JPS63142377A - Automatic density adjusting device - Google Patents

Abstract

PURPOSE:To obtain an image with proper density at all times by controlling image formation conditions according to the density of a document and varying parameters of this control with the output signal of a sensor. CONSTITUTION:A reference plate 1 with reference density, the sensor 2, and a control means 3 are provided. A photosensitive body 4 is exposed to an image of the reference plate 1 to form its latent image and the density of the latent image after development is detected by the sensors 2. The control means 3 controls the image formation conditions according to the density of the document and varies the parameters of this control with the output signal of the sensor 2. Consequently, an image with proper density is obtained without reference to the image formation conditions and the kind of the document.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to an automatic density adjustment device in an image forming apparatus such as a copying machine.

(Prior Art) Automatic Density in Image Forming Apparatus: Some gR leveling devices detect the document density and control the developing bias voltage based on the detection signal.

However, with this automatic density adjustment device, images with appropriate density can be obtained when the image forming conditions (electrophotographic process conditions) are constant, but if the image forming conditions change, images with appropriate density cannot be obtained. .

(Objective) It is an object of the present invention to provide an automatic density adjustment device that eliminates the above-mentioned drawbacks and can always obtain images with appropriate density.

(Structure) The present invention relates to an automatic density adjustment device for an image forming apparatus that performs image exposure on a photoreceptor to form a latent image, develops this latent image, and transfers it to a transfer material. It has a reference plate 1 having a concentration as follows, a sensor 2, and a control means 3. A latent image is formed on the photoreceptor 4 by image exposure of the reference plate 1, and the density of this latent image after development is detected by the sensor 2. The control means 3 controls the image forming conditions according to the density of the original, and changes the parameters of this control according to the output signal of the sensor 2.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 2 shows an example of a copying machine to which the present invention is applied.

This example uses a reference plate lO (third
(see figure) is provided to detect the density of the toner image corresponding to this base plate 10 and the document's degree to determine the image forming conditions.When the print key of the operation section 34 is pressed, the photoreceptor As the drum 11 is rotated by the main motor, the charging corona discharger 12 is turned on to uniformly charge the photosensitive drum 11.

Then, the exposure lamp 22 is turned on and illuminates the reference plate 10, and the reflected light is reflected from the mirrors 24 to 26. The latent image of the reference plate 10 is formed by irradiating the photosensitive drum 11 through the lens 27 and the mirror 28. This latent image is
4 to form a toner pattern.

The density of this toner pattern is determined by the lamp 30 and the light receiving element 3.
1 is detected by a toner pattern density detector. In front and behind it (the front and back relationship differs depending on the configuration of the machine) a lamp 229 and a reflector 23. A scanner 29 equipped with a mirror 24 moves from its home position and starts scanning the original 21 on the original table 20. Therefore, the photosensitive drum 11
The original image is exposed to light to form a latent image, which is developed by a developer 14 and transferred to a transfer paper 15 from a paper feeder by a transfer corona discharger 16. In this case, the toner pattern of the reference plate 10 is not transferred to the transfer paper 15, and the separation corona is emitted after the original image is transferred. , vessel 1
The toner is separated from the photoreceptor drum 11 by 7, and the toner is fixed by a fixing device (not shown). Also, the photosensitive drum 1
After the original image has been transferred, charge is removed from charge removal device 1 by corona discharger 18, and cleaning device 19 cleans the charge removal device 1, so that it can be reused.

Further, as shown in FIG. 3, a concentration sensor consisting of a light receiving element 35 and a flexible optical fiber 36 is provided, and the tip of the optical fiber 36 is fixed to a scanner 29. The original 21 on the original platen 20 is irradiated with light 33, and the reflected light is received by the light receiving element 35 via the optical fiber 36. Here, the illumination light 33 for document density detection is shifted in the forward movement direction of the scanner 29 from the illumination light 32 for exposing the reference plate and the document image, and when the scanner 29 is located at the home position, the illumination light 32 is deviated from the illumination light 32 for exposing the reference plate and the document image. When the illumination light 32 is irradiating a position P, which is further shifted from the original 21, the position P within the original 21 is irradiated, and when the illumination light 32 is irradiating the starting edge P of the original 21, the original 21 is also irradiated.
Irradiate the position within.

The distance between p, , p, has a larger value, +L, than the distance between P, , P, and when the scanner 29 starts scanning the original, the light receiving element 30 detects ( Before the illumination light 32 reaches the starting edge position fiP,1 of the original 21), the density of p, , p and the intermediate portion of the original 21 is detected. After the scanner 29 finishes scanning the original 21, it returns to its home position.

Further, in Fig. 3, 37.38 is an operational amplifier, 39 is a transistor, 40 is a variable resistor for adjusting the output voltage, 41.42 is a capacitor, 43 to 46 are resistors, 47 is a reset terminal, 4
8 is a diode, and these 32 to 48 constitute a peak hole circuit 49. A current flows through the light receiving element 35 in accordance with the amount of light received, and a peak hold circuit 49 detects and holds the peak of the current, thereby detecting the background density of the original and converting it into a voltage, which is then sent to the CPU (microcomputer) 50 (microcomputer) 50. output to the analog/digital conversion input section (see Figure 2).

Something that can be made constant under the image forming conditions when creating and developing a latent image on the reference plate 10 (corona discharge W for charging, device 1
2, the voltage of the lamp 22, the developing bias voltage applied from the CPU 50 to the developing sleeve of the developing device 14, etc.), if kept constant, will change over time and with the environment. Changes in the density of the toner pattern due to the reference plate 10 can be detected by the output VTD of the toner pattern density detector. So CPU5
0 is the reference value VT of the developing bias voltage Vn during copying, which is determined by the output VTD of the toner pattern density detector as shown in FIG.
It is determined from the D vs. VT characteristics, density fluctuations are corrected by variations in image forming conditions, and the developing bias voltage Vo is determined according to the output VOD of the peak hold circuit 49 based on the VoD vs. V vs. n characteristics shown in FIG. For example, original image density ○D=0.1
VT at 7! +: 2.8 to 3.4■ (1-ner concentration 2.5
~3.1%), V o = V T +60 = 29
0+60 = 350 (V).

FIG. 6 shows a part of the processing flow of the CPU 50.

cpuso is activated when the print key of the operation unit 34 is turned on.

A signal from the print key moves the scanner 29 from the home position to scan the original, and when the scanning distance of the scanner 29 reaches a certain distance, VT is fetched from the RAM. cpus here.

detects the output VTD for the toner pattern on the reference plate 10 of the toner pattern density detector including the lamp 3o and the light receiving element 31 once every 10 copying operations, converts it from analog to digital, and stores it in the RAM. Next, the CPU 50 uses the VTI (VTI) fetched from the RAM.
T is calculated according to the characteristics shown in FIG. 5, and the output VOD of the peak hold circuit 49 is inputted and subjected to analog/digital conversion, and Vn is calculated from this VoD and the calculated VT according to the characteristics shown in FIG. 4. Then, this Va is delivered to the developing sleeve of the developing device 14 to perform development.

In the above example, the image density is controlled by controlling the developing bias voltage, but this control is based on the amount of charge on the photoreceptor drum 11 by the charging corona discharger 12, and the amount of light n.

It is only necessary to perform this for at least one of the image forming conditions such as the developing bias voltage.

(Effects) As described above, according to the present invention, the image forming conditions are controlled based on the density of the original, and the parameters of this control are changed by the sensor output for the toner pattern on the reference plate, so that it is possible to control the image forming conditions depending on the image forming conditions and the type of the original. It is possible to obtain an image with an appropriate density.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing the configuration of the present invention, Fig. 2 is a sectional view showing an example of a copying machine to which the invention is applied, Fig. 3 is a schematic diagram showing a part of the copying machine, and Fig. 4 is a OD and V of the same copier
FIG. 5 is a characteristic diagram showing the relationship between OD and Vo, FIG. 5 is a characteristic diagram showing the relationship between VTD and VT of the copying machine, and FIG. 6 is a flowchart showing a part of the CPU processing flow of the copying machine. 1...Reference plate, 2...Sensor, 3...
- Control means, 4... photoreceptor. IP) 4 Country CV) IP) 6 Mouth

Claims (1)

[Claims] In an automatic density adjustment device in an image forming apparatus that performs imagewise exposure on a photoconductor to form a latent image, develops this latent image, and transfers it to a transfer material, the photoconductor is imagewise exposed to a latent image with a reference density. A reference plate for forming an image, a sensor for detecting the density of the image of the reference plate on the photoconductor after development, and controlling the image forming conditions according to the density of the original, and changing the parameters of this control according to the output signal of the sensor. An automatic concentration adjustment device characterized by comprising a control means for controlling the concentration.