JPS6152658A - Image forming device - Google Patents

Abstract

PURPOSE:To form satisfactorily an image under a correct condition corresponding to a density of an original by operating a detecting value of the original density and a reference value, and controlling a developing bias signal and a light quantity correcting signal, 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, a developing bias value is operated by the computer 7 by referring to a density of the corresponding original point and an area of this side of said point, and it is corrected so that this value becomes within a reference value range. Thereafter, the voltage is controlled by inputting the developing bias value to a developing drum 108 from the computer 7. Also, the light quantity is controlled by inputting a light quantity correcting signal to a lamp LA1. Accordingly, since the detecting value of the original density and the reference value are operated, an image forming condition can be corrected, and an image of a good quality is obtained.

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, transfer l1lUi
To adjust the image density to an appropriate amount, adjust the volume 300 in the operation unit as shown in Fig. 1, change the variable resistor VRI shown in Fig. 2, and change the lighting voltage of the original exposure lamp LAI to obtain an appropriate image. It was common to obtain

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 thereof is to provide an image forming apparatus that can set image forming conditions according to a document with extremely high accuracy.

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 an original platen cover, 103 is an operation unit and an original platen, 104 is a lamp for exposing the original, 105a to 105d are reflective 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 1;
A charger 08 uniformly charges the photosensitive drum 108 in a positive or negative manner, and a blank exposure lamp 111 removes charges from a non-image area on the photosensitive drum 108.

112 a developing device for developing the electrostatic latent image on the photosensitive drum 108; 113 a paper feed cassette containing transfer paper; 114 a transfer charger for transferring the toner image on the photosensitive drum 108 onto the transfer paper; 115 1 is a transfer roller; 116 is a conveyance roller; 117 is a fixing device that fixes the toner image on the transfer paper;
18 is a copy tray; 119 is an image tip sensor that outputs a signal indicating the leading edge of the original; 120 is a registration roller; 121
122 is a power switch; 123 is a home position sensor; 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 current by the photodiode 1 which is lost 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 1-chip microcomputer with a built-in AD converter.

The microcomputer 7 operates a developing device 11 which is calculated based on 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, the output capo-h0
1 outputs a PWM (pulse width modulated) pulse, which is level-converted through an integrator and used as a development bias control signal input to the high voltage transformer 8. Here, volume 5 is the photosensitive drum 108, in this embodiment. T.P.
It determines the developing bias DC value to be applied to a predetermined reference density determined for the document according to the sensitivity change of the C drum, and the volume 6 is used to determine the developing bias DC value to be applied to a predetermined reference density determined on the document. This is to determine the variable range of the developing bias DC value corresponding to the two basic degrees.

Further, 9 is a transformer, which rectifies the aftereffects on the secondary side, and performs zero cross detection by an operational amplifier 11.

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 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. It is effective in pink amplifying accurate data. Switch 14.1
5 selects the light intensity of the halogen lamp (4 levels) and selects D/
The A converter sends a lighting voltage control signal to the lamp regulator LRI. A lamp lighting signal is output from the output port 102.

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 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 (ADZ) and the magnification for the same density original is linear as shown in Figure 9. It is shown by the formula. Therefore, the sampled sensor output value (ADZ) needs to be corrected 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 uses a sequential control method, in which the amount of reflected light from the document surface is detected by the optical sensor l while scanning the document, and
The output is sampled at the zero cross point, and development/heas is controlled by an appropriate development bias value calculated based on the sampled data. First, while the original platen is moving forward, the image edge signal of the original is input from the image edge sensor 119, and according to the optical sensor output sampled at the zero cross point, when the power frequency is 50 Hz, the first developing bias value is determined by sampling 8 points. v1
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.
The next sampling section is started in parallel from the 5th point in the case of z and the 6th point in the case of 60 Hz, and the next bias DC value v2 is calculated at the 8th point or the 10th point, respectively. Thereafter, by repeating the same control, v3, v4, etc. are calculated.

The developing bias DC value Vn obtained in this manner is sequentially output from 1 at the bias switching timing as shown in FIG. 8. The timing of bias switching is the distance 3 between exposure position A on the photosensitive drum and the developing sleeve.
The timing is when a time of 320 m5, which is 2 mm divided by the process speed of 100 mm/s, has elapsed after the image tip signal was input.

As is clear from the above, the sequential control AE according to this embodiment
Regarding the latent image area developed by the developing bias value Vn, the latent image area 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 wood AE control controls the developing bias in units of a specific temporal width (40 m at 50 Hz and 41.5 m at 60 H2), so the developing bias value is changed to ■. This is the result of consideration taken to prevent an extreme change in density from occurring in the image at the boundary between switching from vn+1 to vn+1.

The control timing of this 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 accomplished within the zero-crossing interrupt process shown in FIG. The developing bias specifications of the high-speed transformer 8 used in this example are as shown in FIG. -50 to -6
It is controlled linearly up to 00V. In this embodiment, in order to obtain this control signal, a pulse width modulated (PWM) pulse is output from the output port core 1 as shown in FIG. The level is converted to . The situation is shown in Figure 11 of fjs. In this example, the pulse duty ratio is divided into 43,
It controls the developing bias DC value control signal. Therefore, the minimum resolution of the developing bias DC value is (600-50)/44=12.5V. In this way, pulses having a duty ratio corresponding to the developing bias A1a calculated by the bias calculation routine shown in FIG. Appropriate image density control is achieved by outputting from the 51 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 representing the function. That is, if the average value Vn when the magnification is X% is the data Vn when the magnification is 100%, Vn=Vn/(0,57β+0.43)=V n /
(0,57X,...-+0.43), which is the magnification correction process in FIG.

Next, a light amount correction process is performed.As shown in FIG. 15, as the number of copies increases, the light potential of the photosensitive drum (OPG drum) on which the present invention is applied increases and the contrast decreases. There is a tendency that In order to correct this, switch 14.
15 selects the light amount 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 FIG. I! Based on this data, the microcomputer 7 sets the D/A converter 16 to 8.
Bit information is transmitted, and the D/A converter converts this information into an analog value and outputs it, thereby providing a halogen lamp lighting voltage control signal to the lamp regulator LRI.

Therefore, the standard lighting voltage is EO1 and the other three types of lighting voltage.
Assuming El, E2, E3 (representatively 8 sentences), the calculated value Vn obtained by the 1 magnification correction process is V after the light amount correction.
n' and Vn are determined as follows.

Through this light amount correction processing, the original density shown in FIG. 13 is determined, and the final processing of the flow shown in FIG. 12, that is, calculation of the developing bias DC value for the optical abrasion correction value V n' is executed. Figure 14 shows the situation. To explain Fig. 14, the development/<Ias DC value is linearly controlled 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. As a result, characters on dark originals are not overlapped, and characters on thin originals are clearly reproduced. However, it is more intense than newspaper! 7. By setting an upper limit to the bias value for originals and setting a lower limit for originals that are lighter than standard density originals, excessive control such as excessive background skipping or overlapping is prevented. Furthermore, as shown in FIG. 15, the photosensitive drum (OPC drum) 108 used in this example has a tendency for the latent image potential with respect to the exposure amount to increase from curve 1 to curve 2 as the number of copies increases. Therefore, as shown in FIG. 14, it is necessary to make the control value of the developing bias for the standard original (the lower limit value described above) variable, and this is set by adjusting the control value of the developing bias shown in FIG.
This is realized by In addition, the changes over time of the photosensitive drum shown in FIG. 15 are the light potential (■L) and the dark potential (
Since the contrast between VD and VD also changes in a decreasing direction, it is necessary to change the developing bias control variable width between the standard density original and the newspaper-equivalent original as shown in FIG. 14 over time. In this embodiment, this variable width is changed from m1n90V to m1 by the volume 6 shown in FIG.
It is controlled up to n90V.

According to this embodiment, optimal image reproduction corresponding to the density of the original is possible, and since the control is performed sequentially within the same original, image control that follows changes in density within the same original is possible. This eliminates the waste of transfer paper due to copy errors and realizes an efficient copying function.

In this embodiment, a copying machine with a movable optical system is used as an example, but the present invention can also be applied to a copying machine 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 detected value of the document density and the reference value are calculated, and the image forming means is controlled according to the calculation results, so that the image forming conditions can be set with extremely high accuracy. This makes it possible to obtain proper playback images.

[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. 5 is an interrupt routine flowchart, FIG. 6 is a diagram showing waveforms of various parts of the present invention, 714 is a timing chart of the present invention, and FIG. 8 is a diagram showing AE sensor output sampling divisions and developing bias output DC value. A diagram showing correspondence relationships. Figure 9 shows the relationship between the copy magnification and the AE sensor output, Figure 10 shows the specifications of the developing bias DC value of the high voltage transformer, and Figure 11 shows the relationship between the developing bias control pulse and the developing bias control signal. 12 is a bias value calculation flowchart in AE sub-control, FIG. 13 is a diagram showing the relationship between the amount of reflected light Q on the original and the AE sensor output, and FIG.
The figure shows the relationship between the amount of reflected light Q on the original and the developing bias DC' value, and FIG. 15 shows the sensitivity change due to the aging of the photosensitive drum. In the figure, l 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. 4 Cows [%] Current aCt Asf〉μσ-t Shise;li (■)/17 Ass@14FP/flL Sq Upper Hi□

Claims (4)

[Claims] (1) An image forming means for forming an image according to the original on a recording medium, a detecting means for detecting the density of the original, determining a correction value according to the output of the detecting means, calculating this correction value and a reference value, An image forming apparatus comprising: a control means for controlling the image forming means according to the calculation result. (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 includes the An image forming apparatus characterized by controlling a developing bias voltage of a developing means. (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. (4) The image forming apparatus according to claim 1, wherein the operation is addition or subtraction.