JPS638664A - Laser beam printer - Google Patents

Abstract

PURPOSE:To obtain a clear color image free from registration shear by allowing a write control means to control image signal writing start synchronously with the initial image writing start signal outputted from a beam detector immediately after the end of counting of a prescribed time from the sending of a paper feed start signal by a counting means. CONSTITUTION:When a counter circuit 2 ends the counting of the prescribed time, a count-up signal UP is outputted to a J terminal of an FF 3. An image writing start signal BD1 outputted from a beam detector 36C is inputted to one input of an AND gate 4 every scanning of a laser beam LBP1, a pulse signal from the Q terminal of the FF 3 is inputted to the other terminal of the AND gate 4, and when AND operation of both the inputs is formed, an image writing timing signal HSYNC is inputted to an unshown printer control part. Consequently, influence to be exerted upon an image based upon the frequency variation or the like of an oscillator can be removed and the generation of registration shear can be prevented.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a photoreceptor that corresponds to each laser beam emitted from a plurality of laser units and an image memory that stores each image information to be written on each of these photoreceptors. The present invention relates to a laser beam printer having a laser beam printer.

[Conventional technology]

FIG. 4 is a sectional view illustrating the configuration of a four-drum laser beam printer, in which 21 is the printer main body, 22
is a paper feed cassette that stores recording paper 23. 24 is a paper feed roller, and the recording paper 2 stored in the paper feed cassette 22 is
3 to the position where the registration rollers 25 are placed. A laser unit 26C forms a latent image on the cyan photosensitive drum 27C in accordance with color image data. 26
M is a laser unit that forms a latent image on the cyan photosensitive drum 27M according to color image data. 26Y is a laser unit that forms a latent image on the cyan photosensitive drum 27Y according to color image data. 26BK is a laser unit that forms a latent image on the cyan photosensitive drum 27BK according to color image data. 28C, 28M, 2
8Y.

28BK has a toner hopper, cyan and magenta.

Filled with yellow and black toner. 29
A conveyor belt 30 conveys the recording paper 23. A fixing device 30 fixes the toner onto the recording paper 24 by applying heat and pressure to the recording paper 23 onto which the toner has been transferred. A paper discharge roller 31 discharges the recording paper 23 on which image formation has been completed to a paper discharge stacker 32 .

Note that the registration roller 25 is driven at a timing when the leading edge of the recording paper 23, which has been fed by the paper feeding roller 24 from the paper feeding cassette 22 and is stopped, coincides with the leading edge of the image formed on the photosensitive drum 27C. The operation of the registration roller 25 will be described below with reference to FIGS. 5 and 6.

Figure 5 shows the photosensitive drums 27C227M, 2 shown in Figure 4.
4 is a schematic diagram illustrating the relative relationship between 7Y and 27BK and the fed recording paper 23, and the same parts as in FIG. 4 are given the same reference numerals.

In this figure, t1 to t4 are the registration rollers 25
The recording paper 23 fed from the photosensitive drums 27C and 27M
, 27Y, and 27BK.

After the registration roller 25 starts driving, for example, A4
It is energized and rotates for a period of time to (see FIG. 6) long enough for the size of the recording paper 23 to pass through.

After a delay of time tl''ta from this start, the image signal VD is applied to each photosensitive drum 27C, 27M, 27Y, 27BK.
Start writing OI to VDO4 and register roller 2.
Write at the same time as the time to when 5 is driven.

FIG. 7 is a perspective view illustrating an image exposure operation in a four-drum laser beam printer, and the same parts as in FIG. 4 are given the same reference numerals.

In this figure, 31G is a semiconductor laser, and the image signal V
A laser beam LBI is generated according to the DOI (for cyan). 32C is a scanner motor that rotates a polygon mirror (rotating polygon mirror) 33C at a constant speed. 34C is an imaging lens that scans the photosensitive drum 27C with the deflected laser beam LBI. 35C is a mirror that receives the scanning laser beam LBI just before the image writing position in the direction of the arrow, and guides it to a beam detector 36C that generates an image writing start signal BDI. 31M is a semiconductor laser that receives the image signal VD.
A beam LB2 is generated according to O2 (for magenta). 32M is a scanner motor that rotates a polygon mirror (rotating polygon mirror) 33M at a constant speed. 34M is an imaging lens that scans the photosensitive drum 27M with the deflected laser beam LB2. 35M is a mirror that receives the scanning laser beam LB2 in the direction of the arrow immediately before the image writing position and guides it to a beam detector 36M that generates an image writing start signal BD2. 31Y is a semiconductor laser, and the image signal VD
A laser beam LB3 corresponding to O3 (for yellow) is generated. 32Y is a scanner motor that rotates a polygon mirror (rotating polygon mirror) 33Y at a constant speed. 34Y is an imaging lens that scans the photosensitive drum 27Y with the deflected laser beam LB3. 35Y is a mirror that receives the scanning laser beam LB3 in the direction of the arrow just before the image writing position and guides it to the beam detector 36Y that generates the image writing start signal BD3. 31BK is a semiconductor laser, and the image signal V
A laser beam LB4 corresponding to DO4 (for yellow) is generated.

32BK is a scanner motor that rotates a polygon mirror (rotating polygon mirror) 33BK at a constant speed. 34BK is an imaging lens that scans the photosensitive drum 27BK with the deflected laser beam LB4.

35BK is a mirror that scans the laser beam LB in the direction of the arrow.
4 immediately before the image writing position and guides it to a beam detector 368K that generates an image writing start signal BD4. Note that the photosensitive drums 27C, 27M, 27Y, and 27BK are arranged at regular intervals.

FIG. 8 is a timing chart explaining the scanning timing of the laser beam.

In this figure, BDI is an image writing start signal, and N
+1st image writing start signal BDI to each line (
This shows a state in which images corresponding to lines 1 to 3456 have been written.

The period 1+ (shown in FIG. 9) until the N image writing start signals BDI are sent out is given by the following equation (1), assuming that the period of the image writing start signal BDI is too.

tl=NXteo ・-(1) However, the rotation speed of one polygon mirror, for example, the polygon mirror 33C, is determined by the oscillator (crystal oscillator) of the driver circuit shown in FIG.
Determined by the frequency of X.

FIG. 10 is a driver circuit diagram of the scanner motor 32C shown in FIG. 7, and the same circuit as this circuit is provided in each of the scanner motors 32M, 32Y, and 32BK. Note that for the sake of explanation, the operation of i circuits will be explained.

In this figure, 41 is a driver circuit, and the zero roller 41a has a rotor 41a made of, for example, a permanent magnet, which rotates the polygon mirror 33C at a constant speed.
A constant angle, for example 135°, relative to the rotational angular position of 1a
It has Hall elements 42a and 42b arranged at . 43a to 43d are stators, the stator 43a,
When a current is applied to the coil 43d, the rotor 41
Stator 43b facing rotor 41a when stators 43a, 43d facing a become south poles and current is applied to the coils of stators 43b, 43c.

The coils are wound such that 43c is the north pole. A Hall IC 44 is disposed near the rotor 41a and feeds back a detected frequency signal FG to the control unit 45. The control unit 45 outputs a frequency signal FG and a signal C (not shown).
From the drive signal M sent out from the PU, the stator 43a~
PLL control unit 45a that controls the current supplied to 43d
, a current amplifier 45b, and a current limiter circuit 45c. Note that the Hall elements 42a and 42b are connected to the rotor 41.
When the N pole of a approaches, one side outputs an electromotive force of rOJ, and the + side outputs an electromotive force of "1". Further, when the S pole of the roller 41a approaches the Hall elements 42a and 42b, one side outputs an electromotive force of "1", and the + side outputs an electromotive force of "0".

[Problem that the invention seeks to solve]

However, the period too of the image writing start signal BDI also fluctuates due to the frequency accuracy and fluctuations of one oscillator X, for example, 0.1
% fluctuation occurs, the period t1 until the N image writing start signals BDI shown in FIG. 9 are sent out is given by tll shown in the following equation (2).

t++=0, IX-XNXtso
(2) For this reason, the recording paper 23 fed from the registration roller 25 is transferred to the photosensitive drum 2 after the elapse of time t1.
When reaching 7C, a deviation of 0.1% occurs with respect to the leading edge of the image.

Converting this into a distance, for example, if the distance between the registration roller 25 and the photosensitive drum 27C is 200 mm, there will be a deviation of 0.2 mm (200 JLm) at the tip, and the color shift will be extremely noticeable and the quality of one image will be significantly impaired. There was a problem. The further away from the registration rollers 25, the more strongly this is affected. Furthermore, if we consider that the frequencies of the oscillators X provided in each driver circuit do not completely match, the effect is doubled.

This invention was made in order to solve the above-mentioned problems, and after a certain period of time has elapsed since the registration roller started driving, an image signal is written in synchronization with the latest image writing start signal. An object of the present invention is to obtain a laser beam printer capable of obtaining clear color images without deviation.

[Means for solving problems]

The laser beam printer according to the present invention includes a timer that counts a predetermined time from a position signal of a recording paper, and an image writing start signal that is outputted from a beam detector immediately after the timer finishes counting. A write control means for controlling the start of writing of a signal is provided.

[Effect]

In this invention, when the timer finishes counting the predetermined time after the paper feeding start signal is sent, the writing control means starts the image writing control means in synchronization with the first image writing start signal outputted from the beam detector immediately after that. Controls the start of signal writing.

〔Example〕

FIG. 1 is a block diagram illustrating the control configuration of a laser beam printer showing an embodiment of the present invention. Reference numeral 1 denotes a CPU that also serves as a writing control means of the present invention, and controls the print sequence in general. . 2 is a counter circuit,
Counting of a predetermined time pp is started in synchronization with a registration signal ST sent from the CPU 1 to a drive means (driver circuit, motor, etc. not shown) that drives the registration roller 25. 3 is a JK type rough flip-flop FF), and when the counter circuit 2 finishes counting for a predetermined time, a count up signal UP is output to the J terminal of FF3. 4 is an AND gate, and to one side of the AND gate 4, an image writing start signal BD1 output from, for example, the beam detector 36C is inputted every scan of the laser beam LBPI;
A pulse signal from the Q terminal of FF3 is input, and when the AND of both is established, one image write timing signal H is generated.
3YNC is input to a printer control section (not shown). Note that a circuit having the same circuit as that in FIG. 1 is provided for each image signal.

Next, the operation shown in FIG. 1 will be explained with reference to FIG.

FIG. 2 is a timing chart illustrating the signal sending timing of each part in FIG. 1. Components that are the same as those in FIG. 1 are given the same reference numerals.

As can be seen from this figure, the image writing start signal BDI
At any timing when the register signal ST is sent to the AND gate 4, the register signal ST is sent from the CPU to the register roller 25.
When the counter circuit 2 starts counting for a preset predetermined time pp, the counter circuit 2 outputs a count up signal UP to the J terminal of the FF 3 after counting is completed. At this time, C is connected to the terminal of FF3.
When a pulse signal is being sent from the PUI, the pulse signal is input to the AND gate 4 from the Q terminal. Immediately after this pulse signal is sent to the AND gate 4, the image writing start signal BDI is input to the AND gate 4.
The AND gate 4 opens, an image writing timing signal H3YNC in the main scanning direction is output to a printer control section (not shown), and processing of image signals input from, for example, external geometry is started. Therefore, it is possible to eliminate the influence on the image due to frequency fluctuations of the oscillator X, etc., and prevent registration roller deviation.

FIG. 3 is a block diagram illustrating the configuration of a laser beam printer according to another embodiment of the present invention, and the same parts as in FIG. 4 are given the same reference numerals.

In this figure, reference numerals 11 to 14 are image memories, which include a cyan image signal 11C, a magenta image signal 12M, a yellow image signal 13Y, which are input from an external device (not shown).
A black image signal 14BK is stored. HSYNC
-C, HSYNC-M, HSYNC-Y, HSYNC-
BK is an image writing timing signal.

As can be seen from this figure, in a device in which image signals 11C, 12M, 13Y, and 14BK for each color are stored in one image memory 11 to 14, an image write timing signal H3YNC-C corresponding to the above-mentioned image write timing signal H3YNC, HSYNC-M, HSYNC-Y,
The image memories 11 to 14 are accessed in synchronization with HSYNC-BK to generate each image signal IIC, 12M, and 13Y.

If 14BK processing is started, the same effect as above can be expected.

Furthermore, in the above embodiment, time measurement is started using the paper feed start signal, but a means for detecting the leading edge position of the recording paper is provided upstream of the first photosensitive drum in the recording paper feeding path, and the output thereof is It may also be used to start timing.

〔Effect of the invention〕

As explained above, the present invention includes a timer that counts a predetermined time from a position signal of a recording paper, and an image writing start signal that is synchronized with the latest image writing start signal that is output from a beam detector immediately after the timer finishes counting. A writing control means for controlling the start of writing of the signal is provided, so that even if the frequency of the oscillator that determines the cycle of the image writing start signal changes, the leading edge of the image on the conveyed recording paper can be adjusted to the image formed on each photosensitive drum. It has the advantage of being able to be accurately superimposed on the tip and forming a clear color image without color shift.

[Brief explanation of the drawing]

FIG. 1 is a block diagram explaining the control configuration of a laser beam printer showing an embodiment of the present invention, FIG. 2 is a timing chart explaining the signal sending timing of each part in FIG. 1, and FIG. A block diagram illustrating the configuration of a laser beam printer illustrating another embodiment, FIG.
FIG. 1 is a cross-sectional view illustrating the configuration of a drum-type laser beam printer. Fig. 5 is a schematic diagram explaining the relative relationship between each photosensitive drum shown in Fig. 4 and the fed recording paper, and Fig. 6 explains the timing of writing images on each photosensitive drum shown in Fig. 4. 7 is a perspective view explaining the image exposure operation in a four-drum laser beam printer, FIG. 8 is a timing chart explaining the laser beam scanning timing, and FIG. 9 is the paper feeding or image forming timing. FIG. 10 is a timing chart explaining the time taken to complete the process, and is a driver circuit diagram of the scanner motor shown in FIG. 7. In the figure, 1 is a CPU, 2 is a counter circuit, 3 is an FF, 4 is an AND gate, 11 to 14 are image memories, and 25 is a registration roller. Figure 1 Resistance *ST Figure 2 Figure 3 Figure 5 Figure 6 Figure 8 No. D1

Claims (1)

[Claims] In a laser beam printer each having a beam detector that receives each laser beam emitted from a plurality of laser units in an image writing straight line and sends out an image writing start signal, a timer counts a predetermined time from a position signal of a recording paper. and a writing control means for controlling the start of writing of an image signal in synchronization with the latest image writing start signal outputted from the beam detector immediately after the counting of the timer ends. printer.