JPS6025787B2 - image forming device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an image forming apparatus that detects image forming power and controls image forming based on its output.

Conventionally, there has been a technology for detecting image forming power and controlling image forming using its output, for example, in USP. No. 2956487.

When such control is performed, a situation may arise where an appropriate image cannot be obtained for some reason. If image formation is continued while such a situation occurs, not only will the recording material and the like be wasted, but in some cases, there is a risk that the apparatus will be damaged. The present invention has been made solely in view of the above points, and includes means for photoelectrically detecting the density corresponding to a grayscale image, means for forming a static latent image based on the grayscale image, means for developing a static latent image, A means for transferring a developed image onto a sheet, a procedure for determining at least one of a latent image potential when forming the electrostatic tower image or a developing bias potential when developing is programmed in advance in the memory, and the detection means detects the image. and a control means for executing a program based on the output, and the control means is characterized in that a limit value is set for the concentration detected by the detection means, and the limit value is adjustable. This makes it possible to prevent recording at an inappropriate density and to select a controllable detection density range. Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 shows a schematic diagram of an electrostatic printing machine using a master.

A master 110 having an image developed in advance by a master creating machine (not shown) is sent to the drum 109 by a pickup roller 111 and a feed roller 112. The drum grips the master with grippers 124 and secures it on the drum. A charger 107 uniformly corona charges the master fixed on the drum. A static latent image appears on the master depending on the image density on the master. If the high voltage transformer (HVTI) 108 has a positive output, a latent image with a positive charge is formed on the master. If negative toner is contained in the developing device 116, the positive charge on the master causes the toner to adhere to the master, forming an image using the toner. On the other hand, the printing paper 101' is fed by a pickup roller 102 and is fed. -Fu 103 sends the image to the transfer section. The printing paper is H from the back side.
Since the drum is uniformly positively charged by VTI', the negative toner is transferred to the printing paper, and at the same time, the drum is again positively charged. The transferred printing paper is transferred to the fixing device 104
and enters the scale paper tray 106. Figure 2 shows the characteristics of the master's reflection density versus surface potential when the voltage applied by the charger is 1V, and Figure 3 shows the relationship between the charging applied voltage and the surface potential in the master's rest and bright areas. .

As a result, when the applied voltage increases, the contrast potential (
It can be seen that the surface potential in the dark area (surface potential in the bright area) increases and the surface potential in the bright area also increases. Therefore, when developing, so-called fog occurs. The disadvantage is that the printing paper gets stained all over. If a bias voltage along the dotted line curve in the figure is applied to the developer, toner will adhere to the master side at the surface potential in the bright area, but toner will remain attached to the developer in the dark area. It does not stick to the master side. This shows that the above drawbacks can be compensated for by applying an appropriate bias to the developing device. FIG. 4 shows the reflection density of the printed paper after printing versus the contrast potential on the master. As described above, in an electrostatic printing machine using a master, depending on the quality of the master, fog may occur when the printing is finished after printing, or sufficient toner may not be applied to the surface.

The present invention automatically corrects these.

First, a reference tension area (hereinafter referred to as check zone) is provided on the master as shown in FIG. That is, a bright area (black area 2) and a dark area (white area 5) are created on the check zone using a pattern provided on the master creating machine. The master image portion created by this check zone is the result of including all variable factors such as the exposure amount of the master creating machine, the temperature of the thermal developing machine, and the material properties of the master. By detecting the reflection density of the bright area 2, the developer bias voltage is determined, and by detecting the reflection density of the dark area S, the voltage applied to the charger is determined.

Also, depending on the quality of the master, if the reflection density of a floor is below a predetermined value or the reflection density of a bright place is above a predetermined value, the contrast in the dark area may be too low and it may be sufficient to run the master on a printing machine. A good image cannot be obtained. In such cases, an interlock is placed to prevent the printing process from entering. The automatic setting of the charger applied voltage and the developing bias voltage will be described in detail below with reference to the drawings.

In FIG. 1, numeral 119 is an automatic voltage setting control section including a microprocessor, the internal details of which are shown in FIG.

120 is a printing press control section (hereinafter referred to as a panel section), and a printing press start signal STA and a printing stop signal STA are sent from the panel section 120 to the control section 119.

On the other hand, a print start command signal CPY, master contrast density abnormality A (floor is too bright - MMI), and master contrast density abnormality B (bright place is too dark - MM2) are sent from the control unit 1 1 9 to the panel unit 1 20. send a signal. In response to these abnormal signals, a warning lamp is lit on the panel to notify the operator of the abnormality, and at the same time an interlock is established to prevent the printing process from proceeding. Reference numerals 121 and 122 are setters SET1 and SET2 for setting the abnormal limit of the master concentration described above.

SETI is a digital switch for setting an abnormal concentration limit value in a dark place, and SET2 is a digital switch for setting an abnormal concentration limit value in a bright place. 1
23 is the interface where the operator removed the abnormal master when the master concentration was abnormal.

This is the glue set switch REST to release the lock.
113 is a photoelectric converter for measuring the reflection density at the master check part; 1 14 (PH-A), 1 1
5 (PH-B) detects the positions of the dark and bright areas of the master check zone (FIG. 5).

The resulting signal is a reference signal for creating a sample signal for sampling the reflection density value of each bright and dark portion of the master. An example of control outside the microcontroller will be explained below with reference to the flowchart of FIG. When the printing machine and the automatic voltage setting control unit 119 are powered on, first, master density limit values SET1 and SET2 are stored in the memory 212. SET until STR signal is sent from panel 120
1. The memory is sequentially revised to the latest set value by SET2. When the printing press is started, an STR signal is sent and the master 110 is fed by the pickup roller 111. When the master passes the feed roller 112, the reflection density detector 1 is detected by the master check sensor 114, 115 arranged between the roller 12 and the drum 109.
Control unit 1 19 indicates that the check position is below the 13 position.
Let me know. When notches 3 and 4 are provided in the master density check zone, PH-A and PH-B are output signals as shown in FIG. When PH-A is at “H” level and PH-B is at “L” level, the master detects the bright part of the concentration check zone and the PH level.
When -A is "L" and PH-B is "H", it indicates that the fat part of the master is under the reflection density detector 113. Those signals are read to CPU 208 via input port 2. Therefore, when PH-A is "H" and PH-B is "L", the CPU 208 holds the A/D converter 206 and converts the reflection density data value XI from the detector 113 in the master photopic area into a digital quantity. and put it in the memory section of 119. The master 11 shown in FIG. 2 is a heat-developable photosensitive sheet member and is composed of a support 202 and a photosensitive layer 203. 113 is a photoelectric element lamp for master reflection density detection and a light receiving element, and 205 is an amplifier.

207 is an input port INI which reads data from the A/D converter.

21 1 is the input port IN2, PH-A, PH-B, S
It is a host for TR, STP, SET1, SET2, and REST signals, and each input terminal is designated by a designation signal from the CPU.

212 is a group of memory elements such as a fixed program memory and a readable/writable memory.

Each memo IJ and the address in the memory are specified by an address designation signal from the CPU, and are negotiated and written by a control signal from the CPU. 209 are output ports 1 to 3, OUTI and 2 are each connected to a D/A converter,
The output digital data is converted to analog data.

Since the analog output is input to the high voltage transformer, the output voltage can be changed according to the input voltage. HVTI is applied to the charger and HVT2 is applied to the developer. Each signal of CPY, MM1, MM2 is sent from output boat 3 to panel 1.
Sent out to 20. Since this signal can be "H", it can be output without converting it to analog data. Each output boat is also CP
It is selected by a designated signal from U. Detection reflection density in bright place
When I passes through the A/D converter and enters the memory, the next step is to release the hold of the A/D converter and cause the A/D converter to output momentary detection data. Check the status of PH-A and PH-B from input port 2, and if PH-A = “L” and PL-B = “H”, A will be turned on again.
/D converter is held, and this time, the reflection density of the master's fat spot is passed through the A/D converter and input from the input port to C.
After passing through PU208, we enter the final stage. The data at this time is
shall be. After reading the data on the floor, release the A/○ converter hold using the program. This means that the measurement of the master density check part is completed. The next step is to check x22SETI.

That is, if the average reflection density value of the floor is greater than or equal to the density limit value SETI, the process proceeds to the next step. However, when x2>SETI, an MMI signal is output from OUT3 to notify the master density abnormality, and the machine is interlocked so as not to enter the printing process. When the plum is normal, the next step is to check if x, Mi SET2 by the CPU, and if > SET2, then MM2
is output and the machine is interlocked as described above. If it is normal, the optimum voltage to be applied to the charger at that time is calculated by the CP river. This is the relationship between the master reflection density x and the optimal charger applied voltage y, or the optimal bias voltage y2, y,=
It is calculated using the experimental formula: f(x), y2=g(x). This calculation procedure is stored in memory 212 in advance. FIG. 7 is an example showing the relationship between the bias voltage and the charger applied voltage with respect to the master reflection density obtained from experiments. From the reflection density x,,x2, the optimum voltage z,=f(x
2), Bo = g (pond) is calculated and each output boat OUT
Output from 1 and 2. The digital data output from the output boats OUTI and 2 is converted into voltage from the D/A converter 21 and then sent to the high voltage transformers HVT1 and H, respectively.
The optimum charger applied voltage and developer bias voltage according to the master density contrast are input to VT2 and HVT1,
Issued from HVT2. Next, after the stabilization period of 2 minutes has elapsed, the printing process step is started, and since the master is not changed, a predetermined number of sheets are printed using the optimal charger applied voltage and developer bias voltage that have been set once. When printing is completed, the main body 120 detects the ejection of the last sheet and outputs STP, and the CPU sends MM.
1. Set all output signals except MM2 to IJ. After that, it returns to the starting state again. As described above, various fluctuation factors during master creation are automatically corrected during the printing process by controlling the voltage applied to the charger and the developing bias voltage, which has a great advantage in improving the stability of printed images.

It should be noted that a person skilled in the art can operate a general-purpose microcomputer to carry out the desired compensation control using the program steps described above, so a detailed explanation of the more detailed steps using command words will be omitted. It is also possible to control HVT1 and HVT2 to appropriate values from the density of the visible image obtained in the printing process in the same manner as in the case of the master. Therefore, in not only printing machines but also so-called copying machines, it is possible to control HVT1 and HVT2 from the density of the original first visible image or the second visible image after development to achieve the appropriate density. Become.

[Brief explanation of drawings]

Fig. 1 is a diagram of the electrostatic printing process to which the present invention is applied, Fig. 2 is a diagram of the density vs. surface potential characteristic of the master, and Fig. 3 is a diagram of the applied voltage vs.
Surface potential characteristic diagram, Figure 4 is a master contrast potential-density characteristic diagram, Figure 5 is a master plan view, Figure 6 is a block diagram of the control section in Figure 1, and Figure 7 is a density-charger voltage/bias voltage characteristic. 8 is a check zone detection signal diagram, and FIG. 9 is a flowchart for executing the process shown in FIG. 6. In FIG. 1, 113 is a master concentration detector;
5 is a check zone detector, 119 is a control unit, HVTI
is a charged voltage source, and HVT2 is a bias voltage source. Kotobuki no Zu Younger Brother Drawing 2 Drawing 3 Drawing 4 Younger Brother Drawing 6 Drawing 7 Drawing 8 Takashi? figure

Claims (1)

[Claims] 1 means for photoelectrically detecting the density corresponding to the grayscale image;
means for forming an electrostatic latent image based on the grayscale image; means for developing the electrostatic latent image; means for transferring the developed image onto a sheet;
A control means for preprogramming in a memory a procedure for determining at least one of a latent image potential when forming the electrostatic latent image or a developing bias potential when developing the electrostatic latent image, and executing the program based on the detection output of the detection means. An image forming apparatus characterized in that the control means sets a limit value for the density detected by the detection means, and the limit value is adjustable.