JPH0256669B2 - - Google Patents

Description

[Detailed Description of the Invention] (a) Technical Field of the Invention The present invention relates to a developing device for a printer using an electrophotographic method, and particularly to a developing bias for appropriately setting a bias voltage that greatly affects the print quality of the developing device. Regarding the setting method.

(b) Prior art and problems The principle of the recording method of printers using electrophotography is to first apply a charger to the surface of the photosensitive drum.
Charges about 500V. Subsequently, when a light beam is applied to the surface by a laser beam, the electric charge is removed from the area that is hit by the light beam, forming a latent image. When a developer applies toner to the latent image, the toner adheres to the latent image and is developed as a visible image. The developed image is transferred to paper, and the transferred image is fused and fixed to the paper. Recording is performed by the above-described operation, but it is necessary to apply a bias voltage to the toner in the developing device via the developer material, and if the bias voltage is not appropriate, the print quality will deteriorate. FIG. 1 is a diagram illustrating the relationship between the bias voltage and print quality. The developing material deteriorates as it is used, and in order to maintain constant printing quality, it is necessary to change the bias voltage as shown by a. Therefore, printing quality is usually maintained by adjusting the bias voltage as shown by b, and the bias voltage is adjusted within a range of about +300V to -300V. However, the state of deterioration shown on the horizontal axis is unknown, and conventionally the development bias has been adjusted by determining the degree of deterioration based on the paper feed amount. The degree of bias is different, and there is a drawback that there are cases where an appropriate bias voltage cannot be obtained.

(c) Object of the Invention In order to eliminate the above-mentioned drawbacks, the object of the present invention is to provide a developing bias setting method that determines the state of developed marks, detects the degree of deterioration of the developing material, and automatically sets an appropriate bias voltage. It is about providing.

(d) Structure of the Invention The structure of the present invention is to develop a latent image formed on an image carrier by adsorbing toner to which a bias voltage is applied, and to print by transferring the developed toner image onto a recording medium. In the apparatus, a latent image of a mark having a plurality of line segments is formed on the image carrier, a change in the resolution of a toner image obtained by developing the latent image of the mark is detected, and corresponding to the detection result, the Something that adjusts the bias voltage.

(e) Embodiments of the Invention In the present invention, a mark as shown in FIG. 2 is recorded at a predetermined position on a photosensitive drum, and the resolution of the mark is determined to determine the bias voltage. For example, a plurality of lines are recorded as shown by A. If the bias voltage is appropriate, each line will have straight edges and no internal unevenness as shown by A. If this line is optically read out, a waveform as shown by B, indicating that the bias voltage is appropriate, can be obtained. When the developing material deteriorates and the bias voltage becomes inappropriate, development occurs such as toner not adhering to the center of the line and appearing white, or the edges of the line becoming blurred, as shown in C, and the difference in shading also decreases. As a result, the optical readout waveform exhibits developments such as an increase in frequency and a decrease in amplitude as shown by D. Therefore, changes in frequency and amplitude are detected, and the amount of change is compared with a predetermined value to automatically adjust the bias voltage.

FIG. 3 is a block diagram of a circuit showing one embodiment of the present invention. The photosensitive drum 1 is charged by a charger 2, and the laser beam 3 forms a latent image at a predetermined position on the photosensitive drum 1 as shown in FIG. 2A. Developer device 4
Toner is mixed with the developing material and stirred, and a developing bias is applied from the bias voltage generator 5. An optical reader 10 reads the latent image at a predetermined position on the photosensitive drum, where the toner is not adhered to the developed latent image. An analog waveform of the image signal read by the optical reader 10 is sampled by an analog/digital (A/D) conversion circuit 9, and voltage values and frequency components are sent out as digital values. The voltage value is sent to the ROM 7, and the frequency component is sent to the frequency analysis circuit 8. The frequency components analyzed by the frequency analysis circuit 8 are sent to the ROM 7. A table is prepared in advance in the ROM 7 in which bias voltage correction amounts for frequencies and voltages are determined, and the bias voltage correction amounts determined by indexing the table are determined by the digital/analog (D/A) conversion circuit 6. It is converted into an analog value and sent to the bias voltage generator 5.
The bias voltage generator 5 sends the bias voltage corrected by the correction amount to the developer 4.

(f) Effects of the Invention As explained above, the present invention automatically adjusts the appropriate bias voltage according to the state of deterioration of the developing material, so it is possible to provide a printer that always prints with good quality.

[Brief explanation of the drawing]

FIG. 1 is a diagram explaining the relationship between bias voltage and print quality, FIG. 2 is a diagram explaining the principle of the present invention,
FIG. 3 is a block diagram of a circuit showing one embodiment of the present invention. 1 is a photosensitive drum, 2 is a charger, 3 is a laser beam, 4 is a developer, 5 is a bias voltage generator, 6 is a digital/analog conversion circuit, 7 is a ROM, 8
9 is a frequency analysis circuit, 9 is an analog/digital circuit, and 10 is an optical reader.

Claims (1)

[Scope of Claims] 1. An apparatus for developing a latent image formed on an image carrier by adsorbing toner to which a bias voltage is applied, and for printing by transferring the developed toner image to a recording medium, comprising: A latent image of a mark having a plurality of line segments is formed on an image carrier, a change in resolution of a toner image obtained by developing the latent image of the mark is detected, and the bias voltage is adjusted or decreased in accordance with the detection result. A developing bias setting method characterized by: