JPS61156265A - Image forming device - Google Patents

Abstract

PURPOSE:To surely form a stable excellent image even at the time of a halftone, by setting conditions similar to the operating conditions of an image forming means immediately after the leading edge section of an original to the leading edge section of the original. CONSTITUTION:The quantity of reflecting light from the surface of an original is detected by means of an optical sensor 1 and, when the frequency of the power supply is 50Hz, the first developing bias value V1 is calculated with a microcomputer 7 at 8-point sampling. Then, the next sampling division is also started in parallel from the 5th point in the course of the first sampling division and the next bias value V2 is calculated at the 8th point. The successive bias values V3, V4... are also calculated in the same manner thereafter. The bias value V2 immediately after the leading edge section of a picture is used as the first developing bias value V1. Therefore, no toner fogging, etc., are produced and excellent images can be formed even if the leading edge section of the picture is in a halftone.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to an image forming apparatus such as a copying machine, and more particularly to an image forming apparatus that controls image forming conditions according to the density of a document so as to obtain a proper image.

Prior Art In a conventional image forming apparatus such as a copying machine, in order to adjust the transferred image density to an appropriate amount, the volume 300 in the operating section as shown in FIG. 1 is adjusted and the variable resistor VR% shown in FIG. 2 is changed. It was common practice to obtain an appropriate image by changing the lighting voltage of the original exposure lamp LA%.

However, the conventional method has the disadvantage that several sheets of transfer paper are often wasted before obtaining a proper image, and the amount of transfer paper used increases beyond the required number.

Purpose The present invention has been made in view of the above points, and an object thereof is to provide an image forming apparatus that is capable of extremely accurately and reliably setting the operating conditions of an image forming means according to the document. do.

Example The present invention will be explained in detail below with reference to the drawings.

FIG. 3 is a schematic cross-sectional view of a copying machine which is an embodiment of an image forming apparatus according to the present invention.

In FIG. 3, 101 is the main body, 102 is a document platen cover, 103 is an operation unit and document table, 104 is a lamp for exposing the document, 105a to 105d are reflection mirrors, 106 is a zoom lens for variable magnification, and 107 is for heat exhaust. 108 is a photosensitive drum; 109 is a cleaner for removing toner remaining on the photosensitive drum 108; 110 is a photosensitive drum 10;
A charger 8 uniformly charges the photosensitive drum 108 positively or negatively; 111 a blank exposure lamp for removing charges from a non-image area on the photosensitive drum 108; and a developer 112 for developing the electrostatic latent image on the photosensitive drum 108. 113 is a paper feed cassette containing transfer paper; 114 is a transfer charger for transferring the toner image on the photosensitive drum 108 onto the transfer paper; 115 is a transfer roller;
116 is a transport roller, 117 is a fixing device that fixes the toner image on the transfer paper, 118 is a copy tray, 119 is an image edge sensor that outputs a signal indicating the leading edge of the document, 120 is a registration roller, and 121 is a device that detects the density of the document. 122 is a power switch, and 123 is a home position sensor. The copying process of this copying machine is not much different from that of conventional machines, so the details will be omitted.

FIG. 4 shows a circuit for detecting the original density. The operational amplifier 2 performs current-to-voltage conversion on the photodetection power source from the photodiode cover 1 corresponding to the light receiving sensor 121, and the operational amplifier 3 adjusts the gain of the input voltage to the microcomputer 7.

The microcomputer 7 is a one-chip microcomputer with a built-in AD converter. The microcomputer 7 controls the ADI input level and volume 5. and the developing bias DC of the developing device 112 calculated based on the input from 6.
In order to output the value, a PWM (pulse width modulated) pulse is output from the output port 1, and this is sent to the integrator 5.
is the photosensitive drum 1089 in this embodiment, which determines the developing bias DC value to be applied to a predetermined reference density determined on the document according to the sensitivity change of the oPC drum, and the volume 6 is the one described above. Developing bias DC corresponding to the first reference density and a separately determined second reference density
This determines the variable range of values. Further, 9 is a transformer, which performs full-wave rectification on the secondary side and uses an operational amplifier 11 to detect zero cross. The zero loss pulse is inputted to the interrupt terminal 1 of the microcomputer 7, and ADl is sampled by the interrupt processing as shown in FIG. 5. As shown in FIG. 6, the ADI waveform changes in synchronization with the lighting voltage waveform of the halogen lamp LAI, which is the document exposure lamp 104, and is changed in synchronization with a half wave of the power supply frequency as shown in the figure, so it is sampled at the zero cross point. This is effective in picking up accurate data. Switches 14 and 15 select the light intensity of the halogen lamp (
4 levels) and the lamp regulator L with the D/A converter.
It sends a lighting voltage control signal to the RI. A lamp lighting signal is output from the output port core 2.

FIG. 7 shows a timing chart of the automatic appropriate density adjustment function (hereinafter abbreviated as AE function) according to the present invention. A copying machine embodying the present invention has a zoom lens 10 as shown in FIG.
6, it has a continuous magnification function that enlarges and reduces the original in 1% increments, and the relationship between the sensor output (ADI) and the magnification for the same density original is linear as shown in Figure 9. It is shown by the formula. Therefore, as will be described later, the sampled sensor output value (ADI) must be corrected using the linear equation shown in FIG. 9 in accordance with the copy magnification to the value at the same magnification. To explain FIG. 7, the AE function according to this embodiment uses a sequential control method, in which the optical sensor 1 detects the amount of light reflected from the document surface while scanning the document.
The output is sampled at the zero cross point, and the developing bias is controlled by an appropriate developing bias value calculated based on the sampled data. First, the first developing bias value v1 is calculated by sampling 8 points when the power supply frequency is 50H2, according to the optical sensor output sampled at the zero cross point after receiving the image edge signal of the original from the image edge sensor 119 while the document table is moving forward. do. When the frequency is 60Hz, it is calculated using 10 points. The next sampling section starts in parallel from the middle of the first sampling section, that is, from the 5th point in the case of 50 Hz and the 6th point in the case of 60 Hz, as shown in FIG.
The next bias DC value ■2 is calculated at the 8th point or the 10th point, respectively. Thereafter, by repeating the same control, V3. Calculated as V4 life/kai.

The developing bias DC value Vn thus obtained is outputted sequentially from vl at the bias switching timing as shown in FIGS. 7 and 8. The timing of bias switching is based on the exposure position A on the photosensitive drum and the pressure between the developing sleeve of 932 mm and the process speed F of 100 mm /
This is the timing when the time 320 m5 divided by S has elapsed after the image tip signal was input. However, data v1 cannot be treated as proper data because it includes a margin of about 2 mm at the leading edge of the image. Therefore, as shown in FIGS. 7 and 8, the initial developing bias data V1 is substituted with data 2 immediately after the leading edge of the image. As a result, even if the leading edge of the image is a halftone chart or the like, image formation can be performed without toner overlapping.

As is clear from the above, the sequential control AE according to this embodiment
The latent image area to be developed using the developing bias value Vn is determined by referring to the document density of the document portion to which the bias value corresponds and the area on the near side thereof. This is because this AE control controls the developing bias in units of a specific temporal width (40 m5.60 I at 50 Hz (41.5 m5 at z)). Based on the results taken into consideration to avoid extreme changes in concentration.

The control timing of this sequential AE control has been described above, and next, the method for determining the developing bias DC value Vn will be described. The calculation of the bias DC value is performed within the zero-cross interrupt process shown in FIG. The developing bias specifications of the high voltage transformer 8 used in this embodiment are linearly controlled from -50 to -600V with respect to a control signal of 10 to 15V, as shown in FIG. In this embodiment, in order to obtain this control signal, a pulse width modulated (PWM) pulse is output from the output port 01 as shown in FIG. Level conversion. The situation is shown in FIG. In this embodiment, the duty ratio of the pulse is divided into 43, and the development/<IAS DC value W control signal is controlled. Therefore, the minimum resolution of the developing bias DC value is (800-50)/44-12.5V. In this way, the duty corresponding to the developing bias value calculated by the bias calculation routine shown in FIG.
Appropriate image density control is realized by sequentially outputting pulses having a ratio from the o1 output port.

Next, the contents of the bias calculation routine shown in FIG.
This will be explained with a diagram. After passing the image edge sensor while the document is advancing, the average value is calculated for each output of 8 samplings when the power frequency is 50 Hz, and 10 times when the power frequency is 60 Hz. The data is corrected to the same size using a linear equation that shows the following. That is, the magnification X
%, the data Vn when the magnification is 100% is Vn=Wn/(0,57β+0.43)=Vn
/ (0,57X −+ 0.43). This is the magnification correction process in FIG.

The next step is light amount correction processing. As shown in FIG. 15, in the photosensitive drum (COPC drum) according to the present invention, as the number of copies increases, the light potential increases and the contrast tends to decrease sharply. 4th to handle this
As shown in the figure, the light intensity of the halogen lamp serving as the document exposure lamp is selected by switches 14 and 15. In other words, as the number of copies increases, the Lig of the photosensitive drum increases.
As the ht potential increases, the reduction in contrast and last is alleviated by increasing the lighting voltage of the halogen lamp. This lighting voltage can be selected from four types by combining switches 14 and 15 shown in FIG. 14, and the microcomputer 7 transmits 8-bit information to the D/A converter 16 based on this data. D/
The A converter converts this information into an analog value and outputs it, thereby providing a /\logen lamp lighting voltage control signal to the lamp regulator LRI.

Therefore, the standard lighting voltage is EO1 and the other three lighting voltages are E
l, E2. E3. (Representatively, Ex), the calculated value Vn obtained by magnification correction processing is Vn' after light amount correction.
and Vn' are determined as.

This light amount correction process determines the original density shown in FIG. 13, and the final process in the flow shown in FIG. 12, that is, calculation of the developing bias DC value for the light amount correction value Vn'' is executed. FIG. 14 shows the process. To explain Fig. 14, the developing bias DC value is linearly set for densities ranging from the amount of reflected light Q = 0.76 for a standard density original to Q = 0.5 for an original with a dark background equivalent to a newspaper. By controlling the bias value, characters on dark originals are not overlapped and characters on thin originals are clearly reproduced. However, for originals that are darker than newspapers, an upper limit is placed on the bias value, and for originals that are lighter than standard density originals, the characters are clearly reproduced. By setting a lower limit even when the base material is removed, excessive control such as excessive removal of the undercoat or over-covering of the base material is prevented.
8, as the number of copies increases, the latent image potential with respect to the exposure amount tends to increase from curve 1 to curve 2, as shown in FIG. 14. Therefore, as shown in FIG. It is also necessary to make the control value (the lower limit value mentioned above) variable, and this is realized by the volume 5 shown in FIG. In addition, the aging of the photosensitive drum shown in FIG. 15 also changes in a direction that reduces the contrast between the light potential (V) and the dark potential (VD).
As shown in FIG. 4, it is also necessary to change the variable width of the development bias control between the standard density original and the newspaper equivalent original with the passage of time. In this embodiment, this variable width is changed from m1n90V to m1n90V by the volume 6 shown in FIG.
It is controlled up to.

Using Shikijime as an example, it is possible to perform optimal image reproduction according to the density of the original, and since it is sequentially controlled within the same original, image control that follows changes in density within the same original is possible. Although this has been described above as being more efficient as it eliminates the waste of transfer paper due to copy errors, it can also be applied to copying machines with a movable document table. It is also applicable to a device that copies a document while it is being read.

Effects As described above, according to the present invention, the same operating conditions as the operating conditions of the image forming means immediately after the leading edge of the document are set for the leading edge of the document, so even in the case of a halftone chart, etc. Operating conditions can be set reliably and stable image formation can be performed.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a scanning section of a copying machine, FIG. 2 is a conventional density adjustment circuit diagram, FIG. 3 is a sectional view of a copying machine to which the present invention is applied, and FIG. 4 is a document density detection according to the present invention. A circuit diagram, FIG. 5 is an interrupt routine flowchart, FIG. 6 is a diagram showing waveforms of each part of the present invention, FIG. 7 is a timing chart of the present invention,
Figure 8 is a diagram showing the correspondence between the AE sensor output sampling division and the developing bias output DC value, Figure 9 is a diagram showing the relationship between the copy magnification and the AE sensor output, and Figure 10 is a diagram showing the relationship between the developing bias DC value of the high voltage transformer. Diagram showing specifications, No. 11
The figure shows the relationship between the developing bias control pulse and the developing bias control signal, Figure 12 is a bias value calculation flowchart in AE sub-control, and Figure 13 shows the amount of reflected light Q on the original and the AE
FIG. 14 is a diagram showing the relationship between the sensor output, FIG. 14 is a diagram showing the relationship between the amount of reflected light Q on the original and the developing bias DC value, and FIG. 15 is a diagram showing the sensitivity change due to the aging of the photosensitive drum. In the figure, 1 is a photodiode, 7 is a microcomputer, 8 is a high voltage transformer, 104 is an original exposure lamp, 108 is a photosensitive drum, 112 is a developing device, and 121 is a light receiving sensor.

Claims (3)

[Claims] (1) An image forming means that forms an image corresponding to the original image on a recording medium, a detecting means that detects the density of the original image, and operations of the image forming means sequentially according to the density of the original image detected by the detecting means. An image forming apparatus comprising: a control means for controlling conditions, wherein the control means sets operating conditions for a leading edge of a document similar to operating conditions of the image forming means immediately after the leading edge of the document. (2) In claim 1, the image forming means includes a latent image forming means for forming a latent image on the recording medium and a developing means for developing the latent image, and the control means is configured to control the developing means for developing the latent image. An image forming apparatus characterized in that the developing bias voltage of the means is controlled. (3) The image forming apparatus according to claim 1, wherein the detection means detects the density of the original based on the amount of light from the original.