JPS6257990B2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to an image forming apparatus.

Conventionally, when controlling the exposure amount in an image forming apparatus such as an electrophotographic copying machine, the basic idea is to control the amount of light emitted by the light source using a photodetector element to control the amount of light emitted by the photoreceptor so that the time integral value of the amount of light is constant. detect,
A method that turns off the light source when the time-integrated value reaches a predetermined value, or a method that keeps the brightness of the light emitting source constant against external fluctuation factors such as power supply voltage, and also keeps the exposure time constant. There was a method to keep the integral constant. Various automatic exposure devices have been invented based on the same idea in the field of cameras and the like. However, in electronic copying machines, the characteristics of the photoreceptor, corona charger, etc. used vary greatly depending on the usage environment (temperature, humidity fluctuations, fluctuations in power supply, changes over time, etc.) It has become difficult to maintain good and stable copies for a long time using a control method that maintains a constant integral value of the amount of light to the photoreceptor. That is, in an electrophotographic device, a primary charger uniformly charges a photoreceptor by corona discharge, and then the aforementioned charge is removed by exposure, and an electrostatic latent image is created by exposing the entire surface to light. . FIG. 1 is a graph showing how the amount of charge on a photoreceptor is removed depending on the amount of light exposure, where the horizontal axis represents the amount of light and the vertical axis represents the amount of charge or potential of the photoreceptor. When the amount of light is zero, a potential determined by the charge applied to the photoreceptor by the primary charger appears, and as the amount of exposure increases, the potential of the photoreceptor decreases. The photoreceptor has the same primary charge amount depending on usage environmental conditions (temperature, humidity, etc.), changes over time, etc., and even if the photoreceptor is exposed to the same amount of light, the charge level of the photoreceptor varies. In the same figure, if the center light intensity for characteristic 1 is E6, then the center light intensity is E5 for characteristic 2, E4 for characteristic 3, the dynamic range of the largest surface potential Vp is obtained, and the gradation is sufficient. You should get something. When the characteristic of the photoreceptor changes as shown in characteristic 3 when the central light intensity is fixed at E6, the dynamic range of the bright area is compressed and the potential contrast of the latent image is reduced, and the potential of the dark area is also decreased and it becomes a visible image. This causes the maximum image density to decrease. Conversely, when the central light intensity is E4 and the photoreceptor characteristics become 1, the dynamic range of the dark area is compressed, and the potential of the bright area is relatively high and when a visible image is created, the so-called "fogging" phenomenon occurs. arise.

That is, the present invention provides an image forming means including an exposure means for forming an image on a photoreceptor, a reference signal generating means for generating a reference signal, a counting means for counting the reference signal, and a method that sequentially processes images according to the count value of the counting means. a pattern signal generating means for generating a signal whose level changes sequentially in order to form a potential pattern corresponding to a density change; An image forming apparatus comprising: a control means for controlling exposure conditions of the exposure means; and means for detecting a pattern in which the potential on the photoreceptor changes sequentially to determine optimal operating conditions for the image forming means. This is what we provide.

Other objects of the present invention will become clear from the description of the embodiments given below in conjunction with the drawings.

FIG. 2 is a configuration diagram showing the main parts of the electronic copying machine. Reference numeral 100 denotes a document table, which consists of an effective image area 101 on which a document is placed and a non-image area 102 provided with a white pattern for checking. Reference numeral 103 denotes an exposure source, and a light source such as a fluorescent lamp or a halogen lamp is used. The light emitted from the light source 103 is reflected by the document table 100, becomes a signal light, passes through the reflective lens system 105 by the first reflective mirror 104, is reflected by the second reflective mirror 113, and is further reflected by the third reflective mirror 114, and is charged for AC charge removal. The image is formed on the photosensitive drum 112 via the device 116. A non-image area (hereinafter referred to as a check pattern) 102 provided on the document table 100 is imaged onto a check pattern recording section 117 on a photosensitive drum 112. 1
09 is a rotary encoder that is mechanically connected to the photosensitive drum 112 and the document table 100 and operates;
08, it is composed of a light receiving element 110 and a photoelectric conversion circuit 111, and generates various drive signals for the copying machine. 115 is a primary charger, 116 is an AC static eliminator, and 118 is a full-surface irradiation lamp. Reference numeral 106 indicates a probe for detecting the surface potential of the photosensitive drum 112 of the check pattern recording unit 117 for the full path light diameter, and 107 indicates an amplification circuit. Regarding the latent image forming process,
It is described in detail in No. 23910, etc. The check zone 102 is imaged on a check pattern recording section 117 by a photosensitive drum 112. Check pattern 1
Since 02 is a white portion, the amount of primary charge on the drum shape is removed together with the AC charge, and a latent image potential Vp is generated in the check pattern recording portion 117 by full exposure. Since the reflection density of the check zone 102 of the document table 100 is constant, the surface potential Vp is the same as that of the light source 10.
The potential changes depending on the brightness of 3. That is, the light emitted from the light source 103 is reflected by the check zone 102 of the document table 100, passes through the optical system, and the illuminance e at the position of the check pattern recording section 117 and the photosensitive drum 112 pass through the slit exposure width by the AC static eliminator 116. When the amount of light multiplied by the required time t is E=ext, the Vp-E characteristic is changed as shown in FIG. 1 described above. As is clear from FIG. 1, if the brightness of the exposure source 103 is constant for the time it takes to pass through the exposure width of the static elimination slit, then the brightness of the exposure source 103 is
The electrostatic latent image (surface potential) Vp formed on the surface of the photosensitive drum 112 by the white pattern 02 should reach its maximum brightness at the point when the slope dVp/dE of the Vp-E curve begins to decrease. . That is, in characteristic 2 of Fig. 1, A
2-Although dVp/dE is quite large for A11,
1 To the right of 1, that is, when the amount of light is increased, the increment of the surface potential Vp starts to decrease. Therefore, A11 should be the maximum brightness under the usage conditions of the photoreceptor, that is, the exposure source brightness. In FIG. 1, the point A11 is such a point, and it is good to give the exposure source luminance e ₁₁ =E ₁₁ /t. In reality, there are cases in which dVp/dE does not decrease rapidly, and in such cases, the maximum value of dVp/dE should be determined, and the point at which it decreases to some percentage of that value should be set as the exposure limit. FIG. 3 and subsequent figures are explanatory diagrams for concretely realizing the above basic idea. In FIG. 2, a pre-idle rotation for determining the optimum exposure amount is performed before starting the copying process. During forward rotation, the document table 100, photosensitive drum 112, exposure source 103, and various chargers are operated, and the light source 1
The surface potential Vp on the photosensitive drum 112 corresponding to the amount of light at that time is stored in the data storage section, and the surface potential Vp on the photosensitive drum 112 corresponding to the amount of light at that time is stored in the data storage unit, and the characteristic table shown in FIG. to be created. FIG. 3 is a circuit block diagram for sequentially increasing the amount of light from the exposure light source 103. The oSp signal is a signal sent from the control section shown in FIG. 5, and is generated by a copy start command, etc., and this starts the sequential exposure amount switching operation during forward rotation. When oSp=H level, pulse generator 302
is activated and emits a pulse. Pulse generator 30
2 can be constructed from a normal multivibrator circuit. 305 is a counting circuit for counting pulses from the pulse generator 302, and is composed of a commercially available IC (integrated circuit) such as a decade counter. 303 is a D/A converter (digital-to-analog conversion circuit) that converts the digital quantity from the counting circuit 305 into an analog quantity. 306
1 is a circuit that controls the cut-off angle of the power supply using a bidirectional thyristor or the like according to an input signal, and dims the light source 307. A photoelectric element 309 detects the brightness of the light source 307, and uses elements such as phototransistors and solar cells. 308 is the light receiving element 3
This is a circuit that amplifies the signal from 09, and the output is D/A.
It is included in a differential circuit with the output of converter 303. The light source 307 is dimmed according to the output of the D/A converter 303 by the above circuit. 304 is a delay circuit, which emits a pulse with a delay of time TD after the pulse from the pulse generator 302 is sent out. The output pulse of this delay circuit
DLp uses the surface potential value on the photosensitive drum as a signal to store data in the data storage section of the control section.

FIG. 4 is a diagram illustrating time-series changes in signal generation in each part of FIG. 3, and the signal oSp is shown at 401 in FIG. Pulse generator 3 depending on oSp=H level
02 outputs a pulse, and the situation is shown at 402. 40 shows the output of the D/A converter 303.
Shown in 3. The output pulse that has passed through the delay circuit 304 is output with a time delay of TD as shown in 404. An electronic copying machine usually causes the drum to idle, which is called forward rotation, after pressing the copy button. This period is a period in which all other copying devices except the original scanning drive, the paper feed pick-up roller, the developer drive, etc. are operated. This is the period necessary to properly sensitize the drum and clean the drum surface.

If the automatic exposure execution period of the present invention is executed during this preemption period, the time until the start of copying does not become long due to automatic exposure. Third
As is clear from FIGS. 4 and 4, during the pre-idling period, the exposure source is dimmed by the program according to FIG. 3, and gradually becomes brighter than dark. This is because the DLp pulse needs to have a time delay because, as is clear from the configuration diagram in FIG. 2, there is a positional shift between the photosensitive drum imaging section and the drum surface potential detection probe 106.

FIG. 5 is a block diagram of the control section. In the figure, CPU is a processing circuit, for example, composed of a 4040 (manufactured by Intel). Figure 6 shows the processing circuit.
The block diagram of CPu is shown.

MIF is a memory interface, for example 424
4 (manufactured by Intel). The RAM is a memory, for example, 4002 (manufactured by Intel), and this memory RAM stores surface potential data, data on differences therebetween, etc., as shown in FIG. CLOCK is a signal generator that applies a clock signal to the processing circuit CPu.

The above-mentioned elements are connected as shown in FIG.
The IU is an input device, which detects the surface potential of the photosensitive drum 112 with a probe P, as shown in a detailed diagram in FIG. It is input to multiplexer MPX1. Also signal DP,
DLP and CSP signals are applied to multiplexer MPX2. The outputs of multiplexers MPX1 and MPX2 are applied to inverter INV ₁ via wired OR, and the outputs are applied to the buffer shown in FIG.
Applied to Buff. DE ₁ in FIG. 9 is a decoder that selects multiplexers MPX ₁ and MPX ₂ and controls inverter INV ₁ .

In FIG. 5, OU is an output device, the detailed diagram of which is shown in FIG. 10. In the same figure, L ₁
~ _L4 is a latch circuit, which contains storage elements of 4 bits and 2 bits, respectively, and is connected as a set of 4 bits. The above latch circuits L ₁ to L ₄
is set by the output of the buffer Buff in FIG. 5 via the inverter _INV2 . Decoder _DE2 outputs a signal for selecting latch circuits _L1 to _L4 . The outputs of the latch circuits L ₁ to _{L 4} supply the OR circuit 310 with an OES signal representing data on the optimum exposure amount, also output a signal HVT for driving various chargers, and output a signal OSp to the pulse generator 302. , are connected to supply a copy signal CSSP as a start signal for the copying process.

In Figure 5, the memory ROM is in Figure 11 and 1.
Commands and data for executing control procedures as shown in FIG. 2 are stored. DE ₃ is a decoder that generates a signal to select a memory ROM.

The operation of the embodiment having the above configuration will be explained with reference to the drawings.

When the start button of the copying machine is pressed, the copy start signal generator 901 generates the signal CSP=H,
The copier starts copying. Processing circuit CPU
detects CSP=H through the input device IU, and sends control signals to various chargers by the output signal HVT of the latches L ₂ and L ₃ of the output device OU. Further, a drum drive motor, a full-surface irradiation lamp, etc. are also driven by means not shown. Thereafter, in order to determine the optimum exposure amount, the processing circuit CPU sets the start address in the program counter PC. This initiates control to determine the optimum exposure amount, and first clears the memory RAM. In step 003, the signal OSP is outputted through the latch circuit _L3 of the output device OU. This causes the pulse generator 302 to start operating. Therefore, the exposure lamp 103 is sequentially dimmed from dark to bright by the circuit shown in FIG. In the next step 004, the index register IRO inside the CPU is set to zero. The index register IRO is a counter that indicates a value equivalent to the amount of exposure, and indicates an address where a data value of the surface potential is stored. Step 005
checks the state of signal DLP through multiplexer MPX ₂ . Proceed to step 006 with DLP=L
Check and wait for DLP=H. That is, the third
By the circuit shown in the figure, light with an exposure amount equivalent to the first pulse is applied to the check pattern recording section 117 of the photosensitive drum 112, and a time delay is created until the light reaches the surface potential detection probe 106, and the first pulse is generated. This is the timing adjustment for reading the potential on the drum surface when the exposure amount corresponds to . DLP
=H A/D converter 90 that converts the surface potential detection probe 902 analog quantity into a digital quantity
3, the multiplexer MPX ₁ and the processing circuit CPU, and the data is stored at address 0 of the memory RAM. FIG. 7 is a diagram showing the contents of each data with respect to the addresses of the memory RAM. In the above case IRO
This shows how photoreceptor surface potential data D ₀ when receiving an exposure amount corresponding to the first pulse is stored at memory address 0 from =0. The above-mentioned surface potential data is obtained by the A/D converter 903, for example, 8
It is converted into bits, the upper 4 bits are input, and the lower 4 bits are input. By step 009, index register IRO is increased by +1,
IRO=1. At step 010, it is determined whether the contents of IRO have reached n, and if n=13, in this case IRO≠n, and the process returns to step 005. That is, a routine is entered in which the photosensitive drum surface potential data corresponding to the second exposure amount is stored in the memory RAM.
The control of steps 005 to 009 is repeated in the same manner as described above, and the surface potential data is input to the memory RAM by the device IU.
According to the contents of read IRO from multiplexer MPX ₁ , surface potential data Di is stored in memory address i. The surface potential data is sequentially stored in the memory RAM until IRO=n. Step 01
By completing step 0, a characteristic table of exposure amount versus surface potential corresponding to FIG. 1 has been stored in the memory RAM. The value of the memory address, ie, IRo, corresponds to the exposure amount. Next, in order to calculate the maximum value of dVp/dE, the difference in surface potential with respect to the change in exposure amount is calculated. That is, the maximum value of dVp/dE is determined from the maximum value of dmax=(Dn-Dn _-1 ). Step 01
2 to 019 are routines for finding the maximum value of dVp/dE. Step 001 sets index register IRo to 1. This allows memory
By step 012, which points to address 1 of RAM, the data at address 1 of memory RAM is stored in the accumulator in the processing circuit CPU.
Data is transferred to ACC. In step 013, the contents of Acc ( _i.e.
D ₁ data value) is stored. Step 014
In , subtract IRO by -1. This points to address 0 of the memory RAM. Step 01
In step 5, the data Do at address 0 is transferred to Acc as in step 012. In step 016, a difference calculation of (Acc-IR ₁ ) is performed. That is, (Do-
D ₁ ) difference calculation is performed. In step 017, the calculation result of (D ₀ -D ₁ ) is stored in the address indicated by the contents of IRO. In the above case, data (Do-D ₁ ) is stored at memory RAM address 0. That is, it becomes like B in FIG. Index register in step 018
Increase IRO by +2. This can be done, for example, by executing the +1 instruction twice. When n=13, the process returns to step 012 again from IRO=2, calculates (D ₁ -D ₂ ) in the same manner as described above, and stores the result at address 1. Similarly (D ₁₁
−D ₁₂ ), IRO=13 and complete the Vp difference calculation. The index register _IR2 is a register that stores the maximum value of the potential difference dn=D _o+1 -Dn. Steps 020 to 028 are a routine for determining the maximum value dmax of the differential potential. Set IR2=0 initially. From IRO=0, data do enters Acc as shown in B in Figure 7. In step 023, the difference between Acc and IR2 is calculated.
At 024 steps from do≧0, Acc≧0. Therefore, the process advances to step 026 and the contents of Acc are transferred to IR2. In other words, data do will be stored in IR2. At step 027, the address is incremented by 1 and the content _d1 of memory RAM address 1 is placed in Acc.
(d ₁ -d ₀ ) is calculated in step 023, and it is determined in step 024 whether the result is positive or negative. _d1 >
If d ₀ , the contents of IR2 will be d ₁ , and the address will be 1.
Take a step forward. Then, the process returns to step 022 again.
Thereafter, the operation of replacing the maximum value in register IR2 is executed in the same manner. As is clear from FIG. 1, as the exposure amount increases, the increment of Vp reaches its maximum value and then decreases. In that case, step 0
At step 23, Acc>0, and step 024 is entered. At this time, the contents of IR2 are not changed, so when IR0=9 is reached, dmax will be stored in IR2. Steps 029 to 038 represent control for determining the optimum exposure amount from the maximum value of dVp/dE. Step 029 clears the contents of IR0 to memory
Pointing to address 0 in the RAM, data do at address 0 is placed in Acc at step 030. In step 034, do and dmax are compared, and since do<dmax, the index register IR0 is incremented by +1 (step 031), and the process returns to step 030. The optimal exposure exists after the maximum value of dVp/dE (provided that E is switched from dark to bright) as shown in Figure 1.
Since this is the first light intensity when the potential increment in the area excluding the area to the left of A ₁ and A ₂ becomes equal to or less than the dmax×C value, the light source 103 exists in a place brighter than the light intensity that becomes dmax. The routine for checking this consists of steps 030-032. Calculate dmax×C in step 033 and repeat
Store the value in IR2. Naturally, IR2 no longer remembers the value of dmax. In step 034, the next address after the address that becomes dmax is specified, and in step 035, the contents are entered into Acc in step 03.
In step 6, compare the magnitude relationship between the potential difference and dmax×C.
IR0 is incremented until it becomes dmax×C or less. In the case of Figure 1, d11, which becomes IR0 = 11, is dmax x C
If it is smaller, IR0=11 and the step moves to 037. That is, IR0=11 indicates the address of the memory RAM, but is also a factor that determines the amount of exposure light.
Therefore, by 037, the contents of IR0 are transferred to the latch circuit L ₁ ~
It is outputted from _L2 and enters the OR gate 310 in FIG. 3 and is passed through the D/A converter 303 to set an input value so that the light source 103 has an optimum exposure amount. This allows one to determine the optimum exposure amount under the usage conditions of the photoreceptor.
An example was explained in detail. Step 038 is the 10th
The figure shows that the copy signal CSSP is output from the latch circuit _L3 , and the copying process is started after the exposure amount has been determined.

The above description shows a specific example of the optimal exposure amount control system, and the application of the above idea depending on the difference in the latent image creation process can be easily realized and falls within the scope of the present invention. Although the check pattern on the document table is a white pattern in the above embodiment, it is clear that it may be a pattern of alternating black and white.

In the embodiment, the light source brightness was gradually increased, but the exposure source is kept constant, the exposure slit width or the exposure aperture is sequentially varied, and the resulting exposure amount on the photosensitive drum surface is changed to determine the optimum exposure amount from the drum surface potential. Also within the scope of the present invention.

Although the drum surface potential is detected by 106 probes, it is clear that the surface potential meter does not need to be used as long as the detection device can determine the state of the electrostatic latent image.

As described above, according to the present invention, since it is possible to automatically form a pattern in which the density changes sequentially, the operator is not troubled when forming the pattern, and it is possible to accurately recognize fluctuations in image forming conditions. This makes it possible to always obtain appropriate images.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the relationship between the amount of charge and the amount of lightning, FIG. 2 is a perspective view of a copying machine for explaining the automatic exposure apparatus according to the present invention, and FIG. 3 is a control circuit diagram of the light source 307. Figure 4 is a time series diagram of signals, Figure 5 is an automatic exposure control circuit diagram according to the present invention, Figure 6 is a block diagram of the processing circuit CPU, Figure 7 is a diagram showing the data area of memory RAM, and Figure 8. is a detailed diagram of the processing circuit CPU and memory interface MIF, Figure 9 is a block diagram of the input device Iu, and Figure 10 is the output circuit.
Ou block diagram, Figures 11 and 12 are memory
FIG. 3 is a diagram showing a control procedure stored in a ROM. ROM...memory, CPU...processing circuit.

Claims (1)

[Scope of Claims] 1. An image forming means including an exposure means for forming an image on a photoreceptor; a reference signal generating means for generating a reference signal; a counting means for counting the reference signal; pattern signal generating means for generating a signal whose level changes sequentially in order to form a potential pattern corresponding to a sequential density change; forming a pattern on the photoreceptor in which the potential changes sequentially by the signal from the pattern signal generating means; An image forming apparatus comprising: a control means for controlling the exposure conditions of the exposure means, and a means for detecting a pattern in which the potential on the photoconductor sequentially changes to determine optimal operating conditions for the image forming means. Device.