JPH05100535A - Image forming device - Google Patents

Abstract

PURPOSE:To shorten the time for image formation as a whole when a multiple number of image formations are carried out consecutively. CONSTITUTION:Potential is measured in a multiple number of spots of an electrostatic latent image of a photosensitive body 16 by a potential sensor 37 at the start of copying of a first piece, initial photosensitive characteristic is detected based on this data, and grid voltage is controlled based on the detected result. This control is carried out by a basic control means C1 of a control device 35. From a second piece onward, the spots where potential is measured is reduced less than at the time of basic control based on the data at the basic control, and simplified control is carried out by a simplified control means C2 based on the data. Because the simplified control can be carried out in a shorter time than the basic control, the time for image formation as a whole can be shortened.

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 for detecting a photosensitive characteristic of a photosensitive member by measuring a latent image potential of the photosensitive member and adjusting image forming conditions based on the detection result. The present invention relates to an image forming apparatus capable of shortening the entire image forming time including a latent image potential measuring process and an image forming condition adjusting process.

[0002]

2. Description of the Related Art In an image forming apparatus such as a copying machine, a photosensitive member, which is one of the main constituent members of an image forming section, has a photosensitive characteristic such as temperature and humidity in an external environment or repeated charging and exposure. Changes subtly by. Since the density of the final copy is greatly affected by this change in the photosensitivity, in order to obtain a stable high-quality copy, the photosensitivity of the photoconductor during copying is accurately grasped and The image forming conditions suitable for the photosensitive characteristics are set.

A general method for ascertaining the photosensitivity of a photoconductor is to expose the surface of the photoconductor uniformly charged by a charging device to form an electrostatic latent image, and the potential of the electrostatic latent image at this time. To measure. For example, as an electrostatic latent image, a dark portion and a bright portion corresponding to a white portion and a black portion of an original image are formed on the surface of the photoconductor, and the potential thereof is measured. It is known that the potentials of the dark portion and the bright portion change according to the photosensitive characteristics of the photoconductor. Then, the difference in potential between the dark portion and the light portion, that is, the magnitude of the contrast is directly reflected in the density of the final copy. For example, if the contrast is high, the amount of toner as a developer adhered increases, and the density of the copy increases accordingly. On the other hand, the toner adheres to the light areas where the toner should not adhere, and fog tends to occur. Conversely, when the contrast is low, there is no fog, but the copy density is low.

When a scorotron type charging device is used, a grid is interposed between the charging wire of the charging device and the surface of the photosensitive member. The typical charging voltage is regulated by the voltage applied to this grid, the so-called grid voltage. It is known that the voltages of the dark part and the bright part on the surface of the photoconductor increase substantially linearly as the grid voltage increases. Also, looking at the way of rising, the way of rising in the dark part is large, but that of the bright part is small. That is, the difference in potential between the dark portion and the bright portion, that is, the contrast, tends to increase as the grid voltage increases. If the contrast is controlled to an appropriate value, the final copy density can be improved.

The relationship between the grid voltage and the contrast can be obtained as follows. First, the grid voltage is kept constant and the photoconductor is uniformly charged, and then a dark portion and a bright portion are formed by exposure, and the respective potentials at that time are measured. Then, the grid voltage is changed and the potentials of the dark and bright areas are measured as in the previous time. Based on these four potential data, if the dark part and the dark part when the grid voltage is changed and the bright part and the bright part are connected by straight lines, respectively, a straight line showing the change of the dark part when the grid voltage is changed, And a straight line representing the change in the bright part when the grid voltage is changed. The straight line that represents the change between the dark portion and the bright portion represents the photosensitive characteristic of the photoconductor at that time. When the photosensitive characteristic changes, the straight line moves in parallel with the change. That is, assuming that the slope of the straight line in the dark part is α and the slope of the straight line in the bright part is β, the slopes α and β of these straight lines are
Does not change. Actually, these straight lines are calculated by a computer based on the above-described four potential data indicating the surface potential of the photoconductor.

In consideration of the photosensitivity of the photoconductor obtained by these potential data and calculation, the image forming conditions are controlled to the optimum ones such as adjusting the grid voltage so that the contrast becomes a predetermined value. There is.

The control process including the measuring process and the adjusting process is performed not only when the image forming apparatus is first installed, but in order to obtain a stable copy image, one copy ( It may be performed for each image formation).

[0008]

However, according to the above-mentioned conventional technique, when the control process is performed for each image formation in order to obtain a stable copy image, the image forming process (contribution to the actual image formation Charging process, exposure process, developing process, etc.) and a control process are alternately performed, and there is a problem that the entire image forming time tends to be long.

Therefore, in the first invention, for example, the basic control is performed at the beginning of the image formation (for example, the first sheet), and thereafter the simple control is performed (for the second sheet and thereafter), and the second invention is An object of the present invention is to provide an image forming apparatus capable of shortening the entire image forming time by performing part or all of the control process in parallel during the image forming process.

[0010]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and a first aspect of the present invention is a charging device for regulating a charging potential of a photoconductor by a grid voltage and exposing the photoconductor. An image including: an exposing unit that forms an electrostatic latent image by means of the above; an electric potential measuring unit that measures the electric potential of the electrostatic latent image; and a controller that adjusts the grid voltage based on the output of the electric potential measuring unit. In the forming apparatus, the control device detects the initial photosensitive characteristics of the photoconductor based on a plurality of potential data measured by the potential measuring device, and a basic control device that adjusts the grid voltage based on the detection result. A storage unit for storing the initial photosensitivity characteristic of the photoconductor obtained by the basic control unit, and an electric charge less than that for the basic control measured by the electric potential measuring unit and the initial photosensitivity characteristic stored by the storage unit. Characterized in that it and a simple control means for detecting the photosensitive characteristics of the photosensitive member on the basis of the data.

A second aspect of the invention is a charging device for regulating a charging potential of a photoconductor by a grid voltage, an exposing unit for exposing the photoconductor to form an electrostatic latent image, and a potential of the electrostatic latent image. An electric potential measuring unit for detecting the electric potential, and a control device for adjusting the grid voltage based on the output of the electric potential measuring unit, in an image forming apparatus, a potential measuring process of the electrostatic latent image by the electric potential measuring unit, Part or all of the control process including the process of adjusting the grid voltage by the control device is performed during the image forming process.

[0012]

Based on the above construction, the first aspect of the invention is to know the initial photosensitivity of the photoconductor (for example, the photosensitivity at the time when the power is turned on and the copying of the first sheet is started. The same applies hereinafter). The potential measuring means measures a plurality of potentials on the surface of the photoconductor, detects the photosensitivity of the photoconductor at this point based on the potential data, and controls to obtain the best copy for the density based on this result. The basic control means of the device regulate the grid voltage. And then (eg 2
For the copies after the first sheet, a simple control unit that can control the grid voltage in a shorter time than the basic control unit when adjusting the grid voltage is used. That is, since the initial photosensitivity of the photoconductor is already known by the basic control of the photoconductor, the subsequent copy is based on this photosensitivity and the electrostatic latent image of the photoconductor measured to obtain the photosensitivity is obtained. The photosensitive characteristics of the photoconductor can be known by measuring the potential data smaller than the potential data of 1., and the control process including the potential measurement process is shortened compared to the basic control. Therefore, the entire copy time is shorter than in the case where the basic control is performed for each copy.

According to a second aspect of the present invention, a part or all of a control process including a photoconductor potential measuring process for changing an image forming condition and a grid voltage adjusting process is performed in parallel with the image forming process. As a result, the copy time can be shortened as compared with the case where the control process and the image forming process are alternately performed in time.

[0014]

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

FIG. 2 shows an outline of a four-color digital color copying machine (hereinafter simply referred to as copying machine) 1 as an image forming apparatus embodying the present invention. This copying machine 1 is a document D
The reader unit 2 for reading the image information and the printer unit 3 for copying the image information.

The reader unit 2 includes a document illumination lamp 6 mounted on a carriage 5 that reciprocates in the direction of arrow A, a short focus lens array 7, and a CCD (image sensor) 9, and CC
An image processing device 10 to which image data from the CCD 9 is input is connected to D9.

The printer unit 3 includes the image forming apparatus 10 described above.
It has an exposure means 11 to which an image signal from is input. The exposure unit 11 includes a laser unit 12, a polygon mirror 13, a mirror 15 and the like, and the photoconductor 1 is irradiated with laser light.
6 is exposed.

The photoconductor 16 is rotatably supported in the direction of the arrow, around which the charger 17 uniformly charges the surface of the photoconductor 16 prior to exposure, and the static electricity formed on the surface of the photoconductor 16 by exposure. A developing device 18 that develops the electrostatic latent image is provided.

In the developing device 18, four full color developing devices, that is, yellow, magenta, cyan, and black developing devices 19Y, 19M, 19C, and 19B are loaded on a rotating body 19, respectively.
A developer (toner) corresponding to each color is stored. The latent images on the photoconductor 16 are sequentially developed by the developing devices 19Y, 19M, 19C, and 19B, and the developed toner images are transferred to the transfer material (sheet material) P wound around the transfer drum 20.

The sheet material P is stored in a paper feed cassette 21 mounted below the front side (right side in FIG. 2) of the printer unit 3, but is replaced by a paper feed roller 22, a transport roller 23, a registration roller 25 and the like. It is supplied to the transfer drum 20 via the. The toner images of four colors are sequentially transferred from the photoconductor 16 to the sheet material P by the transfer charger 26, and the transfer drum 2
Then, the toner image is fixed by the fixing device 29, and then the toner image is discharged onto the paper discharge tray 30 to finally complete the copy.

FIG. 1 illustrates components for measuring and controlling the potential of the photoconductor 16. The charger 17 is of a scorotron type having a charging wire 17a and a grid 17b, and is connected to high voltage power sources 31 and 32, respectively. Another high-voltage power source 33 is provided for each developing device 19.
The developing cylinders 19a of Y, 19M, 19C, and 19B are connected. These high-voltage power sources 31, 32, 33
Are all CPU35a, ROM35b, RAM3
5c is connected to the control device 35, and the control device 35 includes a laser driver 12a and a laser oscillator 1
A potential measuring means (potential sensor) 37 via the laser unit 12 having 2b and the like, and the potential control unit 36.
Are connected.

The potential sensor 37 measures the surface potential of the photoconductor 16, and the potential control unit 36 converts the digital signal from the potential sensor 31 and inputs it to the control device 35. The potential data input to the control device 35 is read by the CPU 35a, and the high voltage power supply 31,
32 and 33 are controlled.

Next, the control flow of the surface potential control of the present invention will be described.

FIG. 3 shows a basic flow chart.

First, when the power of the copying machine 1 is turned on (S
1), the counter of the potential control counting means is reset to N = 0 (S2). Next, when the copy start button is pressed (S3) and N = 0 in S4, the control device 3
Basic control C1 by the basic control means 5 is performed. The basic control means C1 will be described later. Then, a normal image forming process is performed (S5), and the potential control counter is set to N = 1 (S6).

When the next copying operation is performed without turning off the power of the copying machine 1, in step S4, a simple control means C described later is provided.
2 is selected.

Next, the operation of the basic control means C1 will be described with reference to FIG.

In FIG. 4, the horizontal axis corresponds to the grid (bias) voltage, and the vertical axis corresponds to the surface potential V _S. In the figure, V _D corresponds to the surface potential when not exposed (dark part potential), and V _L corresponds to the surface potential when exposed (bright part potential). Now, when the range of the dark space potential V _D is limited, the dark region potential V _D is proportional to the grid bias V _G, and _VL also has the same tendency. That is, the amount of change in V _D and V _L is proportional to the amount of change in V _G , and if the proportional constants are α and β, α> β
Have a relationship. Therefore, before the print sequence is performed, the Vs according to the preset grid voltages V _G1 and V _{G2 are} applied.
_D and V _L are measured by the potential sensor 37, and V _D and V with respect to the grid voltage V _G as shown in FIG.
Assume the _L charge curve. After that, when actually forming an image, the development contrast, that is, DC component V _DC and V _L of the developing bias, which will be described later, is calculated from the charging curve obtained by the above operation.
Of the grid voltage V _G such that the difference V _cont or the latent image contrast (V _D −V _L ) becomes a desired value, and the grid bias is controlled. Further, the portion corresponding to the white background of the image, in the case of the present embodiment, is V because it is the reversal development.
_In order to prevent the toner from adhering to the portion corresponding to _D , a developing bias having a value (V _B ) lower than the constant potential by V _D is obtained and the developing bias is controlled.

Next, the simplified control means C2 will be described with reference to FIG.

When the simple control C2 is performed, the basic control C1 is already performed, and the basic control C1 controls the slope α of the dark potential V _D and the slope β of the bright potential V _L with respect to the grid voltage V _G. It is stored in the RAM 35c of 35. In the operation of the basic control C2, only V _D ′ with respect to a certain one point of the grid bias V _G ′ is measured, and a new charging curve of V _D and V _L is assumed by using the above-described inclinations α and β. After that, perform the same calculation as the basic control C1,
The grid voltage V _G and the developing bias V _B during image formation are calculated. Here, since the charging potential on the photoconductor 16 is measured at only one point of V _D ′ because V _L hardly changes, the control process is completed in a much shorter time than the basic control C1.

In the above-described first embodiment, 1 is set after the power is turned on.
The first invention has been described in which the potential control is performed differently for the first and second sheets.

Next, the second invention in which the potential control is performed at different timings for the first and second sheets will be described.

FIG. 6 shows the flowchart.

Steps S1 to S4 are the same as in the first embodiment. In the case of N = 0, that is, after turning on the power switch, if it is the first sheet, the potential is controlled and the image forming process is started. The control method is the same as in the first embodiment,
The dark portion potentials V _D1 and V _D2 and the light portion potentials V _L1 and V _L2 are stored in the RAM 35.
It is stored in c. For the second and subsequent copies, the grid voltage V _G and the developing bias V _B are set by using V _D1 , V _D2 , V _L1 , and V _L2 obtained by the previous potential control without performing the potential control. The desired image is formed.

After the image forming process is completed, the photoconductor 1
The potential is controlled during the post-processing operation such as the cleaning of 6, the V _D1 , V _D2 , V _L1 , and V _L2 are newly measured, and the content of the RAM 35c is rewritten. This data is used when forming the image of the next copy.

If the potential control is performed at the above timing, the control process including the potential measuring process and the grid voltage adjusting process can be performed during the post-processing operation such as cleaning which is one process of the image forming process. No need to devote special time for control process.

The case where the present invention is applied to an image forming apparatus having a plurality of image forming stations will be described below.

FIG. 7 shows a four-drum laser beam printer which is an example of a laser beam printer having a plurality of optical scanning means.

The printer is provided with four image forming stations around the image carrier which is an electrophotographic photosensitive member, the image forming means having image forming means, and the image formed by each image forming station. The image on the carrier is transferred to a transfer material carried and conveyed by a moving body that moves adjacent to the image carrier.

Magenta, cyan, yellow, and black image forming stations Pm (first station), P
c (second station), Py (third station),
The photosensitive drums 51 are respectively provided on Pk (fourth station).
M, 51C, 51Y and 51K are arranged and rotated in the arrow direction. In addition, the photosensitive drums 51M, 51C, 51Y,
Chargers 52M, 52C, 52Y, 5 are provided around 51K.
2K, scanning optical devices 53M and 53 as optical scanning means
C, 53Y, 53K, developing devices 54M, 54C, 54
Y, 54K, cleaner 55M, 55C, 55Y, 55K
An image forming unit including the above is disposed.

Further, the transfer portion 56 which constitutes one of the image forming means includes the image forming stations Pm, Pc, Py, and
Transfer belt 56a and transfer charger 56 common to Pk
M, 56C, 56Y, 56K, and full-color image formation is performed on the transfer material P supported on the transfer belt 56a.
This is achieved by sequentially transferring the toner images of the respective colors formed on the photosensitive drums 51M, 51C, 51Y and 51K. The transfer material P is supplied from the paper feed cassette 57, and the transfer material P that has completed the transfer process is separated and fixed in the fixing device 5.
8 to the tray 59.

The scanning optical devices 53M, 53C, 53
Reference numerals Y and 53K denote a laser device which is a light source (not shown), a rotating polygon mirror which scans the laser device, an fθ lens which focuses the scanning beam on the generatrix of the surface of the photosensitive drum, and a reflection mirror which redirects the light beam. , A beam detection device for detecting a specific position of the scanning beam. 60M, 60C, 60Y and 60K are potential sensors.

In such an image forming apparatus, after the power switch is turned on, during the copying operation of the first sheet, for example, basic control C1 is performed before image formation for all four stations.
The copy operation for the second and subsequent sheets will be described with reference to FIGS. 8 and 9. In the figure, the direction of the arrow indicates the passage of time.

In FIG. 8, in the second and subsequent copies, before the image formation in each image forming station, the simple control C2 similar to that described in the first embodiment is performed to set each image forming condition. It means to do.

Similarly, FIG. 9 shows the copying operation for the second and subsequent sheets after the power is turned on. Here, the first image forming station is V _D1 , V _D2 , V obtained during the previous copying operation.
_The image forming conditions are set using data such as _L1 and _VL2 . After the second image forming station, the potential control is performed during the image forming process of the first image forming station Pm to set the image forming conditions. Then, in the first image forming station Pm, after the image forming process is completed,
The potential is controlled during the image forming process of another image forming station, and the data is used in the next copy. By doing this, copying is completed in a shorter overall image forming time than in FIG.

Of course, the simple control C2 in FIG. 9 may be replaced with the basic control C1 to obtain the same effect.

[0047]

As described above, according to the first aspect of the invention, the control performed for each copy at the time of image formation, for example, the basic control performed for the first copy and the second and subsequent copies are performed. By performing the simple control for the image forming process, the entire image forming time can be shortened. According to the second aspect of the invention, the image forming time can be shortened by performing a part or all of the control process for changing the image forming condition in parallel with the image forming process.

[Brief description of drawings]

FIG. 1 is a block diagram showing potential control for a photoconductor.

FIG. 2 is a schematic view showing a vertical section of the image forming apparatus.

FIG. 3 is a basic flowchart of potential control.

FIG. 4 is an explanatory diagram of basic control.

FIG. 5 is an explanatory diagram of simple control.

FIG. 6 is a flowchart of the second embodiment.

FIG. 7 is a schematic view showing a vertical section of an image forming apparatus according to a third embodiment.

FIG. 8 is a flowchart of the third embodiment.

FIG. 9 is another flowchart of the third embodiment.

[Explanation of symbols]

 11 exposure means 16 photoconductor 17 charging device 17b grid 35 control device 37 potential measuring means (potential sensor) C1 basic control means C2 simple control means

Claims (2)

[Claims] 1. A charging device that regulates a charging potential of a photoconductor by a grid voltage, an exposure unit that exposes the photoconductor to form an electrostatic latent image, and a potential measurement that measures the potential of the electrostatic latent image. In the image forming apparatus, a control unit that adjusts the grid voltage based on an output of the potential measuring unit, wherein the control unit controls the photosensitivity based on a plurality of potential data measured by the potential measuring unit. A basic control unit that detects the initial photosensitivity of the body and adjusts the grid voltage based on the detection result; a storage unit that stores the initial photosensitivity of the photoconductor obtained by the basic control unit; A simple control means for detecting the photosensitive characteristic of the photoconductor based on the initial photosensitive characteristic stored by the means and the potential data measured by the potential measuring means which is smaller than that at the time of the basic control. Image forming apparatus characterized by. 2. A charging device that regulates a charging potential of a photoconductor by a grid voltage, an exposing unit that exposes the photoconductor to form an electrostatic latent image, and a potential measurement that detects the potential of the electrostatic latent image. An image forming apparatus comprising: means for adjusting the grid voltage based on the output of the potential measuring means; and a process of measuring the potential of the electrostatic latent image by the potential measuring means, An image forming apparatus, wherein part or all of a control process including a grid voltage adjusting process is performed during an image forming process.