JPH04269778A - Toner concentration controlling method - Google Patents

Abstract

PURPOSE:To prevent faulty toner concentration immediately after developing device is activated, that is when printing is started, and carrying out stable toner concentration control in a developing device such as an electrophotographic printer, etc., utilizing two component developer consisting of non-magnetic toner and magnetic carrier. CONSTITUTION:The developing device for the two component developer is provided with a concentration sensor to carry out the toner concentration control and a temperature sensor to detect developer temperature and carries out replenishing of the toner according to the output level of the concentration sensor against a specified threshold value. In this device, the initial threshold value against the output level of the temperature sensor according to the developer temperature from the temperature sensor is set to be a different value at the starting of activation of the developing device according to the developer temperature from the temperature sensor, and the threshold value is gradually varied from a differing initial threshold value to the specified threshold value according to the temperature sensor output at a different timing.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a toner density control method for controlling toner density at a constant level in a developing device such as an electrophotographic printer using a two-component developer consisting of a non-magnetic toner and a magnetic carrier.

[0002] In recent years, the print quality of copying machines and printers has improved,
There are demands for barcode compatibility (face-to-face image printing) and higher speed. Therefore, stable control of toner concentration is required to always perform the best development.

0003

2. Description of the Related Art A conventional developing device for determining toner concentration is equipped with a magnetic permeability sensor that periodically detects the mixing ratio of toner and carrier to determine the concentration. A predetermined slice level is set in advance for the value of the sensor output. In the magnetic permeability sensor, there is a relationship between the toner concentration and the sensor output as shown in FIG. 3. As the toner concentration becomes lighter, the sensor output increases, and conversely, as the toner concentration increases, the sensor output decreases.

Toner concentration control uses the above relationship to compare the slice level and sensor output, and if the sensor output becomes higher than the slice level value, toner is replenished, the sensor output is lowered, and the slice level is used as a reference. Toner density is always controlled to be constant.

[0005] The slice level is set at a state where air is mixed in the developer by stirring the developer to some extent after the developer is started, and the density of the developer is stabilized. After this, the magnetic permeability sensor operates stably. However, when the developing device is started up, the air mixed by stirring is removed from the developer, which increases the density of the developer.

[0006] Therefore, the density of magnetic carriers detected by the magnetic permeability sensor also increases, and even if the concentration is the same (same mixing ratio), the sensor output of the magnetic permeability sensor becomes high, causing overshoot. After the developer is sufficiently agitated and mixed with air, the original sensor output is obtained.

In order to correct this overshoot of the sensor output, first, a temporary slice level is determined from when the developer is started until the sensor output becomes the original output, and the value of that slice level is set as the true slice level. A method has already been proposed in which the temperature is gradually lowered to .

FIG. 4 shows an example of the above-mentioned overshoot correction. This method is a method of lowering the correction slice level in stages. Note that the sensor output A indicates a value output by the magnetic permeability sensor when the toner concentration is always constant.

First, the value after Δt1 seconds is set as the initial threshold value Vs (V) of the sensor output, and the value obtained by subtracting ΔV1 (V) from the initial value is set as the slice level at the time of overshoot. After that, after Δt2 seconds, ΔV2(V
) is the next slice level.

[0010] This slice level is compared with a predetermined slice level Vc (V), and the predetermined slice level Vc (
The slice level is successively lowered until it reaches V). ΔV
If the value subtracted by n(V) becomes a value lower than the true slice level, the predetermined slice level Vc(V) becomes the next slice level.

[0011]

However, the overshoot that appears on the magnetic permeability sensor changes depending on the developer temperature, and may cause deterioration of print quality, and this change cannot be ignored. The overshoot that appears in the magnetic permeability sensor is caused by a combination of errors that occur in the magnetic permeability sensor due to changes in fluidity caused by changes in developer temperature, and errors that occur in the magnetic permeability sensor itself due to temperature changes. .

[0012] However, the overshoot of the sensor output of the sensor that occurs at the time of start-up for toner concentration control is corrected in a uniform manner even when the temperature of the developer changes. Therefore, as shown in a, b, c, and d of FIG. 5, when the developer temperature differs, the overshoot amount B of the sensor output and
The slope C when the sensor output changes from overshoot to normal changes.

For example, the slope C when the sensor output changes from overshoot to normal is the slope C' of the sensor output curve c.
If the temperature of the developer is such that the sensor output curve c is outputted when the correction A is fixed, the overshoot can be stably corrected by using the correction A.

However, if the same correction A is used when the developer temperature is such that the sensor output curve d is output, the correction A
Since the toner density is corrected as shown by 'd', the toner density is controlled to create a curve like the broken line shown by d'.

That is, in order to increase the sensor output as shown by the upward arrow in the figure, the toner is consumed to reduce the toner density. This causes printing problems such as blurred printing. On the other hand, when correction A is used for sensor output curves a and b, the toner density becomes too high.

An object of the present invention is to prevent toner density defects immediately after starting the developing device, that is, immediately after printing starts, and to perform stable toner density control.

[0017]

[Means for Solving the Problems] In order to solve the above problems, the present invention has a density sensor for controlling toner density and a temperature sensor for detecting developer temperature. In a developing device for two-component developer that replenishes toner according to the output level of the developing device, the initial threshold value for the output level of the temperature sensor is set to a different value depending on the developer temperature from the temperature sensor when the developing device starts operating. Set,
The threshold value is also configured to be changed stepwise from a different initial threshold value to a predetermined threshold value at different times depending on the temperature sensor output.

[0018]

[Function] By varying the initial threshold value, threshold change amount and/or change time depending on the temperature, the threshold value can be set according to the initial fluidity and density of the developer, so that good concentration can always be achieved. can be developed.

[0019]

[Embodiment] Fig. 1 shows an embodiment of the present invention, which is a method of lowering the slice level during correction step by step.
, A2°C, and A3°C. (A1>
A2>A3) This is a case where the slope of the sensor output curve at the time of overshoot becomes steeper as the developer temperature becomes higher.

ΔV1ΔV2ΔV3..., Δt1Δt2 for the sensor output at each developer temperature
Change Δt3... In other words, from A1℃ to A2℃,
By increasing the values of ΔV and Δt as the developer temperature decreases, such as from A2° C. to A3° C., stable toner concentration control can be performed.

FIG. 2 shows a toner density control device that performs such control. 1 is a magnetic sensor whose output changes depending on the amount of carrier in the developer, 2 is a temperature sensor that detects the temperature of the developer, 3 is a threshold generator that sends out the slice level, and 4 is a magnetic sensor. A replenishment control device that drives a toner replenishment motor by comparing a sensor 1 and a threshold value generator 3;
is a timer that counts a predetermined time; 6 is a threshold memory that stores initial threshold levels and threshold change information that change depending on temperature information; 7 is a timer memory that stores time information that changes depending on temperature information; sets a predetermined time determined by the value of the temperature sensor 2 from the timer memory 7 to the timer 5, and transmits the threshold value information determined by the value of the temperature sensor 2 from the threshold value memory to the threshold value generator 3 at the timing obtained from the timer 5. This is a threshold value control device that sets the value to .

When the developing unit is started, the threshold control device 8 takes in temperature information A3° C. from the temperature sensor 2 and sends the address of timing data Δt1 corresponding to the sensor output curve 1c shown in FIG. 1 to the timer memory 7. Then, Δt1 is set in the timer 5, and the address of the slice level data Vs, which is the initial threshold, is sent to the threshold memory 6, and Vs is set in the threshold setting device 3.

The threshold value setting device 3 in which the slice level data Vs has been set sends the slice level of Vs (V) to the supply control device 4. Further, the timer 5 set to Δt1 starts counting, and sends a timing signal to the threshold value control device 8 when the timer elapses.

Then, the threshold control device 8 stores the addresses Δt2Δt3... in the timer memory and the addresses ΔV1 in the threshold memory.
Addresses of ΔV2... are sequentially sent out. The temperature information used when sending an address in this way may be input from the temperature sensor 2 each time, or the temperature information input first may be retained and the same data may be used.

In this way, the threshold value setting device 3 sends out a slice level that takes temperature into account. Then, when ΔVn is subtracted from the slice level value and the slice level becomes lower than the original slice level Vc, Vc (V) is maintained as it is and the overshoot correction ends.

Even during such processing, the magnetic permeability sensor 1 and the replenishment control device 4 operate in the same manner as in the prior art, and an appropriate toner concentration can be obtained.

In addition, in the above embodiment, the slope of the sensor output curve becomes steeper as the developer temperature increases, but the fluidity may vary depending on the installation position of the magnetic permeability sensor, the particle size of the developer, etc. Contrary to the embodiment shown in FIG. 1, the slope of the sensor output curve may become gentler as the developer temperature becomes higher.

In this case, contrary to the first embodiment, the values of ΔV and Δt may be made smaller as the developer temperature becomes lower. Also, these ΔV and Δt have been determined to be 1 by experiment etc.
It can be easily calculated by obtaining sensor output curves such as those shown in a, 1b, and 1c.

[0029]

As explained above, according to the present invention, when the temperature of the developer differs when the developer is started, it is possible to prevent the toner concentration from running out of control due to the overshoot of the sensor output being unable to be corrected, and to reduce the toner concentration. Printing problems caused by runaway can be prevented.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an embodiment of the present invention.

FIG. 2 is a diagram showing a toner density control device to which an embodiment of the present invention is applied.

FIG. 3 is a diagram illustrating characteristics of a toner concentration sensor.

FIG. 4 is a diagram illustrating conventional overshoot correction.

FIG. 5 is a diagram explaining a conventional problem.

Claims (1)

[Claims] 1. Two-component development comprising a density sensor for controlling toner density and a temperature sensor for detecting developer temperature, and replenishing toner according to the output level of the density sensor relative to a predetermined threshold value. In a developing device for a developer, an initial threshold value for the output level of the temperature sensor is set to a different value depending on the developer temperature from the temperature sensor when the developer starts operating, and the threshold value is set as the temperature sensor output. A toner density control method characterized in that the different initial threshold values are changed stepwise from the different initial threshold values to a predetermined threshold value at different times.