EP1156390B1 - Apparatus for developing an electrostatic image - Google Patents

Description

The present invention relates to an apparatus for electrostatic image development, and more particularly to an apparatus in which a magnetic brush cooperates with a photoconductor drum.

Development devices and methods that use a magnetic brush to place toner on the photoconductor have been known for years. Development apparatuses and methods using a magnetic brush having hard magnetic carrier particles are disclosed in U.S. Patent Nos. 5,496,074 and 4,802,866 US 4,473,029 and the US 4,546,060 described. The devices disclosed in these patents include a rotating housing coated with a mixture of hard magnetic carrier particles and toner, a rotating magnetic core having a plurality of magnetic poles disposed within the housing, and a thin, planar, photoconductive one Movie on. The rotating magnetic core brings the hard magnetic carrier particles onto the surface of the housing, which provides for increased movement and contact of the toner with the photoconductive film.

The in the US 4,546,060 The disclosed two-component dry developer composition comprises charged toner particles and opposite charge magnetic carrier particles comprising (a) a magnetic material having hard magnetic properties characterized by a coercivity of at least 30 mT and (b) an induced magnetic moment of at least 200 mC / kg when in a field of 100 mT Gauss. As described in this patent, the developer is used in conjunction with a magnetic applicator comprising a rotatable magnetic core and an outer non-magnetizable housing for developing electrostatic images. When hard magnetic carrier particles are used and exposed to a series of magnetic fields emanating from the rotating core applicator element, the particles rotate and roll over in each new field and are thus each moved into magnetic alignment. Any overturning will moreover as a consequence both the magnetic moment of the particles as well as the coercivity of the magnetic material accompanied by a rapid jump of each particle in the circumferential direction against the direction of movement of the rotating core. The observed result is that the developers of the US 4,546,060 flow around the housing with no problems and at a fast flow rate as the core rotates in the opposite direction, rapidly transferring fresh toner to the photoconductor for high-performance copying and printing applications.

Previous uses for hard magnetic carrier particles provided a flexible photoconductor in the form of a thin, sheet-like film. Flexible photoconductors or photoconductor films have several important advantages for high-speed photocopiers. In a typical device, the photoconductor film is positioned under light tension with a series of rollers. The film has an inherent compliance which allows it to respond to changes in the thickness of the magnetic brush.

Photoconductive drums are state of the art but have not yet been used with magnetic brushes having hard magnetic carrier particles. The reason photoconductors were not used is largely because they are much stronger than film photoconductors and the increasing thickness of the magnetic brush can damage the surface of the drum. Conversely, a decreasing thickness of the magnetic brush may cause inadequate contact with the photoconductor and thus result in poor image development.

The document US 5,484,680 shows a magnetic brush with hard magnetic carrier particles which is arranged opposite a photo drum. The centers of rotation of the non-magnetic sleeve and the magnetic core are superimposed.

The invention is accordingly based on the object to provide a improved device for developing an electrostatic image.

This object is achieved according to the invention by an apparatus for developing an electrostatic image according to claim 1 and by a method for developing an electrostatic image according to claim 6.

In one embodiment of the invention, an apparatus for developing an electrostatic image comprises a photoconductive drum and a magnetic brush which contacts the photoconductor and comprises a mixture of toner and hard magnetic carrier particles.

According to another embodiment of the invention, a toner unit comprises a support rail, a slide rail located in the support rail, the slide rail being adapted to receive the toner unit, a pair of dowel pins, the slide rail positioning the toner unit relative to the dowel pins, and a servomotor, which aligns the toner unit in register with the dowel pins.

The invention will be described below with reference to the drawings based on preferred embodiments.

Fig. 1

eine Seitenansicht einer erfindungsgemäßen Entwicklervorrichtung einschließlich einer Querschnittsansicht einer erfindungsgemäßen Tonereinheit,

Fig. 2

eine vergrößerte Ansicht einer erfindungsgemäßen Entwicklungszone,

Fig. 3

eine vergrößerte Ansicht einer Entwicklungszone mit einem Rückstaubereich,

Fig. 4

eine auseinandergezogene perspektivische Ansicht der Tonereinheit aus Fig. 1,

Fig. 5

eine auseinandergezogene perspektivische Ansicht der Tonereinheit aus Fig. 1 von deren entgegengesetztem Ende aus gesehen,

Fig. 6

eine Seitenansicht der erfindungsgemäßen Tonereinheitträgeranordnung,

Fig. 7

eine perspektivische Ansicht der Trägeranordnung aus Fig. 6,

Fig. 8

eine Ansicht einer seitlichen Draufsicht auf eine Gleitschiene, die in der Trägeranordnung aus Fig. 6 angeordnet ist,

Fig. 9

eine perspektivische Ansicht der Trägeranordnung aus Fig. 6 von dem entgegengesetzten Ende, zu dem in Fig. 7 dargestellten Ende,

Fig. 10

eine Seitenansicht der Trägeranordnung aus Fig. 6 mit der Tonereinheit aus Fig. 1 registerhaltig mit einer Fotoleitertrommel ausgerichtet,

Fig. 11

eine vergrößerte Ansicht eines Passlaufreifens und eines Passstiftes in einem nicht-registerhaltigen Zustand, und

Fig. 12

eine vergrößerte Ansicht eines Passlaufreifens und eines Passstiftes in einem registerhaltigen Zustand.

In the drawings show:

Fig. 1

a side view of a developer device according to the invention including a cross-sectional view of a toner unit according to the invention,

Fig. 2

an enlarged view of a development zone according to the invention,

Fig. 3

an enlarged view of a development zone with a Rückstaubereich,

Fig. 4

an exploded perspective view of the toner unit of Fig. 1,

Fig. 5

an exploded perspective view of the toner unit of Figure 1 seen from the opposite end,

Fig. 6

a side view of the toner unit carrier assembly according to the invention,

Fig. 7

a perspective view of the carrier assembly of Fig. 6,

Fig. 8

4 is a side elevational view of a slide rail disposed in the carrier assembly of FIG. 6;

Fig. 9

6 is a perspective view of the carrier assembly of FIG. 6 from the opposite end to the end shown in FIG. 7;

Fig. 10

1 in register with a photoconductor drum, FIG. 3 shows a side view of the carrier arrangement from FIG. 6 with the toner unit from FIG.

Fig. 11

an enlarged view of a registration race and a dowel pin in a non-registered condition, and

Fig. 12

an enlarged view of a registration race and a dowel pin in a registered condition.

Various embodiments of the invention are illustrated in FIGS. 1-12, which are not drawn to scale, and in which the parts in the several views are numbered alike. 1 shows a toner unit 10 according to the invention, comprising a photoconductive drum 12 and a magnetic brush 14 which brings a mixture of toner and hard magnetic carrier particles into contact with the outer surface of the photoconductor drum 12. Magnetic brush 14 includes a housing 16, preferably of non-magnetizable material, and a core 18 having a rotating plurality of magnetic poles. The photoconductive drum 12 rotates in the direction indicated by the arrow 20, the sleeve 16 rotates in the direction indicated by the arrow 22, and the core 18 rotates in the direction indicated by the arrow 24.

The toner unit 10 and the photoconductor drum 12 are attached to the frame 28, which is configured as needed for a specific copying machine or a printer application / printer. The toner unit 10 comprises a sleeve 16, a catch basin 30, four augers 32 rotatably mounted in the catch basin 30, a transport roller 34 disposed over the augers 32 adjacent to the sleeve 16, and a refill unit 36 which perforates a stationary one Tube 38 and a Auffüllbürste 40 within the tube 38, which rotates in the direction indicated by the arrow 42 comprises. The refill unit 36 directs toner into the toner / carrier particle mixture according to the Information from a toner concentration monitor 44 to maintain the weight ratio of toner and carrier particles, eg 1/10. Some of these parts may be added or removed depending on the particular application. The additional mixing by the four-screw system improves mixing and even toner distribution over the entire image width. The toner concentration gradients are preferably minimized and represent only a few percent.

In use, the mixture of hard magnetic carrier particles and toner covers the screws 32 to a level approximately equal to the level of the bottom of the transport roller 34. The worms 32 include a plurality of angled paddles 46 mounted on the shafts 48. The mixers mix the carrier particles and the toners to provide frictional charging and homogeneity and to provide a generally similar level of toner / carrier particle mixture in the sump 30. The transport roller 34 rotates in the direction indicated by the arrow 50 and raises the mixture from the catch basin 30 to the sleeve 16.

FIG. 2 is an enlarged view of the nip portion of FIG. 1, showing where the toner / carrier particle mixture 52 surrounding the sleeve 16 contacts the photoconductive drum. The flow of the toner / carrier particle mixture 52 has a thickness T and contacts the drum 12 over a length L. The flow shown in Fig. 2 is highly desirable.

In Fig. 3, an unwanted flow of the toner / carrier particle mixture 52 is shown, with a Rückstaubereich 54 has arisen. It is believed that a back pressure region 54 is formed when the flow of the toner / carrier particle mixture 52 is greater than the amount that can flow through the gap between the sleeve 16 and the roller 12. The backpressure area may cause disturbances in image development on the drum 12 and also damage the surface of the drum 12. The back-up area 54 is not passive because the rotating core 18 tends to drive the mass of material in the back-pressure area 54 into the gap with active force.

According to one embodiment of the invention, the development of a Rückstaubereiches is bypassed. Referring to Figure 1, it can be seen how the register-containing position of the housing 16 is controlled to the drum 12 by mounting a pair of dowel pins 56 on each side of the drum 12. The drum 12 includes a shaft 58 which is mounted in a pair of bearings 60, which in turn are secured to the frame 28. The toner unit 10 includes a pair of registration fittings 62 on each end into which the pins 56 fit. According to a preferred embodiment of the invention, the toner unit 10 is secured in register with the pins 56, thereby rendering it immobile during operation of the drum 12 and the magnetic brush 14. The registration fitting 62 shown in FIG. 1 is for the most part hidden behind the toner unit 10. A better reproduction can be found in FIG. 12.

According to a further embodiment of the invention, the centers of rotation of the core 18 and the sleeve 16 are not superimposed, but the centers of rotation of the core 18 relative to the center of rotation of the sleeve 16 on the drum 12 to (eccentric), wherein a region 64 is formed in the inner surface of the sleeve 16 is closest to the outer surface of the core 18 (slightly below the point where the drum 14 and the sleeve 16 are closest to each other.) A metering element 66 is disposed opposite the region 64 in which the sleeve 16 farthest from the core 18. The metering element 66 meters a predetermined thickness of the toner / carrier particle mixture on the sleeve 16. The magnetic field applied to the toner / carrier particle mixture is weakest in that point, so it will not The thickness of the mixture decreases as it passes around the housing to the drum 12. Thus, j Any change in thickness with the thickness of the mixture, with a more precise thickness T is created. According to a preferred embodiment, an imaginary line extends horizontally from region 64 to metering element 66 and the two elements are at 180 ° to each other (one element at the 9 o'clock position and the other at the 3 o'clock position).

Figures 4 and 5 show exploded views of the toner unit 10 from opposite ends to illustrate additional detail and the relationship between the components.

The rotating magnetic core 18 may cause eddy current losses in the photoconductive drum 12. A combination of relatively fine magnetic pole frequency (e.g., a 14-pin array of about 4 cm [1.6 inch] diameter) and a relatively thin wall of 4 to 8 mm for the photoconductor drum 12 reduces the resulting eddy current losses. In addition, the choice of materials for a relatively hard aluminum (T3 or T6) for the drum wall minimizes the conductivity of the wall and thus the eddy current losses.

According to a further embodiment of the invention, the metering element 66 is provided at both ends with vanes 67 which reduce the flow of the toner / carrier particle mixture in the vicinity of the ends of the photoconductive drum 12. Reducing the flow in this way prevents damage that can occur at the ends of the development zone due to the edge effects that locally increase the flow. Further reductions in the formation of backpressure regions at the ends of the development zone are achieved by placing small permanent magnets on the metering element 66 at the position of the wings 67.

A DC bias is applied to the sleeve 16 to create an electric field that brings the toner onto the surface of the photoconductor drum 12. An AC bias can also be used to improve the rate of development, and thus the level and consistency of image quality. In solid surface development systems, an electrical bias is applied between the base layer of the photoconductor and the sleeve of the developer unit. When a high frequency, or high voltage (eg, 1000 to 2000 hertz and 500 to 1500 volt effective voltage) signal is added to the constant bias voltage, the rate of development is significantly increased.

FIGS. 6-12 illustrate a carrier assembly 100 according to one embodiment of the invention that may be used with the toner unit 10 (FIGS. 1 and 10) to precisely register the toner cartridge with the photoconductor drum 12 (FIGS ). The carrier assembly 100 compensates for displacements of the photoconductor drum 12. As shown in FIGS. 6 to 9, the carrier unit comprises a support rail 102 and a slide rail 104 which is held and guided by the three rods 106, 108 and 110. The support rail is fixed to a structure, e.g. connected to the frame 28 of FIG. As best seen in FIG. 8, the slide rail 104 includes two horizontally elongated holes 132 which receive the outer rods 106 and 110 and a slightly oversized hole 134. The center rod 108 limits movement of the slide rail 104 in the longitudinal direction while allowing lateral movement of the slide along the rod 108. The two outer rods 106 and 110 serve to maintain the planarity of the slide rail 104.

In Figs. 6 to 9, the slide rail 104 is attached to the side plate 116. An eccentric shaft 112 is driven by an electric servomotor 114, is mounted between two parts of the side plate 116, and provides the means for positioning the slide rail 104 relative to the photoconductor drum 12. The electric actuator 114 is fixedly attached to the same support structure as the support rail 102. The eccentric shaft 112 includes an eccentric bearing 113. A load arm 122 is also attached to the side plate 116 and pivoted about a vertical axis about a load arm pivot point 124. The position of the eccentric shaft 112 is controlled by the use of two solid state microswitches 126 and one eccentric positioning clutch 118.

When the eccentric shaft 112 is rotated from a parked position to a deployed position, it pushes against a detected eccentric securing plate 120 which is secured to the side plate 116. The movement pushes the slide 104 into its adjusted position (see Fig. 6) as indicated by arrow 142. While the slide rail 104 is brought into its set position, the load arm 122, which abuts against the side plate 116 attached to the toner unit 10 (Figures 1 and 10) and deflected to provide a spring force which aligns the toner cartridge 10 with the registration pins 56 (Figures 1 and 10). The detected eccentric securing plate 120 causes a force such that the eccentric shaft 112 is not rotated away when the device is in the engaged position.

6 to 9, a positive vertical lifting force is achieved through the use of two angled pressing blocks 128 mounted on the load arm 122 and a mating angled wedge 130 attached to the toner unit 10 (see Figures 1 and 10). is attached. The pressing blocks 128 pass through a pair of windows provided in the side plate 116. In Fig. 10, an angled pressing block 136 is fixed to the bottom of the toner unit 10, and a mating presser plate 138 is attached to the frame of the machine such as the machine. the frame 28 of FIG. 1, attached. The angled pressure block 136 and the mating pressure block 138 provide additional vertical lifting force. The net force is directed toward the drum 12 upwards, as the arrow 140 in Fig. 1 indicates. As shown in FIGS. 11 and 12, the registration fittings 62 attached to each end of the toner unit 10 preferably include pointed notches 63, and the registration pins 56 are received in the notches 63 as the toner unit moves in the direction of arrow 140 becomes. The force that holds the toner unit 10 in position may exceed about 450 N and in one particular embodiment is about 700 N.

The slide rail 104 includes a track 105 in which the toner unit 10, as it is inserted into the apparatus, lies and is guided until all the electrical and mechanical interfaces are connected. The slide rail 104 and the track 105 serve to accurately position the toner unit 10 relative to the pins 56, so that when the eccentric shaft 12 is activated, the dowel pins 56 are received in the notches 63.

List of reference numbers

10

toner unit

12

Photoconductor drum

14

magnetic brush

16

shell

18

core

20

arrow

22

arrow

24

arrow

28

frame

30

catch basin

32

snails

34

transport roller

36

restocking

38

perforated tube

40

Auffüllbürste

42

arrow

44

Toner concentration monitor

46

angled paddles

48

wave

50

arrow

52

Toner / carrier particle mixture

54

backwater area

56

dowels

58

wave

60

bearing pair

62

Registration fitting

63

V-notch

64

Area

66

metering

67

wing

100

carrier assembly

102

support rail

104

slide

105

track

106, 108, 110

rods

112

eccentric shaft

113

eccentric

114

servomotor

116

side plate

118

Exzenterpositionierkupplung

120

Exzentersicherungsplatte

122

load arm

124

Lastarmschwenkpunkt

126

Solid microswitch

128

pressing block

130

angled wedge

132

elongated holes

134

oversized holes

136

Andrückkonsole

138

pressure plate

140

arrow

142

arrow

Claims (9)

1. Apparatus for developing an electrostatic image, comprising the following:

   a drum photoconductor (12);

   a magnetic brush (14) contacting said drum photoconductor (12), said magnetic brush (14) comprising a mixture of toner and hard magnetic carriers, wherein said magnetic brush (14) comprises a magnetic core (18) within a shell (16) having a center of rotation, and said magnetic core (18) is offset relative to said center of rotation toward said drum photoconductor (12); and,

   located adjacent said shell, a metering element (66) for metering the mixture, said metering element being located in an area where said shell (16) is furthest from said magnetic core (18).
2. The apparatus as set forth in Claim 1, wherein said shell (16) is closest to said magnetic core (18) in an area (64), said drum photoconductor (12) can be rotated in one direction of rotation, and wherein the drum photoconductor (12) is closest to said shell (16) at a location upstream of said area (64) in which said shell (16) is closest to said magnetic core (18) with respect to said direction of rotation.
3. The apparatus as set forth in Claim 1 or 2, wherein said metering element (66) and said area (64) in which said shell (16) is closest to said magnetic core (18) are 180° apart with respect to the circumference of said shell (16).
4. The apparatus as set forth in Claim 1, 2 or 3, wherein an imaginary line drawn from said metering element (66) to said area (64) in which said shell (16) is closest to said magnetic core (18) is horizontal.
5. The apparatus as set forth in any one of the preceding Claims, wherein a carriage assembly (100) is provided, said carriage assembly (100) comprising:

   a support rail (102);

   a sliding rail (104) received within said support rail (102), said sliding rail (104) being adapted to receive a toning station (10) of said apparatus;

   a pair of registration pins (56), said sliding rail (102) positioning said toning station (10) relative to said registration pins (56); and,

   an actuator (114) that forces said toning station (10) into registration with said registration pins (56).
6. Method for developing an electrostatic image, comprising the following steps:

   applying a mixture of toner and hard magnetic carrier particles to a drum photoconductor (12) with a magnetic brush (14) comprising a magnetic core (18) within a shell (16) having a center of rotation, and whereby said magnetic core (18) is offset relative to said center of rotation toward said drum photoconductor (12), and

   metering said mixture of toner and hard magnetic carrier particles with a metering element (66) located adjacent said shell (16) in an area where said shell (16) is furthest from said magnetic core (18).
7. The method as set forth in Claim 6, wherein said drum photoconductor (12) is rotated in one direction of rotation and wherein said mixture of toner and hard magnetic carrier particles are applied to said drum photoconductor (12) at a location upstream of said area (64) in which said shell (16) is closest to said magnetic core (18) with respect to said direction of rotation.
8. The method as set forth in any one of Claims 6 through 7, further comprising the step of:

   reducing a flow of said mixture of toner and hard magnetic carrier particles to prevent the formation of roll-back.
9. The method as set forth in Claim 8, wherein said flow is reduced by said metering element (66).

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