JP2737009B2 - Image forming device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an image forming apparatus using an electrophotographic method, such as a copying machine and a laser beam printer.

(Prior Art) Conventionally, as this type of apparatus, for example, the one shown in FIG. 6 is known. That is, in this apparatus, the surface of a photosensitive drum 101 as an image carrier uniformly charged by a primary charger 100 is irradiated with image light 102 guided by an optical system (not shown) for scanning a document. To form an electrostatic latent image. On the other hand, the developing device 103 contains a one-component developer 103a. The developer 103a is electrostatically attracted to a surface of a sleeve 103b as a developer holding member to which a developing bias is applied, and is rotated in a direction indicated by an arrow.
The photosensitive drum 101 is conveyed to the photosensitive drum 101, and adheres to the electrostatic latent image portion to perform development.

The development proceeds to the transfer section a by the rotation of the photosensitive drum 101 in the direction of the arrow, and is transferred by the transfer charger 104 onto the transfer paper b conveyed at a timing by the paper supply means 106, and then transferred to the transfer means 107. Is transported to a fixing unit (not shown).

The developer 102 remaining on the surface of the photosensitive drum 101
Is scraped off and collected by the cleaner 105, and is reused.

(Problems to be Solved by the Invention) However, in the above-described conventional example, the development characteristics formed on the surface of the photosensitive drum 1 change depending on the image ratio of the document. That is, there is no problem in the case of a document having a high image ratio, but in the case of a document having a low image ratio, the consumption of the developer 103a is extremely small.
The developer 103a that stays for a long time on the surface of 3b is present, and the developer 103a has a very strong electrostatic attraction to the sleeve 103b.

As a result, there is a problem that the developer 103a does not easily adhere to the electrostatic latent image formed on the surface of the photosensitive drum 101, and the developing density is reduced. This problem was particularly remarkable when a high resistance having negative polarity electric charge, which is the intrinsic tribo characteristic of the resin, that is, an insulating developer having a small proportion of a magnetic material was used.

An object of the present invention is to solve the above-mentioned problem, and to prevent the developer from staying in the sleeve for a long time due to a change in development characteristics formed on the image carrier and increasing the electrostatic attraction force. It is intended to provide a forming apparatus.

(Means for Solving the Problems) In order to achieve the above object, the present invention provides an image carrier on which an electrostatic latent image is formed, and an image carrier for developing the electrostatic latent image on the image carrier. An image forming apparatus having an opposing developer holding member, the image forming apparatus having a detecting unit for detecting a characteristic related to a consumption amount of the developer in the image forming, and detecting that the detected value by the detecting unit is smaller than a standard value. A control means for forcibly consuming the developer on the developer holding member in the non-image area of the image carrier based on the detection value when the detection is performed is provided.

(Operation) According to the operation of the present invention based on the above configuration, first, an electrostatic latent image is formed on the surface of the image carrier. This electrostatic latent image is developed by the developing material held by the developer holding member. The detecting means detects a characteristic related to the consumption amount of the developer. A predetermined amount of the developer held by the developer holding member is forcibly consumed in the non-image forming area of the image bearing member based on the detection value of the detecting means, and is removed from the developer holding member.

(Embodiment) Next, the present invention will be described with reference to FIG. 1 to FIG.

FIG. 2 is a schematic configuration diagram of an image forming apparatus to which the present invention is applied. In the figure, reference numeral 1 denotes a photosensitive drum as an image carrier, and the photosensitive drum 1 rotates in the direction of an arrow. Around the photosensitive drum 1, a primary charger 2, a developing device 3, a transfer / separation charger 4, a cleaner 5, a neutralizing lamp 6, and an LED for erasing charges in a non-image forming area on the surface of the photosensitive drum 1. A so-called blank exposure lamp (removal means) 15a composed of a lamp array is provided.

The developing unit 3 contains a one-component magnetic developer 3a. Reference numeral 9 denotes a cylindrical sleeve as a developer holding member;
Is a magnet arranged in the sleeve 9, and 15c is a doctor blade. The sleeve 9, doctor blade 15
c is connected to a high-voltage power supply (developing bias means 15b described later), and alternately (vibration) such as AC, AC + DC (sine wave, rectangular wave)
It is configured so that a voltage can be applied.

8a is a position facing the photosensitive drum 1, and
A toner sensor as a detecting means 8 provided between the separation charger 4 and the cleaner 5. The toner sensor 8 a detects a developing characteristic (density) formed on the surface of the photosensitive drum 1. The toner sensor 8a can be satisfied by using a known reflective photocoupler or the like.

In the drawing, reference numeral 12 denotes a feeding unit for feeding the transfer paper P to the transfer unit B, and 13 denotes a conveying unit.

FIG. 1 is a block diagram showing a main circuit configuration of the present invention. The detection means 8 for detecting the development characteristics is connected to a CPU 14 having a control unit and a calculation unit. Further, the removing unit 15 is connected to the CPU 14 via the driving unit 16. Note that 17
Is an external memory connected to the CPU 14.

Next, the operation of the above embodiment will be described with reference to the flowchart of FIG.

First, when a copy button (not shown) is turned on (step), image light A illuminating a document (not shown) is guided to the surface of the photosensitive drum 1 to form an electrostatic latent image. This electrostatic latent image is developed by the developer 3a electrostatically attracted to the surface of the sleeve 9 to which a voltage is applied from the developing bias means 15b, and is transferred to the transfer section B by rotation of the photosensitive drum 1. Then, this developing is performed on the transfer paper P fed by the feeding means 12 in a timely manner on the transfer / separation charger 4.
After the transfer (step), the transfer paper P is separated from the photosensitive drum 1 and is conveyed to the fixing means (not shown) by the conveying means 13. Then, the residual image agent 3a remaining on the surface of the photosensitive drum 1 is scraped off by the cleaner 5, and thereafter, the same image forming operation is repeated.

During the above operation, during the pre-rotation or post-rotation of the photosensitive drum 1 at which the image forming operation starts or ends, the blank exposure lamp 15a is turned on while the image light A is turned off,
Although unnecessary charges in the non-image forming area are erased,
During this time, the blank exposure lamp 15a is turned off for a predetermined time on the surface of the photosensitive drum 1 at least at a position corresponding to the toner sensor 8a to form a standard dark area potential of a predetermined area in the non-image forming area (step). Then, this is developed (step) by the developing device 3. Then, the density of the development is detected by the toner sensor 8a, and is stored in the external memory 17 as a standard density.

Thereafter, in the image forming operation to be performed, the developing density on the photosensitive drum 1 is detected (step) by the toner sensor 8a, and the detected density is compared with the standard density in the external memory 17; When the image ratio of the document is small and the consumption of the developer 3a is small), the dark exposure potential is formed in the non-image forming area of the photosensitive drum 1 by turning off the blank exposure lamp 15a. 3a
May be removed by adhering to the photosensitive drum 1 or the sleeve 9 may be formed regardless of the formation of the dark potential region.
The developer 3a on the sleeve 9 is forcibly developed (stepped) and removed by forcibly applying a DC voltage having the same polarity as the charging polarity from the developing bias means 15b applied to the sleeve 9 to the sleeve 9. If the detected density is higher than the standard density, the normal developing operation may be continued.

In this way, even for a document having a small image ratio, the developer 3a held on the sleeve 9 is consumed by an appropriate amount. Therefore, it is possible to prevent the developer 3a from staying for a long time to increase the electrostatic attraction force to the sleeve 9,
The developing density formed on the surface 1 of the photosensitive drum 1 becomes stable.

FIG. 4 shows another embodiment. This is because, when the image ratio of the original is low (the consumption of the developer 3a is small), the developing characteristic is deteriorated. If it is lower, the developer 3a on the sleeve 9 is removed in the same manner as described above. That is, the potential of the electrostatic latent image formed on the photosensitive drum 1 is located between the opening 20 where the image light A of the document is irradiated onto the surface of the photosensitive drum 1 and the developing device 3 and in the vicinity of the photosensitive drum 1. A potential sensor 8b is provided as a detecting means 8 for measuring, and a latent image potential is stabilized by controlling a dark portion potential and a bright portion potential. Other configurations are the same as in the above embodiment.

In this embodiment, the standard potential measured by the potential sensor 8b is stored in the external memory 17 in advance. Then, the copy button is turned ON (step) and the copying operation is started (step) in the same manner as described above, and the potential of the electrostatic latent image detected (step) by the potential sensor 8b is higher than the standard potential in the external memory 17. If it is low, the developer 3a on the sleeve 10 is operated in the non-image forming area when the photosensitive drum 1 is rotated at the end of the copying operation or at the start of the copying operation (step), and the developing bias means 15b is operated in the same manner as described above. (Step) to forcibly move the photosensitive drum 1 to the surface.

If the potential of the surface of the photosensitive drum 1 detected by the potential sensor 8b in the step is higher than the standard potential, the copying operation ends (step).

If the detected average potential is lower than the standard potential and the frequency is higher than a predetermined value, the developer 3a on the sleeve 10 is forcibly attached to the non-image forming area during the standby until the apparatus is started again the next morning. It may be configured as follows. Further, the developing device 3 using the one-component developer 3a is provided with a remaining amount detecting means 8c for detecting the remaining amount of the normal developer.
Developer 3a from a hopper container (not shown)
Is provided to the developing device 3. In this case, the frequency of the signal of the remaining amount detecting means 8 may be detected, and if appropriate, the developer 3a on the sleeve 10 may be attached to the non-image area and removed as described above.
Further, the amount of reflected light of the original can be detected by an appropriate detecting means, and in a copying machine having an automatic original exposure function, the amount of reflected light can be used as a substitute for the image ratio.

In the above embodiment, the toner sensor 8a, the potential sensor 8b, and the remaining amount detecting sensor 8c as the detecting unit 8 corresponding to the blank exposure lamp 15a as the removing unit 15 and the developing bias unit 15b may be provided collectively. Alternatively, the corresponding removing means 15 and detecting means 8 may be provided independently.

(Effect of the Invention) Since the present invention is configured as described above, the developer holding member holds the developer based on the detection value of the characteristic related to the consumption of the developer in the image formation detected by the detection unit. The developing agent is forcibly consumed in the non-image forming area on the image carrier and is appropriately removed from the developer holding member, and the electrostatic attraction force to the developer holding member becomes extremely strong. I won't. Therefore, an excellent effect that an image having a stable development density can be always formed on the image carrier is exhibited.

[Brief description of the drawings]

1 to 5 show an embodiment of the present invention, FIG. 1 is a block diagram showing a main circuit configuration, FIGS. 2 and 4 are front sectional views showing a schematic configuration, and FIGS. FIG. 6 is a flowchart showing the operation, and FIG. 6 is a front sectional view showing a schematic configuration of a conventional example. DESCRIPTION OF SYMBOLS 1 ... Photosensitive drum (image carrier) 3a ... Developer 8 ... Toner sensor, potential sensor, remaining amount detection means (detection means) 9 ... Sleeve (developer holding body) 15 ... Blank exposure Lamp, developing bias means (removal means)

Claims (1)

(57) [Claims] An image forming apparatus comprising: an image carrier on which an electrostatic latent image is formed; and a developer holding member facing the image carrier for developing the electrostatic latent image on the image carrier. A detecting unit for detecting a characteristic related to a consumption amount of a developer in image formation; and when detecting that a detection value by the detecting unit is smaller than a standard value, the image carrier based on the detection value. An image forming apparatus comprising: a control unit for forcibly consuming the developer on the developer holding member in the non-image area.