JPS63309978A - Image forming device - Google Patents

Abstract

PURPOSE:To accurately detect an electric potential and to control it with high precision even if unevenness in electrification occurs in the main scanning direction of an image carrier by detecting the surface electric potential of the image carrier with the aid of an electric potential sensor at plural spots in the main scanning direction of the image carrier. CONSTITUTION:Electrification is sequentially and uniformly executed on a photosensitive drum 1 which rotates in a direction shown with an arrow by a primary electrifier 2, and other electrifiers 5-7 being in off-state, turn a preexposure unit 9 on. Meanwhile, an electric potential sensor 11 starts the measurement of the surface electric potential from one end of the photosensitive drum 1 while fetching data and it is moved in the main scanning direction of the photosensitive drum 1 with the aid of an electric potential sensor driving means 12 to measure to another end. Next, the data is inputted in an electric potential control circuit 14 through an electric potential measurement circuit 13 and it is arithmetically processed to transmit a signal to a primary electrifying transformer 17 and control the corona total current which is impressed on the primary electrifier 2, so that the specified proper surface electric potential can be obtained on the photosensitive drum 1. Even if the unevenness of the surface electric potential occurs in the main scanning direction, the accurate measurement can be possible, thereby executing the excellent control.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Object of the Invention [Field of Industrial Application] The present invention relates to an image forming apparatus such as an electrophotographic copying machine or a laser beam printer.

[Conventional technology]

In this type of image forming apparatus, a potential sensor is provided near an image carrier such as a photosensitive drum to detect the surface potential of the image carrier, and based on an output signal from the sensor, an image of the discharge characteristics of the charger, etc. Methods for controlling the formation conditions are known (for example, Japanese Patent Application Laid-Open No. 53-37025, Japanese Patent Publication No. 56-77).
No. 850 and Japanese publication No. 58-77851).

An example thereof will be explained based on FIG. High voltage transformer 1
A drum-shaped photoreceptor (hereinafter referred to as photoreceptor drum) 103 as an image carrier is charged by a primary charger 102 connected to
Charge is accumulated on the surface of the The surface potential of the photosensitive drum 103 caused by this accumulated charge is measured by a potential sensor 104 and a potential measuring circuit (not shown) disposed near the drum. The measured surface potential is transferred to the amplifier lO
5 and its output 106 is applied to one input terminal of a comparator 107. A reference potential 109 is applied from a reference potential generator 108 to the other input terminal of the comparator 107, and an output proportional to the difference between the output 106 of the amplifier 105 and the reference potential 109 is sent from the comparator 107 to the potential control circuit 110. applied.

The potential control circuit 110 controls the high voltage transformer 101 so that the output of the comparator 107 approaches zero, and the surface potential of the photosensitive drum 103 is controlled to a potential specified by a reference potential 109. That is, when the surface potential is below a certain value, the potential control circuit 110 acts to increase the surface potential by increasing corona discharge, and on the other hand, when it is above a certain value, it decreases the corona discharge and lowers the surface potential. As a result, the surface potential of the photosensitive drum 3 is maintained at a predetermined appropriate potential and the image quality is stabilized regardless of dirt on the charging wire or changes in the charging characteristics of the photosensitive member.

[Problem that the invention seeks to solve]

However, conventionally, a potential sensor that measures the surface potential of an image carrier such as a photosensitive drum is fixedly placed at one location in the main scanning direction of the image carrier. When unevenness of surface potential occurs in the main scanning direction of the image carrier, there are problems such as failure to perform good control.

The present invention aims to solve the above problems.

1. Structure of the Invention [Means for Solving Problems] The present invention provides a potential sensor for detecting the surface potential of the image carrier in the vicinity of the image carrier, and performs image formation based on the detection output of the sensor. An image forming apparatus that controls conditions is characterized in that the potential sensor detects surface potentials at a plurality of locations in the main scanning direction of the image carrier.

[For production]

By measuring the surface potential at multiple locations in the main scanning direction of the image carrier using a potential sensor, even if unevenness in the surface potential occurs in the main scanning direction, the above measurement values can be averaged, making it more accurate. This measurement becomes tiT sparrow.

〔Example〕

Hereinafter, the present invention will be specifically explained based on embodiments shown in the drawings.

Embodiment 1 FIG. 1 is a schematic diagram of a first embodiment in which the present invention is applied to a laser beam printer as an image forming apparatus.

In the figure, reference numeral 1 denotes a photosensitive drum made of amorphous silicon or the like, which is rotated at a predetermined circumferential speed in the direction of arrow a in the figure.

The photosensitive drum 1 is surrounded by a negative charger 2, a laser unit 3 as a latent image forming means, a developing sleeve 4, a pre-transfer charger 5, a transfer charger 61, a separation charger 7. Cleaner 8
, pre-exposure device 9 are arranged in this order.

The laser unit 3 is driven by a laser driver 10, and irradiates the photosensitive drum surface with laser light according to desired image information. Reference numeral 11 denotes a potential sensor for detecting the surface potential, which is provided close to the circumferential surface of the photosensitive drum between the negative charger 2 and the developing sleeve 4. It is configured to move back and forth in the direction). Reference numeral 13 denotes a potential measuring circuit that measures the surface potential of the photosensitive drum l based on the output from the potential sensor 11, and its output is input to the potential control circuit 14. 15
is a DC controller that controls the potential control circuit 14 and the laser driver IO.

The above-mentioned developing sleeve 4 is disposed in a developing device (not shown), and toner (powder developer) is applied to the circumferential surface of the sleeve.
is coated. 16 is a developing bias transformer for applying a bias voltage to the developing sleeve 4; 17-
Reference numeral 20 denotes a DC transformer for applying a high voltage to each of the chargers 2-5-6-7, and each of the transformers 16 to 2o is configured to be controlled by the potential control circuit 14. 21 is a high-voltage AC transformer for superimposing a female wave voltage on the transfer charger 6 and separation charger 7; 22 is a pair of registration rollers; 23 is a pair of feeding guides for the transfer material P; and 24 is a transfer material conveying belt.

In the above configuration, the potential sensor 11 detects whether or not the photosensitive drum l is charged to a predetermined surface potential by the primary charger 2 during forward rotation of the photosensitive drum before executing the image forming process, and the primary charging is performed based on the detection. First, the primary charger 2 sequentially and uniformly charges the photosensitive drum 1 rotating in the direction of the arrow, while the other chargers 5 to 7 remain off. When the charged portion of the photosensitive drum 1 comes close to the pre-exposure device 9, the pre-exposure device 9 is turned on and continues to be turned on. - potential sensor 1 for measuring the surface potential of the force photosensitive drum l;
1 starts measurement with one end of the photosensitive drum 1, for example, the near end in FIG. move it to Then, when the measurement reaches the other end of the photosensitive drum 1, the data acquisition is completed, the potential sensor 11 is returned to the home position, and the primary charger 2 is turned off.

FIG. 2 is a developed view of the drum surface showing the movement locus of the potential sensor 11 with respect to the photosensitive drum surface at that time, and shows the movement of the potential sensor 11 in the main scanning direction (direction b in the figure) and the arrow direction of the photosensitive drum 1. By rotating in the direction a, the potential sensor 11 moves in a direction apparently inclined with respect to the main scanning direction as shown in the figure, and the potential is measured. Note that the potential sensor 11 may perform reciprocating measurements, or may perform measurements continuously or discontinuously (stepwise).

Next, the data captured by the potential sensor 11 is input to the potential control circuit 14 via the potential measurement circuit 13, and arithmetic processing (
For example, by taking an average value), a signal is sent to the primary charging transformer 17 to control the total corona current applied to the primary charger 2 so that a predetermined appropriate surface potential is obtained on the photosensitive drum.

FIG. 3 is a graph showing the relationship between the surface potential of the amorphous silicon photosensitive drum and the total corona current of the primary charger. , and controls the total corona current applied to the primary charger 2 based on the data.

As described above, the image forming process is executed by appropriately setting the total corona current to the primary charger 2. The laser beam emitted from the unit 3 performs image exposure according to desired image information, and an electrostatic latent image is formed on the drum surface.

The electrostatic latent image is visualized by toner being attached thereto by the action of a developing bias voltage applied to the developing sleeve 4 in the developing device. In this way, a toner image is formed on the photosensitive drum, and the pre-transfer charger 5 increases the charge of the toner.

On the other hand, the transfer material P is timed with the movement of the toner image by a pair of registration rollers 22, and is fed between the photosensitive drum 1 and the transfer charger 6 via a pair of transfer material feeding guides 23. The transfer charger 6 applies a corona charge with a polarity opposite to that of the toner to the back surface of the transfer material P, so that the toner image on the photosensitive drum 1 is sequentially transferred to the transfer material PJ:, and then the transfer material P is separated. The toner image is neutralized by the charger 7 and separated from the photosensitive drum 1, and sent to a fixing device (not shown) by the conveyor belt 24, where the toner image is fixed on the transfer material. On the other hand, the toner and paper powder remaining on the photosensitive drum without being transferred are neutralized by a cleaner 8, and the electric charge remaining on the photosensitive drum is eliminated by exposure from the pre-exposure device (lamp) 9, and the next It is prepared for image formation, and the above-described image formation process is repeatedly performed.

As described above, by controlling the total corona current to the primary charger 2 so that the photosensitive drum l is charged to a predetermined surface potential by the primary charger 2, the discharge wire of the charger 2 can be prevented from becoming dirty, Good images can always be obtained even if the charging characteristics of the photosensitive drum change due to changes in humidity.

Embodiment 2 In the first embodiment, the primary charger 2 is controlled, but other chargers may also be controlled.

FIG. 4 shows an embodiment in which the transfer charger 6 is controlled, and a potential sensor 11 similar to that described above is disposed downstream of the transfer charger 6 in the rotational direction of the photosensitive drum. The other configurations are the same as those in the example shown in FIG. The surface potential on the photosensitive drum is measured, and based on the measured value, the transformer 19 of the transfer/transfer charger 6 is appropriately controlled to execute the image forming process. Even if the discharge wire becomes dirty, good transfer conditions can always be obtained. Other chargers (e.g. separation charger 7)
, pre-transfer charger 5, other pre-cleaner charger, etc.) can be similarly controlled.

Embodiment 3 The present invention can also be applied to a multicolor image forming apparatus, and FIG. 5 shows an embodiment applied to a two-color laser beam printer having two developing units.

The photosensitive drum 1 is uniformly negatively charged by the primary charger 2, and a first laser unit 31 serving as a first exposure means emits image information with a laser beam, exposing it to negative light to form a first latent image (negative latent image). image) is formed. Reference numeral 41 denotes a developing sleeve having a two-component developer mixed with magnetic particles such as ferrite and chromatic toner such as red on its surface, and is placed in a first developing device (not shown) for visualizing the first latent image. It is arranged. The two-component developer is transferred to the developing sleeve 41 which rotates in the direction of the arrow.
A first toner image is formed by forming a magnetic brush by the magnetic force of a magnet roller fixed in the sleeve above and reversingly developing the first latent image with negatively charged toner.

25 is a second charger (hereinafter referred to as a re-charger) that uniformly charges the photosensitive drum 1 negatively again; 32 is a second exposure means similar to the first laser unit 31; Laser Unit/ ) performs negative exposure with a laser to form a second latent image (negative WJ image). 42 is a second developing sleeve provided in a second developing device (not shown), and a negatively charged one-component magnetic toner such as black is coated on its circumferential surface.
A thin layer of 0 to 100 g is applied, and a developing bias is applied to visualize the second latent image to form a second toner image. Note that the single layer of toner applied on the second developing sleeve 42 is developed without contacting the surface of the photosensitive drum. Thereafter, the first and second toner images are simultaneously transferred onto the transfer material P by the same steps as in Example 1 to obtain a desired print image.

The reason why the recharging device 25 is provided is that if the recharging device 25 is not provided, the first latent image will be subjected to the second development during the second development, resulting in color mixing, as shown in FIG. 6(b). However, by providing the negative charger 25, color mixing as shown in the figure (&) can be prevented.

As described above, it is very important to stabilize the potential in one-pass transfer for two-color development, and before executing the image forming process, the surface potential of the photosensitive drum 1 by the primary charger 2 and the potential after recharging are kept constant. need to be kept. Therefore, in the illustrated example, a potential sensor 11 similar to that in the first embodiment is provided downstream of the primary charger 2 and the recharger 25 to control the two chargers 25. In this case, - Although the potentials of the charger 2 and the recharging device 25 may be controlled individually, it is also possible to turn on both the negative charger and the recharging device to keep the potential after recharging constant.

Also, since the recharging process ($25) involves a developing device in the immediately preceding process, the discharge wire is likely to get dirty with toner and the discharge current flowing to the drum tends to be unstable, so controlling it as described above will form a good multicolor image. It is extremely effective in doing so.

In the above embodiment, the potential sensor 11 was moved in the main scanning direction of the photosensitive drum 1 to detect the surface potential at multiple locations or continuously. However, as shown in FIG. A plurality of chargers may be fixedly provided in the scanning direction, and the total current applied to the charger may be controlled based on the average value of the potential detected by the chargers.

The present invention can also be applied to a system in which the surface potential of the photosensitive drum is detected by a potential sensor to control the developing bias voltage, the amount of exposure light, and other image forming conditions.

Furthermore, the present invention is applicable not only to laser beam printers but also to various image forming apparatuses such as other printers (LED, liquid crystal, etc.) and electrophotographic copying machines.

C. Detailed Description of the Invention According to the present invention, the surface potential of an image carrier such as a photosensitive drum is detected at a plurality of locations in the main scanning direction of the image carrier by a potential sensor. Even if charging unevenness occurs in the main scanning direction, more accurate detection becomes possible, and there is an effect that control can be performed with high precision.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram showing a first embodiment of an image forming apparatus to which the present invention is applied, FIG. 2 is a developed view of the drum surface showing the movement locus of the potential sensor relative to the photosensitive drum, and FIG. 3 is a primary band A graph showing the relationship between the total corona current of the tube and the surface potential of the photosensitive drum, FIG. 4 is a schematic configuration diagram of the second embodiment,
FIG. 5 is the same diagram as above of the third embodiment applied to a multicolor image forming apparatus, FIGS. 6(a) and (b) are explanatory diagrams of the image forming process, and FIG. FIG. 8 is an explanatory diagram of a conventional example. 1 is an image carrier (photosensitive drum), 2 is a primary charger, 3 is a laser unit, 4 is a developing sleeve, 5 is a pre-transfer charger,
6 is a transfer charger, 7 is a separation charger, 8 is a cleaner, 9
1 is a pre-exposure device, 10 is a laser driver, 11 is a potential sensor, 12 is a potential measurement circuit, and 13 is a potential control circuit. Figure 2 1 q Figure 1 q

Claims (1)

[Scope of Claims] 1. An image forming apparatus in which a potential sensor for detecting the surface potential of the image carrier is provided in the vicinity of the image carrier and image forming conditions are controlled based on the detection output of the sensor, An image forming apparatus characterized in that a sensor detects surface potential at a plurality of locations in a main scanning direction of an image carrier. 2. The image forming apparatus according to claim 1, wherein the potential sensor is configured to be movable in the main scanning direction of the image carrier. 3. The image forming apparatus according to claim 1, wherein the potential sensor is provided on two or more sides of the image carrier in the main scanning direction.