JPH0158509B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a density adjustment device for an image forming apparatus, and particularly to one suitable for adjusting image density in an apparatus capable of forming images in multiple modes.

For example, with a microfilm reader printer, the original image taken on microfilm may be a negative image or a positive image. Regardless of the original image, the copy obtained from it must be a positive image. In order to meet such demands, an image forming apparatus that can switch between a mode for forming a positive image from a negative original image (N-P mode) and a mode for forming a positive image from a positive original image (P-P mode) has been developed. It has been known.

The process of forming images in the NP mode and the PP mode using the image forming apparatus shown in FIG. 1 will be described. In the case of the N-P mode, first, a photoreceptor 1 whose conductor is covered with a photoconductive layer is negatively charged by a primary charger 2 in a dark place, and a negative original image light 3 is projected thereon.
Forms a negative electrostatic latent image. This electrostatic latent image is reversely developed using negatively charged toner supplied from the developing device 4. A bias voltage (biased AC voltage HAC) in which a negative DC voltage is superimposed on an AC voltage is applied to the developing sleeve 4a and the blade 4b.
The negatively charged toner jumps to the image-exposed bright area (surface potential approximately OV) of the photoreceptor 1 and is developed. A negatively charged toner image is transferred by a transfer charger 5 by generating positive corona discharge from the back side of the transfer material P. Switch to P-P mode,
When forming an image, first, the developing device 4 is replaced with one that can supply positively charged toner. Then, positive original image light 3 is projected onto the negatively charged photoreceptor 1 to form a positive electrostatic latent image, and the positive electrostatic latent image is developed with positively charged toner. biased ac voltage
The positively charged toner supplied from the developing device 4 to which HAC is applied is the image-exposed dark part of the photoreceptor 1 (surface potential negative).
Develop. The positively charged toner image is transferred onto the transfer material P by negative corona discharge of the transfer charger 5. In both the NP mode and the PP mode, the image on the transfer material P is fixed and a hard copy is obtained. On the other hand, after the transfer, the residual toner on the photoreceptor 1 is cleaned by a cleaner device 6, and the residual charge is irradiated with uniform light 7 to be short-circuited (discharge removed), and the next image forming process begins. In addition, 9
is a slit, and 10 is a shutter.

In order to adjust the density of the obtained copy image in such an image forming apparatus, the DC component voltage (hereinafter referred to as "developing bias voltage") of the biased AC voltage HAC applied to the developing sleeve 4a etc. is increased or decreased.
However, as shown in FIG. 2, in the NP mode, the higher the developing bias voltage is, the higher the density becomes, whereas in the PP mode, conversely, the higher the developing bias voltage is, the lower the density is. In addition, there are various types of film whose original image is a negative image, and the density of the base part (background part) of the image varies greatly depending on the film, so adjusting the developing bias voltage with a common variable resistor will produce a negative image. It is not possible to form a positive image of appropriate density from this film. If you try to increase/decrease the developing bias voltage using one variable resistor, the increasing/decreasing range of the developing bias voltage will be the same in both modes, making it impossible to cover the appropriate image density range in both modes. .

The present invention has been made in view of the above situation, and it is an object of the present invention to provide a density adjustment device that can adjust the density to an appropriate density in any mode of image formation.

The present invention that achieves this object is switchable between a first mode in which a positive image is formed from a positive original and a second mode in which a positive image is formed from a negative original;
In an image forming apparatus that adjusts image density by increasing or decreasing a developing bias voltage, there is provided a density adjustment means for adjusting the image density, and an adjustment to an appropriate image density in a first mode according to the adjustment of the density adjustment means. a first bias adjusting means for increasing or decreasing the developing bias voltage within a first range; and a first bias adjusting means for increasing or decreasing the developing bias voltage within a first range, and a first bias adjusting means for increasing or decreasing the developing bias voltage within a first range, and a first bias adjusting means for increasing or decreasing the developing bias voltage within a first range; a second bias adjustment means for increasing or decreasing the range of 2; a selection means for selecting either the first bias adjustment means or the second bias adjustment means according to mode switching; and means for associating the increasing and decreasing direction of the developing bias voltage by the first bias adjusting means and the increasing and decreasing direction of the developing bias voltage by the second bias adjusting means so that they are in opposite directions. It is an adjustment device.

Examples of the present invention will be described in detail below.

FIG. 3 is a circuit block diagram of an image density adjusting device to which the present invention is applied. In the figure, 20 is a microcomputer with a central processing unit CPU,
The storage device ROM/RAM, input/output section I/O, etc. are all integrated into one chip. 21 is the drive circuit,
Based on the command from the microcomputer 20, the charger 2.
Drive voltages HV ₁ , HV ₂ , and HAC are sent to the charger 5, developing sleeve 4a, and blade 4b, respectively. A switching detection circuit 22 sends an N-P mode and P-P mode switching signal to the microcomputer 20. Also
IN is an inverter, VR1 and VR2 are interlocking variable resistors, and R1 to R4 are fixed resistors. These circuits are operated by the output signal OUT of the microcomputer 20, and the developing bias voltage remote signal V _REM.
is sent to the drive circuit 21. relay
When the control coil L of RY is energized and the normally open terminal NO is conducting with the common terminal C, the constant voltage v+ is divided by the resistor R1, variable resistor VR1, and resistor R2,
Emit remote signal V _REM . When relay RY is de-energized and normally closed terminal NC becomes conductive, constant voltage v+ is divided by resistor R4, variable resistor VR2, and resistor R3, and a remote signal V _REM is output. In the NP mode, the voltage range of the remote signal V _REM is determined by the ratio of the value of the resistor R3 and the value of the resistor R4. On the other hand, in P-P mode, the value of resistor R1 and resistor R
The voltage range of the remote signal V _REM is determined by the ratio of the two values.

The relationship between the remote signal voltage V _REM and the developing bias voltage is shown in FIG. Normally, in an image forming apparatus such as a microfilm printer, the increase/decrease range of the developing bias voltage to obtain a proper image density in the NP mode is -150 to -800V. On the other hand, in the PP mode, the range of increase/decrease in the developing bias voltage for obtaining proper image density is 0 to -400V.
Therefore, the corresponding remote signal voltage V _REM
is 1.5~8V in N-P mode, 0 in P-P mode
~4V. The values of the variable resistors VR1, _VR2 and the fixed resistors R1 to R4 are determined according to the constant voltage v+ so that they vary within this range.

For example, the interlocking variable resistors VR1 and VR2 are sliding type,
As shown in FIG. 5, by moving a common adjustment knob 10, the image forming apparatus can be slid along the density scale on the operation panel of the image forming apparatus. Therefore, P
-When in P mode, move knob 10 to 1 on the density scale.
(high concentration side) to 9, variable resistance VR1
The voltage of the remote signal V _REM output from the normally open terminal NO/common terminal C increases in a low range. However, in N-P mode, the variable resistor
The voltage of the remote signal V _REM output from VR2 through the normally closed terminal NC and common terminal C decreases in a relatively high range.

Each function of the microcomputer 20 operates according to program procedures stored in its ROM area. FIG. 6 shows a flowchart for executing a program for a portion of the image forming sequence that includes the configuration of the present invention. The operation will be explained below according to this flowchart. According to a series of image forming sequences, the photoconductor 1 is primarily charged by applying a negative output high voltage HV ₁ to the drive circuit 21;
The shutter 10 is opened and image exposure is performed to form an electrostatic latent image. In step 101 of the flowchart, it is determined based on the output of the switching detection circuit 22 whether the image forming mode is the N-P mode or the P-P mode. N-
If it is the P mode, the output signal out is set to "0" in step 102. Since the output of the inverter IN becomes "1", the normally closed terminal NC of the relay RY becomes the common terminal C.
It is conducting. Therefore, the variable resistor VR2 becomes adjustable. The remote signal V _REM at this time,
As the density adjustment knob 10 is moved from scale 1 to scale 9, the density becomes lower. Correspondingly, the developing bias voltage also decreases, so the image density decreases. In step 103 of the flowchart, a command is issued to the driver circuit 21 to make the voltage HV ₂ applied to the transfer charger 5 positive. If step 101 indicates P-P mode, step 104
Then, set the output signal out to “1”. Inverter IN
Since the output of relay RY becomes "0", normally open terminal NO of relay RY conducts with common terminal C, and variable resistor VR1
becomes adjustable. At this time, the remote signal
V _REM increases as the knob 10 is moved from scale 1 to scale 9. Correspondingly, since the developing bias voltage also increases, the image density decreases. step
At 105, a command is issued to the driver circuit 21 to make the voltage HV ₂ applied to the transfer charger 5 negative. Step 103・
After step 105, the normal image forming sequence returns.

Because of this operation, as shown in FIG. 7, the display of the density scale matches the density of the image to be copied in both the NP mode and the PP mode.

FIG. 8 shows another embodiment of the portion of the circuit shown in FIG. 3 that generates the remote signal V _REM . Output signal out of microcomputer 20
The contacts of relay RY2, which operates in
The adjustable variable resistor is an example of a single variable resistor VR. In N-P mode (state shown), the relay
Normally closed contact NC ₁ of RY2 and common contact C ₁ , normally closed contact
NC ₂ and common contact C ₂ are respectively conductive, and the constant voltage V+ is divided by resistor R4, variable resistor VR, and resistor R3 and output as a remote signal V _REM . In P-P mode, normally open contact NO ₁ , common contact C ₁ and normally open contact C ₂ conduct, respectively, and constant voltage V+ is connected to resistor R1 and variable resistor.
The voltage is divided by VR and resistor R2 and output. variable resistance
Even if VR is changed in the same direction, the increase or decrease in remote signal _VREM will be opposite depending on both modes.

FIG. 9 also shows another embodiment of the portion generated by the remote signal V _REM . In this example, using operational elements such as operational amplifiers, an addition/subtraction circuit, a multiplication/division circuit,
It is constructed by combining inverting and non-inverting amplification circuits. Voltage obtained by dividing constant voltage v+ with variable resistor VR3
v _p is input to the non-inverting adder circuit 11, and a constant voltage
Add v ₁ (v _p + v ₁ ). A voltage of V _REM =α(v _p +v ₁ ) (where 0<α≦1) is obtained by using the voltage dividing circuit 13. On the other hand, the voltage v _p is input to the inverting/subtracting circuit 12, and the constant voltage v ₂ is subtracted and simultaneously inverted and amplified (v ₂ −v _p ). This is done by the voltage dividing circuit 14.
A voltage of V _REM =β(v ₂ −v _p ), (0<β≦1) is obtained.
These two resulting output voltages α(v _p +v ₁ ) and β
(v ₂ −v _p ) are output as remote signals V _REM from the contacts NO and NC of relay RY, respectively.

FIG. 10 shows another embodiment of the adjustment device. The divided voltage output of the variable resistor VR3 is converted into a digital signal by the A/D converter 24 and input to the microcomputer 20. microcomputer 20
The ROM starts operating upon receiving a signal from the switching detection circuit 22, and uses the digital signal of the divided voltage output to detect the second voltage.
As shown in the figure, a program has been written to output a digital signal DV _REM that changes the developing bias voltage. Digital signal DV _REM to D/
Analog remote signal with A converter 25
After returning to V _REM , it is output to the driver circuit 21.
In this way, even if the relationship shown in FIG. 2 is not linear, it can be easily corrected by simply rewriting the data in the ROM. Therefore, there is no need for hardware measures such as correction using a variable resistor intermediate tap as in the past. Furthermore, the output variable range can be easily changed.

As described above, according to the image density adjustment device of the present invention, image density adjustment for different image forming modes can be performed using one operation knob and scale, making adjustment easy and preventing erroneous operations.

Further, regardless of whether the image density of the negative original or positive original is low or high, images with appropriate density can always be formed using a common adjustment means.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of an image forming apparatus to which the present invention can be applied, FIG. 2 is a diagram illustrating the relationship between image density scale and developing bias voltage, and FIG. 3 is a circuit diagram of an image density adjustment device to which the present invention is applicable. 4 is a diagram explaining the relationship between remote signal voltage and developing bias voltage,
Fig. 5 is a diagram of the density scale and adjustment knob, Fig. 6 is a flowchart of the adjustment device, Fig. 7 is a diagram explaining changes in image density with respect to the density scale, and Figs. 8 to 10 are diagrams of the adjustment device. A circuit diagram of another embodiment. 1 is a photoreceptor, 2 is a primary charger, 4 is a developer, 5
is a transfer charger, 10 is an adjustment knob, 20 is a microcomputer, 21 is a drive circuit, VR1,
VR2 is a variable resistor, R1 to R4 are fixed resistors, RY
is the relay and V _REM is the developing bias voltage remote voltage.

Claims (1)

[Claims] 1. In an image forming apparatus that can be switched between a first mode for forming a positive image from a positive original and a second mode for forming a positive image from a negative original, and adjusts image density by increasing/decreasing the developing bias voltage, a density adjustment means for adjusting the image density; a first bias adjustment means for increasing or decreasing the developing bias voltage within a first range so as to adjust the image density to an appropriate image density in the first mode according to the adjustment of the density adjustment means; a second bias adjustment means that increases or decreases the developing bias voltage in a second range wider than the first range so as to adjust the image density to an appropriate image density in the second mode according to the adjustment of the adjustment means; 1. selection means for selecting one of the second bias adjustment means;
The increasing/decreasing direction of the developing bias voltage by the first bias adjusting means and the increasing/decreasing direction of the developing bias voltage by the second bias adjusting means are in opposite directions with respect to the density adjustment in the same direction by the density adjusting means. 1. A concentration adjusting device comprising: means for associating.