JPS6345109B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to scaling processing of image information in an image forming apparatus, and particularly to an image forming apparatus that obtains a clear image in enlargement mode.

Conventional copying machines have often made reduced copies. On the other hand, when it comes to enlarging, it would be extremely useful if a drawing in a newspaper could be enlarged to transparency film to make it easier to see the projected image on an overhead projector, or if a B5 size manuscript could be enlarged to A4 size and formatted. Although it is convenient and there is a strong demand for it, very few devices have been realized. The reason for this is as follows. In general, copying machines are designed to achieve maximum performance for normal-sized copies in order to reduce costs, and lenses are no exception, using their full resolution. For this reason, simply enlarging the image will directly affect the blur due to insufficient resolution.
The enlargement actually worsens the image. Of course, this can be solved by increasing the resolving power of the lens, but since the angle of view is particularly large for lenses used in copying machines, lens design is not easy, and the number of lenses required to correct aberrations increases, resulting in a significant increase in cost. This is not desirable.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to obtain a good enlarged image at a low cost using a lens that has been used in a conventional conventional image forming apparatus.

In summary, the present invention applies an appropriate developing bias to an enlarged and blurred latent image.
A clear enlarged image is obtained by increasing the contrast of the image, that is, by making the shading boundaries stand out. Thus, the present invention provides a developing device including a developer holding member disposed opposite to a latent image holding member on which either a same-size latent image or an enlarged latent image of image information is formed. It is characterized by having means for applying a developing bias that changes periodically to the holding member, and means for increasing the frequency of the developing bias in the enlarged mode for developing the enlarged latent image than in the same-size mode for developing the same-size latent image. The present invention provides a developing device.

The present invention will be explained below with reference to the drawings.

Figure 1a shows the original density. An enlarged latent image obtained from this original using a lens designed as a full-size copying device is shown in FIG. 1c.
However, in order to clarify the so-called blur, the horizontal direction (spatial axis)
The size of is normalized by the original image length. FIG. 1a can also be seen as a latent image during full-size copying. In this case, the contribution of the developed density due to the edge effect at the edge of the image can be illustrated as shown in FIG. 1b. From this viewpoint, the developed density can be expressed as a composite of FIG. 1a and FIG. 1b. By multiplying FIG. 1b by an appropriate coefficient during synthesis, it is possible to evaluate that the edge effect differs depending on the development method.

Even if the latent image shown in FIG. 1c is converted into a developed density as it is, an image in which the periphery of the black part of the image is blurred will naturally be obtained. The contribution of the edge effect to the latent image in FIG. 1c is shown in FIGS. 1d-f. These d~f
Accordingly, the image density is shown as shown in FIG. 1 g to i. Of these, visually the one shown in Figure 1g is the best.

Now, when making a full-size copy, you can obtain an image with extremely excellent gradation without any edge effect, and when making an enlarged copy, despite using a lens designed for a full-size copying device, No device has been realized that can obtain visually sufficient image quality by emphasizing some edges. However, according to the present invention, the above-mentioned problem can be solved by simply switching the bias potential applied to the developing electrode. Therefore, it greatly contributes to downsizing and lowering the cost of the device.

The applicant proposed patent application No. 53-92105, etc.
A developing method with very little fog in non-image areas and with good gradation has been clarified. According to this, by applying an appropriate periodic alternating developing bias voltage, an image with extremely excellent gradation can be obtained. Of course, if such development is used, a good image cannot be obtained because the development is too faithful to the latent image shown in FIG. 1c. This indicates that the development method is disadvantageous for small-sized enlargement reproduction devices. However, according to experiments conducted by the present inventors, the bias used in the development method was
By increasing the AC frequency and slightly shifting the DC component of the bias, it is possible to continuously increase only the edge effect without changing the developed density or background fog, and furthermore, as shown in Figure 1. It is possible to obtain image densities as shown in FIG. 1g to i even for a latent image such as that shown in FIG. It has also been found that by changing the DC component of the bias, it is possible to obtain the developed density only in the portion above the dashed-dotted line in FIGS. 1g to 1i. Therefore, even for a blurred latent image as shown in FIG. 1c, the image quality improvement effect shown above the dashed line in FIG. 1g can be achieved. As described above, by using the present invention, it is possible to obtain a visually good image without an extreme change in the image line width even if the image is blurred.

2 to 5 illustrate embodiments of the invention. FIG. 2 shows its overall arrangement, and in the figure, 1 is a latent image holding member (in the illustrated embodiment, a photosensitive drum), and 2 is a developer holding means ( In the illustrated embodiment, a developer sleeve) is shown. On the latent image holding member, that is, the photosensitive drum 1, a latent image in a magnified form of part or all of the image information is held. Toner 5 is regulated by a doctor blade 3 and placed in the developer holding means, that is, the developing sleeve 2 so as not to come into contact with the photosensitive drum 1 . The photosensitive drum 1 and the sleeve 2 rotate in the direction of the arrow at the same circumferential speed, and the toner on the sleeve is triboelectrically charged by contacting the doctor blade 3 or the sleeve 2 and holds a predetermined electric charge. Flying development is performed according to the electric field formed by the image (not shown) and the sleeve 2.
Reference numeral 4 designates a hopper wall, and reference numeral 6 designates a magnet that is fixedly installed within the sleeve 2 and holds the toner 5 therein.
For this reason, a one-component magnetic toner is used as the toner 5.

According to the present invention, the means 10 for generating the variable magnification of the latent image or a physical quantity corresponding to the variable magnification, and the bias potential corresponding to the variable magnification or the physical quantity generated by the variable magnification generating means are determined or selected. means 9, bias potential generation means 8, and connection means 7 for applying a bias potential to the developer holding means, that is, the developer sleeve 2.
The connecting means 7 is formed by a sliding brush or the like, and the bias potential determining means 9 applies the bias from the bias potential generating means 8 to the sleeve 2 by controlling the bias on and off. The means 10 for generating a physical quantity proportional to the magnification may be a keyboard with electrical contacts when the magnification is fixed. In that case, 9 may be a simple wire connection depending on the needs of the bias generating means 8.

3 to 5 show bias potential generation means 8,
Bias potential determination and selection means 9, physical quantity generation means 1
0 embodiment is shown.

In FIG. 3, the physical quantity generating means 10 is a switch 1.
This circuit consists of switch 1 and power supply 14.
3 OFF represents the same magnification mode, and ON represents the enlarged mode. This means 10 generates OV when the image is enlarged to the same size, and generates a power supply voltage V when the image is enlarged. The bias determination selection means 9 consists of a relay. Bias generation means 8
includes circuits 11-1 and 11-2 that generate necessary bias potentials in equal magnification and enlargement modes, respectively;
The outputs of circuits 11-1 and 11-2 are relay contacts 12
The voltage is applied to the sleeve 2 through the connecting means 7 shown in FIG.

FIG. 4 shows an example applied to a copying apparatus that reads an original with an image sensor and exposes it to a laser beam. A voltage corresponding to the magnification ratio is outputted from the amplifier 19 by the volume 13', this voltage is converted into a digital signal by the AD converter 16, and the time base φ is converted by the digital amount.
The clock _φ0 , which determines the CCD readout signal and process speed, is obtained. On the other hand, the output of the amplifier 19 is sent to the AD converter 18, multiplexer 17, and gates 12-1 to 12-
8 selects eight biases 11-1 to 11-8 corresponding to the magnification ratio and applies them to the sleeve 2 when the bias is enabled.

Figure 5 shows how to determine the bias frequency and DC component of the bias voltage in detail according to the magnification ratio.
The output of the VF converter 23 is amplified to approximately 1 KV _pp by the power amplifier 22, and a DC shift is obtained by one of the float amplifiers 21.

By using the above configuration, a good enlarged image can be easily obtained just by changing the bias voltage.

The implementation data is as follows. In the case of the same magnification mode, the process speed is 100 mm, the gap between the photosensitive drum and the sleeve is 250 μm, and the bias frequency is 200
Hz, bias voltage AC min 1200V _pp , bias voltage
At DC +200V, I was able to get a very good image. When enlarging the image twice in this state and setting the bias frequency to 600 Hz, a much better image was obtained than when developing with the bias described above.

As described above, the present invention provides a developing device that can obtain clear enlarged images at a low cost by using lenses used in conventional copying devices.

[Brief explanation of the drawing]

Figures 1 a-i are diagrams showing density distributions of originals and images, Figure 2 is a side view showing an apparatus for implementing the present invention, and Figures 3 to 5 are diagrams showing details of each part thereof. be. DESCRIPTION OF SYMBOLS 1...Latent image holding body (photosensitive drum), 2...Developer holding means (developing sleeve), 3...Doctor blade, 4...Hopper wall, 5...Toner, 6...
...Magnet, 7... Connection means, 8... Bias potential generation means, 9... Bias potential determination selection means, 10... Physical quantity generation means, 11-1, 11-
2...Bias potential generation circuit, 12...Relay contact, 13...Switch, 14...Power supply, 13'...
...Volume, 15...Preset counter, 1
6...AD converter, 17...Multiplexer, 18...AD converter, 19...Amplifier,
12-1 to 12-8...gate, 20...DC amplifier, 21...float amplifier, 22...power amplifier, 23...VF converter.

Claims (1)

[Scope of Claims] 1. A developing device equipped with a developer holding member disposed opposite to a latent image holding member on which either a full-size latent image or an enlarged latent image of image information is formed, wherein the developer It has means for applying a periodically changing developing bias to the holding member, and means for increasing the frequency of the developing bias in an enlarged mode for developing the enlarged latent image than in a same-size mode for developing a same-size latent image. A developing device characterized by: 2. The developing device according to claim 1, wherein the developer on the developer holding means and the latent image surface are not in contact with each other.