JPH04163165A - Laser beam scanning device for laser printer - Google Patents

Abstract

PURPOSE:To prevent excessive electrostatic latent image from being formed on a sensitive drum by a method wherein feeding of a driving control signal to a driving means is prohibited from when a count value reaches a first specified value which corresponds with timing right after the generation of a horizontal synchronous signal to when the count value reaches a second specified value which corresponds with latent image forming start timing. CONSTITUTION:A discrimination circuit 29 feeds a discrimination signal Sj at an 'L' level to an AND gate 25, based on a count value of a counter 28, from when the count value reaches a count value N1 which corresponds with timing right after the input of a horizontal synchronous signals HSYN to when the count value reaches a count value N2 which corresponds with a scanning position P2, and also from when the count value reaches a count value N3 corresponding with a scanning position P3 at which reading of printing data in a serial buffer 22 is completed, and latent image forming is completed to when the count value reaches a count value N4 corresponding with a scanning position P4 at which scanning of laser beam B in A direction is completed. Therefore, a driving control signal Sc is not output from a laser beam driving circuit 26 to a semiconductor laser element 3.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a laser beam scanning device for a laser printer, and in particular, to a laser beam scanning device for a laser printer, and in particular, to a laser beam scanning device for a laser printer. Regarding things that are prevented from forming.

[Prior art]

Recently, in order to output characters and symbols on printing paper, contour data obtained by digitizing the contours of many characters such as letters and symbols is stored in non-volatile memory such as ROM, and this contour data is scaled. After performing conversion processing such as processing, converting the converted contour line data into dot data using a data conversion control device, and forming an electrostatic latent image on the photosensitive drum using the dot data using a laser beam scanning device, Laser printers and laser facsimiles have been put into practical use that use a developing device to create character images on printing paper.

By the way, as shown in FIG. 2 according to the embodiment, the laser beam scanning device is generated from a semiconductor laser element 3.
The light beam (hereinafter referred to as a laser beam) B passes through a collimating lens 4, is reflected by a hexahedral mirror (polygon mirror) 5 rotating at a constant speed in a predetermined direction, and is further reflected by an imaging lens 6 and a cylindrical lens. 7, the photosensitive drum 8 rotating at a constant speed is repeatedly scanned in the direction of arrow A, and an electrostatic latent image is formed on the photosensitive drum 8. Furthermore, the scanning range E of the laser beam B
A small reflecting mirror 9 is provided inside, and when the laser beam B is at the scanning position PO on the photosensitive drum 8, the laser beam B reflected by the reflecting mirror 9 is received by a laser light receiving element 10. Video controller circuit and D
A horizontal synchronizing signal is output to a control device consisting of a C controller circuit.

Therefore, every time the control device inputs this horizontal synchronization signal,
While the laser beam B scans from the scan position P1 immediately after the scan position PO to the scan position P2, which is the timing to start latent image formation, the print data for one dot line supplied from the page buffer or the serial buffer ( The print data stored in the serial buffer is stored in the serial buffer from the scan position P2 to the scan position P3 where the storage of the print data is completed, and the print data is stored in the serial buffer at the beginning of the print data in synchronization with the synchronization clock signal supplied from the oscillation circuit. One dot data is read out from the address, and a drive control signal corresponding to this dot data is sequentially outputted to the semiconductor laser element 3 (=sequentially. As a result, the semiconductor laser element 3 turns on or off the laser beam B based on the drive control signal. Since the light is turned off, an electrostatic latent image corresponding to one page of dot data stored in the page buffer is formed on the photosensitive drum 8. However,
The control device selects the scanning position P, which is the right end position of the scanning range E of the laser beam B, so that the horizontal synchronization signal is always input.
4 to the scanning position P1, the semiconductor laser element 3 is controlled to be forcibly illuminated with the laser beam B. The serial buffer is provided with a memory capacity sufficient to store dot data corresponding to the electrostatic latent image formed from the scanning position P2 to the scanning position P3, which is the end timing of latent image formation. .

[Problem to be solved by the invention]

As described above, while the laser beam B is scanned from the scanning position P2 to the scanning position P3, an electrostatic latent image corresponding to one dot line worth of print data stored in the serial buffer is formed on the photosensitive drum 8. However, while the laser beam B scans from the scanning position P3 through the scanning position P4 to the scanning position P2 where the printing data for the next one dot line is completely stored in the serial buffer, the serial buffer is Since the stored print data is repeatedly read out from the first address, especially between the scanning position P3 and the scanning position P4 of the laser beam B, and from the scanning position P1 to the scanning position P2 corresponding to the right end position of the reflecting mirror 9. An extra electrostatic latent image is formed on the photosensitive drum 8 corresponding to the gap. In other words, when this electrostatic latent image is formed on the printing paper by the developing device, the part corresponding to the scanning position P2 from the left end position of the printing paper and the part corresponding to the right end position of the printing paper from the scanning position P3 are serialized. The problem is that extra dots or "smudges" are printed based on the print data stored in the buffer. However, scanning position P2
If a serial buffer is provided with a large memory capacity capable of storing a large number of dot data corresponding to scanning position P4, "stains" may occur only on the left edge of the printing paper.
is printed.

SUMMARY OF THE INVENTION An object of the present invention is to provide a laser beam scanning device for a laser printer that prevents unnecessary electrostatic latent images from being formed on a photosensitive drum.

[Means to solve the problem]

As shown in the functional block diagram of FIG. 1, a laser beam scanning device for a laser printer according to the present invention includes a light emitting unit that generates a beam of laser light, a scanning unit that scans a photosensitive drum with a beam of light, and a light emitting unit that scans a photosensitive drum with a beam of light. The drive means includes a drive means for driving the means, and a memory means for storing print data for each dot line for printing, and outputs a drive control signal corresponding to the print data to the drive means from a predetermined latent image formation start timing for each scan. In a laser printer, the oscillation means generates a synchronization clock signal for synchronizing and outputting a drive control signal, and the light reception means receives a light beam and generates a horizontal synchronization signal. a counter means that counts the supplied synchronization clock signal and whose count value is cleared by a horizontal synchronization signal received from the light receiving means; and a counter means that receives the output of the counter means and whose count value corresponds to the timing immediately after generation of the horizontal synchronization signal. and prohibiting means for prohibiting the supply of the drive control signal to the driving means from the time when the first predetermined value is reached until the time when the second predetermined value corresponding to the latent image formation start timing is reached. .

[Effect]

In the laser beam scanning device for a laser printer according to the present invention, the scanning means scans the photosensitive drum with the laser beam generated by the light emitting means, and the light receiving means receives this beam and generates a horizontal synchronization signal. do. When the control means receives the horizontal synchronization signal, the control means stores print data for one dot line to be used for printing in the memory means, and
Since the drive control signal corresponding to this print data is output to the drive means in synchronization with the synchronous clock signal from the oscillation means from the predetermined latent image formation start timing when the storage of this print data is completed, the light emitting means is activated by the drive means. The luminous flux is turned on or off through driving. Here, the control means outputs a drive control signal corresponding to the updated new print data in the memory means from the latent image formation start timing, or prints the already outputted print data until the next latent image formation start timing. Read data repeatedly. As a result, an electrostatic latent image corresponding to the regular print data is formed on the photosensitive drum from the latent image formation start position, and in particular, from the left end of the photosensitive drum to a position corresponding to the latent image formation start timing. There is a possibility that part of the print data in the memory means will be formed as an extra electrostatic latent image. That is, if this extra electrostatic latent image is formed on the photosensitive drum, it will be printed on printing paper through a phenomenon process.

On the other hand, the counter means counts the synchronization clock signal supplied from the oscillation means, and its count value is cleared by the horizontal synchronization signal received from the light reception means. The inhibiting means receives the output of the counter means, and controls the count value from when the count value reaches a first predetermined value corresponding to the timing immediately after generation of the horizontal synchronizing signal to when it reaches a second predetermined value corresponding to the latent image formation start timing. Throughout this period, supply of drive control signals to the drive means is prohibited. Therefore, among the extra electrostatic latent images formed from the left end of the photosensitive drum to the position corresponding to the latent image formation start timing, from the position immediately after the horizontal synchronization signal is generated to the position corresponding to the latent image formation start timing. No electrostatic latent image is formed. Here, an electrostatic latent image is formed on the photosensitive drum from the left end to the position immediately after the horizontal synchronization signal is generated, or this electrostatic latent image is a portion that does not normally correspond to the printing paper. . As a result, only an electrostatic latent image corresponding to regular print data is formed on the portion of the photosensitive drum corresponding to the print paper.

〔Effect of the invention〕

According to the laser beam scanning device for a laser printer according to the present invention, as explained in the light section [Operation], the counter means and the inhibiting means are provided, and the count value of the counter means corresponds to the timing immediately after the horizontal synchronization signal is generated. Since the supply of the drive control signal to the drive means is prohibited from the time when the first predetermined value corresponding to the latent image formation start timing is reached to the time when the second predetermined value corresponding to the latent image formation start timing is reached, Only an electrostatic latent image corresponding to regular print data can be formed on the corresponding photosensitive drum from the latent image formation start position.

Therefore, "stain" is not printed on the printing paper that has been developed based on this electrostatic latent image.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

First, the laser beam scanning device 1 will be explained based on FIG. 2. This laser beam scanning device 1 is similar to the existing one, so it will be briefly explained. On the substrate 2, there are provided a semiconductor laser element 3 that generates a beam of laser light (hereinafter referred to as a laser beam) B, a collimating lens 4, Scanner motor (
(See Figure 3) A hexahedral mirror (polygon mirror) 5 is rotated at a constant speed in a predetermined direction F at 23, and an imaging lens 6 and a cylindrical lens 7 are arranged behind the polygon mirror 5. Immediately behind this cylindrical lens 7, there is a main motor (third
(See figure) Photosensitive drum 8 rotated at a constant speed by 24
It is arranged parallel to the cylindrical lens 7. The collimating lens 4 is for correcting the laser beam B generated from the semiconductor laser element 3 into parallel light, and the imaging lens 6 is for keeping the scanning speed of the laser beam B scanning on the photosensitive drum 8 constant. The cylindrical lens 7 is used to correct the tilt of the surface of the polygon mirror 5.

Therefore, the laser beam B generated from the semiconductor laser element 3 passes through the collimating lens 4, is reflected by the polygon mirror 5, passes through the imaging lens 6 and the cylindrical lens 7, and repeatedly scans the photosensitive drum 8 in the direction of arrow A. Therefore, an electrostatic latent image is formed on the photosensitive drum 8 according to whether the laser beam B is turned on or off. Note that the symbol E indicates the scanning range of the laser beam B.

Furthermore, a scanning range E of the laser beam B is formed on the substrate 2.
A small reflecting mirror 9 is provided in the optical path of the laser beam B, which is a scanning position near the left end of the photosensitive drum 8 (hereinafter simply referred to as scanning position). receives the laser beam B reflected by the horizontal synchronizing signal H3 to the control device 20.
A laser light receiving element 10 for outputting YN is also provided.

Next, the control system of the laser beam scanning device 1 of the laser printer will be explained based on FIG.

The control device 20 is similar to an existing one consisting of a video controller circuit or a DC controller circuit, and includes an oscillation circuit 21 that outputs a synchronized clock signal CL of a predetermined frequency (for example, about 10 MHz), and an oscillation circuit 21 that outputs print data for printing one dot line at a time. A serial buffer (scan buffer) 22 for storing data is provided, and a scanner motor 23 is provided.
and controls the drive of the main motor 24. As shown in FIG. 2, this serial buffer 22 has a large number of locations corresponding to the maximum latent image formation range from the scan position P2 at the start timing of latent image formation of the laser beam B to the scan position P3 at the end timing of latent image formation. There is a memory capacity capable of storing dot data, and the control device 20 constantly repeatedly reads out each dot data of the print data stored in the serial buffer 22 in synchronization with the synchronous clock signal CL from the oscillation circuit 21.

The video signal Sv based on the print data read out from the serial buffer 22 is supplied to the laser light drive circuit 26 via the AND gate 25, and the laser light drive circuit 26 sends the drive control signal Sc based on the video signal Sv to the semiconductor laser element. 3, the semiconductor laser element 3 turns on or off the laser beam B based on this drive control signal Sc.

The laser beam B generated from the semiconductor laser element 3 hits the polygon mirror 5 and the reflection mirror 9 at the scanning position PO.
When the laser light receiving element 10 outputs a light reception signal to the laser light receiving circuit 27, the laser light receiving circuit 27 outputs a horizontal synchronizing signal H3YN. This horizontal synchronization signal H3YN is supplied to the control device 20 and the reset terminal of the addition counter 28, and the count value of the counter 28 is cleared while counting the synchronization clock signal CL supplied from the oscillation circuit 21.

On the other hand, the discrimination circuit 29 consists of an AND gate, a flip-flop, etc., and based on the count value of the counter 28,
Scanning begins when the count value reaches the count value N1 corresponding to the timing immediately after the input of the horizontal synchronizing signal H3YN, that is, the timing of the scanning position P1 corresponding to the right end of the laser beam B or the reflecting mirror 9 as shown in FIG. Position P
2, and from the time when the count value N3 corresponding to the scanning position P3 is reached, at which reading of the print data in the serial buffer 22 is completed and latent image formation is completed. The determination signal Sj remains at the "L" level until the count value N4 corresponding to the scanning position P4 at which the scanning of the laser beam B in the direction of the arrow A ends is reached.
is supplied to the AND gate 25. Therefore, the output of the AND gate 25 is "L" from the scanning position Pi to the scanning position P2, and from the scanning position P3 to the scanning position P4.
level, and even though the video signal Sv based on the print data of the serial buffer 22 is being output, only the drive control signal Sc is output from the laser light drive circuit 26 to the semiconductor laser element 3. Furthermore, the discrimination circuit 29 performs the following operations from the time when the count value N4 corresponding to the scan position P4 is reached until the time when the count value Nl corresponding to the scan position P1 is reached.
A forced signal Ss of "H" level is output to the input circuit of the drive control signal Sc of the laser light drive circuit 26. This results in
Since the laser beam B is forcibly turned on from the semiconductor laser element 3 from the scanning position P4 to the scanning position P1 of the laser beam B, the laser beam receiving circuit 27 receives the horizontal synchronizing signal H.
Reliably outputs 3YN.

Next, the operation of the laser beam scanning device 1 will be explained based on FIG. 4 without referring to FIG. 2. For convenience of explanation, the explanation will start from when the horizontal synchronization signal H3YN is input from the laser light receiving circuit 27. However, serial buffer 22
The print data within is always read out sequentially from the address indicated by the read pointer in synchronization with the synchronous clock signal CL supplied from the oscillation circuit 21. Furthermore, the synchronous clock signal CL shown in FIG. 4 is illustrated in an exaggerated manner for ease of understanding.

When the laser beam B generated from the semiconductor laser element 3 by the rotation of the polygon mirror 5 is at the scanning position PO, the horizontal synchronization signal HSYN is input from the laser light receiving circuit 27, so that the count value of the counter 28 is cleared and , the control means 20 changes from this scanning position PO to scanning position P.
2, new print data to be printed is sequentially stored in the serial buffer 22 from its leading address. Furthermore, when the count value of the counter 28 reaches Nl corresponding to the scanning position P1, the discrimination circuit 29 cancels the forced signal Ss that was output to the input circuit of the laser beam drive circuit 26, and also cancels the forced signal Ss that has been output to the input circuit of the laser beam drive circuit 26. When reaching N2 corresponding to scanning position P2, the determination signal S of "L" level
j is supplied to the AND gate 25, the output of the AND gate 25 is "L" from the scanning position Pi to the scanning position P2.
J level, and even though the print data is read from the serial buffer 22 and the video signal Sv is output, the laser light drive circuit 26 does not output the drive control signal Sc to the semiconductor laser element 3.

Then, when the count value becomes N2 and the laser beam B is at the scanning position P2, the counter 28 supplies an "H" level discrimination signal Sj to the AND gate 25, and
Since the read pointer is cleared and points to the start address of the serial buffer 22, new print data or the first dot data in the serial buffer 22 is sequentially read out in synchronization with the synchronous clock signal CL, and the data corresponding to this print data is read out sequentially in synchronization with the synchronous clock signal CL. Drive control signal Sc based on video signal Sv
As a result, an electrostatic latent image is formed on the photosensitive drum 8. Thereafter, the counter 28 outputs the "L" level discrimination signal S from the time when the count value becomes N3 and the laser beam B is at the scanning position P3 to the scanning position P4 when the count value becomes N4.
Since j is supplied to the AND gate 25 again, the drive control signal Sc is not output from the laser light drive circuit 26 to the semiconductor laser element 3 even though print data is being read from the serial buffer 22 during this time.

Therefore, since the positional relationship between the printing paper P with the maximum paper width and the photosensitive drum 8 is as shown in FIGS. 2 and 4, a serial buffer is placed on the photosensitive drum 8 corresponding to the printing paper Only the electrostatic latent image corresponding to the new print data stored in 22 is formed, and the print paper P after the development process has "
It is possible to print only character strings of regular print data without any dirt.

By the way, the control system of the laser beam scanning device 1 is configured with a microcomputer, and the series of operations described above is programmed, and this laser beam scanning control program is stored in a program memory (ROM) in the wound surface device 20. You can.

Since this laser beam scanning control routine is complex, the outline of the routine will be briefly explained based on the flowchart shown in FIG. This control program includes a count value N1 corresponding to the scanning position P1 of the laser beam B, a count value N2 corresponding to the scanning position P2, a count value N3 corresponding to the scanning position P3, and a count value corresponding to the scanning position P4. N4 is stored in advance.

When a print command is manually input to the control device 20, this control starts, and first the scanner motor 23 and the main motor 2
4 or driven by a DC controller circuit (S10)
, when the horizontal synchronizing signal H3YN read through the laser light receiving element 10 is at "H" level (S11, S12:
(Yes), the count value C of the counter that counts the synchronous clock signal CL is cleared (S13), and when the count value C is "0" (S14: Yes), new print data or its start address is stored in the serial buffer 22. A write process for storing is executed from S11 (S15).
Return to Note that this write processing is performed by a routine not shown in the drawings based on the input of the synchronous clock signal CL. On the other hand, when the horizontal synchronization signal H3YN is not input (Sll, S1
2.S14: No), when the synchronous clock signal CL supplied from the oscillation circuit 21 is at "H" level (S16,
S17: Yes), the count value C is incremented by one (S18), and when the count value C is rNIJ (
S19: Yes) In order to forcibly drive the semiconductor laser device 3 to turn on, for example, the “H” level forced signal supplied to the video signal input circuit of the laser driver that drives the semiconductor laser device 3 is released. (S20). When the count value C is equal to or greater than "Nl" and smaller than "N2" (S21: Yes), for example, the video signal input circuit of the laser driver is forced to the rLJ level, and the drive control signal for the semiconductor laser element 3 is S
The supply of c is prohibited (S22), and the serial buffer 22
A read process is executed to read the print data in (328
), if the print command has not been canceled (S29
:No), return to Sll. Also, the count value C is “N2
'' and smaller than I'N3J (S23
:Yes), the drive control signal Sc corresponding to the video signal of the laser driver is directly supplied to the semiconductor laser element 3 (S24), and returns to Sll via S28 and S29. Further, when the count value C is greater than or equal to "N3" and smaller than "N4" (S25: Yes), the video signal input circuit of the laser driver is forcibly set to "L" level, and the drive control signal for the semiconductor laser element 3 is The supply of Sc is prohibited again (S26), and the process returns to Sll via S28 and S29. Further, when the count value C is larger than "N4", and when it is larger than "0" and smaller than rNIJ (S25
:No), for example, by supplying an "H" level forced signal to the video signal input circuit of the laser driver that drives the semiconductor laser element 3, the semiconductor laser element 3 is forcibly driven to turn on (S27), and S28 and S29 After that, return to Sll.

The maximum latent image forming range on the photosensitive drum 8 is expanded from the device position P2 of the laser beam B to the scanning position P4, and a large number of dots are stored in the serial buffer 22 corresponding to this expanded forming possible range. In the case where data can be stored, the prohibition period of the drive control signal Sc to the semiconductor laser element 3 may be limited to the period from the scanning position PI of the laser beam B to the scanning position P2. In this case, the inhibition control of the drive control signal Sc can be simplified.

[Brief explanation of the drawing]

Figure 1 is a functional block diagram showing the configuration of the present invention, Figures 2-
Fig. 5 shows an embodiment of the present invention, Fig. 2 is a plan view of the laser beam scanning device, Fig. 3 is a configuration diagram of the control system of the laser beam scanning device, and Fig. 4 is a diagram of the control system of the laser beam scanning device. Time charts of various signals, and FIG. 5 is a schematic flowchart of a laser beam scanning control routine according to a modified example. ■... Laser beam scanning device, 3... Semiconductor laser element, 5... Hexahedral mirror, 10... Laser light receiving element, 20... Control device, 21... Oscillation circuit, 22.
・Serial buffer, 23...Scanner motor,
26... Laser light drive circuit, 28... Addition counter,
25... Ant Kate. Patent applicant: Brother Industries, Ltd. Figure 1 Figure 3

Claims (1)

[Claims] (1) A light emitting device that generates a beam of laser light, a scanning device that scans the photosensitive drum with the light beam, a driving device that drives the light emitting device, and print data for each dot line that is stored for printing. A control means including a memory means and outputting a drive control signal corresponding to print data to the drive means from a predetermined latent image formation start timing for each scan, and a synchronous clock signal for synchronously outputting the drive control signal. In a laser printer comprising an oscillating means for generating a beam, and a light receiving means for receiving a luminous flux and generating a horizontal synchronizing signal, the horizontal synchronizing signal received from the light receiving means is counted while the synchronizing clock signal supplied from the oscillating means is counted. a counter means whose count value is cleared by; and a counter means which receives the output of the counter means and corresponds to the latent image formation start timing from when the count value reaches a first predetermined value corresponding to the timing immediately after generation of the horizontal synchronization signal. A laser beam scanning device for a laser printer, comprising: prohibition means for prohibiting the supply of a drive control signal to the drive means until a second predetermined value is reached.