JPS6114652A - Electrostatic recorder - Google Patents

Abstract

PURPOSE:To detect adequate picture image density even if plural color toners are used by constituting a titled recorder in such a manner that the characteristics of the light emitted from light emitting elements are changed according to the spectral reflectivity of the developer to be used. CONSTITUTION:LED18d1, 18d2 as light emitting elements are arrayed and provided to face the inside of the optical passage 18b formed in the body 18a of a density sensor 18. A phototransistor 18e as a photodetector is provided to face the inside of the optical passage 18c. The light irradiated from the LEDs 18d1, 18d2 passes through the optical passage 18b, is reflected by the surface of a photosensitive drum and is made incident on the phototransistor 18e via the passage 18c. The LED of which the peak wavelength of the irradiation light is in a 600- 800nm range is selected for 18d1 and the LED of which the peak wavelength is <=500nm is selected for 18d2. The phototransistor corresponding thereto is used for 18e. The adequate density is thus detected and the control of the image density is made possible with the color toners A, B having different spectral reflectivities.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention involves forming an image of a document as an electrostatic latent image on the surface of a photoreceptor, developing the electrostatic latent image with a developer, and transferring it to transfer paper. The present invention relates to an electrostatic recording device that fixes images, and more particularly to an electrostatic recording device that detects the density of a developer image formed on the surface of a photoreceptor to control whether or not developer is replenished.

(Prior Art) Among the electrostatic recording devices described above, an electrophotographic copying device is schematically configured as shown in FIG. When the original 81.2 is set on the surface of the platen glass l and the copy start button is operated, the exposure light source 3 scans the original 2 with light relatively, and the optical image of the original 2 is projected onto the mirror 4.5. The light is guided to the surface of a photosensitive drum 6 as an image forming photosensitive member.

The photosensitive drum 6 is a grounded metal cylinder with a photoconductive layer made of selenium or the like provided on the outer peripheral surface thereof, and rotates in the direction of arrow a in conjunction with the exposure scanning.

Before the arrival of the optical image, the photoconductive layer of the photosensitive drum 6 is, for example, uniformly charged by a charging electrode 7 to which a DC high voltage is applied, and the photoconductive layer in this state receives the optical image. Then, the conductivity of the part that receives the light increases, and the electrical charge in that part escapes to the metal cylinder, and a positive charge remains in the dark part depending on the degree of brightness, which causes photoconductivity. An electrostatic charge 111fIA corresponding to the image of the original is formed on the surface of the layer.

When the portion on which this electrostatic latent image is formed reaches the developing sleeve 8a of the developing device 8, the negatively charged developer is attracted to the remaining positively charged portion of the photosensitive drum 6 by electrostatic force. Ru. As a result, a developer image corresponding to the electrostatic latent image is formed on the surface of the photosensitive drum 6.

The transfer paper 9 is sent out by a conveyor belt 11 from a paper feeding force center 10 at a timing such that the leading edge of the transfer paper 9 and the leading edge of the developer image coincide with each other. The developer image on the surface of the photosensitive drum 6 is transferred by the transfer pole 12 to which is applied.

After that, the separation electrode 13 and separation claw 1 to which AC high voltage was applied
The transfer paper 9 is separated from the photosensitive drum 6 by the conveyor belt 15, and the developer image is fixed thereon by the conveyor belt 15.

Reference numeral 18 denotes a light reflection type density sensor that detects the developer concentration (it also detects transfer paper that arrives wrapped around the surface of the photosensitive drum 6 without being separated from it), and 19 a removing electrode that removes the electrical charge on the photosensitive drum 6. , 20 is a cleaning device for removing developer remaining on the surface of the photosensitive drum 6.

The density sensor 18 described above detects the density of the reference image formed on the photosensitive drum 6. This reference image is
The image on the density reference plate 21 is guided to the photosensitive drum 6 and developed by the developing device 8 before the optical system reaches the original exposure scanning speed, and the image is developed by the density signal of this reference image output from the density sensor 18. A solenoid valve 8C serving as a developer replenishment device for the hopper 8b of the device 8 is controlled to control the developer concentration.

This control is called a developer concentration control method using an image density detection method, and the density information detected by the density sensor 18 includes changes in the sensitivity of the photoreceptor of the photoreceptor drum 6, changes in the amount of charge of the developer, and charge - Since information such as fluctuations in lighting conditions is included, the developer concentration can be appropriately controlled against these fluctuations and changes, and the image density can be kept stable.

However, a copying device that can use a plurality of color toners as a developer (a plurality of developing devices filled with developers of different colors are lined up in advance along the rotational direction of the photosensitive drum 6 and one of them is selected) In some cases, the spectral reflectance differs depending on each color toner, so the irradiation light from the light emitting element at the density sensor 18 is Depending on the wavelength and spectral sensitivity of the photodetector,
The detection circuit that receives the output of the light receiving element of the density sensor may become saturated, making it impossible to detect the image density.

(Object of the Invention) The present invention has been made in view of the above points, and its object is to provide an electrostatic recording device that can perform appropriate image density detection even when a plurality of color toners are used. The goal is to provide the following.

(Structure of the Invention) For this purpose, in the present invention, light emitted from a light emitting element is projected onto a developer image formed on the surface of a photoreceptor, and the amount of reflected light from the developer image is detected by a light receiving element to form an image. In an electrostatic recording device that controls density, the wavelength of the light emitted from the light emitting element is changed in accordance with the spectral reflectance of the developer used.

(Example) Examples of the present invention will be described below. FIG. 2 shows the spectral reflectance characteristics of the first color toner A and the second color toner B. As is clear from the figure, the reflectance of both color toners A and B differs greatly depending on the wavelength, and color toner A has a wavelength of about 6
The reflectance is low for irradiation light between 00 and 800 nm,
Furthermore, color toner B has a low reflectance for irradiated light having a wavelength of about 60 Or++++ or less.

Therefore, if the density of any color toner is detected by irradiating it with light of a wavelength with a low reflectance, the light receiving element of the density sensor 18 will be saturated because the amount of reflected light from that color toner is small. This can be prevented.

FIG. 3 shows a cross section of the concentration sensor 18 of this embodiment, in which an LED (light emitting diode) 18d+ as a light emitting element is placed facing into the light path 18b formed in the main body 18a.
, 18d2 are arranged side by side, and a phototransistor 18θ as a light receiving element is provided so as to face into the light 1ffl path 18c. )
and passes through the optical path 18C to the phototransistor 1.
8a. And LED
For 18dl, the peak wavelength of the irradiation light is 600-800n1
1 is selected, and the LED 18d2 has a peak wavelength of 500 nm or less. Furthermore, the phototransistor 18e is sensitive to at least the wavelength of light within the above range.

FIG. 4 shows a detection circuit for processing detection signals from one day of the sensor to obtain an image density signal. The LEDs 18d+ and 18d2 of the concentration sensor 18 are connected to the power supply Vcc.
The resistors R1 and R7 are connected in series in the forward direction between the switch 22 and the selector switch 22, and the switch 22 is connected to ground. The phototransistor 188 is connected between the power supply Vcc and the inverting input terminal of the operational amplifier 23. The power supply voltage Vcc is connected to the non-inverting input terminal of the operational amplifier 23 through a resistor R.
A voltage divided by 2 and R3 is applied, and its output terminal is connected to an inverting input terminal by a resistor R4 and to an inverting input terminal of a comparator 24. A voltage obtained by dividing the power supply voltage Vrc by resistors R5 and R6 is inputted to the non-inverting input terminal of the comparator 24 as a comparison reference voltage.

In this detection circuit, by switching the switch 22, the LED
Either 186+ or 18e2 can be selected. In the above example, when using the first color toner B, select LED18d+ so that the peak wavelength of the irradiated light is between 600 and 800 rv, and when using the second color toner B, selects the LED 13d2 so that the peak wavelength of the irradiated light is 500 nm or less.

The amount of reflected light incident on the phototransistor 8e is small (
When the developer concentration on the photosensitive drum 6 is low, the emitter current of the phototransistor 18e is small, and this current is converted into a voltage by the operational amplifier 23 and amplified. The output from the operational amplifier 23 is output from the phototransistor 1.
The smaller the amount of reflected light to 8e, the higher the amount of light is input to the comparator 24 at the next stage. And this comparator 24
, when the output from the operational amplifier 23 to the inverting input terminal rises above the reference voltage applied to the non-inverting input terminal, the output voltage becomes a low level and the density of the detected developer image becomes higher than a predetermined value. Show that.

A signal indicating the concentration detected in this manner is sent to a solenoid valve of the developing device, and replenishment of developer from the hopper is started or stopped by opening and closing the solenoid valve.

Note that the switching of the changeover switch 22 is carried out depending on the loaded developing device, for example, by providing a different protrusion for each type of color toner on the developing device or hopper of the developing device, and moving the developing device out of alignment. 9JS1J for the purpose of singing! !
It is possible to make it possible to

Further, although the above embodiment is an example in which two types of color toners are used, it goes without saying that the same concept can be applied to cases in which color toners of class 341 or higher are used.

(Effects of the Invention) As described above, according to the present invention, even in an electrostatic recording device that uses color toner of a plurality of colors so as to form a chromatic image, the density of the image by each color toner can be adjusted appropriately. It has the characteristic of being controllable.

[Brief explanation of the drawing]

Figure 1 is a schematic configuration diagram of an electronic copying machine, Figure 2 is a 2ft
FIG. 3 is a sectional view of the density sensor, and FIG. 4 is a circuit diagram of the detection circuit. DESCRIPTION OF SYMBOLS 1...Platen glass, 2...Original, 3...Light source for exposure, 4.5...Blender 16...Photosensitive drum, 7...
...Charging electrode, 8...Developing device, 9...Transfer paper, 10
...Paper feed cassette, 11...Transport belt, 12...
・Transfer pole, 13... Separation pole, 14... Separation claw, 15
. . . Conveyor belt, 16 . . Fixing device, 17 . . Receiver is plate, 18 .
... Cleaning device, 21 ... Concentration reference plate, 22
... Selector switch, 23... Operational amplifier, 24...
·comparator.

Claims (2)

[Claims] (1) The static image density is controlled by projecting light emitted from a light-emitting element onto a developer image formed on the surface of a photoreceptor, and detecting the amount of reflected light from the developer image with a light-receiving element. An electrostatic recording device, characterized in that the wavelength of the light emitted from the light emitting element is changed according to the spectral reflectance of the developer used. (2) Electrostatic recording according to claim 1, characterized in that the wavelength of the light emitted from the light emitting element is changed depending on the developing device filled with the developer. Device.