JPS63243972A - Laser printer - Google Patents

Abstract

PURPOSE:To permit normal image formation of a mark for density detection, etc., even if a host computer transmits a request for changing a picture element density at arbitrary timing by preventing the receipt of a change of the picture element density during the image formation operation of the mark for density detection. CONSTITUTION:A laser printer 1 starts a printing operation upon receipt of a request for starting printing in a printing control part 200. Data is read out at the time of exposing and a laser diode LD 31 is modulated, then a latent image is created on a photosensitive body. The mark (density detection mark) MA for an automatic image density control (AIDC) is formed by a printing data writing control circuit 217 in the control part 200 to the position where a density reader is readable upon lapse of the prescribed time after the end of exposing in this case. The change of the picture element density is not accepted even after the start of the exposing until the writing of the mark MA for AIDC ends. The normal image formation of the mark MA for AIDC is, therefore, permitted even if the host computer or the like transmits the request for changing the picture element density at the arbitrary timing.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a laser printer capable of changing pixel density, and particularly to a laser printer that can appropriately respond to a request to change pixel density during image formation. Regarding Uru laser printer.

(Prior Art and its Problems) A laser printer is a printer device that forms an image using a large number of pixels arranged in a matrix. A latent image is formed by pixels on the paper, a visible image is obtained by toner development, and the visible image is transferred to plain paper and then fixed. Laser printers are capable of high-speed modulation of laser light, so they can print at high speed and with high quality (high density).
Printing and graphic recording can be realized, and therefore, it has a wide range of uses as an output device for various data processing systems and image creation systems using computers.

By the way, there are various image densities of the image signals output from the host combinator, and in order to receive these outputs and print a normal image, the pixel density (printing density) of the laser printer must be set to one of these. It is necessary to make it variable according to the situation. Furthermore, in order to change the print size using character generators having the same pixel configuration, it is necessary to make the pixel density of the laser printer variable.

In order to meet such demands, laser printers with variable pixel density have been proposed (for example, Japanese Patent Application Laid-open No. 198076/1983).

On the other hand, as mentioned above, a laser printer has a process similar to an electrophotographic process, and the density of the image finally printed on plain paper varies depending on the amount of toner. Therefore, the amount of toner must be controlled to keep the image density at its optimum level. To do this, a mark for density detection is formed on the photoconductor using a laser beam, and after this is developed, the density can be read. The concentration is detected by reading it with a device. ′
The seismic intensity detection mark a is formed on the photoreceptor at a position that does not overlap with the image area of the image, and is controlled so that it is always formed at a constant position.

By the way, when the pixel density is changed from a new page of images that are being sequentially processed by a host computer, etc., control data for requesting a change in pixel density is sent from the host computer to the laser printer along with the image data of those images. output for However, if you change the pixel density while an image of the density detection mark or image area is being formed, the image will not be formed correctly, so do not change the pixel density until the image formation has finished. Therefore, in the past, the host computer had to constantly recognize the status of the laser printer and issue a request to change the pixel density at a time when image formation was not in progress. Therefore, the signal processing for changing the pixel density on the host combinator side is complicated, and the processing speed is reduced.

(Means for Solving the Problems) In view of the above-mentioned problems, the present invention is designed to ensure that images such as density detection marks are formed normally even if a host computer or the like issues a request to change the pixel density at any timing. The purpose of this project is to provide a laser printer that can perform the following functions.The technical means is to scan a laser beam to form an image with a large number of pixels on a photoreceptor, and to change the rotation speed of a polygon mirror to form an image on a photoreceptor. A laser printer with variable density has means for forming a density detection mark outside the image area on the photoreceptor, and a request to change the pixel density occurs during the operation of forming the density detection mark. In this case, the pixel density changing operation is not started until at least the image forming operation of the density detection mark is completed.

(Example) The present invention will be explained below based on illustrated embodiments.

FIG. 1 is a sectional view of the laser printer 1. FIG. In the figure, 2 is a photoreceptor on which a latent image is formed by a laser beam;
3 is a charger for uniformly charging the photoreceptor 2; 4 is a developer for developing a latent image formed by a laser beam; 5 is a transfer charger for transferring the developed toner onto paper; 6 7 is a separation belt for separating the paper from the photoreceptor 2; 7 is a cleaner blade that collects excess toner after transfer; 8 is an eraser that irradiates to remove excess charge in order to uniformly charge the charger 3; 9 is a density reader that reads the density of toner; 10 is a paper cassette that stores paper; 11 is a half-moon-shaped paper feed roller for guiding the paper to the conveyance path; 12 is a conveyance roller; 13 is a paper feeder for manual paper. A transport roller 14 also serves as a roller, and 14 is a registration roller that determines the recording position on the paper in the sub-scanning direction (the direction in which the laser beam scans the paper is the main scanning direction, and the direction perpendicular to it is the sub-scanning direction). , 15 is a fixing roller that fixes the toner transferred by -5 on the paper during transfer charging, 16 is a main body ejection roller, 17 is a reversing unit for ejecting the back side of the paper, and 18 is a reversing unit for ejecting the paper from the back side or the front side. It is a paper guiding claw for switching, and can be operated manually. Reference numeral 19 is a conveyance path for back side ejection, and 20 is an ejection roller. Reference numeral 21 is a guide for identifying the paper size in the paper cassette 10. It is a group of magnets, and a sensor 22 detects and identifies whether or not there is a magnet in the 3-pit storage frame. 23 is a paper empty sensor, Psi, PS, which detects the presence of paper in the cassette.
2. Each PS3 has a paper sensor.

FIG. 2 schematically shows the optical system of the laser printer 1. As shown in FIG. Referring to FIG. 1 and FIG. 2, 31 is a laser diode (hereinafter referred to as LD), which will be described later.
It is driven in a variable manner by the driving section.

32 and 33 are so-called collimator lenses and cylindrical lenses for correcting the spread of the laser beam. 3
Reference numeral 4 denotes a polygon mirror, which is configured so that when it rotates, a laser beam scans the photoreceptor 2 and scan light 39 is obtained. 35 is an fθ lens for scanning the laser beam on the photoreceptor at a uniform speed; 36
．． 37 is a folding mirror for guiding the laser beam to the photoreceptor 2; 38 is a beam detector for determining the printing position in the main scanning direction; the scan light 39 passes through the beam detector and then directs the laser beam to the photoreceptor 2; Configured to scan.

FIG. 3 is a system block diagram when the laser printer 1 is actually used, and 400 is a general-purpose data processing device (
300 is a data control unit, and 200 is a print control unit of the laser printer 1 that controls the printing operation of the laser printer 1.

Generally, when a print request occurs in the data processing device 400, printer control data that determines the printing operation mode of the laser printer 1 and print data that determines the actual print content are sent to the data control unit through the interface 301 using code data. 300. The purpose of transmitting the code is to shorten the transmission time as much as possible.

The data control section 300 receives data based on the code data, and if the data is printer control data, it is transmitted as is to the print control section 200 of the laser printer 1 via an interface 201, which will be described later. On the other hand, if the data is print data, the code data is converted into bit image data and then developed into a memory called a bitmap memory that can store bit image data for one page. Once the data has been expanded, the interface 201
A print start request is issued to the print control unit 200 of the laser printer l. The laser printer 1 starts the printing operation when the print control unit 200 receives the print start request, reads data from the bitmap memory through the interface 201 during exposure that actually requires image data, and uses the data to read data from the bitmap memory. LD3
The protocol of the 0-order interface 201 that modulates the 0-order image to create a latent image on the photoreceptor 2 and the print control of the laser printer 1 will be explained.

The interface 201 is for exchanging data between the data control section 300 and the print control section 200 in the laser printer 1, and functionally consists of the following two interfaces.

Referring to FIG. 5, the control interface 201a:
This is used to exchange data related to the operation control of the laser printer 1, and the data control unit 300 sends data for specifying print formats such as the paper feed port and ejection port, and data for determining the timing of print start requests, etc. On the other hand, the print control unit 200 sends data for the internal status of the laser printer 1, such as paper size information and error information, and data for determining the timing of printing completion, paper ejection, etc. . Further, this interface 201a is made up of commands and statuses, and the commands are used to exchange data related to the timing, and the statuses are used to exchange other data. These commands and status are shown in Tables 1 and 2.

(Margin below) Table 1 Command Table 2 Status Next, the image interface 201b controls the data control unit 30 during the so-called exposure time when a latent image is being formed on the photoreceptor 2.
It is used to read image data from the bitmap memory 0.

FIG. 4 shows the configuration of the signal line, where 5100 is a light rasp (referred to as WR3T) signal indicating that exposure is in progress, and 5101 is a signal when the scanning light 39 of the laser beam (see FIG. 2) passes through the beam detector 38. Sensor scan (hereinafter referred to as SSC) signal, S102, indicating that
5103 is a data request (hereinafter referred to as DREQ) signal for requesting 8-bit image data, and 5103 is the DRE.
This is an 8-bit image data signal output by the Q signal.

At the time of exposure, the WRST signal 5100 becomes "L",
Thereby, the data control unit 300 enters the system for transmitting image data. Furthermore, the start of one line is recognized by the falling edge of the 5SCAN signal 5101, and 8-bit parallel data is transmitted to the laser printer 1 in synchronization with the rising edge of the DREQ signal 5102.

FIG. 5 is a block diagram of the print control section 200 of the laser printer 1. As shown in FIG. The configuration is a so-called multi-chip configuration centered around CPU2O5, and data can be exchanged with each chip via bus S10. In the figure, 205 is a system ROM that stores a control program.

206 is a system R serving as a work area for the control program.
AM, 203 is an oscillator that creates a clock to synchronize the operation of the CPU, 204 is a reset circuit to reset the entire circuit when the power is turned on, 208 is various driving parts such as motors, solenoids, heaters, etc., 207 is Drive section 20
8, 210 is a paper sensor, concentration sensor, and other various sensors, 209 is an input port that receives and receives signals from sensor 210, and 212 is a device that has a display element such as an LED or an input element such as a switch. This is a work panel.

A scanner driving unit 215 controls the rotation of the polygon mirror 34, and determines the rotation speed of the polygon mirror 34 in accordance with the clock S12 transmitted from the timer 213, and drives the polygon mirror 34. The setting value of timer 213 is CPU U2O5
It can be set by commands from the CPU U2O.
5 allows the rotation speed to be arbitrarily changed and set. This is the polygon mirror 3 when changing the printing density.
This is because it is necessary to change the rotation speed of No. 4. Also,
The scanner driver 215 sends a polygon lock signal Sll to the input port 209 indicating whether the polygon mirror 34 is rotating at a constant speed.

218 is an LD drive unit that controls the drive of the LD 31;
A print data write circuit 2 that modulates the LD 31 based on a signal sent from the print data write control circuit 217.
Reference numeral 17 designates scanning light 39 at a predetermined position on the photoreceptor 2 from the image data sent from the data control unit 300.
LD modulation data to be sent to the LD drive unit 218 is created so that the LD drive unit 218 turns on and off. Note that image data is exchanged using the image interface 201b, and 219 is an interface control circuit that controls the control interface 201a.

FIG. 6 shows the contents of the output signal from the output port 207. Here, only the details of the objects to be driven are shown, and the circuits and specific connections for actually driving these drive units are omitted. Further, all mechanical drive units (rollers, toner supply unit, etc.) in this embodiment are driven by a chain from the main motor 224, and turned on and off by a clutch using a solenoid.

220 is a solenoid that determines whether or not to transmit the drive of the chain to the paper feed roller 11; 221 is a solenoid for the registration roller 14; and 222 is a solenoid that determines whether or not to drive a portion that replenishes toner to the developing unit 4. Solenoid, 22
3 is an ED attached to the density reader 9, 224 is a main motor, and 227 is a motor relative to the photoreceptor 2 so that the toner in the developer 4 adheres only to the latent image formed on the photoreceptor 2. The potential (hereinafter referred to as developing bias) is applied to the developing device 4.
229 is a heater section of the fixing roller 15. Print data writing control circuit 2
The output signal to 17 will be described later.

FIG. 7 shows the contents of the input signal to the input port 209. Here, like the output signal, only the contents to be detected are shown, and specific connections, comparators, etc. are omitted.

230 is a switch that detects the opening/closing of a door that separates the inside and outside of the laser printer l; 231 is a main motor 22;
The defective detectors 4, 232 and 233 are respectively charged
- defective detector for jar 3 and transfer charging -5, 234
23 is a toner empty detection sensor that detects the amount of toner in the developing device 4; 235 is a density detection sensor in the density reader 9; 236 is a face up/down switch that detects which state the paper guiding claw 18 is in;
Reference numeral 7 denotes an initial setting switch consisting of a double switch for setting the initial value of the print density (pixel density), which allows four settings to be made. Further, 238 is a temperature control section for the heat roller, and the input port 209 is informed of the temperature state of the heater.

FIG. 8 is a detailed circuit diagram of the print data write control circuit 217.

This circuit 217 determines the image printing position in the main scanning direction, determines the printing position of the automatic image density control (hereinafter referred to as AIDC) mark (density detection mark) MA in the main scanning direction, and determines the above printing position. Synchronous signal (SSCA
Forced light emission of the LD31 outside the image area to generate N), determination of the sample timing of automatic power control (hereinafter referred to as APC) of the LD31, and LD310
Table 3 shows the contents of input/output signals to this circuit 217, which are used to emit light and detect abnormalities in the rotation of the polygon mirror 34.

(Margins below) Table 3 In Fig. 8, 250 indicates the clock 5115 (hereinafter referred to as basic clock) which follows the modulation synchronization clock 719 (hereinafter referred to as image clock) of LD31.
This is a clock selector that selects from oscillators 251, 252, 253, and DPISE from CPU U2O5.
Selection is made by LECT signal 5113.

The image clock 511 is activated by a command from the CPU U2O5.
The reason why 9 frequencies can be selected is to make the printing density (pixel density) of the laser printer 1 variable.

To change the printing density, if no changes are made to the mechanical structure of the optical system shown in FIG. It is necessary to change at least two of the rotational speed of the photoreceptor 2), but in the embodiment, a method of changing the rotational speed of the polygon mirror 34 and the modulation frequency of the LD 31 is adopted as the changing means, and when the power is turned on, Initial settings are made using the initial setting switch described above, and subsequent changes are made by setting the DPIRQ flag to a value corresponding to the change request, as described later. It is now possible to do so. Hereinafter, the three types of printing densities will be referred to as printing density 1, printing density 2, and printing density 3 in descending order of density.

Next, Fig. 9, Fig. 10, and Fig. 11 (a) to (C)
The image position determination control will also be explained with reference to .

First, during printing, the 5SCAN signal 5112 is periodically generated as shown in the top row of FIGS. The operation will begin. As shown in FIG. 11(a), the 5SCAN signal S 1
12, the output Q (CTCATEO) S116 of the flip-flop 254a becomes "H", and
As a result, the output Q (CT
GATE 1”) S117 is the basic clock (1/I C
LK) goes high in synchronization with the rise of S115, CT
When GATEI 5117 becomes H”, the clearing (CLR) of the flip-flop 255 is released and the output Q 511
8 to 1/2 divided clock of basic clock 5115 (1
/2CLK) output starts. Furthermore, the load (LD) of the 4-bit counter (CTI) 256 is also released, and 1
/2 When CLKSllB is input, down-counting starts, and clocks obtained by dividing 1/2CLK into 1/2.1/4.1/8.1/16 are output from outputs QA, QB, QC, and QD, respectively. be done.

Start counter (CT2) 257 and end counter (CT2) for determining the start and end of printing in the main scanning direction
The gate of the C70) 258 is opened by the rise of the 5SCAN signal 5112, and then the 4-bit counter 258 is opened.
Counting is started by the inverted clock from the output QD of 6. Start counter 257 and end counter 2
58 output S122. S123 is L'' while counting continues, and becomes H when the countdown from the set value reaches zero, so this output is used to determine the image area in the main scanning direction.End counter When 258 finishes counting, FIG. 11 (C
), the output 5123 rises and an "L" pulse is output from the output 5124 of the monostable multivibrator 259, and the rise causes the output Q of the flip-flop 261 to become "L", which causes the LD DATAS10
4 is forcibly set to "H", and the LD 31 emits light.

Due to the forced light emission of the LD 31, the beam detector 38 is scanned again, and an H'' pulse of the 5SCAN signal 5112 is generated. ) 5138 to flip-flop 2
54a clear (CLR) S140, output of flip-flops 254a and 254b QS116
．． S 117 is set to "L", thereby stopping the output of the clock from the output Q S 118 of the flip-flop 7 255.

The image area in the main scanning direction is the start counter (C
r2) 257 and end counter (C70) 258
(see Figure 19), that is, 5SCA
A start counter 257 determines the start of an image from the rising edge of the N signal, and an end counter 258 determines the end of the image from the rising edge of the SSCAN signal 5112.
, an appropriate value (determined by the paper size) is set in advance from the CPU2O5 before exposure, and the output S L22. An image area is determined from S123. FIGS. 11(b) and 11(c) are detailed time charts near the end of each counter. Between the image areas, a DREQ signal S 102 and a LOAD signal 5131 are generated as shown in FIG. 1θ. The data control unit 300 outputs 8-bit parallel data (L DATA
) to the laser printer. Furthermore, the parallel-to-serial converter 264 takes in the data S 103 due to the “L” level of the LOAD signal 5131, and outputs the image clock (IMCL).
K) LD drive data (LD DA) synchronized with S119
TA) It is sent to the LD drive section 218 as S104.

The image area in the sub-scanning direction is CP as shown in FIG.
5S S T A RT S 114 from 0202
WRST signal S1 which is a signal latched with CAN signal
Determined by 00. That is, the DREQ signal 5102 is sent to the data control unit 300 only when the WR5T signal S 100 is II HII.

Next, a method of generating the AIDC mark MA will be explained. AIDC is created by exposing and developing a solid black mark at a certain position and size on the photoreceptor 2.
The density of the mark is read by the reader 9, and if the density is below a certain level, the developer 4 is supplied with toner. The AIDC mark is a mark for reading. The position of this AIDC mark is
Naturally, it is created outside the image area, but in this embodiment, in the main scanning direction, it is within the area where printing is actually performed, and in the sub-scanning direction, it is outside the area where printing is actually performed. Therefore, since the AIDC mark is formed on the part of the photoreceptor 2 that is actually used for printing, the sensitivity due to the use of the photoreceptor 2 will be reduced. Appropriate concentration control will be performed without being affected by fluctuations.

Positioning of the AIDC mark in the main scanning direction is performed by a start counter 257 that determines the image start and a monostable multivibrator 260, that is, as shown in FIG. When the output 5122 rises due to the completion of the start counter 257 whose value has been set, an H'' pulse is output from the output Q S 125 of the monostable multivibrator 260, and the area between these 'H'' pulses is defined as a mark area.

On the other hand, positioning in the sub-scanning direction is performed by releasing the clear (CLR) of the monostable multi-vibrator 260 only when printing (see FIG. 13). Since the pulse time is constant, the mark width in the main scanning direction changes depending on the print density.

Next, the generation of the 5SCANOUT signal will be explained.

The programmable counter (CT4) 26 has an input GA
Due to the rising edge of the input signal to TE, 5SCAN signal 5
The "L" pulse with a pulse period of 112, that is, a value slightly longer than the beam scan period of the beam detector 38, is the output 0U.
An appropriate timer value is set from CPU2O5 in accordance with the print density so that the timer value is emitted from T136. Input G
Since the 5SCAN signal 3112 is connected to the ATE, as long as the polygon mirror 34 rotates at a normal rotation speed and the LD 31 continues to emit light normally, the output "L" pulses overlap and the "L'" state is maintained. continue. However, L
Since the LD 31 does not emit light during the DBIAS signal S1 signal furnace L'', the AND gate 263 forces the 5SCANOUT signal S107 to be "L" during that time.
is input to the interrupt terminal of the CPU 202.

Next, while referring to the flowcharts in FIGS. 12 to 17 and the time chart in FIG.
The details of control by 2O5 will be explained. First, the flag and internal timer used here will be explained.

PRRJT indicates a state in which print commands are not accepted.

PRNT indicates that this flag is “1” indicating that printing is in progress.
If a print command is accepted at ``, printing can be performed immediately from paper feed without starting up the main motor or photoreceptor 2.

DPIRQ indicates a print density switching (change) request and the print density after switching; 0 indicates no request, ■.

2.3 is a request for switching to printing density 1.2.3, respectively.

PLYCH indicates that it is necessary to determine whether the polygon mirror 34 has reached a constant speed.

EXPEND indicates the end of exposure.

BFEXP indicates that a print command has been accepted, but exposure for printing has not yet started.

1.2.3 DPIAC accepts the print density command and indicates the print density content; 0 indicates that it is not accepted.
indicates that a print density command with a request to switch (change) print density 1, 2, or 3 has been received.

INHCH is a flag that becomes 1'' from the start of exposure to the end of writing of the AIDC mark, and while this flag is 1'', the printing density cannot be changed under any conditions.

TIMO~14. TIMEO~E2. TIMSO~S1
．． TIMNX indicates an internal timer that determines the on/off timing of each element during printing.

t1-t14. tEO~tE2. tSo〜tS
t.

tNX is a timer value, details of which are shown in the time chart of FIG. to will time out as soon as the timer is set to this value.

FIG. 12 shows the main flow of control. When the power is turned on, first the RAM 206 and the interface 201a are activated.

Input/output ports 207, 209, timer 213, start counter (CT2) 257, end counter (C
T3) 258 is initialized. As a result, the timer 213 outputs the clock S12 with a period determined by the set value, and the start counter (CT2) 2
57 and an end counter (CT3) 258 maintain the "L" state while counting clocks input from the outside. Furthermore, the flag and internal timer are cleared (step N1).

Next, initial startup control (step N2) is performed.

FIG. 13 is a flow showing the details. First, turn on the heater 229 of the fixing roller 15 in step N9.
), then read the value of the print density initial value setting switch 237 (step Nl0).Since the switch 237 has two sets, it can take four types of states, 0.1 and 2.3, and each Print density 1, print density 1, print density 2
, printing density 3, and in order to obtain the rotation speed of the polygon mirror 34, the frequency of the basic tarok, and the aforementioned 5SCANOUT signal that match each printing density, a timer 213, a DPISE LCT signal 5113, and a programmable counter ( CT4) Set an appropriate value to 262 (step Nil, N12. N15), l
Therefore, by setting the initial setting switch 237 to match the printing density that the user always uses, the value of the initial setting switch 237 is read in step N2 when the power is turned on, and printing is performed accordingly. The density will be initialized. Note that the print density is subsequently changed by a command from the data control unit 300 as described later (steps N27 to N35).
*tcl, tc2. tc3 is a value set in the timer 213, and is the period of a synchronization pulse that synchronizes the rotation speed of the polygon mirror 34 at a print density of 1°2.3. Also, tssl+t's2. tss
3 is a programmable counter (CT4)
262, and each print density is 1. 2. 3
This is the pulse length of the "L" pulse generated to detect the 5SCANOUT signal at

By the way, the heater 229 and the polygon mirror 34 are
It is not possible to become ready for printing (hereinafter referred to as READY state) immediately; in other words, the heater 229 requires a transition time to reach the set temperature, and the polygon mirror 34 requires a transition time to reach a constant speed. be.

Therefore, in step N14, it is determined whether the heater 229 and the polygon mirror 34 are both in the READY state, and if YES, the READY status is set to "1".
(Step N15).

When the initial startup control (step N2) is completed, that is, R
When the ADY state is reached, the main loop is entered. In the main loop, status transmission and reception control is first performed (step N
3), here the data control unit 300 shown in Table 2
The status of laser printer 1 is read and the status of laser printer 1 is sent out.

Next, command control is performed (step N4), in which processing at the time of receiving or transmitting each command shown in Table 1 is performed.

FIGS. 14(a) to 14(c) are flowcharts showing details of command control. Steps N16 to N27 of these represent processing when a print command is received. When a print command is received (step N16), the PRRJT flag indicating whether an error is occurring (step N17) or a print command cannot be accepted is determined.Step N
18) If there is no error and the state is ready for acceptance, the print command is accepted. If the print command is not accepted, send NAK to the data control unit 300 (step N27). If the print command is accepted (step N9), if the PRNT flag indicating the print status is alON, that is, if it is not in the print status, the NAK is sent to the data control unit 300 (step N27). to (step N20), and also TIMEI, TIME2
(Step N21). On the other hand, if the PRNT flag is 1", set to in 71M5 (Step N22), and clear TIMEO (Step N25). Printing is started by either Step N20 or N22. When printing is started, the PRRJT flag is set to "1" to prohibit reception of print commands (Step N24), and the BFEXP flag, which indicates that exposure has not yet started, is set to "1" (Step N25). , AC to the data control unit 300
K is transmitted (step N26).

Next, steps N28 to N35 show processing when a print density command is received.

When the print density command is received (step N28), it is determined whether an error other than a recoverable error such as paper empty or toner empty is occurring (step N29). If an error is occurring, the data control unit 30
Send NAK to 0 (step N35), accept the command if there is no error, and send NAK to 1 according to the print density request.
．． Step N31.2.3 should be set in the DP IAC flag. N32. N33), data control unit 300
ACK is sent to (step N34).

Next, steps N36 to N38 show processing when sending an exposure end command. If the EXPEND flag indicating the end of exposure is 1''' (step N36), an exposure end command is sent to the data control unit 300 (step N37). Then clear the EXPEND flag (step N5B
), the data control unit 300 uses this command to prepare for sending the next print data.

When the command control (step N4) is completed, the process moves to sequence control (step N5).

FIGS. 15(a) to 15(c) are flowcharts showing details of sequence control. Here, the on/off flow of each element during printing is controlled by connecting internal timers in a chain. The start of this control is by command system W (
This is done by accepting the print command in step N4), and the timer value to is sent to TIMO or 71M5.
is activated by the set of . Detailed timing is on the 18th
This is shown in the time chart in the figure.

In the command system m<step N4), to TIMO
When is set, the time-up immediately occurs in step N39, and thereafter the on/off timing of each element as shown in FIG. When is set, the time-up immediately occurs in step N51, and thereafter the control from N51 to N101 is performed in step N39.
From N50 is a start-up operation for starting the actual printing operation, in which the main motor 224, eraser 8 are turned on, charging mode -3 is turned on, and the developing bias 22 of the developing unit 4 is turned on.
7 is turned on, and on the other hand, the LDON signal is turned on, and the L
When the DB IAS signal is turned on, the LD 31 is forced to emit light, and as a result, the scanning light 39 enters the beam detector 38, and a series of controls within the print data writing control circuit 217 is started. The LDON signal is turned off after a period of time sufficient to initiate the control.

The PRNT flag indicating the print status becomes "bi" immediately when TIMO times out (step N39).

This value becomes 0'' at the end of the series of printing operations (step N96).

Steps N51 to N55 are paper feeding control. After the leading edge of the fed paper passes PSL (steps N56 and N57), exposure is started after a certain period of time (step N5B). However, if the polygon mirror 34 is not at a constant speed, that is, the PLYCH flag is "1". '', the exposure is not started and the check is repeated to see if the PLYCH flag becomes "0" (step N59), the polygon mirror 34 becomes constant speed, and the FLYCH flag becomes "0".
0'', set timer values in the start counter (C70) 257 and end counter (CTa) 258 according to the print density and paper size, and turn on the 5TART signal 5114 to start exposure.Step N6
0), this starts exposure, so the BFEXP flag is set to "0", and in order to prohibit changing the print density, the I
The NHCH flag is set to "1" (step N61).

Therefore, for example, if the rotation speed of the polygon mirror is changed in response to a request to change the print density before exposure, the exposure will be stopped until it is determined that the polygon mirror has reached a constant speed after the change in rotation speed. , exposure is performed as soon as the polygon mirror reaches a constant speed.

5TART at the end of exposure (steps N67 to N70)
EXPEND which turns off the signal 5114 and indicates the end of exposure.
Set the flag to 1″.

Steps N64 to N66 and N71 to N72 are controls regarding the registration roller 14. After exposure, the timing (
Here, it is turned on after tlO time) and turned off when the paper finishes passing through the registration rollers 14.

Steps N73 to N87 are controls related to AIDC. After t11 hours have passed after the end of exposure, a count value that determines the start position of the AIDC mark MA in the main scanning direction is first set in the start counter (C70) 257 (step N74).The count value at this time is set according to the print density. It becomes something. Immediately thereafter, the AIDC signal is turned on (step N75), and turned off after the elapse of time t12 (step N78). As a result, the mark is placed at the position in the main scanning direction determined by the print data writing control circuit 217 during time t12. It is formed. This mark is formed at a position that can be read by the density reader 9 based on the count value, and in order to determine the starting position in the main scanning direction, a start counter is used to determine the starting position of the image area. (C70) 257 is also used,
No dedicated counter or timer is used for this mark. Immediately after the mark is formed, the INHCH flag is set to "0" to permit a change in print density. If there is a change request at this point, a change in print density will be started as described later. Further, after t13 hours have elapsed after mark formation (this is the time when the exposed mark is developed and just reaches the density reading unit 129), the density detection LED 223
Turn on the light (Step N81), judge the density of the mark (Step N82), and if the density is below a certain value, turn on the solenoid 222 for toner replenishment (Step N83), after t14 hours. Turn off (steps N86 and N87).

Steps N88 to N89 perform control to determine the timing for accepting the next print command.

In this embodiment, after tNX has elapsed after the start of exposure, the PRRJT flag that prohibits reception of print commands is cleared at that time.

Steps N90 to N94 are for controlling the timing at which the transfer charger 5 is turned on, and are turned on only when the paper passes through -5 during transfer charging. This is because if the AIDC mark MA is on when it passes the transfer charger 5, there is a risk that the toner will separate from the photoreceptor 2 and pollute the inside of the machine.

Steps N95 to N102 are controls for stopping the printing operation when the printing operation is completed and there is no next print request. When the sequence system '4B (step N5) is finished, the image forming section control (step N6) is completed.
to go into.

FIG. 16 is a flowchart showing details of image forming section control.

Here, image-related parts such as the polygon mirror 34 or the LD 31 are controlled.

Steps N103 to N108 determine the timing to actually change the print density in response to the reception of the print density command. In other words, even if a print density command is accepted, if the time is before the start of exposure of the previously accepted print command, the DPIRQ flag indicating a change request is not set (steps N103 to N106.Furthermore, even after the start of exposure, Also, until the writing of the AIDC mark MA is completed, that is, while the INHCH flag is “1”, the DP
Do not accept requests to change print density using the IRQ flag (
Steps N107, N108), L. Therefore, the actual start of the print density change operation is the exposure of the print according to the print command received before the time when the print density command related to the change is received, and the AI
This is the time when all the writing of the DC mark MA is completed.

When a request to change the print density is accepted, S S CANOU
In order to disable T interrupt (step N109), obtain the rotational speed of the polygon mirror 34 according to the required printing density, the basic tarok frequency, and the above-mentioned 5SCANOUT signal.
Appropriate timer values tcl and tc2 for the timer 213
Alternatively, set tc3 and send the DPISELECT signal to select an appropriate oscillator clock (step N
110 to N113), and even programmable
Appropriate timer value tss for counter (CT4) 262
Set L tsa2+ or tss3+.

After that, the DPIRQ flag is cleared and the PLYCH flag indicating that the polygon mirror 34 is not at a constant speed is set to "1".
(Step N114), and while the FLYCH flag is 1'' (Step N115), the polygon mirror 34
Step N116)
, when the speed becomes constant, the FLYCH flag is cleared and the above 5.
Release the interrupt prohibition of the SCANOUT signal.

Here, the reason why interrupts are prohibited while the polygon mirror 34 is not at a constant speed is because the frequency of the polygon mirror 34 and the basic clock are not matched during this period, so even though there is no abnormality, the interrupt of the 5SCANOUT signal is prohibited. This is because there is a possibility that there will be interference.

FIG. 17 is a flowchart showing the processing at the time of an interrupt of the 5SCANOUT signal. When a 0 interrupt occurs, subsequent interrupts are prohibited (step N119), the power to the LD drive is turned off (step N120), and the LD31 emits light. Try not to.

When the image forming section control (step N6) is completed, error control '411 (step N7) is performed. Here, errors such as paper empty, toner empty, jam, eraser lamp burnout, or high pressure section failure are detected.

Finally, in step N8, other controls related to print control, such as display control, temperature control, and paper size detection, are performed, and then the process returns to step N3, which is repeated thereafter.

In the above embodiment, a presettable down counter is used as a timer means, and the timer function is achieved by inputting pulses of a fixed period to this, but other counters and timers may also be used. often,
In short, it is sufficient if substantially two types of time setting or time measurement are performed, one for the image area and one for the mark.

In the above embodiment, the INHCH flag is set to "0'" immediately after writing of the AIDC mark MA is completed.
I tried to allow changing the print density as AID.
Even after the writing of the C mark is finished, changing the print density is prohibited, and image formation in the next image area is completed, or image formation in the image area before the next AIDC mark is completed. After a series of image forming operations are completed, the print density may be allowed to be changed.

(Effects of the Invention) According to the present invention, even if there is a request to change the pixel density from a host computer or the like during the operation of forming a density detection mark, the pixel density remains unchanged at least until the operation of forming the density detection mark is completed. Since no changes are made, images such as density detection marks can be formed normally even if a host computer or the like issues a request to change the pixel density at any timing. Therefore, there is no need for the host computer to constantly recognize the status of the laser printer or to request changes to the pixel density while checking the timing when image formation is not in progress. Signal processing for this purpose is extremely easy, and image processing can be performed at high speed.

[Brief explanation of drawings]

The drawings show embodiments of the present invention; FIG. 1 is a front sectional view of a laser printer, FIG. 2 is a perspective view schematically showing the optical system of the laser printer, and FIG. System block diagram, Figure 4 is interface 2
01 signal line configuration, Figure 5 is a block diagram of the print control section of the laser printer, Figure 6 is a diagram for explaining the signal content from the output port of the print control section, and Figure 7 is the same. A diagram to explain the connection to the input port,
FIG. 8 is a circuit diagram showing an example of the print data writing circuit of the print control section; FIGS. 9 to 11 (a), (b), and (C) are time charts showing the states and timings of each signal; 17 to 17 are flowcharts showing the control details of the laser printer, FIG. 18 is a time chart showing the operation timing of each part of the laser printer, and FIG. 19 explains the image area on the photoreceptor and the position of the AIDC mark. This is a developed diagram for 1... Laser printer, 2... Photoreceptor, 34...
Polygon mirror, 38... Beam detector (light detection sensor), 39... Scanning light, 128... Laser beam (laser light), 200... Printing control section, MA.
・・AIDC mark (concentration detection mark). Applicant Minolta Camera Co., Ltd. 2 m No. 3 Port No. 4 Fig. A 141 Hole 0 No. 14 + C 1b No. 140C Fig. 15 C Fig. 17 @19!21

Claims (1)

[Claims] In a laser printer that scans a laser beam to form an image with a large number of pixels on a photoreceptor, and also changes the pixel density by changing the rotation speed of a polygon mirror, density detection is performed outside the image area on the photoreceptor. If a pixel density change request occurs during the density detection mark formation operation, the pixel density is changed at least until the density detection mark image formation operation is completed. A laser printer characterized in that a changing operation is not started.