JP3458878B2 - Laser beam scanning device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser beam scanning device, and more specifically, to a laser beam scanning device used in an image forming apparatus such as a digital copying machine, a digital printer, or a facsimile, which is capable of controlling the rotational phase of a polygon mirror. It relates to a technique for controlling.

[0002]

2. Description of the Related Art First, an example of a color image forming apparatus (four-drum type laser beam printer) will be described with reference to FIG. This color image forming apparatus is configured to form an image by a laser beam writing section and image forming sections for four colors of yellow, magenta, cyan and black. That is, in FIG. 23, a laser beam from each laser light source (LD) is emitted by a laser driver (not shown) that operates based on color-separated image information,
It is converted by the OFF signal, and is deflected by the polygon mirrors 231a to 231d while repeating the ON and OFF operations, and passes through the lenses 232a to 232d to expose the photoconductor 233a.
~ D are irradiated respectively. Around the photoconductors 233a-d, the charging chargers 236a-d and the developing unit 2 are provided.
34a-d, transfer chargers 235a-d, etc. are provided. Then, an image is formed on the recording paper 238 by charging, exposing, developing, and transferring, which are normal electrophotographic processes. That is, the recording paper 238 is the transfer belt 2
While being conveyed at 37, the image of the first color is formed on the recording paper, the images of the second color, the third color, and the fourth color are formed in this order, and the images of the four colors are superimposed to form a color image.

In the image forming apparatus as described above, a laser beam scanning device composed of a plurality of laser beams and a polygon mirror is disclosed in, for example, Japanese Patent Laid-Open No. 62-24.
2909 (conventional example 1), JP-A-2-170110.
There are known techniques described in Japanese Patent Application Laid-Open (JP-A) No. 3-175461 (Prior art 3), Japanese Patent Laid-Open No. 5-227383 (Prior art 4), and the like.

In the conventional example 1, a latent image is formed on the photosensitive drum by the laser light which is turned on and off in response to an image signal from the laser unit, and a predetermined image is developed by toner based on the latent image. Here, the laser beam uniformly scans the drum through the polygon mirror and the lens. The drums are arranged at regular intervals, and the laser beam is detected by the mirror. Then, the common reference frequency f0 is applied from the common frequency signal generating means to the signal terminal of the IC chip of the PLL for each color, the frequency signals FG fed back from the respective Hall ICs are compared, and a signal is issued to rotate the scanning motor. By controlling, the uneven rotation of the IC chips of each PLL is eliminated,
Rotation in which the surface phases (directions of mirror surfaces) of the respective polygon mirrors coincide with each other can be obtained, and good image quality can be obtained.

Further, in Conventional Example 2, the first beam detect pulse signal from the first and second laser beam detectors and the second beam detect pulse signal from the second detector have a phase difference. The phase difference is sent out, and the phase difference is measured by the clocking means such as an internal counter circuit in the rotation phase synchronization control device. Then, one of the reference signals is selected by the selection switch, and one reference signal is sent to the second phase synchronization controller as a reference signal for generating a phase close to the obtained phase difference. As a result, the first and second phase synchronization control units perform the phase synchronization control of the first and second motors, and thereafter, the phases of the first and second beam detect pulse signals become substantially the same, 1st and 2nd
The beam-reflecting surface of the rotating polygon mirror is in phase.

In the conventional example 3, a plurality of surfaces for reflecting the light beam to scan the photosensitive drum are provided, and a plurality of polygon mirrors driven by a motor and a plurality of rotation position detectors for detecting the rotation position of the polygon mirrors are provided. Set up. Then, feedback control is performed so that the interval between the rotational position signals detected by the rotational position detector becomes a predetermined value and the time difference between the rotational position signals between different polygon mirrors maintains a predetermined standard value. As a result, the amount of positional deviation between the print colors does not change each time the power is turned on, and the position adjustment can be performed accurately.

In Conventional Example 4, an optical scanning device provided with a scanner motor drive circuit including a PLL control circuit, a motor driver, and a scanner motor is driven by a reference clock from a reference clock generator, and the optical scanning devices output from each optical scanning device. The write position detection signal is supplied to the microprocessor. Then, the microprocessor obtains a time shift of the write position detection signals from the second to fourth light scanning devices with respect to the write position signal from the first optical scanning device, and outputs a phase control signal corresponding to each time shift. The configuration is such that each is added to the outputs of the PLL control circuits of the second to fourth optical scanning devices. Accordingly, it is possible to accurately correct the positional deviation in the sub-scanning direction due to the scanning timing changes of the plurality of optical scanning devices.

[0008]

However, the conventional color image forming apparatus has the following problems. That is, when a color image is created, it is necessary to superimpose the independently created image for each color of yellow, magenta, cyan, and black on a correct position on the recording paper. Then, in order to superimpose the image of each color on the accurate position on the recording paper, the recording start position of the image of each color on the photoconductor in the main scanning direction and the sub scanning direction must be accurately adjusted.

Here, with respect to the adjustment in the main scanning direction, for example, the laser scanning start position is constantly detected by a detector, and the writing timing of the recording data is adjusted for each color so that the laser beam writing in the apparatus is performed. Even if the positions of the insertion portion and the photoconductor do not completely match for each color, a method is used in which color misregistration does not occur when images of each color are superposed.

For the adjustment in the sub-scanning direction (vertical direction), the pitch L of the photosensitive member is kept at an integral multiple of the scanning pitch, and the laser scanning start position is always detected by the detector.
A method is used in which printing is performed at the same scanning frequency by controlling the writing timing of print data, and color misregistration does not occur when images of respective colors are superposed.

However, according to this method, since the recording is performed at the scanning frequency of the same phase, it is impossible to correct the color misregistration of 1 scanning pitch or less (8 at 300 dpi).
4, 67 μm). Therefore, there is a method of controlling the rotational phase of a motor that rotates a polygon mirror as a method of correcting a color shift of one scanning pitch or less.

In the first conventional example, a common frequency is input to each PLL control IC for controlling the rotation of each polygon mirror, and a signal is compared with the frequency signal FG fed back from each Hall IC to generate a signal for scanning. By controlling the rotation of the motor, the surface phases are made to match each other except for the rotation unevenness of each polygon mirror. However, although the polygon mirror can be stably rotated by inputting a common frequency in this way, it is difficult to match the surface phase when the mounting positions and the directions of the polygon mirrors do not match. In addition, if the mounting position and the orientation are to be matched, a complicated structure is required for that purpose, and the cost is increased.

In the conventional example 2, the phase difference between the first beam detect pulse signal and the second beam detect pulse signal is measured by a time measuring means such as an internal counter circuit and is close to the phase difference obtained. A reference signal for generating a phase is generated and sent to the phase synchronization control unit, and the first and second motors are phase-synchronized with the signal for generating the phase difference. The beam reflection surfaces of the first and second rotary polygon mirrors have substantially the same phase, and have the same phase. However, in this case, there is a problem that it is necessary to find in advance a reference signal that generates a phase close to the obtained phase difference, and it is necessary to carry out experiments and evaluations in advance to obtain phase data.

Further, in the conventional example 3, the interval of the rotational position signals detected by the rotational position detector of the polygon mirror is a predetermined value, and the time difference of the rotational position signals between different polygon mirrors holds a predetermined standard value. The feedback control is performed so that the positional deviation amount between the printing colors does not change each time the power is turned on, and the position is accurately adjusted. However, with this configuration, the surface phase cannot be matched when the position of the Hall element that detects the rotational position of each polygon mirror is different, and in order to match it, experiments and evaluations are performed in advance to obtain the phase data. Need to take.

In the conventional example 4, the optical scanning device is driven by the reference clock, and the writing position detecting devices from the second to fourth optical scanning devices respond to the writing position detecting signal from the first optical scanning device. The time shift of the writing position detection signal is obtained, and the phase control signals corresponding to the respective time shifts are added to the outputs of the PLL control circuits of the second to fourth optical scanning devices, respectively, and the position shift in the sub-scanning direction is performed. Is being corrected.
However, the rotation control circuit (P
It is necessary to provide an adder circuit between the LL control circuit) and the motor driver circuit, which causes a problem of circuit change and cost increase.

It is an object of the present invention to provide a laser beam scanning device which can easily control the surface phase of a plurality of polygon mirrors without requiring acquisition of phase control data by experiments or evaluations.

[0017]

According to a first aspect of the present invention, there is provided a laser beam scanning device comprising a plurality of laser beam generating means, a plurality of polygon mirrors for independently deflecting and scanning the plurality of laser beams, and the polygon mirror. A plurality of driving means for rotating at a speed, a plurality of control devices for controlling the rotation of the driving means by an external frequency, a first sensor for detecting the positions of the plurality of laser beams, and a plurality of polygon mirrors. Output signals of the second sensor for detecting the rotational position of the laser beam and the first sensor for detecting the position of the laser beam deflected by the reference polygon mirror, and the position of the laser beam deflected by another polygon mirror. A control for calculating the time difference between the output signals of the first sensors to be detected and for controlling the rotation of the driving means of the polygon mirror as a reference. A frequency whose phase is shifted by the time difference from the input frequency to the device is input to each of the control devices that control the rotation of the driving means for the other polygon mirrors to control the rotational phase between the plurality of polygon mirrors. Rotation phase control means is provided, and the rotation phase control means detects the output signal of the first sensor for detecting the position of the laser beam deflected by the polygon mirror serving as a reference and the laser beam deflected by another polygon mirror. A phase difference detection unit that calculates the time difference from the output signal of the first sensor that detects the position, a reference frequency generation unit, a counting unit that counts the reference frequency, the output of the counting unit, and the rotation of the polygon mirror. A reference polygon mirror rotation control comparing unit for comparing a count value corresponding to the number, and a position corresponding to the output of the counting unit and the calculated time difference. It comprises a polygon mirror rotation control comparison unit for comparing control data and a rotation frequency generation unit for generating a rotation frequency for input to the control device based on the output of the polygon mirror rotation control comparison unit. Characterize.

A laser beam scanning device according to a second aspect of the present invention is characterized in that the rotation frequency is generated based on a count value in the counting section.

According to a third aspect of the present invention, the laser beam scanning device is characterized in that the counting section is set to continue repeating counting up to a value corresponding to the number of rotations of the polygon mirror.

According to a fourth aspect of the present invention, the laser beam scanning device is characterized in that the counting unit is reset when the phase control data is set in the polygon mirror rotation control comparing unit.

According to a fifth aspect of the present invention, the laser beam scanning device is characterized in that the counting unit is reset when the comparison result from the reference polygon mirror rotation control comparing unit is output.

According to another aspect of the laser beam scanning device of the present invention, the output signal of the first sensor for detecting the position of the laser beam deflected by the reference polygon mirror and the laser beam deflected by another polygon mirror are detected. A reference frequency is used when calculating the time difference between the output signals of the first sensor for detecting the position.

According to a seventh aspect of the present invention, in the laser beam scanning device, the phase control data set in the polygon mirror rotation control comparing section is a reference polygon mirror from the data set in the reference polygon mirror rotation control comparing section. The time difference between the output signal of the first sensor for detecting the position of the deflected laser beam and the output signal of the first sensor for detecting the position of the laser beam deflected by another polygon mirror is subtracted. It is characterized by

That is, in the present invention, the rotational phase control means of the polygon mirror similar to the conventional one is used, and the control means includes the first sensor for detecting the position of the laser beam deflected by the reference polygon mirror. By providing a function to calculate the time difference between the output signal and the output signal of the second sensor that detects the position of the laser beam deflected by another polygon mirror, it is possible to obtain phase control data in advance by experiments. In addition, it is possible to control the surface phase of a plurality of polygon mirrors.

That is, as described in claim 1, the rotation phase control means of the polygon mirror is composed of a frequency generation section, a counting section, a comparison section, etc., so that the rotation control circuit of the motor used in the past (that is, the PLL). The orientation of the mirror surface of the polygon mirror can be easily controlled using the control circuit) and the motor driver circuit as they are.

If the reference frequency is counted by the counter and the rotation frequency is generated from the count value as in the second aspect, the rotation frequency can be easily changed only by changing the count value.

By setting the counting unit to continue counting up to a value corresponding to the number of rotations of the polygon mirror, it is not necessary to set or control the value for the counting unit.

When the phase control data is set in the comparator and the counter is reset, the phase control data obtained by measuring the time difference is sent to the polygon mirror rotation control comparator. The counter can be reset and restarted from the initial value regardless of the state.

According to a fifth aspect of the present invention, by resetting the counting unit when the comparison result from the reference polygon mirror rotation control comparing unit is output, a value corresponding to the rotation number of the polygon mirror is previously stored in the counting unit. It becomes unnecessary to set. (Hereafter, margin)

According to a sixth aspect of the present invention, the output signal of the first sensor for detecting the position of the laser beam deflected by the reference polygon mirror and the position of the laser beam deflected by the other polygon mirror are detected. By using the reference frequency when calculating the time difference between the output signals of the two sensors, the count value of the reference frequency can be sent to the reference polygon mirror rotation control comparison unit, and the control flow can be simplified.

According to a seventh aspect of the present invention, the phase control data set in the polygon mirror rotation control comparison unit is a laser beam deflected by the reference polygon mirror from the data set in the reference polygon mirror rotation control comparison unit. By subtracting the time difference of the output signal of the first sensor for detecting the position of the laser beam deflected by another polygon mirror from the output signal of the first sensor for detecting the position of
A normal incrementing counter is used as the counting unit, and the output of the reference polygon mirror rotation control comparison unit is input to the reference frequency generation unit without presetting the value to be counted, and the phase advances by the time difference. Frequency can be generated.

[0032]

DETAILED DESCRIPTION OF THE INVENTION A laser beam scanning device according to an embodiment of the present invention will be described below. Note that the embodiment described below applies the present invention to the phase control of the polygon mirror in the four-drum type laser beam printer illustrated in FIG. 23, but the present invention is also applicable to other types. It is needless to say that can be similarly applied.

FIG. 1 shows an optical system in the laser beam scanning device of the embodiment. In FIG. 1, the polygon mirror 11 is rotated by a polygon motor 12, and the laser beam from the laser light source LD is polygon mirror 11.
The LD scanning range D is scanned by being deflected by the outer surface of. A beam detector mirror 1 is provided at the end of the LD scanning range D.
The laser beam reflected by the beam detector mirror 14 is detected by a laser beam detector (beam detector sensor) 15 and is output as a beam detector pulse signal.

A hall element 13 for detecting a rotational position is provided in the polygon motor 12. Then, as the polygon motor 12 rotates, the rotational position detecting hall element 13 outputs a signal having a frequency corresponding to the rotation. Although not shown, the rotational position detecting Hall element 13 is not shown.
PL from which the frequency from and the rotation frequency from the outside are not shown
By inputting to the L control unit, the phase control of the polygon motor 12 is performed and the polygon mirror 11 rotates at a constant speed.

FIG. 2 shows a block diagram of the polygon mirror phase control circuit according to the first embodiment. This polygon mirror phase control circuit detects the position of the laser beam and outputs the detector pulse signal as described above, and the first to fourth laser beam detectors 15a to 15d and the time difference between the detector pulse signals of the respective laser beams. 21, a first to fourth counter 23a
23d, first to fourth reference frequency generators 22a to 22d for operating the counters 23a to 23d, and the counter 23a.
23a to 23d, and first to fourth comparators 24a to 24d and counters 23a to 2 for comparing the output of the rotation speed control data with the rotation speed control data.
The rotation frequencies / PCLK1 to / PCLK4 are generated based on the outputs from the first to fourth comparators 24a to 24d and the comparators 24a to 24d for comparing the output of 3d and the phase control data from the controller 21, respectively, and this is also generated. PLL for controlling rotation of polygon motor 11
It is composed of first to fourth rotation frequency generators 25a to 25d, etc., which are respectively sent to a controller (not shown).

Next, the operation of the polygon mirror phase control circuit according to the first embodiment will be described with reference to FIGS. In addition, in the following description, the reference frequency is 5 MHz.
The counters 23a to 23d are set to repeatedly count 0 to 1999, the rotation speed control data is '1999', and the required rotation frequency is 1.25 KHz.

As shown in FIG. 3, when the power is turned on,
The reference frequency is output from the oscillator (not shown), and the rotation speed control data '1999' is output from the controller 21 as the second value.
~ Is sent to each of the fourth comparators 24b to 24d. Here, the counters 23a to 23d each start counting after a reset signal is input and reset. Then, referring to FIGS. 4 and 6, each time the counter value becomes '1999', the comparators 24a to 24a
A pulse signal is output to the rotation frequency generators 25a to 25d from d, and the rotation frequency of 1.25 KHz / PC
LK1 to 4 are generated.

The polygon motor 12 is rotated by a motor ON signal (not shown) and a rotation frequency / PCLK1-4. Further, when the laser beam is turned on, the laser beam detector 15 causes the first to fourth detector pulse signals D
P1 to DP4 are output as shown in FIG. 7 and sent to the controller 21.

The controller 21 uses the laser detector pulse signal DP1 deflected by the polygon mirror 11 as a reference, as a reference, and the time difference (delay amount of time) T1, T2 with respect to the other detector pulse signals DP2-4. , T3 are calculated as shown in FIG. The calculated data is converted into a form of data to be sent to the comparator, and the second to fourth comparators 24b to 24b
24d.

FIG. 5 shows a procedure for generating the rotation frequency whose phase is controlled by the setting data to the comparator. In FIG. 5, the rotation frequency / PCLK1 is the same as that shown in FIG. 4 because the setting data of the comparator 24a is not changed. Then, referring to FIG. 7, the time difference between the detector pulse signals DP1 and DP2 is T1, and the data converted for sending this to the comparator 24b is set to '1500'.

In this way, when the setting data of the comparator 24b is changed from "1999" to "1500", when the value of the counter 23b which repeats counting from 0 to 1999 becomes 1500, the comparator 2
A pulse signal is output from 4b.

The rotation frequency generator 2 includes a comparator 24.
As shown in FIG. 5, the pulse signal from b.
Generate a rotation frequency / PCLK2 of 25 KHz. Then, it can be seen that the phase (falling frequency) is advanced by T1 from the rotation frequency / PCLK1. In addition,
The above is the description of the rotation frequency / PCLK2, but the same applies to the rotation frequency / PCLK3 and 4, and the data is converted using the time differences (time delay amounts) T2 and T3, and the same processing as above is performed. Done.

FIG. 8 shows the rotation frequencies / PCLK1 to PCLK4 after the above phase control. Note that in FIG. 8, the amount of advance at the rising portions of the rotation frequencies / PCLK1 to 4 is shown, but the same applies to the falling portions of the rotation frequencies / PCLK1 to PCLK4. Further, in FIG. 8, the rotation frequency / PC
LK1 and / PCLK2 are the rotation frequency / P in FIG.
It is similar to the relationship between CLK1 and / PCLK2. And
The rotation frequency shown in FIG.
When sent to the L control unit, as shown in FIG. 9, the detector pulse signals DP1 to DP4 having no time difference (amount of time delay).
Is obtained.

FIG. 10 shows a rotation frequency generator according to the second embodiment. In this embodiment, a T flip-flop (toggle) 101 is used to generate the rotation frequency from the output of the comparator. And, for example,
First, by resetting the T flip-flop 101 and setting its output Q to LOW, the input D of the T flip-flop 101 becomes HIGH. By inputting the output of the comparator to the clock input of the T flip-flop 101, the output Q of the T flip-flop 101 does not change unless the output of the comparator changes.

Further, as shown in FIG. 11, the output Q (rotation frequency / PCLK) of the T flip-flop 101 is
Initially LOW, comparator output goes from LOW to H
When it changes to IGH, the rotation frequency / PCLK is HI.
It becomes GH (rise), and remains HIGH until the output of the comparator changes from LOW to HIGH again. The output Q of the T flip-flop 101 (rotation frequency / PCLK) is LOW when the output of the comparator is LOW.
When it changes from LOW to HIGH, it becomes LOW (falls) and the output of the comparator is changed from LOW to HIGH again.
It remains LOW until it changes to.

By repeating the above operation, the rotation frequency / PCLK is generated. The output of the comparator is once in the half cycle of the rotation frequency / PCLK, and therefore the output from the counter compared by the comparator may be the time (count value) of the half cycle of the rotation frequency / PCLK.

FIG. 12 shows a block diagram of the phase control circuit of the polygon mirror 11 according to the third embodiment. This phase control circuit is different from that shown in FIG. 2 in that the controller 21 can reset the rotation frequency generators 121a to 121d configured by the T flip-flop 101 as shown in FIG.

FIG. 13 shows a phase control flow of the polygon mirror 11 according to the third embodiment. Note that this phase control flow is the same as that shown in FIG. 3 up to data conversion, and will be omitted. That is, when data conversion is completed and phase control data is sent to the comparator,
By sending the reset signal as shown in FIG. 14 to the rotation frequency generators 121a to 121d, the rotation frequency / PCL
K1 to 4 are once fixed to LOW.

Here, the conversion into the phase control data and the transmission of the phase data to the comparators 24a to 24d may be different in time due to the processing in the controller 21. Therefore, as shown in FIG.
1 to 4 separate reset signals to the rotation frequency generator 1
21a to 121d, respectively.

FIG. 14 shows an example in which the phase control data is sent to the comparator 24b. Here, when the output of the counter 23b reaches the set value of the comparator 24b (in this case, "1500"), the pulse signal is output from the comparator 23b. Due to the rise of this pulse signal, the rotation frequency which was LOW until now / PCLK2)
Changes to HIGH. Then, when the counter 23b reaches "1500" again, a pulse signal is output from the comparator 23b, and at the rising edge of the counter 23b, the rotation frequency / PCLK2, which has been HIGH until now, becomes L.
Change to OW.

By repeating the above, the rotation frequency / P
CLK2 is generated. Rotation frequency / PCLK
The setting values of the comparators 3 and 4 may be different as appropriate, and the other configurations and operations are the same. Then, as in the case of FIG. 2, the rotation frequency / PCL
K2 is a frequency in which the phase (rise of frequency) is advanced by T1 from the rotation frequency / PCLK1, and as a result, detector pulse signals DP1 to DP4 without time difference (delay amount of time) are obtained as shown in FIG. 9 of the first embodiment. To be

FIG. 15 shows a block diagram of the phase control circuit of the polygon mirror 11 according to the fourth embodiment. This phase control circuit is different from the case of FIG. 12 in that the counters 23a to 23d that count the reference frequency are provided in the controller 21.
It is different in that it can be reset from.

FIG. 16 shows a timing chart in this embodiment. That is, when the reset signal from the controller 21 enters the counters 23a to 23d,
The values of the counters 23a to 23d become "0" in synchronization with the rising of the reference frequency from the reference frequency generators 22a to 22d, and the counting is restarted at the reference frequency. The subsequent process is the same as that of the embodiment shown in FIG. 2 or FIG. Note that in the embodiment shown in FIG. 15, the reset signal also enters the flip-flops of the rotation frequency generators 25a to 25d as in the embodiment of FIG. Not something to do.

FIG. 17 shows a block diagram of the phase control circuit of the polygon mirror 11 according to the fifth embodiment. This phase control circuit is similar to that of FIG.
4a is used, and this is output to logic circuits 171a-17
The difference is that the counters 23a to 23d are reset via 1d. The configuration of the embodiment shown in FIG. 17 is not limited to the illustrated configuration.

In the phase control flow of the fifth embodiment, the counters 23a to 23d are output from the comparator 24a which is the reference polygon mirror rotation control comparing section.
15 is the same as that of the embodiment of FIG. Further, FIG. 18 shows a timing chart of the phase control of one polygon mirror 11 in the fifth embodiment. For other polygon mirrors, the setting values of the comparators 24a to 24d may be different,
Further, the timings of the output signals of the comparators 24a to 24d or the timings of the rotation frequency may be different, and the others are the same.

When the value of the counter 23a becomes "1999" which is the set value of the comparator 24a, the pulse signal is output from the comparator 24a. This pulse signal is inverted by the logic circuits 171a to 171d, and the reset signal / RESET2 from the controller 21 is output.
The counters 23a and 23b, and the counters 23c and 23d can be reset by performing a logical product with (a signal that resets the counter 23b and the rotation frequency generator 121b when setting data in the comparator 24b).

Upon receiving the reset signal, each of the counters 23a to 23d becomes "0" at the rising of the reference frequency when the reset signal is LOW. Then, the reset signal becomes HIGH, and the count advances at the rising of the reference frequency. With this configuration, it is not necessary to preset the counter to stop counting at '1999' and return to '0'.

FIG. 19 shows a block diagram of the phase control circuit of the polygon mirror 11 according to the embodiment. This embodiment is different from the embodiment of FIG.
The difference is that the three counters for sending the counter values to b to 23d and the three reference frequency generators for operating the counters do not exist, and the reference frequency generator 22 and the counter 23 substitute these. Since the operation and control flow in the embodiment of FIG. 19 are the same as those of the embodiment of FIG. 17, description thereof will be omitted.

FIG. 20 shows the relationship between the reference frequency and the rotation frequency in the first to fifth embodiments. Here, the reference frequency is generated at the same time when the power is turned on, and thus the four reference frequencies may have different phases as shown in the figure. Further, the rotation frequency that controls the phase of the polygon mirror 11 rises and falls in synchronization with the rise (the same is true for the fall) of the reference frequency. Therefore, as shown in FIG. 20, reference frequencies 1 to 4
If the phases of the rotation frequencies 1 to 4 are deviated, the phases of the rotation frequencies 1 to 4 (/ PCLK1 to 4) are also deviated by the same amount.

Therefore, for example, even when the time difference is calculated and the control for matching the surfaces of the respective polygon mirrors is performed, the surfaces are displaced by a maximum of one cycle of the reference frequency. When only one reference frequency is used as in the sixth embodiment shown in FIG. 20, such a thing does not occur.

FIG. 21 shows a block diagram of a phase control circuit for a polygon mirror according to the seventh embodiment. This embodiment differs from the sixth embodiment shown in FIG. 19 in that data (value set in the comparator 24) for determining the rotation speed of the polygon can be set from the controller 21.

In the first to sixth embodiments described above, the value set in the comparator 24a is "1999".
It is fixed at and the circuit must be changed to change the value. Then, in the seventh embodiment, such a value change can be easily performed by setting by the controller 21.
Such a change in the value is useful for making the phase control unit versatile, and the writing density and speed can be changed by changing the rotation speed of the polygon mirror.

FIG. 22 shows a phase control flow of the polygon mirror in the seventh embodiment. The difference from the sixth embodiment is that, after the power is turned on, first, the controller 21 receives the rotation speed control data from the comparator 24.
The only difference is that it is sent to, and the others are the same.

Another embodiment of the present invention will be described below. First, as an eighth embodiment, first to seventh
In the embodiment of the present invention, the controller 21 uses the laser detector pulse signal DP1 deflected by the polygon mirror as a reference, and the other detector pulse signals DP2 to DP4 with respect to the time difference T1, T2, T3.
When calculating (see FIG. 7), the controller 21 may use the reference frequency to measure the number of counts from when the detector pulse signal DP1 is input to when the detector pulse signal DP2 (DP3, DP4) is input. . With this configuration, since this count number can be sent to the comparator as it is, there is no need to convert it into the form of data to be sent to the comparator as in the above-described embodiments.

Further, as the ninth embodiment, in the phase control of the first embodiment, as shown in FIG.
The detector pulse signal DP2 is the detector pulse signal D
A configuration in which it is delayed from P1 by a time difference T1 can be mentioned. With this configuration, if the phase of the rotation frequency sent to the PLL control unit (rising portion or falling portion) is advanced from the rotation frequency / PCLK1 by the time difference T1, the direction of the polygon mirror surface can be matched (see FIG. 8
And FIG. 9).

As can be seen from FIG. 5, when "1500" is set in the comparator 24b, the rotational frequency / PCLK2 is equal to the rotational frequency / PCLK1 by the time difference T1.
Although the phase (the rising portion or the falling portion) is ahead of that, the value of the counter 23b corresponding to the time difference T1 is '1999-1500', that is, '499'.
Therefore, in order to set '499' in the comparator 24b as it is, when the counter 23b is configured to be decremented, it is necessary to set the value to be counted in advance. Therefore, when a normal incrementing counter is used, a value obtained by subtracting "499" that is time difference data from "1999" that is the data set in the comparator 24a that is the reference polygon mirror rotation control comparator is set, Also, the counter 23a
23d can be freely counted as in the fifth embodiment and returned to "0" by the reset signal. (Hereafter, margin)

In the embodiment described above,
The reference frequency is the minimum unit of rotation frequency, and also the minimum control unit for phase control. Since the reference frequency is 5 MHz in each embodiment,
The period of the rotation frequency can be changed by 0.4 μs. Also,
The time difference of the rising part of each rotation frequency is 0.2
Since it can be changed by μs, phase control can be performed in 0.2 μs units. Further, in the above embodiments, the controller calculates the time difference by software, but in addition, the time difference may be calculated by hardware by combining electronic circuits.

[0068]

According to the first aspect of the present invention, there is provided a laser beam scanning device which can easily control the orientation of the mirror surface of a polygon mirror by using the rotation control circuit and motor driver circuit of a motor which have been conventionally used as they are. it can.

According to the second aspect, it is possible to provide a laser beam scanning device in which the rotation frequency can be easily changed only by changing the count value in the counting section.

According to the third aspect, it is possible to provide a laser beam scanning device which does not require setting or control of a value for the counting section.

According to the fourth aspect of the present invention, when the phase control data is sent to the polygon mirror rotation control comparing section, the counting section can be reset and restarted from the initial value regardless of its state. A device can be provided.

According to the fifth aspect, it is possible to provide a laser beam scanning device in which it is not necessary to preset a value corresponding to the number of rotations of the polygon mirror in the counting section.

According to the sixth aspect, it is possible to provide a laser beam scanning device in which the count value of the reference frequency can be sent to the reference polygon mirror rotation control comparing section, and the control flow can be simplified.

The output of the reference polygon mirror rotation control comparison unit is input to the reference frequency generation unit without using a normal incrementing counter as the counting unit and setting the count value in advance. It is possible to provide a laser beam scanning device that can generate a frequency whose phase is advanced by a time difference only by performing the above.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of an optical system in a laser beam scanning device according to an embodiment of the present invention.

FIG. 2 is a block diagram of a polygon mirror phase control circuit according to the first embodiment of the present invention.

FIG. 3 is a flowchart of phase control of a polygon mirror according to the first embodiment of the present invention.

FIG. 4 is a timing chart according to the first embodiment of the present invention.

FIG. 5 is a timing chart according to the first embodiment of the present invention.

FIG. 6 is an explanatory diagram at the time of measuring a phase difference of a polygon mirror rotation frequency according to the first embodiment of the present invention.

FIG. 7 is an explanatory diagram before phase control of an output signal of the laser beam detector according to the first embodiment of the present invention.

FIG. 8 is an explanatory diagram after phase difference control of a polygon mirror rotation frequency according to the first embodiment of the present invention.

FIG. 9 is an explanatory diagram after phase control of an output signal of the laser beam detector according to the first embodiment of the present invention.

FIG. 10 is an explanatory diagram of a main part of a rotation frequency generation unit according to the second embodiment of the present invention.

FIG. 11 is an explanatory diagram of an operation of a rotation frequency generation unit according to the second embodiment of the present invention.

FIG. 12 is a block diagram of a polygon mirror phase control circuit according to a third embodiment of the present invention.

FIG. 13 is a flowchart of polygon mirror phase control in the third embodiment of the present invention.

FIG. 14 is a timing chart in the third embodiment of the invention.

FIG. 15 is a block diagram of a polygon mirror phase control circuit according to a fourth embodiment of the present invention.

FIG. 16 is a timing chart in the fourth embodiment of the invention.

FIG. 17 is a block diagram of a polygon mirror phase control circuit according to a fifth embodiment of the present invention.

FIG. 18 is a timing chart in the fifth embodiment of the invention.

FIG. 19 is a block diagram of a polygon mirror phase control circuit according to a sixth embodiment of the present invention.

FIG. 20 is a timing chart in the sixth embodiment of the invention.

FIG. 21 is a block diagram of a polygon mirror phase control circuit according to a seventh embodiment of the present invention.

FIG. 22 is a flowchart of polygon mirror phase control according to the seventh embodiment of the present invention.

FIG. 23 is an explanatory diagram of an example of a color image forming apparatus.

[Explanation of symbols] 11 polygon mirror 12 polygon motor 13 Hall element for rotational position detection 14 Beam detector mirror 15, 15a to 15d Laser beam detector 21 Controller 22a to 22d Reference frequency generator 23a-23d counter 24a to 24d comparator 25a to 25d Rotation frequency generator

Claims (7)

(57) [Claims] 1. A plurality of laser beam generating means, a plurality of polygon mirrors for independently deflecting and scanning the plurality of laser beams, a plurality of driving means for rotating the polygon mirrors at a constant speed, and a frequency from the outside. A plurality of control devices for controlling the rotation of the drive means, and a first sensor for detecting the positions of the plurality of laser beams, respectively.
The output signals of the second sensor for detecting the rotational positions of the plurality of polygon mirrors, the first sensor for detecting the position of the laser beam deflected by the reference polygon mirror, and the deflection signals of the other polygon mirrors. The time difference between the output signals of the first sensor that detects the position of the laser beam is calculated, and the phase difference is the same as the time difference with respect to the input frequency to the control device that controls the rotation of the driving means of the polygon mirror. The shifted frequencies are respectively input to a control device that controls the rotation of the driving means for the other polygon mirrors, and the rotational phase control means controls the rotational phase between the plurality of polygon mirrors. The output signal of the first sensor for detecting the position of the laser beam deflected by the reference polygon mirror and the deflection by another polygon mirror A phase difference detection unit that calculates a time difference from the output signal of the first sensor that detects the position of the generated laser beam, a reference frequency generation unit, and a counting unit that counts the reference frequency,
A reference polygon mirror rotation control comparison unit that compares the output of the counting unit and a count value corresponding to the number of revolutions of the polygon mirror, and an output of the counting unit and phase control data corresponding to the calculated time difference. And a rotation frequency generator for generating a rotation frequency for input to the control device based on the output of the polygon mirror rotation control comparator. Scanning device. 2. The rotation frequency is generated based on the count value of the counting unit.
The laser beam scanning device described. 3. The laser beam scanning device according to claim 1, wherein the counting unit is set so as to continue repeating counting up to a value corresponding to the number of rotations of the polygon mirror. 4. The laser beam scanning device according to claim 1, wherein the counting unit is reset when the phase control data is set in the polygon mirror rotation control comparing unit. 5. The laser beam scanning device according to claim 1, wherein the counting section is reset when the comparison result from the reference polygon mirror rotation control comparing section is output. 6. An output signal of the first sensor for detecting the position of a laser beam deflected by a reference polygon mirror and the first signal for detecting the position of a laser beam deflected by another polygon mirror. The laser beam scanning device according to claim 1, wherein a reference frequency is used when calculating the time difference between the output signals of the sensors. 7. The phase control data to be set in the polygon mirror rotation control comparison unit is the position of the laser beam deflected by the reference polygon mirror from the data set in the reference polygon mirror rotation control comparison unit. The first signal for detecting the output signal of the first sensor for detecting and the position of the laser beam deflected by another polygon mirror
2. The laser beam scanning device according to claim 1, wherein the laser beam scanning device is obtained by subtracting the time difference of the output signals of the sensor.