JPH041342B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention involves exposing a reference target on a photoreceptor in advance, developing it, detecting the density of the toner image, and determining the copy density and white background density based on the obtained detection signal. The present invention relates to a control device for an electronic copying machine that comprehensively controls a toner supply device, developing bias voltage, charger, exposure system, etc. according to a preset mode so that the values fall within a range of values.

Conventionally, this type of copying machine has a device that automatically controls the amount of toner supplied, a device that controls the developing bias voltage, etc. in order to maintain the image quality of the resulting copy, especially the density of the copied image, at a constant level. has been adopted. These devices improve the stability of image quality by detecting changes in the amount of transmitted light, electrical resistance, magnetic resistance, etc. of the developer and automatically maintaining the toner content in the developer at a constant level. .
However, in these devices, the toner content is controlled to be constant even when the developer, exposure lamp, etc. deteriorate or when the humidity increases, so the image quality of the resulting copies deteriorates.

In particular, copying machines using magnetic brush developing devices have the drawback of being susceptible to these effects.

Therefore, in order to improve the shortcomings of the conventional control device, the present applicant has developed a copying machine that comprehensively controls the toner supply device, developing bias voltage, charger, exposure system, etc. The image density detected from the image is compared and judged with a preset reference value, and the amount of toner supplied to the developing device is controlled based on the judgment result, and the bias voltage applied to the developing electrode of the developing device or the charging device is controlled. An application has been filed for a control device for an electronic copying machine in which at least one of the charging currents is controlled by a predetermined control mode output from a central control circuit. According to this control device, copies with more stable image quality can always be obtained.

In the control device described above, the greater the number of reference targets, the better the degree of improvement in image quality, and the degree of improvement in image quality is not so good if there is only one reference target.

For example, if the toner density in the image area and the toner density in the background area are high, it is possible that solving the problem in the high density image area will also solve the problem in the high density background area at the same time. It cannot be said with certainty depending on the degree of

Furthermore, if the toner density in the image area is low and the toner density in the background area is high, trying to solve the problem in the low density image area will only make the problem in the high density background area worse, and conversely, the problem in the high density background area will worsen. If an attempt is made to solve the problem, the problem in the low-density image area will become even worse, and there is a limit to the improvement in image quality, and the degree of improvement in image quality is not very good.

However, if there are a plurality of reference targets, it becomes possible to at least independently detect the toner densities of the image area and the background area, which solves the above-mentioned problems and improves the degree of improvement in image quality.

However, when a plurality of reference targets having different densities are placed near the document table and a single detector is used to detect the density of each toner image of each reference target, it is necessary to set the reference targets in the direction of movement of the photoreceptor. They must be arranged in the same direction.

In such a case, the exposure scanning mechanism not only scans the document on the document table but also travels with respect to the reference target, which inevitably increases the scanning area.

Increasing the scanning area of the exposure scanning mechanism in this way is undesirable from a design perspective in terms of space and drive system, and conversely, due to design constraints, it is difficult to arrange multiple reference targets in the positional relationship described above. Sometimes it becomes difficult to do so.

In this case, it is sufficient to arrange the detectors in a direction perpendicular to the moving direction of the photoconductor, but in this case, the detectors for detecting the density of the toner image correspond to the number of reference targets. This has disadvantages in terms of cost and installation space as the number of devices increases.

The present invention has been made in view of the above circumstances, and its purpose is to constantly obtain copies with more stable image quality, and to improve the degree of image quality improvement by providing a plurality of reference targets. It is an object of the present invention to provide a control device for an electronic copying machine that can reduce the scanning range of the electronic copying machine and detect the density of a toner image with one detector.

An embodiment of the present invention will be described in detail below with reference to the drawings. FIG. 1 shows an electronic copying machine employing the control device of the present invention, in which a copying machine main body 1 is provided with a document table 2 on top of which a document (not shown) is placed.
As shown in FIG. 1, the lower side of the document table 2 is provided with a reference target 3 and an exposure lamp 4 that moves along the document table 2 and serves as an exposure scanning mechanism. can now be exposed. The reflected light from the original or the reference target 3 passes through the optical system 5 and reaches the photoreceptor 6 in the copying machine main body 1, and forms an electrostatic latent image on the circumferential surface of the photoreceptor 6, which is charged by the charger 25. The electrostatic latent image on the photoreceptor 6 is developed into a toner image by the next developing device 7. The developing device 7 has a developing electrode 8 to which a high voltage is applied along the circumferential surface of the photoreceptor 6, and the developer containing the toner supplied from the toner supply device 9 causes static on the photoreceptor 6. A detector 10 is provided above the developing device 7 to detect the density of the toner image of the reference target 3 formed on the photoreceptor 6.

The detector 10 includes, for example, a light emitting element 10a such as a diode and a light receiving element 10 such as a photodiode.
b is a reflection type sensor, which is provided at a position corresponding to the toner image of the reference target 3 formed outside the effective copying surface on the photoreceptor 6, and is used to determine the density and background of the toner image from this toner image. It is now possible to detect the concentration of

The reference target 3 is arranged as shown in FIGS. 2 and 3. That is, a guide 30 is provided on one end surface 2a of the document table 2 in the exposure scanning direction, and a movable body 31 is provided on this guide 30 so as to be movable in a direction perpendicular to the exposure scanning direction (photoreceptor movement direction). This movable body 31 has first and second reference targets 3 ₁ and 3 ₂ with different densities arranged side by side in the moving direction, and the movable body 31 has a spring 32 that allows the first reference target 3 ₁ to be fixed on the photoreceptor 6 . When the solenoid 33 is energized by being held at the first position that coincides with the concentration detectable position A, which is opposite to the position orthogonal to the moving direction corresponding to the detector 10, and being connected to the movable part 33a of the solenoid 33, the solenoid 33 is energized. The second reference target ₃₂ is arranged to move to a second position that coincides with the concentration detectable position A.

The detection signal of the detector 10 is amplified to an appropriate level signal by an amplifier circuit 15 as shown in FIG.
It is compared with the reference density signal inputted from 7, and the result is inputted to the central control circuit 18.

The central control circuit 18 selects a control mode according to the density determination result input from the comparison circuit 16, and sends control signals to various control circuits 20 via an output circuit 19. The control circuits 20 include a developing bias control circuit 20a, an exposure lamp control circuit 20b, a toner supply amount control circuit 20c, and a charging current control circuit 20d.

Then, the image density detected from the toner image of the reference target 3 is compared and judged with a preset reference density, and the developing bias voltage is adjusted according to the judgment result.
Since the light intensity of the exposure lamp 4, the amount of toner supplied to the developing device 7, the charging current of the charger 25, etc. are controlled,
Even when the developer, exposure lamp, etc. are deteriorated or humidity is high, the density of the copied image is maintained constant and copies with more stable image quality can be obtained at all times.

Furthermore, in the state shown in FIG. 2, the first reference target ₃₁ is at a position that matches the density detectable position A, so the density of the toner image of the first reference target ₃₁ formed on the photoreceptor 6 is is detected by the detector 10, and when the solenoid ₃₃ is excited from the state shown in FIG. A detector 10 detects the density of the toner image on the target ₃₂ .

Therefore, the detector 1 detects toner images of different densities.
Since it can be detected at 0, the degree of image quality improvement is improved.

Furthermore, since the first and second reference targets 3 ₁ and 3 ₂ reciprocate in a direction perpendicular to the direction of movement of the photoreceptor,
Since the scanning area of the exposure scanning mechanism (that is, the exposure lamp 4) is the same as when one reference target 3 is provided, the scanning area can be shortened.

Therefore, the scanning area of the exposure scanning mechanism becomes shorter, which is preferable in terms of space, drive system, etc., and even if the scanning area cannot be made longer due to design constraints, it is possible to provide a plurality of reference targets 3. I can do it.

Furthermore, since either the first or second reference target 3 ₁ or 3 ₂ is at a position that matches the density detectable position A, it is not possible to detect the toner density of either toner image with one detector 10. It is advantageous in terms of space and cost.

According to the control device of the present invention described in detail above, the following effects are achieved: Since control is performed using a reference target representing the image area and a reference target representing the background area, the degree of improvement in image quality can be improved. is good.

Although two or more reference targets are prepared in the exposure scanning area near the document table, the scanning area may be the same as that of a control device that has only a single reference target, so there is no need to enlarge the optical system.

Although it is controlled using two or more reference targets, it is economically advantageous because only one detector is required.

[Brief explanation of drawings]

The drawings show embodiments of the present invention, and FIG. 1 is a schematic diagram of a copying machine according to the first embodiment, FIG. 2 is a plan view of main parts, and FIG.
The figure is a front view, and FIG. 4 is a block diagram of the control system. 2 is a document table, 3 is a reference target, 6 is a photoreceptor, and 31 and 40 are movable bodies.

Claims (1)

[Scope of Claims] 1. At least two reference targets arranged near the document table and having densities representative of an image area and a background area, respectively; a single detector for detecting the density of a developed reference target toner image projected onto a portion of the photoreceptor; image quality improvement from the output of said detector; A control device for an electronic copying machine, comprising: a device for controlling control elements that contribute to a control element.