JP2573851B2 - Sensor contamination compensator in toner density controller - Google Patents

Abstract

PURPOSE:To control image density automatically and to prevent the density from being overcorrected by comparing reflection factor data on a photosensitive body that a sensor inputs with correction reference data, correcting the sensor voltage and generating an alarm when a correction limit is reached. CONSTITUTION:The sensor 17 inputs reflection factor data on a no-image formation area on a photosensitive drum to an arithmetic part 23 through an output terminal 21. The arithmetic part 23 compares the input data with the sensor correction reference data and data for sensor correction corresponding to the comparison difference is converted by a converter 24 and sent to an LED 17a to correct the voltage of the sensor 17. Therefore, the voltage of the LED 17a is raised correspondingly by a decrease in reflection factor due to the contamination of the sensor 17. Further, when the correction data reaches limit data, an abnormality warning is generated and the machine is stopped. Consequently, variation in image density due to the sensor contamination is corrected automatically to prevent an element from being destroyed owing to overcorrection.

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a toner density control device for a copying apparatus, and more particularly, to a sensor dirt compensating device which issues a warning or a machine stop when dirt exceeds a limit. About.

[Conventional technology]

As shown in FIG. 3, an electrophotographic copying apparatus uses an original (not shown) placed on a platen glass 1 as a light source 2.
And the reflected light from the original is charged in advance by the band electrodes 8 by the optical system such as the mirrors 3 to 6 and the lens 7 and rotated in the direction of the arrow b in synchronization with the scanning. The latent image is formed on the photosensitive drum 9, and the latent image is developed with toner by the developing unit 10 in the next process. Then, the toner is transferred to the transfer paper fed from the direction of arrow c by the transfer pole 11. Transfer the image and then separate the transfer paper
, And is conveyed to the heat fixing unit 14 by the conveying belt 13 to be fixed there and discharged. Reference numeral 15 denotes a cleaning unit for removing toner remaining on the photosensitive drum 9, and reference numeral 16 denotes a charge removing lamp for removing unnecessary charge on the surface of the photosensitive drum 9 charged by the band electrode 8 to prevent waste of toner consumption. And 17 are sensors for detecting toner density.

The toner in the developing unit 10 decreases when it is supplied to the photosensitive drum 9, and when the toner advances, the image becomes thin. Therefore, the toner density is detected by the toner density sensor 17 to control the amount of toner in the developing unit 10. It is supposed to.

That is, in this toner density control, a reference density plate 18 is provided in advance on the starting end side of the platen glass 1, and an image (reference black) of the reference density plate 18 is scanned prior to scanning of an original to scan a latent image. After forming and developing, the sensor 17 detects the density, and when the density is lower than the reference value, the valve 10b of the toner hopper 10a in the developing unit 10 is opened a predetermined number of times, or for a certain time, and the toner is opened. Is supplied to the sleeve 10c side.

FIG. 4 is a diagram showing a circuit for controlling the toner density.
The sensor 17 is configured by a reflection type photocoupler including an LED 17a as a light emitting element and a phototransistor 17b as a light receiving element. VR1 and VR2 are variable resistors for adjusting the current flowing through the LED 17a, Q1 and Q2 are transistors for adjusting the voltage across one of the variable resistors VR2, Q3 is a transistor for amplifying the output of the phototransistor 17b, and R1 is a transistor. The base bias resistor of Q2, R2 and R3 are transistors Q3
Is a resistor for converting the output current into a voltage, and TH is an element for temperature compensation.

In this circuit, when the current of the LED 17a is constant (the amount of emitted light is constant), if the detected toner concentration is high, the amount of reflected light there is small, so the output current of the phototransistor 17b is small and the voltage at the output terminal 21 is low. On the other hand, if the toner concentration is low, the voltage increases.

A comparator (not shown) to which a voltage corresponding to the toner density reference value is applied as a comparison reference value is connected to the output terminal 21, so that when a voltage higher than this comparison reference value is output, the output is output from the comparator. Then, the valve 10b of the toner hopper 10a is driven to supply the toner. This control is repeated for each copy operation,
Control is continuously performed so that the toner concentration becomes appropriate.

[Problems to be solved by the invention]

However, the sensor 17 described above is
It is set at the entrance side of the LED, so that it is considerably contaminated by the toner, and the effective light amount of the light emitted from the LED 17a is reduced, or a part of the light reflected by the patch image does not reach the phototransistor 17b Things can happen.

In such a state, the accurate density of the patch image can no longer be detected, and it is detected that the toner density is high. Therefore, there is a problem that toner supply is not performed and the image density is reduced. .

In this regard, conventionally, when a serviceman replaces the photosensitive drum, the reflectance of the photosensitive drum of the drum is based on the difference, and the light emission amount of the light emitting element is manually changed in order to correct the variation in the reflected light amount there. When adjusting by the resistor VR1, the sensor was manually cleaned. Therefore,
Until the drum replacement, the toner density control was insufficient.

The present invention has been made in view of such a point, and an object of the present invention is to correct the sensor so that the image density does not decrease even when the sensor is contaminated with toner, and to further correct the image density. The warning is to stop the machine.

[Means for solving the problem]

For this purpose, the present invention detects the density of a patch image obtained by developing the image of the reference density plate on the surface of the photosensitive drum with a sensor,
A toner concentration control device configured to control the toner concentration, a unit that controls a power supply voltage of a light emitting element of the sensor according to contamination of the sensor, a unit that detects that the voltage has reached a limit value, and A means for issuing an alarm and stopping the machine based on the output from the detection means is provided.

〔Example〕

Hereinafter, examples of the present invention will be described. FIG. 1 is a diagram showing a circuit for controlling toner concentration according to one embodiment. An output voltage from an output terminal 21 is converted into a digital value of a predetermined number of bits by an A / D converter 22, and the arithmetic unit 23 To enter. Then, various results calculated by the calculation unit 23 are as follows:
The signal is output to the D / A converter 24 as a sensor correction signal, and is output as a toner supply signal, a correction completion signal, final data, and the like.

As shown in FIG. 2, the sensor 17 passes through the patch image B, the non-image forming area C, and the image forming area D as shown in FIG. Then, taking in the toner density information is performed using the patch image B.
Performed between the timing t ₂ and t ₄ when detecting the. Also,
In this embodiment, the reflectance data (density data) of the non-image forming area C of the photosensitive drum 9 is also fetched, and the timing is the timing t ₁ immediately after the copy start and before the patch image B portion or the image forming area C is reached. It is.

(1). The toner density control: a captured data is toner density data between the timing t ₂ ~t _3, this data is compared to the reference level data inside the case of the lower concentration than the input density data is the reference density data , A toner supply signal is output to drive the valve 10b of the toner hopper 10a to perform toner supply.

More specifically, for example, normal replenishment and forced replenishment are performed as follows according to the voltage Va of the output terminal 21.

Here, the normal replenishment is a replenishment performed from the completion of the density data capture to the capture timing of the next copy cycle. The forced replenishment is a replenishment that is performed for 0.3 seconds after the completion of the capture or the completion of the density data, and is executed only in the last copy cycle. This is to prepare for the next copy.

(2). Sensor Dirt Compensation: In this case, the output terminal in the non-image forming area of the photosensitive drum 8 when the copying apparatus is shipped or the drum is replaced.
The voltage of 21 is manually adjusted to a predetermined voltage by the variable resistor VR1.

Then, (data corresponding reference voltage appearing at the output terminal 21, for example, 2.5v) During normal use, the incorporation of the current reflectance data of the non-image forming region C at the timing t _1, the interior of the sensor correction reference data ROM with built-in sensor correction data by comparing data with input reflectance data
(Not shown), sensor correction data corresponding to the comparison difference is sent to the D / A converter 24, where it is converted into an analog voltage, and the voltage is used as the power supply voltage of the LED 17a. When the correction is completed, a correction completion signal is output.

Therefore, in this control, if the sensor is dirty, the reflectance data of the non-image forming area C is also data indicating a low reflectance (for example, 2.5 V or less), and a difference from the correction reference data occurs. , LED17a by the amount corresponding to the difference
By compensating for the increase in the power supply voltage, the decrease in reflectance corresponding to contamination can be compensated. That is, the output terminal
A normal voltage (for example, 2.5 V) appears at 21.
Therefore, also in the toner density control performed by the timing t ₂ ~t ₃ after this, since the control correction supply voltage corresponding to the correction reference data is performed, so that precise control is performed.

The sensor dirt compensation need not be performed every copy, thus in the above embodiment are processing takes in the data at the timing t ₁ immediately before the process proceeds from the copy start to the image forming area C. That is, each time the copy start button is operated, the dirt compensation is performed.

(3). Detection of drum winding jam: The sensor 17 is provided on the input side of the cleaning unit 15, and here, the transfer paper must be separated.
However, when the separation is incomplete, the paper bites into the cleaning unit 15 and needs to be detected.

In the present embodiment, this jam detection is detected by the sensor 17. Sensor 17 captures the data for the timing t ₁ in dirt compensation as described above, captures the data for t ₂ ~t ₃ in the toner density control. Therefore, at a portion other than these timings, the voltage of the output terminal 21 is monitored, and if a voltage of, for example, 3.5 V or more appears, it is determined that a jam has occurred. Since the color of the transfer paper is whiter than the color of the photosensitive drum surface, jam detection can be performed using this difference.

(4). Regarding the correction limit and alarm generation: The system for compensating for the contamination of the sensor 17 can theoretically follow the contamination as much as possible as described above, but this correction method uses the voltage appearing at the output terminal 21 Since the power supply voltage of the LED 17a is increased until the voltage reaches the reference value (for example, 2.5 V), if the voltage is increased beyond a certain limit, the LED may be broken, and the correction completion signal may not be output.

Therefore, in the present embodiment, sensor correction data (data for power supply voltage) is limited, and limit data for maximizing the power supply voltage is prepared in the ROM, and sensor correction reference data and input reflectance data are stored. By the comparison difference of
When data equal to or more than the limit data is selected, the machine is stopped (copy start is stopped) at the same time as determining the correction limit and issuing an audio or visual warning.

〔The invention's effect〕

As described above, according to the present invention, the dirt on the sensor is automatically corrected, so that the toner density control can be normally performed. In addition, when the dirt reaches the limit, the user is notified of the limit, and Since the operation is stopped, there is an advantage that the light emitting element can be prevented from being damaged due to overcorrection, and incomplete contamination compensation can be prevented.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of sensor dirt compensation according to one embodiment of the present invention,
FIG. 2 is a diagram for explaining the timing of taking in sensor dirt compensation data and toner density data, FIG. 3 is a diagram showing the principle of a conventional general electrophotographic copying apparatus, and FIG. 4 is a diagram showing conventional toner density control. It is a circuit diagram. 17 ... Sensor

Claims (1)

(57) [Claims] A toner density control device configured to detect a density of a patch image obtained by developing an image of a reference density plate on a photosensitive drum surface with a sensor and to control a toner density; Means for controlling the power supply voltage of the light emitting element of the sensor, means for detecting that the voltage has reached a limit value, and means for issuing an alarm and stopping the machine based on an output from the detecting means. Characteristic sensor dirt compensation device.