Device and method to lift magnetizable carrier particles from a mixture of toner particles and magnetizable carrier particles

In a device and method for lifting magnetizable carrier particles from a mixture of toner particles, a cover of a collecting element interface device is arranged such that it can be rotated around a stator with a magnet. The cover comprises a spiral that, given rotation of the cover, conveys the carrier particles in an axial direction.

BACKGROUND OF THE INVENTION

The invention concerns a device to lift magnetizable carrier particles. Furthermore, the invention concerns a method to lift carrier particles.

In electrographic printers or copiers, two-component toner systems are frequently used that comprise a mixture of ferromagnetic carrier particles and toner particles. A magnetic roller arrangement transports the two-component mixture in a region with little separation between the magnetic roller arrangement and the surface of an applicator element to be inked with toner particles, for example a roller or a ribbon. The toner particles are transferred to the surface of the applicator element, whereby magnetic forces hold back the ferromagnetic carrier particles. However, in practice it can occur that ferromagnetic carrier particles that adhere to the toner particles are transferred with them or are mechanically flung onto the surface of the applicator element. These very hard magnetizable carrier particles are then active outside of the development process and can damage the print system or copier system or, due to the contamination, can cause print image interference.

A method and a device to clean carrier elements in printers or copiers using magnetic fields is specified from DE 101 52 892, incorporated herein by reference. In this patent application, the development process is specified in detail with the aid of two-component systems and the application of magnetic fields to ferromagnetic carrier particles. The content of this patent application is hereby incorporated in the disclosure contents of the present patent application.

It is known from operational practice to use an angle stripper that exhibits a magnetic field to lift magnetizable carrier particles. The angle stripper faces at the distance of an air gap a carrier surface that carries the mixture of toner particles and carrier particles. With the aid of the magnetic forces, magnetizable carrier particles are captured. The problem hereby exists that toner taken along by the carrier particles or freely straying (vagrant) toner dust deposits on the surface of the angle stripper via adhesion or triboelectric or electrostatic charging. Viewed over a longer operation time, toner layers can assemble increasingly stronger, such that it can lead to function disruption. Furthermore, the lifted carrier particles must again be removed from the surface of the angle stripper and, if possible, are again supplied to the two-component mixture in the developer station so that the ratio of carrier particles and toner particles remains constant in the two-component mixture in the developer station. In the developer station, frequently a very limited space is present, such that the return of the carrier particles and also the lifted toner particles causes problems.

SUMMARY OF THE INVENTION

It is an object of the invention to specify a device and a method that enables a safe lifting of magnetizable carrier particles and ensures a safe delivery of the carrier particles.

In a device and method for lifting magnetizable carrier particles, a cover of a collecting element is rotated around a stationary stator and wherein the stator comprises at least one magnet having a pole arranged approximately radial to the cover and a magnetic field which attracts ferro-magnetic carrier particles located on a carrier at a distance of an air gap. A surface of the cover comprises at least one screw-thread type spiral so that, given rotation of the cover, the carrier particles move in an axial direction relative to the cover.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A cover of a collecting element, preferably a non-magnetic hollow cylinder, can be rotated around a stationary stator. This stator comprises at least one magnet whose one pole is arranged approximately radial to the cover and whose magnetic field attracts the ferromagnetic carrier particles. An air gap is provided between the carrier particles and the surface of the cover. At least one spiral according to a type of threading is present on the surface of the cover, preferably as a spiral elevation or depression which, upon rotating the cover, moves the carrier particles in the direction axial to the cover. The ferromagnetic carrier particles are thereby adhered via the magnetic field, such that between the carrier particles and the surface of the cover a relative motion occurs in the circumferential direction and in the axial direction dependent on the lead of the spiral. Due to the axial motion of the carrier particles on the surface of the cover, the carrier particles are systematically conveyed to a desired location and can there be discarded. At the same time, due to the relative motions the surface of the cover is cleaned of deposited toner particles, whereby a safe operating mode occurs.

According to a further aspect, a method is specified to lift magnetizable carrier particles. The technical effects that can be achieved with this method coincide with those according to the specified device.

It should be noted that the cited device and the method can be used anywhere ferromagnetic carrier particles that are arranged on a flat or curved carrier surface should be selected.

FIGS. 1A and 1Bshow an exemplary embodiment of a collecting roller10designed as a collecting element. InFIG. 1B, a section X ofFIG. 1Ais shown enlarged. The collecting roller10comprises as a spiral a spiral-shaped channel12according to a type of threading. As is to be recognized in the detail cut-out X, the channel12has a specific width and depth that can be adapted to the size of the ferromagnetic carrier particles. On the left edge of the collecting roller10, two grooves14are sunk into the surface of the collecting roller10. These grooves14serve as a discarding device. When the carrier particles conveyed in the direction axial to the collecting roller10reach these grooves14, they are taken away by the grooves14and discarded from the collecting roller10. In place of the grooves14, elevations or carrier ridges or fins can also be arranged as discarding devices. A further variant exists to bring the magnetic field to a value near zero in a region of the discarding location such that the ferromagnetic carrier particles are no longer held to the surface of the collecting roller10, and thus also clean the cover surface via the relative motion.

FIG. 2shows the exemplary embodiment according toFIGS. 1A,1B with carrier particles16that are transported via rotation of the collecting roller10counterclockwise towards the left to a carrier fin18, and are there discarded. In the area20, an accumulation of carrier particles is visible that are moved axially to the left in the channel12via carrier particles.

FIG. 3shows schematically a side view of the collecting roller10. It comprises a cover22that is designed as a hollow cylinder. Inside the cover22, a stator24is arranged with two magnets26,28. The stator24with the magnets26,28is stationary, while the cover22is rotated in the direction of the rotation arrow P1. The magnet26serves as an attracting magnet, i.e. it attracts carrier particles16. The long axis of the magnet26is aligned approximately radial. The magnet28serves as a transporting magnet; its lengthwise axis is aligned radially and has an angular separation of approximately 90° to the pole axis of the magnet26. The poles of the magnets26,28facing outwards have different polarity, i.e. a concentrated magnetic flux occurs from the north pole of the magnet26to the south pole of the magnet28.

Using theFIG. 3, the functional principle is explained. The magnet26attracts ferroelectric carrier particles16with its magnetic field active outwards, such that these adhere to the surface of the cover22. Given rotation of the cover22counterclockwise in the direction P1, the carrier particles16are conveyed to the area of the south pole of the magnet28and are held there by the magnetic force of the magnet28. A relative motion thus occurs between the surface of the cover22and the accumulation of the carrier particles16in the area of the south pole of the magnet28. Due to the screw-shaped channel12(not visible inFIG. 3), the accumulation of carrier particles16is conveyed in the direction perpendicular to the paper plane, whereby a further relative motion occurs. When the conveyed carrier particles16reach the region of the grooves14, they are taken away by the grooves and are discarded in the region of the discarding location30.

FIG. 4shows an example in which a channel32is designed coil-shaped on the surface of the collecting roller10according to a type of right-handed thread, and the channel34is designed according to a type of left-handed thread. The discarding device, for example grooves14or fins, is arranged where both channels32,34meet, here in this example approximately in the middle. In this type of design of the collecting roller10, the discarding location30lies in the middle of the collecting roller10.

FIG. 5shows another example. The channels32,34are likewise designed in the opposite direction and convey the carrier particles16outwards to the edge regions of the collecting roller10where they are discarded by the grooves14. Two discarding locations thus occur here at the edge. Given the axial motion of the carrier particles16, these rub against the surface of the cover22and clean it of deposited toner particles, as this ensues, for example, at the location20. The toner particles adhere due to the triboelectric charge and adhesion to the surface of the cover22to the surface of the carrier particles16. The number of discarding locations30, as well as the lead for a plurality of spiral-shaped channels and the direction of the thread, can only be designed such that the discarding locations30are set where corresponding catch locations or catch devices are present. In this manner, an improvement of the design possibilities occurs, for example, inside of a developer station. Via the selection of a plurality of discarding locations30, the accumulating quantity of carrier particles16and for the most part scarce space within a housing can be accommodated.

FIG. 6shows the example according toFIG. 3with further details. The magnets26,28are designed such that on the one hand the magnet26transports the carrier particles16to the surface of the cover22, and on the other hand the magnet28, given rotation of the cover22, conveys the acquired carrier particles16optimally in the axial direction of the cover22.

FIG. 7shows an example in which a single magnet36undertakes the function of catching the carrier particles16and axially transporting the carrier particles16. A simple and cost-effective assembly thus occurs. This variation is offered when the quantity of carrier particles16to be lifted is relatively small and an accumulation of carrier particles16at this location leads to no problem in the overall system. In the variation according to claim6, the carrier particles16that are attracted by the magnet26are transferred (preferably via the magnetic field lines between the north pole of the magnet26and the south pole of the magnet28) to the transporting magnet28and held there. Such an arrangement is advantageous when the lifted carrier particles can not dwell at the pole location of the magnet26, for example due to the narrow air gap, since the quantity to be lifted is too large. On the other hand, the division of the functions of attracting carrier particles and holding them and axially conveying the carrier particles is advantageous for reasons of design.

FIG. 8shows as an exemplary embodiment of a developer station40with an indicated housing42. The two-component mixture comprising toner and ferromagnetic carrier particles is located in the floor region. This mixture is circulated by a paddle wheel46. A magnetic roller48conveys the mixture made of carrier particles and toner particles to an applicator roller, whereby if at all possible only toner particles should be transferred to the surface of the applicator roller50. The magnetic roller48holds the carrier particles back due to its magnetic field. However, this process is imperfect, such that carrier particles to some degree can also arrive together with toner particles on the surface of the applicator (carrier) roller50. The previously specified collecting roller10is arranged at a distance of an air gap52from the surface of the applicator roller50and catches the carrier particles from the carpet made of toner particles. The caught carrier particles are then again supplied to the two-component mixture. The applicator roller50transfers the toner particles to the location54on the surface of a photoconductor drum provided with latent images. A cleaning roller56removes the untransferred toner particles from the surface of the applicator roller50. It is to be noted that an applicator ribbon100(shown in dashed lines inFIG. 8) can also be used as an applicator carrier element that is arranged opposite the collecting roller10that removes ferromagnetic carrier particles from the carpet of toner particles.

Numerous variations of the specified exemplary embodiments are possible. For example, the coil to transport the carrier particles in the axial direction can also comprise elevations in the form of fins. The fins or channels do not have to be designed connected, but rather can also only be present along the extent of the cover in sections. Additionally, a direct voltage field can also act along the axis of the collecting roller10, for example via application of a high direct voltage. The electrical field is to be selected such that it repels toner particles. In this manner, fewer toner particles are dragged along via the attraction of carrier particles, and free vagrant toner is repelled. An alternating voltage can be overlaid on the direct voltage in order to amplify the effect. The cover22can be coated with an anti-adhesive material in order to ease a removal of deposited toner layers via mechanical friction. Many other variations are also possible.

Although preferred exemplary embodiments are shown and specified in detail in the drawings and in the preceding specification, the invention should not be limited to this. It is to be noted that preferred exemplary embodiments are shown and specified, and all variations and modifications that lie within the scope of protection of the invention now and in the future should be protected.