Toner density sensor, and ink jet head, developing unit and image forming apparatus in which toner density sensor is used

Abstract: A toner density sensor includes a liquid developer tank (1) for accommodating liquid developer (2) to be used for development, a diluting liquid tank (3) for accommodating diluting liquid (4) formed of a base material of the liquid developer (2), and a mixing chamber (5) disposed outside and connected to the tanks (1, 3) through a first valve (7) and a first pump (9), and a second valve (8) and a second pump (10), respectively. The valves (7, 8) and pumps (9, 10) are controlled so as to be opened or closed by a control driver (17). A passage (13) of a circulation type is formed in part of the mixing chamber (5) with a third pump (11) interposed therein, and a transparent cell element (14) for measuring a transmission light amount through fluid passing through the inside thereof is disposed in the passage (13). Further, a light emitting element (15) and a light receiving element (16) are disposed such that the transparent cell element (14) is positioned between them.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a toner density sensor, and an ink jet head, a developing unit and an image forming apparatus in which a toner density sensor same is used, and more particularly to a toner density sensor for a wet type image forming apparatus such as a printer, a facsimile or a copying machine, and an ink jet head, a developing unit and an image forming apparatus in which a toner density sensor is used. Description of the Related Art A wet type image forming apparatus uses liquid developer composed of toner dispersed in solution to develop an electrostatic latent image formed on a photosensitive member to form a visible toner image. In the wet type image forming apparatus, the toner density, that is, the ratio of the toner in the liquid developer, has a very serious influence on the image density, chapping, the resolution and so forth of the developed image. Meanwhile, since the toner in the liquid developer is gradually consumed as development is repeated, in order to always keep an appropriate toner density, the toner density is measured and, when the density drops, either warning information of this is developed or a suitable amount of toner or liquid developer of a high density is automatically supplemented. Thus, a toner density sensor is required to measure the toner density in order to keep the toner density appropriate. One of such toner density sensors is disclosed in Japanese Patent Publication JP-B-41-21435 (1966) wherein liquid developer is flowed in a passage formed from a transparent member and an amount of transmission light through the liquid developer is measured by means of a light emitting element and a light receiving element disposed in an opposing relationship to each other on the opposite sides of the passage and is utilized as a substitute characteristic of the toner density. The toner density sensor, however, is disadvantageous in that toner density detection of an appropriate density is difficult. The reason is that, since liquid developer of an appropriate density is very low in transmission factor, the transmission light through the liquid developer is attenuated by a large amount by the liquid developer. Further, if the light path length through the liquid developer is reduced in order to allow toner density detection of an appropriate density, then retention of the toner in the liquid developer or clogging of the passage with foreign articles in the light path becomes liable to occur and toner becomes liable to stick to the passage in the light path. A toner density sensor according to the preamble of claim 1 is disclosed in PATENT ABSTRACTS OF JAPAN vol. 007, no. 216 (P-225), 24 September 1983 (1983-09-24) & JP 58 111069 A (CANON KK). More specifically, in the disclosed arrangement some of the liquid developer is sent to a developing unit and a reminder is delivered to a cell for performing a concentration measurement. It is one object of the present invention to provide an improved toner density sensor and an improved method for determining a toner concentration in a toner density sensor. According to an aspect of the invention, a toner density sensor according to the subject-matter of claim 1 is provided. According to another aspect of the present invention, a method for determining a toner concentration in a toner density sensor according to claim 8 is provided. Further aspects and embodiments of the present invention are provided according to the subject-matter of claims 2 to 7. The toner density sensor according to the invention is advantageous in that, even where the liquid developer has a very low transmission factor in a density upon measurement, toner density detection of an appropriate density can be performed readily. The reason is that, since the liquid developer is diluted normally at a certain fixed ratio, toner density detection within a density range within which the transmission light is attenuated but by a small amount can be performed even with a light path length within which retention of toner or clogging with foreign articles in the liquid developer does not occur in the light path. Preferably, the diluting liquid is a solution same as a base material of the liquid developer. Preferably, the light emitting element and the light receiving element are covered completely with a transparent member having a low surface energy property and are disposed in an opposing relationship to each other with a certain fixed gap left therebetween in the mixing chamber. According to another aspect of the present invention, there is provided an ink jet head, comprising any of the toner density sensors described above. According to a further aspect of the present invention, there is provided an image forming apparatus, comprising the ink jet head described above. According to a still further aspect of the present invention, there is provided a developing unit, comprising means for making the density of the liquid developer fixed based on the density of the liquid developer detected by any of the toner density sensors described above According to a yet further aspect of the present invention, there is provided an electrophotographic image forming apparatus, comprising charging, exposure, transfer and fixing means, and the developing unit described above. The above and other objects, features and advantages of the present invention will become apparent from the following description and the appended claims, taken in conjunction with the accompanying drawings in which like parts or elements are denoted by like reference symbols. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagrammatic view of a toner density sensor to which the present invention is applied; FIGS. 2(a) to 2(c) are schematic diagrammatic views illustrating operation of the toner density sensor of FIG. 1; and FIG. 3 is a schematic diagrammatic view of another toner density sensor to which the present invention is applied. DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring first to FIG. 1, there is shown a toner density sensor to which the present invention is applied. The toner density sensor shown is incorporated in an ink jet head not shown of an image forming apparatus not shown such as, for example, a printer, a facsimile or a copying machine and includes a liquid developer tank 1 for accommodating liquid developer 2 to be used for development, a diluting liquid tank 3 for accommodating diluting liquid 4 formed of a base material of the liquid developer 2, and a mixing chamber 5 disposed outside and connected to the tanks 1 and 3 through a first valve 7 and a first pump 9, and a second valve 8 and a second pump 10, respectively. The first valve 7, second valve 8, first pump 9 and second pump 10 are controlled so as to be opened or closed by a control driver 17. A passage 13 of a circulation type is formed in part of the mixing chamber 5 with a third pump 11 interposed therein, and a transparent cell element 14 which allows an amount of transmission light through fluid which passes through the inside thereof to be measured is disposed in the passage 13. Further, a light emitting element 15 and a light receiving element 16 are disposed such that the transparent cell element 14 is positioned between them. Operation of the toner density sensor is described below with reference to FIGS. 1 and 2(a) to 2(c). When the toner density is to be detected, the first valve 7 on the liquid developer tank 1 side is opened by the control driver 17 as seen in FIG. 2(a), and the liquid developer 2 is supplied by a predefined amount from the liquid developer tank 1 into the mixing chamber 5. Simultaneously, also the second valve 8 on the diluting liquid tank 3 side is opened by the control driver 17, and an amount of the diluting liquid 4 with which the dilution ratio of the liquid developer 2 to it is to be always kept fixed is supplied from the diluting liquid tank 3 into the mixing chamber 5. After the predefined amount of the liquid developer 2 and the diluting liquid tank 3 are supplied into the mixing chamber 5, the first valve 7 and the second valve 8 are closed by the control driver 17 as seen from FIG. 2(b). The liquid developer 2 and diluting liquid 4 supplied in the mixing chamber 5 are agitated by an agitation member 12 disposed in the mixing chamber 5 to make liquid developer 6 for toner density detection. The liquid developer 6 for toner density detection agitated sufficiently is forcedly circulated between the mixing chamber 5 and the transparent cell element 14 by the third pump 11. Simultaneously, an amount of transmission light through the liquid developer 6 for toner density detection in the transparent cell element 14 is measured by means of the light emitting element 15 and the light receiving element 16, and it is determined by a density calculation circuit 18 whether the liquid developer 2 in the liquid developer tank 1 has a density within an appropriate density range. After the detection of the ink density is completed, the first valve 7 on the liquid developer tank 1 side is opened by the control driver as seen in FIG. 2(c), and the liquid developer 6 for toner density detection in the mixing chamber 5, in the transparent cell element 14 and the passage 13 between them is discharged to the liquid developer tank 1 side. In this manner, even if the liquid developer 2 has such a high density that the transmission light is attenuated by a great amount to such a degree that the transmission light amount cannot be measured unless the light path length of the transparent cell element 14 is made considerably small, the diluting liquid 4 is mixed at a certain fixed ratio into the liquid developer 2 in the mixing chamber 5 while the light path length of the transparent cell element 14 of such a degree that retention of toner or clogging of foreign articles does not occur is assured, and the liquid developer 6 for toner density detection diluted to such a density within a density range within which the transmission light amount can be measured is produced in the mixing chamber 5 and the transmission light amount through the liquid developer 6 for toner density detection is measured at the transparent cell element 14. Then, the transmission light amount thus measured is compared with sample data of the density of the liquid developer 6 for toner density detection, which have been obtained in advance with the liquid developer 2 diluted similarly to a lower limit value and an upper limit value to the appropriate density range, by the density calculation circuit 18 to determine the density of the liquid developer 2. It is to be noted that, in order to prevent a great density variation from occurring with the liquid developer 2 also when the liquid developer 6 for toner density detection is discharged into the liquid developer tank 1, preferably the amount of the liquid developer 6 for toner density detection is considerably smaller than the amount of the liquid developer 2. Further, in order to prevent fixation of remaining toner when the inner face side of the transparent cell element 14 becomes dry after the liquid developer 6 for toner density detection is discharged, preferably the mixing chamber 5 and the transparent cell element 14 are always filled with the diluting liquid 4. Referring to FIG. 3, there is shown another toner density sensor to which the present invention is applied. The toner density sensor of FIG. 3 is a modification to and different from the toner density sensor described hereinabove with reference to FIG. 1 in that the light emitting element 15 and the light receiving element 16 are covered completely with a transparent member 19 having a low surface energy property and disposed in an opposing relationship to each other with a certain fixed gap left therebetween in the mixing chamber 5. When toner density detection is to be performed, the light emitting element 15 and the transparent cell element 14 are immersed in the liquid developer 6 for toner density detection in the mixing chamber 5, and the liquid developer 6 for toner density detection is agitated by the agitation member 12 in the mixing chamber 5. In this condition, the transmission light amount through the liquid developer 6 for toner density detection in the mixing chamber 5 is measured by the light emitting element 15 and the light receiving element 16, and it is determined by the density calculation circuit 18 whether the liquid developer 2 in the liquid developer tank 1 has a density within an appropriate density range. While, in the foregoing description, the toner density sensor is incorporated in an ink jet head of an image forming apparatus such as, for example, a printer, a facsimile or a copying machine, it may otherwise be incorporated in a developer of an electrophotographic image forming apparatus which additionally includes charging, exposure, transferring and fixing means. Where the toner density sensor is incorporated in a developing unit, the density of the liquid developer is controlled fixed based on a result of detection by the toner density sensor. While preferred embodiments of the present invention have been described using specific terms, such description is for illustrative purpose only, and it is to be understood that changes and variations may be made without departing from the scope of the following claims.

Claims: A toner density sensor, comprising: a light emitting element (15); a light receiving element (16) for receiving light emitted from said light emitting element (15); a liquid developer tank (1) for accommodating a liquid developer (2) used for developing; a diluting liquid tank (3) for accommodating a diluting liquid (4); characterized by : means (7, 8, 9, 10) for removing a quantity of developer (2) from the developer tank (1) and for diluting it with the diluting liquid (4) in a mixing chamber (5) at a predetermined ratio to be used for the measurement; a passage (13) to circulate the diluted liquid developer (6) to a transparent cell element (14) disposed in said passage (13) between said light emitting element (15) and said light receiving element (16) for measuring the amount of light transmitted from said light emitting element (15) to said light receiving element (16); and means (18) for determining a density of the liquid developer (6) based on the light amount transmitted through the diluted liquid developer (6) in said mixing chamber (5). A toner density sensor as claimed in claim 1, wherein the diluting liquid (4) is a solution same as a base material of the liquid developer (2). A toner density sensor as claimed in claim 1, wherein said light emitting element (15) and said light receiving element (16) are covered completely with a transparent member (19) having a low surface energy property and are disposed in an opposing relationship to each other with a certain fixed gap left therebetween in said mixing chamber (5). An ink jet head comprising a toner density sensor as claimed in claim 1, 2 or 3. An image forming apparatus comprising an ink jet head as claimed in claim 4. A developing unit comprising means for making the density of the liquid developer fixed based on the density of the liquid developer detected by a toner density sensor as claimed in claim 1, 2 or 3. An electrophotographic image forming apparatus, comprising charging, exposure, transfer and fixing means, and a developing unit as claimed in claim 6. A method for determining a toner concentration in a toner density sensor comprising a light emitting element (15), a light receiving element (16) for receiving light emitted from the light emitting element (15), a liquid developer tank (1) for accommodating a liquid developer (2) used for developing and a diluting liquid tank (3) for accommodating a diluting liquid (4), the method comprising the steps of: a) removing of a quantity of developer (2) from the developer tank (1) and diluting it with the developer diluting liquid (4) at a predetermined ratio to be used for the measurement, b) passing the diluted liquid developer (6) trough a transparent cell element (14) disposed between a light emitting element (15) and a light receiving element (16) and determining a density of the liquid developer (6) based on a light amount transmitted through the diluted liquid developer (6) and calculating whether the measured density is in a predetermined range, and c) discharging the diluted developer (6) used for measurement to the developer tank (1).

Inventors: SHIMA KAZUO, SUETSUGU JUNICHI, YAKUSHIJI TORU, SHIMA, KAZUO, SUETSUGU, JUNICHI, YAKUSHIJI, TORU, Shima, Kazuo c/o NEC Niigata Ltd., Suetsugu, Junichi c/o NEC Niigata Ltd., Yakushiji, Toru c/o NEC Niigata Ltd.
Applicants: NIPPON ELECTRIC CO, NEC CORPORATION
Application year: 1999
Main classification: G03G15
IPC codes: G03G15, G01N21, B41J2