JPS62145260A - Multiple transfer type laser printer - Google Patents

Abstract

PURPOSE:To eliminate the mutual shift of a multiple transfer image based upon respective latent images and to obtain an excellent multiple transfer image by setting the transmission frequency of a video signal properly according to the optical magnification of a laser scanning system. CONSTITUTION:Video signal V1-V4 from respective image processors 31 are transferred to line buffer memories 32 at the same transfer frequency, but video signals V1-V4 from the respective line buffer memories 32 are transferred to laser modulating circuits 3 and laser scanning systems 3 according to video clocks CL1-CL4. At this time, laser beams based upon the video signals V1-V4 illuminate respective photosensitive drums 1 according to the transmission timing of respective video clocks CL1-CL4 while absorbing variance in optical magnification among the respective laser scanning systems 2, and the substantial scanning ranges on the respective photosensitive drums 1 are made constant to form latent images corresponding to the respective video signals. Consequently, latent image formation positions on the respective photosensitive drums 1 are coincident with one another in a scanning direction.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a multiple transfer type laser printer, and in particular,
The present invention relates to an improvement in a multi-transfer type laser printer which is provided with a plurality of laser scanning systems, photoreceptors, developing means, and transfer means, respectively.

[Prior Art] A conventional multi-transfer type laser printer of this type is disclosed in Japanese Patent Application Laid-Open No. 59-62879. This system is equipped with a laser scanning system, a developing device for different color toners, and a transfer device for multiple photoreceptors, and each laser scanning system deflects the beam from the laser light source in the scanning direction using a deflector such as a polygon mirror. The deflected beam is irradiated onto each photoreceptor through an imaging lens, while the latent image formed on each photoreceptor is developed into toner by each developer, and the toner on each photoreceptor is The images are transferred onto a single transfer sheet in a sequentially overlapping manner.

In this type, a latent image can be formed independently on each photoreceptor, so printing speed can be improved compared to a type that forms latent images on a single photoreceptor at different times. It can be done.

[Problems to be Solved by the Invention] However, in such a conventional multi-transfer laser printer, each image is The optical magnification of the laser scanning system may vary.

In such a case, there is a risk that the actual scanning range of each photoreceptor will deviate in the scanning direction, and the latent images written by each laser scanning system will deviate in the scanning direction. When multiple toner images are transferred onto one transfer sheet, a problem arises in that the transferred images are shifted from each other, resulting in a significant deterioration in image quality.

In order to solve this problem, it is possible to match the focal lengths of the imaging lenses of each laser scanning system, but the processing accuracy and installation of the imaging lenses, etc. must be adjusted in consideration of the adjustment accuracy at the time. , it becomes virtually impossible to match the optical magnifications of the laser scanning systems by the above-mentioned means.

Means for Solving Problems] The present invention has been made by focusing on the above problems, and is capable of effectively absorbing variations in optical magnification in a plurality of laser scanning systems. The present invention provides a multi-transfer type laser printer capable of obtaining good multi-transfer images without image shift.

That is, the present invention each includes a plurality of laser scanning systems, a photoreceptor,
Based on the premise of a multi-transfer type laser printer in which developing means and transfer means are provided independently and the toner images on each photoreceptor are superimposed and transferred onto one transfer medium, the video signals sent to each laser scanning system are The transmission frequency is appropriately changed according to the optical magnification of each laser scanning system, and the effective scanning range of each laser scanning system for each photoreceptor is set constant.

In such technical means, the design of the laser scanning system may be changed as appropriate, but in order to improve the scanning accuracy, it is desirable to add means for correcting the surface inclination of the laser beam deflection means.

Further, the photoreceptor may be of any type such as a drum or a belt, the developing means may be selected as appropriate, and the transfer means may be appropriately selected such as a thermal transfer method or an electrostatic transfer method.

Further, as a means for appropriately changing the oscillation frequency of the video signal sent to the laser scanning system, an oscillator that generates a clock of a preset frequency or a voltage variable oscillator that can adjust the clock frequency as appropriate may be used. You may change the design as appropriate.

[Function] According to the technical means described above, if the transmission frequency of the video signal sent to each laser scanning system is set in advance to an appropriate value according to the optical magnification of each laser scanning system,
Even if the optical magnification of each laser scanning system varies,
By effectively absorbing variations in the optical magnification of each laser scanning system, it becomes possible to match the latent image width based on each video signal, in other words, the actual scanning range of each laser scanning system.

[Embodiment 1] Hereinafter, the present invention will be described in detail based on embodiments shown in the accompanying drawings.

In the embodiment shown in FIG. M1, the laser printer includes four photosensitive drums 1 (specifically, one
a to 1d), and each photosensitive drum 1 is provided with a laser scanning system 2 (specifically, 2a to 2d). A pre-charger 3 (specifically, 3a to 3d) that charges the toner, a developing device 4 (specifically, 4a to 4d) having cyan, magenta, yellow, and black toner, and a toner image on each photosensitive drum 1. A transfer device 6 (specifically, 6a to 6d) that transfers the toner to the transfer paper 5 as a transfer medium, a cleaner 7 (specifically, 7a to 7d) that removes residual toner on each photosensitive drum 1, and each photosensitive drum. A static eliminator 8 (specifically, 8a to 8d) for removing the residual charge on the 1 is provided. In FIG. 1, reference numeral 9 denotes a paper transport means for sequentially transporting the transfer paper 5 to the transfer section of each photosensitive drum 1, 10 a paper feed means for supplying the transfer paper 5 to the paper transport means 9, and 11 a transfer paper. 12 is a fixed volume means for fixing the toner image superimposed and transferred on 5, and a paper ejecting means 12 for ejecting the transfer paper 5 after the fixing process.

In this embodiment, each of the laser scanning systems 2 includes a semiconductor laser 21 as a laser light source and a collimator lens 22 that condenses and collimates the beam from the semiconductor laser 21, as shown in FIG. 1, for example. , a polygon mirror 23 that emits the beam from the collimator lens 22 in the scanning direction, an fθ lens 24 that emits the deflected beam onto the surface of the photosensitive drum to form an image, and the polygon mirror 23
It is composed of cylindrical mirrors 25 and 26 that correct the tilt of the surface.

Further, in this embodiment, as shown in FIG. 2, image processing devices 31 (specifically, 31a to 31d) are provided corresponding to each laser scanning system 2 (2a to 2(1)). , each image processing device 31 outputs an appropriate video signal V.
to (4) are sent out, and the line buffer memory 32 (specifically, 32a to 32d) is sent out at a predetermined write clock CL.
). Then, predetermined read clocks (hereinafter referred to as video clocks) CL to CL4 are respectively output from the line buffer 7 memories 32.
A video signal is read out in accordance with this, and this video signal is applied to the semiconductor laser of each laser scanning system 2 via a laser modulation circuit 33 (specifically, 33a to 33d).

Further, each of the video clocks CL1 to CL4 is appropriately set according to the actual measured value of the optical magnification in each radar scanning system 2, and the latent image width based on the video signal read out at the transmission timing of each video clock is set as appropriate. They are set to match each other on each photosensitive drum 1. More specifically, as shown in FIG.
0, and the clock from this R oscillator 40 is appropriately frequency-divided by a frequency divider 42, and each radar scanning system 2
The frequency divider 42 synchronizes with the laser writing start signal 8.
The frequency dividing operation is started. Note that, especially when the clock from the oscillator 40 is set to correspond to a desired video clock, the frequency divider 42
Of course, there is no need to use .

Therefore, according to the multiple transfer laser printer according to this embodiment, the video signals V 1 to V 4 from each image processing device 31 are transferred to the line buffer memory 32 at the same transfer frequency; The video and audio signals @v1 to v4 are transferred to the laser modulation circuit 33 and the laser scanning system 2 in accordance with the video clocks C[ to C[4].

At this point, according to the transmission timing of each of the video clocks CL1 to CL4, the laser beam based on each of the video signals v1 to 4 is applied to each photosensitive drum 1 while absorbing variations in the optical magnification of each laser scanning system 2. irradiated with
On each photosensitive drum 1, a latent image corresponding to each video signal is formed with a substantially constant scanning range.

In this state, the latent image forming portions of each photosensitive drum 1 are aligned with each other in the scanning direction, so after the latent image on each photosensitive drum 1 is developed with toner, each toner image is transferred to one transfer sheet. When multiple transfer is performed on the image data 5, the width of each transferred image in the scanning direction becomes constant, and the multiple transfer images are transferred in a good condition without shifting in the scanning direction.

In the above embodiment, the oscillator 40 is one that generates a clock of a predetermined frequency, but the oscillator 40 is not limited to this. For example, as shown in FIG. By using a variable voltage oscillator 43 as an oscillator and making the reference voltage of this variable voltage oscillator 43 variable as appropriate with the voltage regulator 44, the task of setting the video clock for each laser scanning system 2 can be made similar to that of the embodiment. It's easier compared to

[Effects of the Invention] As explained above, according to the multiple transfer laser printer according to the present invention, the transmission frequency of the video signal is appropriately set according to the optical magnification of the laser scanning system, so that each photosensitive It becomes possible to match the real scan ranges of the body with each other. For this reason, the latent image forming portions on each photoreceptor are aligned in the scanning direction, eliminating mutual misalignment of multiple transfer images based on each latent image, and making it possible to obtain a good multiple transfer image.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing an embodiment of a multi-transfer type laser printer according to the present invention, FIG. 2 is a block diagram showing a control unit of the laser printer according to the embodiment, and FIG. 3 is a diagram showing the control system of the laser printer according to the embodiment. FIG. 4 is an explanatory diagram showing an example of means for setting the read timing of the line buffer memory. FIG. 4 is an explanatory diagram showing another example of the means for setting the read timing of the line buffer memory according to the embodiment. [Description of symbols] (CLl to C10)...Video clock (v, to v4)...Video signal (1)...Photosensitive drum (photosensitive member) (2)...Laser scanning system (4) ... Developing device (developing means) (5) ... Transfer paper (transfer medium) (6) ... Transfer device (transfer means) (31) ... Image processing device (32) ... Line buffer Memory (33)... Laser modulation circuit (40)... Oscillator (43)... Voltage variable oscillator Patent applicant Representative of Fuji Xerox Co., Ltd.
Patent attorney Tomohiro Nakamura (2 others) 31 Image error? Noshi f
ffffi Figure 3 Figure 4

Claims (1)

[Claims] In a multi-transfer type laser printer in which a plurality of laser scanning systems, photoreceptors, developing means, and transfer means are independently provided, and the toner images on each photoreceptor are superimposed and transferred onto one transfer medium, each laser scan The oscillation frequency of the video signal sent to the system is appropriately changed according to the optical magnification of each laser scanning system, and the effective scanning range of each laser scanning system with respect to each photoreceptor is set to be constant. Multi-transfer type laser printer.