JPS62242968A - Forming device for electrostatic latent image for detecting image density - Google Patents

Abstract

PURPOSE:To execute a stable process control by providing a temperature detecting means so as to contact or to be adjacent to a photosensitive body, and calculating the light quantity of a laser beam at the time of forming an electrostatic image for detecting an image density, in accordance with a detected temperature. CONSTITUTION:A timing control circuit 8 selects an image signal supplying circuit 9 and forms an electrostatic latent image on the surface of a photosensitive body 5. When the circuit 8 selects an image signal generating circuit 10, an electrostatic latent image for detecting an image density is formed on the surface of the photosensitive body 5, based on a signal from the circuit 10, developed and becomes a reference toner image 17. In this case, a laser beam quantity calculating circuit 13 calculates a laser beam quantity in accordance with a detected temperature from a temperature detecting circuit 12 and output is to the circuit 10. Accordingly, the surface potential of the electrostatic latent image for detecting the image density is kept constant irrespective of a temperature variation. The toner image 17 is irradiated by a light source 10, and a signal corresponding to the image density of the toner image 17 is supplied to a toner replenishment control circuit 23 by an image density detecting circuit 20. In this way, a stable process control can be executed.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a laser printer that performs exposure by scanning a laser beam, and is used to create a latent image for forming a reference toner image for image density detection on a photoreceptor. The present invention relates to an electrostatic latent image creation device for density detection.

2. Description of the Related Art Conventionally, it has been known in an electrophotographic copying machine to form a reference toner image on a photoreceptor and detect the image density to control the density of a recorded image. To form this reference toner image, a reference density piece is provided in advance on a part of the document table of the copying machine, and this reference density piece is exposed onto the surface of the photoconductor using an optical system for reading the original. This is done by forming a corresponding electrostatic latent image on the strip and then developing it into a toner image. Here, the standard density piece used is a peta black image and an optical reflection density of 1.2.
The gray ones shown below, and those with a combination of white parts and black parts, as seen in Utility Model Publication No. 60-4188, are known.

Recently, a laser printer has been developed that scans the surface of a photoreceptor with a flashing or modulated laser beam according to an image signal using a polygon mirror, forms an electrostatic latent image, and then develops and transfers the latent image. It is used. Image density control is also necessary in this laser printer, and it is conceivable to form a reference/reference toner image on the surface of a photoreceptor and detect its density, as in the above-described copying machine. In this case, to form an electrostatic latent image for image density detection, a reference density piece such as that used in copying machines is used, which is illuminated with a light source, and the reflected light is directed onto the photoreceptor using an optical device. The method of forming an image on the latent image requires a large amount of optical equipment such as a light source, lenses, and mirrors just for the purpose of forming the latent image, and is not practical. Therefore, in view of the fact that copying machines use an optical device for image formation as part of an electrostatic latent image creation device for detecting image density, laser printers also use a laser beam scanning device for image formation. It is conceivable to use this as part of an electrostatic latent image forming device for detecting image density.

Now, in order to use a laser beam scanning device to create an electrostatic latent image for image density detection, image signal generation is required to generate a predetermined signal so that an electrostatic latent image of the desired image is formed on the photoreceptor. The circuit may be connected to a laser emitting circuit to control the laser emitting circuit. By developing the electrostatic latent image created by this method, a reference toner image for image density detection is formed.

The reference toner images formed in this case include a low-density, non-patterned reference toner image created by adjusting the amount of laser light scanning the photoreceptor, and a white part formed by blinking the laser light. There are two reference toner images having patterns formed by combinations of black parts, and an example of the latter is JP-A-60-49363. Of these two reference toner images, when using a reference toner image with a pattern, a complex pattern signal must be generated by an image signal generation circuit in order to create a predetermined pattern image. In addition, the configuration of the image signal generation circuit becomes complicated, and the increase in cost cannot be ignored. Therefore, from an economic standpoint, it is considered preferable to use a patternless, plain, low density reference toner image.

Problems to be Solved by the Invention However, the light intensity of the laser beam is set to a predetermined value lower than the light intensity during recording, and this laser light creates an electrostatic latent image for image density detection to form a reference toner image. In some cases, it has been found that even if the electrophotographic process conditions to be controlled are constant, such as the toner concentration in the two-component developer, the optical density of the reference toner image after development is not constant. did.

The inventor investigated the cause of this problem and found that the density of the reference toner image changes due to changes in the temperature of the photoreceptor. The reason for this will be explained below.

Since semiconductor lasers used as light sources for laser printers have an oscillation wavelength in the near-infrared region, photoreceptors used in laser printers are subjected to infrared sensitization treatment. Because of this infrared sensitization treatment, the sensitivity changes significantly with respect to environmental temperature changes compared to conventional photoconductors for copying machines.

FIG. 5 is a graph showing the relationship between the amount of laser light scanning the photoreceptor and the surface potential of the photoreceptor after scanning with the laser light. As the amount of laser light increases, the surface potential decreases, but the degree of decrease varies depending on the temperature of the photoreceptor.
For the same amount of light, it is greater at low temperatures. As for the laser light during image recording, the laser is turned on when the light amount = P in Fig. 5.
state, and two values are used: this and the OFF state. For example, when black development is performed using the -reversal development method, the light amount = P is the black area, and the light amount is zero (that is, the laser beam is 0FF).
) corresponds to the white image area. The electrostatic latent image for image density detection is created by scanning a laser beam with an intensity Q lower than the amount of laser beam used during image recording. However, because the sensitivity curves differ between low and high temperatures,
The surface potential after exposure is vH at low temperature and Vl at high temperature.
, and is not constant.

This situation is illustrated in FIG. When the amount of laser light is P and when the amount of light is zero (no laser emission), there is little influence from changes in the photoreceptor temperature, and the surface potential is maintained at a roughly constant value. However, when the amount of light Q is less than P,
As shown in the figure, the surface potential is high at low temperatures and low at high temperatures, and the optical reflection density of the reference toner image obtained by reversal development is lighter at lower temperatures and darker at higher temperatures. The electrophotographic process conditions to be controlled, such as the toner concentration in a two-component developer, are not reflected correctly. If regular development is performed instead of reversal development, exposure for the reference toner image will be performed near the light amount = R in Figure 5, but in this case also, it is shown by the dotted line in Figure 6. The optical reflection density of the reference toner image after development becomes darker at lower temperatures and lighter at higher temperatures, which is just the opposite of that in the case of reversal development. This results in a problem that the electrophotographic process conditions, such as the toner concentration in the two-component developer, are not correctly reflected.

The present invention has been made in view of the above-mentioned problems, and it is possible to control the electrophotographic process conditions to be controlled, for example, in a two-component developer, without being affected by changes in the sensitivity of the photoreceptor due to changes in environmental temperature, etc. It is an object of the present invention to provide an electrostatic latent image forming device for detecting image density, which can form a reference toner image that appropriately reflects toner density.

Means for Solving the Problems In order to solve the above-mentioned problems, the present invention forms an electrostatic latent image for image density detection by scanning a laser beam whose light intensity is set to be lower than that required for image recording. In the apparatus, a temperature detecting means is provided in contact with or in close proximity to the photoreceptor, and the amount of the laser beam when creating an electrostatic latent image for image density detection is controlled according to the temperature detected by the temperature detecting means. It is equipped with the following.

According to the above-described structure, the present invention allows the value of the light amount of the laser beam when creating an electrostatic latent image for image density detection to be adjusted depending on the temperature of the photoconductor or its vicinity even if the sensitivity of the photoconductor changes due to changes in environmental temperature or the like. Because of this control, the surface potential of the electrostatic latent image for image density detection is kept constant regardless of the environmental temperature. Therefore, the optical reflection density of the reference toner image after development is:
By properly reflecting the electrophotographic process conditions to be controlled, for example, the toner concentration in the two-component developer, stable process control, for example, toner concentration control, becomes possible.

Embodiments Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

FIG. 1 shows a schematic configuration of an electrostatic latent image forming device for image density detection according to an embodiment of the present invention, in which 1 is a laser diode as a laser light source, 2 is a collimator lens,
3 is a polygon mirror for scanning a laser beam in the main scanning direction, 4 is an f/θ lens, 5 is a photoreceptor having a photosensitive layer on its surface, and 6 is a reflecting mirror. A laser emitting circuit 7 that blinks the laser diode 1 according to an input signal is connected to the laser diode 1, and an image signal supply circuit 9 and an image signal generation circuit 10 are connected to the laser emitting circuit via a timing control circuit 8. be done. The image signal supply circuit 9 supplies signals related to images to be recorded, and the image signal generation circuit 10 generates and supplies signals for creating an electrostatic latent image for image density detection. These circuits9.
The signal from 10 is selected by the timing control circuit 8 and supplied to the laser emission circuit 7, and an image based on the signal from the image signal supply circuit 9 is formed in the image area of the photoreceptor 5. The image signal generation circuit 1 is located at the position of
An electrostatic latent image for image density detection is formed based on the signal from zero. A temperature detector 11 is arranged near the photoreceptor 5, a temperature detection circuit 12 is connected to the temperature detector 11, and a signal corresponding to the detected temperature is given as an input to a laser light amount calculation circuit 13. The laser light amount calculation circuit 13 receives this signal, calculates the appropriate value of the laser light amount when creating the electrostatic latent image for image density detection, and outputs the value to the image signal generation circuit 10.

On the outer periphery of the photoreceptor 5, a charging device 15 for performing a normal electrophotographic process, a developing device 16, a recording paper supplying means (not shown), a transfer means (not shown), a fixing means (not shown), Photoreceptor surface cleaning means (not shown) and the like are arranged. Further, near the photoconductor 5, there is an LE that irradiates a reference toner image 17 for image density detection formed on the photoconductor 5.
A light receiving element 19 that receives reflected light from a light source 18 such as a D lamp and a reference toner image 17 is arranged, and an image density detection circuit 20 is connected to the light receiving element 19. On the other hand, the developing device 16 is provided with a toner replenishment device 21 and a toner replenishment motor 22 for driving the toner replenishment device 21, and the toner replenishment motor 22 is controlled by a toner replenishment control circuit 23 which inputs a signal from an image density detection circuit '20. It has become so.

Next, the operation of the apparatus having the above configuration will be explained.

When the timing control circuit 8 selects the image signal supply circuit 9, the laser emission circuit 7 drives the laser diode 1 to emit blinking laser light in accordance with the image signal from the image signal supply circuit 9. scans the surface of the photoreceptor by rotating the polygon mirror 3 to form an electrostatic latent image in accordance with an image signal. This electrostatic latent image is developed by a developing device 16, transferred to recording paper, and then fixed on the recording paper and discharged.

On the other hand, when the timing control circuit 8 selects the image signal generation circuit 10, an electrostatic latent image for image density detection is formed on the surface of the photoreceptor 5 based on the signal from the image signal generation circuit 10. The reference toner image 1 is developed by the developing device 16.
It becomes 7. The amount of laser light at this time is determined by the laser light amount calculation circuit 13, and is smaller than the amount of laser light used when recording is performed based on the image signal from the image signal supply circuit 9. Note that details will be described later.

The created reference toner image 17 changes as the photoreceptor rotates 50 times.
The light is irradiated by the light source 18, and the reflected light enters the light receiving element 19, and the light receiving element 19 and the image density detection circuit 20 send a signal corresponding to the image density of the reference toner image 17 to the toner replenishment control circuit 2.
Output to 3. The toner replenishment control circuit 23 determines whether toner should be replenished based on this signal, controls rotation and stop of the toner replenishment motor 22, and controls toner replenishment by the toner replenishment device 21. As a result, the toner concentration in the two-component developer in the developing device 16 is maintained within an appropriate range.

Next, the amount of laser light for creating a reference toner image calculated by the laser light amount calculation circuit 13 of this embodiment will be explained in detail.

FIG. 2, like FIG. 5, is a graph showing the relationship between the amount of laser light scanning the photoreceptor and the surface potential of the photoreceptor after laser scanning. Assume now that the appropriate surface potential of the electrostatic latent image for image density detection is v□. At this time, in order to maintain the surface potential of the photoreceptor at a substantially constant Vo, it is necessary to change the amount of laser light depending on the temperature change of the photoreceptor or its vicinity. In other words, when the temperature of the photoreceptor or its vicinity is high (1H), the laser light intensity is
When the temperature is low (11), it is necessary to set the amount of laser light to QH. FIG. 3 shows the relationship between the amount of laser light Q (t) and temperature for obtaining a constant surface potential ■o. The relationship shown in FIG.
3 is pre-entered. Laser light calculation circuit 13
calculates the amount of laser light Q (t) according to the temperature signal from the temperature detection circuit 12, and sends the value to the image signal generation circuit 1.
Output to 0. Therefore, the laser light scene when creating an electrostatic latent image for detecting image density is based on the calculated laser light amount Q(t).
The surface potential of the latent image formed on the surface of the photoreceptor is always maintained at Vo regardless of temperature changes.

FIG. 4 is a graph showing the relationship between photoreceptor temperature, surface potential, and amount of laser light. The amount of laser light when recording an image based on the signal from the image signal supply circuit 9 is the amount of light P (
(laser ON) and light intensity zero (laser 0FF).

On the other hand, the amount of laser light when creating an electrostatic latent image for image density detection is controlled to the amount of light Q (t) calculated by the laser light amount calculation circuit 13 as described above, and the surface potential is always vo
is maintained.

In this embodiment, an example of an optical system using a combination of a collimator lens, a polygon mirror, and an f.0 lens is shown as a means for scanning the laser beam, but it is obvious that a galvanometer mirror or other optical system may also be used. . Furthermore, the electrophotographic process conditions to be controlled are not limited to the toner concentration in the two-component developer, and may be other electrophotographic process conditions, such as the amount of charge by a charger, etc. A similar effect can be obtained.

Effects of the Invention As is clear from the above description, the present invention provides the following advantages when forming an electrostatic latent image for detecting image density by scanning a laser beam with an amount of light set to be less than that required for image formation. The light intensity of the laser beam is controlled based on the temperature detected by a temperature detection means placed in contact with or close to the photoreceptor, so that the temperature of the photoreceptor does not change due to changes in environmental temperature, etc. Even if the sensitivity characteristics change, the surface potential of the electrostatic latent image for image density detection can be kept constant, and the optical reflection density of the reference toner image created by developing this electrostatic latent image can be controlled. This appropriately reflects the electrophotographic process conditions, for example, the toner concentration in the two-component developer, and has the effect of enabling stable process control, for example, toner concentration control.

[Brief explanation of drawings]

FIG. 1 is a block diagram schematically showing a laser printer equipped with an electrostatic latent image forming device for detecting image density according to an embodiment of the present invention, and FIG. 2 shows the amount of laser light and after laser scanning in the above embodiment. Figure 3 shows the relationship between the surface potential of the photoreceptor and the temperature of the photoreceptor in the above embodiment using the amount of laser light as a parameter.
, Figure 4 shows the relationship between the amount of laser light necessary to obtain a constant surface potential and the temperature of the photoreceptor in the above example. Figure 5 shows the amount of laser light and the photoreceptor surface potential in a normal photoreceptor. Figure 6 shows one side of the relationship between the photoreceptor temperature and surface potential in a conventional example using the amount of laser light as a parameter. 1...Laser diode, 3...Polygon mirror,
5... Photoreceptor, 7... Laser emission circuit, 8...
Timing control circuit, 10... Image signal generation circuit, 1
1... Temperature detector, 12... Temperature detection circuit, 13.
...Laser light amount calculation circuit, 16...Developer, 17...
- Reference toner image, 18... Light source, 19... Light receiving element, 21... Toner replenishing device, 22... Toner replenishing motor. Name of agent: Patent attorney Satoshi Nakao and one other person 1 1! 7 - (7A) 4th
Review 5I! L trace - drop) hanging 59] L - power fall 1□

Claims (1)

[Claims] a latent image forming means that scans a laser beam on a photoreceptor to form an electrostatic latent image for density detection; a temperature detection means disposed in contact with or close to the photoreceptor; and a temperature detected by the temperature detection means. an electrostatic latent image creation device for image density detection, comprising a laser light amount calculation means for calculating the amount of laser light when creating the electrostatic latent image for image density detection.