeds to the image forming process (STEP 3 in FIG. 4).

After the printing operation is completed, the executed print mode is stored in the memory (STEP 5 in FIG. 4).

Thus, also in this embodiment, the same effect as that of the first embodiment can be obtained.

The means for detecting the pressurization state of the developing device and the pressurization switching mechanism are not limited to those shown in the above embodiments, and any other means can be adopted. Further, in the above embodiment, an example in which the present invention is applied to a negative / positive compatible microreader printer has been described. However, the present invention can be similarly applied to a twin color copying machine or a full color copying machine. it can.

[0046]

As is apparent from the above description, according to the present invention, a plurality of image forming modes can be selected, and an image carrier carrying a toner image and at least one non-contact developing device are provided. An image forming apparatus that has a plurality of developing devices including the image forming apparatus and presses the corresponding developing device to the image bearing member in each image forming mode and separates the other developing devices from the image bearing member. The pressure state of is maintained even after the image forming operation is completed, and when the image forming mode is changed, the pressure state of the developing device is switched, and the developing device corresponding to the changed image forming mode is used as the image carrier. Since the pressure is applied to separate the other developing devices from the developing device, it is possible to reduce the number of pressure switching operations of the developing devices and maintain the developing gap with high accuracy for a long period of time.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an image forming apparatus according to a first embodiment of the present invention.

FIG. 2 is a schematic configuration diagram of the image forming apparatus according to the first embodiment of the present invention.

FIG. 3 is a flowchart showing an operation of the image forming apparatus according to the first embodiment of the present invention.

FIG. 4 is a perspective view of a developing device pressure switching mechanism of the image forming apparatus according to the first embodiment of the present invention.

FIG. 5 is a front view of the operation panel of the image forming apparatus according to the first embodiment of the present invention.

FIG. 6 is a flowchart showing an operation of the image forming apparatus according to the second embodiment of the present invention.

FIG. 7 is a schematic configuration diagram of a conventional image forming apparatus.

FIG. 8 is a perspective view of a developing sleeve of the developing device.

FIG. 9 is an explanatory diagram of a developing gap.

FIG. 10 is a flowchart showing the operation of a conventional image forming apparatus.

[Explanation of symbols]

 1 Photoreceptor (Image Carrier) 5 Positive Developer 6 Negative Developer 13 Pressure Cam 14 Pressure Cam Drive Shaft 15 Positive Developer Pressure Arm 16 Negative Developer Pressure Arm 17 Pressure Arm Shaft 18N Negative Mode Selection Key 18P Positive mode selection key 19 Copy key 20 CPU 21 Operation part 22 Detection means 30 Pressurization switching mechanism

Claims (1)

[Claims] 1. A plurality of image forming modes are selectable, and an image carrier carrying a toner image and a plurality of developing devices including at least one non-contact developing device are provided, and in each image forming mode, In an image forming apparatus in which a corresponding developing device is pressed against the image bearing member and other developing devices are separated from the image bearing member, the pressing state of the developing device used for image formation is maintained even after the image forming operation is completed, When the forming mode is changed, the pressing state of the developing device is switched, the developing device corresponding to the changed image forming mode is pressed against the image carrier, and the other developing devices are separated from the developing device. Image forming apparatus.