JPH04238366A - Output density control system for image recorder - Google Patents

Abstract

PURPOSE:To obtain stable image density without becoming incapable of control because of the occurrence of toner crowding by controlling to such toner concentration that the output image density is not saturated. CONSTITUTION:The toner concentration in a developing device is detected by an optical toner concentration sensor 25 or a magnetic method, and a dispensing motor 18 is controlled based on the detected result, so that the toner concentration in the developing device is controlled to be a value that the output image density is not saturated. In such a state, the density of a patch part formed in a non-image part is detected by a density sensor 16 and the grid voltage of an electrostatic charger 11, exposure or the bias voltage of the developing device 14 are controlled so that the image density may be a target value, and the output density is controlled to be constant in the constant toner concentration.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an output density control method for an image recording apparatus such as a copying machine.

0002

2. Description of the Related Art FIG. 3 is a diagram for explaining a conventional image density control system used, for example, in a copying machine.

The sensitive material drum 10 is charged to a predetermined potential by a charger 11, and exposed through a mirror 13 by a laser light source 12 controlled by an image reading device (not shown) to form an electrostatic latent image. The electrostatic latent image is developed by the developer 14.
The toner is developed by a charger 15 including a transfer corotron and a detack corotron, and an image is transferred onto a sheet (not shown) and recorded. Image density control at this time is based on the reference potential area (patch) formed in the non-image area.
The image density is optically detected by the ADC sensor 16, and based on the detection result, the toner dispensing motor 18 is controlled through the drive circuit 17, and the supply of toner from the toner box 19 to the developing device 14 is controlled, so that the image density becomes constant. That's what I do.

0004

By the way, the relationship between toner concentration (TC) and output density has a characteristic as shown in FIG. 4 when, for example, the surrounding relative humidity is used as a parameter. In the figure, when the output density D0 is the target density,
The image density is detected by the ADC sensor 16, and if the humidity is 30% and the TC is controlled to be C0, and if the humidity changes from 30% to 70%, the output density will change from the operating point A. Moving to point B, the ADC sensor detects that the image density has become darker, and the toner dispense motor 18
The driving of the developing device 17 is stopped, and the supply of toner into the developing device 17 is stopped. Since copying is performed with toner supply stopped, TC decreases and the output density also decreases, and the operating point shifts from B to C as shown by the arrow, and the target density D0 is achieved. Next, at operating point C, the relative humidity is 70%.
When changing from 30% to 30%, the output concentration decreases and reaches the operating point C
At this time, the ADC sensor detects that the density is low, so the dispense motor 18 is driven to supply toner, and the toner density and output density change from operating point D to operating point A. When the image density D0 is detected by the ADC sensor 16, toner supply is stopped and the target density is achieved.

[0005] As described above, in concentration control when an environmental parameter such as humidity changes, there is a history phenomenon between TC and output concentration. With this method, it takes a certain amount of time to obtain the target density, and the output density is saturated at high toner density, so TC control becomes impossible depending on the density detection by the ADC sensor, and toner cloud There was also the problem that the system would become uncontrollable due to the occurrence of

The present invention is intended to solve the above-mentioned problems, and it is possible to avoid the inability to control the density due to excessively high toner density or the occurrence of toner clouds, and to perform stable and highly accurate output image density control. The purpose of the present invention is to provide an output density control method for an image recording apparatus that can be used in an image recording apparatus.

[0007]

[Means for Solving the Problems] The present invention provides an image recording apparatus that charges a sensitive material to a predetermined potential, forms an electrostatic latent image by image exposure, develops it with toner, and then transfers and records it onto paper. , a toner density control means that detects the toner density in the developing device and controls it to a value that does not saturate the image density, and a toner density control means that detects and detects the image density of a reference potential portion formed in a non-image area on the photosensitive material. Charger grid voltage, depending on the result
The image density control means controls at least one of the exposure amount and the developing bias voltage.

[0008]

[Operation] The present invention detects the toner concentration in the developing device using an optical or magnetic method, and controls the dispense motor according to the detection result, thereby adjusting the toner concentration in the developing device to the output image density. Control the value to avoid saturation. In this state, the density of the patch portion formed in the non-image area is optically detected by an ADC sensor, and the grid voltage of the charger, the exposure amount, or the bias voltage of the developer is controlled so that the image density becomes the target density. By doing so, the output density is controlled to be constant at a constant toner concentration. In this way, the toner density is controlled to a value that does not saturate the output image density, so there are no problems such as loss of control or toner cloud formation, and the image density is detected and kept constant. Since the grid voltage of the charger, the exposure amount, or the bias voltage of the developer is controlled, it is possible to obtain a stable output image density.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a diagram showing an embodiment of the output image density control system of the present invention, and FIG. 2 is a diagram illustrating the principle of the control system. In the figure, the same numbers as in FIG. 3 indicate the same contents. 2
0 is a control means, 21 is a high voltage power supply, 22 is an exposure amount drive circuit, 23 is a surface potential sensor, 25 is an optical toner concentration sensor (ATC sensor), and 26 is a trimmer.

In this embodiment, before the amount of toner on the surface of the mag roll is made uniform by the trimmer 26, A
The TC sensor 25 detects the toner concentration. For example, in a color two-component developer, the ATC sensor is 9
When using 00 nm infrared rays, the carrier is an absorbing material,
Toner particles act as a reflective material, and when an ATC sensor irradiates infrared rays and detects the reflected light, the reflectance is proportional to the toner concentration, so the toner concentration can be detected by detecting the amount of reflected light. In addition, a magnetic permeability type detector may be used to detect the toner concentration, and since the magnetic permeability changes depending on the concentration of magnetic toner particles, the toner concentration can be similarly detected.

The toner concentration detection signal is fed back to the drive circuit 17 of the dispense motor 18, and when the toner concentration decreases, the dispense motor 18 is driven and toner is supplied from the toner box 19 into the developing device 14.
The toner concentration within the developing device 14 is always controlled to be constant.

At the same time, the ADC sensor 16 detects the image density of the patch formed in the non-image area. For example, Figure 2
As shown in (a), the ADC sensor output and contrast potential (Vcont) (dark potential (VH) - exposure potential (VL)
)), a contrast potential V0 such that the ADC sensor output becomes the target value is determined in advance, the surface potential sensor 23 detects the potential of the sensitive material, the detected potential is read, and the control means 20 sets the high voltage. The grid potential of the charger 11 is changed by controlling the power source 21, and the contrast potential is controlled to become the target potential V0 as shown in FIG. 2(b).

Of course, the contrast potential may be changed not only by the charger's crid potential, but also by controlling the exposure amount drive circuit 22 to control the amount of light from the laser light source 12, or by controlling the amount of light from the laser light source 12 by controlling the control means 20. By controlling the bias power supply 27, the developing bias may be controlled to obtain a predetermined image density.

[0014] Through such control, TC is maintained at a constant value C0 as shown in Fig. 2(c).
If the relative humidity changes to 70% while the output density is controlled to D0 at 0%, the output density shifts to D1, and this image density is immediately detected by the ADC sensor.
By changing the charger grid bias, exposure amount, or development bias, the output density is controlled from D1 to D0, resulting in a constant image density.

[0015]

[Effects of the Invention] As described above, according to the present invention, since the toner density is controlled so that the output image density is not saturated,
There is no toner cloud, no loss of control, and the ADC sensor detects the actual image density.
It becomes possible to accurately and stably control the output image density to a constant value.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing one embodiment of an output image density control method of the present invention.

FIG. 2 is a diagram for explaining the principle of the control method of the present invention.

FIG. 3 is a diagram for explaining a conventional image density control method.

FIG. 4 is a diagram showing the relationship between toner density and output density.

[Explanation of symbols]

16 ADC sensor 12 Laser light source 20 Control means 21 High voltage power supply 22 Exposure amount drive circuit 23 Surface potential sensor 25 Optical toner density sensor 27 Developing bias power supply

Claims (1)

[Claims] Claim 1: In an image recording apparatus that charges a sensitive material to a predetermined potential, forms an electrostatic latent image by image exposure, develops it with toner, and then transfers and records it onto paper. A toner density control means detects and controls the image density to a value that does not saturate the image density, and a toner density control means detects the image density of a reference potential area formed in a non-image area on the photosensitive material and adjusts the charger grid according to the detection result. 1. An output density control method for an image recording apparatus, comprising an image density control means for controlling at least one of a voltage, an exposure amount, and a developing bias voltage.