JP2941982B2 - Image forming device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus using an electrostatic process, such as an electrostatic copying machine and a printer, and more particularly to an image forming apparatus having a contact type transfer means.

[0002]

2. Description of the Related Art In a well-known image forming apparatus including a step of transferring a toner image formed on the surface of an image carrier to a transfer material such as paper, a photoreceptor is formed by a contact transfer means such as a transfer roller pressed against the photoreceptor. A transfer bias voltage is applied to the transfer means, and the toner image on the photoreceptor side is transferred to the transfer material by the action of an electric field formed by the transfer material. It has already been proposed.

The image forming apparatus has a developing device for developing an electrostatic latent image to form a toner image on a photosensitive member. As means for detecting the remaining amount of toner contained in the developing device, there is means for utilizing a bias voltage applied to the developer carrying member. In this method, a conductive member (antenna) is provided in opposition to a developer carrying member, and a change in electrostatic capacity between the two is detected by detecting the amount of developer present between the two, thereby detecting a remaining amount of toner. Is what you do.

When the bias voltage is applied to the developer carrying member for the purpose of detecting the remaining amount of toner during non-development of the electrostatic latent image, that is, during non-printing, the toner adheres to the image carrier. . This toner adheres to and stains the contact transfer means, and stains the back surface of the transfer material when the transfer material enters the nip portion between the image carrier and the contact transfer means.

[0005]

SUMMARY OF THE INVENTION An image forming apparatus for detecting the remaining amount of toner in a developing device using a bias voltage, wherein the image forming apparatus has a transfer unit in contact with an image carrier. To prevent back contamination of the transfer material due to the detection operation.

[0006]

A main aspect of the present invention is a charging means for charging an image carrier, a developing device for developing a latent image formed on the image carrier, and a developer developed by the developing device. In an image forming apparatus having a transfer unit for transferring an image to a transfer material and detecting a remaining amount of the developer in the developing unit by applying a voltage to the developing unit, during a non-printing operation, the charging unit A voltage applied to the developing device during a printing operation when the image carrier is charged to a potential corresponding to a non-image portion and the charged region faces the developing device as the image carrier moves. Is applied to detect the remaining amount of the developer in the developing device.

[0007]

FIG. 1 is a schematic view of a laser beam printer according to an embodiment of the present invention, which has a drum-shaped image carrier (hereinafter referred to as a photoreceptor) having an axis perpendicular to the paper surface and rotating and running in the direction of the arrow shown in the drawing. OPC electrophotographic photosensitive layer is formed on one surface. The layer is uniformly negatively charged by a primary charging roller 3 connected to a power supply 4 whose application of each voltage is controlled by a DC controller 9 having a CPU as described later. (In addition to the primary charging transformer 41, the developing bias voltage AC transformer 42 and D
There are a C transformer 43, a transfer bias voltage transformer 44, and a transfer roller cleaning bias voltage transformer 45. Next, the charged surface is irradiated with a laser beam 5 modulated with an image signal, the potential of the portion is attenuated to form an electrostatic latent image, and the latent image is further transferred to the photosensitive member 1 and the developing roller of the developing device 6. When the developing unit 61 reaches the developing site opposed thereto, the developing unit 61 rotates in the direction of the arrow to supply the negatively charged toner from the developing roller 61 that carries and transports the toner 62 in the developing unit 6 to the latent image portion. Is done.

Here, the reversal development is a development method in which toner charged to the same polarity as that of the latent image is visualized by adhering it to a bright portion potential region (a region exposed to light) of the latent image. Areas (areas not exposed to light) are substantially free of toner. On the other hand, in normal development, the toner charged to the polarity opposite to the polarity of the latent image is made visible by attaching it to the dark potential region of the latent image, and the toner is not substantially attached to the bright potential region. That is, in the reversal development, the bright portion potential region is a so-called image portion, and the dark portion potential region is a so-called background portion, that is, a non-image portion. In normal development, the dark portion potential region is a so-called image portion and a bright portion potential. The region is a so-called background portion, that is, a non-image portion.

In the following, embodiments of the present invention will be described with respect to an apparatus employing a reversal development method in order to avoid complication, but the present invention can be applied to an apparatus employing regular development.

A bias voltage having an AC voltage component obtained by superimposing the AC voltage of the transformer 42 on the DC voltage of the transformer 43, that is, an oscillating bias voltage is applied to the developing roller 61, whereby the toner oscillates at the developing portion. It is caused to move and adhere to the latent image portion. In order to prevent fog, the DC bias component is set to a value between the potential of the latent image portion and the potential of the non-image portion. (Note that the oscillation bias voltage includes not only a voltage that oscillates up and down the OV but also a voltage that oscillates only within a range of one polarity.) The thickness of the toner layer carried and transported by the developing roller 61 in the developing area is as follows. Although it is smaller than the minimum gap between the photosensitive member 1 and the developing roller 61 in the developing area, that is, a layer thickness regulating member (blade) (not shown)
Thus, the so-called non-contact development is performed with the toner layer thickness being regulated in such a manner. However, an image having high development efficiency, high density and little fog can be obtained by the vibration bias voltage. For example, the dark portion potential V _D of the latent image is −600 V,
If the bright potential V _L and -100 V, -300-500V as the DC voltage component V _DC of the developing bias voltage, peak-to-peak voltage V _PP as an AC component 1600 V, frequency 1
800 Hz is available.

As seen in the direction of rotation of the photosensitive member 1, a transfer portion is formed on the downstream side of the developing portion by elastically pressing the photosensitive member 1 and a transfer roller (which may be a belt or the like) 2 rotating in the direction of the arrow. As the photosensitive member 1 rotates, the toner image arrives at the transfer site, and at the same time, the transfer material P supplied from the transport path 7 arrives at the transfer site. A transfer bias voltage V _T (for example, +1.5 KV) having a polarity opposite to that of the toner is applied, and the toner image on the photoconductor is transferred to the transfer material P.

Thereafter, the transfer material P carrying the toner image is separated from the photoreceptor 1 and conveyed to a fixing portion (not shown), and the residual toner partially remaining on the surface of the photoreceptor 1 is removed by a cleaner 8, and For the next printing process (primary charging,
(Image light exposure, development, transfer).

As described above, in this embodiment, the transfer roller is used as the contact transfer means.

The material of the transfer roller 2 includes rubber materials such as urethane rubber, silicone rubber, EPR, EPDM, and IR. Examples of the conductive fine particles dispersed in the rubber include carbon, zinc oxide, tin oxide, and the like. The conductive rubber material is coated on a cored bar and pressed against the photoreceptor.

Reference numeral 63 denotes a developing roller 6 in the developing container 6.
1 are conductors (antennas) arranged opposite to each other. When a sufficient amount of toner is present in the developing device, a sufficient amount of toner exists between the developing roller 61 and the antenna 63, but when the toner is consumed in developing the latent image and the remaining amount of toner in the developing device becomes small. Alternatively, when the toner runs out, the toner also runs out between the developing roller 61 and the antenna 63. That is, as the toner in the developing device is consumed, the developing roller 61 and the antenna 63
The capacitance between them changes. This change in capacitance is detected by the detection circuit 64 using the bias voltage applied to the developing roller 61, and when the amount of toner in the developing device falls below a specified value, a warning unit 65 such as a light emitting element is driven. And / or a known replenishing means for replenishing the developing unit 6 with toner from a toner replenishing container (not shown) is operated (Japanese Patent Publication No. Sho 62
-62352).

The graph shown in FIG. 3 is measured using the capacitance detecting circuit shown in FIG. In the circuit shown in FIG. 2, the voltage meter 68 reads a change in the output voltage of the detection resistor 67 that changes according to the electrostatic capacity (PF) of the toner between the roller 61 and the antenna 63. The vertical axis in FIG. 3 is plotted by converting the output voltage level into capacitance. Here, when the output level falls below a certain value, the user can be notified of toner supply by turning on the out-of-toner lamp 65.

The detection circuit 64 of FIG. 1 includes a comparison circuit for comparing the reference voltage with the output voltage of the resistor 67, instead of the meter 68 of FIG.

FIGS. 4 and 5 show operation sequences of two embodiments of the present invention.

Since the developing site and the transfer site are located at a predetermined distance from each other on the downstream side of the photosensitive member in the rotation direction of the photoreceptor, the application site of the developing bias voltage, the application time of the transfer bias voltage, Actually, the transfer roller cleaning bias voltage is applied at a time delayed (rightward) from the position shown in FIGS. 4 and 5 by the time required for the photoconductors to move the above distances, respectively. For easy understanding, FIGS. 4 and 5 show the application time of each bias voltage shifted to the left by the above-described time. Accordingly, for example, in FIG. 4, the application time point of the primary charge for detecting the remaining amount of toner, the application time point of the developing bias voltage, and the application time point of the transfer bias voltage coincide with each other in the drawing, in fact, This means that the developing bias voltage and the transfer bias voltage act on the photoreceptor region acted upon by the application. In FIG. 5, the application time of the developing bias voltage for detecting the remaining amount of toner and the application time of the transfer roller cleaning bias voltage are the same. What is shown is that the transfer roller cleaning bias voltage acts on the photoreceptor area which is acted upon by the application of the developing bias voltage.

The preparatory rotation in FIGS. 4 and 5 is as follows.
After the main switch for connecting the image forming apparatus to the external power supply is closed, but before the print operation is enabled by closing the print switch, preferably, the fixing device is locked and warmed up (fixable temperature). This is an operation for rotating the photoreceptor at the completion of or before the completion, and cleaning the photoreceptor, and preferably further cleaning the transfer roller.

The term "pre-rotation" refers to a print switch closing operation, that is, an operation caused by a print start command, in which the photoreceptor is rotated, and a photoreceptor uniform exposure lamp and a primary charging roller (not shown) are actuated. In order to adjust the sensitivity of the photoreceptor, to make it uniform, to perform cleaning, etc., post-rotation is
After the printing is completed, the photoconductor is continuously rotated for a predetermined time, and the sensitivity history of the photoconductor is eliminated by operating the unillustrated photoconductor uniform exposure lamp and the primary charging roller.

During the preparatory rotation, the pre-rotation, and the post-rotation, the transfer roller 2 and the primary charging roller 3 rotate in conjunction with the photoconductor 1 in the same manner as during printing, in order to prevent the photoconductor from being damaged by rubbing. Let it.

4 and 5 occur after the pre-rotation operation. At this time, the above-described image light is applied to the primary charged photosensitive member to form an electrostatic latent image. The developing roller 61 is driven to rotate, and the above-described developing bias voltage is applied to the developing roller 61 to develop the electrostatic latent image, and a transfer bias voltage (in the opposite polarity to the toner) is applied to the transfer roller 2. At the same time, the transfer paper P is fed to the nip portion between the transfer roller 2 and the photoconductor 1 to transfer the toner image formed on the photoconductor to the transfer paper P. That is, a printing operation is performed.

The developing roller 61 is used for preparing a photosensitive member,
The rotation may be performed in synchronization with the rotation of the photoconductor at the time of the front rotation and the rear rotation. When the developing roller is rotated during the pre-rotation or during the preparatory rotation, the toner in the container is loosened, and the toner is sufficiently rubbed with the sleeve, so that a high triboelectric charge for developing the latent image on the toner can be given. preferable. On the other hand, it is preferable to stop the rotation of the developing roller during preparation, before and after rotation of the photoconductor in order to suppress toner scattering.

4 and 5, the transformer 42 is connected to the developing roller 61 for a predetermined time during the preparatory rotation of the photosensitive member.
The remaining amount of toner is detected by applying a bias voltage from 43. This is performed in a portion indicated by oblique lines in the drawing, and the developing bias voltage and the transfer bias voltage (the output voltage of the transformer 44 having a polarity opposite to that of the toner) are applied to the portion where the primary charging is performed on the photoconductor surface. The voltage is applied to the developing roller 61 and the transfer roller 2 respectively. This is because even if the developing bias voltage is turned on, the toner is not attached to the photoreceptor because the surface of the photoreceptor has a high potential due to primary charging. However, since the component having the inverted polarity of the toner (referred to as inverted toner) may adhere, a transfer bias having the same polarity (+) as that of the inverted toner, that is, a polarity opposite to that of the normally charged toner is applied, and Adhesion to the transfer roller 2 is prevented. After the detection of the remaining amount of toner, the transfer roller cleaning bias voltage is applied to the transfer roller from the transformer 45, and the toner of normal charge polarity adhering to the transfer roller surface is removed from the roller 2 for cleaning, and the preparatory rotation ends.

The transfer roller cleaning bias voltage has the same polarity as the toner.

Here, the same polarity as the toner or the polarity opposite to the toner in the present specification means the polarity for developing the image portion of the latent image, that is, the same polarity or opposite polarity to the charging polarity of the toner charged to the normal polarity. In other words, the polarity is not used in the sense that the polarity is the same as, or opposite to, the polarity of a small amount of toner (reversed toner) charged to the opposite polarity to the normal polarity for some reason.

In the embodiment shown in FIG. 4, the primary charging roller 3 charges the photosensitive member facing the developing roller 61 to which the vibration bias voltage is applied from the transformers 42 and 43 for detecting the remaining amount of toner. The potential of the lever is set to the dark portion potential V _D
The potential is set to be equal to (background portion potential), that is, a potential for preventing adhesion of toner of normal polarity, thereby preventing toner contamination of the transfer roller 2. However, in the embodiment of FIG. For this reason, the photosensitive member portion facing the developing roller 61 to which the vibration bias voltage is applied is not subjected to primary charging, and the potential of this portion is equal to or higher than the light portion potential V _L (image portion potential). Has a potential at which the toner is more likely to adhere. Therefore, when the toner remaining amount is detected, the toner on the developing roller 61 adheres to the photosensitive member portion. In order to prevent the toner (normal polarity) from adhering to the transfer roller 2, the transfer roller 2 A transfer roller cleaning bias voltage having the same polarity as that of the toner is applied to electrostatically prevent the toner from adhering to the roller 2.

However, when the toner remaining amount is detected, a very small amount of reversal toner may adhere to the photosensitive member, and the reversal toner adheres to the transfer roller 21 electrostatically by applying a transfer roller cleaning bias voltage. Therefore, in order to discharge the reversal toner from the transfer roller 2 onto the photoreceptor 1 electrostatically again, after the portion of the photoreceptor facing the developing roller to which the developing bias voltage has been applied passes the transfer portion, the transfer is performed. The application of the roller cleaning bias voltage is temporarily interrupted, and the transfer bias voltage from the transformer 44 is applied to the transfer roller 2 for a period of time equal to or more than one rotation of the transfer roller 2. This can prevent the back surface of the transfer material from being stained with the reversal toner during printing.

In FIGS. 4 and 5, the detection of the remaining amount of toner is performed during the preparatory rotation, but may be performed during the pre-rotation or post-rotation. When the example of FIG. 4 is performed at the time of pre-rotation or post-rotation, the application of the transfer roller cleaning bias voltage is temporarily interrupted at that time, and instead, the transfer bias voltage is temporarily applied to the transfer roller for the required time. Apply. On the other hand, FIG.
When the above example is performed at the time of pre-rotation or post-rotation, the charging potential to the primary charging roller 3 is temporarily suspended at that time.
Preferably, after the time corresponding to that time, the application of the transfer roller cleaning bias voltage is temporarily stopped, and the transfer bias voltage is temporarily applied to the transfer roller 2.

Although the above embodiment has been described with respect to an image forming apparatus that performs reversal development, the present invention can be applied to an image forming apparatus that performs regular development. For this normal development, charged photoconductor portion at the primary charger is a comparable dark potential V _D,
The portion where the normally charged toner (the polarity opposite to the latent image) is likely to adhere, and the portion where the primary charging device does not act is equivalent to the light portion potential VL, or a portion where the normally charged toner is less likely to adhere. However, in any case, the reversal toner is a portion that is likely to adhere.

Accordingly, in the case of regular development, when the remaining amount of toner is detected when the primary charge is deactivated as shown in FIG. 5, it is necessary to respond to the application of the developing bias voltage for that. Unlike FIG. 5, a transfer bias voltage having a polarity opposite to that of the toner is applied to the transfer roller 2 for a predetermined time to prevent the reverse toner from adhering to the transfer roller 2.

On the other hand, when the primary charge is energized at a time corresponding to the time when the toner remaining amount is detected as shown in FIG. 4, the normal polarity toner adheres to this portion. 4, a transfer roller cleaning bias voltage is applied to the transfer roller 2 for a required time to prevent the normal polarity toner from adhering to the roller 2.

Although the developing bias voltage is the vibration bias voltage in the above embodiment, the present invention can be applied to an apparatus using a non-vibration DC bias voltage.

Although the above-described embodiment uses a one-component developer, the present invention can be applied to an apparatus using a two-component developer. In this case, the remaining amount of toner means the ratio of the toner to the carrier particles, that is, the toner concentration.

[0036]

According to the present invention, it is possible to prevent useless contamination of the transfer means when detecting the remaining amount of the developer in the developing device.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of an embodiment of the present invention.

FIG. 2 is an explanatory diagram of an example of a toner remaining amount detection circuit.

FIG. 3 is an explanatory diagram of a relationship between a detection output and a remaining amount of toner.

FIG. 4 is a diagram illustrating an operation sequence according to an embodiment of the present invention.

FIG. 5 is a diagram illustrating an operation sequence according to another embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photoconductor 2 Transfer roller 4 Power supply 61 Developing roller

Continuation of the front page (56) References JP-A-63-208885 (JP, A) JP-A-1-319078 (JP, A) JP-A-54-63838 (JP, A) JP-A-54-114248 (JP) JP-A-61-226773 (JP, A) JP-A-1-234874 (JP, A) JP-A-1-292385 (JP, A) JP-A-2-244081 (JP, A) (58) Field surveyed (Int.Cl. ⁶ , DB name) G03G 15/06-15/095 G03G 15/16 G03G 15/00 303

Claims (2)

(57) [Claims] A charging unit configured to charge an image carrier; a developing unit configured to develop a latent image formed on the image carrier; and a transfer unit configured to transfer a developer image developed by the developing unit to a transfer material. An image forming apparatus that detects the remaining amount of the developer in the developing device by applying a voltage to the developing device, wherein the non-printing operation causes the charging unit to move the image carrier to a non-image portion. The developing device is charged to a corresponding potential, and when the charged region faces the developing device along with the movement of the image carrier, a voltage applied during a printing operation is applied to the developing device to thereby cause the developing device to be charged. An image forming apparatus for detecting a remaining amount of the developer. 2. When the area facing the developing device at the time of detecting the remaining amount of the developer faces the transfer unit with movement of the image carrier, the transfer unit has a polarity opposite to that of the developer. The image forming apparatus according to claim 1, wherein a voltage is applied.