JPH01204083A - Toner concentration control method - Google Patents

Abstract

PURPOSE:To keep developer concentration constant by forming an electrostatic latent image on a photosensitive body in a reference pattern and visualizing it with toner, and then using information obtained from the reference pattern and another piece of information obtained at the time of previous image formation together when measuring light reflection characteristics of the image and controlling the toner concentration according to the measurement result. CONSTITUTION:A transfer charger 2 is energized at specific timing for a rotating photosensitive drum 1 and corona discharge is caused to hold the surface of the drum 1 at a specific high potential. Then reflected light from an original which is not shown in a figure is made incident through an optical scanning system 3 to form the electrostatic latent image on the surface of the drum, and the image is visualized with toner. At this time, the output signal of an optical sensor 9 provided to the drum 1 is applied to a controller 100 and a detection level measuring instrument 110 provided to the controller 100 measures the voltage of an electric signal and supplies the result to a developing bias selecting device 120 to switch the output voltage of a developing bias power source 130 according to the output.

Description

Detailed Description of the Invention [Field of the Invention] The present invention is directed to forming an electrostatic latent image on a photoreceptor, for example in an electrophotographic copying machine, and visualizing the electrostatic latent image with toner to produce a visible image. The present invention relates to toner density control in a recording device that transfers images onto recording paper, and particularly relates to a toner density control method that forms a visible image of a reference pattern on a photoreceptor and measures the light reflection characteristics of the visible image to adjust toner density. .

[Prior Art] In an electrophotographic copying machine, an electrostatic latent image corresponding to an image to be recorded is formed on a photoreceptor, and toner is attracted to this electrostatic latent image, thereby forming a visible image. A developing unit that visualizes the electrostatic latent image contains a developer. in general,
The image agent is composed of two components: resin-coated iron powder and powdered toner. Then, due to the friction between the iron powder and the powder toner, the powder toner is charged to a polarity opposite to that of the photoreceptor, and is attracted to the electrostatic latent image. Therefore, since only the powder toner is attracted to the electrostatic latent image, when the developing operation is performed,
The ratio of iron powder to powdered toner, that is, the developer concentration (toner concentration) changes. Therefore, if the developer concentration decreases, replenish powder toner from the toner replenishment tank.
It is necessary to control the developer concentration to be constant.

As this type of control method, for example, the method described below is known.

That is, a reference density pattern is provided at the edge of the ljX document reading surface,
The pattern is read with a scanner along with the original, an electrostatic latent image corresponding to the read image is formed on a photoreceptor, and this electrostatic latent image is developed to form a visible image.

Then, the optical reflectance, that is, the density, of the visible image of the reference density pattern formed on the photoreceptor is read by a reflective optical sensor. Then, the toner replenishment control system is energized so that the read density approaches a predetermined target value. That is, when the density of the toner image of the reference density pattern formed on the photoreceptor is low, it is considered that the density of the developer has decreased, and therefore toner is replenished.

However, this type of control method has the following disadvantages. That is, variations in the charging potential of the photoreceptor and variations in the gap size between the photoreceptor and the developing device have a large effect on the developing ability of the developing device, resulting in variations in the image density of the reference density pattern. As a result, when the developing capacity is relatively large, the toner density is reduced too much by toner density control, resulting in poor image density and poor uniformity of solid images. Further, when the developing ability is relatively small, the toner density is increased too much by toner density control, and the background portion of the image becomes smudged.

In this type of control method, the control toner density is almost determined depending on the developing ability, resulting in large variations in the quality of recorded images among individual copying machines.

An object of the present invention is to control toner density so as to reduce variations in recorded image quality between apparatuses.

[Structure of the Invention] In order to achieve the above object, in the present invention, conditions other than the toner concentration in the process of forming a visible image of a reference pattern are changed from those of a visible image of a reference pattern formed during previous image formation. Set according to the information obtained by measuring the light reflection characteristics.

For example, the charging potential of the photoreceptor surface in the charging process and the bias potential in the developing process are set according to the measurement result of the visible image density of the reference density pattern. As a result, the developing ability of the device is adjusted in a direction that keeps the visible image density of the reference density pattern constant, so after the charging potential on the photoreceptor surface and the developing bias potential are set,
If the visible image density of the reference density pattern is measured again and the toner density is controlled based on the result, the toner density is controlled to a constant value and variations in characteristics between devices are eliminated.

Other objects and features of the present invention will become apparent from the following description of embodiments with reference to the drawings.

[Embodiment] Fig. 2 shows the configuration of the main machine parts of an electrophotographic copying machine of one type in which the present invention is implemented.The image forming operation will be briefly explained with reference to Fig. 2.

The photosensitive drum 1 rotates in the direction of the arrow in the figure. The charger 2 is energized at a predetermined timing, and corona discharge occurs between it and the photosensitive drum 1.

The surface of the photoreceptor drum 1 is charged to a predetermined high potential (for example, 800V) by the current. When reflected light from an original (not shown) enters the highly charged surface of the photoreceptor drum l via the optical scanning system 3, a potential distribution corresponding to the original image, that is, an electrostatic latent image, is transferred to the photoreceptor. It is formed on the surface of the drum 1. Eraser 5 is.

Erases electrostatic latent images in unnecessary image areas.

The electrostatic latent image on the photosensitive drum 1 is developed by a color developer 6 or a black developer 7 and made visible. That is, an amount of toner depending on the potential level of each part of the electrostatic latent image adheres to that part, and a toner image corresponding to the electrostatic latent image is formed on the surface of the photoreceptor drum 1.

On the other hand, a transfer sheet fed from a predetermined sheet feeding system is sent to the surface of the photosensitive drum 1 via the registration rollers 11, and is superimposed on the toner image. Then, the toner image is transferred onto the transfer paper side by the biasing force of the transfer charger 8. The transfer paper onto which the toner image has been transferred passes through the separation charger 12, separates from the photoreceptor drum 1, and is discharged after the toner image is fixed by a fixing system (not shown). Toner remaining on the photosensitive drum 1 is removed by a cleaning unit 10.

What is the standard density pattern that serves as the basis for toner density control?

It is placed at the end of a contact glass for placing a document (not shown), and is read together with the image of the document when the optical scanning system 3 scans. Therefore, the reflected light from the reference density pattern is also irradiated onto the photoreceptor drum 1, and a toner image with a density corresponding to that is formed on the photoreceptor drum 1. The density of this toner image, ie, the light reflectance, is read by a reflective optical sensor 9.

The result of reading the toner image of the reference density pattern is normally used to control a replenishment device that replenishes toner from a tank into the color developer 6 or black developer 7, thereby controlling the amount of toner used for development. concentration control is performed.

However, in this embodiment, the reading result of the toner image of the reference density pattern is also used to control the developing bias voltage of the developing units 6 and 7.

That is, as shown in FIG. 1, the electrical signal output by the optical sensor 9 is applied to the control device 100.

Detection level measuring device 110 provided in control device 100
measures the voltage Vout of the electrical signal output by the optical sensor 9. The measurement result of the detection level measuring device 110 is applied to the developing bias selection device 120. This device 12
0 switches the output voltage of the developing bias power supply 130 according to the measurement result of the voltage Vout.

Specifically, processing is performed as shown in FIG. However, in this embodiment, the processing shown in FIG. 5 is performed only immediately after the operator replenishes the developer into the tank of the developing device 6 or 7. This will be explained with reference to FIG. First of all,
A value IV called the inching value is measured. This value is 1
Find it as follows. That is, 1 obtained when the optical sensor 9 reads the toner image corresponding to the reference density pattern.
The voltage Vo when the optical sensor 9 reads the part where the electrostatic latent image has been erased by the eraser, with the voltage V out being Vsp.
Let ut be Vsg, and calculate from the following equation (1).

Iv=vsP/vsgX100 (1
) In the actual process shown in Fig. 5, the image forming process (
However, all parts other than the reference density pattern are erased with an eraser) to obtain the inching values obtained during each image formation, and further calculate the inching values obtained during the 11th to 18th image formation. The average value of the obtained inching values is set as the final inching value IV.

Then, a developing bias level is set according to the obtained inching value. That is, if IV is less than 7, level 1, I
If V is 7 or more and less than 11, level 2° IV is 11 or more and 15
If the IV is less than 15, it is level 3. If the IV is 15 or more and less than 21, it is level 4. If IV is 21 or more, the developing bias voltage is set to level 5.

Each level of the developing bias voltage is set as shown in FIG. That is, processing is performed such that the developing bias voltage is changed by 20 V for one difference in level. In this example, level 3 is the standard level.

Figure 3 shows the relationship between the image forming conditions, the amount of toner adhering on the photoreceptor, and the amount of toner adhering and the sensor output voltage Vout.The development potential VP is the difference between the surface potential of the photoreceptor drum and the developing bias voltage. It is. Gp is the gap between the surface of the photoreceptor drum and the developing sleeve, and in this example, it is 0.6, 0.8, and 1. The characteristics of [Orim] are shown below.

Referring to FIG. 3, it can be seen that when the development potential VP or gap GP changes, the density of the toner image formed with respect to the reference density pattern changes. Since the development potential Vp changes depending on the charging potential of the photoreceptor drum surface determined in the charging process, it will vary from device to device unless a special charging voltage automatic adjustment device is used.

Furthermore, as a matter of course, the gap GP also varies from device to device. Therefore, the detected visible image density (Vou
If the toner density is adjusted according to t), the controlled toner density will vary from device to device.

FIG. 4 shows the relationship between the inching value, the image density, and the degree of scumming (toner adhesion to areas that are not originally an image) when the controlled toner density is in a stable state. Regarding the rank of scumming, a larger number indicates a better condition, and a smaller number indicates a worse condition. Referring to FIG. 4, it can be seen that when the inching value is very small, background stains are good, but on the other hand, the image density becomes low.

Furthermore, it can be seen that when the inching value is quite large, the image density is good, but the background smudge becomes worse.

Therefore, in order to obtain good image quality, it is necessary to maintain the inching value at an appropriate value.

In this embodiment, as shown in FIG. 6, the developing bias voltage is adjusted based on the detected inching value.
The development potential Vp shown in FIG. 3 changes. Therefore, the conditions of the image forming process are changed so that the density of the toner image on the photoreceptor approaches a proper state. As a result, the inching value is also adjusted to an appropriate level, and variations in characteristics between devices regarding image quality are reduced.

Normally, the detection level measuring device 11O shown in FIG. 1 outputs a toner density adjustment signal at a predetermined period according to the toner image density of the reference density pattern detected by the optical sensor 9, and outputs a toner density adjustment signal to a toner replenishment solenoid (not shown). is energized to replenish toner. That is, the toner supply amount is adjusted and the developer concentration is automatically adjusted according to the toner image density of the reference density pattern. In this embodiment, since the developing ability is controlled to reduce the variation between devices,
The voltage Vout of the signal detected by the optical sensor 9 is constant, and therefore the toner concentration does not vary greatly between devices.

Next, another embodiment will be described with reference to FIG.

In this embodiment, the control device 200 is equipped with a charging bias selection device 220.

This selection device 220 selects the charging bias power source 24 according to the inching value detected by the detection level measuring device 21O.
Controls 0. In this example, the charger 2 is equipped with a charge wire 2a and a grid electrode 2b, a charging main power source 230 is connected to the charge wire 2a, and a charging bias power source 240 is connected to the grid electrode 2b. There is.

That is, by adjusting the voltage applied to the grid electrode 2b, the charging potential of the surface of the photoreceptor drum 1 that has undergone the charging process is adjusted. The setting state of the voltage applied to the grid electrode 2b by the charging bias power supply 240 is changed according to the inching value similar to the embodiment described above. By adjusting the charging potential of the photoreceptor drum 1, the development potential Vp shown in FIG. can be maintained.

In the above embodiment, the development bias voltage and the grid bias voltage of the charger were set at the current 8F.
Although this is done when the toner supply to the tank of /6-7 is completed, it may be done at any other time.

[Effects] As described above, according to the present invention, since the concentration of the developer is maintained constant, variations in image recording characteristics between devices are reduced.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of the main parts of an electric circuit of a device embodying the present invention. FIG. 2 is a front view showing the configuration of the main mechanical parts of a copying machine embodying the present invention. FIG. 3 is a graph showing the relationship between changes in image forming conditions, toner image density, and optical sensor output voltage. FIG. 4 is a graph showing the relationship between inching value and recorded image quality. FIG. 5 is a flowchart showing a general procedure for developing bias setting processing in the apparatus shown in FIG. FIG. 6 is a graph showing the relationship between the inching value and the developing bias adjustment amount of the apparatus shown in FIG. FIG. 7 is a block diagram showing the electrical circuit configuration of a device in another embodiment of the present invention. 1: Photosensitive drum 2: Charger 2a: Charge wire 2b = Grid electrode 3: Optical scanning system
5: Eraser 6: Color developer 7: Black developer 8: Transfer charger 9: Optical sensor 10: Cleaning unit 11 Ni registration roller 12: Separation charger 100.
200: Control device 110. 210: Detection level measuring device 120: Developing bias selection device 130: Developing bias power source 220: Charging bias selection device 230: Charging main power source 240: Charging bias power source Voice 1 Figure 12 Figure Voice 3 Image sense Voice 4 Inashi 5 Diagram Takashi 6 Diagram Inner/But vsp/■5GX100 Voice 7 Diagram

Claims (3)

[Claims] (1) Form an electrostatic latent image of a reference pattern on a photoconductor, visualize the electrostatic latent image with toner, measure the light reflection characteristics of the visualized image, and determine the toner concentration according to the measurement results. In the toner density control method for controlling: Conditions other than the toner density in the process of forming the visible image of the reference pattern are obtained by measuring the light reflection characteristics of the visible image of the reference pattern formed during previous image formation. 1. A toner density control method, characterized in that setting is performed according to received information. (2) Form an electrostatic latent image of a reference pattern on a photoreceptor, visualize the electrostatic latent image with toner, measure the light reflection characteristics of the visualized image, and determine the toner concentration according to the measurement results. In the toner concentration control method for controlling: When replenishing developer or replacing developer, the light reflection characteristics of the visible image of the reference pattern are measured, and the toner concentration in the image forming process is adjusted according to the measurement result. The present invention is characterized by setting conditions other than the above, and after completing the settings, forming a visible image of the reference pattern, measuring the light reflection characteristics of the visible image, and adjusting the toner density according to the measurement results. Toner concentration control method. (3) Form an electrostatic latent image of a reference pattern on a photoreceptor, visualize the electrostatic latent image with toner, measure the light reflection characteristics of the visualized image, and determine the toner concentration according to the measurement results. In the toner density control method, the light reflection characteristics of the visible image of the reference pattern are measured, and according to the measurement results, at least the charging characteristics of the charging process for charging the photoreceptor and the bias voltage of the developing process are adjusted. One of the parameters is set, and after the setting is completed, a visible image of the reference pattern is formed, the light reflection characteristics of the visible image are measured, and the toner density is adjusted according to the measurement result. Toner concentration control method.