JPH06236084A - Image forming device - Google Patents

Abstract

PURPOSE:To transfer an image having no distortion to a recording medium even when a photosensitive drum irregularly rotates by setting a phase angle between a recording position where an electrostatic latent image is formed on the photosensitive drum and a transfer position where a visible image on the photosensitive drum is transferred to the recording medium to the integer multiple of a pitch angle between the teeth of a drum gear for driving the photosensitive drum. CONSTITUTION:The rotating speed of the photosensitive drum 28 is consecutively changed every pitch angle alpha between two adjacent gear teeth 41a according to the working accuracy of the drum gear 41. Meanwhile, the phase angle beta between the recording position P where the electrostatic latent image is recorded on the drum 28 by the incidence of a laser beam 35 and the transfer position T where the toner sticking to the visible image on the drum 28 is transferred to the recording paper 33 through a transfer roller 36 is set to the integer multiple of the pitch angle alpha between the gear teeth 41a. As a result, meshing relation between the gear tooth 41a and a gear tooth 42a for driving the gear tooth 41 a becomes the same at the recording position P and the transfer position T, and the increase/decrease of the rotating speed of the drum 28 also becomes the same at both positions P and T.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus having a photoconductor drum driven by a gear, and more particularly, an accurate image recording medium having no distortion even with respect to periodical rotation unevenness occurring on the photoconductor drum. It is related to what can be transferred to.

[0002]

2. Description of the Related Art Conventionally, in an image forming apparatus such as a copying machine, a printer or a facsimile, a laser beam as an image signal is made to enter a photosensitive drum while being scanned in the left-right direction, and the photosensitive drum is driven by a gear mechanism. There are various proposals for those which are driven to rotate. For example, Japanese Patent Laid-Open No.
In Japanese Patent Laid-Open No. 166470, a process cartridge and a photoconductor drum are provided, and a laser beam emitted from a laser scanning optical system unit is projected onto the photoconductor drum from above by a reflection mirror to form an electrostatic latent image. On the other hand, the first gear (drum gear) fixed to one end of the photoconductor drum is rotationally driven by the second gear (drum drive gear) that is rotationally driven in a predetermined rotation direction by the electric motor, and the toner adhered on the photoconductor drum is rotated. There is described a laser printer in which the image is transferred to a recording sheet conveyed below the photosensitive drum. In this case, the recording position where the electrostatic latent image is formed on the photosensitive drum and the transfer position where the toner on the photosensitive drum is transferred to the recording paper are determined based on the positional relationship and shape of various devices provided inside. It is provided at a predetermined position.

[0003]

As described above, in the conventional image forming apparatus such as the laser printer disclosed in Japanese Patent Laid-Open No. 2-166470, the drum gear for driving the photosensitive drum is meshed with the drum gear. When driving with a drum drive gear that operates, the gear teeth of the drum drive gear and the gear teeth of the drum gear mesh with each other. Since it is repeated every time, the rotation speed of the drum gear, that is, the photosensitive drum is determined by the predetermined rotation speed (V) for each pitch angle between two adjacent gear teeth of the drum gear, depending on the processing accuracy and material of the drum gear. A rotational speed (V + ΔV1) slightly higher than (V) by ΔV1 and a rotational speed (V + ΔV1) slightly slower than (V) by ΔV2. ΔV2) and over the continuously changes as a sine curve.

As a result, an image having a normal image density corresponding to a predetermined rotation speed (V), an image sparser than the normal image density corresponding to a rotation speed (V + ΔV1), and a rotation speed are formed on the photosensitive drum. An image in a denser state than the normal image density corresponding to (V-ΔV2) is periodically recorded, and the image including the sparse or dense state is transferred onto the recording paper, so that the image is printed particularly on the recording paper. In an image such as "picture", there is a problem that an image portion which is contracted in the conveying direction of the recording paper or is enlarged and distorted conspicuously appears. In the above publication, the first and second gears are helical gears. However, uneven rotation of the photosensitive drum is unavoidable, and image distortion cannot be eliminated.

An object of the present invention is to provide an image forming apparatus capable of transferring an accurate image onto a recording medium without distortion even if periodical rotation unevenness occurs on a photosensitive drum that receives a beam as an image signal. Is to provide.

[0006]

An image forming apparatus according to a first aspect of the present invention is directed to a beam output means for outputting a beam as an image signal, a photosensitive drum for receiving the beam to form an electrostatic latent image, and a photosensitive drum. In an image forming apparatus provided with a developing means for converting the electrostatic latent image formed on the body drum into a visible image, and a transfer means for transferring the visible image on the photosensitive drum onto a recording medium,
The phase angle between the recording position where the beam forms an electrostatic latent image on the photosensitive drum and the transfer position where the transfer unit transfers the visible image on the photosensitive drum to the recording medium is the drum gear for driving the photosensitive drum. Is configured to be an integral multiple of the pitch angle between adjacent gear teeth.

[0007]

In the image forming apparatus according to the first aspect of the present invention, the photosensitive drum is rotatably driven by the drum driving gear driven by the electric motor through the drum gear for driving the photosensitive drum, and the beam is emitted. The electrostatic latent image formed on the photoconductor drum by receiving the beam as the image signal output from the output means is developed into a visible image by the developing means, and this visible image is transferred to the recording medium by the transfer means. . Here, since the phase angle between the recording position and the transfer position on the photosensitive drum is configured to be an integral multiple of the pitch angle between adjacent gear teeth of the drum gear for driving the photosensitive drum, the drum gear The gear teeth of and the gear teeth of the drum drive gear that drives the same are the same at the recording position and the transfer position on the photoconductor drum, and the rotation speed of the drum gear depends on the period of the pitch angle between the gear teeth. Even if the rotation unevenness occurs, the increase and decrease of the rotation speed at these two positions are similar.

That is, the case where an image by the image beam is recorded on the photosensitive drum at every predetermined time will be described. When the rotation speed of the photosensitive drum at the recording position is slightly increased with respect to the predetermined speed, Although the image density is recorded on the body drum at a density lower than the image density corresponding to the predetermined speed, the rotation speed of the photosensitive drum at the transfer position is also slightly increased, and the recording medium conveyance speed is Since it corresponds to the predetermined speed of the drum, it is transferred in a dense state at the transfer position, so that it is transferred to the recording medium at the same original recording density as the image formed by the image beam that has eliminated the sparse state. . On the other hand, when the rotation speed of the photosensitive drum at the recording position is slightly reduced with respect to the predetermined speed, the operation is reverse to the above. As a result, even in the case of uneven rotation of the photoconductor drum, in the image such as "picture" or "character" printed on the recording medium, the image is partially shrunk in the conveying direction of the recording medium or conversely enlarged. It is possible to print an image that accurately corresponds to the image signal on the recording medium without distortion.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. This embodiment is an embodiment in which the present invention is applied to a laser printer which receives data from the outside and stores it in a memory and prints the data. First, the laser printer will be briefly described. As shown in FIG. 1, the laser printer 1 is provided with a printer casing 4 including an upper casing 2 and a lower casing 3, a laser scanner device 5 provided in the upper casing 2, and a detachable mount in the lower casing 3. Process cartridge 6
A transfer / separation device 9 including a transfer charger 7 and a charge elimination needle 8; a fixing device 12 including a heating roller 10 and a pressure roller 11; a paper feed roller 13; a registration roller 1
4, a transfer roller 36 that transfers the visible image on the photosensitive drum 28 to the recording paper 33, a conveyance roller 15, and a paper discharge roller 16
The transport device 17 is provided with the above.

Upper casing 2 of printer casing 4
Can be opened and closed via a hinge 19 between the closed position and the open position shown in FIG. The laser scanner device 5 includes a case 21 formed integrally with the upper casing 2, and a case 2
Semiconductor laser 22 and hexahedral mirror 2 arranged in
3, a focusing lens 24, a reflection mirror 25, and a lens member 27 made of synthetic resin, which is disposed at a laser light outlet portion 26 that is formed so as to project downward at the front end of the case 21. The process cartridge 6 is detachably arranged in the lower casing 3, and the photosensitive drums 28, 1
Next charger 29, developing cylinder 30, and exposure lamp 31
Etc. are assembled together. Incidentally, reference numerals 32, 33,
34 is a paper feed cassette, a recording paper, and a paper discharge tray, respectively. A fixing heater 18 including a halogen lamp is provided at the center of the heating roller 10 of the fixing device 12, and a thermistor 20 for detecting the temperature of the heating roller 10 is provided.

Next, the operation of the laser printer 1 will be briefly described. The laser light 35 emitted from the semiconductor laser 22 and incident on the hexahedral mirror 23 is deflected by a predetermined angle for each mirror surface of the hexahedral mirror 23 that rotates at a constant high speed, so that the laser light 35 is mainly distributed over a predetermined angular range. The light beam is scanned, then reflected vertically downward by the reflection mirror 25 through the imaging lens 24, and then enters the photoconductor drum 28 through the elongated lens member 27 in the scanning direction of the laser light 35. The laser beam 35 incident on the photoconductor drum 28 is rotated at a constant speed by a drum driving mechanism 40 described later, and the photoconductor drum 2 is rotated.
Sub-scanning is performed by 8 to form an electrostatic latent image on the peripheral surface of the photosensitive drum 28. Although the main scanning direction of the laser light 35 varies due to the variation in surface accuracy of the hexahedral mirror 23, the variation in the scanning direction is corrected by the lens member 27 when passing through the lens member 27. There is.

The electrostatic latent image formed on the photosensitive drum 28 is developed by the toner supplied from the developing cylinder 30, and this visible image is conveyed in synchronization with the rotation of the photosensitive drum 28. 33 is charged with a positive charge by the transfer charger 7, and the toner on the photosensitive drum 28 is transferred onto the recording paper 33 by the transfer roller 36 which is being pressed. It is separated from 28 and conveyed to the fixing device 12. In the fixing device 12, toner is fused and fixed on the recording paper 33 by the heating roller 10 and the pressure roller 11, and then the conveying roller 1
The sheet is conveyed to the sheet discharge tray 34 via the sheet discharging roller 5 and the sheet discharge roller 16.

Next, the drum drive mechanism 40 will be described with reference to FIG.
A brief description will be given based on. A large-diameter drum gear 41 made of synthetic resin is fixed to the drum shaft 28a of the photosensitive drum 28, and a small-diameter drum drive gear 42 that meshes with the drum gear 41 is connected to a main motor (not shown) by a connecting mechanism. It is driven to rotate. On the other hand, the carrying device 17 is also connected to the main motor, and the paper feed roller 13, the registration roller 14, the transfer roller 36, the carrying roller 15, the paper discharge roller 16 and the like rotate the photosensitive drum 28 by the main motor. It is configured to be rotationally driven in synchronization with the speed. That is, the recording paper 33 is conveyed in synchronization with the rotation of the photosensitive drum 28.

When the drum gear 41, that is, the photosensitive drum 28 is rotationally driven by the rotation of the drum drive gear 42, the gear teeth 42a of the drum drive gear 42 and the gear teeth 41a of the drum gear 41 are engaged with each other. Therefore, since the meshing operation from the meshing start phase angle of the gear tooth 42a to the gear tooth 41a to the meshing end phase angle is repeated for each gear tooth 41a, as shown in FIG. ,
The rotational speed of the drum gear 41, that is, the photosensitive drum 28, is a predetermined rotational speed (V) for each pitch angle α between two adjacent gear teeth 41a, and a rotational speed (V + ΔV1) slightly faster than this speed (V) by ΔV1. And from this speed (V) Δ
With a rotational speed slightly slower by V2 (V-ΔV2),
It changes continuously like a sine curve. However, it is assumed that the recording paper 33 is conveyed at a predetermined conveying speed corresponding to this rotation speed (V).

By the way, a recording position P where an electrostatic latent image is recorded on the peripheral surface of the photosensitive drum 28 by the incidence of the laser beam 35, and a toner adhered to the visible image on the photosensitive drum 28 is transferred to a transfer roller. The phase angle β with the transfer position T transferred onto the recording paper 33 via 36 is configured to be an integral multiple (for example, 14 times) of the pitch angle α between the gear teeth 41a. As a result, when the rotation speed of the photosensitive drum 28 at the recording position P is “V”, the rotation speed at the transfer position T is also “V”, and when the rotation speed of the photosensitive drum 28 at the recording position P is “V + ΔV1”. The rotational speed at the transfer position T is also "V + ΔV1". Similarly, when the rotational speed at the recording position P is "V-ΔV2", the rotational speed at the transfer position T is also "V-ΔV2".

That is, when the rotational speed of the photosensitive drum 28 at the recording position P and the transfer position T is "V", the transport speed of the recording paper 33 at the transfer position T is a predetermined speed corresponding to this rotational speed (V). So there is no problem. However, the photosensitive drum 2 at the recording position P and the transfer position T
A case where the rotation speed of No. 8 is “V + ΔV1” will be described with reference to FIG. However, in FIG. 5, it is assumed that a plurality of horizontal ruled lines K are recorded at predetermined intervals L by the laser beam 35 as an image signal on the photosensitive drum 28 driven at the rotation speed “V”. Since the rotation speed of the photosensitive drum 28 at the recording position P is “V + ΔV1”, the interval between the horizontal ruled lines K recorded at this recording position P is the speed “V”.
The ruled line interval obtained by adding only the ruled line interval increase “ΔL1” corresponding to the speed increase “ΔV1” to the ruled line interval “L” corresponding to “L”, that is, a sparse state. However, at the transfer position T,
Although the rotation speed of the photosensitive drum 28 is “V + ΔV1”, the recording paper 33 is conveyed in the conveyance direction A at the conveyance speed corresponding to the rotation speed “V”, so that the ruled line intervals in the sparse state become dense. , The ruled line interval increase “ΔL1” corresponding to the speed increase “ΔV1” is eliminated, and the recording paper 33
Each of the plurality of horizontal ruled lines K is transferred at the ruled line interval “L” on the upper side.

On the other hand, the case where the rotation speed of the photosensitive drum 28 at the recording position P and the transfer position T is "V-ΔV2" will be described with reference to FIG. However, in FIG. 6, a plurality of horizontal ruled lines K are formed at a predetermined interval L by the laser light 35 on the photosensitive drum 28 driven at the rotation speed “V”.
It shall be recorded for each. Since the rotation speed of the photosensitive drum 28 at the recording position P is “V−ΔV2”, the interval between the horizontal ruled lines K recorded at the recording position P is the speed decrease amount from the ruled line interval “L” corresponding to the speed “V”. The ruled line interval obtained by subtracting "ΔL2", which is the reduced ruled line interval corresponding to "ΔV2", is the dense state. However, at the transfer position T, the rotation speed of the photosensitive drum 28 is “V−ΔV2”, but the recording paper 33 is conveyed in the conveyance direction A at the conveyance speed corresponding to the rotation speed “V”. The dense ruled line spacing becomes sparse, and the reduced ruled line spacing “ΔL2” corresponding to the speed reduction “ΔV2” is eliminated, and the recording paper 3
Each of the plurality of horizontal ruled lines K is transferred onto the pattern 3 at the ruled line interval “L”.

As described above, the phase angle β between the recording position P and the transfer position T on the photosensitive drum 28 is such that the adjacent gear teeth 41a of the drum gear 41 for driving the photosensitive drum.
Since the gear teeth 41a of the drum gear 41 and the gear teeth 42a of the drum drive gear 42 for driving the gear teeth 41a are configured to be an integral multiple of the inter-pitch angle α, the recording position on the photosensitive drum 28 is The same applies to P and the transfer position T, and even if the rotational speed of the drum gear 41, that is, the photosensitive drum 28 is unevenly rotated in the cycle of the gear tooth pitch angle α, the rotational speed increases and decreases at these positions as well. Become. That is, even if the image density recorded on the photoconductor drum 28 is recorded in a dense state or a sparse state due to uneven rotation of the photoconductor drum 28 with respect to the image signal by the laser light 35, the recording paper 33 is conveyed in a predetermined manner. Depending on the speed, the recording paper 33
Is transferred at the same original image density as the image signal by the laser beam 35 that has eliminated the dense or sparse state. As a result, an image such as a "picture" or a "character" printed on the recording paper 33 will not be partially shrunk in the transport direction A of the recording paper 33, or conversely will be enlarged and distorted, and thus an image signal will be obtained. The corresponding image can be accurately transferred onto the recording paper 33.

The drum gear 41 and the drum drive gear 42 may be helical gears. It should be noted that the phase angle β between the recording position P and the transfer position T is determined by the gear teeth 41
It can be configured to an arbitrary integral multiple of the pitch angle α between a.
It is needless to say that the present invention can be applied to various image forming apparatuses such as a facsimile machine and a copying machine configured to gear-drive the photosensitive drum 28 that receives laser light.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of a laser printer.

FIG. 2 is a schematic side view of a drum drive mechanism.

FIG. 3 is a diagram showing fluctuations in the rotation speed of a photosensitive drum.

FIG. 4 is a view corresponding to FIG. 2 showing a recording position and a transfer position on a photosensitive drum.

FIG. 5 is an explanatory diagram of a transfer state onto a recording sheet when the rotation speed of the photosensitive drum is reduced.

FIG. 6 is a view corresponding to FIG. 5 when the rotation speed of the photosensitive drum is increased.

[Description of Reference Signs] 1 laser printer 5 laser scanner device 6 process cartridge 28 photosensitive drum 30 developing cylinder 33 recording paper 35 laser light 36 transfer roller 41 drum gear 42 drum drive gear

Claims (1)

[Claims] 1. A beam output means for outputting a beam as an image signal, a photosensitive drum for receiving the beam to form an electrostatic latent image, and a visible electrostatic latent image formed on the photosensitive drum. In an image forming apparatus including a developing unit for forming an image and a transfer unit for transferring the visible image on the photosensitive drum onto a recording medium, a recording position at which the beam forms an electrostatic latent image on the photosensitive drum. And a transfer position at which the transfer means transfers a visible image on the photosensitive drum to a recording medium, an integer multiple of a pitch angle between adjacent gear teeth of the drum gear for driving the photosensitive drum. An image forming apparatus having the above structure.