Device For Automatically Regulating The Concentration Of Developing Solution

Abstract

A device for automatically regulating the concentration of a developing solution, consisting of toner dispersed in a carrier solution, maintains developing solution having a predetermined concentration in a wet type developing device. The concentration of the solution is photoelectrically detected, and, when the concentration decreases to less than the predetermined valve concentrated toner from a container is supplied by negative pressure generated by the falling of developing solution then remaining in a concentration regulating device into a developing solution reservoir under the action of gravity. Such concentration adjustment occurs in response to the interruption of the circulation of the solution and disconnection of the concentration regulating device from the surrounding atmosphere.

Description

The present invention generally relates to electrophotographic devices and particularly to a wet type developing device used in electrophotographic devices. More specifically, the present invention relates to an automatic developing solution concentration regulating device for use with wet type developing devices.

In electrophotographic processes, the developing solution, consisting of toner dispersed in a carrier solution, is applied to the exposed surface of a photosensitive element for developing an electrostatic latent image formed thereupon. The toner particles are attracted to and held upon the surface of the photosensitive element in correspondence with the pattern of the latent image by electrostatic force. Such developed electrophotographic toner image is fused upon the photosensitive element by fixing means, such as a heater. Alternately, the developed image may be transferred to and fused upon a suitable recording element such as a paper sheet. In the wet type developing method used in the electrophotographic process, toner concentration is decreased as the developing operations are repeated and the concentration of the developing solution must be maintained at a predetermined value so as to enable the production of copies having high quality images without any irregular adhesion or attraction of the toner particles. As described above, the developing solution consists of two components, the toner particles and a carrier solution. The toner particles will be consumed, as described above, so that the concentration of the developing solution, that is, the concentration of the toner particles therein, must be detected and toner supplied for maintaining a predetermined concentration during the developing operation.

In the conventional automatic concentration regulating device for use with wet-type developing devices for electrophotography, the concentration of the developing solution is photoelectrically detected and toner concentrate is supplied or added to the developing solution from a concentrated toner storage container depending upon the detected concentration. For example, toner concentrate is added to the developing solution from an inverted concentrated toner storage container by opening and closing the toner supply opening thereof, thereby dropping the toner concentrate into the developing solution. In this case, it is very difficult to add the toner concentrate in exact quantity in response to detected concentration and, in some cases, there is the possibility that toner concentrate may be forced into the developing solution because of thermal expansion of air inside the storage container. There has been proposed another method in which the concentrated toner storage container is arranged upright and air under pressure is forced into the container through an air port formed in the upper portion thereof, thereby forcing the toner concentrate out of the container through a toner concentrate supply port formed also in the upper portion thereof. In this case, it is also very difficult to add the toner concentrate in exact quantity. Furthermore, an air pump must be provided for introducing air under pressure into the storage container and the device must be designed to operate with a high degree of accuracy, thus resulting in high manufacturing cost. In still another method an air port and a toner concentrate supply port are formed in the upper portion of a concentrated toner storage container and a pump is provided to pump toner concentrate therefrom. However, it is also difficult to add the toner concentrate in exact quantity and there is the possibility that the pump and its piping may become clogged with toner particles.

The primary object of the present invention is to provide an automatic developing solution concentration regulating device which can constantly supply developing solution having a predetermined concentration to a wet type developing device.

Another object of the present invention is to provide an improved automatic developing solution concentration regulating device which can detect the toner concentration and constantly maintain it at a predetermined value by supplying toner concentrate or the like depending upon detected concentration.

A further object of the present invention is to provide an improved automatic developing solution concentration regulating device which can positively circulate developing solution between a developing solution reservoir and a developing solution container (in a developing device) by use of a pump.

A still further object of the present invention is to provide an improved automatic developing solution concentration regulating device which can effect its whole operations automatically with a high degree of accuracy based upon static hydrodynamic principles.

The above and other objects, features and advantages of the present invention will become more apparent from the following description of one illustrative embodiment thereof taken in conjunction with accompanying drawing, in which:

FIG. 1 is a longitudinal sectional view of one embodiment of an automatic developing solution concentration regulating device in accordance with the present invention; and

FIG. 2 is a circuit diagram of a developing solution concentration detecting device used therein.

Referring to FIG. 1, within a developing solution reservoir 1 is contained a developing solution, consisting of toner dispersed in a carrier solution, and a developing solution circulating pump 3 is disposed securely in position within the developing solution reservoir 1 below the level of the developing solution therein. At the bottom of the circulation pump 3 is formed an aperture or port 4 for the suction of the developing solution therein and two pipes or ducts 5 and 6 for supplying the developing solution extend upwardly from the upper portion of the circulation pump 3. The pipe 5 is adapted to supply the developing solution into a developing solution tank 8 or the like disposed within a developing device 7, from which the developing solution may be returned to the reservoir 1. The pipe 6 communicates with a developing solution concentration regulating tank 9 so that the developing solution discharged from the circulation pump 3 is circulated through the pipe 6, the regulating tank 9, a discharge pipe 10 extending downwardly from the regulating tank 9 to the developing solution reservoir 1. Preferably, the lower open end of the discharge pipe 10 is slightly above the level of the developing solution in the solution reservoir 1 so that the level, that is the volume of the developing solution in the developing solution reservoir 1, may be determined depending upon the position of the lower open end of the discharge pipe 10.

Within the developing solution concentration regulating tank 9 is disposed a photoelectric transducer means 13 consisting of a light source 11, connected to a supply E by a switch S, and a photoconductor element 12. When the concentration of the developing solution rises above a predetermined value, the developing solution is circulated from the reservoir 1 through the circulation pump 3, the developing solution concentration regulating tank 9 and the discharge pipe 10 to the reservoir 1 again. On the other hand, when the concentration of the developing solution falls below the predetermined value, signals indicating this decrease in concentration of the developing solution and generated by the photoelectric transducer means are transmitted to an electromagnet 14 disposed above the concentration regulating tank 9, thereby energizing this electromagnet 14 so as to close a valve 16 in a pipe 15, connected between the concentration tank and the surrounding atmosphere and to close a valve 17 between the duct 6 and the concentration regulating tank 9, thereby opening a circulation pipe 18.

The head between the normal level of the solution within the concentration regulating tank 9 and the lower opening end of the discharge pipe 10 is designated by H.sub.1. The head between the average height designated by the line A-B connecting the vertices of a siphon 20 intercommunicating the concentration regulating tank 9 and a toner storage tank 19 and the level of the toner solution within the toner storage tank 19 is designated by H.sub.2. The head between the upper wall of the concentration regulating tank 9 and the above described line A-B is designated by H.sub.3. In this case, it should be noted that the parts of the device of the present invention are so arranged that the following relation will be held:

H.sub.1 > H.sub.2 > H.sub.3.

Therefore, the developing solution present in the concentration regulating tank 9 flows down into the developing solution reservoir 1 through the discharge pipe 10 by the action of gravity of head H.sub.1 so that a negative pressure is produced in the concentration regulating tank 9. Thus, because of the relation:

H.sub.1 > H.sub.2 the toner concentrate within the toner storage tank 19 is forced into the concentration regulating tank 9 through the siphon 20, whose bottom end is disposed in closely spaced apart relation with the bottom of the toner storage tank 19, which is hermetically closed except for a vent 21 in the cover thereof. When the toner solution is supplied into the concentration regulating tank 9 in the manner as described hereinabove, the pressure within the tank 9 is increased and the toner solution is mixed with the developing solution. Thereafter, the mixed developing solution flows into the reservoir 1. Thus, it is seen that when the above described steps occur, the concentration of the developing solution may gradually approach a predetermined value. When the developing solution concentration reaches such predetermined value, the photoelectric means is deenergized and the electromagnet 14 is also deenergized thereby returning the valves 16 and 17 to their normal positions. In this case, it should be noted that the flow of the toner solution from the toner storage tank 19 through the siphon 20 stops 4432>H.sub.3.

Next referring to FIG. 2, when the concentration of the developing solution is above the predetermined value, the light emitted by the light source 11 will not be incident upon the photoconductor element 12, such as CdS, and the element because of the relation:

H.sub.2 > has a 3. resistance, as is well known in the art. Therefore, in the transistorized balancing circuit, the potentials at the points A and B are substantially equal. Since the transistors Tr.sub.1 and Tr.sub.2 are temperature-responsive, that is their characteristics are easily susceptible to variations due to temperature change, a thermistor Th is interconnected, thereby compensating for the variation due to the temperature change. When the concentration of the developing solution drops below the predetermined level, the light from the light source 11 is incident upon the element 12 so that its resistance is decreased. Consequently, the current flowing from the point A into the transistor Tr.sub.1 and the resistor r.sub.3 is decreased and current flows from the point C through the transistor Tr.sub.3 and a resistor 5 into the transistor Tr.sub.2 and the resistor r.sub.3. Furthermore, current flows through the electromagnet 14 and the transistor Tr.sub.3 so that the electromagnet 14 is energized, thereby closing the valve 17 so as to close the passage 23 between the pipe 6 and the concentrating regulating tank 9 while opening the circulation pipe 18. An armature 22 is attracted by the electromagnet 14 so that the valve 16 closes the pipe 15 thereby interrupting the interior of the concentration regulating tank 9 and the surrounding atmosphere.

In the instant embodiment shown in FIG. 1, the photoelectric means 13 has been described as being disposed within the concentration regulating tank 9, but it is understood that it may be disposed within the developing solution reservoir 1 or the developing device 7 as desired.

From the foregoing, it will be understood that the present invention is based upon static hydraulics principles, in which the concentration of the developing solution circulating between the developing device and the developing solution reservoir is photoelectrically detected so that when the concentration falls below a predetermined value, normal circulation of the developing solution is stopped and toner solution is supplied from a concentrated toner storage container into the concentration regulating tank under the influence of the negative pressure produced therein due to gravity flowdown of the developing solution remaining in the tank 9. Thus devices in accordance with the present invention are very simple in construction yet highly reliable in operation for supplying and constantly maintaining the concentration of the developing solution at a predetermined value because the toner concentrate may be supplied in exact quantity to maintain the concentration of the developing solution at the predetermined value. Therefore, better quality copies may be continually provided.

Claims

What is claimed is:

1. An automatic developing solution concentration regulating device comprising:

a developing solution reservoir;

a developing solution concentration regulating means in communication with the surrounding atmosphere;

a toner concentrate storage container;

means for circulating the developing solution between said developing solution reservoir and said developing solution concentration regulating means when the concentration of the developing solution is higher than a predetermined value;

means for detecting the concentration of the developing solution;

means for interrupting the circulation of the developing solution through said concentration regulating means when the concentration of the developing solution decreases to less than said predetermined value;

means for disconnecting the communication of said concentration regulating means with the surrounding atmosphere; and

means for supplying toner concentrate from said toner concentrate storage container to said concentration regulating means only upon the decreasing pressure generated by the falling of the developing solution remaining in said concentration regulating means into said developing solution reservoir under the action of gravity in response to said interruption of the circulation of the developing solution and said disconnection of said communication of said concentration regulating means with the surrounding atmosphere.

2. The automatic developing solution concentration regulating device claimed in claim 1 wherein said means for detecting the concentration of the developing solution is a photoelectric means providing electrical signals indicative of variations in intensity of light emitted from a light source due to the variations in concentration of the developing solution.

3. The automatic developing solution concentration regulating device claimed in claim 1 including

means for concurrently actuating said means for interrupting the circulation of the developing solution through said concentration regulating means and said means for disconnecting the communication of said concentration regulating means with the surrounding atmosphere when the concentration of the developing solution decreases to less than said predetermined value.

4. The automatic developing solution concentration regulating device claimed in claim 1 wherein

said means for supplying toner concentrate from said toner concentrate storage container to said concentration regulating means is a siphon.

5. The automatic developing solution concentration regulating device claimed in claim 2 including an electromagnet and means for energizing said electromagnet where said signals indicate a decrease of the concentration of the developing solution to below said predetermined value, said electromagnet concurrently actuating said means for interrupting the circulation of the developing solution through said concentration regulating means and said means for disconnecting the communication of said concentration regulating means with the surrounding atmosphere.

6. An automatic developing solution concentration regulating device comprising:

a developing device;

a developing solution reservoir;

developing solution concentration regulating means in communication with the surrounding atmosphere;

a toner concentrate storage container;

means for circulating the developing solution between said developing solution reservoir and said developing device;

means for circulating the developer solution between said reservoir and said developing solution concentration regulating means when the concentration of the developing solution is higher than a predetermined value;

means for detecting the concentration of the developing solution;

means for interrupting the circulation of the developing solution through said concentration regulating means when the concentration of the developing solution decreases to less than said predetermined value;

means for disconnecting the communication of said concentration regulating means with the surrounding atmosphere; and

means for supplying toner concentrate from said toner concentrate storage container to said concentration regulating means only upon the decreasing pressure generated by the falling of the developing solution remaining in said concentration regulating means into said developing solution reservoir under the action of gravity in response to said interruption of the circulation of the developing solution and said disconnection of said communication of said concentration regulating means with the surrounding atmosphere.

7. The automatic developing solution concentration regulating device claimed in claim 6, wherein said means for detecting the concentration of the developing solution is disposed in said developing solution concentration regulating means.

8. Apparatus for use in maintaining a predetermined concentration of toner in developing solution contained in a reservoir, comprising:

a vessel containing concentrated toner and having a first port communicating with ambient atmosphere and a second port;

a tank having a top wall disposed vertically above the level of toner in said vessel and including a first tank port and a second tank port, a bottom wall providing a third tank port disposed vertically below said toner level and a side wall including a fourth tank port;

toner supply means sealably connecting said vessel second port and said tank second port and extending into said vessel below said toner level;

developing solution circulating means comprising a pump disposed in said reservoir, a first valve in said tank, a first conduit extending from said pump to said first valve, and a second conduit extending from said first valve to said reservoir;

a second valve connecting said first tank port to ambient atmosphere;

means for detecting the concentration of toner in developing solution in said tank; and

circuit means responsive to said detecting means for actuating said first and second valves to first positions to provide communication respectively between said first conduit and said tank and between said tank first port and ambient atmosphere when detected toner concentration is greater than said predetermined concentration and for actuating said first and second valves respectively to second positions to provide communication between said first conduit and said second conduit and to discontinue communication between said tank first port and ambient atmosphere when detected toner concentration is less than said predetermined concentration.