JPH0375674A - Developing device - Google Patents

Abstract

PURPOSE:To always inform correct toner replenishing timing by detecting a current flowing between a developer carrier and an image carrier at a developing position and judging whether or not a toner concentration drops to a tolerance or below, based on the detected current position. CONSTITUTION:A developing device is provided with a developer carrying means 2 carrying toner (d) along a prescribed route including a developing region, a developing bias source 8 applying a bias voltage to the developer carrying member 2, a current detecting means 7 detecting the value of a current flowing into the developer carrying member 2 from the developing bias source 8, a concentration deciding means 9 deciding whether the toner concentration in the toner (d) is high or low based on the detected current value of the current detecting means 7, and a means informing a result decided by the concentration deciding means 9. A signal generating circuit 10 serving as the informing means generates a signal indicating the decided result to an optical writer/printer control part 11. Thus, the lack of the toner (d) can be always and correctly detected and informed regardless of the presence of absence of the toner (d).

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a developing device using magnetic toner.

[Prior art and its problems]

Dry developing methods can be roughly divided into two-component developing methods that use a two-component developer consisting of toner and carrier, and one-component developing methods that use a one-component developer that does not contain a carrier. The latter one-component development method does not require precise control of toner density as does the former two-component development method. Therefore, there is no need to provide a toner degree detection means or a mechanism for replenishing toner based on the detected value, and the developing device becomes small and simple.

An example of a conventional developing device is shown in FIG. The developing device of this example uses developer d, which is a mixture of magnetic toner and magnetic particles. The developer d is conveyed to the development position Pd by the development sleeve 42 containing the magnet 41, where the toner is transferred to the acid 7! formed on the surface of the photoreceptor drum 43. Supplies the latent image and develops it. In this case, the appropriate range of the toner concentration in the developer d is 50 to 95 wt%, which allows for a considerably wider allowable range than in the two-component development system. Therefore, the developer management mechanism may be simpler than in the two-component development system, and a method is usually adopted in which the toner concentration is estimated from the remaining amount of developer. In this example, a piezoelectric sensor 45 is installed at the bottom of the toner hopper 44, and when the remaining amount of developer d decreases from level 1 to level L2, the piezoelectric sensor 45 indicates that the toner is insufficient. A signal is emitted. In response to this 1 toner out signal, for example, a 'toner out 9' display is displayed on the operation panel, and the user who sees this displays toner and replenishes toner.

In the case of the above-mentioned development device, although the developer management mechanism is simple, the piezoelectric sensor 45 is relatively expensive, and the wiring structure from the piezoelectric sensor 45 is as complicated as in the two-component development method. Requires considerable installation space. As a result, −
Even though a developing method similar to the component developing method is adopted, the developing device becomes larger. In addition, the piezoelectric sensor 45 is normally arranged at the center of the developing device in the longitudinal direction (axial direction of the developing sleeve), but if the residual developer is biased to either the left or right side, it can be Unable to detect amount. Specifically, even though there is still enough developer d left,
'No toner' signal may be emitted. In particular, as the image forming apparatus becomes larger and the developing device becomes longer, the above-mentioned remaining amount detection failure is more likely to occur.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a small and inexpensive developing device that can always accurately detect and notify a toner shortage condition regardless of the presence of developer.

[Key points of the invention]

In order to achieve the above object, the present invention provides a developing device that uses a developer made of a mixture of insulating magnetic toner and conductive magnetic particles, in which the developer is conveyed along a predetermined path including a developing area. A developer transporting member, a developing bias power supply that applies a bias voltage to the developer transporting member, a current detection means that detects a current value flowing from the development bias power supply to the developer transporting member, and a detection current of the current detection means. The main feature of the present invention is to include a concentration determination means for determining whether the toner concentration in the developer is high or low based on the value, and a means for notifying the determination result by the concentration determination means.

[Embodiments of the invention]

Embodiments of the present invention will be described in detail below with reference to FIGS. 1 to 3.

FIG. 1 is a schematic cross-sectional view showing a developing device used in an optical writing printer as an embodiment of the present invention. In this example, the average particle size of the developer d containing the magnetic component is 14
Insulating magnetic toner of about μm and average particle size of about 10 μm
A material prepared by mixing conductive magnetic particles with a volume resistivity of 10'Ω and am is used. A developer supply opening 1a is formed diagonally below the hopper 1 for temporarily storing the developer d. A developing sleeve 2 serving as a developer conveying member is rotatably disposed in this developer supply opening 1a. The developing sleeve 2 is driven and rotated at a predetermined speed in the direction of arrow A by a drive device (not shown). A draught blade 3 as a layer thickness regulating member is disposed above the developing sleeve 2. The drata blade 3 has its sharpened end close to the surface of the developing sleeve 2 over substantially the entire width direction (axial direction), and its opposite end is fixed to the hopper casing 1b.
It is supported vertically. A gap G maintained between the tip of the doctor blade and the upper peripheral surface of the developing sleeve 2 regulates the layer thickness of the developer d. That is, the developer d, which moves following the rotation of the developing sleeve 2, is forced to pass through the gap '/AG, thereby being thinned to a predetermined layer thickness. As the developing sleeve 2 rotates, the thinned developer is conveyed to a developing position Pd closest to the surface of the photoreceptor drum 4, where it is used to develop an electrostatic latent image.

Inside the hopper 1, a developer stirring member 5 is rotatably disposed. The developer stirring member 5 of this example is rotated at a predetermined speed in the direction of arrow B by a drive device (not shown) about the shaft 5a. As a result, the developer d stored at - time is stirred, its coagulation and solidification are prevented, and the magnetic toner is triboelectrically charged to a predetermined polarity.

A toner supply port 1C is formed above the developer stirring member 4. This toner supply port IC is covered with a lid 6 so as to be openable and closable. When replenishing magnetic toner, use the M6
Open it and put it in.

A developing bias power source 8 is connected to the developing sleeve 2 via a current detection circuit 7. As a result, a developing bias voltage is applied to the developing sleeve 2, and the developing position Pd
A developing electric field can be formed. Along this developing electric field, magnetic toner is selectively transferred from the thin developer layer being conveyed to the electrostatic latent image on the surface of the photoreceptor drum 4, and the electrostatic latent image is developed.

The current detection circuit 7 includes a comparison calculation circuit 9 and a signal generation circuit 1.
0 are connected in series. The current detection circuit 7 detects the current supplied to the developing sleeve 2 (referred to as a developing current).

The comparison calculation circuit 9 compares the detected developing current with a reference current stored in advance, and determines whether the toner concentration of the developer exceeds an allowable lower limit value. The theory on which this determination is based will be explained in the eleventh section. The signal generation circuit 10 transmits a signal representing the determination result of the comparison calculation circuit 9 to the optical writing printer control section 11. Printer control unit 11
When receiving the signal 'No Toner 9', a display to that effect is displayed on the operation panel (not shown).

Here, a theory for determining whether the developer d is in a ``toner-free'' state and an operation based on the theory will be explained.

FIG. 2 is a schematic explanatory diagram showing the developing current i3. In the figure, the developing current i3 can be divided into two types of currents 11+12 at the developing position Pd. One is the toner current i+ that flows when the charged magnetic toner t is transferred along the development electric field, and the other is the toner current i+ that flows due to the transfer of the charged magnetic toner t along the development electric field. This is an electric field current 12 that flows due to a decrease in the electrical resistance value of the developer R layer.

As the toner is consumed as printing is repeated and the toner concentration in the developer d decreases, the proportion of conductive magnetic particles present in the developer d increases and the electrical resistance value decreases. As the electrical resistance value of the developer d decreases, the electric field current 12 increases and the development current i3 increases. Therefore, the toner density can be estimated from the value of the developing current i3.

Figure 3 shows the above three types of current 1 with respect to toner concentration.
FIG. 3 is a graph diagram showing each change characteristic of trl 2+13. From this, the toner current 11 has a toner concentration of 63 to 9.
It can be seen that it is approximately constant (2, OμA) in the range of 0 vt%, and rapidly decreases when the toner concentration becomes 60 wt% or less. Further, the electric field current 12 increases rapidly as the toner concentration decreases.

Therefore, the developing current i3, which is the sum of the toner current il and the electric field current 12, changes approximately along the electric field current i2 when the toner concentration is in the range of 63 to 90 wt%, and when the toner concentration is 80 wt%
% or less, and the electric field current is rapidly approaching 12.

From the above-mentioned change characteristics of the developing current, it is possible to determine the threshold value of the developing current 13 when the toner density is out of the permissible range. In this example, when the toner density is around 70vt%, the developing current i, ]=5. oμA is used as a threshold value, and this value is stored in the comparison calculation circuit 9 as a comparison reference value.

Therefore, the comparison calculation circuit 9 compares the detected value of the current detection circuit 7 with the stored reference value, and if the detected value exceeds the reference value, it is determined that there is no toner, and the signal generation circuit 10
A signal to that effect is sent to the printer control unit 11 from the printer controller 11.

Printer control unit 11 is displayed on the operation panel 9 No toner 9
is displayed to prompt the user to replenish toner.

In FIG. 1, in the developing device of this example, 250 g of developer d, indicated by level L, is put into the toner hopper 1 at the initial stage of operation. As printing is repeated, the toner is gradually consumed, and when the developer d has decreased to approximately 60 g as indicated by level L2, the toner concentration is 67.
It has decreased to wt%. At this point, the developing current i3 has increased to 5 μA, and "No Toner" is displayed. During this time, image quality defects such as a decrease in image density do not occur. By replenishing the supply, it is possible to stably obtain good printed images over a long period of time.

It should be noted that the present invention is not limited to the specific embodiments described above, and it goes without saying that various modifications can be made within the technical scope of the present invention. For example, the notification means for notifying the user that there is no toner is not limited to visual means such as a panel display, but may also be audible means using audio.

〔Effect of the invention〕

As described above in detail, according to the present invention, the current flowing between the developer conveying member and the image bearing member at the development position is detected, and the toner concentration is determined to be lower than the allowable range based on the detected current value. By adopting a configuration that determines whether or not the toner is present, it is possible to know when toner is to be replenished without using a detection means that directly corresponds to the developer, such as a piezoelectric sensor. Therefore, even if the developer is present in one side of the developing device, it is possible to accurately detect the point in time when the toner concentration has decreased beyond the allowable range. Therefore, even if the developing device is of an elongated type, it is possible to always accurately notify the timing of toner replenishment and to stably obtain good images.

Further, since it is not necessary to provide a detection means such as a piezoelectric sensor directly to the developing device, it is possible to promote miniaturization and cost reduction of the developing device.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view showing a developing device for an optical writing printer as an embodiment of the present invention, FIG. 2 is a schematic explanatory diagram showing the developing current in the case of using the above developing device, and FIG. FIG. 4 is a graph showing the relationship between the developing current and toner concentration of the device, and FIG. 4 is a schematic cross-sectional view showing a conventional developing device. 1... Toner hopper 2.42... Developing sleeve 4.43... Photosensitive drum 7... Current detection circuit 8... Development bias power supply 9... Comparison calculation circuit 10... Signal generation circuit 11... Toner current 12... Electric field current i3... Developing current patent Applicant Casio Computer Co., Ltd. Same as above
Casio Electronics Co., Ltd.W42DiagramW41Diagram

Claims (1)

[Claims] In a developing device using a developer made of a mixture of insulating magnetic toner and conductive magnetic particles, a developer transporting member that transports the developer along a predetermined path including a development area; a developing bias power source for applying a bias voltage; a current detecting means for detecting a current value flowing from the developing bias power source to the developer conveying member; and a current detecting means for detecting a current value detected by the current detecting means. A developing device comprising: a density determining means for determining whether the density is high or low; and a means for notifying a determination result by the density determining means.