JPH04136876A - Beam power control method for laser printer - Google Patents

Abstract

PURPOSE:To obtain a sure synchronizing signal without out-of-synchronism and the defective a scanning line by controlling a laser output controller regardless of a set condition so that beam power may be at a previously set level for detection. CONSTITUTION:The content of a U/D counter 73 is corrected by loading a level corresponding value for detection which is latched in a latch circuit 71 as an initial value when the synchronizing signal DETP is inputted and thereafter adding or subtracting power correction data inputted from a latch circuit 72 every time an I counter 74 outputs. The content of the counter 73 is always converted into an analog signal by a D/A converter 76 and power-amplified by a power amplifier 77, and it becomes a driving signal for driving an LD. Since the line of the driving signal is connected to the line of an on/off control signal coming from a write control circuit 45 through a diode 78 before it reaches an LD 30a, the level of H is set at or above the maximum voltage level of the driving signal when a control signal is H, a driving current all flows to the LD 30a, and the power beam in accordance with the current value is outputted.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a beam power control method for a laser printer.

[Conventional technology]

A laser printer is a device that forms images on plain paper using electrostatic latent image technology, and is also called a laser beam printer.
In addition to being connected to personal computers, EWSs, etc. as external peripheral devices, they are also used as integrated output devices in digital copying machines, color copying machines, high-speed facsimile machines, etc.

As is well known, the principle is that a laser beam (hereinafter referred to as ``beam'') modulated and output from a light source such as a laser diode (hereinafter also referred to as LDJ) is optically deflected according to image data. The main scanning is performed by repeatedly deflecting the deflected beam by means (for example, a rotary deflector such as a polygon mirror rotating at a constant speed) and focusing the deflected beam as a spora 1 on a charged photoreceptor surface that moves in the sub-scanning direction. to form an electrostatic layer image.

The electrostatic latent image is converted into a visible toner image by development,
By transferring and fixing the toner image onto paper,
An image is formed on plain paper.

In this way, an image is formed by the main scanning of the spot and the sub-scanning of the photoreceptor that moves in the perpendicular direction, so if the synchronization of optical writing in the main scanning direction is out of synchronization, the formed image will be distorted. A photodetecting element such as a photodiode or phototransistor is provided at a position immediately before irradiating the effective image area, and when it receives the beam, it outputs a synchronizing signal and generates an image clock synchronized with it.

Since optical writing is performed according to the image clock, an image without vertical line distortion can be obtained.

On the other hand, the beam power output by the LD and other parameters are set according to image density or ambient conditions such as temperature and humidity specified by the operator, and the laser output control device controls the beam power according to the set conditions.

However, if the power of the main scanning beam remains at the above-mentioned setting value, the illuminance of the spot will be high at the center of the effective image area and low at the periphery, causing density unevenness in the image.

Therefore, the laser output control device knows the position of the spot being scanned on the screen by clocking the image clock, and as shown in Figure 8, the laser output control device lowers the power at the periphery of the screen and lowers the power at the center of the screen. So-called parabola correction is performed to control the output of the LD so that the illuminance of the entire screen is constant.

Therefore, depending on the setting conditions, output control is performed such that the spot is shifted down by 1 in proportion to the position of the spot, as shown in FIGS.

[Problems to be Solved by the Invention] However, as shown in FIG. 8, the power beam for the peripheral area is input to the photodetecting element, so the human power level changes according to the setting conditions.

Therefore, as shown in Fig. 9, which shows the change in the output of the photodetector element over time, each characteristic curve H to D (corresponding to Fig. 8 A to D, respectively) has a strong In the case of input level A, a saturated portion appears in the output, and the time at which the threshold voltage, which is predetermined for outputting the synchronizing signal, is reached is earlier by Δ゛F.

That is, the timing at which the synchronization signal is output changes depending on the input level, that is, the setting conditions.

Even if there is a positional shift due to such an input level, there is no problem with "2" in practical use because the input level fluctuation is small for images on the same paper, but in the case of a weak input level C, slight input level fluctuations Even if there is, jitter or non-detection occurs, and problems such as vertical line distortion and scanning line dropout due to main scanning synchronization deviation occur.

In the case of an even weaker input level D, the peak of the output does not reach the threshold voltage, so a synchronizing signal is not output, resulting in a problem in which an image cannot be formed.

Furthermore, in the conventional example, as shown in Fig. 8, the light emission time of the LD is longer at the peripheral level where the beam power is highest under the same setting conditions, so the life of the LD is shortened accordingly. There was also.

The present invention has been made in view of the above-mentioned points, and an object of the present invention is to provide a beam power control method for a laser printer by which a reliable synchronization signal can be obtained.

[Means to solve the problem]

In order to achieve the object stated in ``--, the present invention includes a photodetecting element that detects a laser beam that is main-scanned by an optical deflection means, and a standard for writing timing in the main scanning direction according to the output of the photodetecting element. A synchronization signal circuit outputs a synchronization signal, an image clock generation circuit generates an image clock synchronized with the synchronization signal, and the beam power of the laser beam is adjusted according to setting conditions such as image density and the count number of the image clock. In a laser printer equipped with a laser output control device, the laser output control device controls the beam power to a preset detection level when the laser beam is incident on the photodetecting element, regardless of setting conditions. It is something to control.

[Function] In the beam power control method for a laser printer according to the present invention, when the laser beam is incident on the photodetecting element, the laser output control device controls the beam power to a preset detection level. Regardless of the conditions, the optimal level of laser beam is always input to the photodetecting element,
A reliable synchronization signal without synchronization deviation or scanning line dropout can be obtained.

[Example] Hereinafter, an example of the present invention will be specifically described with reference to the drawings.

FIG. 3 is a schematic diagram showing the internal mechanism of a laser printer that is an embodiment of the present invention.

Around the photosensitive drum 10 rotating clockwise as shown by the arrow, chargers 11 . Optical writing unit 12. Phenomenon unit 13, transfer charger 1
4. Cleaning units 15 are arranged respectively.

The surface of the photosensitive drum 10 is first uniformly charged by a charging charger 11, and then modulated by image data from an optical metering unit 12 and deflected in the main scanning direction. is scanned to form an electrostatic latent image.

The electrostatic latent image is developed by the developing unit 13 and converted into a visualized toner image, and then the toner image is transferred by the transfer charger 14 to the paper that has been conveyed along the route shown by the dashed line. transcribed.

The toner and charge remaining on the photosensitive drum 10-h are removed by the cleaning unit 15, and the removed toner is collected by the cleaning unit 15.

The paper is fed by a paper feed roller 19 from a paper stack 18 on a paper feed cassette 17, and is fed by a pair of registration rollers 2.
0, the toner image is conveyed to the position of the transfer charger 14 by a pair of registration rollers 20 at a timing that matches the image written on the photoreceptor drum 10 by the optical writing unit 12. is transcribed.

The paper onto which the toner image has been transferred is conveyed to the fixing unit 21, pressed against the fixing roller 21b heated by the pressure roller 21a, and fixed by the heat and pressure, and then conveyed to the paper ejection roller 22. The paper is discharged from the paper discharge port 23 onto the paper discharge tray 24 .

FIG. 4 is a perspective view of essential parts showing an example of the optical writing unit 12.

The optical writing unit 12 includes an LD (laser diode) unit 30, which is a modulated light source, and a first cylinder lens 31. First mirror 32. A pre-object type imaging lens 33, a rotary deflector 36 which is a light deflecting means consisting of a polygon motor 34 and a polygon mirror 35 rotationally driven in the direction of arrow A, and a second mirror 37. Second
a scanning imaging optical system consisting of a cylinder lens 38, and a third mirror 40. It is constituted by a synchronous optical system consisting of a light receiving lens 4+ and a synchronous sensor 42 which is a light detecting element.

The LD unit 30 has an L I) inside and this L D
A collimator lens that converts a diverging beam emitted from the beam into a parallel beam, and an aperture that regulates the thickness of the beam are integrated.

The parallel light beam emitted from the LD unit 30 passes through the first cylinder lens 31 and is reflected by the first mirror 32, and then passes through the imaging lens 33 and enters the reflective surface 35a of the polygon mirror 35.

The imaging lens 33 acts to form an image of the parallel main scanning direction component of the incident beam on a photoreceptor drum l01-, which will be described later.
The combined power of the sub-scanning direction component of the parallel beam acts to form an image once on the reflective surface 35a of the polygon mirror 35.

The beam reflected by the polygon mirror 35 and repeatedly deflected in the main scanning direction is reflected by the second mirror 37, passes through the second cylinder lens 38, and reaches the photosensitive drum 10 rotating in the direction of arrow B.

The second cylinder lens 38 converts the sub-scanning direction component of the beam focused on the reflecting surface 35a1- to the photoreceptor drum 10''.
Therefore, the beam is imaged into a spot along with the main scanning direction component imaged by the imaging lens 33, and the main scanning line of photoreceptor drum] Oa-, , I: is directed in the direction of arrow C. main scan.

Further, just before the beam deflected by the rotary deflector 36 enters the effective image area of the main scanning line 10aJ-, the beam is reflected by the third mirror 40 and focused on the light receiving surface by the light receiving lens 41. A synchronization sensor 42 that outputs a main scanning synchronization signal is also provided.

FIG. 5 is a block diagram showing an example of a control section of this laser printer.

The controller 50 is a main microcomputer (
Programs and constant data required by rMPUJ)51 and its Ml)U5].

A ROM 52 that stores character fonts, etc., and a RAM 2S that stores temporal data, dot patterns, etc.
It consists of a T1054 that controls input/output of commands and data, an operation panel 55 connected to the MPU 51 via its l105/l, and an internal interface (1/F) 56, which are connected to each other by a data bus, address bus, etc. connected with.

In addition, the host machine 58 that outputs print commands, character data, and image data is also connected to the MPU via I/054.
51.

The engine driver 60 includes a sub microcomputer (hereinafter referred to as "CPU") 61 and a ROM 6 that stores programs and constant data required by the CPU 6.
2, a RAM 63 for storing temporal data, and an I1064 for controlling data output, and are connected to each other by a data bus, an address bus, etc.

A reference numeral 11064 is connected to the internal interface 56 of the controller 50, and inputs video signals from the controller 50 and the states of various switches on the operation panel 55, and outputs status signals such as image clock and paper end to the controller 50.

Also, this l1064 is the printer engine 6.
5, the optical writing unit 12 and other sequence equipment group 66, and various sensors 67 including the synchronization sensor 42.
It is also connected.

The controller 50 receives print commands, character codes, and image data from the host machine 58, edits those codes and data, and if it is a character code, uses the character phono stored in the ROM 52 to write the data necessary for image writing. After converting into dot patterns, the dot patterns of those characters and images (hereinafter collectively referred to as "images") are stored in a VRAM (video RAM) area in the RAM 53.

When the image clock is input together with the ready signal from the engine driver 60, the controller 50 outputs the dot pattern stored in the VRAM area to the engine driver 60 serially or in parallel as a video signal synchronized with the image clock.

The engine driver 60 controls the optical writing unit 12 of the printer engine 65 based on data from the controller 5o.
A video signal necessary for controlling the sequence equipment group 66 and image writing is input from the controller 50 and output to the optical writing unit 12, and signals indicating the status of each part of the engine are sent from the synchronization sensor 42 and other sensors 67. is processed manually, and necessary information and error signals are output to the controller 50.

FIG. 6 is a circuit diagram showing an embodiment of the laser output control device together with an example of its related parts.

The laser output control device 70 includes two latch circuits 71.7.
2 and three counters, namely a U/D (up/down) counter 73. T (interval) counter 74. A
(address) counter 75 and ■]/A converter 7
6 and a power amplifier 77.

The related parts include the CPU 61 of the engine driver 60 that performs sequence control, and the power control data area (rPcD area hereinafter) that stores a series of power control data for correcting the beam power set in advance in the ROM 62. ) 68, and the optical writing unit 1
2 (FIG. 4), each polygon mirror 35. LID (laser diode) 30a in the LD unit 30,
There are a synchronization sensor 42, a synchronization signal circuit 43, and a write control circuit 45.

CI) tJ 6 ] outputs the initial value set Pth immediately before the start of printing for -page to the latch circuit 71 and latches it, and also sets the setting conditions among the plurality of data groups in the I) CI) area 68. Specify the start address of the pair corresponding to .

The beam output from the LD 30a is reflected by the polygon mirror 35, and the beam is reflected by the main scanning line 1 indicated by a dashed line.
When the beam is incident on the synchronous sensor 42 located at the extension -1- of the effective image area indicated by the arrow 0a''-, the synchronous sensor 42 detects the beam and outputs a detection signal to the synchronous signal circuit 43.

For example, when the detection signal input from the synchronization sensor 42 exceeds the threshold voltage, the synchronization signal circuit 43 consisting of a Schmitt circuit set to a threshold voltage (FIG. 9) and a monostable multi-circuit synchronizes a single pulse. Write signal DETP control circuit 45 and laser output control device 7
0 U/D counter 73. They are output to the A counter 75, respectively.

The write control circuit 45 forms image clocks WC+, . It processes a video signal for image writing that is manually inputted from the controller 50 in synchronization with , and outputs an on/off control signal for controlling the on/off of LI) via the diode 78 .

When the synchronization signal DETP is input manually, the A counter 75 (
I) CD area 68 specified by the CPU 61
The start address of one set of data is loaded, and thereafter the contents are incremented by 1 in accordance with the output of the counter 771.

The data in the PCD area 68 at the address specified by the A counter 75 is latched by the latch circuit 72, and the power correction data, which will be described later, is sent to the U/D counter 73, and the interpulpator is sent to the counter 74. Each of them will appear.

■The counter 74 loads manually input interval data from the latch circuit 72 and decrements its contents every time the image clock WCT is input from the write control circuit 45. For example, when rOJ becomes "-1", The resulting amplifier carry is output to the U/I') counter 73 and the A counter 75.

The U/D counter 73 is loaded with the value corresponding to the detection level latched as an initial value in the latch circuit 71 when the synchronization signal D ETP is input manually, and thereafter, the value corresponding to the detection level is loaded as an initial value in the latch circuit 71. The power correction data inputted from the circuit 72 is added or subtracted to correct the contents.

The contents of the U/D counter 73 are always converted into an analog (voltage) signal by the D/A converter 76, power amplified by the power amplifier 77, and used for driving the LD (
current) signal.

This drive signal line is connected to the on/off control signal line that comes from the write control circuit 45 via the diode 78 before reaching the LD 30a, so the on/off control signal is " When the control signal is "H", all the drive current flows to the write control circuit 45 and the LD 30a does not emit light, and when the control signal is "H", the level of IIHII is higher than the maximum voltage level of the drive signal. - Since it is set to
All drive currents flow through L+) 30a, and a beam with a power corresponding to the current value is output.

FIG. 7 is an explanatory diagram showing an example of data in the PCD area 68.

Each data is 1 byte (8 bits) long, the lower 5 bits (0 to 4) are interval data, and - is the 1st and 3rd bits.
Bits (5-7) are power correction data, MSD
When the second digit (7) is ``1'', it instructs addition, and when it is ``0'', it instructs subtraction, and the following two digits (1-(5, 6)) indicate the increase or decrease.

When the interval data is Oh (hexadecimal number), the counter 74 counts the image clock W C+-+ K by 1 and outputs a carry, so the interval is "1", and when the data is the maximum IF h The interval is “3”
2".

Power correction data can be specified from 0 (no correction) to a maximum of ±3.

Therefore, A and B of the PCD area 68 shown in FIG.
, C address data is [Image clock WCLK
It has instructions such as ``count 5 and then add 1 to the contents of the U/D counter 73'', ``take an interval of 32 counts and do not change the contents'', and ``count 1 and subtract 3 from the contents''. .

In the conventional example, as the beam power (time) characteristics are shown in FIG. The data CEPD latched in the latch circuit 71 is output to the synchronizing signal D.
Each ETP is loaded into the U/D counter 73, the image clock WCLK is counted, and after reaching (the left end of) the effective image area, the latch circuit 72. ■Counter 74. The A counter 75 is activated, and the content of the U/D counter 73 is subtracted so that the beam power attenuates in a parabolic manner toward the center of the image, and after passing the center, it decreases in a parabolic manner toward the periphery (at the right end). was performing the addition.

Generally, the left and right peripheral powers are equal, so at the end of main scanning of the image area, the contents of the U/I) counter 73 return to data CEPD, which is input to the synchronization sensor 42 when the next synchronization signal is generated. This is the power of the beam.

FIG. 1 is a diagram showing an example of the time characteristics of beam power according to the first embodiment of the present invention.

That is, regardless of the setting conditions, the CPU 61 initially sets the optimum level (for example, FIG. 9B) of the beam power input to the synchronous sensor 42 at which no jitter, non-detection, or oversaturation occurs, that is, the value CMSD corresponding to the detection level. It is output as a value to the latch circuit 71 and latched.

Therefore, as shown in FIG. 1, the beam is always at a constant detection level before and after it enters the synchronization sensor 42, and just before the beam hits the effective image area, it is corrected to the peripheral level according to each setting condition. do.

In the example shown in Figure 1, like the data at address C shown in Figure 7, the maximum negative correction is performed several times in the shortest time to obtain the peripheral level corresponding value CE I) of D. Then, within the effective image area, a parabolic characteristic is obtained by increasing/decreasing correction.

In the example shown in Figure 1A, the M of the data at address C in Figure 7
All you have to do is repeat the maximum positive correction with SD set to "l".

Once outside the effective image area, the maximum plus or minus correction is similarly repeated to return to the original corresponding value CMSD.

In this way, as shown in FIG. 1, the beam power entering the synchronous sensor 42 can be kept at a constant detection level regardless of the setting conditions.

FIG. 2 is a bond diagram showing an example of the time characteristics of beam power according to the second embodiment.

In the first embodiment, the CPU 61 simply sets the corresponding value CMSD and the start address of the set corresponding to the setting conditions of the PCD area 68 as initial values immediately before starting printing of -pages.

In this second embodiment, the CPU 61 alternately outputs the optimum level corresponding value CMSD and the peripheral power corresponding value CEPD according to the setting conditions to the latch circuit 71 at a timing for each main scan, and latches it. let

That is, when the beam finishes optical writing and leaves the effective image area, the CPU 61 outputs the optimum level corresponding value CMSD and causes the latch circuit 71 to latch it, and at the same time output the U/D
After the synchronization signal DETP is output, the image clock WCLK is counted, and just before the beam reaches the effective image area, the peripheral power corresponding value CE is loaded into the counter 73.
The PD is output and latched by the latch circuit 71, and simultaneously loaded into the U/D counter 73.

In this case, the CPU 6
1 and each corresponding value may be directly loaded into the U/D counter 73. In addition, in place of the latch circuit 71, two latch circuits (7] a, 711) (not shown) are provided, and the corresponding values CMSD and CHPD are latched, respectively, and the LJ/D counters are alternately used depending on the timing. It may be set to low 1 at 73.

The parabolic data correction within the effective image area is the same as in the first embodiment, so the explanation will be omitted.

- As explained above, since the beam power of the laser beam is always maintained at a constant detection level outside the effective image area regardless of the setting conditions, the output of the synchronous sensor 42 may become saturated or the threshold voltage There are no problems such as jitter when the value is close to the value, or non-detection when the value is too low.

Furthermore, since the detection level is generally much lower than the maximum output level of the laser diode, the life of the laser diode can be extended.

[Effects of the Invention] As described in 1-1 above, according to the beam power control method for a laser printer of the present invention, a reliable synchronization signal can be obtained.

[Brief explanation of drawings]

1 and 2 are diagrams showing an example of the time characteristics of the beam power according to the present invention, FIG. 3 is a schematic diagram showing the internal mechanism of a laser printer according to an embodiment of the present invention, and FIG. FIG. 5 is a block diagram showing an example of the control unit; FIG. 6 is a circuit diagram showing an example of the laser output control device; FIG. is an explanatory diagram showing an example of the power control data, FIG. 8 is a line diagram showing an example of the time characteristic of the beam power according to the conventional example, and FIG. 9 is a line diagram showing an example of the time characteristic of the output of the photodetector element f. It is a diagram. 10... Photosensitive drum IOa... Main scanning line 3
0a...LD (laser diode) 6...Rotary deflector (light deflection means) 2...Synchronization sensor (light detection means) 3...Synchronization signal circuit 5...Write control circuit (image clock generation circuit) 1...
CI) tJ (microcomputer) 8...PCD area (power control data area) 0...laser output control device

Claims (1)

[Claims] 1. A photodetecting element that detects a laser beam that is main-scanned by an optical deflection means, and outputting a synchronization signal that serves as a reference for writing timing in the main-scanning direction in accordance with the output of the photodetecting element. a synchronization signal circuit, an image clock generation circuit that generates an image clock synchronized with the synchronization signal, and a laser output that controls the beam power of the laser beam according to setting conditions such as image density and the count number of the image clock. In a laser printer equipped with a control device, when the laser beam is incident on the photodetecting element, the laser output control device is configured to adjust the beam power to a preset detection level regardless of the setting conditions. A beam power control method for a laser printer characterized by controlling the beam power.