JPH0423265B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a color image recording apparatus, and more particularly to a color image recording apparatus that sequentially transfers and records a color image formed based on color image information onto a conveyed recording paper for each color.

As a method for recording color images, color image information is output using an electronic copying device (laser beam printer) that includes a plurality of photosensitive drums arranged side by side, and the color images formed by this electronic copying device are sequentially printed in different colors. Conventionally, methods have been proposed in which images are recorded in overlapping colors.

Figure 1 is an explanatory diagram of such a recording method.
1d is a scanning optical system, which extracts required image information from an image memory (not shown) as a light beam (laser beam), and this light beam is divided into cyan C, magenta M, yellow Y,
Photosensitive drum 2 arranged in parallel corresponding to black Bl
It is configured to form images on a to 2d. Developing devices 3a to 3 are located near the photosensitive drums 2a to 2d.
3d, and each of the photosensitive drums 2a to 2d is arranged on the conveyor belt 7 side for conveying the recording paper.
Chargers 4a to 4d are disposed to face each other.
To explain the operation of the above configuration, the modulated light beams output from the scanning optical systems 1a to 1d form optical images on the respective photosensitive drums 2a to 2d,
Thereafter, this formed image becomes an electrostatic latent image through an electrophotographic process, which is developed by developing devices 3a to 3d, and each color is sequentially transferred to the recording paper held on the conveying belt 7 by chargers 4a to 4d. A color image is formed.

Figure 2 shows the four scanning optical systems 1 shown in Figure 1.
1 is a schematic perspective view showing details of one of the
The light beam modulated by the semiconductor laser 11 is collimated by the collimating lens 10 and subjected to optical deflection by the rotating polygon mirror 12. The deflected light beam forms an image on the photosensitive drum 2 by an imaging lens 13 called a θ lens, and beam scanning is performed. During this beam scanning, the tip of the one-line scanning light beam is reflected by a mirror 14 and guided to a detector 15 . As is well known, the detection signal from the detector 15 is used as an ID (index) of the image signal or a cue signal, and is used as an output timing control signal.

Conventional color image recording is performed using the method described above, but when images corresponding to each color are sequentially superimposed on the conveyed recording paper, the output timing of the image signal depends on the position of the recording paper. Regardless, it is set in advance, so due to misalignment of the recording paper caused by deviation of the conveyance belt, etc.
The overlapping images of each color transferred to the recording paper are misaligned. That is, there is a drawback that a high-quality color image cannot be obtained due to failure of registration.

Therefore, when recording an image of the first color, a mark for alignment is recorded at a predetermined position on the recording paper, and by detecting the mark, the position of the recording paper is detected, and based on that, the second color image is recorded. Japanese Patent Laid-Open Publication No. 153634/1983 discloses a method in which images of first and second colors are recorded at predetermined positions on recording paper by recording an image of a color of .

However, since the method disclosed in JP-A-54-153634 records marks for positioning on the recording paper, there are defects and marks that are recorded on the recording paper such that redundant information is recorded on the recording paper. The drawback was that the desired image could not be recorded. Furthermore, there is a possibility that an image near the mark may be detected as a mark, and as a result, accurate positioning on the recording paper may not be possible.

The present invention eliminates the above-mentioned drawbacks of the conventional technology.The present invention directly optically detects the recording medium being conveyed and, based on the detection result, adjusts the output start timing of the laser beam for image formation vertically and horizontally. By controlling the color images in the vertical and horizontal directions, it is possible to form high-quality color images in which color images are accurately superimposed at predetermined positions in the vertical and horizontal directions on the recording medium without recording unnecessary marks on the recording medium. The purpose is to provide a color image recording device that can.

That is, the present invention comprises: an image forming means having a plurality of image forming stations that modulate a laser beam based on color image information and form an image on a photosensitive drum for a plurality of color image information; and conveying the medium to the plurality of image forming stations. a moving means for moving with a recording medium placed thereon; and a recording device for sequentially transferring and recording images of each color formed by a plurality of image forming means stations of the image forming means onto a recording medium conveyed by the moving means. and detecting directly and optically the recording medium placed on the moving means and conveyed, thereby determining the timing of passage of the recording medium at a predetermined position with respect to the moving direction and the amount of lateral deviation in a direction substantially perpendicular to the moving direction. The present invention is characterized by comprising a detection means for detecting the laser beam, and a control means for controlling the output start timing of the laser beam in the vertical and horizontal directions based on the passage timing and the amount of lateral deviation detected by the detection means.

An embodiment of the present invention will be described below with reference to the attached drawings. FIG. 3 is a schematic perspective view showing a paper position detection system employed in the color image recording apparatus of the present invention. Before explaining this paper position detection system, the reason why the position of the transported paper shifts will be explained. The recording paper 20 is held on the conveyor belt 7 and is attached to each of the photosensitive drums 2a to 2a shown in FIG.
2d, and undergoes a copying process of electrostatic latent image, development, and transfer by a charger as shown in FIG. In this case, in order to facilitate corona transfer by the chargers 4a to 4d shown in FIG. 1, the belt 7 is made of nylon or polyethylene woven into a mesh shape. Therefore, the recording paper 20 is deformed by the belt 7 and easily changes its position. Therefore, as described above, in order to accurately superimpose each color, it is important to detect the position of the recording paper and adjust the output timing of image information.

For this purpose, a light source 22 is disposed on the conveyor belt 7 as a position detection system for the recording paper 20 conveyed by the conveyor belt 7, as shown in FIG. An optical system 23 and a line sensor 24 such as a CCD are arranged to receive light from the sensor. FIG. 4 shows details of this paper position detection system. The same reference numerals as in FIG. 3 indicate the same parts, and an image of the recording paper 20 illuminated by a light source 22 such as a lamp is formed on a line sensor 24 by an optical system 23 composed of a self-occurring lens array or the like. be done. Assuming that the recording paper 20 is now being fed in the direction of the arrow, the output signal from the line sensor 24 will have a waveform as shown in FIG.

Now, if the repetition frequency of one line of the line sensor 24 is _L , the period of one line △T ₁ is △T ₁ =
1/ _L sec. When the image of the recording paper 20 does not reach the line sensor 24, repetitive pulses A, B, and C having a predetermined duty ratio of, for example, about 80% are output within the line period _ΔT1 described above.
In this case, the rising edge of each pulse, from “L” to “H”
The number of bits maintained at "H" from the time when the line sensor changes to "H" is counted as will be described later, and if this counted value is greater than a predetermined value, it is determined that the image of the recording paper 20 has not reached the line sensor. On the other hand, when the leading edge of the recording paper 20 reaches the line sensor 24, it changes from "H" to "L" after a predetermined period of time ΔT ₂ and ΔT ₃ , respectively, from the pulse rising point as described above, as in the cases D and E of the figure. fall In this case, the number of bits maintained at "H" is counted in the same way, and if the counted value does not exceed a predetermined value, the above-mentioned pulse rising time is recognized as the vertical synchronization signal, and the number of bits from the first bit is recorded. The amount of lateral displacement of the recording paper 20 can be determined by detecting whether the recording paper 20 becomes "L" when it comes to the shadow part of the paper.

Next, the details of detecting the amount of lateral shift will be explained. Now, when the optical system 23 is an optical system that creates a same-size erect image, the paper position is given by Y=P×N, where Y is measured from the tip of the line sensor.

However, P is the pitch of the line sensor, and N is “H”.
This is the number of bits of the output line sensor.

If the optical system is composed of a normal lens with a magnification β (β<0), the direction of the line sensor must be reversed because it is an inverted image. Therefore, in this case, by reversing the reading direction of the line sensor and determining Y=P×N×β ⁻¹ , the amount of lateral deviation of the paper can be accurately determined. Based on the above detected amount, the output timing of the image signal is adjusted by the following method.

The sixth figure is a block diagram of a circuit for adjusting the output timing of this image signal. First, the vertical synchronizing signal obtained by signal processing from the line sensor 24 is delayed by a predetermined number of counts by the counter 31.
It becomes an image synchronization signal in the vertical direction. On the other hand, the horizontal position correction signal 33 obtained by signal processing from the line sensor 24 is obtained by setting a value proportional to the above-mentioned horizontal shift amount, Y, in the counter 35, and using the horizontal synchronization signal 34 shown in FIG. 2 as a reference. The subtraction count is started, and when the count reaches 0, the above-mentioned image synchronization signal is output.

The repetition frequency of such a line sensor 24
If _L is synchronized with the line frequency to the optical scanning of the laser beam printer, it is possible to correct the lateral deviation line by line, but if the above-mentioned processing takes time, a method of reading each line of recording may be used.

Next, a description will be given of how to provide a vertical synchronization signal for an image signal in this embodiment. Currently, the recording laser beam printer has a paper feed speed of 30 mm/sec.
Assuming that it is written at a pitch of 50 μm, the time required for one line △T ₀ is △T ₀ =50×10 ^-3 /30≒1.7 msec. Therefore, when synchronized with the reading cycle of one line by the line sensor, one cycle of the line sensor △T ₁ is also △T ₁ = 1.7 msec, and if a 512-bit CCD sensor 3 is used, the driving clock for each bit is Frequency ₁ is ₁ > 512/1.7×10 ^-3 301KHz. FIG. 7 is a circuit block diagram for obtaining the above-mentioned vertical synchronization signal, and shows the line sensor 2.
The output signal from 4 is read out bit by bit in synchronization with the read clock ₁ from the clock generator 36, and is binarized by the binarization circuit 40. Next, only "H" level outputs from the binarization circuit 40 are counted. The final count from the counter 41 is compared with a set value by a comparator 42, and if it is smaller than a predetermined number, it is assumed that the recording paper is coming and a vertical synchronizing signal is generated. The predetermined number required for the comparison by the comparator 42 described above may be a value smaller than 512, but it is desirable to give it experimentally in order to increase the accuracy of the stroke of the horizontal displacement of the paper and the authenticity of the data. Although the vertical synchronization signal can be obtained as described above, the horizontal position correction signal may be used by using the output of the counter 41 as it is or by multiplying it by a constant.

In this way, in one embodiment of the present invention, the output timing of the image synchronization signal is controlled based on the detection signal from the recording paper position detection means, and the vertical synchronization signal and horizontal synchronization signal for this image signal are generated. , color image registration can be performed with high precision regardless of the positional deviation of the recording paper.

In the above-mentioned embodiment, the skew (tilt) of the recording paper was not mentioned in relation to the positional shift of the recording paper, but the amount of lateral shift from the line sensor is expressed as Y after a certain time Δt (here Δt is the same recording From the measured Y', the skew angle θ (rod) is θ=(Y'-Y)/ν·Δt. However, ν is a value determined from the paper feeding speed. Such skewing of paper can be corrected by software by appropriately changing the way the scanning optical system retrieves image information from the image memory contents.

As explained above, the color image recording apparatus of the present invention directly optically detects the conveyed recording medium when sequentially transferring and recording a color image for each color onto the conveyed recording medium. Since alignment is performed, there is no need to record extra marks on the recording medium. This also makes it possible to record a desired image in a wide area of the recording medium. Furthermore,
The present invention detects the passing timing of a predetermined position with respect to the moving direction of the recording medium and the amount of lateral shift in a direction substantially orthogonal to the moving direction, and based on the detection results, output timing of a laser beam for image formation is adjusted in vertical and horizontal directions. Since it is controlled to the vertical direction of the recording medium,
A color image can be reliably recorded at a predetermined position in the horizontal direction.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram of a color image forming method on recording paper via a plurality of photosensitive drums by a laser beam printer, Fig. 2 is a schematic perspective view of a scanning system adopted in the method shown in Fig. 1, and Fig. 3 is a schematic perspective view of a scanning system adopted in the method shown in Fig. 1. The figure is a schematic perspective view of a paper position detection system employed in a color image recording apparatus according to the present invention, FIG. 4 is a perspective view showing details of the paper position detection system shown in FIG. 3, and FIG. 3 and 4 are waveform diagrams of output signals from the line sensor, FIG. 6 is a block diagram of the image signal output timing adjustment circuit adopted in the present invention, and FIG.
The figure is a block diagram of a vertical synchronization signal generation circuit employed in the present invention. 1... Scanning optical system, 2... Photosensitive drum, 3...
Developing device, 4... Charger, 7... Conveying belt, 2
0...Recording paper, 22...Light source, 23...Optical system,
24...Line sensor.

Claims (1)

[Scope of Claims] 1. An image forming means having a plurality of color image information, including an image forming station that modulates a laser beam based on color image information and forms an image on a photosensitive drum, and a recording medium for the plurality of image forming stations. a moving means for moving a recording medium on top of the recording medium to convey the image, and sequentially transferring and recording images of each color formed by a plurality of image forming stations of the image forming means onto the recording medium conveyed by the moving means. By directly optically detecting the recording means and the recording medium placed on and conveyed by the moving means, the passage timing and the amount of lateral deviation in a direction substantially perpendicular to the moving direction of the recording medium are determined at a predetermined position with respect to the moving direction of the recording medium. A color image recording device comprising: a detection means for detecting; and a control means for controlling output start timing of the laser beam in vertical and horizontal directions based on the passage timing and the amount of lateral shift detected by the detection means. .