JP2840249B2 - Color image forming equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention forms different images on a plurality of recording media,
The present invention relates to a multiplex image forming apparatus that obtains a multiplex image by transferring each color image onto one recording medium.

[Conventional technology]

First, FIG. 29 shows a conventional color copying apparatus using one photosensitive drum, and further shows its operation.

In FIG. 29, reference numeral 1200 denotes a one-drum type color copying apparatus main body. Reference numeral 1201 denotes a photosensitive drum which rotates in the direction of arrow a. 1202 is a charger, 1203 is a laser oscillator, 1204 is an exposure charger, and 1205 is a surface position sensor. 1206,1
Reference numerals 207 and 1208 denote Y (yellow), M (magenta) and C (cyan) color developing units.

The operation in this configuration will be described. First, the photoconductor surface of the rotating photosensitive drum 1201 is charged by the charger 1202 (corona discharge). The laser light generated by the laser oscillator 1203 passes through the reflection mirror and
Irradiated at 01. Here, the laser oscillation unit includes a polygon mirror (not shown). As the polygon mirror rotates, the laser light is scanned in the main scanning direction to form one line. When the laser light is turned on or off, an electrostatic latent image is formed as a pixel on the surface of the photosensitive drum of the photosensitive drum 1201. Thereafter, one of the three color developing units 1206, 1207, and 1208 attaches the color toner, and the latent image is developed. Then, the toner image is transferred by the transfer charger 1209 to the transfer paper 1210 sent from the paper supply cassette by the paper supply roller 1211. Here, the difference from the monochrome copying apparatus is that the transfer paper 1210 is held by the holding drum 1215 and is rotated in the direction of the arrow b. This holding drum 1215
The latent image is rotated to transfer the latent image of the color toner to the transfer paper 1210 in the order of Y, M, and C, and its rotation speed is equal to the peripheral speed of the photosensitive drum 1201.

Next, the transfer paper after the transfer of the three primary color toners is
The toner is peeled off from the holding drum 1215 and transported to the heat fixing device 1214. The transfer paper fixed by this is discharged to a paper discharge roller 12.
By 13, it is discharged to the copy tray 1212.

[Problems to be solved by the invention]

However, from the viewpoint of copy speed, the method using a plurality of photosensitive drums as shown in FIG. 3 is more advantageous than the conventional example as shown in FIG. However, for example, in the embodiment using four photosensitive drums in the embodiment shown in FIG. 3, there is a problem of color shift (color registration) as a color image output and a screen memory is required due to a distance shift of the photosensitive body. There are still many problems to be solved, such as control of sensitivity variations by a plurality of photoconductors.

[Means and actions for solving the problems]

The present invention provides a plurality of image forming units each having a recording body and forming an image of a different color on the recording body, and transferring each color image formed by the plurality of image forming units onto a single recording medium. A transport unit that mounts and transports the recording medium to read the registration marks of each color formed by the plurality of image forming units and transferred onto the transport unit; and a reading result of the reading unit. Detecting means for detecting the amount of positional deviation of each color image based on the amount of positional deviation detected by the detecting means; determining whether or not the amount of positional deviation is within a correctable range; Control means is provided for correcting the displacement of each color image, and prohibiting image formation when correction is impossible.

〔Example〕

Since the color copying apparatus of the present embodiment is composed of various components, there are many component technologies to be described. Therefore, the description will be made in the following order.

1. Outline of the device (1-1) Block diagram (1-2) Overall device (1-3) Reader unit (1-4) Memory unit (1-5) Printer unit 2. Automatic color registration correction (2-1) ) Algorithm (2-2) Elemental technology (2-3) Correction timing (1. Outline of device) (1-1) Overall block diagram FIG. 1 is an overall block diagram of the device of this embodiment. 100
Denotes a reader unit, 115 denotes a reading sensor, and 118 denotes a light source for irradiating a document.

Reference numeral 103 denotes an amplifier unit for amplifying an analog video signal output from the reading sensor. The amplified analog video signal is input to the A / D converter 104. Here, the sensor 115 is a CCD color sensor, and one pixel is R
(Red), G (green), and B (blue) signals are sequentially transferred and output serially. A latch circuit 105 latches and holds B, G and R in the order of B, G and R, and simultaneously outputs color signals B, G and R for one pixel.

Reference numeral 106 denotes a color conversion unit for generating L ^* , a ^* , and b ^* signals from B, G, and R, and is configured by, for example, a look-up table using a ROM (Read Only Memory) or the like.

Therefore, the output of the reader unit 100 is a signal of L ^* , a ^* , b ^* .

300 is a memory unit. The signals received as L ^* , a ^* , b ^* are L ^* (brightness signal) and a ^* , b ^* (chromaticity signal), which are separately compressed, and finally, information of a predetermined number of pixels. Is compressed to 32 bits and input to the screen memory 301.

 A detailed description of these will be given later.

The image signal provided in the screen memory 301 is output to the outside through the communication interface 320 or is output to the printer unit 200.

When the image signal is output to the printer unit 200, the image signal stored in the screen memory 301 is read out by the decompressor 304, decoded, returned to the original L ^* , a ^* , b ^* signal, and sent to the printer unit 200. Is output.

The printer unit 200 switches and supplies the image signals received at L ^* , a ^* , and b ^* in response to requests for asynchronous write timing signals from a plurality of photoconductors by the color conversion unit 255. ^The image signals marked with ^* , a ^* , and b ^* are converted into image signals of printing toners C (cyan), M (magenta), Y (yellow), and K (black).

Reference numerals 201C, 201M, 201Y, and 201K denote laser units, each having four laser units in the present embodiment, and exposing C (cyan), M (magenta), Y (yellow), and K (black) images. Write on the body.

211C, 211M, 211Y, and 211K are their photoconductors, and in the case of this embodiment, they are drums, and correspond to laser units, respectively.

(1-2) Entire Apparatus FIG. 2 is a perspective view of the entire apparatus of the digital color copying machine of the present embodiment. As described above, 100 is a color reader unit for reading a color original, 300 is a memory unit for storing a compressed image signal, and 200 is a color printer for forming and outputting a color image.

As an application device, reference numeral 21 denotes a sorter for collating output color copy paper.

Reference numeral 25 denotes an ADF (auto document feeder) for automatically feeding a sheet document.

Reference numeral 23 denotes a paper deck for storing and feeding a large amount of transfer paper.

Also, 22A and 22B are paper cassettes, in this case a two-stage cassette.

FIG. 3 shows the internal structure of the apparatus of this embodiment. The operation of each part will be described later, but FIG. 3 shows a minimum configuration for performing the basic operation.
Application devices such as a sorter 21 and a paper deck 23 shown in the figure are omitted.

(1-3) Reader Unit Next, the reader unit will be described.

In FIG. 3, reference numeral 112 denotes a document irradiating lamp which is a light source; 113, a reflection mirror; 114, a rod lens for condensing reflected light from a document 122 placed on a document table glass 121 onto a reading sensor 115; An array. Reference numeral 118 denotes the original irradiation lamp, a reflection mirror 113, a rod lens array 114,
A scanning body mounted with a reading sensor 115 and an A / D conversion circuit board 117 having an A / D conversion circuit for A / D converting an image signal transmitted from the reading sensor 115 via a signal line 116, The mounted objects 112 to 117 and the scanning body 118 integrally perform the same linear motion in the direction of the arrow. 120 is the A / D conversion circuit board 117
Processing control circuit for storing / calculating and outputting an 8-bit image signal in this example transmitted through a signal line 119
This is a processing control circuit board having 120 (described later).

FIG. 4 is a schematic configuration diagram of the color reader shown in FIG. 3, and the same components as those in FIG. 3 are denoted by the same reference numerals. In the figure, reference numeral 123 denotes a stepping motor serving as a drive source for moving the scanning body 118, reference numeral 124 denotes a motor pulley fixed to a shaft of the stepping motor 123, and reference numeral 125 denotes a stepping motor 123.
And 128, a drive pulley fixed to the shaft 127. 129
The scanning body 118 slides on the surface with two rails. 130
Is fixed to both side surfaces of the scanning body 118 by a bracket 132 and a member 131 via a driving pulley 128 and an idle pulley 133 by a driving wire, and the idle pulley 133 is pulled by a spring 134 in a direction for applying tension to the driving wire 130. ing. 135 includes a motor driver circuit for generating a drive signal for driving the stepping motor 123 based on a signal sent from the processing control circuit 120 via a signal line 136, and a pulse generation circuit for generating a pulse for timing the drive signal. The motor control board is connected to the stepping motor 123 via a signal line 137.

In the above configuration, the rotation of the stepping motor 123 is controlled by the motor pulley 124, the belt 125, the pulley 126,
7, is converted into a linear motion of the scanning body 118 on the rail 129 via the driving pulley 128, the wire 130, the metal fitting 132, and the member 131. The direction of the linear movement of the scanning body 118 at this time is controlled by the forward rotation and the reverse rotation of the stepping motor 123.

When reading an image of a document, an image reading unit (irradiation lamp 112, reflection mirror 113, rod lens array 114, reading sensor 115, etc.) that is integral with the movement of the scanning body 118 scans the document 122 at a certain constant speed. It is performed by The actual reading operation is performed from the leading edge position of the document.

FIG. 5 is a block circuit diagram relating to the reader section. Since the reading system is almost the same, avoid it. However, on the original 122, the direction MS shown in FIG.
S is the sub-scanning direction.

The rod lens array 114 is simply represented as a lens.

Now, the image signal output from the 115 reading sensor is sent to the A / D conversion circuit board 117 described above. The B, G, and R analog signals are sequentially input serially, amplified by a 701 preamplifier, and then input to a 703 sample hold. φ _B ,
φ _G and φ _R are timing pulses for sampling and holding serial B, G, and R analog signals. Also, 702 is C
This is a pulse generator that generates a timing pulse for sampling and holding an image signal, including generation of a CD sample and hold pulse.

Amplifier 103 is a gain adjuster to balance R, G, B
103 '. An A / D converter 104 converts an analog signal into a digital signal.

Here, the image signals of each color of R, G and B are digital signals of 8 bits each.

FIG. 6 is a block diagram of a control circuit for operating the reader unit.

1150 is a CPU (for example, a micro computer), 115
Reference numeral 1 denotes a driving unit that operates each load of the reader unit, and is, for example, the above-described stepping motor 123 or the like. Reference numeral 1152 denotes a power switch signal of the printer unit. However, if a jam (paper jam) or the like occurs in the printer unit, it is expected that the power switch will be turned off in the printer unit during a jam processing operation.

Reference numeral 1153 denotes a keyboard input circuit which operates in response to a key input operation from the operation panel shown in FIG.

Reference numeral 1154 denotes a display, which includes a copy number display 1103 and a jam warning light 1102 shown in FIG.

Reference numeral 1156 denotes a signal indicating "no toner" sent from the printer unit, and there are "no toner" signals of C (cyan) toner, M (magenta) toner, Y (yellow) toner, and K (black) toner. In this case, the CPU 1150 turns on the "no toner" lamp on the display 1154 to give a warning. Specifically, the lamp 1101 on the operation panel shown in FIG. 7 is turned on.

Four lamps 1101 are provided, each of which is a “no toner” lamp of C (cyan) toner, M (magenta) toner, Y (yellow) toner, and K (black) toner.

If any one of them is turned on and there is no toner in one color, color reproducibility as a color copy becomes impossible. Therefore, it is impossible to start the copy operation with the normal copy key 1107. However, the slight color imbalance is when the user wants to copy with knowledge,
For example, a case of a single color copy or the like is included, but in such a case, the copy operation can be started by the single color copy key 1113.

When "no toner" is turned on for all four colors, it goes without saying that single-color copying is also impossible.

Numeral 1106 in FIG. 7 is used to set the number of copies and the like. Reference numeral 1108 denotes a clear key, which is used to clear the number of sheets set by the numeric keypad 1106.

Reference numeral 1103 denotes a number display, which is used to display the number of copies described above.

1102 is a jam display. Reference numeral 1105 denotes a weight indicator. These will be described later.

A stop key 1120 is used to stop the operation during the copy operation.

Reference numerals 1110 and 1111 denote an upper cassette selection key and a lower cassette selection key, respectively, for selecting 22A and B (upper cassette, lower cassette) in FIG. Reference numeral 1121 denotes a paper deck selection key for selecting a paper deck 23 as shown in FIG.

Reference numeral 1112 denotes a density lever, which changes the brightness of a color copy. In this example, this is realized by selectively generating L ^* (brightness signal).

The memory clear key 1122 is used for forcibly clearing the contents of the image memory. This is mainly for deleting the image signal remaining in the image memory when copying is not resumed after the jam processing when a jam occurs. It is for doing.

When detecting the memory clear key 1122, the CPU 1150 sends a memory clear signal 1155 shown in FIG. 6 to the memory section 300 to erase the contents of the memory.

1123 is a saturation knob. This is for adjusting the chromaticity signals of a ^* and b ^* to vary the saturation. 1157 is A.
This is an input of a PC ready signal, and indicates that a potential control described later and an APC (auto power control) operation subsequent thereto have been completed.

Reference numeral 1158 denotes an input of an automatic registration ready signal, which indicates that an automatic registration operation described later has been completed. These 1157 and 1158 ready signals must be executed before the copy operation is performed, and the conditions for the copy operation include the temperature control of the fixing device heater and the presence of paper on the transfer paper, which are the same as in a normal copying machine. In addition to the conditions (not shown), 1156
The copy operation can be performed in a state in which all of the toner and the like are prepared, and the weight display 1105 indicating this is disappeared.

(1-4) Memory Unit The memory unit is provided between the reader unit and the printer unit and serves to store image signals. A4 size (210
X297 mm), 16 pixels / mm for both main and sub-scanning and 8 bit gradation per pixel, requires a memory capacity of 16 MB (byte) per screen. This is a color signal
If you have all R, G, B screens, 16 × 3 = 48 MB, and Y, M,
In the case of having C and K screens, 16 × 4 = 64 MB does not result in a large amount.

For example, when storing these using 1M bit DRAM
384 (48MB) or 512 (64MB) required, 4Mbi
This 1/4 is necessary even when DRAM of t is used.

In addition, as a copier, it is a necessary condition to support up to A3 size. Therefore, twice as many memory IC chips are required.

Therefore, in this example, data compression is performed,
We considered reducing the memory capacity to reduce the number of memory chips and the data processing time including transmission.

The algorithm of the data compression will be described later. When the compression ratio is 12, 48 MB (A4) x 2 ^ 12 as A3 size
= 8MB is enough.

This is 64 1M-bit DRAMs, which is a practical range.

In addition, the data bit width is made up of 32 bits to enable high-speed access.

FIG. 8 is a configuration example of a memory in this example. 1 to
64 is a 1M bit IC memory chip. Since the data is input with a data width of 32 bits, 32 IC memory chips are arranged, and they are used separately in the first half of the 1st to 32nd and the second half of the 33th to 64th.

As mentioned above, the total number of memory bits is 8 MB, so
When accessing with a 2-bit width, a total of 21 addresses are required.

In FIG. 8, reference numeral 801 denotes an address counter which generates these 21 addresses. In addition, since the DRAM of the 1M-bit IC memory chip requires 20 address inputs, the lower 20 addresses (A _{0 to} A ₁₉ ) of the number of addresses generated by the 801 address counter may be input. This is 804
Address buses A _{0 to} A ₁₉ . The bit configuration of a 1M bit DRAM is often 1048576 per bit.
Further, 20 pieces of address inputs, not to have a terminal of the IC chip, RAS, the Fu that _{CAS A 0 ~A 9, A 10} ~A
Normally, the input is divided into the addresses of the upper 10 bits and the lower 10 bits of ₁₉ , respectively, but the explanation is omitted here. In the DRAM, a refresh operation for retaining the memory contents is indispensable, but is omitted here.

By the way, we have already mentioned that 64 memory IC chips are divided into 32 chips, but the choice between the first half and the second half is ▲
▼ was made in the (Chitsupuserekuto), as the signal input, and using the address bus A _20.

Address A ₂₀ are indicated by 805 in FIG. 8, the logic of the inverters 806, either the first half or second half is selected.

That is, the highest address 805 of the address bus 804 is “0”
At this time, the first half of the IC memory chip is selected by ▲ ▼.

 FIG. 9 shows an 8 MB memory map.

If the data width of 32 bits is one block, there are 1995840 blocks, so the address is 1E7440 (Hex). These addresses, but are generated from the address counter 101, the clock input at this time there are two readout clock f ₁ and write clock f _2, these switching is performed by 802.

Reference numeral 803 denotes an R / W (read / write switching) signal. When the signal is "0", a write mode is set, and when it is "1", a read mode is set.

The memory IC chip has a data input (Din) and a data output (Dout).
Is connected. In particular, since the data output (Dout) becomes high impedance when not selected (when ▲ ▼ = 1), there is no problem even if the output terminals are connected.

A3 size explained that the total memory was 8MB (bytes).
The address advances only up to E7440 (Hex). This is an A3 size area (297 x 420mm) which is 8MB in binary
(Byte), which is 1013
The remaining 12 blocks. This is slightly larger than the A3 size and corresponds to an image area of about 21 mm x 297 mm.

In FIG. 8, the memory clear signal 1155 is for erasing the contents of the memory as described above, and is applied to all the clear terminals (（) of the memory chip IC.

(1-5) Printer section As shown in FIG. 3, a four-drum type color printer 20
0, consisting of four units centered on the photosensitive drum. Each unit has its own color developer
The toner stored in 205 differs by color.

In FIG. 3, reference numerals 201C, 201M, 201Y and 201K denote laser oscillators for K (black), Y (yellow), M (magenta) and C (cyan) color signals. This includes a polygon mirror (not shown), and the laser light scans in the main scanning direction by the rotation of the polygon mirror, forming one line.

Here, one unit of photosensitive drum 211 having the same configuration
Is rotated clockwise, and the surface of the photoreceptor is charged by the charger 212.

Laser light is irradiated, and pixel information is written by turning on and off. At this time, a latent image is still being formed, but a color toner is adhered by the developing sleeve 206 to form a visible image (visible image).
From 08, the toner image is transferred to the transfer paper sent by the paper feed roller 207.

In this case, the register roller 250 adjusts the optical edge margin of the image.

The transfer paper is conveyed from the C (cyan) color development to the next color M (magenta) by the conveyance belt 209. And one after another, Y (yellow) and K
(Black) is superimposed on the toner image, and is conveyed to the heat fixing device 213 when the four color toners are aligned. here,
The heat is fixed by the heating roller 214. Then, the sheet is placed on the copy tray 215 by the sheet discharging roller 216.

By the way, in the one-drum type color copying apparatus shown in FIG. 29, the number of the photosensitive drums is one, so that the deterioration of the image quality due to the deterioration of the sensitivity of the photosensitive member has the same effect on all the color development. Therefore, in terms of color balance, even if there is deterioration, the balance is maintained. Therefore, it is possible to prevent the image quality from deteriorating by simple surface potential control.

On the other hand, in the case of a four-drum type color copying apparatus, the sensitivity deterioration of the four drums varies. In addition, the color balance is often lost when a certain drum is replaced with a new one. In this embodiment,
The problem in this regard has been solved.

FIG. 10 is an enlarged view showing the periphery of the photosensitive drum 211 having only one unit. Reference numeral 1008 denotes a potential sensor for measuring the surface potential of the photosensitive drum 211.

The surface potential of the general photosensitive drum by a corona discharge of the charger 212, the drum surface potential is charged until V _0. Then, dark decay occurs before the exposure point A. The exposure point A is the laser light irradiation point A in FIG. Here, exposure is performed by a laser beam, and the surface potential changes depending on the amount of exposure, that is, the intensity of the laser power. In the case of analog recording, the density of the recorded image can be represented by the intensity of the laser power.

230 is a high-voltage transformer. With a predetermined laser power and a constant beam diameter, the photosensitive drum 211
Irradiation. By measuring the surface potential of the drum, the sensitivity of the drum at that time can be known.

By emitting light with a predetermined laser power, as described above,
When the surface potential is measured by the potential sensor, the surface potential is _VL0 . This is a value of the target actually sometimes becomes narrow dynamic range without Citara only to V _L1. This is the photosensitive drum 211
This is considered to be caused by deterioration of the laser beam or decrease in the exposure amount, that is, insufficient laser power.

Either cause can be solved by increasing the laser power.

This potential control method will be described in section (2-3).

(2) FIG. 11 shows the timing to start writing an image.

Recording paper 2 fed by the 250 register roller as described above
08 The t ₁ ~t ₄ hours after the paper leading end respectively corresponding photoreceptors 211
C, 211M, 211Y and 211K are reached, and the transfer of the toner image starts.

FIG. 12 shows this state in a timing chart.

After the register roller 250 starts, for example, in the case of A4 size recording paper, the register roller 250 is energized and rotated for a time sufficient for the recording paper to pass. The image signal is started to be written to the photosensitive member with a delay of t ₁ to t ₄ hours from the start, and is written for the same time as the register roller.

Since there is such a problem peculiar to the four-drum type printer, it is necessary to change the read access of the screen memory accordingly.

FIG. 13 shows that the optical system of the reader unit advances, the timing of writing to the memory and the registration roller of the printer unit are rotated,
This shows the timing at which an image is written by the laser unit.

FIG. 13 shows the timing at which the optical system 118 shown in FIG. 3 moves forward to read a document. ,, is the fifth
7 is R, G, B image signals of the 117 A / D conversion circuit board shown in FIG. Is sent to the memory unit 300 by the memory write clock f _WR , color-converted and data-compressed, and then written to the memory unit.

The image signal stored in the memory unit is sent to the printer unit.

At this time, since the four photoconductors are displaced as described above, it is necessary to separately and asynchronously extract the C (cyan) signal, M (magenta) signal, Y (yellow) signal, and K (black) signal. .

Fig. 13 shows this situation.
,... Are the respective read clock signals f _RD .

This is the color conversion circuit 250 of the printer unit 200 shown in FIG.
Can be realized by switching at high speed.

For the memory section, as shown in FIG. 8, the memory write clock f _WR (850) and the memory read clock f _RD (85)
1) is applied to the multiplexer 802, and is switched and added to 801 according to the timing of writing and reading. Thus, an address is generated from the address counter 801 to the memory chip. However, in this case, the address is incremented (incremented) by one in 4 × 4 pixel blocks, instead of addressing in pixel units.

2. Automatic Color Registration Correction In a four-drum digital color copying machine as shown in this embodiment, the most basic condition is to correct the color registration deviation and form a color image with a good hue. It goes without saying that it is one. For this reason, the apparatus of this embodiment has means for automatically correcting the color resist.

(2-1) Correcting means An unfixed register marker is formed on the conveyor belt using an actual image forming means, and after reading this, the color misregistration of each color image is measured to write the image. By controlling the timing, a laser beam printer that can output a clear color image without color shift can be obtained.

More specifically, image forming control means for forming a predetermined image to be formed on each photosensitive member in each area of the recording medium having the main scanning direction divided into a plurality of parts, and the image forming control means Color shift measuring means for measuring the relative position shift of each image formed in each area,
Color shift correcting means for correcting the timing of writing a laser beam to each photoconductor in accordance with the color shift measured by the color shift measuring means.

FIG. 14 is a block diagram of the displacement correction circuit,
Is a CPU for forming a predetermined image in each area of the recording medium being conveyed in which the main scanning direction is complicatedly divided, and a position shift detector 1402C, 1402M, 140 configured by, for example, a CCD or the like.
The relative color shift amount of each image is calculated according to the output of 2Y, 1402K. 1403a to 1403d are counters (CNT).
3a counts the time from the start of transfer paper transfer from the register roller to the timing of starting to write a cyan image. The counter 1403b counts the timing calculated by the CPU 1401, for example, the writing start timing of the image including the amount of displacement of the cyan image from the magenta image. Similarly, the counter 1403c is calculated by the CPU 1401. For example, the amount of displacement between the cyan image and the yellow image is counted,
1403d counts the amount of displacement between the black image and the cyan image calculated by the CPU 1401, for example.

When the counters 1403a to 1403d count up and a carry signal is issued, they are set by the J terminals of the JK flip-flops 1405a to 1405d, and the write enable signal VD
Oa to VDO-d go to the “H” level.

At this time, since the input gates of the AND gates 1404a to 1404d are opened, the aforementioned beam detect signals (BD-C to BD-
K) is output from the AND gate. This is a HSYNC signal, which is a horizontal synchronization signal, and indicates the synchronization of the laser beam in the main scanning direction.

 This HSYNC signal is sent to the image memory.

FIG. 15 is a perspective view for explaining a displacement detection operation according to this embodiment.

In this figure, reference numeral 1505 denotes a recording medium, which in this example corresponds to a position on a transport belt. Each laser unit 201C, 2
The latent images formed on the respective photosensitive drums 211C, 211M, 211Y and 211K are developed by laser beams from 01M, 201Y and 201K to form 1501C, 1501M, 1501Y and 1501K. Reference numeral 1506 denotes a sensor substrate, as will be described later.
M, 1402Y and 1402K are arranged at predetermined positions. The photosensitive drums 211C, 211M, 211Y and 211K are disposed with a certain distance L, the image forming timing of the photosensitive drum 211C is after t ₁ hours from the delivery of the transfer sheet of the registration roller 250, in addition the photosensitive drum 211M Image formation timing is t ₂
After a lapse of time.

Similarly, the image forming timings on the photosensitive drums 211Y and 211K are after elapse of t ₃ and t ₄ hours, respectively. FIG. 18 shows this in a timing chart. In FIG. 18, after the transfer paper is sent out by the registration roller 250, for example, in the case of A4 size transfer paper, a time t ₀ just for passing the transfer paper is used.
To rotate. VDO-C, VDO-M, VDO-Y, and VDO-K are image permission write-in signals. As described above, after the registration roller 250 starts rotating and starts feeding the transfer paper, t ₁ and t ₁ , respectively. t
Writing of an image is permitted after elapse of ₂ , t ₃ and t ₄ hours. However, the timing relationship does not change even when there is no transfer paper as in this example.

This will be described more specifically with reference to FIG. In this figure, the BD signal (beam detect) signal from the beam detector 1513 is constantly output while the polygon scanner is rotating.

As described above, when the above-mentioned counters 1403a to 1403d count up and the J terminals of the JK flip-flops 1405a to 1405c shown in FIG. 14 are set, the count-up signal becomes "H". It is. Also, it indicates that the BD signal is extracted only during image formation by the AND gates 1404a to 1404d and becomes an HSYNC signal.

The image signal is read from the image memory 300 in synchronization with the HSYNC signal to form an image. This is shown in FIG.

In FIG. 17, HSYNC-C, HSYNC-M, HSYNC-Y, HSY
The NC-K signal accesses the memory unit 300 to extract C (cyan), M (magenta), Y (yellow), and K (black) image signals, and outputs the laser units 201C, 201M, 201Y, and 201.
This shows the state of writing in K.

255 is a color converter, L ^* (brightness signal), a ^* , b
^* (Chromaticity signal) for converting into C (cyan), M (magenta), Y (yellow), and K (black) signals, respectively.

 This is the same as that shown in FIG.

FIG. 16 is a plan view showing the arrangement of the sensor substrate 1506 shown in FIG. 15, and the same components as those in FIG. 16 are denoted by the same reference numerals.

In this figure, 1600C, 1600M, 1600Y, and 1600K are color-specific areas divided in the main scanning direction of the recording medium 1505, and the respective color-specific areas 1600M and 1600Y based on an image 1501C formed in the color-specific area 1600C , Each image formed at 1600K 1501M, 150
The case where the relative positional deviation amounts of 1Y and 1501K are Δy ₂ , Δy ₃ and Δy ₄ is shown. Reference numeral 1602 is a reference plate, which is a displacement detector 1402C, 1402
Cancels the variation error due to mounting of M, 1402Y and 1402K. Note that an arrow 1604 indicates the transport direction (sub-scanning direction) of the recording medium 1505.

Thus, a plurality of displacement detectors 1402C, 1402M, 1402Y, 14
Since the 02K is mounted on the same substrate 1506, the positions of the plurality of detectors do not change with respect to the substrate and can be accurately adjusted.

First, the CPU 1 controls the recording medium 1505 conveyed by the photosensitive drums 211C, 211M, 211Y, and 211K disposed at a constant interval L.
Predetermined images 1 in the color-specific regions 1600C, 1600M, 1600Y, 1600K
When forming a 501C～1501K, i.e. the time t ₄ has passed, is conveyed to a position where the sensor substrate 1506 is disposed. Here, the images 1501C to 1501K formed in the respective color regions 1600C, 1600M, 1600Y, and 1600K are used as position shift detectors 1402C and 1402.
Detected by M, 1402Y, 1402K. At this time, for example, image 1
501C calculates the relative positional deviation of each image 1501M~1501K based on its positional deviation amount [Delta] y _2, [Delta] y _3, by adding the time t ₂ and time corresponding to Δy _4, t _3, t ₄ and respectively Time (t ₂ + | Δ
y ₂ |), (t ₃ + | Δy ₃ |) and (t ₃ + | Δy ₄ |) are calculated and set as counter values in the counters 1303b to 1303d. At the time of main image formation, after completion of counting of each of the counters 1403b to 1403d, that is, after the corrected time has elapsed, each laser unit
For 201M, 201Y, 201K, permission signals VDO-C, VDO-M,
Generate VDO-Y and VDO-K. Thereby, the shift of the color resist is automatically corrected.

As described above, the marker reading method has been proposed as a method for automatically correcting the displacement of the color resist. However, in consideration of the stability of the marker formation itself, the formation of a reliable marker is premised.

 The factors that support this premise are as follows.

(I) The rotation speeds of the four polygon scanners are completely the same.

(Ii) The sensitivity variation of the four photoconductors is controlled, and no extreme density difference is observed in the formation of markers.

The problem (i) can be solved by using a common reference oscillator (for example, a crystal oscillator) in a plurality of polygon scanner control circuits. The problem (ii) can be solved by controlling the surface potential.

In the present embodiment, these points have been solved and are important technical elements constituting means for automatic registration correction.
Because, as shown in Fig. 16, the registration correction marker
Recording width Y ₁ to Y ₄ of 1501C~1501K is proportional to the number of main scanning of the scanning lines, which is obtained by multiplication of the process speed in the time represented by t ₁ = N × t _BD in Figure 20 is there.
Y ₁ to Y ₄ is intended to be formed by irradiation of a laser beam from the four polygons sukiya toner, respectively. Therefore
Needless to say, the time lag of t _BD directly affects Y ₁ to Y ₄ . In addition, by controlling the density of the resist correction marker to be constant by controlling the surface potential, the detection accuracy of the marker can be improved.

(2-2) The common st of the reference oscillator As shown in FIGS. 1, 3, and 15,
201C, 201M, 201Y and 201K are laser units. This will be described in more detail. However, only one laser unit 201C will be described, and the rest will be omitted.

In FIG. 15, a laser beam emitted from a semiconductor laser chip 1005 is reflected by a 1510 polygon mirror, irradiated on a photosensitive drum 211C via an f · θ lens 1511, and uniformly scanned. The scanning direction is as shown by the arrow. Reference numeral 1512 denotes a reflection mirror which receives the laser beam emitted from the laser unit 201C before the image writing position, enters the beam detection signal generation unit (BD signal generation unit) 1513, and extracts the signal as a BD-C signal.

The same applies to the crotch and other laser units. 1514
Is a scanner motor.

FIGS. 21 and 22 show the scanner motor shown in FIG.
FIG. 14 is a block diagram illustrating a control configuration of 1514.

In these figures, reference numeral 61 denotes a driver circuit, which has a rotor 61a for rotating the polygon mirror 1510, for example, composed of a permanent magnet. The rotor 61a has Hall elements 62a and 62b arranged at a fixed angle, for example, 135 ° with respect to the rotation angle position of the rotor 61a. 63a to 63d are stators, and when current is applied to the coils of the stators 63a and 63d, the stators 63a and 63d facing the rotor 61a become S poles,
When current is applied to the coils of the stators 63b and 63c,
The coils are wound so that the stators 63b and 63c facing the rotor 61a have N poles. A Hall IC 64 is disposed near the rotor 61a and feeds back the detected frequency signal FG to the control unit 65. The control unit 65 controls the frequency signal FG
And a drive signal M sent from a CPU (not shown), and a PLL control unit 65a that controls a current supplied to the stators 63a to 63d.
It has a current amplifier 65b and a current limiter circuit 65c. When the N pole of the rotor 61a approaches, the Hall elements 62a and 62b output an electromotive force of "0" on the negative side and output an electromotive force of "1" on the positive side. Further, when the S pole of the rotor 61a approaches, the Hall elements 62a and 62b output an electromotive force whose-side is "1",
The + side outputs an electromotive force of “0”.

At the position shown in FIG. 21, since the rotor 61a of the Hall element 62a faces the N pole, the output Ha becomes “0”, current flows through the stator 63a, and the stator 63a is magnetized to the S pole. The S-pole of the rotor 61a repels, the N-pole is attracted and a rotational force is generated to rotate in the direction of the arrow. When the rotor 61a rotates, the Hall element 62a loses the electromotive force as the N pole on the Hall element 62a moves away, and the stator 63a is cut off. On the other hand, since the S pole of the rotor 61a approaches the Hall element 62b, the output Hb becomes "0", and a current flows through the stator 63b to be magnetized to the N pole. Therefore, the S pole is sucked. Thus, output Ha → output Hb → output Hc → output
It becomes “0” in the order of Hd, and in response, the stator
63a to 63d are sequentially magnetized, and the rotation of the rotor 61a is continued.

On the other hand, the rotation speed is controlled by the frequency signal FG detected by the Hall IC 64 mounted near the rotor 61a.
The current sent to the motor 65 and applied to the stators 63a to 63d is controlled so that the rotation of the rotor 61 is maintained at a constant speed.
Needless to say, one rotor 61a is provided for each polygon mirror 1510.

In FIG. 22, reference numeral 71 denotes a PLLIC chip (PLL control means) composed of, for example, HA12032 (manufactured by Hitachi, Ltd.), which is fed back from a reference frequency signal FV supplied from a reference frequency oscillator (crystal oscillator) 72 and a Hall IC 64. And the current supplied to the stators 63a to 63d is controlled. The PLLIC chip 71 is connected to each scanner motor 151
It is provided for every four.

For this reason, since the PLLIC chip 71 controls the rotation of each scanner motor 1514 in synchronization with the reference frequency signal FV supplied from each reference frequency oscillator 72, each scanner motor 1514 is accurately controlled by the variation of each reference frequency signal FV.
Cannot be controlled in the same manner. Therefore, the line widths Y1 to Y4 of the registration correction markers are not uniform, and there is an inconvenience in reading the correction and correcting the registration.

In order to solve the above-mentioned problems, the color registration deviation is automatically corrected by sharing the oscillation source of the reference frequency signal supplied to the PLLIC chip, and a color image without color deviation can be output. A common frequency signal generating means for supplying a common reference frequency signal to a plurality of PLL control means is provided.

FIG. 23 is a PLL control circuit diagram of a laser beam printer showing an embodiment of the common use of the oscillation source, and the same components as those in FIG. 22 are denoted by the same reference numerals.

In this figure, 2300 is a common frequency signal generating means,
It supplies a common reference frequency signal f ₀ to the signal input terminal X of each color of PLLIC chip 71.

As can be seen from this figure, each PLLIC chip 71 compares the frequency signal FG which is fed back to the reference frequency signal f ₀ from each of the Hall IC, for controlling the rotation of Sukiyanamota 1514.

For this reason, the rotational speeds of the PLLIC chips 71 are exactly the same, and the inconvenience such as the different image widths Y1 to Y4 of the registration correction markers as described above is eliminated.

(2-3) Surface potential control The formation of a resist correction marker is very important because the edge of the marker is captured and the amount of deviation between colors is measured. Therefore, it is necessary to solve this problem by keeping the density of the marker constant. As the means, it is conceivable to control the surface potential of the photoconductor.

In FIG. 10, reference numeral 211 denotes a photosensitive drum which rotates in the direction of the arrow. Reference numeral 212 denotes a primary charger, which uniformly charges the photosensitive drum 211 by corona discharge. 230 is a high voltage transformer, which supplies power to the temporary charger 212. Reference numeral 1004 denotes an auto power controller (APC) serving as a current control means and a current correction means according to the present invention, and a laser substrate 10 having a laser driver circuit 1005a, a D / A converter 1005b, and a semiconductor laser 1005c.
Drive current data for supplying the reference drive current to 05
For example, it is transmitted at 8 bits. Reference numeral 1006 denotes a power detector serving as monitoring means of the present invention, which detects the emission power of the semiconductor laser 1005c on the laser substrate 1005, amplifies the output with an amplifier 1006a, and converts the emission power data via an A / D converter 1006b. The data is sent to the CPU 1004a of the APC 1004. 1
A laser beam 007 is emitted from the laser substrate 1005 to the exposure point A of the photosensitive drum 211. A potential sensor 1008 measures the surface potential of the photosensitive drum 211 by the laser beam 1007 irradiated at the exposure point A. The surface potential is measured at a potential measurement point B. Reference numeral 1009 denotes a potential measuring device serving as a surface potential measuring means of the present invention, and the output of the potential sensor
The data is converted into a digital value by the A / D converter 1009a, and the surface potential data is fed back to the CPU 1004a of the APC 1004 from the micro computer 1009b. Reference numeral 206 denotes a developing sleeve, which is supplied with the developer by driving the supply rollers R ₁ and R ₂ . The transport belt 209 is transported in the direction of the arrow. Reference numeral 210 denotes a transfer charger that transfers the registration correction marker developed on the photosensitive drum 211 to the transport belt 209.

FIG. 24 is a block diagram of a circuit for realizing the surface potential control and the APC function.

The same elements as those in FIG. 10 are given the same numbers. The operation will be described in detail in an operation flowchart described later, and the second is described regarding the surface potential control and the APC function.
The circuit operation will be described with reference to FIGS. 4 and 25.

First, in FIG. 24, the potential sensor 1008 → A / D converter 1009a →
Microcomputer 1009b → APC CPU 1004a → D / A converter 1005b → Laser driver circuit 1005a → Semiconductor laser 1005
c ... A series of control systems of light receiving diode 1006c, amplifier 1006a, A / D converter 1006b, and APC CPU 1004a are shown. The purpose of the APC operation is to keep the photoconductor surface potential constant.

The purpose is achieved by storing the value measured by the surface potential sensor and keeping the amount of light required at this time constant. Further, in the case of this example, since four photoconductors are provided, it is desirable that these controls be handled in a unified manner. Figure 25 shows AP
Four potential measuring devices are connected around a center C1004, and four laser substrates 1005, laser light emitted by a semiconductor laser 1005c, four light receiving diodes 1006c for receiving the laser light, and a beam detector 1006 are shown. As a result, the CPU 1004a in the APC can grasp all situations related to latent image formation.

FIG. 26 is a flowchart for explaining an example of the surface potential measuring operation. In addition, (1) to (11) show each step.

First, the surface potential of the photosensitive drum 211 is
v Charge to _D , and when it reaches exposure point A, APC1
004 is the reference drive current data and D / A converter of laser board 1005
By sending a 1005 b, the reference drive current I ₀ to the semiconductor laser 1005c
To irradiate the photosensitive drum 211 with the laser beam 1007 (1). Next, it is determined whether or not the number of adjustments N has reached the predetermined number a (2). If YES, an error flag is set and the control is terminated (3). If NO, the photosensitive drum 211 moves to the potential measurement point B. It waits for the arrival at the surface potential measurement timing (4), and when it arrives, detects the surface potential of the potential sensor 1008 (5), and outputs the output of the potential sensor 1008 to the A / A of the potential measurement device 1009. D converter 100
9a converts the data into digital values, and the microcomputer 1009b converts the data into table data. Next, it is determined whether or not the measured potential matches the desired potential _VL (6). If YES, the applied laser drive current (reference drive current I ₀ + Δα) is stored in a memory (not shown) and control is terminated. (7).

On the other hand, if the determination in step (6) is NO, the number of measurements N is incremented by "1" (8), and then it is determined whether the measured potential is greater than the desired potential _VL (9). If YES, a laser drive current (reference drive current I ₀ + ΔI ₀ ) is applied so as to increase the laser light amount (10),
Returning to step (2), if NO, the laser drive current (reference drive current I ₀ −ΔI ₀ ) so as to increase the laser interference
Is applied (11), and the process returns to step (2). Note that ΔI ₀
Is the minimum unit of current that can be increased or decreased by one control, and D / A
This is a current unit corresponding to a change in the LSB (minimum bit) of the converter 1005b. Δα is ΔI ₀ which is N times the number of adjustments.

In this way, the laser amount P _{0 with} respect to the surface potential of the photosensitive drum to _VL is the laser drive current (reference drive current I ₀ −Δα).
Can be caused by:

Therefore, although the same as to keep the laser light intensity P ₀ constant to hold the surface potential of the photosensitive drum 211 constant, semiconductor lasers 1005c laser substrate 1005 is dependent on the environmental variations of the temperature of the ambient likely, the relationship between the laser light quantity P ₀ and the laser drive current (reference drive current I ₀ -Δα) is dependent on how the environmental change, to hold the laser light amount P ₀ constant, the laser drive current ( Reference drive current I ₀ -Δα)
, It is necessary to apply a current in consideration of the environmental fluctuation correction value Δβ to the laser driving current (reference driving current I ₀ −Δα). Therefore, the semiconductor laser 1005c
The amount of light is constantly monitored by the power detector 1006c, and the fluctuation in the amount of light is transmitted to the CPU 1004a of the APC 1004 via the A / D converter 1006b.

Next, the monitor control of the laser emission power will be described with reference to FIG.

FIG. 27 is a flowchart for explaining an example of monitor control of laser emission power. In addition, (1) to (8) show each step.

First, the surface potential of the photosensitive drum 211 executes the image forming operation in a state of outputting a laser light amount P ₀ in the laser driving current to be V _L (1), between the recording sheet and the recording sheet, for example is fed It waits until the laser power measurement timing set at a non-image area or at a predetermined time interval is reached (2), and when it reaches, the power detector 1006c measures the emission power of the semiconductor laser 1005c on the laser substrate 1005 (monitor). do it,
The output is amplified by the amplifier 1006a, and the light emission power data PD is transmitted to the CPU 1004a of the APC 1004 via the A / D converter 1006b (3). Then, the light emitting power data PD to determine if it matches the initial laser light amount P ₀ (4), to control application of a YES if the laser drive current (reference drive current I ₀ + Δα + Δβ) in the laser driver circuit 1005a. Then, the APC ready signal 1157 is set, and the process ends (5).

On the other hand, if NO in the judgment of step (4), to determine if emission power data PD is greater than the initial laser light amount P ₀ (6), a laser driver circuit for reducing the YES if laser light amount 1005a A laser drive current (reference drive current I ₀ + Δα−ΔI ₀ ) is applied to the step (7), and the process returns to step (2). If NO, the laser drive current (reference drive Current I
₀ + Δα + ΔI ₀ ) and returns to step (2) (8). ΔI ₀ is the minimum unit of current that can be increased or decreased by one control, and is a current unit corresponding to a change in the LSB (minimum bit) of the D / A converter 1005b. Δβ is ΔI ₀ which is N times the number of adjustments.

By the way, although the displacement detector 1402 is configured by a CCD sensor or the like, the stability of the light amount of the light source is extremely important. Because the amount of light is not constant, the registration correction marker
This is because when the light is irradiated to the 1501 and the reflected light is received by the CCD sensor, the edge of the registration correction marker 1501 is shifted.

In FIG. 14, the light emitting element 1603 is a light emitting diode (CED), and each of them is provided with a constant current circuit 1406 to stabilize the light quantity. In addition, when the transport belt 209 that forms the registration correction marker 1501 becomes dirty and the SN ratio cannot be obtained sufficiently, such as when the light amount is increased, the light emitting elements 1603C, 1603M, 1603Y, and 1603K need to simultaneously increase the light amount to maintain balance. The constant voltage circuit 1409 has an output voltage
A variable volume 1407 that can change V ₀ is provided.

Reference numeral 1408 denotes a power supply for driving these light emitting elements 1603.

As described above, since the light amounts of the plurality of light sources 1603 for the detectors 1402 are kept constant, the registration mark of each color can be detected with high accuracy, and the registration control can be performed accurately.

Incidentally, the reading accuracy of the correction registration mark 1501 is extremely important. This is because if the reading accuracy is lower than the resolution of the original color print, the color resist cannot be adjusted. Needless to say, the reading accuracy is greatly affected by the stability of the formation accuracy of the registration mark 1501, the resolution of the reading CCD sensor 1402, and the relative mounting accuracy of the four CCD sensors, and changes with time. This is a problem to be solved if these four CCD sensors are firmly fixed and integrated.

16 is a cross-sectional view of the sensor substrate 1506. Reference numeral 1606 denotes a housing, and 1605 denotes a lamp for irradiating the correction registration mark 1501. Reference numeral 1404 denotes a CCD sensor, reference numeral 1608 denotes a printed circuit board on which these are mounted, and reference numeral 1606 denotes a short focus lens array. As a result, the correction registration mark 1501 can be accurately read, and the accuracy of registration correction can be improved.

Next, the change with time of the CCD sensor 1402 and the irradiation lamp 1605 is very susceptible to temperature and humidity. To prevent this, it is best to read and calibrate the standard reflector. Reference numeral 1602 in FIG. 16 denotes a standard reflection plate, for example, which is white, and can read and calibrate reference light without being largely influenced by the spectral sensitivity of the CCD sensor.

(2-4) Correction Timing Next, the automatic color registration correction timing operation according to the present invention will be described with reference to FIG. 14 and FIG.

FIG. 28 is a flowchart for explaining the image forming timing correcting operation according to the present invention. In addition, (1)-(1
2) shows each step.

In FIG. 14, CPU1 1401 has counters 1403a to 1403d.
Is set to the initial value. This is the photosensitive drum 211
Image, ie, color registration correction marker
1501C~1501K is of order to be recorded after the initial value t ₁ ~t ₄ hours is started on the transport belt 1505. This corresponds to step (1) in the flowchart of FIG.

As described above, the state in which all of these color registration correction markers are formed is shown in FIG.

1505 is handled as a conveyor belt, and is an endless belt. However, when measuring the color register correction markers, they are formed on the transport belt 1505. Therefore, some reference time is required to measure the relative color shift, and it can be obtained as a difference from this reference time. This corresponds to the time when the original transfer paper should be the leading edge of the paper. It waits for the temporary paper end of 1505 shown in FIG. 16 to be detected by any one of the displacement detectors 1402C to 1402K (2), and when it is detected, each marker is operated by an internal timer circuit (not shown). Image of
Time Δx ₁ , Δx ₂ , Δx ₃ , until 1501C to 1501K are detected,
Measure Δx ₄ and store in internal memory (3) ～
(6), relative time difference (difference) from time Δx ₁ Δy ₂ (Δx ₁ −
Δx ₂ ), Δy ₃ (Δx ₁ −Δx ₃ ), and Δy ₄ (Δx ₁ −Δx ₄ ) are sequentially obtained (7) to (9). Then, Step (7) ~
The time differences Δy ₂ , Δy ₃ and Δy ₄ obtained in (9)
Correction time t ₂ + Δy ₂ , t ₃ + Δy considering t ₂ , t ₃ , and t ₄ respectively
_3, t ₄ + _{Δy 4} calculates the to excisional counter 1403a~1403d (10) ~ (12) .

Then, it is checked whether or not the counter set value is within the correctable range (13). That is, it is checked whether or not the correction allowable amount of the counters 1403a to 1403d is exceeded. If not, the automatic registration ready signal 1158 is set because correction is possible (14). If it is over, the correction is not possible and the automatic registration ready signal 11
Reset 58.

Therefore, if correction is not possible, the automatic registration ready signal 1158 remains reset, the weight display lamp 1105 (FIG. 7) remains lit, and copying cannot be started. The display is not limited to the weight display lamp, and may be displayed on another display.

In the case of this embodiment, the registration correction marker of the cyan image is detected first, and the difference is calculated based on this. However, when other colors are detected earlier, the color is used as the reference. Just do it.

In addition, although an electrophotograph has been described as an example, the present invention can of course be applied to any color recording apparatus of a type in which a plurality of colors are sequentially transferred regardless of recording formation. For example, various applications such as thermal transfer and a lithographic printer can be applied.

[Other embodiments]

The light emission amount is varied while maintaining the balance of the plural light emission amounts in the registration correction detecting means, for example, when the ratio (SN ratio) between the sensor output of the registration mark and the sensor output of the conveyor belt is reduced.

〔The invention's effect〕

As described above, according to the present invention, it is possible to suppress the formation of a color image having a color shift.

[Brief description of the drawings]

1 is a block diagram of a digital color copying machine to which the present invention is applied, FIG. 2 is a perspective view of the digital color copying machine of FIG. 1, FIG. 3 is a cross-sectional view of the digital color copying machine of FIG. 4 is a perspective view of a reader unit, FIG. 5 is a circuit diagram of a reader unit, FIG. 6 is a block diagram showing an example of a reader unit CPU circuit, FIG. 7 is a top view of an operation panel, and FIG. 9 is a diagram showing a memory map, FIG. 10 is a circuit diagram of an APC circuit, FIGS. 11, 12, and 13 are explanatory diagrams of registration control, and FIG. 14 is misregistration detection and correction. Circuit diagram, FIG. 15 is a perspective view showing occurrence of misalignment, FIG. 16 is a schematic diagram showing the principle of misalignment, FIG. 17 is a diagram showing an interface between the memory circuit and the printer unit, and FIG. 18 is a registration mark FIG. 19 shows the timing of generation of the HSYNC signal. FIG. 20, FIG. 20 is a diagram showing the relationship between the recording width and the beam detect signal BD, FIGS. 21 and 22 are drive circuit diagrams of the scanner motor, FIG. 23 is a PLL control circuit diagram, FIG. 24, FIG. Is an automatic laser power control circuit (AP
C), FIG. 26 and FIG. 27 are flowcharts of APC control, FIG. 28 is a flowchart of resist control, and FIG. 29 is a sectional view of a conventional one-drum color copying machine.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hiroaki Ishii 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Yutaka Udagawa 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon (56) References JP-A-62-242969 (JP, A) JP-A-56-161556 (JP, A) JP-A-57-23954 (JP, A) JP-A-59-93462 (JP, A A) (58) Field surveyed (Int. Cl. ⁶ , DB name) G03G 15/00

Claims (1)

(57) [Claims] 1. A plurality of image forming units each having a recording body and forming images of different colors on the recording body, and each color image formed by the plurality of image forming units on a single recording medium. A carrier for placing and transporting the recording medium for transfer, reading means for reading registration marks of each color formed by the plurality of image forming means and transferred onto the carrier, and a reading result of the reading means Detecting means for detecting the amount of displacement of each color image based on the amount of displacement, determining whether or not the amount of displacement detected by the detecting means is within a correctable range. A color image forming apparatus comprising: a control unit configured to correct a positional shift of each color image by using the control unit, and to prohibit image formation when correction is not possible.