JPS63144366A - Density control unit - Google Patents

Abstract

PURPOSE:To eliminate the generation of character disappearance, etc., and to exactly attain ground color correction, by selecting a measuring element, based on an original size, and controlling a light source or an applied voltage of a developing electrode in accordance with a detected value of the selected measuring element. CONSTITUTION:An original 12 is irradiated by a light source 13, and a reflected light L is led onto a photosensitive drum 15 through an optical system 14. Also, concentration detecting sensors 17a-17d provided in the vicinity of an enlargement projection position of a projection lens 16 photodetect a reflected light by a photometric area portion of a prescribed width, respectively, and the detected reflected light quantity is inputted to an exposure quantity detecting circuit 18. An original size detecting circuit 22 outputs a signal for showing an original size, to a CPU 21, and the CPU 21 changes a measuring area by turning on and off a switch, based on said signal, and controls a detecting output voltage outputted to the CPU 21 from the exposure quantity detecting circuit 18. The CPU 21 controls an applied voltage to the light source 13 in phase through a phase controlling circuit 27.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a high-resolution apparatus for copying, etc., which automatically controls the voltage applied to a light source or a developing electrode based on the weight of light reflected from an original. Regarding.

[Prior Art] Conventionally, such devices include, for example, Japanese Patent Application Laid-Open No. 60-216
As shown in Publication No. 347, there was a method in which the reflected light irradiated from the original onto the photosensitive drum was photometered approximately on average using one sensor, and the voltage applied to the light source was automatically controlled according to this photometric value. .

[Problem that Hokumon tries to solve] However, in the above method, the photometric area of the sensor is fixed, so if the original is small, reflected light other than the anti-Q = 1 light from the original, such as reflection from the platen cover The image is averaged including light, and the background stains on the original cannot be corrected completely.
Scratches appear on the copied image. Furthermore, as shown in Figure 8(a), if there is a large black area in one part of the document, the photometric value of the sensor will drop significantly as shown in Figure 8(b), and based on this photometric value, the illumination of the light source will be If the IJ (light display) was changed, the exposure amount would increase significantly, resulting in a situation where characters, etc. near the black area would become wet due to overexposure.

The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to provide a density control device that can accurately correct the background color without causing characters to disappear.

[Means and effects for solving the problems] The present invention has the following features:
By selecting a measuring element based on the size of the original and controlling the voltage applied to the light source or developing electrode according to the detected value of the selected measuring element, overexposure can be eliminated and the reflected light indication can be set as the target value. Accurate feedback control of color.

[Example] An example of the present invention will be described in detail based on the drawings of FIGS. 1 to 7.

FIG. 1 is a schematic diagram of an embodiment of a concentration control device according to the present invention. In the figure, an original 12 placed on a platen glass 11 is illuminated by a light source 13, and the reflected light is guided onto a photosensitive drum 15 via an optical system 14 to form an electrostatic latent image. . Further, as shown in FIG. 2, near the enlarged projection position 16A of the projection lens 16 of the optical system 14, there are a plurality of density detection sensors 17a for detecting reflected light indicators.
~17d are arranged. These sensors 17a-17
d is configured such that the respective photometric areas touch or do not overlap, and receives reflected light only from the photometric area valves having a constant width. Note that this reflected light indication is an average of document density corresponding to an area of a constant width.

The reflected light signals detected by the sensors 17a to 17d are input to the exposure amount detection circuit 18.

As shown in an embodiment of FIG. 3fa, the exposure amount detection circuit detects output voltages corresponding to input light indications from each of the sensors 17a to 17d, and amplifies the detected output voltages using OP amplifiers 19a to 19d. The largest voltage among these output voltages is output to a control circuit (hereinafter referred to as CPU) 21 via diodes 20a to 20d and switches 1 to 4. This is because a potential difference is generated between each diode due to each output voltage amplified by the OP amplifiers 19a to 19d, and a reverse current is applied from the diode with the highest output voltage to the other diodes. As a result, the other diodes are cut off, and for example, for the document shown in FIG. 8(a), the CPU 21 receives only the voltage corresponding to the largest light display, as shown by the solid line in FIG. 8(C), as in the conventional example. The output is as follows.

Further, as shown in another embodiment of FIG. 3(b), the exposure amount detection circuit detects the output voltage according to the input light indication of each sensor 17a to 17b, and
Amplify with. On the output side of the OP amplifiers 198-19d, resistors R1-R8 and diodes D1-D8 are connected in series for each set, and the series-connected resistors and diodes form parallel circuits, respectively. Each resistor has a relationship of R1>R2, R3>R4, R5>R6, R7>R8, and diodes D1. D3, Ds.

D7 is a diode D2, D4, D6 . It is connected in the opposite direction to Ds. This detection circuit detects the output voltage V1. A so-called weighted average is applied to V2, V3, and V4, and the average voltage Vo is (a1V1+a2V2 +a3V34-a4V4)/
(a1+a2+a3+a4) (al, 'a2.a3.a4 are arbitrary values determined by the resistance values of each resistor R1 to R8), and as above, the 8th
It is output to the CPU as shown by the broken line in Figure (C).

The switches 1 to 4 above are the original size detection circuit 2.
On/off control is performed by the CPU 21 based on the document size detected in step 2.

In other words, the document size detection circuit 22 is connected to a platen cover 23 that opens and closes the platen glass 11 as shown in FIG.
The document size is detected based on the output signals of the size detection sensors 24a to 24d disposed in the document controller 24, and a signal indicating the document size is output to the CPU 21. CPLI 21 immediately activates relays 1 to 4 shown in FIG. 5 in response to this signal. For example, as shown in Figure 6, the activation control of relays 1 to 4 is performed for each document size, and when the document size is A5 or less, only relay 1 is activated and the switch In the case of A3, relays 1 to 4 are activated and switches 1 to 4 are turned on. As a result, from the exposure Φ detection circuit 18,
Switches 1 to 4 are turned on and off according to the document size to change the photometry area and control the detection output voltage output to the CPU 21.

The CPU 19 sets the detection output voltage of the exposure amount detection circuit 18 to A.
/D conversion A/D converter, input/output interface,
It incorporates a memory for storing these operating programs and data, a central processing unit, etc. CPU
In addition to the exposure amount detection circuit 18 and original size detection circuit 20, a zero cross detection circuit 26 connected to an AC power supply 25, a phase control circuit 27, and an effective value detection circuit 28 are connected to the reference numeral 19.

The zero cross detection circuit 26 outputs a cutting signal @ to the CPU 21 at the timing when the voltage of the AC power supply 25 starts to drop. The CPU 21 takes in the detected output voltage of the exposure amount detection circuit 18 at the timing when the interrupt signal is input.

Then, the CPU 21 controls the phase control circuit 27 so that the difference between the predetermined target value and the detected output voltage becomes zero so that the detected output voltage becomes an optimal value for good copying. The phase control circuit 27 controls the phase of the voltage applied to the light source 13 according to a command from the CPU 21 and outputs the voltage.

The phase-controlled voltage signal is also input to the effective value detection circuit 28, and the effective value detection circuit 28 processes the voltage signal and outputs the effective value to the CPU 21. CPU
21 takes in the effective value at the timing when the interrupt signal is input. Then, the CPU 21 selects the phase control condition for the effective value so that the detected output voltage from the exposure amount detection circuit 18 becomes equal to the target value, and performs feedback control.

Next, light amount control according to the present invention will be explained based on the flowchart shown in FIG.

In the figure, first, when the CPU 21 inputs a synchronized input signal to the AC power supply 25, it monitors the voltage applied to the light source in step 101, and determines whether the voltage is equal to or higher than the rated voltage n, which is the limit of the applied voltage. . The reason for setting this rated voltage is to avoid problems such as disconnection of the light source lamp if the voltage applied to the light source becomes high and the bright spot temperature exceeds a predetermined limit. be.

Here, when the applied voltage is below the rated voltage n, the process proceeds to step 102, and when it is above the rated voltage n, the process proceeds to step 103. In step 103, it is determined whether the amount of reflected light from the document is less than a predetermined target value, and when it is less than the target value, the process proceeds to step 104, and a control signal is output to the phase control circuit 25 to delay the dot hole phase. After that, he returned to the main role. Further, if the amount of reflected light is equal to or greater than the target value in step 103, the process proceeds to step 102, similar to when the applied voltage is equal to or less than the rated voltage in step 101.

In step 1.02, it is determined whether the amount of reflected light from the document is greater than or equal to the target value, and when it is greater than or equal to the target value, the phase control circuit 27 is feedback controlled to delay the dot hole phase in step 105. In the following cases, the phase control circuit 27
feedback control. After step 105 or 106, a return to the main routine is performed.

In the present invention, the density of the copy was controlled by controlling the voltage applied to the light source according to the amount of light reflected from the original, but it is also possible to control the density of copies by keeping the voltage applied to the light source constant and controlling the voltage applied to the developing electrode. It is also possible to perform concentration control. Alternatively, the photometric values of each sensor may be directly input to the CPLI and processed by software in the CPU for selection/averaging. In addition, the sensor for detecting the document size was placed on the platen cover, but if a narrow document is copied while the platen cover is open, the density detection sensor will detect it as if a solid black area had occurred, and the In correction will be over-copied. becomes thinner. Therefore, it is possible to prevent excessive correction when the platen cover is opened by disposing a sensor for detecting the cost size inside the copying machine, for example, near the platen glass. Furthermore, the number of document size detection sensors can be increased or decreased according to the document size.

Therefore, the present invention prevents overexposure by controlling the ground color by feedback using the q] light exposure as a target value.

[Effects of the Invention] As explained above, the present invention selects a measuring element based on the document size and controls the voltage applied to the light source or the developing electrode according to the detected value of the selected measuring element. etc. did not occur, exactly 1t! Single color correction can be performed.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram of an embodiment of a moisture level control device according to the present invention, and FIG. 2 is a diagram showing the arrangement position of a concentration detection sensor.
Fig. 3 is a circuit diagram of an embodiment of the exposure amount detection circuit according to the present invention, Fig. 4 is a diagram showing the arrangement position of the document size detection sensor, Fig. 5 is an operating circuit diagram of the relay, and Fig. 6 is FIG. 7 is a diagram showing the relationship between document size and relays, FIG. 7 is a flowchart diagram for optical control, and FIG. 8 is a diagram showing conventional photometric values and photometric values of the present invention for a document. 12... Original, 13... Light source, 17a-17d...
・Temperature detection sensor, 18... Exposure amount detection circuit, 21.
...Control 1 circuit (CPLI), 22...Document size detection circuit, 24a to 24d...Size detection sensor, 2
5... AC power supply, 26... Zero cross detection circuit, 2
7... Phase suppression circuit, 28... Effective value detection circuit. Tatami 7 Soeki Ii 1 Place 2 Figure 4 Figure 5 ○ ON

Claims (3)

[Claims] (1) In a density control device having means for detecting the size of an original and means for detecting the amount of exposure from the original using at least two measuring elements, a detection value of the measuring element is selected based on the detected size of the original. and means for controlling a voltage applied to a light source or a developing electrode according to a detected value of the selected measuring element. (2) The concentration control device according to claim 1, wherein the controlling means controls the largest detected value among the detected values of the measuring element as a target value. (3) The concentration control device according to claim 1, wherein the controlling means performs a weighted average of the detection values of the measuring elements and controls the average value using the target value.