Device For Automatically Regulating The Concentration Of Developing Solution

Abstract

Device for automatically regulating the concentration of developing solution in a wet type electrophotographic machine. Stirrer means is used to stir the developing solution for circulation through a developing tray and a reservoir, and a concentration detector is disposed in the stream of developing solution. The concentration detector has a source of radiation such as light and two elements sensitive to the radiation and the detection circuit including two elements. The concentration detector provided within the stream can effect the regulation of concentration with high accuracy and stability.

Description

This invention relates to a wet electrophotographic machine, and more particularly to a device for automatically regulating the concentration of a developing solution used with such a machine.

In a wet type electrophotographic machine, it is important to automatically maintain the concentration of a developing solution at a predetermined level in order to prevent the uneveness of the resultant image and provide an excellent quality of the image as well as to simplify the manipulation of the machine.

There are the following two methods of detecting the concentration of the developing solution in a wet type electrophotographic machine and supplying concentrated developer from an auxiliary tank in accordance with the detection signal.

1. Concentrated liquid is continuously supplied from the auxiliary tank when the means for detecting the concentration of the developing solution is producing a signal representing an insufficient concentration.

2. A predetermined amount of concentrated liquid is supplied once or more from the auxiliary tank when the means for detecting the concentration of the developing solution is producing a signal representing an insufficient concentration.

While the present invention may be applicable to both of the foregoing methods, a description will now be made briefly with respect to the application of the invention to the second method mentioned above.

Stirrer means is provided to stir the developing solution for circulation through a developing tray and a reservoir and there is disposed a concentration detector in the stream of the developing solution. The concentration detector comprises a source of radiation, and elements sensitive to said source of radiation and disposed at both sides thereof and a detection circuit including these elements. Between the source of radiation and one of the elements sensitive thereto the developing solution is introduced and circulated. Between the source of radiation and the other element sensitive thereto there is interposed means for regulating the quantity of light so that equal quantities of light reach the two elements when the developing solution in the reservoir has a standard or proper concentration. The detection circuit is in a balanced state when the developing solution has the standard concentration. If the concentration of the developing solution is decreased, a switching circuit including the detection circuit is operated to actuate a plunger and associated valves of an auxiliary tank so that a predetermined amount of concentrated liquid is supplied from the auxiliary tank through its valves into the reservoir to increase the concentration of the developing solution therein to the standard level.

In contrast, according to the prior art, the concentration detector is disposed exteriorly of the developing machine and this arrangement requires the provision of means such as a pipe or the like for introducing the developing solution into the concentration detector. Such means presupposes a space therefor which results in a larger size and higher cost of the entire device. Furthermore, the measurement of concentration is not effected directly with the developing solution circulating in the reservoir but with a portion of it which is introduced through the pipe or like means, and this results in a lower accuracy of the measurement.

It is an object of the present invention to provide a device for automatically regulating the concentration of a developing solution by means of a concentration detector disposed directly in the path of the developing solution circulating in a developing tray or a reservoir to effect the regulation of the concentration with high accuracy and stability.

It is another object of the present invention to provide a less expensive device for automatically regulating the concentration of a developing solution which has a concentration detector disposed in a developing tray or a reservoir thereby eliminating the need to provide any additional space for such detector and the need to use any additional means such as pipe or the like required by the prior art.

The invention will now be described in greater detail with respect to an embodiment thereof shown in the accompanying drawings, in which:

FIG. 1 is a partly broken-away perspective view of a wet type developing machine incorporating the device of the present invention;

FIG. 2 is a plan view of the machine shown in FIG. 1;

FIG. 3 is a sectional view taken along line III--III of FIG. 2;

FIG. 4 is a cross-sectional view taken along line IV--IV of FIG. 2;

FIG. 5 is a front view, in vertical section, of the detector portion for detecting the concentration of the developer;

FIG. 6 is a front view, in vertical section, of the valve portion for supplying concentrated liquid; and

FIG. 7 diagrammatically shows the electric circuit for detecting the concentration of the developing solution.

Referring to FIGS. 1 to 4, a reservoir 1 contains therein a developing solution 2 which is stirred by stirrer means 4 such as pump or the like driven by a motor 3. The developing solution 2 thus stirred is moved through a pipe 5 into a substantially trough-shaped developing tray 6. The portion of the developing solution which has been brought to the developing tray 6 flows down into the reservoir 1 through discharge holes 7 formed in the developing tray 6. The reservoir 1 is divided into two compartments by a partition wall 25, that is, compartment 28 just underlying the developing tray 6 and compartment 29 having the stirrer means 4 disposed therein. The partition wall 25 is formed with cut-aways 26.sub.1 and 26.sub.2 for permitting the developing solution which has flowed down from the developing tray 6 into the compartment 28 to circulate between the two compartments 28 and 29 of the reservoir 1. According to the present invention, a concentration detector 8 is disposed in the developing solution within the reservoir 1. The concentrations detector 8 comprises a detection circuit constituted by a source of radiation L and elements CdS1 and CdS2 sensitive to the source of radiation, as shown in FIG. 5. In the flow passage of the developing solution which is provided by the cut-away 26.sub.1 formed in the reservoir, there is disposed an auxiliary tank 10 for containing concentrated liquid therein. As shown in FIG. 6, the auxiliary tank 10 is formed with a discharge port 9 for supplying a predetermined amount of concentrated liquid, and at the inner and outer ends of the discharge port 9 there are provided valves 12 and 13 mounted on a valve rod 11. The open inner end of the discharge port 9 is normally closed by the valve 12 urged downwardly by a spring 18 mounted in the upper portion of the valve rod 11.

Turning to FIG. 7, there is provided a rectifier circuit comprising a power source transformer T.sub.1, diodes D.sub.1 to D.sub.4 and a capacitor C.sub.1. The d.c. output of the rectifier circuit is applied to a bridge circuit comprising resistors R.sub.1 and R.sub.2 , a variable resistor R.sub.3 and elements CdS1 and CdS2 sensitive to the source of radiation L. When the concentration of the developing solution 2 in the reservoir 1 is at a proper level, equal quantities of radiation reach the two elements CdS1 and CdS2 sensitive to the source of radiation L. Thus the bridge circuit is maintained in balanced state.

If the developing solution 2 decreases its concentration after a great deal of development has been effected, the element CdS2 sensitive to the source of radiation also decreases its resistance value to thereby destroy the balance of the bridge circuit, whose output thus triggers an oscillation circuit comprising a transistor Tr, an oscillating transformer T.sub.4 and a capacitor T.sub.4 and a capacitor C.sub.2 . The output of the oscillation circuit is applied to the gate of a bidirectional silicon controlled rectifier element FLS, which is thereby turned on to actuate a plunger 14. In this case, an input is intermittently applied to the plunger 14 through a microswitch MS in synchronism, for example, with action of the operating mechanism of the image reproducing machine.

As shown in FIG. 1, the lower end of the plunger 14 is connected to an arm 15 at one end thereof. The other end of the arm 15 is connected to one end of an arm 17 by means of a rod 16 so that the other end of the arm 17 controls the movement of the valve rod 11. Thus, the movement of the plunger 14 is transmitted through the arm 15 and rod 16 to the arm 17 which in turn raises the valve rod 11 against the force of the spring 18 so that the valve 13 mounted on the valve rod 11 closes the outer open end of the discharge port 9 for supplying a predetermined amount of concentrated liquid. Thus, a predetermined amount of concentrated liquid fills the discharge port 9. If the plunger 14 is released, the valve rod 11 is urged downwardly by the spring 18 so that the valve 12 mounted on the valve rod 11 closes the inner open end of the discharge port 9 while the outer open end of the discharge port is opened so as to allow the predetermined amount of concentrated liquid filling the discharge port 9 to fall into the reservoir 1. The described sequence of operation is repeated with each actuation of the plunger 14 so as to enable the concentrated liquid stored in the auxiliary tank 10 to be supplied in predetermined amounts into the reservoir 1. The concentrated liquid thus supplied into the reservoir 1 is circulated by stirrer means 4 such as pump or the like. When the concentration of the developing solution 2 thus reaches the optimum level, it is detected by the concentration detector 8 to thereby stop the actuation of the plunger 14.

According to the present invention, the concentration detector 8 is disposed in the developing solution 2 within the reservoir 1 as described above, and this arrangement eliminates the cumbersome provision of pipe or like means and enhances the appearance of the machine as compared with the prior art arrangement which included the concentration detector disposed exteriorly of the reproducing machine. Thus the arrangement of the present invention economizes the space over the reservoir and is very advantageous in designing.

In the illustrated form of the present invention, the concentration detector 8 comprises, as shown in FIG. 5, a detection circuit comprising a source of radiation L and elements CdS1 and CdS2 sensitive thereto, both contained in a casing 20 formed of transparent material. The concentration detector 8 may be mounted through an opening 21 formed in the cover plate 1.sub.1 of the reservoir 1 in such a manner that the detector lies in the developing solution 2 within the reservoir 1. Lead-out wires are led out from the concentration detector elements L, CdS1 and CdS2 through a hole 23 formed in the lid member 22 of the casing 20. The casing 20 and its lid member 22 may be constructed so as not to allow the admission of the liquid thereinto by providing a tight fit between the casing and lid member, so that developing solution cannot enter the casing during the normal operation of the machine and thereby the elements L, CdS1 and CdS2 of the concentration detector can be readily protected from the liquid. Also, the lid member 22 may be removed to change the source of radiation L within the casing 20 and this means a great convenience in maintenance of the device. Means 24 such as slit, filter or the like for regulating the quantity of light may be provided in the light path between the source of radiation L and the element CdS2. If the means 24 is a slit, it will eliminate the problem of light transmittivity which would result from the use of a filter, and the provision of the slit itself can be simply achieved by ordinary machining. Also, the use of the slit 24 leads to a further advantage that the width thereof may be suitably selected so as to select a proper resistance value for the radiation-sensitive element CdS2 when the concentration of the developing solution is proper. Further, a recess 27 for receiving therein the developing solution to be measured may be formed in the bottom of the casing 20 and the casing 20 may be disposed in such a manner that the recess 27 therein is in alignment with or closely proximate to the cutaways 26, thereby allowing the developing solution 2 to flow through the recess quickly enough to prevent the inner peripheral surface of the recess 27 from being contaminated by the developing solution. Thus, a highly accurate detection of the concentration of the solution is accomplished.

Claims

What is claimed is:

1. A device for automatically regulating the concentration of developing solution in a wet type electrophotographic machine which comprises:

a reservoir for said developing solution;

a developing tray in fluid connection with said reservoir;

means for detecting the concentration of said developing solution disposed in said reservoir, said detecting means including a source of radiation and means sensitive to said radiation arranged to produce a signal upon changes in the concentration of said solution; and

means for supplying concentrated developing solution operable in response to said signal from said detecting means.

2. The device of claim 1 which further includes stirring means arranged in said reservoir to maintain circulation of said solution through said developing tray and reservoir.

3. The device of claim 1 wherein said means sensitive to said radiation comprises at least two elements sensitive to radiation, one of said elements being disposed at one side of said source of radiation with the developing solution flowable therebetween and said second element being disposed at the other side of said source of radiation with means for regulating said radiation interposed therebetween, said elements being in circuit to produce said signal, and said detection means further includes a switching circuit activated by said signal to operate said supply means.

4. The device of claim 3, wherein said means for regulating said radiation comprises a plate defining a predetermined sized slit.

5. A device for automatically regulating the concentration of a developing solution as defined in claim 3 wherein said detecting means is contained in a casing having a radiation passage formed of a light transmitting material through which said developing solution flows.

6. A device for automatically regulating the concentration of a developing solution in a wet type developing machine for electronically picked-up images, said device comprising a reservoir, a developing tray, means for stirring the developing solution in said reservoir, means for detecting the concentration of said developing solution disposed in the flow passage of said developing solution, and means for supplying concentrated solution to said reservoir, said means for detecting the concentration of a developing solution having a switching circuit including a detection circuit having a source of radiation and at least two elements sensitive to the radiation from said source of radiation, one of said elements being disposed at one side of said source of radiation with the developing solution flowing therebetween, the other element being disposed at the other side of said source of radiation with means for regulating the quantity of radiation interposed therebetween, said means for supplying concentrated solution actuating a plunger and a valve rod in response to the output of said means for detecting the concentration of the developing solution so as to actuate valves located in a discharge port of a supply of concentrated solution for supplying a predetermined amount of concentrated solution into said reservoir.