JPH02116561A - Scanning position detector of image forming device - Google Patents

Abstract

PURPOSE:To obtain a high quality image which is always free from color dislocation and wandering of a fine line by a comparatively simple structure by a method wherein an optimum phase pulse signal corresponding to a state of light beams is selected as an image scan synchronous clock signal by a clock selective means. CONSTITUTION:A light intensity detector 27 is arranged to a main scan start point side outside a main scan area of scan beams, which detects a scan beam prior to each main scanning. The detector 27 emits a synchronous detection signal SPD as its output and applies it to a latch circuit 24. A delay circuit 23 has a same frequency as that of an image scan clock, and emits pulse signals of which phases are successively shifted. A selective circuit 25 judges a state of light beams based on intensity signals po-pm of the light beams inputted from a light intensity measuring circuit 21 and selects a corresponding optimum pulse signal as an image scan synchronous clock signal to be outputted.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a scanning position detection device for an image forming apparatus, and more particularly to a scanning position detection device for an image forming apparatus that compensates for variations in scanning position due to changes in the state of a light beam.

[Conventional technology]

For example, in an image forming apparatus such as a laser printer, the scanning start position of a light beam modulated by an image signal on the scanned surface,
That is, it is necessary to keep the writing start position constant in order to obtain a high quality image.

FIG. 12 is a perspective view illustrating the setting of the writing start position in the radar printer.

As shown in the figure, in order to keep the writing position constant for each line (main scanning direction), the laser beam from the laser diode 17 is transmitted to the polygon mirror 18 in the pre-scanning stage of image recording.
, a beam detection means 19 (for example, a PIN photodiode) is provided to detect arrival at a specific position via the lens 20 and mirror 12 and form a detection signal, and the output signal from the beam detection means 19 is used as a reference. A method is used in which after a predetermined period of time (counted by counting a predetermined number of T@image clocks) has elapsed, recording of an image with a laser beam onto the photosensitive drum 8 is started.

With a PIN photodiode as beam detection means 19,
The laser light is converted into an electrical signal, and the waveform is shaped by a waveform shaping circuit (not shown) to obtain a rectangular wave that rises and falls in accordance with a predetermined darkness value.

FIGS. 13(a) and 13(b) are time charts showing the relationship between the output waveform A of the PIN photodiode, the output waveform B of the waveform shaping circuit, and the threshold value C. FIG.

The figure (a) shows when the intensity of the laser beam is weak, and the figure (b) shows (
This is a timing chart of portions A and B when the intensity of the laser beam is stronger than in (a), and in (b) the pulse widths of both A and B are wider than in (a).

For this reason, considering the case where the counter starts counting at the rising edge of signal B, when the intensity of the laser beam is strong (B in (b)), when the intensity of the laser beam is weak (B in (a)) ) The printing start timing is earlier by a considerable amount of time than Δ.

Therefore, when the intensity of the laser beam is strong and when it is weak,
The writing start position will shift, and the quality of the image will deteriorate.

In order to compensate for the shift in the writing start position due to such changes in the intensity of the laser beam, an optical scanning position detection device configured using a monostable multivibrator was proposed in Japanese Patent Laid-Open No. 58-49962. There is.

In this proposed method, a monostable multivibrator is provided at the output stage of the optical scanning position detection device, and the inverted signal of the photodetection signal of the photodetector is used as the bias voltage of this monostable multivibrator. Therefore, the pulse width of the output signal of the monostable multi-bi break becomes narrower as the laser light intensity decreases, and widens as the laser light intensity increases. By synchronizing the write start position at the falling edge, it is possible to compensate for the shift in the write start position.

[Problem to be solved by the invention]

In the method proposed above, the design of the circuit for changing the pulse width of the output signal of the monostable multi-bibreak within a desired range in response to changes in laser light intensity is relatively complicated, and furthermore, Changes in set values due to changes in set values or changes over time are also relatively likely to occur.

Also, for example, yellow (like a laser color printer)
When attempting to compensate the writing position using the method proposed above for each of three-color images of Y), magenta (M), and cyan (C), or four-color images with black (BK) added to these, Is the circuit extremely? I become sloppy.

The present invention has been made in view of the current state of the scanning position detection device for this type of image forming apparatus as described above, and its purpose is to provide a relatively simple configuration, and for example, to provide a scanning position detection device for multiple image forming devices such as a laser color printer. An object of the present invention is to provide a scanning position detection device for an image forming apparatus in which compensation of the image writing position is appropriately performed in response to light beam conditions such as fluctuations in laser light intensity and placement errors of each rape light source.

[Means to solve the problem]

In order to achieve the above object, the present invention periodically deflects a light beam modulated with an image signal to perform raster scanning on a surface to be scanned within an optical scanning area, and performs image scanning at a scanning start position on a scanning line. In a scanning position detection device of an image forming apparatus, which generates a synchronization clock signal, starts the modulation based on the image scanning synchronization clock signal, and writes the image signal onto the scanned surface, a light intensity detector arranged to detect the intensity of the light beam;
determining means for determining the state of the light beam based on the detection signal of the light intensity detector; pulse signal generating means for generating a plurality of pulse signals having equal frequencies and sequentially shifted phases; and the determining means and clock selection means for selectively outputting one pulse signal from the pulse signal generation means as the image scanning synchronization clock signal in accordance with the state of the light beam determined by.

[Effect]

In the present invention, the intensity of the light beam or, when multiple light beams are used as in a laser color printer, the condition of the light beam, such as the mutual positioning error of the light sources of the light beams, is determined by the light intensity detector. The determination is made by the determination means based on the detection signal.

Corresponding to the state of the light beam determined by this determining means,
The clock selection means selects one of the plurality of pulse signals generated from the pulse signal generation means, which have the same frequency and are sequentially shifted in phase, as an image scanning synchronization clock signal, and the image signal is synchronized with this pulse signal. An image signal is written onto a surface to be scanned, for example, a photosensitive drum.

In this way, the pulse signal with the optimum phase corresponding to the state of the light beam is selected as the image scanning synchronization clock signal by the clock selection means, thereby writing an image signal without color shift or wobbling of thin lines. will be carried out.

〔Example〕

Embodiments in which the present invention is applied to a laser color printer will be described in detail below with reference to the drawings.

FIG. 11 is an explanatory diagram showing the configuration of the laser color printer portion of each embodiment.

In the figure, 4 is a paper feed roller, 5 is a tray, 11 is a fixing unit, 16 is a tray, 178, 17Y, 17M,
17C is a laser light source, IBK, IY.

LM, IC is rotating motor, 18BK, 18Y, 18M,
18C is a rotating polygon mirror, 208, 20Y, 20M, 20
C is an imaging lens, 88, 8Y, 8M.

8C is a photoreceptor lens; 7BK, 7Y, 7M, and 7C are corona dischargers; 28, 2Y, 2M, and 2C are developing devices; 13 is a conveyor belt; 9BK, 9Y, and 9M.

9C is a transfer discharger.

A color printer capable of outputting full-color images separates the image to be output into yellow (abbreviated as Y), magenta (abbreviated as M), and cyan (abbreviated as C), and outputs each image signal. The signals are received through a suitable interface, and based on the signals, Y, M, and C monochrome images are generated, and these are superimposed and combined to obtain a full-color image.

Y again.

Black (abbreviated as BK) is sometimes used for M and C.

This is to perform black output corresponding to the corner plate used in the printing industry. A color expressed using the three colors Y, M, and C includes equal amounts of BK corresponding to Y, M, and C, so the same color can be expressed using BK and any two of Y, M, or C. It can be expressed by

Removing equal amounts of Y, M, and C corresponding to BK is undercolor removal (UCR), and the replaced BK is a corner plate. In laser color printers, in addition to color reproduction, UCR reduces toner consumption.
This has the advantage that the thickness of the output image is reduced and the fixing load is also reduced. Therefore, in general, a toner image is formed four times and transferred four times.

In FIG. 11, exposure of a laser color printer will be explained using exposure of black (BK) information as an example. The laser light modulated by the image signal is transmitted to a laser light source 17.
8K and is deflected by a rotating polygon mirror 18BK rotated by a rotating motor IBK. The deflected laser beam scans a predetermined position π on the photosensitive drum 8BK via the imaging lens 20BK. This beam scanning is called main scanning, and its direction is called the main scanning direction. Rotating polygon mirror 18
By rotating the photosensitive drum 8BK, the laser beam is scanned back in the same direction on a straight line on the photosensitive drum 8BK.

By rotating the photosensitive drum 88K in the direction of arrow e,
The laser light is also scanned in the same direction on the photosensitive drum 8BK (this scanning is called sub-scanning, and this direction is called the sub-scanning direction), and the laser light raster-scans the photosensitive drum 8BK. When the photosensitive drum 8BK, which is initially charged by the corona discharger 78K, is scanned with laser light in accordance with the image signal, the charge in the portion that has received a predetermined exposure energy is removed, and an electrostatic latent image is formed on the drum 8BK. be done. Developing device 2BK transfers the charged toner to photosensitive drum 8.
It is attached to the exposed area on BK and the electrostatic latent image is developed.

This visible image is transferred to transfer paper. Exposure is performed in a similar process for each of the colors cyan, magenta, and yellow. On the other hand, the transfer paper fed from the tray 5 by the paper feed roller 4 and the transfer paper fed from the tray 5 by the paper feed roller 4 are conveyed in the direction of arrow Y by the conveyance belt 13.

The conveyor belt 13 is made of Mylar, for example, and is rotationally driven by several rollers. The contact point between the photosensitive drum and the conveyor belt 13 is the transfer position, and is the transfer discharger 9BK.

Each color toner is sucked onto the transfer paper by 9Y, 9M, and 9C.

The transfer paper onto which the toner images of each color have been transferred is separated from the conveyor belt 13 by a separating claw, passes through a fixing unit 11 using a heat roll, and the overlapping color toner images are fixed thereon. The paper is ejected.

For the laser color printer described above, in each embodiment, each laser light source 178 shown in FIG.
A light intensity detector is provided outside the optical scanning area of 7Y, 17M, and 17'C, and when this light intensity detector detects the light beam, a black synchronization detection signal (BKSPD) is output from each light intensity detector. ), yellow synchronization detection signal (YSPD), magenta synchronization detection signal (MSPD), and cyan synchronization detection signal (C3PD).

FIG. 1 is a block diagram showing the configuration of the main parts of the first embodiment, in which 27 is a light intensity detector, 21 is a light intensity measurement circuit, 23 is a delay circuit, 24 is a latch circuit, and 25
is a selection circuit.

The light intensity detector 27 is disposed outside the main scanning area of the scanning beam on the main scanning start point side and detects the scanning beam prior to each main scanning, and outputs a synchronization detection signal SPD, which is sent to the latch circuit 24. to be applied. Delay circuit 23
generates pulse signals having the same frequency as the image scanning clock and whose phases are sequentially shifted.

In this way, pulse signals with the same frequency and sequentially shifted phases as the image scanning clock are prepared in advance,
Select one of the prepared pulse signals according to the state of the light beam based on the negative output signal of the light intensity detector 20,
This is the actual image scanning clock.

FIG. 2 is a circuit diagram showing the configuration of the light intensity measuring circuit 21 in the first embodiment, in which 26 is a clock signal generation circuit, 27 is a photodiode 2, and an amplifier 2.
9. A light intensity detector consisting of a comparator 30; 31. 32 is a counter that counts a count value corresponding to the pulse width of the output signal pulse that varies with changes in the incident light intensity of the photodiode 28; 33 to 34, Data selector that defines the range of count values of counters 31 and 32, 36 to 38 are AND
It is a circuit. From the light intensity measuring circuit 21, the count values of the counter are O=B+, B+ -Bz, B! ~B3...
...corresponding to the intensity signal P, respectively. ~P is output and input to the selection circuit 25.

FIG. 3 is a circuit diagram showing the configuration of a main part of the phase selection circuit which is the main component of FIG. 1. In the figure, 23 is a delay circuit, 24 is a latch circuit, and 40 to 45 are NAND circuits.

FIGS. 4 to 6 are circuit diagrams showing circuits that constitute a phase selection circuit in combination with FIG. 3, and in these figures, 46 to 52 are NAND circuits.

As is clear from these figures, in FIGS. 4 to 6, the delay circuit 23 is connected to the input terminals of the NAND circuits 46 to 51.
The delay terminals t0 to t are connected in a different order. For example, when the circuit number in FIG. 3; the circuit in FIG. 4 is connected, the signal a0 of the delay terminal t2 is output, and the third
When the circuit of FIG. 5 is connected to the circuit of the figure, the delay terminal t,
When the circuit of FIG. 6 is connected to the circuit of FIG. 3, the signal a of the delay terminal t4 is output.

In this way, in the phase selection circuit, by changing the connection of the delay terminals t0 to t of the delay circuit 23, a pulse signal having a constant phase relationship with respect to the image scanning clock is selected.

In order to make this selection, in the first embodiment, the selection circuit 5 shown in FIG. A clock selection means is provided for determining the pulse signal and selecting and outputting the corresponding optimum pulse signal as the image scanning synchronization clock signal.

FIG. 7 is a timing chart showing the adjustment of the image scanning synchronization clock by the apparatus of the present invention including a clock setting circuit. To generate the cyan image scanning clock: CCLK and the magenta image scanning clock MCLK, complementary basic clocks whose phases differ by a quarter cycle each: CLK (C1""C4 and Ml-M4)
Cyan synchronization detection signal; C3PD and magenta synchronization detection signal: MSPD according to the above C1
One basic clock: CLK is selected from ~C4, M, and ~M4, and used as the image scanning clock.

In this way, when the light beam intensity changes, the cyan light detection signal: C3 as the cyan image scanning clock: CCLK and the magenta image scanning clock: MCLK.
PD and magenta light detection signal: MSPD, :! : Clocks C7 and M2 with the closest phase (022 in Fig. 7)
M2) is selected.

Furthermore, according to the embodiment, it is also possible to compensate for differences in writing positions caused by placement errors of the respective light intensity detectors and optical path differences.

FIG. 8 is a time chart of cyan and magenta signals in a laser color printer. As is clear from the figure, the position of the cyan light intensity detector and the magenta light intensity detector or the optical path difference between the cyan image signal: CDATA and the magenta image signal: MDAT.
The positions of A's heads are shifted from each other by a distance corresponding to Δt. This difference Δt hardly changes unless there is an abnormality in the system or unless optical parts or the like are replaced. This can be said to be completely unchanged considering the accuracy of the specifications of the device.

Therefore, it is sufficient to implement some method of correcting by Δt at the time of initial adjustment. In the embodiment, as shown in FIG. 7, the photodetection signal: SPD and the image scanning clock:
Basic clocks with slightly different phases (C, ~C4 or M1~) prepared for phase synchronization with CLK
M4) is selected so as to correct a deviation of Δ.

That is, for magenta, the magenta synchronization detection signal: MS
If it is fixed to select M2 that rises earliest after the rise of PD, the cyan cycle detection signal for C: C3 If it is set at the time of initial adjustment to select C3 that rises second after the rise of PD, Magenta image signal: MDATA and cyan image signal: CDATA
The writing start position is always the same for both, and an image without color shift can be obtained.

However, since the phase difference between the clocks with different phases prepared in advance is 1/4, the writing position will be shifted by this amount at most. In order to achieve even more precise positioning, it is sufficient to prepare a larger number of clocks with different phases.

FIG. 9 is a block diagram showing the configuration of the main parts of the second embodiment of the present invention. In the figure, 55 is a phase selection circuit, 56 is a data selector, and 57 is a delay circuit.

In the embodiment shown in FIG. 8, the intensity of the light beam corresponding to the pulse width of the SPD is measured by the circuit shown in FIG. be done.

Then, the phase selection circuit selects a clock synchronized with the timing after the pulse width has changed. The delay circuit 57 again generates clocks having the same frequency and different phases.

The generated clock is input to the data selector 56, and an image scanning synchronization clock signal is finally selected in accordance with the light intensity signals p0 to pn.

According to the second embodiment shown in FIG. 8, it is possible to compensate the writing position more precisely.

FIG. 10 is a block diagram showing the configuration of the main parts of the third embodiment of the present invention, in which 27 is a light intensity detector;
7 is an AD converter, 58 is a ROM table, and 59 is a latch circuit.

In this third embodiment, the light intensity is directly measured, and the analog signal of the light intensity detected by the light intensity detector 27 is
It is converted into a digital signal by a D converter and input to the ROM table 58.

Since the values of the optical intensity signals p0 to p corresponding to each level are written in the ROM table 58, the values are latched and used in any of the above-mentioned FIGS. 3 and 4 to 6. It is input to the phase selection circuit configured.

In this way, according to each embodiment, fluctuations in laser light intensity,
By compensating for deviations in writing positions caused by placement errors of each laser light source or optical path differences, it is possible to obtain high-quality images without color shift or twisting of thin lines.

〔Effect of the invention〕

As described in detail above, according to the present invention, with a relatively simple configuration, it is possible to compensate for deviations in the writing position due to fluctuations in laser light intensity, placement errors of the laser light source, or optical path differences, and to always prevent color misregistration and thin lines. A scanning position detection device for an image forming apparatus is provided that can obtain high quality images without wobbling.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of the main parts of the first embodiment of the present invention, FIG. 2 is a circuit diagram showing the configuration of the light intensity measuring circuit in the first embodiment, and FIG. 4 to 6 are circuit diagrams showing the configuration of the main parts of the phase selection circuit in the embodiment.
The figure is a circuit diagram showing a part of the configuration of the phase selection circuit in the first embodiment, FIG. 7 is a time chart showing adjustment of the image scanning synchronization clock according to each embodiment of the present invention, and FIG. Time charts of cyan and magenta signals in each embodiment, FIG. 9 is a block diagram showing the configuration of the main part of the second embodiment of the present invention, and FIG. 10 is a time chart of the third embodiment of the present invention. FIG. 11 is an explanatory diagram showing the configuration of a laser color printer portion according to an embodiment of the present invention; FIG. 12 is a perspective view illustrating setting of a writing start position in the laser printer; FIG. The figure is an output waveform diagram of a PIN photodiode. 21......Light intensity measurement circuit, 23...
...Delay circuit, 24...Latch circuit, 25...Selection circuit, 27...
・・・・Light intensity detector, 31.32・・・・・・・・・
Counter, 33-35... Data selector. agent

Claims (1)

[Claims] A light beam modulated by an image signal is periodically deflected to perform raster scanning on the surface to be scanned within the optical scanning area, and an image scanning synchronization clock signal is generated at the scanning start position on the scanning line. In a scanning position detection device of an image forming apparatus that starts the modulation based on a signal and writes the image signal on the scanned surface, the scanning position detection device is arranged outside the optical scanning area and detects the intensity of the light beam. a light intensity detector for detecting the light intensity, a determining means for determining the state of the light beam based on a detection signal of the light intensity detector, and a pulse signal for generating a plurality of pulse signals having equal frequencies and sequentially shifted phases. It is characterized by comprising a generating means, and a clock selecting means for selectively outputting one pulse signal from the pulse signal generating means as the image scanning synchronization clock signal in accordance with the state of the light beam determined by the determining means. A scanning position detection device for an image forming apparatus.