JPH0668599B2 - Image forming device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention 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 document density so that an appropriate image can be obtained.

2. Description of the Related Art In an image forming apparatus such as a conventional copying machine, in order to adjust the transfer image density to an appropriate amount, the volume 300 in the operation unit as shown in FIG. 1 is adjusted to change the variable resistance VR1 shown in FIG. It was common to obtain a proper image by changing the lighting voltage of the exposure lamp LA1.

Therefore, a configuration has been considered in which the document density is detected based on the amount of light reflected from the document and the image forming conditions are controlled.

However, in this configuration, when the exposure lamp is supplied with an alternating current of 50 Hz, for example, a ripple of 100 Hz is generated, and there is a drawback that the document density cannot be accurately detected depending on the timing of sampling the reflected light amount of the document.

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 capable of extremely accurately setting image forming conditions according to a document.

EXAMPLES Hereinafter, the present invention will be described in detail with reference to the drawings.

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

In FIG. 3, 101 is a main body, 102 is a document table cover, 103 is an operation unit and a document table, 104 is a document exposure lamp, 105a to 105d are reflection mirrors, 106 is a zoom lens for zooming, and 107 is heat exhaust. Fan, 108 is a photosensitive drum, 109 is a cleaner for removing toner remaining on the photosensitive drum 108, and 110 is a photosensitive drum 1.
08 is a charger that uniformly charges positive or negative, 111 is a blank exposure lamp for removing charges in a non-image area on the photosensitive drum 108, and 112 is a developing device for developing an electrostatic latent image on the photosensitive drum 108. Numeral 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 a transfer roller, 116 a conveying roller, 117 a toner on the transfer paper A fixing device for fixing an image, 118 is a copy tray, 119 is an image sensor for outputting a signal indicating the leading edge of a document, 120 is a registration roller, 121 is the intensity of light reflected from the document for detecting the density of the document. A light receiving sensor, 122 is a power switch, and 123 is a home position sensor. Since the copying process of this copying machine is not so different from the copying machine of the related art, its details are omitted.

FIG. 4 shows a circuit for detecting the document density. The photodetection current from the photodiode 1 corresponding to the light receiving sensor 121 is converted from current to voltage by the operational amplifier 2, 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 outputs PWM from the output port 1 in order to output the developing bias DC value of the developing device 112 calculated by the input level of AD1 and the inputs from the volumes 5 and 6.
The (pulse width modulated) pulse is output, the level of this pulse is converted through an integrator, and the resultant is used as a developing bias control signal input to the high voltage transformer 8. Here, the volume 5 determines the developing bias DC value to be applied with respect to a predetermined reference density determined for the original according to the sensitivity change of the photosensitive drum 108, in this embodiment the PC drum, and the volume 6 Is for determining the variable width of the developing bias DC value corresponding to the second reference density determined separately from the first reference density described above. 9 is a transformer, 2
The next side is full-wave rectified and the zero cross detection is performed by the operational amplifier 11. The zero-cross pulse is input to the interrupt terminal of the microcomputer 7, and AD1 is sampled as shown in FIG.
The waveform of AD1 is as shown in FIG.
The half-wave of the power supply frequency changes in synchronization with the lighting voltage waveform of the halogen lamp LA1 which is 4 as shown in the figure, so sampling at the zero cross point is effective for picking up accurate data. . The switches 14 and 15 select the light quantity of the halogen lamp (4 levels) and send a lighting voltage control signal to the lamp regulator LR1 by the D / A converter. A lamp lighting signal is output from the output port 2.

FIG. 7 shows a timing chart of the automatic proper density adjusting 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.
, And has a continuous variable magnification function that has an enlargement and reduction function for each 1% with respect to the original, and the relationship between the sensor output (AD1) and the magnification for the same density original is a linear expression as shown in FIG. Indicated by. Therefore, it is necessary to correct the sampled sensor output value (AD1) by a linear equation shown in FIG. Referring to FIG. 7, the AE function according to the present embodiment employs a sequential control system, 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 a 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 50 Hz according to the optical sensor output sampled at the zero-cross point after the document edge signal is input from the image sensor 119 while the document table is moving forward. To do. At 60 Hz, calculate with 10 points. In the middle of the first sampling segment, that is, as shown in FIG.
The next sampling segment is started in parallel from the 5th point in the case of 0 Hz and the 6th point in the case of 60 Hz, and the next bias DC value V2 is calculated at the 8th or 10th point. Hereinafter, the same control is repeated to calculate V3, V4 ....

The developing bias DC value Vn thus obtained is sequentially output from V1 at the bias switching timing, as shown in FIG. The bias switching timing is the distance 3 between the exposure position A on the photosensitive drum and the developing sleeve.
2mm divided by 100mm / S process speed 32
This is the timing when 0 mS has elapsed after the image destination signal was input.

As is clear from the above, the sequential control AE according to the present embodiment
With regard to (1), the latent image area to be developed with the developing bias value Vn is determined by referring to the original portion corresponding to the bias value and the original density of the area on the near side. This is because the AE control controls the developing bias in units of a specific time width (40 mS at 50 Hz, 41.5 mS at 60 Hz), so the developing bias value is Vn.
This is based on the result of consideration so as not to cause an extreme density change in the image at the boundary where the image is switched from to Vn + 1.

The control timing of the sequential AE control has been described above. Next, the method of calculating the developing bias DC value Vn will be described. The calculation of the bias DC value is carried out in the zero-cross interrupt processing shown in FIG. The developing bias specification of the high-voltage transformer 8 used in this embodiment is linearly controlled from -50 to -600 V with respect to the control signal 10 to 15 V 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 1 as shown in FIG. Level conversion. This is shown in FIG. In the present embodiment, the duty ratio of the pulse is divided into 43 parts 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. The duty corresponding to the developing bias value calculated by the bias calculation routine shown in FIG.
Proper image density control is realized by successively outputting pulses having a ratio from one output port.

Next, the contents of the bias calculation routine shown in FIG.
This will be described with reference to the figure. During the document advance, after passing through the image sensor, an average value is calculated for each output of sampling 8 times when the power supply frequency is 50 Hz and 10 times when it is 60 Hz, and the average value is the magnification shown in FIG. 9 as described above. The data at the same size is corrected by a linear expression showing the relationship. That is, the magnification x
Assuming that the average value Vn is%, the data Vn when the magnification is 100% is Becomes This is the magnification correction process in FIG.

The light amount correction process is performed next. The photosensitive drum (PC drum) embodying the present invention has a tendency that the Light potential increases and the contrast decreases as the number of copies increases, as shown in FIG. In order to correct this, the switches 14 and 15 as shown in FIG.
Is used to select the light amount of the halogen lamp which is the original exposure lamp. That is, as the Light potential of the photosensitive drum rises as the number of copies progresses, the lighting voltage of the halogen lamp is raised to mitigate the decrease in contrast. This lighting voltage can be selected from four types of voltages by combining the switches 14 and 15 shown in FIG. 4, and the microcomputer 7 transmits 8-bit information to the D / A converter 16 based on this data. Then, the D / A converter converts this information into an analog value and outputs it, thereby giving the halogen lamp lighting voltage control signal to the lamp regulator LR1. Therefore, the standard lighting voltage is E ₀ , the other three kinds of lighting voltages are E ₁ ,
If E ₂ and E ₃ (representatively E ₁ ), the calculated value Vn obtained by the magnification correction processing is Vn ′ and Vn after the light amount correction.
n'is Is obtained as.

By this light amount correction process, the document density shown in FIG. 13 is determined, and the final process of the flow of FIG. 12, that is, the calculation of the developing bias DC value for the light amount correction value Vn ′ is executed. The situation is shown in FIG. Referring to FIG. 14, the developing bias DC value is linearly controlled with respect to the density from the reflected light amount Q = 0.76 of the standard density original document to the dark original document Q = 0.5 corresponding to the newspaper. As a result, the characters are clearly reproduced on the thin original without covering the dark original. However, by setting an upper limit for the bias value for documents that are darker than newspapers and setting a lower limit for documents that are brighter than standard-density documents, excessive control of over-blowing and overfogging of the background can be prevented. ing. In addition, the photosensitive drum (PC drum) 1 used in this embodiment
As shown in FIG. 15, since the latent image potential with respect to the exposure amount tends to rise from the curve 1 to the curve 2 as shown in FIG. 15, control of the developing bias for the standard original is shown in FIG. The value (lower limit value described above) also needs to be variable, and this is realized by the volume 5 shown in FIG. Further, since the change over time of the photosensitive drum shown in FIG. 15 is changed so as to reduce the contrast between the Light potential (V _L ) and the Dark potential (V _D ), as shown in FIG. It is also necessary to change the variable width of the developing bias control between the originals with the lapse of time. In this embodiment, the variable width is changed from min90V to max18 by the volume 6 shown in FIG.
It is controlled to 0V.

According to the present embodiment, the optimum image reproduction corresponding to the density of the original can be performed, and since the sequential control is performed within the same original, it is possible to perform the image control following the density change within the same original. Therefore, the waste of transfer paper due to miscopy is eliminated and an efficient copying function is realized.

In the present embodiment, the optical system moving type copying machine has been described as an example, but the present invention is also applicable to a document table moving type copying machine.
It can also be applied to an apparatus for copying while flowing a document.

Effect As described above, according to the present invention, the document density can be accurately and accurately detected by sampling the output of the document density detection means in synchronization with the detection of the zero level of the AC voltage supplied to the exposure means. As a result, it is possible to set the image forming conditions with good accuracy, and it is possible to obtain an image with an appropriate density.

[Brief description of drawings]

FIG. 1 is a diagram showing a scanning unit of a copying machine, FIG. 2 is a conventional density adjusting 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. Circuit diagram, fifth
FIG. 6 is a flowchart showing an interrupt routine, FIG. 6 is a diagram showing waveforms of respective parts of the present invention, FIG. 7 is a timing chart of the present invention, and FIG. 8 is a correspondence relationship between AE sensor output sampling section and developing bias output DC value. FIG. 9 is a diagram showing the relationship between the copy magnification and the output of the AE sensor, FIG. 10 is a diagram showing the specifications of the developing bias DC value of the high voltage transformer, and FIG. 11 is a relationship between the developing bias control pulse and the developing bias control signal. FIG. 12, FIG. 12 is a flowchart for calculating a bias value in AE control, FIG. 13 is a diagram showing the relationship between the reflected light amount Q of the document and the output of the AE sensor, and FIG. 14 is a relationship between the reflected light amount Q of the document and the developing bias DC value. FIGS. 15A and 15B are diagrams showing sensitivity changes due to changes with time 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 (1)

[Claims] 1. An image forming means for forming an image of an original on a recording medium, including an exposing means for exposing the original, a detecting means for detecting the original density by detecting reflected light from the original, and a power source. Supply means for supplying an alternating voltage from the supply means to the exposure means, an output means for detecting a zero level of the alternating voltage supplied from the supply means and outputting a detection pulse, and a detection pulse from the output means Control means for repeatedly sampling the output of the detecting means in synchronism with the above, and controlling the operating conditions of the image forming means in accordance with a plurality of sampled values so as to make the density of the image formed on the recording medium appropriate. An image forming apparatus comprising: