JPH0456876A - Image forming device - Google Patents

Abstract

PURPOSE:To make detection of surface potential of a photosensitive body stable and accurate, to miniaturize the device, and to make it light weighted by varying developing bias voltage to the vicinity of non image range potential Vo of the photosensitive body after exposure immediately before passing a pattern state electrostatic latent image through a developing means. CONSTITUTION:A surface potential sensor S is inserted and installed between a developing means 16 and a transfer means 17 where there is comparatively more space, and the developing bias voltage is varied to the vicinity of the non image forming range voltage Vo of the photosensitive body 14 after exposure immediately before the pattern state electrostatic latent image is passed through the developing means 16. Thus, the device can be miniaturized, the weight and cost can be reduced, and the detection of the surface potential of the photosensitive body 14 can be carried out stably and accurately without any influence to the charge of toner at the developing means 16 by the operation of a bias voltage adjustment means.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention forms an electrostatic latent image in a fixed pattern on a photoreceptor, detects the potential of this electrostatic latent image, and adjusts the detected potential to the detected potential. The present invention relates to an image forming apparatus configured to control various image forming conditions based on the present invention.

[Conventional technology]

In various image forming devices such as copying machines and printers,
The surface of a photoconductor that is transported in a certain direction is uniformly charged, an electrostatic latent image is formed by exposing the photoconductor, and toner is supplied from a developing section to this electrostatic latent image. Visualize the latent image. The obtained toner image is transferred to a sheet of paper, and the transferred toner image is fixed to the sheet of paper so that a final image is obtained on the sheet of paper.

In the above steps, charging conditions, exposure conditions, development conditions, transfer conditions, and fixing conditions are controlled and adjusted by a central control section.

On the other hand, the photoreceptor has a property that characteristic values such as charging characteristics and sensitivity characteristics change over time.

Therefore, in order to maintain desired image quality, it is necessary to adjust (correct) image forming conditions such as charging conditions, exposure conditions, development conditions, and transfer conditions in accordance with changes in the characteristics of the photoreceptor.

Therefore, conventionally, an electrostatic latent image of a certain pattern is formed on a photoconductor, and the potential of this latent image is detected by a surface potential sensor.
By measuring this detection voltage, changes in the photoreceptor over time can be ascertained. Based on this, target set values for various image forming conditions are adjusted, and various image forming conditions are controlled in response to changes in the photoreceptor over time. Particularly in a full-color copying machine that superimposes images of a plurality of colors, a high degree of image stability is required, and therefore, the above-mentioned target setting values are frequently adjusted.

Incidentally, in a conventional image forming apparatus, the surface potential sensor is provided upstream of a developing section in the direction in which the photoreceptor is transported. Therefore, the measurement of the surface potential in the electrostatic latent image forming section is performed at a position upstream of the developing section. Therefore, toner is not supplied from the developing section to the electrostatic latent image.

That is, the surface potential is measured without toner being attached to the latent image. The reason why the surface potential sensor is placed upstream of the developing section is because if toner adheres to the electrostatic latent image, the detected potential of the electrostatic latent image becomes inaccurate due to the charge that the toner has. be.

[Problem to be solved by the invention]

However, normally, on the photoreceptor side of a copying machine, there is actually almost no extra space between the exposure position from the optical system and the development position. Therefore, it is structurally difficult to insert the surface potential sensor between the exposure position and the development position, and insertion of the surface potential sensor necessitates an increase in the size of the apparatus, which is not preferable.

On the other hand, in an image forming apparatus such as a color copying machine in which a plurality of image forming stations are arranged side by side, from the viewpoint of memory cost, it is desirable that the distance between the photoreceptors in each image forming station be as close as possible.

That is, the buffer memory provided in the image processing section is required to correspond to the product of the image width in the main scanning direction and the distance between each photoreceptor. Therefore, from the perspective of reducing memory costs, by reducing the diameter of the photoreceptor as much as possible, or by partially overlapping the developing section of one image forming station and the photoreceptor cleaning section of the adjacent image forming station, Efforts have been made to shorten the distance between the photoreceptors.

Therefore, inserting and arranging the surface potential sensor on the upstream side of the developing section necessitates increasing the distance between the photoreceptors. Furthermore, when inserting a surface potential sensor between the charged part and the exposed part, it is necessary to ensure safety against high-pressure discharge of the charged part, to avoid the influence of noise, and to avoid the influence of the magnetic field generated by the developing sleeve. It is desirable that the distance between the charging section and the potential sensor and the distance between the potential sensor and the developing section be as large as possible.

For this reason, there are drawbacks such as an increase in the size of the device and an increase in memory cost.

The present invention has been made based on this background, and its purpose is to eliminate the drawbacks of the prior art described above, to stably and accurately detect the surface potential of a photoreceptor, and to miniaturize the device. Therefore, it is an object of the present invention to provide an image forming apparatus that can reduce weight and cost.

[Lessons to solve problems]

In order to achieve the above object, the present invention includes a charging means for uniformly charging the surface of a photoreceptor, such as a photoreceptor tram, which is transported in a fixed direction, and a charging means for uniformly charging the surface of a photoreceptor, such as a photoreceptor tram, which is transported in a fixed direction; an exposure means for forming an electrostatic latent image by exposing a light image corresponding to the image to be imaged; a developing means for supplying toner to the electrostatic latent image to visualize the electrostatic latent image; a transfer means for transferring the obtained toner image onto a recording material such as a transfer paper; a pattern exposure means for exposing the photoreceptor to a light image of a certain pattern to form a patterned electrostatic latent image; A surface potential sensor detects the surface potential of the photoconductor portion on which the patterned electrostatic latent image is formed, and various adjustments such as charging conditions, development conditions, and transfer conditions are made based on the detected value of the surface potential sensor. The present invention is directed to an image forming apparatus equipped with a control means for adjusting image conditions.

The surface potential sensor is disposed downstream of the developing means in the direction of conveyance of the photoreceptor and upstream of the transfer means, and immediately before the patterned electrostatic latent image passes through the developing means,
The present invention is characterized in that a bias voltage adjusting means is provided for changing the developing bias voltage to around the non-image forming area voltage vo of the photoreceptor after exposure.

[Effect]

As described above, in the present invention, the surface potential sensor is inserted and arranged between the developing means and the transfer means, which have a relatively large space, and is therefore compared to the conventional one in which the surface potential sensor is inserted and arranged upstream of the developing means. This makes it possible to reduce the size, weight, and cost of the device.

Furthermore, even if a surface potential sensor is placed downstream of the developing section,
Due to the operation of the bias voltage adjusting means, the surface potential of the photoreceptor can be stably and accurately detected without being affected by the charge of the toner in the developing means.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

Figure 1 is a schematic configuration diagram of a digital full-color copying machine, Figure 2
3 and 3 are block diagrams of the control section, and FIG. 4 is a diagram showing an example of setting the charging potential and the developing bias potential.

First, the schematic configuration of a digital full-color copying machine will be explained using FIG. 1.

This copying machine is roughly divided into a scanner section 1 for reading originals,
An image processing section 2 that electrically processes the image signal output as a digital signal from the scanner section 1, and a printer section 3 that forms an image on transfer paper based on the image recording information of each color from the image processing section 2. It is composed of.

The scanner section 1 includes a lamp 5.5 that optically scans a document placed on a contact glass 4.

The light reflected from the original illuminated by this lamp 5.5 is reflected by a mirror 6.7.8, passes through an imaging lens 9, and enters a dichroic prism 10. The dichroic prism 10 separates the light into three types of wavelength light, for example red (R), green (G), and blue (B), and enters the light receiving element 11. As shown in the figure, this light receiving element 11 is composed of a red CCD 11R, a green CCDIIG, and a blue CCDIIB, and each of the wavelengths separated into three types as described above is incident on each CCD 1l. The red CCD 11R, green CCD 11G, and blue CCDIIB convert the received light into digital signals and output them to the image processing section 2.

In the image processing section 2, the input image signal is converted into recording color information signals of four colors, for example, black (BK), yellow (Y), magenta (M), and cyan (C). Although this embodiment shows the case where images are formed using the four colors, it is also possible to form a color image using three colors.

The output signal from the image processing section 2 is input to the printer section 3, and the recording devices 138K, 13C113M,
Sent to L3Y. These 4 sets of parallel recording devices @1
3 have almost the same configuration, the recording device 13C
The configuration will be explained using as an example.

As shown in the figure, the recording device 13C includes a laser beam recording device l.
A 12C1 photosensitive drum 14C, a charging charger 15C, a developing section 16c, a surface potential sensor SC, a transfer charger 17C, and the like are arranged in this order around the photosensitive drum 14C. As shown in the figure, the surface potential sensor SC is arranged downstream of the developing section 16C in the rotational direction of the photosensitive drum 14C.

In this embodiment, a negative/positive development process method (reversal development process method) is adopted. First, the surface of the photoreceptor drum 14C is approximately -8
It is uniformly charged to 00V, and then the laser beam emitting device 1.2
Exposure is performed using C, and an electrostatic latent image corresponding to a cyan light image is formed.

The surface potential of the electrostatic latent image portion formed by this exposure becomes approximately zero potential. This electrostatic latent cyan image is developed and visualized by the developing section 16C having a negative potential developing bias of approximately -500 .

On the other hand, the transfer paper fed from the paper feed unit 19 by the drive of the paper feeder 018 is sent onto the transfer belt 21 by the registration roller 20 at the timing when it is aligned with the leading edge of the image, and is electrostatically attracted on the transfer belt 21. Ru. This transfer belt 21
The transfer paper conveyed by the transfer paper passes directly under the photosensitive drum 14C on which a cyan toner image is formed, and the toner image is transferred to the transfer paper by the action of the transfer charger 17C.

Thereafter, the toner image is transferred onto the transfer paper by the fixing roller 22 and discharged to the outside of the machine by the paper discharge roller 23.

Next, a block diagram of the entire control system of the printer section 3 is shown in FIG.

The main control section 40 for the printer section 3 includes a CPU, a ROM, a RAM, an I10 interface, etc., and controls the entire system. On the input side of the main control unit 40, a paper discharge sensor 41.
A paper end sensor 42 that detects the presence or absence of transfer paper in the paper feed section 19, a registration sensor 43 that controls paper feeding to the registration rollers 20, a cassette size sensor 44 that detects the cassette size, BK, C, M, and Y. 45C for the photosensor 458 that detects the density of each toner.

45M, 45Y, a thermistor 46 that detects the temperature of the fixing heater, and surface potential sensors SBK, SC, SM, and SY that detect the surface potential of the photosensitive drum 14, etc. are connected, respectively.

On the output side of the main control unit 40, a charger 15,
Transfer charger 17 and belt static elimination charger 47
(See Figure 1) is 48.49.50 for each high voltage power supply.
connected via.

Further, a heater 51 provided within the fixing roller 22
It is connected via a heater control section 52. Furthermore, the main motor 53, the photosensitive drum 14 and the transfer belt 2
The drive motor 54 that drives the DC motor driver 5
5.

Further, a video control section 54 is provided to take in image data from the image processing section 2.

This video control unit 56 includes semiconductor lasers 57BK, 57C, 57M, and 57Y for BK, C, M, and Y (12G, 12M in the laser beam emitting device 128).

12Y) is connected to the LD driver 58. Further, a mirror drive motor 59 for driving a polygon mirror is connected to this video control section 56 via a polygon motor driver 60.

Furthermore, in the main control section 40, the developing sleeves 268 provided in the developing section 168, 16G, 16M, and 16Y are provided with 26C and 26M.

A developing bias high voltage power supply 61 that applies a developing bias voltage is connected to 26Y. Further, the developing section 16BK
, ], toner supply rollers 29BK and 29C provided in 6C, 16M, and 16Y.

A replenishment bias high voltage power supply 62 that outputs a toner supply signal is connected to 29M and 29Y.

On the other hand, as shown in FIG. 2, the charging high voltage power source 48C (
The same applies to other colors BK, M, and Y) and the developing bias high voltage power supply 61 (same applies to other colors BK, M, and Y) has four signal lines 0 that can change the output voltage from the main control unit 40. , 1, 2.3 are connected to the trigger signal line. By combining H and rLJ by these four signal lines 0, 1, and 2.3, the charging high-voltage power supply 48C and the developing bias high-voltage power supply 61C can be set to the output voltage as shown in FIG. It has become.

Further, the video control unit 56 reads the data of the potential detection pattern after exposure when the pattern trigger signal from the main control unit 40 is set to rLJ, and based on this data, the data of the potential detection pattern is sent to the laser emitting device 128 such that 12C, 12M, 12C, 12M, 1
It has a function of lighting each 2Y semiconductor laser.

Next, the operation of detecting the surface potential of the photosensitive drum 14 will be explained.

To form an electrostatic latent image of a potential detection pattern.

The pattern triggers of each color become rl-J at the same time. Then, data is read from the pattern memory in the video control unit 56, the semiconductor lasers 57 of each color are changed, and the photosensitive drum 14 is exposed. At this time, a timer counter included in the CPU in the main control section 40 monitors the elapsed time from the start of exposure of the pattern (starting from star 1), controls the bias voltage applied to the developing section 16, which will be described later, and controls the voltage of the photoreceptor 14. The timing of surface potential detection is determined.

Immediately before the electrostatic latent image portion of the potential detection pattern passes under the developing section 16, the developing bias voltage reaches a value near the voltage (dark area voltage) v0 of the non-image forming area of the photoreceptor 14 (in this embodiment, V. -40V value). By doing this, the surface potential sensor S generates a voltage of V. The potential can be accurately detected without being affected by the charge of the toner.

Note that the bright area voltage (VL) on the surface of the photoreceptor drum 14 after exposure is
), but if left as is, toner would adhere to the electrostatic latent image part of the detection pattern.
Accurate voltage cannot be detected.

On the other hand, detecting the v0 potential as in the present invention is advantageous because there is no fear of toner adhesion.

Based on the potential detected by the surface potential sensor S in this way, the power temperature of the semiconductor laser is changed, for example. That is, when the detected potential is higher than a preset reference value, the power of the semiconductor laser is reduced according to the difference, and on the other hand, when it is lower than the reference value, the power is increased according to the difference. controlled as follows. Note that since these control methods are conventionally known, detailed explanations will be omitted.

Furthermore, when the potential detection pattern passes under the developing section, stopping the rotation of the developing sleeve will more reliably eliminate the influence of the toner charge, making it possible to measure the Vo potential more accurately.

〔Effect of the invention〕

As described above, by arranging the surface potential sensor on the downstream side of the developing means where there is sufficient space, the present invention can reduce the size of the device compared to the case where the surface potential sensor is arranged on the upstream side of the developing means. , weight reduction and cost reduction can be achieved.

Furthermore, even if the surface potential sensor is placed downstream of the developing means, there is no effect of the charge of the toner in the developing means, and the surface potential of the photoreceptor can be detected stably and accurately. Even if the characteristic value of the image changes over time, it is possible to appropriately control the image forming conditions accordingly. For this reason, it is possible to provide an image forming apparatus with high operational reliability.

[Brief explanation of the drawing]

The drawings are all for explaining the present invention in detail. Figure 1 is a schematic configuration diagram of a digital full-color copying machine, Figures 2 and 3 are block diagrams of a control section, and Figure 4 is a diagram of a charging unit. FIG. 3 is an explanatory diagram showing an example of setting a potential and a developing bias potential. 3... Image processing unit, 12... Laser beam emitting device, 13... Recording device, 14... Photosensitive drum, 15... Charger, 16...
Developing section, 17, old transfer charger, 40...
- Main control section, 56...Video control section, 61
...Development bias high voltage power supply, S...Surface potential sensor. Diagram: Lord Hoami

Claims (2)

[Claims] (1) A charging means that uniformly charges the surface of a photoreceptor that is transported in a certain direction, and an electrostatic latent image that is formed by exposing the charged photoreceptor to a light image corresponding to the image to be formed. an exposure means for forming an electrostatic latent image, a developing means for supplying toner to the electrostatic latent image to visualize the electrostatic latent image, and a transfer means for transferring the toner image obtained by development onto a recording material. a pattern exposure means for exposing a light image of a certain pattern on the photoreceptor to form a patterned electrostatic latent image; and a surface potential of a portion of the photoreceptor on which the patterned electrostatic latent image is formed. In an image forming apparatus comprising a surface potential sensor for detecting a surface potential, and a control means for adjusting various image forming conditions based on the detection value of the surface potential sensor, the surface potential sensor is located at a lower surface of the photoreceptor than the developing means. disposed downstream in the transport direction and upstream of the transfer means, immediately before the patterned electrostatic latent image passes through the development means;
Non-image area potential V of photoreceptor after exposure to developing bias voltage
An image forming apparatus characterized in that it is provided with a bias voltage adjusting means for changing the bias voltage to around o. (2) In claim (1), the developing means includes a rotating developing sleeve, and the developing sleeve is configured to stop rotating when the patterned electrostatic latent image passes through the developing means. An image forming apparatus characterized by: