JPH0452665A - Image forming device - Google Patents

Abstract

PURPOSE:To control image forming conditions finely and to increase image quality by controlling the light quantities of plural light beams to individually set values. CONSTITUTION:A CCD read part 130 processes and outputs image data as an analog picture element signal, which has its density converted and is converted into a digital signal; and the shading is corrected. The image data is converted by a gamma converting circuit 134 and a modulating circuit 135 imposes modulation on a semiconductor laser 136 with said image data. The output light intensity of the laser 136 is detected by a photodetector 137, whose detected value is inputted to a power correcting circuit 138. This circuit 138 corrects the value of a current, supplied from a constant current power circuit 139 to the laser 136 at specific timing other than the optical power modulation of the laser 136, with the output signal of a detector 137 and the light intensity of the laser 136 is controlled.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention forms an electrostatic latent image in a fixed pattern on an image bearing member such as a photoreceptor drum, and detects the potential of this electrostatic latent image. The present invention relates to an image forming apparatus configured to control various image forming conditions based on the detected potential. [Prior Art] In various image forming devices such as copying machines and printers, the surface of a photoreceptor that is transported in a certain direction is uniformly charged, and an electrostatic latent image is formed by exposing the photoreceptor to light. Then, toner is supplied from the developing section to this electrostatic latent image to visualize the latent image. The obtained toner image is transferred to a sheet of paper, and the transferred toner image is fixed to the sheet of paper so that a final image is obtained on the sheet of paper.

In the above steps, charging conditions, exposure conditions, development conditions, transfer conditions, and fixing conditions are controlled and adjusted by a central control section.

On the other hand, the photoreceptor has a property that characteristic values such as charging characteristics and sensitivity characteristics change over time.

Therefore, in order to maintain desired image quality, it is necessary to adjust (correct) image forming conditions such as charging conditions, exposure conditions, development conditions, and transfer conditions in accordance with changes in the characteristics of the photoreceptor.

Therefore, conventionally, an electrostatic latent image of a defined pattern is formed on a photoconductor, and the potential of this latent image is detected by a surface potential sensor.
By measuring this detection voltage, changes in the photoreceptor over time can be ascertained. Based on this, target setting values for various image forming conditions are adjusted, and various image forming conditions are controlled in response to changes in the photoreceptor over time.

The present invention has been made based on this background, and its purpose is to improve the image forming apparatus, which forms an electrostatic latent image on an image carrier using a plurality of light beams, such as a full-color copying machine, compared to conventional image forming apparatuses. It is an object of the present invention to provide an image forming apparatus in which narrower and more appropriate image forming conditions can be set.

[Issues to be solved]

In order to achieve the above object, the present invention has the following features.

In an image forming apparatus that obtains one image output by forming an electrostatic latent image on at least one image bearing member such as a photoreceptor drum using a plurality of light beams, each of the plurality of light beams is used to write a predetermined image. Modulate and scan in a predetermined pattern at the timing.

an electrostatic latent image forming means for forming a patterned electrostatic latent image on an image carrier; a surface potential sensor for measuring the surface potential of a portion where the electrostatic latent image is formed; and a surface potential sensor for measuring the amount of light of the plurality of light beams. A light amount control means for controlling each independently set value; and a light amount control means configured such that the set value of the light amount control means can be changed as appropriate based on externally provided data, and a detection signal of the surface potential sensor is configured to This is characterized in that the setting values of each light beam can be changed independently based on the above.

[Effect]

As described above, the present invention can independently control the light intensity of a plurality of light beams so that each has an individually set value, so image forming conditions can be controlled more finely and appropriately, resulting in improved image quality. It is possible to provide an image forming apparatus with high performance.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

Figure 1 is a schematic configuration diagram of a digital full-color copying machine, Figure 2
3 and 3 are block diagrams of the control section, and FIG. 4 is a diagram showing an example of setting the charging potential and the developing bias potential.

First, the schematic configuration of a digital full-color copying machine will be explained using FIG. 1.

This copying machine is roughly divided into a scanner section 1 for reading originals,
An image processing section 2 that electrically processes the image signal output as a digital signal from the scanner section 1, and a printer section 3 that forms an image on transfer paper based on the image recording information of each color from the image processing section 2. It is composed of.

The scanner section 1 includes a lamp 5.5 that optically scans a document placed on a contact glass 4.

The light reflected from the original illuminated by this lamp 5.5 is reflected by a mirror 6.7.8, passes through an imaging lens 9, and enters a dichroic prism 10. The dichroic prism 10 separates the light into three wavelengths, for example, red (R), green (G), and blue (B), and enters the light receiving element 11. As shown in the figure, the light receiving element 11 is composed of a red CCD 11R, a green CGDIIG, and a blue CGDIIB, and each of the wavelengths separated into three types as described above is incident on each CCD 1l. The red CCD 11R, green CCDI IG, and blue CCDIIB convert the received light into digital signals and output them to the image processing section 2.

In the image processing section 2, the input image signal is converted into recording color information signals of four colors, for example, black (BK), yellow (Y), magenta (M), and cyan (C). Although this embodiment shows the case where images are formed using the four colors, it is also possible to form a color image using three colors.

The output signal from the image processing section 2 is input to the printer section 3, and the recording devices 138K, 13C113M,
Sent to 13Y. These four sets of parallel recording devices 1
3 have almost the same configuration, so the recording device L3C
The configuration will be explained using as an example.

As shown in the figure, the recording bag [13C is the laser beam emitting device 1
2G, photosensitive drum 14C, and this photosensitive drum 1
Charger 15C, developing section 16C1 surface potential sensor SC and transfer charger 1 arranged around 4C
7C etc. are arranged sequentially. As shown in the figure, the surface potential sensor SC is arranged downstream of the developing section 16C in the rotational direction of the photosensitive drum 14G.

In this embodiment, a negative/positive development process method (reversal development process method) is adopted. First, the surface of the photoreceptor drum 14C is approximately -8
It is uniformly charged to 00V, and then the laser beam emitting device it
Exposure is performed by 2C, and an electrostatic latent image corresponding to the cyan light image is formed.

The surface potential of the electrostatic latent image portion formed by this exposure becomes approximately zero potential. This electrostatic latent cyan image is developed and visualized by the developing section 16G having a negative potential developing bias of approximately -500V.

On the other hand, the transfer paper fed from the paper feed section 19 by the drive of the paper feed roller 18 is sent onto the transfer belt 21 by the registration rollers 20 at the timing when it is aligned with the leading edge of the image, and is electrostatically attracted on the transfer belt 21. Ru. This transfer belt 21
The transfer paper conveyed by passes directly under the photosensitive drum 14C on which a cyan toner image is formed, and the toner image is transferred to the transfer paper by the action of the transfer charger 17G.

Thereafter, the toner image is transferred onto the transfer paper by the fixing roller 22 and discharged to the outside of the machine by the paper discharge roller 23.

Next, a block diagram of the entire control system of the printer section 3 is shown in FIG.

The main control section 40 for the printer section 3 includes a CPU, a ROM, a RAM, a ■/○ interface, etc., and controls the entire printer. On the input side of this main control unit 4-0, there is a paper discharge sensor 41 that detects the discharge of transfer paper to the outside of the machine.
, a paper end sensor 42 that detects the presence or absence of transfer paper in the paper feed section 19, a registration sensor 43 that controls paper feeding to the registration roller 20, a cassette size sensor 44 that detects the cassette size, BK, C, M, Y. 45C in a photosensor 458 that detects the density of each toner.

45M, 45Y, a thermistor 46 that detects the temperature of the fixing heater, and surface potential sensors SBK, SC, SM, and SY that detect the surface potential of the photosensitive drum 14, etc. are connected, respectively.

On the output side of the main control unit 40, a charger 15,
Transfer charger 17 and belt static elimination charger 47
(See Figure 1) is 48.49.50 for each high voltage power supply.
connected via.

Further, a heater 51 provided within the fixing roller 22
It is connected via a heater control section 52.

Further, a main motor 53, a drive motor 54 that drives the photosensitive drum 14, and the transfer belt 21 are connected via a DC motor driver 55.

Further, a video control section 54 is provided to take in image data from the image processing section 2.

This video control unit 56 includes semiconductor lasers 57BK, 57C, 57M, and 57Y for BK, C, M, and Y (12C, 12M in the laser beam emitting device 128).

12Y) is connected to the LD driver 58. Further, a mirror drive motor 59 for driving a polygon mirror is connected to this video control section 56 via a polygon motor driver 6o.

Further, in the main control section 40, the developing sleeves 268, which are provided in the developing section 168, 16C, 16M, and 16Y, are provided with 26C and 26M.

A developing bias high voltage power supply 61 that applies a developing bias voltage is connected to 26Y. Further, in the developing section 168, toner supply rollers 29BK and 29G are provided in the toner supply rollers 16G, 16M, and 16Y.

A replenishment bias high voltage power supply 62 that outputs a toner supply signal is connected to 29M and 29Y.

On the other hand, as shown in FIG. 2, the charging high voltage power source 48C (
The same applies to other colors BK, M, and Y) and the developing bias high voltage power supply 61 (same applies to other colors BK, M, and Y) has four signal lines 0 that can change the output voltage from the main control unit 40. , 1, 2, and 3 are connected to trigger signal lines. By combining rH] and rLJ by these four signal lines 0.1 and 2.3, the charging high-voltage power supply 48C and the developing bias high-voltage power supply 61C can be set to the output voltage as shown in FIG. ing.

In addition, the video control unit 56 reads the data of the potential detection pattern after exposure when the pattern trigger signal from the main control unit 40 is set to “L”, and based on this data, the data of the potential detection pattern is sent to the laser emitting device 128. 12M, 1
It has a function of lighting each 2Y semiconductor laser.

Next, the detection operation of the surface potential on the photosensitive drum 14 will be explained with reference to FIG.

In the figure, 71 is a semiconductor laser, 72 is a collimating lens,
73 is a polygon mirror, 74 is an fθ relleno, 75 is a dustproof glass plate, 76 is a synchronization detector, 77 is a photosensitive drum, 7
8 is a surface potential sensor, 79 is a light amount control means, 80 is a semiconductor laser drive means, 81 is a pattern generation means, 82 is a pattern output timing signal, and 83 is image data.

The output light intensity of the semiconductor laser 71 changes depending on the amount of injected current, and even if the amount of injected current is constant, the output light intensity changes greatly due to temperature changes and the like. Therefore, the amount of injected current is generally controlled so that the output light intensity is constant (APC). In this embodiment, the light amount setting means 79
The injection current value is determined, and the semiconductor laser driving means 80 controls the injection current to the semiconductor laser 71 according to image data 83 from the outside.

Since the light from the semiconductor laser 71 is diffused light, the collimating lens 72 converts it into parallel light. The polygon mirror 73 constantly rotates and linearly scans the aforementioned parallel beam. The fθ relleno 74 functions to keep the beam scanning speed on the photoreceptor drum 77 constant and to condense the beam. The dustproof glass plate 75 is for protecting the optical system from floating particles such as toner.

A pattern generating means 81 is driven by a pattern output timing signal 82 outputted from a main control section (not shown), thereby forming an electrostatic latent image of a fixed pattern on the photoreceptor drum 77.

The surface potential of this patterned electrostatic latent image portion is measured by the surface potential sensor 78, and the light amount control means determines the required light amount while referring to an internal data table according to the detection signal from the surface potential sensor 78. is set. Note that the patterned electrostatic latent image is formed on the photoreceptor drum 7.
7 is formed in an area outside the normal image forming area. Also,
When the patterned electrostatic latent image portion passes through the developing section, the developing process is stopped to prevent variations in surface potential due to toner adhesion and toner consumption.

In normal image formation, the amount of toner attached depends on the potential difference between the latent image potential and the developing bias potential.

When the charging potential fluctuates and approaches the developing bias value, the background portion of the photoreceptor drum is developed and so-called background smear occurs, so the difference between the charging potential vO and the latent image potential remains constant for each color. It is preferable to control it so that

FIG. 5 shows an example of the surface potential measurement results in the case of multi-value output (4 levels of V o = V:l), for example, V. The amount of light from the semiconductor laser 71 is controlled so that the difference between VO and YO (vo - 3) is constant. In addition, by appropriately setting the value of V o -V 3 according to the type of toner, environmental changes such as temperature and humidity, or changes over time of the photoreceptor drum, and controlling the output light amount of the semiconductor laser, the above-mentioned It is possible to cancel out differences in characteristics such as

Also, depending on the environment, if the potential difference between vO and developing bias voltage is not large enough, background stains may become severe.As a countermeasure, adjust vO and developing bias voltage respectively, and change ■1 to v3. The method is advantageous. A simple method for changing the surface potential is to adjust the amount of light, and advantageous methods for adjusting the amount of light include a method of changing the beam light intensity, a method of changing the lighting time of the semiconductor laser, and a combination of the two.

Next, a method of controlling the beam light intensity will be explained.

Fig. 6 is a control block diagram for controlling the beam light intensity, Fig. 7
The figure is a circuit diagram of the optical output setting means, and FIG. 8 is a schematic configuration diagram of the printer section.

First, the schematic configuration of the printer section will be explained using FIG. 8. In the figure, a semiconductor laser 71, a collimating lens 72, a polygon mirror 73, an F.theta. mirror 74, a synchronization detector 76, a photosensitive drum 77, a semiconductor laser driving means 80, etc. are the same as those shown in FIG. In the figure, 84 is a photodetector, 85 is a control circuit, and 86 is a signal processing circuit.

The signal processing circuit 86 applies the image data 83 to the semiconductor laser driving means 80, and its timing is controlled by a synchronization signal from the synchronization detector 76.

A laser beam emitted backward from the semiconductor laser 71 is incident on a photodetector 84, and its light intensity is detected.

According to this detection signal, the control circuit 85 controls the semiconductor laser driving means 80 so that the beam light intensity of the semiconductor laser 71 becomes a desired value.

Next, the detailed configuration of the control circuit 85 will be explained with reference to FIG.

When the timing signal Tx for starting the output control operation is input, the JK flip-flop 87 is cleared and its output signal goes to L level, thereby permitting the up/down counter 88 to perform the counting operation. Comparator 89
The output signal of the D flip-flop 90 is latched by the clock signal from the oscillator 91, and the output signal of the D flip-flop 90 is applied as a counting mode signal to the up/down counter 88, and at the same time the D flip-flop 90 controls the counting mode. It is latched at 92 by the clock signal from the oscillator 91.

The non-inverted output of the D flip-flop 90 and the inverted output of the D flip-flop 92 are input to a NOR circuit 93, and the output signal of the NOR circuit 93 sets the JK flip-flop 87.

The output proportional to the laser beam intensity detected by the photodetector 84 and amplified by the amplifier 94 is compared with the reference voltage Vref by the comparator 89, and the output of the comparator 8 is determined according to the comparison result.
9 outputs a high level or low level signal.

For example, when the output of the comparator 89 is at a high level (that is, the optical output of the semiconductor laser 71 is higher than the reference voltage Vref), the up/down counter 8
When the count operation of 8 is permitted, the up/down counter 88 operates as a down counter due to the high level output of the D flip-flop 90.

The output of the up/down counter 88 is converted into an analog signal by a digital-to-analog converter 95, and the driving current value of the semiconductor laser 71 output from the semiconductor laser driving means 80 changes according to the output. . Therefore, in this case, the driving current value of the semiconductor laser 71 decreases, and the output voltage of the amplifier 94 decreases. When the output of the comparator 89 is inverted from high level to low level, the output of the D flip-flop 90 becomes low level, the output of the NOR circuit 93 becomes high level, and the JK flip-flop 8
7 is set to prohibit the up/down counter 88 from counting.

On the other hand, when the output of the comparator 89 is at a low level (that is, the optical output of the semiconductor laser 71 is lower than the reference voltage Vref), the up/down counter 88 is activated by the timing signal T1.
Once the counting operation is allowed.

The up/down counter 88 is a D flip-flop 9
It operates as an up counter by outputting a low level of 0.

The output of the up/down counter 88 is converted into an analog signal by a digital-to-analog converter 95, and the drive current from the semiconductor laser drive means 80 increases in accordance with the output, and the output voltage of the amplifier 94 increases. Then, when the output of the comparator 89 is inverted from low level to high level,
The output of the D flip-flop 90 becomes high level. This causes the up/down counter 88 to operate as a down counter. At this time, the output of the NOR circuit 93 remains at a low level, the JK flip-flop 87 is not reset, and the up/down counter 88 remains enabled to perform counting operations. That is, when the optical output of the semiconductor laser 71 increases and exceeds the reference voltage Vref, the up/down counter 88 does not prohibit the counting operation, but when the optical output of the semiconductor laser 71 decreases and exceeds the reference voltage Vref.
Colorite operation is prohibited only when f is exceeded. Therefore, the driving current of the semiconductor laser 71 is always constant.

On the contrary, when the optical output of the semiconductor laser 71 decreases and exceeds the reference voltage Vref, the up/down counter 88 does not prohibit the counting operation, but the optical output of the semiconductor laser 71 increases and the reference voltage Vref is exceeded. Even if it is set so that the counting operation is prohibited when the value exceeds ref, the drive current of the semiconductor laser 71 is always maintained constant.

That is, the portion surrounded by a frame 96 in FIG. 6 corresponds to an edge detection circuit that detects a change in the output from the comparator 89 and permits or prohibits the counting operation of the up/down counter 88. As described above, the optical output from the semiconductor laser 71 is controlled so that the output voltage of the amplifier 94 is a constant value with reference to the reference voltage Vref (the optical output is always maintained at a constant value).

In this way, the optical output from the semiconductor laser 71 becomes an optical output when the optical output is detected by the photodetector 84 and the output amplified by the amplifier 84 matches the reference voltage Vref. Therefore, in this embodiment, when the reference voltage Vref becomes large, the output of the amplifier 94 becomes large together with the reference voltage Vref, and the optical output of the semiconductor laser 71 also becomes large. Conversely, when the reference voltage Vref becomes small, the optical output of the semiconductor laser 71 also becomes small so that the output to the amplifier 94 becomes small together with the reference voltage Vref.

The scanning beam output data that is input from the outside, for example from the printer main body control unit or image processor unit, may be analog data, but digital data is more resistant to noise than analog data, and data processing and retention are difficult. It is better to provide digital data because it is easier. If it is digital data, a method such as inputting multiple bits in parallel or serially may be used.

The scanning beam power data given in this way is held in the optical output setting means 97 (note that it is not necessary to hold it when changing the optical output constantly), and the reference voltage according to the scanning beam output data is held. Vref is set and input to comparator 89.

As shown in FIG. 7, this optical output setting means 97 is configured such that n-bit scanning beam output data PDATA inputted from the outside in synchronization with the strobe signal 5TRB is transferred to a latch circuit 98.
The signal is latched at and input to the digital-to-analog converter 99. This digital-to-analog converter 99 is, for example, HA17.
In the case of a current output type like 008, n=8, and the output terminal is connected according to the output of the latch circuit 98. A current i is output. Here, the comparator 89 is, for example, LM31.
In the case of a general-purpose voltage comparator such as 1, the output current i of the digital-to-analog converter 99 is equal to the amplifier lOO
According to the resistance value r, a reference voltage Vref of Vref = ir is generated.

Note that the output current i of the digital-to-analog converter 99 when the scanning beam output data PDATA reaches its maximum value can be set with a resistance value, so by appropriately setting this value, the desired variable range of the reference voltage Vref can be adjusted. You can also set it to a range.

As described above, by being able to set the light intensity of the scanning beam in accordance with external data, it is possible to change one imaging condition and to correct (adjust) changes in various characteristics over time.

Next, a method for controlling the lighting time of the scanning beam will be explained.

As methods for modulating a scanning beam into multiple values, there are a power modulation method that changes the laser power and a pulse width modulation method that changes the pulse width. By the way, in the former method, since a margin is required for the temperature characteristics of the power supply and optical output of the semiconductor laser, providing many levels is essentially a perversion.

On the other hand, the latter method does not have the above-mentioned problems,
Many levels can be achieved depending on the modulation circuit. This embodiment employs a pulse width modulation method and is an example in which this is digitally processed.

FIG. 9 is a block diagram of the pulse width modulating means, and FIG. 10 is a timing chart of signals of various parts in the pulse width varying means.

In this example, the data is 2 bits DO and DI, and the selector selects 4 levels of values including 0 (OFF).
11 so that it can be selected. The D latch 101 is
This is for synchronizing data Do and DI with CLK.

The block shown in the figure consisting of the delay element 102, phase selection means 103, and logic circuit 108 is a block consisting of the delay element 104, phase selection circuit 105, and logic circuit 109, as well as the block consisting of the delay element 106, phase circuit 107, and logic circuit. Since it is functionally equivalent to the block constituted by 110, one block will be explained.

The data clock signal CLK is input to the delay element 102, and a plurality of phase-shifted clock signals a o ""
generate a m. These clock signals a o - a m
are respectively input to the phase selection means 103, and one of the clock signals is selected and output as C1. A pulse signal P1 shorter than the clock duty is obtained by ANDing the data clock signal CLK and the tarlock signal CI (logic circuit 108). Note that the logic circuit 11
0 is an OR circuit, in which case a pulse signal P3 longer than the clock duty is obtained.

The timing chart in FIG. 10 shows the timing when the phase selection means 103 selects the clock signal al as CI from among a plurality of clock signals a0 to am having different phases generated by the delay element 108 based on CLK. Showing a chart. Therefore, in this example, the logic (
AND) The outputs of circuits 1 and 08 are CLK and clock a1
The AND output P1 is obtained. The phase selection means 103 selects the signal 8.
The pulse width of Pl can be adjusted depending on which signal is selected from 1 to am. This means that other pulse signals Pz, P
The same applies to s.

The pulse signal P o ” P 3 created in this way
One of them is data DO with select 111.

Pn is selected by DI and output, and the semiconductor laser is directly modulated by this signal Pn.

In this way, the multilevel level can be set completely digitally, the stability and reproducibility of the level can be improved, and the variation during mass production can be reduced. Although the phase selection means is combined with the phase selection means, it is also possible to combine a plurality of delay elements with different delay amounts and the switch means instead of this combination.

Next, another embodiment of the pulse width modulation method will be described.

FIG. 11 shows that 2-bit parallel signal lines are assigned to gray scale signals,
FIG. 2 is a block diagram of a configuration for obtaining output of four gradations using two bits. D1 to D4 in the diagram are dial lines, Gl, G2
is an AND gate, G3. G4 is an OR gate, S is a selector, 80 is a semiconductor laser driving means, and 71 is a semiconductor laser.

This method uses the pixel clock CLK and the pixel clock C
A configuration is prepared in which the logical product or logical sum of LK delayed at any time by the delay line D is prepared as many as the number of gradations (four types in this embodiment). Then, the selector S obtains an output with a pulse width corresponding to the gradation signal, and supplies this to the semiconductor laser driving means 80 to drive the semiconductor laser 71. FIGS. 12 and 13 show the delay line and AND FIG. 3 is an explanatory diagram of a method for obtaining an arbitrary pulse width output from a pixel clock CLK using a gate and an OR gate. 1st
Figure 2 (a) is a configuration diagram of a combination of delay line D and AND gate G, Figure 1 (b) is its operating waveform diagram, and Figure 13 (a) is a diagram of a combination of delay line D and OR gate G. The configuration diagram and FIG. 3(b) are its operating waveform diagrams.

In Figure 12, the pixel clock CLK■ and the delay signal ■ passed through the delay line D (T1 to delay time) are ANDed.
By inputting it to the gate G, a signal (2) having a pulse width of (T-TΔl) can be obtained. Therefore ΔT1
By arbitrarily selecting , any pulse width (T-Δ
A signal ① having T1) can be generated.

Next, a description will be given of means for detecting the surface potential of the electrostatic latent image formed on the photoreceptor and changing the set value of the pulse width.

As shown in FIG. 14, an area of the photoreceptor drum 77 that is not an effective image forming area (that is, an area where no image is transferred to the transfer paper, for example, an area adjacent to an effective image forming area in the main scanning direction,
Alternatively, an electrostatic latent image having a certain pattern can be created by lighting a laser beam at a certain duty in the area between the image forming area to be transferred to the transfer paper and the image forming area to be transferred to the next transfer paper. 120 is formed. Then, the surface potential of the portion where the electrostatic latent image 120 is formed is measured by the surface potential sensor 121.

The detection output of the surface potential sensor 121 is amplified by an amplifier 122 and inputted to a pulse width setting means 123. This pulse width setting means 123 changes the set value of the pulse width according to the signal from the surface potential sensor 121, inputs the signal having the changed pulse width to the sector 124, and inputs the signal having the changed pulse width to the sector 124. A multilevel pulse signal is applied to the single conductor laser driving means 125, and based on it, the semiconductor laser 12
6 is driven. FIG. 15 is a block diagram showing an example of the configuration of the pulse width setting means 123 shown in FIG. 14. G1~Dn are day line.

61 to Gn are AND or OR gates, 124a;

124b is a selector, 125 is a semiconductor laser driving means,
126 is a semiconductor laser.

In the figure, the operation of this configuration is the same as that explained in FIG. 11 above, except for the selector 124a.

Note that the selector 124b in FIG. 15 has the same function as the selector S in FIG. 11.

The output signal of the surface potential sensor 121 shown in FIG. 14 is input to the selector 124a in addition to signals having arbitrary pulse widths created by the delay lines D1 to Dn and the gates 61 to Gn. In this selector 124a, 1
A signal having a pulse width corresponding to the output signal of the surface pattern position sensor 121 is selected, and the signal having the selected pulse width is input to the selector 124b. As described above, this selector 124b supplies a signal with a pulse width corresponding to the gradation signal to the semiconductor driving means 125 to drive the semiconductor laser 126.

Next, an embodiment of the combined control of the control of the beam light intensity and the control of the lighting time of the laser beam will be described.

FIG. 16 is a block diagram of this control system.

The CCD reading unit 130 shown in the figure processes image data read by a line sensor (not shown) and outputs it as an analog pixel signal, and this signal is an analog logarithmic (LO) signal.
G) Concentration conversion is performed by the conversion circuit 131. The image data from this analog/logarithmic conversion circuit 131 is converted into a 6- to 8-bit digital signal by an analog-to-digital converter 132, and shape ink correction is performed by a shading correction circuit 133. The image data from this shading correction circuit 133 is γ-converted by a γ-conversion circuit 134, and the modulation circuit 135 modulates a semiconductor laser 136 using the image data from the γ-conversion circuit 135. The output light intensity of the semiconductor laser 136 is detected by a photodetector 137, and the detected value is input to a power correction circuit 138.

This power correction circuit 138 corrects the value of the current supplied from the constant current power supply circuit 139 to the semiconductor laser 136 at a predetermined timing other than when modulating the optical power of the semiconductor laser 136, using the output signal of the photodetector 137. , the light intensity of the semiconductor laser 136 is controlled to be the same for the same image data output from the γ conversion circuit 134.

FIG. 17 is a diagram showing details of the modulation circuit 135 and constant current power supply circuit 139.

Image data Vid output from the γ conversion circuit 134
eo is multivalued data, and in this embodiment is 3 bits. This image data Video is input to a pulse width modulation circuit 140 and an amplitude determination table 141, respectively, as shown in FIG.

This pulse width modulation circuit 140, as shown in FIG.
Delay elements 142 to 145, AND circuit or OR
It is composed of a logic circuit 146 and a selector circuit 147.

The pixel clock signal VCLK input to the pulse width modulation circuit 140 is input directly to the logic circuit 146, and is also input to the logic circuit 146 after being delayed by delay elements 142 to 145. By performing an AND or OR operation in this logic circuit 146, pulse signals with eight different pulse widths can be obtained. Of these eight types of pulse signals, one of them is sent to the selector 147.
is selected by the image data Video from the γ conversion circuit 134 and output as a pulse width modulation signal Vin. This pulse width modulation signal Vin is a signal having eight different pulse widths (including a pulse width of 0) corresponding to the 3-bit image data Video.

On the other hand, the amplitude determination table 141 is composed of a read-only memory (ROM) as shown in FIG. Table data as shown in FIG. 19 is written in this ROM, and image data (Video) is given as an address input.

takes eight values from O to 7, and outputs amplitude data PDATA corresponding to each address input. In this embodiment, the amplitude data PDATA is 2 bits.

Therefore, it takes a value of 0 to 3. In this way, image data Vi
Corresponding to the value of eo, a pulse width modulation signal Vin and amplitude data PDATA for determining its amplitude are simultaneously output. As shown in FIG. 17, the pulse width modulation signal Vi
n is given to the switch circuit 148, and the data PDATA
is applied to a voltage generating circuit 151 via inverters 149 and 150. The switch circuit 148 is a circuit that switches the current of the semiconductor laser, and includes field effect transistors 152, 153 and resistors 154 to 15.
It consists of 6. The constant current circuit 157 is a circuit for setting the current when the semiconductor laser is on, and is composed of a transistor 158 and a resistor 159. The voltage generating circuit 151 is a circuit that determines the setting current of the constant current circuit 157, and is a circuit that determines the set current of the constant current circuit 157, and is a circuit that determines the setting current of the constant current circuit 157, and is a circuit that determines the setting current of the constant current circuit 157.
and resistors 162 to 165.

The output signal Vs of this circuit is not only the image signal PDATA but also the power correction circuit 138 or the amplitude data PD in the embodiment.
ATA is 2 bits and therefore takes values from 0 to 3. In this manner, the pulse width modulation signal Vin and the amplitude data PDATA for determining the amplitude thereof are simultaneously output in accordance with the value of the image data Video.

As shown in FIG. 17, pulse width modulation signal Vin is applied to switch circuit 148, and data PDATA is applied to voltage generation circuit 151 via inverters 149 and 150. The switch circuit 148 is a circuit that switches the current of the semiconductor laser, and is a circuit that switches the current of the semiconductor laser.
52, 153 and resistors 154 to 156. The constant current circuit 157 is a circuit for setting the current when the semiconductor laser is on, and the transistor 158
and a resistor 159.

The voltage generating circuit 151 is a circuit that determines the setting current of the constant current circuit 157, and is a circuit that determines the setting current of the constant current circuit 157, and includes a field effect transistor 160.16.
1 and resistors 162 to 165. The output signal Vs of this circuit is controlled not only by the image signal PDATA but also by the correction voltage Cv inputted from the power correction circuit 138 via the buffer 166 and the capacitor 167.

The voltage generating circuit 151 is basically a resistive voltage dividing circuit,
The partial pressure ratio is the image signal PDATA (PO.

This image signal PO, P1 controlled by PI) is 0
, 0, the outputs of inverters 149 and 150 both become high level, and field effect transistors 160 and 16
1 are both turned on, and the input voltage Cvo from the buffer 166 is divided at a voltage division ratio such that the combined resistance value of the resistor 162 and the resistors 163 to 165 becomes the output voltage Vs.

Further, when the image signals PO and PI are 1 and 1, the outputs of the inverters 149 and 150 are both low level, the field effect transistors 160 and 161 are both turned off, and the input voltage Cvo from the buffer 166 is changed to the resistor 162. The voltage is divided by the voltage division ratio with the resistor 165, and the output voltage Vs is obtained.

Furthermore, when the image signals PO and PI are 1 and 0, the input voltage CVo is divided by the voltage division ratio of the resistor 162 and the resistor 164.degree. 165, and becomes the output voltage Vs.

Furthermore, when the image signals PO and PI are 0.1,
Input voltage CVo is between resistor 162 and resistor], 63.16
The voltage is divided at a voltage division ratio of 4 to obtain the output voltage Vs.

If the value of the resistor 163 is set larger than the value of the resistor 164, the output voltage Vs changes according to each voltage division ratio, and the output voltage Vs changes to four values from 1, 0 to 1.1 of the image signals PO, PI. Correspondingly, four values of the output voltage Vs are obtained and can be applied to the constant current circuit 157. In this constant current circuit 157, the collector current of the transistor 158 has a current value approximately proportional to the output voltage Vs of the voltage generation circuit 151, and becomes a current load on the switch circuit 148.

On the other hand, the pulse width modulation signal Vin from the pulse width modulation circuit 140 is applied to the switch circuit 148.

This switch circuit 148 is an actuation type switch circuit,
One of the field effect transistors 152 and 153 operates to turn on in response to the input voltage Vin of "0" and rlJ. For example, when the input voltage Vin is "1", the field effect transistor 152 on the semiconductor laser side turns on and drives the anticonductor laser, and its on-current value is equal to the current set by the constant current circuit 148 and the voltage generation circuit 151. value. In other words, the current value of the constant current circuit 157 determined by the correction voltage Cv corresponding to the detected optical output value of the semiconductor laser and the image data PO, PL is equal to the input voltage Vin.
0" and "1", and the driving current of the semiconductor laser is multi-valued.

〔Effect of the invention〕

The present invention has the above-described configuration, and since the light intensity of a plurality of light beams can be controlled independently, it is possible to adjust (correct) more detailed and appropriate image forming conditions in, for example, a full-color copying machine. , image quality can be improved.

[Brief explanation of the drawing]

All the drawings are for explaining the present invention in detail, and FIG. 1 is a schematic configuration diagram of a digital full-color copying machine, FIGS. 2 and 3 are block diagrams of a control section of the copying machine, and FIG. The figure is a diagram for explaining the surface potential detection operation on the photoreceptor drum. Figure 5 is a diagram showing an example of surface potential measurement results in the case of multi-value output. Figure 6 is a diagram for controlling the beam light intensity. FIG. 7 is a circuit diagram of the optical output setting means; FIG. 8 is a schematic configuration diagram of the printer unit. FIG. 9 is a block diagram of the pulse width modulation means, FIG. 10 is a timing chart of each part of the signal in the pulse width modulation means, FIG. 11 is a block diagram of a configuration for obtaining output of four gradations, and FIG. 12 (a), (b) and FIG. 13(a). (b) is an explanatory diagram for explaining a method of obtaining an arbitrary pulse width output from a pixel clock using a delay line, an AND gate, and an OR gate, and FIG. 14 is an illustration of an electrostatic latent image formed on a photoreceptor. 15 is a block diagram showing an example of the configuration of the pulse width setting means shown in FIG. 14; FIG. A block diagram of another control system for controlling the amount of light; FIG. 17 is a detailed diagram of a modulation circuit and a constant current power supply circuit; FIG. 18 is a block diagram of a pulse width modulation circuit and an amplitude determination table. FIG. 19 is an explanatory diagram showing the contents of the amplitude determination table. body laser driving means, 81...pattern generation section, 8
2...Pattern output timing signal, 83...
····image data. 3...Printer section, 12...Laser beam emitting device, 13...Recording device, 14.77...
...Photosensitive drum. 40... Main control section, 54... Video control section. 57.71... Semiconductor laser, 78. S...
...Surface potential sensor, 79...Light amount control unit,
80... Semiconductor Fig. 7 Fig. Fig. Fig. Fig. Fig. t (Ct = σl) Fig. Fig. 1

Claims (5)

[Claims] (1) In an image forming apparatus that forms an electrostatic latent image on at least one image carrier using a plurality of light beams to obtain an image output, the plurality of light beams are sent at predetermined timings at respective predetermined writing timings. an electrostatic latent image means for modulating and scanning in a pattern to form a patterned electrostatic latent image on an image carrier; and a surface potential sensor for measuring the surface potential of a portion where the electrostatic latent image is formed. , a light amount control means for controlling the light amount of the plurality of light beams so that they each have independently set set values; and a set value of the light amount control means that can be changed as appropriate based on externally provided data. An image forming apparatus comprising: a set value of each light beam can be changed independently based on a detection signal of the surface potential sensor. (2) The image forming apparatus according to claim (1), wherein the light amount control means is configured to be able to control the intensity of the light beam. (3) The image forming apparatus according to claim (1), wherein the light amount control means is configured to control the lighting time of the light beam. (4) Claim (1), characterized in that the set value of the light amount is determined such that the difference between the charging potential of the image carrier and the surface potential of the patterned electrostatic latent image portion is constant. image forming apparatus. (5) The image forming apparatus according to claim (1), wherein the patterned electrostatic latent image is formed in an area other than a normal image forming area of the image carrier.