JPS6343471Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a device for adjusting the toner mixing ratio of a developer in a laser beam printer.

The developer in a laser beam printer is a mixture of toner and carrier. By changing the mixing ratio of toner and carrier in this developer, the printing density of the laser beam printer is adjusted. Therefore, the developing machine of the laser beam printer is provided with a toner concentration adjustment mechanism for the developer. The toner concentration is expressed by the toner weight ratio of the developer, but since it is difficult to detect the weight ratio, the volume ratio is detected and the toner concentration is adjusted. A schematic diagram of an example of a method for detecting the toner volume ratio of developer is shown in FIG. In the figure,
1 is a concentration detection coil, 2 is a carrier, and 3 is a toner.

In Figure 1, the area around the concentration detection coil is
The mechanism is such that a fixed amount of developer always falls. As the number of carriers falling per unit time changes, the magnetic permeability around the coil changes, and the inductance of the concentration detection coil changes. This change in inductance is detected as a change in the terminal voltage of the coil of the series resonant circuit. An example of a toner density adjustment circuit is shown in FIG. In the figure, 4 is a comparator, and 5 is a variable resistor.

In FIG. 2, if the coil terminal voltage is lower than the reference voltage, a toner supply signal is generated and is supplied by the operator or automatic supply device. When toner is supplied and the terminal voltage of the coil increases, the toner supply signal stops. The reference voltage applied to the comparator is changed by a variable resistor to adjust the toner concentration. With this method, it takes time for the toner density to change after setting the resistance value of the variable resistor, and the change in toner density is determined by print density, which makes adjustment difficult. It was hot.

An object of the present invention is to eliminate the above-described drawbacks of the prior art and to improve the operability of the developer toner concentration adjustment mechanism by immediately displaying the appropriate toner concentration.

In the present invention, the toner concentration adjustment mechanism is devised so that it can be displayed that the toner concentration of the developer has reached a set value.

An example of a specific embodiment of the present invention is shown in FIG.
In the figure, 1a and 1b are comparators connected in parallel with the concentration adjustment coil, and the reference voltage of comparator 1b is set higher than that of comparator 1a. The adjustment completion display circuit consists of an inverter 12 and a NAND gate 13.

In FIG. 3, when the developer concentration is lower than the set value, the terminal voltage of the concentration adjusting coil becomes lower than the reference voltage applied to the + side of the comparator 1a, and a toner supply signal is output. When toner is supplied and the terminal voltage of the density adjustment coil becomes higher than the reference voltage, the toner supply signal stops and a toner density adjustment completion signal is output. This signal can indicate that the toner concentration of the developer has reached the set value. When the toner concentration is higher than the set value, the terminal voltage of the concentration adjustment coil applied to one side of the comparator 1b is higher than the reference voltage applied to the + side, so the toner concentration adjustment completion display signal is not output. In other words, the toner concentration adjustment completion display signal is output only when the toner concentration becomes approximately equal to the toner concentration set by the variable resistor. The range of toner density at which this signal is output can be easily changed by changing the resistance value of the resistor R2.

The toner concentration adjustment completion display signal is used for the purpose of notifying the apparatus operator that the toner concentration has reached the set value, such as by turning on an indicator light.

According to the present invention, since it is possible to display that the toner concentration of the developer has reached a set value, the operability of the developer toner concentration adjustment mechanism is improved and the toner concentration adjustment time can be significantly shortened.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of an example of a method for detecting a toner volume ratio of a developer, and FIG. 2 is a conventional developer toner concentration adjustment circuit. FIG. 3 is a circuit diagram showing an embodiment of the present invention.

Claims (1)

[Scope of utility model claims] In a developing device for a laser beam printer comprising a series resonant circuit having a toner concentration detection coil, the output of the series resonant circuit is connected to a first comparator having a reference potential adjusted by a variable resistor; An adjustment completion display circuit is connected in parallel with a second comparator having a high reference potential and outputs a toner concentration adjustment completion signal when the output of the series resonant circuit is between the two reference potentials. Connected toner density adjustment mechanism.