JPH02118588A - Laser bean printer - Google Patents

Abstract

PURPOSE:To record a multicolor image by simple constitution with high accuracy without any color shift by detecting the position of a position detection area scanning beam by a beam position detector and starting recording operation according to its detection signal. CONSTITUTION:A photoconductive drum 1 is charged electrostatically by an electrostatic charger 2, a 1st beam 5 is scanned on the surface of a drum 1 axially to form a 1st latent image, and a 1st developing device 8 develops the image with a 1st color. Then, a latent image is formed with a 2nd beam 6 and developed by a 2nd developing device 9 with a 2nd color, and a latent image formed with a 3rd beam 7 is developed similarly with a 3rd color. For example, a beam from a semiconductor laser 18 is scanned on the drum 1 though a lens 19, a mirror 3, and a lens 4 and the position detection area scan ning beam 15 is projected on the beam position detector 17 through a mirror 16 to detect the beam position. Then the recording operation is started at a specific time later according to the detection signal.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a laser beam printer using electrophotography.

Laser beam printers, which combine electrophotography and laser beam scanning technology, can print complex figures, characters, and formats at high speed, and have become widely used as printer output devices.

In such laser beam printers, there is a demand for printing characters, formats, and graphics in two to three colors.

Conventional laser beam printers that produce prints in multiple colors combine a laser beam modulated with text information and a laser beam modulated with format information into one laser beam, as described in Japanese Patent Laid-Open No. 55-84664. There is one in which two charge latent images are formed on a photoconductive drum by deflection scanning using a rotating mirror, and these are developed with different color toners.

However, although this conventional device (the above-mentioned patent publication) specifically refers to a two-color electrophotographic process, it proposes a specific means for accurately aligning two-color toner images in the horizontal and vertical directions. I haven't. In particular, when a plurality of laser beams are deflected by a single rotating mirror and charge latent images are formed at different positions in the same area on the photoconductive drum while the beam position is detected by a beam start point detector, the structure is It is difficult to record images without color shift unless the processing precision and assembly precision of parts are maintained at a very high level, which is impractical.

It is an object of the present invention to solve the problems of the conventional apparatus and to make it possible to relatively easily record multicolor images with no color shift and high precision with a simple configuration.

In order to achieve this object, the present invention develops a charge latent image formed by scanning and exposing a uniformly charged photoconductive drum with a laser beam multiple times to obtain a toner image. forming a multi-color toner image on a photoconductive drum;
A laser beam printer that transfers this toner image onto recording paper includes a scanning mirror that deflects and scans a plurality of laser beams corresponding to the plurality of colors, and one of the plurality of laser beams.
One laser beam position detector detects the deflection position of the laser beam of the book, and the output signal of this laser beam position detector is delayed in correspondence with each of the plurality of laser beams, and each laser beam is connected to the photoconductive drum. A plurality of horizontal delay circuits generate a horizontal recording start signal for each color synchronized with the time when deflection is performed to a predetermined recording start position in the horizontal scanning direction parallel to the axis of the A plurality of vertical delay circuits generate a vertical recording start signal for each color to align the recording start position in the rotational direction of the photoconductive drum, and input the horizontal recording start signal and vertical recording start signal for each color to generate a vertical recording start signal for each color. The present invention is characterized in that it is provided with a plurality of recording start timing signal generators that determine the reading start timing of each recorded information, and a means for modulating a laser diode with the read recorded information signal.

According to such a configuration, the output signal from one laser beam position detector and the recording command signal are delayed in correspondence with the horizontal and vertical scanning exposure positions of the laser beam of each color, and are transmitted for each laser beam of each color. A horizontal recording start signal and a vertical recording start signal can be obtained,
A recording start timing signal for each color is obtained from the horizontal recording start signal and vertical recording start signal for each color, and a recording information signal can be generated at a timing corresponding to an accurate recording position (scanning exposure position). Therefore, high-precision multicolor image recording without color shift can be achieved relatively easily by electrical signal processing with a simple configuration.

FIG. 1 explains the configuration of the apparatus of the present invention. The surface of the photoconductive drum 1 rotating in the direction of arrow A is uniformly charged by a charger 2, and then the drum 1 is charged with a first beam 5, which is a laser beam, by a rotating main scanning mirror 3 and a scanning lens 4. A first charge latent image is created by main scanning the surface in the axial direction.

At this time, a semiconductor laser (not shown) is used as the laser,
It is directly modulated by the information signal to be recorded. Next, the first developing device 8 develops this first charge latent image in a first color.

Next, the second beam 6 is main scanned to create a second charge latent image,
A second developing device 9 develops the image in a second color. Furthermore, the third beam 7 performs main scanning, and the third developing device 1° develops the image in a third color. The three color toner images thus created are simultaneously transferred onto the recording paper 11 under the transfer device 12. Thereafter, the toner remaining on the surface of the photoconductive drum 1 is removed by a cleaner 13, and the drum is used again. In this way, three-color images are continuously transferred to the recording paper 11, and finally the toner image is fixed on the paper 11 and used.

In such a configuration, three scanning beams are projected from three semiconductor lasers (not shown) onto substantially the same surface of the rotating main scanning mirror 3 at different angles, and are deflected and scanned at the same angular velocity. After passing through the reflection mirror, it is divided into three pieces before reaching the photoconductive drum 1. Therefore, only one expensive rotating main scanning mirror 3 and one scanning lens 4 are required, and it is preferable to use a small and inexpensive semiconductor laser as the laser.

FIG. 2 shows a method of detecting the position of the scanning beam. In the present invention, the beam position may be detected at any one of the three beams, but for convenience of explanation, the position of the scanning beam can be detected at any one position. The case where this is done will be explained below.

The beam from the semiconductor laser 18 passes through a condensing lens 19, a rotating mirror 3, and a scanning lens 4 (this may be omitted depending on the case), and then main scans the photoconductive drum l in the direction of the arrow. 14 is a recording area scanning beam, and 15 is a position detection area scanning beam, which are distinguished by the deflection area of one scanning beam. The beam position of the scanning beam 15 is detected by a beam position detector 17 after passing through a mirror 16, and recording is started t4 seconds after this detection signal is used as a reference.

In order to record images of two or three colors using the configuration shown in FIG. 1, it is necessary that the images of each color be recorded correctly at desired positions. To do this, it is necessary to correctly control the horizontal (main scanning) and vertical (sub scanning) positions of each beam.
It is necessary to adjust t4 in the figure for each beam so that the recording start position of each beam in the horizontal direction on the surface of the photoconductive drum is almost the same. Time t1. until the recording position by the first beam 5 or the second beam 6 on the surface reaches the recording position of the next beam. It is necessary to adjust the overlapping position of the plurality of images by adjusting tt and setting the main scanning start position at almost the same point on the drum. +1! +1. The recording start time of the first beam must be controlled so that the subsequent position of the drum surface coincides with a fixed position of the recording paper 11 (the position of each member of the paper).

The above is the same whether there are two colors or more, but below, the case of three colors will be explained.

FIG. 3 shows an embodiment of adjusting the beam position according to the present invention.

First, the recording start time of horizontal scanning of the beam is controlled as follows. The signal BD caused by the beam being detected by the beam position datater 17 is sent to a delay circuit (timer).
H+, Hg, Hs, first, second . third beam 5,
6. Adjust the horizontal recording start time in 7. On the other hand, the recording start time in the vertical direction is determined by delay circuits V, , V, , V, which transmit a print command signal TOP, which is one of the signals controlling the entire printer, and which means the beginning of the recording page to each beam. The page recording start position is controlled according to the leading position in the recorder. The delay circuit v1 controls the position of the image and the recording paper 11 by the scanning of the first beam 5, and the delay circuits V, , V, control the position of the recording paper 11 by the scanning of the first beam 5. The positional relationship between the image scanned by the third beam 6.7 and the image scanned by the first beam 5 is controlled. In this way, the first. Second. When the third vertical recording start position is determined, the BD signal detected as being scanned in the horizontal direction is extracted from the signal, and the horizontal recording start timing signal generator 711'rz.

A recording start timing signal is generated at T.

Recording start timing signal generator 'rt,'rg,'rs
A timing signal commanding the start of recording for each of the beams is sent from the recording information source DATA and sent to the buffer memories M*, M! , determines the timing to read out the information stored in M s. The memory M is activated at the timing from the recording start timing signal generator 'r+, Tg, 'rs.
, , Mt, the recording information signals sent out from M2 are transmitted through amplifiers DA, DA! , DA3, the diode laser DL, is shaped and amplified for diode laser modulation.

DLs, modulate the DLs.

By controlling the timing of modulating each diode laser as described above, each color image can be recorded at the correct position. The accuracy of the 1/1 adjustment varies depending on the recorded image, but is approximately 1/4 to 10 dots of the recorded image.

FIG. 4 shows the signal relationships in the control method described in FIG. 3, and such relationships are adjusted and controlled for each beam.

The delay circuit V generates a signal V delayed by tv in order to determine the vertical position of the print start command signal TOP, and
After a delay time t4 of the next beam position detector signal BD by the pulse delay circuit H6, the timing signal generator TI issues a recording start timing signal to start recording. ■D represents a laser modulation signal.

FIG. 5 shows the timing of the operation of the developing devices, which is one way to prevent toners of other colors from getting mixed into each developing device when operating a color laser beam printer configured as shown in FIG. 1. This is what is shown. Charging CH of charger 2
The operation of the first developing device 8 is started after a period of time t, during which the charged drum at least passes through the first developing device. Similarly, the second developing device 9 is operated after t, and the third developing device 10 is operated after t. In this case, if t is passed through the third developing device 10, then tb ”t
It is also possible to set y=O.

Next, a case will be described in which the colors to be printed are appropriately selected and changed using the color printing laser beam printer according to the present invention.

(1) If you want to change each of the three colors: change the data information for modulating the first to third beams.

(2) When combining two colors: The operation of the developer and the operation of each beam are selected and the data information to be modulated is replaced. However, at this time, the laser that operates the beam position detector 17 needs to emit light for at least the period necessary to operate the beam position detector 17, even if it is not modulated by the recording signal.

(3) In the case of one color: Put all the recording information into the first beam (other beams are not operated) and select the operation of the developer, or modulate the beam corresponding to each color with the recording information. In the latter case, the laser operating the beam position detector 17 is operated at least in the same manner as in (2).

As described above, colors can be changed or combined, but if you want to print in a color other than the preset color plate, make the developer unit removable and replace it. More demands can be met by automatically or manually replacing and setting developing devices for other colors built into the apparatus.

As described above, according to the present invention, the output signal from one laser beam position detector and the recording command signal are respectively delayed in correspondence with the horizontal and vertical scanning exposure positions of the laser beam of each color, and the laser beam of each color is A horizontal recording start signal and a vertical recording start signal can be obtained for each color, and a recording start timing signal for each color can be obtained from the horizontal recording start signal and vertical recording start signal for each color to determine the accurate recording position ( Since the recording information signal can be generated at a timing corresponding to the scanning exposure position), highly accurate multicolor image recording without color shift can be achieved relatively easily by electric signal processing with a simple configuration.

[Brief explanation of drawings]

Fig. 1 is a configuration diagram of a color printing laser beam printer to which the present invention is applied, Fig. 2 is a detection mechanism diagram for detecting the laser beam position, Fig. 3 is a beam control circuit diagram of the laser beam according to the present invention, and Fig. 4 is the beam modulation control time chart, fifth
The figure is a time chart for operating the developing device. 1...Photoconductive drum, 3...Rotating main scanning mirror 5...First beam, 6...Second beam, 7...・3rd beam, 8...
First developing device, 9...Second developing device, 10...
...Third developer, 11...Recording paper, 17...
・・・Beam position detector, H, -H, ・・・・・・
Delay circuit, ■, ~v3...Delay circuit. Figure 'l Figure Figure

Claims (1)

[Scope of Claims] 1. The step of developing a charged latent image formed by scanning and exposing a uniformly charged photoconductive drum with a laser beam to obtain a toner image is carried out multiple times with different toner colors. A laser beam printer that forms toner images of a plurality of colors on the photoconductive drum and transfers the toner images to a recording sheet, comprising: a scanning mirror that differentially scans a plurality of laser beams corresponding to the plurality of colors; one laser beam position detector for detecting the deflection position of one of the plurality of laser beams; and the output signal of this laser beam position detector is delayed in correspondence with each of the plurality of laser beams, and each a plurality of horizontal delay circuits that generate a horizontal recording start signal for each color in synchronization with the time when the laser beam is deflected to a predetermined recording start position in a horizontal scanning direction parallel to the axis of the photoconductive drum; and a recording command signal. a plurality of vertical delay circuits that generate a vertical recording start signal for each color to delay the recording start position in the photoconductive drum rotation direction for each color, and the horizontal recording start signal and vertical recording start for each color. A plurality of recording start timing signal generators inputting signals to determine the readout start timing of recorded information for each color; and means for modulating a laser diode with the read recorded information signal. Laser beam printer.