JPH0135344B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a device for controlling the density of a printed image in a recording device applying electrostatic recording or electrophotographic technology.

In electrostatic recording and electrophotographic techniques, an electrical latent image is developed with a developer and visualized. A widely used developer is a mixture of toner and carrier, and comes in liquid and powder forms. Since the colored toner concentration (toner mixing ratio in the developer) of these developers decreases as printing is performed, the density is adjusted to within a certain range. The visualized toner image is fixed as it is, or is transferred to another recording paper and then fixed. In this type of recording apparatus, the image printing density of a recorded toner image may be increased or decreased depending on the intended use. The image printing density can be controlled by changing the toner density in the developer, but in order to thin the toner density, the only option is to rely on the natural reduction (reduction due to consumption) of the toner density, which has poor responsiveness. In addition, if the toner concentration is increased to make it darker, there may be problems such as the image being smudged, a thin toner film being formed on the photoreceptor, the device becoming dirty, and the life of the developer being shortened. Ta.

An object of the present invention is to provide a print density control device that can quickly control the density of a print image without increasing the toner density in the developer.

A feature of the present invention is that a toner concentration detection means in the developer is provided, and on condition that the toner concentration is within a predetermined range, the toner concentration and electrical latent image potential or electrical latent image contrast or Print density is controlled by changing at least one of the developing bias potentials.

The present invention can be applied to a liquid developer or a powder developer, to the case where a toner image is directly recorded and fixed on a recording medium, or to the case where it is fixed after being transferred to another recording paper. The following is an example of a recording apparatus in which a toner image obtained by developing an electrical latent image on a photoconductor is transferred to another recording sheet and then fixed using a dry powder developer consisting of the following.

FIG. 1 is a schematic diagram of a recording apparatus implementing the present invention. Reference numeral 1 denotes a photoconductive photosensitive drum for electrophotography.As the drum rotates, its surface is uniformly charged by a charger 2, and then a photoimage 3 is exposed to form a charge latent image. The developing device 4 is rotated so that a developer 4a, which is a mixture of a magnetic carrier and toner, is attracted by a magnetic roller 4b, adheres to a non-magnetic rotating sleeve 4c, and comes into continuous contact with the surface of the photosensitive drum 1. A portion of the developer 4a is stripped off from the sleeve 4c by the scraper 4b and acts on the toner concentration detection coil 5 when it rotates. Since the magnetic permeability of the developer 4a changes in inverse proportion to the toner concentration, the toner concentration is detected as a change in the inductance of the detection coil 5. The photosensitive drum 1, on which the toner has adhered to the latent image to form a toner image, comes into contact with the recording paper 6, and transfers the toner image onto the recording paper 6 under the application of a corona charge from the transfer device 7. Thereafter, the surface of the photosensitive drum 1 is cleaned with a cleaner 8 and reused. As the toner in the developer is consumed, new toner 4e is replenished from the toner box 4f.

FIG. 2 shows a toner mark image for detecting the density of a printed image recorded on the paper 6. As shown in FIG. A regular toner mark image 11 is recorded on a portion of the recording paper 6. A latent image of the toner mark image is optically created on the photosensitive drum 1 and transferred and fixed after development.
The image density of the toner mark image 11 is detected by the optical detector 9.

FIG. 3 shows an electrical circuit diagram of the toner concentration detection means. An oscillating voltage of, for example, 100 KHz is applied to a capacitor C coupled in series with the detection coil 5 (L), so that a voltage that changes depending on the inductance is generated from the terminal of the coil L as an LC resonant circuit. This voltage can be rectified, smoothed,
A detection voltage V ₁ is obtained by voltage division, and a detection difference voltage V _d is obtained by comparing it with a reference voltage V ₂ . usually,
The variable resistor V _R is adjusted so that V _d =0 at the set reference toner concentration.

FIG. 4 shows the relationship between the toner concentration of the developer 4a and the output voltage _V1 of the toner concentration detection means. It is desirable that the toner concentration be adjusted between T _nio and T _nax , and in particular, T _nax must be avoided to exceed, for example, 5%. In order to obtain a constant image, for example, the toner density T ₀ = 3±
It is desirable to adjust it to 0.5%.

FIG. 5 is a block diagram of a control means for controlling the image printing density within a range in which the toner density does not exceed a certain range (particularly an upper limit) in the recording apparatus shown in FIG. In the drawing, toner concentration detection voltage
The level comparison circuit 12 determines whether V ₁ is within a certain range (for example, whether it is below the voltage corresponding to T _nax in FIG. 4). 13
is a timer that disables the output from the comparison circuit 12 until the toner concentration detection means is in a normal operating state, and an output is obtained from the AND circuit 14 when the toner density detection means is in a normal operating state. . Reference numeral 15 denotes a timer for determining the timing of print image density detection, and outputs the output at the timing when the optical detector 9 outputs the output. The printed image density detection voltage output by the optical detector 9 is compared by an image density level comparison circuit (density setting circuit) 16, and the comparison circuit 16 outputs an output when the density is below the set density. The output of the comparison circuit 16 is input to the AND circuit 18 via the AND circuit 17 under the AND condition with the output of the timer 15.
Only when there is a signal from 4, that is, when the toner density is within a predetermined range, the output of the AND circuit 17 is passed through and output as the control signal _Vc .

Next, image printing density control using this control signal _Vc will be explained with reference to FIG. This example is a laser beam printer, and the basic configuration is the same as that shown in FIG. 1, so some detailed explanations will be omitted. A charger power supply 19 whose output voltage can be adjusted is connected to the charger 2 . The laser beam image 3 is scanned by a polygon mirror 21 and illuminates the photosensitive drum 1 through a lens 20 . The laser beam is modulated by a signal from a print signal source 24 by a modulator 22 in accordance with the print signal. Further, the light amount is controlled by a variable transmission filter 23 to a light amount suitable for printing. Further, the signal from the print signal source 24 is input to a dot counter 25, which counts the number of dots corresponding to the area of the printed characters. The rotating sleeve 4c of the developing device 4 is connected to a voltage-variable developing bias power source 28, and the toner 4e in the toner box 4f is introduced into the developer 4a by a rotary metering valve 4g driven by a motor 26. be done.

In such a configuration, each control element is controlled as follows by the image printing density control means shown in FIG.

The motor 26 is driven by the control signal V _c of the print density control means. The toner 4e is added and the toner density increases, and when the print image density reaches the set level, the toner 4e is stopped being added.
At this time, it is preferable to add the toner 4e in small amounts intermittently since there is a delay in density detection (delay from the time the toner is added until the detection result is output). The image printing density is set by the comparison circuit 16. In such image printing density control, when the toner density reaches a predetermined upper limit, the output of the comparator circuit 12 disappears, so the AND circuit 18 stops outputting the control voltage _Vc , and excessive toner density is prevented.

The drive of the toner replenishment motor 26 is controlled by the control voltage V _c of the image printing density control means, and the voltage of the charger power supply 19 is also controlled in conjunction with the image printing density setting (change) given to the level comparator 16. change. The change in toner density due to toner density control is slow as shown in FIG. 7A. Therefore, during the transition period, the density change of the printed image is slow as shown by the broken line in FIG. 7C. Therefore, the desired print density cannot be obtained during this period. To prevent this, the output voltage of the charger power source 19 is changed at the density change time _t1 to lower the charging potential of the photosensitive drum 1 as shown in FIG. 7B. In this way, the electrical latent image potential formed on the surface of the photosensitive drum 1 is reduced. If this is done, the density of the printed image will drop rapidly. Thereafter, the output voltage of the charger power supply 19 is gradually restored. This recovery speed is set to a value that allows the print density to be changed by toner density control, and is preferably controlled by a program measured in advance.
In this way, the supply of the toner 4e is substantially stopped and the toner density naturally decreases due to consumption, and when the latent image potential returns to the original level, the print density control based on the toner density is completed. Voltage recovery control is
It is also possible to use the output of the dot counter 25 to determine the amount of toner consumed. When the image printing density is to be increased, the setting level applied to the level comparator 16 and the voltage of the charger power supply 19 are simultaneously changed at _t2 . As a result, the potential of the electrical latent image formed on the photosensitive drum 1 rises rapidly, resulting in an increase in the density of the printed image. After that, if the voltage of the charger power supply 19 is lowered according to the toner replenishment capacity of the toner replenishment motor 26, a decrease in concentration due to the drop is detected, toner replenishment is performed, and the voltage returns to its original state. Image printing density control using toner density is completed.

In this way, the latent image potential control by the charger power supply 19 with quick response is also used during transient periods, so that the image printing density can be quickly controlled. Since the change in the latent image potential is temporary, there is little adverse effect on the characteristics of the photosensitive drum 1.

Instead of controlling the voltage of the charger power supply 19, the developing bias voltage is similarly controlled by changing the transmittance of the filter 23 or the output voltage of the bias power supply 28.

As described above, according to the present invention, the toner concentration in the developer is controlled by a combination of toner concentration control within a predetermined range and control for changing at least one of the potential or contrast of the electrical latent image or the development bias potential. It is possible to quickly control the image printing density without increasing the density excessively.

Note that the present invention is not limited to laser beam printers, but can be applied to any electrostatic recording device or electrophotographic device that uses a developer consisting of toner and carrier.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of an electrophotographic recording apparatus embodying the present invention, FIG. 2 is a plan view of recording paper on which toner mark images are recorded, FIG. 3 is an electric circuit diagram of toner density detection means, and FIG. 4 is its output characteristic curve diagram, No. 5
This figure is a block diagram of the image printing density control means, FIG. 6 is a schematic diagram of a laser beam printer, and FIGS. 7A to 7C are control characteristic curve diagrams thereof. 1... Photosensitive drum, 2... Charger, 3... Optical image, 4...
Developing device, 4a... Developer, 4e... Toner, 4g... Measuring valve, 5... Toner concentration detection coil, 9... Optical detector, 12... Toner density level comparison circuit, 16...
Image density level comparison circuit, 19...charger power supply.

Claims (1)

[Claims] 1 A device that develops an electrical latent image into a visible image with a developer consisting of toner and carrier, which includes a toner concentration detection means for detecting the toner concentration in the developer, and a visible image obtained by the development. In a control device provided with a print density control means for controlling the print density of
The print density control means includes a print density setting means, and the print density setting means sets the print density when the toner concentration in the developer is within a predetermined range with respect to the print setting density set by the print density setting means and in a steady state. means for replenishing toner so that the toner concentration corresponds to the toner concentration, and an electric latent image that is operated in conjunction with the print density setting means to compensate for a delay in controlling the toner concentration in the developer when changing the print setting density. A print density control device comprising compensation means for changing at least one of potential, electrical latent image contrast, and development bias potential.