JP2900741B2 - Image forming device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus for printing characters and images using four colors of yellow, magenta, cyan and black, and more particularly to a case where a structure in which four process units are arranged and operated in parallel. In addition, the present invention relates to an image forming apparatus for preventing the occurrence of mutual displacement of toner images formed for each process unit.

2. Description of the Related Art In a color printer used as a color image forming apparatus, four color toner images of yellow, magenta, cyan and black are sequentially formed on one photosensitive drum, and each time a single color toner image is formed. A one-drum method in which a multicolor toner image is sequentially transferred to one intermediate transfer member to form a multicolor toner image on the intermediate transfer member, and then transferred from the intermediate transfer member to recording paper and fixed to print a color image. And four
Four color toner images of yellow, magenta, cyan and black are formed in parallel on one photosensitive drum, respectively.
There is a four-drum type in which a color image is printed by transferring and fixing in parallel on a recording paper with a time difference corresponding to the interval between the photosensitive drums and the recording paper conveyance speed.

In the case of the one-drum system, four color toner images are sequentially formed on the photosensitive drum, so that a single color image is not formed unless the photosensitive drum rotates at least four times. One color image is formed by one rotation of the drum, so that high-speed printing is possible as compared with the one-drum method. Therefore, the four-drum system is also advantageous for product series.

The four-drum system naturally requires four optical systems, and among various optical systems such as a laser exposure system, an LED exposure system, and a liquid crystal exposure system, the laser exposure system is most often used for products. Therefore, cost reduction measures are in progress, which is advantageous.

In this laser exposure system, a laser beam that is reflected by a polygon mirror and scans in the main scanning direction is detected by a sensor provided outside the printing area, and based on this detection signal, a laser beam in the main scanning direction is detected. The exposure start position has been determined.

In the four-drum system, since four process units operate in parallel to form one toner image on recording paper, the above-described exposure start position must be the same in the four process units. There is.

[0007]

2. Description of the Related Art FIG. 7 is a view for explaining a configuration example of an image forming apparatus. FIG. 7 shows a configuration example of a 4-drum system, in which Y, M,
Four process units indicated by C and K are arranged and operated in parallel, and a Y process unit for forming a yellow toner image includes a photosensitive drum 1, a developing unit 2, a laser diode exposure unit 3, a charging unit 4, , A static elimination lamp 5, a cleaner 6, an AC static eliminator 7, and a transfer device 8.
The developing device 2 stores yellow toner.

The M process unit for forming a magenta toner image has the same configuration as the Y process unit, but a magenta toner is stored in a developing unit, and a C process unit for forming a cyan toner image is The K process unit, which has the same configuration as the Y process unit, stores cyan toner in the developing device, and forms a black toner image, has the same configuration as the Y process unit. Is stored.

The photosensitive drum 1 rotates in the direction shown by the arrow A. First, the photosensitive drum 1 is uniformly charged by the charger 4, and the yellow electrostatic latent image is formed by the light beam projected by the laser diode exposure unit 3. Is formed on the photosensitive drum 1.

When the yellow toner supplied from the developing device 2 adheres to the electrostatic latent image, the yellow toner image is developed, and at the timing when the toner image reaches the position of the transfer device 8, the sheet feeding cassette Pick roller 14 from 15
The recording paper (not shown) which has been fed out and is waiting by the standby roller is inserted between the transfer unit 8 and the photosensitive drum 1 by the belt 9.

The yellow toner image formed on the photosensitive drum 1 is transferred to the recording paper inserted between the transfer unit 8 and the photosensitive drum 1 by the transfer potential provided by the transfer unit 8.
It is transported to the next M process unit.

After the photosensitive drum 1 is neutralized by the AC neutralizer 7, the remaining toner is removed by the cleaner 6.
Further, the charge is removed by the charge removing lamp 5, and the above process is repeated again.

The belt 9 attracts and holds the recording paper by the potential applied by the belt charger 10, and conveys the recording paper as described above. Then, at the timing when the recording paper conveyed by the belt 9 is inserted between the transfer unit 8 of the M process unit and the photosensitive drum 1, the laser diode of the M process unit is transferred so that the magenta toner image is transferred. The exposing unit 3 starts exposing, and the magenta toner image formed on the photosensitive drum 1 is transferred onto a recording sheet in the same manner as described above.

Subsequently, at the timing when the recording paper conveyed by the belt 9 is inserted between the transfer device 8 of the C process unit and the photosensitive drum 1, the C process is performed so that the cyan toner image is transferred. The laser diode exposure unit 3 of the unit starts exposure, and the cyan toner image formed on the photosensitive drum 1 is transferred to a recording sheet as described above.

Subsequently, at the timing when the recording paper conveyed by the belt 9 is inserted between the transfer device 8 of the K process unit and the photosensitive drum 1, the K process is performed so that the black toner image is transferred. The laser diode exposure unit 3 of the unit starts exposure, and the black toner image formed on the photosensitive drum 1 is transferred to a recording sheet in the same manner as described above.

As described above, the recording paper that has passed through the four process units of Y, M, C, and K has the toner fixed by the fixing unit 13 and is discharged to the discharge tray 16. Further, the belt 9 is neutralized by a belt neutralizer 12 and is cleaned by a belt cleaner 11.
Charge.

Each of the laser diode exposure units 3 of the four process units Y, M, C, and K operating as described above.
The exposure start position in the main scanning direction, that is, the print start position, based on the pulse width of the BD signal indicating that the light beam has been detected by the photo sensor provided near the end of the photosensitive drum 1, I have decided.

That is, the printing start position is determined by counting a predetermined number of dot clocks based on the pulse width of the BD signal.

[0019]

FIG. 8 is a diagram for explaining the problems of the prior art. Since the light intensity of the laser beam is represented by a Gaussian distribution, the output of the photosensor when not saturated has a waveform similar to the light intensity of the laser beam.
Accordingly, the output waveform of this photosensor varies as shown in FIG. 8 due to the difference in the power of the laser diode and the difference in the sensitivity of the photosensor, as shown in FIG.

For this reason, if a BD signal is created by binarizing with the threshold value shown below, the pulse width of the BD signal is constant even if the level of this threshold value is fixed or the fixed ratio of the peak value of the waveform is set. Since the power of the laser diode and the sensitivity of the photosensor are not the same for each of the four process units M, C, and K, they differ from each other.

As described above, each of the laser diode exposure units 3 of the four conventional process units determines the printing start position based on the pulse width of the BD signal, so that the pulse width is always constant. Is required, but FIG.
Since the pulse widths of the BD signals are different from each other, the printing start position in the main scanning direction slightly shifts for each process unit as shown in FIG.

Even if the print start position can be finely adjusted with a switch or the like for each process unit, the pulse width of the BD signal is always kept constant due to the environmental change of the laser diode or the photo sensor or the characteristic change due to the aging. Is difficult to perform, and there is a problem that the print quality is deteriorated due to the shift of the print start position for each process unit.

The present invention has been made in view of the above-described problems, and the pulse width of the BD signal is made to coincide with the reference pulse width so that the BD signal always formed of a pulse having a constant width is supplied. The purpose is to match the print start positions of the process units.

[0024]

FIGS. 1 and 2 are block diagrams for explaining the principle of the present invention. The image forming apparatus is shown in FIG.
As shown in FIG. 7, the electrostatic latent images formed by scanning the plurality of image carriers 47 to 50 in the main scanning direction by the electrostatic latent image forming means 52 to 55 are developed, and sequentially transferred onto the recording medium 51. Print one toner image.

Generating means 5 for generating a reference pulse
6, signal transmission means 57 for transmitting a BD signal which is a reference of a start position of forming an electrostatic latent image in the scanning in the main scanning direction,
Based on the difference between the scanning cycle in the main scanning direction obtained from the BD signal sent by the signal sending means 57 and a predetermined reference scanning cycle, and the phase difference between the reference pulse sent by the generating means 56 and this BD signal. A synchronization means 58 for synchronizing the BD signal with the reference pulse, and a difference between the reference pulse sent from the generation means 56 and the pulse width of the BD signal synchronized by the synchronization means 58, and removing the difference in the pulse width. And a pulse width matching means 59 for performing the operation.

By making the pulse width of the BD signal the same as the pulse width of the reference pulse, the electrostatic latent image forming means 52 to 5 for each of the plurality of image carriers 47 to 50 can be obtained.
5 are synchronized in the main scanning direction.

As shown in FIG. 2, the image forming apparatus scans a plurality of image carriers 47 to 50 by electrostatic latent image forming means 52 to 55 in the main scanning direction to form an electrostatic latent image. The toner image is developed, sequentially transferred onto the recording medium 51, and one toner image is printed.

A signal transmitting means 57 for transmitting a BD signal serving as a reference for the start position of forming an electrostatic latent image in the scanning in the main scanning direction, and a pulse width of the BD signal transmitted by the signal transmitting means 57 is set to a threshold. Changing means 60 for changing and changing
Counting means 61 for counting the pulse width of the BD signal transmitted by the changing means 60; and control means 62 for controlling a threshold value supplied to the changing means 60 so that the counting result of the counting means 61 matches the reference value. Are provided.

By making the pulse width of the BD signal equal to the reference value, the plurality of image carriers 47 to
The scanning periods in the main scanning direction of the electrostatic latent image forming means 52 to 55 for every 50 are all synchronized.

[0030]

With the above arrangement, the pulse width of the BD signal can be made to coincide with the pulse width of the reference pulse, so that a BD signal formed by a pulse having a constant width can always be supplied. Therefore, each of the image carriers 47 to 5
The print start position on 0 can be matched.

[0031]

FIG. 3 is a block diagram of a circuit showing an embodiment of the present invention, and FIG. 4 is a time chart for explaining the operation of FIG.

The generating means 56 shown in FIG.
The signal transmitting means 57 shown in FIG. 1 is constituted by the equipment indicated by reference numeral 23 in FIG. 3, and the synchronizing means 5 shown in FIG.
8 is composed of devices indicated by reference numerals 26 to 30 in FIG.
The pulse width matching means 59 is constituted by devices indicated by reference numerals 34 to 40 in FIG.

When a motor start signal is input to the motor drive circuit 33 from a host device (not shown), the motor drive circuit 33 supplies a drive current to the polygon motor 21, so that the polygon motor 21 starts rotating.

The encoder 22 is constituted by a Hall element, and sends a voltage signal corresponding to the rotation of the polygon motor 21 to the motor drive circuit 33. Therefore, the motor drive circuit 33 switches the current applied to the motor coil according to the voltage signal. Therefore, the polygon motor 21 rotates at a predetermined rotation speed.

When the host device drives the laser diode, it causes the polygon mirror 20 to project laser light.
When the light reflected by the polygon mirror 20 scans the BD sensor (photo sensor) 23, a signal having a waveform shown in FIG. 8 is transmitted to the amplifier 31 and the comparator 37.

When the amplifier 31 amplifies this signal and creates a pulse as shown by BD in FIG. 4, it sends it to the phase comparator 26 and the FV converter (frequency-voltage converter) 30.
The crystal oscillator 24 supplies a reference signal as shown in the reference pulse of FIG. 4 to the phase comparator 26 and the comparator 38 via the frequency divider 25.

The phase comparator 26 outputs B
The phase of the D pulse is compared with the phase of the reference signal. If there is a phase difference, an output voltage corresponding to the phase difference is sent to the amplifier 28 via the amplifier 27.

On the other hand, the FV converter 30 outputs a voltage corresponding to the frequency of the BD pulse and sends it to the amplifier 29. The amplifier 29 compares this voltage with a voltage corresponding to the rotation speed of the polygon motor 21 set by the variable resistor 32, and sends a voltage corresponding to the difference to the amplifier 28.

Therefore, a signal that changes according to the phase difference detected by the phase comparator 26 and a signal that changes according to the frequency difference detected by the FV converter 30 are amplified by the amplifier 28.
And amplified.

The amplifier 28 amplifies the phase difference signal and the frequency difference signal and sends them to the motor drive circuit 33.
The motor drive circuit 33 adjusts the rotational speed of the polygon motor 21 by changing the current supplied to the polygon motor 21 in accordance with the output voltage of the amplifier 28.

Therefore, the reference signal transmitted by the frequency divider 25 is shared by the four process units Y, M, C, and K, so that the phases of the BD signals of all the process units can be adjusted as shown in FIG. It can be synchronized with the pulse phase.

Accordingly, the rising timing of the reference pulse shown in FIG. 4 coincides with the rising timing of the BD pulse shown in FIG. The comparator 37 is D
The threshold value is changed according to the output of the / A converter (digital / analog converter) 36 to pulse the signal transmitted from the BD sensor 23, and the pulse is transmitted to the CLK terminal of the register 35, the B terminal and the BD terminal of the comparator 38 as a BD pulse. I do.

The comparator 38 is connected to the NOT circuit 4 from the CLK terminal.
It operates by a clock input through the terminal 1 and compares the pulse width of the reference signal input from the A terminal with the pulse width of the BD pulse.
If the BD pulse width is large, as shown in the output of the comparator 38 in FIG. 4, the period corresponding to the magnitude of the pulse width difference, A <B
In order to send a logical "1" from the terminal to the AND circuit 40,
The logic "1" is input to the up / down counter 34 from the AND circuit 40 in synchronization with the clock.

The up / down counter 34 sends an output value that increases by the number of clocks to the register 35, and the register 35 takes in this output value at the falling edge of the BD pulse.

As shown in the register output of FIG. 4, the register 35 sends the fetched output value to the D / A converter 36, so that the output of the D / A converter 36 is the output of the DA converter of FIG. As shown in (2), since the signal increases in synchronization with the fall of the DA pulse, the comparator 37 slices the signal transmitted from the BD sensor 23 at a threshold value corresponding to this output. Therefore, the width of the BD pulse transmitted to the BD terminal is gradually reduced.

The comparator 38 operates in response to a clock input from the CLK terminal via the NOT circuit 41 and compares the pulse width of the reference signal input from the A terminal with the pulse width of the BD pulse. In a period corresponding to the magnitude of the width difference, a logical "1" is sent from the A> B terminal to the AND circuit 39, so that the logical "1" enters the up / down counter 34 in synchronization with the clock from the AND circuit 39. .

The up / down counter 34 sends an output value reduced by the number of clocks to the register 35, and the register 35 takes in this output value at the falling edge of the BD pulse.

The register 35 sends the fetched output value to the D / A converter 36, and the output of the D / A converter 36 decreases in synchronization with the falling edge of the DA pulse. Slices the signal sent by the BD sensor 23 with a threshold value corresponding to this output. Therefore, the width of the BD pulse sent to the BD terminal increases sequentially.

The reason why the comparator 38 is clock-synchronized is to prevent the up / down counter 34 from malfunctioning due to glitches. The output side of the BD terminal is connected to an exposure start position determination circuit (not shown).

FIG. 5 is a block diagram of a circuit showing another embodiment of the present invention. The changing means 60 in FIG.
The counting means 61 in FIG. 2 is constituted by the equipment indicated by reference numeral 46 in FIG. 5, and the control means 62 in FIG. 2 is constituted by the equipment indicated by reference numerals 42 to 44 in FIG.

The processor 42 receives the counter 4 via the bus.
A signal is sent to the RST terminal 6 to reset the counter 46. Further, a clock is input to the counter 46 via the NOT circuit 41.

The comparator 45 changes the threshold value according to the analog signal level sent from the D / A converter 44 to pulse the signal sent from the BD sensor 23 and sends it to the EN terminal of the counter 46 to enable the counter 46 and Then, an interrupt is issued to the processor 42 via the bus, and the interrupt is sent to the BD terminal as a BD pulse.

The enabled counter 46 counts the width of the signal sent from the comparator 45, that is, the BD pulse width, and sends it to the bus of the processor 42. Processor 42
Writes the initial value to the register 43, and the register 43 sends the initial value to the D / A converter 44. Therefore, the D / A converter 44 sends an analog signal of a level corresponding to the initial value to the comparator 45. The comparator 45 generates a BD pulse with the threshold value corresponding to the analog signal level as described above.

When detecting an interrupt from the comparator 45, the processor 42 reads the count value of the counter 46, compares it with a reference value stored in an internal ROM or the like. The write value is increased, and if smaller than the reference value, the write value of the register 43 is decreased.

Therefore, in the same manner as described above, the D / A converter 4
The comparator 45 creates a BD pulse by changing the threshold so that the difference between the width of the BD pulse and the reference value is eliminated according to the level of the analog signal transmitted by 4.

FIG. 6 is a flowchart for explaining the operation of FIG. The processor 42 writes the initial value into the register 43 in step (1), checks whether an interrupt has come in step (2), and reads the value of the counter 46 in step (3) when the interrupt comes.

Then, in step (4), comparison with the reference value is performed, and in step (5), it is checked whether the value is larger than the reference value. If it is larger than the reference value, the write value of the register 43 is increased in step (7), written in the register 43 in step (9), and the process returns to step (2).

If it is not larger than the reference value in step (5), it is checked in step (6) whether it is smaller than the reference value. If it is not small, the process returns to step (2).
In (8), the write value of the register 43 is reduced. Then, in step (9), the data is written into the register 43, and the process returns to step (2).

It is needless to say that the above operation may be realized by hardware.

[0060]

As described above, the present invention automatically adjusts the pulse width of the BD signal from each optical system of a plurality of process units for outputting two or more colors to the reference value. Even when the characteristics of the laser diode or the photo sensor change between solids or due to environmental changes, the printing start position in the main scanning direction can be automatically made the same for each color.

Accordingly, it is possible to prevent a decrease in print quality due to a shift in the print start position for each process unit.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating the principle of the present invention (part 1).

FIG. 2 is a block diagram illustrating the principle of the present invention (part 2);

FIG. 3 is a block diagram of a circuit showing one embodiment of the present invention.

FIG. 4 is a time chart for explaining the operation of FIG. 3;

FIG. 5 is a block diagram of a circuit showing another embodiment of the present invention.

FIG. 6 is a flowchart for explaining the operation of FIG. 5;

FIG. 7 illustrates a configuration example of an image forming apparatus.

FIG. 8 is a diagram illustrating a problem of the related art.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photosensitive drum 2 Developing device 3 Laser diode exposure part 4 Charger 5 Static elimination lamp 6 Cleaner 7 AC static eliminator 8 Transfer device 9 Belt 10 Belt charger 11 Belt cleaner 12 Belt static eliminator 13 Fixing device 14 Pick roller 15 Paper cassette 16 Output tray 20 Polygon mirror 21 Polygon motor 22 Encoder 23 BD sensor 24 Crystal oscillator 25 Divider 26 Phase comparator 27, 28, 29, 31 Amplifier 30 FV converter 32 Variable resistor 33 Motor drive circuit 34 Up / Down counter 35, 43 Register 36, 44 D / A converter 37, 38, 45 Comparator 39, 40 AND circuit 41 NOT circuit 42 Processor 46 Counter 47-50 Image carrier 51 Recording medium 52-55 Electrostatic latent image formation Means 56 Generating means 57 Signal sending means 58 Synchronizing means 59 Pulse width matching means 60 Changing means 61 Counting means 62 Control means

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-3-149576 (JP, A) JP-A-1-186327 (JP, A) JP-A-3-175461 (JP, A) JP-A-63-1988 8662 (JP, A) JP-A-60-57316 (JP, A) JP-A-6-227038 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) B41J 2/525 B41J 2 / 44

Claims (2)

(57) [Claims] An image for developing an electrostatic latent image formed by scanning a plurality of image carriers (47) to (50) in a main scanning direction by electrostatic latent image forming means (52) to (55), respectively. Generating means (56) for generating a reference pulse; and a laser beam detection signal (hereinafter referred to as a BD signal) serving as a reference for a start position of forming an electrostatic latent image in the scanning in the main scanning direction.
Signal transmitting means (57) for transmitting a signal, a difference between a scanning cycle in the main scanning direction obtained from the BD signal transmitted by the signal transmitting means (57) and a predetermined reference scanning cycle, and the generating means (56) And the reference pulse transmitted by
A synchronizing means (58) for synchronizing the BD signal with the reference pulse based on a phase difference from the D signal; a reference pulse transmitted by the generating means (56);
8) determining a pulse width difference of the synchronized BD signal and removing the pulse width difference, and a pulse width matching means (59), and providing the pulse width of the BD signal with the pulse width of the reference pulse. By the same as the above, the plurality of image carriers (47) ~
(50) An image forming apparatus, wherein all the scanning periods of the electrostatic latent image forming means (52) to (55) in the main scanning direction are synchronized. 2. An image for developing an electrostatic latent image formed by scanning a plurality of image carriers (47) to (50) in the main scanning direction by electrostatic latent image forming means (52) to (55), respectively. A signal transmitting means (57) for transmitting a BD signal serving as a reference of a start position of forming an electrostatic latent image in the main scanning direction; and a BD signal transmitted by the signal transmitting means (57). Changing means (60) for changing the pulse width by changing the threshold value, counting means (61) for counting the pulse width of the BD signal transmitted by the changing means (60), and counting results of the counting means (61) Is equal to the reference value,
Control means (6) for controlling a threshold value supplied to the change means (60);
2), and by setting the pulse width of the BD signal to be equal to the reference value, electrostatic latent image forming means (52) to (52) to (52) to (50) for each of the plurality of image carriers (47) to (50). 55) An image forming apparatus wherein all the scanning periods in the main scanning direction are synchronized.