JPS6198370A - Electrophotographic copying machine - Google Patents

Abstract

PURPOSE:To control the concentration of toner always at a constant value even in a humidity environment by arranging a humidity detector near a two- component developer. CONSTITUTION:In the relation between humidity and the inductance of a developer, the inductance is increased in accordance with the increase of humidity. Even if the toner concentration is fixed, the characteristic of the humidity detector kept at a high temperature reduce the sensor resistance like exponential function in accordance with the rise of humidity. The output of the humidity detector 8 can be extracted as voltage change by an AC regulated power supply 9. In addition, an output having a negative characteristics to humidity by a logarithmic amplifier 10 and a rectifying circuit 11. Since the humidity characteristic of the humidity detector 1 is positive, arithmetic weighted in accordance with respective variables is executed by an arithmetic circuit 12, so that the humidity change of a detecting level of the density detector 1 can be canceled.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an electrophotographic copying machine equipped with a function of controlling toner concentration in a developer in a two-component development system.

Conventional Structure and Problems Conventionally, as a means for detecting toner concentration in a developer in a two-component development system, a method of detecting a change in magnetic permeability of the developer by a change in inductance has been common, but this method has been unsuccessful. In other words, the difference in magnetic permeability between the carrier and the toner constituting the developer is utilized. Since the carrier usually has higher magnetic permeability,
The apparent magnetic permeability changes depending on the mixing ratio. This is detected as a change in inductance by a concentration detector consisting of a magnetic circuit including a recoil with an iron core and a developer.

A conventional detection method will be described below with reference to the drawings. Fig. 1 is a functional diagram of a recoil with an iron core that detects inductance as a concentration detector, and Fig. 2 is a functional diagram of a recoil with an iron core that detects inductance as a concentration detector. FIG. 1i toner concentration detector, 2a AC constant current source, 3a
AC cross section, 41d rectifier circuit, 6-voltage comparator, 6(d
Drive circuit, shows a DC motor as a 7Il-r actuator.

The operation of the conventional toner density control system configured as described above will be described below.

When the detection surface of the density sensor 1 is installed in a place where the developer flows well, as indicated by the arrow, the inductance of the coil serving as the density sensor 1 changes in a direction inversely proportional to the toner density. By connecting the concentration detector 1 to the AC constant current source 2, the change in inductance appears as a voltage change, and the toner concentration is detected by comparing it with a preset reference value in the voltage comparator 6. . Based on the result, the direct reading motor 7, which is an actuator, is operated to supply the toner that has been reduced due to the copying operation so as to always obtain a constant toner density.

However, in the above configuration, due to the nature of the developer being a powder, its composition state changes slightly depending on humidity, and the magnetic permeability is also affected.
This method has a major drawback in that the detected inductance has an error due to humidity.

OBJECTS OF THE INVENTION It is an object of the present invention not only to eliminate the drawbacks of the above-mentioned conventional examples, but also to provide an electrophotographic copying machine capable of always stably controlling toner density without being affected by humidity.

Structure of the Invention In order to achieve the above object of the present invention, a humidity detector is disposed near the two-component developing device, thereby making it possible to always control constant toner density even in a humid environment.

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 3 is a block diagram of a toner density control system in one embodiment of the present invention, and FIG. 2 shows the same components with the same reference numerals.

8 is a humidity detector, 9 is an AC constant current source, 1o is a logarithmic amplifier, 11 is a rectifier circuit, and 12 is an arithmetic circuit.

The operation of the toner density control of this embodiment configured as described above will be described below.

Figure 4 shows the relationship between humidity and developer inductance.
As shown in 1□, when the humidity increases, the inductance increases. Therefore, even if the toner concentration is constant, when the temperature becomes high, Vr- is set so that it is detected that the toner concentration is low. Furthermore, the humidity detector has a characteristic that the sensor resistance decreases exponentially as the humidity increases, as shown in FIG. The AC stabilized power supply 9 outputs the humidity detector 8 as a voltage change. Further, the logarithmic amplifier 10 and the rectifier circuit 11 provide an output with negative humidity characteristics.On the other hand, since the humidity characteristics of the concentration detector 1 are positive, the arithmetic circuit 12 outputs an output that has negative humidity characteristics. By performing calculations with weighting, it is possible to cancel humidity changes in the detection level of the concentration detector 1.

As described above, according to this embodiment, by detecting the humidity near the developing device, it is possible to correct the detection error of toner concentration caused by the change in magnetic permeability due to the humidity of the developer. Effects As is clear from the above explanation, the present invention has a means for detecting the toner concentration based on changes in the magnetic permeability of the developer, and a humidity detector for detecting the humidity near the developer. This provides an excellent effect in that stable toner density control is possible. As a result, it is possible to realize an electrophotographic copying machine with stable image quality at all times.

[Brief explanation of the drawing]

Fig. 1 is a functional diagram of the density detector, Fig. 2 is a block diagram of a conventional toner density control system, and Fig. 3 is a block diagram of a toner density control system in an embodiment of the present invention.
FIG. 4 is a correlation diagram between the inductance and relative humidity of the concentration detector, and FIG. 5 is a correlation diagram between the AC resistance value and relative humidity of the humidity detector. 1... Concentration detector, 2... AC constant current source, 3... AC amplifier, 4... Rectifier circuit, 5... Voltage comparison device, 6...Drive circuit, 7...DC motor, 8...Humidity detector, 9...AC constant current source, 10...・Logarithmic amplifier, 11... Rectifier circuit, 12...
・Arithmetic circuit 0 Name of agent: Patent attorney Toshio Nakao and 1 other person 1st
Figure 2 Figure 3

Claims (2)

[Claims] (1) An electrophotographic copying machine characterized in that a humidity detector is provided near a developing unit for a two-component developer. (2) The humidity detector constitutes a means for correcting changes in magnetic permeability due to humidity of the developer in an operation control system for keeping the toner concentration of the developer in the developing device constant. An electrophotographic copying machine according to claim 1.