JPH0695508A - Copying machine - Google Patents

Abstract

PURPOSE:To shorten FCOT by using a different criterion for patch display for the first copy from that for the second and subsequent copies. CONSTITUTION:A control portion 43 compares a patch density signal given from an A/D convertor 47 with a first threshold X1 stored on a threshold table 55. The first threshold X1 is exclusively for the first copy and greater than a normal threshold (second threshold X2). For the first copy, rotation of a photoreceptor drum 20 is slow so that the amount of electrification by a charged electrode 21 increases, generally resulting in density enhancement; to prevent the density from being enhanced, i.e., to make the density equal to that for the second and subsequent copies, the threshold X1 is made greater so that the amount of supply of toner is reduced. For the first copy, copying operation is therefore started before the photoreceptor drum 20 reaches a constant rate, and so FCOT is shortened.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a copying machine, and more particularly to FCOT (First Copy Out Tim).
The present invention relates to a copying machine designed to shorten the item e).

[0002]

2. Description of the Related Art FIG. 5 is a diagram showing an example of a conventional structure of a copying machine. At the center of the upper portion of the main body of the copying machine, a transparent glass original placing table 1 on which the original D is placed is arranged. At the left end of the original placing table 1, a scale plate 2 for designating the placing position according to the size of the original D is placed. Is provided. Further, an original cover 3 for covering the placed original D is provided on the original placing table 1 so as to be tilted forward.

The original D is placed on the original table 1 on the scale plate 2
The original cover 3 is placed according to the scale specified by
The movement is restricted by being covered with. A display unit 4 using a reflective liquid crystal is arranged near the intermediate position on the lower surface side of the scale plate 2.

A first mirror unit 12 having an exposure lamp 10 and a first mirror 11 is provided below the original placing table 1 and inside the main body of the copying machine. The first mirror unit 12 is parallel to the original placing table 1 and in the left-right direction in the drawing. It is provided so as to be linearly movable to, so that the entire surface of the document D can be scanned. The second mirror unit 15 configured by integrating the second mirror 13 and the third mirror 14 is arranged at a speed half that of the first mirror unit 12 in the left-right direction and in the left-right direction so as to maintain a predetermined optical path length. It can be moved linearly in parallel to the mounting table 1.

The main lens 16 is used for the document D on the document placement first.
Is a lens which is incident after being reflected by the first mirror 11, the second mirror 13 and the third mirror 14, and the light emitted from the main lens 16 is passed through the fourth mirror 17 to serve as an image support. Slit 1 on the photoconductor drum 20 of
It is designed to be incident via 8.

The strip electrode 21 serves to uniformly charge the photosensitive drum 20. Therefore, the photosensitive drum 20 that rotates clockwise due to the incidence of light from the optical system.
An electrostatic latent image will be sequentially formed on the top. The developing device 22 converts the electrostatic latent image on the photosensitive drum 20 into a visible toner image.

On the other hand, the sheet feeding device for feeding the transfer sheet is a sheet feeding cassette 23 for storing the transfer sheet P (two are shown here).
A first paper feed roller 24 for feeding the transfer paper P one by one from the paper feed cassette 23; a second paper feed roller 25 for feeding the fed transfer paper P to the photosensitive drum 20 side;
The guide plates 26 and 27 are arranged between the paper feeding cassette 23 and the second paper feeding roller 25 and between the second paper feeding roller 25 and a transfer pole described later.

At the time of copying, the selected paper feed cassette 23
The transfer paper P inside is fed out by the first paper feed roller 24,
Although guided by the guide plate 26 to the second paper feed roller 25, the second paper feed roller 25 has a timing such that the leading edge of the toner image on the photosensitive drum 20 and the leading edge of the transfer paper P coincide with each other. Driven by.

The transfer pole 28 transfers the toner image on the photoconductor drum 20 onto the transfer paper P, and the separation pole 29 separates the transfer paper P from the photoconductor drum 20. The transfer paper P separated by the separation electrode 29 passes through a transfer paper transporting means 30 and a fixing device 31.
Then, after being melted and fixed by the heat fixing roller and the pressure bonding roller, the sheet is discharged onto the sheet discharge tray 33 by the sheet discharge roller 32.

After the transfer process, the photosensitive drum 20
Is subjected to a cleaning device 34 to remove residual toner present on the drum surface. Then, the residual toner existing on the surface is scraped off by the blade 34a in the cleaning device 34. In this case, in order to facilitate the removal of the residual toner, a cleaning removal electrode 35 that performs AC corona discharge is provided in the front portion thereof. Further, a charging erasing section 36 for erasing the non-image area with light is arranged at the rear of the strip electrode 21 so as to face the photoconductor drum 20. Reference numerals 37 and 38 are a pre-charge exposure lamp and a pre-transfer exposure lamp, respectively. Pre-transfer exposure lamp 38
Is also called PTL and is a lamp for increasing the transfer efficiency.

Next, the toner density control operation before entering the copy mode will be described. FIG. 6 is an explanatory diagram of toner density control. The same parts as those in FIG. 5 are designated by the same reference numerals. In the figure, reference numeral 51 is a patch attached to the back surface of the scale plate 2 as a reference for toner density adjustment. The patch 51 is applied to a certain standard density. The optical system 50 is configured to include the first mirror unit 12 and the second mirror unit 15 shown in FIG.

Now, the patch 51 is irradiated with the exposure lamp 10. The reflected light is transmitted through the optical system 50 to the mirror 17
The surface of the photoconductor drum 20 is exposed. This allows
An electrostatic latent image of the patch 51 is formed on the drum surface. When the photoconductor drum 20 rotates and reaches the position of the developing device 22,
Toner is attracted to the electrostatic latent image of the patch 51 and the patch image 5
1a is formed.

This patch image rotates clockwise and reaches the bottom of the cleaning device 34. In this portion, the light emitting element 41 and the light receiving element 42 are arranged at predetermined positions. As the light emitting element 41, for example, a light emitting diode (L
ED) is used, and as the light receiving element 42, for example, a phototransistor is used. The patch image 51a is emitted from the light emitting element 41, and the reflected light enters the light receiving element 42.
The light receiving element 42 generates an electric signal (density signal) according to the density of the patch image.

This density signal enters the controller 43 and is compared with a predetermined reference value. Then, a toner density control signal according to the comparison result is output from the control unit 43 and fed back to the toner replenishment motor 44. That is, when the density of the patch image measured by the light receiving element 42 is higher than the reference value, the toner is not replenished, and when the density of the patch image is lower than the reference value, the toner replenishment motor 44 is driven and the toner replenishment unit 45 is operated. Toner is supplied to the developing device 22. In this way, the toner density is controlled to be constant.

[0015]

The toner density changes depending on the potential applied to the surface of the photosensitive drum from the strip electrode 21 and the exposure amount of the PTL 38 disposed below the developing device 22. For example, at the start of copying, it takes time for the photosensitive drum 20 to reach a constant speed, but during this period, since the rotational speed of the photosensitive drum 20 is slow, the potential on the drum surface rises, so that the developing device 22 causes the drum surface to move. The amount of toner adsorbed on the toner increases and the density increases.

Therefore, in the conventional apparatus, the toner density control is performed after the rotation of the photosensitive drum 20 reaches a constant speed. Therefore, there is a problem that it takes time to start copying.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a copying machine capable of shortening FCOT.

[0018]

According to the present invention for solving the above-mentioned problems, the output of a patch density detecting section for detecting the density of a patch image is detected in the step of performing the toner density control in the stage before shifting to the copy mode. In a copying machine that compares a predetermined patch density determination reference value and controls the toner density supply amount to the developing device in accordance with the comparison result, when copying the first sheet and the second sheet It is characterized in that the patch density determination reference value is changed at the time of the subsequent copying and the threshold value is made high at the time of the first copy so that a copied image having a constant density can be obtained.

[0019]

As described above, at the time of copying the first sheet, it takes time for the photosensitive drum to reach a constant speed. Therefore, if waiting until then, the FCOT does not become short. Therefore, copying is started at a stage before the photosensitive drum reaches a constant speed, that is, at a stage when the rotation of the drum is slow. Therefore, in the toner density control stage, the reference value for comparing the densities of patch images is set higher than the reference values for the second and subsequent sheets. As a result, toner is not replenished until the density of the patch image exceeds the reference value, so that it can be matched with the copy density of the second and subsequent sheets. As a result, the copying operation can be started before the photosensitive drum reaches a constant speed, and FCOT can be accelerated.

[0020]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention. The same parts as those in FIG. 6 are designated by the same reference numerals. In the figure, 51 is a patch provided on the back surface of the scale plate 2, 41 is a light emitting element for irradiating the patch image 51a formed on the surface of the photosensitive drum 20, and 42 is the patch image 5
The light receiving element receives the reflected image from 1a. As described above, the light emitting element 41 is, for example, a light emitting diode, and the light receiving element 42 is, for example, a phototransistor.

Reference numeral 46 is an amplifier for amplifying the output of the light receiving element 42, and 47 is an A / D converter for receiving the output (analog signal) of the amplifier 46 and converting it into a digital signal. The output of this A / D converter 47 enters the control unit 43. In the control unit 43, 55 is a threshold value table that stores the first threshold value X1 and the second threshold value X2 of the toner density. Control unit 4
The output of No. 3 is fed back to the toner replenishment motor 44, and the toner replenishment motor 44 drives the toner replenishment section 45 to control the on / off of toner replenishment. The operation of the apparatus configured as described above will be described below.

Now, assume that the copy button (not shown) is pressed. A short time after the copy button is pressed, the photosensitive drum 20 starts rotating. On the other hand, in the optical system, the patch 51 is irradiated with the exposure lamp 10. The reflected light exposes the surface of the photoconductor drum 20 from the mirror 17 via the optical system 50. As a result, the patch 51 is
Electrostatic latent image of is formed. When the photoconductor drum 20 rotates in the clockwise direction shown in the figure to reach the position of the developing device 22, toner is adsorbed to the electrostatic latent image of the patch 51 to form a patch image 51a.

This patch image rotates clockwise and reaches the bottom of the cleaning device 34. The patch image 51a is emitted from the light emitting element 41, and the reflected light enters the light receiving element 42. The light receiving element 42 generates an electric signal (density signal) according to the density of the patch image.

This density signal is amplified by the amplifier 46 and then enters the A / D converter 47 to be converted into a digital signal. This digital density signal enters the control unit 43. The control unit 43 compares the patch density signal given from the A / D converter 47 with the first threshold value X1 stored in the threshold value table 55. Here, the first threshold value X1 is a threshold value dedicated to the first copy, and is a normal threshold value (second threshold value X2).
Is taken larger than. Since the rotation of the photosensitive drum 20 is slow at the time of copying the first sheet, the charge amount by the band electrode 21 increases, and the density generally increases. Therefore, in order to prevent the density from increasing, that is, in order to make it equal to the copy density of the second and subsequent times, the threshold value X1 is increased and the toner density supply amount is decreased.

FIG. 2 is a diagram showing the relationship between the threshold value and toner supply. X1 is used as a threshold when copying the first sheet.
When the patch density is higher than X1, toner is not replenished, and when the patch density is lower than X1, toner is replenished. Also, when copying the second and subsequent sheets,
X2 (X1> X2) is used as the threshold. When the patch density is higher than X2, the toner is not replenished, and when the patch density is lower than X2, the toner is replenished.

If the measured density signal is smaller than the threshold value X1, the control unit 43 activates the toner replenishment motor 44 to replenish the toner from the toner replenishment unit 45. As a result, the toner density is controlled in the direction of increasing the density.

On the other hand, when the measured patch density signal is larger than the first threshold value X1, the controller 43 does not activate the toner replenishment motor 44. That is, the toner is not replenished. As described above, the toner density control by the control unit 43 is an on / off control as to whether or not toner is replenished.

At the time of copying the first sheet, the copying operation is performed before the rotation of the photosensitive drum reaches a constant speed.
The change in density due to this is dealt with by controlling copy density so that it does not change. In this way, according to the present invention, the copying operation is started before the photosensitive drum reaches the constant speed, so that FCOT is shortened.

At the time of copying the second and subsequent sheets, the second threshold value X2 is used as a reference value. At this time, the photosensitive drum 2
The rotation of 0 is a constant speed. Then, when the measured density signal is smaller than the threshold value X2, the control unit 43 activates the toner replenishment motor 44 to replenish the toner from the toner replenishment unit 45. As a result, the toner density is controlled in the direction of increasing the density.

On the other hand, the measured patch density signal is the threshold value X2.
If it is larger than this, the control unit 43 does not activate the toner replenishment motor 44. That is, the toner is not replenished. In this way, a copy image having a constant density can be obtained.

FIG. 3 is a flow chart showing the operation of the present invention. First, it is checked whether it is the first copy (S1). If it is the first sheet, the measured density value> X
It is checked whether it is 1 (S2). If this is the case, the density is too high, so toner is not replenished (S3). When the density measurement value <X1, the density is low, so toner is replenished (S
4).

In step S1, if it is the second or subsequent sheet, it is checked whether the density measurement value> X2 (S5). If this is the case, the density is too high, so toner is not replenished (S7). If the density measurement value <X2, the density is low, so toner is replenished (S8).

FIG. 4 is a time chart showing the operation of the present invention. (A) shows the state of the photoconductor drum, and (b) shows the operating state of the charger or the PTL 38. It is assumed that the copy button is pressed at time t1 to start copying. Then, at a time t2 after a lapse of a predetermined time, the drum is turned on and starts rotating. Then, at time t3 before the rotation of the drum reaches a constant speed, the first patch image forming process is performed, and then the first image forming process is performed. Then 2
The patch image formation processing for the first sheet is performed, and the image formation processing for the second sheet is performed. The same applies hereinafter.

Needless to say, the present invention can be applied to both monochromatic copying machines and color copying machines.

[0035]

As described above in detail, according to the present invention, it is possible to provide a copying machine capable of shortening FCOT.

[Brief description of drawings]

FIG. 1 is a configuration block diagram showing an embodiment of the present invention.

FIG. 2 is a diagram showing a relationship between a threshold value and toner density.

FIG. 3 is a flowchart showing the operation of the present invention.

FIG. 4 is a time chart showing the operation of the present invention.

FIG. 5 is a diagram showing a conventional configuration example of a copying machine.

FIG. 6 is an explanatory diagram of toner density control.

[Explanation of symbols]

 1 Document Placement Table 10 Exposure Lamp 20 Photosensitive Drum 21 Band Electrode 22 Developer 27 Transfer Electrode 34 Cleaning Device 38 PTL 41 Light Emitting Element 42 Light Receiving Element 43 Control Section 44 Toner Supply Motor 45 Toner Supply Section 46 Amplifier 47 A / D Converter 50 optical system 51 patch 51a patch image

Claims (1)

[Claims] 1. In a step of performing toner density control in a stage before shifting to a copy mode, an output of a patch density detecting section for detecting the density of a patch image is compared with a predetermined reference value for patch density determination. In a copying machine in which the toner density supply amount to the developing device is controlled according to the comparison result, the patch density determination reference value is set for the first copy and the second and subsequent copies. Change, when copying the first sheet,
A copying machine characterized in that a copy image having a constant density can be obtained by increasing the threshold value.