JPS6152660A - Image forming device - Google Patents

Abstract

PURPOSE:To form satisfactorily an image under a correct condition corresponding to a density of an original by controlling a developing bias signal and a light quantity correcting signal in accordance with a detecting value of the original density and a sensitivity shift of a recording body, in a copying machine. CONSTITUTION:An intensity of a reflected light from an original is detected by a photodiode 1, and a density of the original is detected. This photodetecting signal is inputted to a computer 7. In this case, the original density is sampled by several points each by a zero crossing detection, and a developing bias value is operated by the computer 7 by referring to a density of the corresponding point and an area of this side of said point. Also, when copying is continued plural times, a sensitivity of a recording body is shifted, therefore, the bias value is corrected by the computer 7. Also, the voltage is controlled by inputting the developing bias value to a developing drum 108, and the light quantity is controlled by inputting a light quantity correcting signal to a lamp LA1. Accordingly, since an image forming condition is corrected in accordance with a shift of the recording body, a good image is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to an image forming apparatus such as a copying machine, etc. 12) In particular, it relates to an image forming apparatus that controls image forming conditions according to the original fIc 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 operation section as shown in FIG. 1 is adjusted and the variable resistor VRI shown in FIG. It was common practice to obtain an appropriate image by changing the lighting voltage of the exposure lamp LAI.

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

OBJECTS The present invention has been made in view of the above points, and an object of the present invention is to provide an image forming apparatus that can set image forming conditions according to a document with extremely high accuracy.

Example The great 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, IO is the main body, 102 is a document table cover, and 103 is an operation section and document table.

104 is a lamp for exposing an original, 105a to 105d are reflecting mirrors, 106 is a zoom lens for variable magnification, 107 is a fan for exhausting heat, 108 is a photosensitive drum, and 109 is a photosensitive drum 1
Cleaner for removing toner remaining on 08, 1
10 is a charger that uniformly charges the photosensitive drum 108 positively or negatively; 111 is a blank exposure lamp for removing electric charge from a non-image area on the photosensitive drum 108; and 112 is an electrostatic latent image on the photosensitive drum 108. 113 is a paper feeder 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 conveyance roller;
17 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 sensor that detects the density of the document. A light receiving sensor detects the intensity of reflected light, 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.

Figure tjS4 shows a circuit for detecting the original density. The photodetection current by the photodiode l, which corresponds to the light receiving sensor 121, is converted from current to voltage by the operational amplifier 2, and the gain of the input voltage to the microcomputer 7 is adjusted by the operational amplifier 3. do. The microcomputer 7 is a one-chip microcomputer with a built-in AD converter.

The microcomputer 7 operates a developing unit 11 which is operated by the input level of the ADI and the inputs from the volumes 5 and 6.
In order to output the developing bias DC value of 2, a PWM (pulse 1 inversion iM) pulse is output from the output port 1, and this is level-converted through an integrator to provide a developing bias control signal to the high voltage transformer 8. Use as input. Here, the volume 5 is the photosensitive drum 108, and in this embodiment, v
It determines the developing bias DC value to be applied to a predetermined reference density determined for the original according to the sensitivity change of the 5pc drum, and the volume 6 is determined separately from the first base aW degree mentioned above. This is to determine the variable width of the developing bias DC value corresponding to the second reference density.

Further, 9 is a transformer, which performs full-wave rectification on the secondary side and uses an operational amplifier 11 to detect zero cross.

Zero cross pulse is lNTl of microcomputer 7
The signal is input to the interrupt terminal, and ADI is sampled as shown in FIG. 5 by the interrupt processing. As shown in Fig. 6, the ADI waveform changes in synchronization with the lighting voltage waveform of the halogen lamp LAI, which is the original f1% exposure lamp 104, and changes at a half-wave of the power supply frequency as shown in the figure, so it changes at the zero cross point. Sampling is effective in picking up accurate data. switch 1
4.15 selects the light intensity of the box lamp (4 levels) I
,, A lighting voltage control signal is sent to the lamp regulator LRI by the D/A converter. Lamp lighting No. 4.3 is output from the output boat 02.

FIG. 7 shows a timing chart of the automatic appropriate density adjustment function (hereinafter referred to as AE function) according to the present invention. A copying machine embodying the present invention has a zoom lens 106 as shown in FIG.
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, it is necessary to correct the sampled sensor output value (ADl) according to the copy magnification using the linear equation shown in FIG. 9, as will be described later, to the value at the same magnification. To explain FIG. 7, the AE function according to this embodiment employs a sequential control method, in which the optical sensor 1 detects the amount of light reflected from the surface of the document while scanning the document.
The output is sampled at the zero cross point, and the developing bias is controlled by an appropriate phenomenon/heias value calculated based on the sampled data. According to the optical sensor output sampled at the zero cross point after input, when the power frequency @ 50 Hz, the first developing bias value Vl is sampled at 8 points.
Calculate.

When the frequency is 60Hz, it is calculated using 10 points. In the middle of the first sampling section, that is, at 50H as shown in FIG.
In the case of z, the next sampling section starts from the 5th point, and in the case of 60Hz, the next sampling section starts from the 6th point, resulting in 8 points each!・Or the next bias DC at the 10th point
Calculate the value V2. Thereafter, by repeating the same control, v3, v4, etc. are calculated.

The developing bias DC value Vn obtained in this manner is outputted sequentially from vl at the bias switching timing as shown in FIG. The timing of bias conversion is the timing when a time of 320 m5, which is the distance between the fog light position A on the photosensitive drum and the developing sleeve of 32 mm divided by the process speed of 100 mm/S', has elapsed after the image tip signal was input.

As is clear from the following, sequential control A according to this embodiment
Regarding E, the latent image area to be developed with 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 the present AE control controls the developing bias in units of a specific temporal width (40 m S at 50 Hz and 41.5 m S at 5.60 Hz). This is the result of taking into consideration that extreme e-degree changes will not occur in the image at the switching boundary.

The control timing of the tree sequential AE control has been described above, and next, the method of calculating the developing bias DC value Vn will be described. The calculation of the bias DC value is performed within the zero-crossing interrupt process shown in Figure i5. The developing bias specifications of the high transformer 8 used in this example are -50 to -600V for the control signal 1O-15V), as shown in the fJSIO diagram.
controlled linearly up to In this embodiment, in order to obtain this control signal, the output port '?' is used as shown in FIG. A pulse width modulated (PWM) pulse is output from 51, and the level is converted into a control signal by inputting it to an integrator. The situation is shown in FIG. 11. In this embodiment, the duty ratio of the pulse is divided into 43, and the developing bias DC value control signal is controlled. Therefore, the minimum resolution of the developing bias DC value is (600-50)/44=12.5V. In this way, dut corresponding to the developing bias value calculated by the bias operation q routine shown in FIG.
Appropriate image density control is realized by sequentially outputting pulses having the y ratio from the 101 output ports.

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, and the average value is 1γI as described above, as shown in Figure 9 The data is corrected to the same magnification using a linear equation representing a magnification function. That is, if the average value Vn is the magnification of X%, then the magnification is 100.
%, the data Vn is Vn=Vn/(0,57β+0.43)=Vn/
(o, s 7 X Hh+ 0.43), which is the magnification correction process in Figure 812.

The next step is a light amount correction process.As shown in FIG. 15, in the photosensitive drum (OPC drum) to which the present invention is applied, as the number of copies increases, the light potential increases and the contrast decreases. There is a tendency. To correct this, the switch 14.1 as shown in FIG.
5 selects the light intensity of the halogen lamp serving as the document exposure lamp. That is, as the potential of the photosensitive drum L gh increases as the number of copies increases, the reduction in contrast is alleviated by increasing the lighting voltage of the halogen lamp. This lighting voltage is selected by the combination of switches 14 and 15 shown in Figure 14.
It is possible to select different voltages, and based on this data, the microcomputer 7 sends 8 bits to the D/A converter 16.
The D/A converter converts this information into an analog value and outputs it to the lamp regulator L.
A halogen lamp lighting voltage control signal is given to RI.

Therefore, the sign lighting voltage is EQ, and the other three types of lighting voltages are E
1, E2, and E3 (representatively 8 sentences), the calculated value Vn obtained by magnification correction processing is Vn after light amount correction.
and V n' are determined as.

Through this light amount correction process, the document density shown in FIG. 13 is determined, and the final process of the flow shown in FIG. 12, that is, calculation of the developing bias DC value for the light amount correction value Vn is executed. The situation is shown in Fig. 14. To explain Fig. 14,
By linearly controlling the developing bias DC value for densities between the reflected light 1Q = 0.76 for standard density originals and Q = o, 5 for originals with a dark background equivalent to newspapers, it is possible to prevent dark originals from overlapping. The characters on thin originals are clearly reproduced. However, by setting an upper limit to the bias value for originals that are darker than newspapers, and setting a lower limit for originals that are lighter than standard density originals, excessive control such as excessive background skipping or over-covering can be prevented. ing. Also,
Photosensitive drum (VPC drum) 108 used in this example
As shown in Fig. 15, as the number of copies increases, the latent image potential with respect to the exposure amount tends to rise from curve 1 to curve 2. Therefore, as shown in Fig. 14, the developing bias for standard originals 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 change over time of the photosensitive drum shown in FIG. 15 also changes in a direction that decreases the contrast between the Lfght potential (vL) 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.

According to this embodiment, optimal image reproduction corresponding to the density of the M document is possible, and since the control is performed sequentially within the same document, image control that follows density changes within the same document is possible. This enables efficient copying at@ without wasting transfer paper due to copy mistakes.

Although this embodiment has been described using a moving optical system type copying machine as an example, the present invention can also be applied to a copying machine having a moving document table. It is also applicable to a device that copies a document while it is being read.

According to the present invention, the operating conditions of the image forming means can be adjusted in accordance with the sensitivity shift of the recording medium, and the detected output of the original density is corrected in accordance with the adjusted operating conditions. ,
Image forming conditions can be set extremely accurately regardless of environmental changes, changes over time, etc., and an appropriate reproduced image can be obtained.

[Brief explanation of drawings]

Fig. 1 is a diagram showing the scanning section of a copying machine, Fig. 2 is a conventional C degree 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 diagram showing the original density adjustment according to the present invention. Detection circuit diagram, FIG. 5 is an interrupt routine flowchart, FIG. 6 is a diagram showing waveforms of various parts 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 control, and Figure 13 shows the amount of reflected light Q on the original and the AE
Figure 14 is a diagram showing the relationship between the sensor output, and Figure 14 is a diagram showing the relationship between the B1 draft reflected light ff1Q and the developing bias DC' value.
FIG. 5 is a diagram showing changes in sensitivity due to changes in the photosensitive drum over time. In the figure, 1 is a photodiode, 7 is a microcomputer, 8 is a high-voltage transformer, 104 is an original fog light lamp, 108 is a photosensitive drum, 112 is a developer, and 74 and 121 are light receiving sensors.

Claims (5)

[Claims] (1) An image forming means that forms an image according to the document on a recording medium, a detection means that detects the density of the document, and an adjustment that can change the operating conditions of the image forming means according to the sensitivity shift of the recording medium. An image forming apparatus comprising: means for correcting the output of the detecting means in accordance with changes in the operating conditions, and controlling the image forming means in accordance with the correction value to obtain an appropriate image. . (2) The image forming apparatus according to claim 1, wherein the image forming means includes an exposing means for exposing a document, and a developing means for developing a latent image on the recording medium. (3) The image forming apparatus according to claim 2, wherein the adjustment means is capable of changing the lighting voltage of the exposure means. (4) The image forming apparatus according to claim 2, wherein the control means controls a developing bias voltage of the developing means. (5) 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.