JPH09169135A - Light scanning device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the number of data bits of a memory into which frequency information of an image clock signal required for electrically correcting a distortion at both of ends in a scanning face is stored beforehand. SOLUTION: A RAM 23 stores beforehand frequency information for determining a frequency of an image clock signal by each address information corresponding to a respective scanning position on a photosensitive body in one scanning of a beam light. A counter 22 outputs the address information of the RAM 23 corresponding to the present scanning position of the beam light on the photosensitive body. A divider 24 fetches from the RAM 23 the frequency information corresponding to the address information outputted from the counter 22 and varies the frequency of the image clock signal based on the frequency information. The frequency information stored in the RAM 23 is bit information that represents increase or decrease with respect to the frequency of the image clock signal at the previous timing by one clock.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical scanning device which forms an image on a photoconductor by scanning a light beam from a light emitting element such as a laser diode with a rotating mirror in a fixed direction on the photoconductor.

[0002]

2. Description of the Related Art Conventionally, as this type of optical scanning device, there is a laser scanner unit of a laser printer using an electrophotographic system. Incidentally, the laser printer using the electrophotographic method, the surface of the photoconductor made of a photoconductive material is uniformly charged by the charging section, and the laser beam is scanned from the laser scanner unit onto the charged photoconductor. Image information is electrostatically recorded, the electrostatic latent image recorded on the photoconductor is developed into a toner image by a developing device, the toner image is transferred to a transfer material by a transfer section, and the transferred transfer image is transferred. The image of the material is fixed by a fixing device.

The laser scanner unit has a structure shown in FIG. That is, the laser scanner unit 40 includes a laser diode 41 that emits a laser beam light 42, a rotating mirror 44 that reflects the laser beam light 42 emitted from the laser diode 41 to a mirror 43, and the rotating mirror 44 that rotates in a fixed direction. A driving polygon motor 45, a start sensor 46 which receives a part of the reflected light from the mirror 43 and gives a synchronization signal to a laser diode control circuit 47, and drives the laser diode 41 in response to the synchronization signal from the start sensor 46. A laser diode control circuit 47, a polygon motor drive circuit 48 for controlling the drive of the polygon motor 45, and a PLL control circuit 49 for controlling the rotation speed of the polygon motor 45. In the laser scanner unit having this configuration, the laser diode control circuit 47 outputs an image clock signal corresponding to image data for one line in response to the synchronizing signal from the start sensor 46.
Then, a laser beam light 42 is emitted from the laser diode 41 at the on / off timing of the image clock signal, and the laser beam light 42 is reflected by the rotating mirror 44 that rotates at a high speed by the polygon motor 45, and the mirror surface of the mirror 43 is directed in a fixed direction. To scan. In response, the mirror 43
The reflected beam of light scans the surface of a photoreceptor (not shown) in a certain direction, and image information is electrostatically recorded on the surface of the photoreceptor.

By the way, in the conventional laser scanner unit 40, in order to correct the distortion of the laser beam light 42 for scanning the surface of the photosensitive member at both ends of the scanning surface, it is deflected at a constant angular velocity by the rotating mirror 44. An f-θ lens 50 having distortion is installed in the optical path of the laser beam light 42.

Recently, the frequency of the image clock signal generated in the laser diode control circuit 47 is set to 1
A laser scanner unit that does not require the f-θ lens 50 is considered by electrically correcting the distortion at both ends of the scanning surface by changing the length so that it becomes gradually shorter as it approaches both ends of the scanning. In such a laser scanner unit, the frequency information of the image clock signal is preliminarily provided in the RAM (random access memory) in the laser diode control circuit 47 for each address information corresponding to each scanning position on the photoconductor in one scanning of the laser beam light. )
Alternatively, it is stored in a ROM (Read Only Memory). Then, in response to the synchronization signal from the start sensor 46, the frequency information is read in the order of addresses, the clock width of the image clock signal is determined so that the frequency of this frequency information is obtained, and when there is image data, this clock width is used. The image clock signal is output to the laser diode 41.

Here, a multiple of the reference clock has been set as the frequency information of the image clock signal. Therefore, by increasing the frequency of the reference clock, the change width of the frequency can be set finely, so that fine-tuned correction can be performed.

[0007]

However, in an optical scanning device such as a conventional laser scanner unit which electrically corrects the distortion at both ends of the scanning surface, a multiple of the reference clock is used as the frequency information of the image clock signal. However, since the multiple as the frequency information increases as the finer correction is performed, the number of data bits of the semiconductor memory that stores the frequency information increases. The semiconductor memory becomes more expensive as the number of data bits increases, which in turn increases the cost of the product.

The present invention has been made under such circumstances, and an object thereof is to store in advance the frequency information of the image clock signal necessary for electrically correcting the distortion at both ends of the scanning surface. Another object of the present invention is to provide an optical scanning device capable of reducing the number of data bits of the memory and reducing the cost of the product.

[0009]

SUMMARY OF THE INVENTION According to the present invention, a light emitting element is controlled to be turned on and off in synchronization with an image clock signal, and a light beam from the light emitting element is scanned by a rotating mirror in a certain direction on a photoconductor. In an optical scanning device for forming image information on a photoconductor, a storage unit that stores in advance frequency information that determines the frequency of an image clock signal for each address information corresponding to each scanning position on the photoconductor in one scanning of a light beam. , An address information output unit for outputting address information of a storage unit corresponding to the current scanning position of the light beam on the photosensitive member, and frequency information corresponding to the address information output by the address information output unit are fetched from the storage unit. A clock frequency changing unit that changes the frequency of the image clock signal based on the frequency information, and stores the frequency information stored in the storage unit,
This is bit information that represents an increase / decrease in the frequency of the image clock signal one clock before.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment in which an optical scanning device of the present invention is applied to a laser scanner unit of a laser printer using an electrophotographic system will be described below with reference to FIGS.
This will be described with reference to FIG. FIG. 1 is a block diagram of a laser scanner unit 10 according to this embodiment. That is, the laser scanner unit 10 includes a laser diode 11 as a light emitting element, a rotary mirror 14 for reflecting a laser beam light 12 emitted from the laser diode 11 to a mirror 13, and a polygon motor for rotationally driving the rotary mirror 14 in a fixed direction. 15, a start sensor 16 which receives a part of the reflected light from the mirror 13 and gives a synchronization signal to a laser diode control circuit 17, and a laser diode control which drives the laser diode 11 according to the synchronization signal from the start sensor 16. A circuit 17, a polygon motor drive circuit 18 for controlling the drive of the polygon motor 15, and a P for controlling the rotation speed of the polygon motor 15.
It is composed of an LL control circuit 19.

FIG. 2 shows the laser diode control circuit 17
FIG. 3 is a block diagram of the configuration of FIG. That is, the laser diode control circuit 17 is reset to "0" in response to the CPU (central processing unit) 21 which gives the reference reference data A of the preset image clock signal to the frequency divider 24 and the synchronizing signal, After that, the counter 22 that counts up by "1" each time the image clock signal output from the frequency divider 24 is input, the count value of the counter 22 is taken in as address information ADD, and the area corresponding to the address information ADD is acquired. RAM (random access memory) for giving the bit data bit stored in
23, head reference data A given from the CPU 21
Is held as a frequency division value, and in response to the synchronization signal from the start sensor 16, a clock signal having a frequency division value times the reference clock supplied from an oscillator (not shown) is output as an image clock signal, and the RAM 23 outputs bits. A frequency divider 24 that increases / decreases the frequency division value based on the bit data bit when receiving a data bit, and timing control for outputting image data as laser on / off data to the laser diode 11 in synchronization with the image clock signal. It is composed of a circuit 25.

In the RAM 23, the address information A corresponding to each scanning position of one scanning on the surface of the photosensitive member by the laser beam light 12 scanned by the high speed rotation of the rotary mirror 14.
For each DD, as frequency information for determining the frequency of the image clock signal, bit data representing increase / decrease with respect to the frequency division value in the frequency divider 24 corresponding to the frequency of the image clock signal one clock before is stored in advance. . Incidentally, in this embodiment, “± 0” is set as bit data “0” = (00) H for the frequency division value, and “+1” is set for the frequency division value.
Is set as bit data “1” = (01) H, and “−1” is set as bit data “2” = (10) H for the frequency division value.

Here, the RAM 23 constitutes a storage section, the counter 22 constitutes an address information output section,
The frequency divider 24 constitutes clock frequency varying means. An example of the operation timing of the laser diode control circuit 17 having such a configuration will be described with reference to the timing chart of the main part of FIG. In FIG. 3, (a) shows the synchronization signal from the start sensor 16, (b) shows the count value of the counter 22, and (c) shows the bit data bit stored in the RAM 23. And (d) is frequency divider 2
4 shows the frequency division value, and (e) shows the image clock signal.

First, the CPU 21 sets, for example, "11" as the head reference data A of the image clock signal in the frequency divider 24. Next, when the laser beam 11 is emitted from the laser diode 11 and the synchronization signal p1 is output from the start sensor 16 (time point t0), the synchronization signal p1 is generated.
Is provided to the counter 22 and the frequency divider 24. As a result, the frequency divider 24 uses the clock signal 11 times the reference clock as the image clock signal S0.
And output to the counter 22.

The counter 22 is reset to "0" in response to the rise of the synchronizing signal p1 and gives the count value "0" to the RAM 23 as address information ADD. As a result, the RAM 23 outputs the bit data bit = "0" stored in the address 0 to the frequency divider 24. The frequency divider 24 receives the bit data bit = "0" and maintains the frequency division value "11". As a result, the image clock signal S
Similarly to 0, the timing control circuit 24 also uses a clock signal 11 times the reference clock as the image clock signal S1.
And output to the counter 22.

On the other hand, the counter 22 counts up the count value to "1" when the first image clock signal S0 is input. As a result, the RAM 23 outputs the bit data bit = "0" stored in the address 1 to the frequency divider 24. Also in this case, since the bit data bit is "0", the frequency divider 24 maintains the frequency division value "11". Therefore, the image clock signal S1 is followed by 11 of the reference clock.
The doubled clock signal is output to the timing control circuit 24 and the counter 22 as the image clock signal S2.

On the other hand, the counter 22 counts up the count value to "2" by the input of the second image clock signal S1. As a result, the RAM 23 outputs the bit data bit = "1" stored in the address 2 to the frequency divider 24. The frequency divider 24 receives the bit data bit = "1" and updates the frequency division value to "12". As a result, next to the image clock signal S2, a clock signal 12 times the reference clock is output to the timing control circuit 24 and the counter 22 as the image clock signal S3.

Thereafter, similarly, the counter 22 increments the count value by "1" each time the image clock signals S2, S3, ... Are input. As a result, RA
M23 is a frequency divider 2 for bit data bit “0”, “1” or “2” of an address (address) corresponding to the count value.
4 is output. The frequency divider 24 maintains the current frequency division value if the bit data bit is "0", and the bit data bi
If t is "1", "1" is added to the current frequency division value, and if the bit data bit is "2", "1" is calculated from the current frequency division value.
Is subtracted. The image clock signals S4, S5, ...
.. are sequentially changed so as to be multiplied by the division value of the reference clock.

When the image data is input, the timing control circuit 25 synchronizes the image data with the image clock signal so that the laser diode 11 is turned on,
Output as off data. As a result, the laser beam 11 is emitted from the laser diode 11 with the clock width of the image clock signal.

When the above operation is performed until the next synchronizing signal p2 is input, one scanning of the laser beam light 12 on the surface of the photosensitive member is completed, and one line of image data is formed on the surface of the photosensitive member. . At this time, the counter 22 is reset to "0" in response to the input of the synchronizing signal p2, and the bit data bit at address 0 is given to the frequency divider 24. As a result, the above operation is repeated. That is, the image data for the next one line is formed on the surface of the photoconductor by the time the next synchronization signal p3 is input. In this way, the above operation is repeated each time the synchronization signal is input, and image data for one page is formed on the surface of the photoconductor.

As described above, in the present embodiment, the image clock signal of the address clock ADD corresponding to each scanning position of the laser beam light 12 scanned by the high speed rotation of the rotating mirror 14 on the surface of the photoconductor is scanned. As frequency information for determining the frequency, bit data representing increase / decrease with respect to the frequency division value in the frequency divider 24 corresponding to the frequency of the image clock signal one clock before is stored in advance.

The frequency of the image clock signal necessary for electrically correcting the distortion at both ends of the scanning surface must be changed so as to become gradually shorter as it approaches both ends of one scanning. In this case, the smaller the change width is set, the higher the correction accuracy becomes. That is, regardless of the frequency of the reference clock, the increase / decrease range for the frequency division value is ± 1.
Within the range of. Therefore, as the data representing the increase / decrease with respect to the frequency division value, "± 0", "+1" and "-
There are only three types of "1", and 2-bit data can handle all of them.

Conventionally, a multiple of the reference clock is set as the frequency information of the image clock signal stored in the RAM. Therefore, for example, in the case of the example of FIG. 3 in the present embodiment, bit data “1” is assigned to addresses 0 and 1.
1 ”= (1011) H, bit data“ 12 ”at 2nd address
= (1100) H, bit data “1” at addresses 3 and 4
A RAM capable of storing at least 4 bits of data, such as 3 ″ = (1101) H, is required, resulting in an increase in price of the RAM.

On the other hand, according to the present embodiment, RA
Since the frequency information stored in M23 can be 2-bit data regardless of the frequency of the reference clock, RA
It is possible to reduce the price of the M23 and thus the price of the product.

In the above-described embodiment, the head reference data written by the CPU 21 in the frequency divider 24 is set to "11", but it goes without saying that it is not limited to this value. Further, in the above-described embodiment, the RAM is shown as the storage unit for storing the frequency information, but the ROM or the EEPROM is used.
It may be a non-volatile memory such as. Further, the present invention is not limited to the laser scanner unit, but can be applied to an apparatus that requires the distortion correction at the end portion of the scanning surface when scanning the light beam in a fixed direction on the photoconductor. In addition, it goes without saying that various modifications can be made without departing from the spirit of the present invention.

[0026]

As described above in detail, according to the present invention, the number of data bits of the memory for pre-storing the frequency information of the image clock signal necessary for electrically correcting the distortion at both ends of the scanning surface is reduced. Therefore, it is possible to provide an optical scanning device capable of reducing the price of a product.

[Brief description of the drawings]

FIG. 1 is a block configuration diagram of a laser scanner unit that is an embodiment of the present invention.

FIG. 2 is a block configuration diagram of a laser diode control circuit according to the same embodiment.

FIG. 3 is a timing chart showing an example of operation timing of the laser diode control circuit in the same embodiment.

FIG. 4 is a block configuration diagram of a conventional laser scanner unit.

[Explanation of symbols]

 10, 40 ... Laser scanner unit 11, 41 ... Laser diode (light emitting element) 12, 42 ... Laser beam light 14, 44 ... Rotating mirror 15, 45 ... Polygon motor 16, 46 ... Start sensor 17, 47 ... Laser diode control circuit 21 ... CPU 22 ... Counter (address information output section) 23 ... RAM (storage section) 24 ... Frequency divider (clock frequency varying means) 25 ... Timing control circuit

Claims (1)

[Claims] 1. A light emitting element is controlled to be turned on and off in synchronization with an image clock signal, and a light beam from the light emitting element is scanned in a fixed direction with respect to a photoconductor by a rotating mirror to display image information on the photoconductor. In the optical scanning device for forming, a storage unit that stores in advance frequency information that determines the frequency of the image clock signal for each address information corresponding to each scanning position on the photoconductor in one scanning of the light beam,
From the storage unit, an address information output unit that outputs address information of the storage unit that corresponds to the current scanning position of the light beam on the photoconductor and frequency information that corresponds to the address information that the address information output unit outputs. A clock frequency changing means for changing the frequency of the image clock signal on the basis of this frequency information, and the frequency information stored in the storage section is a bit indicating an increase / decrease with respect to the frequency of the image clock signal one clock before. An optical scanning device characterized by being information.