JPH01237575A - Printer - Google Patents

Abstract

PURPOSE:To eliminate the generation of uneven density by measuring an interval value of a void between a photosensitive drum and a developing sleeve of a developing device, and controlling a developing bias voltage by its interval value. CONSTITUTION:A part of a laser light 10 which is scanned onto a photosensitive drum 2 is reflected to the void direction by using a reflecting mirror 5 and a lens 6. Subsequently, the width of the laser light which has passed through the void is detected by a photodetector array 7, and an interval value of the void is recognized by a void measuring circuit 8. The inverval value which is obtained in such a way is fed back to a developing bias potential supply circuit 9, and a developing bias is varied successively. In such a way, the image density is corrected so as to be kept constant, and printing can always be executed by prescribed density.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a printing device, and particularly to a printing device using an electrophotographic method.

[Prior Art] A conventional electrophotographic printing device is used as an output device for an information processing device, and is required to be able to use plain paper and to have stable image quality such as high density and geometric accuracy. In a conventional printing apparatus, as shown in FIG. 2, a photosensitive drum 2 is charged by a negative charger 1 and then irradiated with a laser beam 10 to neutralize the charges. As a result, the toner positively charged with respect to the electrostatic latent image on the photosensitive drum 2 is caused to fly from above the developing sleeve 4 by using the latent image potential in the developing device 3 and the AC bias from the developing bias voltage supply circuit 9. Developing is done by.

[Problem to be solved by the invention]

In the above-mentioned conventional printing apparatus, the distance between the photosensitive drum 2 and the developing sleeve 4 for causing the toner in the developing device 3 to fly is not constant due to "distortion" caused by heat and distortion due to manufacturing, and the density is uneven. The disadvantage is that it occurs.

In addition, the strain is caused by the developing sleeve 4 and the photosensitive drum 2.
Both tend to be distorted coaxially.

Therefore, an object of the present invention is to provide a printing apparatus that does not cause density unevenness.

[Means to solve the problem]

According to the present invention, a printing apparatus includes means for measuring the distance value of the gap between the photosensitive drum and the developing sleeve of the developing device, and a developing bias voltage supply circuit, and the developing bias voltage is controlled by the distance value. is obtained.

〔Example〕

Next, the present invention will be described in detail with reference to the drawings showing one embodiment of the present invention.

Referring to FIG. 1, in one embodiment of the present invention, a portion of the laser beam 10 scanned onto the photosensitive drum 2 is reflected toward the gap using a reflective mirror 5 and a lens 6. The width of the laser beam passing through the gap is detected by the light receiving element array 7, and the gap measurement circuit 8 recognizes the gap interval value.

The obtained interval value is fed back to the developing bias potential supply circuit 9, and the developing bias is successively changed. This corrects the image density to be constant.

In this embodiment, a laser light source is used to create an electrostatic latent image on the drum, but it is also possible to use a separate laser light source.

〔Effect of the invention〕

As described above, according to the present invention, a printing device that can always print at a constant density can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of an embodiment of the present invention, and FIG. 2 is a cross-sectional view of a conventional electrophotographic printing apparatus. 1.1' knee charger, 2.2': photosensitive drum, 3.3': developer, 4.4': developing sleeve,
5: Reflection mirror, 6: Lens, 7: Photodetector array, 8
: Gap measurement circuit, 9: Development bias voltage supply circuit, 10
．． 10': Laser light. Agent Patent Attorney Susumu Uchihara

Claims (1)

[Claims] An electrophotographic printing apparatus, comprising means for measuring a gap distance between a photosensitive drum and a developing sleeve of a developing device, and a developing bias voltage supply circuit, and controlling the developing bias voltage according to the gap value. A printing device characterized by: