JPH0555869B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an image forming apparatus such as a copying machine. Conventionally, in order to adjust the transferred image density of a copying machine to an appropriate amount, the volume VR1 in the operation section as shown in Figure 1 was used.
The original exposure lamp shown in Fig. 2 was adjusted.
It was common practice to obtain an appropriate image by changing the lighting voltage of LA1. However, in this conventional method, there are many cases in which several sheets of transfer paper are wasted before obtaining a proper image, and there is a drawback that the amount of transfer paper used increases beyond the necessary number.

The present invention has been made to eliminate this kind of conventional drawback.When exposing an original, the light reflected from the original surface is detected by a photodetector or the photoreceptor potential is detected by an electrometer, and the original is detected according to the output level. It attempts to obtain an image with an appropriate density by determining the density and controlling the appropriate amount of developing bias or voltage of the original exposure lamp.In detail, it includes a scanning means for exposing and scanning the original, and a scanning means for forming an image corresponding to the original image. image forming means,
A timing detection means for detecting a scanning timing signal of the scanning means, which divides the document into several regions in the exposure scanning direction, and samples the document density within each divided region multiple times at a predetermined period. a first timer means that starts a timing operation in synchronization with the scanning timing signal and sets a first scanning period corresponding to the end of the next divided area from the beginning of the odd-numbered divided area for detection;
a second timer means for setting a second scanning period corresponding to the end of the next divided area from an even-numbered divided area in the middle of the first scanning period; a plurality of density detection outputs in the first scanning period; a first sampling means for sampling the density detection output a plurality of times during the second scanning period, and a second sampling means for sampling the density detection output a plurality of times in the second scanning period, and converting each sample value of the concentration detection means into a digital value. digital conversion means, said first;
A calculating means for adding the outputs of the digital converting means of the second sampling means to obtain an average value of the document density of adjacent two divided areas, and repeating and parallel operations of the first and second sampling means, respectively. and set the image forming conditions of the image forming means of each divided area corresponding to a part of the first or second scanning period to the document area sampled during the first or second scanning period. It is an object of the present invention to provide an image forming apparatus, which has a control means that performs control by sequentially using the calculation results of the calculation means, and the calculation means and the control means repeat calculations for obtaining an average value and control of image forming conditions, respectively.

In this way, by using two timer means, the image forming conditions of the area corresponding to a part of the density sampling period are determined from the average value of the digital density of the sampling period. Since large changes in detected density can also be prevented, joints between regions can be made less noticeable, and image quality can be improved.

FIG. 3 shows an embodiment of the present invention. In front of the in-mirror lens IM, an optical sensor PH, in the present invention a photodiode, is installed to detect the intensity of reflected light from the original glass PL. D is a photosensitive drum, and L is an original exposure lamp. Figure 4 shows the detection circuit. The detection signal from the photodiode 1 of the PH is amplified by the operational amplifier 2, the gain is adjusted by the operational amplifier 3, and the signal is input to the AD1 input of the microcomputer 7 with a built-in AD converter. The microcomputer 7 outputs a pulse width modulated pulse from the output port 1 according to the AD1 input level and the AD2 input level determined by the volume 5 described later, and integrates this pulse and inputs it to the operational amplifier 6, thereby changing the output of the operational amplifier 6. The level is output in proportion to the pulse width, and the developing bias of the high voltage transformer 8 is
Control the DC component. A transformer 9 performs full-wave rectification on the secondary side, and an operational amplifier 11 performs AC zero-cross detection. The zero cross pulse is input to the 1 interrupt terminal of the microcomputer 7, and by the interrupt processing thereof, the program shown in FIG. 5 reads the input of AD1 and controls the developing bias.

FIG. 5 will be explained. The relationship between each flag (indicated by FG) and the sequence is shown in FIG. First, when the copy button is pressed, the main motor starts rotating,
When the pre-rotation for removing the charge on the drum and cleaning is completed, the optical system starts moving forward and notifies the leading edge of the document.When there is an input from the sensor S in the middle of forward movement (Step 1), the leading edge of the image is activated for development. The CNTO counter is incremented (step 2), and the time from when the leading edge of the document is exposed to light until the latent image is developed is measured based on the count-up value of the CNTO counter. Before starting development, a bias equal to the preset value FF plus AD2 is applied to prevent toner from adhering to the drum (step 0). Meanwhile, sample AD1 and Σ1
(Step 3), and when the above-mentioned time has elapsed and FG is set indicating that development is in progress (Step 4), the value of Σ1 is divided by CNTO to calculate the average value of AD1 and the fine adjustment volume is adjusted. 5 (Figure 3), and set this value to N (Step 5). As shown in Figure 6 of routine a, the H level pulse width control value T in PWM determined by the value of N is determined. demand. CNT0, CNT1, CNT2 are
Increment every INT input pulse.

The reason why the value of N is divided by 30 in Figure 6 is because the N (←L/P1+AD2) mentioned earlier is 0 at the minimum and 510 at the maximum because the A/D converter is 256LSB, and this is divided in units of 30LSB. This is because it can be divided into 18 parts. Therefore, by controlling the pulse width output to the port 1 in FIG. 4 for each value of N←N÷30, the developing bias DC component can be changed as shown in FIG. 9. Development bias DC
The component varies from -50 to -600V as shown in Figure 10 by the developing bias control voltage _VB shown in Figure 4, and in order to control this _VB , the pulse width output from one output port of the microcomputer is controlled. ing.
The control flowcharts are shown in FIGS. 6 and 7. FIG. 7 shows a timer internal interrupt program that starts when the power is turned on and then starts when an interrupt occurs due to its own time-up.

By the way, the counter CNT2 starts in the middle of the time from the input of the image front edge signal from the sensor S until the start of development. CNT1 and CNT2
As shown in Figures 8 and 12, V _M serves to distinguish the sampling areas for calculating and determining the bias voltage.
The image area to be controlled is the control area shown in Figure 12.
(n) and one area before (n-1) or after (n+1) during original exposure.
It is controlled by a value V _o calculated from the average value of input data from the photodetector sensor 1 in the figure. Here, the bias control voltage V _o is not limited to sampling only the control area (n), but the bias control voltage V o is not limited to sampling only the control area (n);
1) or the data including sampling up to the subsequent area (n+1) is used for the purpose of providing appropriate continuity to the developing bias value to be controlled in response to changes in document density between control areas. be. The bias output is determined by averaging Σ1 for CNT1 (step 5) and averaging Σ2 for CNT2 (step 6).

By the way, the photosensitive drum is a PC drum and the primary charge is negative, so the developing bias DC
When the component is increased to the negative side, the amount of development decreases, resulting in a thinner copy image. Therefore, as shown in FIG. 9, as the value of N increases, that is, as the density of the original becomes thinner, the negative value of the developing bias DC component is made smaller and the amount of development is increased, and the density of the original becomes thinner. Control is aimed at improving character reproduction and, conversely, increasing the development bias CD component for documents with high density, such as newspapers, to eliminate fog in the copied image.

As shown in FIG. 11, the volume 5 shown in FIG. 4 adjusts the DC component of the developing bias in order to obtain a proper copied image when the EV characteristic of the drum changes from one curve to two curves due to drum deterioration. This is a means for appropriate correction.

Note that in the present invention, the development bias is controlled by dividing the document scanning period based on the time from the input signal from the document leading edge detection sensor until the leading edge of the image is developed, and calculating the sampling data. The method is not limited to this, but for example, the scanning section may be divided based on another suitable predetermined scanning time width, or the scanning speed of the optical system differs depending on the magnification in a copying machine having a variable magnification function. Control such as dividing the scanning section based on , etc. becomes effective. It is also possible to measure the potential on the photosensitive drum immediately after exposure and perform the above-mentioned calculations to control it.

According to the present invention, the reproducibility is good for original images with light characters, and copies of dark originals such as newspapers can be obtained without overlapping, eliminating the hassle of adjusting the conventional density adjustment lever, etc., and making mistakes in copying. This eliminates the wastage of transfer paper and realizes an efficient copying function.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the operation section of the copying machine, Fig. 2 is a conventional density adjustment circuit diagram, Fig. 3 is an explanatory diagram of the optical system, Fig. 4 is an example circuit diagram for realizing the present invention, and Figs. 7th
The figure is a flow chart of the present invention, FIG. 8 is a sequence timing chart, FIG. 9 is a relationship diagram between calculated values and developing bias, FIG. 10 is a relationship diagram between developing bias control voltage and developing bias, and FIG. 11 is a diagram showing the relationship between developing bias control voltage and developing bias. FIG. 12, which is an EV characteristic diagram of the drum, is a diagram showing the relationship between the bias control voltage and the document density sampling area, and numeral 1 in the diagram is a photo sensor.

Claims (1)

[Scope of Claims] 1. Scanning means for exposing and scanning a document; Image forming means for forming an image corresponding to the document image; Timing detection means for detecting a scanning timing signal of the scanning means; Several documents are scanned in the exposure scanning direction. In order to detect the document density in each divided area by sampling multiple times at a predetermined period within each divided area, a timing operation is started in synchronization with the scanning timing signal, and the odd-numbered a first timer means for setting a first scanning period corresponding from the beginning of a divided area to the end of the next divided area; from an even-numbered divided area in the middle of the first scanning period to the end of the next divided area; a second timer means for setting a corresponding second scanning period; a first sampling means for sampling the density detection output a plurality of times in the first scanning period; and a plurality of density detection outputs in the second scanning period. concentration detection means having a second sampling means for sampling twice; digital conversion means for converting each sample value of the concentration detection means into a digital value; and outputs of the digital conversion means of the first and second sampling means, respectively. an arithmetic means for calculating the average value of the document density of adjacent two divided areas; and the operations of the first and second sampling means are repeatedly executed in parallel, and one of the first or second scanning periods is control means for controlling the image forming conditions of the image forming means for each divided area corresponding to the set by sequentially using the calculation results of the calculation means corresponding to the document areas sampled in the first and second scanning periods; An image forming apparatus, characterized in that the calculation means and the control means each repeat calculation for obtaining an average value and control of image forming conditions.