JPS6367184B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a toner density detection method in electrostatic recording such as electrophotographic copying, in which a developing bias voltage is changed between when developing an original to be recorded and when developing a reference density piece. A developing method using a two-component developer consisting of a carrier such as iron powder and a toner, which is a colored resin powder, is known as a developing method for electrostatic recording systems such as electrophotographic copying machines and facsimiles. In the developing method, only the toner in the developer is consumed as the number of recordings increases, so in order to keep the recording density constant, it is necessary to maintain the toner concentration in the developer within a predetermined range. If the toner density becomes too high, the background of the recorded material becomes dirty, and if it becomes too low, the image density decreases and the contrast worsens. Various methods have been proposed to maintain a constant toner density, one of which is electrophotography, as disclosed in Japanese Patent Publication No. 43-16199, Japanese Patent Application Laid-open No. 52-119233, and Japanese Patent Application No. 53-43303. For copying devices,
The density of the developed toner image is optically measured by developing a control image consisting of a belt-shaped control image provided on the peripheral edge of the photoreceptor or a reference density patch provided at a position where the image is developed before the effective image area. This is detected as a toner concentration signal, and the amount of toner is replenished according to this signal. However, in this method, when developing a toner density control image such as a band-shaped area or patch, the same developing bias voltage as when developing an electrostatic latent image in an effective image area is applied, so the peripheral edge of the patch area as a toner density control image is applied. Alternatively, the developed image has a noticeable so-called edge effect in which the density at the peripheral edge of the band-shaped region is high. Furthermore, since the toner is scraped off by the carrier, it is difficult to obtain an image with uniform density. Therefore, when such a developed image is optically detected, there is a problem in that it is difficult to accurately detect the image density because the intensity of reflected light from the peripheral portion and other portions is extremely different. Furthermore, as the photoreceptor and developer deteriorate, the edge effect becomes more pronounced, making it even more difficult to accurately detect image density. Furthermore, when a carrier with high electrical resistance is used or when the specific resistance of the carrier increases in low humidity conditions, the edge effect also increases, so optical detection may become inaccurate in image conditions where the edge effect is significant. The present invention has been made in view of the above drawbacks.
Set the development bias voltage applied when developing the electrostatic latent image on the standard density strip to a voltage of the same polarity, a voltage of opposite polarity, or a ground voltage that is lower than that when developing the electrostatic latent image corresponding to the original. This is how it was done. DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to the drawings. FIG. 1 is a diagram for explaining the process of the present invention. In the figure, reference numeral 1 denotes a document table, and a reference density piece, that is, a patch section 2 for controlling toner concentration is attached to the lower surface of the tip of the document table 1. FIG. 2 is a diagram showing an embodiment of the patching section 2, in which 1 is a document table;
is the document table glass. Reference numeral M denotes an original placed on the original platen glass 1a, and 3 denotes an exposure device equipped with a lamp 3a and a reflector 3b for irradiating light onto the original M, and the original platen 1 moves during recording. Alternatively, the exposure device 3 is configured to move along the document table 1. Reference numeral 5 denotes a photosensitive drum that rotates at a constant speed in the direction of the arrow in synchronization with the movement of the document table 1 or the exposure device 3. Now, when the photoreceptor drum 5 rotates and is uniformly charged by the charger 4, the patch portion 2 and the document M, including the patch portion 2, are subjected to image exposure by the exposure device 3, and the surface of the photoreceptor drum 5 is exposed. An electrostatic latent image corresponding to the patch portion 2 and the document M is formed on the wafer. When the photosensitive drum 5 having the electrostatic latent image is developed by the developing device 6, when developing the electrostatic latent image on the patch portion 2 formed on the drum 5, a voltage is applied to prevent fogging during development. The bias voltage is controlled to the ground potential, a voltage with a polarity opposite to the polarity of the latent image charge of the patch section 2, or a developing bias voltage smaller than that during development of the effective image section, and then the effective image, that is, the electrostatic latent image of the document M is controlled. When developing, the developing bias applied voltage is controlled so that the developing bias voltage has the same polarity as the electrostatic latent image charge and is sufficiently higher than the potential of the background portion. If the bias voltage is controlled in this manner and development is performed, the developed image of the patch portion, which is a toner density control image, will be an image having uniform density with very little edge effect. The following table shows the state of the edge effect in comparison with the conventional technique when using a square patch with a side of 20 mm and a reflection density of 1.0.
The photoreceptor used was a selenium photoreceptor, and the latent image charge was positive, and the surface potential for a reflection density of 1.0 was +.
It was developed at 700V with a toner density of 2%.
The bias applied voltage when developing the electrostatic latent image on the original is +
It is 250V.

[Table] In the table, η _e indicates the ratio of the reflection density at the center of the patch to the reflection density at the periphery of the patch. Therefore, when η _e is 1.0, there is no edge effect, and as it is smaller than 1.0, the edge effect is more pronounced. Of the developed images of the patch portion and the document developed in this way, only the developed image of the document is transferred onto the recording paper 10 by the transfer pole 7, and the recording paper 10 is separated from the photoreceptor drum 5 by the separation pole 8 and transported. The toner image on the recording paper 10 is transferred to the recording paper 1 by the fixing device 11.
Fixed to 0. On the other hand, the uniform toner image in the patch portion that is not transferred passes through the transfer pole 7 and separation pole 8 while remaining attached to the photoreceptor drum 5, and the density detector 12 irradiates this toner image with light to detect the reflected light. Receives light, outputs a signal corresponding to the amount of light received,
In this way, the density of the patch portion is detected. Based on the signal output from the density detector 12, a certain amount of toner is supplied from the toner supply device 13 to the developing device 6 to control the toner density to be constant. The developed image on the patch portion 2 and the residual toner after transfer are removed from the surface of the photosensitive drum 5 by a cleaning device 9. In this way, one copy cycle is completed. By the way, it is necessary that the patch area is a toner image of uniform density, but in the present invention, the developing bias voltage is set to the ground potential, a voltage with the opposite polarity to the latent image charge of the patch area, or a voltage smaller than that during original development. By simply controlling the developing bias voltage, a uniform toner image can be easily obtained, allowing accurate density detection. As a result, the toner density can be accurately controlled within a predetermined range, making it possible to always obtain copies with stable image density. Furthermore, in the present invention, it is only necessary to switch the developing bias voltage between developing the patch portion and developing the document.
It has the advantage of not requiring complicated detection methods or control devices.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of an electrophotographic copying apparatus that implements the method according to the present invention, and FIG. 2 is a bottom view of a document table showing the position of a patch section. DESCRIPTION OF SYMBOLS 1... Document stand, 1a... Document stand glass, 2... Patch section, 3... Exposure device, 3a... Lamp, 3b... Reflector, 4... Charger, 5... Photosensitive drum, 6... Developing device, 7... Transfer pole , 8... Separation electrode, 10... Recording paper, 1
1... Fixing device, 12... Density detector, 13... Toner supply device.

Claims (1)

[Claims] 1. Develop the electrostatic latent image of the reference density strip formed on the charge carrier using a two-component developer containing toner and carrier, and calculate the reflection density of the developed image of the reference density strip. In the toner concentration detection method of detecting the toner concentration in the developer, the development bias voltage applied when developing the electrostatic latent image of the reference density piece is equal to the voltage applied when developing the electrostatic latent image corresponding to the document. A toner concentration detection method characterized in that the voltage is set to a voltage of the same polarity, a voltage of opposite polarity, or a ground voltage lower than .