JP2565879B2 - Laser printer - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser printer having a variable pixel density, and more particularly to a laser printer capable of appropriately responding to a request for changing the pixel density before exposure. is there.

(Prior Art) A laser printer forms a latent image by pixels on a photosensitive drum with laser light deflected by a polygon mirror that rotates at high speed, obtains a visible image by toner development, transfers it to plain paper, and then fixes it. Since the laser light can be modulated at high speed, high speed and high quality (high density) printing and graphic recording can be realized. Therefore, the laser printer has a wide range of applications as an output device of various data processing systems and image processing systems using computers.

By the way, there are various image densities of image signals output from a host computer or the like, and in order to print a normal image by receiving these outputs, the image density of the laser printer is variable according to these. There is a need. Further, it is necessary to change the pixel density of the laser printer in order to change the printing size by using the same pixel forming character generator.

In order to meet such demands, laser printers having variable pixel densities have been conventionally proposed (for example, Japanese Patent Laid-Open No. 59-198076), and the rotation speed of the polygon mirror is changed to change the pixel density. It is like this. However, the rotation speed of the polygon mirror that is driven by the motor and rotates at a high speed is changed, and it takes time to reach a stable state, so if exposure starts during this time,
There was a problem that the image was disturbed and a normal image was not printed. In order to avoid such a situation, the timing of the image density change request signal transmitted from the host computer to the laser printer is calculated so that the rotation of the polygon mirror is stable before the laser printer starts exposure. It had to be timed. But,
It is difficult to output the image density change request signal at such an appropriate timing, and the pixel density (print density) change request cannot be received from the host computer at any timing before exposure. It was

(Means for Solving the Problems) The present invention has been made in view of the above problems,
In a laser printer that feeds paper according to a predetermined sequence and then forms an image on the paper by an exposure operation, a unit that receives a request for changing the pixel density, and a unit that changes the rotation speed of the polygon mirror in response to the request. When,
Detection means for detecting whether or not the rotation speed of the polygon mirror changed in response to the change request is in a constant speed state, and the detection means at the timing before the exposure operation after the paper feed is started by the predetermined sequence. It is detected whether or not the rotation speed of the polygon mirror is in a constant speed state, and when the rotation speed of the polygon mirror is in a constant speed state, the exposure operation is continuously performed according to a predetermined sequence to perform the image forming operation, while the polygon mirror If the rotation speed of is not constant speed, the exposure operation is suspended until the rotation speed of the polygon mirror becomes constant speed, and as soon as the rotation speed of the polygon mirror becomes constant speed, the exposure operation is started immediately and the image is displayed. Means for performing a forming operation.

(Operation) The rotation speed of the polygon mirror is detected in response to the request for changing the pixel density at the timing after the start of the paper feeding operation according to the predetermined sequence and before the exposure operation, and the rotation speed of the polygon mirror is kept constant. When the polygon mirror rotation speed is not constant, the exposure operation is performed according to a predetermined sequence to perform the image forming operation.
The exposure operation is suspended until the rotation speed of the polygon mirror reaches a constant speed state, and as soon as the rotation speed of the polygon mirror reaches the constant speed state, the exposure operation is immediately started to execute the image forming operation.

(Example) Hereinafter, the present invention will be described based on illustrated examples.

FIG. 1 is a sectional view of the laser printer 1. In the figure, 2 is a photoconductor on which a latent image is formed by a laser beam, 3 is a charging charger for giving a uniform charge to the photoconductor 2, and 4 is a developing device for developing the latent image formed by the laser beam. 5 is a transfer charger for transferring the developed toner onto the paper, 6 is a separation belt for separating the paper from the photoconductor 2, 7 is a cleaner blade for collecting the residual toner after the transfer, 8 is the charging charger 3 The eraser that irradiates to remove the residual charge in order to make the charge even in 9 is a density reader that reads the density of toner, 10 is a paper cassette that stores paper, and 11 is a half-moon type that guides the paper to the transport path. Paper feed roller, 12 is a feed roller, 13 is a feed roller that also serves as a feed roller for manual paper, and 14 is a sub-scanning direction (the direction in which the laser beam scans the paper is the main A registration roller that determines the recording position on the paper in the scanning direction and the direction perpendicular to the scanning direction) is a fixing roller that fixes the toner transferred by the transfer charger 5 onto the paper, 16 is a main body discharge roller, Reference numeral 17 denotes a reversing unit for ejecting the paper on the back surface. Reference numeral 18 denotes a paper guide claw for switching the back side or front side discharge, which can be manually operated. Reference numeral 19 is a conveyance path for discharging the back side, and 20 is a discharge roller. Reference numeral 21 is a magnet group for identifying the paper size in the paper cassette 10, and the sensor 22 detects whether or not a magnet is present in the 3-bit housing frame for identification. twenty three
Is a paper empty sensor that detects the presence of paper in the cassette, and PS1, PS2, and PS3 are paper sensors.

FIG. 2 schematically shows an optical system of the laser printer 1. Referring to FIG. 1 and FIG. 2, reference numeral 31 is a laser diode (hereinafter, referred to as LD), which is modulated and driven by an LD drive unit described later. Reference numerals 32 and 33 are so-called collimator lenses and cylindrical lenses for correcting the spread of the laser beam. Reference numeral 34 denotes a polygon mirror, which is configured so that the laser beam scans the photoconductor 2 to obtain scan light 39 by rotating. Reference numeral 35 is an fθ lens for scanning the photoconductor on the photoconductor at a uniform speed, 36 and 37 are folding mirrors for guiding the laser beam to the photoconductor 2, and 38 is for determining a printing position in the main scanning direction. It is a beam detector, and the scanning light 39 is configured to scan the photoconductor 2 after passing through the beam detector.

FIG. 3 is a system block diagram when the laser printer 1 is actually used, and 400 is a general-purpose data processing device (for example, a word processor or a personal computer,
Other host computers, etc.), 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, in the data processing device 400, the laser printer 1 is passed through the interface 301 where a print request is generated.
Printer control data, which determines the print operation mode in
Also, print data for determining the actual print content is transmitted to the data control unit 300 by code data. The reason why the code is transmitted is to shorten the transmission time as much as possible. In the data control unit 300, the data based on the code data is received, and if the data is printer control data, the data is directly transmitted to the print control unit 200 of the laser printer 1 by the interface 201 described later. On the other hand, if the data is print data, the code data is converted into bit image data, which is then expanded into a memory called bit map memory that can store one page of bit image data, and the data for one page is expanded. Then, the interface 201 issues a print start request to the print control unit 200 of the laser printer 1. The laser printer 1 has a print control unit 20.
When the print start request is received at 0, the print operation is started, and at the time of exposure when image data is actually required, data is read from the bitmap memory through the interface 201, LD31 is modulated by the data, and the latent image is transferred to the photoconductor 2. Create an image. Then interface 201
The protocol and print control of the laser printer 1 will be described.

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

Referring to FIG. 5, the control interface 201a is used for exchanging data relating to the operation control of the laser printer 1, and the data control unit 300 sends data for designating a print style such as a paper feed port and a discharge port. And data for determining the timing of print start request etc. is sent,
On the other hand, the print control unit 200 sends data such as paper size information and error information for the internal condition of the laser printer 1 and data for determining the timing of printing end, paper discharge and the like. The interface 201a is composed of a command and a status. The command is used for exchanging the timing data and the status is used for exchanging other data. These commands and status are shown in Tables 1 and 2.

Next, the image interface 201b is used to read image data from the bitmap memory of the data control unit 300 at the time of so-called exposure during formation of a latent image on the photoconductor 2.

Fig. 4 shows the configuration of the signal line, and S100 is the light last (indicated by ▲ ▼) indicating that exposure is in progress.
A signal, S101 is a sensor scan (hereinafter referred to as ▲ ▼) signal indicating that the scanning light 39 (see FIG. 2) of the laser beam has passed through the beam detector 38, and S102 is 8
Data request (hereinafter referred to as ▲ ▼) signal for requesting bit image data, S103 is the ▲
▼ An 8-bit image data signal output by a signal. At the time of exposure, the signal S100 becomes "L", which causes the data control unit 300 to enter the system of image data transmission. Furthermore, the start of one line is recognized by the fall of the signal S101, and the signal S102 is detected.
The 8-bit parallel data is transmitted to the laser printer 1 in synchronization with the rising edge of.

FIG. 5 is a block diagram of the print control unit 200 of the laser printer 1. The configuration is a so-called multi-chip configuration centered on the CPU 202, and data can be exchanged with each chip by the bus S10. In the figure, 205 is a system ROM that stores the control program, 206 is a system RAM that is a work area of the control program, 203 is an oscillator that creates a clock that synchronizes the operation of the CPU, and 204 is the entire circuit when the power is turned on. A reset circuit for setting a reset state, 208 is a motor,
Various drive units such as solenoids and heaters, 207 is an output port that gives a signal to the drive unit 208, 210 is various sensors such as a paper sensor and a density sensor, 209 is an input port that receives a signal from the sensor 210, and 212 is an LED or the like. It is an operation panel having an input element such as a display element or a switch.

Reference numeral 215 denotes a scanner drive unit that controls the rotation of the polygon mirror 34, and a clock S12 transmitted from the timer 213.
The rotational speed of the polygon mirror 34 is determined in accordance with the above and driven. The set value of the timer 213 can be set by a command from the CPU 202, and the CPU 202 can arbitrarily change and set the rotation speed. This is because it is necessary to change the rotation speed of the polygon mirror 34 when changing the print density. Further, the scanner driving unit 215 sends to the input port 209 a polygon lock signal S11 indicating whether or not the polygon mirror 34 is rotating at a constant speed.

Reference numeral 218 denotes an LD drive unit that controls the drive of the LD 31, and based on a signal sent from the print data writing control circuit 217, L
Performs D31 modulation. The print data writing circuit 217 controls the scan light 39 to be turned on and off at a predetermined position on the photoconductor 2 based on the image data sent from the data control unit 300.
Create LD modulation data for the LD drive unit 218. The image data is exchanged at the image interface 201b. 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 contents of the objects to be driven are shown, and the circuits for actually driving these driving units and concrete wirings are omitted. Further, all mechanical drive units (each roller, toner replenishment unit, etc.) in this embodiment are driven by a chain from the main motor 224, and on / off thereof are performed by a clutch using a solenoid. 220 is a solenoid that determines whether or not the chain drive is transmitted to the paper feed roller 11, and 221 is a registration roller 14
Solenoid for use, 222 is a solenoid for deciding whether or not to drive a portion for supplying toner to the developing device 4, 223 is an LED attached to the density reader 9, 224 is a main motor, 227
Is a voltage applying device for applying a potential (relative to a developing bias) relative to the photosensitive member 2 to the developing device 4 so that the toner in the developing device 4 adheres only to the latent image formed on the photosensitive member 2. A high-voltage power source, 229 is a heater portion of the fixing roller 15. The output signal to the print data writing control circuit 217 will be described later.

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

230 is a switch for detecting opening / closing of a door separating the inside and the outside of the laser printer 1, 231 is a defect detector of the main motor 224, 232 and 233 are defect detectors of the charging charger 3 and the transfer charger 5, respectively, and 234 is a developing device 4. Toner empty detection sensor to detect the amount of toner inside, 235
Is a density detection sensor in the density reader 9, 236 is a face-up / down switch for detecting which state the paper guiding claw 18 is in, and 237 is print density (pixel density)
This is an initial setting switch consisting of a double switch for setting the initial value of, and by this, four kinds of settings can be performed.
A heat roller temperature controller 238 informs the input port 209 of the temperature of the heater.

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

This circuit 217 determines the image print position in the main scanning direction, determines the print position of the mark for automatic image density control (hereinafter referred to as AIDC) in the main scanning direction, and generates a synchronization signal (SSCAN) for determining the print position. L outside the image area
D31 forced flash, LD31 automatic power control (A
Determination of sample timing) and LD31
For detecting abnormalities in the light emission of and the rotation of the polygon mirror 34. Table 3 shows the contents of input / output signals to / from the circuit 217.

In FIG. 8, reference numeral 250 denotes a modulation synchronization clock S119 of the LD 31.
The clock S115 that is the source of the image clock
(Hereinafter referred to as the basic clock) with three oscillators 251,252,25
It is a clock selector that selects from 3 and is selected by a DPI SELECT signal S113 from the CPU 202. CPU202
The reason why the frequency of the image clock S119 can be selected by a command from is to make the printing density (pixel density) of the laser printer 1 variable.

In order to change the print density, if no change is made to the mechanical structure of the optical system shown in FIG. 2, the rotation speed of the polygon mirror 34, the modulation frequency of the LD31, or the conveyance speed of the paper ( At least 2 of the rotation speed of the photoconductor 2)
However, in the embodiment, the method of changing the rotation speed of the polygon mirror 34 and the modulation frequency of the LD 31 is adopted as a changing means, and the initial setting at the time of power-on is performed by the above-mentioned initial setting switch. As will be described later, the change is made by setting a value corresponding to the change request in the DPIRQ flag, and in each case, three types of print density (pixel density) can be selected. Hereinafter, the three types of print densities will be referred to as print density 1, print density 2, and print density 3 in ascending order of density.

Next, the image position determination control will be described with reference to FIGS. 9, 10 and 11 (a) to (c).

First, during printing, the SSCAN signal S112 is periodically generated as shown in the uppermost row of FIGS. 9 and 10, but a series of characters for printing in the main scanning direction is generated by the rising of the SSCAN signal. The operation will be started. First
As shown in Fig. 11 (a), the rising edge of SSCAN signal S112 causes
Output Q (CTGATE0) S116 of flip-flop 254a is "H"
And the output Q of the flip-flop 254b (CT
GATE1) S117 goes "H" in synchronization with the rise of the basic clock (1 / 1CLK) S115. When CTGATE1S117 becomes “H”, clear (CLR) of flip-flop 255 is released and output QS
From 118, 1/2 frequency-divided clock of basic clock S115 (1 / 2CLK)
The output of is started. 4 bit counter (CT1) 2
When the code (LD) of 56 is released and 1 / 2CLKS118 is input, downcounting starts, and 1 / 2CLK is 1/2, 1/4, 1/8, from output QA, QB, QC, QD respectively. The clock divided by 1/16 is output.

Start counter (CT2) 257 and end counter (CT3) 258 for determining the start and end of printing in the main scanning direction
The gate is opened by the rising of SSCAN signal S112,
After that, counting is started by the inverted clock from the output QD of the 4-bit counter 256. Start counter 25
The outputs S122 and S123 of 7 and the end counter 258 are "L" while the count continues, and become "H" when they become zero due to the countdown from the set value. Determine the image area of. When the end counter 258 finishes counting, FIG. 11 (c)
As described above, the output S123 rises and an "L" pulse is output from the output S124 of the monostable multivibrator 259, and the output Q of the flip-flop 261 becomes "L" due to the rise.
This forces LD DATAS 104 to go "H" and LD 31 emits light.

The beam detector 38 is scanned again by the forced light emission of the LD 31, and the "H" pulse of the SSCAN signal S112 is generated. The output pulse from the monostable multivibrator 259 is the pulse from the borrow (BR) S138 with a 4-bit count of 256 and the clear (CLR) S14 from the flip-flop 254a.
Send to 0 and output QS11 of flip-flops 254a and 254b
6, Set S117 to "L". This makes the flip-flop 255
The output of the clock from the QS118 stops.

The image area in the main scanning direction is determined by the start count (CT2) 257 and the end counter (CT3) 258 (see FIG. 19). That is, the start counter 257 that determines the start of the image from the rising edge of the SSCAN signal.
And an end count 258 that determines the end of the image from the rising edge of the SSCAN signal S112, an appropriate value (determined by the pacer size) is preset from the CPU 202 before exposure, and the image area is determined from the outputs S122 and S123. To do. FIGS. 11 (b) and 11 (c) are detailed time charts near the end of each counter. Between the image areas, as shown in Fig. 10, ▲ ▼
Signal S102 and ▲ ▼ signal S131 are issued. The data control unit 300 transmits 8-bit parallel data (L DATA) to the laser printer at the rising edge of the signal S102. Furthermore, the parallel-serial converter 264 takes in the data S103 by "L" of the signal S131, and sends it to the LD drive unit 218 as LD drive data (LD DATA) S104 synchronized with the image clock (IMCLK) S119.

The image area in the sub-scanning direction, as shown in FIG.
It is determined by the signal S100, which is a signal obtained by latching STARTS 114 from U202 with the SSCANS signal. That is ▲
The signal S102 is sent to the data control unit 300 only when the signal S100 is "H".

Next, a method of generating an AIDC mark will be described. AI
The DC is created by exposing a black solid mark at a certain position and a certain size on the photoconductor 2 and then developing it. The density of the mark is read by the reader 9, and if it is below a certain density, the developing unit 4 The control is to replenish the toner. The AIDC mark is the reading mark. The position of the AIDC mark is naturally formed outside the image area, but in the present embodiment, it is within the range in which printing is actually performed in the main scanning direction, and in the sub-scanning direction. This is the position immediately outside the range where printing is performed (see Fig. 19).

Positioning of the AIDC mark in the main scanning direction is performed by a start counter 257 and a monostable multivibrator 260 that determine the start of an image. That is, as shown in FIG. 10, when the output S122 rises due to the end of the start counter 257, an “H” pulse is output from the output QS125 of the monostable multivibrator 260, and the mark area is defined between these “H” pulses. On the other hand, positioning in the sub-scanning direction is performed by releasing the clear (CLR) of the monostable multivibrator 260 only when printing (see FIG. 13). Since the pulse time from the monostable multivibrator 260 output by the AIDC signal S108 from the CPU 202 is constant, the mark width in the main scanning direction changes depending on the print density.

Next, generation of the SSCANOUT signal will be described. The monostable multivibrator 262 has a "L" value that is slightly longer than the pulse period of the SSCAN signal S112, that is, the beam scan period of the beam detector 38, due to the rise of the input signal to the input B.
A pulse is emitted from output S136. SSCAN to input B
Since the signal S112 is connected, as long as the polygon mirror 34 rotates at a normal rotation speed and the LD 31 continues to generate normally, the output "L" pulses are overlapped and the "L" state continues. However, since the LD 31 does not emit light while the LDBIAS signal S109 is "L", the AND gate 263 forces it to "L" during that time. The SSCANOUT signal S107 is input to the interrupt terminal of the CPU 202.

Next, the control content of the CPU 202 will be described with reference to the flowcharts of FIGS. 12 to 17 and the time chart of FIG. First, the flag and internal timer used here will be described.

PREJT indicates that the print command is not accepted.

PRRT indicates that a printing operation is being performed. If the print command is accepted when this flag is "", printing can be performed immediately from the paper feed without starting the main motor or the photoconductor 2.

DPIRQ indicates a print density switching (change) request and the print density after switching. 0 is no request, and 1, 2 and 3 are requests to switch to print densities 1, 2 and 3, respectively.

PLYCH indicates that it is necessary to determine whether or not the polygon mirror 34 has reached a constant speed.

 EXPEND indicates the end of the exposure.

TIM0 to 14, TIME0 to E2, TIMS0 to S1, and TIMNX represent internal timers that determine the on / off timing of each element during printing.

_{t 1 ~t 14, tE0~tE2, tS0~tS1} , tNX is a timer value, are details shown in the time chart of Figure 18. t0
Will time up as soon as this value is set by the timer.

FIG. 12 is a main flow of the control. When power is turned on, RAM206, interface 201a, I / O port
207,209, timer 213, and start counter (CT2) 2
57, Initialize the end counter (CT3) 258. As a result, the timer 213 outputs the clock S12 having a cycle determined by the set value, and the start counter (C
The T2) 257 and the end counter (CT3) 258 are kept in the "L" state while counting the clocks input from the outside. Further, the flab and the internal timer are cleared (step N1).

Next, initial activation control (step N2) is performed. FIG. 13 is a flowchart showing the details. First, turn on the heater 229 of the fixing roller 15 (step N9), and then read the value of the print density initial value setting switch 237 (step N1).
0). Since the switch 237 has two lines, it can take four kinds of states of 0, 1, 2, and 3, and each corresponds to the print density 1, the print density 1, the print density 2, and the print density 3, In order to obtain the number of revolutions of the polygon mirror 34 and the frequency of the basic clock that match each print density, the timers 213 and D
Set an appropriate value to PISELCT signal S113 (steps N11, N
12, N13). Therefore, by setting the initial setting switch 237 so as to match the print density that the user always uses, the value of the initial setting switch 237 is read at step N2 when the power is turned on, and the print density corresponding to this is read. It will be initialized. The change of the print density thereafter is performed by a command from the data control unit 300 as described later (steps N27 to N35). tc1,
tc2 and tc3 are values to be set in the timer 213, respectively.
This is the period of a synchronization pulse that synchronizes the rotation speed of the polygon mirror 34 at print densities 1, 2, and 3.

By the way, the heater 229 and the polygon mirror 34 cannot be ready for printing (hereinafter referred to as READY state) immediately. That is, the heater 229 needs a transient time to reach the set temperature, and the polygon mirror 34 needs a transient time to reach a constant speed. Therefore, in step N14, it is determined whether or not both the heater 229 and the polygon mirror 34 are in the READY state, and if YES, the status READY is set to "1" (step N15).

When the initial startup control (step N2) ends, that is, RE
When it enters the ADY state, it enters the main loop. In the main loop, status transmission / reception control is first performed (step N3).
Here, the status of the data control unit 300 shown in Table 2 is read and the status of the laser printer 1 is sent out.

Next, command control is performed (step N4). Here, processing is performed when each command shown in Table 1 is received or transmitted.

FIG. 14 is a flowchart showing details of command control. Of these steps, steps N16 to N26 show the processing when the print command is received. When the print command is received (step N16), the PRRJT flag indicating whether an error is occurring (step N17) or the print command cannot be accepted is determined (step N18). Accept print commands. If it is not accepted, NAK is sent to the data control unit 300 (step N2
6). When a print command is accepted (Step N9)
, If PRNT flag is "0" indicating a print condition, that is, if a printed state, set to t ₀ to TIM0 (step N20), further TIME1, TIME2 clearing (step N21). On the other hand, if the PRNT flag is "1", t ₀ is set in TIM5.
Is set (step N20), and TIME0 is cleared (step N23). Printing is activated by either step N20 or N22. When print is activated,
The PRRJT flag is set to "1" to prohibit acceptance of the print command (step N24), and ACK is transmitted to the data control unit 300 (step N25).

Next, steps N27 to N35 show the processing when the print density command is received.

When the print density command is received (step N27), it is determined whether or not there is an error other than the recoverable error such as paper empty or toner empty (step N28). If there is an error, the data control unit 300 To NAK
Is transmitted (step N35). If there is no error, the command is accepted. If the print density request is not the same as the current print density (step N30), the DPIRQ flag indicating the print density change request is set to 1,2 depending on the print density request. , 3 values are set (steps N31, N32, N33), and the data control unit 3
ACK is sent to 00 (step N34).

Next, steps N36 to N38 show the processing when the exposure end command is transmitted. If the EXPEND flag indicating the end of exposure is "1" (step N36), the exposure end command is issued to the data control unit 300.
To (step N37) and then clear the EXPEND flag (step N38). The data control unit 300 prepares to transmit the next print data by this command. When the command control (step N4) is completed, the sequence control (step N5) is performed.

FIG. 15 is a flowchart showing details of the sequence control.
Here, the on / off flow of each element associated with printing is controlled by connecting internal timers in a chain. Start of this control is performed by reception of the print command in the command control (step N4), it is activated by a set of timer values t ₀ to TIM0 or TIM5.
The detailed timing is shown in the time chart of FIG.

If t ₀ to TIMO in command control (step N4) is set, immediately a time-up in step N39, then the control of the step N39 to N101,
Create the on / off timing of each element as shown in FIG. On the other hand, in command control (step N4), TI
If t ₀ is set to M5, immediately a time-up in step N51, then performs control from N51 to N101. Steps N39 to N50 are start-up operations for starting the actual printing operation, and the main motor 224 and the eraser 8
Is turned on, the charging charger 3 is turned on, and the developing bias 227 of the developing device 4 is turned on. On the other hand, the LD31 signal is forcibly emitted by turning on the LDON signal and turning on the LDBIAS signal, which causes the scanning light 39 to enter the beam detector 38 and start a series of control in the print data writing control circuit 217. To do. LDO
The N signal turns off after a sufficient time has elapsed to start the control.

The PRNT flag indicating the print state becomes "1" immediately after TIMO times out (step N39). This becomes "0" at the time when the series of printing operations is completed (step N95).

Steps N51 to N55 are paper feed control. The leading edge of the fed paper must pass through PS1 (steps N56, N5
7) Start exposure after a certain time (step N58). However, if the polygon mirror 34 is not at a constant speed, that is, PLYCH
If the flag is "1", the exposure is not started, and the PLYCH flag is repeatedly checked whether it is "0" (step N59). When the polygon mirror 34 becomes constant speed and the PLYCH flag becomes "0", the timer value according to the print density and the paper size is set in the start counter (CT2) 257 and the end counter (CT3) 258, and the exposure is performed. START to start
The signal S114 is turned on (step N60).

Therefore, for example, when the rotation speed of the polygon mirror is changed in response to a print density change request before exposure, the exposure is stopped until it is determined that the polygon mirror has become constant speed after the change of rotation speed. The exposure is performed as soon as the polygon mirror becomes constant speed.

At the end of exposure (steps N66 to N69), START signal S114
To OFF and set the EXPEND flag indicating the end of exposure to "1".

Steps N63 to N65 and N70 to N71 are controls relating to the registration roller 14. After exposure, the timing at which transfer to the paper is performed at a predetermined position (here, t ₁₀
It turns on after a lapse of time) and turns off when the paper has finished passing through the registration rollers 14.

Steps N72 to N86 are controls relating to AIDC. After t ₁₁ hours from the end of exposure, first start count (CT2)
A count value for determining the start position of the AIDC mark in the main scanning direction is set in 257 (step N73). Immediately thereafter, the AIDC signal is turned on (step N74) and turned off after t ₁₂ hours have passed (step N77). This allows for t ₁₂ hours,
A mark is formed at a position in the main scanning direction determined by the print data writing control circuit 217. It goes without saying that this mark is formed at a position where the density reader 9 can read it according to the count value. Further, after t ₁₃ hours have elapsed since the mark was formed (this is the time when the exposed mark is developed and just reaches the density reading unit 129), the LED 223 for density detection is turned on (step N80) to check the density of the mark. Judge (step N81). Solenoid for replenishing toner if the density here is below a certain value
Turn on 222 (step N83) and turn off after t ₁₄ hours (steps N85, N86).

Steps N87 to N88 control the determination of the timing for receiving the next print command. In this embodiment, it is assumed that TNX has elapsed after the start of exposure, and the PRRJT flag that prohibits the reception of print commands is cleared at that point.

Steps N89 to N93 are for controlling the timing at which the transfer charger 5 is turned on, and are turned on only when the sheet passes through the transfer charger 5. This is because if the mark for AIDC is turned on at the time when it passes the transfer charger 5, the toner may be separated from the photoconductor 2 and contaminate the inside of the machine.

Steps N94 to N101 are controls for stopping the print operation when the print work is completed and there is no next print request. Sequence control (Step N5)
Is completed, the flow enters the image forming unit control (step N6).

FIG. 16 is a flowchart showing details of control of the image forming unit. Here, control is performed on a portion related to the image, such as the polygon mirror 34 or the LD 31.

If there is a print density change request (step N102), it is determined whether or not exposure is in progress (step N103). If it is not in exposure, SSCANOUT interrupt is prohibited (step N104), and the print density is changed according to the required print density. In order to obtain the rotation speed of the polygon mirror 34 and the frequency of the basic clock, the timer 213 is set to an appropriate timer value tc1, tc2 or tc3, and a DPISELECT signal for selecting an appropriate oscillator clock is sent (step N105 to N108).

As a result, even if a print density change request is received during exposure, the print density is not immediately changed, but the print density is changed after the exposure is completed. Then, the DPIR0 flag is cleared and the PLYCH flag indicating that the polygon mirror 34 is not at a constant speed is set to "1" (step N109). While the PLYCH flag is "1" (step N110), it is determined whether or not the polygon mirror 34 has become a constant speed (step N111), and if it becomes a constant speed, the PLYCH flag is cleared and the SSCANOUT signal interrupt is prohibited. To cancel.

Here, the reason why the interrupt is prohibited while the polygon mirror 34 is not at a constant speed is that the polygon mirror 34 and the frequency of the basic clock are not matched during this period. This is because it may be complicated.

FIG. 17 is a flow chart showing the processing when the SSCANOUT signal is interrupted. When an interrupt occurs, subsequent interrupts are prohibited (step N114) and the power supply to the LD drive is turned off (step N11).
5) Make LD31 not emit light.

When the image forming unit control (step N6) is completed, error control (step N7) is performed next. Here, an error such as a paper empty, a toner empty, a jam, an eraser lamp burnout, or a high voltage section defect is detected.

Finally, in step N8, control other than the above regarding print control such as display control, temperature control control, paper size detection, etc. is performed, and then the process returns to step N3 again, and this is repeated thereafter.

As described above, according to the present embodiment, when there is a request for changing the print density (Yes in step N102), and during the exposure (No in step N103), the rotation speed of the polygon mirror 34 is changed. Instead, the clock is switched to change the rotation speed after the exposure is completed (step
N105-108). At the same time, in step N109, P
Set the LYCH flag to "1" and output that the rotation speed of the polygon mirror is in a non-constant state. After that, when the polygon mirror rotates at a constant speed (YES in step N111), the PLYCH flag is reset to "0" (step N11).
2) Outputs that the speed is constant.

When the internal timer TIMO is set to t ₀ by receiving a print command (YES in step N16) (step N20), TIMO immediately times up in step N39 of the sequence control, and paper feeding operation and charging are performed. A series of image forming sequences such as operations are started (steps N39 to N58).

In the image forming sequence, while the PLYCH flag is "1", that is, while the rotation speed of the polygon mirror is in the non-constant speed state, the result of step N59 is NO and the exposure is not started. Then, after the polygon mirror is in the constant speed state, the START signal turns on in step N60.
Then, the exposure is started.

Therefore, it is possible to accept the print density change request regardless of whether or not the exposure is being performed, and after the print density change request is received, it is detected whether or not the rotation speed of the polygon mirror is constant. The exposure is not started when the rotation speed of the polygon mirror is in the non-constant speed state, so that there is no problem in image formation.

(Effect of the Invention) According to the present invention, even if the rotation speed of the polygon mirror is in a non-constant state due to the change of the pixel density, the paper feed operation in which the rotation speed of the polygon mirror does not influence is executed, and the rotation speed of the polygon mirror is executed. Since the exposure operation is immediately started as soon as the state becomes the constant speed state, there is an effect that the loss time of image formation is minimized.

Further, when the rotation speed of the polygon mirror is in the non-constant speed state, the exposure operation is not started, and there is an effect that no inconvenience occurs in image formation.

BRIEF DESCRIPTION OF THE DRAWINGS The drawings show an embodiment of the present invention. FIG. 1 is a front sectional view of a laser printer, FIG. 2 is a perspective view schematically showing an optical system of the laser printer, and FIG. System block diagram when using a laser printer, Fig. 4 shows interface 20
FIG. 5 is a block diagram of a print control unit of the laser printer, FIG. 6 is a diagram for explaining signal contents from an output port of the print control unit, and FIG. FIG. 8 is a circuit diagram showing an example of a print data writing circuit of a print control unit, and FIGS. 9 to 11 are diagrams for explaining signal contents to an input port. 12 to 17 are flow charts showing control contents of the laser printer, FIG. 18 is a time chart showing operation timing of each part of the laser printer, and FIG. 19 is a photoconductor. FIG. 4 is a development view for explaining the upper image area and the position of the AIDC mark. 1 ... Laser printer, 2 ... Photoconductor, 39 ... Scan light, 200 ... Print control unit, 215 ... Scanner drive unit, 21
7: Print data writing control circuit.

Claims (1)

(57) [Claims] 1. Paper feeding is performed according to a predetermined sequence,
After that, in a laser printer that forms an image on paper by an exposure operation, a means for receiving a change request for pixel density, a means for changing the rotation speed of a polygon mirror in response to the change request, and a change for the change request A detecting means for detecting whether or not the rotation speed of the polygon mirror is in a constant speed state; and a rotation speed of the polygon mirror by the detecting means at a timing before the exposure operation after the paper feeding is started by the predetermined sequence. If the rotation speed of the polygon mirror is in the constant speed state, the exposure operation is continuously performed according to a predetermined sequence to perform the image forming operation, while the rotation speed of the polygon mirror is not in the constant speed state. At this time, the exposure operation is suspended until the polygon mirror rotation speed becomes constant, and the polygon mirror rotation speed becomes constant. And a means for immediately starting an exposure operation to execute an image forming operation.