Method for controlling an electrolytic silver recovery system for a photographic processor

Abstract: The invention relates to a method and apparatus for controlling an electrolytic silver recovery system (11) for a photographic processor, the control being effected in response to the surface area of the photosensitive material (8, 9, 10) moved through the processing solutions. By means of the apparatus (3) the amount of silver deposited in the fixing bath (9) of the processor is determined from the width, length and density of the photosensitive material and used as an electrical signal for controlling the electrolytic current of the silver recovery system (11).

Description: The invention relates to a method for controlling an electrolytic silver recovery system for a photographic processor, the control being effected in response to the surface area of the photosensitive material moved through the processing solutions. Methods of this type in which a signal is gained from the processor which is proportional to the processed film or paper area and, thus, also proportional to the amount of silver deposited in the fixing bath of the processor, are known. In DE-PS 1 188 822, for example, a method is described for electrolytically recovering silver in which recovery is controlled by turning on and off the electrolytic current in response to the amount of photographic material moved through the fixing bath. The surface area of the material to be processed is the basic parameter therefor, assuming that on average always identical amounts of silver are dissolved from the material. In DE-PS 1 237 789 the operating cycle of the silver recovery system is determined by a pulse generator activated by the film material moved through the processor, with the possibility of storing the pulses. In this case as well, the surface area of the material to be processed is the decisive factor and, as a result, only an average amount of silver to be recovered from the photosensitive material is used as a basic parameter. An improved method for detecting the area of the photosensitive material is described by the US 4,506,969. A film processor includes a scanner which measures the transmittance of light through the film material along a line with respect to the direction of film travel. Thus, the film width can be determined whereas the film length is determined by the transport speed of the film. US 4,341,453 discloses an automatic control system for a photographic processor. For detecting the width of an unprocessed film, an array of reflective infrared sensors is used which are positioned across a path of the film. The disadvantage of such methods is that the amount of silver in the fixing bath is averaged and used as a basic parameter by means of which the electrolytic silver recovery system is controlled. On the other hand, silver recovery systems are known that operate in response to the silver content of the fixing solution forming an electronic reference value. The reference value may be, for example, the cathode potential of a reference electrode that is proportional to the silver concentration. There is a disadvantage, however, in that a continuity of the value determined by the silver content can hardly be realized over an extended period of time so that the recovery system is not very reliably and exactly controlled. It is the object of the invention to provide a method for controlling a silver recovery system for a photographic processor in which method the amount of silver deposited in the fixing bath is reliably and exactly determined and used for controlling the system. According to the invention, the above object is attained by the features of claim 1. The invention advantageously achieves that the electrolytic current is adapted to the actual amount of silver and thus an optimum silver recovery is possible. When a perdetermined amount of silver has been deposited on the cathode, the power supply of the recovery system is cut off. The method according to the invention permits, within a large density range of the photosensitive material, a reliable and accurate determination of the density and the surface area of the material and, thus, of the amount of silver contained in the fixing bath. As a result, the electrical signal used for controlling the silver recovery system is also proportional to the amount of silver contained in the fixing bath so that advantageously a control is realized in that the recovery of the silver is based on the actual amount of silver gained from the photosensitive material. Moreover, a substantial reduction of replenishment of the fixing bath will be obtained. The invention will now be described in detail with reference to the drawing. Fig. 1 shows the apparatus for performing the method and Fig. 2 shows a known processor with the apparatus according to the invention installed therein. In advancing direction 7 of the photosensitive material the apparatus 3 shown in Fig. 1 comprises two rows of IR transmitters 2, 2' with oppositely arranged receivers 4, 4' and IR reflective sensors 1, 1' spaced at regular intervals. Arrangement of the IR sensors with respect to the longitudinal side 6 of the apparatus is such that in each of the two rows an IR transmitter 2, 2' with a receiver 4, 4' is followed by an IR reflective sensor 1, 1'. The IR transmitters 2, 2' consist of infrared LED's and the receivers 4, 4' are formed of photocells. Across the total width of the apparatus 3 at least eight IR transmitter/receiver sensors and eight IR reflective sensors are arranged per row. By means of rollers not illustrated the photosensitive material is moved through slot 5 in direction 7. As shown in Fig. 2, the apparatus 3 is placed downstream of a processor substantially formed of three main assemblies: the processing tanks containing a developing bath 8 and a fixing bath 9 provided with level sensors, a water bath 10 and a drying station, a silver recovery system 11 and a replenishing means consisting of pumps 15 and 17 and a pressure switch 16, supply tanks 13, 14 for developing and fixing solutions and a control unit 12 operable via a computer 18 and comprising a microprocessor. The developing bath 8 is connected to supply tank 13 by means of pipes with parallelly operating pumps 15 and 17 interposed. The fixing bath 9, on the one hand, is connected via pipes to the electrolytically operating silver recovery system 11 and, on the other, to supply tank 14 with pumps 15 and 17 interposed as well. The method is described as follows: The photosensitive material, film or paper, moves through the processor in a known way, that is to say from the developing bath 8 to the fixing bath 9, the water bath 10 and then to the drying station from which it is advanced into slot 5 of the apparatus 3. As soon as the leading edge of the material moves beneath the first row of the reflective IR sensors 1 a signal is produced and a time measurement is started by the microprocessor control unit 12. Then the density of the photosensitive material is measured by the transmitted light operated IR transmitter/receiver sensors 2, 2' and 4, 4'. When the leading edge of the material moves through the IR reflective sensors 1' in the second row, the time lapsed since the start of the time measurement is determined. Using the values from the time lapse and the known spacing between the first and second row of the IR reflective sensors 1, 1', the transport speed is calculated. The width of the film or paper is determined from the number of IR transmitter/receiver sensors 2, 4 and 2', 4' that detect light reflected by the material and produce a signal. When the trailing edge of the material moves through the first row of the IR reflective sensor, time measurement is terminated. The total time then corresponds to the duration the film has taken to move through the processing solutions by means of which value the length of the material is calculated in response to the transport speed. The surface area processed will result from the length and width of the material. During the time the material moves between the IR transmitter/receiver sensors 2, 2' and 4, 4' its density is determined. If no spot on the material shows a density below a predetermined value stored in the microprocessor of the control unit, the type of the material, film or paper, can be determined. The surface area, density and type of material being known, the control unit 12 calculates - by means of a program stored in the microprocessor - the required amounts of replenisher for the developing and fixing sulutions. Depending on the amounts calculated, the replenishing pumps for developer, fixer and water are switched on for a predetermined period. Moreover, a value is determined in the control unit 12 the calculation of which is based on the surface area and the density of the material and corresponds to the amount of silver deposited in the fixing bath. Said value is fed to the silver recovery system 11. When further film material is fed into the processor, the value corresponding to the amount of silver actually contained in the fixing bath is added to the aforementioned value, the total being used as a signal for controlling the electrolytic current of the silver recovery system 11 so that the electrolytic current is controlled as a function of the silver concentration in the fixing bath. Every ten seconds the actual amount of silver contained in the fixing bath is determined and the electrolytic current adapted accordingly. By means of a program stored in the microprocessor of the control unit 12 and considering experimentally determined efficiency values also the amount of silver electrolytically recovered and deposited on the cathode is calculated and subtracted from the amount of silver contained in the fixing bath. When a perdetermined amount of silver has been deposited on the cathode, the silver recovery system is cut off.

Claims: Method of controlling an electrolytic silver recovery system for a photographic processor, the control being effected in response to the surface area of the photosensitive material which is moved through the processing solutions by measuring its widths, length and density, characterized by the steps of: a) measuring the width and length of the photosensitive material by means of an IR reflective light-operated sensor arrangement (1, 1'); b) measuring the density of the photosensitive material by means of an IR transmitted light-operated sensor arrangement (2, 2'), whereby both sensor arrangements are arranged in rows and alternately across the width of the path of said photosensitive material; c) generating an electrical signal by means of an microprocessor unit (12) which is determined from the steps a) and b) and d) using said electrical signal for controlling the electrolytic current of the silver recovery system. Method according to claim 1, characterized in that the amount of silver contained in the fixing bath and the electrolytic current controlled accordingly are determined every ten seconds. Method according to claims 1 and 2, characterized in that the power supplied to the silver recovery system is cut off when a predetermined amount of silver has been deposited on the cathode.

Inventors: GREEN ANDREW, HOITZ GERD, UEFFINGER GERHARD DR, GREEN, ANDREW, HOITZ, GERD, UEFFINGER, GERHARD, DR., GREEN, ANDREW, C/O KODAK LIMITED, Üffinger, Gerhard, Dr.
Applicants: EASTMAN KODAK CO, KODAK AG, EASTMAN KODAK COMPANY, KODAK AKTIENGESELLSCHAFT
Application year: 1993
Main classification: G03D3
IPC codes: G03C11, G03C5, G03D3, C25C1, C25C7