JPS59157659A - Image density adjusting device - Google Patents

Abstract

PURPOSE:To perform image formation with invariably proper density by performing a preliminary scan at intervals of a specific number of copies and measuring the density of an original picture repeatedly. CONSTITUTION:A decision on whether the number of taken copies attains to a specific number NO or not is performed in a step S801. Then, when so, an original lighting lamp is turned on. The amount of exposure is determined by a lighting voltage VAC. Then, the contents of a copy quantity counter CN are stepped by one and an advance to a step S802 is made. A copying process from paper feed and the forward movement of an optical system to the backward movement of the optical system is carried out in the step S802. When the decision that the copy quantity counter CN attains to NO=20 is made in the step S802, an advance is made according to a flow of YES, and the contents of the counter CN are cleared after a remeasurement flag FLG is set. Consequently, the picture density of the original is measured again. The succeeding copies are taken with the reset density on the basis of the remeasurement result.

Description

TECHNICAL FIELD The present invention relates to an image forming apparatus such as a copying machine, and more particularly to an image density adjusting apparatus that measures the density of a document and determines appropriate image forming conditions during image formation based on the measured density.

Conventional technology There are two types of devices of this type:

(1) Read the original density once, hold and memorize this value,
A method of appropriately setting image forming conditions, such as the light intensity of an exposure lamp, developing bias, etc., based on this value during image formation.

(2) A so-called successive approximation method that simultaneously reads the document density during image formation and immediately feeds it back to the image forming conditions.

In the case of method (1), in which preliminary scanning is performed to read the original density prior to image formation, the original image density value set by the preliminary scanning is applied regardless of the number of copies. Continuous copying is performed based on the AE value (hereinafter referred to as AE value). However, when making continuous copies with a large number of sheets, the image forming conditions often change between the beginning and the end, so even if the AE value is constant, the actual image on the copy paper There is a possibility that the concentration will differ.

OBJECTS In view of the above, an object of the present invention is to provide an image density adjustment device that can always maintain an appropriate image density regardless of the number of copies.

Example Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 shows an embodiment of the invention. here.

100 is a high-voltage transformer, which is controlled by a control signal output from a potential control circuit 101 to be a negative charger 1o2. Secondary charger 103. 10EI is a developing bias cylinder which controls the high voltage output of the pre-static eliminator 104 and the transfer charger 105, and is controlled by the developing bias circuit 107.

The light reflected from the original 1011 exposed by the original illumination lamp 10B passes through the lens 110 and then passes through the mirror lit.
, 112 and 113 are imaged onto the photosensitive drum 114. Here, since the photosensitive drum 114 is rotated in the direction of arrow 115 in the figure in synchronization with the exposure of the original, an electrostatic latent image of the original image is formed on the surface of the photosensitive drum.

121 is a control circuit that controls the load of each part, and is composed of a microcomputer, and includes a central processing unit CPU,
It has a memory RO which stores control programs shown in FIGS. 5 and 8, which will be described later, and a memory RAM 1 which temporarily stores various data such as the number of copies. Further, the control circuit has a built-in copy number counter CN for counting the number of copies. Further, as will be described later, a remarriage flag FLG is formed in the memory RAL, which is set when the copy number counter CN counts N1 copies.

From this control circuit 121 to the potential control circuit 101 and image exposure circuit 122 (hereinafter referred to as AE circuit),
A control signal is provided. 123 is a potential sensor that measures the surface potential on the photosensitive drum, and this sensor output (surface potential) 123S is amplified via an amplifier 127 and then supplied to the potential control circuit 101 and the AE circuit 122. . The AE circuit 122 calculates the document density from the sensor output 123S, and outputs a control signal 122S to the lighting circuit 124 based on this result. The lighting circuit 124 lights the illumination lamp 10B with a predetermined lighting voltage based on this signal 122s. Next, reference numeral 125 is a transfer paper storage section for storing transfer paper, which is a recording member.
From there, the stored transfer paper size signal 125S is supplied to the control circuit 121. Reference numeral 12G denotes an operation section disposed on the main body of the apparatus, on which various keys are arranged, and the operator sets the number of copies, commands to start copying, etc.

FIG. 2 shows a time chart of various parts during copying of an A4 size document in this embodiment. Here, L is the preliminary scanning width (
AE measurement width), and over a period corresponding to this L,
The AE circuit 122 reads the output 123S of the potential sensor 123. This scanning width is often set to the width of a transfer sheet (A4 size in this example) on which an image is to be formed, as will be described later. In other words, the size of the transfer paper is usually the same as the size of the document to be read, and if the scanning width is made to match the size of the transfer paper on which the image is to be formed, preliminary scanning will be performed over the entire surface of the document to be read. It turns out.

FIG. 3 shows an example of the configuration of the AE circuit. Here, 301 is 1
It is a chip microcomputer, and has a memory ROM2. Accumulator ALU, memory RAM2 for temporarily storing data, etc.
It has an A/D converter A/D. In the memory RAM2, there is a data table TBL (VAc table) shown in Fig. 7.
, register R(VAi) and R(VAυ. 302 is an integrating circuit, and potential sensor output 123S
is taken in, and its output 123S is integrated over a period corresponding to the preliminary scanning width. An example of the configuration of this integrating circuit is shown in the fourth example.
The output 302S of the integrating circuit 302 shown in the figure is supplied to the microcomputer 301.

303 is a D-A converter, and the microcomputer 3
After converting the digital signal VAC, which is the calculation result output from 01, into an analog signal 122S, it is output to the lighting circuit 124.

In the AE circuit having such a configuration, the lighting voltage of the document illumination lamp 108 is determined based on the measurement output 123S of the photosensitive drum surface potential, as will be described later.

FIG. 5 shows the operation of this embodiment configured in this manner.

This will be explained according to FIGS. 8 and 8.

First, in FIG. 5, in step 5501, when a copying operation is started after copying conditions such as the number of copies N and transfer paper size are set, a preliminary scanning width is determined based on the transfer paper size. That is, in the control circuit 121, the transfer paper size is detected from the signal 125s from the transfer paper storage section 125, and the size width is set as the pre-scanning width, and the reversal position of the optical system is determined. After this,
The optical system begins to advance, and preliminary scanning for determining the exposure amount of the original begins (time TI in FIG. 2). Step 5502
Now, measure the original image density by the width of the transfer paper size (AE
Measurements are taken (between T1 and T2 in Figure 2). That is, A
The E circuit 122 takes in the potential sensor output 123S over a period corresponding to the width, and stores the digital conversion values DV and IB of the integrated value VAt in the memory RAM2. In step 5503, the optical system that has finished measuring the original density returns to its home position (between T2 and T3 in FIG. 2). That is, in the AE circuit 122,
The potential sensor output 123s is captured over a period corresponding to the width, and the digital conversion value Dv of the integrated value V is stored in the memory R.
Store in AM. In step 5503, the optical system that has finished measuring the original density returns to the home position 2 (times T2 and T3 in FIG. 2). In step 5504, while the return operation is being performed, an operation is performed to determine the lighting voltage of the document illumination lamp 108, the details of which will be described later, based on the integral value DVA'a.

In step 5505, after the backward movement of the optical system is completed, a copy sequence to be described later is entered, and - an autumnal equinox copy is performed.After the copy is completed, it is determined whether or not the re-measurement flag FLG is set. , if it has not been set, the process returns to step 5501 to perform preliminary scanning and measure the document density. On the other hand, when the flag FLG is in the reset state, it is determined whether or not the copying of the set number N of sheets has been completed, and the recopy operation is stopped when the copying of N sheets is completed.

"FIG. 6 shows an arithmetic routine (step 5504 in FIG. 5) executed in the AE circuit 122. In the figure,
In step 5601, the integral value DV obtained by preliminary scanning is transferred to the accumulator ALU. Step 5
At 602, the VAc table TBL in the memory RAM is retrieved using this value DVg as an offset value.

FIG. 7 shows this table TBL. Now, suppose that the density of the pre-scanned document is light<, and DVAv: =2 is obtained, then in this table TBL, DVM! =2
A voltage value Vhc=84 (V) corresponding to is selected.

In step 5603, the selected voltage value V is stored in the register R(V- in the memory RAM. In this way, from the measured value of VA@, the value VAc of the lighting voltage of the illumination lamp 108 is calculated. Here, when the image density of the original is low, the obtained DvAa value is small;
Therefore, the value of the lighting voltage can also be kept low.

In the opposite case, the value of the lighting voltage is set high.

After the lighting arithmetic position is set in this way, the process moves to the copy sequence (step 5505 in FIG. 5) as described above.

Figure 8 shows this copy sequence? Indicates low. In the figure, in step 5801, first, the number of sheets that have already been copied is changed to the number of sheets N@ (in this example, N,
=20) is determined. If the determination is negative, the process proceeds along the flow of "NO" and the document illumination lamp 10 is turned on (time T3 in FIG. 2). At this time, the exposure amount is determined by the value of the lighting voltage 'Jg calculated as described above. That is, as shown in FIG. 3, the set value of VA is converted from a digital value to an analog signal 122S via the DA conversion circuit 302, and is supplied to the lighting circuit 124. The lighting circuit 124 lights the illumination lamp 10 days in response to the supplied signal 122S. . Thereafter, the contents of the sheet number counter CN are incremented by "1" and the process proceeds to step 5802. In step 5802, paper feeding starts and the optical system starts moving forward. When the optical system reaches the inverted position, forward movement is stopped and backward movement begins (time T4 in FIG. 2), and the optical system returns to the home position. In this way, the copy sequence ends.

On the other hand, if it is determined in step 5801 that the sheet number counter ON has reached N,=20, the process proceeds along the flow of rYESJ, sets the re-measurement flag FLG, and then clears the contents of the sheet number counter CN. As a result, as described above (step 5505 in FIG. 5), the image density of the document is remeasured. Subsequent copies are performed using the density reset based on the remeasurement results.

Effects As explained above, according to the present invention, when performing continuous copying, preliminary scanning is performed every time a predetermined number of copies are made, and the image density of the original is remeasured, so that the image density of the original is always maintained at an appropriate density. Image formation can be performed.

Note that the present invention is not limited to controlling only the exposure amount described above, and it goes without saying that the amount of charge and the developing bias may be controlled.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an embodiment of the present invention, Fig. 2 is a time chart of each part of the device shown in Fig. 1, Fig. 3 is a block diagram showing the AE circuit in the device shown in Fig. 1, and Fig. 4 is a block diagram showing an embodiment of the present invention. Third
A circuit diagram showing the integration circuit in the AE circuit shown in Fig. 5,
FIGS. 6 and 8 are flowcharts showing the operation of the apparatus shown in FIG. 1, and FIG. 7 is a diagram showing the table TBL. 100... High-voltage transformer, +01... Potential control circuit, 102... - charger, 103... Secondary charger, 104... Pre-static eliminator, 105... Transfer charger, 106 Developing bias cylinder, 107 Developing bias circuit, 108 Original illumination lamp, 108 Original, 110 Lens, 111, 112, 113 Mirror, 114 Photosensitive Drum, 115...Arrow, 121...Control circuit, 122...Image exposure circuit (AE circuit 0.123...
Position sensor, 124...Lighting circuit, 125...Transfer paper storage unit, +213...Operation unit, 127...Amplifier, 301...Microcomputer, 302...Integrator circuit, 303...・D-A converter, 123S, 302S, VAc, 122s,
125S=signal, RAMI, RAM2. ROMI, RO
M2...-Memory, A/D...A-D converter, Cptl...Central processing unit, FLG...Re-measurement flag, CN...Number of sheets counter. Figure 7

Claims (1)

[Claims] 1) Prior to exposure of the original to form an image on a recording member, a preliminary scan of the original is performed, and an image is formed based on the measurement result of the image density of the original obtained by the preliminary scanning. In an image density adjustment device that controls image recording conditions for
When continuously forming images on multiple recording members,
An image density adjusting device characterized in that the preliminary scanning is performed every predetermined number of sheets. 2. An image density adjusting device according to claim 1, wherein the image recording condition is an exposure amount of a document.