JPS63243911A - Laser printer - Google Patents

Abstract

PURPOSE:To maintain the period of a picture element density or printing density at a desired value by providing a photodetecting sensor and means for detecting the abnormality of laser light to a laser printer. CONSTITUTION:The laser printer which maintains the picture element density or printing density at the desired value by changing the scan period of laser light is constituted as follows: The laser light from a laser diode 31 subjected to modulation driving is corrected in the spread of the light by a collimator lens 32 and a cylindrical lens 33 in series thereto and is entered to a polygon mirror 34. The scan light to a photosensitive body 2 is formed by rotating the mirror 34. The scan light is thereafter made into a beam 128 by an ftheta lens 35. This beam is adjusted to a uniform speed and is reflected by folding mirrors 36 and 37 so that the photosensitive body 2 is scanned by the scan light 39 via a beam detector 38 for determining the printing position in the main scanning direction. The scan period meeting the picture element density is thus determined and is made to deal with defective light emission of a diode and defective rotation of the polygon mirror.

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 capable of changing the pixel density, and in particular, a laser printer capable of detecting abnormalities in laser light caused by laser diodes, polygon mirrors, etc. related to laser printers.

(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 that use combinators.

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 adjusted to these. It is necessary to make it variable. 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, in order to detect abnormalities in laser light caused by laser diodes, polygon mirrors, etc., the scanned laser light is detected by a photodetection sensor for each scan, and the output from the photodetection sensor is output at a constant cycle. In other words, it is detected whether the laser beam is passing over the photodetection sensor within a certain period of time. However, in the past, the cycle (time) that is the standard for determining the quality of laser light is fixed, so laser printers with variable laser light scan cycles cannot accurately detect abnormalities in the laser light. I couldn't do it. In other words, the time used as the criterion for judgment must be set longer than the longest cycle (time) of the laser light scan cycles, so if the scan cycle is short, critical detection cannot be performed and normal Even in abnormal cases where the scan period was longer than the state, this could not be detected.

(Means for Solving the Problems) In view of the above-mentioned problems, the present invention provides a laser printer in which the pixel density (printing density) is variable by changing the scan period of the laser beams, and which accurately detects abnormalities in the laser beams. The technical means for this purpose is to use a photodetection sensor that detects the scanned laser light, and the output of the photodetection sensor to detect when the laser light scans within a certain period. The present invention is characterized in that it includes a detection means for determining whether or not there is a laser beam and detecting an abnormality in the laser beam, and a changing means for changing the period for determination by the detection means in accordance with the pixel density.

(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 is a separation belt for separating the paper from the photoreceptor 2; 7 is a cleaner blade for collecting excess toner after transfer; 8 is for removing (irradiating) excess charge to make the charging uniform in the charging 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 that guides the paper to the transport path, 12 is a transport roller, and 13 is a manual paper feeder. A conveyance roller that also serves as a paper roller, and 14 a resist that determines the recording position with respect to 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 thereto is the sub-scanning direction). 15 is a fixing roller that fixes the toner transferred by the transfer charger 5 onto the paper; 16 is a main body discharge roller; 17 is a reversing unit for discharging the paper from the back side; 18 is a roller for switching between back and front side discharge; It is a paper guide claw and can be operated manually. 19 is a conveyance path for surface ejection, 20 is an ejection roller. 21 is a group of magnets for identifying the paper size in the paper cassette 10. The sensor 22 detects and identifies whether or not there is a magnet in the 3-bit storage frame. 23 is a paper empty sensor that detects the presence of paper in the cassette, Psi, P
S2. 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 modulated and driven by a 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. When the data has been expanded, the ink-face 201 issues a print start request to the print control unit 200 of the laser printer 1. 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 at the time of exposure that actually requires image data, and uses the data to read data from the bitmap memory. L.D.
The protocol of the zero-order interface 201 that modulates the 31 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, 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 so-called exposure 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 5SCAN) signal 5102 indicating that
5103 is a data request signal (hereinafter referred to as DRQ) for requesting 8-bit image data, and 5103 is the DRE signal.
This is an 8-bit image data signal output by the Q signal.

At the time of exposure, the WR3T signal S100 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 I. 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 SIO. In the figure, 205 is a system ROM that stores the control program, 206 is a system RAM that is a work area for the control program, and 203 is a CP
An oscillator that creates a clock that synchronizes the operation of U, 20
4 is a reset circuit that resets the entire circuit when the power is turned on; 208 is a motor, solenoid, heater, and other various drive units; 207 is an output port that provides signals to the drive unit 208; 210 is a paper sensor, concentration sensor, etc. 209 is a human-powered boat that receives and receives signals from the sensor 210, and 212 is an operation panel having display elements such as LEDs or input elements such as switches.

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 set value of the timer 213 can be set by commands from the CPU 202, and
The rotation speed can be changed and set arbitrarily.

This is the polygon mirror 34 when changing the printing density.
This is because it is necessary to change the rotation speed of the Further, the scanner driving unit 215 sends a polygon rotor signal Sll to the input boat 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.
17, scanning light 39 is transmitted from the image data sent from the data control unit 300 to a predetermined position on the photoreceptor 2.
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 boat 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 boat 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 1; 231 is a main motor 22;
4 defect detectors, 232 and 233 are defect detectors of charging charger 3 and transfer charger 5, respectively; 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, which notifies the input boat 209 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 in the main scanning direction, and generates a synchronization signal (SSCAN) for determining the above printing position. Forced light emission of the LD31 outside the image area, determination of sample timing of automatic power control (hereinafter referred to as APC) of the LD31, and control of light emission of the LD31 and polygon mirror 34
Table 3 shows the contents of the input/output signals to this circuit 217, which is used to detect abnormalities in the rotation of the circuit 217.

(Margin below) Table 3 In Fig. 8, 250 indicates the clock 5115 (hereinafter referred to as basic clock) that follows the modulation synchronization clock 5119 (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 l 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, The initial settings are made using the above-mentioned initial setting switch, and subsequent changes are made by setting the DPIRQ flag to a value according to the change request, as will be described later. It is possible to select different printing densities (pixel densities). 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. 5SCAN signal 511 as shown in FIG. 11(a)
2 rises, the output Q (CTGATEO) S116 of the flip-flop 254a becomes H', which causes the output Q (CTGA
TE-1) SILT is the basic clock (1/I CLK)
It becomes "H" in synchronization with the rise of 3115. CTGA
When TEL 3117 becomes H”, flip-flop 25
5 clear (CLR) is released and the output Q S 11B
1/2 frequency division clock (1/2) of the basic clock 5115 from
2CLK) is started. Furthermore, the load (LD) of the 4-bit counter (CTI) 256 is also released, and 1/
2 The down count starts when CLKS118 is input, and 1 is output from each of the outputs QA, QB, QC, and QD.
A clock obtained by dividing /2CLK into 1/2.1/4.1/8.1/16 is output.

A start counter (C70) 257 and an end counter (C70) are used to determine the start and end of printing in the main scanning direction.
) 258 has its gate opened by the rise of the 5SCAN signal 5112, and then starts counting by the inverted clock from the output QD of the 4-bit counter 256. Output S of start counter 257 and end counter 258 122. S123 is " while counting continues.
The output is L'', 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. When the end counter 258 finishes counting, the output 5123 rises as shown in FIG. 11(C), and the output 5124 of the monostable multivibrator 259 outputs an "L" pulse. but"
This forces the LD DATAS 104 to become "H" and the LD 31 emits light.

By forcing the LD 31 to emit light, the beam detector 38 is scanned again, and an "H" pulse of the 5SCAN signal 5l12 is generated. The output pulse from the monostable multipibrator 259 further sends a pulse from the borrow (BR) 313B with a 4-bit count 256 to the clear (CLR) S140 of the flip-flop 254a, and outputs Q S 11 of the flip-flops 254a and 254b.
6. Set S 117 to L II. As a result, the output of the clock from the output QS118 of the flip-flop 255 is stopped.

The image area in the main scanning direction is the start counter (C
70) 257 and end counter (C70) 25B
(see Figure 19). In other words, 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 5SCAN signal 3112.
, an appropriate value (determined by the paper size) is set in advance from the CPU2O5 before exposure, and the output S122. 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 5102 and a LOAD signal 5131 are generated as shown in FIG. 1θ.

The data control unit 300 outputs 8-pit parallel data (L DATA) in response to the rise of the DREQ signal 5102.
to the laser printer. Furthermore, the LOAD signal 5131 goes “L”, causing the discrete converter 264 to take in the data 5103 and output the image clock (IMCLK) S1.
LD synchronized to 19! S1 dynamic data (LD DATA
) is sent to the LD drive section 218 as S104.

The image area in the sub-scanning direction is CP as shown in FIG.
It is determined by the WR3T signal 5100, which is a signal obtained by latching the 5TARTS 114 from U2O5 with the 5SCAN signal. That is, the DREQ signal S102 is sent to the data control unit 300 only when the WR3T signal s too is "H".

Next, a method of generating an AIDC mark will be explained.

AEDC is produced by exposing and developing a solid black mark at a certain position and size on the photoconductor 2, and reading the density of the mark with a reader 9. If the density is below a certain level, the developing device 4 It is also controlled when replenishing toner.

The AIDC mark is a mark for reading. The position of this jIDcID-mark is naturally created outside the image area, but in this embodiment, it is located within the range where printing is actually performed in the main scanning direction, and within the actual printing range in the sub-scanning direction. Therefore, the mark for AIDC is formed on the part of the photoreceptor 2 that is actually used for printing (see Fig. 19). , photoreceptor 2
Appropriate concentration control can be performed without being affected by changes in sensitivity due to the use of .

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 when the start counter 257 whose value has been set ends, an H" pulse is output from the output Q S 125 of the monostable multi-bi break 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 multivibrator 260 only when printing (see FIG. 13).The monostable multivibrator 260 is output by the AIDC signal 3108 from the CPU 202. 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, which is slightly longer than the beam scan period of the beam detector 38, is output as 0UT.
136, an appropriate timer value is set from CPU2O5 according to the print density. Input GA
Since 5SCAN signal 5112 is connected to TE,
The polygon mirror 34 rotates at a normal rotation speed, and
As long as D31 continues to emit light normally, the output "L" pulses overlap and the "L" state continues. However, LDBI
Since the LD 31 does not emit light while the AS signal 5109 is "L", the AND gate 263 forces it to "L" during that time.
”.This 5SCANOUT signal 5107 is
It is input to the interrupt terminal of U2O5.

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.

- If the PRNT accepts a print command when this flag, which indicates that printing is in progress, is 1'', it can immediately print from paper feed without starting up the main motor or photoreceptor 2.

DPIRQ indicates a request to switch (change) the print density and the print density after switching; 0 is no request, and 1°2.3 is a request to switch to print density 1.2.3, respectively.

FLYCH 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.

TIM 0-14. TIME O~E2. TIM
SO to SL and TIMNX indicate internal timers that determine the on/off timing of each element during printing.

t1-t14. tEo~t E2. tSo〜ts
1°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 a clock 312 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 Nl).

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 N10). Since there are two switches 237, O, l, 2. 3, each corresponds to print density 1, print density 1, print density 2, and print density 3, and the polygon mirror 340 rotation speed and basic tarot that match each print density. In order to obtain the frequency and the aforementioned 5SCANOUT signal, appropriate values are set in the timer 213, the DP I 5ELCT signal 5113, and the programmable counter (CT4) 262 (steps Nil, N12. Nl3).
, I. 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 the value of the initial setting switch 237 is read in accordance with this. The print density will be initialized to the specified print density. Note that the subsequent change in printing density is performed by the data control unit 300 as described later.
(Steps N27 to N3
5), tel, tc2. tc3 is a value set to the timer 213, and the printing density is 1°2.3.
This is the period of the synchronization pulse that synchronizes the rotation speed of the polygon mirror 34 in . Also, 1ssl+ tss2+
tss3 is a programmable counter (C
T4) is the value set to 262, and each print density is 1. 2
．． This is the pulse length of the "L" pulse generated for the detection of the 5SCANOυT signal in 3.

By the way, the heater 229 and the polygon mirror 34 cannot immediately become ready for printing (hereinafter referred to as READY state). 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. 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 system m (step N2) is completed, that is, R
When the EADY 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 the laser printer l is read and the status of the laser printer l 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 II. Steps N16 to N27 of these represent processing when a print command is received. When the print command is received (step N16), it is determined whether there is an error (
Step N17) or check the PRRJT flag indicating whether the print command cannot be accepted or not. If there is no error (and if the print command can be accepted), the print command is accepted. If not, the print command is not accepted.
K is sent to the data control unit 300 (step N27), and when the print command is accepted (step N9), if the PRNT flag indicating the print status is "0", that is, if it is not in the print status, 10 is set to TTMQ. Set step N20), then TIMEL, TIME2
(Step N21), On the other hand, if the PRNT flag is 1'', set LO to 71M5 (Step N22), further clear TIMEO (Step N25), and start printing by either Step N20 or N22. When printing is started, the PRRJT flag is set to "l" 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). ), A for the data control unit 300
CK 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 N3B show processing when sending an exposure end command. If the EXPEND flag indicating the end of exposure is "!" (step N36), an exposure end command is sent to the data control unit 300 (step N37). After that, the EXPEND flag is cleared (step N38).
), the data control unit 300 uses this command to prepare for transmitting the next print data.

When the command system m<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 the command control l
(Step N4), the timer value 1 is sent to TIMO or T[M5.
Activated by setting 0. Detailed timing is first
This is shown in the time chart in Figure 8.

To TIMO in command system W (step N4)
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 10 is set,
Step N3 immediately times up in step N51, and then controls from N51 to N101.
9 to N50 is a start-up operation for starting the actual printing operation, which turns on the main motor 224 and eraser 8, and
Charger 3 on, developing bias 2 of developing device 4
27 is turned on, and on the other hand, the LDON signal is turned on,
When the LDBIAS 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 1'' immediately after TIMO times up (step N39). It becomes 0'' at the end of the series of print operations (step N96).

Steps N51 to N55 are paper feeding control. After the leading edge of the fed sheet passes through 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, if the PLYCH flag is 11tN. If so, do not start exposure and repeatedly check whether the FLYCH flag becomes MO'' (step N59), the polygon mirror 34 becomes constant speed, and the PLYCH flag becomes 0.
'', set timer values in the start counter (Cr2) 257 and end counter (CTa) 258 according to the print density and paper size, and turn on the 5TART signal 3114 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)
EXPEN which turns off the signal S114 and indicates the end of exposure.
Set the D 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 the 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 starting position of the AIDC mark 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 printing density. Become 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, but in order to determine the starting position in the main scanning direction, the starting point for determining the starting value 1 of the image area is The counter (C70) 257 is also used, and 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. Furthermore, after t13 hours have elapsed since the mark was formed (this is when the exposed mark has just been developed and the density reading section 12
9), the density detection LED 223 is turned on (step N81), and the density of the mark is determined (step N81).
Step N82) If the density is below a certain value, the solenoid 222 for toner replenishment is turned on (Step N83) and turned off after ti4 hours (Steps N86 and N87).

Steps N8B to 889 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 mark for AIDC 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 control (step N5) is completed, the image forming unit control m<step N6) is entered.

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 DP I RQ flag indicating a change request is not set (steps N103 to N106.Furthermore, after the start of exposure Even if there is, the D
A request to change the print density using the PIRQ flag is not accepted (steps N107 and N108). Therefore, the print density change operation actually starts for prints that were received before the time when the print density command related to the change was received. Exposure of prints by command and AI
This is the time when all the DC marks have been written.

When a request to change the print density is accepted, S S CANOU
In step N109), an appropriate timer value tcl + t is set in the timer 213 to obtain the rotation speed of the polygon mirror 34, the frequency of the basic tarokk, and the above-mentioned 5SCANOUT signal according to the requested printing density.
Set c2 or tc3, send the DP I5ELECT signal to select the appropriate oscillator clock (steps Nll0 to N113), and further set the programmable counter (CT4) 262 to the appropriate timer value tssL Lss2'+ or Set tss3+.

After that, the DPIRQ flag is cleared, and the PLYCH flag, which indicates that the polygon mirror 34 is not at a constant speed, is set to 1'' (step N114), and the FLYCH flag is set to 1.
” (step N115') 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 image forming unit side m<step N6) is completed, error control m (step N7) is performed. Here, errors such as paper empty, toner empty, jam, eraser lamp burnout, or high voltage 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.

(Effects of the Invention) According to the present invention, when the pixel density is changed, the period for determining whether the laser beam is scanning within a certain period based on the output of the photodetection sensor is changed. Since it has a changing means for changing the laser beam, it is possible to accurately detect abnormalities in the laser beam, and it is possible to precisely detect abnormalities such as a failure in light emission of a laser diode or a failure in rotation of a polygon mirror.

[Brief explanation of the drawing]

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), (c), and (c) are time charts showing the states and timing 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, 38...
Beam detector (light detection sensor), 39...Scanning light, 128...Laser beam (laser light), 200
. . . Print control unit, 217 . . . Print data writing control circuit (detection means for detecting abnormalities in laser light), 262.
...Programmable counter (change means). Applicant: Minolta Camera Co., Ltd. No. 2 W No. 3 Kuchiki 4 Kuchi No. 6 171 141. 'i0 Figure 14b Figure 14C Figure 15-〇 I7 rJ 191

Claims (1)

[Claims] A laser printer that has variable pixel density by changing the scanning period of the laser beam has a photodetection sensor that detects the scanned laser beam, and an output of the photodetection sensor that allows the laser beam to scan within a certain period. The present invention is characterized by comprising a detection means for determining whether or not the laser beam is being used and detecting an abnormality in the laser beam, and a changing means for changing the period for determination of the detection means according to the pixel density. laser printer.