The invention concerns a device and a method to replace at least one component of a pourable medium. Furthermore, the invention concerns the use of such a device in a printer or copier.
Examples of systems in which pourable medium are used are electro-photographic or ionographic printers or copiers. The pourable medium used therein is a developer, especially a two-component developer that contains a toner and a magnetic carrier respectively in particle form.
In printers or copiers operating according to the electro-photographic principle, charge images of characters (such as texts or drawings) to be printed are generated on an intermediate carrier, for example a drum with an electro-photographic layer. The intermediate carrier with the charge images is directed into a development station in which the charge images are developed and thereby made visible. Upon the development, the toner particles of a two-component developer are conveyed in the direction of the intermediate carrier and are electrically attracted onto the intermediate carrier by the charge carrier. The carrier particles are conveyed back to the development station. The developed charge images are transferred and fixed upon a recording medium, for example a paper web. The toner material within the two-component developer is used in the development valve. Fresh toner material is refilled corresponding to this use. The carrier material conveyed back is subject to an aging process, whereby the print quality or copy quality can suffer. Therefore, it is also necessary to renew the carrier material little by little.
A printer device or copier device is specified in WO 98/39691 (of which reference is made here to its entire disclosure) in which a recording medium can be printed upon in monochrome and/or color. A plurality of developer stations are thereby provided for which, respectively, one color is associated for one colored print. In order to maintain the print quality in printers of such a type, a replacement must occur at specific time intervals due to the expiration of the developer or the expired components contained therein in the form of the carrier. For example, this could hitherto occur such that development stations are completely emptied and subsequently filled, which is very time-consuming and is associated with an interruption of the operation of the printer or copier.
Replacement of the developer with expired carrier with fresh developer can also occur such that developer stations are supplied with fresh toner and fresh carrier separate from one another, such that a definite amount of the toner and carrier ensuring the print quality or copy quality is always present in the developer, such that the printer operation or copier operation must not be interrupted.
A device for the replacement of expired developer with fresh developer in a development station of an electro-photographic device is known from U.S. Pat. No. 4,358,196. This known device comprises two metering devices, via one of which fresh developer is supplied to the developer station, and via the other of which expired developer is removed from the development station, such that a developer ensuring good print quality is always present in the development station.
Given replacement of the developer with expired carrier, it is important that a specific volume of developer with a defined toner concentration and carrier concentration (meaning a defined proportion of toner to carrier) is always present in a development station. Over the entire lifespan of a printing device, a total fill quantity of developer guaranteeing proper functioning must always be present. The toner concentration can be regulated in its own regulation cycle, such that an amount of toner ensuring the print quality is always present in the development station. The regulation can occur such that the toner concentration is detected and regulated either directly by means of a sensor, or indirectly via detection of the inking of the printing. However, given direct regulation, the toner concentration cannot be precisely determined due to inevitable control deviations, and given indirect regulation, the toner concentration can in part not be determined at all, whereby losses in quality can arise.
Typically, the ratio of toner to carrier for the volume of the supplied two-component developer is known. However, the ratio of toner to carrier in the volume of the removed developer can vary from the ratio in the supplied developer, because the toner concentration in the development station can vary higher or lower than the toner concentration of the supplied developer due to the control deviations. However, because both volumes are equal, the proportion of the carrier in the removed developer can vary higher or lower than the proportion of the carrier in the supplied developer.
If the replacement of the developer is implemented uniformly and constantly, as is the case in the device according to the US patent specification cited above, the carrier quantity in the developer station can drift ever further higher or lower, given a large number of alternating cycles. This means that the development station can overflow or run empty in the extreme case, whereby the printer or copier is incapable of functioning.
A device and a method for the replacement of at least one component of a pourable medium is known from EP 0 043 505 A2. The pourable medium with the expired component is removed from a container, and a quantity of fresh pourable medium is supplied into the container. Two metering devices are provided, from the first of which the developer station is constantly supplied fresh developer, and from the other of which used developer is constantly removed from the developer station in an equal quantity.
A developer station is known from U.S. Pat. No. 5,450,178, in which a mix of toner and carrier particles is present in an upper chamber according to the exemplary embodiment according to FIG. 4. The proportion of toner is higher than is necessary for the typical usage. The mix from the upper chamber is transferred little by little into a container, whereby an expired mixture in this container is dispensed into a lower chamber, dependent on the signal of a sensor that analyzes the contents in the container. In this manner, the total quantity of the mixture can be maintained at a constant value.
A developer unit is known from U.S. 5,095,338, in which a mixture of toner particles and carrier particles is present in a chamber (compare in particular FIG. 2). A quantity of carrier particles and toner particles is supplied from the container to the development material in the chamber. The ratio of toner particles to carrier particles in the container is greater than in the chamber, such that expired developer material is continually renewed. A sensor system observes the composition of the development material in the chamber and initiates via a controller the supply of fresh developer material.
A copier with at least two developer stations for at least two different colors is known from EP 0 043 505 A2, in which a fresh developer component is supplied from a common reservoir container to these developer stations at the respective supply intake. This developer is a liquid developer.
Reference is made to the documents JP 59 100 471 A, JP 2000 122 424 A, and WO 01/06325 A as further relevant prior art.