JPH0326835B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a novel control method for controlling the developing bias voltage of an electrophotographic copying machine. Figure 1 shows a general electrophotographic copying machine. In the figure, 1 is a platen glass, 2 is a document, 4 is an exposure lamp such as a fluorescent lamp or a linear halogen lamp, and mirrors 5, lenses 6, etc. The image is projected onto a photosensitive material 7 made of selenium through an optical system consisting of. Sensitive material 7
is positively charged in advance by the charging corotron 8 and forms an electrostatic latent image corresponding to the image of the original 2 after exposure. This electrostatic latent image is developed using a developer 18 by a developing roll 10 in a developing device 9, and is transferred by a transfer corotron 14 onto a sheet 19 fed in advance by a sheet tray 13. This paper 19 is fixed by a fixing roll 15. On the other hand, toner remaining on the photosensitive material after transfer is cleaned by a cleaner 11, and charged by a charging corotron for the next copy. Further, a bias voltage is applied to the developing roll 10 from a bias power supply 17, thereby preventing fogging and making it possible to obtain an appropriate image density. Note that 12 is cleaned toner. Conventionally, this developing bias has been set to a constant value, or as an automatic control method, a patch image of a constant density is developed on a photosensitive material, its reflected density is detected, and an appropriate bias voltage is applied. The thing was publicly known. Setting it to a constant value in advance and leaving it unchanged has the disadvantage that it cannot respond to changes in the temperature of the photosensitive material, cycle characteristics, etc., and even if the bias is changed according to the developed density, the patch density of the reference input will not change. Densities that are close to each other are controlled with relatively good accuracy, but as the input patch density deviates, the variation becomes large. In order to prevent this, a method of using a plurality of batches has been proposed, but this method has the disadvantage that the device becomes complicated and expensive. In order to further improve this problem, there is a method of reading the electrostatic latent image of a patch with a constant density and applying that value as a developing bias voltage, but this method provides good copy quality control at a low cost. However, even this method has the following drawbacks. In other words, if the density of the patch is low, printing errors inevitably have a large effect. For example, an error of about 0.05 usually occurs in absolute density, but if you want to use a patch density of 0.15, you won't know which density it will actually be between 0.10 and 0.20 until you get it. In terms of performance
A value of about 0.15±0.01 is required. concentration is 0.15
Although it is possible to select a value of ±0.01, there are problems in terms of reduced efficiency and high inspection costs. The present invention has been made to solve the above-mentioned drawbacks, and it involves forming a patch image of a constant density as an electrostatic latent image on a sensitive material, detecting the potential of the latent image, and adjusting the developing bias voltage accordingly. The present invention aims to provide a developing bias voltage control method that can always apply a stable bias voltage even if the patch density used varies to some extent. Embodiments of the present invention will be described below based on FIG. 2. Note that in FIG. 2, members that are the same as those in the conventional system are designated by the same reference numerals as those shown in FIG. 1, and explanations thereof will be omitted. A potential sensor 16 detects the surface potential of an electrostatic latent image of a fixed density patch 3 provided on the platen 1;
When adjusting the copying machine at the time of factory shipment or during adjustment by a service person at the customer's location, the difference between this patch potential (when adjusting V _PATCH ) and the optimum bias potential (when adjusting V _BIAS ), V _D = (when adjusting V _PATCH) -V _BIAS adjustment)
Remember this, and from now on when using the copy machine,
Detect the patch potential (V _PATCH ) at that time and set the bias voltage V _BIAS to the developing roll 10 as V _BIAS =
It is applied through the controller 17 so that V _PATCH -V _D. In explaining the embodiments below, terms will be defined as follows. V _DDP : Potential of the sensitive material when unexposed V _IM : Potential of the sensitive material corresponding to the input density V _BKG : Potential of the sensitive material after exposure of the blank area (all of the above are potentials at the development position) Also, the potential of the sensitive material corresponding to the input density. The specs are that the input density of 0.7 solids is outputted on the copy as 0.7 or higher, the input of 0.2 line is outputted as 0.3 or higher, the input of 0.7 line is outputted as 1.1 or higher, and the fog is 0.01.
It is assumed that the output concentration is as follows. The copying machine used in the example is Fuji Xerotx.
The photosensitive material, developer, and other consumables for the 3500 were all made for the same machine, and all were commercially available from Fuji Xerox Co., Ltd. Example V _DDP = 900V, V _BKG = 50V, V _BIAS adjustment = 200V
The charging current value, light intensity, etc. were adjusted so that The copy quality at this time was fog density → none 0.7 solid input → 0.7 output copy 0.2 line input → 0.6 output copy 0.7 line input → 1.2 output copy, all of which satisfied the specifications. In addition, a patch with a density of 0.25 is used, and the patch part potential V during adjustment is 255V when _PATCH is adjusted. Therefore, the difference between the patch potential and the optimum bias potential is V _D = V _PATICH adjustment - V _BIAS adjustment = 255 - 200 = 55 V, and after that, the voltage is applied to the developing device through the controller 17 so that V _BIAS = V _PATCH - 55 V. When the bias voltage V _BIAS was applied to the developing roll 10 in the image forming apparatus 9, the following differences in copy quality appeared compared to those without control. During adjustment (22℃) V _DDP = 900V V _BKG = 50V V _BIAS = 200V, 500 copies were taken continuously, the quality of the 500th copy was determined, and the quality of the 500th copy was left overnight at 5℃, and the first copy was taken in the morning. The following table shows the results of comparing copy quality.

[Table] As can be seen from this table, it can be seen that fogging is particularly improved. Furthermore, there is no need to check the patch density, and if it is around 0.2, there is no need to limit the density to a particularly narrow range. On the other hand, in the case of the Fuji Xerox 3500, where the patch potential and bias voltage are made the same, the patch density had to be kept at about 0.16±0.01. As described above, the present invention forms a patch image of a constant density as an electrostatic latent image on a sensitive material, detects the potential of this electrostatic latent image, and adjusts the developing bias voltage set at the time of adjusting the copying machine. The difference in electrostatic latent image potential due to this patch (V _D = V _PATCH adjustment - V _BIAS adjustment) is memorized, and when copying, the memorized potential difference V _D is subtracted from the electrostatic latent image potential V _PATCH . Value (V _PATCH −
Since V _B is applied to the developing roll as the developing bias voltage V _BIAS , a stable bias voltage can always be applied even if the patch density used varies somewhat.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of the structure of a general electrophotographic copying machine, and FIG. 2 is an explanatory diagram of the structure of an embodiment of the present invention. 1 is a platen, 3 is a patch, 4 is an exposure lamp,
7 is a photosensitive material, 9 is a developing device, 10 is a developing roll, 16
17 is a potential sensor, and 17 is a bias potential controller.

Claims (1)

[Claims] 1 A patch image of a constant density is created as an electrostatic latent image on a sensitive material, the potential of this electrostatic latent image is detected, and the developing bias voltage set when adjusting the copying machine and the electrostatic latent image potential due to this patch are detected. difference (V _D = V _PATCH adjustment -
V _BIAS adjustment) is memorized, and the potential of the electrostatic latent image V _PATCH
The value obtained by subtracting the potential difference V _D stored above from (V _PATCH
-V _B ) to a developing roll as a developing bias voltage V _BIAS .