A supply means for supplying magnetically attractive developing powder

Abstract: The invention relates to a supply means for magnetically attractive developing powder, comprising a reservoir (9) provided with an outflow opening (13) for supplying a magnetically attractive developing powder (21) from the reservoir to a developing unit. The reservoir is provided with two magnetic systems (15,16) each rotatable about an axis of rotation and each at least partially being surrounded by a stationary enclosure over which the developing powder can be displaced under the influence of the rotating magnetic systems. The magnetic systems are disposed opposite one another with the axes of rotation parallel to one another. The stationary enclosures of the two magnetic systems together form the outflow opening, while in a supply mode the magnetic systems are adapted to effect transport of developing powder through the outflow opening by rotation and in a stationary mode the magnetic systems are adapted to prevent transport of developing powder through the outflow opening.

Description: The invention relates to a means for supplying magnetically attractive developing powder, comprising a reservoir provided with an outflow opening and a magnetic system for supplying the magnetically attractive developing powder from the reservoir to a developing unit. A supply means of this kind is known from US patent 5 181 074, wherein a developing device is described for a developing powder of toner and carrier particles. The carrier particles are magnetically attractive. In this device, the developing powder is transported to a supply unit the underside of which is closed by a magnetic roller. Rotation of the magnetic roller causes developing powder to be supplied to a mixing chamber of a developing unit of an electro-photographic printing unit, such chamber being situated beneath the supply unit. In practice with this device it has been found that the quantity of developing powder that can be supplied is limited, even in the case of developing powder consisting solely of magnetically attractive toner. For example, when such so-called one component or unary toner is used, a supply speed of 30 to 35 grams per minute is the maximum obtainable. This quantity is insufficient for copiers and printers operating at very high speeds (in excess of 100 copies or prints per minute). Other methods of supplying large quantities of toner rapidly, for example using rotating mechanical valves, have the disadvantage that the toner for supply comes into contact with the mechanical valve. This is a disadvantage for toners of the kind that have now been developed. These toners generally have relatively low fusing properties, i.e. the toner is fixed on the paper at a relatively low temperature, this being advantageous In energy terms. However, these toners have the disadvantage that they are mechanically vulnerable. Lumping or caking rapidly occurs due to mechanical load. This results in an unacceptable distortion of the image. The advantage of using a magnetic system such as a magnetic roller for supplying magnetically attractive toner or a toner-carrier mixture is the low mechanical load of the toner, so that caking is avoided as far as possible. The above objects are achieved in a means according to the invention wherein the reservoir is provided with two magnetic systems each rotatable about an axis of rotation and each at least partially being surrounded by a stationary enclosure over which the developing powder can be displaced under the influence of the rotating magnetic systems, the magnetic systems are disposed opposite one another with the axes of rotation parallel to one another, the stationary enclosures of the two magnetic systems together form the outflow opening, while in a supply mode the magnetic systems are adapted to effect transport of developing powder through the outflow opening by rotation and in a stationary mode the magnetic systems are adapted to prevent transport of developing powder through the outflow opening. With this system it is possible to supply large quantities of developing powder while caking due to mechanical loading is avoided. Supply takes place during the rotation of the magnetic rollers. If the developing powder used is relatively strongly magnetisable and/or has poor flowing properties, a first embodiment according to the invention is characterised in that the outflow opening is located beneath the reservoir In an operative state and the direction of rotation of the magnetic system in the supply mode coincides with the developing powder supply direction. In the stationary mode, the strongly magnetisable developing powder forms a developing powder bridge extending across the outflow opening, so that the transport of the powder Is prevented. In the supply mode this bridge is broken because the developing powder is drawn through the outflow opening by the rotating magnetic systems. If the developing powder used Is relatively weakly magnetisable and/or has good flowing properties, a second embodiment of the invention is characterised in that the outflow opening is located beneath the reservoir in an operative state and the direction of rotation of the magnetic systems in the supply mode is in the opposite direction to the developing powder supply direction. With developing powder of this kind, passage of the developing powder through the outflow opening will occur at standstill. This passage Is further intensified and a large supply is obtained by the direction of rotation of the magnetic systems extending in the opposite direction to the direction of supply. Another advantageous embodiment is characterised in that each magnetic system comprises on an outside two diametrically opposite magnets extending parallel to the axis of rotation and wherein the connecting line between the magnets of the one magnetic system is substantially perpendicular to the connecting line between the magnets of the other magnetic system when a magnet is situated opposite the outflow opening. One effect of this is that the magnetic field between the magnetic poles is reduced, so that developing powder can drop from the enclosure to the developing device. More than two magnets per magnetic system gives an increased chance of complete coverage of the enclosure with developing powder. On the other hand, during rotation, a separate magnetic pole comes along the outflow opening four times per revolution during rotation, and this magnetic pole entrains developing powder without magnets being situated opposite one another. Another advantageous embodiment is characterised in that In the stationary mode one of the magnets is situated opposite the toner outflow opening. In the case of developing powder which is strongly magnetically attractive and/or has good flowing properties, with no spontaneous bridge formation occurring, the passage of developing powder can be prevented in this way. In another advantageous embodiment, the reservoir is provided with means contained therein for keeping the developing powder loose, such means being inoperative in the stationary mode and operative in the supply mode. Particularly in the case of strongly magnetisable toner and/or developing powder which has poor flowing properties, the above-mentioned bridge formation In the stationary mode can be so great that the connection between the developing powder particles first has to be broken before the magnetic systems can transport them. One advantageous embodiment for the purpose of achieving a large supply is characterised in that the stationary enclosure of the magnetic systems defining the outflow opening merges, via a transition plane extending continuously at an angle of inclination, into a straight outflow duct, wherein the transition plane tangentially adjoins that part of the enclosure which forms the outflow opening and also the outflow duct. The developing powder transported by a first magnetic pole must be given the opportunity of remaining out of the influence of a following magnetic pole of the opposite magnetic system. Otherwise the transported developing powder will again be drawn back by the next magnetic pole. As a result of the shape of the transition plane the developing powder can flow out rapidly so that a higher speed of revolution of the magnetic system is possible. Another advantageous alternative embodiment for obtaining a large supply is obtained for the same reasons in an embodiment characterised in that the stationary enclosure of the magnetic system defining the outflow opening merges, via a straight transition plane having a constant angle of inclination, into a straight outflow duct wherein the transition plane tangentially adjoins the part of the enclosure forming the outflow opening. The supply means according to the invention will be explained in detail hereinafter with reference to the following drawings wherein: Fig. 1 shows a developing unit with a supply means according to the invention. Fig. 2 shows the supply means of Fig. 1 in accordance with a first embodiment. Fig. 3 shows the supply means of Fig. 2 in accordance with a second embodiment. Fig. 4 shows a first embodiment of the outflow opening of the supply means and Fig. 5 shows a second embodiment of the outflow opening of the supply means. Fig. 1 diagrammatically illustrates a developing unit 1 for developing an image of developing paper on a charge carrier 2 of the kind used in copying machines or laser or LED printers. For this purpose the charge carrier 2 is provided with photoconductive or dielectric material. In the case of photoconductive material, a charge image is obtained on the charge carrier 2 by means of direct image exposure as in the case of conventional or analogue copying machines or by means of a laser or LED exposure in the case of digital copying apparatus or printers, local developing powder being adapted to be deposited on the charge image by the developing unit 1. In the case of dielectric material, a charge image is obtained by an electrode system suitable for the purpose. The developing powder can be of the unary conductive type with only toner, or of the binary type in the form of a combination of carrier and toner. Both types of toner adhere electrically to the charge present on the charge carrier 2. Unary toner comprises magnetisable material to enable the same to be applied to the charge carrier 2 by means of a magnetic developing roller 3. In the description hereinafter, for the sake of convenience the term "toner" will be used to indicate different types of developing powder. For application purposes, the developing roller 3 comprises a number of magnets 4 where a sleeve 5 trained around the same rotates in the direction indicated. The magnets 4 ensure that the toner is attracted to the sleeve 5 while the latter ensures the transport of the toner. Suitable feed means such as a similar magnetic intermediate roller 6 and a mechanical feed roller 7 with blades or wires 12 ensure transport of toner from a reservoir space 8 to the developing roller 3. The reservoir space 8 is filled with toner from a toner reservoir 9 having sufficient capacity to make a required number of copies or prints. The toner reservoir 9 can be constructed as an exchangeable bottle or as a fixed reservoir which can be replenished via a filling opening 10. The capacity required for such a toner reservoir 9 will be in the region of 1 to 2 litres for example. The toner reservoir 9 is connected to the developing unit 1 via a tube or flexible hose 11. The toner can be moved by means of spirals in the tube 11 but this is preferably effected by gravity in order to avoid mechanical loading of the toner as far as possible. Preferably, known means for keeping the toner loose are provided in the toner reservoir 9 although not shown in detail. Such means may, for example, be a mixer mill having a rotating set of mixer wires disposed at a specific angle and located a short distance away from the wall. These prevent toner from caking or eliminate any caking after long stationary periods. Such means also provide mixing of old and new toner. The arrangement shown in Fig. 1, i.e. a toner reservoir 9 with the toner outflow opening 13 extending downwardly, comprises a toner supply means 14 on the one hand to prevent unwanted passage of toner to the developing unit 1 and, on the other hand, to supply a required predetermined quantity of toner to the developing unit 1. Said supply means 14 must be capable of supplying a required quantity of toner per unit of time of the order of 50 to 100 grams per minute. Such quantities are in fact required for copying machines and printers making more than 100 copies per minute. On the other hand, the supply means must exert the minimum possible mechanical loading on the toner in order to avoid its lumping or damage. Fig. 2 shows the toner supply means 14 of Fig. 1 in greater detail in accordance with a first embodiment of the invention. The drawing shows two magnetic rollers 15 and 16 comprising bar magnets 17, 18, 19 and 20. The magnets 17 - 18 have a magnetic strength of about 3400 Gauss and a dimension of 50 mm in the direction of the longitudinal axis of the magnetic rollers. The width B is 6 mm and the thickness D is between 3 and 6 mm. By varying the thickness D it is possible to adjust the effective magnetic force exerted on the toner. The pole-pole direction of the magnets 17 - 20 passes through the axis of the magnetic rollers 15 and 16. The magnetic rollers 15 and 16 are partly closely enclosed by part of the toner reservoir 9, a toner outflow opening 13 being formed with a minimum gap width S of 0.5 to 2 mm. It must be remembered that the toner has characteristic cross-sections of about 10 µm. The magnetic forces exerted by the magnets 17 - 20 are operative on the toner 21 in the toner reservoir 9 located near said magnets 17 - 20. The size of the toner outflow opening 13 in the axial direction of the magnetic rollers 15 and 16 corresponds to the length of the magnets 17 - 18 and is 50 mm. Although the magnetic rollers 15 and 16 are in this case constructed as rollers of non-magnetic material with the separate magnets 17 - 20 embedded therein, a magnetic roller can also be constructed in the form of a magnetised roller of magnetic material. It should also be noted that the enclosure forming the toner outflow opening 13 is of course not of magnetic or magnetisable material. A gearwheel 24 is fixed to the magnetic roller 15 and a gearwheel 25 to the magnetic roller 16. Gearwheel 25 is driven by a motor 23 via a toothed drive belt 22. The gearwheels 24 and 25 are also so coupled that the connecting line 26 between the magnets 17 and 18 is always perpendicular to the connecting line 27 between the magnets 19 and 20. As a result, a magnetic pole comes along the toner outflow opening 13 four times per revolution. The variations in the mechanical load of the drive are acceptable in this case. The magnetic rollers 15 and 16 are driven at a speed of between 50 and 175 revolutions per minute, depending on the required amount of toner to be supplied. In the case of toner which is relatively strongly magnetisable and/or has poor flowing properties, a toner bridge will be formed across the toner outflow opening 13 when the magnetic rollers 15 and 16 are stationary, so that no toner is supplied in such a stationary mode. In the stationary mode, the above-mentioned means for keeping the toner loose In the toner reservoir 9 are not active in order not to destroy the bridge that has been formed. By rotating the magnetic rollers 15 and 16 in the directions 29 and 30 shown in Fig. 2 together with the toner supply direction, by means of a motor 23, toner is displaced through the toner outflow opening 13. The toner loosening means are now also activated in order to break the bridge that has formed. The toner is attracted in the form of a brush to the wall of the toner reservoir 9 and rolls and/or slides over the same as a result of the force of attraction of the rotating magnetic fields. The maximum quantity of toner to be supplied Is in this case determined primarily by the maximum speed of rotation at which complete coverage with toner of the parts of the toner reservoir 9 adjoining the magnetic rollers 15 and 16 is obtained. The toner must have time to drop by gravity before the next rotating magnet can again engage the toner. Until this maximum speed of rotation is reached, the quantity of supplied toner increases with an increase in the speed of rotation of the magnetic rollers 15 and 16. With a gap width S of about 2.5 mm there is also complete coverage with toner. On the other hand, for complete supply the gap width S must not be less than about 0.5 mm. Toner supplies of more than 50 g per minute are obtained with gap widths S between 1 mm and 2 mm at a speed of the magnetic rollers 15 and 16 in excess of 100 rpm. Within these limits, the toner supply increases with the use of stronger magnets to a maximum of 90 g per minute at 150 rpm. In the case of relatively weakly magnetisable toner and/or toner having good flowing properties, the mechanisms that occur are different. Such toner occurs, for example, in the form of a colour toner, in which the percentage of magnetic material is preferably kept as low as possible. In a stationary mode, in which the magnetic rollers 15 and 16 do not rotate, no toner bridge will form in a neutral state, i.e. no magnetic pole at the toner outflow opening 13. The toner will then run spontaneously through the toner outflow opening 13. Consequently, in a second embodiment of the invention, the magnetic rollers 15 and 16 in the stationary mode are so positioned that there is always one magnetic pole opposite the toner outflow opening 13. This can be achieved by known position sensors such as magnetic sensors or optical sensors in combination with a marker on one of the gearwheels 24 and 25. In Fig. 3 this is shown by a sensor 31 which controls the motor 23 via a control circuit 32. The maximum gap width is determined in this case by spontaneous passage of the toner while the minimum gap width is determined by the minimum supply required. In practice, the gap width S for a supply greater than 50 g per minute is between 1.3 mm and 1.9 mm for a gap length of 50 mm. Also, with such weakly magnetisable toner, the magnets of the magnetic rollers 15 and 16 are unable to attract the toner over the surrounding wall of the reservoir 9. However, by rotating the magnetic rollers 15 and 16 in the upward direction, In opposition to the toner supply direction, In the directions indicated by the arrows 32 and 33 in Fig. 3, the spontaneous passage of the toner is Intensified. For a speed of rotation of more than 100 rpm, a toner supply of more than 50 g per minute can also be achieved here up to a maximum of 80 g per minute for a speed of rotation of 150 rpm. Fig. 4 is a more detailed embodiment of the advantageously formed transition plane 35 from the toner outflow opening to a further toner transport conduit. As already stated, the transported toner must come out of the range of a following rotating magnet as quickly as possible. As a result of the transition plane 35, which extends with a continuous angle of inclination, the toner does not stop and the required distance is achieved more quickly. Fig. 5 shows another advantageous form of a transition plane 36 between the toner outflow opening and a further toner transport conduit. In this case the angle of inclination of the transition plane 36 is constant and it tangentially adjoins the toner outflow opening and the toner transport conduit. A greater supply of toner can be obtained with the shape of the transition planes 35 and 36 shown in Figs. 4 and 5.

Claims: A supply means for magnetically attractive developing powder (21), comprising a reservoir (9) provided with an outflow opening (13) and a magnetic system for supplying a magnetically attractive developing powder from the reservoir to a developing unit, characterised in that the reservoir (9) is provided with two magnetic systems (15, 16) each rotatable about an axis of rotation and each at least partially being surrounded by a stationary enclosure over which the developing powder can be displaced under the influence of the rotating magnetic systems, the magnetic systems are disposed opposite one another with the axes of rotation parallel to one another, the stationary enclosures of the two magnetic systems together form the outflow opening (13), while in a supply mode the magnetic systems are adapted to effect transport of developing powder through the outflow opening by rotation and in a stationary mode the magnetic systems are adapted to prevent transport of developing powder through the outflow opening. A supply means according to claim 1, characterised in that the outflow opening (13) is located beneath the reservoir (9) in an operative state and the direction of rotation of the magnetic systems in the supply mode coincides with the developing powder supply direction. A supply means according to claim 1, characterised in that the outflow opening is located beneath the reservoir in an operative state and the direction of rotation of the magnetic systems in the supply mode Is in the opposite direction to the developing powder supply direction. A supply means according to any one of the preceding claims, characterised in that each magnetic system (15, 16) comprises on an outside two diametrically opposite magnets (17, 18; 19, 20) extending parallel to the axis of rotation and wherein the connecting line between the magnets of the one magnetic system is substantially perpendicular to the connecting line between the magnets of the other magnetic system when a magnet is situated opposite the outflow opening. A supply means according to claim 4, characterised in that in the stationary mode one of the magnets is situated opposite the toner outflow opening. A supply means according to any one of the preceding claims, characterised in that the reservoir is provided with means contained therein for keeping the developing powder loose, such means being inoperative in the stationary mode and operative in the supply mode. A supply means according to any one of the preceding claims, characterised In that the stationary enclosure of the magnetic systems defining the outflow opening merges, via a transition plane (35) extending continuously at an angle of inclination, into a straight outflow duct, wherein the transition plane tangentially adjoins that part of the enclosure which forms the outflow opening and also the outflow duct. A supply means according to any one of claims 1 to 7, characterised in that the stationary enclosure of the magnetic systems defining the outflow opening merges, via a straight transition plane (36) having a constant angle of inclination, into a straight outflow duct wherein the transition plane tangentially adjoins the part of the enclosure forming the outflow opening.

Inventors: BAKKER ROBERT ERIC, BAKKER, ROBERT ERIC
Applicants: OCE TECH BV, OCE-TECHNOLOGIES B.V.
Application year: 1998
Main classification: G03G15
IPC codes: G03G15, G03G9