JPH0526584Y2 - - Google Patents

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to an improvement of an electrostatic copying machine having a function of automatically controlling the copying density according to the density of the original.

(Prior art) Conventionally, as shown in Japanese Patent Publication No. 54-36502, for example, a white light-shielding portion is provided at the reference position of a contact glass to form a non-image area of about 0.5 to 20 mm at the leading edge of copy paper. This prevents the leading edge of the copy paper from wrapping around the fixing roller when the copy paper is brought into pressure contact with the heat fixing roller for fixing, and prevents any hindrance to the separation action of the copy paper by the peeling claw. It is known what has been done.

By the way, there is an automatic density control function that sequentially controls the copy density by detecting the reflected light from the original, reading its density, and changing the light intensity of the optical system section or the bias voltage of the developing section according to that value. In an electrostatic copying machine equipped with the above-mentioned electrostatic copying machine, there is a problem in that when the above-mentioned white light shielding part is provided, the leading edge of the copy paper becomes black. That is, since the amount of reflected light increases when the white light-shielding portion is exposed, the automatic density control function operates to adjust the exposure amount in the section A-B corresponding to the light-shielding portion as shown in FIG. However, after the optical system passes through the light-shielding section, even though there is a document in section B, there is a delay in the operation of the automatic density control function. The copy density in the section B-C becomes darker until it returns to the value corresponding to the original density, and the image becomes darker.
In order to prevent this problem, it may be possible to set a timer to stop the automatic density control function when exposing the white light-shielding area, but in this case, the structure of the control unit becomes complicated and the magnification change In copying machines equipped with such functions, there is a problem in that accurate control is difficult because the scanning speed of the optical system changes.

In addition, in a type of device that measures and averages the original density using a pre-scan, and sets the exposure amount based on this averaged value to perform the copying operation, the average exposure amount decreases due to the presence of a white light-shielding part. However, there is a problem in that the entire image formed on the copy paper becomes dark.

(Purpose of the invention) The present invention was devised to solve the above-mentioned problems, and it is necessary to adjust the image density at the leading edge of copy paper with a simple configuration in an electrostatic copying machine equipped with an automatic density control function. The object of the present invention is to appropriately prevent the image density from becoming too dark and from increasing the image density on the entire copy paper.

(Structure of the invention) The present invention includes an optical system unit that exposes and scans a document placed on a contact glass, and a part of the document in a direction perpendicular to the scanning direction based on the exposure scan of the optical system unit. and a control means for controlling the copy density according to a detection signal outputted from the detection means, in the scanning direction of the contact glass on which the leading edge of the document is placed. Including the document leading edge reference position,
In an electrostatic copying machine in which a band-shaped white light-shielding portion is formed in a direction perpendicular to the scanning direction, at least a portion of the white light-shielding portion whose density is detected by the detection means prior to the original; A color light shielding portion whose amount of reflected light is smaller than the amount of light reflected by the white light shielding portion is provided closer to the starting end in the scanning direction than the document leading edge reference position.

With this configuration, the amount of light irradiated from the optical system portion and reflected from the chromatic light shielding portion having a small amount of reflected light is detected by the detection means, and the copy density is controlled based on this detected value. As a result, it is possible to prevent the image at the leading edge of the copy paper from becoming dark despite the provision of the white light shielding section. Further, when the density is measured by pre-scanning, it is possible to prevent the entire image from becoming dark.

(Embodiment) FIG. 1 schematically shows the internal structure of an electrostatic copying machine. In the figure, a contact glass 1 is provided on the top surface of the machine body, and inside the machine body there is an optical system section 2, a photoreceptor drum 3, and its surroundings. equipment is provided. The optical system section 2 includes a document irradiation lamp 21 and a reflector 2.
2. First to third mirrors 23 to 25, condensing lens 2
6 and a fourth mirror 27, the document irradiation lamp 21 and the like move back and forth along the lower surface of the contact glass 1, and are configured to expose the document 10 on the contact glass 1 during the forward movement.

The photosensitive drum 3 is rotationally driven in the direction of arrow X by a drum drive device (not shown). Around the photosensitive drum 3, there are a main charging section 32 having a charge wire 31, a developing section 34 having a developing roller 33, a transfer charging section 35, and a separation charging section 3.
6 and a cleaning section 37 are provided. As the photoreceptor drum 3 rotates, the main charging section 32
Charge wire 31 to which a high voltage is applied
After the surface of the photoreceptor drum 3 is charged, an original image is irradiated onto the photoreceptor drum 3 from the optical system section 2 to form an electrostatic latent image. After this electrostatic latent image is developed in the developing section 34, it is transferred to the paper feed cassette 11.
The transfer charging unit 35 transfers the image onto a transfer paper fed by the transport mechanism 12. After this transfer paper is separated from the photosensitive drum 3 by the separation charging section 36, it is sent to the fixing device 14 via the ejection belt 13, and is led out onto the paper ejection tray 15.

The optical system section 2 includes an original density detection means 2 including a photodiode or the like for detecting a part of the reflected light of the light irradiated toward the contact glass 1 from the exposure lamp 21 and reading the density of the original 10.
7 is provided. That is, as shown in FIG.
Light is irradiated from 1, and the reflected light is detected by the detection means 27. This detection signal is input to the light amount detection circuit 41 of the control means 4 and converted into a voltage signal. The voltage signal output from the light amount detection circuit 41 is input to a comparison circuit 42 and compared with a reference voltage output from a reference voltage circuit 43. For example, if the background density of the original is high and the amount of reflected light from the original is small, and the voltage signal output from the light amount detection circuit 41 is smaller than the reference voltage, the amount of light from the exposure lamp 21 is increased. A command signal is inputted to the lamp voltage generation circuit 45 via the limiting circuit 44, and a voltage corresponding to the light amount command signal is applied to the exposure lamp 21 to perform scanning exposure while controlling the amount of irradiated light. There is. The limiting circuit 44 is provided to prevent a voltage exceeding a limiting value from being applied to the exposure lamp 21 when the density of the original is extremely high, thereby preventing the lamp from burning out.

Further, the lower surface of the reference position of the contact glass 1 on which the leading edge of the original 10 is placed, that is, the optical system section 2
As shown in FIG. 3, a light shielding portion 5 is provided on the lower surface of a portion corresponding to the vicinity of the starting position.
The light-shielding portion 5 includes a white light-shielding portion 51 formed by adhering a white tape having a width a over substantially the entire width of the contact glass 1, and a portion of the contact glass 1 on which the document density detection means 27 is disposed. It consists of a gray light shielding section 52 formed on the lower surface of the white light shielding section 51 at approximately the center in the width direction. This gray light shielding part 52 is made of a tape material or the like having a width b and a length c, and is located at a position Y serving as a reference for the leading edge of the document.
It is placed further outward than the In addition, the gray light-shielding portion 52 has a brightness corresponding to the density of an average original (from N3 to
7).

Further, the gray light-shielding portion 52 is not necessarily limited to gray, but may be any colored light-shielding portion whose amount of reflected light is smaller than the amount of light reflected by the white light-shielding portion, for example, the sensitivity of the exposure sensor constituting the document density detection means 27. Any color having a wavelength outside the wavelength band can be used. In the following explanation, the case of a gray light-shielding part is cited.

The operation of the electrostatic copying machine having the above configuration will be explained below. The original 10 is placed on the upper surface of the contact glass with the leading edge of the original 10 aligned with the reference position Y of the contact glass 1. As a result, the lower surface of the leading edge of the original document 10 is covered over the length d in the scanning direction by the rear end portion of the white light-shielding portion 51, and when this portion is exposed by the optical system portion 2, the copy paper is exposed. A non-image area corresponding to the length d is formed at the tip.

Then, start the optical system section 2 and read the original 10.
At the same time, the light intensity of the reflected light is detected by the original density detection means 27, and the developing and transfer operations are performed while controlling the light intensity of the exposure lamp 21 by the control means 4 based on the detected value. When the exposure operation is started, the reflected light from the white light shielding section 51 enters the document density detection means 27, and the comparison circuit 42
Since it is determined that the amount of light is excessive in , as shown in FIG.
In this step, control is performed so that the amount of light emitted from the exposure lamp 21 is gradually reduced and then stabilized. Thereafter, when exposure of the gray light-shielding portion 52 begins, the amount of reflected light incident on the detection means 27 rapidly decreases, so a command is issued from the control means 4 to increase the voltage applied to the exposure lamp 21. Section D- corresponding to the gray light shielding part 52
At B', the amount of light irradiated from the exposure lamp 21 gradually increased and reached almost the standard amount of light without being affected by the section B'-B corresponding to the white light-shielding part having a small width d as described later. In this state, exposure of the original 10 is started from section B.

As described above, since the gray light shielding part 52 is provided in the center of the white light shielding part 51, even when the exposure operation is performed while performing automatic density control via the control means 4, the influence of the white light shielding part 51 is reduced. Accordingly, it is possible to prevent control failures from occurring when the irradiation light to the leading edge of the document decreases and the image density at the leading edge of the copy paper becomes higher. Furthermore, in the case of a device that performs a pre-scan, it is possible to prevent the entire image from becoming dark. Further, since a white light-shielding portion 51 having a length d is left in a portion corresponding to the leading edge of the document, a non-image area for preventing copy paper from wrapping is secured. In addition, the amount of reflected light increases temporarily at the length d of the white light-shielding portion 51, but this length d is sufficient if it is about 5 mm, and there is no need to make it so large. There is no control to reduce the amount.

In the above embodiment, a case has been described in which the copy density is controlled by changing the light amount of the exposure lamp 21, but in an apparatus configured to control the copy density by changing the bias voltage of the developing section 34. The configuration of the present invention can also be applied. In addition, by applying paint to the lower or upper surface of the contact glass 1, the white light shielding portion 51 can be
A gray light shielding portion 52 may also be formed. Further, the position, size, etc. of the gray light-shielding portion 52 can be varied as necessary, and the gray light-shielding portion 52 may be configured to exist at least in a portion corresponding to the detection position of the document density detection means 27. Bye.

Further, the present invention can be applied not only to copying machines of the above optical system traveling type but also to document table traveling types.

(Effects of the invention) The present invention provides at least a portion of the white light-shielding portion on the contact glass whose density is detected prior to the document by the detection means, and which is located on the starting edge side in the scanning direction from the document leading edge reference position. Even with a simple configuration in which a colored light shielding part is provided whose amount of reflected light is smaller than the amount of light reflected by the white light shielding part, it is possible to prevent the leading edge of the copy paper from wrapping around the fixing roller, and to sequentially control the copy density. When the exposure operation is performed using automatic density control, the amount of light irradiated to the leading edge of the document will not be reduced due to the influence of the white light-shielding area, and therefore the image at the leading edge of the copy paper will become dark. Furthermore, in an apparatus that measures document density by pre-scanning, problems such as darkening of the entire copied image do not occur, and appropriate automatic density control becomes possible. Moreover,
There is no need to adopt a complicated structure such as installing a timer to stop the copy density control function of the part corresponding to the white light shielding part, and it is possible to always perform appropriate control even in a device equipped with a variable magnification function. This has the advantage that.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing an embodiment of an electrostatic copying machine according to the present invention, FIG. 2 is a block diagram showing an embodiment of the control means, and FIG. 3 is a bottom view showing an embodiment of the light shielding part.
FIG. 4 is a characteristic diagram showing the exposure amount during the exposure operation according to the present invention, and FIG. 5 is a characteristic diagram showing the exposure amount during the exposure operation using the conventional apparatus. 1...Contact glass, 2...Optical system section, 4
...Controlling means, 27...Document density detection means, 51
...White light shielding part, 52...Gray light shielding part.

Claims (1)

[Scope of Claim for Utility Model Registration] 1. An optical system unit that exposes and scans a document placed on a contact glass, and based on the exposure scan of the optical system unit, a part of the document in a direction perpendicular to the scanning direction. and a control means for controlling the copy density according to a detection signal outputted from the detection means, in the scanning direction of the contact glass on which the leading edge of the document is placed. In an electrostatic copying machine in which a band-shaped white light-shielding portion is formed in a direction perpendicular to the scanning direction including a document leading edge reference position, the density of the white light-shielding portion is detected prior to the document by at least the detection means. 1. An electrostatic copying machine, characterized in that a color light shielding part is provided on the starting edge side in the scanning direction of the original document leading edge reference position, the amount of reflected light being smaller than the amount of light reflected by the white light shielding part. 2. The electrostatic copying machine according to claim 1, wherein the color light-shielding portion is a gray light-shielding portion having a brightness corresponding to the density of an average original. 3. The electrostatic copying machine according to claim 1, wherein the color light-shielding portion has a color having a wavelength outside the sensitivity wavelength band of the detection means. 4. The stationary device set forth in claim 1 of the utility model registration claim, characterized in that the detection means for detecting the density of the original is configured to detect the amount of reflected light when the original is exposed by an optical system section. Electric copying machine. 5. The electrostatic copying machine according to claim 1, wherein the control means is configured to control the amount of light from the exposure lamp in order to control the copy density. 6. The control means includes a light amount detection circuit that receives a detection signal from the document density detection means and converts it into a voltage signal, a reference voltage circuit, and a voltage signal output from the light amount detection circuit and the reference voltage circuit. a comparison circuit that compares the reference voltage output from the exposure lamp with a reference voltage, a limiting circuit that prevents a voltage exceeding a limit value from being applied to the exposure lamp, and a lamp voltage generator that receives the output of the comparison circuit and determines the amount of light from the exposure lamp. An electrostatic copying machine according to claim 5, characterized in that the electrostatic copying machine is comprised of a circuit. 7. The electrostatic copying machine according to claim 1, wherein the control means is configured to control the bias voltage of the developing section in order to control the copy density.